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

We fabricate a 20 um 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 microm in horizontal direction and +290 microm in vertical direction. The 1 dB alignment tolerance is measured at +-4.2 microm in horizontal direction and +125 microm 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 microm wide grating coupler which is also fabricated in this experiment.