Research On Sensing Characteristics Of Photosensitive Polymer-Based Micro-Nano Long-Period Fiber Grating

The performance of the sensor depends on its signal carrier and structure.After decades of development,long-period fiber grating(LPFG)has become an important part of the sensor,with the advantages of small size,mature production process,high sensitivity,no backward reflection,and low loss.LPFG shows a good application prospect in life,production and technology.The development of LPFG sensors is mainly reflected in the areas of high sensitivity,miniaturization,and low cost.Although a great deal of work has been done on LPFG research,the design of excellent LPFGs with different structures and fabrication methods is still one of the important research goals in the field of sensing.The development of microfabrication techniques and materials provides a good basis and ideas for LPFG sensor design.Using a micromachined 3D adjustment frame to manipulate the carrier with a suspended polymer,the polymer is brushed axially across the tapered waist region of the polished micro-nano-fiber(MNF)at a uniform speed.According to the Plateau-Rayleigh instability(PRI)effect,the liquid film on the MNF surface rapidly splits spontaneously into a series of polymer dots,and form a cladding perturbation structure,resulting in a kind of LPFG based on MNF and photosensitive polymer.The LPFG has a high flexibility with the grating parameters.Simulations are used to optimize the grid parameters and LPFG performance.The size of our LPFG is small because of the strong refractive index(RI)of the cladding structure.Based on the strong evanescent field of MNF,the strong coupling of cladding modulation structure and the excitation of high-order cladding modes,our LPFG can achieve high sensing sensitivity.The photosensitive polymer material can be cured quickly.By combining LPFG with sensitive materials,the LPFG is used to complete RI,humidity,and temperature sensing experiments.Through theoretical derivation and simulation,the feasibility of the LPFG proposed in this thesis is verified.This thesis obtains the transmission spectrum and RI sensing results of the LPFG are compared and analyzed for different grating parameters,which include MNF diameter,grating period,polymer dot height and RI.The PRI effect is investigated by completing brush coating experiments based on polymers on the surface of MNFs with different diameters.Combining the results of simulation optimization and brush coating comparison experiments,LPFG samples were fabricated.The RI sensing experiments were completed with a maximum RI sensitivity of 10419 nm/RIU.This dissertation also completed experiments and analyses of invertibility,temperature crosstalk and time stability related to the RI sensing experiment.The moisture-sensitive material coated LPFG monitored the humidity-sensing response.The polymer was replaced by a curable temperature-sensitive material,and the samples were monitored for a temperature-sensing response.The LPFG proposed in this thesis has the advantages of high sensitivity,small size,a wide range of sensing applications,flexibility in fabrication method,and fast production,which have the prospect of application and advancement in the fields of environmental testing,biochemical research,and food safety.