Low-Back-Reflection Grating Couplers Using Asymmetric Grating Trenches

We propose a design of grating couplers having low back-reflections on silicon-on-insulator (SOI). The grating trenches are etched asymmetrically on the grating coupler. The asymmetric grating trenches help change the angle of reflected light path. Consequently, back-reflections can be reduced. The design concept has been verified by three-n-dimensional finite-difference time-domain simulations. The average back-reflection of 1-dB bandwidth in the proposed grating coupler is -44 dB. Only less than 0.3-dB penalty in fiber coupling efficiency occurs comparing with a conventional SOI-grating coupler.