Impurity modes in one-dimensional periodic systems: The transition from photonic band gaps to microcavities

Abstract

We present a unified model of photonic-band-gap impurities and optical microcavities by using a one-dimensional distributed Bragg reflector. A variable-width center layer creates impurity photon states within the photonic band gap. We show that the best optical features (light localization, electric-field strength, linewidth, and laser threshold gain) are obtained when the layer thickness is half-wave (or a multiple), in which case the photon impurity state is located at the middle of the photonic band gap and the structure is a \ensuremath{\lambda}/2 (or higher-order) Fabry-P\'erot microcavity.