Research On Highly Sensitive Temperature Sensor Technology Based On Micro/Nano Fiber Knot Ring

In recent years,optical fiber sensors have been widely concerned by domestic and foreign scholars because of their electromagnetic interference,chemical corrosion resistance,high integration,high sensitivity,long-distance sensing,low price and easy mass production.With the development of the science and technology,the demand for miniature and integrated sensor components is gradually increasing.Fiber sensors based on micro/nano fiber play the leading role.The evanescent field generated by the micro/nano fiber results in the high sensitivity response to the changes of the external environment.In addition to the advantages of the optical fiber sensors mentioned above,micro/nano optical fiber sensors also have the advantages of fast response,low transmission loss and small size,which are outstanding compared with that of the ordinary optical fiber sensors.In this thesis,based on the optical characteristics of micro-nano fiber and the structural characteristics of the ring resonator,a knot sensor based on micro/nano fiber is fabricated,and experimentally demonstrated with the excellent temperature sensing performance.In view of the advantages of the high ratio evanescent field of the micro/nano fiber being sensitive to external changes,and the disadvantages of the extremely small diameter and easy to break,the surface being easily contaminated with dust,the difficulty of storage and the low practicability,this thesis will improve the performance of the knot micro/nano fiber resonator.Theoretical study and experimental research are carried out to study the corresponding sensitivity,structural stability,service life and practicality of the knot micro/nano fiber resonator.The main contents are listed as follows:(1)The evanescent field transmission principle and optical characteristics of the micro/nano fiber are analyzed theoretically,as well as the optical transmission principle of the micro/nano fiber ring resonator.The commonly methods for preparing micro/nano fiber were compared and analyzed.The high efficiency flame scanning method and taper drawing machine were chosen to prepare the micro/nano fibers with high uniformity of diameter.(2)The structure characteristics,optical sensing characteristics and preparation methods of three kinds of ring micro/nano fiber resonators were analyzed and compared.In this thesis,the knot resonance model was selected and the preparation method was the direct knotting method with simple process and low loss.The research assumption of applying knot micro/nano fiber resonator to explore the temperature probe was proposed.The output spectrum of the knot micro/nano fiber resonator was obtained by theoretical analysis and simulation to study the depending relationship between the sensing performance and the structural parameters.(3)The sensitivity and stability of the knot micro/nano fiber resonator were improved by analyzing and selecting appropriate packaging materials.PDMS with high thermal expansion coefficient and high thermal optical coefficient was selected as packaging material.The temperature sensing principle of the knot micro/nano fiber resonator encapsulated with PDMS film was studied.(4)The PDMS solution was prepared,and the micron scale micro/nano fiber with smooth surface and uniform diameter was prepared by flame scanning method.The knot micro/nano fiber resonator was prepared by direct knotting method.By selecting the appropriate heating method at high temperature to cure PDMS solution,the temperature sensor chip was finally obtained.(5)The temperature measurement experiment system based on the knot micro/nano fiber resonator was built.The highest sensitivity of the knot micro/nano fiber resonator was experimentally demonstrated with 12nm/℃.Where,the probe has a loop length of 95 μ m,and the coupling area micro/nano fiber diameter is 2 μm.The effects of the ring length and the micro/nano fiber diameter of the coupling area on the temperature sensing performance were compared.The experimental results meet well with that of the theoretical analysis.(6)An elliptical knot micro/nano fiber resonator was fabricated,and temperature measurement experiments were carried out.The highest sensitivity of elliptical knot micro/nano fiber resonator was obtained as 28.12nm/℃ with a good linearity.The experimental results show that the structure has high sensitivity and good stability.