The all-fiber optic current sensor is applied to realize the measurement of the leakage current of ships. The analytical model is established in a two-dimensional cartesian coordinate system. The magnetic field distribution of the weak current of a single long straight wire and the leakage current formed by two wires are modeled and simulated, respectively. The correctness of the analytical model is verified by the finite element method. The conditions of the formula application of the all-fiber current sensor are studied. It is determined that no magnetic field mutation, sensing fiber coil closure, transmission fiber insensitive to the magnetic field, and stable operation of the Verdet constant are the prerequisites for the combination of the Faraday effect and Ampere loop theorem. Finally, the experiments are conducted to prove the feasibility of the proposed method. The sensor achieves an accuracy of 1% and good linearity when the leakage current is from 1mA to 99mA.

Acousto-optic modulator (AOM) and electro-optical modulator (EOM) are applied to realize the all-fiber current sensor with a pulsed light source. The pulsed light is realized by amplitude modulation with AOM. The reflected interferometer current sensor is constructed by the mirror and phase modulation with EOM to improve the anti-interference ability. A correlation demodulation algorithm is applied for data processing. The influence of the modulation frequency and duty cycle of AOM on the optical system is determined by modeling and experiment. The duty cycle is the main factor affecting the normalized scale factor of the system. The modulation frequency mainly affects the output amplitude of the correlation demodulation and the system signal-to-noise ratio. The frequency multiplication factor links AOM and EOM, primarily affecting the ratio error. When the frequency multiplication factor is equal to the duty cycle of AOM and it is an integer multiple of 0.1, the ratio error of the system is less than 1.8% and the sensitivity and the resolution of AFOCS are 0.01063 mV/mA and 3 mA, respectively. The measurement range of AFOCS is from 11 mA to 196.62 A, which is excellent enough to meet the practical requirements for microcurrent measurement.

We present a method to simultaneously measure the temperature and electric current, which can be applied for the all-fiber optic current sensor (AFOCS) temperature compensation. The Faraday rotation mirror is introduced as the temperature sensing unit based on the all-fiber dual-modulation optic current sensor. The temperature and electric current could be distinguished by the sequence of pulse light received by the photodetector. The working principle of temperature and electric current sensing are analyzed by modeling and simulation. The experiments are designed to confirm the temperature compensation scheme. The relative error of AFOCS decreases from 14% to 2% by temperature compensation, which meets the requirements of micro-current fiber sensing.

The effects of the Faraday rotation mirror on the all-fiber optic current sensor (AFOCS) are studied in this paper. The reflectivity degradation of FRM with the long-term operation, the misalignment of the optical axis between FRM and the sensing fiber, and the influence of temperature fluctuation on FRM are modeled and simulated in this paper. The effect of temperature is the biggest obstacle to the application of the Faraday rotation mirror, while other factors can be easy to overcome by the data processing method. The experiments are designed and realized for verification. The temperature fluctuation range is related to the measured electric current to satisfy the required accuracy for IEC 60044-8 class 0.2S.