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The use of optical feedback for improving response linearity of electrooptic light modulators has been investigated. The modulator is configured as a straight channel waveguide flanked by electrodes in a lithium niobate (LiNbO3) substrate. Light is coupled into the waveguide in both TE and TM polarizations, and a voltage applied across electrodes causes a relative phase shift between two polarization components. An output analyzer converts the phase modulation to intensity modulation. Optical feedback of light in both polarization modes results from reflection of light at the polished edges of the substrate. Channel waveguides supporting a single guided mode for TE and TM polarizations were fabricated in x-cut LiNbO3 substrates using titanium-indiffusion technique. The waveguides and modulators were characterized at a wavelength of 1.55 ??m using a distributed feedback laser. The modulators were driven with a sinusoidal voltage waveform. To minimize harmonics of the modulating frequency in the intensity output, the magnitude of the optical feedback and the substrate temperature were adjusted. The feedback level was altered by applying refractive index-matching liquid to one or both ends of the waveguide at the edges of the crystal. It was found that a high degree of response linearity in the presence of feedback was achievable at certain substrate temperatures. The spurious-free dynamic range (SFDR) relative to the noise floor was measured at different feedback levels and substrate temperatures in an effort to maximize the modulator response linearity. An SFDR of 68.04 dB, limited by third-order nonlinearity, was achieved by applying index-matching fluid to the input end of the substrate. This compares with an SFDR of 64.84 dB limited by second-order nonlinearity when index-matching fluid was applied at both ends of the substrate. By changing the temperature of the same substrate to adjust the phase shifts experienced by TE and TM polarizations, the SFDR with index-matching fluid at the input end increased to 71.83 dB, limited by third-order nonlinearity. In tests at constant modulation depth, an improvement of as much as 9.6 dB in SFDR vs. the theoretical value for an interferometric modulator without feedback was achieved.

The coherence of a semiconductor laser subjected to a coherent optical feedback of greater than -30 dB will collapse, causing the laser¡¦s performance in many applications to be severely degraded. This research investigated the feasibility of suppression the coherence collapse with orthogonal-polarization optical feedback. In the experiments, we first studied the characteristics of coherence collapse state of semiconductor laser. Under an operational condition of 63.9 mA, 21.9¢J and -11 dB of coherent optical feedback, a Hitachi HLP 7806G semiconductor laser would be conducted from its solitary single-mode state into a multimode oscillation state with a very broad linewidth. At the same time, the relative intensity noise measured from the RF spectrum analyzer drastically raised about 15 dB. When a -16 dB and a -23 dB orthogonal-polarization optical feedback were fed back into the laser¡¦s cavity. The coherence collapse could be effectively suppressed, while the laser was conducted back to its solitary single-mode state stably. This result will greatly increase the application of the laser. Some experiments were also reported to explore the interaction between the laser and the orthogonal-polarization feedback light.

This work investigated the characteristics of transverse modes and polarization of a VCSEL and attempted to control its transverse mode with optical feedback. The fundamental studies indicated that this solitary VCSEL's output consisted of two mutually orthogonal linear polarizations with different threshold currents and different transverse mode distributions. Furthermore, the temperature dependence of the transverse modes of the VCSEL revealed a better stability than that of edge-emitted lasers. In the mode controlling experiments, an iris was employed to select a specific transverse mode for feedback, resulting in an enhancement in the power of the feedback mode. A significant improvement was accomplished in the feedback of the fundamental mode of the major polarization component: the laser oscillated in a single mode with a side mode suppression ratio greater than 19.8 dB and with a depression of the relative intensity noise more than 20 dB/Hz. Nevertheless, a week feedback in the minor polarization component would stimulate more competition among transverse modes and degraded the performance of the VCSEL. Finally, no effect was observed in the orthogonal-polarization optical feedback experiment due to the excessively small of feedback ratio.

