Optimization of AC Sensing using In-line Sagnac Fiber Current Sensor System

Abstract

Optimization of AC sensing of the optical fiber current sensor comprised of the fiber sensing configuration with the light source, the detector, and the current sensing fiber was investigated upon application of the alternating current from 0 to 16,000 A by the toroid type current supplier. The types of fiber sensing configurations, light sources, sensing fibers, and temperature were investigated to find the best current sensing performance. The characteristics of Faraday rotation of the fibers sensing configuration and the subsequent current sensitivity were evaluated by measuring the Faraday rotation angle using the polarization analyzer. The Faraday rotation angle of the fiber sensor probe with the polarimetric configuration was 14.1°, that with the modified in-line Sagnac configuration was 48°, and that measured by the in-line Sagnac configuration was 62.5° upon application of the alternating current to 16,000A. As for the current sensitivity, while the in-line Sagnac configuration showed linear output voltage over the range of 0~250A, the modified in-line Sagnac configuration showed better linearity and stability at 2,000~16,000 A. The stability of the current sensor was found to depend on the characteristics of the light sources but the sensitivity was dependent on the characteristics of the fibers used and temperature change. While the single mode fiber pigtailed superluminescent diode (SMFSLD) showed the negligible change in voltage fluctuation and thus most stable, the amplified spontaneous emission (ASE) and the polarization maintaining fiber superluminscent diode (PMFSLD) showed ±15 mV and ±20 mV, respectively upon application of the alternating current to 16,000 A. In the case of the optical fiber type on the sensitivity, the spun high birefringence fiber (SHB) showed the largest sensitivity with the change of 2,287 mV, the spun low birefringence fiber (SLB) 1,575 mV and the un-spun fiber 1,377 mV. Temperature dependence on the sensing characteristics was also investigated. When temperature was changed from 20℃ to 80℃ to the fiber sensor probe, the SHB fiber showed the smallest sensitivity change -2%, the SLB fiber showed -8.8%, and the un-spun fiber showed largest change -22.4%. The SHB fiber was the most insensitive to the temperature change. In summary, the optimization of the present optical fiber current sensor was obtained by using the SMFSLD as a most suitable light source and the SHB fiber as a most suitable optical fiber.