A Demodulation Scheme Based On Tunable F-P Filter

In the past20years, the development of the fiber grating was rapid. It has become hundreds of million dollars industry; it is widely used in optical fiber communication and optical fiber sensor. Since1989, the American Morey researched the temperature-strain sensor of the fiber Bragg grating at the first time. The fiber grating has became the fastest growing technology in the sensing field, and has made a successful application in many fields, such as aerospace, civil engineering, composite materials, petrochemical and so on. It is important the application of fiber grating in the optical fiber sensor. It has many advantage, such as resist electromagnetic interference, good electrical insulating performance, corrosion resistance, small volume, light weight, geometric shape plastic, transmission loss is small, large transmission capacity, wide measuring range, etc. At present, the fiber Bragg grating sensor mainly includes the fiber Bragg grating strain sensor, the temperature sensor, acceleration sensor, displacement sensor, pressure sensor, etc.This article mainly talks about the demodulation method of the FBG temperature-strain sensor, the mainly content of the research is as follows:1. Introduce the development, classification and production methods of the FBG.2. Analysis the spectral characteristics based on the coupling theory of FBG and SFBG, and simulate the reflection spectrum of them3. Introduce the sensing principle of temperature and strain sensors and the principle of temperature, strain cross sensitive issues, provide some solutions people use.4. Introduces some common signal demodulation methods of fiber Bragg grating sensor, and compares the advantages and disadvantages of various methods.5. In the reference, on the basis of previous work, put forward an improved method based on tunable F-P filter demodulation schemeThis paper is mainly devoted to solve two problems:one is the temperature and strain cross-sensitivity problem; The other one is to improve the signal demodulation precision of the sensor system with keeping low cost. To solve the two problems above, the article accomplish it with SFBG, specific solution is as follows:About the temperature-strain cross sensitive problem, this paper make use of the reflectivity of the first main peaks of SFBG and center wavelength of SFBG are affected by the strain and temperature, so as to solve the synchronization measurement of strain and temperature.On signal demodulation, the demodulation methods are compared, and finally select tunable F-P filter method, the precision of this method restricted demodulation factors mainly have two aspects:(1) tunable F-P cavity length of filter will produce because of the change of the environment temperature drift.(2) The relationship of actual elongation of original drive PZT and the voltage is non-linear. To solve these two problems, the method this article use is:the introduce the original SFBG as a reference, It has a lot of larger peaks with large reflectivity, and the peaks are intense, so the neighboring peaks of sensing sensor can be the gap of the reference grating peaks, then use the interference conditions of sensing grating subtract the interference conditions of reference grating, then the cavity length of tunable F-P filter is cut, It means the center wavelength demodulated is nothing to do with the initial cavity length, the influence of cavity length drift on the demodulation accuracy is eliminated. About the problem elongation PZT and driving voltage is nonlinear, I choose a parameter known SFBG used as reference, fit a real-time curve of wavelength-voltage, then bring the voltage values of sensing grating back to this curve, so realize the real-time correction of wavelength-voltage is realized.