Mid-infrared frequency combs and staggered spectral patterns in $\chi^{(2)}$ microresonators

TL;DR

This paper introduces a novel method for generating mid-infrared frequency combs using cascaded three-wave-mixing in a microresonator, enabling integrated, low-power mid-IR comb sources compatible with telecom lasers.

Contribution

It demonstrates a new approach for mid-IR microcomb generation via cascaded three-wave-mixing in a $ ext{chi}^{(2)}$ microresonator, producing combs at 3.1 μm with staggered spectral patterns.

Findings

Generated $ ext{chi}^{(2)}$ frequency combs at 3.1 μm from 1.55 μm pump.

Observed both ordinary and staggered comb states with distinct spectral patterns.

Potential for integrated, low-power mid-IR comb sources compatible with telecom technology.

Abstract

The potential of frequency comb spectroscopy has aroused great interest in generating mid-infrared frequency combs in the integrated photonic setting. However, despite remarkable progress in microresonators and quantum cascade lasers, the availability of suitable mid-IR comb sources remains scarce. Here, we present a new approach for the generation of mid-IR microcombs through cascaded three-wave-mixing. By pumping a CdSiP$_2$ microresonator at 1.55 $\mu$m wavelength with a low power continuous wave laser, we generate $\chi^{(2)}$ frequency combs at 3.1 $\mu$m wavelength, with a span of about 30 nm. We observe ordinary combs states with a line spacing of the free spectral range of the resonator, and combs where the sideband numbers around the pump and half-harmonic alternate, forming staggered patterns of spectral lines. Our scheme for mid-IR microcomb generation is compatible with integrated telecom lasers. Therefore, it has the potential to be used as a simple and fully integrated mid-IR comb source, relying on only one single material.