Narrow-linewidth quarter-wavelength-shifted DFB laser based on coupling-coefficient distribution engineering

Area of Science:

• Photonics
• Semiconductor Lasers
• Optical Engineering

Background:

• Distributed feedback (DFB) lasers are crucial for optical communications.
• Narrow linewidths are essential for high-performance applications.
• Longitudinal spatial hole burning (LSHB) broadens the linewidth in conventional DFB lasers.

Purpose of the Study:

• To propose and demonstrate a novel narrow-linewidth quarter-wavelength-shifted distributed feedback (QWS-DFB) laser.
• To suppress linewidth broadening caused by LSHB through coupling-coefficient distribution (CCD) engineering.
• To improve longitudinal field uniformity within the laser cavity.

Main Methods:

• Designed a QWS-DFB laser utilizing CCD engineering with symmetric apodized-coupling regions.
• Tailored the longitudinal coupling profile to modify intracavity optical field distribution.
• Performed numerical analysis to understand the effect of coupling-coefficient profile on mode characteristics.
• Experimentally fabricated and tested the proposed CCD QWS-DFB laser.

Main Results:

• Suppressed strong central optical-field localization in conventional QWS-DFB cavities.
• Achieved improved longitudinal field uniformity.
• Demonstrated a minimum Lorentzian linewidth of 75 kHz.
• Observed significantly reduced linewidth compared to a uniform-coupling reference laser.

Conclusions:

• Coupling-coefficient distribution engineering effectively regulates intracavity field distribution and mode characteristics.
• The proposed CCD QWS-DFB laser design offers a robust method for achieving narrow linewidths.
• This approach provides an effective and fabrication-robust route toward narrow-linewidth DFB lasers.