Study On High-speed Fiber Bragg Grating Demodulation System Based On Diffraction Grating

Fiber Bragg grating sensor and demodulation technology has become a major researchdirection in the field of detection technology. With the continuous expanding of FBGapplication field, the demand of demodulation precision and demodulation speed are moreand more high, which greatly promote the research about optical fiber grating sensordemodulation technology.There have been different fiber Bragg grating demodulation products based ondifferent solution, but these products are mainly in static demodulation, demodulation speedis not high, the structure is complex and the price is relatively high. The high speed andhigh precision fiber Bragg grating demodulation system will be the trend of development inthe future.The high speed fiber Bragg grating demodulation system based on diffraction gratingis studied in this article. Also the fiber Bragg grating demodulation system structure and theprinciple of diffraction gratings are introduced. The demodulation speed and demodulationaccuracy is mainly considered in this article. Thus, a fiber Bragg grating demodulationsystem which using IBSEN I-MON series diffraction grating module and FPGA asdevelopment platform is proposed. The demodulation make full use of FPGA’s advantagesof parallel computing, customizability and simple structure to realize high speed and highprecision demodulation and transmission of fiber Bragg grating signal.This research includes the hardware circuit design, the embedded data processing andcontrol program, and data receiving and display software. The hardware circuit includesdata acquisition, FPGA minimum system, Ethernet transmission, temperature compensation,channel switch and power supply circuit. Then the fiber Bragg grating sensor wavelengthdemodulation algorithm is discussed in detail. For the high speed demodulation problem,the characteristics of fiber Bragg grating sensor signal is analyzed and an improvedGaussian fitting algorithm is proposed, which reduces the curve fitting computationeffectively. Also the Cholesky matrix method is used in the least squares problem involvedin the algorithm.The experiment shows that the high-speed fiber Bragg grating demodulation system measuring accuracy and resolution can be±1pm, and the demodulation frequency is2kHz.Also the improved Gaussian fitting algorithm is proved reliable and effective.