Research On Key Technologies Of Photonic A/D And D/A Conversion

With the increasing demand of signal transmission rate and system bandwidth in microwave communication system,analog-to-digital converter(ADC)and digital-to-analog converter(DAC)as the key components of the system,conversion rate and conversion resolution have an important impact on system performance.Although the manufacturing process of electronic ADC and DAC is mature,the conversion performance cannot be further improved due to inherent bottlenecks such as electromagnetic interference and clock jitter.Therefore,using the advantages of photonic technology such as high speed,low sampling jitter and stable transmission to improve the system rate and resolution has attracted wide attention of researchers.This paper first introduces the existing photonic ADC and DAC schemes,and analyzes their advantages and disadvantages.The conversion basis between digital signals and analog signals are described.Meanwhile,the key technical indicators of the conversion system are analyzed and discussed.Secondly,the key technologies of photonic ADC and DAC are studied in this paper.A photonic quantization scheme based on the weighted transfer function of Mach-Zehnder modulator(MZM)is designed.A DAC approach based on Dual-Drive Mach-Zehnder modulator(DDMZM)is also proposed.Complete mathematical modeling and theoretical analysis are conducted for the above two systems respectively.The effectiveness of the above two approaches for the conversion between analog signals and digital signals is proved by simulation.Meanwhile,a verification experiment is built to further prove the validity of the conversion function of the above two schemes.The key performance indicators of the above two systems are analyzed.Two conversion systems are described as follows:1.Combined with the weighted multi-wavelength sampling and phase-shifting optical quantization technology,a photonic ADC scheme based on the MZM weighted transfer functions is proposed.Combined with N-wavelength sampling and MZM weighted transfer functions with expected phase shift,the input analog signal can be uniformly quantized into 2N +1 quantization levels.The feasibility of the scheme is verified by building a photonic ADC system with 17 quantization levels.Compared with the traditional photonic ADC schemes,the proposed approach improves the conversion resolution of the conversion system with a more concise implementation structure.Through theoretical research,simulation results and experimental demonstration,the advantages of the scheme in improving the conversion resolution of the system are demonstrated.2.Based on the transmission characteristic function of DDMZM,a novel photonic DAC is proposed.Combined with theoretical analysis and simulation verification,the proposed 2-bit photonic DAC module can be extended to realize the conversion of 2N-bit digital signal to analog signal,that is,N DDMZMs can be used to construct 2N-bit photonic DAC system.A 4-bit photonic digital-to-analog conversion experiment is built,and the differential nonlinearity and integral nonlinearity are 0.08 and 0.36,respectively.Compared with most of the current photonic DAC schemes,the proposed approach based on DDMZM can improve the system conversion resolution with a relatively simple system structure.Finally,the photonic ADC and DAC are summarized,and the improvement direction of highperformance photonic ADC and DAC schemes and the prospect of subsequent research work are given.