Design And Application Of Micro And Nano Fiber Optic Sensors Based On Polyvinyl Alcohol Sensitized Materials

The rapid development of modern society and economy has put forward higher requirements on the accuracy and real-time information.Fiber optic sensing and fiber optic communication promote and complement each other,and together promote the development of fiber optic technology.Fiber optic sensing technology provides monitoring and protection functions for fiber optic communication systems.The development of fiber optic sensing technology has also benefited from the advancement of fiber optic communication technology.The demand of fiber optic communication has driven the innovation and application expansion of fiber optic sensing technology,which has promoted the performance improvement of sensors and the continuous development of sensing technology.Fiber-optic sensors have received widespread attention because of their compact size,multiplexing,chemical inertness and resistance to electromagnetic interference.Among these sensors,micro-nano fiber-optic sensors are more popular for their real-time,miniaturization,accuracy and applicability.In this paper,based on the understanding of the principle of micro-nano optical fiber,we make deep work on the device structure and sensitization mechanism,and then design and study the application of micro-nano optical fiber sensor based on polyvinyl alcohol sensitization for relative humidity and ion detection.A fiber optic sensor based on polyvinyl alcohol film is designed and prepared that can be used to measure relative humidity.The sensor consists of winding a uniform girdle region into a ring structure after flame pulling cone using a fiber twister,and a uniform and stable polyvinyl alcohol film is formed on the surface of the ring micro-nano fiber using dip-coating method.The flame pulling taper achieves core-packet mode interference in one micro-nano fiber,and then the micro-nano fibers are wound together with a fiber twister to form a ring-shaped resonant cavity,making the sensor exceptionally sensitive to changes in the surrounding refractive index.The polyvinyl alcohol film is dip-coated on the surface of the ring structure.The change of ambient humidity affects the physical morphology and refractive index of the film material,and then changes the transmission of the optical signal.The environmental relative humidity monitoring is realized by demodulating the spectral data.Experimental results show that the sensitivity is 0.533 nm/%RH at 40%-76%RH.The sensor has a low temperature cross-sensitivity（0.0075 nm/°C）.With the advantages of low cost,high sensitivity,good stability and fast response,this sensor provides a new option for relative humidity monitoring.A sensor based on a polyvinyl alcohol composite film is designed and prepared to measure the concentration of copper ions in aqueous solutions.The sensor consists of a micro-nano optical fiber and a ternary composite sensitive film.Flame pulling cones are realized in a micro-nano optical fiber to produce core-packet mode interference,which makes it sensitive to the change of surrounding refractive index.The ternary composite sensitive film is formed by 3-aminopropyltriethoxysilane as a cross-linker between imidazole-2-carboxaldehyde and polyvinyl alcohol.The ternary composite sensitive film generates different amounts of chelates in different concentrations of copper ion solutions.The refractive index of the medium on the surface of the sensor will change to affect the transmission of optical signals.By demodulating the spectral data,the concentration of copper ions can be detected.The experimental results show that the sensitivity of the sensor is up to 7.715×10⁶ nm/M and the detection limit can reach 0.0576 ppm when the copper ion concentration changes from 0 to 10^-6 M.The sensor has good specificity,high stability and low temperature cross-response,which has guiding significance for the design of optical pollutant sensor.