Research On Optical Fiber Sensor For Water Pollution Detection

Water pollution detection is generally the concentration detection of pollutants.From the 1970 s,research on online detection systems suitable for various purposes has been conducted internationally.But up to now,chemical analysis is still the main research method in the field of water quality detection,which can not achieve fast detection.The frequent occurrence of water pollution incidents requires the development of water pollution detection towards miniaturization,in-situ and portability.The optical fiber sensing technology has the unique advantages of corrosion resistance,electrical insulation,and online monitoring in the field of water pollution detection.Microfibers stand out due to their excellent performance such as fast response,high sensitivity,low energy consumption,strong evanescent field,and real-time monitoring.For the detection of water pollution detection,this paper uses the strong evanescent field characteristics of microfibers to build microfiber sensors.By designing the sensing structure of different types of microfibers,the propagation characteristics of light are analyzed,and the sensing characteristics are analyzed theoretically and experimentally,and high precision and sensitivity sensing are realized,which provides a new method for online detection of water pollution.The main contents of this paper includes:(1)The basic structure of tilted fiber grating(TFBG)and the fabrication method of microfiber are summarized.The mode characteristics of tilted fiber grating and the mode distribution characteristics of microfiber are analyzed theoretically.For TFBG,due to the inclination angle,in addition to the mode coupling between core modes,there are also core and cladding mode couplings.For microfibers,as the fiber diameter decreases,the core’s ability to confine the light field weakens,the energy of the evanescent field increases,and it becomes more sensitive to changes in the external environment.(2)A tilted fiber Bragg grating sensor and a micro-fiber coupler-based sensor for detecting the BOD concentration in water pollution were proposed and implemented.The sensing mechanism of these two sensors is analyzed,and the characteristics of these two sensors under different BOD concentrations are experimentally studied.(3)Three kinds of micro-fiber sensors for detecting chloride ion concentration were proposed and implemented,and the real-time monitoring of chloride ion concentration changes was realized.The mode interference of the micro-fiber structure was analyzed theoretically,and the sensor structure was numerically calculated by Rsoft and Matlab.The response relationship between the three kinds of optical fiber sensors used to detect the chloride ion concentration and the chloride ion solution concentration change was experimentally studied.