Research On The Demodulation Of Fiber Grating Sensor Based On F-P Filter

Fiber Bragg gratings (FBG) are one type of developing fast passive fiber devices in recent years. Especially in sensing field, it caused people strong concern. As a sensing element, optical grating transforms information measured to the movement of reflected wavelength that is wavelength coding. As a result, it can not be influenced by the fluctuation of optical source power and system loss. How to enhance the accuracy of demodulation technology is a key to make the fiber grating sensors promising in actual industry. This paper focuses on FBG sensor system, and emphatically discussed the demodulation scheme of tunable F-P filter. Then put forward autocorrelation demodulation and improved it.First, the technical characteristics of optical fiber sensors and fiber grating sensors are analyzed; fiber grating sensor and its development trend has been studied. From the basic theories, the sensor models under the influence of the temperature and stress are established. The basic principles and main parameters of tunable F-P filter are analyzed, and through numerical simulation, the impact of parameters on tunable F-P filter is found. So a theoretical basis is provided for the selection of tunable F-P filter.Then, several network multiplexing technique and common demodulation scheme are analyzed and compared, after that, tunable F-P filter demodulation is selected as the main demodulation scheme in this paper. The basic principle of tunable F-P filter method is studied, through theoretical analysis and numerical simulation, the relationship between the PD and the bandwidth of F-P filter, the sensitivity curve of PD are obtained. Based on the basic principles, the sensor array is focused. The research shows that when the wavelength of adjacent Bragg less than 0.4nm, a serious impact will interference the output of demodulation system and make demodulation fail. The study has a certain significance on the selection of grating demodulation system.At last, according to the deficiency of tunable F-P filter demodulation, autocorrelation demodulation based on tunable F-P filter is carried out. Analyzed the performance of this demodulation method and put forward some improvement on it. Finally, a numerical simulation is performed by using Matlab, to prove the program can not only eliminate the negative impact by wavelength of adjacent Bragg but also reduce the delay by autocorrelation demodulation to large extent. This algorithm increases the accuracy and real-time of demodulation system, provides a better theoretical basis to practical application.