Metasurfaces for manipulating terahertz waves

 

The associated THz responses include focusing, holograms, polarization modulation, special beams and active controlling. Credit: Xiaofei Zang, Bingshuang Yao, Lin Chen, Jingya Xie, Xuguang Guo, Alexei V. Balakin, Alexander P. Shkurinov, and Songlin Zhuang

https://phys.org/news/2021-03-metasurfaces-terahertz.html

by Chinese Academy of Sciences

THz waves have a plethora of applications ranging from biomedical and medical examinations, imaging, environmental monitoring, to wireless communications, because of abundant spectral information, low photon energy, strong penetrability, and shorter wavelength. THz waves with technological advances not only determined by high-efficiency sources and detectors but also decided by a variety of high-quality THz components/functional devices. However, traditional THz devices should be thick enough to realize the desired wave-manipulating functions, hindering the development of THz integrated systems and applications. Although metamaterials have shown groundbreaking discoveries due to tunable electric permittivity and magnetic permeability of a meta-atom, they are limited by technical challenges of fabrication and high loss of the metal-based unit cell.

In a new paper published in Light: Advanced Manufacturing, a team of scientists, led by Professor Songlin Zhuang from Terahertz Technology Innovation Research Institute, University of shanghai for Science and Technology, and co-workers have summarized recent advancements of metasurfaces for the manipulation of THz waves. These ultra-compact devices with unusual functionalities render metasurface devices very attractive for applications such as imaging, encryption, information modulation and THz communications.

Actually, metasurfaces typically consist of planar antennas that enable predesigned EM responses. The antennas are made of metals or traditional high-refractive index dielectrics that can be easily fabricated based on standard fabrication processes. In addition, metasurfaces with functionality in manipulating EM waves are dependent on abrupt phase changes at planar antenna interfaces, and thus the thickness of metasurfaces is much thinner than the incident wavelength. Metasurfaces can locally control the wavefront of EM waves at subwavelength resolution, leading to various practical applications such as metalenses, waveplates, vortex beam generators, beam steering and holograms. The ultrathin nature of metasurfaces, ease of fabrication, and subwavelength resolution in manipulation of EM waves make metasurfaces ideal candidates for THz device miniaturization (ultra-compact THz devices) and system integration.

The metasurface-based approach for manipulatig THz waves enables remarkable contributions in designing ultra-thin/ultra-compact and tunable THz components. The main advantages/contributions of THz metasurfaces can be concluded as follows: (1) THz components with reduced size: The functionalities of focusing, OAM, and polarization conversion realized by metasurfaces can be traditionally obtained by using a THz lens, helical phase plate, and half-wave (or quarter-wave) plate, respectively; (2) THz components with multiple functions: The traditional THz devices, e.g. THz lenses, waveplates, etc, always show a single function. Metasurfaces not only provide a flexible platform to realize ultra-thin/ultra-compact THz devices with single function, but also enable the unprecedented capability in designing multifunctional THz devices. (3) THz components with tunable function: Metasurfaces combined with VO2, graphene, etc, open a new avenue for designing THz components with active functions.

In conclusion, metasurfaces with planar structures can locally modify the wavefront of THz waves at subwavelength resolution. Metasurfaces not only provide an ultra-compact platform for manipulating the wavefront of THz waves, but also generate a plethora of applications that are difficult to achieve with conventional functional devices. As an overview, the recent developments of metasurfaces for manipulating THz waves were presented in this paper, and this progress report may open a new avenue to design ultra-thin or ultra-compact THz functional devices and systems.

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Metasurfaces for manipulating terahertz waves

                                              
LIGHT PUBLISHING CENTER, CHANGCHUN INSTITUTE OF OPTICS, FINE MECHANICS AND PHYSICS, CAS

The associated THz responses include focusing, holograms, polarization modulation, special beams and active controlling.

