Humidity Sensing Application Based On Tilted Fiber Bragg Grating

In recent years,more and more researchers have devoted themselves to the research of TFBG,because it has many unique advantages.It is a passive device written in the fiber,so it has the advantages of the fiber itself: corrosion resistance,immunity from electromagnetic interference,and it can also couple the light transmitted by the core into the cladding to detect external parameters,including temperature,strain and refractive index.Change.In this paper,the research of tilted fiber Bragg grating includes two aspects: lithography technology and humidity sensing application.There is a certain angle between the grating plane and the fiber axis of tilted FBG,which has a great influence on the properties of TFBG.At present,TFBG with small angle is the most reported,while other angles of TFBG also have the properties that small angle FBG does not have.Recently,more and more researchers have paid attention to it.We also use small angle tilted fiber grating to make humidity sensor.Compared with traditional sensors,it has great advantages.At present,capacitive and resistive sensors which are most used are less resistant to corrosion and electromagnetic interference,while F-P fiber-optic sensors have the effect of temperature cross-sensitivity.Therefore,we have studied the humidity sensor based on TFBG.In this paper,the coupling mode analysis of fiber Bragg grating and tilted fiber grating is introduced,and their sensing principle is also introduced.In chapter 3,the research work of fiber grating lithography technology is introduced.The purpose of this paper is to realize the lithography of all-angle tilted fiber grating.The phase mask method and the intensity mask method are mainly introduced.The phase mask method is the most widely used one at present.This method is more economical,but it is suitable for writing large angle TFBG.If we use this method to write small angle TFBG(e.g.when theta < 45 degrees),the period of intensity mask is several hundred nanometers.Ultraviolet light will produce high-order diffraction light in grating lithography,which is no longer the only method.At present,this method is only used in the writing of large angle TFG.We have studied the method of coating graphene oxide on the surface of fiber,each method has its own advantages,and the method of physical deposition is most suitable in this experiment.A functionalized tilted fiber grating(TFBG)sensor based on graphene oxide(GO)and multi-walled carbon nanotubes(MNCNT)was proposed for the detection of environmental relative humidity(RH).GO is hydrophilic to detect the concentration of environmental water molecules,and MWCNT act as a support in GO to increase the sensitivity of the sensor.In this paper,the sensitivity of humidity sensor is increased by using GO/MWCNT composite material.The test results show that the relative humidity(RH)detection range is 30%-90%,the maximum sensitivity is 0.32/%RH.Furthermore,the proposed humidity sensor exhibits good performance in terms of repeatability and stability.