Spatial multiplexing of soliton microcombs

TL;DR

This paper demonstrates the generation of multiple coherent frequency combs from a single microresonator, enabling advanced dual- and triple-comb spectroscopy with improved stability and potential for integrated photonic applications.

Contribution

It introduces a novel method to generate multiple soliton microcombs simultaneously in different spatial or polarization modes within a single microresonator, simplifying dual-comb systems.

Findings

Up to three simultaneous combs produced with high mutual coherence

Successful dual-comb spectroscopy and optical sampling demonstrated

System compatible with integrated photonic resonators

Abstract

Dual-comb interferometry utilizes two optical frequency combs to map the optical field's spectrum to a radio-frequency signal without using moving parts, allowing improved speed and accuracy. However, the method is compounded by the complexity and demanding stability associated with operating multiple laser frequency combs. To overcome these challenges, we demonstrate simultaneous generation of multiple frequency combs from a single optical microresonator and a single continuous-wave laser. Similar to space-division multiplexing, we generate several dissipative Kerr soliton states - circulating solitonic pulses driven by a continuous-wave laser - in different spatial (or polarization) modes of a $\mathrm{MgF_2}$ microresonator. Up to three distinct combs are produced simultaneously, featuring excellent mutual coherence and substantial repetition rate differences, useful for fast acquisition and efficient rejection of soliton intermodulation products. Dual-comb spectroscopy with amplitude and phase retrieval, as well as optical sampling of a breathing soliton, is realised with the free-running system. Compatibility with photonic-integrated resonators could enable the deployment of dual- and triple-comb-based methods to applications where they remained impractical with current technology.