Linearly polarized light from substrate emitting ring cavity quantum cascade lasers

The authors report on substrate emitting ring cavity quantum cascade lasers that feature linearly polarized emission beams at an emission wavelength of 8.8 μm. A central lobed far field is achieved by a modification of the distributed feedback grating, at which two π phase-shifts at an angular distance of 180° are applied. In this central lobe, 80% linear polarization is measured. In order to extend this polarization property to the whole far field, an on-chip wire grid polarizer is used. These devices show linearly polarized substrate emission with an extinction ratio higher than 1:16.