Search

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.

CLEO Topic 14 " Optical Metrology ", session CMH " Ultrahigh-Resolution Spectroscopy " [CMH1]; International audience; A new method using optical injection is proposed to measure spectral linewidth of coherent single mode lasers. Theoretical model and experimental measurement of a 50 kHz full width half maximum linewidth fiber laser are presented.

conference 5452 « Semiconductor Lasers and Laser Dynamics » [5452-63], proceedings of SPIE (ISBN 9780819453754); International audience; Feeding light inside a semiconductor laser gives rise to a wealthy set of dynamics that have been largely described. The two fundamental parameters are the detuning and the injected power. We present here theoretical and experimental evidence that other parameters may play a role. For instance, injecting with an orthogonal polarization is not equivalent to nullify the effect of optical injection as demonstrated by our experimental map. We will focus the main part of the talk on the influence of coherence. Some part of this study has been made possible by the use of a single-frequency fibre laser which enables us to establish an enlightening comparison between these two different types of lasers and also to surround the influence of coherence.

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; A new configuration of micro-lensed fibre that consists of a quarter pitch length of 125/125 /spl mu/m graded index section with a hyperbolic end shape is proposed. Low loss and long working distance for laser diode and singlemode fibre coupling have been verified.

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.

The main control parameters of a single mode semiconductor laser submitted to an injected external signal are the power and the frequency of the injected signal. Following their magnitude, many phenomena can be observed such as phase locking, frequency locking, frequency generation, push-pull effects, hysteresis phenomena and chaos,... We show here that the spectral signature of the slave laser enables a better understanding of the the nonlinear interaction between the two competing sources: the spontaneous emission and the external field for which spectra are equally amplified through the active medium. This amplification is then strongly dependent on their coherency. We describe the role of the injected laser as a filter and an amplifier. It follows that the laser can be used to process information in ways that are not yet completely exploited. To cite this article: S. Blin et al., C. R. Physique 4 (2003).

EQEC session EP1 " EQEC Postdeadlines " [EP1-2-THU]; International audience; This work shows that at high injected power (> 0 dBm), huge bistable area (extending over 11 dB and 35 GHz) for a slave laser operating at four times its threshold (the optical output power is equal to 5 dBm). Moreover, for moderate injected power (-10 dBm), that are usually presented in the literature, the authors observe multistability that has been already predicted.

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.

Summary form only given. The main idea of optical injection is to give a reference to the injected laser from another laser. The injected laser can become slaved onto the master and frequency-locking occurs following the injected intensity and the frequency difference between both lasers. Phase locking is a different phenomenon which manifests itself in the locking of the linewidth of the slaved laser onto that of the master. The topics of this communication is to describe the power spectral density of the injected laser when the injected power is decreased to very low level (/spl sim/picowatt) with a central frequency identical for both lasers but each of them having very different linewidths. The study follows from an interpretation of the laser as a filter and amplifier as recently given.

We present a new scheme to obtain chaotic synchronization of two semiconductor lasers. We show synchronization even for a large range of values of injected power. The synchronization is shown to be very sensitive to the spectral signature of the master laser.

Summary form only given. An injected (slave) laser can become slaved onto another one (master) and frequency locking occurs following the injected intensity and the frequency difference between both lasers. Optical injection can give a frequency reference or transfer to a slave the spectral properties (linewidth) from a master. For lasers tuned on the same central frequency, decreasing the injected power implies a partial linewidth transfer, when the master linewidth is larger than the slave linewidth. In the converse case (master linewidth smaller than slave linewidth), the laser amplifies at the sample rate both the spontaneous emission from the slave and the external injected field. We have in this way characterized optical spectra of signals in the picowatt range. In our experiment, two single mode lasers are used: a tunable source with a linewidth of 80 kHz for the master and a DFB laser for the slave with a linewidth much wider (2-200 MHz) depending on the bias current. Adding to the laser detector a heterodyne technique, signals in the femtowatt range were detected. The aim is to study the amplification of the laser detector.

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.

COLOQ 7 " 7ème COloque sur les Lasers et l'Optique Quantique " (Rennes, France, september 2001); National audience; Nous proposons une méthode simple pour obtenir les fonctions de base des représentations irréductibles. Une procédure automatisée est proposée pour exprimer les opérateurs de projection comme combinaisons d'harmoniques sphériques. L'application de cet automate permet l'obtention des harmoniques cubiques (fonctions associées à la symétrie cubique) à partir desquelles les fonctions propres des bandes de conduction et de valence dans GaAs sont exprimées.

COLOQ 7 " 7ème COloque sur les Lasers et l'Optique Quantique " (Rennes, France, september 2001); National audience; Les résultats concernent l'injection optique d'un laser à semi-conducteurs de type DFB émettant à la longueur d'onde de 1550 nm. Nous dressons des cartographies intra et intermodes présentant les différents comportements d'un laser soumis à injection optique (accrochage total, mélanges multi-ondes, chaos...) dans le plan (puissance injectée / désaccord en fréquence entre le maître et l'esclave). Nous montrons la différence notable entre un laser esclave polarisé prias ou loin du seuil et nous précisons également les zones de bistabilités.

