Parity-time–symmetric microring lasers

TLDR

Controlling modes in a laser resonator is essential, as competing modes degrade beam quality and spectral purity, leading to spatial and temporal fluctuations. By exploiting parity‑time symmetry in coupled microring lasers, the authors achieve stable single‑longitudinal‑mode operation, increase output power in the desired mode, and enable broadband mode selectivity without additional components, paving the way for advanced synthetic optical devices.

Abstract

The ability to control the modes oscillating within a laser resonator is of fundamental importance. In general, the presence of competing modes can be detrimental to beam quality and spectral purity, thus leading to spatial as well as temporal fluctuations in the emitted radiation. We show that by harnessing notions from parity-time (PT) symmetry, stable single–longitudinal mode operation can be readily achieved in a system of coupled microring lasers. The selective breaking of PT symmetry can be used to systematically enhance the maximum attainable output power in the desired mode. This versatile concept is inherently self-adapting and facilitates mode selectivity over a broad bandwidth without the need for other additional intricate components. Our experimental findings provide the possibility to develop synthetic optical devices and structures with enhanced functionality.