Frequency noise reduction of delay-coupled quantum cascade lasers.

Area of Science:

• Quantum optics and laser physics.
• Semiconductor device physics.

Background:

• Quantum cascade lasers (QCLs) are crucial for mid-infrared applications.
• Understanding noise characteristics is vital for high-performance laser operation.
• Delay-coupled lasers offer unique noise-reduction possibilities.

Purpose of the Study:

• To theoretically investigate frequency noise and spectral linewidth in mutually delay-coupled QCLs.
• To analyze the impact of mutual injection on noise performance.
• To explore the influence of various operational parameters on laser noise.

Main Methods:

• Theoretical analysis of mutually delay-coupled quantum cascade lasers.
• Simulation of frequency noise and spectral linewidth.
• Investigation under stable locking regime conditions.

Main Results:

• Mutual injection significantly reduces frequency noise at optimal coupling phases.
• Relative intensity noise is largely insensitive to mutual injection.
• Pump current, linewidth broadening factor, coupling phase, and delay time influence frequency noise.
• Multiple compound laser modes were found to degrade frequency noise performance.

Conclusions:

• Mutual delay coupling is a viable strategy for reducing frequency noise in QCLs.
• Careful selection of coupling parameters is necessary for optimal noise reduction.
• The presence of multiple modes presents a challenge for achieving low-frequency noise QCLs.