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We realize a fiber Bragg grating InGaN-based laser diode emitting at 400 nm and demonstrate its high coherency. Thanks to the fabrication of a narrowband fiber Bragg grating in the near-UV, we can reach single-mode and single-frequency regimes for the self-injection locked diode. The device exhibits 44 dB side-mode suppression ratio and mW output power. Detailed frequency noise analysis reveals sub-MHz integrated linewidth and 16 kHz intrinsic linewidth. Such a narrow linewidth laser diode in the near-UV domain with a compact and low-cost design could find applications whenever coherency and interferometric resolutions are needed.

International audience; Nowadays, narrow linewidth lasers are unavoidable tools for fundamental and applied physics. One promising approach to generate coherent laser emission is based on stimulated Brillouin scattering (SBS) optical nonlinearity. Implementing SBS in an optical cavity gives rise to coherent emission with impressive performances in terms of noise and linewidth. Cascading the SBS process can even, under given conditions, improves the coherent emission specifications. To achieve such performances it is crucial to determine the Brillouin gain coefficient. Usual pump-probe methods are carried out in single pass waveguides. The probe intensity is proportional to e gBP in L eff / A eff where P in is the incident pump power, A eff the effective mode area and L eff the usual effective interaction length. To observe significant probe amplification one needs either long waveguides or strong pump power to reach the SBS threshold. We propose a method, based on the cavity ringdown spectroscopy, to directly characterize the Brillouin gain coefficient inside a resonator. This configuration allows to extract Brillouin parameters from the light recirculation with both a reduced waveguide length and input pump power when compared to usual methods.

International audience; We report a technique based upon the cavity ringdown method that enables to characterize the Brillouin gain coefficient directly in a laser cavity. Material gain, optical cavity parameters and lasing properties can be extracted from measurements whithin a single experiment.

International audience; We provide numerical verification of a feed-forward, heterodyne-based phase noise reduction scheme using single-sideband modulation that obviates the need for optical filtering at the output. The main benefit of a feed-forward heterodyne linewidth reduction scheme is the simultaneous reduction of the linewidth of all modes of a mode-locked laser (MLL) to that of a narrow-linewidth single-wavelength laser. At the heart of our simulator is an MLL model of reduced complexity. Importantly, the main issue being treated is the jitter of MLLs and we show how to create numerical waveforms that mimic the random-walk nature of timing jitter of pulses from MLLs. Thus, the model does not need to solve stochastic differential equations that describe the MLL dynamics, and the model calculates self-consistently the line-broadening of the modes of the MLL and shows good agreement with both the optical linewidth and jitter. The linewidth broadening of the MLL modes are calculated after the phase noise reduction scheme and we confirm that the phase noise contribution from the timing jitter still remains. Finally, we use the MLL model and phase noise reduction simulator within an optical communications system simulator and show that the phase noise reduction technique could enable MLLs as optical carriers for higher-order modulation formats, such as 16-state and 64-state quadrature amplitude modulation.

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 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. 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. 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.

International audience; We demonstrate that multi-Stokes operation is essential to get low intensity noise Brillouin fiber ring laser. 20 dB/Hz noise reduction compared to input pump laser is confirmed by a numerical modal replicating experimental observation. Stimulated Brillouin Scattering (SBS) initiated in an optical cavity is an attractive phenomenon to generate narrow linewidth lasers. Multi-Stokes waves generated through cascade process allow to reach better coherence properties. We build a Brillouin multi-Stokes fiber laser with 20 meters Polarization Maintained fiber. This fiber ring cavity is resonantly pumped using a continuous wave laser. The circulating pump wave initiates Brillouin amplification in Stokes 1 (S1) wave traveling in the opposite direction. We show characteristics of cascade Brillouin laser on the Figure (left axis). S1 (blue), S2 (green), and S3 (yellow) output power are plotted as function of input pump power. When the power in S1 reaches the normalized output power needed to compensate linear losses of S2, coherent emission of S2 takes place; the cascaded process is on. In that regime, the S1 circulating power is clamped. Relative intensity noise (RIN) of individual Stokes are characterized and normalized by the pump RIN. RIN behavior of the three first individual Stokes lines as function of the input pump power are plotted on the Figure (right axis). Above, which corresponds to the S2 lasing threshold, the S1 experiences an abrupt RIN reduction up to 20 dB/Hz compared to the input pump RIN level. This reduction originates from the clamping effect of S1 line due to the appearance of the stimulated S2 emission. Dotted lines correspond to measured RIN and starred lines to numerical simulations based on a set of coupled-mode equations. Numerical results even predict 40 dB/Hz reduction. We assume that the discrepancy is due to experimental bench limitation. We finally show that Stokes RIN follows the noise distribution similar to a class B laser featuring relaxation of oscillations, originating from the coupling between phonons and photons. Our study gives inputs to design optimized Brillouin fiber laser in term of RIN reduction.

