Looking back over the past two decades, a number of gratifying achievements in the photonics field can be listed in discovering new mechanisms, inventing new structures/materials, and exploring new applications. All the optoelectronic devices operate based on the interaction between light and matter, which is essentially the interaction between various fundamental particles and quasiparticles. Over the past 20 years, significant advances have been made in the understanding of the new mechanisms by which these particles interact with each other. Benefits from the progress of micronano processing technology, new structures, or materials help us to validate these new mechanisms and use them to develop devices. First, beyond the classical interaction between electrons and photons, a series of quasiparticles have stepped onto the stage and, together with nanostructures or metamaterials, contributed to realizing new functions of photonic devices. For example, phonons, typical quasiparticles, can interact with photons through an optomechanical crystal, which is a kind of nanostructure combining with a photonic crystal and a phononic crystal and deals with the interaction between photons (light) and phonons (mechanical motion). It opens the door to the quantum ground state of macro-/mesoscopic objects, “ultimately-precise” measurement for a broad range of physical properties, such as mass, force, torque, magnetic field, and acceleration, and other fundamental investigations and applications. Excitons are another representative quasiparticle, whose transitions have been identified to present the basis of all recombination processes in quantum dots due to the overlap of the strongly localized electron and hole wavefunctons, and make quantum dots show plenty of advantages even at room temperature. The two-dimensional materials, such as transition metal dichalcogenides or black phosphorus, also can keep the exciton state at room temperature and provide a new platform for studying excitonic devices. On the other hand, surface plasmon polariton (SPP), which is a special electromagnetic form formed by coupling an electromagnetic wave with metal-free electron density oscillation, is also considered as a kind of quasiparticle. The transport, coupling, and resonance properties of various SPP modes in metal nanostructures, as well as the interaction properties between SPP-enhanced light and matter, have been extensively studied. Different types of SPP waveguides, couplers, resonant cavity structures, high-sensitivity SPP biochemical sensor chips, SPP-enhanced light absorption solar cells, nanoscale SPP lasers, and nanoscale photolithography are reported using SPP to break the optical diffraction limit. Except for these quasiparticles, free electrons have also become the new role of photonic devices breaking through the traditional device principle based on the interaction between bound electrons and light field in crystal. Through nanostructures or metamaterial, a new mechanism of interaction among the flying electrons on a chip, bound electrons in the crystal, and light field can be realized and opens a new way for the future photonic devices. The research achievements of the past 20 years on new mechanisms, structures, and materials are important foundations for the development of photonic devices in the next 20 years. It is reasonable to expect “quasiparticle devices”, such as phonon, exciton, and SPP devices, or on chip-free electron devices, to realize new functions that traditional photonic devices cannot achieve and to take a place in future photonic devices. In terms of application, although it is hard to enumerate anything as socially influential as optical communication technology at the end of the last century, the penetration of many photonic technologies into the application field is commendable. Since entering the new century, the application of photonic technology has been extended from a mature optical communication to other fields, such as sensing, energy, medical, aerospace, and so on, and brought out a batch of notable technologies. One of them is the on-chip spectral measurement technology and even one-shot optical spectral imaging technology that enables real-time dynamic spectral imaging. This is not only very significant for almost all areas, such as hyperspectral remote-sensing imaging, noninvasive portable medical testing, and environmental monitoring, but will also provide a new paradigm for future intellisense. When it comes to optical intelligence, a related topic is optical computing. A lightwave can carry and process information due to light propagation, parallel processing, and coherent control. With the development of deep learning and an artificial neural network (ANN), the optical neural network (ONN) has become a new research hotspot. Due to the limitation of optical–electric and electric–optical conversion, all-optical ONN is a very important development trend for the future. While another trend that should be noticed is to realize ONN on a photonic chip. With photonic integrated devices, it is helpful to release the requirement of optical alignment as well as the environmental vibration and temperature variation. Moreover, more devices can be integrated on a single chip to perform more complex functions. Another application worth mentioning is optical quantum information. A photon is an ideal carrier of quantum information because of its fast propagation speed, difficult coupling with the outside world, easy to maintain quantum coherence, and it is easy to manipulate its quantum state. Actually, quantum computing has achieved considerable progress with a photonic platform at the same period of ONN and some hard computational problems, which are difficult to deal with by classical computers based on the von Neumann structure, can be efficiently solved. Of course, more research is being reported on quantum communication, such as quantum key distribution, quantum teleportation, quantum networks, and other quantum communication advances. Considerable progress has been made in the miniaturization and integration of key devices needed for the optical quantum system, including but not limited to a quantum light source, single photon detection, on-chip optical quantum state controlling, and so on. The integrated optical quantum chip technology, with significant advantages such as high stability, strong controllability, and easy expansibility, is regarded as an important platform to realize the functions of quantum communication, quantum computing, quantum simulation, and quantum precision measurement. The next 20 years will usher in an era of vigorous development of photonic technology, both in cutting-edge research and technology applications. The accumulation of research in the field of photonics will bear fruit in the next 20 years. Breakthroughs at the device level will revolutionize the system. New devices will emerge in the new wavelength band, such as in the ultraviolet or terahertz range. Lidar may be ready for widespread use, and virtual/augmented reality technology will bring people different experiences. The research of optical computing will attract more attention. Optical quantum technology will be active in the field of precision measurement and sensing, including the quantum-effect-based electromagnetic field, gravity field detection technology, single photon imaging, and so on. Let us look forward to the future. Views expressed in this editorial are those of the author and not necessarily the views of the ACS. Views expressed in this editorial are those of the author and not necessarily the views of the ACS.
