Tunable single-mode two-section semiconductor lasers with photolithography-patterned low-order surface gratings

Low-cost single-mode semiconductor lasers are critical optoelectronic components for optical communication networks. Here, we demonstrate wavelength-tunable single-mode two-section semiconductor lasers. These lasers incorporate optimized low-order surface gratings, fabricated using I-line projection photolithography without requiring epitaxial regrowth. The grating parameters are carefully balanced for simultaneous low optical loss and high reflectivity, thereby directly enhancing device performance. The fabricated laser achieves a maximum side-mode suppression ratio (SMSR) exceeding 58 dB. It maintains stable single-mode operation with an SMSR >50 dB over a 30-mA current-tuning range without mode hopping. Notably, independent current biasing of the two sections enables continuous wavelength tuning over 8.2 nm, highlighting robust tunability. Additionally, the laser delivers an output power exceeding 14 mW and demonstrates a 3-dB modulation bandwidth greater than 10 GHz.