Research And Application Of Optical Fiber Chemical Sensing Technology

Optical fiber chemical sensing technology is an important branch in the sensing field,combined with optical and chemical related technologies,together with optical fiber technology and chemical membrane.Optical fiber chemical sensor with miniaturization,anti-electromagnetic interference,transmission of information and other characteristics,can be widely used in chemical reaction monitoring and detection,biological research,biochemical reaction monitoring,environmental protection and ecological monitoring,medical and clinical aspects.In this paper,the preparation and application of three kinds of optical fiber chemical sensors are studied.The main contents are as follows:1.An optical fiber heavy metal ion sensor based on M-Z interferometer is proposed.The M-Z interferometer is composed of two cascaded fiber tapers.The surface of the fiberstructurewasfunctionalizedwithchitosan/polyacrylicacid?PAA?multi-membrane by the layer-by-layer self-assembly technique,the sensor was modified by multi-walled carbon nanotubes to improve the sensitivity.When the multi-membrane structure adsorbs the nickel ions(Ni²⁺)in the test solution,the dip wavelength changes due to the variation of the refractive index of the multi-membrane structure.Finally,the concentration of Ni²⁺in the solution is measured by the demodulation of light intensity.2.A volatile organic compound?VOC?optical fiber gas sensor based on polypyrrole thin film was proposed.The end of the fiber structure was coated with polypyrrole film through the interface polymerization technology.When the film absorbs the gas,a chemical effect occurs,thereby changing the resistance of the film,causing a change in the refractive index of the film,resulting in a resonance peak shift.By using intensity demodulate,we can get the concentration changes of VOC.3.An optic fiber pH sensor based on PAH/PAA multi-membrane structure was proposed.The coreless fiber was spliced in the middle of the two single-mode fiber together as the sensing structure.The pH-sensitive multi-membrane structure was coated on the fiber by layer-by-layer self-assembly technique.When the pH of the test solution changes,the swelling/shrinkage of the polymer film causes the refractive index to change due to the protonation and deprotonation of the arboxyl group.The effects of different pH of the PAH/PAA solution on sensitivity were compared.