This PDF file contains the front matter associated with SPIE Proceedings Volume 10683 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

This paper provides a road-map for the development of simple core/clad optical fibers whose enhanced performance - in particular, marked reductions in optical nonlinearities - is achieved materially and not through the more conventional present routes of geometrically complex fiber design. More specifically, the material properties that give rise to Brillouin, Raman, and Rayleigh scattering, transverse mode instabilities (TMI), and n2-mediated nonlinear effects are compiled and results on a wide range of optical fibers are discussed with a focus on trends in performance with glass composition. Further, optical power scaling estimations as well as binary and ternary property diagrams associated with Rayleigh scattering, the Brillouin gain coefficient (BGC) and the thermo-optic coefficient (dn/dT) are developed and employed to graphically represent general trends with composition along with compositional targets for a single intrinsically low nonlinearity, silica-based optical fiber that can achieve the powerscaling goals of future high energy fiber laser applications.

In this presentation we discuss the developed solutions based in both monitoring as well as control strategies for the use of laser in two applications in which we profit from the laser advantages by developing sensors and detectors that can be used to either provide in-situ information or establish closed-loop controls. The first application is the removal of excess of material with laser cutting in parts fabricated by forging related techniques. Since burrs and other defects are not regular, the most optimal cutting parameters do not always guarantee successful cutting of the excess of material. A home-made monitoring system based on the capture of the scattered light of the laser beam can provide information about the effective removal of material and hence, it can be employed for automated operations. The second application deals with the micro-drilling of large surfaces. In fact, in this application it is highly desirable to have a tool that could inform somehow about the performance of the process in order to obtain a feedback about the final quality. For this, an optical sensor monitoring the scattered light of the processing laser has been placed at the top and bottom of the processed panel. Deviations of the signal during micro-drilling can be correlated with local defects of the process performance.

Fiber lasers with fiber Bragg grating (FBG) mirrors inscribed directly into the active fiber, hereinafter referred to as monolithic fiber lasers, are of great interest thanks to simpler resonator design and thanks to elimination of fiber splices between the active fiber and passive fibers with FBGs that could lead to breakdown. In order to build such monolithic fiber laser configuration, different methods for FBG inscription were reported in literature, including phase mask inscription using UV light or fs lasers in deep UV light, visible and IR spectrum, and by point-by-point technique with IR fs radiation, for details see [1, 2] and references herein. We report to our knowledge first application of monolithic fiber laser with FBGs inscribed by so-called plane-by-plane method using femtosecond laser pulses operating in visible region [3, 4]. We used erbium and ytterbium co-doped double-clad fibre fabricated in-house. The fibre was drawn from preforms manufactured by modified chemical vapour deposition method and solution-doping of erbium and ytterbium ions with phosphorous oxide. Since the inner cladding cross-section of the fibre had a circular shape, a tailored coiling had to be applied in order to improve pump absorption [5, 6]. Indeed, the peak absorption at 976 nm increased from 3.5 dB of the standard coil to 17 dB for a tailored coil of 5 m long fibre sample. The high reflectivity mirror reflects more than 99 % and the reflectance of the low-reflective FBGs varied from 10 % to 50 % in the various samples. The laser characteristics were measured using 976 nm pump laser diode with the pump wavelength stabilized by volume Bragg grating. We report 30 % efficiency of the experimental fibre laser setup. The relatively low laser efficiency can be attributed to non-optimal absorption due to circular cross-section of the inner cladding and to non-optimized erbium-to-ytterbium concentration

Brillouin fiber ring lasers (BFRLs) are based on the amplification of the Stokes signal wave generated by a pump signal seeded inside a fiber-ring cavity. Brillouin fiber ring lasers have already been extensively studied [1] and results have shown that the generated first order Stokes wave has less intensity and phase noise than the seeded pump. This increase in coherence is attractive for many sensing applications, whether in the field of fiber sensors or remote sensing systems such as LIDAR. For input pump powers few times the 1rst order Stokes Brillouin lasing threshold, stimulated Brillouin scattering (SBS) in the fiber acts as a low-pass filter and reduces both frequency and intensity noise of the Stokes-1 signal relative to that of the pump [1], [2], [3]. Brillouin fiber lasers with several Stokes components can further increase the coherence through a cascading effect, the 1st Stokes component being the pump for the 2nd Stokes order and so on [4]. In this communication, we experimentally demonstrate up to 40 dB FN reduction of a non-resonant pumping BFRL compare to that of the pump and show that it can reach even higher values (50 dB). To our knowledge, this is the first demonstration of such experimental FN (so its linewidth) reduction using non-resonant BFRLs. Using resonant pumping, and multi-Stokes Brillouin fiber lasers, we show that the RIN reduction is exceptionally increased (20 dB) through the cascading effect due to the saturation process of the Stokes signal used as an optical pump. We stated that the multi-Stokes operation is mandatory to obtain high RIN-Reduction, while the frequency noise reduction is maintained at a high level (30 dB). Analytical expressions obtained for the noise power density enables us to predict this reduction showing the effect of the cavity (Q-factor) and of acoustic damping rate. Chalcogenide and silica fibers are compared. [1] L. Stepien, S. Randoux, and J. Zemmouri, “Intensity Noise in Brillouin fiber ring lasers,” J. Opt. Soc. Am. B-Optical Phys., vol. 19, pp. 1055–1066, 2002. [2] A. Debut, S. Randoux, and J. Zemmouri, “Experimental and theoretical study of linewidth narrowing in Brillouin fiber ring lasers,” J. Opt. Soc. Am. B, vol. 18, no. 4, pp. 556–567, 2001. [3] J. Geng, S. Staines, Z. Wang, J. Zong, M. Blake, and S. Jiang, “Highly stable low-noise Brillouin fiber laser with ultranarrow spectral linewidth,” IEEE Photonics Technol. Lett., vol. 18, no. 17, pp. 1813–1815, 2006. [4] K. H. Tow, Y. Léguillon, S. Fresnel, P. Besnard, L. Brilland, D. Méchin, P. Toupin, and J. Troles, “Toward more coherent sources using a microstructured chalcogenide Brillouin fiber laser,” IEEE Photonics Technol. Lett., vol. 25, no. 3, pp. 238–241, 2013.

Glass is a widely used material in different industrial domains thanks to some of its main properties such as high thermal and chemical resistance, biocompatibility and transparency. Glass bonding methods have a lots of applications in various domains such as architecture and design, optics, microfluidics or pharmaceutical. Compared to conventional glass bonding methods e.g. adhesive, fusing or anodic junction, ultrashort laser glass welding presents many advantages in terms of mechanical, chemical and thermal resistance, absence of additive material, process speed and miniaturization. Ultrashort laser pulses glass welding consists in irradiating the interface of the samples to weld through the glass with a focused beam. Glass is initially transparent to the laser beam, until a nonlinear absorption of the laser energy due to the high intensity reached in the focusing volume, which increases locally the temperature inside the material. A thermal accumulation effect is induced at high repetition rate (> 100 kHz), increasing the temperature up to the melting point of the glass. The junction is obtained by the blending of the material at the interface, followed by a fast cooling of the melting pool. Our study focuses on the relevance of using a long focal length focusing device, as opposed to a more classical microscope objective, for femtosecond laser glass welding at high repetition rate. Femtosecond laser welding is performed on borosilicate glass plates using a scanner head with a 100 mm F-theta lens. The low numerical aperture focusing device generates a wide elongated focusing spot at the interface of the glass plates. Compared to a microscope objective as a focusing device, such an F-theta lens presents several advantages. The long Rayleigh length, up to hundreds of micrometers, reduces the level of accuracy generally needed when positioning the focusing spot at the interface. The integration of the lens in a scanner head gives a large freedom of geometries and patterns, at high scanning speed, with a high positioning accuracy. Our thermomechanical modeling shows that the wide elongated focusing spot, combined with the thermal accumulation effect occurring at high repetition rate (500 kHz), generates a low temperature increase at each pulse arrival, up to the melting temperature. On the opposite, in the literature, the use of a microscope objective induces single pulse material modifications by reaching temperature largely over the melting point. Our experimental characterizations by photoelasticimetry confirm that the low temperature increase reduces the residual thermal stress inside the material. On this basis, a design of experiments has been carried out considering the influence of pulse duration, pulse energy, wavelength and repetition rate with tensile tests, photoelasticimetry and transmission measurement characterizations.

The synthetic µ-diamonds powder was synthesized using high pressure high temperature technique. The metal-catalyst effect was used to reduce the pressure and temperature of diamonds synthesis. The irradiation of diamonds by focused beam of 975 nm laser diode lead to obtain intense broadband white emission with maximum at 620 nm. This type of white emission generation were described earlier for graphene ceramic and graphene foam. The emission of μ-diamonds is characterized by low threshold of power excitation and strong dependence of ambient pressure. It was suggested that the white light emission observed from graphene samples may originate from the laser-induced sp²↔sp³ hybridization change as a result of the mechanism analogous to the intervalence charge transfer in Sr₂CeO₄ nanocrystals. Similar sp²↔sp³ hybridization change can occur in µ-diamonds resulting in intense, bright white light emission.

In this paper we present high stimulated Brillouin scattering (SBS) gain in a chip-scale device. Narrowband gain of >50 dB is achieved in a chalcogenide waveguide with a bandwidth of ~10 MHz. Such a large gain is promising for on-chip amplification for the realization of integrated structures with many optical components, as well as for RF photonic and optical signal processing applications. We harness the highly efficient SBS interaction in the photonic chip to realize low-power RF filters, phase shifters and delay lines. Through the concept of RF interference an enhancement in the delay by almost a factor of 6 compared to pure SBS-based slow light is observed, making this technology promising for lowpower-budget RF photonic systems.

Distributed meandering waveguide based fiber optic components are introduced, categorized, and numerically analyzed in the near-infrared. The building block of all meandering waveguide components is the meandering loop mirror. The other components are the meandering resonator, meandering distributed feedback structure, symmetric and antisymmetric meandering resonator, symmetric and antisymmetric meandering distributed feedback structures giving rise to transmission spectra with Lorentzian, Rabi, Fano, coupled resonator induced transparency, and winged Lorentzian lineshapes. With this variety of spectral responses, distributed meandering waveguide fiber optic components are suitable as filters, and delay line elements in fiber optic communication, and as sensor elements in fiber optic diagnostics.

Phase change memory thin films from Ge-Sb-Te system with large (GeTe):(Sb₂Te₃) ratio have been deposited via UV pulsed laser deposition technique. The studied compositions were Ge₆Sb₂Te₉, Ge₈Sb₂Te₁₁, Ge₁₀Sb₂Te₁₃, and Ge₁₂Sb₂Te₁₅. Physico-chemical properties of the Ge-Sb-Te thin films, based on the scanning electron microscopy with energydispersive X-ray analysis, X-ray diffraction and reflectometry, atomic force microscopy, optical reflectivity, sheet resistance temperature dependences, and variable angle spectroscopic ellipsometry measurements, were studied in order to assess the effect of chemical composition of the deposited layers. All the obtained data confirm the importance of GeTe content in (GeTe)_1-x(Sb₂Te₃)_x thin films.

The spectral response of a distributed-feedback resonator with a thermal chirp is investigated. An Al₂O₃ channel waveguide with a surface Bragg grating inscribed into its SiO₂ top cladding is studied. A linear temperature gradient along the resonator leads to a corresponding variation of the grating period. We characterize its spectral response with respect to wavelength and linewidth changes of the resonance peak. Simulated results show good agreement with the experimental data, indicating that the resonance wavelength is determined by the total accumulated phase shift. The calculated grating reflectivities at the resonance wavelength largely explain the observed changes of the resonance linewidth. This agreement demonstrates that the linewidth increase is caused by the increase of resonator outcoupling losses.

The continuously rising demands in the today’s photonic market towards increasing precision, high surface finish, geometrical complexity yet low cost for thin microstructure glass optics require advanced fabrication technologies. The conventional method via grinding and polishing is limited to those applications mainly due to the unavoidable deformation caused by mechanical stress between lenses and clamping parts. Over the last decade, replication technology such as thermal slumping has become an advanced method in manufacturing complex and precision thin lenses. However, the technology efficiency is strongly diminished by incomplete glass flow into mold cavity and extremely long processing time. In contrast, such deficits can be avoided by a novel molding process with vacuum assistance, recently developed at Fraunhofer IPT. The vacuum-assisted molding promises an effective and reliable technology in the fabrication of high precision thin glass optics for mass production. In this paper, the newly developed molding concept is firstly presented. Besides, this research introduces a numerical implementation based on an enhanced material model characterizing glass behavior at high temperature near softening point, which is crucial to study the internal stress, surface tension and form accuracy of the thin glass. With the help of simulation, the influences of process parameters will be discussed. Experiments were performed for the validation, and the accuracy of the molded glass with microstructure features is discussed in detail. Finally, the experiment results of both thermal slumping and vacuum-assisted molding are compared to illustrate the process efficiency and guidance for industrial applications is delivered.

In this paper we numerically investigate the effect of the reverse cross-relaxation process on the inversion population of laser levels in Tm-doped glass based active system. We show the impact may be significant when high inversion population is required.

We present an indirect and non-destructive optical method for domain statistic characterization in disordered nonlinear crystals, having a spatially random distribution of ferroelectric domains with homogeneous refractive index. This method, based on a combination of numerical simulations and experimental measurements, analyses the wavelengthdependent second harmonic spatial distribution. We apply this technique to the characterization of two different random media, with drastically different statistical distributions of ferroelectric domains.

Surface tension induced whispering gallery mode (WGM) micro-resonators can be made in glass with very high quality factor Q. In fact, low losses amorphous glassy dielectrics can be easily shaped in high-surface-quality spheroids by thermal reflow. Since the pioneering works on fused silica microspheres showing several orders of magnitude higher Qs compared to previous findings, a large number of studies have been performed in the last years on glass based microresonators. Main results include frequency conversion through non-linear effects and micro-lasers, filtering and optical switching, RF photonics and sensing. Besides spheres, alternatives shapes like micro-bottles and micro-bubbles have been implemented to improve the resonator performances depending on the application. Other glasses rather than silica have been considered in order to enhance properties like transparency windows and non-linear effects. This presentation will review the main results we obtained on micro-laser sources in erbium doped microcavities, parametric conversion in silica microspheres, and stimulated Brillouin scattering in silica microbubbles. Potentials of coated silica microspheres implemented to add the functionalities of the coating material will be also presented.

Optical microresonators are a very promising component for use in optoelectronics. They have very high quality factors and low mode volumes which makes them suitable for many applications such as lasing, sensing or non-linear optics. We will present our work on microspheres coated with sol-gel Er³⁺ activated 70SiO₂ - 30HfO₂. In particular the lasing properties of such microspheres will be presented. Different coating thicknesses will be employed and the peak lasing power will be discussed in respect to the coating thickness. The lasing peaks will be identified in respect to the radial and azimuthal numbers of the whispering gallery modes and the assignments will be discussed in terms of mode selectivity.

