Multi-bounce self-mixing in terahertz metasurface external-cavity lasers

Area of Science:

• Optics and Photonics
• Quantum Electronics
• Metamaterials

Background:

• Terahertz (THz) quantum-cascade lasers (QC-lasers) are crucial for various applications.
• Vertical-external-cavity surface-emitting laser (VECSEL) architectures offer unique advantages over traditional designs.
• Understanding optical feedback effects is essential for laser stability and performance.

Purpose of the Study:

• To investigate the impact of optical feedback on a THz quantum-cascade metasurface VECSEL (QC-VECSEL) using self-mixing techniques.
• To develop a theoretical model for self-mixing in QC-VECSELs.
• To analyze the stability of the QC-VECSEL under varying optical feedback conditions.

Main Methods:

• A single-mode 2.80 THz QC-VECSEL was subjected to controlled optical feedback.
• Variations in terminal voltage due to self-mixing were monitored under different feedback strengths, round-trip times, and angular misalignments.
• A new theoretical model was established to describe the observed self-mixing phenomena.

Main Results:

• The QC-VECSEL demonstrated strong susceptibility to optical feedback, even with external optics misalignment, due to its large aperture and beam shape.
• High feedback levels, including multiple round-trips, were observed, differing from typical ridge-waveguide QC-lasers.
• Mechanical instabilities in the external cavity were amplified by feedback, causing low-frequency voltage oscillations.

Conclusions:

• The QC-VECSEL architecture exhibits a distinct self-mixing response compared to other QC-laser designs.
• The findings provide insights for systems where optical feedback is a critical factor.
• This research opens avenues for novel self-mixing applications utilizing QC-VECSELs.