Frequency-Shifted-Feedback Mode-Locked Fibre Lasers are not as common as SESAM-based or figure 8/9 mode-locked ultrafast fiber lasers. It is mainly because that type of lasers requires a frequency-shifter like Acousto-Optics Modulator (AOM) which increases the complexity of the system for similar operation. Here, we took benefit of the optical transmission modulation and wavelength shifting effects of the AOM to build a fiber laser that can operate at different repetition rates. Pulsed operation (100ps) at the fundamental repetition rate (3.5MHz) of the laser cavity as well as first and second harmonics regimes have been obtained and show stable behaviour over hours.

Solid state dewetting (SSD) is a natural shape instability occurring in thin solid films when heated at high temperature: it transforms a flat layer in isolated islands. SSD can be efficiently exploited in several fields, including flexible photonics, photocatalysis or dielectric Mie resonator, to form perfectly ordered and complex nano-architectures over large scales, as well as randomly organized, isolated islands. Among the dewetting systems reported in literature, in our group SiGe dewetting, i.e. SiGe structures directly formed on an electrically insulating and optically transparent substrate, has been efficiently exploited to realize arrays of nanostructures with footprint ranging from few nm up to several μm. Additionally, dewetting of Ge, which is of particular interest for photonic devices working at near and mid-infrared frequency, has recently started to be investigated. This work purpose is to study dewetted SiGe and Ge islands and to exploit them to produce flexible films for photonic sensing applications. In particular, also an innovative approach to transfer SiGe and Ge dewetted islands into a flexible substrate such as polydimethylsiloxane (PDMS) will be presented.

This conference presentation was prepared for SPIE Photonics Europe, 2024.

Multi-scale 3D architecture with highly localized fluorescence contrast in photosensitive silver-containing glasses by means of femtosecond laser writing can be obtained. We will present results obtained on electron-irradiated glass samples by EPR spectroscopy and in-situ cathodoluminescence. This allowed for understanding the initial phenomena of electron deposition and charge trapping by identifying the nature of point defects and Ag species. In addition, a careful point defects analysis of fs-laser written silica glass as a function of the laser deposited energy for [50-500 fs] pulse durations was leaded highlighted the role of certain defects in the chemical etching of fused silica glass

We obtained 51 W of UV laser light at 343nm for 8 ns temporally square-shape pulse at 400 kHz repetition rate which corresponds to a peak power of 42.5kW and a conversion rate of 38% from a 133W linearly polarized signal at 1030nm. This high UV power is achieved by third harmonic generation of infrared beam which is generated thanks to a newly developed Ytterbium-doped rod-type high-power amplifier effectively singlemode fiber with a hybrid hexagonal and aperiodic cladding design. Two fibers with MFD at 47µm and 67µm were tested. The 47µm MFD fiber allow to reach up to 200W of singlemode signal before the TMI appearance. This fiber can deliver 150 W of 1030 nm signal with a 250 W pump light, for different nanosecond pulse durations and repetition rates with excellent beam quality (M²<1.1).

In this conference, we show the realization of a high power 2.12 μm Ho3+-doped fiber (HDF) laser integrating for the first time to our knowledge a 1.94 μm triple clad fiber (3CF) combiner. This 3CF combiner, specifically developed for the above mentioned HDF laser, presents low losses properties thanks to a low-index glass capillary implemented in the component. Moreover, in this contribution we will discuss the power scalability of such a HDF laser monolithic architecture based on a triple clad fiber combiner pumped at 1.94 μm using Tm3+-doped fiber lasers.

Lately, yellow lasers have been showing promising results for the treatment of diabetic retinopathy. In this study, a numerical model for Dy-doped yellow fiber lasers has been developed to analyze the impact of the most significant input parameters. The impact of input pump power, cavity length, and reflectivities of the mirrors on the output signal power has been studied, by evaluating the impact of the lifetime of Dy-energy levels. Additionally, an investigation of excited state absorption has been conducted. Simulation results provide valuable insights into both the qualitative and quantitative influence of these input parameters on the performance and efficiency of Dy-doped fiber lasers for yellow emission.

Currently, the development of lasers operating in the mid-infrared (MIR), is of greater interest for a wide range of applications. All pump diodes are supplied with silica fibres. Together with the high water absorption of fluoride fibers catalyzed by high pump power density, this makes it impossible to use external butt-coupling techniques to inject pump source radiation into a fluoride fiber. We proposed and implemented the idea of the side-polished (D-shaped) fiber-based pump combiner. The pump combiner with 75% efficiency has been developed. The TEC system of cooling and heating with temperature feedback allowed for a reduction in losses in the system from 1.32 dB to 1.02 dB.