Relative Intensity Noise in Er:ZBLALiP Whispering Gallery Mode Laser : Theory and Experiments Patrice Féron(1)*, Jean-Baptiste Ceppe(1,2), Michel Mortier(3), Yannick Dumeige(1). (1) CNRS, UMR 6082 Foton, Enssat, 6 rue de Kerampont, CS 80518, 22305 Lannion, France. (2) IRCICA (CNRS USR 3380) - PhLAM (CNRS UMR 8523), 50 Avenue du Hallay, 59650 Villeneuve d'Ascq, France (3) IRCP (CNRS-UMR 8247), Chimie-Paristech, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05, France. *corresponding author patrice.feron@enssat.fr +33296469042 ceppe@enssat.fr +33359632258 dumeige@enssat.fr +33296469110 michel-mortier@chimie-paristech.fr+33153737927 EPE113 Fiber Lasers and Glass Photonics: Materials through Applications Fibers and Waveguide Sources – metrology and testing methods for laser sources Abstract: Micro spherical resonators have attracted significant attention in recent years due to their interesting optical properties and the range of applications for which they can be used. Most of the publications dedicated to micro spherical Laser are devoted to lasing effects in different materials where the spectral properties of the emission depends on (i) the choice of dopant (e.g. Er3+, Yb3+, Tm 3+) and (ii) the host matrix (e.g. silica, fluoride, phosphate or telluride glass) in which the dopant is embedded. Yet, the dynamics of theses Lasers are still to be studied. This paper shows experimental and theoretical results on the amplitude fluctuations of a Whispering Gallery Mode Laser, also known as relative intensity noise (RIN). It gives information about the dynamics inside the cavity, such as photon lifetime, effective pumping rate and noise sources. We use as active medium Er3+ doped fluoride ZBLALiP glass. Theses glasses are well adapted to the development of micro spherical Laser operating in the infrared region, in particular with emission wavelengths falling respectively in the C-band. In this paper we report on the RIN measurements for several pumping configurations of Erbium doped fluoride glass WGM micro-lasers. Due to the unique properties of WGM resonators, harmonics of the spiking frequency are observed in the RIN spectrum. Usual model of class B laser has been extended to take into account WGM specificities in order to exploit the experimental results. The model including nonlinear coupling of population inversion and photon number fluctuations is well suited for the description of low mode volume WGM lasers for which this coupling is not negligible. The comparison between experiments and our model allow relevant physical parameters to be extracted from the fitting of the RIN spectrum (as example mode volume and quantum numbers of the WGM). Our approach could be extended to WGM laser frequency noise and exploited in the analysis of the whole noise properties of micro-lasers used in sensor applications.

Lithium niobate (LiN bO₃) microresonators have attracted much interest over the last decade, due to the electrooptical, acousto-optic and non-linear properties of the material, that can advantageously be employed in combination with thin resonances of optical microcavities for applications as varied as integrated gyrometers, spectrometers or dynamic filters. However the integration of micrometer scale cavities with an input/output waveguide is still a critical issue. Here we propose an innovative approach, allowing low insertion losses and easy pigtailing with SMF fibers. The approach consists in producing and optimizing separately a membrane-based LiNbO₃ waveguide with Spot-Size Converters, and a thin microdisk. The two elements are dynamically assembled and fixed in a second step. Additionally to the proposed integrated microresonator, this approach opens the way to the production of 3D hybrid photonic systems.

A Dy³⁺-doped ZBLAN fiber amplifier based on an in-band pumped configuration is designed and optimized via an evolutionary approach. In the proposed model, the rate equations are coupled with the power propagation equations for the pump and signal beams. The complete amplifier model allows the definition of the fitness function to be optimized. Realistic values for optical and spectroscopic parameters are considered. For a fiber with dopant concentration of 2000 ppm, by employing an input pump power of 1 W at 2.72 μm wavelength, an optical gain of about 15.56 dB at 2.95 μm wavelength is obtained.

This paper presents a short review of the results obtained by the authors in the field of the sol–gel-derived glass nanoparticles activated with lanthanides ions. The attention is focused on the systems that are particularly interesting for photonic structures and bioapplications. We discuss how the sol–gel technology allows to prepare different kind of active nanoparticles and how is possible to use them in specific applications. Some examples showing fabrication techniques of spherical micro- and nanoparticles are given, including preparation of rare-earth-doped silica and silica-calcia glass. The proper structures are mentioned to tailor the optical and spectroscopic properties of microresonators. Glass-ceramics systems are also reminded where nanocrystalline particles are derived. Fabrication and spectroscopic assessment of rare earth doped HfO₂ and SnO₂ nanoparticles are presented as well. Finally, it is discussed how bioactive properties of SiO₂– CaO nanoparticles can be used in medicine, for example in tracking using their luminescent properties.

A type of a random laser with a feedback organized by a number of randomly distributed fiber Bragg gratings (FBG) can demonstrate single-mode, or low threshold operation. Nevertheless, the spectrum of such lasers can be unstable. Here we study temporal variations of the spectra of random fiber laser with a set of Bragg gratings and show that they depend on the level of surrounding noise.

A tuning of the light transmission properties of 1D photonic structures employing an external stimulus is very attracting and opens the way to the fabrication of optical switches for colour manipulation in sensing, lighting, and display technology. We present the electric field-induced tuning of the light transmission in a photonic crystal device, made by alternating layers of silver nanoparticles and titanium dioxide nanoparticles. We show a shift of around 10 nm for an applied voltage of 10 V. We ascribe the shift to an accumulation of charges at the silver/TiO₂ interface due to electric field, resulting in an increase of the number of charges contributing to the plasma frequency in silver, giving rise to a blue shift of the silver plasmon band, with concomitant blue shift of the photonic band gap. The employment of a relatively low applied voltage gives the possibility to build a compact and low-cost device ¹ . We also propose the fabrication of 1D photonic crystal and microcavities employing a magneto-optical material as TGG (Tb₃Ga₅O₁₂). With these structures we can observe a shift of 22 nm with a magnetic field of 5 T, at low temperature (8 K). The option to tune the colour of a photonic crystal with magnetic field is interesting because of the possibility to realize contactless optical switches ² . We also discuss the possibility to achieve the tuning of the photonic band gap with UV light in photonic crystals made with indium tin oxide (ITO).

Temperature sensors are used across a broad spectrum of human activities such as in medicine, home appliances, meteorology, agriculture, and industrial and military contexts, resulting in temperature being by far the most commonly measured physical quantity. New concepts in temperature measurement methods and probes are needed for contemporary applications, the most important of which are nanotechnology, biotechnology, and integrated optics. Additionally, non-contact thermometry of moving or contact-sensitive objects, difficult to access pieces, or bodies in hazardous locations, is of a growing interest. Since the size of devices rapidly decreases making them more sensitive to thermal overstress, the reliable detection of hot-spots in electrical devices is becoming even more important. For surface luminescence temperature measurements, phosphor materials in forms of films and coatings are the most promising ones. If sufficiently thin, coatings and films rapidly equilibrate with their surroundings, and local temperature can be monitored in real-time. Also, it enables thermal imaging over the complete surface of interest. Such coatings and films can be prepared from almost all luminescence thermographic materials mixed with appropriate binders by different methods: spin-, spray-, dip-coating, doctor blade method, electrophoretic, etc. Inorganic phosphor materials for use could be rare earth or/and transition metal doped oxides, silicates, titanates, phosphates, etc. The most frequently used temperature read-out scheme in current practice is founded on luminescence intensity ratio (LIR – the ratiometric intensity reading) of different emission bands in luminescent material. This method may exploit emissions from two emission centers in binary luminescence thermometric material. Here, we aimed to develop the supersensitive luminescence thermometric binary film and coatings which utilize the ratio of two spectrally distinct emissions from two luminescence centers. Transition ion Mn4+ was one center whose emission intensity rapidly quenches with temperature, and rare earth ion Ho3+ was the one whose luminescence is insensitive to temperature changes over the temperature range up to 100°C. As powder precursors, Mg2TiO4:1%Mn4+ and Y2O3:1.5%Ho3+ were prepared by Pechini and Polymer complex solution methods, respectively. To avoid spectral overlapping, the powders were selected based on its efficient luminescence in different spectral regions and similar powder morphologies. Various ratios of starting powder precursors were studied to optimize probe.   Luminescence emissions were measured by 465nm excitation from 450W Xenon lamp on Fluorolog-3 Model FL3-221 spectrofluorometer system (Horiba Jobin-Yvon), and the LIR was calculated to obtain the calibration curve. To test the thermographic performance of the newly developed probe, an uncertainty analysis is conducted and repeatability measurements were performed. By using electrophoretic deposition of the probe, a film was formed on ITO glass, while brush coating was applied on the glass substrate with an organic (PVA) and inorganic (SHMP) binder. For such obtained probes, luminescence thermometry parameters were evaluated based on the LIR method.

All Er³⁺ doped dielectric 1-D microcavity are fabricated by RF sputtering technique. The microcavity is composed of half wave Er³⁺ doped SiO₂ active layer inserted, between two Bragg reflectors consisting of seven pairs of SiO₂/TiO₂ layers also doped with Er³⁺ ions. The morphology of the structure is inspected with scanning electron microscopy. Transmission measurements show the third and first order cavity resonance at 530 nm and 1535 nm, respectively. The photoluminescence measurements were obtained by optically exciting at the third order cavity resonance using 514.5 nm Ar⁺ laser with an excitation angle of 30°. The Full Width at Half Maximum of the emission peak at 1535 nm decrease with the pump power until the spectral resolution of the detection system of 2.3 nm. Moreover, the emission intensity presents a non-linear behavior with the pump power and a threshold at about 4 μW.

The ring-core refractive-index profile in RO-Al₂O₃-SiO₂ glass (R = Ca and Ba) was formed by the manipulation of a platinum (Pt) microsphere via continuous-wave laser irradiation method (the CW-LM3 method). The homogeneously modified area could be obtained in the CAS glass (R = Ca) with a wide velocity of the microsphere, though the BAS glass (R = Ba) showed inhomogeneous modified area with periodic structure. The even-width modified line was fabricated by controlling the velocity of the Pt microsphere, and the ring-core structure with the highest refractive index change was fabricated in the CAS glass with the Pt-microsphere speed of 46 μm/sec.

The investigated Bi₂ZnOB₂O₆ nonlinear optical single crystals doped with Nd³⁺ or Pr³⁺ ions were grown by the Kyropoulos method. Bi₂ZnOB₂O₆ single crystals doped with selected RE³⁺ ions are characterized by high values of nonlinear optical coefficients as well as the effective luminescence of excited RE³⁺ ions, which make this system a unique candidate for laser converters. The vibrational properties of Bi₂ZnOB2O₆:Nd₃₊ and Bi₂ZnOB₂O₆:Pr³⁺ single crystals were investigated with the use of μ-Raman spectroscopy. The strong emission of Bi₂ZnOB₂O₆:Nd³⁺ single crystals with maximum at about 1062 nm (⁴F_3/2→⁴ I_11/2 transition) was detected under the excitation at 514 nm. Emission spectrum of Bi₂ZnOB₂O₆:Pr³⁺ show enhancement of emission with maxima at about 1350 and 1470 nm ( ¹D₂→³H₄ and ¹G₂→³H₅ transition). The effective luminescence of excited Nd³⁺ or Pr³⁺ ions in Bi₂ZnOB₂O₆ single crystals as well as excellent nonlinear optical properties of Bi₂ZnOB₂O₆ host suggest that the investigated system can be very useful as a bifunctional crystals for new integrated optical systems such as self-frequency doubling lasers.

Rare earth ions (RE³⁺) have typical photoluminescence emissions due to internal 4f orbital transitions. These emissions are narrow, with long excited state lifetimes and have the capability of spectral manipulation like wavelength shifting, down-conversion or up-conversion processes. Therefore, RE-doped materials are widely used for optical applications. However, the narrow absorption bandwidths and the small excitation cross sections for their optical transitions are major limiting factors for the full exploitation of their potentials. In this work, we show that the addition of metal nanoaggregates as broadband and efficient sensitizers can be a viable strategy to overcome these limits. Silica-zirconia (70% SiO₂ – 30% ZrO₂) glass-ceramic films doped by Tb³⁺/Yb³⁺ ions and an additional 5 mol.% of Na₂O were prepared by sol-gel synthesis followed by a thermal annealing at 1000°C. Ag introduction was then obtained by ion-exchange in a molten salt bath and the samples were subsequently annealed in air at 380°C or 430°C to induce the migration and aggregation of the metal. The structural, compositional and optical properties of the materials were investigated, providing evidence for efficient broadband sensitization of the rare earth ions by energy transfer from Ag-dimers or multimers, which could have applications for increasing the efficiency of silicon solar cells.

In this paper we present on-chip mode-locked waveguide lasers fabricated in Yb-doped phosphate glass and Er, Ybdoped phosphate glass. At 1 micron wavelength, pulse repetition rates of up to 15 GHz with pulses ~800 fs were demonstrated and at 1.5 micron, picosecond pulses with a repetition rate up to 7 GHz were demonstrated. Dispersion was controlled in the cavity by varying the spacing between the waveguide and the SESAM, while the repetition rate could be controlled by varying the optical power. The average power can also be scaled using an integrated optical amplifier and on-chip gain of up to 10 dB was demonstrated. All these individual components can be integrated in a single platform to achieve a high-power on-chip multi-GHz optical frequency comb. Furthermore, we discuss an application of such laser sources in high-capacity telecommunications applications.

The paper describes the techniques and instrumentation employed in characterization metrology of devices used in THz communication links, addressing primarily transmitters and receivers, and also applicable to passive elements. THz wireless links are rapidly approaching industrial implementation within specified user-scenarios, such as data centres. Rigorous characterization of emitter and receiver devices utilized in THz wireless links is an essential part of link and network design, and is also a pre-condition for industrial implementation and regulatory acceptance. Deployment will require the ability to manufacture and supply reliable, reproducible emitter and receiver devices in compliance within agreed specifications and international standards. As enabling steps, calibration procedures and standards for these devices must be agreed; suitable instrumentation must be developed; and calibration services must be established providing customer accessibility. Widespread adoption of standards and calibration services must be encouraged. Measurements and applications at THz frequencies employ two disparate classes of devices and instrumentation platforms: photonics-based, which are predominantly free-space; and electronic, which are generally waveguide-coupled. THz wireless communications utilize both electronic and photonic devices, and both waveguide-coupled interconnects and free-space propagating signals. To date, photonics-based free-space THz systems have strongly dominated applications and uptake; while in recent years THz electronics has also been experiencing rapid growth. Conversely, waveguide-coupled electronic THz systems have enjoyed strong predominance in robust metrology and traceable measurements. However, because wireless signals propagate in free space, the relevant device characterization also has to be performed in free space. In order to fully characterize emitter and detector devices, a variety of measurements must be performed. It is highly desirable that these measurements be carried out using calibrated instruments and applying traceable techniques. Commercial instrumentation is available for some of the necessary measurements; this is supplemented where needed by laboratory-built equipment. In addition, several types of characterization techniques and instruments have been custom-developed. The paper details the device characterization techniques and their metrological aspects. Emitters require measurements of power, spectrum, and beam profile. Whereas calibrated power meters are commercially available, bespoke emitter-specific techniques for determining noise and stability for both amplitude and phase had to be developed. Similarly, the centre frequency and linewidth of an emitter can be measured using a traceably calibrated commercial signal analyser. In addition, a laboratory-built lamellar interferometer was employed in order to reveal the broadband spectral profile (e.g. features such as harmonics and side-lobes). Emitter beam profile and divergence was determined using two different approaches: first, and aperture raster-scan, revealing the power profile; and second, electro-optic imaging, revealing field amplitude and phase profiles. Receivers or detectors require measurements of spectral responsivity and spectral NEP (noise-equivalent power), response time, and beam acceptance cone. A calibrated broadband source with known emission spectrum and noise spectrum, such as a black-body, is necessary to determine detector responsivity and NEP. Such source was used together with the lamellar interferometer to obtain spectral response of receivers. The acceptance cone was determined using a well-collimated source and a goniometer-like arrangement where the receiver axis was rotated relative to the beam axis.

