This thesis presents the development of a refractometric sensor based on quantum dot-embedded polystyrene microspheres. The technique uses optical resonances within a microsphere, known as Whispering-Gallery Modes (WGMs), which produce narrow spectral peaks. The basic theory of WGMs is reviewed and specifically discussed for biosensing application. The spectral shifts of WGM peaks are sensitive to changes in the local refractive index. In the experiments, two-photon excited luminescence from the quantum dots couples into several WGMs within the microresonator. By optimizing the detection area, the spectral visibility of the WGMs is improved. The spectral shifts are measured as the surrounding index of refraction changes. The experimental sensitivity is about five times greater than that predicted by Mie theory. The sensor element is based on commercially available dielectric microspheres with a diameter about 10 μm. Thus, the technique is more economic and suitable for sensing applications, compared to microspheres of 100 μm in size which can only be made in the laboratory.

Significant technical barriers currently prevent the wide spread adoption of WGM lasers as building blocks in large-scale photonic integrated circuits. The first challenge is to reduce the electrical power consumption at desirable levels of light output power. The second target is to obtain directional light emission without sacrificing other laser performance metrics. The best opportunity for success lies in the pursuit of small micro-Pillar lasers with spiral-geometry cavities. Process technology has been demonstrated for making high-performance WGM lasers including a refined ICP etching process for fabricating micro-Pillar cavities with sidewall roughness less than 10 nm and a new hydrogenation based approach to achieving current blocking that is compatible with all other processing steps and robust in comparison with earlier reports. A comprehensive photo-mask has been designed that enables investigation of the interplay between device geometry and WGM laser performance. Emphasis has been placed on enabling experiments to determining the impact of diffraction and scattering losses, current and carrier confinement, and surface recombination on electrical/optical device characteristics. In addition, a methodology has been developed for separating out process optimization work from the task of identifying the best means for directional light out-coupling. Our device fabrication methods can be proven on WGM lasers with pure cylindrical symmetry, hence results from these experiments should be independent of any specific light output coupling scheme. Particular attention has been paid to the fact that device geometries that give the best performance for purely symmetrical cavities may not yield the highest level of light emission from the spiral output notch. Such considerations seem to be missing from much of the earlier work reported in the literature. Finally, our processing techniques and device designs have resulted in individual WGM lasers that outperform those made by competitors. These devices have been incorporated into multi-element, coupled-cavity optical circuits thereby laying the groundwork for construction of digital photonic gates that execute AND, OR, and NOT logic functions. / Ph. D.

This thesis presents a novel method to fabricate metallic nanostructures on whispering gallery mode (WGM) cavity surfaces. The unique properties of WGM cavities have shown their promising future in both fundamental research and engineering applications. High sensitivity biosensors are one of the most important applications. Thanks to their ultra high quality factor (Q) and small optical mode volume, the resonant frequency shift of a single nanoparticle binding becomes detectable. The basic principles of a WGM cavity and its coupling mechanism with an optical coupler are discussed in detail. From the WGM sensing principle, people have demonstrated the positive contributions of the surface plasmon to the sensitivity. Furthermore, we implement the localized surface plasmon resonance (LSPR) on the cavity surface by depositing metallic dots. We use the focused ion beam (FIB) to directly deposit metallic nanodots on the spherical cavity surface for the first time. The quality factor of the cavity with metallic dots is above 10^7 in both air and water, which is more than one order larger than other published results. Also, the new method is much more controllable and repeatable than previous methods. It reveals a new fabrication method for potential ultra sensitive sensors based on WGM cavities. In addition, we offer a new mode solver for the toroidal WGM cavity. The microtoroid is a better platform for further investigation of WGM sensing than the microsphere. By expanding cavity modes to a set of normal fiber modes, we formulate the new mode solver based on simple physical principles. The simulation results of the radiative quality factor based on the new mode solver are presented as well. / Graduate

This thesis covers the construction and characterisation of microlasers based on whispering gallery modes in ytterbium-doped microsphere resonators. The microlasers were made by drawing and fusing Yb-doped silica optical fibre into microspheres of approximately 100 μmin diameter using CO2 laser-induced melting. Access to whispering gallery modes was accomplished using a prism coupled to the evanescent field of the internal cavity modes. Microspheres with Q-factors of up to 10^7 were made using this technique. CW multimode lasing was observed at 1050 nm, with a pump threshold required for lasing estimated to be of the order of 100 μW for a 900 nm pump. Both TE and TM modes were identified in the laser emission and the ability to selectively excite each mode family (TE or TM) is shown to be directly controlled by the pump. Pulsed lasing was also observed at 975 nm and 1050 nm.

