| Due to its unprecedented structure design and unique light-controlling capability.Photonic crystal fiber?PCF?has attracted extensive attention in the optical fiber field.Especially,the PCF based on functional material filling provides a broader space for the development of the optical fiber sensing field.The sensing measurement of external parameters can be realized by filling different functional materials in cladding holes of the PCF,which greatly enriches the means of the sensing detection.Based on the existing research status,this paper starts from the sensor design of PCF,the sensing properties of PCF sensors based on different functional materials and sensing methods are investigated based on finite element method.The main research contents are as follows:Firstly,a highly sensitive bending sensor with temperature-compensation based on magnetic fluids?MF?infiltrated PCFis presented.Specific cladding air-holes are filled with MF material to form defective channels and introduce new degrees of freedom for fiber sensing.The structure designed in such way can achieve simultaneous measurement of bend-curvature and bend-direction with temperature compensation.The bending sensitivity can reach to-6.544nm/m-11 with a high linearity within the range of curvature from-10 m-1 to 10m-1.The proposed two-dimensional?2D?bending vector sensor cannot only improve the sensing precision and measurement range,but also reduce the metrical difficulty and simplify the process.Secondly,a high-sensitive refractive index?RI?measuring method is proposed through the combined use of elliptical core PCF and Sagnac interferometer.We analyze the phase birefringence and group birefringence to obtain the dependence of RI sensitivity on the operable wavelength?.The RI sensitivity can be enhanced 10 to 20times by introducing a liquid-filled elliptical hole into the fiber core.Additionally,the single-core structure can convert to twin-core just through decreasing the RI of filling liquid,and the spectral response is adjustable via changing main structural parameters.Within the RI range of 1.463-1.467,the average sensitivity up to 114967nm/RIU,which corresponds to a resolution of 1.74×10-6 RIU.Finally,the sensing method is applied to magnetic-field measurement for an example,and the magnetic-field sensitivity can reach up to 3.45 nm/Oe within the range of 89.9-271.0 Oe.The measurement principle also applies to other sensing fields,and the proposed sensor is insensitive to fiber bending without fabrication complexity.Thirdly,a modified D-shaped PCF based on Sagnac interferometer is designed for methane concentration sensing.Two ultra-large air holes with methane-sensitive film are distributed horizontally in the PCF to shorten response time.Besides,a defect hole is introduced into the fiber core and theoretical analysis is carried out to enhance the sensing sensitivity.The dependence of gas sensitivity on the operable wavelength?is obtained by analyzing the phase birefringence B??,C?and group birefringence Bg??,C?.The average gas sensitivity is as high as 36.64 nm/%in the sensing range of 0 to 3.5%.The modified D-Shaped and highly sensitive PCF sensor exhibits immunity to cross-sensitivity,and provides a new design idea for methane gas monitoring.Finally,a high-sensitive methane sensor based on a twin-core PCF is proposed and analyzed.Two ultra-large side-holes of the PCF are polished and coated with methane-sensitive film to achieve fast response and high sensitivity.The finite element method?FEM?is used to analyze the relationship between gas sensing performance and structural parameters.Within the detection range of 0%-3%,the gas sensitivity and low detection limit can reach to 4.60nm/%and 435ppm,respectively.The proposed sensor with high sensitivity and simple structure has great practical value and application prospects for environmental gas monitoring.The paper has 53 graphs,13 tables,and 130 references. |
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