Optical waveguide grating couplers: 2nd-order and 4th-order finite-difference time-domain analysis

Output optical waveguide grating couplers are rigorously analyzed using the 2-order and the 4-order finite-difference time-domain (FDTD) method in conjunction with the total field/scattered field (TF-SF) approach and special averaging and regularization techniques for the mitigation of permittivity discontinuities. Volume-holographic and surface-relief grating couplers are analyzed for both TE and TM polarizations. The 2- and 4-order FDTD results are compared in terms of computational efficiency and accuracy. In addition, the FDTD results are compared to the approximate ones obtained by the rigorous coupled-wave analysis in conjunction with the leaky modes.