Optical resonators such as silica micro-spheres and micro-toroids can support whispering gallery modes (WGMs), where light circulates near the resonator surface and is confined by the total internal reflection at the dielectric boundary. Such resonators can exhibit very high quality (Q) factors, since the resonator surface can maintain atomic level smoothness. The combination of high Q factors and small resonator volumes has led to a wide range of applications in sensing, optomechanics, nonlinear optics, and quantum optics. In this dissertation, we introduce a new type of whispering gallery resonators (WGRs) based on micro-droplets in an immiscible liquid-liquid system. Within such an all-liquid platform, it is possible to achieve highly nonlinear coupling between light and liquid that can potentially lead to single-photon level optical nonlinearity. Specifically, we experimentally characterize a droplet (D~500um) of index matching fluid submerged in the water as a high-Q optical resonator, where we use an optical fiber taper to couple light into the droplet through non-contact evanescent coupling. The highest Q-factor observed in the experiment is 2x10^7 which closely matches the upper limit of intrinsic Q-factor set by the material absorption. Given with such a high Q factor, the WGM can exert strong radiation pressure on the droplet interface, push it outward, increase the length of optical path, and produce a red-shift in WGM resonance. Our experimental results have found that the ratio of those resonance shifts and the optical power coupled into the resonator is approximately 60 fm/μW. The result closely matches to our steady-state estimation based on solving the coupled Maxwell-Navier-Stokes equation. To investigate the dynamic interplay of light and liquid, we develop a harmonic oscillator (HO) model to describe the time-domain behaviors of the coupled optofluidic system. We find a good agreement between theoretical predictions and our experimental data. The shift of WGM resonance can potentially be induced by thermal effects. To estimate the magnitude of thermal effects, we also investigate the thermally induced nonlinear behaviors of WGMs in a cylindrical fiber resonator (D~125um), where we change the mechanism of heat dissipation by changing the cladding material (e.g. air and water). For direct temperature measurements, we use a fiber optical resonator with a fiber Bragg grating (FBG) inscribed in the fiber core to observe temperature shifts induced by the high-Q WGMs. Our result shows that the temperature increase in the fiber resonator in the water is 0.13 C, whereas the fiber resonator in air shows ~4.5 C increase in temperature. Our results suggest that the relatively high thermal conductivity of water suppresses thermal nonlinearity by ~50 times, and that the red-shifts of WGMs can largely be attributed to radiation pressure effect. / Ph. D.

Ce travail porte sur l'étude de propriétés optiques des fluides à échelle micrométrique. A cet effet, nous avons conçu, réalisé et étudié différents types de micro-résonateurs optofluidiques, sous forme de laboratoires sur puce. Notre analyse est fondée sur la modélisation analytique et numérique, ainsi que sur des mesures expérimentales menées sur des micro-cavités optiques; nous utilisons l'une d'entre elles pour des applications de réfractométrie de fluides homogènes et de fluides complexes ainsi que pour la localisation par piégeage optique de microparticules solides. Nous nous sommes d'abord concentrés sur l'étude d'une nouvelle forme de micro-cavité Fabry-Pérot basée sur des miroirs courbes entre lesquels est inséré un tube capillaire permettant la circulation d'une solution liquide. Les résultats expérimentaux ont démontré la capacité de ce dispositif à être utilisé comme réfractomètre avec un seuil de détection de 1,9 × 10-4 RIU pour des liquides homogènes. De plus, pour un liquide contenant des particules solides, la capacité de contrôler la position des microparticules, par des effets de piégeage optique ou de liaison optique, a été démontrée avec succès. Dans un second temps, un résonateur optique est formé simplement à partir d'une goutte de liquide disposée sur une surface super-hydrophobe. La forme quasi-sphérique résultante est propice à des modes de galerie. Il est démontré que, jusqu'à des tailles de gouttelettes millimétriques, la technique de couplage en espace libre est toujours en mesure d'accéder à ces modes à très faible queue évanescente d'interaction, contrairement à ce qu'indiquait jusqu'ici la littérature. De tels résonateurs optofluidiques à gouttelette devraient trouver leur application notamment comme capteur d'environnement de l'air ambiant ou encore comme incubateur de micro-organismes vivants pouvant être suivis par voie optique / This work focuses on the study of optical properties of fluids at the micrometer scale. To this end, we designed, implemented and studied different types of optofluidic micro- resonators in the Lab-on-Chip format. Our analysis is based on analytical and numerical modeling, as well as experimental measurements conducted on optical microcavities; we use one of them for refractometry applications on homogeneous fluids and on complex fluids, as well as for the localization of solid microparticles by optical trapping. We first focused on the study of a new form of Fabry-Perot micro-cavity based on curved mirrors between which a capillary tube is inserted for injecting a fluidic solution. Experimental results demonstrated the ability of this device to be used as a refractometer with a detection limit of 1.9 × 10-4 RIU for homogeneous liquids. Furthermore, for liquid containing solid particles, the ability to control the microparticles position either by optical trapping or optical binding effects has been successfully demonstrated. In a second step, an optical resonator is simply formed from a liquid droplet placed on top of a superhydrophobe surface. The resulting quasi-spherical shape supports resonant whispering gallery modes. It is shown that, up to millimeter size droplets, the proposed technique of free-space coupling of light is still able to access these modes with very low evanescent tail interaction, contrary to what was indicated in the literature so far. Such optofluidic droplet resonators are expected to find their applications for environmental air quality monitoring, as well as for incubator of living micro-organisms that can be monitored optically