Dynamically controlling terahertz wavefronts with cascaded metasurfaces

Abstract

Dynamically controlling terahertz (THz) wavefronts in a designable fashion is highly desired in practice. However, available methods working at microwave frequencies do not work well in the THz regime due to lacking suitable tunable elements with submicrometer sizes. Here, instead of locally controlling individual meta-atoms in a THz metasurface, we show that rotating different layers (each exhibiting a particular phase profile) in a cascaded metadevice at different speeds can dynamically change the effective Jonesmatrix property of the whole device, thus enabling extraordinary manipulations on the wavefront and polarization characteristics of a THz beam impinging on the device. After illustrating our strategy based on model calculations, we experimentally demonstrate two proof-of-concept metadevices, each consisting of two carefully designed all-silicon transmissive metasurfaces exhibiting different phase profiles. Rotating two metasurfaces inside the fabricated devices at different speeds, we experimentally demonstrate that the first metadevice can efficiently redirect a normally incident THz beam to scan over a wide solid-angle range, while the second one can dynamically manipulate both the wavefront and polarization of a THz beam. Our results pave the way to achieving dynamic control of THz beams, which is useful in many applications, such as THz radar, and bio-and chemical sensing and imaging.

Active spintronic-metasurface terahertz emitters with tunable chirality

“…Metasurfaces, two-dimensional (2D) metamaterials composed by subwavelength planar micro-structures (e.g., "metaatoms") with tailored electromagnetic responses, have greatly enriched our capability of wave manipulation in the terahertz regime. [24][25][26][27][28][29] By engineering the electromagnetic properties of individual meta-atoms and the collective coupling between them, metasurfaces can precisely control the field transformation and achieve predesigned functionalities. [30][31][32] However, functional meta-devices so far achieved in the terahertz regime are mostly separated from the generation source, which makes it difficult to make the entire device compact.…”

Recent Advancement in Optical Metasurface: Fundament to Application

“…However, increasing the layers from two to four will make the fabrication costly and complex. The system is multi-layered (layer number) [128]. (B) (a) Illustrates a meta-atom composed of dual silicon (Si) posts.…”

“…FDTD simulated results, (b) transmission phase, (c) average transmission amplitude |t i av| against the parameters Wx and h3 of the bottom post. The computed average transmission and average transmission amplitude against l and h1 are illustrated in d) and (e), receptively [128] [128]. (A-C) Reprinted/adapted with permission from Ref.…”

Rotational Multiplexing Method Based on Cascaded Metasurface Holography

“…Integrated multilayer metasurface layouts have often been used to achieve kaleidoscopic wavefront control, [38] multispectral achromatic metalenses, [39] image differentiation, [40] Janus metasurfaces with bidirectional functionality, [41][42][43] holography with asymmetric transmission, [44] holography with color printing, [45] and all-optical machine learning frameworks. [46] For cascaded metasurfaces, whose components can be replaced, translated, or rotated, impressive functionalities such as prescribing light trajectories, [47] Moiré metalens for adjustable focal length, [48] dynamical wavefront modulators, [49] etc., have been demonstrated. Furthermore, the cascaded holography method allows for physical separation and combination of encoded information.…”