Study Of A Highly Precise FBG Sensor Interrogation System With Magneto-optical Crystal Wavemeter Calibration

Because FBGs(Fiber Bragg Gratings)have the advantages of anti-electromagnetic interference,waterproof,dustproof and light weight,these have been widely applied in construction safety,petrochemical,aerospace and other fields nowadays.FBG interrogation technique is one of the key technologies of fiber optic sensors,and the accuracy of interrogation determines the measurement accuracy of FBG.As the light sources of FBG demodulators,the tunable lasers usually sweep at high speed over a range of wavelength with a constant optical power.The center wavelength of FBG is obtained after detecting and building the reflection spectrum by the interrogator.However,when tunable lasers continuously sweep at high speed,the fluctuations of wavelength often appear.These wavelength drifts can hardly be avoided and cause the deviations of demodulation.Because of high-cost and equipment complexity,the traditional wavelength calibration methods were difficult to be utilized in practical engineering.So we have demonstrated a highly precise FBG sensors interrogator with magneto-optical crystal wavemeter calibration.The wavelength calibration device has advantages of simple structure,high accuracy and quick response.In this paper,we have combined the wavemeter and the demodulator to calibrate the fluctuation during the laser scan and improve the performance of the FBG interrogator.The main study of this paper as follow:1.This paper introduced the development of fiber optic sensors and FBG interrogation schemes.We compared and summarized previous wavelength calibration methods and analyzed their advantages and characteristics.2.We proposed a wavelength calibration scheme which combined a magneto-optic wavemeter with the interrogation system.The working principle and characteristics of the interrogation system are given.3.General hardware design scheme of the system is given.The hardware structure of the system was introduced.We have built the circuit boards and optical path of wavelength calibration module and main control module.4.The software design of the system is introduced.The PID temperature controller was applied to maintain the temperature of the crystals.Also the system flow charts of uC/OS were demonstrated.We have analyzed and compared the algorithm of wavelength calibration and fitting,and the final schemes were given at last.5.We present experimental verification of real-time wavelength calibration of tunable lasers and measurement corrections.In the measurement demonstrations,the experimental results show that the FBG interrogation accuracy was raised from ±3 pm to±1 pm,and better long-term stability was achieved,corresponding to the temperature accuracy of ±0.1 °C.