The Research Of Portable Fiber Bragg Grating Demodulation System With Large Measurement Range

The research and application in fiber Bragg grating (FBG) in sense field attracts more and more attention in recent years, the FBG wavelength demodulation is one of most important technology which extends the application of FBG sensor. Though many methods of wavelength demodulation have been presented, less of them are applied in practice, so that it is much valuable to develop the FBG wavelength demodulation system according to practical application demand, which can also develop and extend the application of FBG sensor. Based on this idea, a portable FBG wavelength demodulation system with large measurement range according to the demand of architecture structure inspection is introduced in this article, which is characterized by large measurement range, simply structure and low cost. The main contents of this thesis are listed as follows:1. The fiber system part of FBG wavelength demodulation system is designed. The demodulation system is based on passive proportion demodulation method, ASE light source based on Erbium -Doped Fiber is adopted as light source, Wavelength Division Multiplexing (WDM) based on fused taper technology is used as linear filter, and the parameters of WDM are designed, which desire more than 7nm linear work range; The performance test about WDM splitting ratio is done with optical power meter and tunable laser, the experiment result shows that WDM can achieve more than 10nm wavelength measurement, meanwhile, the splitting ratio of optical signal and FBG wavelength have favorable linear relation.2. The optical attenuation is used as optical modulator of demodulation system, which solves the problem of optical modulation. The modulation frequency can achieve 4kHz, the driver circuit is designed, and the modulation frequency is 2kHz.3. Optical signal measurement part is designed. Optical signal measurement is achieved based on lock- in technology, special orthogonal vector lock- in amplifier is designed, the influence caused by the phase difference of double lock- in amplifiers is eliminated, and the amplitude is detectd directly, which reduces the system error; The microcontroller ADuC847 with 24-bitΣ-ΔA/D completes data collection, data processing and peripheral controlling, LCD is used to display the real-time FBG wavelength information, and data storage is achieved through the USB interface; The driver for microcontroller and its peripheral is developed, gain compensation is...