Femtosecond Laser-Induced in-Fiber Composite Micro-Cavity Array for High-Performance Distributed High-Temperature Sensing

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 hotspots or microlesion. Here, we proposed and experimentally demonstrated in-fiber composite micro-cavity array (CMCA) assisted by using spatial-reflection-correlation spectra mapping design method (SRCSM) 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 was used for temperature demodulation. With optimal SRCSM, the composite micro-cavities (CMCs) displayed great suppression of sub-peaks and large envelope of the cross-correlation spectra, hence illustrated the better stability and larger dynamic range in temperature sensing compared with single micro-cavity with same density. The standard deviation decreases from 1.6 GHz to 0.033 GHz. The dynamic range was increased by 10 times with similar accuracy while the length of the sensing unit is same as 1 mm. The correct demodulation of the optimal designed CMCA show great robustness improvement. Moreover, the accuracy improvement at high temperature of 700 ℃ was nearly 30-fold with the spatial resolution of 1 mm and the dynamic range of ~700 ℃. The demodulation accuracy could be low as 0.0016 ℃ 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.