We first carry out a stability analysis on the standard two-wave STRS process in frequency-detuned two-mode fiber amplifiers, in the presence of pump/signal quantum defect thermal load. We show that the standard two-wave STRS process is stable against small modal perturbations, and as such it does not describe adequately the widely observed thermally-induced TMI process. We further show that inclusion of FWM effects and three-wave interaction, through the addition of an anti-Stokes LP11 wave, is required to describe modal instabilities above a power threshold, and a previously derived TMI power threshold formula is recovered. This work sheds new light on the standard STRS process and adds new insight into its connection with TMI effects in high power fiber amplifiers.

Fiber lasers are reliable and flexible sources of high laser power with excellent beam quality. However, limitations due to nonlinear and thermal effects, hamper further power scaling. We will give an overview over relevant influencing factors for these limitations, on the component side as well as regarding system design. Experimental examples in the 1µm and 2µm spectral region will be shown for the proposed techniques to tackle several of these obstructions, with a focus on ways to suppress transverse mode instabilities. Remaining limitations for single fiber systems can be overcome by parallelization of amplification, using multiple actively doped cores running below the critically power threshold each. Such fiber cores can be housed separately or in a single multi-core fiber. We will address coherent and spectral methods to (re-)combine multiple fiber laser output beams while maintaining beam quality and discuss scaling aspects and potential limitations to these architectures.

In the era of high-power laser systems, there is a constant demand for compact and efficient short-pulsed amplifiers delivering high power with an excellent beam profile and high polarization stability. In this presentation, I will review the advantages of active tapered double-clad fiber amplifier technology and different geometrical concepts. The special geometrical architecture of tapered fibers enables the direct amplification of picosecond pulses from tens of milliwatts to hundreds of watt levels in a single amplification stage. The recent technological progress in tapered fibers led to a doubling of the average power level, preserving excellent output spatial and polarization characteristics. The spun tapered fiber features low birefringence resulting in improved polarization stability at high power levels. Moreover, this geometrical architecture is exploited for the amplification of structured light, maintaining complex polarization profiles and spatial intensity distribution.

We will report on recent advances in fabrication of large volume silica based, doped fiber preform materials synthesized via powder-based processes. Recently, there has been increased interest for power scaling in fiber based laser applications that requires large core volumes with excellent homogeneity in refractive indices, but also chemical variety (in terms of high dopant concentrations, different dopants). A structural fiber variety requires dedicated large volume core material of reproducible and tailorable chemical composition. Established technologies such as modified chemical vapor deposition (MCVD) or crucible melting rely on complex thermal processing, and are limited in accessible chemistries, dopant concentration, achievable functionalities, and in case of MCVD in achievable core sizes. The current process development thus targets to overcome such draw-backs by including novel approaches to enable extreme material combinations, enhanced reactivity, or novel functions.

Thulium-doped fiber lasers working in the 2-μm wavelength range are particularly important because they belong to the group of so-called eye-safe lasers. Although their efficiencies are getting closer to the efficiencies of the matured ytterbium fiber lasers, the record output power of thulium fiber lasers is still orders of magnitude below its potential, looking for technology breakthroughs that would overcome the current limitations. Novel fiber designs, e.g., using structured core of the active fiber, and new ways of mitigating thermal and temperature effects may enable further increase of the output power. In the paper, we will review our proof-of-concept experiment of the pedestal-free thulium doped silica fiber with a large nanostructured core, where the initial preforms of the active medium were made by the nanoparticle-doping and MCVD methods. Next, measurement of temperature-dependent thulium cross sections will be reviewed as well as application of these cross-section spectra for prediction of thulium fiber laser operation using recently derived closed form expressions for the laser threshold and slope efficiency under pumping at 790 nm by the two-for-one process.

Experimental results on optical properties of Tm-doped oxide glass fibres based on different technologies and host materials are presented. Silica fibres and crystal-derived fibres (CDF) are compared. Crystal-derived fibres offer potentially higher doping levels than those made by Modified Chemical Vapor Deposition technology providing the ability to tune optical properties towards new applications. A detailed analysis of absorption and fluorescence properties of the 3F4 and 3H4 levels within a concentration range from 0.08 up to 1.52 mol% Tm2O3 is provided resulting in an extensive and specific energy level scheme for 789nm core-pumping.

Fluoride-based fibres have attracted notable attention for their thermal properties, such as a thermal expansion coefficient that is 30 times larger than that of silica fibres. In this work, we discuss the thermal behaviour of FBGs inscribed in different fluoride-based fibres, such as ZBLAN and InF3, for application as thermal sensors for cryogenic temperatures. The FBGs were inscribed utilizing the Talbot interferometer with a Ti:Sapphire fs-laser combined with frequency-doubling crystal.

