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简单直接新方法增强光线纳米聚焦——光子晶体光纤耦合金属纳米天线 光纤由于具有长距离传输低损耗、应用灵活等优点，从而成为使用范围最为广泛的光波导。其在诸如光纤生物传感器、化学传感器、光纤激光器以及光纤内近场成像等一系列应用中，起到照明和收集光线的作用。随着人们对纳米量级光子器件以及量子通讯需求的日益提升，亟需一种可以将光纤中传输的光线（光子模式）聚焦至纳米尺度的方法。表面等离激元（SPP）波导在光线沿金属-介电表面传播时，能够控制并约束光束在纳米尺度，但其光学损耗过大，因此传播距离仅有微米级。因此，如何将低损耗光子波导模式耦合至高约束SPP模式，反之亦然，是纳米尺度光纤光学实际应用中必须要解决的问题。此类光纤纳米聚焦器件的研发难点在于：如何实现模场大小不同、模场分布不同的光子模式和等离子体模式之间的相位匹配（光子模式在微米量级，而等离子体模式在纳米量级，且通常沿径向偏振）；此外，目前已有的将金属纳米线等纳米量级的等离子体纳米波导集成到微米量级光纤的方法，都需要工序繁多、精度要求高的复杂加工过程。针对以上研究现状，贝勒大学张臻蓉副教授和加州大学欧文分校Howard Lee 副教授合作，将研究重点放在了一种简单且直接的方法上，可高效地将光纤光子模式耦合、聚焦到纳米量级等离子体模式（图1（a））。该装置是一个电子束诱导蒸发技术在光子晶体光纤（PCF）端面上制作的针状等离子体纳米天线（图1（b）），其相关的制作流程、实验表征、理论仿真发表于Photonics Research2021年第2期上（Khant Minn, Blake Birmingham, Brian Ko, Ho Wai Howard Lee, Zhenrong Zhang. Interfacing photonic crystal fiber with a metallic nanoantenna for enhanced light nanofocusing[J]. Photonics Research, 2021, 9(2): 02000252）。在贝勒大学 Khant Minn发明的实验平台上，PCF的基模沿光纤传播，通过端射耦合，耦合至铂金纳米天线上的SPP模式中。这种直接耦合的方式放宽了光子模式与等离子体模式严格的相位匹配要求，在宽带宽范围内实现耦合的同时，还降低了传输损耗。耦合后的SPP模式随后沿着天线向锥形端传播，并汇聚在纳米量级的尖端上，产生一个高度增强且受限的场。在聚焦离子束扫描电子显微镜（FIB-SEM）腔内，仅需一步就可直接将纳米量级的金属尖端刻写到光纤上，进而实现对等离子体天线位置和大小的精确操控。图1 光子晶体光纤(PCF)-纳米天线混合探针。(a)器件原理图及金属纳米线波导上等离子体模式的强度分布仿真。(b)电子束诱导沉积过程示意图；PCF及纳米线制备的SEM图像该合作研究组提出的光纤-等离子体探针的单步制作方法，除了可以实现设计出的具有纳米量级分辨率3D天线的量产，还能够以高精度实现任意配置的光纤-天线耦合。比如在加工过程中，在金属纳米天线底部开一个金薄膜矩形孔，从而将光纤中常见线性偏振通过非对称耦合和聚焦，耦合至尖端径向偏振纳米聚焦等离激元中。该装置对输入偏振的选择性可在散射光的侧面成像中观察到，证实了聚焦SPP模式的等离子体特性。贝勒大学的张臻蓉副教授和加州大学欧文分校Howard Lee副教授认为，光纤-等离子体探针将为遥感、近场光谱仪、单光子激发、量子传感器、纳米级光刻以及Lab-on-fiber集成器件等新型光纤设备和应用的研发奠定基础。下一步工作将放在优化耦合和聚焦效率，以及将光纤探针集成到扫描探针显微镜中，以用于纳米级化学成像技术如基于光纤的针尖增强拉曼光谱、荧光光谱等。 Interfacing photonic crystal fiber with a metallic nanoantenna for enhanced light nanofocusing Optical fiber is the most broadly used optical waveguide for transmitting light because of its low loss transmission even over long distances and its flexibility, which has been used for illumination and collection of light in various applications including optical fiber biosensors and chemical sensors, fiber lasers, and in-fiber near-field imaging. With the increasing demand for nanoscale photonic devices and quantum communication, an efficient way is needed to focus the light transmitted by optical fiber (the photonic mode) down to nanoscale-confined light. Surface plasmon polariton (SPP) waveguides can control and confine light in the nanometer scale as the light is propagating along the metal-dielectric interface. However, the travel distance of SPP is in the micrometer scale due to the high optical loss. Thus, efficient coupling of low-loss photonic waveguide modes to the highly-confined SPP mode and vice versa is necessary for practical nanoscale fiber optics. The development of these optical fiber nanofocusing devices has been challenging as it requires the phase matching of photonic mode and plasmonic mode that exhibit different mode sizes (microscale vs nanoscale) and mode profiles (with the plasmonic mode being naturally radially polarized). Additionally, current attempts to integrate a nanometer-sized plasmonic nano-waveguide, e.g. a metal nanowire, onto a micrometer-sized fiber have required a challenging fabrication process with multiple procedures and precise alignments.The collaborative research between Prof. Zhenrong Zhangs group at Baylor University and Prof. Howard Lees group at the University of California, Irvine in the United States focuses on a simple and straightforward method of efficient coupling and focusing of the optical fiber photonic mode to the nanoscale plasmonic mode (Fig. 1a). The device involved is a needle-like plasmonic nano-antenna fabricated on the end facet of a photonic crystal fiber (PCF) by an electron beam induced evaporation technique (Fig. 1b). The fabrication, experimental characterization, and theoretical simulation of the device are published in Photonics Research Vol. 9, No. 2, 2021 (Khant Minn, Blake Birmingham, Brian Ko, Ho Wai Howard Lee, Zhenrong Zhang. Interfacing photonic crystal fiber with a metallic nanoantenna for enhanced light nanofocusing[J]. Photonics Research, 2021, 9(2): 02000252).In this platform, introduced by Khant Minn from Baylor University, the fundamental core mode of the PCF propagates through the fiber and couples to the SPP mode on the platinum nano-antenna via the end-fire coupling. Such direct coupling relaxes the challenging phase-matching requirement of the photonic mode and the plasmonic mode, enables broadband coupling, and reduces propagation losses. The coupled SPPs then propagate along the antenna toward the tapered end where they converge to produce a highly enhanced and confined field at the nano-scale apex. The precise control of the position and size of the plasmonic antenna is achieved by directly writing a nanoscale metallic tip onto the fiber in a single step inside a focused-ion and scanning electron microscope (FIB-SEM) chamber.Fig. 1. The photonic crystal fiber (PCF)-nanoantenna hybrid probe. (a) Schematics of the device and simulated intensity profile of plasmonic mode on metallic nanowire waveguide. (b) Schematics of the electron beam induced deposition process and SEM image of PCF and fabricated nanowireThis work presented a single-step fabrication of a fiber-plasmonic probe which allows for any fiber-antenna coupling configuration to be realized with high precision, in addition to the high yield of the designer 3D antenna with nanometer resolution. For example, during fabrication, a gold thin film rectangular aperture was opened at the base of the metal nanoantenna to enable the asymmetrical coupling and focusing of the commonly-accessible lineally-polarized light from the optical fiber to the radially-polarized nano-focusing plasmons at the tip apex. Input polarization selectiveness of the device observed in the side images of the scattered light demonstrated the plasmonic nature of the focused SPP.Prof. Zhenrong Zhang from Baylor University and Prof. Howard Lee from the University of California, Irvine believe that the fiber-plasmonic probe is a promising platform for the development of novel optical fiber devices and applications such as remote sensing and nearfield spectroscopes, single photon excitation and quantum sensors, nano-scale optical lithography, and lab-on-fiber devices.Future work will focus on the optimization of the coupling and focusing efficiencies and the integration of these fiber probes in scanning probe microscopes for nanoscale chemical imaging such as fiber-based tip-enhanced Raman and fluorescence spectroscopies.

