Suppression of quantization noise in fibre optic Sagnac interferometer

Two light beams are modulated by a phase modulator provided in fiber coil (1). An analog-to-digital converter (2) is arranged to convert analog phase shift signal of light beam detected by photodetector into digital output signal. An adder (5) is arranged to add the digital output signal with amplified sign corrected residual value signal output by delay element (12). The added output signal is outputted to digital-to-analog converter (3). The digital phase reset signal is calculated based on assistance of main control circuit of evaluation circuit and output of digital-to-analog converter. An independent claim is included for interferometric sensor.