Silicon photonics interconnects have emerged as a promising way to exceed the capacity limits imposed by copper interconnects, exploiting different multiplexing technologies like wavelength division multiplexing (WDM) and polarization division multiplexing (PDM). However, the bandwidth demand is still growing and new multiplexing technologies like Mode division multiplexing (MDM) are required to overcome these limitations, enabling the transmission and reception of multiple modes through a single multi-mode waveguide. Several architectures have been proposed to perform mode multiplexing like asymmetrical directional couplers and architectures based on conventional MMIs, which show a narrowband performance. Recently, adiabatic and counter-tapered couplers have been presented showing a broader bandwidth, but both architectures suffer from large footprints. For this reason, a compact mode multiplexer with low insertion losses and low crosstalk over a broad bandwidth is still sought after. In this work, we present an ultra-broadband two-mode division (de)multiplexer (DE/MUX) that overcomes the restrictions imposed by conventional MMIs by means of sub-wavelength grating waveguides (SWG). SWG structures are composed by a disposition of different alternating materials that are repeated periodically with a pitch smaller than the operation wavelength enabling dispersion engineering. The structure of our broadband mode multiplexer is composed by a sub-wavelength engineered MMI, a 90º phase shifter (PS) and a symmetric Y-junction supporting the first two modes (TE0 and TE1) at the stem. By properly choosing the duty cycle (DC) and the pitch (Λ) of the SWG section of the sub-wavelength engineered MMI, an almost flat beat length can be achieved and, subsequently, a broader operation bandwidth. SWG tapers are included in order to perform an adiabatic transition between the non-periodic waveguides and the periodic structures of the SWG-MMI. On the other hand, the PS consists of two parallel waveguides, where the upper arm comprises two tapers in back-to-back configuration, whereas the lower arm is a straight waveguide. The operation principle of the device working as a MUX is as follows: the TE0 mode injected through the lower (upper) port of the SWG-MMI is equally split with the same amplitude and a phase difference of -90º between the two output ports. The PS generates a +90º phase shift between the upper and lower arms. Therefore, the modes arrives in-phase (out-of-phase) at the Y-junction, producing the output TE0 (TE1) mode. Silicon on Insulator (SOI) platform was considered for the design of the proposed two-mode DE/MUX with 220-nm-thick and 500-nm-wide waveguides surrounded by SiO2 substrate and cover. Full-3D-simulations of the device working as DEMUX show that insertion loss are less than 0.84 dB (0.61 dB) for the TE0 (TE1) mode in the [1.4 - 1.7] μm wavelength range, and less than 0.49 dB within [1.5 – 1.6] μm. The crosstalk of the two modes is below -20.29 dB in the [1.4 - 1.7] μm wavelength range and decreases down to -27.41 dB within [1.5 – 1.6] μm. In conclusion, we have proposed a SWG based ultra-broadband two-mode DE/MUX with a 300 nm bandwidth and a footprint as small as 36 x 3.7 μm.

Primary standards of optical radiation total radiant flux are traditionally realized by absolute cryogenic radiometers [1] working on the principle of electrical substitution with a relative total uncertainty of 1e-4 in the power measurement. The current cryogenic radiometers though operate over a limited spectral range, usually from 350 nm to 800 nm and working with free space beam. For fibre optics telecom spectral range 1300 nm - 1650 nm this scale is then extended in several steps, typically via application of other standard detector systems such as spectrally flat room temperature pyro detectors [2] and spectrally dependent temperature stabilized solid state detectors [3], which adversely affects the scale accuracy by a factor of approximately one order of magnitude. The typical relative total uncertainty of state-of-the-art transfer standard fibre coupled detectors reaches 0.5 %. Recently published results on planar electrical-substitution carbon nanotube cryogenic radiometer (PCBR) [4] brought the opportunities for using these systems as new absolute primary standards in telecom spectral range directly in fibre coupled configuration. This shortens the traceability chain, with a potential improvement in the total uncertainty to below 0.1 %. CMI in collaboration with NIST are developing the first prototypes of fibre coupled PCBR systems. First both free space and fibre coupled measurements have confirmed radiometric The paper will present both the core physical parameters of these PCBR electrical-substitution systems and initial results including the currently achieved agreement of traditional transfer standards with the PCBR at the level of 0.2 %. The work reported in this abstract was partially funded by project EMPIR 14IND13 PhotInd. This project has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme. References: [1] Martin J E, Fox N P and Key P J 1985 Metrologia 21, 147 [2] Lehman J., Theocharous E., Eppeldauer G., and Pannel C., “Gold-black coatings for freestanding pyroelectric detectors” Measurement Science and Technology, 14, 916-922, 2003 [3] E. Theocharous, M. Šmíd, T. Ward, N. Fox, “The establishment of an absolute infrared scale using cavity pyroelectric detectors”, in preparation. [4] N A Tomlin, M White, I Vayshenker, S I Woods and J H Lehman, Planar electrical-substitution carbon nanotube cryogenic radiometer 2015 Metrologia 52 376

In recent years, silicon-on-insulator (SOI) technology has focused remarkable attention due to its high index contrast, which enables a high confinement of the propagating waveguide mode and a great integration density. However, the sub-micron waveguide dimensions imply a large difference between the transverse electric (TE) and the transverse magnetic (TM) modes, giving rise to a strong birefringence. The extremely wide range of applicability of this platform increases the interest in the enhancement of the current polarization beam splitters (PBS) performance. Different approaches such as Mach-Zehnder interferometry based PBSs [1], Bragg grating waveguides [2], directional couplers [3], photonic crystals [4], slotted [5] and plasmonic [6] waveguides or multimode interference couplers (MMI) [7] have been proposed with this purpose. Nevertheless, these schemes present different drawbacks like large footprints, experimental set-up limitations, limited bandwidths, efficiency restrictions, tight fabrication tolerances or complex fabrication techniques. In this work, the novel PBS proposed is a MMI based on sub-wavelength grating (SWG) technology. SWGs are periodic structures of alternating materials, most commonly silicon and silicon dioxide, with a pitch much smaller than the wavelength of the propagating light, hence suppressing diffractive effects. These widely used structures can be considered as a homogeneous medium with an equivalent refractive index which is the average between the indices of both materials. By adjusting their geometric parameters, particularly the duty cycle, the equivalent index can be engineered opening the way to enhanced ultra-compact devices. SWGs have recently been demonstrated to be especially interesting in MMI couplers providing ultra-broadband bandwidths and notably efficiencies [8]. Therefore, the present design not only benefits from the inherently low losses of MMI devices, but also from the index engineering of subwavelength structures. Furthermore, the high degree of inherent birefringence of these structures provides our MMI with an anisotropic character, which can be advantageously engineered by tilting the SWG structures in the multimode region. The SWG segments in the multimode region are tilted with respect to the optical axis of the device. Progressively-tilted input and output inverse tapers are also implemented, improving coupling efficiency and reducing losses. By selectively tuning the propagation constants of each polarization, large differences in their Talbot self-imaging length can be implemented. As a result, the beat length for the TE and TM polarizations are highly disparate, enabling a compact polarization splitter configuration. With this technique, a more efficient device is obtained with a reduced footprint, low insertion losses and extinction ratios, and broad bandwidth. The polarization splitter implemented on SOI platform allows a one-step and simple fabrication process.

For most extreme light applications, a reliable and stable driver laser is crucial to successful experiments. As lasers grow in energy and peak power they become increasingly complex and more failure modes are introduced to the system as a whole. For this reason it is prudent to develop a laser with simplicity, repeatability, and durability in mind. With the wide commercial availability of high quality, inexpensive fiber components, much of the required pulse conditioning for seeding high energy laser systems can take place entirely in fiber. This allows for much of the laser front end to be compact, alignment-free, and computer controlled with potentially dramatic savings in cost and space on the optical table. Here we explore some of the current trends in fiberbased front ends for high peak power laser systems. The requirements for any given high peak power laser are always quite different and fiber front ends are enormously customizable, so here we present two basic versions of fiber front ends which are used at the ELI-Beamlines facility which resemble other common fiber front end architectures.

Advanced microscopy requires excitation light with coherence, monochromaticity and control of pulse duration. The ideal laser source should be tuneable with continuity over a wide spectral range, capable of emitting short pulses and amenable to fibre coupling. All these requirements are met by supercontinuum lasers that can generate highly coherent picosecond pulses at wavelengths spanning from blue light to NIR and beyond. A supercontinuum laser (SuperK EXTREME - NKT photonics, Denmark) was used to perform fluorescence lifetime imaging of human osteosarcoma cells labelled with a new probe (DCHQ5). DCHQ5, in addition to quantify the total intracellular Mg concentration in cell populations, allows one to visualize the intracellular Mg distribution in single cells. Using an acousto-optic filter, a 10 nm spectral band, centred at 480 nm was sliced from the white light exiting the supercontinuum source. The excitation light, made by a 20 MHz train of few-picosecond-long pulses, was coupled to a 400 μm fibre using a wide aperture microscope objective in order to excite all modes. The flat top light source consisting in the distal end of the fibre was imaged onto the object plane of the microscope (Leica DM-RM) to provide uniform illumination over the whole field of view. This approach, which required a home-made optical system, implemented the epifluorescence scheme with a 63X immersion objective lens, used to deliver the excitation light and collect the fluorescence signal through a dichroic mirror @500 nm and a long pass filter @505 nm. The fluorescence images were acquired with a fast picosecond camera (Picostar, LaVision Germany) made by a light intensifier coupled to a low noise CCD. A sequence of images was collected at different delays (in the interval 0-60 ns) with respect to the laser pulses, from each microscope field. Data analysis was performed using a custom written software based on the Matlab engine. The dataset, made by all the gated images, was processed using a non-linear algorithm for bi-exponential fit, operated in parallel mode. Amplitude and lifetime maps were recovered for both the fluorescent components that characterise the emission of the DCHQ5 probe. Additionally, to better estimate a possible variation of the decay dynamics of the probe in different cell comportments with alike magnesium concentration, two AOIs were isolated on the basis of the fluorescence intensity. All the pixels within the AOIs were binned to a single decay curve, which was fitted with a non-linear algorithm based on the NAG mathematical package. The fluorescence lifetime maps show a uniform pattern over the whole cell, for both the short and long living components of the fluorescence, while the amplitude maps reveal a minimum in correspondence of the nucleus and a high value in the cytoplasm. This result is confirmed by the analysis of the AOIs. Therefore, the intracellular distribution of the fluorescence intensity depends on amplitude variations of both DCHQ5 fluorescent components, and not on lifetime variations. Thus, fluorescence intensity maps reflect the concentration of the complex DCHQ5-Mg, and can be effectively used to quantify intracellular Mg2+.

Hi-tech industrial or biotechnological laser applications request for picosecond pulsed 2-μm laser generating sub-1-J pulses in >kHz repetition range. At HiLASE center the development of the laser system with target to generate 1-J picosecond pulses with 1-kHz repetition rate has started. In this paper, we present a concept of the laser system and demonstrate recent results from the first part of the laser – the holmium fiber oscillator. The holmium fiber front-end is pumped by a continuous wave <1-W thulium fiber laser generating at wavelength of 1950-nm. Mode-locking operation in the oscillator is reached by dispersion management in the laser cavity. In this self-starting configuration we reached 45-mW of average power with repetition rate of 22.5-MHz with pulse energy of 2-nJ.

Structural and optical properties of Eu³⁺ doped barium-gallo-germanate glasses modified with antimony and tellurium oxides were investigated. Barium ions are gradually replaced by antimony and tellurium ions to create two glass series. Structural properties of prepared series were established with help of FT-IR spectroscopy, X-ray diffraction method and observation under Scanning Electron Microscope (SEM). MIR spectra of studied glasses indicate a tendency to glass structure polymerization through the observed shift of main band assigned to Ge-O-Ge and Ge-O bonds vibrations. Simultaneously luminescence spectrum of Eu³⁺ ion (Electric/Magnetic – ED/EM dipole transition intensity ratio) for both glass series presented the increasing tendency to ordering of Eu³⁺ local environment. It was also proved that tetrahedral [TeO₄] units were created in glass structure which were modified with TeO₂ when addition exceed 10 mol%. The result indicates decrease of ED/MD ratio as a function of TeO₂ content above its 10 mol%.