International audience; We report on the frequency noise reduction performance of a feed-forward technique. The Letter is based on frequency noise measurements that allow the spectral response of the feed-forward phase noise correction to be determined. The main limitation to the noise compensation is attributed to the local oscillator flicker noise and the noise added by the optoelectronic loop elements. The technique is applied to an actively mode-locked laser diode demonstrating, at the output of the system, an optical frequency comb source with 14 comb lines reduced to sub-kilohertz intrinsic linewidth.

International audience; Summary form only given. Brillouin fiber ring lasers have already been extensively studied 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. 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. In this communication, we investigate the noise properties of a multi-Stokes Brillouin fiber laser. We present numerical simulations from a model that is an extension of the usual three-waves model of stimulated Brillouin scattering in agreement with experimental results.

International audience; The onset of the coherence collapse (CC) regime, which is incompatible with data transmission, is investigated both theoretically and experimentally in a 1.55-um InAs/InP quantum dash semiconductor laser. It is numerically shown that the filling from the excited state produces an additional term, which accelerates the route to chaos. This contribution can be seen as a perturbation that reduces the overall CC threshold.

International audience; We present here for the first time experimental bifurcation diagrams of a self-pulsing dual wavelength erbium-doped fiber laser. New type of generalized bistabilities are observed such as 3T-chaos and 1T-chaos. Theoretical calculation based on the two-mode ion-pair model shows a very good agreement with the experimental results.

International audience; Laser spectra are strongly modified by the optical feedback which is provided by external cavities; here we give a preliminary experimental result describing the optical spectrum of a fibre laser having two identical end cavities, which appear between the external mirrors and fibre ends. One observes a channelled spectrum including mode clusters separated by empty regions. We use the optical Airy function defined in the pure frequency domain to study these spectra. An optical Vernier effect allows the description of this structure. The linewidth of each mode is calculated as a function of the gain, by using the same Airy function.

We propose in this communication an experimental study of the relaxation oscillations behavior in mode-locked lasers. The semiconductor self-pulsating laser diode is composed by two gain sections, without saturable absorber. It is made of bulk structure and designed for optical telecommunication applications. This specific device allows two different regimes of optical modulation: the first one corresponds to the resonance of the relaxation oscillations and the second one, to the mode-locking regime at FSR value. This singular behavior leads us to characterize the self-pulsations which are coexisting in the laser and to describe two regimes of output modulation: the first one appears thanks to the resonance of the oscillation relaxation and the other one corresponds to the FSR of the Fabry-Perot laser at 40 GHz., poster session, SPIE Photonics Europe, Strasbourg : France (2008)

We give an analysis of the spectrum around the laser line of vertical-cavity surface-emitting lasers. We show that they contain sidebands which are not symmetrically located on each side of the laser frequency and that this asymmetry corresponds to a non-degeneracy of relaxation oscillations of the carriers. A model which explains this non-degeneracy is introduced.

The amplification response of a laser to a weak, narrow line width signal is measured above the laser threshold and below the minimum injection power condition for locking. This signal has the same resonant frequency as the laser but a smaller line width which allows to separate its effect from that of the spontaneous emission in the laser output spectral density. Optical powers as low as −117 dBm or 0.2 photon per correlation time are experimentally detected. Phenomena are theoretically explained by using simple semiclassical formulas based on the laser transfer function.

The process of amplification of light by a laser set above its oscillation threshold is studied. This laser has a wide bandwidth (typically 100 MHz) and is injected by a signal whose bandwidth is much narrower, which allows to separate the amplified signal from the ordinary laser spectral density. Theoretical calculations are based on simple semiclassical formulas and agree with the experimental results which are performed at 1.55 μm using single-mode semiconductor lasers. The amplification arises from a progressive channeling of energy from the wider laser line onto the narrow injected signal.

