INVESTIGATION OF OUTPUT SIGNAL AMPLITUDE DEPENDENCE IN HOMODYNE DEMODULATION SCHEME FOR PHASE FIBER-OPTIC SENSOR

The method of homodyne demodulation is widely used in interferometer fiber optic sensors. The paper deals with modeling results of output signal amplitude dependence on the amplitude of the measured phase-shift signal and phase modulation depth at the carrier frequency. Optimal phase modulation depth at the carrier frequency, which corresponds to the maximum value of the output signal, is defined as C=2.373 rad. Nonlinear character of the amplitude dependence of the output signal on the amplitude of the measured phase-shift signal is shown for the first time. Detailed mathematical analysis of obtained dependencies is given, which shows the opportunity for increasing of the linear part of the homodyne demodulation scheme amplitude response by widening the lowpass filter passband, favoring the input signal dynamic range increase. According to received results, for the measured phase-shift signal at frequency 500 Hz, low-pass passband increasing from 500 Hz to 1500 Hz leads to increasing of the size of the amplitude response linear part from 1.1 rad to 2.9 rad, i.e. input signal dynamic range increases up to 8.42 dB. Mathematical method of optimal low-pass passband calculating is proposed, providing the linearity of the demodulation scheme amplitude response in the specified range of input impact.