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.

Scalability in terms of both capacity and energy are gaining increasing focus as potential bottlenecks for future optical communication networks. Traffic growth is outpacing the rate of network efficiency improvements as well as the rate of optical system capacity improvement. Laboratory results are rapidly approaching the fiber transmission spectral efficiency limits. The energy efficiency benefits derived from Moore's law scaling are slowing. Research is under way today to address these challenges, covering the full range of technologies from devices to systems and networks. While many problems can be tackled by working independently within these areas, often important innovation comes from solutions that cut across such topical boundaries. Understanding device performance impacts and likewise network requirements can be essential to unlocking the critical ideas that lead to progress.

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.

We describe an all-fiber ytterbium-doped laser followed by a double-stage ytterbium-doped double-clad fiber amplifier of 10-W output power for helium pumping. Different cavity designs are investigated with the goal of achieving high-power multimode emission at 1083 nm, wavelength tunability over the helium absorption bands, and linewidth envelope control over the range 1-3 GHz. We point out the domains with unstable output power and discuss their origin.

We demonstrate simultaneous mode locking of more than 24 wavelengths at 3 GHz in an actively mode-locked erbium-doped fiber laser operating at room temperature. The multiwavelength operation is achieved when a frequency shifter and an all-fiber 50-GHz periodic filter are inserted into a ring cavity. Active mode locking is performed with an amplitude modulator, and pulses with a FWHM of 30 ps are obtained.

Experiments are described that show that polarization of light in a vertical-cavity surface-emitting laser subjected to isotropic optical feedback can jump regularly back and forth between two orthogonal states when the injection current is increased. The polarization-resolved light-current characteristic curves are thus channeled. This effect occurs when the dichroism of the laser is weak enough to allow the effective (isotropic) reflectance to impose the polarization. A comparison of a model introduced by San Miguel [Phys. Rev. A52, 1728 (1995)] and the standard equations indicates that the best description is given when no spin relaxation is included.

Lasers that are almost optically isotropic may operate on more than one polarization mode. Here we report on the polarization states of microchip YAG lasers, their control by polarized feedback, and the dynamics of the polarization flips. Switching and polarization relaxation oscillations are observed, both of which are much faster than the inverse of the population decay rate.

Summary form only given. An erbium-doped fiber laser exhibits self-pulsing behavior when the ion-pair concentration x is large enough (x>5%). For high concentration (x>10%), this behavior is observed for any pump level while for intermediate values, it is dependent on the pumping rate. In this case, when the laser is operating on two wavelengths, antiphase dynamics and chaos have been reported. A generalized bistability has been predicted and observed. However in all these experimental results, only the temporal traces were recorded. In this communication, experimental bifurcation diagrams will be presented with respect to the pumping rate.

International audience; In this study we report, through a comparative analysis of static and dynamic measurements, on the impact of mode hopping on the overall intensity noise dynamics of InGaN edge emitting lasers. Mode clustering usually observed in InGaN lasers enhances the mode competition and then the laser intensity fluctuation. Variations as large as 20 dB have been observed. The coexistence of longitudinal modes induces mode competition and then unstable bimodal lasing. This mode competition is mediated by temporal fluctuations of spontaneous emission through nonlinear cross saturation of the optical gain. The subsequent enhancement of the relative intensity noise can be detrimental for applications where the intensity stability of InGaN lasers is a key parameter. Our experimental observations are supported by a simple rate equation model. We point out the major importance of the different modal gain in the bimodal regime on the overall intensity noise of the laser.

conference 6603 « Noise and Fluctuations in Photonics, Quantum Optics, and Communications » session « Posters-Wednesday » [6603-92]; International audience; A sensitive technique to measure the relative intensity noise of a laser is described. Such experiment is a useful tool for laser characterizations, allowing direct measurement of physical parameters like relaxation oscillation frequencies and damping factor. Examples of determination of such parameters are given.

A class of laser which exhibits ultra-narrow sub MHz linewidth emission necessary for numerous applications in optical communications and sensors is described. The spectral performance of commercial discrete mode (DM) and distributed feedback (DFB) lasers is compared. The devices used in this work are asymmetrically coated ridge waveguide Fabry Perot lasers which incorporated etched slot features and emitting around lambda = 1.55 mum. The active region of the devices consisted of a strained compensated InAlGaAs MQW structure.

