Multiplexable intrinsic Fabry-Perot interferometers inscribed by femtosecond laser for vibration measurement in high temperature environments

This paper reports fabrication technique and demodulation algorithm developments to use multiplexable intrinsic Fabry-Perot interferometer (IFPI) fiber sensor array for distributed vibration measurements at high temperatures. Using femtosecond laser direct writing scheme, IFPI array were fabricated through laser-induced Type II scattering points in single mode fiber cores. Reflection spectra of IFPI array were demodulated in real-time using modified Bunemen frequency analysis. The demodulation algorithm, which was implemented using a photodetector-array spectrometer, achieves 64-n epsilon dynamic strain resolution at 1-kHz spectral acquisition rate and 2-kHz maximum vibration bandwidth. Performance and stabilities of IFPI sensor array were characterized from room temperatures to 800 degrees C. The static strain resolution was 0.6 mu epsilon and the minimum detectable dynamic strain amplitude was 23 n epsilon/root Hz at 800 degrees C. The multiplex performance was also tested by measuring dynamic strain in time domain through six IFPI sensor array fabricated in one fiber. This paper presents an integrated and low-cost sensing solution to perform distributed vibration measurements in harsh environments. (C) 2021 Published by Elsevier B.V.