We study a vertical-cavity surface-emitting laser with external feedback through a quarter-wavelength plate. We show that the effect of a rotation of the quarter-wavelength plate is to shift one comb of modes with respect to the other one. The dependence of the frequency on the rotation angle is calculated and shown to be in good agreement with experimental results.

The polarization state of a vertical cavity surface emitting laser (VCSEL) output was driven by means of optical injection from another VCSEL. The bistability inherent to polarization locking allowed us to generate a memory effect. The control parameter was the modulated bias current of the maser laser and effects were shown to exist at frequencies up to 1 GHz.

An injected microchip laser is theoretically studied, with the use of two models: in the first model, which is traditional, the field is represented by a single frequency component in the slowly-varying envelope approximation. In the second model, referred to as the Fabry-Perot model, two field components are considered which are respectively centered around the frequency of an eigenmode of the injected laser and the frequency of the injected field. Computation of locking ranges, bistability do mains are performed and the results compared. They show not only an improved precision of the second model but also a necessity to use it to describe some effects such as the bistable domains in the limits of the locking domains.

Vertical-cavity surface-emitting lasers (VCSELs) are known to exhibit a small birefringence and dichroism whose axes are directed along the crystal axes of the quantum wells and which fix the polarization of the oscillating light. In this paper, we consider the dynamics of the polarization of light in such a laser, extended by means of a quarter-wavelength plate in an external cavity. Periodic variations are experimentally observed. A theoretical analysis and numerical results are proposed, using a recent model which includes the carriers' spin interaction. A good match is found between experimental and numerical results.

For underwater surveillance applications, an all-optical acoustic array technology allows enhanced capabilities compared to conventional piezoelectric antenna in terms of compactness, robustness and large distance remote interrogation through small diameter optical cable. This paper presents the results obtained on a first full optical antenna panel based on an innovative wideband pressure and temperature compensated fiber laser hydrophone. The presented mock-up includes 12 fiber-laser optical hydrophones interrogated through a 4 km lead optical cable.

A compact second-order Stokes Brillouin fiber laser made of microstructured chalcogenide fiber is reported for the first time. This laser required very low pump power for Stokes conversion: 6 mW for first order lasing and only 30 mW for second order lasing with nonresonant pumping. We also show linewidth-narrowing as well as intensity noise reduction for both the 1st and 2nd order Stokes component when compared to that of the pump source.

International audience; A compact second-order Stokes Brillouin fiber laser made of microstructured chalcogenide glass is reported for the first time. This laser has very low optical pump-power threshold for Stokes conversion: 6 mW for first order and only 30 mW for second order with nonresonant pumping.

Almost fifty years after the first experiment by Stover [1], optical injection has been the subject of intense analysis in the last decade, especially for single-frequency laser [2,3]. This paper focuses on the properties of a single-mode quantum dash laser emitting at 1.55 µm, submitted to optical injection. Recent results concern mainly multi-frequency quantum dot or dash lasers emitting at 1.55 µm [4] or single-mode quantum-dot laser emitting at 1.3 µm [5,6]. However, our devices, DFB quantum-dash laser emitting at 1.55 µm [7], doesn't reveal the same behaviour as the one described in [5]. The general properties of this DFB quantum-dash laser are close to the ones of quantum-well lasers [3]. Nevertheless the strong damping factor associated to the quantum-dash lasers modifies totally the response with respect to the pumping parameter of the slave laser. In a conventional laser (bulk or quantum wells), close to threshold, the laser behaves like an optical amplifier, while at a larger pump current, more regimes appear as illustrated in the figure 1, which compares the different regimes in the chart “detuning”- “injected power”. On the contrary, for quantum-dash laser, the tendency is opposite as shown in figure 2. We propose in this communication to detail these trends experimentally and theoretically.

International audience; We propose a novel design for a semiconductor microcavity nonlinear detector, based on two-photon absorption, for high-speed signal processing applications in future wavelength division multiplexing (WDM) systems. By inserting a phase section and a gain section in the resonant cavity, we could achieve wavelength and bandwidth tunability of the nonlinear detector. Theoretical investigation is carried out in the frame of an extended transfer matrix formalism, leading to the selfconsistent calculation of the device properties. We model the design and characteristics of a GaAs/AlGaAs microcavity suitable for selective processing of different WDM channels, operating at various data rates and modulation formats.

