Input-grating couplers for narrow Gaussian beam: influence of groove depth.

Input-grating coupling characteristics have been studied for narrow Gaussian beam incidence and finite-length grating coupler with an electromagnetic full-vector field model based on the finite-difference time domain (FDTD) method. Analytic analysis based on perturbation theory has been compared to the FDTD technique. The influences of the variation in grating period, modulation depth, corrugation, and beam size have been investigated. Certain aspects of the calculated results have been confirmed with experiments.