A method of starting fiber optic gyroscope outside its optical measuring range

Abstract

Increasing the length and diameter of the fiber ring of fiber optic gyroscope (FOG) can improve the accuracy of FOG, and the optical measuring range of FOG will be reduced accordingly. High-precision FOG usually uses cross-fringe modulation and demodulation algorithm to increase its measuring range, but it can only be started in its optical measuring range, otherwise it will output the wrong angular rate, which limits the FOG's application. When the FOG is powered outside its optical measuring range, it works in non-zero-order fringes, but its modulation and demodulation algorithm can't distinguish its work fringe level and wrongly consider that it works in the zero-order fringe, which results in wrong output of angular rate. According to Sagnac effect, the interference light intensity in the optical path of FOG is in cosine relation with the rotation rate, and the peak intensity of the interference fringes is the same at all levels. In practice, the wide-spectrum light source used in FOG will cause the interference peak intensity of the fringes weakened with the increase of fringe level. According to the FOG interference characteristic, this paper proposes a method of starting FOG outside its optical measuring range. The method firstly demodulates the interference peak intensities of adjacent fringes of FOG's working fringe through circuit modulation and demodulation, and then judges the level of the FOG's working fringe by these peaks. Finally the FOG's output angular rate is corrected according to its working fringe level. In this way, the FOG can still output the correct angular rate when it is started outside its optical measuring range. The mechanism that FOG outputs error angular rate when started outside its optical measuring range, was analyzed, and a method of starting FOG outside its optical measuring range was proposed in this paper. The experiment results show that the method can effectively solve the problem of FOG's abnormal output when started outside its optical measuring range.