Micromachined microphones with diffraction-based optical displacement detection are presented. A compliant membrane is made part of a phase sensitive diffraction grating, and the deflection resulting from external acoustic pressure alters the intensities of the diffracted orders which are monitored with integrated photodiodes. The scheme provides the displacement sensitivity of a Michelson interferometer and can be integrated without beam splitters or critical alignment problems into volumes on the order of 1mm³. The method is implemented and characterized using microphone membranes with integrated diffraction grating back electrodes fabricated on silicon using Sandia National Laboratories' dedicated processing platform. Detailed response characterization in both air and vacuum environments is performed to extract the diaphragm properties and high frequency cutoff frequencies of the microphone. Results from a finite element model of the microphone structure are in good agreement with measured data. The sensor's internal noise is characterized with measurements performed in the anechoic acoustic test facility at Georgia Tech. While utilizing 2.4mW of laser power, an (A) weighted displacement resolution of 6×10⁻⁴Å/√Hz is measured which is limited by thermal acoustic noise caused by the microphone's back-plate flow resistance.

The extension of Multi-mode Absorption Spectroscopy (MUMAS) to the infra-red spectral region for multi-species gas sensing is reported. A computationally efficient, theoretical model for analysis of MUMAS spectra is presented that avoids approximations used in previous work and treats arbitrary and time-dependent spectral intensity envelopes, thus facilitating the use of commercially available Interband Cascade Lasers (ICLs) and Quantum Cascade Lasers (QCLs). The first use of an ICL for MUMAS is reported using a multi-mode device operating at 3.7 μm to detect CH₄ transitions over a range of 30 nm. Mode-linewidths are measured using the pressure-dependent widths of an isolated absorption feature in HCl. Multi- species sensing is demonstrated by measurement of partial pressures of CH₄, C₂H₂ and H₂CO in a low-pressure mixture with uncertainties of around 10%. Detection of CH₄ in N₂ at 1 bar is demonstrated using a shorter-cavity ICL to resolve spectral features in pressure-broadened and congested spectra. The first use of a QCL for MUMAS is reported using a commercially available device operating at 5.3 μm to detect multiple absorption transitions of NO at a partial pressure of 2.79 μbar in N₂ buffer gas. The revised model is shown to enable good fits to MUMAS data by accounting for the time-variation of the spectral intensity profile during frequency scanning. Individual mode-linewidths are derived from fits to pressure- dependent MUMAS spectra and features from background interferences due to H₂O in laboratory air are distinguished from those of the target species, NO. Data obtained at scan rates up to 10 kHz demonstrate the potential for achieving short measurement times. The development of a balanced ratiometric detection scheme for MUMAS with commercially available multi-mode lasers operating at 1.5 μm is reported for simultaneous detection of CO and CO₂ showing improved SNR performance over previous direct transmission methods and suitability for a compact field-employable instrument. In addition, MUMAS spectra of CO₂ are used to derive gas temperatures with an uncertainty of 3.2% in the range 300 - 700 K.

Souvent considéré néfaste dans le domaine de la télécommunication car il limite la puissance d'un système de transmission optique, l'effet Brillouin peut être utilisé pour la réalisation de lasers. Un laser à fibre Brillouin peut potentiellement être très cohérent et très peu bruité ; ce qui incite son utilisation dans plusieurs domaines incluant la défense, la métrologie et les télécommunications. L'objectif de cette thèse, qui s'insert dans le cadre du projet ATOS (Antenne acoustique en technologie Tout Optique pour la Surveillance), est d'obtenir un laser Brillouin à la fois compact et avec un seuil laser relativement bas. Pour respecter ces deux conditions, il est nécessaire de disposer d'une fibre avec un très fort coefficient de gain Brillouin gB et ayant une très petite aire effective de manière à concentrer la puissance optique dans le cœur de la fibre. Nous avons ainsi choisi d'utiliser une fibre faite à partir de verres en chalcogénure, qui ont un gB de deux ordres de grandeurs supérieures au gB d'une fibre monomode silice classique avec une microstructure dans le coeur. Ces travaux de recherche contribuent donc, d'une part, à démontrer qu'il est expérimentalement possible de réaliser des lasers Brillouin compacts, bas seuils et exhibant des caractéristiques remarquables en termes de bruit et de cohérence avec des fibres microstructurées en verre de chalcogénure et, d'autre part, à étudier la potentialité de ces cavités lasers dans le cadre du projet ATOS tout en proposant d'autres applications possibles pour la métrologie, l'instrumentation et les télécommunications. / Although stimulated Brillouin scattering (SBS) in optical fiber is a penalizing nonlinear effect in optical communication systems, it is possible to make good use of SBS in other applications such as in Brillouin fiber lasers (BFLs). A BFL can potentially have a very narrow linewidth and very low relative intensity noise (RIN) and frequency noise, making them excellent coherent laser sources that can be used in telecommunications, defense and metrology. The goal of this research work, which is in the framework of ATOS (Antenne acoustique en technologie Tout Optique pour la Surveillance, All Optical Acoustic Antenna for Security) project, is to obtain a compact Brillouin laser with a very low threshold power. In order to match these two conditions, it is essential to use a fiber with a very high Brillouin gain coefficient gB and with a small effective mode area to ensure a stronger light confinement in the fiber core. For this research work, we have combined both alternatives by using a microstructured optical fiber made of chalcogenide glass. These materials are known to have very high gB, which can be two orders of magnitudes higher than in the case of a standard silica fiber. In this work, we have, first of all, experimentally demonstrated that it is possible to obtain a compact, low threshold and low noise Brillouin laser using microstructured chalcogenide fibers. Then, we have studied the feasibility of using this laser cavity in the framework of the ATOS project while proposing alternative applications for metrology and telecommunications.

