Birefringence analysis in photonic crystal fibers with germanium-doped core

Abstract

We present the results of numerical analysis of birefringence in photonic crystal fibers with germanium-doped inclusions in the core. In such fibers, geometrical birefringence induced by holey cladding interplays with the birefringence induced by shape and composition of doped inclusions. The latter gives rise also to stress birefringence associated with different thermal expansion coefficients in doped and non-doped regions. In our analysis, we consider elliptical and circular inclusions and demonstrate that, by proper selection of the inclusions' geometry, it is possible to increase significantly the phase modal birefringence to a level greater than 10−4 in the short wavelength range. Moreover, it is possible to shape the dispersion of the phase modal birefringence in such a way that the group birefringence crosses zero value at a certain wavelength.