A terahertz photomixer based on plasmonic nanoantennas coupled to a graphene emitter.

We propose the concept of a graphene-based nanoantenna-enhanced photomixer to realize wideband-tunable terahertz (THz) frequency generation. When two laser beams are focused on the graphene nanoemitter of a planar field-emission diode, THz current oscillations can be created at the emitter tip through the optical heterodyne. Graphene's optical transparency allows suitably designed plasmonic nanoantennas to boost the mixing of laser radiation at the emitter tip, significantly increasing the overall produced photomixing current. The THz wave generated at the graphene emitter is then coupled to a loading circuit, thanks to the THz wave confinement in the graphene nanostructures. Our design is ideally suited for THz sources that may be tuned from DC to 10 THz by simply shifting the frequency offset of two pumping lasers.