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On-chip integration of optical comb sources is crucial in enabling their widespread use. Integrated photonic devices that can be mass-manufactured in semiconductor processing facilities offer a solution for the realization of miniaturized, robust, low-cost, and energy-efficient comb sources. Here, we review the state of the art in on-chip comb sources, their applications, and anticipated developments. (C) 2022 Author(s).

Time-delay signature (TDS) suppression of semiconductor lasers with external optical feedback is necessary to ensure the security of chaos-based secure communications. Here we numerically and experimentally demonstrate a technique to effectively suppress the TDS of chaotic lasers using quantum noise. The TDS and dynamical complexity are quantified using the autocorrelation function and normalized permutation entropy at the feedback delay time, respectively. Quantum noise from quadrature fluctuations of vacuum state is prepared through balanced homodyne measurement. The effects of strength and bandwidth of quantum noise on chaotic TDS suppression and complexity enhancement are investigated numerically and experimentally. Compared to the original dynamics, the TDS of this quantum-noise improved chaos is suppressed up to 94% and the bandwidth suppression ratio of quantum noise to chaotic laser is 1:25. The experiment agrees well with the theory. The improved chaotic laser is potentially beneficial to chaos-based random number generation and secure communication., 4 pages, 5 figures

Die Messung von Spurengasen ist für viele Bereiche essentiell. So werden beispielsweise industrielle Verfahren anhand der Konzentration von Prozessgasen gesteuert oder ärztliche Diagnosen durch den Befund von Spurengasen im menschlichen Atem gefällt. Viele moderne Spurengasanalysen setzen auf optische Messmethoden. Hierfür wird i.A. ein Laser als Lichtquelle verwendet. Für die Bestimmung von Gaskonzentrationen werden die wellenlängenabhängigen Absorptionslinien der Atome/Moleküle verwendet. Viele Moleküle haben ihre stärksten Absorptionslinien im NIR (780 nm < λ < 3 µm). Eine nahezu vollständige Abdeckung von Laserquellen im Spektrum von 250 nm bis 10 µm wurde bereits erreicht. Hierdurch verschieben sich nun auch die Ziele der modernen Laserchip Forschung. Es werden jetzt Optimierungen an bestehenden Materialsystemen angestrebt. Einer dieser zu überarbeitenden Bereiche liegt bei λ ~ 2 µm. Hier ist momentan Indiumphosphid (InP) als aktives Medium Stand der Technik. An der höherwelligen Grenze verliert InP stark an optischer Leistungsfähigkeit (z.B. P < 3 mW). Deshalb wird in dieser Arbeit der Ansatz untersucht, GaSbbasierte Laser an deren unterer Wellenlängengrenze weiter zu verbessern. Die Galliumantimonid-Laserchips konnten erfolgreich prozessiert und in Lasersystemen aufgebaut werden. Die Eigenschaften dieser Lasersysteme zeigen Verbesserungen bezüglich der Ausgangsleistung sowie des Einzelmodenverhaltens im Vergleich zu den bisher gängigen Indiumphosphid-basierten Lasersystemen. Die anvisierten Laserleistungen von PDFB > 5-10 mW bzw. PFP > 30 mW wurden erreicht. Die aus diesem Ansatz resultierenden Laserdioden wurden dann auch im weiteren Verlauf der Arbeit an einer spektroskopischen Anwendung getestet. Eine recht junge und vielversprechende Anwendung ist die Quarz-verstärkte photoakustische Spektroskopie (engl. quartz enhanced photoacoustic spectroscopy, kurz QEPAS). Bei der QEPAS wird der photoakustische Effekt an Gasen ausgenutzt. Akustische Wellen werden hierbei mit einer Quarzstimmgabel detektiert. Dadurch können sehr kleine Messkammern mit entsprechend kleinen Probenvolumina realisiert werden. Die neuen GaSb Laserdioden sind entscheidend, da in der Photoakustik die Signalstärke proportional zur eingestrahlten Lichtleistung ist. Durch die hohe Leistung der neuen GaSb Laser konnte moderne photoakustische Spektroskopie an relevanten Treibhausgasen und an medizinisch relevanten Gasen (CO2, N2O) durchgeführt werden. Desweiteren wurden vergleichende Messungen an Methan (1650 nm, 2300 nm, 3300 nm, 7900 nm) durchgeführt. Für die QEPAS Messungen wurden reine Gase im Laborumfeld verwendet. Außerdem konnte eine Miniaturisierung eines QEPAS-Sensors realisiert werden. Zu ersten Mal erfolgte eine Zusammenführung einer Quarzstimmgabel mit der Anregungsquelle in einem ButterflyGehäuse. Dies schafft neue Möglichkeiten der Spurengasdetektion im mobilen Einsatz. Hier konnte Methan bei 1650 nm gemessen werden., Trace gases measurements are essential for many areas. For example, industrial manufacturing is controlled based on the concentration of process gases or medical diagnoses are made based on trace gases found in human breath. Many modern trace gas analyzes rely on optical measurement methods. Lasers are used as a light source for optical techniques generally. The wavelength-dependent absorption lines of the atoms / molecules are used to determine gas concentrations. Many molecules have their strongest absorption lines in the NIR (780 nm 5-10 mW or PFP> 30 mW were achieved. For this thesis the resulting laser diodes were then also tested for spectroscopic application. A very recent and very promising application is quartz-enhanced photoacoustic spectroscopy (QEPAS). QEPAS uses the photoacoustic effect of gases. Acoustic waves are detected with a quartz tuning fork. As a result, very small measuring chambers with correspondingly small sample volumes can be realized. The new GaSb laser diodes are crucial because in photoacoustics the signal strength is proportional to the radiated light input. Thanks to the high performance of the new GaSb laser, modern photoacoustic spectroscopy could be performed on relevant greenhouse gases and medically relevant gases (CO2, N2O). Furthermore, comparative measurements on methane (1650 nm, 2300 nm, 3300 nm, 7900 nm) were carried out. Pure gases in the laboratory environment were used for the QEPAS measurements. In addition, a miniaturization of a QEPAS sensor was realized. For the first time, a quartz tuning fork was combined with the excitation source in a butterfly housing. This creates new possibilities for trace gas detection in mobile use. Here methane was measured at 1650 nm.

