  A novel plasmonic waveguide-coupled nanocavity with a monopole antenna is
proposed to localize the optical power from a hybrid plasmonic waveguide and
subsequently convert it into electrical current. The nanocavity is designed as
a Fabry-P\'erot waveguide resonator, while the monopole antenna is made of a
metallic nanorod directly mounted onto the metallic part of the waveguide
terminal which acts as the conducting ground. The nanocavity coincides with the
antenna feed sandwiched in between the antenna and the ground. Maximum power
from the waveguide can be coupled into, and absorbed in the nanocavity by means
of the field resonance in the antenna as well as in the nanocavity. Simulation
results show that 42% optical power from the waveguide can be absorbed in a
germanium filled nanocavity with a nanoscale volume of 220x150x60nm$^3$. The
design may find applications in nanoscale photo-detection, subwavelength light
focusing and manipulating, as well as sensing.
