Simultaneous Measurement Of Temperature And Strain By Two LPFGs

With the development of society, people have an increasing demand for information. As one of the three mainstays of modern information technology, the information collection technology (sensor technology) is becoming more and more important, its production capability and application level influence development and application of the information technique directly.As a rising technique in photon research, it is concerned all-pervading for the research and application of sensor technique that have fiber grating for the radical sensor parts of an apparatus lately. Long period fiber grating is a new type of passive optical components that appear lately,it achieve coupling between core mode and cladding mode that transmit equidirectional. Long period fiber grating is concerned by home andoverseas extended scholar,for it have some unique excellence. For example technics simple,insertion loss little,no retroreflection, reaction sensitivity high when external environment change,capacity small,integration and connect with other optic communications device.It has displayed jolly vastitude development foreground in the fibre communication and fibre sensor area for short years.This thesis base on coupling theory of long period fiber grating,it achieved simultaneous measure of temperature and shape change by two longperiod fiber gratings in experiment. It consists several aspects hereinafter mainly:1. Firstly,it make a total statement from the development story of fiber grating, classify fiber gratings idiographic by different manners, and then describe various facture methods of long period fiber grating detailed2. Secondly, introduce two most application of long period fiber gratingin sensor and fibre network.And detrude theory model and numerical calculation method of long period fiber grating,we have a total cognition to long period fiber grating by summing these basic knowledge.3. It is about 0.01nm/℃for the temperature sensitivity of a simple FBG,and strain sensitivity is 5nm/ε. It is very low for measure of precision to use that fiber grating to detect temperature and strain. It is impossible to make a accurate measure of precision in practical production and living. For improving sensitivity, I deduce expression of temperature and strain according to tuning principle of long period fiber grating.We know that sensitivity of temperature and strain are connect with material and magnitude of fiber grating period, at the meantime we know that it is no influence between the two sensitivity. We find that the wavelength of long period fiber grating will move to long wavelength with rising of temperature and enlargement of strain from theory and experiment. So this experiment achieve measurement of temperature simultaneous and strain very well by use those character. Figure 1 is its principle of work: Figure 1 As figure 1, the two fiber gratingλ1 andλ2 are connection in series, then they are relocated in a drying cabinet to have them temperature accordant.Thereintoλ1 induces temperature only but no strain, not onlyλ2 induces temperature but strain. So magnitude ofλ1 indicates temperature, and that D-valueλ1 andλ2 indicate magnitude of strain. We should make scaling for temperature of two fiber gratings and strain ofλ2 before we achieve simultaneous measurement. In this way we achieve simultaneous measurement of temperature and strain by contrasting two transmission spectrum with three scaling figure. As figure 2, 3, 4 show: figure 4 relation curve of wavelength and strain Figure 2 and 3 are fitting curve of two fiber gratings about temperature sensitivity, we find that it is linearity relation between wavelength and temperature nearly from the two figure, the sensitivity is about 0.11nm/℃, is about 10 times than bare FBG. Although it is not good linearity relation between wavelength and strain, sensitivity is very high, is about 7 times than FBG. The fiber grating is written after decolling cladding, so environment will impact shift of wavelength a certain extent, it is better if the part of grating is encapsulated.We can measure temperature and strain simultaneous by scalling for temperature of two fiber grating and strain ofλ2. As figure 5 showing:As figure 5 showing, it is two spectral line when temperature is 20℃and strainε=0.16. The left isλ1 , the right isλ2.λ1 denotes the temperature in condition, and the D-value ofλ2 toλ1 indicates magnitude of strain . So that achieve measurement of temperature and strain simultaneous. The premise is that we know the wavelength will move to long wavelength along with hoist of temperature and accretion of strain. Figure 5 anastomoses with the three scalling images. This work offers thereunder significant and referrence for research of this area in the future, we could improve device material and facture craftwork ulteriorly on the base, make it applied more extensive in the high degree of accuracy measurement area.