由法拉第效应原理,通过测量磁场引起光纤布拉格光栅(FBG)的偏振相关损耗(PDL),可以测得磁感应强度大小。FBG中线双折射的存在,同样改变了光的偏振特性,仿真并实验验证了FBG固有偏振相关损耗的特点。利用琼斯矩阵法理论推导了FBG在既有双折射又有磁场影响时,输入线偏振光偏振态的变化规律。通过对偏振相关损耗与线偏振光起偏角和双折射大小的仿真分析可知,不同起偏角的线偏光对线双折射的敏感度不同。在线双折射的影响下,偏振相关损耗峰值随起偏角大小呈周期性变化,对磁场测量的灵敏度产生影响,而与磁感应强度的线性关系并未发生变化。

According to the principle of Faraday effect,the magnetic field can be measured with the polarization dependent loss (PDL) of the fiber Bragg gratings FBG. The polarization of light is changed by the liner birefringence existing in(FBG). The intrinsic PDL in the different structure gratings is simulated and measured,and the validity of the result is proved. The change of the state of polarization with the magnetic field and birefringence is theoretically analyzed and simulated by using the Jones matrix. The influences of liner birefringence and polarizing angle on the measurement system are compared. The peak of PDL and the cross sensitivity of the system vary with different polarizing angle. The linear relation between the magnetic field and the peak of PDL is not affected by these factors.