Optical fiber systems have been developed during the past twenty-five years with primary applications in long distance, high speed digital information communication. Optical fiber sensors have also been developed over the past fifteen years for the nondestructive inspection and evaluation of materials used in the aerospace, energy, transportation, and medical industries. Optical fibers may be used as the field-sensitive elements in sensors for the measurement of environmental parameters such as displacement, strain, temperature, vibration, chemical concentrations and electromagnetic fields. Their advantages for such measurements include 1) an inherent immunity to electromagnetic interference (EMD), 2) avoidance of ground loops, 3) the capability of responding to a wide variety of measurands, 4) excellent resolution, 5) the avoidance of sparks, especially important for applications within explosive environments, and 6) operation at temperatures of approximately 800°C for silica waveguides and above 1900°C for sapphire waveguides. Phase-modulated optical fiber sensors have been shown to possess the highest sensitivities to a given measurand. This dissertation describes several novel phase-modulated optical fiber sensors. The sensors described include a strain gage, a temperature sensor for applications up to and including 1700°C, a displacement sensor with sub-Angstrom resolution, and a vibration mode filter. For each sensing concept, a description and method of operation is given, followed by fabrication methods and experimental results. / Ph. D.

Two new fiber optic magnetostrictive phase modulators and magnetometers using the highly magnetostrictive rare-earth iron compound Tb_xDy_l-xFe₂ are investigated. They demonstrated to have a high sensitivity, dynamic range, minimum field detectability, and a better structural suitability than metallic glasses. For the first sensor, the experimental linear phase shifting coefficient was 1.102 rad/Vp-m with the corresponding phase shift nonnalized to the magnetic field of 0.306 radiO-m. For the second sensor, the experimental linear phase shifting coefficient was 0.5 rad/Vp-m with the corresponding phase shift nonnalized to the magnetic field of 0.136 rad/G-m. A minimum detectable phase shift of better than 1 μrad was obtained, which corresponds to 2 μG/m for a 4 Hz bandwidth and 1 μG/â HZ per meter of fiber interaction length. The projected minimum detectable magnetic field for 30 meters, for the first sensor, is thus seen to be 3pT/â HZ. The experimental results presented have clearly demonstrated the utility of the Terfenol based magnetostrictive fiber optic phase modulator and magnetometer. / Master of Science

International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada / System performance can be ascertained via a number of parameters; one of which is Signal-to-Noise ratio (SNR). SNR is the ratio of the value of the signal to the value of the noise. It is generally expressed in decibels and usually a function of the system bandwidth. Another measure of performance is the Noise-Power ratio (NPR). NPR is the ratio of the noise level within a specific measurement channel when noise is applied to all channels, to the level that is measured within the specific channel with noise applied to all of the channels but not the specific channel.

International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / One of the charters of the Advanced Range Telemetry (ARTM) program was to develop more spectrally efficient waveforms while trying to maintain similar performance to the legacy waveform, Pulse Code Modulation/Frequency Modulation (PCM/FM). The first step toward this goal was the ARTM Tier I family of waveforms which include Feher patented, quadrature phase shift keying, -B version (FQSPKB) and shaped offset quadrature phase shift keying, Telemetry Group version (SOQPSK-TG). The final step was development of Tier II, an even more spectrally efficient waveform, multi-h Continuous Phase Modulation (CPM). This paper characterizes the performance of this waveform when applied in an airborne telemetry environment and, where appropriate, comparisons are made with existing Tier 0 and Tier I waveforms. The benefits, drawbacks, and trade-offs when applying this waveform in an airborne environment will also be discussed.

This thesis explores the theoretical foundations of cross-phase modulation (XPM) between optical fields in the N-configuration atom. This is the process by which the refractive index experienced by one field can be modulated by controlling the intensity of another. The electro-optical version of this effect was first discovered by John Kerr in 1875 and found applications in photonics as a means of very rapidly modulating the phase and intensity of electromagnetic fields. Due to recent advances in experimental techniques there has been growing interest in generating nonlinear optical interactions in coherently prepared atomic ensembles. The use of coherently prepared media brings the possibility of achieving a much larger cross-phase modulation than is possible using classical materials. This is particularly useful when trying to create large optical nonlinearities between low-intensity electromagnetic fields. Much of the current research into cross-phase modulation is directed towards realising potential applications in the emerging field of quantum information processing. Above all, the possibility of constructing an all-optical quantum computer has been at the heart of much research and controversy in the field. In this thesis the theory of steady-state, transient and pulsed cross-phase modulation is developed. Moreover, care has been taken to relate all research back to experimentally feasible situations. As such, the relevance of the theory is justified by consideration of the situation present in rubidium-87. Due to the close relationship between XPM in the N-configuration atom and electromagnetically induced transparency in the Lambda-atom, many similarities and insights act as link between these two fields. Indeed, it is frequently demonstrated that the key to understanding the various properties of XPM in the N-configuration atom is by comparison with the situation in the corresponding Lambda-atom equivalent.