Advances in microfabrication and surface chemistry techniques have provided a new paradigm for the creation of in vitro systems for studying problems in biology and medicine in ways that were previously not practical. The ability to create devices with micro- to nano-scale dimensions provides the opportunity to non-invasively interrogate and monitor biological cells and tissue in large arrays and in a high-throughput manner. These systems hold the potential to, in time, revolutionize the way problems in biology and medicine are studied in the form of point-of-care devices, lab-on-chip devices, and biological microelectromechanical systems (BioMEMS). With new in vitro models, it will be possible to reduce the overall cost of medical and biological research by performing high-throughput experiments while maintaining control over a wide variety of experimental variables. A critical aspect of developing these sorts of systems, however, is controlling the device/tissue interface. The surface chemistry of cell-biomaterial and protein-biomaterial interactions is critical for long-term efficacy and function of such devices. The work presented here is focused on the application of surface and analytical chemistry techniques for better understanding the interface of biological elements with silica substrates and the development a novel Bio-MEMS device for studying muscle and neuromuscular biology. A novel surface patterning technique based on the use of a polyethylene glycol (PEG) silane self-assembled monolayer (SAM) as a cytophobic surface and the amine-terminated silane diethyeletriamine (DETA) as a cytophilic surface was developed for patterning a variety of cell types (e.g. skeletal muscle, and neural cells) over long periods of time (over 40 days) with high fidelity to the patterns. This method was then used to pattern embryonic rat skeletal muscle and motor neurons onto microfabricated silicon cantilevers creating a novel biological microelectromechanical system (BioMEMS) for studying muscle and the neuromuscular junction. This device was then used to study the effect of exogenously applied substances such as growth factors and toxins. Furthermore, a whispering-gallery mode (WGM) biosensor was developed for measuring the adsorption of various proteins onto glass microspheres coated with selected silane SAMS commonly used in BioMEMS system. With this biosensor it was possible to measure the kinetics of protein adsorption onto alkylsilane SAMS, in a real-time and label-free manner.

Ever-increasing interest in millimeter-wave and terahertz spectrum has prompted research and development of novel passive components working at these frequencies. Compared with the conventional planar components, non-planar dielectric devices become more attractive as frequencies increase due to their higher quality factors and dimensional tolerances. In this thesis, we present fast methods to analyze the millimeter-wave dielectric resonator and rod antenna. First, an analytical method has been developed to evaluate resonant frequencies, quality factors of the Whispering Gallery Mode (WGM) disk resonators and also the resonator-waveguide coupling. A numerical solver based on full-wave finite element method is implemented to verify the analytical result. This analytical model provides a solution for fast design and optimization of WGM resonators in filter and sensor applications. Secondly, a fast analytical approach based on local mode theory is introduced to calculate the radiation from tapered dielectric rod antenna. This efficient approximate model consumes much less computing resources and time, and demonstrates good agreements with full-wave numerical results. It supplies a quantitative way to understand the radiation mechanism and interaction between different parts of the antenna. Based on this, design criteria for the taper profile of rod antennas are given.

Ever-increasing interest in millimeter-wave and terahertz spectrum has prompted research and development of novel passive components working at these frequencies. Compared with the conventional planar components, non-planar dielectric devices become more attractive as frequencies increase due to their higher quality factors and dimensional tolerances. In this thesis, we present fast methods to analyze the millimeter-wave dielectric resonator and rod antenna. First, an analytical method has been developed to evaluate resonant frequencies, quality factors of the Whispering Gallery Mode (WGM) disk resonators and also the resonator-waveguide coupling. A numerical solver based on full-wave finite element method is implemented to verify the analytical result. This analytical model provides a solution for fast design and optimization of WGM resonators in filter and sensor applications. Secondly, a fast analytical approach based on local mode theory is introduced to calculate the radiation from tapered dielectric rod antenna. This efficient approximate model consumes much less computing resources and time, and demonstrates good agreements with full-wave numerical results. It supplies a quantitative way to understand the radiation mechanism and interaction between different parts of the antenna. Based on this, design criteria for the taper profile of rod antennas are given.