The use of optical feedback for improving response linearity of electrooptic light modulators has been investigated. The modulator is configured as a straight channel waveguide flanked by electrodes in a lithium niobate (LiNbO3) substrate. Light is coupled into the waveguide in both TE and TM polarizations, and a voltage applied across electrodes causes a relative phase shift between two polarization components. An output analyzer converts the phase modulation to intensity modulation. Optical feedback of light in both polarization modes results from reflection of light at the polished edges of the substrate. Channel waveguides supporting a single guided mode for TE and TM polarizations were fabricated in x-cut LiNbO3 substrates using titanium-indiffusion technique. The waveguides and modulators were characterized at a wavelength of 1.55 ??m using a distributed feedback laser. The modulators were driven with a sinusoidal voltage waveform. To minimize harmonics of the modulating frequency in the intensity output, the magnitude of the optical feedback and the substrate temperature were adjusted. The feedback level was altered by applying refractive index-matching liquid to one or both ends of the waveguide at the edges of the crystal. It was found that a high degree of response linearity in the presence of feedback was achievable at certain substrate temperatures. The spurious-free dynamic range (SFDR) relative to the noise floor was measured at different feedback levels and substrate temperatures in an effort to maximize the modulator response linearity. An SFDR of 68.04 dB, limited by third-order nonlinearity, was achieved by applying index-matching fluid to the input end of the substrate. This compares with an SFDR of 64.84 dB limited by second-order nonlinearity when index-matching fluid was applied at both ends of the substrate. By changing the temperature of the same substrate to adjust the phase shifts experienced by TE and TM polarizations, the SFDR with index-matching fluid at the input end increased to 71.83 dB, limited by third-order nonlinearity. In tests at constant modulation depth, an improvement of as much as 9.6 dB in SFDR vs. the theoretical value for an interferometric modulator without feedback was achieved.

This research accomplished a series of investigations on the polarization switching of Vertical-Cavity Surface-Emitting Lasers (VCSEL). The research was preceded experimentally and theoretically to observe the variation of the VCSEL¡¦s polarization switching under various polarization optical feedback and various feedback ratios. A VCSEL with significant polarization-switching hysteresis loop was employed in the experiments to study the interaction between the optical feedback and polarization switching. The experimental results matched the theoretical simulations very well. These results could be interpreted with the graphic analysis of the linear gain model of the VCSEL. In the investigation of the polarization-switching hysteresis loop, experiments found that, inside the loop and at some constant current, the polarization switching would be conducted with a switching delay time. The switching delay time was shortened under stronger optical feedback, revealing an exponential dependence between the switching delay time and optical feedback ratio. In the experiments of small current modulation to continuously switch the laser¡¦s polarization, optical feedback could improve the success of the current-driven polarization switching, significantly enhancing its bandwidth. For a large-range tuning of the laser¡¦s current, as the current modulation frequency increased, the polarization-switching current in the increasing-current process would significantly shift toward the high current end, while the polarization-switching current in the decreasing-current process was affected less. These results greatly contribute to the understanding of the VCSEL¡¦s polarization switching.

Microstructure manipulation is a fundamental process to the study of biology and medicine, as well as to advance micro- and nano-system applications. Manipulation of microstructures has been achieved through various microgripper devices developed recently, which lead to advances in micromachine assembly, and single cell manipulation, among others. Only two kinds of integrated feedback have been demonstrated so far, force sensing and optical binary feedback. As a result, the physical, mechanical, optical, and chemical information about the microstructure under study must be extracted from macroscopic instrumentation, such as confocal fluorescence microscopy and Raman spectroscopy. In this research work, novel Micro-Opto-Electro-Mechanical-System (MOEMS) microgrippers are presented. These devices utilize flexible optical waveguides as gripping arms, which provide the physical means for grasping a microobject, while simultaneously enabling light to be delivered and collected. This unique capability allows extensive optical characterization of the structure being held such as transmission, reflection, or fluorescence. The microgrippers require external actuation which was accomplished by two methods: initially with a micrometer screw, and later with a piezoelectric actuator. Thanks to a novel actuation mechanism, the “fishbone”, the gripping facets remain parallel within 1 degree. The design, simulation, fabrication, and characterization are systematically presented. The devices mechanical operation was verified by means of 3D finite element analysis simulations. Also, the optical performance and losses were simulated by the 3D-to-2D effective index (finite difference time domain FDTD) method as well as 3D Beam Propagation Method (3D-BPM). The microgrippers were designed to manipulate structures from submicron dimensions up to approximately 100 µm. The devices were implemented in SU-8 due to its suitable optical and mechanical properties. This work demonstrates two practical applications: the manipulation of single SKOV-3 human ovarian carcinoma cells, and the detection and identification of microparts tagged with a fluorescent “barcode” implemented with quantum dots. The novel devices presented open up new possibilities in the field of micromanipulation at the microscale, scalable to the nano-domain.

