Abstract-Scattering of spoof surface plasmon polaritons in defect-rich THz waveguides

Andreas K. Klein, Alastair Basden, Jonathan Hammler, Luke Tyas, Michael Cooke, Claudio Balocco, Dagou Zeze, John M. Girkin, Andrew Gallant

https://www.nature.com/articles/s41598-019-42412-6

We report on the first observation of ‘Spoof’ Surface Plasmon Polariton (SPP) scattering from surface defects on metal-coated 3D printed, corrugated THz waveguiding surfaces. Surface defects, a result of the printing process, are shown to assist the direct coupling of the incident free-space radiation into a spoof SPP wave; removing the need to bridge the photon momentum gap using knife-edge or prism coupling. The free space characteristics, propagation losses and confinement of the spoof SPPs to the surface are measured, and the results are compared to finite-difference time domain simulations. Angular resolved THz spectroscopy measurements reveal the scattering patterns from surfaces and are compared with Mie theory, taking into account the shortened wavelength of the photons in their bound SPP state compared to their free space wavelength. These results confirm yet another similarity between the properties of THz spoof SPPs and their natural, non-spoof, counterparts at optical and infrared frequencies which also, unexpectedly, adds functionality to the structures.

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

Abstract-Study of terahertz spoof surface plasmons on subwavelength gratings with dielectric substance in grooves

V.V.Bulgakova, V.V.Gerasimov, B.G.Goldenberg, A.G.Lemzyakov, A.M.Malkin, 

http://www.sciencedirect.com/science/article/pii/S1877705817341711

Terahertz (THz) plasmonic devises based on periodical corrugated structures are promising for sensing applications in biology and medicine but have not been developed so far because spoof surface plasmons (SSPs) on such structures were studied insufficiently in the THz spectral range. In the paper, the propagation of THz SSPs along one-dimensional subwavelength rectangular plane gratings with a dielectric substance in the grooves was studied and optimal parameters of gratings (period, aspect ratio and groove depth) for sensing of dielectric were found. First grating samples were made and tested using the THz radiation of the Novosibirsk free electron laser.

Abstract-Trapped spoof surface plasmons with structured defects in textured closed surfaces

Hong-Wei Wu, Hua-Jun Chen, Hui-Ying Fan, Yang Li, and Xian-Wen Fang

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-4-791&origin=search

We demonstrate that a defect unit in periodic textured closed surfaces is able to trap spoof surface plasmons (SPs) into a deep subwavelength scale. The resonant frequency of a trapped spoof SP can be tuned freely by properly tailoring the dimension of the defect unit. By introducing multiple defect units with different dimensions at different positions of the textured closed surfaces, the spoof SPs with different frequencies trapped effectively at desired places are also demonstrated. In addition, we further design a graded defect structure with continuously variable dimensions to trap the spoof SPs over an ultrawide spectral band. The interval between the trapped waves on the closed surfaces can be tuned conveniently by changing the grade of the defect dimensions. The designer structures may indicate potential applications in the optical switch and storage in the microwave and terahertz frequencies.

© 2017 Optical Society of America

Abstract-Switching terahertz wave with grating-coupled Kretschmann configuration

Li Jiu-sheng

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-16-19422

We present a terahertz wave switch utilizing Kretschmann configuration which consists of high-refractive-index prism-liquid crystal-periodically grooved metal grating. The switching mechanism of the terahertz switch is based on spoof surface plasmon polariton (SSPP) excitation in the attenuated total reflection regime by changing the liquid crystal refractive index. The results highlighted the fact that the feasibility to “tune” the attenuated total reflection terahertz wave intensity by using the external applied bias voltage. The extinction ratio of the terahertz switch reaches 31.48dB. The terahertz switch has good control ability and flexibility, and can be used in potential terahertz free space device systems.

© 2017 Optical Society of America

Abstract-Ultrasensitive terahertz metamaterial sensor based on spoof surface plasmon

• 
  
  
• Xu Chen & 
• Wenhui Fan

https://www.nature.com/articles/s41598-017-01781-6

A planar terahertz metamaterial sensor consisting of a corrugated metal stripe perforated by three rectangular grooves is proposed and investigated numerically. Due to the formation of Fabry-Perot resonance of the spoof surface plasmons mode on the corrugated metal stripe, the extremely sharp resonance in transmission spectrum associated with strong local field enhancement and high quality factor can be realized and exploited for ultrasensitive sensing. Since the intense interaction between electromagnetic waves and analyte materials, the frequency sensitivity of 1.966 THz per refractive index unit and the figure of merit of 19.86 can be achieved. Meanwhile, the film thickness sensitivity of this metamaterial sensor is higher than 52.5 GHz/μm when the analyte thickness is thinner than 4 μm. More interestingly, we find that the metal thickness has a great effect on the sensor performance. These findings open up opportunities for planar metamaterial structures to be developed into practical sensors in terahertz regime.

Abstract-Enhanced terahertz sensing with a coupled comb-shaped spoof surface plasmon waveguide

Xiaomei Shi, Jianyuan Qin, and Zhanghua Han

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-1-278

A comb-shaped waveguide based on the excitation of coupled spoof surface plasmon (CSSP) mode is investigated, and is found to have a pronounced effect for the enhancement of fingerprint detection sensitivity in the terahertz (THz) regime. Composed of two oppositely oriented metal stripes with single-side comb-shaped corrugations, the waveguide is formed due to the coupling of SSP modes supported by metal corrugations on both sides and the mode is tightly localized between the central gap, which provides a perfect site for accommodating the samples in THz sensing. The effective detection of thin-layer lactose is given as an example to demonstrate the sensitive detection of it at a thickness of only a few microns. A transmission spectrum through the waveguide with a pronounced dip at its characteristic absorption frequency of 0.529THz is shown, which can never be observed using the transmission through a lactose layer with the same thickness.

© 2017 Optical Society of America

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