Design And Implementation Of Single-shot Photonic Time-stretch Analog-to-digital Converter

Analog-to-digital converter (ADC) is a central component in the modern digitalsignal processing (DSP) technique, and it is widely used in the high-speedcommunication system, radar system, biomedical imaging system and advancedlaboratory instrument. However, the sampling rates and bandwidth of electronic ADCare limited by factors such as timing jitter in the sampling clock, settling time of thesample-and-hold circuit and comparator ambiguity. Recent years, many kinds ofphotonic analog-to-digital converters (PADC) have been proposed for they haveultra-low timing jitter and wide bandwidth in comparison with electrical ADC.Photonic time-stretch analog-to-digital converter (PTS-ADC) is one kind of PADCs,and it has ultra-high sampling rates and ultra-wide bandwidth, although its effectivenumber of bit (ENOB) is relatively low due to the limitation of the large transmissionloss. This thesis mainly studies the single-shot PTS-ADC system, including: digitaldomain filtering technique, the impact of nonlinearity effect on the performance ofPTS-ADC system, modified PTS-ADC system that utilizes the self-phase modulationeffect, the prototype design of the system and its performance test.Firstly, the thesis analyzes and simulates about the mathematical model ofPTS-ADC system. Then it mainly studies the digital domain filtering technique, whichis used to remove the amplitude distortion caused by nonuniformity of optical pulsespectrum. By utilizing this method, the PTS-ADC system with the sampling rates of200GSa/s, intrinsic bandwidth of65GHz has been realized experimentally, and itsSNR and ENOB are24.2dB and3.73bit respectively. Additionally, the thesis alsointroduces the prototype design and performance test of the single-shot PTS-ADCsystem.Next, this thesis analyzes the impact of nonlinearity effect on the performance ofPTS-ADC system, including: power transfer function and carrier-to-interference ratio (CIR) from the theoretical, numerical and experimental results. The theoretical,numerical and experimental results all show that the nonlinearity effect occurring in thefirst spool of fiber has almost no influence on the sampled signal. On the Contrary, itcan improve the system’s bandwidth and CIR. However, the nonlinearity effect in thesecond spool of fiber will deteriorate the system performance and should be refrained.Finally, the thesis demonstrates a modified PTS-ADC scheme that utilizes theself-phase modulation (SPM) effect together with the group-velocity dispersion (GVD)effect to promote the system stretching ability. This scheme can significantly shortenthe length of DCF used in the system, hence, it can enhance the SNR and ENOB of thesystem. In comparison with the traditional system, the total dispersion amountsdecreases from-2790ps/nm to-1750ps/nm, and the SNR and ENOB increase by3.3dB and0.53bit respectively in the modified PTS-ADC system.