Single-mode fiber dispersion characterization from ultraboradband white-light spatial-spectral interferogram During the recent years the optical fiber industry has seen a considerable growth not only to due the telecommunication but also medicine, military and sensing [1]. This has in turn has increased the development of new types of fibers, which has established a need for convenient and quick dispersion measurement technique over a wide spectral range. Among various methods for measuring dispersion in optical fibers, e.g. time of flight and phase modulation techniques, interferometric methods suit best for characterizing short (tens of centimeters in length) and specialty optical fibers [2]. Spectral interferometry (SI), the most widespread arrangement, involves scanning delay between two consequent pulses and registering intensity or modulation pattern in spectral domain [3]. The stability issues of SI can be overcome by recording a two-dimensional trace, where the delay is mapped to the axis perpendicular to the spectral one. This method is called spatial-spectral interferometry (SSI) and it allows to retrieve spectral phase, group delay, and dispersion from a single trace without scanning, and is estimated to be most precise method to characterize dispersion [4]. In this work we used a customized fiber fed SSI arrangement, called SEA TADPOLE [5] for characterizing chromatic dispersion of single-mode fibers. In the SEA TADPOLE the light from interferometer’s measurement and reference arm is guided to spectrometer using endlessly single mode photonic crystal fibers to address the stability issues of the technique. To enhance the bandwidth we balance the dispersion of the fiber by placing known dispersion to the reference arm. In the spectrometer the output pulses are combined so that one would get spatial fringes in vertical axis and resolve the pulses spectrally in horizontal axis. That would yield a single shot measurement with a spectral phase for all the measured wavelengths [6]. From that one could easily calculate the dispersion. In this paper we present the design based on SEA TADPOLE and demonstrate proof of principle experiments. In combination with spatially coherent supercontinuum laser source (Fianium WL-SC400-4-PP), and silicon CMOS matrix detector we can perform dispersion measurement from 400 to 1000 nm. We characterize the dispersion of single mode fiber Thorlabs 630HP in its single-mode regime 630-770 nm and compare it with dispersion curve provided by the manufacturer. From the results we can see that our measurement quite well coincides with the provided dispersion date for this specific fiber. In the future we plan to use a more elaborative dispersion balancing and we are expecting to be able to extencd the spectral sensitivity range and to separate modes in multi-mode regime. Also it is possible to extend the working range of SEA TADPOLE interferometer to telecom range in near infrared spectral band with appropriate matrix sensor or suitable filtering. All in all we find that this method has high potential for commercialization. [1] Fiber Optics Market Analysis By Type (Single Mode, Multimode, Plastic Optical Fiber), By Application (Telecom, Oil & Gas, Military & Aerospace, BFSI, Medical, Railway), By Region, And Segment Forecasts, 2014 – 2025 http://www.grandviewresearch.com/industry-analysis/fiber-optics-market [2] Cohen "Comparison of Single-Mode Fiber Dispersion Measurement Techniques" J. of Lightwave tech. 1985 http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=1074327 [3] Froehly, C., Lacourt, A. and Vienot, J.C., 1973. Time impulse response and time frequency response of optical pupils.: Experimental confirmations and applications. Nouvelle Revue D'Optique, 4(4), p.183. http://iopscience.iop.org/article/10.1088/0335-7368/4/4/301/meta [4] A. Börzsönyi, A. P. Kovács, M. Görbe, and K. Osvay, “Advances and limitations of phase dispersion measurement by spectrally and spatially resolved interferometry,” Opt. Commun. 281, 3051–3061 (2008) http://www.sciencedirect.com/science/article/pii/S0030401808001235 [5] Pamela Bowlan, Pablo Gabolde, Aparna Shreenath, Kristan McGresham, Rick Trebino, and Selcuk Akturk, "Crossed-beam spectral interferometry: a simple, high-spectral-resolution method for completely characterizing complex ultrashort pulses in real time," Opt. Express 14, 11892-11900 (2006) https://doi.org/10.1364/OE.14.011892 [6] Peeter Piksarv, Andreas Valdmann, Heli Valtna-Lukner, Roland Matt, and Peeter Saari, "Spatiotemporal characterization of ultrabroadband Airy pulses," Opt. Lett. 38, 1143-1145 (2013). https://doi.org/10.1364/OL.38.001143

Online measurement of diameters and concentricities of optical fibre layers, and the coating layer in particular, is one of the challenges in fibre manufacturing. Currently available instruments can measure concentricity and diameter of layers offline, and are not suitable for precise monitoring or control of the manufacturing process in real time. In this work, we use two laser beams, positioned orthogonally to illuminate the fibre from two sides, and calculate deviations from the expected geometry by analysing the scattering pattern. To measure the diffraction pattern we use two 8K linear array detectors, with the scattered light incident directly on the sensors. Each detector is capturing approximately 90° angular range directly behind the fibre. The two measurement channels are positioned at different heights. The scattered pattern is modelled mathematically with finite-element and Fourier-modal methods, with various diameter and concentricity deviations. The sensitivities of the changes in the scattering pattern are identified in respect to these deviations. Since calculations are computationally intensive, the sensitivities are pre-calculated in advance, and the realtime measurement is based on pattern recognition. The symmetry of the pattern is used to differentiate between diameter and concentricity variations. We performed online measurements with the prototype instrument in production conditions, and show that this method is sensitive enough to measure deviations of under 1 µm in diameter and concentricity of the coating layer.

Spatial heterodyne Fourier transform (SHFT) spectroscopy is based on simultaneous interferometric measurements implementing linearly increasing optical path differences, hence circumventing the need for mechanical components of traditional Fourier transform spectroscopy schemes. By taking advantage of the high mode confinement of the Siliconon-Insulator (SOI). platform, great interferometric lengths can be implemented in a reduced footprint, hence increasing the resolution of the device. However, as resolution increases, spectrometers become progressively more sensitive to environmental conditions, and new spectral retrieval techniques are required. In this work, we present several software techniques that enhance the operation of high-resolution SHFT micro-spectrometers. Firstly, we present two techniques for mitigating and correcting the effects of temperature drifts, based on a temperature-sensitive calibration and phase errors correction. Both techniques are demonstrated experimentally on a 32 Mach-Zehnder interferometers array fabricated in a Silicon-on-insulator chip with microphotonic spirals of linearly increasing length up to 3.779 cm. This configuration provides a resolution of 17 pm in a compact device footprint of 12 mm2. Secondly, we propose the application of compressive-sensing (CS) techniques to SHFT micro-spectrometers. By assuming spectrum sparsity, an undersampled discrete Fourier interferogram is inverted using l1-norm minimization to retrieve the input spectrum. We demonstrate this principle on a subwavelength-engineered SHFT with 32 MZIs and a 50 pm resolution. Correct retrieval of three sparse input signals was experimentally demonstrated using data from 14 or fewer MZIs and applying common CS reconstruction techniques to this data.

We report on the development of an instrument for the measurement of the Encircled Angular Flux (EAF) and on establishing its metrological traceability at the required level of uncertainty. We designed and built for that purpose two independent EAF measuring instruments, both based on the analysis of the two-dimensional far field intensity profile observed at the output of an optical fibre, using either CMOS or CCD cameras. An in depth evaluation of the factors influencing the accuracy of the measurements was performed and allowed determining an uncertainty budget for EAF measurements, which was validated by a first series of inter-comparisons. Theses comparisons were performed between the two independent EAF measuring systems, using a 850 nm LED coupled into a gradient index fibre as a test object. We demonstrated a very good equivalence between the two systems, well within the absolute measurement uncertainties that were estimated at the 10^-3 level. Further inter-comparisons using light sources coupled to step-index, large core and small core multimode fibres are still ongoing, with the aim to confirm the performances of the instrument under various illuminating conditions.

We employ mirror enhanced grating couplers as convenient output ports for ridge Si3N4 waveguide to detect single photons emitted from Dibenzoterrylene (DBT) molecules coupled into propagating modes at room temperature. The coupling ports are designed for waveguide structures on transparent silica substrates for light extraction from the chip backside. Thus the coupling ports enable contact free readout of the waveguide devices by imaging through the silica substrate. Optimized grating structures provide maximum out-coupling efficiency at 785nm (the central emission wavelength of DBT) with a bandwidth of 50 nm and fulfill mode-matching to a Gaussian mode in free space (FWHM ≈ 4μm). Covering fully etched grating devices with a Hydrogen silsesquioxane buffer layer and a gold mirror increase the coupling efficiency compared to bare grating structures. The maximum single coupler efficiency predicted by finite element simulations is 90% which reduces to 60% when adapted to fabrication constrains, whereas the average measured coupling efficiency is 35±5%. We employ such grating ports to read out optical waveguides designed for single-mode operation at λ=785 nm. DBT molecules are coupled evanescently to the waveguides and transport emitted single photon signals to the coupling region upon optical pumping. Using a Hanbury Brown and Twiss setup we observe pronounced antibunching with g(2)(0)=0.50±0.05 from the grating couplers by excitation (λ=767nm) of a single DBT molecule which confirms the quantum nature of the outcoupled fluorescent light.

Lasers and amplifiers based on thulium-doped silica fibers require improved spectroscopic properties. In this context, one of the most promising approaches is based on the embedding of thulium ions in nanoparticles of tailored composition and structure. This paper presents various methods used to produce thulium-doped nanoparticles inside silica-based optical fibers. Effects of solution doping method during the elaboration of Modified Chemical Vapor Deposition preform and doping solution composition are studied. A comparison is made between the use of solutions containing LaF₃:Tm³⁺ or YAG:Tm³⁺ nanoparticles and aluminum-lanthanum-thulium chlorides. Results show that for similar lanthanum content, lanthanum-thulium chlorides doping allows for similar enhancement of ³H₄ level of Tm3+ than LaF3:Tm³⁺ doping. Also, effects of aluminum on ³H₄ lifetime enhancement and inhibition of nanoparticle’s formation is discussed.

In recent years, BiVO4 based-materials have attracted much attention because of their fascinating multifunctional physicochemical properties, such as pigmentation, ferroelelasticity, semiconductivity, optical, luminescent and (photo)catalytic properties. Their potential at various applications is exceptionally broad. For example, BiVO4 can be useful in improving photovoltaic cell efficiency through solar spectral conversion by shifting short-wavelength sunlight (ultraviolet and blue) to longer wavelengths (downshifting), or by shifting long-wavelength near-infrared (NIR) radiation to visible light (up-conversion), which provides more radiation in the spectral region wherein the solar cell shows the largest quantum efficiency. Also, BiVO4 has proved to be an excellent material for use (under visible-light illumination) in photocatalytic water splitting and photocatalytic degradation of organic compounds (air/water pollutants). Brilliant yellow color of non-toxic ms-BiVO4 makes it a good commercially available substitute for toxic cadmium- and lead-based yellow pigments. Herein, colloidal synthesis of BiVO4 nanoparticles and their multifunctional physicochemical properties, such as photoluminescence (down-conversion and up-conversion) emission properties, pigmentation, (photo)catalytic and adsorptive features are presented. Prepared colloid solutions have been characterized by UV-VIS spectroscopy. Measured absorption spectra, for lower concentrations of the precursors, showed blue shift and calculated band gap of the colloid particles ranged from 3.07 to 3.12 eV. Obtained colloid solutions have been mixed with water, centrifuged, and the residue washed with methanol. X-ray diffraction (XRD) patterns show that the BiVO4 nanoparticles crystallize in pure tetragonal phase. In order to improve their crystallinity and to investigate in more detail the structural and photocatalytic properties, the obtained BiVO4 nanoparticles have been annealed at 450°C for 3 hours. Thermogravimetric analysis has been utilized to obtain the optimal annealing temperature. In annealed samples, tetragonal phase completely transits to monoclinic structure for which it has been reported in the literature to be photocatalytically more active. BET surface analysis showed greater specific surface of the samples obtained from the less concentrated colloids. This difference is even more noticeable after the annealing of the samples. In order to investigate photocatalytic activity of the samples, their ability to degrade organic dyes has been tested. Photoluminescence spectra of BiVO4 show two broad emission bands in the range of 450–800 nm: greenish-yellow emission band centered at 530 nm and red emission centered at 678 nm under excitation at 425 nm. This luminescence emission is considered to originate from the radiative recombination of photo-generated electrons and holes. Namely, under the UV/Vis irradiation the electron–hole pairs are generated, holes are formed in the Bi (bismuth) 6s orbitals, or hybrid orbitals of Bi 6s and O (oxygen) 2p, while the electrons are elevated to the V (vanadium) 3d orbitals. Photoluminescence spectra of co-doped samples of BiVO4: Ho/Yb show up-conversion properties and characteristic Ho3+ emission bands centered at 542 nm 659 nm and 755 nm under excitation at 980 nm. BiVO4 nanoparticles as mesoporous material prepared by this technique of synthesis show great photocatalytic activity and further improvements as well as some other applications are to be expected in the future.

Chalcogenide glasses appear as good candidates to build all optical gas sensors due to their wide infrared transparency and the possibility of incorporate rare earth active in MWIR spectral range. To detect and quantify gases, one way is to develop chalcogenide glasses presenting transparency compatible with the molecules absorption band frequency. Two domains of interest can be distinguished: MWIR and LWIR corresponding respectively to the 3–5 μm and 8–12 μm spectral ranges. Selenide and sulfide based chalcogenide glasses are known for their excellent infrared transmission properties in the 1-15 µm region with good thermo-mechanical properties. Doped with Dy3+or Pr3+, sulfide glass fibers have been used as MWIR source for gas sensor for CO2 detection. To probe the far infrared beyond 12 µm, telluride chalcogenide glasses appear as a very interesting material due to it low phonon energy and a broad transparency (up to 25 µm). While these attractive optical properties of telluride glasses, particularly for LWIR, there is few study about rare earth incorporation for luminescence explained a challenging synthesis process avoiding crystallization. To get more stability in the glass state it is essential to add selenium. Thus for each system, it is required to determine the best compromise between the transparency domain and the glass state stability by playing on the ratio between selenium and tellurium atoms. Regarding the energy level of Tb3+, we can expect to have a radiative emission from 3.1 µm up to 8 µm. For gas sensor application, it is a range of interest regarding the LWIR absorption band of some hazardous gases. Thus, Tb3+ doped chalcogenide glasses with nominal composition of Ga5Ge20Sb10Se(65-x)Tex (x = 0, 10, 20, 25, 30, 32.5, 35, 37.5) were synthetized. Their physico-chemical properties (chemical composition, density, thermal characteristics) and optical properties (transmission and ellipsometry spectroscopies) are clearly modified by tellurium substitution to selenium. Based on a detailed study of the Ga5Ge20Sb10Se(65-x)Tex bulk glass and fiber properties, the optimal composition of seleno-telluride glass fiber was found to be Ga5Ge20Sb10Se45Te20. The luminescence properties of Tb3+ (500, 1000 and 1500 ppm) doped Ga5Ge20Sb10Se65 and Ga5Ge20Sb10Se45Te20 were studied in glass bulk and fiber samples. Radiative transitions calculated from Judd-Ofelt (J-O) theory were compared to the experimental values. Although an expected lower phonon energy for telluride glasses, selenide glasses stay more suitable for MWIR emission with a strong emission at 4.8 and 3.1 µm. The emission at 8 µm was successfully observed with careful luminescence investigations.

While CaF₂:Nd³⁺,Lu³⁺ spectroscopic features are now well-known for its broadband laser operation near 1 µm and its good quantum efficiency, this material is appealing for a number of applications such as mode-locking operation. In this paper, we investigate this crystal for dual-wavelength picosecond and femtosecond operations by using a semiconductor saturable absorber mirror (SESAM). In dual-wavelength picosecond operation, synchronous mode-locking is demonstrated at 1054 and 1059 nm when pumping at 797nm and when using a high reflective mirror as an output coupler. Only one pulse train at 93,8MHz was formed and the intensity autocorrelation trace shown a period beat frequency of 1.34 THz. Pumping at 791 nm led to the formation of two asynchronous mode-locked pulses probably because the two emission lines at 1049 nm and 1061 nm were too far to be coupled. Hence by spectral filtering it is possible to make a single train mode locked laser at 1061 nm generating femtosecond pulses. The laser generated modelocked pulses with pulse duration of 435 fs, average power of 10 mW, and central wavelength of 1061 nm. More output power could be obtained by using a more transmissivity for the output coupler however degrading other performances. These results open the way for further investigation on CaF₂:Nd³⁺,Lu³⁺ crystals, with the aim of their implementation as active components in high power femtosecond lasers.

