This thesis concerns some experimental and theoretical issues in fiber optics. In particular, properties and devices based on photonic crystal fibers (PCFs) are investigated. The work can be grouped into three parts. In the first part we use sound to control light in PCFs. The lowest order flexural acoustic mode of various PCFs is excited using an acoustic horn. The acoustic wave acts as a traveling long-period grating. This is utilized to couple light from the lowest order to the first higher order optical modes of the PCFs. Factors affecting the acoustooptic coupling bandwidth are also investigated. In particular, the effect of axial variations in acoustooptic phase-mismatch coefficient are studied. In the second part of the thesis we use an electric field to control transmission properties of PCFs. Tunable photonic bandgap guidance is obtained by filling the holes of an initially index-guiding PCF with a nematic liquid crystal and applying an electric field. The electric field introduces a polarization-dependent change of transmission properties above a certain threshold field. By turning the applied field on/off, an electrically tunable optical switch is demonstrated. The third part consists of two theoretical works. In the first work, we use relativistic causality, i.e. that signals cannot propagate faster than the vacuum velocity of light, to show that Kramers-Kronig relations exist for waveguides, even when material absorption is negligible in the frequency range of interest. It turns out that evanescent modes enter into the Kramers-Kronig relations as an effective loss term. The Kramers-Kronig relations are particularly simple in weakly guiding waveguides as the evanescent modes of these waveguides can be approximated by the evanescent modes of free space. In the second work we investigate dispersion properties of planar Bragg waveguides with advanced cladding structures. It is pointed out that Bragg waveguides with chirped claddings do not give dispersion characteristics significantly different from Bragg waveguides with periodic claddings.

Pillar-array based optical cavities have unique properties, e.g., having a large and connected low dielectric index space (normally air space), exhibiting a large band gap for transverse magnetic modes, having a large percent of electric field energy in air and standing on a substrate. These properties make them well suitable for applications such as optical sensing and terahertz quantum cascade lasers. However there has been rare research in it due to the common belief that pillar arrays have excessive leakage to the substrate. With careful design, we provided several methods to reduce such a leakage and experimentally proved a high quality factor (Q) pillar-array based cavity is practical. We also explored the usage of such a cavity for optical sensing. Numerical methods such as finite-difference time-domain and plane-wave expansion were used in the design of the cavity. Then in microwave spectrum, cavities consisting of dielectric rods were used to test the validity of the theory. Additionally, we observed that a high-Q cavity for modes above light line is feasible and it is very suitable to measure the optical absorption of materials introduce inside the mode volume. Finally in the optical domain, pillar arrays were fabricated in Si/SiO2 material system and measured. Q as high as 27,600 was shown and when applying accurate refractive indices, for every delta n = 0.01, the peak wavelength shifted as large as 3.5 nm, testifying the ultra sensitivity of the cavity to the environmental dielectric change.

