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Janus metasurfaces, offering versatile light manipulation contingent on incident direction, are explored across microwave to mid‐infrared spectra. Nonetheless, prior designs often resort to spatial multiplexing or vertical stacking, entailing complex fabrication. Metallic Janus metasurfaces, owing to material properties, suffer notable Ohmic losses in the visible spectrum. In this study, Single‐layer TiO2‐based Janus metasurfaces with arbitrary polarization control is experimentally demonstrated, exhibiting directionally asymmetric functionalities in spin and orbital angular momentum (OAM). A novel Jones matrix formulation tailored for Janus metasurfaces is presented, enabling efficient generation of two asymmetric, high‐purity OAM states of vortex beams at wavelength of 532 nm, contingent on incidence direction. This innovation facilitates compact and versatile phase manipulation, encompassing applications such as lasers and optical combiners, thereby expanding its utility across diverse domains. [ABSTRACT FROM AUTHOR]

Janus metasurfaces, exemplifying two‐faced 2D metamaterials, have shown unprecedented capabilities in asymmetrically manipulating the wavefront of electromagnetic waves in both forward and backward propagating directions, enabling novel applications in asymmetric information processing, security, and signal multiplexing. However, current Janus metasurfaces only allow for directional phase manipulation, hindering their broader application potential. Here, the study proposes a versatile Janus metasurface platform that can directionally control the phase and polarization of terahertz waves by integrating functionalities of half‐wave plates, quarter‐wave plates, and metallic gratings within a cascaded metasurface structure. As a proof‐of‐principle, the study experimentally demonstrates Janus metasurfaces capable of independent and simultaneous control over phase and polarization, showcasing propagation direction‐encoded focusing and polarization conversion. Moreover, the directionally focused points are utilized with distinct polarization states for advanced applications in direction‐ and polarization‐sensitive detection and imaging. This unique strategy for simultaneous phase and polarization control with direction‐dependent versatility opens new avenues for designing ultra‐compact devices with significant implications in imaging, encryption, and data storage. [ABSTRACT FROM AUTHOR]

Janus metasurfaces emerge as a promising platform for implementing multiple wave functionalities by fully exploiting the inherent propagation direction of electromagnetic waves. Their out‐of‐plane asymmetric structures enable different wave functions depending on the propagation direction. Herein, a multiplexed Janus metasurface is proposed, which operates in the microwave region to flexibly manipulate the transmission and reflection wavefronts for same linearly polarized (LP) incidence propagating along the two opposite directions. A meta‐lens is constructed to validate the concept of full‐space shared‐aperture transmission‐reflection‐independent focusing of electromagnetic (EM) waves, exhibiting four distinct focusing performances. Experiments are conducted in the microwave region that agree well with the simulation results. The proposed full‐space Janus metasurface may provide a platform for asymmetric imaging, multichannel information processing, and encrypted communication. [ABSTRACT FROM AUTHOR]

Abstract Janus metasurfaces, exemplifying two‐faced 2D metamaterials, have shown unprecedented capabilities in asymmetrically manipulating the wavefront of electromagnetic waves in both forward and backward propagating directions, enabling novel applications in asymmetric information processing, security, and signal multiplexing. However, current Janus metasurfaces only allow for directional phase manipulation, hindering their broader application potential. Here, the study proposes a versatile Janus metasurface platform that can directionally control the phase and polarization of terahertz waves by integrating functionalities of half‐wave plates, quarter‐wave plates, and metallic gratings within a cascaded metasurface structure. As a proof‐of‐principle, the study experimentally demonstrates Janus metasurfaces capable of independent and simultaneous control over phase and polarization, showcasing propagation direction‐encoded focusing and polarization conversion. Moreover, the directionally focused points are utilized with distinct polarization states for advanced applications in direction‐ and polarization‐sensitive detection and imaging. This unique strategy for simultaneous phase and polarization control with direction‐dependent versatility opens new avenues for designing ultra‐compact devices with significant implications in imaging, encryption, and data storage.

Janus metasurfaces emerge as a promising platform for implementing multiple wave functionalities by fully exploiting the inherent propagation direction of electromagnetic waves. Their out‐of‐plane asymmetric structures enable different wave functions depending on the propagation direction. Herein, a multiplexed Janus metasurface is proposed, which operates in the microwave region to flexibly manipulate the transmission and reflection wavefronts for same linearly polarized (LP) incidence propagating along the two opposite directions. A meta‐lens is constructed to validate the concept of full‐space shared‐aperture transmission‐reflection‐independent focusing of electromagnetic (EM) waves, exhibiting four distinct focusing performances. Experiments are conducted in the microwave region that agree well with the simulation results. The proposed full‐space Janus metasurface may provide a platform for asymmetric imaging, multichannel information processing, and encrypted communication.

