Fabrication And Characterization Of High Sensitive Fiber-polymers Integrated Temperature Sensing Structures

Temperature monitoring has important significance in the field of industry, agriculture and bio-medicals. The fiber optic sensors have attracted more and more attention in temperature sensing owing to the advantages of small size, fast response, corrosion resistance and immunity to electromagnetic interference. At present, the different fiber temperature sensors have been proposed, such as fiber gratings and fiber interferometers. The sensors based on the fiber optic interferometers have the advantages of small size, light weight, easy manufacture and good transmission performance, etc. But their temperature sensitivities are not high enough due to the small thermo-optic coefficient(TOC) and thermo-expand coefficient(TEC) of silica. In this paper, the fiber-polymer integrated temperature sensing structure based on SU-8 photoresist is proposed and fabricated by the femtosecond laser two-photon polymerization method. The main of research work has been summarized as follow:Firstly, we have proposed and fabricated a fiber-polymer integrated temperature sensing structure based on SU-8 photoresist, which could be used for measurement of temperature and refractive index(RI). It is formed by fabricating a suspended waveguide structure based on SU-8 photoresist in an optical fiber microcavity, which forms a fiber in-line Mach-Zehnder interferometer. We analyze the optical transmission properties of the fiber-polymer integrated temperature sensing structure based on SU-8 photoresist. Its interference spectrum is simulated by using Rsoft software. Then the temperature sensitivity and refractive index sensitivity of the fiber-polymer integrated temperature sensing structure based on SU-8 photoresist are calculated. Then, the temperature and refractive index sensing properties of the structure were investigated experimentally. The temperature sensitivity is-478pm/°C(based on the wavelength shift in the temperature range of 25oC-65oC), which is one order of magnitude higher than that of pure optical fiber temperature sensor. The refractive index sensitivity reaches as high as-8178.086nm/RIU(based on peak intensity measurement in the RI range of 1.333-1.342).Secondly, we have proposed and fabricated fiber-polymer integrated temperature sensing structure based on double SU-8 photoresist, which could be used for measurement of temperature. The non-exposed liquid SU-8 photoresist was sealed in the sensing structure in order to decrease the refractive index difference and increase the thermo-optic coefficient difference. By this way a fiber-polymer integrated temperature sensor with higher sensitivity was achieved. Experimental results of the temperature sensing experiment show that the temperature sensitivity reaches as high as 2.529nm/°C, which is one order of magnitude higher than that of the above optical fiber temperature sensor with air-filled cavity.