Design and investigation of a dual-layer grating coupler for efficient vertical fiber-chip coupling

A novel dual-layer grating coupler was designed for efficient vertical coupling between a single-mode fiber and silicon nanowires, with characteristics of polarization diversity and both wavelength bands of 1.3 and 1.55 μm. Theoretical analysis and two-dimensional finite-difference time-domain simulations were applied to verify the performance of the design. Optimized results show that the coupling efficiencies of a dual-port output of 41% (-3.87 dB) for transverse-electric polarization at 1.56 μm, 32.88% (-4.83 dB) for transverse-magnetic (TM) polarization at 1.58 μm, and 27.06% (-5.68 dB) for TM polarization at 1.32 μm can be achieved. Dual-layer Fabry-Perot resonance was also investigated for high coupling efficiency.