Research On High Stability And Multi-channel Phase Demodulation Technology Of Fiber-optic Sensor Based On FPGA

The phase generation carrier(PGC)demodulation algorithm is the most widely used in Fiber-optic interferometric sensors(FOISs).However,the accuracy of the PGC algorithm is often affected by external factors,such as detected light intensity fluctuations,the drift of phase modulation depth,carrier phase delay,etc.These problems greatly limit the practical process of phase demodulation methods and fiber-optic interference sensors.This paper proposes a self-reference-based PGC demodulation algorithm,focusing on the improvement of the stability and anti-interference ability of the demodulation algorithm.For the practical application of multi-component simultaneous measurement requirements,the four-channel phase demodulation system based on FPGA were developed.The combination and test of FOISs were completed,and the demodulation system was applied in multi-component optical fiber accelerometer,which laid the technical foundation for the instrumentation and practicality of high-precision optical fiber interference sensors,and has important practical value.The main work of this paper includes:Firstly,the PGC demodulation technology development and research status was summarized,and the classical PGC algorithms were analyzed.Aiming at the stability optimization of the algorithm,a self-reference PGC algorithm(SR-PGC)was proposed.The interference signal is mixed frequency and filtered by two low-pass filters to obtain a pair of orthogonal components,which are selected as the reference signals,and divided by their own differential signals.The final demodulation result only contain the phase-shift caused by the measurand,and the influence related to modulation depth,light intensity and carrier signal phase delay can be theoretically eliminated,and the the stability of the algorithm can be improved.On the basis of simulation,the anti-interference performance was compared with several typical improved PGC algorithms,and the stability characteristics of SR-PGC algorithm are verified.Secondly,the hardware of demodulation system based on FPGA was developed.The Zynq chip(FPGA+ARM)was selected as the core,and based on the signal parallel processing ability of FPGA and the file and network management ability of ARM,the high precision clock synchronization module was selected to develope the FPGA hardware system construction including synchronous signal acquisition,generation,demodulation,transmission and control functions.In addition,the construction of the debugging platform was completed,and the modular function debugging of the demodulation system hardware was implemented to ensure that the system function meets the practical application requirements.Finally,the combination and performance test of FPGA demodulation hardware and optical fiber sensors for seismic observation are completed.The phase resolution of the system is 2?rad/Hz^1/2,the dynamic range is 178.2 dB@200 Hz,and the phase static drift is less than 1 mrad@6 h,which verify the high stability of the system.The optical fiber sensor was drived by the vibrostand,and the correctness of the demodulation result was verified;The percussion test was implemented to verify the response synchronization of the four-channel demodulation.The software and hardware of the FPGA demodulation system are tested by small signal detection experiments,and the practicability of FPGA hardware equipped with PGC algorithm is further verified.Through the above work,the stability of the phase generation carrier algorithm was improved,and the prototype of the demodulation system was developed.It is hoped that it can provide some references for better research in the future.