Ce travail de thèse présente les caractéristiques optiques et électriques de dopants dans des couches de CdHgTe, CdZnTe et CdS. Ces 3 matériaux II-VI ont pour point commun d'être utilisés dans des dispositifs de détection, que ce soit la détection de lumière infrarouge pour les couches de CdHgTe et CdZnTe ou la détection visible comme c'est le cas pour le CdS. La caractérisation optique de ces couches de matériaux II-VI a été réalisée par la technique de photoluminescence et corrélée à des mesures électriques effectuées par effet Hall en température. Dans un premier temps, une étude du dopage intrinsèque par les lacunes de mercure et du dopage extrinsèque par incorporation d'arsenic de l'alliage CdHgTe, couche active des détecteurs IR a été réalisée. Pour cela, des mesures optiques par photoluminescence (sur un banc mis en place au laboratoire pendant la 1ere année de thèse permettant de travailler depuis les basses températures jusqu'à l'ambiante entre 1µm et 12 µm dans l'IR) sur des couches de CdHgTe réalisées par épitaxie en phase liquide (EPL) de différentes compositions en Cd ont été effectuées. La corrélation de ces mesures optiques avec des mesures électriques par effet Hall en température a permis d'identifier les énergies d'activation des 2 niveaux de la lacune de mercure ainsi que de démontrer le phénomène de U-négativité de la lacune de mercure dans le CdHgTe. De plus, la comparaison de spectres de PL d'échantillons dopés arsenic pendant la croissance par épitaxie par jets moléculaires (EJM) avec des mesures disponibles réalisées par absorption de rayons X (EXAFS) a permis d'observer des transitions optiques associées aux différents complexes arsenic formés avant et après le recuit d'activation. Par ailleurs, un travail de modélisation du phénomène de désordre d'alliage dans le CdHgTe a été réalisé. Plus précisément, un modèle basé sur une statistique gaussienne associée aux fluctuations d'alliage autour d'un gap moyen et une statistique de Boltzman a été développé pour ajuster dans un premier temps des spectres d'absorption puis pour ajuster les spectres de photoluminescence. Ce modèle nous a permis d'ajuster étroitement les spectres de photoluminescence et d'absorption, tout en prenant en compte intrinsèquement le désordre d'alliage du matériau. Nous avons ainsi constaté que l'ajustement des spectres par des fonctions gaussiennes comme il est réalisé communément dans la littérature permet de trouver les bons écarts entre les pics d'émission et donc les bonnes énergies d'ionisation.. Dans un deuxième temps, toujours dans le cas de la détection infrarouge, le travail a porté sur l'étude du substrat CdZnTe utilisé pour l'épitaxie du CdHgTe. Des comparaisons des spectres de PL avec les paramètres de croissance ont été effectuées. Plus particulièrement, une étude sur une zone spécifique de certains échantillons présentant une absorption du rayonnement IR a été réalisée afin d'en comprendre l'origine. Enfin, nous nous sommes intéressés à la couche de CdS, matériau II-VI dopé intrinsèquement (type n) utilisé comme fenêtre transparente et formant la jonction p-n avec le CdTe dans les cellules solaires, détecteurs de lumière visible. Dans cette partie, nous avons chercher à étudier l'influence des différentes méthodes de dépôts, sublimation ou bain chimique de la couche de CdS sur un substrat de verre, en comparant les spectres d'émission de photoluminescence obtenus ainsi que les types de traitements thermiques effectués après dépôts. Ces mesures ont été corrélées avec le rendement des cellules solaires finales.

Pillar-array based optical cavities have unique properties, e.g., having a large and connected low dielectric index space (normally air space), exhibiting a large band gap for transverse magnetic modes, having a large percent of electric field energy in air and standing on a substrate. These properties make them well suitable for applications such as optical sensing and terahertz quantum cascade lasers. However there has been rare research in it due to the common belief that pillar arrays have excessive leakage to the substrate. With careful design, we provided several methods to reduce such a leakage and experimentally proved a high quality factor (Q) pillar-array based cavity is practical. We also explored the usage of such a cavity for optical sensing. Numerical methods such as finite-difference time-domain and plane-wave expansion were used in the design of the cavity. Then in microwave spectrum, cavities consisting of dielectric rods were used to test the validity of the theory. Additionally, we observed that a high-Q cavity for modes above light line is feasible and it is very suitable to measure the optical absorption of materials introduce inside the mode volume. Finally in the optical domain, pillar arrays were fabricated in Si/SiO2 material system and measured. Q as high as 27,600 was shown and when applying accurate refractive indices, for every delta n = 0.01, the peak wavelength shifted as large as 3.5 nm, testifying the ultra sensitivity of the cavity to the environmental dielectric change.

Ce mémoire présente un système de recalage visuel adapté aux pièces mécaniques. Il s'agit d'estimer, de manière automatique et précise, la position et l'orientation d'un objet connu, à partir de son image vidéo. Les objets considérés possèdent la particularité d'être complexes, généralement métalliques et non-texturés. La solution proposée exploite un modèle d'objet caractérisant à la fois l'apparence et la géométrie de l'objet. Afin de pouvoir estimer la pose de l'objet, nous proposons un processus de mise en correspondance exploitant conjointement les informations d'apparence et de géométrie du modèle. Cette étape exploite la capacité à estimer une pose approximative de l'objet à partir d'un seul appariement pour filtrer efficacement les faux appariements. Un processus d'estimation précise de la pose est ensuite proposé. L'évaluation du processus complet sur des pièces mécaniques issues de l'industrie souligne la précision et la robustesse de ce dernier

