In this paper

a kind of THz single-polarization single-mode PCF is proposed.The dependence of refractive index matching coupling on several parameters（diameter of the micro air holes d3

lattice constantΛ3

lattice shapes in cladding）are investigated with a full-vector Finite Element Method（FEM）.Simulation results show that the best-optimized parameters of fiber are supposed to be d3 =27.7μm

Λ3=38μm and triangular lattice.The fiber exhibits large polarization-dependent loss ratio（>100）and wide bandwidth（0.281 THz）.The polarization-dependent loss ratio will be larger than 100 when the frequency is higher than 0.719 THz

and single-polarization single-mode transmission is realized.At the frequency of 0.95 THz

the polarization-dependent loss ratio reaches the maximum of 479 and the confinement loss is 2.4 e-3 dB/km.Compared with the liquid filling method

the structural adjustment method achieves larger polarization-dependent loss radio

lower confinement loss

and wider bandwidth.