Orientador: Hugo Luis Fragnito / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-19T18:29:41Z (GMT). No. of bitstreams: 1 CastanedaTutestar_JuanAndres_M.pdf: 6184459 bytes, checksum: 92c32f647e9f3cbb607992b021c7924d (MD5) Previous issue date: 2012 / Resumo: Estudamos a interação entre laser e ruído em fibras ópticas, sua dependência com dispersão cromática e sua aplicação para caracterizar flutuações dos parâmetros de dispersao ao longo da fibra. A interacao é governada pela polarização não-linear de terceira ordem e, nesta tese, consideramos especificamente o processo de mistura de quatro ondas ou FMW (de Four-Wave Mixing) descrito por termos de ordem cúbica na amplitude do campo elétrico aplicado. Em particular, nós estamos interessados em termos que são lineares na amplitude do laser e quadraticos na do ruído. Devido a este processo, são geradas novas ondas que apresentam picos bem definidos no espectro e muito sensíveis aos parâmetros de dispersão de alta ordem (até quarta ordem e demonstrada nesta tese). Medidas com pulsos de curta duração (~ 100 ps para o laser e ~ 40 ps para o ruído em nossos experimentos) nos permitem caracterizar como os parâmetros de dispersão variam ao longo da fibra com boa resolução espacial (< 1 km). Apresentamos também uma resolução numérica das equações exatas para determinar como os parâmetros de dispersão, em fibras de perfil de índice degrau, dependem do raio do núcleo da fibra. Encontramos que variações de 0.1 µm (± 1%) do raio do núcleo da fibra produzem mudancas no comprimento de onda de dispersão nula (?0) e no pico de FWM (?FWM) que são consistentes com os resultados experimentais. Também verificamos a existencia de um valor do raio do núcleo da fibra o qual oferece propriedades de dispersao robustas para processos paramétricos. Este trabalho visa contribuir para a compreensão dos processos nao-lineares e campos estocásticos e, do ponto de vista prático, para o desenvolvimento de um método eficiente para medir variações na dispersão de alta ordem ao longo da fibra / Abstract: We study the interaction between laser and noise in optical fibers, its dependence on chromatic dispersion and its application to characterize the parameters of dispersion fluctuations along the fiber. The interaction is governed by the nonlinear polarization of the third-order and, in this thesis, we consider specifically the process of four-wave mixing (FWM) described by cubical terms in the amplitude of the applied electric field. In particular, we concern linear terms in the amplitude of the laser and quadratic in the noise. Due to this process, new waves are generated that have well-defined peaks in the spectrum and very sensitive to the parameters of highorder dispersion (up to fourth order is demonstrated in this thesis). Measurements with pulses of short duration (~ 100 ps for the laser and ~ 40 ps for the noise in our experiments) allow us to characterize how the dispersion parameters vary along the fiber with good spatial resolution (< 1 km). We also present an exact numerical solution of the equations to determine how the parameters of dispersion, in a stepindex fiber, depending on the radius of the fiber core. We found that variations of 0.1µ m (± 1%) of the fiber core radius produce changes in the wavelength of zero dispersion (?0) and at the peak of FWM (?FWM) that are consistent with experimental results. We also verified the existence of a value of the radius of the fiber core which provides robust dispersion properties for parametric processes. This work aims to contribute to the understanding of nonlinear processes and stochastic fields, and the practical point of view, to develop an efficient method for measuring variations in the high-order dispersion along the fiber / Mestrado / Mestre em Física