The Dynamic Real-Time FBG Wavelength Demodulation System Based on FPGA

Due to the temperature drift characteristics and drive element nonlinear characteristics, the detection accuracy of FBG wavelength demodulation system based on tunable F-P filter is insufficient. In order to enhance the detection accuracy, the dynamic real-time correction technology for FBG wavelength was studied. Two kinds of real-time correction methods with series and parallel structure were analyzed and compared respectively. Then the real-time correction system with improved series system was proposed. The high order polynomial function between transmitting wavelength and driving voltage of tunable F-P filter was adjusted in dynamic real time by low-cost reference FBGs model. As a result the demodulation precision of the system was improved. The signal processing was designed based on FPGA as the core. All digital circuits, such as data acquisition unit, peak-searching unit, triangle wave driving unit, data calculation and transmission unit were integrated in the FPGA, so the real-time performance of demodulation system is guaranteed. The experimental results show that the wavelength demodulation range is 1526-1566 nm, scanning frequency is up to 100 Hz and maximum error is +/- 3 pm. Being compared with reported real - time correction method and direct voltage method, the FBG wavelength detection accuracy of demodulation system is improved by 70% and 83.3% respectively.