Conventional wireless communication schemes indiscriminately transmit information into the whole space and pose inherent security risks. Recently, directional information modulation (DIM) has attracted enormous attention as a promising technology. DIM generates correct constellation symbols in the desired directions and distorts them in undesired directions, thus ensuring the security of the transmitted information. Although several DIM schemes have been reported, they suffer from defects of bulkiness, energy consumption, high cost, and inability to support two-dimensional (2D) and high-order modulations. Here, we propose a DIM scheme based on a 2-bit programmable metasurface (PM) that overcomes these defects. A fast and efficient discrete optimization algorithm is developed to optimize the digital coding sequences, and the correct constellation symbols can be generated and transmitted in multi-directional beams. As a proof-of-concept, three sets of constellation diagrams (8 phase shift keying (PSK), 16 quadrature amplitude modulation (QAM), and 64QAM) are realized in the multi-channel modes. This work provides an important route of employing DIM for ensuring physical-layer security and serves as a stepping stone toward endogenous secure communications.

传统的无线通信方案不加区别地将信息传输到整个空间，并带来固有的安全风险。近年来，定向信息调制（DIM）作为一项有前途的技术引起了极大的关注。 DIM在需要的方向上生成正确的星座符号，并在不需要的方向上扭曲它们，从而保证传输信息的安全。尽管已经报道了几种DIM方案，但它们存在体积大、能耗高、成本高以及无法支持二维（2D）和高阶调制的缺陷。在这里，我们提出了一种基于 2 位可编程超表面 (PM) 的 DIM 方案，克服了这些缺陷。开发了一种快速高效的离散优化算法来优化数字编码序列，并且可以生成正确的星座符号并在多向波束中传输。作为概念验证，在多通道模式下实现了三组星座图（8 相移键控 (PSK)、16 正交幅度调制 (QAM) 和 64QAM）。这项工作提供了使用 DIM 确保物理层安全的重要途径，并作为实现内生安全通信的垫脚石。