Magnetic-Free, Non-Reciprocal Integrated Nanophotonic Components Based on Angular-Momentum Bias

基于角动量偏置的无磁、非互易纳米光子元件光学隔离器，即允许光子沿一个方向传播但禁止反向传播的装置，对于在光纤网络中路由光信号并提供激光器操作的稳定性起着至关重要的作用。目前市售的隔离器完全基于偏磁石榴石或铁磁材料。然而，由于磁光效应的弱特性，它们通常基于笨重的光学元件，它们基于昂贵的材料，并且由于与传统基底的晶格失配，它们不可能集成在纳米光子平台中。这项工作的目标包括引入新的理论概念和设计原理，以及通过实验实现无需磁效应即可隔离的集成纳米光子器件。我们的方法以塞曼效应的纳米光子模拟为中心，塞曼效应是利用磁性材料实现传统隔离的物理机制：我们将能够通过时空调制纳米环谐振器形式的角动量适当设计的“元原子”进行偏置，从而在芯片上产生强隔离。该项目的研究结果预计将引起纳米光子学行业的极大兴趣，因为不可逆纳米器件的单片集成可以极大地降低这些基本器件的成本和占地面积。更广泛地说，拟议的研究结合了电气工程中众多令人兴奋的主题，可以直接让本科生和研究生参与一些最重要的电气工程领域，如纳米光子学、超材料、集成电子学、纳米制造和建模，为激励下一代科学家和研究人员提供独特的机会，特别关注代表性不足的少数群体。拟议的研究引入了纳米光子学的颠覆性概念，允许实现可以打破洛伦兹互易性的无磁光学元件无需磁偏置或特殊的铁磁响应。新提出的非互易组件完全基于传统纳米光子板中已有的组件和材料（例如介电波导和半导体结），可以直接集成到传统纳米光子系统中。此外，所提出的结构将最大程度地受益于快速发展的硅光子学、纳米光学和电子学领域的最新进展。完成这项工作后，我们将展示基于角动量偏置的非互易光学元件，这是通过基于电射频信号的谐振纳米环的适当时空调制来实现的。强共振和方位角方向上的精确形式的时空调制的仔细组合将能够极大地增强负责时空调制的微弱电光效应，从而导致与波长相当或更小的足迹内的巨大非互易性。我们对等离子体和石墨烯平台中的角度时空调制的进一步研究将为能够在深亚波长范围内以新颖的方式处理和控制光的新技术平台奠定基础。

Magnetic-Free, Non-Reciprocal Nanophotonic Components Based on Angular-Momentum BiasOptical isolator i.e., devices that allow photons to travel in one direction, but prohibit reverse propagation play a crucial role to route optical signals in optical fiber networks and to provide stability in laser operation. Commercially available isolators today are exclusively based on magnetically-biased garnets or ferromagnetic materials. However, because of the weak character of magneto-optical effects, they are typically based on bulky optical components, they are based on expensive materials, and they are impossible to integrate in a nanophotonic platform due to lattice mismatch with conventional substrates. The objective of this effort consists in introducing new theoretical concepts and design principles, as well as experimentally realizing integrated nanophotonic devices that can isolate without requiring magnetic effects. Our approach is centered on the nanophotonic analog to the Zeeman effect, the physical mechanism based on which conventional isolation is realized with magnetic materials: we will be able to induce a strong isolation on-chip by biasing with angular-momentum suitably designed "meta-atoms" in the form of spatio-temporally modulated nanoring resonators. The findings of this project are expected to attract significant interest from the nanophotonics industry, since monolithic integration of non-reciprocal nanodevices can dramatically minimize the cost and footprint of these essential devices. More broadly, the proposed research combines a plethora of exciting topics in electrical engineering, that can directly involve undergraduate and graduate students in some of the most important fields of electrical engineering such as nanophotonics, metamaterials, integrated electronics, nanofabrication, and modeling, opening unique opportunities to inspire the next generation of scientists and researchers, with special attention to under-represented minorities.The proposed research introduces disruptive concepts for nanophotonics, allowing the realization of magnetic-free optical components that can break Lorentz reciprocity without requiring magnetic bias or special ferromagnetic response. Being fully based on components and materials that are already available in conventional nanophotonic boards, such as dielectric waveguides and semiconductor junctions, the newly proposed non-reciprocal components can be directly integrated into conventional nanophotonic systems. In addition, the proposed structures will optimally benefit from recent advances in the quickly growing fields of silicon photonics, nano-optics and electronics. At completion of this effort, we will have demonstrated non-reciprocal optical components based on angular-momentum biasing, achieved with suitable spatio-temporal modulation of resonant nanorings based on electric radio-frequency signals. The careful combination of a strong resonance and of a precise form of spatiotemporal modulation in the azimuthal direction will be able to drastically enhance the otherwise weak electro-optical effects responsible for spatio-temporal modulation, thus leading to giant non-reciprocity within a footprint comparable or smaller than the wavelength. Our additional investigations of angular spatio-temporal modulation in plasmonics and graphene-based platforms will set the basis for a new technology platform able to process and control light in novel ways at a deeply subwavelength scale.