High Sensitivity Refractive Index Sensor Based on the Cladding Mode of Long-Period Grating Inscribed in Few-Mode Fiber

The surrounding refractive index (SRI) sensing characteristics of cladding mode in a few-mode fiber are investigated experimentally. In the range of
$\mathbf{1.33 \sim 1.43}$
, the SRI sensitivity of
$\mathbf{LP_{05}}$
mode is 5.30 times that of single-mode fiber.