High-efficiency 1.55-µm DFB laser with a 600-µm short cavity and sub-20-kHz linewidth

Area of Science:

• Photonics and Laser Technology
• Semiconductor Device Engineering

Background:

• Distributed Feedback (DFB) lasers are crucial for optical communications.
• Conventional DFB lasers often require long cavities to achieve narrow linewidths and high power.
• Shortening laser cavities presents challenges in maintaining performance metrics.

Purpose of the Study:

• To develop a 1.55-µm narrow-linewidth (NL) DFB laser with a significantly shortened cavity length (600 µm).
• To optimize the epitaxial structure and waveguide design for enhanced laser performance.
• To demonstrate high optical power, ultra-narrow linewidth, and wide frequency tuning range in a compact DFB laser.

Main Methods:

• Utilized an optimized epitaxial structure and waveguide design for the DFB laser.
• Fabricated a 600-µm cavity length 1.55-µm NL-DFB laser.
• Measured laser performance including threshold current (Ith), optical power, power conversion efficiency (PCE), and side-mode suppression ratio (SMSR) at room temperature.
• Employed long- and short-delay fiber delayed self-heterodyne interferometry (DSHI) for intrinsic linewidth measurements.

Main Results:

• Achieved a low threshold current (Ith) of 8.7 mA.
• Obtained high optical power of 61.54 mW and a power conversion efficiency (PCE) of 28.49%.
• Demonstrated a wide frequency tuning range of 331 GHz with an SMSR > 50 dB.
• Confirmed linewidth suppression below 100 kHz, reaching as low as 19.10 kHz using DSHI.

Conclusions:

• The optimized short-cavity DFB laser achieves excellent performance, rivaling and exceeding conventional long-cavity designs.
• The developed laser offers a significant advancement in compact, high-performance light sources for optical applications.
• The novel design demonstrates the feasibility of achieving ultra-narrow linewidth and high power in miniaturized DFB lasers.