Surface states in one-dimensional photonic band gap structures

We study, both theoretically and experimentally, the existence and behavior of surface localized modes in a one-dimensional (1D) comblike photonic band gap structure. The structure is composed of a waveguide, along which dangling side branches are grafted periodically. We demonstrate a theoretical rule about the existence of surface states in such 1D periodic structures; namely, when one considers together two semi-infinite structures obtained by cutting an infinite one along a plane perpendicular to the axis of the structure, one always has as many localized surface states as minigaps. We propose an original method to observe the surface modes, namely, by measuring the transmission through a guide along which a finite comb is attached vertically. The surface modes of the comb are obtained as maxima or minima of the transmission spectrum. The experiments are performed by using coaxial cables in the frequency range of a few hundred MHz. (C) 2001 Elsevier Science Ltd. All rights reserved.