Research On The Signals Processing System Of Wavelength Demodulation Of FBG

FBG sensor is one of the current heat research fields in the optical fiber grating sensing technique fields. Fiber Bragg grating is produced in fiber core. It has small volume and Bragg reflect wavelength can be modulated by temperature, strain and so on. So it is widely used in fiber sensor field. As a sensor, FBG can be immune from light source disturbance and system loss by transforming sensing information into its reflecting wavelength shift, that is wavelength coding. Besides, FBG is of good reliance, immune from electromagnetic signals and corruption, and can be constructed as Fiber Bragg Grating network by being put together on a single fiber so as to realize distributed sensing, which is an unexampled merit for FBG. The extensive interest has been produced because of attractive application of the new sensor in health inspection of large complex structures, such as aviatic space implements, oceanic flat, many-floor builds, and large-span bridges.The key to make FBG use more widely is to demodulate the wavelength signal of FBG. The precision of the whole system is based on the precision of demodulating wavelength shift. The method to using OSA to detect the wavelength is not so good because of traditional OSA with its low-precision and high-precision OSA with its high cost and big body. Furthermore, it can not give the electric signal relative to wavelength for display and save in the automatic systems. And now many researches focus on the instruments with low cost, simple structure ,high speed and high precision to interrogate the wavelength. The data acquisition and processing card based on MCS-51 is not so good to obtain good reputation for its high performance, reliability and flexibility because of its lower speed. So the board based on DSP and CPLD is designed to substitute for it. In this paper FBG and the theory of sensing with FBG are introduced systematically with the characteristics and applications of FBG sensor. Contrast study of some typical demodulation methods is made in this paper and method of Fiber Fabry -Perot Tunable Filter (FFP-TF) is confirmed. It is ofadvantage to get a high sensitive wavelength displacement detection method with the features as high efficiency, easy to be operated, inexpensive, and suitable for engineering application. Then with both FFP and high-speed data processing board the experiment system is built up. The software of acquisition and processing of DSP is given.At first, the principle of fiber Bragg Grating is analyzed, and the temperature and strain -sensing characteristic of FBG is systematically investigated. Secondly, contrast and comparison of current demodulation methods is done. On the basis of choice of the method of F-P Tunable Filter, how to design the signal acquisition and processing board is told in detail. Every part of the board is analyzed specifically. Finally experiments setup are performed to testify the resolution of the system. Furthermore, approach to improve the performance of the system is put forward.