Sensing Characteristics of Helical Long-Period Grating Inscribed in Graded Index Few Mode Fiber

Helical long-period grating fabricated in graded-index few-mode fiber was experimentally demonstrated. The high sensitivities corresponding to torque, curvature, temperature and surrounding refractive index are up to 0.293 nm/rad/m, 2.486nm/m
^-1
, 0.095 nm/□ and 1242 nm/RIU, respectively.