Programmable integrated photonics is an emerging new paradigm that aims at designing common integrated optical hardware resource configurations, capable of implementing an unconstrained variety of functionalities by suitable programming, following a parallel but not identical path to that of integrated electronics in the past two decades of the last century. Programmable integrated photonics is raising considerable interest, as it is driven by the surge of a considerable number of new applications in the fields of telecommunications, quantum information processing, sensing, and neurophotonics, calling for flexible, reconfigurable, low-cost, compact, and low-power-consuming devices that can cooperate with integrated electronic devices to overcome the limitation expected by the demise of Moore’s Law. Integrated photonic devices exploiting full programmability are expected to scale from application-specific photonic chips (featuring a relatively low number of functionalities) up to very complex application-agnostic complex subsystems much in the same way as field programmable gate arrays and microprocessors operate in electronics. Two main differences need to be considered. First, as opposed to integrated electronics, programmable integrated photonics will carry analog operations over the signals to be processed. Second, the scale of integration density will be several orders of magnitude smaller due to the physical limitations imposed by the wavelength ratio of electrons and light wave photons. The success of programmable integrated photonics will depend on leveraging the properties of integrated photonic devices and, in particular, on research into suitable interconnection hardware architectures that can offer a very high spatial regularity as well as the possibility of independently setting (with a very low power consumption) the interconnection state of each connecting element. Integrated multiport interferometers and waveguide meshes provide regular and periodic geometries, formed by replicating unit elements and cells, respectively. In the case of waveguide meshes, the cells can take the form of a square, hexagon, or triangle, among other configurations. Each side of the cell is formed by two integrated waveguides connected by means of a Mach–Zehnder interferometer or a tunable directional coupler that can be operated by means of an output control signal as a crossbar switch or as a variable coupler with independent power division ratio and phase shift. In this paper, we provide the basic foundations and principles behind the construction of these complex programmable circuits. We also review some practical aspects that limit the programming and scalability of programmable integrated photonics and provide an overview of some of the most salient applications demonstrated so far.

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可编程集成光子学的原理、基础和应用

可编程集成光子学是一种新兴的新范式，旨在设计通用的集成光学硬件资源配置，能够通过合适的编程实现不受约束的各种功能，遵循与过去二十年集成电子学并行但不完全相同的路径。上世纪。可编程集成光子学引起了极大的兴趣，因为它受到电信、量子信息处理、传感和神经光子学领域大量新应用的推动，要求灵活、可重构、低成本、紧凑和可以与集成电子设备配合以克服摩尔定律消亡所预期的限制的低功耗设备。利用完全可编程性的集成光子器件有望从特定应用的光子芯片（具有相对较少的功能）扩展到非常复杂的应用无关的复杂子系统，这与现场可编程门阵列和微处理器在电子产品中的运行方式大致相同。需要考虑两个主要区别。首先，与集成电子器件相反，可编程集成光子学将对要处理的信号进行模拟操作。其次，由于电子和光波光子的波长比所施加的物理限制，集成密度的规模将小几个数量级。可编程集成光子学的成功将取决于利用集成光子器件的特性，尤其是 研究合适的互连硬件架构，可以提供非常高的空间规则性以及独立设置（以非常低的功耗）每个连接元件的互连状态的可能性。集成的多端口干涉仪和波导网格提供规则和周期性的几何形状，分别通过复制单位元素和单元形成。在波导网格的情况下，单元可以采用正方形、六边形或三角形等形式。单元的每一侧由两个集成波导形成，这些波导通过马赫-曾德干涉仪或可调谐定向耦合器连接，可通过输出控制信号作为纵横开关或作为具有独立功率分配比的可变耦合器进行操作和相移。在本文中，我们提供构建这些复杂可编程电路背后的基本基础和原理。我们还回顾了一些限制可编程集成光子学的编程和可扩展性的实际方面，并概述了迄今为止展示的一些最突出的应用。