CREDIT

by Xiaofei Zang, Bingshuang Yao, Lin Chen, Jingya Xie, Xuguang Guo, Alexei V. Balakin, Alexander P. Shkurinov, and Songlin Zhuang

https://www.eurekalert.org/pub_releases/2021-03/lpcc-mfm032221.php

THz waves have a plethora of applications ranging from biomedical and medical examinations, imaging, environment monitoring, to wireless communications, because of the abundant spectral information, low photon energy, strong penetrability, and shorter wavelength. THz waves with technological advances not only determined by the high-efficiency sources and detectors but also decided by a variety of the high-quality THz components/functional devices. However, traditional THz devices should be thick enough to realize the desired wave-manipulating functions, hindering the development of THz integrated systems and applications. Although metamaterials have been shown groundbreaking discoveries due to the tunable electric permittivity and magnetic permeability of a meta-atom, they are limited to technical challenges of fabrication and high loss of the metal-based unit cell.

In a new paper published in Light: Advanced Manufacturing, a team of scientists, led by Professor Songlin Zhuang from Terahertz Technology Innovation Research Institute, University of Shanghai for Science and Technology, and co-workers have summarized the recent advancements of metasurfaces for the manipulation of THz waves. These ultra-compact devices with unusual functionalities render metasurface devices very attractive for applications such as imaging, encryption, information modulation and THz communications.

Actually, metasurfaces typically consist of planar antennas that enable predesigned EM responses. The antennas are made by metals or traditional high-refractive index dielectrics that can be easily fabricated based on the standard fabrication process. In addition, metasurfaces with the functionality in manipulating EM waves are dependent on the abrupt phase changes at planar antenna interfaces, and thus the thickness of metasurfaces is much thinner than the incident wavelength. Metasurfaces can locally control the wavefront of EM waves at subwavelength resolution, leading to various practical applications such as metalens, waveplates, vortex beam generators, beam steering and holograms. The ultrathin nature of metasurfaces, the ease of fabrication, and the subwavelength resolution in manipulating of EM waves make metasurfaces ideal candidates for THz device miniaturization (ultra-compact THz devices) and system integration.

The metasurface-based approach for manipulatig THz waves enables remarkable contributions in designing ultra-thin/ultra-compact and tunable THz components. The main advantages/contributions of THz metasurfaces can be concluded as follows: (1) THz components with reduced size: The functionalities of focusing, OAM, and polarization conversion realized by metasurfaces can be traditionally obtained by using a THz lens, helical phase plate, and half-wave (or quarter-wave) plate, respectively; (2) THz components with multiple functions: The traditional THz devices, e.g. THz lenses, waveplates, etc..., are always show a single function. Metasurfaces not only provide a flexible platform to realize ultra-thin/ultra-compact THz devices with single function, but also enable the unprecedented capability in designing multifunctional THz devices. (3) THz components with tunable function: Metasurfaces combined with VO2, graphene, etc, open a new avenue for designing THz components with active functions.

In conclusion, metasurfaces with planar structures can locally modify the wavefront of THz waves at subwavelength resolution. Metasurfaces not only provide an ultra-compact platform for manipulating the wavefront of THz waves, but also generate a plethora of applications that are difficult to achieve with conventional functional devices. As an overview, the recent developments of metasurfaces for manipulating THz waves were presented in this paper, and this progress report may open a new avenue to design ultra-thin or ultra-compact THz functional devices and systems.

Abstract-Terahertz-frequency temporal differentiator enabled by a high-Q resonator

Jingya Xie, Xi Zhu, Hongxiang Zhang, Xiaofei Zang, Lin Chen, Alexey V. Balakin, Alexander P. Shkurinov, and Yiming Zhu

Schematic of the experimental setup for measurements of THz integrated temporal differentiator. AWG: arbitrary waveform generators. RF&MSG: radio frequency microwave source. SGX Module: signal generator extension module. HA: horn antenna. DD: direct detector. The insets (a) and (b) are the schematic drawing of the TRR and cross-sectional view of waveguides, respectively.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-6-7898

Terahertz (THz) fundamental “building blocks” equivalent to those used in multi-functional electronic circuits are very helpful for actual applications in THz data-processing technology and communication. Here, we theoretically and experimentally demonstrate a THz temporal differentiator based on an on-chip high-quality (Q) factor resonator. The resonator is made of low-loss high-resistivity silicon material in a monolithic, integrated platform, which is carefully designed to operate near the critical coupling region. The experiment demonstrates that the device can perform the first-order time derivative of the input signal electric field complex envelope at 214.72 GHz. Our investigation provides an effective approach for terahertz pulse re-shaping and real-time differential computing units.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-A Multi‐Foci Metalens with Polarization‐Rotated Focal Points

