Non-Hermitian Symmetry and Wave Transport in Whispering-Gallery-Mode Microresonators
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. I will discuss recent exploration of fundamental physics associated with non-Hermitian physics, such as parity-time symmetry (PT-symmetry) and light-matter interactions around an 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. In this talk, non-Hermitian physics will be presented as an alternative guideline to design resonator structures with new physical behavior and innovative functionality. Specifically, I will talk about nonreciprocal light transmission in a parity-time-(PT)-symmetric resonator system. I will also explain how to enable chiral modes and directional lasing by operating a laser resonator around an EP. Of special note, sensing is an intriguing application that will benefit from unique features of non-Hermitian resonators operated around an EP. A non-Hermtian phonon laser tuned in the vicinity of EPs will be discussed briefly. 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.