皮秒光脉冲与纳秒电脉冲协同作用开辟将药物、疫苗输送到细胞和组织的新方法 自20世纪50年代以来光击穿和电击穿一直受到研究人员的广泛关注，其描述了在极端光场或电场作用下材料的变性。然而此前从未有人研究过光场和电场相结合，特别是其在生物相关系统中的应用。得克萨斯A&M大学的Vladislav V. Yakovlev教授提出，通过研究电脉冲和光脉冲的协同作用，研究人员能够更好地实现高局域击穿，同时降低击穿阈值。这种新发现的协同效应，在以高局域方式选择性破坏细胞膜方面尤其重要。此前常用的是电穿孔技术，即对细胞施加电场，以增加细胞膜通透性；还有一种常用的方法是光穿孔，即用超短激光脉冲在细胞膜上钻一个小孔。将两种方法结合起来，取二者之长，将能开辟一种将药物、疫苗输送到细胞和组织的新方法。近日，Vladislav V. Yakovlev教授等在Photonics Research2021年第3期发表的文章（Zachary N. Coker, Xiao-Xuan Liang, Allen S. Kiester, Gary D. Noojin, Joel N. Bixler, Bennett L. Ibey, Alfred Vogel, Vladislav V. Yakovlev. Synergistic effect of picosecond optical and nanosecond electrical pulses on dielectric breakdown in aqueous solutions[J]. Photonics Research, 2021, 9(3): 03000416）中表明在纳秒电脉冲和皮秒光脉冲同时激励下，可产生一种协同效应，进而降低击穿的阈值。图1 (a)用于预测电脉冲和光脉冲对介电击穿阈值协同效应的理论模型；(b)用于触发、监测介质中介电击穿的实验装置示意图；(c)图中实验结果显示了击穿概率与输入激光能量的关系该研究是在三个不同研究团队的共同努力下完成的，生物材料光学击穿研究领域的领军专家——Alfred Vogel教授领导的德国团队提出了一个理论模型（如图1（a）），该理论模型为得克萨斯A&M大学和美国空军研究实验室的研究人员提供了实验上实现协同作用的指导。实验装置包括纳秒电脉冲发生器，以及聚焦皮秒光脉冲激励源 （如图1（b））。并且通过在一些生物相关介质上进行实验，验证了协同效应理论（如图1（c））。图2 细胞实验的初步结果。荧光图像所示的是YO-PRO-1染料在(a)控制、(b)纳秒电脉冲单独作用、(c)皮秒光脉冲单独作用以及(d)皮秒光脉冲和纳秒电脉冲同时作用条件下的吸收情况。图（c）中的黄色虚线圈中为培养层细胞被击穿移除的位置培养层细胞。（d）中的橙色虚线圈表示，与周围暴露在纳秒电脉冲下的细胞相比，皮秒光脉冲聚焦处目标细胞中YO-PRO染料的吸收减少。从目前的全球形势来看，这种协同效应与普罗大众最息息相关的作用是其可以提高COVID-19疫苗接种的准确性。在初步实验中，合作团队使用电脉冲和光脉冲照射细胞（如图2），并使用一种沿用已久的染料YO-PRO-1来监测细胞膜的完整性；一旦细胞膜被破坏，这种染料就会渗入细胞。尽管此项技术目前并不存在于实验室已有的技术范畴内，但该合作团队指出，产生协同效应无需复杂的设备，因此可以在大多数实验设施中使用。而且认为，这类把新型基础科学研究与高影响力技术（比如极端光－物质相互作用，纳米生物技术等）结合起来的研究，必将会得到广泛关注。 Synergistic effect of picosecond optical and nanosecond electrical pulses on dielectric breakdown in aqueous solutions Optical and electrical breakdown of materials, which describe material modification in the presence of extreme optical or electrical fields, have been studied since the 1950s. However, simultaneous application of optical and electrical fields, especially, to biologically relevant systems hasnt been explored before. Prof. Vladislav V. Yakovlev from Texas A&M University said by investigating the synergistic action of electrical and optical pulses, they were able to promote highly localized breakdown, while reducing the threshold for such breakdown.The newly discovered synergistic effect is particularly important if there is a need to selectively disrupt cellular membrane in a highly localized manner. Typically, an electroporation, a technique that applies an electrical field to cells to increase the permeability of the cell membrane, is used. Alternatively, an optoporation, which uses ultrashort laser pulses to form a small hole in the cell membrane, can be employed. A powerful combination of electroporation and optoporation can provide the benefits of both of approaches, leading to new ways drugs and vaccines can be delivered to cells and tissues.The cooperative teams recent publication in Photonics Research vol. 9 No. 3 (Zachary N. Coker, Xiao-Xuan Liang, Allen S. Kiester, Gary D. Noojin, Joel N. Bixler, Bennett L. Ibey, Alfred Vogel, Vladislav V. Yakovlev. Synergistic effect of picosecond optical and nanosecond electrical pulses on dielectric breakdown in aqueous solutions[J]. Photonics Research, 2021, 9(3): 03000416) demonstrated that upon simultaneous excitation by nanosecond electrical pulse and picosecond optical pulse, a synergetic effect occurs, leading to reduced threshold for such breakdown.Figure 1. (a) A theoretical model, which predicts the synergistic effect of electrical and optical pulses on the threshold of dielectric breakdown; (b) a schematic of experimental setup which used for initiating and monitoring dielectric breakdown in a medium; (c) experimental results demonstrating the probability of breakdown on the input laser energy.The research was completed with the joint efforts of three different teams. The German team led by Prof. Alfred Vogel, the leading expert in the optical breakdown studies of biological materials, developed a theoretical model (Fig. 1a) which provided Texas A&M University and Air Force Research Laboratory researchers with guidelines for experimental realization of the proposed synergistic interactions. An experimental setup, which included both the nanosecond electrical pulser and a focused beam picosecond optical pulse excitation, was constructed (Fig. 1b), and the proposed effect was experimentally demonstrated for a number of biologically relevant media (Fig. 1c).Figure 2. Preliminary results for cell-based studies. Fluorescent images showing YO-PRO-1 dye uptake under (a) control, (b) nanosecond electrical pulse alone, (c) picosecond optical pulses alone, and (d) combined picosecond optical and nanosecond electrical exposure conditions. Yellow dashed circle in c indicates where cells were removed from culture layer by breakdown event. Orange dashed circle in d indicates where picosecond optical pulse was focused and the reduced YO-PRO dye uptake in targeted cells, compared to surrounding cells exposed to nanosecond electrical pulse.One of the impacts of paramount significance of this effect, which can be of great interest to a general audience, is improved accuracy of vaccine delivery for COVID-19. In preliminary data, the team performed cellular exposure to both electrical and optical pulses (Fig. 2) monitoring the integrity of the cellular membrane using a well-established dye, YO-PRO-1, which upon membrane disruption penetrates the cell.While this technology would be a new addition to a laboratory, the research team noted that creating the effect doesnt require sophisticated equipment, allowing it to be used in a broad range of facilities.As the research team states, a unique combination of a new fundamental science and a broad range of high-impact applications ranging from extreme light-matter interactions to nano- and biotechnology would be of great interest for a broad audience.

