Passive thermal fine-tuning of whispering gallery mode for nonlinear optics in a microcavity

TL;DR

This paper presents a passive, remote thermal tuning method for whispering gallery mode microcavities that achieves MHz precision, enabling enhanced control of nonlinear optical processes like frequency comb generation and Brillouin scattering.

Contribution

A novel passive thermal tuning scheme using an external probe for precise resonance control in WGM microcavities, improving tunability for nonlinear optics applications.

Findings

Achieved MHz-level resonance tuning precision.

Demonstrated tunable optical frequency comb generation.

Enabled variable-frequency stimulated Brillouin scattering.

Abstract

Whispering gallery mode (WGM) microcavities strongly enhance nonlinear optical processes like optical frequency comb, Raman scattering and optomechanics, which nowadays enable cutting-edge applications in microwave synthesis, optical sensing spectroscopy, and integrated photonics. Yet, tunability of their resonances, mostly via coarse and complicated mechanism through temperature, electrical or mechanical means, still poses a major challenge for precision applications as above. Here we introduce a new passive scheme to finely tune resonances of WGMs at MHz precision with an external probe. Such probe remotely transfers heat through a gap from an optical microcavity, effectively tuning its resonances by thermal-optic nonlinearity. Moreover, we explore this unique technique in microcavity nonlinear optics, demonstrating the generation of a tunable optical frequency comb and backward stimulated Brillouin scattering with variable beating frequencies. This new technique addresses the core problem of WGM microcavity's fine-tuning, paving the way for important applications like spectroscopy and frequency synthesis.