Strong Refractive Index Modulation LPFG Sensor Based on the Periodically Cascaded S-Shaped Fiber Core Structure

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Abstract
Strong refractive index (RI) modulation type long-period fiber grating (LPFG) has the advantages of requiring fewer modulation period and shorter sensing area length. However, during the production process, multiple types of optical fibers need to be precisely cut to a fixed length and spliced together, which leads to problems such as low fabrication repeatability and poor mechanical strength. This article proposes a strong RI modulation LPFG (SCS-LPFG) that uses only single-mode fiber and periodically constructs an S-shaped fiber core. Owing to the high degree of curvature of the S-shaped fiber core, fiber core light will directly enter the cladding in the middle of the S-shaped core for transmission, thereby achieving strong refractive index modulation. Results of the experiments demonstrate that the sensing area length of SCS-LPFG is only 2.12mm, and its sensing performance is excellent. The strain, curvature, and temperature sensitivities are 25.8pm/με, 15.6nm/m-1, and 89.7pm/°C, respectively. SCS-LPFG offers a novel approach for the fabrication of strong RI modulated LPFG, which can be integrated into precision instruments and structures with small object volumes for the detection of various physical quantities.
Funding Information
  • National Natural Science Foundation of China (61705025)
  • Technology Project Affiliated to the Education Department of Chongqing Municipality (KJZD-M202201201)
  • Natural Science Foundation of Chongqing Municipality (CSTB2023NSCQ-MSX0020)
  • Chongqing Talent Project (cstc2024ycjh-bgzxm0227, cstc2024ycjh-bgzxm0057)
  • Open Project Program of Chongqing Key Laboratory of Development and Utilization of Genuine Medicinal Materials in Three Gorges Reservoir Area (KFKT2022005)
  • Foundation of Intelligent Ecotourism Subject Group of Chongqing Three Gorges University (zhlv20221008)
  • Chongqing Three Gorges Medical College Project (XJ2023000704)
  • Fundamental Research Funds for Chongqing Three Gorges University of China (19ZDPY08)

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