Dans ces travaux de thèse, nous avons étudié les propriétés dynamiques et spectrales d’une diode laser puissante à 980 nm qui est soumise à un retour optique provenant d’un réseau de Bragg fibré (FBG). Dans cette configuration, le FBG est un élément clé de la thèse d’une part il permet de former une cavité externe par réflexion comme un miroir et d’autre part il est un filtre qui fournit un retour optique sélectif en fréquence (FOF : Filtered Optical Feedback) aux alentours de 980 nm. Nous nous sommes intéressé à étudier cette configuration FOF dans le cadre d’un projet de collaboration entre la société 3S Photonics Group et le Laboratoire de Physique des Lasers. Il s’agit plus particulièrement d’étudier expérimentalement les séries temporelles par un oscilloscope, les spectres RF par un analyseur de spectre RF et les spectres optiques par un analyseur de spectre optique et par un interféromètre Fabry-Perot, afin d’observer, identifier et comprendre ses comportements dynamiques, notamment fluctuations basses fréquences (LFF). Ce système laser FOF est très peu étudié et ces travaux de thèse permettront de nouvelles connaissances techniques ou scientifiques dans un domaine d’application relativement récent, notamment pour l’application dans les systèmes EDFA (Erbium Doped Fiber Amplifier). / In this thesis, we have studied spectrums and the dynamics properties of a high-powerlaser diode emitting at 980 subject to optical feedback via a fibre Bragg grating (FBG). In such a configuration, FBG is a key element of this work because it establishes an ex-ternal cavity with a reflection like a mirror on one hand and it is a filter which provides frequency selective optical feedback (FOF : Filtered Optical Feedback) at around 980 nm on the other hand. We are interested in investigating this FOF configuration for a project in a collaboration between 3S Photonics Group and the Laboratoire de Physique des Lasers.In order to observe, identify and understand its dynamical behaviours, especially low frequency fluctuations (LFF), the experimental studies have been undertaken particularly with time series from an oscilloscope, RF spectra from an RF spectrum analyser and optical spectra from an optical spectrum analyser and Fabry-Perot interferometer. Onlyfew studies have been done with this FOF laser system and our thesis work may allow new technical and scientific understanding for recent application, particularly application to Erbium-doped fibre amplifier.

Nesse trabalho estudamos um laser de estado sólido sujeito a realimentação optica de frequência modificada de um ponto de vista da teoria de bifurcações. Fizemos uma an alise bastante ampla da dinâmica desse laser no espaço de dois parâmetros de injeção (a dessintonização de frequência e a intensidade da injeção) utilizando métodos de integração direta e continuação numérica. Enquanto o método de integração numérica nos possibilitou analisar as dinâmicas mais complexas, incluindo transições para o caos e hipercaos, o método de continuação numérica nos permitiu estudar curvas de bifurcações estáveis e instáveis. A análise foi realizada estudando os efeitos causados pela mudança dos parâmetros que representam o tempo de vida da inversão populacional e a saturação cruzada, responsável pelo acoplamento dos campos dentro do meio ativo. Mostramos que o parâmetro que descreve o tempo de vida da inversão populacional e responsável pelo surgimento de diversas instabilidades no sistema, como o fenômeno de multiestabilidade, surgimento de orbitas periódicas e quase-peri odicas, assim como rotas para o caos via dobramento de período e torus. Para o parâmetro de acoplamento dos campos, mostramos que ele possibilita a presença de hipercaos em nosso sistema, este podendo se apresentar no que denominamos de hipercaos \fraco" e \forte". Dentro da região de hipercaos \forte", mostramos transições determinísticas de dois regimes, em que num deles o laser opera no modo de Q-switching, enquanto que no outro o laser apresenta pequenas oscilações irregulares. Por m, mostramos a existência de uma estatística de eventos extremos dentro do regime hipercaótico. / In this work we studied a solid state laser subjected to frequency-shifted optical feedback from a bifurcation theory point of view. We performed a very broad analysis of the dynamics of this laser in the space of two injection parameters (frequency detuning and injection intensity) using direct integration and numerical continuation methods. While the numerical integration method allowed us to analyze the more complex dynamics, including chaos and hyperchaos transitions, the numerical continuation method allowed us to study stable and unstable bifurcation curves. The analysis was carried out by studying the e ects caused by the change of the parameters that represent the life time of the population inversion and the cross saturation, responsible for the coupling of the elds within the active medium. We show that the parameter that describes the life time of the population inversion is responsible for the appearance of several instabilities in the system, such as the multistability phenomenon, the appearance of periodic and quasi-periodic orbits, as well as routes to chaos via period doubling and torus . For the eld coupling parameter, we show that it allows the presence of hyperchaos in our system, which may present in what we call "weak"and "strong"hyperchaos. Within the "strong"hyperchaos region, we show deterministic transitions of two regimes, in which one laser operates in the Q-switching mode, while in the other the laser presents small irregular oscillations. Finally, we have shown the existence of a extreme events statistic within the hyperchaotic regime.