Diffraction field simulation of waveguide grating coupler with variable periods

In order to realize the high efficiency and high focusing coupling and steering of optical waveguide, a variable period focused grating coupler is designed by using the Bragg condition and the Finite Difference Time Domain (FDTD) method. Firstly, the relationship between the structural factors of the grating and the diffraction angle of the coupled light is derived based on the Bragg condition and the plane waveguide eigenmode equation. The effects of etching depth, grating period, duty cycle and other structural factors on the coupled light passing through the grating are obtained. Then, FDTD is used to simulate the diffraction field of uniform grating with different structure parameters. The uniform grating with different structures is combined and the variable period grating coupler are obtained. Finally, the structure parameters of variable-period grating coupler are optimized, and the optimum coupling efficiency and focusing angle are obtained. The coupling efficiency of the optimized variable period grating coupler is 62.37%. It provides a theoretical basis for the practical application of optical interconnection.