Research On Cholesterol Biosensing Based On Tilted Fiber Bragg Grating

Fiber grating is a new type of passive device.It has the advantages of light weight,less susceptibility to electromagnetic interference,corrosion resistance,low loss,good reusability,and the ability to seamlessly couple with optical fibers.It can be widely used in the field of optical fiber communication and sensing.Among them,tilted fiber Bragg gratings(TFBGs)is an emerging member of the fiber grating family.TFBGs has a special structure with a certain angle between the wave vector direction of the grating surface and the axial direction of the fiber core,resulted in a complex mode coupling between the fiber core and the cladding.Therefore,it is sensitive to the external environment and can be widely used in the field of sensing.Cholesterol is an indispensable and important substance in human and animal tissue cells.The detection of cholesterol solution concentration plays a very important role in the field of biomedicine.Therefore,based on the sensing mechanism of tilted fiber Bragg grating,this thesis designs a simple and efficient tilted fiber Bragg grating sensor through theoretical analysis,simulation and experiment.It is used for sensing and detecting the concentration of cholesterol solution,and explores the concentration sensing when temperature changes.A method is proposed to solve the cross-sensitivity of TFBGs cladding mode to temperature and concentration.The research conclusion provides a simple and new method for the detection of cholesterol solution,and provides a reference for future research on fat-soluble solutions.The main contents are as follows:1.The Opti Grating optical simulation software was used to simulate the transmission spectrum of the tilted fiber Bragg gratings,and the effects of grating inclination,grating length,grating period,core radius,cladding radius,etc.on the transmission spectrum of the tilted fiber Bragg gratings were analyzed and simulated.Summarized the mutual compensation effect between various parameters.The sensing properties of tilted fiber grating to the change of refractive index of the external environment are studied.The results show that the resonant wavelength of the core mode and the transmission loss of the resonant peak are not affected by the refractive index of the external environment,but the resonant peak of the cladding mode increases with the increase of the refractive index of the external environment,and the effective area of the cladding mode gradually decreases.Wavelength drifts to the long wavelength direction.2.A simple and practical sensor based on tilted fiber grating was designed to detect cholesterol solution with a target concentration range of 0.2?4.0 mg/ml.The TFBGs embedded in the fiber core makes the multiple cladding modes and the core mode coupled,and generates a large number of resonance peaks in the transmission spectrum,which is used to sense changes in the external environment.The results show that as the concentration of the cholesterol solution increases,the refractive index increases,and the resonance wavelength of the cladding mode drifts toward the long wavelength with the increase of the concentration of the cholesterol solution,and its sensitivity is 0.12325 nm/(mg/ml).Based on the cholesterol solution sensing experiment,we explore the influence of external temperature changes on concentration sensing.In the temperature range of 25??70?,with the increase of temperature,the resonant wavelength drifts toward the long-wavelength direction.The cladding mode and the core mode are basically similar in sensitivity to temperature and have good linearity.Therefore,the differential wavelength of TFBGs core mode and cladding mode can be used to eliminate the interference of temperature on solution concentration measurement,which can solve the cross-sensitivity of TFBGs cladding mode to temperature and concentration.