International audience; Nous présentons un système d’imagerie hyperspectrale active basée sur l’illumination par un laser à cascade quantique largement accordable dans l’infrarouge moyen. Une méthode de réduction du « speckle », présent dans nos images acquises, est développée.

technical session OThG " Future WDM-PON " [OThG6]; International audience; A novel WDM-PON delivering 10-Gb/s downstream based on L-band loss-less reflective-amplified-modulator and 2.5-Gb/s upstream based on C-band injection-locked Fabry-Perot laser is experimentally demonstrated for 24 channels over 25-km, using quantum-dash mode-locked laser-based multiple-wavelengths seeding sources.

session We3.P « posters » [We3.P.12], ISBN 2-912328-34-9; International audience; We report 570-fs pulse generation based on soliton-effect compression in a 22 m-long non-linear holey fibre. Using soliton-effect compression, we propose a simple method to measure second-order dispersion of fibres in the anomalous dispersion regime.

We report the triple-functionality at 10-Gb/s of an integrated R-EAM-SOA, including modulation, detection and noise-mitigated 2R all-optical signal regeneration. The obtained results demonstrate its high potential for a multi-operation device in colorless WDM access networks.

International audience; We demonstrate 100 km transmission at 28 Gbit/s/channel of 4 DWDM channels using a single quantum-dash mode-locked laser. The amplitude noise of each filtered laser line is improved using limiting amplification in an SOA.

Round-Robin measurements on the linewidth enhancement factor are carried out within several laboratories participating to EU COST 289 Action. The a-factor is measured by applying up to 7 different techniques. The obtained results are compared. (C) 2007 Optical Society of America

Stimulated Brillouin Scattering (SBS) is a coherent interaction process in which light is scattered from optically generated acoustic waves. It is a powerful tool for microwave and optical signal processing, distributed sensing and spectroscopy. Brillouin lasers are attracting a lot of interest for their ability to produce ultra coherent linewidths.This thesis is devoted to the understanding of noise properties of Brillouin fiber ring lasers, operating with multiple Stokes orders. First, we present a technique based on the cavity ringdown method, which allows to characterize the Brillouin gain coefficient directly from probing the laser cavity. Its advantages are to obtain parameters from a single experiment with low optical powers (some 10 milliwatts) for short cavities (a few meters long, or integrated cavities).Secondly, it is shown that an intrinsic linewidth of a few tens of mHz can be easily obtained by cascading two non-resonant Brillouin lasers (for which the pump performs a single pass inside the cavity). In order to obtain these results, the long-term stability has been improved by using a Pound-Drever-Hall servo loop, which allows us to compare our analytical and experimental results. Unfortunately, we were unable to explore the fundamental limits of noise reduction due to the noise floor of our bench.Thirdly, one of the major works of this thesis is the theoretical and experimental study of the noise properties, including frequency noise and relative intensity noise, of a resonant Brillouin laser (for which pump and Stokes waves are resonant inside the cavity). In particular, the impacts of the fiber-ring-cavity quality factor, Brillouin gain detuning, are evaluated very precisely on the laser RIN features such as amplitude noise reduction and relaxation frequency.We emphasize the fact that many characteristics of the frequency noise are related to the RIN properties by a coupling between intensity and phase. We show that the cascade process modifies the dynamics of the Brillouin laser when compared to those of a single-mode Brillouin laser with a single first-order Stokes component. Our experimental results are in excellent agreement with our numerical simulations, obtained thanks to our non-linear system describing the operation of a multi-Stokes Brillouin laser. This good match is mainly due to our ability:* to obtain very precise values of the cavity parameters and the Brillouin gain coefficient using the CRDM technique;* to achieve long-term stability (hours);* to finely control the detuning between the laser Stokes resonance and the frequency of the Brillouin gain maximum.We demonstrate experimentally for the first time that frequency noise is degraded in the presence of anti-Stokes Brillouin scattering. We also show that a gain detuning of the order of a few hundred kHz can degrade the intensity noise reduction or also increase the linewidth by amplitude-phase coupling. All these very fine observations thus allow us to set the fundamental limits of such laser systems such as: the increase in noise due to anti-Stokes orders; the role of pump noise and its possible interrelation with cavity finesse; the effect of the detuning inherent to higher Stokes orders.All these conclusions are key to the design and engineering of these Brillouin fiber lasers, which are currently attracting a great deal of interest as evidenced by the work in progress in the scientific community. This PhD thesis contributes to a better under-standing of multi-Stokes Brillouin lasers., La diffusion Brillouin stimulée (SBS) est un processus d’interaction cohérent, pour lequel la lumière est diffusée à partir des ondes acoustiques générées optiquement. C’est un outil puissant pour le traitement des micro-ondes et des signaux optiques, la détection distribuée et la spectroscopie. Les lasers Brillouin suscitent un très grand intérêt pour leur capacité à produire des largeurs de raie ultra cohérentes.Cette thèse est consacrée à la compréhension des propriétés de bruit des lasers à fibre Brillouin en anneau, fonctionnant avec de multiples ordres de Stokes. Tout d’abord, nous présentons une technique basée sur la méthode de ringdown de la cavité, qui permet de caractériser le coefficient de gain Brillouin directement à partir du sondage de la cavité laser. Ses avantages sont d’obtenir des paramètres à partir d’une seule expérience avec de faibles puissances optiques (quelques 10 milliwatts) pour des cavités courtes (quelques mètres de long, ou cavités intégrées).Deuxièmement, il est démontré qu’une largeur de raie intrinsèque de quelques dizaines de mHz peut être facilement obtenue en cascadant deux lasers Brillouin non résonants (pour lesquels la pompe effectue un seul passage à l’intérieur de la cavité). Afin d’obtenir ces résultats, la stabilité à long terme a été améliorée en utilisant une boucle d’asservissement de type Pound Drever Hall, ce qui nous permet de comparer nos résultats analytiques et expérimentaux. Malheureusement, nous n’avons pas exploré les limites fondamentales de la réduction du bruit en raison du plancher de bruit de notre banc de mesure.Troisièmement, un des travaux majeurs de cette thèse est l’étude analytique et expérimentale des propriétés du bruit, y compris le bruit de fréquence et le bruit relatif d’intensité, d’un laser Brillouin résonant (pour lequel, les ondes de pompe et de Stokes sont résonantes à l’intérieur de la cavité). En particulier, les impacts du facteur de qualité de la cavité fibrée en anneau, le désaccord de gain Brillouin ont été évalués très précisément sur les caractéristiques du RIN du laser telles que la réduction de l’amplitude du bruit et la fréquence de relaxation.Nous soulignons le fait que de nombreuses caractéristiques du bruit de fréquence sont liées aux propriétés du RIN par un couplage entre l’intensité et la phase. Nous montrons que le processus en cascade modifie la dynamique du laser Brillouin par rapport à celle d’un laser Brillouin monomode avec une seule composante de Stokes de premier ordre. Nos résultats expérimentaux sont en excellent accord avec nos simulations, obtenues grâce à notre système non linéaire décrivant le fonctionnement d’un laser Brillouin multi-Stokes. Cette bonne concordance est principalement due à notre capacité :* à obtenir des valeurs très précises des paramètres de la cavité et du coefficient de gain Brillouin en utilisant la technique CRDM ;* à atteindre une stabilité à long terme (plusieurs dizaines d’heures) ;* à contrôler finement le désaccord entre la résonance de Stokes du laser et la fréquence du maximum de gain Brillouin.Nous démontrons expérimentalement pour la première fois que le bruit de fréquence est dégradé en présence d’une diffusion Brillouin anti-Stokes. Nous montrons également qu’un désaccord de gain de l’ordre de quelques centaines de kHz peut dégrader la réduction du bruit d’intensité ou également augmenter la largeur de raie par un couplage amplitude-phase. Toutes ces observations très fines nous permettent donc de fixer les limites fondamentales de tels systèmes laser comme : l’augmentation du bruit due aux ordres anti-Stokes ; le rôle du bruit de pompe et son interrelation possible avec la finesse de la cavité ; l’effet du désaccord inhérent aux ordres de Stokes plus élevés.Toutes ces conclusions sont les clés de la conception et de l’ingénierie de ces lasers à fibre Brillouin, qui suscitent actuellement beaucoup d’intérêt comme en témoignent les travaux en cours dans la communauté scientifique. Cette thèse de doctorat contribue à une meilleure compréhension des lasers Brillouin multi-Stokes.

