Graphene
plasmonics is a promising alternative for on-chip high
speed communication that integrates optics and electronics, where
the strong confinement of the electromagnetic energy at subwavelength
scale and the tunability of the plasmon frequency via an external
gate voltage are key advantages. The main drawback of graphene plasmons
is their rather short decay and propagation length, which is due to
intrinsic losses and substrate-related defects. Toward plasmonic devices,
noble metal antennas represent a viable approach for plasmon launching
in graphene waveguides, with the challenge of efficient coupling and
plasmon propagation that are feasible for on chip communication. Here
we discuss and analyze, using numerical simulations, different designs
of metal antennas and their coupling to graphene plasmons (GP), as
well as graphene based nanopatterned waveguides that can lead to a
more efficient GP propagation. A Yagi-Uda antenna leads to stronger
coupling to GPs and allows for directive propagation as compared to
a simple dipole antenna. This is especially advantageous to launch
plasmons in graphene nanowire waveguides, where propagation up to
3 μm and frequency and phase control can be achieved. In tapered
graphene waveguides, the constructive interference of the plasmon
reflection at the edges can lead to strong plasmon signals up to 8
μm distant from the launching dipole antenna. Nanostructuring
of rectangular waveguides into asymmetric chains of truncated triangles
greatly enhances directionality of GP propagation and conserves phase
information. A comparison of the propagation length and electric near-field
strength of these different approaches is presented, and confronted
with the efficiency of GP launching by light scattering on scanning
near field optical microscopy (SNOM) tips
