Demodulation of EFPI-FBG Hybrid Optical Microphone Based on Spectrum Analysis

Based on spectrum analysis technology, a fast demodulation method is proposed to sense the acoustic and temperature with EFPI-FBG hybrid optical microphone accurately. Separating the EFPI and FBG spectrum from the obtained EFPI-FBG superimposed spectrum, frequency estimation based on total phase method and peak-searching based on quadratic polynomial fitting method were adopted to calculate the F-P cavity's length and the central wavelength of the FBG. The detailed simulation showed that the proposed method has the capabilities to detect the change of the F-P cavity's length and the drift of the FBG's central wavelength with a high speed and accuracy. By applying the proposed method to a homemade diaphragm-based EFPI-FBG hybrid optical microphone, the acoustic and temperature could be recovered successfully. The acoustic sensing error caused by the temperature could be reduced from 75% to 10%.