Intrinsic stability of quantum cascade lasers against optical feedback

Area of Science:

• Optics and Photonics
• Semiconductor Lasers
• Quantum Electronics

Background:

• Diode lasers often suffer from coherence collapse and instabilities under optical feedback.
• Quantum cascade lasers (QCLs) operate differently, potentially offering enhanced stability.
• Understanding QCL behavior with optical reinjection is crucial for advanced laser applications.

Purpose of the Study:

• To investigate the time-dependent optical power of terahertz (THz) and mid-infrared (mid-IR) QCLs.
• To analyze the impact of optical reinjection on QCL emission stability.
• To identify the factors contributing to the observed CW stability in QCLs.

Main Methods:

• Experimental study of THz and mid-IR QCLs.
• Application of controlled optical reinjection.
• Analysis of time-dependent optical power output.
• Characterization of laser dynamics and stability metrics.

Main Results:

• Demonstrated unprecedented CW emission stability in QCLs even with strong optical feedback.
• Observed the absence of coherence collapse and typical diode laser instabilities.
• Correlated stability with a high photon to carrier lifetime ratio.
• Linked stability to a negligible linewidth enhancement factor in QCLs.

Conclusions:

• QCLs exhibit superior CW stability compared to diode lasers under optical feedback.
• The inherent properties of QCLs (high photon/carrier ratio, low alpha factor) are key to this stability.
• These findings pave the way for robust QCL applications requiring high power and stability.