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Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (leaves [137]-142).

Theoretical and experimental studies of real-time interrogation of optical sensors based on wavelength-to-time (WTT) mapping are presented. The sensing information is encoded in the spectrum of an optical sensor, and transferred to the time domain by using WTT mapping. Utilizing digital electronics for post processing, the sensing information can be interrogated at an ultra-high speed and resolution. Two sensors based on WTT mapping are proposed and demonstrated. First, a random grating sensor for simultaneous measurement of the temperature and strain is investigated. An ultra-short pulse from a mode-lock laser is spectrum shaped by a high-birefringence random grating to generate two orthogonally polarized spectrums, which are then fed to an optical loop in which a linearly chirped fiber Bragg grating is incorporated. Linear WTT mapping is implemented, and two temporally separated optical pulses are generated, and then converted to two electrical waveforms at a photodetector. Pulse compression is then employed. By measuring the temporal intervals of the temporally compressed pulses, the strain and temperature information can be retrieved. Conventional fiber based sensors are not sensitive to the refractive index change of the environment. In the second sensor, a silicon photonic microdisk resonator (MDR) for temperature and liquid refractive index sensing is proposed and demonstrated. By using the notches in the spectrum of the MDR, a microwave photonic filter (MPF) is implemented. By feeding a linearly chirped microwave signal to the MPF, a filtered signal with its temporal location representing the spectrum is generated. By monitoring the time location of the filtered signal, the temperature or the refractive index information is revealed.

The work was carried out with the aim of developing an optical interferometric detection system. This was to be applied to the quantative measurement of low amplitude, high frequency surface displacements (< 1nm at several MHz). Two forms of interferometric detector are investigated. The performance and limitations in particular measurement situations are assessed for both types of interferometer. The first type of detector investigated is a miniature stabilised interferometer. The design of a stabilisation system is given, along with ways in which it can be optimised for a particular environment. The second type of detector studied is a quadrature interferometer. Various methods of processing the two channels of information from this device are discussed. The design of a new method of processing the signals is given, and its performance determined. The interferometric sensor is combined with a waveform digitiser and microcomputer to form an integrated detection system. Analysis of the waveforms obtained is performed by a system of Pascal programs developed for this purpose. The detection system is applied to tasks such as the calibration of other forms of transducer and the characterisation of artificial sources of acoustic emission. The results of experimental studies are given and the applications of such a system discussed.

There have been few theoretical advancements in the theory of light-scattering from particles since the days of Rayleigh and of those who have come later in the early twentieth century such as Mie, Lorenz and Born. The lack of progressive advancements in this area is a clear indication of the difficulties faced. However, the advancement of optical sensor technology and computer systems, representing thus an empirical advancement, have managed to produce effective means for collecting large amounts of high quality data in a relatively short time. Such difference in advancement between these two approaches signifies the necessity for establishing generic approximations and tools that can be used effectively in both domains.

