Hybrid Electro-Optically Modulated Microcombs

TL;DR

This paper introduces a hybrid electro-optic and microcomb system that enables direct control and stabilization of large mode spacing microcombs, advancing chip-scale optical frequency comb technology.

Contribution

It demonstrates the first method to stabilize large mode spacing microcombs by interleaving with an electro-optic comb, eliminating the need for an external mode-locked laser.

Findings

Achieved microcomb stabilization with residual 1-second instability of 10^-15.

Controlled microcombs with mode spacing over 140 GHz.

Reduced dependence on external mode-locked lasers.

Abstract

Optical frequency combs based on mode-locked lasers have proven to be invaluable tools for a wide range of applications in precision spectroscopy and metrology. A novel principle of optical frequency comb generation in whispering-gallery mode microresonators ("microcombs") has been developed recently, which represents a promising route towards chip-level integration and out-of-the-lab use of these devices. Presently, two families of microcombs have been demonstrated: combs with electronically detectable mode spacing that can be directly stabilized, and broadband combs with up to octave-spanning spectra but mode spacings beyond electronic detection limits. However, it has not yet been possible to achieve these two key requirements simultaneously, as will be critical for most microcomb applications. Here we present a key step to overcome this problem by interleaving an electro-optic comb with the spectrum from a parametric microcomb. This allows, for the first time, direct control and stabilization of a microcomb spectrum with large mode spacing (>140 GHz) with no need for an additional mode-locked laser frequency comb. The attained residual 1-second-instability of the microcomb comb spacing is 10^-15, with a microwave reference limited absolute instability of 10^-12 at a 140 GHz mode spacing.