Photonic crystals (PCs) are nano-structured materials in which a periodic variation of the dielectric constant of the material results in a photonic band gap. By introducing defects into PCs, it is possible to build waveguides that can channel light along certain paths. It is also possible to construct micro-cavities that can localize photons in extremely small volumes. In this dissertation, to begin with, we computed the photonic crystals dispersion relations and found the photonic band gap (PBG) by the plane wave expansion method (PWE) in the frequency domain. Then, the finite difference time domain method (FDTD) along with the perfectly matched layer boundary conditions was adopted to solve Maxwell¡¦s equations, equivalent to simulate the movement behavior of the Photonic crystals. By properly varying the size of the defect on the PCs, it could really drop the particular wavelengths and guide them to output channels by PCs waveguides. We proposed the structures that would function as Wavelength-Division-Multiplexer (WDM). Secondly, coupled cavity waveguide of PC was used to control group velocity that achieved the slow light property. By calculating dispersion curve with PWE, we obtained group velocity characteristics in PCs waveguide. Meanwhile, we designed a novel Time-Division-Multiplexer (TDM) system by controlling the group velocity characteristics. Finally, we designed cascade ring resonators and expected to obtain an extendable delay line. Conventional delay line devices are propagating in a long waveguide to obtain the delay line property. An excellent delay line and ultra-small size properties are expected in the proposed structure. Because nano-technology has been making great progress steadily, it surely can be used to demonstrate a practical breakthrough in which the devices based on the PC integrated circuits are realized. These devices will be a potential key component in the applications of ultra-high-speed and ultra-high-capacity optical communications and optical data processing systems.

This paper discussed a way of applied stress to control the photonic crystal fiber dispersion curve, so that it can act on the anomalous dispersion or normal dispersion region area. By this way, we can design the pulse compressor and pulse stretcher for higher peak power laser system. Recently, high-power shortpulse laser has become an indispensable tool in many field, using short-pulse laser oscillator, combined with chirped-frequency amplification technology to produce high-power short-pulse laser system can be used for industrial or medical applications. The all-fiber laser system not only provide better pulse quality and also increased pulse laser system on the stability of the environment.

The fabrication of one-dimensional (1-D) polymeric photonic crystals from the self-assembly of ultra-high-Mw polystyrene-b-polyisoprene (PS-PI) block copolymers (BCPs) were conducted in this study. Well-ordered microphase-separated lamellar structures can be observed in the ultra-high-Mw PS-PI BCPs in the bulk by transmission electron microscopy (TEM) and ultra-small angle X-ray scattering (USAXS). To fabricate large-area and well-oriented lamellar microstructures with parallel orientation to the substrate, substrate-induced microstructural orientation with the accompanying solvent annealing method (i.e., solvent-induced orientation) was carried out in the PS-PI film. By grazing-incidence ultra-small angle X-ray scattering (GIUSAXS), scanning probe microscope (SPM) and cross-sectional TEM morphological observation, identification of the microstructural orientation in the PS-PI film can be achieved. A disordered wormlike morphology is observed in the as-spun PS-PI thin film from toluene on the PS-grafting substrate and on neat glass or wafer. This is attributed to the fast solidification of the disordered microstructure due to fast evaporation rate of the toluene solvent. After solvent annealing by the PS-selective or PI-selective solvents such as divinylbenzene (DVB) (neutral but highly PS-selective), benzene (PS-selective) and cyclohexane (PI-selective), parallel lamellar microstructures can be obtained in the PS-PI films on the PS-grafting substrate. By contrast, the coexistence of parallel and perpendicular lamellar microstructures is obtained in the PS-PI film from toluene after solvent annealing by neutral toluene on the PS-grafting substrate or by PS-selective benzene on the neat glass or wafer. This indicates that the formation of the parallel lamellar microstructures is mainly determined by both solvent-induced and substrate-induced orientation. In contrast to the as-spun disordered morphology from toluene, well-ordered parallel lamellar microstructures with few defects was found in the as-spun PS-PI film from DVB on the PS-grafting substrate, whereas parallel lamellar microstructures with many defects was observed in the as-spun PS-PI film from DVB on the neat glass or wafer. This further demonstrates that the PS-grafting substrate indeed plays an important role on the fabrication of well-ordered parallel lamellar microstructures. Interestingly, once the initial morphology of the PS-PI BCP reaches a relative stable state (i.e., parallel lamellar microstructures versus disordered wormlike morphology), it is hardly to trigger the microstructural reorientation by the subsequent solvent annealing. We suggest that the stable initial morphology in the PS-PI film may create high energy barrier for microstructural reorientation. With the controllable microstructural orientation, a PS-PI thick film having large-area and well-oriented parallel lamellar microstructures can be successfully carried out. Therefore, 1-D polymeric photonic crystals from the self-assembly of the lamella-forming PS-PI BCPs can be achieved. The in-situ UV reflectance spectra show that the reflective band shifts from ultraviolet wavelength to visible wavelength was observed in the lamella-forming PS-PI thick film with elapse of time by solvent annealing. Notably, the band gap can be recovered to the initial state once the solvent is removed, indicating the reversible process. As the results, the solvatochromic BCP photonic crystals can be successfully carried out by the manipulation of the solvent swelling in the large-area and well-oriented lamella-forming PS-PI BCP film.

