High-efficiency focusing waveguide grating coupler with parallelogramic groove profiles

A high-efficiency focusing waveguide grating coupler (FWGC) using parallelogramic group profiles is proposed, designed and fabricated. A new waveguide grating structure has been employed which consists of bilayered grating with one grating etched into the guiding layer and the other into a high-index cladding layer. Computer simulation shows that both high directionality and large radiation decay factor are obtainable with this structure. Fabrication of this FWGC by electron beam lithography is described. A coupling efficiency of 86% and focusing spot size full-width at half maximum (FWHM) of around 10 /spl mu/m have been achieved.