Performance Optimization And Realization Of Real-time Instantaneous Frequency Measurement Based On Stimulated Brillouin Scattering

Instantaneous frequency measurement(IFM)is an important technique of measuring unknown microwave signal.It has been widely used in radar and electronic reconnaissance.With the increasing of radar signal bandwidth,the pressure for signal processing of traditional electrical analog-to-digital converters(ADC)and superheterodyne receivers are more severe.On the contrary,the IFM system based on stimulated Brillouin scattering(SBS)has a larger bandwidth and can effectively reduce the backend load.However,its measurement speed is quite slow.Recently,in order to solve this problem,a new type of real-time IFM system by SBS has been proposed.By applying a nonlinear signal as pump signal,it realizes an amplitude compared function(ACF),hence implements the real-time IFM.However,the measurement result of this solution suffers from severe noise interference,which leads to an unsatisfactory resolution and dynamic range.In order to improve its performance,this thesis analyzes the performance of real-time IFM system by SBS and proposes several effective schemes to optimize the resolution and dynamic range of the previous system.This thesis contains three aspects as follows:Firstly,this thesis introduced the principle of real-time IFM system by SBS briefly and analyzed the influence of polarization and signal-to-noise ratio on system performance.Meanwhile,by optimizing the structure of real-time IFM system,the requirements of modulation accuracy of the single sideband Mach-Zehnder modulator are reduced,which facilitates the subsequent optimization of the system.Secondly,theoretical analysis and experimental studies have been made to confirm the influence of random polarization deflection on the resolution of real-time IFM system.Besides,this thesis proposed a solution by using polarization maintaining fiber(PMF)instead of single mode fiber(SMF)to perfect the resolution.The experimental results show that the realtime IFM system using PMF has better stability and finer resolution than the real-time IFM system using SMF.During the tests,the frequency resolution was improved from 225 MHz to 90 MHz.Finally,the scheme has been proposed to improve the dynamic range of input microwave signal by adjusting modulation voltage based on the principle of real-time IFM system and Mach-Zehnder modulator.Experiment results show that under the same experimental conditions,the lower limit power of the real-time IFM system in the experiment can be reduced from >13dBm to 9.7dB by selecting appropriate modulation voltage,which significantly improve the lower limit power of the real-time IFM system.