Continuous demand for compact and efficient laser sources, specifically those operating in short-wavelength spectral range, have resulted in dynamic development of both semiconductor and diode pumped solid state lasers. Undoubtedly, semiconductor lasers are presently the most intensively investigated field of active materials and a number of impressive results has been achieved, including violet GaN laser diodes. Nevertheless, solid state lasers are constantly considered as irreplaceable in all applications requiring excellent optical parameters of the beam together with high power levels. The short-wavelength emission and lasing in solid state lasers is typically obtained via harmonic generation or up-conversion phenomena. The latter method, involving either stepwise absorption of photons or energy transfer processes, is specifically applicable to fiber geometry, where high intensity of radiation and waveguiding effect guarantee high up-conversion efficiency. Trivalent thulium is the activator ion, which energy structure in certain conditions specifically favours a multi-photon or multi-ion pumping mechanisms resulting in emission within the UV-VIS part of spectrum. In low phonon glasses and fibers, luminescence from 1G4 (480 nm), 1D2 (455 nm), as well as 1I6 (287 nm) has been reported, typically involving ESA-type consecutive absorptions of 650 nm photons (3H6→3F2+3F3, 3F4→1G4, 3H4→1D2, 1G4→3PJ) [1]. UV-VIS emission has been also observed under multi-wavelength pumping at 1112 nm, 1116 nm and 1127 nm [2]. Several years ago laser action at 287 nm in Tm3+:ZBLAN fiber was obtained under consecutive ESA of 1064 nm delivered by an Nd3+:YAG laser [3] – which is to date the shortest wavelength of stimulated emission generated in an optical fiber. Laser experiments with thulium-activated fluoride fibers, however very promising, were all severely hindered by photodarkening effects accompanying excitation of UV-violet radiation in the fibers. In this work we present our latest results on UV emission properties of bulk ZBLAN glasses doped with thulium and co-doped with ytterbium ions in different concentrations. In particular, we carefully examined the absorption characteristics, as well as concentration-dependant spectra of UV emission from the 1I6 and 1D2 levels obtained under direct and up-conversion excitation. The fluorescence dynamics profiles, recorded for all concentrations, together with excitation spectra enabled discussion of mechanisms responsible for upper levels populating. Moreover, the multi-ion processes resulting in non-radiative depopulation of excited states have been carefully examined and appropriate cross-relaxation rates have been determined, giving further impact to better understanding of the short wavelength optical properties of the investigated system. This work has been supported by the National Science Centre, Poland, grant number 2011/03/B/ST7/01917. [1] J. Y. Allain, M. Monerie, H. Poignant. Blue upconversion fluorozirconate fibre laser, Electronics Letters 26 (1990), 166–168. [2] S. G. Grubb, K. W. Bennett, R. S. Cannon, W. F. Humer, CW room-temperature blue upconversion fibre laser, Electronics Letters 28 (1992), 1243–1244 [3] R. M. El-Agmy, Upconversion CW Laser at 284 nm in a Nd:YAG-Pumped Double-Cladding Thulium-Doped ZBLAN Fiber Laser, Laser Physics 18 (2008) 1-4.

The evanescent field coupling between fibers plays an important role in many different applications such as novel sensors to detect variations of the environmental refractive index [1] or broad fiber-based band-pass filters [2]. We are particularly interested in fused fiber couplers that allow for coupling light into higher order modes via evanescent field coupling [3]. Such devices are very attractive for increasing the number of channels in large-scale telecommunication networks by an implementation of spatial multiplexing. For the fabrication of fused fiber couplers, the diameter of the fiber cores is reduced constantly during the fusion process. As a consequence, the effective refractive indices of the guided modes are decreasing as well. If the core diameters become too small the modes break out of the fiber core before any evanescent field coupling occurs, in particular when fibers with standard 125 µm diameter are used. In this case, the coupling between the fiber cores is due to the super-mode coupling phenomena, which is unwanted for our application. Thus, if evanescent field coupling shall be obtained, the diameter of the optical fibers has to be reduced before the fusion process. We developed an easy-to-use and reliable etching process based on hydrofluoric acid, which results in a uniform and reproducible reduction of the fiber diameter on a length of around 50 mm. Within the etched fiber section the diameter of the fiber can be as small as 40 µm and the deviation of the diameter is below one micron. A uniform diameter is critical during the fabrication process of the fused fiber couplers since it guarantees a sufficiently good contact and fusion of the outer fiber surfaces. We also developed a sophisticated numerical beam-propagation-method (BPM) simulation which allows us to predict, for a given etched fiber diameter, the extension at which the evanescent field coupling starts. Since the evanescent field coupling is difficult to detect during the fabrication step, the numerical simulations are very crucial. We also optimized the experimental parameters of the fusion process, such as the processing temperature, the fiber tension and the extension speed, for the etched fibers. Currently, we are focusing on two different types of fused fiber couplers: (i) symmetric couplers consisting of two identical single mode fibers (SMF) and (ii) asymmetric couplers consisting of a SMF and a few-mode fiber. Experimental results recorded during and after the fabrication processes, in particular for the symmetric couplers, match perfectly with the predictions of our simulations. In conclusion, we have developed an etching-process and a numerical simulation, which allows us to fabricate evanescent field coupled fused fiber couplers with a reliable, reproducible and controllable process. The asymmetric couplers are going to be used in a joint project with the Hannover Center for Optical Technologies (HOT) to fabricate mode selective fused fiber couplers. [1] Z. Cai et al., Opt. Express 23, 20971-20976 (2015) [2] Q. Wu et al., Opt. Express 20, 3098-3109 (2012) [3] G. Pelegrina-Bonilla et al., Opt. Express 23, 22977-22990 (2015)

Amplified spontaneous emission (ASE) and laser effect in β-NaYF4: Ce,Tb nanocrystals E. Pavel (Storex Technologies, Bucharest, Romania), V. Marinescu (National Institute for R&D in Electrical Engineering, Bucharest, Romania) and M. Lungulescu (National Institute for R&D in Electrical Engineering, Bucharest, Romania) Miniaturization of coherent light sources, such as nanolasers and random lasers, has great potential for applications in nanoelectronics , nanophotonics, microscopy and biomedicine. Some micro- and nanocrystals are laser-active media for random laser, whispering-gallery-mode (WGM) laser or spaser (plasmonic laser). NaYF4 is one of the best optical materials due to its low phonon energy (< 350 cm-1), high refractive index and thermal stability. Hexagonal form of NaYF4, β-NaYF4 is an efficient host material for rare-earth ions. Doped micro- and nanocrystals could be produced by hydrothermal method as described in Ref. [1]. β-NaYF4:Ce,Tb crystals have interesting optical properties. In the present work we shall present our results regarding studies regarding amplified spontaneous emission (ASE) and laser effect in β-NaYF4: Ce,Tb nanocrystals. Lasing was observed in a plane parallel optical microcavity Research regarding new laser-active media is important in developing practical applications for small coherent light sources. Reference [1] E. Pavel, V.Marinescu, M. Lungulescu and B. Sbarcea, ”Hydrothermal synthesis of β-NaYF4: Ce,Tb crystals doped with different cerium concentrations”, Materials Letters, ( 2018) 210, 12-15

Recent advances in ultrafast laser and supercontinuum generation technology have enabled the development of novel types of compact fiber based ultrafast lasers and frequency combs operating above 2 microns. The first prototypes of these lasers have successfully gone through the industrial feasibility studies and are entering the market. These sources are characterized by ultrashort pulse duration down to few optical cycles, Watt level output power, tens of nanojoules pulse energy, and up to GHz repetition rate. Important aspect of the new technology is the tunability of the laser output. The emission wavelength of the femtosecond laser is selectable by the customer in the wide spectral range, roughly from 2 to 3 um. In the case of all-fiber design, the emission wavelength could be also made electronically tunable up to 2.5 micrometres, while keeping the pulse duration in femtosecond range. Alternatively, if demanded by application, the laser can be configured as a coherent supercontinuum light source with spectrum reaching wavelengths well beyond 3 um. The built-in tunability of femtosecond pulses, high quality frequency combs as well as the ability to produce supercontinua directly from the laser allows using these light sources in a range of new and exciting application areas in science and industry. The application areas include, but are not limited to microelectronics, photovoltaics, THz generation, confocal nonlinear microscopy and surgery, as well as environmental, oil and gas sensing. The talk will overview the proprietary ATLA Lasers AS laser technology of the mid-infrared ultrashort pulse lasers and supercontinuum sources. Focus will be made on the specific aspects of the technology making it particularly attractive for industrial applications demanding either high quality processing or ultrahigh sensitivity measurements.

Generation of ultrashort pulses with high average power and moderately high pulse energy generally requires a modelocked laser followed by several fiber amplifiers in a master-oscillator power-amplifier configuration. Recently, gainswitched diode lasers have emerged as a viable replacement to mode-locked oscillators as sources of sub-100 ps pulses in these systems, but the low output power available from the diodes necessitates the use of multiple costly amplifier stages. Here, we demonstrate the generation of 1.7 μJ pulses at 1030 nm, and 11.7 μJ pulses at 1064 nm from a gain-switched diode seeded compact MOPA with only two amplification stages. The final stage is a tapered fiber amplifier, whose geometry efficiently suppresses amplified spontaneous emission and allows reaching a gain of ~40 dB. This research work is still in progress, and further increase in pulse energy should be possible by optimizing the setup.

We report on industrial-grade femtosecond Yb fiber lasers with >100μJ pulse energy and <300fs pulse duration using a tunable all-fiber pulse shaper. The rugged, compact phase modulator is a lossless addition to the standard chirped-pulseamplification scheme. The automated multichannel phase control across the optical bandwidth enables generation of near transform-limited pulses at the laser output, improves unit-to-unit reproducibility of laser pulse characteristics, and reduces laser build time.

We developed a compact femtosecond fiber laser operating at 1064 nm. The laser delivers 80 fs pulses at a repetition of 43 MHz and average power of 1 Watt. It has been used in a two photon microscope for imaging a rabbit bone sample.

Numerous areas, both in science and industry level, have benefited in recent years from the application of ultrafast mode-locked lasers. The introduction of a saturable absorber (SA) in the cavity is a convenient and simple way to achieve passive self-starting mode-locking in fibre lasers. The applicability of such passively mode-locked ultrafast fibre sources is mainly limited by the achievable energy and peak power, the latter usually going up to only a few kW in the femtosecond pulse range. In our current study we rely on a novel InN-based SA, recently presented and studied in [1,2], to set-up an ultrafast, high peak power ultrafast passively mode-locked fibre laser with operation wavelength at 1.56 μm in telecommunication C-band. The fibre laser is implemented as a ring resonator. It is based on a commercial EDFA as gain medium and the aforementioned SA [1], that consists of InN grown by molecular beam epitaxy on a GaN-on-sapphire template, used in reflection configuration as SESAM, which is located in free space and connected to the ring through an optical circulator. The outstanding properties of this material are here further validated, especially its tolerance to extremely high fluences (>1TW/cm2). The cavity length is increased introducing a 1-km standard single mode fibre (SSMF). Note that no polarization control is needed in the system and, as shown in [2], the basic ring configuration around 40-m-long can achieve stable mode-locking with sub-250 fs pulses and a repetition rate around 5 MHz. However, if polarization control is introduced, it is possible to tune the temporal and spectral widths of the pulses, from 150 fs to 320 fs. With a 1 km-long cavity, fundamental mode-locking is easily achievable increasing cavity losses with a VOA. Since symmetric Gaussian pulse spectra are generated, very similar to those delivered in the basic ring configuration, it is possible to assume that all the energy is contained in the pulse spectrum, without significant contribution of continuous white noise. This results in pulses with a temporal width at FWHM of 239 fs and a spectral width of 25.4 nm. Since the repetition rate is 196.4 kHz and the average power is 30.5 mW, pulses with peak power of 650.5 kW and pulse energy of 155.3 nJ are produced. If losses in the cavity are gradually reduced, mode-locking to higher harmonics is obtained in cavities up to 6-km-long, proving the excellent stability of the system. This allows a broad choice of high peak powers and repetition rates. To summarise, for the first time to our knowledge, it has been experimentally demonstrated a polarization-independent passive ultrafast harmonic mode-locked ring fibre laser operating at 1.56 μm achieved with a simple low-cost set-up and the use of an InN-based SESAM, which in combination with a 1-km-long SSMF cavity, delivers femtosecond pulses with a peak power of 650.5 kW, the highest obtained to date, to our knowledge, in this kind of lasers. References [1] F. B. Naranjo et al., Appl. Phys. Lett., Vol. 98, no. 3, p. 031902 (2011). [2] M. Jimenez-Rodriguez et al., Opt. Express, Vol. 25, no. 5, p. 5366 (2017).

Mode-locked fibre lasers are stable, compact, and are capable of producing ultra-short pulses. Because of these desirable salient characteristics, the range of fibre laser applications are on the rise, and so too is the need for improved performance [1]. We present here a new design for mode-locked fibre laser operating in the all-normal dispersion regime. Previously we have presented a mode-locked fibre laser design that contains two segments; the main loop cavity that is uni-directional and a bi-directional nonlinear amplifying loop mirror (NALM) that acts as the mode-locking mechanism of the laser[2]. Here we demonstrate that incorporating a third Yb-doped fibre third gain medium inside the main cavity significantly improved both the output power and the ease of mode-locking. Remarkable both the additional gain segment and the NALM can be pumped by the same laser diode making this design more efficient than the previous one. Previous endeavours have shown that with the two gain media architecture, the laser successfully mode-locks at repetition rates between 500 KHz and 10MHz, however, this architecture suffered from lack of pulse energy, hence requiring additional amplifiers before they could be used in practical applications. The incorporation of a third gain medium has proved useful in improving the output power and bandwidth, and because the new design utilises the same number of components (which are all polarizing-maintaining), we also preserve costs. Operating at 1030nm and with a repetition rate of 5.6MHz, we characterised and compared the laser before and after the insertion of the third gain media. We saw an improvement of average output power from 4mW to 9mW of power corresponding to 1.6 nJ of pulse energy. The spectral bandwidth is about 17 nm and upon taking a FROG trace, we find a pulse width of 16ps with a linear chirp. The linear chirp of the pulse allows us to compress the pulse using a single transmission grating (1600 lines/mm). The prism-grating compressor has an efficiency of 70%, and produced a compressed pulse duration of 291fs with an output pulse energy of 1.1nJ. The autocorrelation shows that the bulk of the energy is contained in the centre of the peak and that the side-lobes, although noticeable, hold little energy. It has been observed that the laser mode-locks and single pulses more easily with a third gain medium. We attribute this to the bi-directional pumping of the gain medium in the NALM which produces a more uniform inversion profile. In conclusion the incorporation of a third gain medium has shown favourable results; increased output pulse energy, reliability in self-starting, ease of mode-locking and output pulses exhibiting linear chirp which allows for compression. Said features are largely attributed to the interactions of the third gain medium with the NALM to create uniform gain. All the while, utilising the same number of components and preserving costs. Further work will be done to test and optimise the laser architecture which will be tailored towards the purposes of micro-machining. [1] M. E. Fermann and I. Hartl, “Ultrafast fiber laser technology,” IEEE Journal of Selected Topics in Quantum Electronics, vol. 15, no. 1, pp. 191–206, 2009. [2] C. Aguergaray, N. G. R. Broderick, M. Erkintalo, J. S. Y. Chen, and V. Kruglov, “Mode-locked femtosecond all-normal all-pm yb-doped fiber laser using a nonlinear amplifying loop mirror,” Opt. Express, vol. 20, pp. 10545– 10551, May 2012.

