Non-Interleaved Bilayer Complex-Amplitude Janus Metasurface Enabling Energy-Tailorable Bidirectional Wave Modulation

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.