In this paper the mode property of a photonic crystal fiber with triangle-lattice array in a silica matrix has been simulated by fast multipole method. The PCFs studied in this paper have a silica core, obtained by introducing a defect, that is by removing three holes in the center of the fiber transverse section. The model fields, effective index and confinement loss about the fundamental mode in the fibre are analysed and compared. It is demonstrated that lower confinement loss and higher

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... fringence can be realized in the condition of fewer rings of air holes. At the wavelength of 1.55 µm the confinement loss is 7.3×10 −6 dB/m and the birefringence is 1.65 × 10 −3 in this fiber. The simulation results show that birefringence of this triangle-lattice PCF is dominated by inner-ring air holes in the fibre effectively. The simulation results in this paper have important meaning for instructing the fabrication of birefringent photonic crystal fiber.