Since the 1970s, optical fibers have undergone considerable development and are now used in a very wide range of applications, covering telecommunications, environment, medical applications, etc., thanks to the development of amplifiers, lasers and sensors. Such progress has been made possible by the considerable work carried out to improve the transparency of optical fibers. In recent years, a new family of optical fibers has been developed incorporating nanoparticles. Such fibers were first envisaged as a means of locally modifying the chemical environment of luminescent ions (rare-earth and transition metal ions) in order to offer new lasers. However, the light scattering induced by nanoparticles limits this application. More recently, light scattering has instead been exploited to develop sensors (temperature, stress, chemistry, biology, etc.). This presentation will review these fibers, presenting the fabrication processes, the fundamental issues involved in nanoparticles formation and their different applications.

The integration of flexible photonics into high value composite structures, such as those made of Carbon Fibre Reinforced Polymer (CFRP) offers new intelligent sensing capability for sustainable manufacture and through-life structural monitoring. Through utilisation of the planar functionality offered by flexible photonics, within these composite matrices, enables the creation of new intelligent structures for a host of sectors including aerospace, clean energy infrastructure and automotive. This presentation highlights the design considerations needed when integrating flexible photonics into fibre reinforced polymers (FRPs) and highlights some promising opportunities that showcase specific demonstrations achieved for flexible planar doped silica. Notable applications, such as scalable tri-axial strain sensing and the implementation of a branching optical network architecture within an FRP composite, will be presented to illustrate the new functionality offered.

This presentation explores the interdisciplinary realm of nanocomposite material design, integrating materials engineering, chemistry, and photonics. Focusing on the innovative use of nanocomposite glasses containing noble metal nanoparticles, the discussion delves into the novel opportunities these materials present for developing sensing structures based on LSPR (Localized Surface Plasmon Resonance). Additionally, transparent glass-ceramics are spotlighted as high-performing materials in functional photonic applications for optical fiber technology.

We examined the potential of amorphous Ge-Bi-Se chalcogenide films prepared from RF magnetron co-sputtering.(Co)-sputtered films’ compositions were analysed using EDX spectroscopy. Pre-deposition calculations were used to find the expected composition, and a good agreement with experimentally determined compositions were observed. The amorphous to crystalline phase change in films were closely examined by XRD analysis and Raman spectroscopy in terms of atomic % of Ge by slowly increasing the GeSe2 contribution during co-sputtering. The influence of the composition on the optical band gap energy, refractive index and transmission spectra were also analysed using variable angle spectroscopic ellipsometry(VASE) and spectrophotometry analysis from visible to mid-IR. Third-order nonlinear optical parameters of the co-sputtered films were estimated using Sheik-Bahae formalism. The ridge waveguides were fabricated from RF magnetron co-sputtered Ge-Bi-Se films on Si/SiO2 substrate to obtain single-mode waveguides at 1.55 μm.

Financial support from Czech Science Foundation and European Union’s Horizon Europe Framework Programme under grant agreement No 101092723 is greatly acknowledged.

We report the first demonstration of excitability in all-fiber lasers with 1550 nm. We present clear numerical evidence in this passive Q-switched device with gain and absorption sections to determine excitability properties, including a threshold-based stimulus response and not much response delay between the input pulse and the excitable response with increasing noise amplitude. Our numerical results are consistent with the excitability basis as demonstrated by a study of Yamada’s model; they pave the way for new and reliable all-fiber architectures for photonic memory and neural-inspired computing applications

In this paper, we report on a high-energy, high-power quasi-continuous wave (QCW) operation of a double-clad thulium (Tm) fiber laser. We constructed an efficient high-power Tm fiber laser which produced rectangular-shaped pulses at 1940 nm with a > 6 J pulse energy and a 10 ms pulse duration at a 10 Hz repetition rate, corresponding to an average power of > 60 W and a peak power of > 600 W for ~ 110 W of incident pump power at 793 nm. The detailed laser characteristics and the ablation of stones with a constructed laser are discussed.

Various applications in the medical, defence and industrial fields exist for thulium-doped fibre lasers (TDFL) emitting in the 2 µm spectral region. All-fibre laser architectures represent optimized designs especially for applications that require high reliability in harsh environments. These architectures can be further improved by reducing the amount of fibre components and therefore reducing the failure probability. We investigate mode field adaption techniques between an active and passive fibre by changing the refractive index profiles of both fibres. The findings of this investigation are used to optimize a core-pumped TDFL with up to 75% slope efficiency.