为了测量高双折射保偏光纤的拍长,采用偏光干涉效应的方法,构建由宽谱光源、带保偏尾纤的起偏器和光谱分析仪组成的全光纤光路测试系统。从理论上用Mueller传输矩阵方法推导了到达光谱仪的光强公式,利用该方法构建实验系统对熊猫型保偏光纤的拍长进行了测试,获得了该保偏光纤拍长的测量数据。结果表明,由待测保偏光纤的偏光干涉效应引起的光强波动以一定的周期间隔表现在光谱变化上,波动的相对幅度与待测保偏光纤主轴与起偏器的保偏尾纤主轴夹角有关,当夹角均为±45°时波动的相对幅度最大。只要在实验中测量出光谱波动的周期,就能够根据理论计算出给定波长处的保偏光纤的拍长。

In order to measure the beat length of high-birefringent polarization-maintaining fibers,an all-fiber optic system,comprised of broadband light source,in-line polarizer with polarization-maintaining pigtail and optical spectrum analysis,was be constructed based on conoscopic interference effect.The expression of optical intensity arrived at the optical spectrum analyzer was derived with Mueller transfer matrix.The measured data of the beat length of a kind of panda high-birefringent polarization-maintaining fiber was acquired in experiments.It is found that the intensity fluctuation due to conoscopic interference effect makes the spectrum variance in a certain period.The relative amplitude of the spectrum variance is decided by the angles between the chief axes of the polarization-maintaining fiber and the pigtail of in-line polarizer.When the angle is ±45°,the relative amplitude is maximal.Hence,the beat length of the panda high-birefringent polarization-maintaining fiber can be calculated as long as the spectrum fluctuation period is measured in experiments.