纳米压印光刻：小芯径中红外硫系光纤端面的抗反射结构 热纳米压印光刻技术，简称为纳米压印，是一种通过将材料加热到特定温度，使之具有延展性、可被塑造定形，从而将纳米或微观结构构造到材料上的过程。由于硫系化合物玻璃的转变温度较低，因此纳米压印技术广泛应用于硫系玻璃的加工中，在常规加热炉可达到的温度范围内即可对玻璃进行构造。因此，热纳米压印已被应用于平面波导、衍射光栅和环形谐振器等各类光子器件的制造中。然而，由于硫系玻璃折射率较高，光在硫系波导和光纤中传输时，会在光纤与空气或其他低折射率材料的界面处发生强烈的菲涅耳反射。目前已有的抗反射（anti-reflective, AR）方法包括布儒斯特角连接器、镀薄膜涂层、以及采用纳米蛾眼减反结构等。2-10 μm的常规As40Se60硫系玻璃的布儒斯特角在70°左右，实施起来相对简单。然而，其AR只对p线性偏振光有效，对偏振的波动异常敏感，但对圆偏振和非偏振光的减反效果并不理想。在光纤端面沉积薄膜可以改善硫系光纤的传输性能，但由于沉积的涂层材料和光纤材料的热机械性能不同，光纤损伤阈值相应降低，造成在光纤端面在加热时涂层开裂和脱层。此外，单层涂层只能在几百纳米的窄带波长范围内抗反射，且中心波长随图层厚度的变化剧烈改变；多层涂层可以扩展抗反射带宽覆盖范围，却增加了工艺的复杂性，降低了热机械的稳健性。（a）热纳米压印原理示意图，（b，c）光纤照片：（b）压印期间（c）压印之后；不同的颜色来源于纳米结构的角度和不同波长的反射相比之下，蛾眼减反结构可以直接压印在光纤的端面上实现宽带宽，不受偏振影响的高吞吐量传输，且不会因开裂和脱层造成光纤损伤。此前的研究已证实，纳米压印技术可在宽带宽范围内增加单材料硫系光子晶体光纤（photonic crystal fiber, PCF）的传输性能。然而，对于传统阶跃折射率光纤(step-index fibers, SIF)来说，还存在另一个问题：即纤芯和包层玻璃的热机械性能不同。迄今为止，有关在SIF端面上纳米压印AR结构的文献报道仅限于硫系玻璃型的大芯径多模光纤，这种光纤的纤芯和包层玻璃之间组分差异非常小。而对于玻璃材质差别非常大的小芯径阶跃折射率光纤不同热机械性能的影响，在已知范围内尚未有相关研究成果发表。丹麦技术大学光子工程系、国家纳米制造与表征中心的Christian R. Petersen及同事与英国诺丁汉大学乔治·格林电磁研究所的中红外光子学小组合作，通过实验测试了不同的纤芯和包层玻璃成分的纳米压印SIFs的动态响应和热机械性能，相关研究成果发表在Chinese Optics Letters第19卷第3期（C. R. Petersen, et. al., Thermo-mechanical dynamics of nanoimprinting anti-reflective structures onto small-core mid-IR chalcogenide fibers [Invited]）。该研究挑战了小芯径SIFs上进行纳米压印的难题，特别是压印过程中纤芯玻璃的收缩问题，提出了一种在不过度变形光纤尖端的情况下实现较高质量压印的方法，从而大大提高传输的性能。此外，研究人员还验证提出了在聚合物/硫族化合物多材料光纤上可压印AR结构。该研究指出，纳米压印是一种通用且实用的方法，可以提高小芯径和大芯径硫系SIFs的传输性能，无需无尘室沉积设备即可进行工业规模制造。此项技术在由不同的聚合物、玻璃和金属组成的多材料光纤端面制备中具有未来应用的潜力，尤其可以在各种硬度不同的光纤中大显身手。 Thermo-mechanical Dynamics of Nanoimprinting Anti-ReflectiveStructures onto Small-core Mid-IR Chalcogenide Fibers Thermal nanoimprint lithography, or nanoimprinting in short, is the process by which nano- and microscopic structures are transferred onto a material by heating it up to a specific temperature, such that it becomes malleable and can be molded into a desired shape. The technique has proven particularly useful for chalcogenide glasses due their low glass transition temperatures (e.g. 185 ºC), that allow for structuring of the glasses at temperatures that are easily obtained by conventional heaters. For this reason, thermal nanoimprinting has been applied in the fabrication of various photonic devices, including planar waveguides, diffraction gratings, and ring resonators.Unfortunately, due to the high refractive indices of chalcogenide glasses, transmission of light in chalcogenide waveguides and optical fibers are limited by strong Fresnel reflections at the interfaces with air or other low index materials. Several methods have been proposed to obtain anti-reflective (AR) properties, including Brewster angle connectors, thin-film coatings, and nanoimprinting of moth-eye structures. The Brewster angle for typical As40Se60 at. % chalcogenide glass is around 70 degrees from 2-10 µm, which although inconvenient is relatively simple to implement. However, the AR effect works only for linearly p-polarized light, making it sensitive to polarization fluctuations and reducing its effectiveness for circular or unpolarized light sources.Thin film deposition on the fiber end faces has been demonstrated to improve the transmission of chalcogenide fibers, but tends to reduce the damage threshold of the fiber due to differences in thermo-mechanical properties between the deposited coating material and the optical fiber. This causes the coating to crack and delaminate as the fiber end face heats up during use. Furthermore, single layer coatings can only provide AR properties over a relatively narrow wavelength region of a few hundred nanometers, and the peak wavelength is very sensitive to the layer thickness. Multilayer coatings are therefore needed to extend the bandwidth, which increases the complexity and reduce the thermo-mechanical robustness.(a) Illustration of the thermal nanoimprinting principle. (b), (c) Photograph of the fiber (b) during and (c) after imprinting. The different colors are due to the angle and wavelength dependent reflection of the nanostructures.In contrast, so-called moth-eye AR structures can be directly imprinted on the end face of optical fibers to achieve broadband-, polarization-independent-, and high throughput transmission without the risk of damage due to cracks and delamination. In a previous report, an increase in transmission over a broad bandwidth was achieved in single-material chalcogenide photonic crystal fiber (PCF) via nanoimprinting. However, traditional step-index fibers (SIF) have the additional challenge of having different core and cladding glasses, each with its own thermo-mechanical properties. Reports from the literature on nanoimprinting of AR structures onto SIF end faces have so far been limited to large-core multi-mode fibers of the sulphide-glass type, with small variation between core and cladding glass compositions. Consequently, the effect of different thermo-mechanical properties in highly disparate glasses and small-core SIFs has, to our knowledge, not been explored until now.Christian R. Petersen and co-workers from Technical University of Denmark, Department of Photonics Engineering and the National Centre for Nanofabrication and Characterization, experimentally tested the dynamics of nanoimprinting SIFs with different core/cladding glass compositions, and therefore different thermo-mechanical properties. The work was performed in collaboration with the Mid-Infrared Photonics group at the George Green Institute for Electromagnetics Research, Nottingham University, United Kingdom, and published in Chinese Optics Letter, Volume 19, Issue 3, 2021 (C. R. Petersen, et. al., Thermo-mechanical dynamics of nanoimprinting anti-reflective structures onto small-core mid-IR chalcogenide fibers [Invited]). The study highlights some of the challenges of nanoimprinting on small-core SIFs, in particular the contraction of the core glass during imprinting, and propose a method for achieving good imprints and greatly improved transmission without excessive deformation of the fiber tip. The conclusion of this investigation is, that nanoimprinting is a versatile and practical method for achieving high transmission in both small-core and large-core chalcogenide SIFs, that can be scaled to industrial-scale fabrication without the need for cleanroom deposition facilities.The research team hints at a future application of the technology within end face preparation of multi-material fibers, composed of different polymers, glasses, and metals. Such fibers are very difficult to polish due to the different hardness of the materials, and would therefore benefit greatly from thermal nanoimprinting. Here, the researchers present a proof-of-concept result with imprinting the AR-structure on a polymer/chalcogenide multi-material fiber.

