The mid-infrared (mid-IR) spectral region is of great interest to many areas of science and technology as it contains two important transparency windows (3-5 and 8-13 μm) of the Earth’s atmosphere and strong characteristic vibrational transitions displayed by a large number of molecules. Praseodymium (Pr3+) and dysprosium (Dy3+) ions feature characteristic transitions in the mid-IR and transmission range of chalcogenides-based materials spans a large part of the mid-IR. The combination of efficient waveguiding properties with mid-IR light emitters would therefore be a key enabler of the development of mid-IR sensors-on-a-chip for health, security and environmental applications. In this paper, RF magnetron co-sputtering is used to deposit a Dy3+/Pr3+-doped chalcogenides guiding layer based on the quaternary system composed of Ga, Ge, Sb and Se atoms on silica cladding layer. The fabrication process of straight ridge waveguides using photolithography and RIE/ICP dry etching is then described. Finally, Dy3+ and Pr3+ mid-IR guided photoluminescence around 2.5 and 4.5 μm is demonstrated at room temperature using co-propagating pumping at telecommunication wavelengths (respectively around 1.3 and 1.55 μm).
An optical resonator like a fiber ring (FR) or a whispering gallery mode (WGM) resonator with two couplers along its loop is referred to be in the add-drop configuration, in analogy with the add-drop multiplexer in telecom networks. Both for practical applications as well as in several fundamental studies involving high-Q resonators, this configuration is of great interest and the assessment of the intrinsic properties of the resonator and of its interaction with the coupling systems is extremely important. We developed an original method able to fully characterize high-Q resonators in an add-drop configuration. The method is based on the study of the two cavity ringdown (CRD) signals, which are produced at the transmission and drop ports by wavelength sweeping a resonance in a time interval comparable with the photon cavity lifetime. All the resonator parameters can be assessed with a single set of simultaneous measurements. We implemented the model describing the two CRD profiles from which a best fit process of the measured profiles allows deducing the key parameters. We successfully validated the model with an experiment based on a FR resonator of known characteristics. Finally, we fully characterized a high-Q, home-made, MgF2 WGM disk resonator in the add-drop configuration, assessing its intrinsic and coupling parameters.
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.
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.
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+, Tm3+) 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 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 and also industrial IOG-1 Yb3+- Er3+ co-doped phosphate 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 and C+L band. We have observed that the RIN can provide insurance about the emission of the Laser. Moreover, we have shown that a single-mode emission comes with the presence of multiple harmonics of the relaxation frequency, which is the signature of a Laser with high noise levels. In this particular case, the second and higher orders of intensity fluctuations cannot be neglected any longer in the small-signal analysis.
We study both theoretically and experimentally the dispersive properties of single whispering gallery mode resonators. We present a simple experimental protocol which allows us to obtain in detail its coupling regime and thus their dispersive properties. We demonstrate a compact optical amplifier with a gain up to 20dB in an Erbium doped fluoride microsphere of 135μm in diameter coupled via a tapered fiber. The model is also applied to analyze the dynamic behavior of the modal coupling between two degenerate resonances of the same cavity. In particular, this can be used to describe the coupling of counterpropagating whispering gallery modes (WGM) by Rayleigh scattering. The theory is successfully compared to experiments carried out in silica microspheres
We show both theoretically and experimentally that the lifetime of an active semiconductor photonic crystal nanocavity is enhanced thanks to the combination of two cooperative effects: slow light propagation based on coherent-population-oscillation effect and optical bistability. In particular we develop an analytical analysis enabling us to clearly show the physical mechanisms producing the enhancement of the cavity lifetime.
We demonstrate that the lifetime of a nanocavity can be enhanced by inserting a medium with a strong index
dispersion in the cavity. The strong dispersion is achieved through coherent population oscillations effect in the
quantum wells of a two-dimensional photonic crystal nanocavity. The initial cavity lifetime of ~3-6ps has been
extended to a maximum value of about 336 ps.
