Brillouin lasers in Bragg grating microresonators

TL;DR

This paper demonstrates a method to inhibit cascaded Brillouin scattering in chip-scale microresonators using a reconfigurable intracavity Bragg grating, enabling higher power and coherence in Brillouin lasers.

Contribution

It introduces a reconfigurable intracavity Bragg grating to suppress cascaded scattering, enhancing the performance of chip-scale Brillouin lasers.

Findings

Six-fold increase in threshold for Brillouin laser oscillation.

Complete inhibition of cascaded scattering at 399 mW pump power.

Reconfigurable modes of operation for on-chip Brillouin lasers.

Abstract

Chip-scale coherent light sources are required in applications spanning metrology and sensing to telecommunications. Brillouin lasers (BLs) offer a route to ultra-coherent optical sources in compact microresonators with free spectral range (FSR) matched to the Brillouin frequency shift (BFS). However, BFS - FSR matching typically facilitates cascaded Brillouin scattering, constraining achievable BL output power and coherence. Here, we demonstrate inhibition of cascading in a planar-integrated chalcogenide microresonator by exploiting the photonic bandgap (PBG) associated with a post-fabrication inscribed, reconfigurable intracavity Bragg grating. The PBG inhibits energy transfer within the target Brillouin scattering pathway, such as from pump to first-order Stokes wave. As a quantitative measure of Brillouin scattering inhibition, we report at least six-fold increase in threshold for onset of BL oscillation, which is ultimately limited by thermorefraction. For on-chip pump power of 399 mW, sufficient for a tenth-order Brillouin cascade, complete inhibition was achieved. Our work positions Bragg grating microresonators as an enabling platform for high performance on-chip BL sources, with reconfigurable modes of operation.