Unclosed fiber optic current sensor based on helically wound spun highly birefringent fiber half waveplate

In the application of the fiber optic current sensor that is mounted on tunnel boring machine (TBM) for measuring the probe current in tunnel geological prediction, the field installation and the influence of the linear birefringence caused by external perturbations are problems needing to be solved. In this paper, an unclosed fiber optic current sensor (UFOCS) based on the helically wound spun highly birefringent (SHB) fiber half waveplate is proposed and demonstrated. The UFOCS is designed to coil the fiber around the measured current clockwise and counter clockwise alternately in order to be mounted on the measured object with large diameter easily. The all -fiber half waveplate made by the helically wound SHB fiber is used to accumulate the Faraday effect. The simulation is carried out based on the polarization model and a linear response is obtained. The laboratory experiment is conducted and the results confirm the good performance of the UFOCS.