An analytical study of dynamical properties of a semiconductor laser with optical injection of arbitrary polarization is presented. It is shown that if the injected field is sufficiently weak, then the laser has nine equilibrium points, however, only one of them is stable. Even if the injected field is linearly polarized, six of the equilibrium points have a state of polarization that is elliptical. Dependence of the equilibrium points on the injected field is described, and it is shown that as the intensity of the injected field increases, the number of equilibrium points decreases, with only a single equilibrium point remaining for strong enough injected fields. As an application, a complex-valued optical neural network with working principle based on injection locking is proposed., Final version, to appear in SIAM Journal on Applied Dynamical Systems (SIADS)

International audience; We experimentally and theoretically demonstrate the variety of the nonlinear dynamics exhibited by a single frequency semiconductor laser subjected to optical injection from a frequency comb. The injection parameters (the detuning and the injection strength) and the comb properties (comb spacing and the amplitude of the injected comb lines) are varied to unveil several dynamics such as injection locking, wave-mixing, chaotic dynamics, and unlocked time-periodic dynamics corresponding to new comb solutions. The asymmetry of the injected comb is shown to modify the size of the injection locking region in the parameter space, as well as the common properties between the new comb solutions observed and the injected comb.

International audience; This work reports on numerical analysis of the nonlinear dynamics of a semiconductor laser subject to an optical injection with a frequency comb. We identified the fundamental difference between the single mode injection and frequency comb injection. By varying the injection parameters (detuning and injection ratio), the results show that the slave laser is able to reproduce the injected frequency comb (new comb) in different parameters regions. The appearance of the new comb depends on the number of injected comb lines for fixed comb properties.

