Substrate emitting index coupled quantum cascade lasers using biperiodic top metal grating

We report on the design and experimental demonstration of a specific metal grating profile that enables a substrate emission of a quantum cascade laser. A low loss, index coupled, and horizontal cavity surface emitting laser (HCSEL) design is proposed, which is very robust against technological spreads. The detailed analysis of the metallic top grating is performed, enabling the laser still to operate as a distributed feedback laser while emitting from the substrate. Following this concept, HCSEL with InP cladding layers and InGaAs/AlInAs active regions have been fabricated. Room temperature HCSEL emitting at 5.65 mu m with a low beam divergence is demonstrated.