Investigation On The Tapered Fiber Evanescent-field Of Liquid

In1966, Charles Kuen Kao of Chinese scientists first proposed the basic principle of optical fiber applications in the communications, optical fiber communications began to be widely accepted. With the successful invention of the first fiber-optic system in1981, the world began to set off a revolution of a fiber-optic communication, accompanied by the advent of optical fiber sensing technology. At present, the fiber optic sensors is varied, although the sensitivity of these devices can also achieve a higher order of magnitude, but due to the complex structure of their systems, modulation and demodulation of the signal is very troublesome, so it is not conducive to the promotion of these applications.In order to overcome this suffering, fiber optic evanescent field sensor was made. This sensor is on the basis of ordinary optical fiber tapered to obtain an evanescent field, the signal will transmission to the fiber outside through the evanescent field, interaction with the outside material, then through the analysis of the received signal processing, we can accurately obtain the useful information of the outside material, such as concentration, refractive index, etc. Compared to other sensors, this sensor production process is simple. It also has high accuracy, and easy integration. In the future of internet things, relying on fiber-optic network, these sensors will play the role of the nerve center of life, and closely related with each one of us.This thesis studied the characteristics of optical fiber evanescent field of liquid sensors, we did numerical simulation first, and then established the theoretical basis, finally carried out the experimental verification. The thesis includes the following basic points:1, the introduction section includes the basic principles of fiber optic evanescent field sensor, development status and the problems faced by.2, introduce the basic principles of fiber optic evanescent field sensor. Introduces the reasons of the evanescent field formed by, study the parameters which affect the evanescent field characteristic.3, introduce the principle of the finite element analysis method and how to use it, we set ordinary step-index fiber as an example to demonstrate how to use the COMSOL MULTIHYSICS.4, we use COMSOL MULTIPHYSICS software to study the tapered fiber which was removed cladding, the parameters include launch angle, taper length, taper ratio, etc. Then calculate the penetration depth of their evanescent wave and their energy loss, so we can get the best matching parameters of them, these can help to improve the sensitivity of the sensor device.5, the experimental section, on the basis of the numerical simulation, we calculate the fiber sensitivity of different tapered structure through the measurement of refractive index for the sodium chloride liquid, discovery that the experiment and the theory of the numerical simulation are in good agreement.