Physical curiosity at the beginning, optical chaos is now attracting increasing interest in various technological areas such as detection and ranging or secure communications, to name but a few. However, the complexity of optical chaos generators still significantly hinders their development. In this context, the generation of chaotic polarization fluctuations in a single laser diode has proven to be a significant step forward, despite being observed solely for quantum-dot vertical-cavity surface-emitting lasers (VCSELs). Here, we demonstrate experimentally that a similar polarization dynamics can be consistently obtained in quantum-well VCSELs. Indeed, by introducing anisotropic strain in the laser cavity, we successfully triggered the desired chaotic dynamics. The simplicity of the proposed approach, based on low-cost and easily available components including off-the-shelf VCSELs, paves the way to the wide spread use of solitary VCSELs for chaos-based applications.

Spectral dependence of Lamb coupling constant C is experimentally investigated in an InGaAlAs Quantum Wells active medium. An Optically-Pumped Vertical-External-Cavity Surface-Emitting Laser is designed to sustain the oscillation of two orthogonally polarized modes sharing the same active region while separated in the rest of the cavity. This laser design enables to tune independently the two wavelengths and, at the same time, to apply differential losses in order to extract without any extrapolation the actual coupling constant. C is found to be almost constant and equal to 0.84 +/- 0.02 for frequency differences between the two eigenmodes ranging from 45 GHz up to 1.35 THz. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

We present experimental and theoretical results of noise-induced attractor hopping between dynamical states found in a single transverse mode vertical-cavity surface-emitting laser (VCSEL) subject to parallel optical injection. These transitions involve dynamical states with different polarizations of the light emitted by the VCSEL. We report an experimental map identifying, in the injected power-frequency detuning plane, regions where attractor hopping between two, or even three, different states occur. The transition between these behaviors is characterized by using residence time distributions. We find multistability regions that are characterized by heavy-tailed residence time distributions. These distributions are characterized by a -1.83±0.17 power law. Between these regions we find coherence enhancement of noise-induced attractor hopping in which transitions between states occur regularly. Simulation results show that frequency detuning variations and spontaneous emission noise play a role in causing switching between attractors. We also find attractor hopping between chaotic states with different polarization properties. In this case, simulation results show that spontaneous emission noise inherent to the VCSEL is enough to induce this hopping., This work has been funded by the Ministerio de Economía y Competitividad (MINECO/FEDER, UE), Spain under project TEC2015-65212-C3-1-P. A.Q. acknowledges FWO for support from a Postdoc fellowship and K.P. is grateful to the Methusalem Foundation for financial support.

We report an experimental study of the polarization nonlinear dynamics in a 1550 nm single-mode vertical-cavity surface-emitting laser (VCSEL) subject to parallel optical injection. Experimentally measured stability maps identifying regions of different nonlinear dynamics for various values of bias current are reported. We show that VCSELs with more than a 35 dB polarization mode suppression ratio can have rich nonlinear dynamics in both linear polarizations, including periodic and chaotic behaviors appearing simultaneously in both polarization modes., Ministerio de Economía y Competitividad (MINECO) (TEC2015-65212-C3-1-P); Fonds Wetenschappelijk Onderzoek (FWO); Agence Nationale de la Recherche (ANR) (ANR-12-JS03-005); Prefecture de Region Grand-Est (Chair in Photonics, FEDER [PHOTON, APOLLO], FNADT[APOLLO, PIANO]); AIRBUS-GDI Simulation; Metz Metropole; Conseil Departemental de Moselle; Conseil Regional Grand-Est.

