Study of higher-order modes for waveguide grating coupler

Abstract

The vector two-dimensional finite difference time domain method is applied to analyze the higher-order modes of waveguide grating couplers (WGCs). The phase matching function of WGC is deduced based on diffraction equation. The stable field distributions and mode patterns of TE1, TE2 and TE3 in WGCs are obtained by using Gaussian beam as a driving source. It is found that the optical mode is determined by grating parameters and waveguide structures. According to the mode field distribution, the optimum coupling efficiency can be predicted, and thus highly-efficient WGCs which are of practical use in integrated optical circuits and optoelectronic devices can be designed conveniently.