Comparison of three-dimensional photonic crystal slab waveguides with two-dimensional photonic crystal waveguides: Efficient butt coupling into these photonic crystal waveguides

Abstract

Butt coupling into photonic crystal waveguides is computationally investigated for a three-dimensional photonic crystal slab and a two-dimensional photonic crystal. The photonic crystal slab consists of a silicon-on-insulator substrate with a triangular array of holes, in which the silicon layer is the optical guiding layer. The transmission spectra of the two-dimensional system and the slab system differ significantly. The slab system supports only a small range of frequencies in which a guided mode exists. In this frequency range, the transmission is comparable with that of the two-dimensional system, and its value is around 0.8. For the other frequencies, where for the slab system only resonances exist, the transmission is much lower than that of the two-dimensional system because of losses in the photonic crystal waveguide. Therefore, we conclude that complete three-dimensional computations have to be performed to obtain quantitative results for photonic crystal slab systems.