Fast Demodulation Technology Of Optical Fiber Bragg Grating

In recent years, fiber grating, as an important device, is used widely and developedrapidly in fiber communications and sensing field. The refractive index of fiber corepresentes periodic change in axial direction. Fiber grating has many advantages, such aseasy for multiplexing, immunity of electronmagnetic interference, properties of specificfiltering and wavelength sensitive. This device has different responding sensitivities fordifferent environment parameters (temperature, stress and strain). By using FiberGrating Array Sensor System, a Fiber Grating Array has built up. Combined with TDM(time division multiplexing), WDM (wavelength division multiplexing) and spatialdivision multiplexing, optial fiber Network Sensor System can realize. For manytraditional demodulate systems of optical fiber Bragg grating (FBG), they are expensive,large volume (spectral analysis) and almost impossible applied in industrial practices. Itis a research focus to achieve high speed and precision demodulation, low cost etc inoptical fiber sensing area.Based on the virtual instrument technology, compared with some demodulationmethods of FBG sensors, we propose a Quadrature Signals processing method based onan unbalanced Mach-Zehnder (M-Z) interferometer, and used cantilever beam drawingFBG, and verified the feasibility of dynamic strain FBG Sensor.The detailed contents as follows:â‘ The theory model is built up by coupled-mode theory (CMT) at first, and thenthe reflection spectrum curve of FBG is gained, next the FBG sensing theory oftemperature and strain is discussed, and some common demodulate methods areanalyzed in sensing fields. The relationship between wavelength shift and temperatureor strain is verified by experiments.â‘¡The basic principle of quadrature time-delay sampling is established. Thecorrectness verification is tested by a program simulation in compiling environment ofLabVIEW.â‘¢The demodulation system of FBG is built up based on an unbalancedMach-Zehnder interferometer and using Quadrature Signals processing method. Byapplying phase compensation and phase unwrapping method, the demodulation ofwavelength shift is realized. The method of using cantilever beam to draw FBG verifiesthe feasibility of dynamic strain sensor system. Compared with the traditional demodulate methods, there are many advantages in the demodulate system using thenovel method.