A comparative study of birefringence in photonic crystal fiber employing various lattice geometries with all-circular air holes

Abstract

This article presents a detail theoretical investigation on birefringence characteristics for various highly birefringent photonic crystal fiber designs based on triangular, square, and circular-lattice geometry. In order to compare the results, a systematic comparative study is then performed. It is shown that the birefringence of any particular lattice geometry can be modulated by modifying the structural anisotropy (asymmetry) of that geometry. The variations of birefringence with normalized wavelength have been evaluated for various asymmetric designs of a lattice geometry and variation for other lattice geometries have thereby been determined and compared. These photonic crystal fibers are composed of a solid silica core surrounded by cladding of circular air-holes. The birefringence is due to large axial anisotropy introduced into the fiber by a prefer arrangement of air-holes in the fiber cladding. A finite difference mode-convergence analysis is implemented to determine the required modal indices of the photonic crystal fiber, which is then used to calculate the birefringence of the fiber. Based on the results, the birefringence is found to be largely dependent on the lattice geometry associated as well as the degree of asymmetry. Numerical results show that for a particular type of asymmetric design triangular-lattice geometry is the best choice in terms of high birefringence. One of the considered designs based on triangular-lattice geometry, formed by omitting three adjacent air-holes at the centre, can considerably enhance the birefringence as high as 12.6×10−3 at normalized frequency 0.48.