<p>Nonlinear optical microscopy serves as a great tool for biomedical imaging due to its high resolution, deep penetration, inherent three dimensional optical sectioning capabilities and superior performance in scattering media. Conventional nonlinear optical microscopy techniques, e.g. two photon fluorescence and second harmonic generation, are based on detecting a small light signal emitted at a new wavelength that is well separated from the excitation light. However, there are also many other nonlinear processes, such as two-photon absorption and self-phase modulation, that do not generate light at new wavelengths and that have not been extensively explored for imaging. This dissertation extends the accessible mechanisms for contrast to the later nonlinear optical processes by combining femtosecond laser pulse shaping and homodyne detection. We developed a rapid pulse shaper with a relatively simple and compact instrument design that modifies the spectrum of individual laser pulses from an 80 MHz mode-locked laser. The pulse shaper enables simultaneous two-photon absorption and self-phase modulation imaging of various nanoparticles in-vitro with high sensitivity. We also applied this imaging technique to study the nonlinear optical response in graphene. Because our technology detects the nonlinear signature encoded within the laser pulse itself, we achieve intrinsic contrast of biological and non-biological samples in highly scattering media. These capabilities have significant implications in biomedical imaging and nanophotonics.</p> / Dissertation

Si les drones militaires connaissent un développement important depuis une quinzaine d’année, suivi depuis quelques années par les drones civiles dont les usages ne font que se multiplier, en réalité les drones ont un siècle avec le premier vol d’un avion équipé d’un système de pilotage automatique sur une centaine de kilomètre en 1918. La question des règles d’usage des drones civiles sont en cours de développement malgré leur multiplication pour des usages allant de l’agriculture, à l’observation en passant par la livraison de colis. Ainsi, leur intégration dans l’espace aérien reste un enjeu important, ainsi que les standards de communication avec ces drones dans laquelle s’inscrit cette thèse. Cette thèse vise en effet à étudier et proposer des solutions pour les liens de communications des drones par satellite.L’intégration de ce lien de communication permet d’assurer la fiabilité des communications et particulièrement du lien de Commande et Contrôle partout dans le monde, en s’affranchissant des contraintes d’un réseau terrestre (comme les zones blanches). En raison de la rareté des ressources fréquentielles déjà allouées pour les futurs systèmes intégrant des drones, l’efficacité spectrale devient un paramètre important pour leur déploiement à grande échelle et le contexte spatiale demande l’utilisation d’un système de communication robuste aux non-linéarités. Les Modulations à Phase Continue permettent de répondre à ces problématiques. Cependant, ces dernières sont des modulations non-linéaire à mémoire entraînant une augmentation de la complexité des récepteurs. Du fait de la présence d’un canal multi-trajet (canal aéronautique par satellite), le principal objectif de cette thèse est de proposer des algorithmes d’égalisation (dans le domaine fréquentiel pour réduire leur complexité) et de synchronisation pour CPM adaptés à ce concept tout en essayant de proposer une complexité calculatoire raisonnable. Dans un premier temps, nous avons considéré uniquement des canaux sélectifs en fréquence et avons étudier les différents égaliseurs de la littérature. En étudiant leur similitudes et différences, nous avons pu développer un égaliseur dans le domaine fréquentiel qui proposant les mêmes performances a une complexité moindre. Nous proposons également des méthodes d’estimation canal et une méthode d’estimation conjointe du canal et de la fréquence porteuse. Dans un second temps nous avons montré comment étendre ces méthodes à des canaux sélectifs en temps et fréquence permettant ainsi de conserver une complexité calculatoire raisonnable.

Soft matter, self-assembled 3D photonic structures such as blue phase liquid crystals have of great interest to the displays industry and are highly desirable as spatial light modulators because of their polarisation independence and fast switching. However, these types of devices suffer from multistep fabrication conditions and require high threshold voltages. To overcome these limitations, two key points were considered: High flexoelectric liquid crystals are capable of uniform 3D self-assembly, with a wide temperature range but have high threshold voltages, whereas, other classes of high dielectric liquid crystals have fast electro-optic response times with low threshold voltages but show poor 3D self-assembly. In this work, new mixture formulations have been devised having both properties in moderation in order to achieve simple yet stable 3D self-assembled blue phases with fast response times at as low as possible applied fields. Dielectric materials were considered from a commercial source whereas, miscible flexoelectric soft materials were synthesised in-house. These synthesised materials were fully characterised. Then mixtures were formulated in commercial high dielectric hosts to study their miscibility, new mesogenic transitions and electro-optic responses in terms of flexoelectric and dielectric properties. The selected mixtures were further investigated for the rapid growth of blue phases and their compatibility with reactive mesogens to form stable blue phases at room temperature. This new formulation of materials has given rise to mixtures and devices which are inherently easy to fabricate allowing the robust and resilient growth of blue phases under an hour in standard laboratory conditions. Furthermore, polarisation independent electro-optic switching has been characterised at fields < 1V micron m-1. For phase modulation studies of these stabilised blue phase devices, phase shift was measured using a modified Young's slit interferometer. The observed results were very promising, with a full 2.5 pi phase shift observed at a field of 9.25 V micron m-1 when compared to earlier reported devices (which required complicated multistep fabrication processes) giving values of full 1.8 pi phase shifts at 20 V micron m-1.

by John Reed.

No description available.