Abstract-Multi-Beam Steering for 6G Communications Based on Graphene Metasurfaces

 

Huifang Ai, Qianlong Kang, Wei Wang, Kai Guo, Zhongyi Guo

 (a) Indoor THz communication scheme for multi-user scenarios. (b) Schematic of a graphene metasurface that consists of a metal substrate, a dielectric layer, and top graphene ribbons. (c) A sectional view of the graphene metasurface. p is the grating period, w is the width of the graphene ribbon and s is the thickness of the SiO2 dielectric layer.

https://www.mdpi.com/1424-8220/21/14/4784/htm

As communication technology is entering the 6G era, a great demand for high-performance devices operating in the terahertz (THz) band has emerged. As an important part of 6G technology, indoor communication requires multi-beam steering and tracking to serve multi-users. In this paper, we have designed a graphene metasurface that can realize multi-beam steering for directional radiations. The designed metasurface consists of graphene ribbons, dielectric spacer, and metal substrate. By designing the graphene ribbons and controlling the applied voltage on them, we have obtained single-, double-, and triple-beam steering. In addition, we have also numerically calculated the far-field distributions of the steered multi-beam with a diffraction distance of 2 m. Our design has potential applications in future indoor directional 6G communications.

Abstract-High power Continuously Frequency-tunable Terahertz Radiation Sources and Transmission Lines for DNP-enhanced NMR System

Diwei Liu, Tao Song,  Hao Shen,  Jie Huang, Ning Zhang, Chenghai Wang, Wei Wang, Shenggang Liu

https://ieeexplore.ieee.org/document/8510299

The effect of the electron beam quality of a 250GHz continuously frequency-tunable gyrotron used for Dynamic Nuclear Polarization enhanced Nuclear Magnetic Resonance is tuned by changing the operating voltage Vo or the operating magnetic field Bo on the operating frequency and the beam-wave interaction efficiency is investigated. Meanwhile, an improved transmission and mirror system with a well-focused Gaussian-like output beam is designed to match the DNP-NMR sample.

Abstract-Terahertz nonvolatile in situ electrically erasable-rewritable photo-memory based on indium oxide/PEDOT:PSS

Bin Liu, Jingyu Liu, Hongyu Ji, Wei Wang, Jingling Shen, and Bo Zhang

 (a) Schematic of the terahertz time-domain spectroscopy (THz-TDS) system and structure of the electrically-erasable rewritable THz device. (b) Scanning electron microscopy (SEM) images of the indium oxide sample.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-20-28792

A terahertz (THz) nonvolatile in situ electrically erasable-rewritable photo-memory based on indium oxide (In2O3) nanoparticles is reported. The In2O3/PEDOT:PSS/quartz sample increases its conductivity and attenuates its THz transmission under optical excitation. When this optical excitation is terminated, the modulated THz transmission recovers to its original value in an air environment slightly. The modulated THz transmission recovered more rapidly with increasing bias voltage. Nonvolatile digital information storage is enabled when the In2O3/PEDOT:PSS/quartz structure is encapsulated in nitrogen. The photo-memory can be rewritten after in situ electrical erasure. The results show that in situ electrically erasable terahertz nonvolatile rewritable photo-memories are feasible.

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

Abstract-Terahertz read-only multi-order nonvolatile rewritable photo-memory based on indium oxide nanoparticles

Applied Physics Letters

Hongyu Ji, Wei Wang, Luyao Xiong, Dandan Liu, Longfeng Lv, Bo Zhang, Jingling Shen,

(a) Schematic of the terahertz time-domain spectroscopy (THz-TDS) system. (b) Absorption spectrum and scanning electron microscopy (SEM) image of the indium oxide sample

https://aip.scitation.org/doi/abs/10.1063/1.5051029

We investigate terahertz (THz) read-only multi-order nonvolatile rewritable photo-memory based on indium oxide (In2O3) nanoparticles. Optical excitation of an In2O3/quartz sample increases its conductivity, which attenuates its THz transmission. When the optical excitation is terminated, the modulated THz transmission can recover back to its original value in air. However, the THz transmission shows no obvious change over a long-term when In2O3/quartz is encapsulated in an inert gas (nitrogen). Multi-order nonvolatile digital information storage is obtained at different light intensities, and the photo-memory can be rewritten after thermal annealing. Different THz transmissions are used as coded signal units, which are programmed to store information. These results show that THz read-only multi-level nonvolatile rewritable photo-memory can be realized.

