In this paper

we propose and study a novel structure of Photonic Crystal Fiber（PCF）with improved birefringence and single-mode propagation condition in a broad range of wavelength.The birefringence of the fundamental mode and single mode property in such a PCF is numerically investigated by Full Vector Finite Element Method（FVFEM）and Anisotropic Perfectly Matched Layers（APML）.The simulation results show that by filling the silica into one line elliptical air holes parallel to xaxis and rotated by an angle of θ=45°

and introducing one line elliptical air holes parallel to yaxis without any material and rotated by an angle of θ=45°to other direction

the birefringence can be 4.65×10

-2

with good single mode condition.Obviously

the proposed PCF has the potential application in optical instruments and devices.