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在矩形晶格多孔光纤的基础上,通过加入一对大直径圆孔,并进一步优化结构参数可以得到宽带稳定的双折射拍长。采用有限差分波束传播法计算了多孔光纤的模式双折射特性,分析了不同参数变化对模式双折射的影响。计算表明,这两种非对称结构分别具有正值和负值双折射,两者相互作用能够控制模式双折射随波长的变化斜率,在一定的波长范围内使模式双折射与波长呈现等比例的线性变化关系,从而得到基本不随波长变化的双折射拍长。通过优化结构参数,分别在1310 nm和1550 nm波长窗口获得了中心拍长为10 mm的平坦拍长曲线,相对带宽达到12%以上,这种光纤非常适合制作集成于全光纤大电流传感器之中的宽带光纤波片。
On the basis of the rectangular lattice porous optical fiber, the broadband stable birefringence beat length can be obtained by adding a pair of large diameter circular holes and further optimizing the structural parameters. The mode birefringence characteristics of porous optical fiber are calculated by finite difference beam propagation method. The influence of different parameters on mode birefringence is analyzed. Calculations show that the two asymmetric structures have positive and negative birefringence, respectively. The interaction between the two structures can control the slope of mode birefringence with wavelength, and make the mode birefringence equal to the wavelength in a certain wavelength range Linear relationship between the changes, resulting in basically no wavelength change birefringence beat length. By optimizing the structural parameters, a flat beat curve with central beat length of 10 mm was achieved at 1310 nm and 1550 nm wavelength windows, respectively, with a relative bandwidth of over 12%. This fiber is very suitable for integration into all-fiber high-current sensors Broadband fiber wave plate.