Photons can be trapped in optical microresonators with extended lifetime proportional to the resonators' quality (Q) factors. Over the past two decades the Q of microresonators have been progressively improved, with over 100 billion and 1 billion Q achieved respectively in discrete and chip-based devices. These high-Q microresonators are essential photonic engines that are currently driving science and technology towards scalable quantum circuitry, high-speed telecommunication industry and miniaturized coherent optical systems. We are developing high-Q microresonators in a wide-range of material systems, with a focus on integrated silicon photonic platforms.

Central to modern AMO physics is the precise measurement of optical frequencies, or equivalently, the "color" of light. The most accurate rulers of optical frequencies are optical frequency combs (OFCs), a ground-breaking technology which was awarded Nobel Prize in 2005 (John Hall and Theodor Hänsch). An OFC consists of hundreds to thousands of equally-spaced, phase-coherent lasers, which are typically derived from femtosecond mode-locked lasers. While table-top OFCs have been commerically available, the recent realization of optical solitons in high-Q microresonators paves the way towards integrated OFCs, which feature remarkable advantages in size, cost and scalability. Our mission is to create high-performance OFCs in CMOS-compatible photonic platforms, as well as their implementation in cutting-edge applications spanning miniaturized precise metrology systems, microwave photonics and optical interconnects.

The combination of long photon lifetime and compact form factors has made high-Q microresonators an attractive platform in the study of nonlinear optical phenomena, including stimulated Raman and Brillouin scattering, coupling between photons and mechanical oscillators, and optical parametric oscillations. We are investigating these toxic nonlinear physics, especially complex dynamics of optical solitons in microresonators.