High efficiency diffraction grating coupler for low cost optical interconnect

Abstract : The original device presented in this paper is designed for coupling a free space optical wave under quasi-normal incidence in- and out of- a highly multimode waveguide with minimum losses. It uses two resonant diffraction gratings at the substrate-waveguide interface that are made of a shallow metal grating, covered with a high refractive index layer. It is shown that the resonant structure can theoretically diffract up to 90 % of the incident energy in and out of the waveguiding layer. The geometrical parameters of the structure and the tolerances can easily be achieved by conventional technology means.