Real-Time Self-Calibrating Phase-Shifted Demodulation Method Based on Polarized Low-Coherence Interference for Optical Fiber Acoustic Sensor

Abstract

A real-time self-calibrating quadrature phase-shift demodulation method for external Fabry–Perot interferometric (EFPI) sensors is proposed and demonstrated. Two birefringent crystal blocks with matching lengths are used to generate two orthogonal interference signals, and the third rotating birefringent crystal block is used as a compensation path for real-time normalization of two orthogonal interference signals. The signals are finally processed by the differential cross multiplication (DCM) algorithm demodulation. Experimental results show that the demodulation scheme can not only correctly demodulate low-frequency dynamic signals but also demodulate ultrasonic signals with high stability and high speed, and has a signal-to-noise ratio (SNR) of up to 90 dB. When the sensor cavity length drifts between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 4.94\,\,\mu \text{m}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.584 ~\mu \text{m}$ </tex-math></inline-formula> , it still has stable demodulation performance and is suitable for EFPI sensors with different diaphragms. The demodulation scheme provides a simple, effective, high-speed, and robust solution for dynamic signal measurement in complex environments based on real-time self-calibrating, which demonstrates great potential in practical engineering applications.