Research On All-fiber Current Sensor Based On Loop Archcture

All fiber current sensor (AFCS) that combining optical technology with current sensor is a kind of electronic transformers. Fiber in AFCS is not only a sensitive element but a signal carrier. The advantages of AFCSs include immunity against electromagnetic interferences, electrical isolation, absence of saturation effects, and small size. And it has more flexible configuration, easier fabrication and lower cost than other optical current sensors. However, there are still some problems hinder the applications of AFCSs.This dissertation focused on the theoretical analysis and configuration of AFCSs, and researched the solutions of two crucial problems-the current sensitivity of AFCS is very low and the environment sensitivity of AFCS is very high. The innovations in the paper include three aspects as follows:Firstly, we demonstrated an all-fiber current sensor based on the fiber loop architecture to improve current sensitivity. A fiber solenoid is employed as a current sensor head in the fiber loop architecture. The optical signal can traverse the sensor head repeatedly so that the Faraday rotation angle is increased and the current sensitivity is enhanced correspondingly. The design can enhance the current sensitivity of AFCS effectively, and has advantages including simple configuration and good expansibility. Both theory and experiment prove that the improvement in sensitivity increases periodically with the number of round trips K and an appropriate K can be selected to measure a specific current range.Secondly, we analyzed the temperature and vibration features of AFCSs using the common single mode fiber (SMF), and tried to find a method to improve the temperature and vibration robustness of AFCSs. Using the SMF as sensitive element of AFCSs can cut the cost effectively. But, it is important to note that the structure and the birefringence conditions of SMF are more uncertain than special fibers. The SMF may have multiple birefringences including linear birefringence, irreciprocal circular birefringence and reciprocal circular birefringence. And the size of linear birefringence of SMF may lie between that of the High birefringence and Low birefringence fibers. According to the situation, the Jones matrix of fiber sensor head was modified via dividing the circular birefringence in the matrix into irreciprocal birefringence and reciprocal birefringence. We deduce the transmission matrices of AFCSs using different schemes, and illustrate the temperature and vibration robustness of these configurations in different birefringence conditions based on the modified matrice. The theoretical analysis and experience results show that the temperature and vibration sensitivity of the AFCS based on a Faraday rotation mirror (FRM) are almost entirely independent of the birefringence condition of the fiber. Thus, the FRM scheme can be used with a common SMF.Finally, we demonstrated a temperature and vibration insensitive AFCS, which combines the FRM reflection scheme with the fiber loop architecture. The design not only possesses the current sensitivity, but also has the temperature and vibration robustness. The theory and experiment prove the construction can reduce the temperature and vibration sensitivity of system and improve the linearity degree of measured results. Moreover, the design can effectively cut down the cost in fabrication via using the SMF and common fiber components.