We report on highly efficient energy conversion between off-plane Gaussian beam and in-plane surface plasmon waves (SPWs). The finite-difference time-domain method was used to analyze the conversion efficiency. In contrast to the single plasmonic rib structure, coupled ribs provide broadband and highly efficient SPW-conversion due to enlarged coupling zone. The simulation shows that Gaussian beam-to-SPWs conversion efficiency can be higher than 50% for the wavelength range from 750 to 950 nm. Compared to in-plane excitation, the present structure is superior in terms of the critical dimension of fabrication, showing promise as an efficient SPW generator in plasmonic nano-circuritry.
