Silicon Photonics Optical Frequency Synthesizer

Abstract

The knowledge of the exact frequency of an optical source has always been one of the ultimate goals in optics. Since the discovery of the laser, complex systems have been developed to address this challenge. That effort reached a significant milestone with the advent of the femtosecond laser frequency comb that reduced the system size from an entire lab down to the bench-top. That spurred interest in the development of integrated optical frequency synthesizers that can generate precisely different optical frequencies on demand and can be deployed widely. In this work, such an optical frequency synthesizer using supercontinuum waveguide and second harmonic generator on silicon photonics platform is demonstrated. Integrated silicon photonics based tunable continuous wave laser is phase-locked to a microwave reference, to synthesize absolute optical frequencies in the telecom band. A relative frequency instability of 1 × 10−12 at 1 s level is achieved by utilizing an integrated self-referencing scheme that exploits the strong 3rd order and electric-field-induced 2nd order nonlinearities of silicon waveguides. With this work, an all on-chip silicon photonics based frequency synthesizer seems promising for mass production of next generation broad-band coherent optical communication systems, spectroscopic, detection, and ranging systems and future integrated quantum systems with Hz-level precision.