We present an ultrafast fiber laser system at a central wavelength of 1750 nm for imaging applications, in particular 3-photon microscopy. It generates an output pulse train with an adjustable repetition rate ranging from 1 MHz to 21 MHz. After temporal compression the pulse duration is 220 fs and the maximum achieved pulse energy is 20 nJ. The laser system consists of a polarization maintaining (PM) Erbium-doped fiber oscillator which emits a stable output pulse train at a fixed repetition rate of 42 MHz. The oscillator generates soliton pulses centered at a wavelength of 1560 nm and a spectral width of 7 nm. Mode-locking is initiated and stabilized by a semiconductor saturable absorber mirror. The output pulses are picked in a PM fiber coupled acousto-optic modulator to an adjustable repetition rate of 1 – 21 MHz. A consecutive Erbium-doped PM fiber amplifier (EDFA) boosts the energy of the soliton pulses from pJ to nJ level. The directly emitted pulses have a duration of 2 ps which can be compressed to a pulse duration of 115 fs by using a passive standard fiber. The uncompressed pulses are soliton-self-frequency shifted by Raman scattering to wavelengths longer than 1700 nm in 7 m of passive PM1550 fiber at a pulse energy of 1.1 nJ. The central wavelength can be adjusted by the pump power of the EDFA. To boost the pulse energy of the wavelength shifted pulses, the Raman stage is followed by a single-clad Thulium-doped fiber (TDF) amplifier. It consists of a 1560/1750 nm wavelength division multiplexer (WDM) and 0.9 m of TDF. To diminish nonlinear effects during amplification, the pulses are stretched with 25 m of normal dispersion fiber (NDF) inserted between the WDM and the TDF. Although on the very short wavelength amplification band, the pulses are amplified up to more than 40 nJ of pulse energy at an injected pump power of 4.1 W. After the fiber amplifier, the pulses are coupled out and propagate through a spectral filter, a triplet of l/4, l/2, and l/4 waveplates, an isolator, and a grating compressor. As the WDM, NDF, and TDF are not PM, the polarization state has to be readjusted to linear with the waveplates before entering the isolator. The added group delay dispersion of 2.17 ps2 by the NDF is compensated in a free space standard grating compressor built of two 600 lines/mm gratings. The transmission of the grating compressor is 60 %. To achieve optimum compression to a pulse duration of 220 fs at a pulse energy of 20 nJ, the compressor in combination with spectral filtering around 1750 nm has to be carefully adjusted. The maximum output pulse energy of 20 nJ is constant ranging from 1 MHz to 7 MHz, but is reduced at higher repetition rates down to 8.7 nJ. The output pulse duration is nearly constant at 220 fs for all repetition rates. Further amplification of the pulses is currently under investigation. This system will be used in future for the application of 3-photon microscopy.

Laser facility such as Megajoule Laser dedicated to laser-matter interaction including inertial fusion need pre-amplification modules (PAM) which must respect a high beam quality. The actual Nd:Phosphate is used in high energy laser system because of its capacity to be produced in big size. The current PAM work at a repetition rate of 1 shot/5 min limited by a low thermal conductivity of the Phosphate glass. However, it would be interesting to increase the shot rate for alignment and diagnostics purposes. Therefore we propose to change this amplification material by some Nd:crystal in the PAM with a higher thermal conductivity and working at 1053 nm to match the power chain wavelength. For long time Nd: CaF2 has been abandoned because of quenching between Nd ions. The lutetium is “buffer” ion used to break Nd clusters and allow high emission cross section. The Nd Lu:CaF2 thermal conductivity is ten times higher than actual Nd:Phosphate and would permit to achieve a repetition rate at 10 Hz. Nevertheless, this material must fulfil the beam specifications to be integrated in the actual amplification chain. We report a characterization of the thermal induced effects on a parallelepiped rod pumped transversally by laser diodes. The pomp-probe beam configuration contains laser diodes emitting at 797 nm with a fluency of 13 J/cm2 and a probe beam passing through the rod at 1053 nm We study the spatially resolved induced birefringence under a mono-shot pump or variable repetition rates. The experimental setup is composed with a cross-rotating polarizer-analyzer and a camera that measures the intensity signal transmitted by the analyzer. A post numerical analysis consists in fitting the intensity signal transmitted for several polarizer-analyzer angles all over the camera picture. Hence the birefringence can be determined spatially at the end front of the rod. These measures are resolved in time to compare the relaxation behaviour of these two materials. Then we simulate the experiment setup with COMSOL software that includes the thermal and mechanic multiphysics interaction. The objective is to assess physical effects we cannot determine by measures like the mechanical stress induced at the origin of the birefringence pattern. We numerically solve the thermal equation. The thermal source defined must fit the experimental pump geometry and time mono-shot pulse rate or variable repetition rates. We take in account of the Beer-Lambert’s absorption law and supergaussian profile for geometry and time definition. Then we use Hooke’s law in general case for free-elastic material linked to the thermal distribution to deduce the stress and strain induced in the material. The induced birefringence is directly associated to the piezo-optic tensor and the stress material. The stress tensor COMSOL computes allow reconstructing the Jones matrices throughout the rod and thus the spatial birefringence. The numerical spatially and time resolved birefringence is in good agreement with experimental measures. This numerical model allows us to optimize the spatial geometry of cooling in transverse pumping as in longitudinal pumping in thick disk amplifier. CPER#16004205 FEDER#2663710

Energy-transfer processes strongly affect the performance of lanthanide-doped photonic devices. In this work, we introduce a simple stochastic model of energy-transfer processes and successfully apply it to the example of crossrelaxation (CR) and energy-transfer upconversion (ETU) in amorphous Al₂O₃:Tm³⁺ waveguides on silicon intended for lasers operating at ~2 μm. The stochastic model is based on the rate-equation formalism and considers two spectroscopically distinct ion classes, namely single ions and ions with neighbours (pairs and clusters), with the corresponding ion fractions being dependent on the doping concentration. We prove that a more accurate description of the luminescence properties of amorphous Al₂O₃:Tm³⁺ is obtained when accounting for the presence of these distinct ion classes. Based on the developed model, we derive microscopic CR and ETU parameters of CCR = 5.83×10^-38 cm⁶ s ^-1 , C_ETU1 = 0.93×10^-40 cm⁶ s ^-1 , and C_ETU2 = 7.81×10^-40 cm⁶ s ^-1 , and determine the laser quantum efficiency η_q of excitation of Tm³⁺ ions in the upper laser level. For the maximum Tm³⁺ concentration of 5.0×10²⁰ cm^-3 studied experimentally in this investigation, η_q reaches 1.73. Furthermore, the transition cross-sections at the pump and laser wavelengths are determined. For the ³H₆ → ³F₄ transition, the maximum stimulated-emission cross-section is σ_e = 0.47 × 10^-20 cm² at 1808 nm.

In this paper, we focused on the size effects of GdVO₄:2mol% Dy³⁺ and DyVO₄ particles on their structural and optical properties. Highly crystalline particles of different sizes and morphologies with tetragonal zircon-type phase were successfully synthesized by using different techniques of synthesis, such as reverse micelles, co-precipitation and hightemperature solid-state methods. The prepared samples exhibited a number of similarity and diversity in structural and optical properties with a decreasing in particle diameter.

This article draws a parallel between the development of electronics and the rise of photonics. Two technologies whose components are based on the same raw material: sand, which is used both to produce glass used in almost optics components and silicon for all integrated electronics devices. The analogy does not end there: carriers, information vectors, transport cables, generators ... photonic reach gradually all the basic elements that made the success of electronics. The last missing element was the transistor, which is at the heart of electronics but, the first optical transistor was realized in 2009. Beside inorganic materials, the new research attainments show that organic materials or carbon based materials like graphene could be also successfully use for electronics and photonics. Hence, the new trends in physics and technology are the plastic electronics and plastic photonics and carbon will replace maybe in the future the silicon technology. Today we transform the solar energy in electricity energy because most of the devices that we use are based on. Withal, the progress in photonics integrated circuits shows that the photonics informatics could be one day possible too. The progress in photonics provides the opportunity to replace the electron flow, for transmission and computing, with a photonic flow or a plasmonic flow; harnessing the interaction between the surface electrons of nanostructured circuits and photons and in the future maybe the light will replace electricity to run our computers. The optical manipulation and optical engines concept were also already demonstrated experimentally. If the laser propulsion will be achieved, and the optical engines will work, the next questions that could rise are “It will be still necessary to transform the solar energy in electricity?” or, “Will be possible to use directly solar energy by creating new devices runs by photons or plasmons and not by electrons?”

Single-frequency Yb³⁺ and Er³⁺:Yb³⁺ fiber amplifiers (YDFA/EYDFA) in MOPA configuration operating at 1064 nm and around 1550 nm are promising candidates to fulfill the challenging requirements on laser sources for the next generation of interferometric gravitational wave detectors (GWDs). They offer high beam quality, long-term stability and allow for excellent thermal management. We developed an engineering fiber amplifier prototype at 1064 nm emitting around 200W of linearly-polarized light in the TEM₀₀ mode. The system consists of three modules: the seed source, the pre-amplifier and the main amplifier. The modular design ensures reliable long-term operation, decreases system complexity and simplifies maintenance procedures and repair. In addition, commercial available fibers increase the flexibility of the entire system. We also developed and characterized a fiber amplifier prototype at 1556 nm that emits 100W of linearly-polarized light in the TEM₀₀ mode. The EYDFA is pumped off-resonantly at 940 nm to enhance the Yb³⁺-to-Er³⁺ energy transfer efficiency and enable a higher amplified spontaneous emission (ASE) threshold. In addition to that, we performed measurements to study phase to intensity noise coupling via the Kramers-Kronig relation above the stimulated Brillouin scattering (SBS) threshold, as it was proposed based on numerical simulations. This effect is based on an asymmetric gain spectrum, which we measured experimentally and used for the reconstruction of the broadband excess intensity noise.

The importance of average power scaling of fiber lasers (FL) is well known. However, power scaling is strongly limited by factors such as thermal load, and non-linear effects. An alternative path for reaching high powers utilizes the stimulated Raman scattering mechanism, and harnesses its power and brightness enhancement potential to reach high average power, high brightness FL. kW scale Raman FLs have been demonstrated, however they are in core-pumping configurations, meaning that they require an a-priori existing brighter kW laser that acts as their pump modules. There have been only a few publications of Raman FLs where the generated signal has a higher brightness than the pump source at levels of ≥100W, the highest, being at 250W. Here we report a strictly all-fiber clad pumped Raman FL with a CW power output of 800 W with a conversion efficiency of 80%. To the best of our knowledge this is the highest power and highest efficiency Raman FL demonstrated in any configuration allowing brightness enhancement (i.e clad pumped or graded index fiber, excluding step-index core pumped), thus being the first kW-class Raman FL with brightness enhancement. This result was achieved with a specially designed triple-clad fiber (TCF). The core was 25 μm, 0.065 NA, and the inner cladding was 45 μm 0.22NA. The choice of the small inner clad allows obtaining sufficient Raman gain without requiring too long a fiber, as well as being compatible with the waist size of the pump source fiber. In addition this diameter complies with the inner-clad/core ratio which prevents generation of a 2nd Stokes laser beam. Two fiber Bragg gratings at 1120 nm written onto the TCF, were employed as the oscillator’s reflectors. The cavity was pumped by a lower beam-quality source with an M² of ~8 at 1070 nm. The Raman signal generated in the core, at the first Stokes wavelength of 1120 nm, showed an improved beam-quality in relation to the pump.

The recent MINERVA project set out to develop new supercontinuum sources operating from 2μm up to (and beyond) 10µm together with related enabling technologies, and deploy them in a spectral-imaging system aimed at the early detection of certain cancers. As part of the project a number of Acousto-Optic devices suitable for operation with the new generation of supercontinuum sources were developed. The design and performance characteristics of any AO device are influenced by the operational wavelength. In particular, the acoustic power and hence the RF drive power required to achieve efficient diffraction scales non-linearly with increasing wavelength. As a result, care must be exercised when designing an AO device for operation at wavelengths above about 1µm, and at wavelengths beyond about 2μm the drive power requirement and consequential management of RF/acoustic energy becomes a significant issue. The criteria for selecting the most appropriate AO interaction medium is reviewed, with an emphasis on factors affecting operation at IR wavelengths. We describe some of the devices developed for operation in the 2μm-4·5μm region. These include an AO Q-Switch for operation at 2·9μm and its deployment in a record peak-power Er:ZBLAN fibre laser. Together with a series of narrowband AO Tunable Filters specifically configured for operation with single spatial-mode white-light sources. The devices, based on the quasi-collinear AO interaction utilise the acoustic power with good efficiency, reducing the required drive power. Finally we describe a technique that is particularly suited to large-aperture AO devices such as imaging AO Tunable Filters.

Development of broadband supercontinuum sources has been studied since decades for its high application potential in various fields like spectroscopy, medical science and others. First experiments were made with silica but the results shown the need to find new materials for supercontinuum generation in the IR wavelength range. Two types of materials have been found interesting for supercontinuum generation: chalcogenide and tellurite glasses. These materials have a high non-linear refractive index and a good transmission in infrared which provides a high potential for applications. Bulks tellurite glasses transmit until 5µm while bulks chalcogenide glasses transmit until 12-20µm depending on their composition. We report here the synthesis of low-OH step-index tellurite fibers and their linear and non-linear characterization. The synthesis is firstly realized by build-in-casting in a glovebox which allows to get a large-core preform(∅clad/∅core  2) and a large core corresponding fiber(∅core  60µm). Then, the rod-in-tube technique allows, from the jacketing of the stretched initial preform, to get a small-core preform and subsequently a small core fiber (∅core  3.5µm). The minimum of losses of the large-core fiber is below 1dB/m, the IR transmission wavelength exceeds 4 µm on several meters of fibers and reaches more than 5 µm on small samples (several centimeters long). We have developed core-clad composition with a large refractive index difference (∆n=0.132) which provides a high confinement in our step-index fibers. We discuss the supercontinuum generation in these fibers exploiting numerical simulations based on the generalized nonlinear Schrödinger equation and then we present the supercontinuum experimental results obtained between 1 and 5µm. Most of pollutant and greenhouse gases emitted by human activity, including methane, carbon dioxide and nitrous oxide, absorbs in the mid-IR. The spectroscopic experiments realized on the gases through supercontinuum generation between 1 and 5 µm are presented.

