Amplified feedback and spontaneous emission injection in quantum cascade ring laser systems

Area of Science:

• Physics
• Quantum Optics
• Semiconductor Lasers

Background:

• Ring lasers exhibit complex operational regimes, including unidirectional, bidirectional, and bistable operation.
• The dynamics of counter-propagating modes (clockwise and counterclockwise) in the mid-infrared have garnered interest, but the switching mechanisms remain underexplored.

Purpose of the Study:

• To model the mode switching dynamics in a ring quantum cascade laser (QCL) with an active outcoupling waveguide.
• To investigate the influence of spontaneous emission and amplified optical feedback on mode selection.

Main Methods:

• Application of the Lang-Kobayashi framework to model the ring laser system.
• Analysis of spontaneous emission in waveguide arms and amplified optical feedback from facets.
• Comparison of model predictions with experimental data.

Main Results:

• Coherent feedback from facet reflections accurately predicts experimental behavior (upwards of 93% agreement).
• Amplified feedback is identified as the primary mechanism responsible for mode selection dynamics.
• The Lang-Kobayashi model effectively captures the observed mode switching phenomena.

Conclusions:

• The study elucidates the dominant role of amplified optical feedback in driving mode selection in ring QCLs.
• The findings provide a theoretical framework for understanding and controlling mode switching in these devices.
• This research contributes to the fundamental understanding of laser dynamics and offers insights for designing advanced laser systems.