Micro--structured crystalline resonators for optical frequency comb generation

TL;DR

This paper introduces a novel micro-resonator design with dispersion control and high quality factor, enabling broader optical frequency combs at lower power, advancing applications in precision measurement and communications.

Contribution

The study presents a new resonator design that combines dispersion engineering, mode crossing suppression, and ultra-high quality factor for improved frequency comb generation.

Findings

Achieved 700 nm comb span with 60 mW pump power

Generated nearly 2000 lines separated by 46 GHz

Demonstrated efficient octave spanning combs without external broadening

Abstract

Optical frequency combs have recently been demonstrated in micro--resonators through nonlinear Kerr processes. Investigations in the past few years provided better understanding of micro--combs and showed that spectral span and mode locking are governed by cavity spectrum and dispersion. While various cavities provide unique advantages, dispersion engineering has been reported only for planar waveguides. In this Letter, we report a resonator design that combines dispersion control, mode crossing free spectrum, and ultra--high quality factor. We experimentally show that as the dispersion of a MgF2 resonator is flattened, the comb span increases reaching 700 nm with as low as 60 mW pump power at 1560 nm wavelength, corresponding to nearly 2000 lines separated by 46 GHz. The new resonator design may enable efficient low repetition rate coherent octave spanning frequency combs without the need for external broadening, ideal for applications in optical frequency synthesis, metrology, spectroscopy, and communications.