Abstract-Multiband terahertz absorber and selective sensing performance

Yue Wang, Zijian Cui, Dongying Zhu, Xinmei Wang, Suguo Chen, and Pengcheng Nie

Fig. 1 (a) Illustration of multiple-band THz metamaterial absorber. (b) Photograph of the metamaterial absorber. (c) Optical microscopy image of the absorber. (d) Reflection time-domain waveforms in the TE and TM polarization cases. Inset: Designed structure and geometric parameters of the unit cell.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-10-14133

Multiband terahertz absorbers are essential photonic components for responding to, manipulating, and modulating terahertz waves. In this work, improved electric split resonant ring arrays are used to demonstrate multiband terahertz wave absorption. The proposed design strategy is simple, practical, and significant. Experiments and simulations reveal perfect absorption at 0.918 THz and 1.575 THz for the transverse magnetic (TM) polarization and at 0.581, 1.294, and 1.556 THz for the transverse electric (TE) polarization. In addition, the weak resonant peaks that occurred in the experiments in both polarization states have been verified by the simulations. Furthermore, five concentration gradients of 2, 4-dichlorophenoxyacetic acid solutions and six concentration gradients of chlorpyrifos have been detected using the absorber. The lowest detectable concentration that could be monitored was 0.1 ppm. The absorption, intensity, and frequency shift values for the different solution concentrations at the resonant peaks were analyzed. The highest linear regression coefficients were 0.9862 and 0.9565 for the TE and TM polarizations, respectively. This multi-band absorber was demonstrated to be highly efficient in detecting pesticides for food safety applications.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Tailoring terahertz surface plasmon wave through free-standing multi-walled carbon nanotubes metasurface

Yue Wang, Zijian Cui, Dongying Zhu, Xianbin Zhang, and Li Qian

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-12-15343

Surface plasmons have a fundamental role in the dynamics of photon–electron interactions and in optical metamaterials. Terahertz (THz) time-domain spectroscopy was used to characterize the complex dielectric constant, index of refraction, and conductivity of super-aligned, free-standing, multi-walled carbon nanotube films over the range 0.2-2.5 THz. These complex parameters were in excellent agreement with Maxwell-Garnett and Drude-Lorentz models. In addition, surface plasmon excitations in engineered, subwavelength, multi-walled carbon nanotube metasurfaces were examined. The observed surface plasmon resonances, reproduced by simulation, could be changed over the THz frequency range by altering the lattice constant of the arrays. The THz transmission was enhanced at the resonance peak. Overall, the results indicate potential applications for THz metasurfaces based on super-aligned, free-standing multi-walled carbon nanotubes.

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

Abstract-Broadband tunable electromagnetically induced transparency analogue metamaterials based on graphene in terahertz band

Yue Wang, Yanbing Leng, Li Wang, Lianhe Dong, Shunrui Liu, Jun Wang and Yanjun Sun

http://iopscience.iop.org/article/10.7567/APEX.11.062001/meta

Most of the actively controlled electromagnetically induced transparency analogue (EIT-like) metamaterials were implemented with narrowband modulations. In this paper, a broadband tunable EIT-like metamaterial based on graphene in the terahertz band is presented. It consists of a cut wire as the bright resonator and two couples of H-shaped resonators in mirror symmetry as the dark resonators. A broadband tunable property of transmission amplitude is realized by changing the Fermi level of graphene. Furthermore, the geometries of the metamaterial structure are optimized to achieve the ideal curve through the simulation. Such EIT-like metamaterials proposed here are promising candidates for designing active wide-band slow-light devices, wide-band terahertz active filters, and wide-band terahertz modulators.

Abstract-Terahertz Dispersion Characteristics of Super-aligned Multi-walled Carbon Nanotubes and Enhanced Transmission through Subwavelength Apertures

