Research On Negative Thermal Expansion Substrate For Fiber Bragg Grating

Fiber Bragg Grating?FBG?is one of the most rapidly developed optical passive devices in recent years.Because of its small size,light weight,immunity to electromagnetic interference and low insertion loss,it has a bright prospec in optical fiber communications and sensors.In the optical fiber sensing field,because of the temperature sensitivity of FBG,the central wavelength of FBG will be affected by stress and temperature when it is used for strain measurement,which seriously affects the accuracy of measurement.Therefore,the temperature compensation of FBG has very important practical significance.On the basis of deeply studying the temperature compensation principle of fiber Bragg grating and a lot of experiments and theoretical calculations,a temperature compensation structure of fiber Bragg grating is designed,the structure basically realizes the complete temperature compensation of fiber Bragg grating.Firstly,ZrW₂O₈ powders with negative thermal expansion coefficient were sintered,and air cooling was found to be the best cooling method by comparison test,ceramic substrates with negative thermal expansion coefficient were obtained through air cooling.Fiber Bragg Grating is bonded to ceramic substrates by a fiber pre-stretching device so that it has a certain pre-strain.When the temperature rises,the ceramic substrate with negative thermal expansion coefficient shrinks,which results in the reduction of the pre-strain of FBG.The negative wavelength drift caused by this shrinkage is offset by the positive wavelength drift caused by the temperature rise,thus realizing the temperature compensation of FBG.The influence of the prestress on the compensation effect is analyzed,and 0.6 nm is a suitably pre-stretching wavelength of FBG.By adjusting the sintering temperature and time of the ceramic substrate,the optimum sintering process parameters is found to be 1180?for 0.5h.The temperature coefficient of the FBG is only 0.25pm/?in the temperature range of 20⁶0?,and the temperature sensitivity of the FBG was reduced by 40 times.Finally,the temperature compensated FBG is connected to the metal stretching plate to simulate the practical application.The temperature sensitivity of FBG is only slightly increased to 0.675pm/?.The linearity and repeatability of the experimental data are good,the FBG sensor can be used for actual strain measurement.