Abstract-Broadband terahertz metamaterial absorber with two interlaced fishnet layers

AIP Advances

Siyu Tan, Fengping Yan,  Ningning Xu, Jingjing Zheng, Wei Wang, Weili Zhang,

Schematic of the proposed broadband metamaterial absorber: (a) the two interlaced square fishnet layers and the ground plane are separated by two identical polyimide spacers with the thickness h = 20 μm. (b) Microscopic graph of the fabricated sample. (c) and (d): The unit cell of the middle layer and the top layer with l = 150 μm, w1 = 35 μm and w2 = 15 μm.

https://aip.scitation.org/doi/10.1063/1.5017099

The realization of broadband absorption in the terahertz regime is of significant interest in high-sensitive signal detection and modulation. Previously, multi-layer metamaterials have been proposed and demonstrated to expand the absorption bandwidth by clustering multiple closely-positioned structures with different absorption peaks. Here, we proposed an alternative design for broadband metamaterial absorption by incorporating two interlaced fishnet layers, and achieved a broadband absorber with a full-width at half-maximum of about 0.99 THz. We also investigated the impact of the relative position of the two fishnet layers in the form of frequency tuning and expanding the absorption band.

Abstract-Determination of pesticides in a flour substrate by chemometric methods using terahertz spectroscopy

Binghua Cao,  Hui Li.   Mengbao Fan,  Wei Wang, Mengyun Wang

https://pubs.rsc.org/en/content/articlelanding/2018/ay/c8ay01728j#!divAbstract

Terahertz time-domain spectroscopy (THz-TDS) is utilized as an effective tool for quantitative analysis of imidacloprid and carbendazim in a flour substrate. The partial least squares (PLS), principal component analysis (PCA), support vector machine (SVM) and PCA-SVM methods were used to construct linear and nonlinear regression models to correlate absorption spectra and concentrations of 21 samples based on the whole absorption spectra (0.2–1.4 THz). The multiple spectra baseline correction (MSBC) method which is based on asymmetric least squares smoothing was adopted to correct the slope baselines. The algorithm can eliminate scatter effects on the spectra and improve the signal-to-noise ratio of the THz spectra. The models were optimized by cross-validation, and their performances were evaluated with respect to root mean square error of prediction (RMSEP), correlation coefficient in the prediction set (Rp) and correlation coefficient in the calibration set (Rc). The results show that PLS delivers the best performance with the lowest errors. The optimized PLS models for both imidacloprid and carbendazim are obtained with RMSEP = 0.5439%, Rp = 0.9992 and Rc = 0.9999. Our experimental results also demonstrate that THz-TDS combined with chemometrics can be used for quantitative determination of pesticides in agricultural products.

Abstract-Ultraviolet light-induced terahertz modulation based on indium oxide thin film

Hongyu Ji, Bo Zhang, Wei Wang, Guocui Wang, Longfeng Lv, and Jingling Shen

https://www.osapublishing.org/abstract.cfm?uri=isuptw-2018-WI19&origin=search

An active ultraviolet light-induced terahertz modulation based on indium oxide thin film was investigated in which exhibit a large absorption modulation of ~50% when illuminated by a low intensity UV laser (11 mW/cm2). The interaction between indium oxide and the metamaterial structure was investigated due to the large enhancement of photo carriers in UV-induced in indium oxide film. We can realize the absorption peak shifts of 37 GHz by changing the UV excited light intensity.

© 2018 The Author(s)

Abstract-Terahertz polarization-maintaining subwavelength filters

Haisu Li, Shaghik Atakaramians, Jin Yuan, Han Xiao, Wei Wang, Yueqin Li, Beilei Wu, and Zhen Han

Fig. 1 Schematic of the THz polarization-maintaining subwavelength grating. Insets: defined geometrical parameters of grating in 𝑦𝑧$yz$ and 𝑥𝑦$xy$ planes.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-20-25617

Terahertz (THz) polarization-maintaining waveguides, which have been considered fundamental elements in polarization-sensitive THz systems, are promising platforms in developing functional THz devices. Here, we propose a THz grating based on a subwavelength rectangular polymer waveguide, which filters two polarization states simultaneously. The proposed gratings are characterized and discussed using numerical simulations. We observe two transmission dips with over a 20.9 dB extinction ratio (ER) and around a 21.1 GHz full-width half-maximum (FWHM), where the reflective frequencies of the two polarization waves and the separation between them can be harnessed with appropriate structure designs. Furthermore, we demonstrate that the grating can operate as a polarization-maintaining narrow bandpass filter (ER>12.3 dB and FWHM<1.7 GHz) by introducing a π-phase shift. This work has the potential to open a new avenue for steering polarized THz radiation using the waveguide-based filters, which could be integrated in THz polarization-sensitive imaging, sensing, and wireless communication systems.