Janus metasurfaces have attracted significant attention due to their key feature of asymmetric transmission in numerous practical applications, such as asymmetric data inscription in communications and dual side displays in smart mobile devices. More compact and integrated spatial wave modulation components call for implementations of non‐interleaved bilayer complex‐amplitude (CA) Janus metasurfaces. Here, by introducing composite geometry phase into propagation phase, direction‐dependent decoupling relation between amplitude and phase engineering is derived, and the mechanism of energy‐tailorable bidirectional wave modulation is elucidated via extremely simple single‐pixeled Janus elements. A non‐interleaved bilayer CA Janus metasurface is thus proposed. Bidirectional amplitude‐phase profiles with both‐transmission (T–T) or transmission–reflection‐integration (T–R) operational modes can readily be achieved. Numerical analysis and experimental verification of direction‐dependent energy allocation and reciprocal asymmetric holograms are performed to demonstrate the excellent manipulation accuracy and decorrelation under bidirectional illuminations. On this basis, a series of coplanar image syntheses, including frequency–polarization multitasking and T–R dual‐channel multiplexing, based on the proposed bidirectional CA modulation mechanism are experimentally demonstrated in the microwave region. This asymmetric transmission mechanism will promote developments of Janus metasurfaces for multichannel processing and information multiplexing applications in miniaturized and highly integrated systems. [ABSTRACT FROM AUTHOR]

The diverse design freedom and exotic electromagnetic properties of metasurfaces enable them to achieve unprecedented capability and superiority with regard to conventional optical elements. Herein, a bifunctional microwave metasurface with an asymmetric bidirection transmission phase that can be controlled is reported. The proposed metasurface is composed of bilayered double‐arrow‐shaped structures sandwiching a subwavelength metal grating. Such design can achieve not only linear polarization (LP) conversion for two oppositely directed wave incidences but also phase control independently by introducing a rotation and adjusting the geometrical parameters of the double‐arrow‐shaped structures. The metasurface breaks the symmetry and realizes different functions for opposite propagation directions, such as deflection and focusing, orbital angular momentum (OAM) mode generation, and holographic imaging. The experimental results suggest that the proposed Janus metasurface can be further exploited as an attractive platform for various applications ranging from microwave reconfigurable beam antenna and multifunctional polarization control to optical imaging, sensing, and information processing.

In this paper, a photoexcited multitasking Janus metasurface (MJM) based on the phase‐changed material vanadium dioxide and the photosensitive materials silicon and germanium in the terahertz (THz) region is proposed, which also exploits the directionality feature of electromagnetic waves. The MJM can switch its functionalities between working band shifting and full‐space polarized wave control, and six functions can be implemented by exciting the switchable materials. By regulating the power of the incident pump beam, it is feasible to complete band adjustment in terms of normal incidence, i.e. the band range of polarization conversion ratio >0.9 changing from 1.23 THz–1.91 THz to 0.98 THz–1.91 THz in the reflection state and axial ratio (AR) <3 dB band range toggling between 0.69 THz–1.08 THz and 0.67 THz–0.96 THz in the transmission state. However, for the backward incidence,, it presents reflective linear‐to‐circle (LTC) polarization conversion (PC), with AR <3 dB domain of 0.99 THz–1.63 THz. The multiple reflection interference theory and electric field distributions are introduced to interpret the high performance. Moreover, the designed device exhibits a high angular tolerance for achieving LTC PC. The integration of numerous functions in a single structure endows the MJM with the great benefit for efficient polarization‐controlled applications. [ABSTRACT FROM AUTHOR]

A thin metasurface has shown powerful capabilities in controlling either incident electromagnetic (EM) waves or radiation waves, but is difficult for both. Here, a self‐feeding Janus metasurface (SFJ‐MS) is proposed to manipulate the incident EM waves and emit the radiated waves simultaneously, which can realize the polarization conversion of incident waves, scattering control, EM wave radiation, and radiation‐beam steering. On the upper of SFJ‐MS, a diagonal‐split square ring and a rectangular patch with rotation for radiation are designed to introduce anisotropy in the meta‐atom for converting the polarization of incident EM waves. On the bottom of SFJ‐MS, a self‐feeding microstructure converts the alternating current into the excitation of SFJ‐MS to emit the EM waves to free space. The multiple functions of SFJ‐MS are comprehensively substantiated by measured results, which are in agreements with the stringent simulations. This SFJ‐MS, with lightweight, compact, low profile, and power‐efficient features, can find potential applications in phased array radar systems, wireless communication systems, polarimetric radar imaging systems, and target detection systems. [ABSTRACT FROM AUTHOR]

Janus monolayers, a class of two-faced 2D materials, have received significant attention in electronics, due to their unusual conduction properties stemming from their inherent out-of-plane asymmetry. Their photonic counterparts recently allowed for the control of hydrogenation/dehydrogenation processes, yielding drastically different responses for opposite light excitation spins. A passive Janus metasurface composed of cascaded subwavelength anisotropic impedance sheets is demonstrated. By introducing a rotational twist in their geometry, asymmetric transmission with the desired phase function is realized. Their broken out-of-plane symmetry realizes different functions for opposite propagation directions, enabling direction-dependent versatile functionalities. A series of passive Janus metasurfaces that enable functionalities including one-way anomalous refraction, one-way focusing, asymmetric focusing, and direction-controlled holograms are experimentally demonstrated., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)