| Summary: | 碩士 === 國立高雄師範大學 === 光電與通訊工程學系 === 102 === If the extinction ratio of the optical pulse is low in the time division multiplexing of polarization insensitive fiber optic Michelson interferometric sensors, the sensor system will suffer the crosstalk and noise to degrade the performance. In addition to adjust the extinction ratio of the optical pulse, in this paper, we use a high-frequency current signal direct modulating the laser to generate high-frequency phase signals in the sensor system. As used herein, a laser, a high frequency modulation signal, time difference of the pulse wave and the interference of crosstalk will be moved to the high-frequency phase noise that can be reduced the phase noise caused by the sensor optical fiber arm and Rayleigh backscattering lead to reduce the phase noise of all the sensor system, but the main sensor signal is almost unaffected. In this paper, in order to verify this method can apply to the sensor systems, we add the third sensor to the system and compare to the previous two sensor systems as control, found that adding the third sensor can effectively reduce crosstalk between the number of sensors, the phase noise, total harmonic distortion, and effectively improve the PGC demodulation of the minimum phase detection sensitivity.
In the part of this article, we use the FPGA digital signal processing for the technique of sensor PGC demodulation. We make the work of the original PGC demodulation by digital processing circuit instead of analog processing circuit with this technology. If interferometric fiber optic sensors use analog circuits for signal demodulation will be due to component aging and other factors lead to distortion , to do further sensor sensitivity normalization process and other signal processing are also more difficult and complicated.In the paper, PGC demodulation of digital system is mainly divided into digital signal conversion and signal processing. Through homemade circuit board (which includes analog to digital converter chip, digital to analog converter chip), we capture the analog signal into a digitized signal for digitizing signal processing. The demodulation signal processed by the digitization operation converts to an analog signal output through the chip. The mainly problem of PGC demodulation techniques in digital conversion circuitry is the signal definition between the state of the output signal ( "0" or "1" ) and the input signal ( "0" or "1" ) which associated with the judgment of logic. Digital signal consists of the FPGA-Xilinx processing program. The programming is composed of mathematical control components and logic control components and makes the MATLAB-Simulink program as Xilinx simulation tools. Finally, the integrated digital system must be given the clock of the ideal frequency separately for each chip according to job requirements, and deal with synchronization issues and inter- chip communication protocol to complete the digitization system.
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