Demodulation of Fiber Bragg Grating Accelerometer Using In-Line Sagnac Interferometers

Abstract

We proposed a fiber Bragg grating (FBG) accelerometer demodulation method based an in-line Sagnac interferometric structure. In this method, an electro-optical phase modulator (EOM) is used as a phase-generating carrier (PGC) modulation module. The principle of in-line Sagnac optical path interference based on EOM is theoretically analyzed by Jones matrix, and the modulation mechanism of EOM is described. The experimental results of an FBG accelerometer based on flexible hinge show that the system background noise is <inline-formula> <tex-math notation="LaTeX">$1 \times {10^{ - 5}}\,\,{{\mathrm {rad}}} \cdot {{\mathrm {Hz}}^{-1 /2}}$ </tex-math></inline-formula>. The EOM based modulation scheme solves the problem of distortion of demodulation response due to the unstable modulation performance of the conventional piezoelectric transducer, which also provides a fast response to the interferometric optical path changes. The sensitivity of the in-line Sagnac based demodulation scheme is doubled compared to the Sagnac ring structure. The proposed scheme provides an integrated phase modulator for demodulation system for FBG sensors.