Simple model for photonic bandgap microstructured optical fibers

Summary form only given. Photonic bandgap microstructure optical fibers (MOF) have attracted significant interest in the past few years. Typically they rely on one of the following guiding mechanisms: total internal reflection or photonic bandgap guidance. The former mechanism is similar to the usual step-index fiber where the refractive index of the core is larger than that of the cladding. The latter guides light in a low-index core through coherent Bragg reflections off periodic layers in the cladding and exhibits a spectral response that is approximately periodic with frequency. In this paper we investigate the spectral characteristics of MOF, in which the lattice constant is larger than the optical wavelength, index contrast is high, and the air-fill fraction is large. In this regime we show that the spectral characteristics are governed by the thickness of the first high index layer rather than the lattice constant. We develop a simple analytic model based on leaky mode guidance in dielectric hollow waveguides, which describes experimental results for spectral features of similar MOF.