Optical Whispering Gallery Mode Cylindrical Micro-Resonator Devices for Sensing Applications

Whispering gallery mode (WGM) micro-resonators are devices attractive for many practical applications including optical sensing, micro-lasers, optical switches, tunable filters and many others. Their popularity is due to the high Q-factors and the exceptional sensitivity of their optical properties to the resonator’s size, refractive index as well the properties of the surrounding medium. The main focus of this thesis is on the cylindrical WGM micro-resonators due to the simplicity of their fabrication and light coupling that they offer in comparison with other WGM devices. At first, an in-depth experimental investigation of the WGM effect in different types of cylindrical micro-resonators was carried out in order to establish the influence of the resonator’s geometry and coupling conditions on the resulting WGM spectrum. As one of the outcomes of this study, a novel method for geometrical profiling of asymmetries in thin microfiber tapers with submicron accuracy has been proposed and demonstrated. The submicron accuracy of the proposed method has been verified by SEM studies. The method can be applied as a quality control tool in fabrication of microfiber based devices and sensors or for fine-tuning of microfiber fabrication setups. The study also resulted in better understanding of the optimum conditions for excitation of WGMs in cylindrical fiber resonators, the influence of the tilt angle between the micro-cylinder and the coupling fiber taper. A novel strain sensor formed by a polymer-wire cylindrical micro-resonator has been developed. Accurate and repeatable measurements of strain have been demonstrated experimentally with the proposed sensor for the upper range of limit of detection up to 3250 με. Practical packaging method for the proposed strain sensor on a glass microscope slide has also been realized making the sensor portable and easy to use. A study of thermo-optic tuning of the WGMs in a nematic liquid crystal-filled hollow cylindrical microresonator has been carried out. A simple and robust packaging has been realized with the proposed tunable device to ensure its stable and repeatable operation. The demonstrated thermo-optic method for the WGMs tuning is potentially useful for many tunable photonic devices. Two novel all-fiber magnetic-field sensors have been designed based on photonic crystal fibers infiltrated with a magnetic fluid and a ferronematic liquid crystal utilizing the magnetic field tunability of WGM resonances. The highest experimentally demonstrated magnetic field sensitivity was 110 pm/mT in the range of magnetic fields from 0 to 40 mT. Finally, a packaged inline cascaded optical micro-resonators (ICOMRs) design is proposed for coupling multiple micro-resonators to a single fiber and simultaneous sensing of multiple parameters (strain, temperature, humidity, or refractive index) at multiple points in space has been demonstrated. The proposed design principle can find applications in quasi-distributed sensing, optical coding, optical logic gates and wavelength division multiplexed optical communications systems

Nonlinear and Quantum Optics with Whispering Gallery Resonators

Optical Whispering Gallery Modes (WGMs) derive their name from a famous acoustic phenomenon of guiding a wave by a curved boundary observed nearly a century ago. This phenomenon has a rather general nature, equally applicable to sound and all other waves. It enables resonators of unique properties attractive both in science and engineering. Very high quality factors of optical WGM resonators persisting in a wide wavelength range spanning from radio frequencies to ultraviolet light, their small mode volume, and tunable in- and out- coupling make them exceptionally efficient for nonlinear optical applications. Nonlinear optics facilitates interaction of photons with each other and with other physical systems, and is of prime importance in quantum optics. In this paper we review numerous applications of WGM resonators in nonlinear and quantum optics. We outline the current areas of interest, summarize progress, highlight difficulties, and discuss possible future development trends in these areas.Comment: This is a review paper with 615 references, submitted to J. Op

Nanostructure-enhanced infrared spectroscopy

While infrared spectroscopy is a powerful technique that provides molecular information such as chemical constituents and chemical structures of analytes, it suffers from low absorption cross-section resulting in low sensitivity and poor signal-to-noise or signal-to-background ratios. Surface-enhanced infrared absorption (SEIRA) spectroscopy, which is supported by nanometer scale structures, is a promising technology to overcome these problems in conventional infrared (IR) spectroscopy and enhances IR signals using the field enhancement properties of surface plasmon resonance. Recently resonant SEIRA technique was proposed, and signal enhancement factor was significantly improved. In this review, we present an overview of the recent progresses on resonant SEIRA technologies including nanoantenna- and metamaterial-based SEIRA, and also SEIRA techniques with nanoimaging capabilities

Nanophotonic split-ring resonators as dichroics for molecular spectroscopy

The unique optical properties of metallic nanostructures have enabled the creation of a new generation of ultra sensitive biosensors based on vibrational spectroscopy. Through strict engineering of structural morphology, a nanometal’s free electrons can be tuned to resonate at a particular frequency, resulting in amplification and confinement of the electromagnetic field around certain areas of the structure. Molecules situated within these areas experience a greater degree of polarisation due to the oscillating plasmon field, a phenomena which, when combined with resonance Raman spectroscopy, has been shown to enable single molecule detection.1, 2 This thesis describes the fabrication and plasmonic characterisation of Au and Ag circular nano split-ring resonators using a combination of electron beam lithography, finite difference time domain simulation and transmission spectroscopy. Through alteration of ring radius, arc length, wall width, metal thickness and metallic composition it is shown that the asymmetric split-ring structures exhibit a multi-modal, polarisation dependent plasmonic response that can be tuned over several microns. Such a response enables these geometries to be employed as novel multi-wavelength biosensors via surface enhanced Raman spectroscopy and surface enhanced resonance Raman spectroscopy. This work goes on to demonstrate that by using electron beam lithography to manipulate the nano-scale geometry of Ag split-ring resonators, their optical properties can be tuned such that the structures exhibit two independently addressable, high frequency plasmon resonance modes for SERRS. In a series of sensing experiments it is shown that this tailored, multi-modal, polarisation dependent activity enables the split-rings to act as discriminating sensors, with each resonance tuned for a particular sensing purpose. Ultimately the structures are used as multi-wavelength, multi-analyte DNA SERRS sensors, with each resonance tuned both to the absorption wavelength of a differently coloured Raman reporter molecule and its corresponding laser excitation wavelength. In doing so, the ability of each resonance to independently sense clinically relevant concentrations of single DNA strand types from within a mixed population on the sensor surface is demonstrated

Plasmonics and its Applications

Plasmonics is a rapidly developing field that combines fundamental research and applications ranging from areas such as physics to engineering, chemistry, biology, medicine, food sciences, and the environmental sciences. Plasmonics appeared in the 1950s with the discovery of surface plasmon polaritons. Plasmonics then went through a novel propulsion in the mid-1970s, when surface-enhanced Raman scattering was discovered. Nevertheless, it is in this last decade that a very significant explosion of plasmonics and its applications has occurred. Thus, this book provides a snapshot of the current advances in these various areas of plasmonics and its applications, such as engineering, sensing, surface-enhanced fluorescence, catalysis, and photovoltaic devices

Integrated optical sensors on the Si₃N₄-organic hybrid (SiNOH) platform

Ein wellenleiterbasierter Sensorchip wird demonstriert, der für Point-of-Care-Anwendungen geeignet ist. Der Biosensor wird mit Hilfe eines mathematischen Modells entworfen, mit dem die Sensitivität der Wellenleiter untersucht wird. Für die Lichteinkopplung in die Wellenleiter wird erstmalig eine neue Klasse von integrierten Laserquellen für sichtbare Wellenlängen untersucht. Die Funktionsfähigkeit des wellenleiterbasierten Biosensorchips durch Detektionsexperimente erfolgreich nachgewiesen