  We report the design, fabrication and characterization of a periodic grating
of shallow rectangular grooves in a metallic film with the goal of maximizing
the coupling efficiency of an extended plane wave (PW) of visible or
near-infrared light into a single surface plasmon polariton (SPP) mode on a
flat metal surface. A PW-to-SPP power conversion factor > 45 % is demonstrated
at a wavelength of 780 nm, which exceeds by an order of magnitude the
experimental performance of SPP grating couplers reported to date at any
wavelength. Conversion efficiency is maximized by matching the dissipative SPP
losses along the grating surface to the local coupling strength. This critical
coupling condition is experimentally achieved by tailoring the groove depth and
width using a focused ion beam.

Optics;Instrumentation and Detectors