Présentation orale; International audience; We investigate wavelength tunable 56 Gbit/s DQPSK systems using comb generation in a quantum-dash mode-locked laser. Relative intensity noise and bit error rate is measured for each mode. Error-free operation is obtained over 9 WDM channels with 100 GHz spacing.

conference 7720 " Semiconductor Lasers and Laser Dynamics ", Posters session [7720-83]; International audience; In this paper we present our recent works on optical injection of Fabry-Perot laser diode for application in access networks. The injection-locked Fabry-Perot laser diode is used as low-cost colorless transmitters for high-speed optical access exploiting wavelength-division-multiplexing technology. The modification of main characteristics of Fabry-Perot laser such as spectral properties, noise and modulation is shown in injection-locking regime. The strong dependence of these properties onto injection parameters is also given. Finally, the operation of injection-locked Fabry-Perot laser diode in a wavelength-division-multiplexed optical access system using a novel multi-wavelength master source based on quantum-dash mode-locked laser is presented and its transmission performances at 2.5Gb/s are reported.

The coherency, which is linked to the spectral linewidth, is an important property of a laser, as it strongly influences the system performances in various domains of application [1]. Several methods have been proposed to measure the laser linewidth, among which the Delayed Self-Heterodyne Technique (DSHT) [2]. In this paper, we propose a novel and simple method to measure the laser linewidth based on Rayleigh Backscattering (RB) effect. Our technique requires relative intensity noise (RIN) measurement. Contrary to DSHT, it avoids the use of an acousto-optic frequency-shifter, which infers the bandwidth detection and of a Mach-Zehnder interferometer.

International audience; We present a novel and simple method to measure both the value of the second-order dispersion coefficient and the nonlinear coefficient in optical fibers. This method is based on the higher-order soliton-effect pulse compression phenomenon and is valid for dispersion values greater than 0.5 ps/km/nm. A non-zero dispersion-shifted fiber, a standard single-mode fiber and a highly-dispersive highly-nonlinear fiber have been measured using this method.

We propose a study of dynamics of edge-emitting semiconductor laser subjected to external optical feedback. The external cavity contains a mirror and a second semiconductor device, which can work as an amplifier or an absorber. The existence of regimes of regular or chaotic pulsations are discussed.

International audience; In this letter, the authors propose a simple source based on mode-locked semiconductor lasers using linearly chirped fiber Bragg gratings external cavities. Using this technique, transform-limited pulses, compatible with 10-Gb/s applications, are generated. Effects of Bragg grating's parameters on the source performances are also experimentally investigated.

topic " Semiconductor lasers ", session: WZ " Grating Feedback Semiconductor Lasers " [WZ6]; International audience; In this paper, we demonstrate the low sensitivity to both external optical feedback and external optical injection of a new type of extremely low cost single-mode lasers, called "discrete mode" (DM) lasers. The DM lasers are obtained from ridge waveguide Fabry Perot (FP) lasers, in which the effective refractive index of the lasing mode has been perturbed. These lasers exhibit a low sensitivity to external optical feedback since the coherence collapse threshold is around 5 dB higher in comparison to a commercial DFB laser.

Topic: Lasers and laser optics, Publisher: OSA (ISSN 0740-3224); International audience; We study a spontaneous Q-switched laser regime obtained with a multiwavelength frequency-shifted-feedback erbium-doped fiber laser. We have developed a traveling wave model to describe the dynamics of this ring cavity laser. The numerical results are in good agreement with experimental measurements. Furthermore, the model gives insight into the origin of this pulsed emission. Unlike in most Q-switched lasers, Q-switched operation does not rely on amplitude modulation of the net cavity gain but is produced by modulation of the optical frequency spectrum. To our knowledge, this is the first demonstration of a fiber laser with frequency-modulated Q-switched operation.

conference 6184 "Semiconductor Lasers and Laser Dynamics II", poster session [6184-67], proceedings of SPIE (ISBN 97808194624043); International audience; The authors propose a simple source based on mode-locked semiconductor lasers using linearly chirped fibre Bragg gratings external cavities to generate transform-limited pulses. Effects of the apodisation of Bragg grating on the source performances are experimentally investigated.