Xiaofei Zang, Hongzhen Ding,   Yuttana Intaravanne,   Lin Chen,   Yan Peng,   Jingya Xie,   Qinghong Ke,   Alexey V. Balakin,   Alexander P. Shkurinov,   Xianzhong Chen, Yiming Zhu,   Songlin Zhuang,

https://onlinelibrary.wiley.com/doi/abs/10.1002/lpor.201900182

Benefiting from the unprecedented capability of metasurfaces in the manipulation of light propagation, metalenses can provide novel functions that are very challenging or impossible to achieve with conventional lenses. Here, an approach to realizing multi‐foci metalenses is proposed and experimentally demonstrated with polarization‐rotated focal points based on geometric metasurfaces. Multi‐foci metalenses with various polarization rotation directions are developed using silicon pillars with spatially variant orientations. The focusing characteristic and longitudinal polarization‐dependent imaging capability are demonstrated upon the illumination of a linearly polarized light beam. The uniqueness of this multi‐foci metalens with polarization‐rotated focal points may open a new avenue for imaging, sensing, and information processing.

Abstract-Metamaterial-enhanced terahertz vibrational spectroscopy for thin film detection

Jingya Xie, Xi Zhu, Xiaofei Zang, Qingqing Cheng, Lin Chen, Yiming Zhu,

Fig. 1 Schematic illustration of (a) the experiment setup, (b) optical image of the metamaterial with L-tartaric acid deposited on it, and (c) the SRR unit cell.

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-8-1-128&origin=search

We present metamaterial-enhanced terahertz vibrational spectroscopy to solve the low sensitivity problem of the THz ray absorption detection in molecular and biomolecular thin film. In a proof-of-principle experiment, we demonstrate the system in split ring resonators (SRRs) metamaterial that is strongly coupled to L-tartaric acid molecular under a low-temperature condition. The experimental results show that the extinction ratio of the detected signal can be significantly improved from 1.75 dB to 4.5 dB. The numerical calculations confirm and explain the experimental observations. By detuning the resonance of metamaterial, the behavior of the spectral signal is modified. When the SRRs and molecular vibrational resonance frequencies are closely aligned, a clear mode splitting is observed resulting in a transparency transmission with enhanced extinction ratio. This method shows great potential for application in thin film sensing by detecting molecular vibrations in the lower-energy terahertz region.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Metasurface for multi-channel terahertz beam splitters and polarization rotators

XiaoFei Zang, HanHong Gong, Zhen Li, JingYa Xie, QingQing Cheng,   Lin Chen,   Alexander P. Shkurinov, YiMing Zhu, SongLin Zhuang,

https://aip.scitation.org/doi/abs/10.1063/1.5028401

Terahertz beam splitters and polarization rotators are two typical devices with wide applications ranging from terahertz communication to system integration. However, they are faced with severe challenges in manipulating THz waves in multiple channels, which is desirable for system integration and device miniaturization. Here, we propose a method to design ultra-thin multi-channel THz beam splitters and polarization rotators simultaneously. The reflected beams are divided into four beams with nearly the same density under illumination of linear-polarized THz waves, while the polarization of reflected beams in each channel is modulated with a rotation angle or invariable with respect to the incident THz waves, leading to the multi-channel polarization rotator (multiple polarization rotation in the reflective channels) and beam splitter, respectively. Reflective metasurfaces, created by patterning metal-rods with different orientations on a polyimide film, were fabricated and measured to demonstrate these characteristics. The proposed approach provides an efficient way of controlling polarization of THz waves in various channels, which significantly simplifies THz functional devices and the experimental system.

