Ultra-narrow linewidth laser across the C-band using polarization-controlled dual-cavity feedback

Area of Science:

• Optics and Photonics
• Semiconductor Laser Technology
• Laser Spectroscopy

Background:

• Semiconductor lasers commonly use external optical feedback (EOF) to reduce linewidth.
• High feedback powers (>1%) typically induce coherence collapse (CC), causing chaotic dynamics and linewidth broadening.

Purpose of the Study:

• To mitigate coherence collapse (CC) in semiconductor lasers subjected to external optical feedback (EOF).
• To achieve ultra-narrow intrinsic linewidths (sub-100 Hz) in tunable semiconductor lasers.

Main Methods:

• Utilized a U-shaped cavity semiconductor laser with sampled grating distributed Bragg reflectors (SG-DBRs) for broad tunability (42 nm).
• Implemented external optical feedback (EOF) into both sides of the laser cavity via an external fiber-based cavity.
• Employed precise dynamic tuning of feedback polarization to manage coherence collapse (CC).

Main Results:

• Achieved an intrinsic linewidth reduction of over three orders of magnitude (MHz to sub-kHz) across the 1513-1555 nm tuning range.
• Demonstrated sub-100 Hz intrinsic linewidths at feedback powers up to 10%, overcoming previous CC limitations.
• Maintained broad tunability and stable laser operation with optimized EOF.

Conclusions:

• Precise polarization control of external optical feedback (EOF) effectively suppresses coherence collapse (CC) in semiconductor lasers.
• This method enables the generation of ultra-narrow linewidth semiconductor lasers with high feedback powers.
• The developed technique significantly enhances semiconductor laser performance for applications requiring high spectral purity.