Programmable VO2 metasurface for terahertz wave beam steering

Phase and amplitude simultaneously coding metasurface with multi-frequency and multifunctional electromagnetic modulations

The integration of multiple functionalities into a single, planar, ultra-compact metasurface has presented significant opportunities for enhancing capacity and performance within compact 5G/6G communication systems. Recent advances in multifunctional metasurfaces have unveiled comprehensive wavefront manipulations utilizing phase, polarization transmission/reflection, and coding apertures. Despite these developments, there remains a critical need for multifunctional metasurfaces with expanded channel capabilities, including multiple operational frequencies, minimal crosstalk, and high-efficiency computable array factors. This study introduces a multifunctional metasurface that integrates phase- and amplitude simultaneous coding meta-atoms at dual frequencies. By altering the polarization of electromagnetic (EM) waves, it is possible to reshape the wave-fronts of reflected waves at these frequencies. The coding metasurface proficiently manipulates both x and y linearly polarized waves through phase and amplitude coding at dual frequencies, thereby enabling distinct functionalities such as anomalous reflection, reflection imaging, and vortex wave beam generation. Both theoretical analysis and full-wave simulation confirm the anticipated functionalities of the designed devices, paving the way for advancements in integrated communication systems with diverse functionalities.

Physics-Informed Inverse Design of Programmable Metasurfaces

Emerging reconfigurable metasurfaces offer various possibilities for programmatically manipulating electromagnetic waves across spatial, spectral, and temporal domains, showcasing great potential for enhancing terahertz applications. However, they are hindered by limited tunability, particularly evident in relatively small phase tuning over 270°, due to the design constraints with time-intensive forward design methodologies. Here, a multi-bit programmable metasurface is demonstrated capable of terahertz beam steering facilitated by a developed physics-informed inverse design (PIID) approach. Through integrating a modified coupled mode theory (MCMT) into residual neural networks, the PIID algorithm not only significantly increases the design accuracy compared to conventional neural networks but also elucidates the intricate physical relations between the geometry and the modes. Without decreasing the reflection intensity, the method achieves the enhanced phase tuning as large as 300°. Additionally, the inverse-designed programmable beam steering metasurface is experimentally validated, which is adaptable across 1-bit, 2-bit, and tri-state coding schemes, yielding a deflection angle up to 68° and broadened steering coverage. The demonstration provides a promising pathway for rapidly exploring advanced metasurface devices, with potentially great impact on communication and imaging technologies.

Terahertz tunable vanadium dioxide metasurface for dynamic illusion and cloaking

Realizing camouflage by illusion and cloaking based on the metasurface has received widespread attention recently. However, existing metasurface-based illusion and cloaking devices are valid for the incident wave with a specific frequency, angle, or polarization, or exhibit a single function. Therefore, a terahertz tunable vanadium dioxide (VO2) metasurface carpet cloak is proposed for dynamic illusion and cloaking. Simulation results show that by controlling the state of the VO2, the metasurface carpet cloak can simultaneously achieve illusion and cloaking functions, working at 0.45 THz and 0.6 THz, and is effective for orthogonal circularly polarized waves with different incidence angles. That is the function, frequency, incident angle, and polarization of the metasurface carpet cloak are dynamically adjustable. Besides, the metasurface carpet cloak is robust to the incident angle and is capable of polarization angle stability. This work has potential value in the real-life application of metasurface-based illusion and cloaking devices.

Directional terahertz holography with thermally active Janus metasurface

Dynamic manipulation of electromagnetic (EM) waves with multiple degrees of freedom plays an essential role in enhancing information processing. Currently, an enormous challenge is to realize directional terahertz (THz) holography. Recently, it was demonstrated that Janus metasurfaces could produce distinct responses to EM waves from two opposite incident directions, making multiplexed dynamic manipulation of THz waves possible. Herein, we show that thermally activated THz Janus metasurfaces integrating with phase change materials on the meta-atoms can produce asymmetric transmission with the designed phase delays. Such reconfigurable Janus metasurfaces can achieve asymmetric focusing of THz wave and directional THz holography with free-space image projections, and particularly the information can be manipulated via temperature and incident THz wave direction. This work not only offers a common strategy for realizing the reconfigurability of Janus metasurfaces, but also shows possible applications in THz optical information encryption, data storage, and smart windows.

Temperature-controlled optical switch metasurface with large local field enhancement based on FW-BIC

Introduction: Many researchers have explored the bound states in the continuum (BICs) as a particular bound wave state which can be used to achieve a very high Q-factor. High-Q factor devices, typically based on the bound states in the continuum (BICs), are well used in the fields of hypersensitive biochemical sensors, non-linear effects enhancement, plasmon lasers, and hi-performance filtering. However, symmetrical-protected BIC is difficult to achieve experimentally high-Q factor because it strongly depends on the geometry and can be destroyed by any slight disturbance in the potential well.

Methods: Therefore, we proposed a parameter-adjusted Friedrich-Wintergen BIC based on the analysis model of time-coupled model theory, where the target system parameters can be tuned to achieve high-Q excitation.

Results: Moreover, considering the tunability and flexibility of the components in various practical applications, we integrate active materials into metasurface arrays with the help of external stimuli to achieve modulation of high-Q resonances. Our results demonstrate that an optical resonator based on FW-BIC can modulate the BIC state by changing the intermediate gap.

Discussion: The BIC state and the high-Q factor Fano resonance can be dynamically tuned by adding temperature-sensitive VO2 material.

Terahertz vortex beam generator carrying orbital angular momentum in both transmission and reflection spaces

Vortex beam generators carrying orbital angular momentum (OAM) with both transmission and reflection modes has broad application prospects in full-space high data capacity communication and orbital angular momentum multiplexing systems. In this work, we proposed a vanadium dioxide (VO₂) assisted metasurface to independently produce and manipulate focused vortex transmission-reflection modes with different number of beams and focal lengths under right-handed circular polarized (RCP) wave incidence. The proposed metasurface generates the diagonal vortex beams, four vortex beams, and focused vortex beam for transmission mode at 1.26THz and reflection mode at 1.06THz by changing phase state of the VO₂. Our work may find many potential applications in future high data capacity information multiplexing communication systems.