Thermal imaging and the recent availability of widely tunable infrared QCL lasers (Quantum Cascade Laser) allow us to propose an active hyperspectral imaging system operating in mid-infrared (MIR) band, where the system output consists in series of narrow band sub-images arranged across the reflectance spectrum of the sample, forming a hypercube data acquired by « staring » acquisition technique. In order to evaluate more precisely the capacities of the active hyperspectral imaging, we propose a system composed of four powerful QCL tunable lasers (in order to cover 3,9 µm to 4,7 µm and 7,5 µm to 11 µm wavelengths) and two cameras: an InSb cooled camera for 3-5 µm range and a bolometer for 7,5-13 µm range. We present the algorithm for image acquisition, image and data processing to obtain spectra of averaged zones of plant leaves. Finally, we present and discuss results using PLS-DA classification technique to characterize health status of different plants under controlled growing conditions, separated in two classes: reference ones were maintained at 80 % of field capacity and stressed ones at 20 %. Initial results have shown the ability of proposed system to separate plants for early water stress detection.; L'imagerie thermique et la récente disponibilité des lasers QCL (Quantum Cascade Laser) largement accordables, nous permettent de proposer un système d'imagerie hyperspectrale active fonctionnant dans l'infrarouge moyen (MIR), où la sortie du système consiste en une série de sous-images à bande étroite disposées sur le spectre de réflectance de l'échantillon, formant un hypercube de données acquises par la technique d'acquisition « staring ». Afin d'évaluer plus précisément les capacités de l'imagerie hyperspectrale active, nous proposons un système de mesure composé de quatre lasers accordables QCL (afin de couvrir les longueurs d'onde de 3,9 µm à 4,7 µm et de 7,5 µm à 11 µm), et de deux caméras : InSb refroidie pour la gamme spectrale 3-5 µm et un bolomètre pour la gamme 7,5-13 µm. Nous présentons également l'algorithme d'acquisition et de traitement des images pour obtenir les spectres des mesures sur la surface des feuilles des plantes. Enfin, nous présentons et discutons les résultats obtenus en utilisant la technique de classification PLS-DA pour caractériser l'état hydrique de différentes plantes dans des conditions de croissance contrôlées au sein de laboratoire, séparées en deux classes : les plantes de témoins ont été maintenues à 80 % de la capacité du champ (CC) et les plantes stressées à 20 %. Des premiers résultats ont montré la capacité du système proposé à séparer les plantes pour une détection précoce du stress hydrique.

