提出了一种在超表面中嵌入二氧化钒（VO₂）从而对太赫兹波进行动态调控的方法。VO₂在68 ℃左右会发生绝缘体到金属的相变，导致其电导率发生4~5个数量级的显著变化。超表面由一个双开口金属谐振环阵列以及金属环开口处嵌入的VO₂结构组成。仿真结果表明，通过改变VO₂的电导率，太赫兹波可以实现高频与低频之间的谐振模式的切换。值得注意的是，这种模式转换不仅可以在实验中通过直接改变环境温度实现，还可以通过激光和强场太赫兹的泵浦完成。这种多样化的激励为该超表面在实际多场景应用中动态调控太赫兹波提供了参考。

在自行搭建的双焦点太赫兹主动成像系统基础上，建立了与角度相关的拟合函数，并利用最小二乘拟合多项式的方法对拟合系数进行计算，成功将扫描轨迹的几何光学追迹计算过程简化成为二元函数计算。该系统为收发同路式像方旋转镜扫描。由于拟合自变量对太赫兹图像的影响很大，采用两种不同的拟合自变量进行计算，并且通过数值分析和成像结果分析比较两者的优劣。实验结果表明，当以旋转镜法向量的坐标分量作为拟合自变量时，计算扫描轨迹的速度减小至3 s/frame，且太赫兹图像非常准确。该系统实现了在约8 m处，50 cm×100 cm视场内达3 cm空间分辨率的快速精确成像。这为扫描式太赫兹快速成像系统提供了有价值的参考，对实时太赫兹安检、无损检测等领域有着实用意义。

We simulate the measurements of an active bifocal terahertz imaging system to reproduce the ability of the system to detect the internal structure of foams having embedded defects. Angular spectrum theory and geometric optics tracing are used to calculate the incident and received electric fields of the system and the scattered light distribution of the measured object. The finite-element method is also used to calculate the scattering light distribution of the measured object for comparison with the geometric optics model. The simulations are consistent with the measurements at the central axis of the horizontal stripe defects.

针对无线光通信中的收发技术，从空间光通信和水下光通信两方面梳理相关的研究进展，根据不同场景从通信波段、调制方式、光电探测器三个方面总结无线光通信收发技术的发展趋势，分析单光子探测在无线光通信中的应用前景，并报道了本研究组将串联型超导纳米线单光子探测器应用于空间光通信取得的结果，为相关研究工作的开展提供借鉴和思路。

Integrated photonics provides a route to both miniaturization of quantum key distribution (QKD) devices and enhancing their performance. A key element for achieving discrete-variable QKD is a single-photon detector. It is highly desirable to integrate detectors onto a photonic chip to enable the realization of practical and scalable quantum networks. We realize a heterogeneously integrated, superconducting silicon-photonic chip. Harnessing the unique high-speed feature of our optical waveguide-integrated superconducting detector, we perform the first optimal Bell-state measurement (BSM) of time-bin encoded qubits generated from two independent lasers. The optimal BSM enables an increased key rate of measurement-device-independent QKD (MDI-QKD), which is immune to all attacks against the detection system and hence provides the basis for a QKD network with untrusted relays. Together with the time-multiplexed technique, we have enhanced the sifted key rate by almost one order of magnitude. With a 125-MHz clock rate, we obtain a secure key rate of 6.166 kbps over 24.0 dB loss, which is comparable to the state-of-the-art MDI-QKD experimental results with a GHz clock rate. Combined with integrated QKD transmitters, a scalable, chip-based, and cost-effective QKD network should become realizable in the near future.

Amorphous materials are attractive candidates for fabricating the superconducting nanowire single-photon detectors (SNSPDs) due to their superior tolerance and scalability over crystalline niobium nitride. However, the reduced superconducting transition temperature degenerates both operating temperature and saturation efficiency. Herein, the SNSPD (6.5 nm thickness and 50 nm width) based on the amorphous Mo0.8Si0.2 film with a high optical absorption coefficient demonstrates close-to-unity intrinsic detection efficiency for 1550 nm photons from 75 mK to 2.2 K. Further, a high-performance array SNSPD with optimized 90 nm-width wires is also demonstrated. As-fabricated uniform 4-pixel SNSPD exhibits a saturation plateau for the photon counts at 2.2 K, which overcomes the limitation of operation at low temperature (<1K) for traditional amorphous SNSPDs. Coupled with superior intrinsic quantum efficiency, highly efficient photon counts, and low dark count ratio, this detector paves a way for achieving high efficiency and superior yield for large array systems.

Laser communication using photons should consider not only the transmission environment’s effects, but also the performance of the single-photon detector used and the photon number distribution. Photon communication based on the superconducting nanowire single-photon detector (SNSPD) is a new technology that addresses the current sensitivity limitations at the level of single photons in deep space communication. The communication’s bit error rate (BER) is limited by dark noise in the space environment and the photon number distribution with a traditional single-pixel SNSPD, which is unable to resolve the photon number distribution. In this work, an enhanced photon communication method was proposed based on the photon number resolving function of four-pixel array SNSPDs. A simulated picture transmission was carried out, and the error rate in this counting mode can be reduced by 2 orders of magnitude when compared with classical optical communication. However, in the communication mode using photon-enhanced counting, the four-pixel response amplitude for counting was found to restrain the communication rate, and this counting mode is extremely dependent on the incident light intensity through experiments, which limits the sensitivity and speed of the SNSPD array’s performance advantage. Therefore, a BER theoretical calculation model for laser communication was presented using the Bayesian estimation algorithm in order to analyze the selection of counting methods for information acquisition under different light intensities and to make better use of the SNSPD array’s high sensitivity and speed and thus to obtain a lower BER. The counting method and theoretical model proposed in this work refer to array SNSPDs in the deep space field.