为提高光纤陀螺干涉仪保偏光纤长度误差量的测量精度，提出了一种基于四态方波调制的新的解决方法，将对光纤陀螺Sagnac干涉仪光纤长度误差量的测量转化为对探测器响应信号中尖峰脉冲的测量，并利用调制频率倍频技术实现了对尖峰脉冲的精细化测量。依据该方法设计制作了一套可检测光纤长度误差量的系统，达到了0.2 m的测量精度(2 000 m光纤)。实验结果表明，与普通保偏光纤测量方法相比，该方法测量精度高、速度快，为光纤陀螺的工程化装配提供了保障。

A novel approach to PM fiber length error measuring of IFOG′s Sagnac interferometer was proposed according to the FOG manufacturing process. Basing on the state four square wave mechanism, the measurement of fiber length error was conversed into the measurement of peak pulses in the detector′s response signal. Meanwhile, fine measurement of the peak pulse was accomplished by modulation frequency multiplying technique. A fiber length error measuring system was developed on the basis of this approach, which achieved the measuring precision of 0.2 m(2 000 m fiber). The experimental results show that a higher precision and a faster measuring speed than original methods, which can increase the efficiency of FOG′s engineering assembly.