Studying relative intensity noise (RIN) of gallium nitride edge emitting laser diodes, the strong correlation between noise dynamics and spectral behavior impacted by mode clustering is highlighted. An analytical model is used to explain experimental results. Then we study single-longitudinal-mode laser diode (LD) emitting around 420 nm. Spectral filtering is achieved using high order aperiodic Bragg grating. A novel approach, involving standard lithography technique with a resolution close to the micron, is proposed unlike most of works of the domain using high resolution e-beam lithography. Release of the resolution constraint paves the way for mass production of low-cost single-mode diode laser devices. Aperiodic grating, mostly used in the telecom range, is designed to 420 nm diode laser using numerical modelling. First single-mode structures are fabricated at EPFL. Measurements of optically pumped devices prove the feasibility of the technique. In the third work we study spectral narrowing of InGaN LD by means of external cavity. Feedback is provided by a specially designed 400 nm Bragg grating optically written on a single-mode fiber. Using that setup, we obtain single-frequency emission with more than 40 dB side-mode suppression ratio, about 50 mW optical power and less than 2.4 MHz linewidth.; Par l'étude du bruit relatif d'intensité (RIN) dans des diodes lasers (DL) en nitrure de gallium à émission par la tranche, nous mettons en évidence la corrélation entre la dynamique du RIN et la structure spectrale, fortement impactée par le phénomène de mode clustering. Cette étude est interprétée grâce à un modèle analytique. Suit une étude de DL InGaN monomode longitudinale émettant autour de 420 nm. La sélection spectrale est obtenue par inscription d'un réseau de Bragg apériodique d'ordre élevé. L'originalité de cette approche tient dans l'utilisation d'une technique de lithographie standard (résolution ≃1 µm), là où la majorité des résultats dans le domaine sont obtenus par lithographie e-beam de haute résolution. Le relâchement de cette contrainte ouvre la voie pour la production de composants monomodes à faible coût. L'adaptation vers 420 nm de la technique de gravure d'un réseau apériodique, principalement employée aux longueurs d'onde télécom, est obtenue par la modélisation numérique du réseau. Des structures monomodes sont caractérisées sous pompage optique démontrant la faisabilité de la technique. Un dernier volet de ce travail concerne l'affinement spectral d'une diode InGaN par l'utilisation d'un réseau de Bragg fibré, à 400 nm, développé dans le cadre de cette thèse. Cette configuration permet d'obtenir une émission monofréquence (taux de suppression des modes latéraux supérieure à 40 dB) avec une puissance de sortie d'une cinquantaine de mW et une largeur de raie inférieure à 2,4 MHz.

Studying relative intensity noise (RIN) of gallium nitride edge emitting laser diodes, the strong correlation between noise dynamics and spectral behavior impacted by mode clustering is highlighted. An analytical model is used to explain experimental results. Then we study single-longitudinal-mode laser diode (LD) emitting around 420 nm. Spectral filtering is achieved using high order aperiodic Bragg grating. A novel approach, involving standard lithography technique with a resolution close to the micron, is proposed unlike most of works of the domain using high resolution e-beam lithography. Release of the resolution constraint paves the way for mass production of low-cost single-mode diode laser devices. Aperiodic grating, mostly used in the telecom range, is designed to 420 nm diode laser using numerical modelling. First single-mode structures are fabricated at EPFL. Measurements of optically pumped devices prove the feasibility of the technique. In the third work we study spectral narrowing of InGaN LD by means of external cavity. Feedback is provided by a specially designed 400 nm Bragg grating optically written on a single-mode fiber. Using that setup, we obtain single-frequency emission with more than 40 dB side-mode suppression ratio, about 50 mW optical power and less than 2.4 MHz linewidth.; Par l'étude du bruit relatif d'intensité (RIN) dans des diodes lasers (DL) en nitrure de gallium à émission par la tranche, nous mettons en évidence la corrélation entre la dynamique du RIN et la structure spectrale, fortement impactée par le phénomène de mode clustering. Cette étude est interprétée grâce à un modèle analytique. Suit une étude de DL InGaN monomode longitudinale émettant autour de 420 nm. La sélection spectrale est obtenue par inscription d'un réseau de Bragg apériodique d'ordre élevé. L'originalité de cette approche tient dans l'utilisation d'une technique de lithographie standard (résolution ≃1 µm), là où la majorité des résultats dans le domaine sont obtenus par lithographie e-beam de haute résolution. Le relâchement de cette contrainte ouvre la voie pour la production de composants monomodes à faible coût. L'adaptation vers 420 nm de la technique de gravure d'un réseau apériodique, principalement employée aux longueurs d'onde télécom, est obtenue par la modélisation numérique du réseau. Des structures monomodes sont caractérisées sous pompage optique démontrant la faisabilité de la technique. Un dernier volet de ce travail concerne l'affinement spectral d'une diode InGaN par l'utilisation d'un réseau de Bragg fibré, à 400 nm, développé dans le cadre de cette thèse. Cette configuration permet d'obtenir une émission monofréquence (taux de suppression des modes latéraux supérieure à 40 dB) avec une puissance de sortie d'une cinquantaine de mW et une largeur de raie inférieure à 2,4 MHz.

