The compact and reliable ultraviolet (UV) source has attracted remarkable attention for its potential use in optical measurement systems, high-density optical storage, and biomedical applications. We demonstrate ultraviolet generation by frequency doubling in a lithium-tantalate-on-insulator (LTOI) microdisk via modal phase matching. The 50-µm-diameter microdisk was milled by a focused ion beam (FIB) and followed by chemo-mechanical polishing (CMP) to smooth the disk surface and edge, and the Q-factor reaches 2.74×105 in the visible band. On-chip UV coherent light with a wavelength of 384.3 nm was achieved, which shows great promise for using LTOIs in integrated ultraviolet source platforms.

中国散裂中子源是中国第一台、世界第四台脉冲型散裂中子源，其已于2020年2月达到100 kW功率的设计指标，运行稳定高效，供束效率位于国际前列。中国散裂中子源二期升级方案中总束流功率将升级到500 kW，其中直线加速器段将采用超导加速腔结构，束流能量由80 MeV提高到300 MeV。其中在80～165 MeV能量段采用324 MHz双spoke超导腔，在165～300 MeV能量段采用648 MHz 6-cell椭球超导腔。采用CST、COMSOL等仿真软件完成324 MHz双spoke超导腔的电磁、机械设计及优化，达到实际运行指标要求。为了提高腔运行的稳定性，在腔的设计中对E_P/E_acc着重进行了优化，使其尽量降低。

设计了一种改进型射频功率源输出功率控制系统，解决了现有射频功率源使用中存在的输出功率稳定性与控制精度不足等问题，预期将应用于中国聚变工程实验堆（China Fusion Engineering Test Reactor，CFETR）负离子源中性束系统（Negative Ion Based Neutral Beam Injection System，NNBI）。采用ARM+CPLD双核设计的软、硬件分离控制结构，保障输出功率控制算法运行效率；采用数字化信号控制方法，实现输出功率的高精度控制；通过精确采样射频功率源实际输出功率和闭环功率控制方法设计，实现输出功率的高稳定性控制。对射频功率源样机进行输出功率控制系统模拟负载测试，结果表明：在额定输出功率为50 kW时，输出功率的控制精度高于0.1%、稳定性波动小于0.5%、人机交互软件功能完善。该方案预期可以搭配阻抗匹配网络满足CFETR NNBI射频功率源对输出功率控制的性能要求。

增强现实（AR）技术将计算机生成的虚拟信息融入现实世界，可为使用者提供沉浸式的体验，被认为是下一代显示技术，但依旧存在一些问题。针对AR显示系统中色差、色彩均匀性、光场均匀性等问题，设计一种基于消色差超构光栅的光波导解决方案。仿真超构光栅的耦出响应，在单层超构光栅的情况下，实现了三种波长光（473，532，620 nm）相同角度入射和相同角度出射，消除了色差。采用双层超构光栅，在实现消色差的基础上，进一步实现了对不同波长光的强度比例可调和耦出效率可调，改善了色彩均匀度，有望用于扩瞳。所提基于消色差超构光栅的AR显示光波导设计有望为头戴式AR显示设备提供全新设计思路。

We investigate the influences of structure parameters and interface shapes on the bandwidth of the edge state of lithium niobate valley photonic crystals. By increasing the size difference of two air holes in the same unit cell, we find that the bandwidth of the lossless nontrivial edge state possesses a peak value of 0.0201(a/λ), which can be used to construct broadband valley photonic crystal waveguides. Mode field distributions verify that the waveguide is robust against sharp bends and exhibits chirality. When the unit cell is arranged in a bearded interface with the top and bottom components showing negative and positive valley Chern numbers, respectively, we find that the lithium niobate valley photonic crystal is more likely to exhibit a lossless edge state, which is difficult to be realized in valley waveguides with low refractive index materials. This work can provide guidance on the design of the high-performance topological waveguide.

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.

对于暗弱目标探测,现有的方法仍然存在探测误差较大的问题,为了提高夏克-哈特曼波前探测器的质心探测精度,提出了一种改进的距离-幂指数质心探测算法。在不同情况下将所提算法与现有的几种质心算法进行对比,仿真结果表明,在不同信噪比、不同光斑直径、子区域不同像素等因素影响下,所提算法的质心探测误差低于其他算法的误差,且更为稳定。