Facet reflectivity reduction of quantum cascade lasers by tilted facets

The authors present a technique to reduce the facet reflectivity in quantum cascade lasers (QCLs) by tilted facets. In order to minimize the Fabry-Pérot resonances, the feedback from the laser facets into the cavity must be minimized. Due to intersubband selection rules, the light generated inside QCLs is TM polarized. This polarization purity in QCLs enables the reduction of the facet reflectivity through the angle of light incidence at the laser facet. We observed a maximum threshold current density when the facet is tilted 17° towards the surface normal. This is in agreement with the calculated Brewster's angle for the QCL heterostructure.

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