Investigation On The Broadband Spectrum Of Evanescent Wave Optical Fiber Chemical Sensor

Compared with traditional optic al fiber sensor,intrinsic evanescent wave optical fiber sensor has the advantages of simple structure,rapid respond,broad spectral range,low cost for detecting element of substance and measuring the amount of the specified substance,and it has became an important direction of research and development.In this paper,a long segmented structure optic fiber sensor is proposed and demonstrated;it is based on evanescent wave absorption theory.The waveguide modes of the intrinsic straight and segmented structure are simulated and analyzed by using beam propagation method(BPM),and build a broadband spectral analysis and detection system,experimental verification is performed.The characteristics of long segmented structure evanescent wave optical fiber chemical sensor are analyzed from three aspects: theory,simulation and experiment.In this essay,the sensing principle of evanescent wave based on ray theory is obtained by optical field distribution and absorption loss.The theory model of evanescent wave optical fiber sensor is built based on sensing principle of evanescent wave.The relationship between sensitivity and geometrical structure parameters of evanescent wave optical fiber sensor are calculated and analyzed by using the FD-BPM.Based on the result of theoretical and numerical analyses and the primary experimental study,a long segmented structure evanescent wave optical fiber sensor is designed and fabricated.The sensors are made by using the chemical corrosion method.The sensitivity of the sensors is tested by using different concentrations methylene blue solution.The experimental results show that with the thinner of core diameters,the longer of the sensing region and the more number of segments,the sensitivity of the sensor will be improved.And the water quality parameters are measured by using fiber evanescent wave sensors.The concentration of permanganate and phosphate ions in water quality monitoring indicators are researched,and establishedthe relation curve of the concentration of a substance and measuring the absorbance,the results show that the two have a good linear relationship.It has an important practical guiding significance for optical fiber evanescent wave sensor provides a theoretical model in the actual water quality monitoring.The process of fabrication and experimental show that the sensitivity of this sensor is higher,the detection limit is lower,and the problems such as sensing fiber is so thin that sensor not easy to packaging,sensing fiber is so long that sensing system not easy to design and construct were solved effectively.The evanescent wave optical fiber sensor has the advantages of high sensitivity,rapid respond,simple structure,easy to fabricated,easy to fabricated,easy to packaging,good repeatability and it has wide prospects for the development and application.