Optical frequency combs obtained from mode-locked laser diodes are potential candidates for WDM networks. However, their lines exhibit usually a broad optical linewidth ( 1-100 MHz). Thus their use is incompatible for high order modulation formats WDM based systems. This thesis investigates one solution to overcome this limitation. It consists of using a feed-forward heterodyne technique to reduce the frequency noise of each comb-line and consequently their optical linewidths. In a first approach, the technique is applied to a single-mode laser. This allowed us to validate its proper working and to identify the intrinsic limits of the experimental device set up. The latter analysis enabled us to reveal that the minimum achievable frequency noise level by our system, corresponds to a 50 Hz intrinsic optical linewidth spectrum and a 1,6 kHz optical linewidth based on 10 ms observation time. This technique is then applied to an actively mode-locked laser diode demonstrating, at our system output, a 21-line optical frequency comb with intrinsic optical linewidths reduced to below 7 kHz. It is worth noting that 9 among them, exhibit sub-kHz linewidths. For an observation time of 10 ms, all lines share the same optical linewidth, almost equal to 37 kHz. We thus show that the timing jitter impacts the technique performances. We also highlight the relevance of such coherence level for coherent optical communication. Lastly, we study a laser frequency pre-stabilization technique based on a locking to an unbalanced fiber interferometer. When applied to a single-mode laser, the technique showed a reduction of its technical frequency noise, thus leading to a clear improvement of its integrated optical linewidth from 224 kHz to 37 kHz for 3 ms observation time. This first result provides a good support towards the exploration of mode-locked laser diodes potential for metrological applications.; Les peignes de fréquences optiques, issus de diodes à blocage de modes, font partie des candidats potentiels pour les réseaux de transmission à multiplexage en longueurs d’onde (WDM). Cependant, les modes composant leur peigne, exhibent généralement des largeurs de raie optiques relativement élevées ( 1-100 MHz), rendant ainsi incompatible leur utilisation sur un réseau WDM employant des formats de modulation avancés d’ordre supérieur. Cette thèse étudie, une solution pour palier à cette limitation. La technique utilisée, dite d’asservissement à correction aval hétérodyne, effectue un traitement du flux lumineux en sortie du laser sans agir sur ce dernier, permettant de réduire le bruit de fréquence présent sur chacune des raies et par conséquent leur largeur de raie optique. Dans une première approche, la technique est appliquée à un laser mono-fréquence. Cela a permis d’une part de valider son fonctionnement et d’autre part d’identifier les limites intrinsèques du dispositif expérimental mis en place. Ainsi, nous démontrons que le niveau de bruit de fréquence minimum permis par notre système, correspond à un spectre optique de largeur de raie optique instantanée de 50 Hz et une largeur de raie de 1,6 kHz pour un temps d’observation de 10 ms. La technique est par la suite appliquée à une diode à blocage de modes actif. Le peigne de fréquences optiques ainsi généré, est composé de 21 modes, ayant tous une largeur de raie optique intrinsèque inférieure à 7 kHz, dont 9 modes sont sub-kHz. Pour un temps d’observation du spectre optique de 10 ms, ces modes exhibent tous une largeur de raie d’environ 37 kHz. Nous démontrons ainsi l’impact de la gigue d’impulsions sur les performances de la technique et nous soulignons l’intérêt d’une telle cohérence, pour le domaine des télécommunications optiques cohérentes (transmissions WDM cohérentes de type m-QAM avec des constellations d’ordre élevé, compatibles avec des débits multi-Tbit/s par raie). En dernier lieu, nous abordons une seconde technique consistant à pré-stabiliser la fréquence d’un laser par asservissement en boucle fermée. Elle repose sur l’utilisation d’un interféromètre à fibre déséquilibré comme référence pour réduire le bruit de fréquence d’un laser, situé particulièrement en basses fréquences. Appliquée à un laser mono-fréquence, elle a permis de réduire son bruit de fréquence technique conduisant ainsi à une nette amélioration de sa largeur de raie intégrée sur 3 ms, de 224 kHz à 37 kHz. Ce premier résultat représente un bon support vers l’exploration du potentiel des diodes à blocage de modes pour des applications métrologiques.

