Optimization of coupling and transmission through finite height SOI photonic crystal slab waveguides

Abstract

Transmission and coupling mechanisms in photonic crystal waveguides have been extensively studied in the last few years to optimize photonic crystal designs. Previous numerical results, using 2D FDTD methods have shown that the technique of tapering the photonic crystal lattice can improve coupling efficiencies up to 80%, as compared to 30-40% efficiencies in butt-coupled waveguides. However, for the 3D structures such as photonic crystal slabs, 2D calculations do not take into consideration the losses in the vertical direction and hence 3D simulations are necessary to obtain more accurate results which can be better compared with experimental data. In this paper 2D and 3D FDTD calculation results obtained for a finite height hexagonal silicon photonic crystal slab waveguide (air as top and bottom cladding) with air holes embedded in a silicon dielectric matrix are presented. Various coupling design configurations were investigated using 3D FDTD and coupling efficiencies of 78% in the photonic crystal waveguide and 72% through the output conventional waveguide were obtained for a conventional waveguide of width 3μm coupled to a step tapered PC waveguide on the input and output ports. Furthermore some designs which show excellent efficiencies with 2D calculations are clearly shown to have significant losses in the vertical direction in 3D simulations.