A Novel Current Sensor Based On Orthogonally Polarized Dual-Frequency Fiber Grating Laser

In recent years, with the rapid development of economy of China, the power demand keeps growing, moreover, the transmission distance of electricity becomes longer than ever before. To improve efficiency of electricity transmission, ultra high voltage transmission lines are being constructed in China. So the demand of current sensors with immunity to high voltage, in-time monitoring, high precision measurement of fault, and digital information management is increasing. Now electromagnetic current transducers, which have been widely used in many areas, can not meet these requirements. Therefore, the research and exploitation of new and immuno-high-voltage current sensors have become particularly important. In this thesis, new current sensors based on an orthogonally polarized dual-frequency fiber grating laser are proposed and fabricated. Their response characteristics have been tested. The details are described as follows:(1) Development and the classification of fiber optical sensors and problems of fiber Bragg grating sensors are briefly referred. Then the principle of the sensors based on orthogonally polarized dual-frequency fiber grating laser is introduced, and the technology about fabrication of orthogonally polarized dual-frequency fiber grating laser is recommended in detail. The orthogonally polarized dual-frequency fiber grating laser is produced by using phase mask method, while 193nm excimer laser is used as a photowriting source in this thesis. Using this technology, an ultra-short fiber laser is fabricated. The total length of the fiber laser could be as short as 8.4 mm, which is the shortest as reported so far, while the laser emits a beat signal with signal-to-noise ratio of 70 dB.(2) The fiber optical current sensor, based on orthogonal polarized dual-frequency fiber grating laser and magnetic force, is proposed and realized experimentally. The relationship between the current and polarization mode beat frequency of optic fiber laser is deduced. The current sensor has been tested under dc and ac current, while the effects induced by vibration and temperature are investigated.(3) The fiber optical current sensor, based on orthogonal polarized dual-frequency fiber grating laser and magnetostrictive effect, is proposed and realized experimentally. The relationship between the current and polarization mode beat frequency of optic fiber laser is deduced. The current sensor has been tested under dc and ac current, while the Earth magnetic field and an exerting magnetic field are regarded as bias magnetic field respectively.