Temperature compensated optical fiber current sensing system based on a two-tap microwave photonic filter

Abstract

In this paper, a two-tap microwave photonic filter (MPF) based temperature compensated optical fiber current sensing system has been proposed and experimentally demonstrated. Two fiber Bragg gratings (FBGs) are employed in the experiment, and the light signals modulated by radio-frequency (RF) signals reflected by two FBGs can be treated as two tap signals, which enter the dispersion-compensated fiber for the delay and beat through the photodetector to recover the RF signals, then a two-tap MPF is formed. Two FBGs are considered as the sensing and temperature compensation elements, respectively. The sensing FBG is affixed on the Terfenol-D. The variation of the current applied to the solenoid changes the magnetic field, and axial stretching strain is generated on the sensing element and sensing FBG's wavelength will change, which results in the shifts of the dip frequency of the MPF, by measuring which the current can be demodulated. Meanwhile, applying current will cause internal heating of the solenoid, and to further reduce the effect of the variation of temperature on current measurement, the temperature compensation FBG is affixed on the temperature compensated material Monel-400, and both two FBGs are placed inside the solenoid and good temperature compensation can be obtained. In the three-time repetitive continuous experiment, the current sensitivity as current increases of the system with temperature compensation is 4.23 MHz/A. The current measurement errors of the systems without and with temperature compensation are 0.83 A and 0.12 A, respectively. Our proposed system offers the advantages of easy fabrication, high current resolution with temperature compensation, good repeatability and high system stability, high current measurement precision, etc.