EQEC topic EC " Dynamics, Instabilities and Patterns ", oral session 6 " Synchronization and feedback " [EC6-5-THU]; International audience; Synchronization of chaotic signals is studied when the chaos is generated through optical injection avoiding optical feedback. The use of optical injection enables a strict comparison when a continuous or a chaotic wave seeds the laser.

The use of coherent optical sources as pumps in solidstate lasers has led to the experimental feasibility of long-fiber lasers, permitting the study of coherent effects on increased time scales. Rare-earth-doped silica-fiber lasers reveal complex static as well as dynamical behaviors. For example, the single polarization Er-doped fiber laser spontaneously operates in a self-pulsing regime as a result of the presence of interacting ion pairs in the medium.' On the other hand, polarization effects are unavoidable for anisotropic2 as well as for quasi-isotropic cavities when no dichroic element is inserted in the experimental setup. These polarization effects were reported in the Nd3 -doped fiber laser for their pumpdependent static properties3 and also in the context of antiphase dynamics.4 In these examples the fiber output beam usually contains two linearly polarized components. As the pump input power is increased, the lower-threshold mode switches on first, followed by the second polarization eigenmode. The relative thresholds of these polarization modes can be adjusted with the orientation of the pump beam polarization.3 At high pump levels the intensity of both modes increases linearly with pump input power in such a way that the intensity of the lowerthreshold mode always exceeds that of the second mode, and we refer to these polarization states as strong and weak modes, respectively. On the other hand, optical feedback was proved to change drastically the static and dynamical properties of laser systems.5 In our study it is used to control the distribution of the total intensity among the eigenmodes. An interesting case is observed when the ratio of the strong-to-weak-mode thresholds is maximized. The purpose of this Letter is to demonstrate that this configuration gives clear evidence of alternate switching between the strong and weak modes when the external feedback loop is suitably adjusted. When the laser is operated between the two thresholds, the weak mode develops at the expense of the strong mode, which is completely washed out by the feedback signal. The experimental setup is schematically represented in Fig. 1. The pump is a laser diode with a collimated output beam at AP = 0.810 juam and an available output power as high as 150 mW. A half-wave plate at AP allows us to rotate the pump polarization. The laser diode optically pumps a 10-mlong silica fiber doped with 500 parts in 106 Nd3 ' by weight. The fiber core diameter is Ic = 2.7 snm, and the cutoff wavelength is A, = 0.86 j.m. The laser oscillation at A = 1.08 /-tm is obtained between mirrors Ml (R= 100% at 1.08 ,-m and T = 80% at Ap) and M 2 (R2 = 80% at 1.08 fum). Index-matching oil suppresses any parasite cavity between the fiber output end and mirror M2. The pump input current at the fiber laser threshold is typically -35-40 mA (corresponding approximately to 23-26-mW input power, measured before mirror Ml). The beam splitter inside the feedback setup is a 6-,tm-thick pellicle oriented at a 10° tilt with respect to the output axis so as to decrease its action as a polarization-selective element. A polarizer is inserted in the feedback loop and adjusted along the Y axis. A half-wave plate at 1.08,um permits calibrated analysis of the two orthogonal polarization components, which are separated by a Glan polarizing prism. The signals are analyzed with two fast-response (2-GHzbandwidth) Ge detectors, monitored with a digital oscilloscope, and then transferred to a microcomputer. We optimize the feedback efficiency by focusing the output beam onto the external mirror with a collimating lens. The effective feedback rate is estimated by the corresponding shift of the laser threshold.5 Before describing our experimental results we recall the following properties of the isolated laser (i.e., without optical feedback): (i) In spite of the highly longitudinal mode operation, in its transient regime the laser behaves as a two-supermode system. Each mode is polarized along an eigenaxis of the fiber (the strong mode along X and the weak mode along Y), and the propagation axes are fixed by the stress-induced birefringence of the medium. (ii)

