A differential-self-multiplication demodulation algorithm for fiber optic current sensor

A fiber optic current sensor (FOCS) demodulation algorithm based on differential-self-multiplication (DSM) is proposed, which is insensitive to the variation in phase modulation depth. It is theoretically analyzed and experimentally verified, compared with two traditional demodulation algorithms in this paper. DSM algorithm reduces demodulation errors caused by phase modulation depth variation that will cause harmonic amplitudes to approach zero. And the variation in phase modulation depth can be simulated by changing modulation voltage. In experiments, where the modulation frequency is 350 kHz and the modulation voltage ranges from 0.5 to 9 V, demodulation currents with DSM algorithms are not only more accurate but also more stable than traditional demodulation algorithms. In addition, the robustness of the DSM algorithm is demonstrated by repeating the experiment at different modulation frequency ranges from 100 to 600 kHz. This work provides a stable demodulation algorithm for FOCS, which can be extended to the applications in demodulation for other phase interferometers.