The Nd3+-doped Silicon Rich Silicon Oxide (SRSO) layers were elaborated by reactive magnetron cosputtering.
We report on refractive index measurements of Nd3+-doped SRSO layers obtained by both m-lines method
and reflectance spectroscopy. From these measurements, the Si volume fraction and also the Nd3+-doped SRSO index
dispersion were deduced by using the Bruggeman model. At 1.06 μm, work wavelength, Nd3+-doped SRSO refractive
index was equal to 1.543 corresponding to a Si volume fraction of 6.5%.
Optical losses measurements were performed on these waveguides at different wavelengths and were about 0.3 dB/cm at
1.55 μm and 1 dB/cm at 1.06 μm. Measurements are confirmed by theoretical models showing that the losses are
essentially attributed to surface scattering.
Guided fluorescence by top pumping at 488 nm on planar waveguides was studied as a function of the distance
between the excitation area and the output of the waveguide and also as a function of the pump power. The guided
fluorescence at 945 and 1100 nm was observed until 4mm of the output of the waveguide and, of course, decreased when
the excitation area moved away from the output. The fluorescence intensity increased linearly for low pump power and
this linear increasing of the guided fluorescence of Nd3+ excited by a non resonant excitation at 488 nm confirms the
strong coupling between the Si- nanoparticles and rare earth ions.
We theoretically analyze the light-storing process in optical microresonator arrays. We propose a passive and
an active schemes to strongly slow light. The two mechanisms rely on microresonator chains whose high order
dispersion is optimized. The unit cell of the systems is a short sequence of two or four resonators. In the passive
process we show that the cancellation of the third order of dispersion allows the propagation of short pulses with
no significant distortion in a microresonator array. The second process needs the use of active microresonators
whose loss and gain are dynamically tuned. The structure is made of only four resonators and is optimized to
avoid pulse distortion as it is the case in the passive scheme. The loss and gain modulations allow the resonant
structure to be isolated from the access waveguide and optical pulse to be stored.
It has been shown that doubly resonant microcavities can be used to obtain miniaturized parametric devices
leading for example to efficient second-harmonic generation (SHG). First we will briefly recall the basic properties
of SHG in III-V semiconductor whispering gallery mode microdisks or microrings. Then we will show theoretically
that by coupling such microresonators and by using the artificial dispersion of a side-coupled integrated spaced
sequence of resonators (SCISSOR) it is possible to adapt the Fresnel phase-matching technique to the case of
highly confining waveguides or to enhance the second order nonlinear properties of a semiconductor waveguide
by slowing fundamental and second-harmonic waves.
We present a simple method to determine simultaneously the transmission and dispersive properties of passive
or active high Q-factor optical resonators. The method is based on cavity ring down spectroscopy where the
probe wavelength is rapidly swept across the resonance. It has already been shown that this technique allows the
loaded cavity lifetime of passive resonators to be obtained. Here we show that we can also infer the dispersion
introduced by the resonator and the resonant gain in the case of active resonators. The method is tested on
a model system consisting of fiber resonators. We applied the method to measure the intrinsic Q-factor of a
passive MgF2 whispering gallery mode resonator. We also used it to characterize the high Q-factor of a system
of coupled fiber resonators. Finally we show that the method can be used to determine the gain and dispersive
properties of selective amplifiers such as Er3+ doped fiber resonators.
Doubly resonant microcavities can be used to enhance optical nonlinearities. We propose a coupled modes
analysis of second-harmonic generation in cylindrical whispering gallery mode III-V microresonators. We show
that microdisks can be used to obtain the quasi-phase-matching condition and that by engineering their refractive
index it is possible to optimize the effective second order nonlinear polarization by maximizing the fundamental
and second-harmonic mode overlap. In a second part we show that the use of side-coupled integrated spaced
sequence of resonators (SCISSOR) can lead to an adaptation of the Fresnel phase-matching to the case of highly
confining waveguides.
