High-Q AlN microresonators for nonlinear near-infrared and near-visible photonics

TL;DR

This paper reports record high Q-factors in AlN microresonators, enabling advanced nonlinear photonics applications like microcomb generation, Raman lasing, and soliton formation in the near-infrared and visible spectrum.

Contribution

The work demonstrates optimized fabrication of AlN microresonators achieving record Q-factors and explores nonlinear dynamics including Dirac solitons and platicon formation.

Findings

Record Q-factors of 5.4×10^6 and 2.2×10^6 achieved in AlN microresonators.

Observation of polarization hybridization of Dirac solitons.

Generation of near-visible Raman laser with linewidth narrower than 220 Hz.

Abstract

High Q-factors of microresonators are crucial for nonlinear integrated photonics, as many nonlinear dynamics have quadratic or even cubic dependence on Q-factors. The unique material properties make AlN microresonators invaluable for microcomb generation, Raman lasing and visible integrated photonics. However, the loss level of AlN falls behind other integrated platforms. By optimizing the fabrication, we demonstrate record Q-factors of 5.4$\times$10$^6$ and 2.2$\times$10$^6$ for AlN microresonators in the near-infrared and near-visible, respectively. Polarized-mode-interaction was used to create anomalous dispersion to support bright AlN Dirac solitons. Measurement of polarization-dependent spectra reveals the polarization hybridization of the Dirac soliton. In a microresonator with normal dispersion, Raman assisted four-wave-mixing (RFWM) was observed to initiate platicon formation, adding an approach to generate normal dispersion microcombs. A design of width-varying waveguides was used to ensure both efficient coupling and high Q-factor for racetrack microresonators at 780 nm. The microresonator was pumped to generate near-visble Raman laser at 820 nm with a fundamental linewidth narrower than 220 Hz. Our work unlocks new opportunities for integrated AlN photonics by improving Q-factors and uncovering nonlinear dynamics in AlN microresonators.