Design of High Brightness Tree-Array Quantum Cascade Lasers With Broad Area Ridge Waveguides and Multimode Interference Couplers

Tree-array quantum cascade lasers (QCLs) are a promising architecture for brightness scaling of midwave infrared (MWIR) and longwave infrared (LWIR) QCLs. Simulations of multimode interference couplers are presented to aid the design of tree-array QCLs based on ridge waveguides. Experimental results are presented for tree-array QCLs at λ = 4.5 μm and λ = 8.6 μm. Nonuniform gain saturation is modeled for tree-array QCLs and is compared to experimental data to further aid in the design of high-brightness tree-array QCLs.