Fig. 1. Schematic diagram of the grating coupler based on the double-groove structure. The green arrow represents the polarization direction, port #1 represents the reflective 1st order, and ports #2, #3, and #4 represent the transmitted +1st, 0th, and −1st orders, respectively.

Fig. 2. Simulation results of the electric field inside the substrate with the double-groove grating coupler when the Gaussian wave from a single-mode fiber is normally incident with TE polarization. The inset (in the red box) is the enlarged electric field distribution within the grating region.

Fig. 3. Relationship between the coupling efficiency calculated by the RCWA, SA algorithms as well as FEM, and the working wavelength λ (a) in the C band and (b) in the C+L band, and (c) electric field distribution diagram at the central wavelength of λ = 1550 nm.

Fig. 4. Simulation results of 1000 samples of the grating couplers based on the Monte Carlo method. The average efficiencies of the couplers in the (a) C and (b) C+L bands for these 1000 samples; statistical distributions of the efficiency of these 1000 samples in the (c) C and (d) C+L bands.