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

This study presents the development of a 1.55-µm narrow-linewidth (NL)-DFB laser with a 600-µm cavity length, achieving high optical power and ultra-narrow linewidth through an optimized epitaxial structure and waveguide design. Despite the significantly shortened cavity, the laser maintains excellent performance, demonstrating a I_th of 8.7 mA, an optical power of 61.54 mW, and a power conversion efficiency (PCE) of 28.49% at room temperature. The laser achieves a 331-GHz frequency tuning range while maintaining a side-mode suppression ratio (SMSR) above 50 dB, ensuring a high-performance single-mode operation. Intrinsic linewidth measurements utilizing both long- and short-delay fiber delayed self-heterodyne interferometry (DSHI) confirm linewidth suppression below 100 kHz, with a further reduction to as low as 19.10 kHz, demonstrating a significant performance enhancement compared to conventional long-cavity DFB lasers.