We demonstrate an asymmetric dual-loop feedback method to suppress external cavity side-modes induced in self-mode-locked quantum-dash lasers with conventional single-and dual-loop feedback. In this Letter, we report optimal suppression of spurious tones by optimizing the delay in the second loop. We observed that asymmetric dual-loop feedback, with large (similar to 8x) disparity in loop lengths, gives significant suppression in external-cavity side-modes and produces flat radio frequency (RF) spectra close to the main peak with a low timing jitter, compared to single-loop feedback. Significant reduction in RF linewidth and timing jitter was produced by optimizing the delay time in the second feedback loop. Experimental results based on this feedback configuration validate predictions of recently published numerical simulations. This asymmetric dual-loop feedback scheme provides simple, efficient, and cost-effective stabilization of optoelectronic oscillators based on mode-locked lasers. (C) 2017 Optical Society of America

Polarization switching in a long-wavelength vertical-cavity surface-emitting laser (VCSEL) under parallel optical injection is analyzed in a theoretical and experimental way. For the first time, to our knowledge, we report experimentally a state in which injection locking of the parallel polarization and excitation of the free-running orthogonal polarization of the VCSEL are simultaneously obtained. We obtain very simple analytical expressions that describe both linear polarizations. We show that the power of both linear polarizations depend linearly on the injected power in such a way that the total power emitted by the VCSEL is constant. We perform a linear stability analysis of this solution to characterize the region of parameters in which it can be observed. Our measurements qualitatively confirm the previous theoretical predictions., Ministerio de Economía y Competitividad (MINECO/FEDER) (TEC2015-65212-C3-1-P); Fonds Wetenschappelijk Onderzoek (FWO); Methusalem Foundation.

We investigate experimentally and theoretically the multi-mode dynamics of a two-color quantum dot laser subject to time-delayed optical feedback. We unveil energy exchanges between the longitudinal modes of the excited state triggered by variations of the feedback phase, and observe that the modal competition between longitudinal modes appears independently within the ground state and excited state emission. These features are accurately reproduced with a quantum dot laser model extended to take into account multiple modes for both ground and excited states. Finally, we discuss the significant impact of such behavior on feedback-based control of two-color quantum dot lasers. (C) 2016 Optical Society of America

© 2015 American Physical Society. We study the occurrence of anticipated synchronization in two complex Ginzburg-Landau systems coupled in a master-slave configuration. Master and slave systems are ruled by the same autonomous function, but the slave system receives the injection from the master and is subject to a negative delayed self-feedback loop. We give evidence that the magnitude of the largest anticipation time, obtained for complex-valued coupling constants, depends on the dynamical regime where the system operates (defect turbulence, phase turbulence, or bichaos) and scales with the linear autocorrelation time of the system. We also provide analytical conditions for the stability of the anticipated synchronization manifold that are in qualitative agreement with those obtained numerically. Finally, we report on the existence of anticipated synchronization in coupled two-dimensional complex Ginzburg-Landau systems., We acknowledge financial support from Ministerio de Economia y Competitividad (Spain) and Fondo Europeo de Desarrollo Regional (EC) under Project No. FIS2012-30634 (INTENSE@COSYP) and European Social Fund and Govern de les Illes Balears under program Grups Competitius.

We present a comprehensive analysis of the technique of Longitudinal-Mode-Filling (LMF) to reduce Stimulated Brillouin Scattering (SBS) limitations in Ytterbium Doped Fibre Amplifiers (YDFA), for the generation of nanosecond, temporally shaped pulses. A basic Master-Oscillator-Power-Amplifier (MOPA) system, comprising an output YDFA with 10 mu m-core active fibre, is experienced for benchmarking purposes. Input pulse-shaping is operated thanks to direct current modulation in highly multimode laser-diode seeds, either based on the use of Distributed Feed-Back (DFB) or of a Fibre Bragg Grating (FBG). These seeds enable wavelength control. We verify the effectiveness of the combination of LMF, with appropriate mode spacing, in combination with natural chirp effects from the seed to control the SBS threshold in a broad range of output energies, from a few to some tens of mu J. These variations are discussed versus all the parameters of the laser system. In accordance with the proposal of a couple of basic principles and with the addition of gain saturation effects along the active fibre, we develop a full-vectorial numerical model. Fine fits between experimental results and theoretical expectations are demonstrated. The only limitation of the technique arises from broadband beating noise, which is analysed thanks to a simplified, but fully representative description to discuss the signal-to-noise ratio of the amplified pulses. This provides efficient tools for application to the design of robust and cost-effective MOPAs, aiming to the generation of finely shaped and energetic nanosecond pulses without the need for any additional electro-optics. (C) 2014 Optical Society of America

