Laterally‐coupled distributed feedback laser with first‐order gratings by interference lithography

The first laterally‐coupled distributed feedback (DFB) laser with first‐order sidewall gratings fabricated by optical interference lithography is experimentally demonstrated. The gratings were first etched into a dielectric mask on the planar top surface of an InP/AlGaInAs laser epiwafer, and then transferred to both sidewalls of a 2 µm deep ridge‐waveguide structure using a novel self‐aligned process. DFB ridge‐waveguide lasers with a cavity length of 650 µm and width of 2.6 µm (with 300 nm gratings on both sidewalls) achieved single longitudinal mode continuous‐wave operation, with a sidemode suppression ratio of 37 dB. The threshold current density is 1.7 kA/cm 2 at room temperature, and the slope efficiency is 0.14 mW/mA per facet (uncoated).