conference 5709 « Fiber Lasers II: Technology, Systems, and Applications », session: « Nanosecond fiber sources » [5709-51]; International audience; Fiber lasers and amplifiers are used in a variety of applications either for scientific (spectroscopy, medicine...) or industrial applications (free space communications, laser marking and drilling ...). The combination of doped double clad fibers (DCF) and high power multimode semiconductors laser diodes technologies allows to achieve very high output power in very compact, robust and maintenance free systems. Yb3+ doped DCF are well suited for 1µm wavelength amplification. In pulsed regime, achievable peak power can be strongly limited by nonlinear effects such as Kerr effect, Stimulated Raman Scattering (SRS) or Stimulated Brillouin Scattering (SBS). Consequently, the optimisation of optical amplifier architecture is required. In this paper, we demonstrate performances obtained for the generation of 2ns optical pulses up to >1.7kW peak power in a Master Oscillator Power Fiber Amplifier (MOPFA) configuration. The laser seed signal at 1060nm is emitted out of a single longitudinal mode source with spectral linewidth 10W average output power with a good beam quality M21.7kW. These high performances are obtained in a fully-integrated device.

It is shown that the light of a commercial vertical-cavity surface-emitting laser submitted to a polarised optical feedback can be switched between two linear polarisation eigenstates.

conference 5452 « Semiconductor Lasers and Laser Dynamics », session 4 « Short Pulses and Mode-Locking » [5452-18]; International audience; A semiconductor laser coupled to a gallium-made non linear mirror may exhibit pulse regime. In order to better understand this coupled cavity, stationary solutions and dynamics are described following the standard Lang and Kobayashi equations for a semiconductor laser submitted to nonlinear optical feedback. It is shown that the nonlinearity distorts the ellipse on which lied the stationary solutions, with a "higher" part corresponding to lower reflectivity and a "lower" part to higher reflectivity. Bifurcation diagrams and nonlinear analysis are presented while the conditions for pulsed operation are discussed.

International audience; Relative intensity noise of a six-channel multiwavelength distributed Fabry-Perot fibre laser is compared to the noise of a singlemode distributed feedback fibre laser. The noise characteristics of individual channels are similar to that of the singlemode laser, offering a low-cost and compact solution for wavelength multiplexing applications without noise penalty.

International audience; A multi mode channeled emission spectrum of Nd3+ and Er3+ doped fiber lasers with two symmetric free space external cavities is experimentally demonstrated. An optical Vernier effect depending on the relative length difference between the two end cavities leads to a controlled number of clusters of oscillating modes.

International audience; We report that a bubble with a radius of a few micrometers may be created at a precise location on a metal-coated optical fiber tip immersed in liquid nitrogen by microsecond optical pulses with peak powers of less than 20 mW. Dynamic optical measurements reveal that after termination of the optical pulse the bubble exhibits stable oscillations for several tens of microseconds, at frequencies up to several megahertz, as it slowly collapses.

International audience; We demonstrate the operation of a CW multi-wavelength erbium-doped fiber laser covering the whole C-band. The laser system consists of a frequency-shifted ring cavity with a new type of periodic filter, namely a fiber Bragg grating array. Careful control of the individual grating strength has allowed us to obtain 17 laser lines, from 1527 to 1562 nm, with output flatness better than 3 dB. We also report on the optimization and characterization of the CW laser emission.

Stationary characteristics and relative intensity noise are simulated for a laser diode with strong filtered optical feedback from an external Bragg reflector. Multiple reflections in external cavity are taken into account through the introduction of Green functions. An analysis of the stationary solutions shows the appearance of new solutions for strong feedback and collapse in the plane frequency-gain of the ellipse which usually contains the modes and so-called antimodes. Numerical result are compared with analytical expressions.

The response of a single mode semiconductor laser to an injected external signal has been studied. The control parameters are the power and the frequency of the injected signal together with the gain of the laser. The injected power varies from 6 down to -120 dBm. Following the magnitude of these control parameters many phenomena can be observed. When both injected field and laser eigenfield are of the same order of magnitude they compete in a non-linear way, leading to frequency generation, push-pull effects, hysteresis phenomena and chaos. For weak dBm the laser behaves with the injected field in the same way as it does for the spontaneous emission which is its natural source. We describe the role of the injected laser as a filter and an amplifier in this case. It follows that the laser can be used to process information in ways that are not yet completely exploited.

