Vertical-cavity surface-emitting laser with a liquid crystal external cavity

A tuneable external cavity consisting of a thin layer of nematic liquid crystal (LC) and a dielectric reflector is placed on the top of a vertical-cavity surface-emitting laser (VCSEL). By changing the voltage across the LC layer, the optical path length of the external cavity can be tuned. As a result, the emitting properties of the LC-VCSEL, including polarization state and emission wavelength, can be controlled by the voltage applied over the LC layer. Stable polarization switching with high contrast is obtained by voltage driving. This device can be integrated in applications which require electrically tuneable VCSEL emission.