深度压缩新方法大幅提高单像素相机的成像速度 提及光学成像，大家通常想到的工具就是具有数百万个像素的相机。但在不可见光谱下，其灵敏度较差，且只有造价非常昂贵的相机才有可能克服这个缺点，从而在此种条件下具有较高灵敏度且经济实惠的单个探测器很快受到了人们的广泛关注。通过单个探测器成像的最直接也是最常见的方法就是对物体进行扫描，逐个像素对其进行测量。另一种非常有趣的方法是利用压缩感测，通常也称为单像素相机成像。与逐个像素采样不同，这种方式通过对不同像素的组合来对物体进行采样。单像素成像使用某一图案照射物体，并用探测器测量那些受到图案照射的物体像素的总强度，通过变换不同的照明图案并进行测量，进而重建物体。在常规相机和基于点扫描的成像系统中，实际的测量次数与像素总数相同（前者通过相机上的所有探测器一次性测量所有像素，而后者则通过单个探测器逐个测量像素）。然而，在压缩感测中，测量的次数与照明图案的数量相同，其远小于像素的数量（1%~10%），同时还可以高质量地恢复成像物体，从而压缩感测具有很高的测量效率。但是，利用压缩感测的单像素相机需要使用DMD（Digital Micromirror Device）去切换不同的照明图案，而这个切换速度限制了整体的成像速度。从而导致在许多情况下，这种单像素相机的成像速度低于基于点扫描或常规相机的成像速度。针对上述研究现状，美国加州大学戴维斯分校的杨暐健教授课题组在Photonics Research 2021年第3期（Kangning Zhang, Junjie Hu, Weijian Yang. Deep compressed imaging via optimized pattern scanning[J]. Photonics Research, 2021, 9(3): 03000B57 ）发表的文章中展示了一种新的压缩成像方式（DeCIOPS）。该成像方式通过在物体上投影并扫描一个被经过优化的图案，再进行深度压缩成像，可以解决现有单像素相机中遇到的困难，大大提高压缩成像的成像速度。DeCIOPS的示意图。DeCIOPS通过一个照明图案对物体进行区块采样, 并利用ISTA-Net（一种基于压缩感测的深度神经网络）重建高分辨率物体（照明图案和ISTA-Net中的参数由自编码器的端到端训练进行优化）DeCIOPS把一个照明图案投影到物体的一个区块上，然后通过照明图案对这个区块上的所有像素进行加权求和而得到一个测量值。只需扫描照明图案，就可以测量物体的不同区块。接着，研究者们开发了一种基于压缩感知的深度神经网络，可以从这种看似低分辨率的区块测量中恢复高分辨率的图像，其从本质上实现了超分辨率成像。此外，研究人员通过自编码器对DeCIOPS进行建模，并对该编码器以端到端的方式进行训练，其在实现了用于图像采集的照明图案和物体重建的深度神经网络优化的同时，也确保了物体的高质量重建。整体而言，DeCIOPS综合了点扫描中的高采集速度和压缩感测中的高测量效率的优势。与点扫描系统相比，DeCIOPS通过高效的采样方式提高了成像速度（几倍到一个数量级）。与需要在许多照明图案之间进行切换的常规压缩成像相比，DeCIOPS只需要在整个物体上扫描单个照明图案，从而将整体成像速度提高多个数量级。杨暐健教授表示，“DeCIOPS紧密集成了成像系统和计算算法，是计算成像中一个很好的例子，并且该成像方法提供的高成像速度使其在生物医学、监视和消费电子领域都有非常大的应用空间。” New imaging modality through deep compressed sensing enables high speed imaging Optical imaging typically relies on a camera with millions of photodetectors. By contrast, imaging can also take place with a single detector. This is particularly advantageous for imaging at non-visible spectrum where the conventional pixelated cameras lose the sensitivity or become very costly for a good performance.A most straightforward way to image through a single detector is to scan the object and measure it pixel by pixel. Yet, another interesting approach, commonly known as single-pixel camera, is to leverage compressed sensing. Instead of being sampled pixel by pixel, the object is sampled through the sum of different combinations of pixels. Typically, the object is illuminated with a pattern, and the detector captures the sum intensity of the object pixels illuminated by the pattern. By performing the measurement through different patterns, the entire object can be reconstructed.In both the conventional camera and the point-scanning-based system, the actual number of measurements is the same as the total number of pixels, though the former measures all pixels at once through different detectors and the latter measures individual pixel sequentially through a single detector. However, the number of measurements, i.e. the number of illumination patterns, can be much smaller than the number of pixels (for example 10~100 times smaller) in compressed sensing. The computation algorithm can then recover the object in high quality through a small number of measurements, by exploiting the natural relationship between adjacent pixels. As a result, compressed sensing has a very high measurement efficiency. The fewer measurements make it promising to reduce the data acquisition time and thus increase the imaging speed.However, the existing implementation of compressed sensing in imaging relies on switching different illumination masks, and the limited speed in the switching device (digital mirror device) restraints the overall speed. In many scenarios, the imaging speed of the switching-mask-based single-pixel camera is actually lower than that based on point scanning or conventional cameras.The research group led by Prof. Weijian Yang from University of California, Davis recently demonstrated a new compressed imaging modality, termed "deep compressed imaging via optimized pattern scanning" (DeCIOPS), which could overcome the challenges in the existing single-pixel cameras, and greatly improve the imaging speed of compressed imaging. The research results are published in Photonics Research, Vol. 9, No. 3, 2021 (Kangning Zhang, Junjie Hu, Weijian Yang. Deep compressed imaging via optimized pattern scanning[J]. Photonics Research, 2021, 9(3): 03000B57 ).Schematics of DeCIOPS (deep compressed imaging via optimized pattern scanning). The object is sampled block by block by an illumination pattern. ISTA-Net, a compressed-sensing-inspired deep neural network is used to reconstruct the object. The illumination pattern and the parameters in ISTA-Net are optimized through an end-to-end trained auto-encoder.In this new imaging modality (DeCIOPS), a block of pixels, weighted by an illumination pattern, are sampled and summed into a single measurement. By scanning the illumination pattern across the object, different blocks of pixels could be measured. A reconstruction algorithm based on a compressed-sensing-inspired deep neural network was developed to recover the high resolution image from this seemingly low-resolution block-by-block measurement. Since the number of measurement blocks can be much