Sensing Characteristics of Long-Period Fiber Grating Inscribed in Double Cladding Fiber

We demonstrate the sensing characteristics of high-order cladding mode by inscribing long-period fiber grating and helical long-period grating in double-cladding fiber. Torsion and surrounding refractive index characteristics were investigated experimentally. The maximum torsion sensitivity is 0.3404 nm/(rad/m).