Dual-cavity feedback assisted DFB narrow linewidth laser.

Area of Science:

• Photonics and Optical Engineering
• Laser Physics and Technology

Background:

• Single longitudinal mode (SLM) distributed feedback (DFB) lasers are crucial for coherent detection systems, requiring narrow linewidths below a few kHz.
• Existing DFB lasers often have linewidths in the MHz range, limiting their application in high-performance coherent systems.

Purpose of the Study:

• To propose and experimentally demonstrate a novel method for compressing the linewidth of SLM DFB lasers.
• To achieve significant linewidth reduction while maintaining SLM output and high side mode suppression.

Main Methods:

• Utilized a dual-cavity feedback structure (DCFS) for optical self-injection feedback to compress laser linewidth.
• Optimized feedback lengths based on the Vernier principle to ensure SLM operation and suppress mode overlap.
• Experimentally validated the DCFS method on DFB lasers with initial linewidths of 1 MHz and 200 kHz.

Main Results:

• Achieved linewidth compression from 1 MHz to approximately 2.7 kHz and from 200 kHz to approximately 1.5 kHz.
• Maintained high side mode suppression ratios (SMSR) of 38 dB and 45 dB.
• Demonstrated stable DCFS output power with fluctuations controlled within ~0.21%.

Conclusions:

• The proposed DCFS method offers a simple, effective, and low-cost approach for DFB laser linewidth compression.
• This technique significantly enhances the performance of coherent detection systems by providing narrow-linewidth laser sources.
• The method is suitable for improving the sensitivity and resolution of various optical sensing and communication applications.