Where, A is the coefficient of amplitude of the interference signal; ∅_s is the phase shift of the Sagnac; ∅_(m )is the phase shift produced by ladder wave (shown in the Fig. 2) ; ∅_(f )is the phase shift produced by the squara wave;〖 ∅〗_o is the phase shift produced by the electrocircuit noises in A/D,D/A and square signal. the phase shift of square wave generated in the positive and negative sphere is ±π/2, which can be got by subtracting the gained signal of the negative sphere from the positive sphere: