基于拉曼自频移效应的高速高精度全光模数转换技术基础研究

High-speed analog-to-digital conversion is urgently needed in application fields such as high-speed measurement, communication, and radar. The performance of state-of-the-art electronic analog-to-digital conversion can hardly be further improved due to the physical limit of carrier migration rate. Optical analog to digital conversion, which gives full play to the characteristics of ultra-high-speed optical signal processing, is considered as an effective way to solve the bottleneck of realizing high-speed digitization, and has become a hot research topic. This project proposes a new scheme to realize high-speed and high-precision optical analog-to-digital conversion of broadband microwave signals. The proposed optical analog-to-digital conversion is implemented through three processes, i.e., optical sampling, optical quantization and optical coding. We will do research on the high-speed linear optical sampling process utilizing electro-optic intensity modulation, the high-precision optical quantization process based on intensity-to-wavelength mapping through Raman-induced frequency shift effect, and the fast optical coding process employing optical filtering after intensity-to-wavelength mapping. In this project, quantization and coding processes are implemented in the optical domain, which can achieve ultra-high-speed conversion with rate larger than 100 GS/s. In addition, the proposed wavelength-based quantization and coding scheme can realize high-precision analog-to-digital conversion. We will conduct deep research on the theoretical modelling, numerical simulation and system experiment of the proposed all-optical analog-to-digital conversion technology. It is hoped that we can make concrete contributions on promoting the analog-to-digital conversion technology.

高速测量、通信、雷达等领域对高速模数转换的需求十分迫切。现有的电子模数转换由于载流子迁移速率已接近物理极限，难以进一步提高性能。光学模数转换充分发挥光信号处理超高速的特点，被认为是解决高速信号数字化瓶颈的有效途径，已成为研究热点。本项目提出一种可实现宽带微波信号高速高精度光学模数转换的新方案，模数转换通过光学采样、光学量化和光学编码三个过程实现。拟研究基于电光强度调制的高速线性光学采样，研究基于拉曼自频移效应的“强度→波长”映射高精度光学量化，研究基于光学滤波的快速光学编码输出。量化和编码过程都在光域内完成，可实现超高速的模数转换（速率大于100GS/s）。所提出的基于光学波长量化编码方案，可实现高精度的模数转换。项目组将在光学模数转换技术的理论建模、数值仿真和系统实验等方面开展深入研究，期待能为解决高速信号数字化瓶颈做出贡献。

本项目针对超宽带无线通信、高速信号采集与测量、高频宽带雷达、电子侦察等民用和国防领域对高速、宽带模数转换（ADC）的亟需，围绕光学ADC技术开展了研究工作，以基于孤子自频移的全光ADC、光学时间拉伸ADC和光采样ADC这三类主要的光学ADC为研究对象，突破了其中的微波光子学和非线性光学等关键理论问题，掌握了高速宽带线性光学采样、高精度光学量化、快速光学编码和光学ADC单元联试等关键技术，形成了一套能够实现宽带信号高速、高精度数字化的光学ADC方法。对于基于孤子自频移的全光ADC，建立了完整的理论模型，设计了采样速率10GS/s、量化位数8bits的系统方案；提出了基于双向梳状光纤和基于时域滤波的两种光谱压缩方案，以提高量化位数，并完成了实验验证；提出了基于Sagnac环梳状滤波的快速光学编码方案，并完成了实验验证。对于光学时间拉伸ADC，建立了完整的理论模型，提出了基于非对称双平行马赫曾德尔调制器（DPMZM）和平衡探测相结合的线性化光学时间拉伸方案，并进行了仿真验证；提出了互补单边带调制结构结合数字域校正补偿的宽带线性化光学时间拉伸ADC方案，同时解决了色散代价、包络导致的信号失真以及调制非线性导致的信号失真等问题；提出了基于耗散孤子的单通道光学时间拉伸ADC方案，并完成了实验验证。针对光采样ADC，建立了完整的理论模型，搭建了“高重频超短光脉冲源+宽带光采样+时分解复用+多路并行量化编码+数字域重组”的光采样ADC实验系统，完成了光学ADC单元联试，并进行了实验研究；提出了利用三个采样率互质的低速光学ADC实现宽频段范围内微波信号频率测量的方案，并完成了实验验证；提出了利用低速光学采样和低频探测实现宽带电光强度调制器和电光相位调制器频响特性测量的方案，并完成了实验验证。