Cascaded metasurfaces for dynamic control of THz wavefronts
Dynamic control of THz wavefronts demonstrated by rotating layers of
cascaded metasurfaces

Date:
July 23, 2021
Source:
SPIE--International Society for Optics and Photonics
Summary:
Researchers have developed a general framework and metadevices for
achieving dynamic control of THz wavefronts. Instead of locally
controlling the individual meta-atoms in a THz metasurface (e.g.,
via PIN diode, varactor, etc.), they vary the polarization of a
light beam with rotating multilayer cascaded metasurfaces.



FULL STORY ========================================================================== Electromagnetic (EM) waves in the terahertz (THz) regime contribute to important applications in communications, security imaging, and bio-
and chemical sensing. Such wide applicability has resulted in significant technological progress. However, due to weak interactions between natural materials and THz waves, conventional THz devices are typically bulky
and inefficient. Although ultracompact active THz devices do exist,
current electronic and photonic approaches to dynamic control have
lacked efficiency.


========================================================================== Recently, rapid developments in metasurfaces have opened new possibilities
for the creation of high-efficiency, ultracompact THz devices for dynamic wavefront control. Ultrathin metamaterials formed by subwavelength planar microstructures (i.e., meta-atoms), metasurfaces enable tailored optical responses for control of EM wavefronts. By constructing metasurfaces that possess certain predesigned phase profiles for transmitted or reflected
waves, scientists have demonstrated fascinating wave-manipulation effects,
such as anomalous light deflection, polarization manipulation, photonic spin-Hall, and holograms.

Moreover, integrating active elements with individual meta-atoms inside
passive metasurfaces allows for "active" metadevices that can dynamically manipulate EM wavefronts. While active elements in deep subwavelengths are easily found in the microwave regime (e.g., PIN diodes and varactors),
and successfully contribute to active metadevices for beam-steering, programmable holograms, and dynamic imaging, they are difficult to create
at frequencies higher than THz.

This difficulty is due to size restrictions and significant ohmic
losses in electronic circuits. Although THz frequencies can control
THz beams in a uniform manner, they are typically unable to dynamically manipulate the THz wavefronts. This is ultimately due to deficiencies
in the local-tuning capabilities at deep-subwavelength scales in this
frequency domain. Therefore, developing new approaches that bypass
reliance on local tuning is a priority.

As reported in Advanced Photonics, researchers from Shanghai University
and Fudan University developed a general framework and metadevices
for achieving dynamic control of THz wavefronts. Instead of locally
controlling the individual meta-atoms in a THz metasurface (e.g., via
PIN diode, varactor, etc.), they vary the polarization of a light beam
with rotating multilayer cascaded metasurfaces. They demonstrate that
rotating different layers (each exhibiting a particular phase profile)
in a cascaded metadevice at different speeds can dynamically change
the effective Jones-matrix property of the whole device, achieving extraordinary manipulations of the wavefront and polarization
characteristics of THz beams. Two metadevices are demonstrated: 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 wavefront and polarization of a THz beam.

This work proposes an attractive alternative way to achieve low-cost
dynamic control of THz waves. The researchers hope that the work will
inspire future applications in THz radar, as well as bio- and chemical
sensing and imaging.

========================================================================== Story Source: Materials provided by SPIE--International_Society_for_Optics_and_Photonics.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Xiaodong Cai, Rong Tang, Haoyang Zhou, Qiushi Li, Shaojie Ma, Dongyi
Wang, Tong Liu, Xiaohui Ling, Wei Tan, Qiong He, Shiyi Xiao,
Lei Zhou.

Dynamically controlling terahertz wavefronts with cascaded
metasurfaces.

Advanced Photonics, 2021; 3 (03) DOI: 10.1117/1.AP.3.3.036003 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/07/210723121456.htm

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