A Multiparameter Sensor Based on Dumbbell-Shaped Double-Cladding Fiber Structure Cascaded Long Period Fiber Grating

A multi-parameter sensor based on dumbbell-shaped double-cladding fiber (DCF) structure cascaded long period fiber grating (LPFG) is proposed and fabricated. It is formed by discharging between single mode fiber (SMF) and DCF to form a waist-enlarged taper and then cascading two LPFGs. When the fiber is affected by the thermal expansion effect, thermo-optic effect and elasto-optic effect, the resonant peaks formed by inter-mode interference will shift, and the shifts generated by different resonant peaks are also different. By demodulating the wavelength shift of the three resonant peaks, the temperature, refractive index and axial strain can be measured by using the coefficient sensitivity matrix. The experimental results show that the temperature sensitivity of the three resonance peaks is 14.79 pm/°C, 69.07 pm/°C and 89.83 pm/°C in the range of 25 °C~80 °C. The refractive index sensitivities of three resonance peaks are 14.27 nm/RIU, −71.39 nm/RIU and −141.07nm/RIU in the range of 1.3355 ~ 1.3715. The axial strain sensitivities of three resonance peaks are −2.26 pm/ $\mu \varepsilon $ , −2.5pm/ $\mu \varepsilon $ and −3.14 pm/ $\mu \varepsilon $ in the range of $75 \mu \varepsilon $ ~ $525 \mu \varepsilon $ . The corresponding resolutions are 0.6905 °C, 0.00054RIU and $36.323 \mu \varepsilon $ , respectively. The sensor is simple and has good linearity. It can be widely used in environmental monitoring for different parameter.