RF Injection Locking of THz Metasurface Quantum-Cascade VECSEL

TL;DR

This paper demonstrates RF injection locking and spectral broadening in a THz QC-VECSEL, achieving a broad spectrum and stable locking, paving the way for ultrafast THz pulse generation.

Contribution

It introduces a novel RF injection locking technique for THz QC-VECSELs with spectral broadening, enabling potential ultrafast pulse applications.

Findings

Achieved spectral broadening from 14 GHz to 100 GHz.

Demonstrated stable RF injection locking near 5 GHz.

Validated experimental results with injection locking theory.

Abstract

RF injection locking and spectral broadening of a terahertz (THz) quantum-cascade vertical-external-cavity surface-emitting laser (QC-VECSEL) is demonstrated. An intra-cryostat VECSEL focusing cavity design is used to enable continuous-wave lasing with a cavity length over 30 mm which corresponds to a round-trip frequency near 5 GHz. Strong RF current modulation is injected to the QC-metasurface electrical bias to pull and lock the round-trip frequency. The injection locking range at various RF injection powers is recorded and compared with the injection locking theory. Moreover, the lasing spectrum broadens from 14 GHz in free-running mode to a maximum spectral width around 100 GHz with 20 dBm of injected RF power. This experimental setup is suitable for further exploration of active mode-locking and picosecond pulse generation in THz QC-VECSELs.