We study polarization switching and hysteresis in a vertical-cavity surface-emitting laser (VCSEL) subject to an orthogonal optical injection, such that the polarization of the injected light is perpendicular to that of the free-running VCSEL. We use the framework of the spin-flip model to characterize the polarization state of the VCSEL as a function of the frequency detuning. With appropriated injection conditions, the orthogonal polarization turns on and locks to the injected field. Increasing and decreasing the detuning across the two locking boundaries results either in narrow or wide hysteresis cycles, or even in irreversible switching. These results are in a good agreement with recent experimental observations. Fil: Salvide, Matias. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Fisica Arroyo Seco; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Masoller, Cristina. Universidad Politecnica de Catalunya; España Fil: Torre, Maria Susana. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Fisica Arroyo Seco; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 104, 021112 (2014) and may be found at https://doi.org/10.1063/1.4861604. Competing approaches exist, which allow control of phase noise and frequency tuning in mode-locked lasers, but no judgement of pros and cons based on a comparative analysis was presented yet. Here, we compare results of hybrid mode-locking, hybrid mode-locking with optical injection seeding, and sideband optical injection seeding performed on the same quantum dot laser under identical bias conditions. We achieved the lowest integrated jitter of 121 fs and a record large radio-frequency (RF) tuning range of 342 MHz with sideband injection seeding of the passively mode-locked laser. The combination of hybrid mode-locking together with optical injection-locking resulted in 240 fs integrated jitter and a RF tuning range of 167 MHz. Using conventional hybrid mode-locking, the integrated jitter and the RF tuning range were 620 fs and 10 MHz, respectively.

Fifty years after the invention of the laser diode and fourty years after the report of the butterfly effect - i.e. the unpredictability of deterministic chaos, it is said that a laser diode behaves like a damped nonlinear oscillator. Hence no chaos can be generated unless with additional forcing or parameter modulation. Here we report the first counter-example of a free-running laser diode generating chaos. The underlying physics is a nonlinear coupling between two elliptically polarized modes in a vertical-cavity surface-emitting laser. We identify chaos in experimental time-series and show theoretically the bifurcations leading to single- and double-scroll attractors with characteristics similar to Lorenz chaos. The reported polarization chaos resembles at first sight a noise-driven mode hopping but shows opposite statistical properties. Our findings open up new research areas that combine the high speed performances of microcavity lasers with controllable and integrated sources of optical chaos., Comment: 13 pages, 5 figures

The effects of disturbances of the flow pattern in front of the fiber facet of a fiber-coupled self-mixing diode-laser Doppler velocimeter system are investigated. This was done by comparing measurements and calculations of the Doppler frequency spectrum with the expected values. The calculated Doppler spectrum was obtained from the calculation of light scattered (with or without Doppler shift) by the moving particles in front of the fiber facet. The velocity profile of the particles was calculated with a finite-element method. Measurements were done with water (with polystyrene spheres) and whole blood as the samples. Good agreement between measurements and calculations were obtained. The velocimeter was modeled as a five-mirror setup. The reflectivity of the fiber facet closest to the laser turns out to have the most influence on the sensitivity and stability of the laser. Direct reflection of unwanted light back into the laser cavity was avoided by placing a glass plate in front of the fiber. Design considerations are presented.

International audience; We study the dynamics of an optically injected quantum-dot laser accounting for excited states. Mapping of the bifurcations in the plane frequency detuning vs. injection strength shows that the relaxation rate scales the regions of locking and single- and double-period solutions, while the capture rate has a minor effect. Within the regions of time-periodic solutions, close to the saddle-node bifurcation boundary, we identify subregions where the output signal resembles excitable pulses as a result of the bottleneck phenomenon. We show that such emission is determined mainly by fluctuations in the occupation of the excited states. The interpulse time follows an inverse square root scaling law as a function of the detuning. In a deterministic system the pulses are periodic regardless of the detuning, but in the presence of noise, close to the locking region, the interpulse time follows a positively skewed normal distribution. For a fixed frequency detuning, increasing the noise strength can shift the mean of the interpulse time distribution and make the pulsations more periodic.

