Photonic crystal slab waveguides are created by inserting a linear defect in two-dimensional (2-D) periodic dielectric structures of finite height. Photonic crystals provide 2-D in-plane bandgaps through which light cannot propagate, however, the fact that the waveguide modes must be index-confined in the vertical direction implies that the propagation loss is strongly dependent on the out-of-plane radiation loss. We present a fully three-dimensional finite-difference time-domain numerical model for calculating the out-of-plane radiation loss in photonic crystal slab waveguides. The propagation loss of the single-line defect waveguide in 2-D triangular lattice photonic crystals is calculated for suspended membranes, oxidized lower claddings, and deeply etched structures. The results show that low-loss waveguides are achievable for sufficiently suspended membranes and oxidized lower cladding structures. The roles of the photonic crystal in out-of-plane loss of the waveguide modes are further analyzed. It is predicted that the out-of-plane radiation loss can be reduced by shifting one side of the photonic crystal cladding by one-half period with respect to the other sides along the propagation direction.
This document was originally published by IEEE in IEEE Journal of Selected Topics in Quantum Electronics. Copyright restrictions may apply. DOI: 10.1109/JSTQE.2006.884785
Kuang, Wan; Kim, Woo J.; Mock, Adam; and O'Brien, John. (2006). "Propagation Loss of Line-Defect Photonic Crystal Slab Waveguides". IEEE Journal of Selected Topics in Quantum Electronics, 12(6), 1183-1195.