smaller than the number of total pixels, the measurement speed can be very high.In addition, the researchers modeled DeCIOPS through an auto-encoder, which was trained in an end-to-end manner and jointly optimized the illumination pattern for image acquisition and the deep neural network for object reconstruction. The end-to-end optimization ensures an overall optimal performance of the entire imaging system and thus a high quality in object reconstruction.Essentially, DeCIOPS synthesizes the strengths of the high acquisition speed of point scanning and the high measurement efficiency of compressed sensing. Compared to the point scanning system, DeCIOPS increases the imaging speed (by a few folds to one order of magnitude) through a highly efficient sampling scheme. Compared to the conventional compressed imaging which requires switching between many illumination patterns, DeCIOPS scans a single illumination pattern across the object, and could increase the overall acquisition speed by orders of magnitude."DeCIOPS represents a nice example in computational imaging with a tight integration of the imaging system and the computation algorithm," said Prof. Weijian Yang. He believes that the high imaging speed offered in DeCIOPS makes it very promising for applications in biomedicine, surveillance, and consumer electronics.

量子调控“尝鲜”方案在混合体系中实现量子逻辑操作和逻辑门 在单量子水平实现对光和物质相互作用的完美控制，不仅仅是量子光学中的一个核心问题，同时也是许多基本物理现象及其应用的研究基础。伴随着先进的光子纳米材料及其加工技术的不断革新，一场基于光学和光子学的量子信息技术革命正在蓬勃发展。近年来，手性量子光学的快速发展得到了科技界的广泛关注，而手性的光与物质相互作用（含不对称性），顾名思义就是跟传播方向有关的光子发射器。基于这个物理现象，人们理所当然地会想到利用这种特殊的现象来实现某种特殊的调控，如非互易耦合。不仅如此，如何将这种手性器件融合到一个混合的量子体系中来实现一整套有趣的量子操作也是一个值得思考的问题。金刚石氮-空位中心（NV）以及基于它来构建的混合量子体系已经成为当前量子信息处理研究领域的宠儿。作为一种点缺陷，NV具备很多优良的物理性质，如优秀的自旋属性、具备原子的一般特点、无需俘获或者囚禁、光学寻址方便、容易集成、室温下仍具有超长相干时间等。因此，在可见光频率范围里，人们可以很方便地将NV集成到光学微腔或者光晶格中，并在单量子水平对其进行高效地相干调控。结合上述研究热点，湖北汽车工业学院理学院周原博士课题组在Photonics Research 2021年第3期发表的文章中（Yuan Zhou, Dong-Yan Lü, Wei-You Zeng. Chiral single-photon switch-assisted quantum logic gate with a nitrogen-vacancy center in a hybrid system[J]. Photonics Research, 2021, 9(3): 03000405）提出了一种有趣且新颖的实现量子逻辑操作和逻辑门的方案。混合器件示意图。该混合器件包含一个手性单光子发射开关，一个NV自旋被放置在一个光学微腔中，微腔和光子开关之间用纳米光纤相连该设计方案中，整个混和器件主要由三部分构成：一个手性的单光子脉冲开关，一个NV自旋，以及一个光学微腔。其中，对于如何实现该手性开关，研究人员提出了三种不同的技术路线，即冷原子体系实现单原子路由器、量子电体系实现路径编码光子发射以及利用表面等离子方案实现手性光子发射。该混和器件中，NV自旋被放置于光学微腔中并且利用纳米光纤将微腔和光子开关相连。接着，在光学微腔中引入双色的微波场来驱动NV自旋的基态，同时进入微腔的手性光子信号也会以光学模式与NV自旋的激发态进行近共振耦合。另外，研究人员还在考虑到各种实际的噪声和实验缺陷等不利因素的影响下，对整个逻辑操作进行了模拟和评估。周原博士表示，这个有趣的研究在利用集成或者混合的光量子器件实现量子调控的领域中可以被看作是一种新鲜的尝试，并希望它能在量子信息技术的研究过程中得到更广泛的应用。 Chiral single-photon switch-assisted quantum logic gate with a nitrogen-vacancy center in a hybrid system In the quantum optics research area, a central goal is to develop techniques for a complete control of light-matter interaction at the single-quantum level, which underlies the essential physics of many phenomena and applications. A new quantum revolution on optics and photonics is also accelerating the progress of quantum information processing (QIP), with the rapid innovation of the advanced photonic nanomaterials and processing technologies.Recently, "chiral quantum optics" which leads to a chiral type light-matter interaction, so-called "propagation-direction-dependent" emission, has quickly attracted widespread attentions. Utilizing this kind of chiral interface, people can surely constitute an interesting quantum control of photon-emitter interaction, i.e. the nonreciprocal interaction, and furthermore fabricate a hybrid quantum system with this exciting photon-emitter setup to function some special and interesting quantum operations.As a point defect in diamond, the nitrogen vacancy (NV) centers integrated in a hybrid quantum system have recently emerged as one of the leading candidates for QIP thanks to their excellent spin properties, such as atom-like properties, solid-state spins without any trap, optical addressable, easy scalability, and longer coherence time even at ambient conditions. In the optical-frequency domain particularly, we can conveniently fabricate the NV center with the optical cavity or optical lattice in a hybrid device, and coherently manipulate the NV center at single-quantum level with enough high efficiency.This investigation proposed by Dr. Yuan Zhou from the quantum physics group from the School of Science, Hubei University of Automotive Technology (HUAT) in Photonics Research, Vol. 9, No. 3, 2021 (Yuan Zhou, Dong-Yan Lü, Wei-You Zeng. Chiral single-photon switch-assisted quantum logic gate with a nitrogen-vacancy center in a hybrid system[J]. Photonics Research, 2021, 9(3): 03000405) is an interesting and novel proposal for realizing a quantum logic operation and logic gate.This hybrid system consists of a chiral switch for emitting photon pulse and an optical microcavity embedded with a single NV center, both of which are connected with an optical nanofiberThis interesting hybrid device is fabricated by a chiral photon-pulse switch, a single NV center, and an optical microcavity. For realizing this chiral photon switch, three major different practical routes are available, i.e. the "one-atom router" with cold atom scheme, "the path-encoded photon" with quantum dot system, and the "chiral photon emitter " with surface plasmon (SP) scheme.The outputs are delivered to the optical microcavity through nanofiber in this hybrid system. A single NV center, driven by a dichromatic microwave field, is planted in the optical microcavity, which will also interact with the optical modes near-resonantly.Besides, taking all of adverse factors into this theoretical investigation, i.e. the practical noise and experimental imperfection, this whole logic operation is evaluated numerically.This work may be a useful attempt for implementing quantum manipulation with integrated or hybrid optical quantum devices owing to its inherent innovative and interesting nature, and may evoke wide and fruitful applications in QIP.

