High-Efficiency Broadband Grating Couplers for Silicon Hybrid Plasmonic Waveguides

Abstract

We report the designs of on-chip grating couplers for the silicon hybrid plasmonic waveguides, which is the first proposal, to the best of our knowledge, for the direct coupling between a standard single-mode fiber and a hybrid plasmonic waveguide. By leveraging the apodized gratings and a two-stage-taper mode converter, we obtain a theoretical coupling efficiency of 79% (−1.03 dB) at the 1550 nm wavelength and a 3-dB bandwidth of 73 nm between the fiber and a 100 nm-wide silicon hybrid plasmonic waveguide with a bottom metal layer. We further propose grating couplers for three other sorts of silicon hybrid plasmonic waveguides with a metal cap and theoretically achieve good performances with coupling efficiencies larger than 47% and bandwidths larger than 51 nm. The proposed direct coupling scheme can avoid extra insertion losses and additional alignment processes that conventional indirect coupling schemes produce. It is believed to be a new step forward to the CMOS-compatible and large-scale integration based on the plasmonic waveguides.