Narrow Linewidth PIC-based Blue-UV Semiconductor Lasers for Optical Atomic Clocks
ABSTRACT
Optical atomic clocks offer 100- to 1000-fold improvements in accuracy and stability over traditional microwave-based clocks. A key obstacle to their miniaturization for field or space deployment is the lack of compact, narrow-linewidth light sources in the blue and ultraviolet (UV) spectral regions - essential for laser Doppler cooling of atoms or ions such as ytterbium and strontium. We present an approach to address this challenge by coupling custom-designed InAlGaN-based laser diodes with photonic integrated circuits (PICs). We developed two types of PICs - one based on CMOS-compatible silicon nitride (SiN) and the other based on UV-friendly aluminum nitride (AlN). Using controlled feedback from ring resonators on the PIC chip to induce laser self-injection locking, we achieved megahertz-level linewidths in the blue, violet, and UV-A bands. Additionally, we demonstrated fast, hysteresis-free frequency tuning via piezoelectric actuation of the PIC waveguides.
BIOGRAPHY
Dr. Christopher Chua is a Principal Scientist at SRI, where he leads the Micro-Technology group conducting advanced applied research in optoelectronics, LEDs, lasers, thin-film transistor electronics, and microfabrication. He designed and built one of the world's most densely packed vertical-cavity surface-emitting laser (VCSEL) arrays and pioneered a VCSEL architecture now used by leading manufacturers. He also invented and developed an on-chip inductor technology that enabled integrated circuit oscillators with world-record Q-factors.
Dr. Chua is the inventor on over 150 U.S. patents and has authored numerous technical publications. His work has been recognized with Best Paper Awards at both the 2003 International Solid-State Circuits Conference (ISSCC) and the 2009 International Microelectronics and Packaging Society (IMAPS) symposium. He holds a Ph.D. in Electrical Engineering from Cornell University and dual bachelor's degrees in Physics and Electrical Engineering from the Massachusetts Institute of Technology (MIT).