Sensitivity-Adjustable Strain Sensor Based on Shrinking Long Period Fiber Grating

In this letter, a novel shrinking long period fiber grating (S-LPFG) is designed. This strain sensor is fabricated through mechanical polishing and arc-discharging, allowing for certain control over its sensitivity to strain. The single-mode fiber (SMF) is first preprocessed into a D-shaped fiber (DSF) through polishing. Then, a periodic melting-induced shrinking is applied to the fiber through arc-discharging modulation. The polishing and shrinking enhance the asymmetry of the single-mode fiber. The discharge modulation enables convenient control of the mode order coupling efficiency and the shrinking level of the sensor, thereby effectively controlling and improving the strain sensitivity. The experimental results indicate that strain sensors with three levels of sensitivity, namely high, medium, and low sensitivity, are obtained by controlling the number of discharges. The high strain sensitivity reaches an ultra-high value of 174 pm/ $\mu \varepsilon $ within the range of $0- 100 \; \mu \varepsilon $ . These adjustable sensitivity sensors have great potential for various application scenarios.