Power stabilization of a terahertz-frequency quantum-cascade laser using a photonic-integrated modulator

Area of Science:

• Terahertz (THz) quantum-cascade lasers
• Integrated photonics
• Optoelectronic devices

Background:

• Quantum-cascade lasers (QCLs) are crucial for THz applications.
• Power drifts and frequency fluctuations limit QCL stability.
• Precise control of THz emission is essential for spectroscopy and imaging.

Purpose of the Study:

• To demonstrate a novel photonic integrated circuit (PIC) for stabilizing THz quantum-cascade laser emission.
• To achieve dynamic power control and long-term frequency locking.
• To explore simultaneous, quasi-independent control of laser power and frequency.

Main Methods:

• Utilized a PIC comprising a racetrack resonator coupled with a ridge waveguide.
• Implemented a proportional-integral control loop for power stabilization.
• Investigated the effect of the resonator on laser emission frequency perturbations.
• Demonstrated integration of the PIC with a micromachined metallic waveguide module.

Main Results:

• Achieved dynamic power control with a range of ±15%.
• Demonstrated stable laser locking for over 600 seconds.
• Observed a 50% weaker perturbation to laser frequency compared to direct modulation.
• Confirmed power modulation of the laser emission line during pulsed operation with the integrated module.

Conclusions:

• The developed PIC structure effectively stabilizes THz quantum-cascade laser emission against power drifts.
• The resonator-waveguide coupling offers a pathway for simultaneous, quasi-independent control of laser power and frequency.
• Further integration with metallic waveguides shows promise for advanced THz system development.