Methods for measuring the auxiliary modulation step in interferometric fiber optic sensor

In the current paper we consider the case of the sawtooth-type of phase modulation of the interference signal argument and demonstrate a method for calculating the phase modulation step of interferometric signal in a fiber optic sensor. Two methods of calculation the modulation step are proposed: for 4-point and 5-point digital demodulation algorithm based on ordinary least squares approach. The effect of target phase on the results of calculating modulation step has been demonstrated. The dependence of the error in the calculation of the auxiliary modulation step on the amplitude of the target signal is also shown. The correspondence between analytical expressions and real modulation step of interferometric signal has been verified by means of numeric simulation.