Broadband Spin-Locked Metasurface Retroreflector.

Retroreflectors are ubiquitously used in a multitude of applications, such as cloaking, wireless communication, radar, and antenna, owing to their ability to augment the reflected electromagnetic (EM) waves in the incident direction. However, Current metasurface retroreflector designs have yet to mature into a practical method due to the limitations of low efficiency and narrow band, which actually originate from the difficulty in simultaneously engineering phase profiles of certain metasurface at distinct wavelengths. Here, a broadband spin-locked retroreflector with high efficiency that relies only on a simple metasurface layer is demonstrated. The metasurface is designed with low-loss dielectric resonators, introducing both the propagation and geometric phases to enable dispersive phase compensation. The results indicate that the proposed metasurface can achieve retroreflection over a broadband spectrum while keeping the spin state identical. Furthermore, a broadband spin-locked cloak is presented for validation. The work builds up a major advance for practice-oriented retroreflector and even envision this approach may open new vistas in the very cutting-edge research of 6G wireless communication network.