Mechanical Control of a Microrod-Resonator Optical Frequency Comb

Abstract

We report on the stabilization of a microresonator-based optical frequency comb (microcomb) by way of mechanical actuation. These experiments use novel CO_{2}-laser-machined microrod resonators, which are introduced here and feature optical Q≳5×10^{8}, less than 1 minute processing time, and tunable geometry. Residual fluctuations of our 32.6 GHz microcomb line spacing reach a stability level of 5×10^{-15} for 1 s averaging, thereby highlighting the potential of microcombs to support modern optical-frequency standards. Furthermore, measurements of the line spacing with respect to an independent frequency reference reveal stabilization of different spectral slices of the comb with a <0.5-mHz variation among 140 comb lines spanning 4.5 THz. Together, these results demonstrate an important step in the development of microcombs, namely, that they can be fabricated and precisely controlled with simple and accessible techniques.