Laterally Coupled DFB Lasers With Self-Aligned Metal Surface Grating by Holographic Lithography

A laterally coupled InGaAsP-InP distributed-feedback (DFB) laser operating around 1.55 mum was fabricated through a novel technique for the formation of metal surface gratings by holographic lithography. The self-aligned Cr DFB gratings were formed on the sidewalls as well as on both sides of the laser ridge by means of angled e-beam evaporation of Ti mask and metal-SiO₂ lift-off on the top of ridges. For an uncoated 3-mum-wide and 300-mum-long cavity, the device emitted an output power of ~9.7 mW/facet at an injection current of 100 mA with a threshold current of 29 mA and a slope efficiency of 0.14 mW/mA per facet at 20 degC under continuous-wave mode. A stable single-mode emission near 1.54 mum with a sidemode suppression ratio of nearly 28 dB was observed and a tuning coefficient of 0.21 nm/K was obtained in the temperature range of 15 degC -55 degC.