# Extending chip-based Kerr-comb to visible spectrum by dispersive wave engineering

## TL;DR

This paper presents a novel silicon nitride microresonator design that uses dispersive wave engineering to extend Kerr frequency combs into the visible spectrum, overcoming material dispersion limitations.

## Contribution

It introduces a new microresonator structure and dispersion engineering method to generate broader Kerr combs reaching visible wavelengths.

## Key findings

- Successful extension of Kerr combs to visible spectrum
- Enhanced bandwidth of Kerr frequency combs
- Optimized dispersive wave properties through dispersion engineering

## Abstract

Anomalous group velocity dispersion is a key parameter for generating bright solitons, and thus wideband Kerr frequency combs. Extension of frequency combs to visible wavelength in conventional photonic materials and structures has been a major challenge due to strong normal material dispersion at the relevant frequencies. Extension of frequency combs toward the normal dispersion region is possible via dispersive waves through soliton-induced Cherenkov radiation. However, this potentially powerful technique has not been used for extending frequency combs to the visible spectrum. In this paper, we demonstrate a new microresonator structure formed by an over-etched silicon nitride waveguide that enables the use of soliton-induced Cherenkov radiation to extend the bandwidth of the Kerr-combs. Furthermore, we show that by careful dispersion engineering in a coupled microring resonator structure we can optimize the properties (e.g., wavelength, and amplitude) of the generated dispersive wave to further extend the Kerr frequency combs to the visible spectrum while increasing the total Kerr-comb bandwidth as well.