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/cm² at room temperature, and the slope efficiency is 0.14 mW/mA per facet (uncoated).