基于可调谐色散介质的光子时间拉伸模数转换系统

传统电子模数转换器受限于噪声、采样时间抖动、比较器模糊等因素，难以接收高频宽带高速信号。具有高重复频率、低时间抖动、窄脉冲宽度等优点的光子模数转换器能够突破上述电子瓶颈。光子时间拉伸模数转换器是一种基于色散傅里叶变换效应的光子辅助型模数转换器。群速度色散效应能够将输入的宽带射频信号拉伸展宽成低速窄带信号，使得后端低速模数转换器能够对高速宽带信号进行采样，可以有效提升模数转换系统的采样率。

本文设计并实现了一种基于可调谐色散介质的高速光子时间拉伸模数转换系统。啁啾光纤布拉格光栅因其反射带宽和色散系数容易受到应变、温度等外界因素影响而发生变化，适合用作可调谐色散介质。将啁啾光纤布拉格光栅的中心点与直角三角形悬臂梁侧面的中性面对齐，能够实现保持中心波长不变的可调谐色散装置。通过调整悬臂梁自由端的垂直位移，即对光栅施加不同的应变，可以间接调节啁啾光纤布拉格光栅的色散系数。在不同色散系数的作用下，输入射频信号在时域上能够被展宽至不同倍数，因而后端电子模数转换器能够采样到相对应的不同采样点，最终使得系统的总采样率提高。本设计结构简单，无需大色散介质和多级光学放大器，在单一通道中实现了多通道采样的等效效果。本设计能够节省额外的通道和多组器件，在实现高采样率的同时，可以大大节省系统的成本。实验中得到了7组不同的拉伸因子(1.882至2.206)，并且成功恢复了频率为2GHz至10GHz的输入射频信号。实验结果表明，系统的总采样率提高了14.4倍，等效采样率提高到288 GSa/s。当输入射频信号频率为2GHz时，得到系统的有效位数为5.55位，拟合所得正弦波形的R平方系数为0.9961，系统具有较好的分辨率。

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