High-Performance Grating Coupler Array on Silicon for a Perfectly-Vertically Mounted Multicore Fiber

High performance grating coupler array for coupling of a silicon photonic chip to a multi-core fiber mounted perfectly vertical to the chip surface is proposed and demonstrated. Experimental results show a low coupling loss of −0.8 dB with 1-dB bandwidth of 47 nm, a low back reflection of <−15.8 dB in about 40 nm wavelength range, a channel non-uniformity of 0.9 dB, and crosstalk of <−40 dB. These improved results attribute to the design of embedding the diffractive grating in a one-port cavity formed by partially and perfectly reflecting Bragg gratings on the silicon chip and a metal mirror on the chip surface.