Optical injection locking of a THz quantum-cascade VECSEL with an electronic source

Area of Science:

• Terahertz (THz) Photonics
• Metasurface Engineering
• Semiconductor Lasers

Background:

• Quantum-cascade lasers (QCLs) are crucial for THz applications.
• Metasurface VECSELs offer tunable THz emission.
• Achieving narrow linewidths and wide locking ranges in THz lasers is challenging.

Purpose of the Study:

• To demonstrate optical injection locking of a metasurface QC-VECSEL at 2.5 THz.
• To characterize the spectral properties and locking bandwidth.
• To investigate the influence of external feedback on the locking behavior.

Main Methods:

• Utilized a Schottky diode frequency multiplier chain as the injection source.
• Employed optical injection locking to synchronize the metasurface QC-VECSEL.
• Measured the locked linewidth using a subharmonic diode mixer.
• Studied the effect of external reflections on locking bandwidth.

Main Results:

• Successfully achieved optical injection locking of the metasurface QC-VECSEL at 2.5 THz.
• Transferred spectral properties of the injection source to the laser output.
• Obtained a locked linewidth of approximately 1 Hz.
• Demonstrated a locking bandwidth of approximately 300 MHz.
• Showed that external reflections can enhance or reduce locking bandwidth based on phase.

Conclusions:

• Optical injection locking is an effective method for controlling the spectral properties of metasurface QC-VECSELs.
• Microwatt power levels from modern diode multipliers enable large locking ranges.
• Understanding the interplay between injected signals and external feedback is critical for optimizing laser performance.