Confinement and manipulation of photons using microcavities have triggered intense research interest in both fundamental and applied photonics for more than two decades. Prominent examples are ultrahigh-Q whispering gallery microcavities which confine photons by means of continuous total internal reflection along a curved and smooth surface. The long photon lifetime, strong field confinement, and in-plane emission characteristics make them promising candidates for enhancing light-matter interactions on a chip. In the first part of this talk, I will introduce some representative photonics applications of ultrahigh-Q microcavities. In the second part, I will focus on a new type of on-chip whispering gallery microcavity which supports both highly asymmetric far-field patterns and ultra-high-Q factors exceeding 100 million. These microcavities not only offer highly directional emission and ultra-broadband coupling desired for various important applications, but also hold great potential to test classical and quantum chaos because they behave like open billiard systems.

Bio：Dr. Yun-Feng Xiao received the B.S. and Ph.D. degrees in physics from University of Science and Technology of China in 2002 and 2007, respectively. After a postdoctoral research at Washington University in St. Louis, he joined the faculty of Peking University in 2009, and was promoted a tenured professor in 2014. His research interests lie in the fields of whispering-gallery microcavity optics and photonics. He has authored or co-authored more than 130 refereed journal papers in Science, Nature Photonics, PNAS, PRL, Advanced Materials et al. He has delivered over 100 plenary/keynote/invited talks/seminars in international/national conferences/universities.