2021年11月 昆明会议官网：https://b2b.csoe.org.cn/meeting/NDTA2021.htm光电探测技术是现代信息获取的主要手段之一，光电探测技术的发展是随着其他关键技术的发展而发展的，由于激光技术、光波导技术、光电子技术、光纤技术、计算机技术的发展，以及新材料、新器件、新工艺的不断涌现，光电探测技术取得了巨大发展。近年来，光电探测技术引起了业内人士的普遍关注，在军事和民用领域占有越来越重要的地位。组委会将于2021年11月在昆明市举办“第八届国际新型光电探测技术及其应用研讨会”，深入研讨近年来涌现出的各种新型探测技术，包括微光探测、偏振探测、量子探测、单光子探测技术等，以促进国际和国内新型光电探测技术及相关产业的可持续、健康发展。大会征文已开通，诚挚欢迎国内外相关领域的科研人员、教师、研究生等踊跃投稿。主办单位：中国光学工程学会微光夜视技术重点实验室承办单位：云南大学西安工业大学北方夜视技术股份有限公司中国宇航学会光电技术专业委员会联办单位：北京理工大学南京理工大学长春理工大学电子科技大学中国科学院半导体研究所中国科学院上海技术物理研究所中国科学院上海微系统与信息技术研究所天津津航技术物理研究所江苏省光谱成像与智能感知重点实验室中国科学院红外成像材料与器件重点实验室中国科学院空间光电精密测量技术重点实验室北京仿真中心航天系统仿真重点实验室复杂产品智能制造系统技术国家重点实验室北京理工大学光电成像技术与系统教育部重点实验室江苏省光学学会大会主席：褚君浩院士，中国科学院上海技术物理研究所于起峰院士，国防科技大学征文方向： Ultraviolet detection technologies and applications/紫外探测技术及应用Visible light detection technologies and applications/可见光探测技术及应用Infrared detection technologies and applications/红外探测技术及应用Terahertz detection technologies and applications/太赫兹探测技术及应用Low level light detection technologies and applications/微光探测技术及应用Single photon detection technologies and applications/单光子探测技术及应用High dynamic imaging technologies and applications/高动态成像技术及应用high-speed imaging technologies and applications/高速成像技术及应用3D imaging technologies and applications/三维成像技术及应用Laser detection technologies and applications/激光探测技术及应用Polarization detection technologies and applications/偏振探测技术及应用Quantum technologies and applications/量子探测技术及应用Multispectral/ highspectral/hyperspectral detection technologies and applications/多光谱/高光谱/超光谱探测技术及应用Optoelectronic devices technologies and applications/光电子器件技术及应用Novel Microwave detection technologies and applications/新型微波探测技术及应用Composite detection technologies and applications/复合探测技术及应用Space detection technologies and applications/空间探测技术及应用Advanced optical design and manufacturing technologies/先进光学设计与制造技术Intelligent optoelectronic detection technologies and applications/智能光电探测技术及应用Intelligent information processing technologies and applications/智能化信息处理技术及应用Intelligent optical detecting-tracking technologies and applications/智能光电探测跟踪技术及应用Others/其他 论文发表：中英文稿件兼收，请作者登录网站提交论文全文，组委会请专家进行审稿。通过审查的稿件被大会录用，择优推荐到正式出版物发表。英文稿件推荐至SPIE会议论文集（EI检索）收录。中文稿件推荐至支持期刊发表。支持期刊： 《红外与毫米波学报》（SCI）《红外与激光工程》（EI）《光学精密工程》（EI）《光子学报》（ESCI，EI）《兵工学报》（EI）《中国光学》（EI）《航空学报》（EI）《遥感学报》（EI）《信息与控制》（中文核心）《电光与控制》（中文核心）《应用光学》（中文核心）《红外技术》（中文核心）《探测与控制学报》（中文核心）《强激光与粒子束》（中文核心）《太赫兹科学与电子信息学报》（中文核心）《现代防御技术》（科技核心）《光学与光电技术》（科技核心）《深空探测学报》 投稿网址：https://b2b.csoe.org.cn/submission/NDTA2021.html截稿时间：2021年5月20日（第一轮） 组委会：刘艳022-58168510liuyan@csoe.org.cn

2021年8月 宁波 会议官网：https://b2b.csoe.org.cn/meeting/IR2021.html 红外及夜视技术在国防、工业和民生领域得到了广泛应用，并促进了我国光电材料、先进器件和集成电路技术的发展，逐步迈向自主化时代。当前随着光电子、微电子和人工智能技术的发展，获取与感知领域方向朝着多手段、多功能、智能化、网络化和信息化迈进，多专业技术交叉融合发展，迫切需要加强产学研密切合作，形成完整的技术创新链，加速技术成果转化，促进技术创新和产业快速发展。 中国光学工程学会红外专家工作委员会联合成员单位，定于2021年8月在宁波市举办“第二届全国红外技术及其应用技术峰会”。组委会将邀请各领域专家共同研讨并交流相关技术，促进行业上下游交流与合作，搭建协同创新的技术交流平台，诚挚欢迎广大科研人员、教师和研究生踊跃投稿并参会。主办单位：中国光学工程学会承办单位：宁波大学中国光学工程学会红外专家工作委员会大会主席：陈良惠院士，中国科学院半导体研究所褚君浩院士，中国科学院上海技术物理研究所王建宇院士，中国科学院上海分院议题方向（不限于此）：红外技术与国防领域应用论坛征文方向：1 自主化光电器件及集成电路芯片技术 2 先进红外光学材料与系统技术 3 新型红外系统探测与识别技术 4 光电传感/射频电子与微系统技术 5 先进红外系统测试评价技术红外技术与工业领域应用论坛征文方向：1 机器视觉与智能检测技术 2 红外技术在工业领域的应用 红外技术与民生领域应用论坛 征文方向：1 红外技术在安防/消防领域的应用2 红外技术在公共安全与卫生健康领域的应用 支持期刊：《红外与毫米波学报》（SCI），《红外与激光工程》（EI），《兵工学报》（EI），《光学精密工程》（EI），《中国光学》（EI），《光子学报》（ESCI，EI），《红外技术》（中文核心），《电光与控制》（中文核心），《太赫兹科学与电子信息学报》（中文核心），《光学与光电技术》（科技核心），SPIE会议论文集 (EI)。 发表须知： 中英文稿件兼收，请作者登录网站提交论文全文，组委会请专家进行审稿，通过审查的稿件被大会录用。英文稿件推荐至SPIE会议论文集（EI收录）发表；中文稿件择优推荐至SCI、EI或中文核心期刊发表。截稿时间：2021年4月30日（第一轮）投稿网址：https://b2b.csoe.org.cn/submission/IR2021.html 组委会：刘艳022-58168510liuyan@csoe.org.cn

会议官网：https://b2b.csoe.org.cn/meeting/SJYJC2021.html

