Research On Fiber Bending Sensor Based On Optical Intensity Modulation

Optical fiber bending sensors has many advantages,so it is widely used in the fields of structural health monitoring,intelligent structural bending angle measurement and so on.In the classification of optical fiber bending sensor,the principle of fiber bending sensor with optical intensity modulation is mainly based on the change of the fiber structure’s bending curvature that causes a change in the intensity of the transmitted light inside the fiber.By detecting the change of light intensity,we can realize the measurement of bending curvature.This kind of optical fiber bending sensors have small size,simple structure,low production cost,and don’t need expensive spectrometer to demodulate.What’s more,they are not affected by temperature,so it can be only sensitive to curvature.With the development of existing optical sensing technology,the higher performance of optical fiber senors is not the only need,reducing the product cost of optical fiber sensors and simplifying the manufacturing process are becoming more and more improtant as well.In this thesis a optical fiber bending senor with SMS(Single Mode Fiber-Multi Mode Fiber-Single Mode Fiber)structure based on light intensity modulation is proposed,and the sensor’s structure is improved to increase the sensitivity.Using the beam propagation method(BeamProp,BMP)to realize the simulation and calculation.The bending characteristics of fiber optical bending sensors of various structures are investigated experimentally.Thesis’s work includes:1、Some basic theories of optical fiber bending sensing based on light intensity modulation in this thesis are described.The analytical method of basic principles which is about the beam transmission method in fiber optical transmission are outlined.The principle of the bend loss of bending optical fiber,the bending transmission characteristics of optical fiber and the connection loss of optical fiber are be described in detail.2、Many kinds of optical fiber sensor’s structure are designed and the bend sensing characteristics of different structure are analyzed.Simulation software is used to model a variety of bending structures and analyze their optical transmission fields.The thesis studies the factors affecting the bending sensing characteristics of the sensor,and makes comparative analysis of the sensor characteristics of different structures by simulation.3、Many kinds of optical fiber sensor’s are fabricated and sensing characteristics of various bending sensors are investigated experimentally.The experimental setups are built,and the relationships between output power and bending curvature of various structures of bend sensors are studied experimentally.The effects of diameter of fiber’s core,misalignment distance,and fiber type on bending characteristics are investigated.