Corrosion Of Fiber Bragg Grating Sensing Characteristics Of The Study

Fiber grating is an optical passive component formed by the periodic perturbation of fiber core refractive index.Optical fiber Bragg grating whose reflection wavelength is associated with its effective refractive index and grating period is a reflection grating.Its bandwidth and reflectivity depend on the length and the amplitude of refractive index change.FBG has special sensitivity to the temperature and the strain,so it has special application in the field of optical fiber communication and sensing.At present,chemical etching method is one of the simplest methods for making optical fiber grating sensor,which is unique in that it needs no exposure.The method changes the waveguide structure of fiber grating,making the manufactured fiber grating sensor more sensitive to the refractive index changes,and having good application prospect in the optical fiber sensing field.The sensor,which has advantages of small volume,low cost and high flexibility,has been widely used in the relative fields like biochemistry,medical chemistry and so on,and gradually become research focus in science in recent years.In this paper,the main work is:First,deriving the wave guided mode of single-mode fiber from Maxwell's equations,through the rules of mode coupling shows that the type and amount of transport mode can be identified if the normalized frequency is determined.Second,discussing the FBG's length and coupling coefficient to spectrum influence.It concludes that the fiber grating is becoming longer,the peak reflectivity of FBG becoming bigger and the spectrum bandwidth becoming litter.On the contrary,the coupling coeffi-cient is becoming bigger,the FBG reflectivity rises faster.In order to verify the sensing rule of the FBG,take one FBG with 1550nm center wavelength to measure the temperature response coefficient is 10pm/? and the stress response coefficient is 1.36N/nm.Third,the paper analyzes the sensing principle of corrosion FBG,using chemical etching method with HF solution about 160min of FBG corrosion and measuring the corrosion process of center wavelength offset is 2.1nm.In order to observe the corrosion process of the FBG response to external refractive index,the original FBG is not sensitive to the refractive index and the etching FBG its response to the external refractive index coefficient is 0.4822nm/riu.Using the etching FBG to measure the brine concentration and density,found that if the brine concentration increases 1%,the center wavelength increases 20.3pm.And if the brine density increases 2.64g/cm3,the center wavelength increases 1nm,It illustrates that can take advantage of the etching FBG to measure the solution concentration and density.Finally,using etching FBG measures the temperature response coefficient is 9pm/?.Fourth,this paper expounds the etching FBG application as the sensor.It is not only can directly measure density and concentration,but also can be used as humidity sensor after coating.At last,it analyzes the cross sensing effect on using the corrosion FBG process.It found that the offset of FBG' s center wavelength has a good linear relationship with the change of external refractive index when etching a little of FBG package layer with chemical reagent.But no processing FBG is insensitive to the refractive index of external environment.It illustrates that it is very necessary to etch FBG package layer in refractive index sensing,which can expand the application of FBG in refractive index sensing field.