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TIR-PCF（the six-fold rotation symmetry total internal reflection photonic crystal fiber）of cladding with hexagonal air column is designed in this paper.The fundamental mode dispersion characteristics are investigated numerically by full vector finite element method.The numerical results show that when other parameters are unchanged

original two fundamental mode polarization are separated if the shape of the cladding air column changes from circular to hexagonal.We can also observe a large mode birefringence and high degree of polarization mode dispersion.The results also show that the wavelength dispersion of the fundamental mode in Xpolarization have the same variation curve with cladding circular air column.It means that the fundamental mode dispersion characteristic has a great influence on the shape of cladding air column.