理论推导了双折射光纤环镜波长变化与轴向应变的公式, 研究表明: 双折射光子晶体光纤环镜轴向应变灵敏度比传统双折射光纤环镜大为减小。 通过监测双折射光子晶体光纤环镜波长的变化, 来实现轴向应变的测量就变得较为困难; 且输出干涉光谱局部呈凹凸不平, 波长监测容易导致数据测量误差。 实验监测双折射光子晶体光纤环镜应变光谱, 对应变光谱分析发现: 随着应变增加, 监测波峰下的绝对积分呈现减小的趋势。 进一步精确计算分析发现: 监测波峰下的绝对积分与应变成线性关系。 基于此, 提出了通过监测波峰下的绝对积分的变化, 来实现轴向应变的测量。 波峰下的绝对积分是表征各波长光强的综合性能指标, 通过监测波峰下的绝对积分的变化, 来实现轴向应变的测量, 不仅可以克服双折射光子晶体光纤环镜监测波长变化的困难, 而且还可以克服波长监测局部寻优导致的测量误差。

In the present paper, the theoretical expression of the wavelength change and the axial strain of birefringence fiber loop mirror is developed. The theoretical result shows that the axial strain sensitivity of birefringence photonic crystal fiber loop mirror is much lower than conventional birefringence fiber loop mirror. It is difficult to measure the axial strain by monitoring the wavelength change of birefringence photonic crystal fiber loop mirror, and it is easy to cause the measurement error because the output spectrum is not perfectly smooth. The different strain spectrum of birefringence photonic crystal fiber loop mirror was measured experimentally by an optical spectrum analyzer. The measured spectrum was analysed. The results show that the absolute integral of the monitoring peak decreases with increasing strain and the absolute integral is linear versus strain. Based on the above results, it is proposed that the axial strain can be measured by monitoring the absolute integral of the monitoring peak in this paper. The absolute integral of the monitoring peak is a comprehensive index which can indicate the light intensity of different wavelength. This method of monitoring the absolute integral of the monitoring peak to measure the axial strain can not only overcome the difficulty of monitoring the wavelength change of birefringence photonic crystal fiber loop mirror, but also reduce the measurement error caused by the unsmooth output spectrum.