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Le besoin croissant de biocapteurs optiques compacts, sélectifs, ultrasensibles, rapides et bas coût dans les domaines médical et environnemental a engendré une émergence de solutions technologiques, notamment les capteurs à bases de microrésonateurs optiques. Ces types de biocapteurs sont capables de fournir une détection sélective de très faibles concentrations de biomolécules si leurs surfaces sont fonctionnalisées. En revanche, les deux méthodes optiques d'interrogation actuelles, balayage spectral et variation de l’intensité, ne peuvent ni fournir la sensibilité de la phase du signal optique propagé dans le capteur, ni les paramètres opto-géométriques (perte par propagation, l'indice effectif, coefficient de couplage, etc) nécessaires pour une modélisation de la réponse du capteur. Pour accéder à ces informations, nous avons proposé d’utiliser l'interféromètre optique à faible cohérence sensible à la phase comme une technique alternative d’interrogation et de caractérisation de microrésonateurs. La première partie des travaux de cette thèse est consacrée à l’étude de conception et de réalisation de microrésonateurs monomodes possédant un facteur de qualité supérieur à 20000 dans l'eau. Cette étude a été validée par la réalisation technologique, à l'aide des procédés de photolithographie classique et de gravure sèche au plasma d'oxygène, de microrésonateurs polymères possédant des facteurs de qualité allant jusqu'à 38 200. La deuxième partie des travaux de thèse est dédiée à l'adaptation du dispositif PS-OLCI, initialement développé au Laboratoire National de Métrologie et d'Essais (LNE) pour interroger les composants des télécommunications optiques, pour la caractérisation de microrésonateurs optiques. Les résultats obtenus en évaluant les performances spatiales et spectrales de différents microrésonateurs ont montré que le dispositif PS-OLCI n'est pas seulement un outil d'interrogation et de caractérisation mais aussi un véritable outil d’aide à la conception de microrésonateurs optiques. Une modélisation, validée par l'ajustement des mesures expérimentales, de la réponse PS-OLCI d'un microrésonateur, met en évidence la relation existant entre l'interférogramme et les intégrales de Fresnel. La dernière partie de nos travaux concerne l'association du dispositif PS-OLCI et d’un composant optofluidique, constitué de microrésonateurs et d’un circuit microfluidique en polymères, pour la détection d’espèces biologiques. A cet effet, la molécule de glucose a été choisie pour démontrer la détection homogène ou volumique en solution aqueuse en obtenant respectivement les limites de détection de l'ordre de 50 µg/ml et de 2 µg/ml en exploitant l’intensité ou la phase des mesures PS-OLCI. Ces performances démontrent la capacité de notre capteur à déceler des biomolécules en faible concentration ainsi que la pertinence de la mesure de la phase, d'où l'intérêt du dispositif PS-OLCI. Pour remédier au problème de sélectivité du capteur en détection homogène, la méthode de détection surfacique est utilisée. La problématique de chimie de surface des polymères, c'est à dire la fonctionnalisation des surfaces des guides polymères en vue d’une détection surfacique, a d'abord été effectuée. Les limites de détection obtenues en détection surfacique sont ensuite évaluées à leur tour pour différents types de molécules particulièrement les protéines telles que la streptavidine ou la biotine. Les performances de détection de streptavidine obtenues sont au moins 10 fois meilleures que celles obtenues à l’aide de la technique de Résonance de Plasmons de Surface considérée à ce jour comme la technique de référence en biodétection sans marqueur. Ces premiers résultats, présentant des marges importantes d’amélioration, contribuent à démontrer que les capteurs à base de microrésonateurs optiques sont des candidats potentiels très prometteurs pour la détection de très faibles concentrations de biomolécules pour l’analyse biochimique. / The increasing need for compact, selective, ultrasensitive, fast and affordable optical biosensors in the medical and environmental sectors gave rise to new technological solutions, especially regarding sensors based on optical microresonators. If their surfaces are functionalized, these biosensors can provide a selective detection of low concentrations of biomolecules. However, two common optical interrogation methods – spectral scanning and intensity variation – cannot provide the same sensitivity as the method using phase detection of the guided modes nor the opto-geometrical parameters (propagation loss, effective refractive index, coupling coefficient), needed for the modeling of the sensor response. To get this information, we proposed to use the Phase Sensitive-Optical Low Coherence Interferometer (PS-OLCI) as a new alternative technical solution for interrogation and characterization of microresonators. The first part of this thesis is dedicated to the conception and fabrication of single mode microresonators with a quality factor higher than 20 000 in water. This work was validated by the manufacture of polymer microresonators with a quality factor up to 38 200, using UV photolithography and Reactive Ion Etching (RIE) processes. The second part of this work covers the adaptation of PS-OLCI setup, initially developed at Laboratoire national de métrologie et d'essais (LNE), to interrogate optical telecommunication devices, for the characterization of optical microresonators. The results, obtained through the analysis of spatial and spectral performances of various microresonators, showed that the PS-OLCI setup is not only an interrogation and characterization tool but also a real support tool for designing optical microresonators. The performed modelling of the PS-OLCI and microresonator association response, validated by the fitting of the experimental data, demonstrated the relation between PS-OLCI measurements and Fresnel integrals. The last part of this work is dedicated to label free biosensing experiments using PS-OLCI setup associated to an optofluidic component, made of polymer optical microresonators and polymer microfluidic circuit, to detect biological species. The glucose molecule was chosen to demonstrate the homogeneous sensing experiments in aqueous solution. The obtained detection limits are around 50 µg/ml when we exploited intensity and around 2 µg/ml when we exploited the PS-OLCI measurements phase. These results demonstrate the high sensitivity of the proposed biosensor as well as the value of the optical phase measurement, hence the interest of PS-OLCI set up. To address the problem of sensor selectivity in homogeneous sensing method, surface sensing experiences were performed. The first step of this method was the functionalization of the sensor surface, by binding adequate recognition molecular sites to the sensor surface in order to immobilize target molecules. Proteins were then chosen to perform this very same type of experiences. The preliminary results in the 0.02 pg/mm2 range clearly show that our sensors is ten times more sensitive than Surface Plasmon Resonance, which is actually considered among the most successful label free sensing methods. These first results, which can be improved, demonstrate that the sensors based on optical microresonators are promising candidates for the detection of low concentrations of biomolecules for biochemical investigation.

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