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

Abstract-Active bidirectional electrically-controlled terahertz device based on dimethyl sulfoxide-doped PEDOT:PSS

Wei Wang, Hongyu Ji, Dandan Liu, Luyao Xiong, Yanbing Hou, Bo Zhang, and Jingling She

Fig. 3 (a) Setup for measurement of the signals of the modulated THz beam based on THz-TDS. (b) Measured signals of the modulated THz beam when the bias is positive (red line) and negative (blue line) for the MPSP sample.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-20-25849

A high-efficiency active bidirectional electrically-controlled terahertz device based on DMSO-doped PEDOT:PSS with low-power photoexcitation is investigated. Under low-power optical excitation of 30 mW (0.5 W/cm2) and under bias voltages ranging from −0.6 V to 0.5 V, spectrally broadband modulation of THz transmission over a range from −54% to 60% is obtained over the frequency range from 0.2 to 2.6 THz in a MEH-PPV/PEDOT:PSS:DMSO/Si/PEDOT:PSS:DMSO hybrid structure. By considering the combined carrier density characteristics of the proposed device, it is found that the large-scale amplitude modulation can be ascribed to the electrically-controlled carrier density in the silicon layer with the assistance of the p-n junction that consists of the DMSO-doped PEDOT:PSS and silicon. Bidirectional modulation has a larger modulation range and is easier to use in communications applications when compared with unidirectional modulation. These results show great potential for application to the design of active broadband terahertz devices.

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

Abstract-Active Optically Controlled Broadband Terahertz Modulator Based on Fe3O4Nanoparticles

 Lu-Yao Xiong,   Bo Zhang,   Hong-Yu Ji,  Wei Wang,   Xin Liu,  Shu-Li He, Jing-Ling Shen

https://ieeexplore.ieee.org/document/8409966/

We report an active broadband terahertz (THz) modulator based on an Fe 3 O 4 nanoparticle/silicon (Si) structure, where the interface effects were measured in a homemade THz time-domain spectroscopy system. An approximately 100-nm Fe 3 O 4 nanoparticle thin film on the high-resistance Si substrate was easily attained by spin-coating ferrofluids. In our experiment, a modulation depth as high as 92% was achieved at an external laser irradiance of 3.6 W/cm 2 . This result can be explained by the accumulation of carriers at the interface of the hybrid structure, which induces intense absorption of the THz transmission. In addition, the limit modulated frequency of the device is ∼12 kHz. The superior performance of this device for THz wave modulation in comparison to other nanomaterial-based THz modulators and the ease of fabrication both illustrate that this is a promising method in the modulation of THz transmission. Furthermore, this modulator could also potentially provide an essential component in a wide variety of technologies, such as THz communications, THz imaging, etc.

Abstract-Tunable terahertz band-stop filter based on self-gated graphene monolayers with antidot arrays

Wei Wang, Dongxiao Yang, Zhenhai Qian, Chuanshan Xu, Chang Wang,

https://www.sciencedirect.com/science/article/pii/S0030401818305066

An electrically tunable terahertz band-stop filter, which is composed of self-gated graphene monolayers with antidot arrays, is proposed and numerically investigated in this letter. Simulation results show that a pronounced resonance trough caused by graphene surface plasmons (0, 1) mode is obtained, which can be used to realize terahertz band-stop filtering efficiently. Center frequency of the resonance trough can be dynamically controlled over a broad frequency range from 6.6 to 8.6 terahertz through changing the voltage from 8.5 to 24.9 volt. Besides, the proposed filter is independent on the polarization state of incident terahertz wave as a result of its high azimuthal symmetry. The influences of structural parameters, substrate properties and misalignment of the two perforated graphene monolayers are also taken into account in further investigations for better understanding characteristics of the terahertz filter. Specifically, the proposed filter can be applied for refractive index sensing as well with a high sensitivity larger than 8.2 μ$\mathrm{}$m/RIU, which is potentially valuable for gas detection and so on.

Abstract-An active optically controlled broadband terahertz modulator based on Fe3O4 nano-particles

Luyao Xiong, Bo Zhang, Hongyu Ji, Wei Wang, Xin Liu, and Jing L. Shen

https://www.osapublishing.org/abstract.cfm?uri=ISUPTW-2018-TuK34

We report an active easily fabricated broadband terahertz modulator based on Fe3O4 nano-particles/Si structure,for which as high as 92% modulation depth was achieved at an external excitation laser of 3.6 W/cm2.

