Study On The DSP Based Fiber Bragg Grating Demodulation System

Fiber Bragg grating (FBG) sensor has been widely used in space industry, ship industry, civil structures, electric industry, oil, chemical industry and medicine fields owing to its wavelength-encode characteristics which helps to be immune from light source disturbance and system loss. Now it is one of the most exciting focuses in the fiber-optic sensors research field. The main bottleneck for the application of FBG sensor is how to measure a small shift of Bragg wavelength accurately, as it is the main factor for this kind of sensor' sensitivity. Therefore to establish a novel wavelength demodulating system with high sensitivity, good stability and cost-effective is of great importance in practical applications.In this paper, an optical fiber Fabry-Perot sensor interrogation system with help of DSP is developed and thoroughly studied based on the inherent wavelength selection property of the tunable Fabry-Perot filter. The spectrum of reflecting signal is obtained using the interrogation of the Fabry-Perot cavity length. DSP (Digital Signal Processor) , as the control kernel, performs data gathering and processing, which is then sent to PC by a serial communication interface (SCI). Hence the system can be controlled with high speed and efficiency. The error source of this demodulation system is carefully analyzed and its accuracy is greatly improved by using a reference FBG to overcome Fabry-Perot filter's bad multiplicity.Both theoretical and experimental results confirm the feasibility of this demodulation system in the application of sensors. Comparing with the traditional optical spectrum analyzer, our system has comparable measuring sensitivity while less complicated and cost effective. Some effective schemes trying to improve the measure accuracy of this system are proposed, which give useful information for further research.