Propagation properties of Bragg fiber analyzed by a Hankel function formalism

This article describes the propagation characteristics of a Bragg fiber whose guiding principle is based on Bragg diffraction due to the periodic cladding. An asymptotic expansion for Hankel function at large arguments is used to express cladding fields with a simple form. A division in matrix calculation enables us to understand the cladding field physically. Condition for getting an asymptotically decaying wave in the cladding is revealed on the basis of property of Bloch wavenumber. It is shown that cutoff effective index giving the cutoff condition determines the lower limit for the cladding index difference.