Modal analysis of optical guides with two-dimensional photonic band-gap boundaries

Guided modes propagating in dielectric material surrounded by periodic two-dimensional photonic band-gap material are theoretically studied using the plane-wave expansion and a supercell. Two opposite boundary designs heavily affecting optical feedback at zone edge (Bragg reflection) are investigated. Limits to the validity range of simple bi-mode coupling schemes in these periodic guides are emphasized and coupling coefficients presented in adequate cases. Mode symmetries are studied and related to dispersion and frequency-width relationship. Finally, the smallest guide thickness allowing for a midgap mode is found to be much smaller than the analogous one-dimensional case, raising prospects for enhanced light-matter interaction. (C) 1996 American Institute of Physics.