| Optical fiber grating is a kind of passive device with refractive index modulation in the core,which realizes the modulation of the transmitted cladding modes of the optical fiber grating.Due to the special structure of the excessively tilted fiber grating with a large tilted angle,which usually exceeds 66.9 degrees,and the circular symmetry of the fiber is destroyed,so it has strong polarization characteristics.The higher order cladding modes transmitted in the grating are sensitive to the external refractive index environment,which makes the excessively tilted fiber grating widely studied in the field of sensing.Concerning on the sensing characteristics and applications of the excessively tilted fiber grating,the dissertation focuses on the mode coupling characteristics,vector refractive index sensing,sensitivity controllable and pH modulated repeatable biochemical sensing applications.The main contents of the dissertation include:（1）Based on the coupled mode theory,the asymmetric mode coupling characteristics of the excessively tilted fiber grating is explained,and the mode coupling mainly occurs between the core symmetric mode and the cladding non-circular symmetric LP1m mode.The theoretical analysis and experimental investigation of the mode distribution of the excessively tilted fiber grating show that the its mode distribution is non-circular symmetric,which caused that the excessively tilted fiber grating has the refractive index vector sensing property according to the refractive index sensing theory.Additionally,the one-sided immersion experiment is designed to verify the vector sensing characteristics of excessively tilted fiber grating.（2）An optical fiber biosensor sensing model based on Langmuir adsorption theory is adopted to explain the sensitization mechanism based on two-dimensional material functionalized excessively tilted fiber grating,and the response state of the biosensor under different adsorption equilibrium constants is also analyzed.By preparing hemoglobin biosensors with excessively tilted fiber grating functionalized different amounts of the graphene oxide,and the results showed that the wavelength drift of the biosensors with 0.57nm,1.14 nm,1.61 nm and 4.34 nm corresponded to the response sensitivity of hemoglobin molecules solution of 2.46 nm/（mg/mL）,3.83 nm/（mg/mL）,4.33 nm/（mg/mL）and 8.21nm/（mg/mL）,while the maximum detection ranges are 1.0 mg/mL,0.8 mg/mL,0.6 mg/ml and0.4 mg/ml,respectively.The experimental results are consistent with the Langmuir adsorption theory,which shows that the slope of linear perception of biosensor increases with the increase of graphene oxide modification and the range of linear variation decreases with the increase of graphene oxide modification.And the results provide a design theory for biosensors with controllable sensitivity and detection range.（3）To address the issue of non-reusable optical fiber biosensors,a sensing theory based on the sensor surface hydroxylation functionalization and desorption is adopted,and a recyclable sensing method of sensor surface functionalization-sensing-desorption-sensing is realized.By designing a hemoglobin biosensor based on hydroxylated excessively tilted fiber grating,the sensing performance is systematically investigated.The experiment research of the desorption of adsorbed hemoglobin is realized by utilizing the pH adjustment function with acetic acid solution and sodium hydroxide solution,and the desorption effect of the biosensor is characterized through monitoring the resonance wavelength of the biosensor,while the completion of desorption of the biosensor is verified by using fluorescent reagents.Employing the method of functionalization-sensing-desorption-sensing can not only correct the measurement error,but also make the prepared biosensor reusable for multiple times with good repeatability,whose sensitivity is about 1.098nm/（mg/mL）,and the maximum measurement error is±0.04nm,the measurement accuracy is improved. |
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