Wang X, Ptitcyn G, Asadchy V S, Díaz-Rubio A, Mirmoosa M S, Fan Shanhui, Tretyakov S A
Department of Electronics and Nanoengineering, Aalto University, P.O. Box 15500, FI-00076 Aalto, Finland.
Ginzton Laboratory and Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA.
Phys Rev Lett. 2020 Dec 31;125(26):266102. doi: 10.1103/PhysRevLett.125.266102.
Physical systems with material properties modulated in time provide versatile routes for designing magnetless nonreciprocal devices. Traditionally, nonreciprocity in such systems is achieved exploiting both temporal and spatial modulations, which inevitably requires a series of time-modulated elements distributed in space. In this Letter, we introduce a concept of bianisotropic time-modulated systems capable of nonreciprocal wave propagation at the fundamental frequency and based on uniform, solely temporal material modulations. In the absence of temporal modulations, the considered bianisotropic systems are reciprocal. We theoretically explain the nonreciprocal effect by analyzing wave propagation in an unbounded bianisotropic time-modulated medium. The effect stems from temporal modulation of spatial dispersion effects which to date were not taken into account in previous studies based on the local-permittivity description. We propose a circuit design of a bianisotropic metasurface that can provide phase-insensitive isolation and unidirectional amplification.
具有随时间调制材料特性的物理系统为设计无磁非互易器件提供了多种途径。传统上，此类系统中的非互易性是通过利用时间和空间调制来实现的，这不可避免地需要一系列分布在空间中的时间调制元件。在本信函中，我们引入了双各向异性时间调制系统的概念，该系统能够在基频下实现非互易波传播，且基于均匀的、仅随时间变化的材料调制。在没有时间调制的情况下，所考虑的双各向异性系统是互易的。我们通过分析无界双各向异性时间调制介质中的波传播，从理论上解释了非互易效应。这种效应源于空间色散效应的时间调制，而在以往基于局部介电常数描述的研究中，这一点尚未被考虑在内。我们提出了一种双各向异性超表面的电路设计，它可以提供相位不敏感隔离和单向放大。
