Intensity-Modulated Optical fiber Sensor Based on Dual-Dip Long-Period Fiber Gratings for Bending and Refractive Index Monitoring

We demonstrate an intensity-modulated bending and refractive index (RI) sensor based on dual-dip long-period fiber gratings (LPFGs) in single-mode fiber using electric arc discharge. As a difference from the conventional LPFGs presenting three resonances, we fabricated dual-dip LPFGs with the same period of 1200 μm in the same wavelength range from 1400 nm to 1600 nm. For the proposed dual-dip LPFGs, there is a middle peak located between the two resonance dips, whose contrast responds and varies regularly with the curvature and surrounding refractive index units (RIU) compared with conventional LPFGs. The dual-dip LPFGs present a bending sensitivity of 3.35 dB/m
^-1
with a curvature range from 1.038 to 2.506 m
^-1
and a RI sensitivity of 79.98 dB/RIU in the RI region of 1.425-1.455 RIU. Moreover, the dual-dip LPFGs shows a negligible variation of contrast on temperature. The proposed dual-dip LPFGs have potential applications for bending monitoring and RI sensing fields.