| Optic current sensor(OCS) based on magnetic sensitive materials has a number of interesting properties, such as inherent insulation, safety, digital output, etc.. Thus, OCS is an important development direction for the current sensor and has attracted many attentions in the world. In order to meet the great requirements for current sensor with good performances in the electrical power system with increasing rated voltage, theoretical and experimental investigations of OCS utilizing Faraday magnetic sensitive materials and magnetic fluid were carried out in this paper. The means for solving the key problems of each kind of sensor were proposed.The main works of this thesis are as follows:1、For the magneto-optic crystal rod OCS, the way of using dual quadrature polarimetric detection scheme to improve the signal to noise ratio was given and the performance of magneto-optic crystal rod OCS manufactured by our research group was measured. When the relative location of sensor and conductor is different, the relation of Faraday rotation angle and current was deduced. Furthermore, the effect of varying distance and orientation of conductor on the current sensing property was studied both theoretically and experimentally.2、For the fiber optic current sensor(FOCS), the mean of jointly using Mueller matrix and Poincare polarization sphere to visually describe the property of polarization light wave was proposed. By utilizing this method the effect of linear birefringence, which is the major problem of this kind of sensor, was analyzed. And then the effect of Faraday mirror on linear birefringence was studied for the FOCS using Faraday mirror, and a time multiplexing method of three different input polarization states was proposed to solve the problem of linear birefringence.3、The multimode interference principle of singlemode-multimode-singlemode(SMS) fiber structure was deeply analyzed, and its temperature cross-sensitivity characteristics were studied as well. The results indicated that the thermo-optic effect of the cladding of the multimode ?ber and thermal expansion effects of the packaging material are the two important contributors to the temperature sensitivity of an SMS structure, respectively. This study can provide basis and reference for investigating the temperature characteristics and compensating the temperature effect for our proposed current sensor based on magnetic fluid(MF) and SMS fiber structure.4、The MF based current sensor was fabricated by combining the magnetically modulated refractive index and absorption properties of MF with the multimode interference principle of SMS fiber structure. The current sensing property of the proposed sensor was measured. The current sensitivities of 7.8pm/A(78pm/Oe) and 0.0092dB/A(0.092dB/Oe), based on dip wavelength and transmission loss demodulations, respectively, were achieved.5、For the MF based current sensor, two kinds of method for improving the current sensitivity were proposed. First, for the demodulation of sensor by measuring the transmission loss, instead of the change of transmission loss at a specific wavelength, the total change of transmission loss during broad wavelength range of source was used to improve the current sensitivity. The results showed that the obtained current sensitivity was at least 344 times larger than that under a specific wavelength. Second, according to the principle that the evanescent field can be enhanced by bend, I fabricated an U-bent sensor to improve the current sensitivity. The obtained current sensitivities were 4.3 and 4.0 times higher than those of straight sensors for the dip wavelength and transmission loss demodulations, respectively. |
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