A Temperature-Insensitive Multipoint Displacement Sensing System Based on Fiber Macro-Bending Loss

We proposed a novel, temperature-insensitive, low-cost multipoint displacement sensing system. The system includes three parts: fiber displacement sensor, fiber loop mirror (FLM), and optical time-domain reflectometer (OTDR). The fiber displacement sensor is designed by cascading single-mode-no-core-single-mode (SNS) fiber, and the SNS is attached to FLM that is constructed by a 3-dB coupler to improve the measurement dynamic range. The variation of displacement will significantly change the value of SNS macro-bending loss, which causes the variation of FLM reflected energy to achieve displacement measurement. Each FLM constitutes a displacement sensing unit, and only 5% pulsed light energy is input for each sensing unit to increase the number of reusable sensors. The results show that each sensor can maintain a similar sensing effect, and the measurement dynamic range can reach 15.613 dB. The peak energy of each FLM is almost unaffected by changes in the external temperature. The proposed system is an ideal solution to engineering problems of displacement measurement, which can be widely used in the field of structural health monitoring.