Broadband frequency comb generation in aluminum nitride-on-sapphire microresonators

TL;DR

This paper demonstrates broadband Kerr frequency comb generation in aluminum nitride-on-sapphire microresonators, enabling UV to MIR coverage with high efficiency and low threshold, advancing chip-scale optical frequency comb technology.

Contribution

The study introduces a crystalline AlN-on-sapphire platform for efficient Kerr comb generation, expanding spectral coverage into UV and MIR regions with high quality factors.

Findings

Achieved near-octave spanning NIR comb with low parametric threshold

Investigated competition between SRS and hyperparametric oscillation

Demonstrated broadband comb generation via Raman-assisted FWM

Abstract

Development of chip-scale optical frequency comb with the coverage from ultra-violet (UV) to mid-infrared (MIR) wavelength is of great significance. To expand the comb spectrum into the challenging UV region, a material platform with high UV transparency is crucial. In this paper, crystalline aluminum nitride (AlN)-onsapphire film is demonstrated for efficient Kerr frequency comb generation. Near-infrared (NIR) comb with nearly octave-spanning coverage and low parametric threshold is achieved in continuous-wave pumped high-quality-factor AlN microring resonators. The competition between stimulated Raman scattering (SRS) and hyperparametric oscillation is investigated, along with broadband comb generation via Raman-assisted four-wave mixing (FWM). Thanks to its wide bandgap, excellent crystalline quality as well as intrinsic quadratic and cubic susceptibilities, AlN-on-sapphire platform should be appealing for integrated nonlinear optics from MIR to UV region.