Phase-shifted demodulation scheme for fiber-optic interferometric sensors with combined waveform phase modulation

Abstract

We propose and demonstrate a demodulation scheme for interferometric optical fiber sensing using combined waveform phase modulation. The method is based on a designed combined waveform and time-division separation technology, which moves the target signal to the sidebands of the carrier signal and eliminates the influence of residual direct current (DC) term and low-frequency intensity noise by filtering the detector signal directly. The effect of the modulation-to-target ratio (MTR) defined as the ratio of the modulation frequency to the target frequency on the demodulation results is also discussed. Both simulations and experiments verify the ability to obtain a pair of quadrature signals. The experimental results indicate that the phase resolution of the system is 1.1 × 10−6 rad/√Hz@2 kHz when the MTR is 625, and 5 × 10−6 rad/√Hz@2 kHz when the MTR is 25, while demonstrating excellent demodulation consistency. This work not only has the advantages of carrier modulation methods, but also does not need to generate analog signals for mixing, which provides guidance for high-sensitivity phase demodulation technology.