Exploiting the formal analogy between the transfer function of a micro-resonator and the optical susceptibility of an
atomic medium, we investigate the spectral and energetic properties of active cavities seen as mesoscopic "photonic
atoms". The resemblance is not limited to linear regime; a structural equivalent can be found for such fundamental
processes as spontaneous emission, stimulated absorption and emission, saturation of the active medium or induced
transparency.
μA simple method based on the sol-gel technology has been developed to coat passive microspheres with an active
coating. The microspheres were prepared by fusion of a standard telecom fiber with a dimension of about 200 μm and
400 μm and have been respectively dipped in a 70SiO2-30HfO2 sol activated by 1 mol% and 0.1 mol% of erbium
ions. Here we first report about the luminescence properties of a silica-hafnia coating doped with erbium ions and then
whispering gallery mode spectra were analysed for different sphere diameters, thickness of coating and erbium
concentration. The thickness of the coating has been chosen in order to support at least one whispering gallery mode at
1.5 μm.
We numerically demonstrate the feasibility of constructing an all-optical pulse restorer by using a microresonator
structure with Kerr nonlinearity. We obtain a clear nonlinear power transfer curve suitable for all-optical regeneration
(reshaping) in the frequency and the time domains. The fully integrated device is based on 2 cascaded sets
of finite chains of 3 coupled nonlinear identical microring resonators side coupled with 3 straight waveguides. The
microrings are constituted by the same instantaneous, dispersive, local Kerr material. The first set suppresses
the noise in "0" and the second limits the amplitude fluctuations in "1" of return-to-zero optical data streams.
For a device made in p-toluene sulphonate (PTS) with n2 = 2.2×10-12 cm2/W with linear losses α = -5 dB/cm
and nonlinear losses α2 = 0.5 cm/GW and considering amplitude, jitter and width fluctuations we evaluate an
amplitude Q-factor improvement of 4.94 dB for a data rate of 40 Gb/s and input intensity n2I0 = 5 × 10-4.
Since we take advantage from field enhancement at resonance, this integrated reshaper could be much smaller
than other gates based on nonlinear fibers or waveguides.
Since the proposition of D.D. Smith et al. [Phys. Rev. A 69 pp. 063804, 2004], the experimental demonstration
of coupled resonator induced transparency has been made using passive fiber or whispering-gallery-mode microspheres.
These demonstrations show that it is possible to integrate delay lines using high quality resonators. The
maximal group delay that it can be introduced depends mainly on the relative value of the intrinsic losses with
respect to the value of the coupling between the resonators. In this paper we experimentally show that the limit
given by the intrinsic losses of the resonators can be circumvented by using active resonators. Our experimental
setup consists in two coupled Er3+ doped fiber resonators. Each resonator can be pumped independently. Consequently,
the values of the residual losses in the two resonators can also be modified independently. We then
show that the transparency of the coupled resonators can be maximized using the right pumping rate in each
resonator. By inserting this device into one arm of a fiber Mach-Zehnder interferometer we are able to optically
measure the phase shift produced by the coupled resonators as a function of the optical frequency. The group
delay can be deduced from this information.
The spectral properties of a single-mode active microring resonator are investigated in the frame of the extended transfer matrix formalism. Spontaneous emission, looked upon as the driving source of the radiation, is described in a semi-classical way in the spectral domain. The internal and emitted fields are filtered into the resonance modes of the whole structure; the spectral density of power is described by the generalized transfer function, which contains all essential mechanisms at work in a laser oscillator: gain, losses and sources. The active zone is saturated through Amplified Spontaneous Emission, integrated over its whole spectral range. Continuously valid across threshold, the method enables one to derive in a simple way the main steady-state properties of the laser oscillation, with the pumping rate as the only external parameter. In this approach, the optical properties of the active medium (the gain, the source and the refractive index) are supposed to be uniquely determined by the steady-state value of the carrier density, obtained within the framework of the rate equation formalism and assumed uniform along the active zone.
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