CMOS平台上实现基于超表面的减色滤波器 随着纳米技术的不断发展革新，基于光和微纳物质结构相互作用的可见光滤波器随之产生，并被视为必不可少的光学组件，广泛应用于日常生活中。这类基于微纳结构的可见光滤波器能够克服基于染料的传统可见光滤波器的缺点，如化学染料对环境的危害、长时间使用后染料褪色导致的性能下降等。基于微纳结构的可见光窄通带滤波器（一般由周期性的圆柱或圆柱形空槽结构组成）已得到广泛研究。其中，增色滤波器（ACF）的通带通过调整亚波长结构的周期、间距或尺寸就可以实现。但是，当ACF和与其对应的减色滤波器（SCF）相比较时，由于SCF是基于互补色去除的工作原理，即不存在光谱中大部分光被滤除的问题，从而具有比ACF更高的透射和反射效率。与此同时，使用先进光刻技术在互补金属氧化物半导体 (CMOS)兼容平台上大规模制造SCF还有待探索。针对以上研究现状，新加坡科技研究局（A*STAR）微电子研究院（IME）的研究团队在Photonics Research 2021年第1期发表的文章中（Zhengji Xu, Nanxi Li, Yuan Dong, Yuan Hsing Fu, Ting Hu, Qize Zhong, Yanyan Zhou, Dongdong Li, Shiyang Zhu, Navab Singh. Metasurface-based subtractive color filter fabricated on a 12-inch glass wafer using a CMOS platform. Photonics Research, 2021, 9(1): 01000013）首次展示了使用CMOS兼容工艺在12英寸(300 mm)玻璃晶圆上制造的SCF。在12英寸玻璃晶圆上的大面积超表面器件该研究团队将经过刻蚀之后的非晶硅层作为超表面层，同时为了在透明玻璃晶圆上制造透射型SCF，还将新开发的薄膜层转移工艺用于解决微纳制造设备中的玻璃晶圆的处理难题。接着使用CMOS兼容工艺制造了三批具有不同高度（110，170和230 nm）的非晶硅纳米柱晶圆，并通过仿真和实验研究了非晶硅纳米柱高度对器件透射光谱的影响。此外，还发现通过对纳米柱高度和间距的改变，可以获得具有不同显示颜色的SCF（所显示的颜色由匹配红、黄、蓝（RYB）色轮内已过滤颜色的互补色来验证）。与此同时，该研究团队还对仿真和实验获得的透射光谱进行了比较和讨论。并通过CIE 1931（由国际照明委员会于1931年创立的最先采用数学方式来定义的色彩空间）颜色匹配函数，绘制了SCF透射光谱的色度坐标。研究团队表示，该工作一方面为大规模生产结构性滤波器奠定了基础，另一方面在大面积超表面光学组件的量产和商业化方面展示了有利的前景。 Metasurface-based subtractive color filter fabricated on a 12-inch glass wafer using a CMOS platform With advanced nanotechnology, the emerging structural color filter which works based on the light-matter interaction is able to overcome the drawbacks of the traditional dye-based color filters including environmental hazards and performance degradation. Therefore, it has been regarded as an essential optical component and widely applied in daily life.The structural color filters with narrow passband contributed by the periodic pillar or hole structure have been widely studied. The passband of the additive color filter (ACF) can be designed by tuning the period, pitch, or dimension of the subwavelength structures. However, ACFs have relatively lower transmission/reflection efficiency compared with its counterpart, which is the subtractive color filter (SCF), since most of the light in the spectrum is filtered out. The SCFs can achieve higher transmission/reflection efficiency since they work based on the removal of the complementary color. In the meanwhile, the SCF fabricated on CMOS-compatible platform in large scale using photolithography patterning technology remains unexplored.In this study conducted by the group from Institute of Microelectronics (IME), Agency for Science, Technology and Research (A*STAR) Singapore, SCFs on 12-inch (300-mm) glass wafer substrate fabricated using the CMOS-compatible process is demonstrated. It was published in Photonics Research, Vol. 9, No. 1, 2021 (Zhengji Xu, Nanxi Li, Yuan Dong, Yuan Hsing Fu, Ting Hu, Qize Zhong, Yanyan Zhou, Dongdong Li, Shiyang Zhu, Navab Singh. Metasurface-based subtractive color filter fabricated on a 12-inch glass wafer using a CMOS platform. Photonics Research, 2021, 9(1): 01000013).Large-area metasurface devices on a 12-inch glass waferAn amorphous Si layer has been patterned and used as a metasurface layer. To make the transmissive-type SCF on a transparent glass wafer substrate, an in-house developed layer transfer process is used to solve the glass wafer handling issue in fabrication tools. Three batches of wafer with pillar height variation (110, 170, and 230 nm) are fabricated. The effect of a-Si nanopillar height on the device transmittance spectra is investigated through both simulation and experiment. With pillar height and pitch variation, SCFs with different displayed colors are achieved. The displayed colors are verified by matching the complementary color of filtered color within red-yellow-blue (RYB) color wheel. The transmittance spectra obtained from simulation and experiment have been compared and discussed. Also, by utilizing the CIE 1931 color matching function, the chromaticity coordinates of transmittance spectra for SCFs are plotted.This work paves the way toward the large-scale mass production of the structural color filters and this is promising for the potential commercialization and large-scale deployment of the metasurface-based optical devices.

