Research On The Performance Of Optical Analog-to-digital Conversion System

The analog-to-digital converters(ADCs)are the bridge connecting and digital signals,and play an important role in the information processing especially in the fields of high-speed communication,radar system and medical imaging.However,due to the limitations of timing jitter and comparator ambiguity,it is difficult for traditional electronic ADCs to meet the two main requirements of modern communication system,which are high sampling rate and high conversion accuracy.In order to overcome these bottlenecks,analog-to-digital conversion schemes based on photonic technologies have become a hot research spot in the field of analog-to-digital conversion.Among the many optical analog-to-digital conversion schemes reported at present,the all-optical analog-to-digital conversion(OADC)scheme based on phase-shifted optical quantization has the advantages of simple structure and great potential of integration.Therefore,this dissertation focuses on the OADC based on phase-shifting optical quantization principle,and analyzes the system performance and quantization enhancement scheme.The main work of this dissertation is as follows.(1)The system simulation platform of cascade step-size multimode interference coupler(CSS-NMI)OADC based on phase-shifting optical quantization and the performance measurement platform of OADC were established.The system performance of the OADC(sampling optical pulse repetition rate of 50 GHz and sinusoidal analog signal of 7.11 GHz)with an effective number of bits(ENOB)of 3.32(10 quantization levels)was analyzed by simulation.By analyzing the influence of the errors of each component on ENOB,the requirements of each component are given when OADC is required to maintain more than 3 bit,which has important guiding significance for the overall design of OADC chip.(2)An OADC scheme to increase the quantization levels was proposed.Compared with the OADC scheme based on CSS-MMI,this scheme not only increases the quantization bits,but also greatly reduces the number of components and optical output ports,as a results,the system complexity is greatly reduced.A 1×4 MMI and a 3×5 MMI were used to achieve phase-shifting optical quantization of 5 ports;Furthermore,an all-optical quantization of 20 quantization levels(4.32 bit)with 6 ports could be achieved by adding a parallel Mach-Zehnder modulator(MZM)and making its half-wave voltage twice that of the front-end sampling phase modulator.However,the CSS-MMI-based OADC requires 9 ports and can only output 18 quantization levels(4.17 bit).By comparing the performance of these two schemes,the simulation results show that the proposed scheme can tolerate up to 9.6%of intensity jitter and up to 0.5 ps of timing jitter of sampling pulses,as well as 16%power imbalance of the MMI output channels when ENOB degrades by 1 bit.In contrast,the 9-port CSS-MMI scheme can tolerate 5.3%of intensity jitter and 0.4 ps of timing jitter of sampling pulses,and 10.9%power imbalance of the MMI.The robustness of the proposed scheme is further verified.