In this study, we study three kinds of surface treatments in the blue phase lasers. Three kinds of surface treatments include no surface treatment, homogeneous alignment ,HA, and vertical alignment ,VA. Blue Phase liquid crystal is a three-dimensional photonic crystal, and it can be used to be a laser cavity. When the blue phase doped with a laser dye, a laser emission can be observed under appropriate pumping energy. In the first part, we fabricate the blue phase lasers with three kinds of surface, there are different surface treatments to study the surface effect of the optoelectronic properties. It is found that the threshold pumping power is significantly decreased under a surface treatment on glass substrate. In the second part, we change cooling rate in the formation of the blue phase liquid crystals, and study the optoelectronic properties of blue phase lasers. The experiment results reveal that the slower cooling rate leads to a order blue phase substrate, resulting in a lower threshold pumping energy of the blue phase laser.

Blue phases have been known to exist in chiral liquid crystals between the cholesteric and isotropic phases. A blue phase as a self-assembled three-dimensional cubic structure with lattice periods of several hundred nanometers exhibits not only selective Bragg reflections of light in the visible wavelength but optically isotropy owning to its highly symmetric molecular structure. Locally, blue phases still exhibit local anisotropic physical properties because of anisotropic structure of the nematic liquid crystal molecules, which make it possible to be easily controlled by an external field. This dissertation studies the effects in blue phases under various external fields, including electrical field, optical field, and temperature. Firstly, we investigated the bistable effect under the influence of an electric field and transition mechanism between various lattice orientations in the negative liquid crystal blue phase. The blue phase exists over a wide temperature range ~16oC, and three lattices (110), (112) and (200) of BPI are confirmed with Kossel diagrams. The red platelet (110) lattice and blue platelet (200) lattice can be stabilized and switched to each other by particular pulse voltages. We also studied the behavior that an electric field induced planar state and electro-hydrodynamatic effect in the blue phase. Additionally, the reflected color of the (200) lattice can be adjusted from 455nm to 545 nm by temperature induced lattice distortions and provided with reversibility. Secondly, we presented an optically switchable band gap of a 3D photonic crystal that is based on an azobenzene-doped liquid crystal blue phase. Two kinds of azobenzene, M12C and 4MAB, were utilized to switch photonic band gap of blue phases and to change the phase transition temperature of blue phase, respectively. For M12C- doped liquid crystal blue phase, the trans-cis photoisomerization of M12C induced by irradiation using 473nm light caused the deformation of the cubic unit cell of the blue phase and a shift in the photonic band gap. The fast back-isomerization of azobenzene was induced by irradiation with 532nm light. The crystalline structure was verified using a Kossel diffraction diagram. Moreover, we also demonstrated an optically addressable blue phase display, based on Bragg reflection from the photonic band gap. For 4MAB- doped liquid crystal blue phase, the trans-cis photoisomerization of 4MAB destabilizes cubic unit cell of the blue phase and reduces the phase transition temperature. We observed the phase sequences of the 4MAB-doped blue phase as a function of the time of UV irradiation. Various distinct phases can be switched to another specific phase by controlling irradiated time and temperature of the sample. Therefore, the corresponding bandgap can be switched on and off between blue phase and isotropic phase, or varied from 3D to 1D between blue phase and cholesteric phase. Finally, we investigated the thermal hysteresis in the phase transition between the cholesteric liquid crystal and the blue phase of liquid crystal. The thermal hysteresis of such a chiral doped nematic liquid crystal occurs over 6oC. Both the CLC phase and the blue phase can stably exist at room temperature and be switched to each other using temperature-controlled processes. Further, we demonstrated two sets of bistable conditions using various surface treatments. In a homogeneous aligned sample, two stable states, CLC with a planar alignment and blue phase with a uniform lattice distribution, reflect light of wavelengths 480-510nm and 630nm, respectively, as determined by the corresponding Bragg¡¦s reflection conditions. In the untreated sample, the CLC phase with a focal conic texture can scatter light and the blue phase with a non-uniform lattice distribution provides high isotropic optical transparency.