A microwave photonics interferometric (MWPI) method for measuring the beat length in high birefringence polarization-maintaining fiber (PMF) is proposed. The approach is based on the radio frequency (RF) interference between the two polarization modes propagating on the polarization axis in the PMF. The period of the RF interference spectral is determined by the optical path difference of the two polarization modes. According to the principle that the phase difference in one free spectral range (FSR) of the interference spectral is 360 degree, the beat length of the PMF can be calculated by recording the RF interference spectral. Two different lengths of PMF have been tested and the measurement results show that the measurement precision is 0.02 mm. The wavelength dependent beat length has also been measured. Furthermore, the measurement precision of this method and the main source of errors are investigated in detail.

中文翻译：

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保偏光纤拍长的射频干涉测量

提出了一种用于测量高双折射保偏光纤 (PMF) 拍长的微波光子干涉 (MWPI) 方法。该方法基于在 PMF 中的极化轴上传播的两种极化模式之间的射频 (RF) 干扰。射频干涉光谱的周期由两种偏振模式的光程差决定。根据干涉光谱在一个自由光谱范围(FSR)内的相位差为360度的原理，通过记录射频干涉光谱可以计算出PMF的拍长。测试了两种不同长度的PMF，测量结果表明测量精度为0.02 mm。还测量了与波长相关的拍长。此外，