基于法拉第效应，正交双频光纤激光器已经被证明可用于实现磁场传感。但这种传感器对磁场的灵敏度与激光器初始的拍频频率相关。因此对这种传感器的磁场灵敏度与拍频频率的关系进行了研究。理论和实验结果表明，传感器对磁场的灵敏度与拍频频率间呈非线性关系，并且灵敏度随着拍频频率的减小而增大。该灵敏度存在一个由费尔德常数决定的上限值。对于实验中基于掺铒光纤制备的短腔光纤激光器，通过将初始拍频频率降至2 MHz，获得了激光器对磁场响应的最大灵敏度43 Hz/μT。此外，激光器初始拍频频率与抽运激光的偏振态也有关系。实验表明，通过调谐抽运激光的偏振态，可以动态地调谐传感器对磁场的灵敏度。

Through Faraday- effect, dual- polarization fiber grating laser based on magnetic field sensor is demonstrated. However, the sensitivity to magnetic field of such sensor is dependent on the initial beat frequency of the laser. Therefore, the relationship between the beat frequency and the sensitivity of such sensor is studied. Theoretical and experimental results show that the dependence of the sensitivity on the beat frequency is nonlinear. Moreover, the sensitivity increases with the decrease of beat frequency. However, there is an upper limit of this sensitivity which is determined by Verdet constant. By lowering the beat frequency to 2 MHz, the maximum sensitivity about 43 Hz/mT to magnetic field is achieved for a dual- polarization fiber grating laser inscribed on an erbium doped fiber. It also shows that the beat frequency is dependent on the polarization of the 980 nm pump. Therefore, dynamical tuning of the sensitivity optically can be demonstrated by tuning the polarization of the 980 nm pump.