In this communication, we present a spectroscopic study of Dy³⁺ -doped and Tm³⁺ -Dy³⁺ codoped CaF₂ as promising candidates to develop solid-state laser sources around 3 μm. In view of the preliminary experimental results, we first demonstrate the advantage of Tm³⁺ ions as sensitizers to improve the excitation of Dy³⁺ ions in CaF₂ and then is highlighted a singular behavior of Dy³⁺ doped CaF₂ crystals that present a multisite character due to clustering of rare earth ions. The spectroscopic characteristics of each site is studied and discussed, as well as the potential of Tm³⁺ codoping for laser applications around 3μm.

The modeling and design of fiber lasers is an essential element of their development process. One of the areas of particular interest during the last years is the development of lanthanide ion-doped fiber lasers which operate at wavelengths exceeding 2000 nm. There are two main host glass materials developed for this purpose: fluoride and chalcogenide. One of the main specific aims of this contribution is therefore to comparatively study the properties of various numerical algorithms applicable to the design and modeling of fiber lasers operating at wavelengths exceeding 2000 nm. Hence, the convergence properties of selected algorithms implemented within various software environments are studied with a particular focus on the CPU time and calculation residual.

This work focuses on the fabrication processes and photonic assessment of SiO₂-SnO₂:Er³⁺ monoliths. To obtain the crack-free and densified system, the sol-gel derived synthesis protocols and heat-treatment processes were optimized. The absorption measurements were employed to assess the effect of the heat-treatment on the samples and specially to estimate the –OH content. The XRD patterns were used to investigate the crystallization as well as the structure of the monoliths. The emission spectra, performed at different excitation wavelengths, evidence the presence of Er³⁺ in the SnO₂ nanocrystals and the energy transfer from SnO₂ to the rare earth ions. In addition, the efficient role of SnO₂ nanocrystals as Er³⁺ sensitizers are also experimentally confirmed in this system.

Tamm plasmon polaritons (TPPs) are excellent candidates for photonic device application for their intriguing properties and simple fabrication design. In this study, optical Tamm structures are fabricated by depositing silver thin film on onedimensional photonic crystals (1DPhCs), constituting twelve pairs of alternating quarter wave thick SiO₂ and TiO₂ thin films. Carbon quantum dots (CQDs) were incorporated in the TiO₂ matrix of the final four pairs of the 1DPhCs. TPPs are observed in the reflectance spectra of the samples with and without CQDs. With the help of transfer matrix method electric field intensity distribution profile is obtained. It is observed that the electric field is confined and enhanced at the metal-1DPhC interface and decays within the 1DPhC. Comparison of PL emission from samples with and without CQDs in the last four layers are presented. Enhanced PL emission from CQDs corresponding to the TPP mode and suppression of emission within the photonic stop band is demonstrated.

In data transmission systems there are applications where lateral coupling light is requested. Fluorescent optical fibers radiate light as a response to incident illumination along the side. Because of photosensitivity along the side, the plastic photo-luminescent fiber is considered a flexible coupling alternative of the light, instead of discrete position coupler or tap. Fluorescent optical fibers have been investigated for data transmission applications. With commercially available fluorescent fiber for the optical bus system and smartphone based data transmission (ASK modulation) the data rates up to 500Mbit/s are feasible, by selecting the right parameters such as short fluorescence lifetime, spectral region of the fibers correlated with light sources and photodetectors and in-fiber low spectral attenuation. The application is useful in automotive applications for data transmission and distributed sensing.

Two realizations of the time-resolved pump-probe method have been applied to study comparatively the nonlinear optical response of chalcogenide glasses of the system As-S-Se illuminated by femtosecond laser pulses near their fundamental absorption band edge and near the two-photon absorption band edge. In such conditions, charge carrier’s photo-excitation is going on with participation of gap states. By comparison of the results of measurements and numerical modeling, we have demonstrated that character of the nonlinear optical response depends on how a glass samples was illuminated. If the pump pulse frequency corresponded to the Urbach tail of a glass sample, the carriers trapping and excitons formation was followed by the excitons absorption and excitation of conduction electrons. If a sample was illuminated at the red-edge of its Urbach tail, the photo-excitation was going through the gap states, but excitation of conduction electrons was followed by excitons formation. Due to these peculiarities, calculated spacial distribution of the photo-induced refractive index variation in the sample was different depending on the illumination conditions.

Fully fibered microwave-optical sources at 1.5 μm are studied experimentally. It is shown that the beat note between two orthogonally polarized modes of a distributed-feedback fiber laser can be efficiently stabilized using an optical phaselocked loop that uses the pump-power induced-birefringence as actuator. Beat notes at 1 GHz and 10 GHz of Erbium doped fiber laser are successfully stabilized to a reference synthesizer, passing from the 3 kHz free-running linewidth to a stabilized sub-Hz linewidth, with a phase noise as low as -75 dBc/Hz at 100 Hz offset from the carrier. An ErbiumYtterbium co-doped fiber laser is also investigated and successfully stabilized. Such dual-frequency stabilized lasers could provide compact integrated components for RF and microwave photonics applications.

This work investigates a concept of coupled fiber lasers exhibiting PT-symmetry and a PT-transition between PTsymmetric and PT-broken lasing states. We consider a system operated via Raman gain comprising two fiber loops (ring cavities) connected to each other by means of two fiber couplers with adjustable phase shift between them. By changing the phase shift or/and amplification (loss) in fiber loops, one can switch between generation regimes, realizing either PTsymmetric or PT-broken solution. In the PT-symmetric lasing regime, equal powers are generated in both cavities despite only active one is pumped. We make theoretical and numerical description of the proposed coupled fiber lasers starting with the simple discrete matrix model taking into account coupling, phase delays, gain (which is assumed to be saturated), losses and nonlinear phase shift. We show how the PT-transition is affected by self-phase modulation inside the fiber cavity and investigate requirements that should be met in order to observe PT-transition experimentally despite Kerr effect that violates exact symmetry conditions. In particular, we show that PT-transition may be observable only near lasing threshold. Further on we adopt more sophisticated model based on Nonlinear Schrödinger equation for PT fiber laser. Taking into account quasi-CW polychromatic radiation with typical spectral bandwidth of fiber Raman lasers, chromatic dispersion and Kerr nonlinearity, we demonstrate both PT-symmetric and PT-broken lasing in a fiber laser.

The propagation of a light beam through a photo-sensitive photopolymer Polyvinyl Alcohol/Acrylamide (PVA/AA), and the creation of self-written waveguides (SWWs), has received much attention. Here we explore the manufacture and characterization of SWWs in PVA/AA for applications at near infrared communication wavelengths 850nm and 1300nm. The SWWs are fabricated using visible light at wavelength 532nm. The insertion and optical loss of the SWWs at different wavelengths will be interrogated. An optical loss and attenuation profile is to be built up for each of the three wavelengths as they propagate down the resulting SWWs.

The numerical simulation of a regenerative amplifier based on codoped Tm,Ho:YAG is presented. Within this work, a maximum pulse energy of 3.1 mJ is observed for 0.9 kW CW end-pumping at 785 nm. The simulation results demonstrate that interionic mechanisms such as upconversion and energy transfer significantly influence the population of states and consequently, the amplification. In detail, the most dominant mechanisms are identified by introducing the rate term k_xN_iN_m as a quantity to compare the strength of all occuring interionic mechanisms. It can then be shown that the energy transfer mechanism E₆₅₁₂ between Holmium and Thulium ions is the greatest source of population loss for the upper lasing state ⁵ I₇ in Holmium. In summary, the presented model represents an efficient tool to characterize the influence of interionic mechanisms on the extractable energy in solid-state media under pulsed operation.

Since an extension of spectral region from near-infrared to mid-infrared covered by fiber lasers belongs to ambitions of today’s research, germanate-based glasses have been proposed, fabricated and their optical properties studied. Glass samples were prepared by Modified Chemical Vapor Deposition method and by conventional glass melting processes. Fabricated preforms suitable for fiber drawing were optically characterized by refractive index and absorption spectra measurements. A limit of rare earths doping of GeO₂-based glasses without phase separation was found comparable to SiO₂-based glasses (thousands of ppm). Preforms prepared by Modified Chemical Vapor Deposition contained only up to 29 mol. % of GeO₂ in core, although pure GeO₂ glass layers were deposited. This effect caused transparency limitation of such materials to 2-2.5 μm. Implementing of effective drying processes during GeO₂-based glass conventional melting lead to decrease of residual OHcontent to the level comparable with optical silica glass HOQ 310. The shift of infrared transmission edge of bulk GeO₂-based conventionally prepared glasses to longer wavelengths towards to 5 μm was observed. These facts support the idea of potential use of GeO₂-based glass matrices for fiber lasers operating in mid-infrared region

Here we discuss the light transmission modulation by periodic and disordered one dimensional (1D) photonic structures. In particular, we will present some theoretical and experimental findings highlighting the peculiar optical properties of: (i) 1D periodic and disordered photonic structures made with two or more materials^1,2; (ii) 1D photonic structures in which the homogeneity³ or the aggregation⁴ of the high refractive index layers is controlled. We will focus also on the fabrication aspects of these structures.

Near-infrared emission in barium gallo-germanate glasses containing rare earth ions for broadband optical amplifiers were studied. Among the rare earths, the trivalent praseodymium and cerium ions were selected as an optically active dopants. In order to examine the spectroscopic properties of these glasses doped with Pr³⁺ and co-doped with Ce³⁺ and Pr³⁺ ions the luminescence spectra were registered. The energy transfer processes between cerium and praseodymium ions in barium gallo-germanate glasses have been also investigated. The intense near-infrared luminescence bands corresponding to characteristic transitions of Pr³⁺ ions in singly and doubly doped glass systems were observed. It has been proved that our glasses exhibit intense 1.5 μm emission originating from ¹D₂ → ¹G₄ transition of Pr³⁺ under direct excitation (445 nm). Moreover, the experimental results indicated that energy transfer between Ce³⁺ and Pr³⁺ is not effective for barium gallo-germanate glasses.

This work demonstrates a new simulation technique, which combines the previously published Dynamic Mode Analysis with the coupling of arbitrary sets of rate equations. Those arbitrary sets include the representation of gain media, which state population is influenced by interionic mechanisms. Especially the state population of Er:YAG is strongly influenced by upconversion and cross relaxation, which impacts the population inversion and the generated heat load. Therefore, the simulation of a resonator based on 50%-doped Er:YAG is performed and compared to experimental results. The accuracy of the presented technique is pointed out by a fine agreement between simulation and experiment with respect to gained cw output power and slope efficiency. Moreover, a finite element analysis of the heat load and the 3-dimensional population inversion in the crystal is illustrated.

To emphasize the scientific and technological interest in the silica-based glassy systems and the versatility of the sol-gel route, nano and micrometer scale structures are discussed focusing the attention mainly on the rare-earth-activated materials and their spectroscopic characterization. We have demonstrated that various SiO₂-based binary systems can be successfully employed for the fabrication of amorphous planar waveguides, glass–ceramic waveguides, and tapered rib waveguide laser. Different technological processes allowed to realize Er³⁺ -activated microspheres that can be exploited as microresonator and it has been evidenced that through specific coating it is possible to modify modal free spectral range and/or modal dispersion of the microresonator and achieve laser action. In the case of rare-earth-doped 3-D colloidal crystals in different configurations (direct and inverse one), it has been shown that the relaxation dynamics of the electronic states can be engineered.

In this paper we show the analysis of Thulium Doped Fibre Amplifier(TDFA) gain dependence on pump laser wavelength and thulium doped fibre length. Thulium doped fibres of lengths varying from 0.5m to 3m are pumped with 785nm and 1550nm lasers in single and dual pumping schemes. Small signal gain up to 16dB was achieved at 2μm for a low pump power of 150mW. A potential wide amplifications bandwidth ranging from 1680nm to 2025nm is observed in the Amplified Spontaneous Emission(ASE) spectrum.

This work focuses on the simulation and modeling of a passively Q-switched dual-cavity fiber laser doped Yb:Yb, to our knowledge, it is for the first time that the progressive wave model is applied to this type of laser, a good agreement between our simulation results and the experimental results published by another team is obtained, two pulse trains are produced by this laser, the first is at the wavelength of 1064 nm, and the second is at 1100 nm, we also show that certain parameters such as the concentration of Yb ions and their length are an important parameters for the optimization of the two laser signals at 1064 nm and 1100 nm.

We report on the characteristics of silicon oxycarbide films deposited by reactive radio frequency magnetron sputtering of a silicon carbide target in the presence of argon and oxygen gases. Quantitative characterization of the silicon oxycarbide films is performed extensively by ellipsometry, scanning electron microscopy and atomic force microscopy. Integrated photonic waveguides are demonstrated in silicon oxycarbide films.

Micro-structures offer superior functions such as superhydrophobicity, selfcleaning, anti-wear and drag reduction. In this paper, various microstructures were fabricated by rear-side picosecond laser irradiation of two-layer materials. The material of underlying layer was commonly commercial available ink; the material of surface layer was PMMA. The high light absorptivity of underlying material result in significantly reduced absorption depth. The laser source could therefore be regarded as plane heat source, leading to better surface morphologies after the mater-laser interaction. The results showed that convex structures were obtained at a lower laser fluence; with increase of laser fluence, a doughnut-like structures were obtained; with further rise of laser fluence, bowl-like structures would be obtained. Moreover, the size of microstructures could be tuned by adjusting laser processing parameters such as laser power, frequency and laser-mater interaction time. This method provides an insight for fabrication of functional surface.

Formation of rare-earth doped nanoparticles into silica matrix has been modelized by Molecular Dynamics simulations. Preforms with molar composition 0.10MgO–0.90SiO₂ and 0.01EuO_3/2–0.10MgO–0.89SiO₂ have been investigated to have an insight on the structure and chemical composition of the nanoparticles, as well as the rare-earth ions local environment and their clustering. We have finally applied a uniaxal elongation of the rare-earth doped preform in order to mimic the drawing step that changes a preform into a fiber. We present herein first results on the modification of the nanoparticles size distribution.

White light emitting devices have attracted great attention for their use in liquid crystal monitor screens and white light emitting diodes (W-LEDs). Glasses singly or doubly doped with lanthanide ions may be good white light emitters. In particular, various glass systems containing Pr³⁺ were studied from this point of view. In this work, germanate glasses doubly doped with Ce³⁺ and Pr³⁺ ions were prepared by traditional melt quenchingtechnique. The excitation and emission spectra of lanthanide ions were measured. The emission bands corresponding to characteristics transitions of Pr³⁺ and transition of Ce³⁺ ions from 5d level to 4f levels (²F_7/2 and ²F_5/2) are quite well observed. It indicates that the energy transfer process between Ce³⁺ and Pr³⁺ ions in germanate glasses occurs. From the emission spectra, the Commission Internationale de I’Eclairage (CIE) chromaticity coordinates (x, y) were calculated in relation to potential application for white LEDs. Luminescence decay analysis is also presented and discussed in details. The obtained results suggest the possibility of using these Ce³⁺/Pr³⁺ co-doped glass systems for future application to white light generation.