Optical frequency combs obtained from mode-locked laser diodes are potential candidates for WDM networks. However, their lines exhibit usually a broad optical linewidth ( 1-100 MHz). Thus their use is incompatible for high order modulation formats WDM based systems. This thesis investigates one solution to overcome this limitation. It consists of using a feed-forward heterodyne technique to reduce the frequency noise of each comb-line and consequently their optical linewidths. In a first approach, the technique is applied to a single-mode laser. This allowed us to validate its proper working and to identify the intrinsic limits of the experimental device set up. The latter analysis enabled us to reveal that the minimum achievable frequency noise level by our system, corresponds to a 50 Hz intrinsic optical linewidth spectrum and a 1,6 kHz optical linewidth based on 10 ms observation time. This technique is then applied to an actively mode-locked laser diode demonstrating, at our system output, a 21-line optical frequency comb with intrinsic optical linewidths reduced to below 7 kHz. It is worth noting that 9 among them, exhibit sub-kHz linewidths. For an observation time of 10 ms, all lines share the same optical linewidth, almost equal to 37 kHz. We thus show that the timing jitter impacts the technique performances. We also highlight the relevance of such coherence level for coherent optical communication. Lastly, we study a laser frequency pre-stabilization technique based on a locking to an unbalanced fiber interferometer. When applied to a single-mode laser, the technique showed a reduction of its technical frequency noise, thus leading to a clear improvement of its integrated optical linewidth from 224 kHz to 37 kHz for 3 ms observation time. This first result provides a good support towards the exploration of mode-locked laser diodes potential for metrological applications.; Les peignes de fréquences optiques, issus de diodes à blocage de modes, font partie des candidats potentiels pour les réseaux de transmission à multiplexage en longueurs d’onde (WDM). Cependant, les modes composant leur peigne, exhibent généralement des largeurs de raie optiques relativement élevées ( 1-100 MHz), rendant ainsi incompatible leur utilisation sur un réseau WDM employant des formats de modulation avancés d’ordre supérieur. Cette thèse étudie, une solution pour palier à cette limitation. La technique utilisée, dite d’asservissement à correction aval hétérodyne, effectue un traitement du flux lumineux en sortie du laser sans agir sur ce dernier, permettant de réduire le bruit de fréquence présent sur chacune des raies et par conséquent leur largeur de raie optique. Dans une première approche, la technique est appliquée à un laser mono-fréquence. Cela a permis d’une part de valider son fonctionnement et d’autre part d’identifier les limites intrinsèques du dispositif expérimental mis en place. Ainsi, nous démontrons que le niveau de bruit de fréquence minimum permis par notre système, correspond à un spectre optique de largeur de raie optique instantanée de 50 Hz et une largeur de raie de 1,6 kHz pour un temps d’observation de 10 ms. La technique est par la suite appliquée à une diode à blocage de modes actif. Le peigne de fréquences optiques ainsi généré, est composé de 21 modes, ayant tous une largeur de raie optique intrinsèque inférieure à 7 kHz, dont 9 modes sont sub-kHz. Pour un temps d’observation du spectre optique de 10 ms, ces modes exhibent tous une largeur de raie d’environ 37 kHz. Nous démontrons ainsi l’impact de la gigue d’impulsions sur les performances de la technique et nous soulignons l’intérêt d’une telle cohérence, pour le domaine des télécommunications optiques cohérentes (transmissions WDM cohérentes de type m-QAM avec des constellations d’ordre élevé, compatibles avec des débits multi-Tbit/s par raie). En dernier lieu, nous abordons une seconde technique consistant à pré-stabiliser la fréquence d’un laser par asservissement en boucle fermée. Elle repose sur l’utilisation d’un interféromètre à fibre déséquilibré comme référence pour réduire le bruit de fréquence d’un laser, situé particulièrement en basses fréquences. Appliquée à un laser mono-fréquence, elle a permis de réduire son bruit de fréquence technique conduisant ainsi à une nette amélioration de sa largeur de raie intégrée sur 3 ms, de 224 kHz à 37 kHz. Ce premier résultat représente un bon support vers l’exploration du potentiel des diodes à blocage de modes pour des applications métrologiques.