圆梦：实现以光钟为频率基准的高精度光学频率合成系统 在通讯、雷达、全球定位系统等应用中，人们不断追求噪声更低、精度更高的电磁波，从而达到通讯容量增大、定位精度提高的目的。其中，微波频率合成器发挥了重要作用，它能在所需要的频率处输出与微波钟性能相当的电磁波信号。近年来，光波波段的电磁波（频率比微波高四个数量级）的性能已超越了微波：低噪声光学振荡器的频率稳定度已达到10−17量级（1s积分时间），光钟的精度已达到10−18量级，比铯喷泉钟还好两个数量级。有了性能如此优异的电磁波，不仅能建立新一代时间频率标准，在高新技术应用中发挥不可替代的作用，还能以前所未有的精度和灵敏度去进行基本物理常数是否随时间变化的探索、厘米量级引力势测量、相对论验证等研究。由于光波振荡器或光钟只工作在特定光频处，故需要利用光学频率合成器，将低噪声和高精度的光钟频率特性传递到所需要的频率处。光学频率合成器的研究关键在于：光频合成过程不能破坏频率精度和相干性。近日，华东师范大学精密光谱科学与技术国家重点实验室的蒋燕义研究员团队在Photonics Research 2021年第2期（Yuan Yao, Bo Li, Guang Yang, Xiaotong Chen, Yaqin Hao, Hongfu Yu, Yanyi Jiang, Longsheng Ma. Optical frequency synthesizer referenced to an ytterbium optical clock[J]. Photonics Research, 2021, 9(2): 02000098）发表的文章中报道了有望采用芯片光梳实现高精度的光学频率合成。以光钟为频率基准的光学频率合成器该研究团队将光梳锁定于铷钟，光梳梳齿的频率稳定度为2×10−11（1s平均时间）。使用频率噪声如此大的光梳，借助光梳频率噪声免疫技术可实现低噪声高精度的光学频率合成：光频合成噪声为6 × 10−18（1s平均时间），光频合成精度为5 × 10−21，表明它能对世界上最低频率噪声或最高频率精度的光波进行频率合成而不影响其性能。利用该技术，研究团队将1064 nm稳频激光的性能传递到578 nm，获得了线宽为Hz量级的镱原子光钟跃迁谱线，并将偏离跃迁中心频率的误差信号反馈给1064 nm稳频激光，最终将镱原子光钟的频率精度高保真地传递到了530~1100 nm范围中。华东师范大学的马龙生教授对此深有感触：40年前当他第一次使用无线电波频率合成器时，他就梦想拥有一台光学频率合成器，用于开展精密光谱研究；2000年光梳的诞生为实现这个梦想铺平了道路；经过20年的奋斗，他们相继研制了窄线宽稳频激光、基于光梳频率噪声免疫技术的光学频率合成器、冷镱原子光钟系统，并将它们集成为一个具有光钟精度的频率合成系统，为光钟应用于精密光谱和精密测量迈出了必要的一步。 An optical frequency synthesizer referenced to an optical clock Electromagnetic waves with higher spectral purity, frequency stability, and accuracy are consistently pursued in communication, radar systems and global position systems for the goal of large communication capacity and high positioning accuracy. Microwave frequency synthesizers are frequently employed for their generation at any desired frequencies in the microwave region with the same excellent frequency stability and accuracy as those of microwave oscillators or clocks, supporting the variety of applications listed above.In the past decade, the frequency stabilities and accuracies provided by electromagnetic waves in the optical domain outperform their microwave counterparts by more than two orders of magnitude: the frequency instabilities of the most stable lasers have reached 10−17, and the frequency accuracies of the most accurate optical clocks have achieved 10−18. Such extraordinary electromagnetic waves emitted from optical oscillators or optical clocks will be the new generation of time and frequency standards, and they constitute extremely sensitive tools for basic research, such as searching for possible time variations of fundamental constants, measurement of changes in gravitational potentials on the centimeter scale, and tests of relativity.However, optical oscillators or clocks only work at a few specific wavelengths. To make use of their full power, we need an optical frequency synthesizer, which can generate optical waves or microwaves at desired frequencies with the same performance as optical oscillators or optical clocks. The key to realize an optical frequency synthesizer is to maintain the coherence and frequency accuracy during frequency synthesis.The team led by Prof. Yanyi Jiang from State Key Laboratory of Precision Spectroscopy, East China Normal University realized low noise, accurate optical frequency synthesis with the help of comb-frequency noise reduction techniques, which provides possibilities to use chip-scale combs.This work was published in Photonics Research, Vol. 9, No. 2, 2021 (Yuan Yao, Bo Li, Guang Yang, Xiaotong Chen, Yaqin Hao, Hongfu Yu, Yanyi Jiang, Longsheng Ma. Optical frequency synthesizer referenced to an ytterbium optical clock[J]. Photonics Research, 2021, 9(2): 02000098).An optical frequency synthesizer referenced to an optical clockTo simulate the large frequency noise of chip-scale combs, they phase-locked a comb to a rubidium (Rb) clock at 10 MHz, resulting in frequency instability of the comb teeth to be 2 × 10−11 at 1 s averaging time. Benefitting from the noise-reduction techniques adopted in optical frequency synthesis, e.g., the transfer oscillator scheme and the optically self-referenced time base, the synthesis noise is largely immune to comb frequency noise. They achieved a synthesis noise of 6 × 10−18 at 1 s averaging time and a synthesis uncertainty of 5 × 10−21, supporting optical frequency synthesis from the state-of-the-art optical clocks.Using the comb phase-locked to the Rb clock, they transferred the coherence from an ultra-stable laser at 1064 nm to 578 nm, and resolved hertz-level-linewidth Rabi spectrum of the ytterbium clock transition. Any frequency deviation from the transition is corrected by adjusting the frequency of the 1064 nm laser, the internal oscillator of the optical frequency synthesizer. Thereby the optical frequency synthesizer acquires frequency stability in the long term as well as high frequency accuracy.Prof. Ma from this research team recalled that about 40 years ago when he used microwave frequency synthesizer for the first time he dreamed of an optical frequency synthesizer for precision spectroscopy. His dream did not come true until optical frequency combs were invited in 2000. Since then, he and his team developed narrow-linewidth ultra-stable lasers, low noise optical frequency synthesis based on optical frequency combs together with comb-frequency-reduction techniques, and cold ytterbium atoms trapped in optical lattices. They combined all these parts together to build an accurate optical frequency synthesizer referenced to the ytterbium optical clock. Such an optical frequency synthesizer enables possibilities to output optical waves with excellent coherence, frequency stability, and accuracy in the region of 530–1100 nm for precision spectroscopy and measurement, supporting many cutting-edge applications of most optical clocks. In the near future, as the SI second is redefined based on the optical clocks, optical frequency synthesizer will become an increasingly indispensable tool to meet the varied applications.