DESIGN AND FABRICATION OF A SINGLE LEAKAGE-CHANNEL GRATING COUPLER

We describe the modeling and fabrication of waveguide grating couplers with theoretical outcoupling efficiencies into a single diffracted or der nearing 100%. Termed single leakage-channel grating couplers (or S LCGC's), these devices utilize a high-reflectivity dielectric stack to reflect the outcoupled beam diffracted toward the substrate and back up into the air region, where it constructively adds with the beam dif fracted into the air region. Computer modeling shows that the branchin g ratio and the leakage rate can be independently controlled, and that the branching ratio is independent of grating depth and grating perio d. A SLCGC with a branching ratio of 97.1% is fabricated by the use of a combination of vacuum-evaporation and wet-chemical techniques.