Brillouin scattering is the inelastic scattering of light by the acoustic waves of a medium. In an optical fiber, stimulated Brillouin scattering occurs, from a certain incident light intensity (pump), for generating a backscattered "Stokes" wave, whose frequency is shifted from that of the pump by a value directly proportional to the acoustic wave propagation velocity in the fiber. The Brillouin shift has a high sensitivity to all effects that can change the speed of the acoustic wave. This property makes it possible to study the composition of the fibers and gives to the SBS the potential for the production of optical fiber sensors. The SBS process is also accompanied by a gain for the backscattered Stokes wave since almost all the power of the Pump wave is transferred there. It can, therefore, be used for the production of optical fiber amplifiers and lasers. As part of this thesis work, we experimentally studied static and dynamic properties of the Brillouin fiber lasers (BFLs). Depending on the damping rate of the acoustic wave and the loss rate of the cavity, the BFL can be very coherent and less noisy, thus promoting its use in multiple fields such as defense, metrology, and telecommunications. When the Pump makes only one turn in the Brillouin cavity, the studied BFL has a frequency noise 10,000 times lower than that of the Pump laser while keeping a similar intensity noise. When the Pump is resonant, it is possible to obtain a BFL with multiple Stokes waves by cascading the Brillouin non-linear effect in the optical fiber. Restricted by our measurement benches, we measured a frequency noise 1000 times lower than that of the Pump and an intensity noise more than 100 times lower.; La diffusion Brillouin est la diffusion inélastique de la lumière par les ondes acoustiques d'un milieu. Dans une fibre optique, la diffusion Brillouin stimulée (DBS) se manifeste, à partir d'une certaine intensité lumineuse incidente (Pompe), par la génération d'une onde Stokes rétrodiffusée dont la fréquence est décalée de celle de la Pompe d'une valeur directement proportionnelle à la vitesse de propagation des ondes acoustiques. Le décalage Brillouin présente une grande sensibilité à tous les effets qui peuvent modifier la vitesse de l'onde acoustique. Cette propriété permet d'étudier la composition des fibres et confère à la DBS la potentialité pour la réalisation de capteurs à fibres optiques. Le processus de DBS s'accompagne aussi d'un gain pour l'onde Stokes rétrodiffusée, puisque presque toute la puissance de l'onde Pompe y est transférée. Il peut donc être utilisé pour la réalisation d'amplificateurs et de lasers à fibres optiques. Dans le cadre de ce travail de thèse, nous avons étudié expérimentalement les propriétés statiques et dynamiques du laser à fibre Brillouin (LFB). Dépendamment du taux d'amortissement de l'onde acoustique et du taux de pertes de la cavité, le LFB peut être très cohérent et très peu bruité, favorisant ainsi son utilisation dans de multiples domaines comme la défense, la métrologie et les télécommunications. Lorsque la Pompe ne fait qu'un tour dans la cavité Brillouin, le LFB étudié présente un bruit de fréquence 10 000 fois plus faible que celui du laser de Pompe tout en gardant un bruit d'intensité similaire. Lorsque la Pompe est résonante, il est possible d'obtenir un LFB à multiples ondes Stokes en cascadant l'effet non-linéaire Brillouin dans la fibre optique. Limités par nos bancs de mesures, nous avons mesuré un bruit de fréquence 1 000 fois plus faible que celui de la Pompe et un bruit d'intensité plus de 100 fois plus faible.

This thesis focuses on laser diodes made of Quantum Dot/Quantum Dash (QD) structures. These devices have attracted considerable attention due to their remarkable properties, such as high gain, high non-linear effects, low laser-threshold, high thermal stability, etc. Our studies based on RIN (Relative Intensity Noise) and optical injection show unusual behaviour of QD lasers. We have compared the RIN of a QDash DFB laser with a ''classical'' (massif or quantum well) DFB laser as well as for Fabry-Perot type QDot/QDash lasers. Analytical simulations have been faced to experimental results and show the role of the wetting layer. Contrary to what is observed with ''classical lasers'', optical injection exhibits many regimes with strong non-linear dynamics when the laser is biased near the threshold, while there is only a very few regimes at moderate pump. All these results demonstrate a strong coupling with strong dumping between the longitudinal modes through the wetting layer, which is a very interesting point for the understanding of mode-locking in these QDot/QDash structures.; Cette thèse porte sur l'étude de structures lasers à semi-conducteurs à base d'îlots et de bâtonnets quantiques, connues pour avoir quelques propriétés remarquables telles leur fort gain, leur effet non-linéaire renforcé, leur faible courant de seuil, leur haute température caractéristique ... Les caractérisations en termes de bruit d'intensité et d'injection optique de ces structures montrent un comportement atypique comparativement aux structures classiques (massives ou à base de puits quantiques). Nous avons pu ainsi comparer le bruit d'un laser DFB à bâtonnets quantiques avec celui d'un laser DFB massif ou à puits quantiques. Des études comparatives de bruit ont aussi été effectuées sur des lasers de type Fabry-Perot. Une modélisation du bruit a été confrontée aux résultats expérimentaux et montre l'importance de la prise en compte de la couche de mouillage. L'injection optique, contrairement aux propriétés d'un laser classique, présente un grand nombre de régimes dynamiques fortement non linéaires près du seuil laser (r~1,1) et peu de régimes à seuil modéré (r~3). Ces résultats nous indiquent finalement que le couplage des modes longitudinaux est à la fois fort et fortement amorti par l'interaction avec la couche de mouillage, ce qui nous donne des pistes très intéressantes pour la modélisation du blocage de modes observé dans ces structures.