5.3 μm-Emitting Diffraction-Limited Leaky-Wave-Coupled Quantum Cascade Laser Phase-Locked Array

A three-element phase-locked array of ~5.3 μm-emitting quantum cascade lasers fabricated by a two-step MOCVD process is demonstrated which operates in a diffraction-limited beam to 5.3 W peak pulsed power. To compensate for overetching at the array edges, the fabrication process was modified such that it resulted in array elements of equal width. Then the array operates in a pure in-phase array mode, in agreement with simulations based on the actual device dimensions, which indicate that resonant leaky-wave coupling occurs for this device's geometry. Measured uniform near-field intensity profiles confirm resonant coupling. Simulations indicate that chirping of the element widths would allow for modification of the near-field intensity profile to mitigate the effects of thermal lensing in continuous-wave operation.