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 ban d gap structure. The structure is composed of a waveguide, along which dang ling side branches are grafted periodically. We demonstrate a theoretical r ule about the existence of surface states in such 1D periodic structures; n amely, when one considers together two semi-infinite structures obtained by cutting an infinite one along a plane perpendicular to the axis of the str ucture, one always has as many localized surface states as minigaps. We pro pose an original method to observe the surface modes, namely, by measuring the transmission through a guide along which a finite comb is attached vert ically. The surface modes of the comb are obtained as maxima or minima of t he transmission spectrum. The experiments are performed by using coaxial ca bles in the frequency range of a few hundred MHz. (C) 2001 Elsevier Science Ltd. All rights reserved.