Cost-effective CMOS-compatible grating couplers with backside metal mirror and 69% coupling efficiency

A highly efficient grating structure for the coupling between standard optical fibers and single-mode waveguides in the silicon-on-insulator platform realized in a CMOS fabrication process is presented. The cost-effective method introduces a backside metal mirror to the grating coupler without need of an extensive wafer-to-wafer bonding. A coupling efficiency of -1.6 dB (around 69%) near the telecommunication wavelength 1550 nm and a large 1 dB-bandwidth of 48 nm are achieved.