Abstract

High efficiency, Gaussian beam input and output waveguide grating couplers are of substantial interest for future applications in optical data storage and guided wave sensors. We have demonstrated that variable depth gratings may be utilized to shape the out-coupled beam profile, and thus enable Gaussian beam out-coupling¹ and optimal in-coupling. Additionally, we have demonstrated that the branching ratio of a constant groove depth grating coupler may be enhanced by depositing a high reflectivity broadband dielectric stack above (or below) the grating/waveguiding region.² The stack reflects the portion of the out-coupled light diffracted toward the cover (or substrate) region, and redirects it to constructively add with the portion of the out-coupled light originally diffracted into the substrate (or cover) region. This produces output coupling efficiencies into a single channel approaching 100%. In this presentation, we will combine the variable depth grating with the high branching ratio design concept to demonstrate a high efficiency Gaussian beam input/output coupler. The modeling, fabrication, and performance characteristics (input coupling efficiency, branching ratio, and output beam profile) of fabricated devices will be presented.

© 1993 Optical Society of America