Light-matter interactions are the fundamental basis for many phenomena and processes in optical devices. Ultra-high-quality whispering-gallery-mode (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, which significantly enhances light-matter interactions, creating the potential for a wealth of new scientific discoveries and technological breakthroughs difficult to achieve by other devices. In this talk, after briefly introducing the physical concepts of WGM microresonators and providing an overview of the research discoveries in the past twenty years, I will report the recent progress in my group towards developing functional platforms using high-Q WGM microresonators and microlasers. 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 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 our recent exploration of fundamental physics, such as parity-time symmetry (PT-symmetry) and light-matter interactions around exceptional points (EPs), in high-quality WGM resonators, which can be used to achieve a new generation of optical systems enabling unconventional control of light flow. Examples including nonreciprocal light transmission, loss engineering in a lasing system, directional lasing emission, and EPs enhanced sensing, will be introduced. 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.
Professor Lan Yang is the Edwin H. and Florence G. Skinner professor in the Preston M. Green Department of Electrical and Systems Engineering at Washington University, St. Louis, MO, USA. She received B.S. from the University of Science and Technology of China and got the Ph.D. in applied physics from Caltech in 2005. Her research interests have been focusing on the fundamental understanding of high-quality photonic whispering-gallery-mode (WGM) resonators and their applications for bio/chemical sensing, lasing, light harvesting, and communications. Recently, her research interests expanded to parity-time-symmetry and non-Hermitian physics in high-quality WGM resonators, which have led to a series of new discoveries for unconventional control of light transport in photonic structures. She received NSF CAREER Award in 2010 for her work on single nanoparticle detection and sizing using an on-chip optical resonator. She is also the recipient of the 2010 Presidential Early Career Award for Scientists and Engineers (PECASE). She has published ~90 papers in peer-reviewed journals including Science, Nature, and Physical Review Letters. She is a fellow of the Optical Society of America (OSA).