The Logic Implementation Of Distortion Suppression Method For Photonic Time-Stretched Signal

Digital signal processing technology has the advantages of high speed and stability.As a bridge connecting continuous analog signals in nature and discrete digital signals,the performance of analog-to-digital conversion is particularly important.With the development of communication technology,people put forward higher requirements for the sampling rate,analog bandwidth and effective number of bits of ADC.However,there is a physical limit in the sampling rate of traditional electronic ADC,which can not meet the sampling requirements of communication system.Photonic time stretched analog-to-digital converter(ts-adc)can break through the physical limit of the sampling rate of traditional electronic ADC,and has better sampling performance in the face of high-frequency and wide-band signals.By preprocessing the analog signal to be measured,the frequency and bandwidth of the analog signal are compressed,and then we sent the analog signal to the electronic ADC for sampling,which improves the sampling rate and analog bandwidth of the ADC equivalently.However,the process of photonic time stretched preprocessing will cause distortion in the analog signal to be measured.In this thesis,the process of photonic time stretched preprocessing uses a dual output Mach-Zehnder modulator structure based on complementary single-sideband modulation,and the output of two channel has complementary characteristics.The main research content of this thesis is to design and implement the corresponding modules to eliminate signal distortion in the digital domain.The main source of signal distortion is the uneven envelope of optical pulse and the phase shift caused by the group velocity dispersion effect.In this thesis,the sampled data rearrangement module is designed and implemented first,which is used to solve the bottleneck between the 10 gsps high-speed data stream and the limited rate of logic chip by the parallel data structure,and get the parallel data form convenient for the subsequent algorithm.On this basis,according to the complementary characteristics of the two channel signals,the elimination of the optical pulse envelope is realized based on the corresponding algorithm,which can improve the signal distortion caused by the uneven optical pulse envelope.The phase shift introduced by group velocity dispersion effect is related to the signal frequency.In this thesis,a hybrid FFT/IFFT algorithm based on parallel structure is studied and implemented.The hybrid FFT algorithm can calculate the frequency-domain sequence of parallel time-domain data in a number of periods,and then correct the phase shift introduced by dispersion in the frequency-domain.The hybrid IFFT algorithm can transform the phase corrected frequency-domain data into time-domain data sequence,so that it can be sent to the upper computer for waveform display.The modules designed and implemented in this thesis were tested on the hardware test platform,and the test results were analyzed with computer software.The analysis results shows that the distortion induced by the optical pulse irregularity is greatly suppressed,and the distortion induced by the phase shift in the time domain is also well suppressed.Each module has achieved the expected result.