Suppression of pointing instability in quantum cascade lasers by transverse mode control

We report on a technique that serves to eliminate pointing instability in Quantum Cascade lasers by suppressing the propagation of higher order transverse modes within the laser cavity. This process, achieved via a short and lossy lateral constriction in the waveguide, only allows the fundamental mode to propagate. The beam pointing fluctuations of the modified devices are greatly reduced, with a 10-fold improvement in standard deviation, indicating a stable emitted beam. The far-field pattern has a Gaussian shape, and the slope efficiency of the received power on a 0.87 numerical aperture detector increases by ∼65, without significant increase in threshold.