| High temperature and ultra-high temperature sensor systems play an important role in the sensing and monitoring of space equipment and other high temperature extreme environment.As one of the key technologies of high temperature environment monitoring,optical fiber high temperature sensor technology is very important for the in-orbit navigation of space equipment and structural health monitoring.To improve the test range,resolution,stability and other performance indicators of optical fiber high temperature sensor is to meet the important requirements of the development of high temperature sensor technology.With the improvement of the preparation technology of optical precision devices,the interferometric fiber sensor has a great application prospect in the field of aerospace because of its characteristics of anti-electromagnetic interference,fast response,compact structure and high sensitivity.However,the low signal-to-noise ratio and wide line width of the interferometric fiber sensor are not conducive to peak searching during signal demodulation.Therefore,by improving the traditional interference sensing system into a laser system,the spectrum has the advantages of high signal-to-noise ratio and narrow line width,so it is of great significance to study the interference laser sensing system oriented to high temperature environment.The specific research is as follows:1.According to the application requirements of high temperature sensing,Mach-Zehnder(MZ)interference of fiber and Fabry-Perot(FP)interference principle components of fiber MZ interference structure and FP interference structure mathematical model are studied respectively,and the influence of temperature and strain on interference spectrum is theoretically studied.The excitation principle of erbium-doped fiber and the sensing principle of fiber laser are studied.The interference structure is used as the filtering structure of fiber laser.The variation of filtering spectrum with the refractive index of interference structure and the length of interference cavity is simulated by spectral simulation.2.The strain and temperature sensing characteristics of erbium-doped fiber laser based on MZ interference structure was studied.The SMF-SCF-SMF structure was formed by cascaded suspension core microstructure fiber(SCF)and single mode fiber(SMF).The optical waveguide mode field in suspension core fiber was simulated by FDTD Solutions and Rsoft,and the influence of cavity length on filtering was studied by testing the transmission spectra of different lengths of suspension core fiber.An erbium-doped fiber laser based on MZ interference filter structure was constructed and the sensing characteristics were studied.With the stretching of the suspended core fiber,the laser spectrum shifted to short wave direction and switched between single wavelength and dual wavelength.The strain sensitivity of the system is 1.80 pm/με and the linearity is98.30%.As the temperature increases,the laser wavelength is redshifted,and the temperature sensitivity of the system is 1.88 pm /℃,and the linearity is 98.58%.3.The temperature sensing characteristics of erbium-doped fiber laser based on the FP structure of the chemical corrosion method was studied..The FP microcavity was prepared by chemical etching method.Its reflection spectra showed multistage interference waveform.The main interference spectrum corresponded to the air FP cavity and the secondary interference spectrum corresponded to the silica cavity.In the high temperature environment,the laser wavelength is redshifted with the increase of temperature,the temperature sensitivity is 13.80pm/℃,and the linear goodness of fit is0.9982.4.The temperature sensing characteristics of erbium-doped fiber laser with FBG-FP structure based on femtosecond laser processing was studied.The fiber FBG-FP filtering structure was prepared by femtosecond laser line-by-line writing technology.The FBG central wavelength of the reflection spectrum has interference characteristics,and it was used as the filtering structure of erbium-doped fiber lasers to achieve stable narrow line-width laser output.With the increase of temperature,the laser wavelength redshifts,and the temperature sensitivity increases gradually.The quadratic goodness of fit between wavelength and temperature is greater than 0.999. |
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