| For all-optical fiber current sensor based on Faraday magneto-optical effect, first, we introduce the basic principles and advantages of optical fiber current sensor. We get the output signal form and characteristics by analysis the whole optics Jones matrix in the system. Secondly,according to the characteristics of the system output signal and weak signal detection theory we determine the coherent demodulation scheme. In this paper, we also discuss the advantages and disadvantages of closed-loop demodulation scheme which be used in most system between open-loop demodulation scheme. We finally decided to use the open-loop demodulation system based on ARM7, because it is more applicable to the system. For the most important module phase sensitive detector, we design it by multipliers and electronic switch. Choose the better one by theoretical analysis and experimental result. In addition, we design the drive circuit of super luminescent diode (SLD) light source, which is the essential module of all-optical fiber current sensor. Piezoelectric ceramic (PZT) phase modulator driver module also be designed. The purpose of matching circuit is integrating all the non-optical parts in the system to a circuit board. Measuring0-500A current, zero bias current is1.89A. drift current is0.0355A. and the correlation coefficient of the entire system is0.99985in laboratory conditions. Finally, according to the problems appeared in the experiments, proposed optimization direction and the possible method to solve the problems.The main innovation of this paper:For Digital lock-in amplifier has high cost. bulky, complex structures and difficult to lock high-frequency, we first used an electronic switch instead of an analog multiplier in analog lock-in amplifier design, not only cost savings but also achieve higher accuracy, and the use of differential structure to reduce the prevalence of analog lock-in amplifier bias problem. The bias voltage of system reduced to250.39μV. zero drift down to59.5μV.Analysis the impact of electronic switch-mode lock-in amplifier in a phase delay error caused. According to GB/T20840.8-2007measurement standard, make phase shifting circuit resistance and capacitance accuracy propose appropriate theoretical requirements.Analysis the relationship between the stability of the interferometer and average wavelength of the light source and the system degree of polarization. On the basis of the design of the multi-stage Lyot fiber depolarizer, effectively improve the stability of its emitted light wavelength and the average degree of polarization to achieve a stable output interferometer. |
