Numerical simulation of sandwich structure photonic crystal fiber with diameter-increasing air holes

A kind of sandwich structure photonic crystal fiber with diameter-increasing air holes is proposed. The sandwich structure is composed of the rectangular lattice in the center and triangular lattice in both sides, which is used to gain high birefringence. The air holes in the cladding, whose diameter in outer ring is always larger than the next inner ring, is used to reduce the confinement loss. The model field, dispersion, birefringence and confinement loss of the fiber fundamental mode are simulated by full-vector finite element method. It was shown from numerical results that it is possible to design a PCF with birefringence B = 3.8 × 10−3 and the fast axis confinement loss less than 10−3 dB/km at wavelength of 1550 nm.