In this project, we have used COMSOL Multiphysics simulations to first investigate how transverse mode propagation can be controlled with cavity spoilers. We have modeled this effect by creating short and lossy lateral constrictions from the top of the laser ridge to perturb the modes distributed more toward the sides of the laser ridge, while leaving the fundamental mode intact. After obtaining optimized dimensions for the constrictions, we have utilized focused ion beam (FIB) milling to etch two small trenches from the top of several laser ridges to create the simulated effect on our devices. We, then, filled them with platinum in an effort to completely suppress the propagation of higher order transverse modes in the cavity. The results obtained show minimal effect on threshold and a Gaussian far-field distribution at various current levels, indicating a complete suppression of the higher order transverse modes.
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Pierre M. Bouzi, Peter Q. Liu, Nyan Aung, Xiaojun Wang, Jen-Yu Fan, Mariano Troccoli, Claire F. Gmachl, "Transverse mode control in quantum cascade lasers via lossy lateral constrictions," Proc. SPIE 8640, Novel In-Plane Semiconductor Lasers XII, 86401V (4 March 2013);