Property And Application Of Sensors Based On Concatenated Fiber Grating And Peanut-shape Structure

Fiber optic sensors have wide applications in sensing fields due to anti-electromagetic interference, high sensitivity, compact and corrosion resistance. In this paper, two fiber optic sensors, namely concatenated fiber Bragg grating(FBG) and peanut-shape structure and concatenated tilted fiber Bragg grating(TFBG) and peanut-shape structure, were put forward. The bending sensing and temperature sensing properties of them were studied. The main results as follows:1. A all fiber optic sensor based on concatenated fiber Bragg grating(FBG) and peanut-shape structure was put forward. The mode-coupled theroy was employed to analyze the bending sensing properties of the sensor. The results show that the introduction of peanut-shape structure can effectively enhance the coupling between core mode and cladding modes inside FBG. Based on beam propagating method, Rsoft software was used to simulate light transmission of peanut-shape structure, which reveals that peanut-shape structure can effectively excite cladding modes. What’s more, core mode power decrease with the diameters of peanut-shape structure.2. The peanut-shape structures were spliced by setting optimized parameters of fiber fusion machine, which was then spliced with FBG to obtain the sensor based on concatenated fiber Bragg grating(FBG) and peanut-shape structure. An all-fiber sensing setup was established and their bending sensing and temperature sensing properties were measured. The results show that cladding modes power decreases with the fiber curvature. However, core mode power keep stable. The cladding modes power falls 4.64 dB when the fiber curvature increases from 0 to 2.2m-1. The reflected spectra shift toward longer wavelength with the increase of environmental temperature. The peak wavelengths of reflected spectra increase 0.6nm when environmental temperature increases from 20℃ to 80℃. However, cladding modes power and core mode power have no obvious changes.3. A all fiber optic sensor based on concatenated tilted fiber Bragg grating(TFBG) and peanut-shape structure was proposed and fabricated. Then an all fiber sensing setup was established. Bending performance of the sensor was studied. The results show that the introduction of TFBG greatly increased the reflection cladding modes power. The collected cladding modes power increased by 38 dB, compared with the sensor based on concatenated fiber Bragg grating(FBG) and peanut-shape structure Besides, with the curvature increasing from 0 m-1 to 1.77 m-1, the collected cladding modes power dropped 2dB.