High-performance 5.5 /spl mu/m quantum cascade lasers with high-reflection coating

A high-reflection coating for 5.5 µm strain-compensated InGaAs/InAlAs quantum cascade lasers is described. Using a high-reflection coating on both facets of a laser cavity, a threshold current density of 0.5 kA/cm2 was observed at liquid-nitrogen temperature, whereas for an uncoated structure of comparable length the threshold current density was 1 kA/cm2. Laser action for a 2.1 mm long and 30 µm wide device with coated facets was achieved in pulsed mode up to the record high temperature of 470 K. A 2.5 mm long and 30 µm wide device with uncoated facets shows lasing action up to 440 K.