Broadband Visible Wavelength Microcomb Generation In Silicon Nitride Microrings Through Air-Clad Dispersion Engineering

TL;DR

This paper demonstrates that air-clad silicon nitride microring resonators can generate broadband visible wavelength microcombs, enabling advances in compact optical clocks and spectroscopy by overcoming dispersion challenges.

Contribution

It introduces a novel air-clad silicon nitride microring design that achieves broadband visible microcomb generation, a significant improvement over traditional silica-embedded resonators.

Findings

Demonstrated broadband microcombs from 680 nm to 1060 nm

Achieved combs pumped at 780 nm reaching 630 nm

Simulations suggest possible extension to 461 nm

Abstract

The development of broadband microresonator frequency combs at visible wavelengths is pivotal for the advancement of compact and fieldable optical atomic clocks and spectroscopy systems. Yet, their realization necessitates resonators with anomalous dispersion, an arduous task due to the prevailing normal dispersion regime of materials within the visible spectrum. In this work, we evince that silicon nitride microring resonators with air cladding on top and sides -- a deviation from the frequently employed silica-embedded resonators -- allows for the direct generation of broadband microcombs in the visible range. We experimentally demonstrate combs pumped at 1060~nm (283~THz) that reach wavelengths as short as 680~nm (440 THz), and combs pumped at 780~nm (384 THz) that reach wavelengths as short as 630 nm (475 THz). We further show through simulations that microcombs extending to wavelengths as low as 461 nm (650 THz) should be accessible in this platform.