Optimizing The Interrogation Method Of A Tilted Fiber Grating For Glucose Measurement

Fiber-optic sensors have the advantages of small size,immunity to electromagnetic field,good biocompatibility,and high sensitivity,making them widely used for temperature,pressure,curvature and biological detection.Among fiber-optic sensors,tilted fiber Bragg grating(TFBG)has attracted great attentions because it simultaneously possesses advantages of a fiber Bragg grating and a long period grating.In this thesis,we first briefly describe the working principle and the spectral response of an TFBG;and then we present an optimizable algorithm for TFBG interrogation;finally,we apply the TFBG for glucose measurement.The optimizable algorithm for TFBG interrogation was based on quickly labelling and measuring the cladding modes within the refractive index-induced spectral responses.The algorithm was carried out in three steps: 1)peak recognition based on serial number and selection of potentially most sensitive cladding mode region;2)select the most sensitive cladding mode from the potentially most sensitive cladding mode region;3)using the Cladding mode fitting technique to improve the efficiency and resolution of Surrounding refraction index(SRI)measurement.The experimental results show that when the wavelength resolution of Optical spectrum analyzer(OSA)decreases,the scanning speed increases,but SRI sensitivity also decreases.Through the calculation of parabolic equation and weighted Gaussian fitting of original data,the reduction of SRI sensitivity caused by the reduction of wavelength resolution can be alleviated,the SRI sensitivity of the sensor can be improved up to 18% in comparison to that directly obtained from the original data.To detect glucose,the fiber surface of an TFBG was covered with a layer of graphene oxide(GO)first,and then the pyrene boric acid(PBA)was immobilized on the GO layer serving as bio-detector for glucose.Experimental results show that our glucose sensor can provide a limit of detection(LOD)of 10 p M,and has a good linearity in the concentration range of 1 – 10 m M.In addition,we also applied our sensor for practical measurement of blood glucose in serums from diabetic patients,and the results were similar to that from a commercial glucose meter.In order to further enhance the sensitivity of our sensor for glucose detection,we coated a 50 nm-thick gold film over the TFBG surface to excite surface plasmon resonance,and then covered successively a GO layer and the PBA on the metallic surface.Experimental results show that the LOD of the sensor can reach 1 f M,and it has a good linearity in the range of 1 f M-10 p M.Additionally,we also used our sensor for blood glucose measurement,providing performances similar to a glucose meter.