Development of a High-Precision Demodulation System for Fiber-Optic Current Sensors

This paper presents the development of a high-precision demodulation system for fiber-optic current sensors (FOCS) based on magneto-optic crystals. The system consists of four key modules: a low-noise power supply, a high-stability amplified spontaneous emission (ASE) light source (1528–1568 nm bandwidth, 0.84 dB flatness, and <0.14% power fluctuation), a high-precision transimpedance amplifier (TIA) module, and a high-resolution data acquisition module based on a 24-bit ADC and STM32 microcontroller. To minimize sampling errors, a threshold detection method is employed to accurately measure signal frequency, with optimal performance achieved when the threshold is set at the midpoint of the peak-to-peak signal amplitude. The demodulation system reconstructs analog signal parameters (phase, period, DC offset, and amplitude) through sinusoidal fitting. A firmware driver written in C enables real-time acquisition of dual-polarization signals, while a C#-based host software processes and visualizes the data via serial communication. Experimental results demonstrate that the proposed system achieves high precision in demodulating polarization signals, making it suitable for industrial current sensing applications.