Highly efficient power extraction in terahertz quantum cascade laser via a grating coupler

We demonstrate the highly efficient power extraction from terahertz quantum cascade laser (THz-QCL) via a grating coupler (GC). The GC, formed in the top metallization of a Fabry-Perot (FP) THz-QCL with a metal-metal (MM) waveguide, diffracts the THz wave into the free space when it oscillates between the two cleaved facets. The radiation loss can be tailored in a wide range by changing the structure of the GC. The asymmetric positioning of the GC enables near-unidirectional emission, the enlarged emission surface reduces the beam divergence, and the MM waveguide keeps the optical confinement factor near unity. Experimental results confirm that, when the operating frequency is near 2.7 THz, the laser with a GC shows superior performances than the conventional FP lasers in terms of output power and operation temperature.