Summary form only given. Optical-spectra of semiconductor lasers contain side bands symmetrically located on each side of the laser line. It corresponds to the relaxation oscillations (RO) of the carriers (1-7 GHz). We have recently shown that these RO are non degenerate and this non degeneracy results in asymmetric side bands of the laser line. This observation of two relaxation frequencies in VCSELs is not unexpected. It is just the same observation as for ROs in class-B multimode lasers. It is well known that these lasers (more precisely soli-state lasers operating with a few modes) have a set of ROs frequencies. The basic model used to describe the dynamics of VCSEL is called spin-flip model (SFM). The SFM model leads to two relaxation processes which are accompanied by damped oscillations of the laser field when laser parameters are disturbed. One is related with the total carrier number and the total photon number inside the cavity. We have modified the SFM model to get agreement with experimental results. We have first introduced the nonlinear-wave coupling on the basis of comparison with other models of laser physics.

We show that lasers can be used as detectors. The experimental set-up consists in optically injecting a slave laser with a laser whose linewidth is smaller. Heterodyne technique allows us to detect signals as small as -1 17 dBm or 0.2 photon per correlation time. We explain the experiment by interpreting the laser as a nonlinear amplifier and filter.

Distributed feedback semiconductor lasers used in optical telecommunication are submitted to an optical injection: various phenomena are experimentally observed, including frequency and progressive phase locking, frequency generation, chaotic behavior, bistability and sensitive detection. The theoretical interpretation is based on the laser transfer function in the frequency domain which is calculated for this kind of laser.

Switching techniques with coherent optical sources are a challenge for telecommunications. One technique is to control the polarization eigenstate of the laser. We have examined the stability of polarized modes in quasi-isotropic laser, such as He-Ne laser at 3.39 μm1 and have proposed a general anisotropy model with applications.2 To test our calculations we have used He-Ne lasers as they are easy to construct in-house and are systems for which all the important parameters are known. For practical applications, however, it is clear that one must use more compact lasers, such as miniature solidstate lasers or semiconductor lasers. To control the polarization eigenstate of such a laser with Polarized Optical Feedback (POF), we need sources, which can run single mode and have weak anisotropies. Possible candidates that satisfy these criteria are microchip Nd:YAG lasers and Vertical Cavity Surface Emitting Lasers.3 However, the orientation of their polarization can vary from laser to laser. That could be a sign of weak anisotropy as the polarization states of quasi-isotropic lasers are highly sensitive to residual cavity anisotropies (most likely strain left during the fabrication process). Previously, we reported on the control of the polarization eigenstates of microchip YAG lasers using POF.4 Here we focus our study on adding POF in order to control the polarization eigenstate of gain-guided VCSELs. A schematic diagram of the experimental setup is shown in Fig. 1.

We propose a real, highly nonlinear, As2Se3-based chalcogenide photonic crystal fiber in which a supercontinuum (SC) spanning more than 2 octaves is generated at =2.8 µm in the femtosecond regime. The designed PCF is characterized for ultrabroadband mid-infrared SC generation in only few millimetres of fiber length. A full modal analysis of the optical properties of the fiber is presented in terms of the effective area, the nonlinearity coefficient, and the chromatic dispersion. A second-order Sellmeier approximation is proposed to estimate the variation of the refractive index of the As2Se3 material as a function of wavelength. The numerical study shows that a SC spanning from 1.9 to 4 µm can be generated in the chalcogenide PCF with an air-hole diameter of 1.26 µm and a pitch of 1.77 µm. We examine the interplay of the nonlinear effects that lead to the construction of the SC as a function of the input power and the fiber length. We find that the dynamics behind the SC generation is mainly ruled by the effects of self phase modulation and stimulated Raman scattering. The intrinsic properties of the chalcogenide glasses and the microstructure provide enhanced optical properties and offer numerous applications in the infrared field.

Topic: Lasers and Laser Optics; International audience; Bistabilities between a steady (or pulsating, chaotic) and different pulsating regimes are investigated for an optically injected semi-conductor laser. Both numerical and experimental studies are reported for continuous-wave single-mode semiconductor distributed-feedback lasers emitting at 1.55 μm. Hysteresis are driven by either changing the optically injected power or the frequency difference between both lasers. The effect of the injected laser pumping rate is also examined. Systematic mappings of the possible laser outputs (injection locking, bimodal, wave mixing, chaos or relaxation oscillations) are carried out. At small pumping rates (1.2 times threshold), only locking and bimodal regimes are observed. The extent of the bistable area is either 11 dB or 35 GHz, depending on the varying parameters. At high pumping rates (4 times threshold), numerous injection regimes are observed. Injection locking and its bistabilities are also reported for secondary longitudinal modes.