Abstract

Electromagnetic propagation is inhibited over the complete solid angle for a finite range of frequencies, and localized modes arise in perfect dielectrics with radially periodic indices of refraction. The electromagnetic properties of such structures are similar to periodic photonic band structures, but radial perturbations scatter weakly away from the Bragg resonance and yield a gap for arbitrarily weak index perturbations. The simplest radial perturbation is δn = Δn_o cos(Kr). In 3-D, this perturbation causes narrow gaps and true localized modes. 2-D systems are constructed by radially perturbing the effective index of slab waveguides. True photon localization is not possible in purely dielectric 2-D systems, but high-Q transparent resonators can be constructed. We discuss solutions to the vector Helmholtz equation under radial dielectric modulation and describe resonance spectra and scattering in 3-D and 2-D structures. We discuss the fabrication of 2-D structures.

© 1992 Optical Society of America