Yue Wang, Guangwu Duan, Liying Zhang, Lihua Ma, Xiaoguang Zhao,  Xin Zhang

https://www.nature.com/articles/s41598-018-20118-5

The terahertz (THz) dielectric properties of super-aligned multi-walled carbon nanotube (MWCNT) films were characterized in the frequency range from 0.1 to 2.5 THz with terahertz time-domain spectroscopy. The refractive index, effective permittivity, and conductivity were retrieved from the measured transmission spectra with THz incident wave polarized parallel and perpendicular to the orientation of carbon nanotubes (CNTs), and a high degree of polarization dependence was observed. The Drude-Lorentz model combined with Maxwell-Garnett effective medium theory was employed to explain the experimental results, revealing an obvious metallic behavior of the MWCNT films. Moreover, rectangular aperture arrays were patterned on the super-aligned MWCNT films with laser-machining techniques, and the transmission measurement demonstrated an extraordinarily enhanced transmission characteristic of the samples with incident wave polarized parallel to the orientation of the CNTs. Surface plasmon polaritons were employed to explain the extraordinarily enhanced transmission with high accuracy, and multi-order Fano profile was applied to model the transmission spectra. A high degree of agreement was exhibited among the experimental, numerical, and theoretical results.

Abstract-Continuous-wave Y-band planar BWO with wide tunable bandwidth

Hongzhu Xi, Jianguo Wang, Zhaochang He, Gang Zhu, Yue Wang, Hao Wang, Zaigao Chen, Rong Li , Luwei Liu

https://www.nature.com/articles/s41598-017-18740-w

A high performance continuous-wave (CW) backward wave oscillator (BWO) with planar slow wave structure (SWS) and sheet electron beam in Y-band is presented in this paper. The mode selection is discussed by studying the dispersion curve of SWSs, distributions of the electric field, and particle-in-cell simulation results, showing that the designed BWO operates in the fundamental mode TM11. The planar SWSs are fabricated by using the UV-LIGA technology with the processing error less than 0.003 mm. The electron gun can provide the 2.5 mm × 0.14 mm sheet electron beam with maximum current density of 57 A/cm2 at the CW mode. Experimental results show that the developed BWO can operate in the fundamental mode TM11 and generate the state-of-art output power of 182 mW at the frequency of 0.3426 THz with a large frequency tuning range from 0.318 THz to 0.359 THz.

Abstract-Development of a novel overmoded sub-terahertz inclined coaxial clinotron with asymmetric mode suppressed

Physics of Plasmas

Zaigao Chen and Yue Wang

http://aip.scitation.org/doi/abs/10.1063/1.5004550

Overmoded coaxial high frequency structures can improve the power capacity of vacuum electron devices (VEDs) and make the fabrication and assembly of the devices easy in the terahertz band, but they also lead to mode competition and deleterious effect on the beam-wave interaction. The numerical investigation on the cold cavity characteristics indicates that the dispersion curve of the quasi-TEM mode almost overlaps with the dispersion curve of the high-order quasi-TE11 mode, and the 3-D numerical simulation results also illustrate that due to the mode competition, the quasi-TEM cannot be excited steadily in the VEDs with traditional coaxial SWSs with the available current density. In order to effectively suppress the mode competition of overmoded coaxial SWSs, novel inclined coaxial slow wave structures (SWSs) are proposed in this paper. As the overmoded ratio of the SWSs reaches 9.7, the 3D particle-in-cell simulation results indicate that this novel device can successfully produce the terahertz wave with the output power of 571 W at the operating frequency of 0.338 THz, and the frequency spectrum of the generated signal is very pure. The field distributions in the inclined coaxial SWSs illustrate that there is no asymmetric mode excited in the proposed device.

Abstract-Broadband extraordinary terahertz transmission through super-aligned carbon nanotubes film

Yue Wang, Xiaoguang Zhao, Guangwu Duan, and Xin Zhang

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-14-15730

We experimentally demonstrate the extraordinary transmission of THz waves through super-aligned multi-walled carbon nanotube (MWCNT) films with one-dimensional arrays of sub-wavelength rectangular gratings in the broad frequency range from 0.2 to 2.5 THz. To achieve this, two kinds of MWCNT films (1 μm and 3 μm in thickness) were fabricated by drawing from a sidewall of super-aligned nanotube arrays synthesized by low pressure chemical vapor deposition. The measured complex refraction index of the film exhibits highly anisotropic transmission of THz waves through the MWCNTs. The anisotropy depends not only on the polarization direction of the THz waves but also on the orientation of the MWCNT gratings. We found that the resonantly extraordinary THz transmission originated from the surface plasmon polaritons supported by periodically patterned carbon nanotube gratings. Our experimental results may provide important insights for emerging THz plasmonic devices based on carbon nanotubes.

© 2016 Optical Society of America

Full Article  |  PDF Article