Research On High Sensitivity Fiber Optic Temperature Sensor Based On Liquid Crystal

Due to the advantages of small size,light weight,high sensitivity and strong anti-electromagnetic interference capabilities,optical devices based on optical fiber have attracted strong interest from researchers in various fields.In the optical field,physical parameter measurement,biochemical field,communication The application in the field is extremely wide,and the research of the optical fiber sensor device occupies a great proportion in it.Liquid crystal(LC),as a unique material with both liquid fluidity and crystal anisotropy,its good response in temperature,electric field,magnetic field and many other aspects make it often used in sensing field.Cholesteric liquid crystal(CLC)is one of them.It can behave as a liquid crystal state at an appropriate temperature.Its molecular layers are arranged in parallel and have a periodic spiral structure.Because cholesteric liquid crystal has the characteristics of selective reflection in Bragg and high photon state density at the edge of the band gap,its application prospect is very broad.In this paper,the combination of CLC and a very small optical fiber probe is used to prepare an optical fiber sensor probe that combines the advantages of both.It also has the advantages of high resolution,high sensitivity,simple manufacturing,and small size.In this paper,a high-sensitivity optical fiber temperature sensor based on liquid crystal is proposed and studied.The fiber probe is filled with CLC,and its Bragg structure is sensitive to temperature.It can convert temperature information into reflected light,and then detect the temperature change by observing the wavelength change of reflected light.The sensor has a high temperature sensitivity,which has been experimentally proven to have a sensitivity of up to 5.71nm/?.The temperature sensor is simple in structure and extremely small in size(suitable for environments such as cells and microfluidic channels),and will become a promising candidate for monitoring temperature fluctuations in small spaces.Specific research contents include:(1)Connect the capillary tube and multimode fiber(MMF)with the fiber fusion splicer,and then prepare the fiber probes with cylindrical and conical structures respectively.A cone-shaped capillary microtube was prepared by flame heating cone pulling method,which was combined with a syringe to make a syringe device,and then the CLC used in the experiment was injected into the optical fiber sensing probe.(2)The temperature sensing characteristics of the two fiber-optic sensor probes were studied respectively,and the sensitivities of 5.71nm/? and 5.64nm/? were obtained respectively.The stability and repeatability of the two probes were also measured.In terms of structure,the tapered structure greatly reduces the volume compared to the cylindrical structure and widens its application range.(3)From the three aspects of the length of filling CLC,clearing point,and type of CLC,the factors affecting the sensing characteristics of the sensor probe are deeply studied.The influence of clearing point on liquid crystal sensing is analyzed and the temperature sensing characteristics are measured.The temperature sensing characteristics of chiral CLCs with different chiral agent concentrations and different types of chiral CLCs are tested.The experiments show that for the same CLC,the higher the chiral agent concentration,the higher the sensitivity.For different types of CLC,as the refractive index of the liquid crystal used increases,its sensitivity to temperature also increases,and the corresponding measurement range also decreases.