A Research Of Photonic Time-stretched Signal Distortion Suppression Technology

Analog-to-digital conversion,which converts continuous analog signals into discrete digital signals,is the basis of high-speed digital signal processing.With the rapid development of technologies such as modern communication,radar system,and electronic warfare,researchers have put higher interest on the sampling rate and quantization accuracy of analog-to-digital converter(ADC).Due to the limitation of carrier mobility in traditional electronic ADC,the effective number of bits is strongly constrained by the time jitter and comparator ambiguity while dealing with highfrequency signals,which makes the electrical ADC fail to meet the needs of modern communications,radar system,electronic warfare and other applications.The photonic time-stretched ADC is a workable scheme to break the limitation that electronic ADC encountered when processing high-frequency signals.The optical timestretched technology preprocesses the analog signal to obtain a low-frequency signal,which equivalently increases the sampling rate and analog bandwidth of the ADC.However,in photonic time-stretched technology,the signal distortions introduced by the optical pulse envelope and the harmonic distortion introduced by the modulation will affect the accuracy of the ADC.In addition,the dispersion-induced power penalty will affect the analog bandwidth of the ADC.The research about signal distortion and dispersion-induced power penalty in photonic time-stretched ADC system is carried out as follows.In order to eliminate the signal distortion introduced by optical pulse envelope and remove even harmonic distortion in photonic time-stretched system,the thesis proposes an photonic time-stretched scheme based on a dual-output Mach-Zehnder modulator(DMZM).The optical pulse envelope is eliminated through the complementary characteristics of DMZM,which is verified by numerical simulations and experiments.The experiments obtain a ten-fold stretch factor of microwave signal from 3 GHz to 6 GHz.In addition,in order to eliminate the limitation to the effective number of bits(ENOB)of time-stretched ADC,which caused by inconsistent frequency response of the two photodetectors,the two outputs of DMZM are coupled and send into the photodetector in the experiment,the ENOB can be up to 4.6bits.In order to improve the bandwidth of time-stretched system which limited by dispersion-induced power penalty,an photonic time-stretched scheme based on single side-band modulation is proposed.The single side-band modulation is employed to eliminates the influence of power penalty on signal power in the output of system.However,a frequency-dependent phase factor is introduced in the signal,causing a phase shift between the different microwave signals,resulting in distortion of the wideband signal in the time domain.A corresponding phase correction method is proposed to ensure the distortion-free of the signal,and eliminate the effect of dispersion-induced power penalty.The validity of the scheme is proved by theoretical analysis and numerical simulation,and experimental verification is carried out.Comparing with the time stretching scheme based on DMZM,the experimental results show that the time-stretched scheme based on single sideband modulation effectively improves the analog bandwidth of the time-stretched ADC system.