International audience; We unveil the bifurcations underlying polarization switching and injection locking in a vertical-cavity surface-emitting laser subject to optical injection. A Hopf bifurcation, not reported for conventional edgeemitting lasers, delimits the injection locking region and influences the polarization switching conditions. We furthermore theoretically show and experimentally observe periodic dynamics at the relaxation oscillation frequency in the noninjected mode together with wave-mixing dynamics in the injected mode. These dynamics precede the polarization switching leading to injection locking and are attributed to a torus bifurcation arising on a two-polarization mode solution.

International audience; We report theoretically on a pure frequency-induced polarization bistability in a vertical-cavity surface-emitting laser (VCSEL) subject to orthogonal optical injection, i.e., the master laser light polarization is orthogonal to that of the slave VCSEL. As the frequency detuning is scanned from negative to positive values and for a fixed injected power, the VCSEL exhibits two successive and possibly bistable polarization switchings. The first switching (from the slave laser polarization to the injected light polarization) exhibits a bistable region whose width is maximum for a given value of the injected power. Such a dependency of hysteresis width on the injected power is similar to that recently found experimentally by Hong et al.[Electron. Lett. 36, 2019 (2000)]. The bistability accompanying the second switching (from the injected light polarization back to the slave laser free-running polarization) exhibits, however, significantly different features related to the occurrence of optical chaos. Interestingly, the width of the bistable region can be tuned over a large range not only by modifying the injection parameters but also by modifying the device parameters, in particular the VCSEL linewidth enhancement factor.

The carrier-induced refractive index in quantum dot (QD) structures due to optical transitions from QD levels to continuum states is considered. It is shown that, for large photon energies, the refractive index change is given asymptotically by the Drude formula. Calculations of the linewidth enhancement factor, alpha, show that alphasimilar to1 due to this contribution to the total refractive index. Furthermore, for highly localized QD states, the absorption coefficient at the photon energies similar to0.8-1.0 eV due to these transitions can be on the order of 10(3) m(-1). (C) 2004 American Institute of Physics. (DOI: 10.1063/1.1639933)

The correspondence between long-delayed systems and one-dimensional spatially extended media enables a direct interpretation of purely temporal phenomena in terms of spatio- temporal patterns. On the basis of this result, we provide the evidence of a characteristic spatio- temporal dynamics —coarsening— in a long-delayed bistable system. Nucleation, propagation and annihilation of fronts, leading eventually to a single phase, are observed in an experiment based on a laser with opto-electronic feedback. A numerical and analytical study of a general phenomenological model is also performed and compared with the experimental findings. Copyright c EPLA, 2012

The effects of disturbances of the flow pattern in front of the fiber facet of a fiber-coupled self-mixing diode-laser Doppler velocimeter system are investigated. This was done by comparing measurements and calculations of the Doppler frequency spectrum with the expected values. The calculated Doppler spectrum was obtained from the calculation of light scattered (with or without Doppler shift) by the moving particles in front of the fiber facet. The velocity profile of the particles was calculated with a finite-element method. Measurements were done with water (with polystyrene spheres) and whole blood as the samples. Good agreement between measurements and calculations were obtained. The velocimeter was modeled as a five-mirror setup. The reflectivity of the fiber facet closest to the laser turns out to have the most influence on the sensitivity and stability of the laser. Direct reflection of unwanted light back into the laser cavity was avoided by placing a glass plate in front of the fiber. Design considerations are presented.