Optofluidic sensing utilizes the advantages of both microfluidic and optical science to achieve tunable and reconfigurable high-performance sensing purpose, which has established itself as a new and dynamic research field for exciting developments at the interface of photonics, microfluidics, and the life sciences. With the trend of developing miniaturized electronic devices and integrating multi-functional units on lab-on-a-chip instruments, more and more desires request for novel and powerful approaches to integrating optical elements and fluids on the same chip-scale system in recent years. By taking advantage of the electrowetting phenomenon, the wettability of liquid droplet on micro/nano-structured surfaces and the Leidenfrost effect, this doctoral research focuses on developing high-performance optofluidic sensing systems, including optical beam adaptive steering, whispering gallery mode (WGM) optical sensing, and surface-enhanced Raman spectroscopy (SERS) sensing. A watermill-like beam steering system is developed that can adaptively guide concentrating optical beam to targeted receivers. The system comprises a liquid droplet actuation mechanism based on electrowetting-on-dielectric, a superlattice-structured rotation hub, and an enhanced optical reflecting membrane. The specular reflector can be adaptively tuned within the lateral orientation of 360°, and the steering speed can reach ~353.5°/s. This work demonstrates the feasibility of driving a macro-size solid structure with liquid microdroplets, opening a new avenue for developing reconfigurable components such as optical switches in next-generation sensor network. Furthermore, the WGM sensing system is demonstrated to be stimulated along the meridian plane of a liquid microdroplet, instead of equatorial plane, resting on a properly designed nanostructured chip surface. The unavoidable deformation along the meridian rim of the sessile microdroplet can be controlled and regulated by tailoring the nanopillar structures and their associated hydrophobicity. The nanostructured superhydrophobic chip surface and its impact on the microdroplet morphology are modeled by Surface Evolver (SE), which is subsequently validated by the Cassie-Wenzel theory of wetting. The influence of the microdroplet morphology on the optical characteristics of WGMs is further numerically studied using the Finite-Difference Time-Domain method (FDTD) and it is found that meridian WGMs with intrinsic quality factor Q exceeding 104 can exist. Importantly, such meridian WGMs can be efficiently excited by a waveguiding structure embedded in the planar chip, which could significantly reduce the overall system complexity by eliminating conventional mechanical coupling parts. Our simulation results also demonstrate that this optofluidic resonator can achieve a sensitivity as high as 530 nm/RIU. This on-chip coupling scheme could pave the way for developing lab-on-a-chip resonators for high-resolution sensing of trace analytes in various applications ranging from chemical detections, biological reaction processes to environmental protection. Lastly, this research reports a new type of high-performance SERS substrate with nanolaminated plasmonic nanostructures patterned on a hierarchical micro/nanostructured surface, which demonstrates SERS enhancement factor as high as 1.8 x 107. Different from the current SERS substrates which heavily relies on durability-poor surface structure modifications and various chemical coatings on the platform surfaces which can deteriorate the SERS enhancement factor (EF) as the coating materials may block hot spots, the Leidenfrost effect-inspired evaporation approach is proposed to minimize the analyte deposition area and maximize the analyte concentration on the SERS sensing substrate. By intentionally regulating the temperature of the SERS substrate during evaporation process, the Rhodamine 6G (R6G) molecules inside a droplet with an initial concentration of 10-9 M is deposited within an area of 450 μm2, and can be successfully detected with a practical detection time of 0.1 s and a low excitation power of 1.3 mW. / Doctor of Philosophy / Over the past two decades, optofluidics has emerged and established itself as a new and exciting research field for novel sensing technique development at the intersection of photonics, microfluidics and the life sciences. The strong desire for developing miniaturized lab-on-a-chip devices and instruments has led to novel and powerful approaches to integrating optical elements and fluids on the same chip-scale systems. By taking advantage of the electrowetting phenomenon, the wettability of liquid droplet on micro/nano-structured surfaces and the Leidenfrost effect, this doctoral program focuses on developing high-performance optofluidic sensing systems, including optical beam adaptive steering, whispering gallery mode (WGM) optical sensing, and surface-enhanced Raman spectroscopy (SERS) sensing. During this doctoral program, a rotary electrowetting-on-dielectric (EWOD) beam steering system was first fabricated and developed with a wide lateral steering range of 360° and a fast steering speed of 353.5°/s, which can be applied in telecommunication systems or lidar systems. Next, the meridian WGM optical sensing system was optically simulated using finite difference time domain (FDTD) method and was numerically validated to achieve a high quality-factor Q exceeding 104 and a high refractive index sensitivity of 530 nm/RIU, which can be applied to the broad areas of liquid identification or single molecule detection. Lastly, a SERS sensing platform based on a hierarchical micro/nano-structured surface was accomplished to exhibit a decent SERS enhancement factor (EF) of 1.81 x 107. The contact angle of water droplet on the SERS substrate is 134° with contact angle hysteresis of ~32°. Therefore, by carefully controlling the SERS surface temperature, we employed Leidenfrost evaporation to concentrate the analytes within an extremely small region, enabling the high-resolution detection of analytes with an ultra-low concentration of ~10-9 M.

