Femtosecond Laser-Induced In-Fiber Composite Microcavity Array for High-Performance Distributed High-Temperature Sensing

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Structural health monitoring is currently facing challenges of precisely capturing high-temperature distribution in some special extremely environment, such as sophisticated power chip, fuel cell, and vortex welding with tiny hot spots or microlesion. Here, we proposed and experimentally demonstrated in-fiber composite microcavity array (CMCA) assisted by using spatial-reflection-correlation spectra mapping (SRCSM) design method and femtosecond laser point-by-point technology for the performance improvement in distributed high-temperature measurement. A correlation-based algorithm by using an optical frequency-domain reflectometry (OFDR) was used for temperature demodulation. With optimal SRCSM, the composite microcavities (CMCs) displayed great suppression of subpeaks and large envelope of the cross correlation spectra, hence illustrated the better stability and larger dynamic range in temperature sensing compared with single microcavity (SMC) with the same density. The standard deviation (STD) decreases from 1.6 to 0.033 GHz. The dynamic range was increased by ten times with similar accuracy, while the length of the sensing unit is the same as 1 mm. The correct demodulation of the optimal designed CMCA shows great robustness improvement. Moreover, the accuracy improvement at high temperature of700~∘C was nearly 30-fold with the spatial resolution of 1 mm and the dynamic range of~ 700~∘C. The demodulation accuracy could be low as0.0016~∘C using multiple MCs as a sensing element. As such, the proposed CMCA by using spectra design method shows a promising method to improve sensor performance in distributed high-temperature sensing technology.