Study On A Novel Demodulation Technology For Fiber Bragg Grating Vibration Sensors

The Fiber Bragg Grating (FBG) sensors are the part and parcel of fiber transducers. Due to its specialty of wavelength modulate, besides some functions as well as the traditional electronic transducers', the FBG sensors have some unique superiority such as immune from electromagnetic signals and corruption, distribute sensing, high precision and good stability, and otherwise. Therefore the FBG sensors have a wondrously wide application outlook. How to accurately measure the FBG reflected wavelength, namely demodulation technology of FBG sensors, is one of the key technique of FBG sensors. The demodulation method contributes in how the sensors work, the range of the sensors' application and their performance. Thus the research of novel demodulation precept is of great essentiality.This paper put forward a demodulation method of FBG sensors based on the voltage drive Fabry-Perot cavity (F-P), on which we have a feedback control voltage to drive. A novel automatic trace method is creatively proposed. By using the operation circuit, the drive voltage of F-P in feedback can automatic trace the reflected FBG wavelength. Not only had an extraordinary wide demodulation range of frequency achieved, but also a problem solved that when the sensing probe is changed, the sensor has the ability to automatic adjust the drive voltage of F-P to keep up with the dramatic change of the reflected FBG wavelength. The sensors designed from this method can meet the need of many testing system of vibration; therefore enlarge the confine of FBG sensors in the vibration sensing field. On account of its low cost while high performance and easy to use, this novel vibration sensor is conceivable to be used in vibration sensing field far and wide.The contributions of this paper are:(1) On basis of analyzed the basic principle of FBG sensing technology, the emphasis was laid on the feasibility of using FBG sensors to measure vibrations.The design factors of FBG vibration sensors were confirmed and the general design method brought forward.(2) A comprehensive expatiation was given to expound the worldwide status in quo of the FBG transducers' demodulation technique. Some basic demodulation methods and theories were explained in detail, indicated their strong point and bound of apply, the limitation of each method was pointed out, thereunder we seeking for a novel demodulation method.(3) An integrity demodulation system of FBG sensors was well designed. Based on a F-P cavity driven by the voltage, a novel automatic trace demodulation technique was carried out. It has the frequency range as wide as 10KHz, of which the traditional demodulation method using F-P can not achieve. This novel FBG sensor can be used to detect the vibrations.(4) Some experiments were set to test the demodulation method above, some problem encountered and solved. As a result the performance of instrument was practically well improved. The outcome of vibration test is given.(5) On the foundation of experimental results, the advantages and shortcoming are commentated, the use of this automatic demodulation technique is been prospected.