We present a comprehensive study of the bifurcation routes in a generic model of a two-polarization-mode semiconductor laser when subject to orthogonal optical injection, relevant to a single-transverse-mode verticalcavity surface-emitting laser. For positive detunings, polarization switching (PS) occurs as the intensity of the noninjected mode gradually decreases and eventually shuts down, in some cases accompanied along the way by the onset and the subsequent vanishing of relaxation oscillations. We identify a Hopf bifurcation on a two-polarization-mode solution, which supports the onset of relaxation oscillation time-periodic dynamics in both injected (x-linearly polarized) and noninjected (y-linearly polarized) modes. For sufficiently large negative detunings, PS is a sharp transition occurring either at the injection-locking point or at a subcritical Hopf bifurcation and is often part of a hysteresis cycle. (C) 2009 Optical Society of America

We investigate the generation of amplitude-squeezed states with degenerate optical parametric amplifiers that are pumped by focused Gaussian beams. We present a model that facilitates the calculation of the squeezing level for an experimentally realistic cofiguration in which there is a Gaussian input signal beam that has the same confocal parameter and waist location as the Gaussian pump beam, with no restriction on the interaction length-to-confocal parameter ratio. We show that the 3-dB squeezing limit that was thought to be imposed by the Gaussian pump profile can be exceeded in the (previously uninvestigated) tight-focusing regime. We find the maximum possible amplitude squeezing in this regime to be 4.65 dB. However, it is possible to increase the squeezing level further by spatially filtering the tails of the output signal beam, resulting in squeezing levels in excess of 10 dB. (C) 2001 Optical Society of America.

The thermal behavior of visible AlGaInP-GaInP ridge laser diodes is investigated numerically and experimentally. It is shown that various parameters critically influence the thermal resistance R of such devices. R is inversely proportional to the thermal conductivity of the heatsink. A substantial improvement in R-quite larger than in the AlGaAs system-is achieved for junction-side-down mounting compared to junction-side-up. R depends strongly on the width w of the ridge and this effect is different for junction-side-up or down mounting. In the first case, R is similar to log (w) and in the second, R is similar to 1/w. The thickness of the soldering material is a sensitive parameter which may increase the value of R by up to 15 K/W. On the other hand, for junction-side-up mounted devices, the top metallization layer has a very favorable effect: a 1 mum thick gold layer reduces R by 30%. The dynamics of thermal phenomena is also studied. It is shown that when a laser is switched on the steady state is reached in the ms time range. Finally, our experimental results show a very good agreement with our numerical data.

International audience; During the last five years, optical chaos-based random bit generators (RBGs) attracted a lot of attention and demonstrated impressive performances with bit rates up to hundreds of Gbps. However all the suggested schemes use external injection schemes (optical injection or feedback) to turn the lasers into chaos, hence strongly increasing setup complexity. On the other hand, we reported that a laser diode can generate a chaotic output without the need for external perturbation or forcing, hence unveiling a highly simplified way to generate an optical chaos at high frequency. However the low dimension and limited number of positive Lyapunov exponent casted doubts about its direct use for chaos-based applications. Here we make a proof-of-concept demonstration for a Random Bit Generator based on polarization chaos. We therefore suggest a highly simplified RBG scheme using only a free-running laser and small-bandwidth acquisition electronics and demonstrate convincing performances with bit rates up to 100 Gbps without unusual or complex post-processing methods. We link these performances to the double-scroll structure of the chaotic attractor rather than the bandwidth of the dynamics, hence bringing new light on the importance of chaos topology for chaos-based applications. In addition our scheme exhibit a strong potential as it enables a low-cost and/or integrated in parallel on-chip scheme.

Optically-pumped vertical external cavity surface emitting lasers (VECSELs) based on flip-chip gain mirrors emitting at the 1.55-mu m wavelength range are reported. The gain mirrors employ wafer-fused InAlGaAs/InP quantum well heterostructures and GaAs/AlAs distributed Bragg reflectors, which were incorporated in a linear and a V-cavity configurations. A maximum output power of 3.65 W was achieved for a heatsink temperature of 11 degrees C and employing a 2.2% output coupler. The laser exhibited circular beam profiles for the full emission power range. The demonstration represents more than 10-fold increase of the output power compared to state-of-the-art flip-chip VECSELs previously demonstrated at the 1.55-mu m wavelength range, and opens a new perspective for developing practical VECSEL-based laser system for applications such as LIDAR, spectroscopy, communications and distributed sensing.