The Study On Interrogation System's Stability Of Interferometric Fiber-Optic Weak Magnetic Field Sensor

Optical fiber sensing technology is a well developed sensor technology with plenty of advantages. It is with high sensitivity to sense weak signal, good flexibility to meet specified requirements of various instruments and structures, immunization to different environment such as high pressure, high temperature, electromagnetic interference, etc., remote sensing to transmit signal via optical fiber, and so on. The optical fiber magnetic/electronic field sensor is one of the most important forefront topics in the research of optical sensing technology. This paper has focused on stability of interferometric optical fiber weak magnetic field sensor. The system has been improved on the basis of previous interrogation system, including experimental research on design of the magnetostriction material, fiber length and the skeleton shape, redesign of the sensing and conditioning circuits for enhancing stability and sensitivity, and cooperation with colleagues on designing electric field transducer. In the end, the tridimensional magnetic field measurements have been done by the directivity of magnetic field transducer.The stability on interferometric optical fiber weak magnetic field sensors has been studied in-depth on both sides of optics and electronics. From Optics side, different structures of the interferometers (M-Z interferometer and Michelson interferometer) have been compared and analyzed, which has been experimentally verified that the good stability of the interferometer with the Faraday rotation in fiber optic sensing system. Most importantly, lots of measures have been made from electronics side in it. The main works focus on the weak magnetic filed sensor interrogation system. In comparison with autocorrelation demodulation, the cross correlation, demonstrates good processing adaptability electronically with the aid of lock-in amplification technology. Meanwhile, the closed-loop feedback circuit based on reversed phase amplification technology has been designed to enhance the stability and sensitivity of the system, which makes the system more practical for application. The improved system can detect weak magnetic field with high performance and reliable repeatability. The system sensitivity reaches 49.4μV/nT, with background noise level at 2.5×10-5V/Hz1/2 and it can detect weak magnetic field as lower as 0.5nT at 1Hz. The performance on sensitivity has been improved about 40 times better than that of the before system we made, whose minimum magnetic field is only 20 nT.