Abstract-Terahertz integrated device: high-Q silicon dielectric resonators

Jingya Xie, Xi Zhu, Xiaofei Zang, Qingqing Cheng, Lin Chen, and Yiming Zhu

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-8-1-50

We design, fabricate, and characterize the terahertz integrated resonators on the silicon platform. Based on mode analysis and selection, the high-Q feature of resonators made of low-loss high-resistivity Si material is achieved due to the excitation of the whispering gallery mode on waveguide-coupled single-mode racetrack rings and disk cavities. The experimental results demonstrate that the Q-factor can reach up to 2839 at 218.345 GHz, which is significantly improved compared with conventional THz cavities. These high Q-factor integrated resonators can be used as on-chip terahertz ultrasensitive sensors and as terahertz functional integrated circuits.

© 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Excitation of dark multipolar plasmonic resonances at terahertz frequencies

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• Lin Chen
• , YuMing Wei
• , XiaoFei Zang
• , YiMing Zhu
•  & SongLin Zhuang

http://www.nature.com/articles/srep22027

We experimentally observe the excitation of dark multipolar spoof localized surface plasmon resonances in a hybrid structure consisting of a corrugated metallic disk coupled with a C-shaped dipole resonator. The uncoupled corrugated metallic disk only supports a dipolar resonance in the transmission spectrum due to perfect symmetry of the structure. However, the dark multipolar spoof localized surface plasmon resonances emerge when coupled with a bright C-shaped resonator which is placed in the vicinity of the corrugated metallic disk. These excited multipolar resonances show minimum influence on the coupling distance between the C-shaped resonator and corrugated metallic disk. The resonance frequencies of the radiative modes are controlled by varying the angle of the C-shaped resonator and the inner disk radius, both of which play dominant roles in the excitation of the spoof localized surface plasmons. Observation of such a transition from the dark to radiative nature of multipolar spoof localized plasmon resonances would find potential applications in terahertz based resonant plasmonic and metamaterial devices.

Abstract-Ultra-broadband terahertz perfect absorber by exciting multi-order diffractions in a double-layered grating structure

Ultra-broadband terahertz perfect absorber by exciting multi-order diffractions in a double-layered grating structure Yan Peng, XiaoFei Zang, YiMing Zhu, Cheng Shi, Lin Chen, Bin Cai, and SongLin Zhuang  »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-23-3-2032

Optics Express, Vol. 23, Issue 3, pp. 2032-2039 (2015)
http://dx.doi.org/10.1364/OE.23.002032

View Full Text Article

Enhanced HTML    Acrobat PDF (1993 KB)

Terahertz (THz) perfect absorber, as a useful functional device, has attracted considerable attention. Traditional metamaterial perfect absorbers are usually in response to single-frequency or multi-frequency owing to the resonance features of the metal-based sub-wavelength structure. In this paper, a simple double-layered doped-silicon grating structure was designed to realize an ultra-broadband and polarization-independent THz perfect absorber. Both theoretical and experimental results demonstrate that the incident THz waves ranging from 0.59 to 2.58 THz can be efficiently absorbed with an absorptivity of more than 95% and a bandwidth of about 2.0 THz. The excellent characteristic of this broad-bandwidth THz perfect absorber is mainly resulted from the air gap mode resonance together with the first-order and the second-order grating diffractions.

© 2015 Optical Society of America

Abstract-Rotatable illusion media for manipulating terahertz electromagnetic waves

XiaoFei Zang, Zhou Li, Cheng Shi, Lin Chen, Bin Cai, YiMing Zhu, Li Li, and XiaoBin Wang  »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-21-25565

Abstract

Based on composite optical transformation, we propose a rotatable illusion media with positive permittivity and permeability to manipulate terahertz waves, and a new way to realize singular parameter-independent cloaks when the incident wave with a certain width propagates from specific incident directions. The fundamental mechanism of this kind of cloak is that the illusion media can be able to avoid the incident wave interacting with the objects. Comparing with traditional transformation-coordinate-based cloaks such as cylindrical-shaped cloaks, our cloaks are independent of singular material parameters. Furthermore, this type of rotatable illusion media can be applied to design tunable miniaturized high-directivity antenna (a small antenna array covered with the rotatable illusion media appears like a large one and meanwhile, the radiation directions of the small antenna array is tunable via this rotatable illusion media). Full wave simulations are performed to confirm these points.

© 2013 Optical Society of America