Enhancing alignment tolerance of silicon waveguide by using a wide grating coupler

Abstract

We fabricate a 20 mu m wide grating coupler for a single-mode thermally-expanded-core (TEC) fiber, in order to enhance positional tolerance in alignment. The minimal coupling loss is measured at 5 dB per facet and the optical 3 dB bandwidth is measured at 40 nm. The 3 dB alignment tolerance is measured at +/- 7.5 mu m in horizontal direction and +290 mu m in vertical direction. The 1 dB alignment tolerance is measured at +/- 4.2 mu m in horizontal direction and +125 mu m in vertical direction. The alignment tolerance is enhanced twice in horizontal direction and four times in vertical direction, compared with the coupling of a standard single-mode fiber to a standard 10 mu m wide grating coupler which is also fabricated in this experiment. (C) 2008 Optical Society of America.