![]() Single-metasurface retroreflectors well release the issue of stringent alignment 11, 12, 13, 14, 15, 16, 17 and even enables adaptability via mechanically altering the geometry of reconfigurable C-shaped resonators 13, switchable metagrating 14, and double C-shaped meta-atoms 16. Although retroreflections can be engineered at various incidences, the slight misalignment of dual plates will significantly undermine the efficiency and even dissolve the retroreflection, as shown in Fig. Recently, there are growing trends to explore the metasurface, a planar structure consisting of artificially engineered subwavelength meta-atoms, for flat and compact electromagnetic devices to offer complete control the amplitude, phase, and polarization (APP) of EM wave or light 4, 5, 6, 7, 8, 9 Employing metasurfaces for retroreflectors has been an intriguing topic most recently 10, 11, 12, 13, 14, 15, 16, 17 In the seminal work 10, dual metasurfaces are utilized, the first of which performs a spatial Fourier transform and its inverse while the other imparts a spatially varying momentum to the Fourier transform. This however renders the bulk size, large weight and nonplanar configuration, hindering the real-world applications where the integration, miniaturization, and compatibility of existing wave systems are favored. Over the decades, the corner reflector and Luneburg lens have been reported 1, 2, 3 via assembling different optical materials or elements for retroreflections. Such peculiar reflective behaviors of waves carrying the information and energy are important for applications including laser tracking, target labeling, navigation safety, radar cross-section/visibility enhancement, remote sensing, satellite communication and others. Retroreflector supports the reflection of electromagnetic (EM) wave back to where it comes from even at oblique incidence. Our strategy opens a new avenue for angle multiplexing and angle-resolved metadevices toward the capacity limit of 2D planar Jones’ matrix. The concept has been experimentally verified by a proof-of-concept super-reflector at microwave frequency, showcasing twelve reflected beams and a high efficiency exceeding 90.6% defined as the ratio of reflected power to incidence for each channel beam. Our compound multiplexed super-reflector allows five degrees of freedom in circular polarization Jones' matrix, approaching the intrinsic upper limit of such planar metasurface. By multiplexing four channels connecting two spin states excited onto each input of three spatial frequencies, a total of twelve channels are engineered, among which three are retroreflected channels and the residual are anomalous reflection ones. Here, we propose a spin-momentum multiplexed paradigm called a super-reflector enabling on-demand control of both retroreflections and anomalous reflections using a non-interleaved single-celled metasurface. It is yet extremely challenging based on passive and compact wave elements, since the wave excitation and scattering channels are exclusively coupled through gradient phases and hence momentum matching condition at the interface. \): The time-dependent intensity of scattered light for (top) large particles and for (bottom) small particles.Electromagnetic wave multiplexing, especially for that occurring at different incidences (spatial-frequency multiplexing), is pivotal for ultrathin multifunctional interfaces and high-capacity information processing and communication. ![]()
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