用于全光纤电流传感器的扭转高双折射光纤设计

Design of spun high-birefringent fiber for fiber optic current sensor

传感光纤中的残余线性双折射、温度和振动敏感性严重影响着Sagnac式全光纤电流传感器的精度。设计了一种可用于全光纤电流传感器的扭转高双折射光纤,该光纤由两端变速率扭转部分和中间匀速率扭转部分组成。其中,变速扭转部分能实现线偏振光和圆偏振光之间的相互转化,具有λ/4波片功能;匀速扭转部分,具有较小的光纤固有线性双折射和圆保偏功能,从而可更为精确地感应法拉第效应。将这种扭转高双折射光纤绕制成特殊结构传感光纤环,解决了Sagnac效应以及电流导体位置对全光纤电流传感器测量结果的影响。理论上建立了扭转高双折射光纤的耦合模方程,模拟了线偏振光入射该光纤时光波偏振状态演化情况。在此基础上设计一种新型的抗振型Sagnac式电流传感器。

The residual linear birefringent of sensing fiber, temperature and vibration sensitivity severely influence the accuracy of Sagnac fiber optic current sensor （S- FOCS）. A sensing fiber can be used in FOCS with spun high birefringent fiber （S Hi- Bi fiber） was designed. This S Hi- Bi fiber includes three sections： two terminal sections with variable spin-rate along fiber were utilized to substitute the fiber quarter-wave plates, respectively converting the light polarization state from the linear one to the circle one, and vice versa; and the middle section with a uniform spin-rate was utilized as the current sensing fiber which maintains the circular polarization state and compress the residual linear birefringent during the light propagation. In addition, the sensing fiber was wound into a special geometric structure so that the Sagnac phase shift was inherently eliminated and the sensing result did not depend on the position of the current conductor. In theory, used the coupled-mode theory the evolution of the light polarization state was simulated when linear polarization states light incident into the sensing fiber. A novel Sagnac fiber optic current sensor with vibration insensitivity based on this spun high birefringent fibers was proposed.