针对太赫兹量子级联激光器光频梳射频信号提取与传输存在的阻抗不匹配问题，设计并提出了一种输入阻抗为20 Ω、输出阻抗为50 Ω的渐变微带线结构，研究了该结构的准TEM模电场分布，并根据S参数建立了相应的LC等效电路模型分析其物理机理。实验中，将渐变微带线结构应用于太赫兹量子级联激光器光频梳射频信号提取与测试，以验证渐变微带线传输射频信号效果，成功测量得到太赫兹量子级联激光器重复频率，其线宽为3.7 kHz，信噪比达到60 dB，在注入电流为700~900 mA范围内重复频率表现为稳定的单模信号，测量得到的最大保持和幅度艾伦方差结果同样表现出重复频率的稳定性。实验结果表明，所设计的渐变微带线具有良好的阻抗匹配效果，能够实现对太赫兹量子级联激光器光频梳射频信号稳定的提取和传输。

Stable operation is one of the most important requirements for a laser source for high-precision applications. Many efforts have been made to improve the stability of lasers by employing various techniques, e.g., electrical and/or optical injection and phase locking. However, these techniques normally involve complex experimental facilities. Therefore, an easy implementation of the stability evaluation of a laser is still challenging, especially for lasers emitting in the terahertz (THz) frequency range because the broadband photodetectors and mature locking techniques are limited. In this work, we propose a simple method, i.e., relative phase locking, to quickly evaluate the stability of THz lasers without a need of a THz local oscillator. The THz laser system consists of a THz quantum cascade laser (QCL) frequency comb and a single-mode QCL. Using the single-mode laser as a fast detector, heterodyne signals resulting from the beating between the single-mode laser and the comb laser are obtained. One of the heterodyne beating signals is selected and sent to a phase-locked loop (PLL) for implementing the relative phase locking. Two kinds of locks are performed by feeding the output error signal of the PLL, either to the comb laser or to the single-mode laser. By analyzing the current change and the corresponding frequency change of the PLL-controlled QCL in each phase-locking condition, we, in principle, are able to experimentally compare the stability of the emission frequency of the single-mode QCL (f_s) and the carrier envelope offset frequency (f_CEO) of the QCL comb. The experimental results reveal that the QCL comb with the repetition frequency injection locked demonstrates much higher stability than the single-mode laser. The work provides a simple heterodyne scheme for understanding the stability of THz lasers, which paves the way for the further locking of the lasers and their high-precision applications in the THz frequency range.

A hybrid integrated 16-channel silicon transmitter based on co-designed photonic integrated circuits (PICs) and electrical chiplets is demonstrated. The driver in the 65 nm CMOS process employs the combination of a distributed architecture, two-tap feedforward equalization (FFE), and a push–pull output stage, exhibiting an estimated differential output swing of 4.0V_pp. The rms jitter of 2.0 ps is achieved at 50 Gb/s under nonreturn-to-zero on–off keying (NRZ-OOK) modulation. The PICs are fabricated on a standard silicon-on-insulator platform and consist of 16 parallel silicon dual-drive Mach–Zehnder modulators on a single chip. The chip-on-board co-packaged Si transmitter is constituted by the multichannel chiplets without any off-chip bias control, which significantly simplifies the system complexity. Experimentally, the open and clear optical eye diagrams of selected channels up to 50 Gb/s OOK with extinction ratios exceeding 3 dB are obtained without any digital signal processing. The power consumption of the Si transmitter with a high integration density featuring a throughput up to 800 Gb/s is only 5.35 pJ/bit, indicating a great potential for massively parallel terabit-scale optical interconnects for future hyperscale data centers and high-performance computing systems.

实现玉米等活体作物叶片不同区域以及近地冠层的水分含量检测, 可为研究作物生长中的水分胁迫响应机制, 以及旱情监测、 精准灌溉等提供有效技术手段。 大体积、 大重量、 低光通量的高光谱仪难以在田间实现活体检测, 将小体积、 小重量、 高光通量近红外相机加装滤光片使其具有波长分辨能力, 有望实现田间活体叶片水分含量成像检测。 基于玉米叶片的近红外高光谱数据, 对实现水分测量的特征波长位置及个数, 以及特征波长带宽和偏移限度等关键参数进行研究; 其中, 不同带宽的仿真数据依据滤光片透光分布函数得到; 固定带宽条件下的中心波长偏移仿真数据依据插值方法得到。 研究结果表明: 特征波长分别为1 150和1 400 nm, 带宽小于100 nm时可满足要求, 能够找到符合参数条件的滤光片产品; 在带宽为25 nm下所建水分含量模型, 其建模集的决定系数(R²)和均方根误差(RMSE)分别达到0.968, 1.245%, 预测集分别达到0.960, 1.298%, 可实现玉米叶片水分的准确检测。 为推测加装滤光片所建模型受环境温度的影响, 应用固定中心波长下的模型预测不同偏移量的仿真数据, 当偏移量为0.05 nm时, 模型预测误差为不漂移条件下3%左右, 可忽略, 由干涉滤光片中心波长漂移与温度的关系, 相当于环境温度在50 ℃的范围对检测结果影响不大。 该研究对近红外相机加装滤光片形成多光谱成像检测装置提供了重要技术参数支撑和环境工作范围建议, 装置的搭建工作已开始, 装置的实现可为现代农业作物生理、 生产研究提供新型、 有效手段。