Terahertz Airy beam generated by Pancharatnam-Berry phases in guided wave-driven metasurfaces

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.

Intensity controlled and multi-multiplexed full-space achromatic metalens and modulated orbital angular momentum

The Fabry-Perot (F-P) interference model was used to make a 6-layer metasurface with cross-polarization that can be changed by heat. The fundamental concept behind the metasurface is to utilize the selectivity of linearly polarized waves by a metal grating to achieve broadband and efficient polarized conversion (PC). It also uses the thermal conversion properties of vanadium dioxide (VO2) to control the amplitude of terahertz (THz) waves in a dynamic way. While achromatic metalenses have been extensively studied, altering the entire spatial incidence angle remains relatively uncommon. Enter modulated orbital angular momentum (MOAM), a promising approach for applications such as holographic encryption, optical communication, and imaging. However, achieving MOAM multidimensional multiplexing has proven to be a significant challenge. In response to this challenge, we have integrated the transmission phase into the metasurface design. This new idea makes it possible to make a full spatially achromatic metalenses with angular multiplexing and makes MOAM multidimensional multiplexing easier by letting you switch between frequency, angle, and MOAM modes. This pioneering approach unveils new prospects for enhancing the capacity, rate, and quality of information exchange in domains such as optical encryption, optical imaging, optical communication, and other related technological fields.

On-chip non-uniform geometric metasurface for multi-channel wavefront manipulations

Metasurfaces integrated with waveguides have been recently explored as a means to control the conversion between guided modes and radiation modes for versatile functionalities. However, most efforts have been limited to constructing a single free-space wavefront using guided waves, which hinders the functional diversity and requires a complex configuration. Here, a new, to the best of our knowledge, type of non-uniformly arranged geometric metasurface enabling independent multi-channel wavefront engineering of guided wave radiation is ingeniously proposed. By endowing three structural degrees of freedom into a meta-atom, two mechanisms (the Pancharatnam-Berry phase and the detour phase) of the metasurface are perfectly joined together, giving rise to three phase degrees of freedom to manipulate. Therefore, an on-chip polarization demultiplexed metalens, a wavelength-multiplexed metalens, and RGB-colored holography with an improved information capacity are successively demonstrated. Our results enrich the functionalities of an on-chip metasurface and imply the prospect of advancements in multiplexing optical imaging, augmented reality (AR) holographic displays, and information encryption.

Metasurfaces integrated with a single-mode waveguide array for off-chip wavefront shaping

Integration of metasurfaces and SOI (silicon-on-insulator) chips can leverage the advantages of both metamaterials and silicon photonics, enabling novel light shaping functionalities in planar, compact devices that are compatible with CMOS (complementary metal-oxide-semiconductor) production. To facilitate light extraction from a two-dimensional metasurface vertically into free space, the established approach is to use a wide waveguide. However, the multi-modal feature of such wide waveguides can render the device vulnerable to mode distortion. Here, we propose a different approach, where an array of narrow, single-mode waveguides is used instead of a wide, multi-mode waveguide. This approach tolerates nano-scatterers with a relatively high scattering efficiency, for example Si nanopillars that are in direct contact with the waveguides. Two example devices are designed and numerically studied as demonstrations: the first being a beam deflector that deflects light into the same direction regardless of the direction of input light, and the second being a light-focusing metalens. This work shows a straightforward approach of metasurface-SOI chip integration, which could be useful for emerging applications such as metalens arrays and neural probes that require off-chip light shaping from relatively small metasurfaces.