Grating-Induced Beam-Tuning in Quantum Cascade Ring Lasers

We describe the fabrication and operation of quantum cascade ring lasers providing grating-coupled surface emission. The devices exhibit tunable far fields, ranging from spot- to ring-shaped symmetric beam cross sections, depending on the grating period. This - along with threshold current densities as low as for comparable Fabry-Perot lasers- demonstrates the compatibility of reduced beam divergence and two-dimensional integrability, resulting in an attractive light source for spectroscopic applications.