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光子学二十年

回顾过去的二十年，在发现新机制，发明新结构/材料以及探索新应用方面，可以列举出光子学领域的一系列可喜成就。所有光电子器件都基于光与物质之间的相互作用进行操作，该相互作用实质上是各种基本粒子与准粒子之间的相互作用。在过去的20年中，在理解这些粒子彼此相互作用的新机制方面已经取得了重大进展。微纳米加工技术，新结构或材料的进步所带来的好处，有助于我们验证这些新机制并使用它们来开发设备。首先，除了电子和光子之间的经典相互作用之外，一系列准粒子还进入了舞台，连同纳米结构或超材料一起，有助于实现光子器件的新功能。例如，声子（典型的准粒子）可以通过光机械晶体与光子相互作用，光机械晶体是一种结合了光子晶体和声子晶体的纳米结构，可以处理光子（光）和声子之间的相互作用（机械运动）。它为宏观/介观物体的量子基态打开了大门，为各种物理性质（例如质量，力，扭矩，磁场和加速度）的“最终精确”测量以及其他基础研究和应用。激子是另一个有代表性的准粒子，由于强局域电子和空穴波函数的重叠，已经确定了它们的跃迁为量子点中所有重组过程的基础，并使量子点即使在室温下也显示出很多优势。二维材料，例如过渡金属二硫属化合物或黑磷，也可以在室温下保持激子状态，并为研究激子器件提供了新的平台。另一方面，表面等离子体激元（SPP）是一种准电磁粒子，它是通过将电磁波与无金属电子密度振荡耦合而形成的特殊电磁形式。金属纳米结构中各种SPP模式的传输，耦合和共振特性，以及增强SPP的光与物质之间的相互作用特性，已经得到了广泛的研究。据报道，使用SPP突破了光学衍射极限，使用了不同类型的SPP波导，耦合器，谐振腔结构，高灵敏度SPP生化传感器芯片，SPP增强的光吸收太阳能电池，纳米级SPP激光器和纳米级光刻。除了这些准粒子以外，自由电子还成为光子器件的新角色，它打破了传统的基于束缚电子与晶体中光场之间相互作用的器件原理。通过纳米结构或超材料，可以实现芯片上飞行的电子，晶体中的束缚电子和光场之间相互作用的新机制，并为未来的光子器件开辟了新途径。过去20年中有关新机制，结构和材料的研究成果是未来20年光子器件发展的重要基础。合理地期望诸如声子，激子和SPP设备之类的“准粒子设备”，或者在无芯片电子设备上实现传统光子设备无法实现的新功能，并在未来的光子设备中占据一席之地。在应用方面，尽管很难列举出上世纪末像光通信技术这样具有社会影响力的事物，但值得赞扬的是许多光子技术在应用领域的渗透。自进入新世纪以来，光子技术的应用已从成熟的光通信扩展到了其他领域，例如传感，能源，医疗，航空航天等等，并带来了一批著名的技术。其中之一是片上光谱测量技术，甚至是一次性光谱成像技术，可实现实时动态光谱成像。这不仅对几乎所有领域都非常重要，例如高光谱遥感成像，无创便携式医学测试和环境监测，而且还将为未来的智能感知提供新的范例。当涉及光学智能时，一个相关的主题是光学计算。由于光传播，并行处理和相干控制，光波可以承载和处理信息。随着深度学习和人工神经网络（ANN）的发展，光学神经网络（ONN）已成为新的研究热点。由于光电转换和光电转换的局限性，全光ONN是未来非常重要的发展趋势。另一个值得注意的趋势是在光子芯片上实现ONN。利用光子集成器件，有助于消除光学对准以及环境振动和温度变化的要求。此外，可以将更多设备集成在单个芯片上以执行更复杂的功能。另一个值得一提的应用是光量子信息。由于光子的传播速度快，与外界的耦合困难，易于保持量子相干性以及易于操纵其量子态，因此它是理想的量子信息载体。实际上，量子计算在ONN的同时期的光子平台上已经取得了长足的进步，并且可以有效解决一些难以解决的计算问题，而这些问题是基于von Neumann结构的经典计算机难以解决的。当然，有关量子通信的研究也越来越多，例如量子密钥分配，量子隐形传态，量子网络以及其他量子通信方面的进展。在光学量子系统所需的关键器件的小型化和集成方面取得了相当大的进展，包括但不限于量子光源，单光子检测，片上光学量子状态控制等。集成的光量子芯片技术，具有稳定性高，可控性强，易于扩展等显着优点，被视为实现量子通信，量子计算，量子模拟和量子精度测量功能的重要平台。未来20年将迎来光子技术蓬勃发展的时代，包括尖端研究和技术应用。光子学领域的研究积累将在未来20年内取得成果。在设备级别的突破将彻底改变系统。新的设备将出现在新的波段，例如紫外线或太赫兹波段。激光雷达可能已准备好广泛使用，虚拟/增强现实技术将带给人们不同的体验。光学计算的研究将吸引更多的关注。光学量子技术将在精密测量和传感领域发挥积极作用，包括基于量子效应的电磁场，重力场检测技术，单光子成像等。让我们展望未来。本社论中表达的观点只是作者的观点，不一定是ACS的观点。本社论中表达的观点只是作者的观点，不一定是ACS的观点。
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