Abstract-Terahertz subwavelength edge detection based on dispersion-induced plasmons

 

Tie-Jun Huang, Jin Zhao, Li-Zheng Yin,  Pu-Kun Liu, 

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-46-11-2746

Terahertz imaging has recently attracted great attention owing to the abilities of high penetration and low ionizing damages. However, the low resolution and low contrast resulting from the diffraction limit and unwanted background illumination significantly hinder the extensive usage. In this Letter, we propose and numerically demonstrate a terahertz subwavelength imaging method capable of extracting only the edges and fine features of the targets. The underlying physics is the efficient transmission of the scattering evanescent waves related to key geometric information while blocking the propagating components. By exploiting the structurally induced plasmons in a bounded metallic waveguide, the transmission channel for evanescent waves is realized by hyperbolic metamaterials through periodically stacking dielectric layers. On this basis, high-contrast edge detection with a resolution up to 0.1𝜆$0.1\lambda$ is demonstrated at terahertz wavelengths. The proposed terahertz imaging method may find important applications in non-destructive testing, weak scattering object detection, and high-contrast microscopy.

© 2021 Optical Society of America

Abstract-Terahertz dual phase gradient metasurfaces: high-efficiency binary-channel spoof surface plasmon excitation

Li-Zheng Yin, Tie-Jun Huang, Di Wang, Jiang-Yu Liu, Yan Sun, and Pu-Kun Liu

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-45-2-411

Spoof surface plasmon meta-couplers are compact antennas that link propagating waves and surface waves. However, most of them are designed with a fixed phase gradient and channel for the incident waves with specific polarization, which limits their further applications in multichannel scenarios. In this Letter, a new, to the best of our knowledge, method that combines the Brillouin zone folding theory with the generalized Snell’s law is proposed. We demonstrate that when the phase gradient of the metasurface is large enough, Brillouin zone folding effect will occur, which will create dual phase gradient space in a single metasurface. With this method, we design two novel terahertz meta-couplers with functionalities of symmetrical and asymmetrical binary-channel spoof surface plasmon (SSP) excitation. Furthermore, finite element method simulations are performed to demonstrate their functionalities. Considering the orthogonality of the incident waves, there can be a total of four independent space channels to excite SSPs on one metasurface. This work may open up new routes in multichannel SSP meta-couplers and multibeam surface wave antennas.

© 2020 Optical Society of America

Abstract-High-efficiency terahertz spin-decoupled meta-coupler for spoof surface plasmon excitation and beam steering

Li-Zheng Yin, Tie-Jun Huang, Feng-Yuan Han, Jiang-Yu Liu, Pu-Kun Liu

https://assert.pub/papers/1904.06133

Spoof surface plasmon (SSP) meta-couplers that efficiently integrate other diversified functionalities into a single ultrathin device are highly desirable in the modern microwave and terahertz fields. However, the diversified functionalities, to the best of our knowledge, have not been applied to circular polarization meta-couplers because of the spin coupling between the orthogonal incident waves. In this paper, we propose and numerically demonstrate a terahertz spin-decoupled bifunctional meta-coupler for SSP excitation and beam steering. The designed meta-coupler is composed of a coupling metasurface and a propagating metasurface. The former aims at realizing anomalous reflection or converting the incident waves into SSP under the illumination of the left or right circular polarization waves, respectively, and the latter are used to guide out the excited SSP. The respective converting efficiency can reach 82% and 70% at 0.3THz for the right and left circular polarization incident waves. Besides, by appropriately adjusting the reflection phase distribution, many other diversified functionalities can also be integrated into the meta-coupler. Our study may open up new routes for polarization-related SSP couplers, detectors, and other practical terahertz devices.

Abstract-Terahertz multichannel metasurfaces with sparse unit cells

Li-Zheng Yin, Tie-Jun Huang, Feng-Yuan Han, Jiang-Yu Liu, and Pu-Kun Liu

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-44-7-1556

Reflective multichannel metasurfaces are flat reflectors that can control incident and reflected waves in a number of propagating directions simultaneously. However, they are always densely discretized with a high spatial resolution, which increases the manufacturing complexity. In this Letter, to the best of our knowledge, a new method that combines the array antenna theory with the metagratings theory is proposed. We demonstrate that the unit cells with a linear gradient phase in each period of the metasurfaces can eliminate specific space harmonics. With this method, multichannel metasurfaces can be designed with sparse unit cells, and high efficiency is maintained simultaneously. As proofs of the method, we design three different terahertz multichannel metasurfaces with no more than three unit cells per period. The simplification of structures can efficiently reduce the manufacturing complexity. This work may open up new routes in designing multichannel metasurfaces.

© 2019 Optical Society of America

Abstract-Superfocusing plate of terahertz waves based on a gradient refractive index metasurface

Journal of Applied Physics

Feng-Yuan Han, Tie-Jun Huang, Li-Zheng Yin, Jiang-Yu Liu, Pu-Kun Liua

Whole view of the proposed metasurface achieving one-dimensional superfocusing, along with identical cells 1−5 as the main components tailoring the incident plane waves. The thickness of the plate is approximately 0.11λ0 at 0.967 THz

https://aip.scitation.org/doi/10.1063/1.5050696

A new scenario to realize superfocusing of terahertz waves based on a gradient index (GRIN) metasurface is proposed. To design the GRIN material, a robust algorithm is presented and numerically demonstrated to retrieve the constitutive effective parameters (permittivity and permeability) of the metasurface from the measurement of S parameters. In addition, a new kind of unit cell with a simple structure is designed to verify the theory of effective parameters. By computing the effective refractive index of the unit cell using the algorithm, we design a plate with a thickness of approximately 0.11λ0 (free-space wavelength) at 0.967 THz to superfocus terahertz waves in one dimension. We also revise the theory of superfocusing to make full use of the coupling effect among the cells in the plate and are able to demonstrate it. Comprehensive simulations of focusing are provided, and the full width at half-maximum beam width reaches up to 0.167λ0 at a distance of 0.2λ0. The focusing depth can be further enhanced by decreasing the cell size of the metasurface. This work is beneficial for metasurface design, super-resolution imaging, and other applications in the near field.

Abstract-Superfocusing of terahertz wave through spoof surface plasmons

Tie-Jun Huang, Jiang-Yu Liu, Li-Zheng Yin, Feng-Yuan Han, Pun-Kun Liu,

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-18-22722

In this paper, we propose and numerically demonstrate a new way to realize superfocusing of terahertz waves via the spoof surface plasmons (SSP). With the assist of a modified subwavelength metallic grating, a near-field rapid oscillation can be formed, originating from the Fabry–Perot resonances due to the reflection of SSP waves at terminations. We show that the field pattern of oscillation on textured metallic surface can be engineered by adjusting groove width and grating number. This produces a desired modulation of phase and amplitude for the radiationless electromagnetic interference (REI) focusing. The effective focusing depth through the corrugated metal is evaluated by the full-width-half-maximum (FWHM) beamwidth. At the situation of third-order Fabry–Perot resonance, the FWMH reaches up to 0.069λ at a distance of 0.1λ, improving the beamwidth by more than 540% compared with a single slit. The FWHM is optimized to 0.06λ as the order of Fabry–Perot resonance becomes seven, leading to the superfocusing metric of 1.67. On the basis of this, we further show the focusing ability can be held on the ultra-thin metallic grating. Two-dimensional subwavelength focusing behavior is also numerically verified. Our study may extend the working distance of sensing and super-resolution imaging devices at terahertz frequency.

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