Microresonators are very suitable for sensing application and investigation of nonlinear effects, due to their enormous quality factor and small mode volume. These properties can be extended to the mid-infrared spectral range by creating microresonators from chalcogenide glasses, which are transparent in the mid-infrared and have large third-order optical nonlinearity. We present the analysis of the nonlinear effects observation in chalcogenide microspheres created by inert gas heating.

We report on the transverse mode selection in an all-fiber CW Raman laser based on a multimode graded-index fiber directly pumped by multimode laser diodes. Selection properties of special fiber Bragg gratings inscribed by UV CW or IR femtosecond radiation in the 100-μm core of graded-index fiber are experimentally compared. It is also theoretically explained why the better fundamental mode selection occurs in the femtosecond fiber Bragg grating inscribed in the fiber with lower core diameter. Fibers with core diameter of 62.5, 85 and 100 um are compared in the experiment. With core enlargement, the output power and slope efficiency increase sufficiently (from 47% to 84%) at the expense of slight beam-quality parameter increase (M² =1.3-3).

In present paper correlations between different parts of spectrum of a fiber laser with randomly distributed feedback (RDFL) were experimentally measured directly. Implemented statistical analysis demonstrate weak cross-correlations between different lines in generation spectrum. These correlations were vizualized by plotting 2-D probability density functions. Linear correlation coefficient (Pearson coefficient) was calculated for each pair of spectrum lines.

We report on the investigation of an approach for modelling light transmission through systems consisting of several jointed optical fibres, in which the analytical modelling of the waveguides was replaced by Finite Element Modelling (FEM) simulations. To validate this approach we first performed FEM analysis of standard fibres and used this to evaluate the coupling efficiency between two singlemode fibres under different conditions. The results of these simulations were successfully compared with those obtained using classical analytical approaches, by demonstrating a maximum loss deviation of about 0.4 %. Further, we performed other more complex simulations that we compared again to the analytical models. FEM simulations allow addressing any type of guiding structure, without limitations on the complexity of the geometrical waveguide cross section and involved materials. We propose as example of application the modelling of the light transmitted through a system made of a hollow core photonic crystal fibre spliced between two singlemode standard optical fibres, and qualitatively compare the results of the simulation with experimental results.

We have developed a comprehensive 3D steady-state numerical model of high power Yb-doped fiber amplifiers which allows the investigation of thermally induced multimode behavior being the reason for the transversal mode instabilities phenomenon. Numerical simulations show that for the pump powers above 3 kW the refractive index grating inscribed as a result of thermo-optic effect supports an efficient energy transfer from the main mode to high order modes. Coupling of the initial Gaussian beam without any shift or tilt to the investigated amplifier leads to the preferential excitation and further growth of symmetrical high order modes (LP₀₂, LP₀₃). Anti-symmetrical modes are not growing. Increasing the pump power leads to stronger mode coupling which is related to the increase of the amplitude and frequency of the temperature oscillations and corresponding refractive index oscillations over the longitudinal axis of the fiber amplifier.

We have developed a fiber-based laser source operating at 515 nm. The experimental setup is composed of a 1030 nm picosecond fiber laser, a Volume Bragg Grating (VBG) based compressor, and a Second Harmonic Generation (SHG) module. The 1030 nm picosecond fiber laser is made with an ANDi mode-lock all-fiber oscillator using a tilted Fiber Bragg Grating (FBG) for spectral filtering. A bandpass filter centered at 1030 nm permits to reduce the bandwidth of the laser to 1.5 nm. A Chirped Fiber Bragg Grating (C-FBG) based stretcher increases the pulse duration to about 90 ps for avoiding nonlinear effects during amplification. A fiber pre-amplifier followed by a double-clad 15 µm core LMA fiber amplifier pumped with a 27 W multimode diode are subsequently used. The total available power at 1030 nm is 14 Watts. SHG is achieved with a type I non-critical phase-matching (NCPM), 15 mm long, Lithium Triborate (LBO) crystal. The 515 nm signal is near diffraction limit (M² < 1.2). The emitted average output power is 5.8 W, the pulse duration is 2.1 ps and the repetition rate is 89 MHz (SHG efficiency is 45%)

We present an experimental study on the suppression of self pulsing in a single stage pulsed master oscillator power amplifier (MOPA), using pump modulation. Many applications require pulsed lasers operating at low repetition rate. Leaving the pump on for long duration without a seed pulse leads to accumulation of amplified spontaneous emission (ASE) and generation of a self-pulse that can damage the laser. For this experiment, the amplifier was fed with peak seed power of 500 mW having a pulse width and repetition rate of 100 ns and 10 kHz respectively. To study the effect of pump modulation on self-pulsing, we carried out the experiment with both a continuous pump and with a pulsed pump. The output was characterized using a constant fractional discriminator (CFD) that generated TTL pulses, in turn fed to a frequency counter. In case of a continuous pump of 2.4 W, with a low repetition rate of 10 kHz for the seed, we noticed self-pulsing of the MOPA. We obtained a maximum amplified signal output peak power of 162 W, or a pulse energy of 7.91 μJ. A further increase in pump power could lead to permanent damage to the system. In case of pulsed pump, the generated pump pulses were synchronized with the seed laser and had a 50 % duty cycle. The resulting output was again characterized with a CFD and counter. We were able to increase the pump power to 6.5 W with an output peak power of 160 W and pulse energy of 9.37 μJ without any sign of self-pulsing. Thus, using a simple method of pump modulation, we were able to reduce the accumulation of ASE and suppressed the phenomenon of self-pulsing at low repetition rates of the seed laser.

Visible light communication (VLC) has been extensively studied for car-to-car (C2C) communication due to its inherent benefits. It is the idea of using light-emitting diodes for both illumination and data communications. The main motivations are longer lifetime of high-brightness light emitting diodes (LED) and growing popularity of the solid state of lighting sources compared to other sources of artificial light. These two features have made a whole range of developing applications such as C2C communication since the level of reliability and power efficiency offered by LED are excellent compared to the traditional incandescent light sources used for lightning. Car industry and automobile lighting market are more and more motivated also to use Laser diodes instead of LED because of higher intensity (Power). Fiber Laser and Glass Photonics could be the next generation components for carto-car VLC. This paper presents the main features of physical layer for VLC based on the IEEE 802.15.7 standard including useful Modulations, Forward Error Correction Coding for single light source also a comparison to wireless RF-Technology and different weather influences are considered. These aspects would also be of main interest for safety, availability and security for autonomous driving in the future applications

Carbon nanotubes (CNTs) are one of the most promising materials for advanced electronic applications, due to its extraordinary chemical and physical properties. Non-linear interactions between photons and carbon bonds provide the possibility to fabricate unique photonic devices. In this paper we present the new technological route of single walled CNTs (SWCNTs) modification using femtosecond (fs) laser pulses to produce junctions in nanotubes through multiphoton oxidation of the carbon lattice with nanoscale resolution. SWCNTs were deposited onto Si/SiO2 substrate using gas-phase process based on thermal decomposition of ferrocene in the presence of carbon monoxide. Source and drain 100/20 nm Au/Ti electrodes were fabricated by photolithography, the gate electrode was p++ Si substrate. Samples were irradiated via fs laser with different energy fluence. Fs laser pulses at low energies were used to perform photocurrent measurements. Not modified SWCNTs and structures modified upon fs laser demonstrate a huge difference for light induced charge generation. We observed significant changes in optical and electrical properties of SWCNTs after the modification. Varying the parameters of power and laser scanning speed we can change the level of local oxidation of SWCNT and photocurrent in produced photodetectors.

We demonstrate a new technique to generate a continuous-wave supercontinuum based on the stimulated Raman effect in an Yb-based ring laser configuration. Continuously pumping this ring cavity with a maximum of 19W optical power, we were able to excite up to 6 Stokes orders and achieved wavelengths up to 1600nm. Due to the feedback mechanism of the ring cavity the generated spectrum does not exhibit plain and separated stokes peaks but the fundamental Raman nature of the spectrum is altered additional nonlinear effects. This results in a dense coverage and an almost complete excitation of the wavelength range from the laser wavelength to the highest stokes wavelength and hence in a continuous-wave supercontinuum. Since the main mechanism of broadening is the Raman effect, we do not rely on anomalous dispersion and modulation instability as typically required to seed continuous wave supercontinuum generation.

In this work, the luminescence properties of silica materials singly- and doubly-doped with Tb³⁺ and Eu³⁺ ions derived by low-temperature sol-gel technique were investigated. The optical properties of prepared samples were evaluated based on photoluminescence excitation (PLE) and emission spectra (PL) as well as luminescence decay analysis. The PL measurements of investigated Tb³⁺/Eu³⁺ co-doped systems were conducted using different excitation wavelengths. Prepared sol-gel materials exhibit bright multicolor, wavelength-tunable luminescence under near-UV illumination. Indicated emission is originated from electronic transitions within 4f6 and 4f8 manifolds of Eu³⁺ and Tb³⁺, respectively. Additionally, based on recorded decay curves, the luminescence lifetimes (τm) for the 5 D0 state of Eu³⁺ and the ⁵D₄ level of Tb³⁺ were also evaluated. Obtained results indicated that co-doping with Tb³⁺ ions led to prolongation of luminescence lifetime of the ⁵D₀ state of Eu³⁺ up to ~24% due to Tb³⁺ → Eu³⁺ energy transfer process. The interpretation of obtained results may suggests the potential usage of fabricated Tb³⁺/Eu³⁺ co-doped sol-gel materials in optical devices operating under near-UV excitation.

The 2-15 μm spectral range hosts many optical sensing applications from biology to environmental monitoring, and infrared spectroscopy is a simple and reliable way to provide fast and in-situ analysis method. Rare-earth ion emissions within chalcogenide glasses with low phonon energies proved to be efficient to address mid-IR luminescence based sensing applications. In particular, they give promising results for the development of all-optical gas sensors in the 3 to 5 μm spectral range based on IR conversion into visible light using rare earth excited state absorption mechanisms. In this article, we report the wavelength conversion of 3.4 μm radiation into 660 nm in Er³⁺:KPb₂Cl₅ bulk crystal, Er³⁺:Ga₅Ge₂₀Sb₁₀S₆₅ and Er³⁺:Ga₅Ge₂₀Sb₅S₇₀ glasses using an excited state absorption process. This wavelength conversion is the result of the excitation of Er³⁺ ions following the excited state absorption of IR photons and the Er³⁺ ions subsequent spontaneous emission in the visible domain. Using an 808 nm pumping, a 3.4 μm photon excited state absorption gives rise to a 660 nm emission. This wavelength conversion device can be further implemented for methane all-optical sensing at 3.4 μm, for the development of remote “all-optical” methane mid-IR sensors with only visible and near-IR input and output signals. This “all-optical concept” enables the use of silica fibers over large distances, thus considerably increasing the scope of possible applications.

In this paper, we report on the potential of silicon oxycarbide (SiOC) for integrated photonic applications. SiOC films are developed by reactive radio frequency magnetron sputtering from a silicon carbide (SiC) target in the presence of argon and oxygen gases. The optical properties of the developed SiOC film are characterized with spectroscopic ellispometry over a broad wavelength range 300-1600 nm. The refractive index n of the SiOC film is 2.2 at wavelength λ = 1550 nm and the extinction coefficient k is estimated to be less than 10^-4 in the near-infrared region above 600 nm. The topography of SiOC films is studied with AFM showing very smooth surface, with rms roughness of 0.24 nm. SiOC film with refractive index n = 2.2 is then patterned by direct laser-writing lithography and etched with reactive ion etching to realize high contrast SiOC core optical waveguides for integrated photonics applications. The waveguide losses are characterized at telecommunication wavelength λ = 1550 nm. As an example of photonic integrated devices integrating SiOC films, a microring resonator is fabricated where a SiOC layer is used as a coating material for the core of a silicon oxynitride (SiON) waveguide.

For the first time films of the As-Se-Te (15≤As≤40, 30≤Se≤65, 5≤Te≤30) chalcogenide system have been prepared by Plasma-Enhanced Chemical Vapor Deposition (PECVD) at low pressure (0.1 Torr). RF (40 MHz) inductively coupled non-equilibrium plasma discharge has been chosen as the initiator of chemical interaction between precursors. Elemental As, Se, and Te of high-purity were used as the initial substances. High-pure argon was utilized as career gas as plasma feed gas. The obtained chalcogenide planar materials have been studied in terms their physical-chemical properties. The films were modified by continuous and femtosecond laser irradiation.

We discuss the fabrication of 1 mol% Eu-doped 70 SiO₂–(30-x) HfO₂–x ZnO (x = 0, 2, 5 and 7 mol%) ternary glass-ceramic waveguides, and the effect of ZnO–HfO₂ hybrid nanocrystals on the optical gain in Eu-doped ternary waveguides. Formation and growth of ZnO–HfO₂ hybrid nanocrystals have been observed in the TEM images with increase of ZnO concentration in the samples. Waveguiding properties of Eu-doped ternary waveguides were measured using lab-built prism-coupling technique. Propagation losses of the waveguides were measured using photometric detection technique and found to be between (0.3 to 0.6)±0.2 dB/cm. We have further investigated the optical amplification of red emission line (⁵D₀ → ⁷F₂) of Eu-ions in these waveguides using the variable stripe length method wherein the waveguides were pumped by continuous wave 532 nm laser in a stripe-like geometry using cylindrical lens The optical gain coefficients are found to be 5.3, 4.8, 3.7 and 0.1 cm⁻¹ for ZnO concentration of 0, 2, 5 and 7 mol% respectively.

Today micromechanical gyroscopes are very popular in different areas. Solid-state micromechanical gyroscopes based on surface acoustic waves (SAW) have good vibration and shock resistance because of absence of elastic suspensions, ability to work at 50 000 g loads, small dimensions, cheap in mass production, etc. Unfortunately, there are some limits for further development of such gyroscopes because it requires prototype production in small series. In this study we are investigating laser ablation method. Earlier existing bidirectional delay line produced by photolithography method was modeled in OOFELIEMultiphysics. Frequency response of modeled bidirectional line was at the same level as for existing prototype which can be a confirmation of correct modeling process. As the next step one more prototype was produced by laser ablation method. For this prototype operational characteristics were examined and compared with photolithography bidirectional delay line and with results of finite element modeling. Results of tests and its comparison with modeling and photolithography method are discussed.

Longitudinal temperature distribution at the surface of the end-pumped Nd:YAG laser crystal was measured using tiny piezoelectric crystals as the temperature sensors. Temperature of each sensor was determined directly by measuring the frequency of its piezoelectric resonance that was noncontactly excited by probe ac electric field. Crystal sensors are transparent to the scattered radiation and can have very small size.