# Ultrabroadband supercontinuum generation and frequency-comb stabilization using on-chip waveguides with both cubic and quadratic nonlinearities

## TL;DR

This paper demonstrates on-chip aluminum-nitride waveguides capable of generating ultrabroadband supercontinuum light and stabilizing frequency combs through multiple nonlinear processes, advancing integrated photonic spectroscopy and metrology.

## Contribution

It introduces a novel on-chip platform using aluminum nitride waveguides that combine quadratic and cubic nonlinearities for supercontinuum generation and frequency comb stabilization.

## Key findings

- Generated supercontinuum from 500 nm to 4000 nm.
- Achieved stabilization of the laser comb's carrier-envelope-offset frequency.
- Produced significant power in the mid-infrared for molecular spectroscopy.

## Abstract

Using aluminum-nitride photonic-chip waveguides, we generate optical-frequency-comb supercontinuum spanning from 500 nm to 4000 nm with a 0.8 nJ seed pulse, and show that the spectrum can be tailored by changing the waveguide geometry. Since aluminum nitride exhibits both quadratic and cubic nonlinearities, the spectra feature simultaneous contributions from numerous nonlinear mechanisms: supercontinuum generation, difference-frequency generation, second-harmonic generation, and third-harmonic generation. As one application of integrating multiple nonlinear processes, we measure and stabilize the carrier-envelope-offset frequency of a laser comb by direct photodetection of the output light. Additionally, we generate ~0.3 mW in the 3000 nm to 4000 nm region, which is potentially useful for molecular spectroscopy. The combination of broadband light generation from the visible through the mid-infrared, combined with simplified self-referencing, provides a path towards robust comb systems for spectroscopy and metrology in the field.