Design of Resonant Leaky-Wave Coupled Phase-Locked Arrays of Mid-IR Quantum Cascade Lasers

A theoretical analysis of the optical and thermal characteristics of planarized phase-locked quantum cascade laser (QCL) arrays emitting at 4.8 μm was performed. Large aperture seven-element designs are established with a reasonably large process window for achieving single in-phase-mode operation. Full-wave optical simulations of these high-index contrast photonic crystal devices were coupled with 2-D heat flow analysis to investigate the influence of thermal lensing on modal behavior. Self-focusing under thermally induced index variations across the array are expected to ultimately limit the single-mode operational range. Anti-resonant reflective-optical waveguide terminations for three-element arrays can decrease the in-phase mode threshold-current density, improve discrimination against array modes composed of coupled first-order element modes, and improve the in-phase-mode near-field uniformity under CW operation.