Modified Effective Index Method to Fit the Phase and Group Index in 3D Photonic Wire Waveguide

A modified effective index method (MEIM), which correctly describes, in a 2D case, both the phase and the group indexes in a 3D photonic wire, is discussed in the paper. MEIM utilizes the combined index profile with two spatial parameters. A central part has a wire index and a width of a nearly wire height. A basic part has a width of 3D wire and a fitting index Nb. Numerical experiments by FDTD of Ring resonator and multi- splitting multiplexer, Fabry-Perot and asymmetric Mach-Zehnder interferometers constructed by silicon wires prove that the MEIM gives an excellent agreement (about 2%) with test 3D simulation in comparison with an about 30%-45% error for EIM. MEIM is preferable for simulation of SOI filtering structures by 2D FDTD.