A New Spring-shaped Long-period Fiber Grating with High Strain Sensitivity

A new type of spring-shaped long-period fiber grating (S-S-LPFG) written with CO ₂ laser is proposed in this letter. A single-mode fiber is etched clockwise in four directions and any two adjacent etched regions are partially coincident in the vertical direction. The special manufacturing method makes that the S-S-LPFG has satisfactory strain sensitivity. The experimental results prove that the strain sensitivity of the S-S-LPFG is up to 30 pm/ ${\mu } \varepsilon $ with the range of 0– $700~{\mu } \varepsilon $ , which is nearly 18 times higher than that of the normal CO ₂ -laser-notched long-period fiber gratings (CO ₂ -LPFGs). The temperature sensitivity of the S-S-LPFG is also calculated from the experimental data as 37 pm/°C. It is strongly believed that the S-S-LPFG could be an excellent candidate for the strain sensors.