Study On OEO System Based On High Temperature Accurate Monitoring Application Requirements

High temperature monitoring has always been an indispensable and important demand for industrial application and scientific research.However,the traditional high temperature measuring equipment has some limitations,such as low sensitivity and poor accuracy.The temperature sensitivity of fiber Bragg grating sensors made of different materials and different periodic structures is generally about 10 pm/℃.However,the accuracy of 10 pm is almost the highest wavelength resolution of spectral analyzer.This means that the temperature change below 1 ℃ is indistinguishable.This cannot meet the demand for higher monitoring accuracy in process production.Such as material forming,crystal growth,chemical and pharmaceutical engineering.Therefore,a high-precision real-time temperature monitoring system suitable for 500 ℃high temperature environment is proposed.A high temperature monitoring system with higher accuracy and more stable output at 500 ℃ is designed by combining phaseshifting fiber Bragg grating(PS-FBG)and photoelectric oscillator(OEO).In order to design this system,the following work has been done:Firstly,the system structure and main components of classical OEO are understood,and the starting vibration principle and measurement principle of OEO loop are analyzed in detail.By adding a fiber Bragg grating sensor to the OEO optical path,the spectral reflection of the grating can regulate the sideband wavelength on the carrier in the OEO optical path.So as to change the optical wavelength difference of the input photodetector.Near the 1550 nm band,the RF signal will have a frequency offset of 125 MHz every time the wavelength of the light wave changes by 1 pm.In this way,the light wave change of the optical fiber sensor is converted to the frequency change of OEO,so that the measurement sensitivity is amplified by at least 125 times,and the measurement accuracy is improved.Secondly,in order to select the appropriate fiber Bragg grating sensor,the characteristics of fiber Bragg grating sensors with different structures are compared,and the grid structure and spectral response of different types of fiber Bragg gratings are studied.PS-FBG concave peak spectrum can be used to construct a fiber Bragg grating sensing system with higher accuracy.The smaller the bandwidth of the spectrum,the higher the measurement accuracy.The sensing characteristics of phaseshifting fiber Bragg grating sensing in temperature and stress are tested by experiments.Therefore,using PS-FBG as the sensor of OEO system provides a reliable device selection for improving the accuracy of system monitoring.Finally,a high temperature real-time and accurate monitoring system based on photoelectric oscillation and phase-shift fiber grating is designed.Stable photoelectric oscillation signal is generated by using the narrow-band characteristics of PS-FBG.The PS-FBG temperature sensor was ceramic encapsulated and annealed at 450 ℃ for 12 hours.The PS-FBG sensor has good high-temperature stability.It can be monitored for20 minutes under the high-temperature environment of 495 ℃,and the maximum offset is no more than 5 pm.In the temperature range of 490 ℃～495 ℃,the sensitivity of fiber Bragg grating reaches 10.17 pm/℃.The experimental results show that the narrow linewidth PS-FBG accurately responds to the wavelength shift caused by temperature change,so it can monitor the change of photoelectric oscillation signal in real time and with high precision.The sensitivity of the method is-1.24 GHz /℃ and the linearity is-0.99953.The resolution of the system is 0.0083 ℃.The test system has good potential application value in the accurate control of high-temperature environment such as metal smelting,crystal growth,chemistry,pharmacy and so on.