Fig. 1. Polarization maintain hollow core negative curvature fiber end view

Fig. 2. （a）y-directional clad tube thickness t_1y and nested tube to the inner diameter of the tube maximum distance Z on the influence of HC-NCF PER ，（b）when t_1y/t_1xis 2.15 （t_1y is 1.60 μm）, Z is 11.76 μm, x and y direction polarization mode

Fig. 3. The effect of core diameter D_core on polarization maintain HC-PCF （a） The confinement loss of the modes changes with D_core, （b） PER and HOMER changes with D_core, （c） Re（n_eff） change with D_core,（d） the mode-field coupling process

Fig. 4. The effect of the cladding tube diameter D_tube on polarization maintain HC-NCF （a） the confinement loss of the mode changes with D_tube, （b） Re（n_eff） changes with D_tube

Fig. 5. Coupling process of mode changing with D_tube: When D_tube=79.57 μm, （a） x-pol core mode， （b） Clad surface mode1; When D_tube=91.14μm, （c） y-pol core mode， （d） Clad surface mode2

Fig. 6. Polarization maintain HC-NCF mode coupling process with wavelength change （a） effective refractive index, （b）coupling process of mode

Fig. 7. Polarization maintain HC-NCF transmission characteristics with wavelength change （a） Mode-limited loss changes with wavelength, （b） PER and HOMER change with wavelength, （c） Birefringence change with wavelength, （d） x-pol core mode（top） and high order mode（bottom）

Fig. 8. Bend loss of polarization-maintaining HC-NCF （a） the loss obtained by bend in the y direction, （b） the loss obtained by bend in the x direction