  An efficient and compact coupler - a device that matches a micro-waveguide
and a nano-waveguide - is an essential component for practical applications of
nanophotonic systems. The number of coupling approaches has been rapidly
increasing in the past ten years with the help of plasmonic structures and
metamaterials. In this paper we overview recent as well as common solutions for
nanocoupling. More specifically we consider the physical principles of
operation of the devices based on a tapered waveguide section, a direct
coupler, a lens and a scatterer and support them with a number of examples.
