Optimization of cavity designs of tapered AlInAs/InGaAs/InP quantum cascade lasers emitting at 4.5 μm

In this work design, fabrication and characterization of mid-infrared AlInAs/InGaAs/InP QCLs taper quantum cascade lasers are presented. In order to increase output power while keeping good beam quality, taper design of resonator was used. We have studied devices emitting at 4.5 μm with different shapes (linear, concave and convex) and angles of taper waveguide section, to optimize the output beam parameters, namely M2 and brightness. Experimental results demonstrate that convex geometry taper laser with 1.7° taper shows the best performance, the highest output power up to 5 W and the smallest horizontal beam divergence of 5.6° in the fundamental mode. This design is also characterized by the highest brightness.