  Graphene plasmons promise exciting nanophotonic and optoelectronic
applications. Owing to their extremely short wavelengths, however, the
efficient coupling of photons to graphene plasmons - critical for the
development of future devices - can be challenging. Here, we propose and
numerically demonstrate coupling between infrared photons and graphene plasmons
by the compression of surface polaritons on tapered bulk slabs of both polar
and doped- semiconductor materials. Propagation of the surface phonon
polaritons (in SiC) and surface plasmon polaritons (in n-GaAs) along the
tapered slabs compresses the polariton wavelengths from several micrometers to
around 200 nm, which perfectly matches the wavelengths of graphene plasmons.
The proposed coupling device allows for a 25% conversion of the incident photon
energy into graphene plasmons and, therefore, could become an efficient route
towards graphene plasmon circuitry.
