Sectional Sensitivity in RI Sensor During Mode Transition With Regenerative Cladding Layer

In this letter, we propose and investigate a refractive index (RI) sensor with sectional sensitivity based on cladding-regenerated long period fiber grating (CR-LPFG). The CR-LPFG is fabricated by using CO2 laser to polish on the composite structure of single-mode fibers(SMFs) spliced with multi-mode fibers(MMFs). The operating mechanism of the CO2 laser results in the removal of the original cladding of the MMFs and the creation of a new refractive index layer on the core. This technique, initially proposed by us, aims to enhance sensitivity to the external environment by facilitating the exposure of evanescent field and increasing the core diameter mismatch. The experimental results demonstrate that the refractive index sensitivity of the sensor is 396.39 nm/RIU, 1878.60 nm/RIU, and 663.32 nm/RIU in the intervals of 1.3321-1.3605 RIU, 1.3605-1.3858 RIU, and 1.3858-1.4190 RIU, respectively. The mode transition results in a phenomenon of sensitivity segmentation, offering various options to meet different needs in practical applications. Therefore, we propose a cost-effective refractive index sensor with high application potential.