Free ultra-high-Q microtoroid: a tool for designing photonic devices

We describe techniques that enable fabrication of a new class of photonic devices based on free UH-Q microresonators. Preliminary results show that free silica microtoroids with Qs above 30 million can be fabricated and transferred to different platforms for integration with a variety of photonic devices

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

Novel Sensing Mechanisms for Chemical and Bio-sensing Using Whispering Gallery Mode Microresonators

Due to their ultra-high quality factor and small mode volume, whispering gallery mode (WGM) microresonators have proven to have exceptional sensing capabilities, with single particle level sensitivity to virions, proteins, and nucleic acids. Current sensing mechanisms rely on measuring the changes in the transmission spectrum of the resonator upon adsorption of the analyte on the surface of the resonator, appearing as either shift, splitting, or broadening of the resonance mode, all of which measure the polarizability of adsorbed analytes. In this dissertation, we present two new sensing mechanisms for WGM microresonators: the measurement of a dynamic chemical reaction around the resonator, exemplified by the polymerization of hydrogel, and the Raman spectroscopy of molecules on the surface of WGM microresonator through WGM-based surface-enhanced Raman scattering. Further, an on-going work on sensing using mesoporous silica micro-bottle resonator is described in the last chapter. Our work on the measurement of gelation of polyacrylamide hydrogel using WGM resonators is the first report of using WGM resonators to continuously monitor a chemical reaction (i.e. gelation) in situ. The results from WGM sensing is compared with rheology, a well-established technique for hydrogel characterization. From the similarities and differences in the measured results from WGM and rheology, we suggest that whereas rheology measures the viscoelastic properties of the hydrogel, WGM resonators measure the hydrogel density indirectly through its refractive index. The two techniques provide data that complement each other, which can be used to study the gelation reaction in more details. Raman spectroscopy is a powerful technique for molecular fingerprinting, but the weak Raman signal often requires enhancement from techniques such as surface-enhanced Raman scattering (SERS). Conventionally, metallic nanostructures are used for SERS, but recently there has been increasing interest in the enhancement of Raman scattering from dielectric substrates due to their improved stability and biocompatibility compared with metallic substrates. The combination of WGM resonator and Raman spectroscopy can be a promising sensing platform with both high sensitivity and specificity. Here, we demonstrate the enhanced Raman scattering from rhodamine 6G molecules coated on silica microspheres, excited through WGMs. A total Raman enhancement factor of 1.4 × 104 is observed

Photonic Molecules Formed by Ultra High Quality Factor Microresonator for Light Control

Whispering-gallery-mode (WGM) optical microresonators with micro-scale mode volumes and high quality factors have been widely used in different areas ranging from sensing, quantum electrodynamics (QED), to lasing and optomechanics. Due to the ultra-high Q and the tight spatial confinement, the cavity provides high intra-cavity field intensity and long interaction time, which enhances the interaction between light and materials. This feature makes WGM microresonator a great candidate for low-threshold nonlinear processes, cavity optomechanics, signal processing, and sensor with ultra-high sensitivity. Also, modification of the modes in these resonators has been of considerable interest for their potential applications and underlying physics. Two or more coupled resonators form a compound structure--photonic molecule (PM)--in which interactions of optical modes create supermodes. This molecular analogy stems from the observation that confined optical modes of a resonator and the electron states of atoms behave similarly. Thus, a single resonator is considered as a photonic atom, and a pair of coupled resonators as the photonic analog of a molecule. Studying the interactions in PMs is critical to understand their resonance properties and the field and energy transfers to engineer new devices such as phonon lasers and enhanced sensors. Further modification of the compound structure with gain mechanism such as rare-earth dopants makes the coupled cavity system a novel Parity-Time symmetric optical device. More surprisingly, the implementation of non-Hermitian on-chip WGM photonic molecule with exceptional points even enables the control and modification of laser emission with just loss tuning. In this dissertation, I present my study and new implementation of applications with ultra-high Q WGM microresonator based photonic molecules. We discuss the on-chip Parity-Time symmetric microresonator and non-Hermitian photonic molecule design for light manipulation and optical isolation, lasing and dissipation control, directional switching and PM-based optical analog of electromagnetically induced transparency, as well as highly sensitive tuning of WGM Raman microlaser with PM loss manipulation

Lightwave planar circuits based on organic materials for filtering and sensing

This thesis investigates in detail optical filters based on two phenomena and their applicability in photonics devices. The first phenomenon is called Whispering gallery modes, discovered in 1912 from Lord Rayleigh. The second phenomenon investigated in this thesis is the Braggs’s law, to develop optical filters

Photonic Sensors Based on Integrated Ring Resonators

This thesis investigates the application of integrated ring resonators to different sensing applications. The sensors proposed here rely on the principle of optical whispering gallery mode (WGM) resonance shifts of the resonators. Three distinct sensing applications are investigated to demonstrate the concept: a photonic seismometer, an evanescent field sensor, and a zero-drift Doppler velocimeter. These concepts can be helpful in developing lightweight, compact, and highly sensitive sensors. Successful implementation of these sensors could potentially address sensing requirements for both space and Earth-bound applications. The feasibility of this class of sensors is assessed for seismic, proximity, and vibrational measurements

Classical and fluctuation-induced electromagnetic interactions in micronscale systems: designer bonding, antibonding, and Casimir forces

Whether intentionally introduced to exert control over particles and macroscopic objects, such as for trapping or cooling, or whether arising from the quantum and thermal fluctuations of charges in otherwise neutral bodies, leading to unwanted stiction between nearby mechanical parts, electromagnetic interactions play a fundamental role in many naturally occurring processes and technologies. In this review, we survey recent progress in the understanding and experimental observation of optomechanical and quantum-fluctuation forces. Although both of these effects arise from exchange of electromagnetic momentum, their dramatically different origins, involving either real or virtual photons, lead to different physical manifestations and design principles. Specifically, we describe recent predictions and measurements of attractive and repulsive optomechanical forces, based on the bonding and antibonding interactions of evanescent waves, as well as predictions of modified and even repulsive Casimir forces between nanostructured bodies. Finally, we discuss the potential impact and interplay of these forces in emerging experimental regimes of micromechanical devices.Comment: Review to appear on the topical issue "Quantum and Hybrid Mechanical Systems" in Annalen der Physi