Ces travaux de thèses portent sur l’étude de la dynamique du laser à mode de galerie dans le but de réaliser une source micro-onde en utilisant un laser à mode de galerie doublement monomode. Nous montrons ici les résultats expérimentaux sur le bruit relatif d’intensité (RIN) d’un laser à mode de galerie en verre ZBLALiP dopé aux ions Er3+. Outre l’aspect performances d’utilisation du laser, le spectre de RIN donne un certain nombre d’informations sur la dynamique du laser (temps de vie des photons, taux de pompage effectif, sources de bruit, ...).Les très forts facteur de qualités de ces résonateurs ainsi que leurs propriétés de confinement spatial amène un couplage non-linéaire etre les photons et les atomes du milieu amplificateur, faisant apparaitre dans le spectre de RIN des harmoniques de la fréquence de relaxation du laser. Le modèle harmonique développé permet d’estimer le volume de mode du mode de galerie en régime laser, quantité difficilement estimable dans ce régime d’émission. D’autre part, les mesures de RIN réalisées sur un verre industriel IOG-1 codopé Yb3+/Er3+ montrent la signature d’un couplage modal, induit par la diffusion Rayleigh, où les deux modes couplés fonctionnent au dessus du seuil laser. La dynamique de ce laser est également étudié et les comportements obtenus sont mis en parallèle avec les études réalisées sur le gyro-Laser à l’état solide. / This thesis presents the studies of whispering gallery mode laser dynamics in order to realize a micro-wave source using simultaneous oscillations in a unique whispering gallery mode micro-laser. We show experimental results on the relative intensity noise (RIN) of a Whispering Gallery Mode Laser in ZBLALiP glass doped with Er3+ ions. Besides the pure laser specifications, the RIN spectrum gives informations about the dynamics inside the cavity, such as photon lifetime, effective pumping rate and noise sources. Moreover, we have shown that a single-mode emission comes with the presence of multiple harmonics of the relaxation frequency. The theoretical model taking account the non-linear coupling between photons and atoms allows us to determine the mode volume of the whispering gallery mode in laser regime, which is quite difficult to evaluate in this regime. On the other hand, we have studied the laser dynamics in an industrial IOG-1 glass codoped with Yb3+/Er3+ ions where the signature of a modal coupling, induced by Rayleigh scattering, lies in the RIN spectrum. In this particular case, the two coupled modes operate above threshold. The observed behavior is compared with thoses of a solid state gyro-laser.

During the past decades, femtosecond laser micro-fabrication has gained growing interests owing to its several unique features including direct and maskless fabrication, flexible choice of materials and geometries, and truly three-dimensional fabrication. Moreover, fiber-optic sensors have demonstrated distinct advantages over traditional electrical sensors such as the immunity to electromagnetic interference, miniature footprint, robust performance, and high sensitivity. Therefore, the marriage between femtosecond laser micro-fabrication and optical fibers have enabled and will continue to offer vast opportunities to create novel structures for sensing applications. This dissertation focuses on design, fabrication and characterization of optical-fiber based interferometric devices for sensing applications. Three novel devices have been proposed and realized, including point-damage-based Fiber Bragg gratings in single-crystal sapphire fibers, all-sapphire fiber-tip Fabry-Pérot cavity, and in-fiber Whispering-Gallery mode resonator / Doctor of Philosophy / Optical fibers are an optical platform with cylindrical symmetry with overall diameter typically within 50 to 500 μm. The miniature footprint and large aspect ratio make it attractive in sensing applications, where intrusion, flexibility, robustness and small size are key design parameters. Beyond that, fiber-optic sensors also possess distinct operational advantages over traditional electrical sensors such as high sensitivity, immunity to electromagnetic interference (EMI), and fully distributed deployment. Owing to the above advances, fiber-optic sensors have been one of the key technologies in the broader sensing field for the past decades. However, the unique cylindrical shape of optical fiber makes it naturally less compatible to those well-developed fabrication technologies in the current sophisticated semiconductor industry. During the past decades, the possibility of three-dimensional (3D) writing inside transparent materials with tightly focused ultrafast laser pulses has attracted attention widely among the academy as well as the industry. Therefore, the marriage between ultrafast laser micro-fabrication and optical fibers have enabled and will continue to offer vast opportunities to create novel structures for sensing applications. This dissertation focuses on design, fabrication and characterization of optical-fiber based interferometric devices for sensing applications. Three novel devices have been proposed and realized, including point-damage-based Fiber Bragg gratings in single-crystal sapphire fibers, all-sapphire fiber-tip Fabry-Pérot cavity, and in-fiber Whispering-Gallery mode resonator.