Whispering gallery micro-cavities

Abstract

Light-matter interactions are the fundamental basis for many phenomena and processes in optical devices. Whispering-Gallery-Mode (WGM) optical resonators trap light in a manner similar to a phenomenon found in the gallery spaces of St. Paul's Cathedral dome in London, where a single whisper (i.e., a sound wave) can be heard along the circular boundary of the architecture. Ultra-high-quality WGM optical micro-resonators provide unprecedented capability to trap light in a highly confined volume smaller than a strand of human hair; a light beam can travel around the boundary of a WGM resonator over 106 times, significantly enhancing light-matter interactions, creating the potential for a wealth of new scientific discoveries and technological breakthroughs difficult to achieve by other devices [2-8]. In the first part of talk, after briefly introducing the physical concepts of WGM microresonators and their coupling with a microfiber waveguide, I will give an overview of the research discoveries in the past fifteen years, which will include examples of optomechanics in high-Q WGM microresonators, frequency comb generation and sensing applications, etc. In the second part of talk, I will present a few cases demonstrating the great potentials of high-Q WGM microresonators and microlasers for both fundamental science and engineering applications. Specifically, I will discuss ultra-high-Q microresonators and microlasers for ultra-sensitive detection of nanoscale objects. I will explain a self-referencing sensing scheme for detection and sizing of single virion, dielectric and metallic nanoparticles. These recent advancements in WGM microresonators will enable a new class of ultra-sensitive and low-power sensors for investigating the properties and kinetic behaviors of nanomaterials, nanostructures, and nanoscale phenomena. Then I will explain an interesting hybrid nanoparticle-resonator system in which the nanoparticles open a new channel to couple light from free space into high-Q WGM resonators. I will present two types of lasers, Raman and rare-earth-ions doped microlasers, achieved by free-space pumping of high-Q resonators via the nanocouplers. Afterwards, I will discuss recent exploration of fundamental physics, such as parity-time symmetry (PT-symmetry) and light-matter interactions around exceptional point (EP), in high-quality WGM resonators, which can be used to achieve a new generation of optical systems enabling unconventional control of light flow, such as nonreciprocal light transmission and directional lasing. In the end, I will present a new generic and hand-held microresonator platform that was transformed from a table-top setup, which might help release the power of high-Q WGM resonator technologies.