Unidirectional mode selection in bistable quantum cascade ring lasers

TL;DR

This paper presents a novel monolithic quantum cascade ring laser design that achieves controllable unidirectional operation and dynamic switching between clockwise and counterclockwise modes, enhancing ring laser functionality.

Contribution

The authors introduce a new coupler design enabling robust unidirectional operation and dynamic mode switching in quantum cascade ring lasers.

Findings

Achieved deterministic unidirectional operation in ring lasers.

Demonstrated dynamic switching with minimal electrical modulation.

Provided an efficient outcoupling and detection mechanism.

Abstract

Ideal ring resonators are characterized by travelling-wave counterpropagating modes, but in practice travelling waves can only be realized under unidirectional operation, which has proved elusive. Here, we have designed and fabricated a monolithic quantum cascade ring laser coupled to an active waveguide that allows for robust, deterministic and controllable unidirectional operation. Spontaneous emission injection through the active waveguide enables dynamical switching between the clockwise and counterclockwise states of the ring laser with as little as 1.6% modulation of the electrical input. We show that this behavior stems from a perturbation in the bistable dynamics of the ring laser. In addition to switching and bistability, our novel coupler design for quantum cascade ring lasers offers an efficient mechanism for outcoupling and light detection.