Abstract

In general, waveguide grating couplers have output coupling efficiencies of ~50% (i.e., a 50/50 split of modal energy into the waveguide’s cover and substrate regions) and input coupling efficiencies of ~40% (due to beam-profile mismatch). Agrawal et al.¹ proposed placing a dielectric stack on the substrate to reflect the light diffracted toward the substrate back up and out of the device, thus creating a single-leakage-channel grating coupler. We demonstrate this concept by showing the design considerations, fabrication, and characterization of such a device. A wet-chemical process, readily adaptable to existing microelectronic fabrication lines, is used to fabricate the dielectric stack on a glass substrate. A solgel buffer layer of appropriate thickness is deposited on top of the reflector stack to isolate the guiding layer from the stack and to provide constructive addition of the reflected light with the light diffracted into the cover region. A variable-depth grating, etched into a solgel processed SiO₂-TiO₂ waveguide, serves to reduce beam profile mismatch, and thus enhance the coupling of Gaussian beams.

© 1991 Optical Society of America