中心博士生陈心佩同学的工作——Sampling bandwidth expansion in channel-interleaved photonic analog-to-digital converters based on optical spectral convolution（基于光谱卷积的通道交织光子模数转换器带宽扩展）的相关成果最近被Optics Express期刊接收，该工作得到了国家自然科学基金（T2225023, 62205203）部分资助。
近年来，随着仪器仪表、无线通信和雷达等领域对宽带信号实时采集与处理需求的不断增长，光子模数转换器（PADC）因其超宽输入带宽和超高采样率的优势，逐渐成为学术界和工业界关注的热点。PADC凭借电光调制器所具备的较大调制带宽，在宽带信号处理方面表现出显著优势。要充分发挥这一优势，光采样脉冲需覆盖足够宽的频率范围，以具备充足数量的平坦电梳，从而有效地将多个奈奎斯特区域的信号折叠回第一个奈奎斯特区域，实现电后端的信号恢复和处理。在平方检测型PADC中，光梳到电梳的转换存在卷积变换，所以即使光学采样脉冲的光谱表现为平坦，电域频谱仍可能出现不平坦，进而降低PADC的带宽性能。
本工作建立了一个光采样脉冲的电域频谱模型，在平方检测中引入光谱卷积来描述光采样脉冲的电谱特性。基于该模型，我们提出可以根据电域频谱来优化光采样脉冲的光谱设计，以实现更平坦的电域频谱。研究表明，单个强度调制器（IM）仅能生成三根锁相电梳线，其平坦度为7 dB。此外，我们推导了级联双驱动马赫-曾德调制器（DPMZM）结构下光采样脉冲的最优光谱分布。 在实验中，我们配置了一个两通道 PADC，并实现了 11 根线性相位电梳线，其平坦度为 3.9 dB。在 4 GHz 输入频率下，PADC 在 0 至 42 GHz 频率范围内的频率响应衰减为 3.9 dB。
摘要: Optical sampling pulses generated by cascade modulators have been widely studied for broadband signal acquisition in photonic analog-to-digital converters (PADCs). In this paper, we establish a comprehensive theoretical optical sampling model that incorporates the photodetection-induced optical spectral convolution, which in turn affects PADCs’ bandwidth. Under sufficient bandwidth conditions of the sampling Mach-Zehnder modulators (MZMs), the bandwidth of the PADC is determined by the electrical spectrum, i.e., the optical power spectrum of the optical sampling pulses, rather than by the optical spectrum. Leveraging the flexibility and adjustability of dual parallel Mach-Zehnder modulators (DPMZMs), we achieve precise control over each optical comb lines. The optimal optical spectrum for the cascaded DPMZM is derived by optimizing the variance of the optical power spectrum, and 11 electrical frequency comb lines with a flatness of 3.5 dB can be obtained. In the experiment, a two-channel PADC is configured and 11 linear-phase electrical frequency comb lines with a flatness of 3.9 dB are achieved. With an input frequency of 4 GHz, a PADC frequency response degradation of 3.9 dB is achieved in a range of 0 to 42 GHz. Furthermore, our model enables large-scale integration of the PADC as the absence of dispersion compensation fiber, making PADC a competitive solution to ultra-wideband signal acquisition in the future.