1 南京大学电子科学与工程学院，超导电子学研究所，江苏 南京 210023
2 紫金山实验室，江苏 南京 211111
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。
光电子学 太赫兹 超材料与超表面 二氧化钒 激光泵浦 强场太赫兹 中国激光
2023, 50(17): 1714015
Author Affiliations
Abstract
1 School of Electronic Science and Engineering, National Laboratory of Solid State Microstructures, Key Laboratory of Intelligent Optical Sensing and Manipulation, School of Physics, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, P. R. China
2 Hefei National Laboratory, Hefei, 230088, China
Fiber components form the standard not only in modern telecommunication but also for future quantum information technology. For high-performance single-photon detection, superconducting nanowire single-photon detectors (SPDs) are typically fabricated on a silicon chip and fiber-coupled for easy handling and usage. The fiber-to-chip interface hinders the SPD from being an all-fiber device for full utilization of its excellent performance. Here, we report a scheme of SPD that is directly fabricated on the fiber tip. A bury-and-planar fabrication technique is developed to improve the roughness of the substrate for all-fiber detectors’ performance for single-photon detection with amorphous molybdenum silicide (MoSi) nanowires. The low material selectivity and universal planar process enable fabrication and packaging on a large scale. Such a detector responds to a broad wavelength range from 405 nm to 1550 nm at a dark count rate of 100 cps. The relaxation time of the response pulse is ~ 15 ns, which is comparable to that of on-chip SPDs. Therefore, this device is free from fiber-to-chip coupling and easy packaging for all-fiber quantum information systems.
1 南京大学超导电子学研究所，江苏 南京 210023
2 网络通信与安全紫金山实验室，江苏 南京 211111
3 江苏亨通太赫兹技术有限公司，上海 200120
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。
成像系统 太赫兹主动成像 最小二乘拟合多项式法 拟合轨迹 快速成像 激光与光电子学进展
2023, 60(12): 1211003
Author Affiliations
Abstract
1 Research Institute of Superconductor Electronics (RISE), School of Electronic Science and Engineering, Nanjing University, Nanjing 210023, China
2 Jiangsu Hengtong Terahertz Technology Inc., Shanghai 200120, China
3 Purple Mountain Laboratories, Nanjing 211111, China
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.
defect detection terahertz terahertz imaging Chinese Optics Letters
2023, 21(6): 061102
1 南京大学超导电子学研究所, 江苏 南京 210023
2 紫金山实验室, 江苏 南京 211111
太赫兹(THz) 波段的高灵敏探测器在诸多前沿领域中有着巨大的应用价值。超导量子电容探测器(QCD) 是一种在 THz 波段具备单光子探测能力的高灵敏直接探测器, 且可实现大规模阵列。对阵列而言, 可靠的读出技术是其性能发挥的基本保障。本研究利用零差读出技术进行了 QCD 信号读出与表征。微波同相正交(IQ) 混频器是零差读出电路的重要组成元件, 故对 IQ 混频器进行了详细表征与校准, 通过排除其不平衡性对探测器信号读出的影响, 提高了测量的可靠性。在此基础上, 对 QCD 的 THz 响应信号进行了测量, 结果显示 QCD 响应信号与理论预期结果高度一致。此外, 所构建的零差读出电路还可用于高灵敏超导微波动态电感探测器(MKID) 阵列等极低温(15 mK 以下) 探测器的信号读出, 为高灵敏 THz 探测器的开发奠定了良好的基础, 具有较高的应用价值。
光电子学 零差读出 高灵敏太赫兹探测阵列 超导量子电容探测器 低温 单光子探测 optoelectronics homodyne readout high-sensitive THz detector array superconducting quantum capacitance detector low temperature single photon detection
1 网络通信与安全紫金山实验室，江苏 南京 211111
2 南京大学超导电子学研究所，江苏 南京 210023
3 中国空间技术研究院通信与导航卫星总体部，北京 100094
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。
光通信 无线光通信 空间光通信 水下光通信 光电探测器 单光子探测 调制解调 激光与光电子学进展
2022, 59(5): 0500001
Author Affiliations
Abstract
1 Nanjing University, National Laboratory of Solid-state Microstructures, School of Physics, Research Institute of Superconducting Electronics, School of Electronic Science and Engineering, College of Engineering and Applied Sciences, Collaborative Innovation Center of Advanced Microstructures, Nanjing, China
2 Sun Yat-sen University, State Key Laboratory of Optoelectronic Materials and Technologies, School of Electronics and Information Technology, Guangzhou, China
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.
quantum key distribution hybrid photonics single-photon detector Bell-state measurement time-multiplexing Advanced Photonics
2021, 3(5): 055002
1 南京大学电子科学与工程学院, 江苏 南京 210023
2 南京大学超导电子学研究所, 江苏 南京 210023
单光子成像技术通过对每个光子携带的时空信息进行探测,实现对物体图像的重构。基于超导纳米线的单光子探测器具有高效率、低时间抖动、宽响应波段的优势,非常适合单光子成像场景的需求。超导纳米线延迟线单光子成像器件是一种新型的单光子成像器件,它利用超导纳米线特有的高动态电感构造低速微波传输线,通过对输出电脉冲进行时间逻辑分析,同步读取光子的到达时刻和空间位置。本文将介绍这种成像器件的设计原理、几何结构和读出方式。同时,介绍基于此成像器件在强背景噪声下的单光子成像实验,证明了通过高性能器件和重构算法的联合优化所实现的成像系统性能增强。
激光与光电子学进展
2021, 58(10): 1011002
Author Affiliations
Abstract
School of Electronic Science and Engineering, Nanjing University, Nanjing 210023, China
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 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 () 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.
Photonics Research
2021, 9(3): 03000389
