Research On Photonic Sampling And Electronic Quantized Analog-to-Digital Conversion Technology

Analog-to-digital converters(ADCs)with sampling rate up to hundreds of GS/s and operation bandwidth up to tens of GHz are urgently required in wideband real time oscilloscope high-speed communication,and electromagnetic spectrum sensing.Electronic ADCs are limited by the carrier migration rate,with operating rates typically only reaching a few GS/s.Additionally,there is a clear constraint between operating bandwidth and conversion accuracy,making it difficult to cope with the rapidly changing signal reception environment in the future.Photonic sampling and electronic quantized ADC utilizes ultra-short optical pulses with high repetition rate and low time jitter to achieve electro-optic modulation-based sampling in the optical domain.Then,the highspeed samping optical pulse is divided into multiple low-speed sampling optical pulses,which are then quantized and encoded by using multiple electronic ADCs,ultimately achieving analog-to-digital conversion of the input signal.Photonic sampling and electronic quantized ADC fully combines the advantages of ultra-high speed and ultrawideband of the photonics technology,as well as the high-precision characteristic of the electronic technology,and is a powerful way to achieve direct sampling and digital reception of high-frequency broadband microwave signals.However,in the photonic sampling and electronic quantized ADC based on cavity-less ultra-short optical pulse source,there are still problems that need to be solved urgently,such as limited analog bandwidth and instantaneous bandwidth,and insufficient dynamic range and sampling rate.This dissertation focuses on the photonic sampling and electronic quantized ADC based on cavity-less ultra-short optical pulse sources.The main research work includes the performance improvement on analog bandwidth,dynamic range,instantaneous bandwidth,and sampling rate.Furthermore,exploration on the integration technology of the photonic sampling and electronic quantized ADC is also carried out.The main research contents of this dissertation are listed as follows.(1)The spectral characteristics of the cavity-less ultra-short optical pulse source have a significant impact on the analog bandwidth of the photonic sampling.This dissertation investigates the influence mechanism and improvement method of the spectral flatness,residual chirp,and pulse width of the ultra-short optical pulses on the analog bandwidth of the photonic sampling.An analog bandwidth enhancement scheme based on the spectral flatness control of the sampling optical pulse has been proposed,which improves the analog bandwidth of the photonic sampling without sacrificing the signal-to-noise ratio of the system by optimizing the bias point and modulation index of the intensity modulator in the cavity-less optical pulse source.In the experiment,the proposed scheme is used to increase the 3-d B bandwidth of the frequency response of the photonic sampling from less than 10 GHz to greater than 35 GHz.On this basis,an analog bandwidth enhancement scheme for the photonic sampling based on residual chirp and spectral width control of the optical pulses is also proposed.By controlling residual chirp of optical pulses and expanding the spectral width of pulses,the frequency response of the photonic sampling in the high frequency range can be further improved.(2)Spurious-free dynamic range is an important indicator for the performance of the photonic sampling and electronic quantized ADC,which is currently mainly limited by the harmonic distortions and noises introduced by the photonic sampling.This dissertation first investigates the sources of the harmonic distortions and noises in the photonic sampling link and their impact on the performance of the system,and focuses on the performance limits of the photonic sampling under the limitation of the noises.On this basis,a scheme for suppressing harmonic distortions in the photonic sampling based on chirp control in the optical pulse is proposed,which achieves harmonic distortion suppression in photonic sampling without sacrificing the signal-to-noise distortion ratio of the system by introducing residual chirp in sampling optical pulse train.In the experiment,a 10.1-GHz single-tone microwave signal is sampled to verify the proposed method,and the spurious free dynamic range of the system is increased by 10.95 d B.In addition,a noise suppression scheme for the photonic sampling based on the Class-AB structure was proposed,which achieves noise suppression in photonic sampling without introducing additional harmonic distortions.In the simulation,by using the proposed method,the suppression ratio of the noises in the link is improved by 15 d B.By effectively suppressing the nonlinear distortions and noises of the photonic sampling link through the above methods,the dynamic range of the photonic sampling ADC can be further improved.(3)Photonic sampling and electronic quantized ADC has the characteristic of large analog bandwidth,which can achieve direct sampling and digitization of high-frequency microwave signals.However,there may be frequency-domain aliasing when receiving broadband signals.This dissertation focuses on the frequency-domain aliasing of the photonic sampling and electronic quantized ADC when receiving broadband linear frequency modulation radar signals.The fractional Fourier transform characteristics and processing methods of the linear frequency modulation signals are studied,and a fractional Fourier transform signal processing method for photonic sampling and electronic quantized ADC is proposed.It effectively solves the frequency-domain aliasing of the photonic sampling and electronic quantized ADC when receiving broadband linear frequency modulation radar signals through twice zero interpolation and bandpass filtering in the fraction Fourier domain.In the experiment,the scheme is used to verify the receiving ability of the broadband linear frequency modulation signals.The instantaneous bandwidth of the photonic sampling ADC with a sampling rate of 5 GS/s is increased from 2.5 GHz to 5 GHz,and the input linear frequency modulation signal with an instantaneous bandwidth of 3 GHz is digitized through direct down conversion without frequency-domain aliasing.In addition,the high-precision ranging ability of the broadband radar is also verified.(4)In response to the problem of insufficient sampling rate in single-channel photonic sampling and electronic quantized ADCs,this dissertation studies two types of high-speed photonic sampling and electronic quantized ADCs based on time division multiplexing technology and time/wavelength interleaving sampling,respectively,effectively improving the sampling rate of the photonic sampling and electronic quantized ADCs by combining the sampling optical pulses with high repetition rate and parallel multi-channel electronic ADCs with low-speed.In the experiment,multi-channel timedivision multiplexing and time/wavelength interleaved photonic sampling analog-todigital conversion systems is built,respectively,both achieving high-speed photonic analog-to-digital conversion with a sampling rate of 20 GS/s.In addition,we also explore the integration and miniaturization solutions for the photonic sampling and electronic quantized ADCs.We develop a cascaded electro-optic intensity/phase modulator chip based on thin film lithium niobate,and the packaging is also completed.The integrated device after packaging is used to achieve an integrated cavity-less ultra-short optical pulse source,the repetition rate of which is 10 GHz.The device is also used in photonic sampling and electronic quantized ADCs,which is the first one internationally.