双螺旋圆单偏振光纤的偏振滤波特性研究

Research on Polarization Filtering Properties of Double-Helix Circularly Polarizing Fibers

双螺旋手征光纤光栅具有波长和偏振的双重选择性,在光纤传感系统中极具应用价值。目前报道的具有圆偏振滤波作用的双螺旋手征光纤光栅螺距仅为几十微米,传输损耗高,机械强度低,限制了其应用范围。基于光纤的复耦合模方程,研究了常用的涂覆光纤,即当涂覆层折射率大于包层折射率时,双螺旋光纤的偏振滤波特性。研究表明,涂覆光纤不仅能增加光纤的机械强度,还能将光纤的螺距增加到数百微米。因此,光纤的传输损耗可被有效降低,有望满足中等距离的传输或传感光纤的要求。分析了光纤参数对双螺旋光纤偏振滤波性能的影响,结果表明增加芯层模和包层模的耦合系数是提高光纤偏振性能的有效途径,对双螺旋圆单偏振光纤的研制有一定的指导意义。

The double-helix chiral fiber grating is a polarization and wavelength selective, which is very potential for applications in the field of optical fiber sensing. However, the spin pitch of the reported chiral fiber grating with circularly polarizing property is only tens of micrometers. The high insertion loss and low mechanical strength limit its application scope. The polarization filtering properties of the normally used coated fiber, whose refractive index of the jacket is higher than that of the cladding, are studied using the complex coupled mode equations. It is revealed that not only the mechanical strength increases in the coated fiber, but also the spin pitch increases to hundreds of micrometers. For this reason, loss can be reduced to meet the transmission requirement of a medium length of fiber. Influence of the parameters of the double- helix circularly polarizing fiber on the polarization filtering properties is analyzed. It is shown that increasing the coupling coefficient of the core mode and the cladding leaky mode is an effective way to improve the polarization filtering performance of the fiber. The results are instructive for the research and developing of the double-helix circularly polarizing fibers.