© 2018 OSA

Abstract-Optically tunable terahertz-band interference fringes shift

Dandan Liu, Bo Zhang, Wei Wang, Hongyu Ji, Guocui Wang, Jingling Shen

https://www.sciencedirect.com/science/article/abs/pii/S0030401818303602


Optically tunable terahertz (THz)-band interference fringes shift in a polymer/silicon structure was investigated. We report an interference phenomenon formed by partial-through measurements and shift of periodic peaks in a terahertz time-domain spectroscopy system. When the terahertz beam passes through the sample edge, equally-spaced interference fringes are obtained in the frequency domain, and the interference fringes can be varied using an external continuous wave laser. This work offers the ability to observe THz-band interference fringes in the frequency domain; these interference fringes change with variations in the applied excitation light intensity

Abstract-Ultrasensitive sensing with three-dimensional terahertz metamaterial absorber

Siyu Tan, Fengping Yan, Wei Wang, Hong Zhou, Yafei Hou,

http://iopscience.iop.org/article/10.1088/2040-8986/aab66e/pdf

Planar metasurfaces and metamaterial absorbers have shown great promise for label-free sensing applications at microwaves, optical and terahertz frequencies. The realization of high-quality-factor resonance in these structures is of significant interest to enhance the sensing sensitivities to detect the minute frequency shifts. We propose and demonstrate in this manuscript an ultrasensitive terahertz metamaterial absorber sensor based on three-dimensional split ring resonator absorber with a high quality factor of 60.09. The sensing performance of the proposed absorber sensor was systematically investigated through detailed numerical calculations and a maximum refractive index sensitivity of 34.40% RIU-1 was obtained. Furthermore, the absorber sensor can maintain a high sensitivity for a wide range of incidence angles up to 60° under TM polarization incidence. These findings would improve the design flexibility of the absorber sensors and further open up new avenues to achieve ultrasensitive sensing in terahertz regime.
© 2018 IOP Publishing Ltd

Abstract-Ultraviolet light-induced terahertz modulation of an indium oxide film

Hongyu Ji, Bo Zhang, Wei Wang, Longfeng Lv, and Jingling Shen

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-6-7204

Active ultraviolet light-induced terahertz modulation of an indium oxide film is investigated. A large absorption modulation of ~66% is achieved upon illumination with a low intensity UV laser (11 mW/cm2). The interaction between indium oxide and a flexible metamaterial structure is investigated owing to the large UV-induced enhancement of photo carriers observed in an indium oxide film. We are able to realize absorption peak shifts of 37 GHz by changing the UV excitation light intensity. We also propose a multi-frequency switch by building a circular metallic split ring resonator whose gaps are filled with silicon, germanium, and indium oxide. In future, a photo-excited tunable multi-frequency metamaterial switch can be realized by irradiating the structure with multi-wavelength laser beam.

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

Abstract-High-precision terahertz frequency modulated continuous wave imaging method using continuous wavelet transform

Yu Zhou, Tianyi Wang,  Bing Dai,  Wenjun Li,  Wei Wang,  Chengwu You, Kejia Wang, Jinsong Liu; Shenglie Wang,  Zhengang Yang

https://www.spiedigitallibrary.org/journals/Optical-Engineering/volume-57/issue-2/023108/High-precision-terahertz-frequency-modulated-continuous-wave-imaging-method-using/10.1117/1.OE.57.2.023108.short?SSO=1

Inspired by the extensive application of terahertz (THz) imaging technologies in the field of aerospace, we exploit a THz frequency modulated continuous-wave imaging method with continuous wavelet transform (CWT) algorithm to detect a multilayer heat shield made of special materials. This method uses the frequency modulation continuous-wave system to catch the reflected THz signal and then process the image data by the CWT with different basis functions. By calculating the sizes of the defects area in the final images and then comparing the results with real samples, a practical high-precision THz imaging method is demonstrated. Our method can be an effective tool for the THz nondestructive testing of composites, drugs, and some cultural heritages.

© 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

Abstract-Strong coherent coupling between graphene surface plasmons and anisotropic black phosphorus localized surface plasmons

Jinpeng Nong, Wei Wei, Wei Wang, Guilian Lan, Zhengguo Shang, Juemin Yi, and Linlong Tang

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-2-1633&origin=search

The anisotropic plasmons properties of black phosphorus allow for realizing direction-dependent plasmonics devices. Here, we theoretically investigated the hybridization between graphene surface plasmons (GSP) and anisotropic black phosphorus localized surface plasmons (BPLSP) in the strong coupling regime. By dynamically adjusting the Fermi level of graphene, we show that the strong coherent GSP-BPLSP coupling can be achieved in both armchair and zigzag directions, which is attributed to the anisotropic black phosphorus with different in-plane effective electron masses along the two crystal axes. The strong coupling is quantitatively described by calculating the dispersion of the hybrid modes using a coupled oscillator model. Mode splitting energy of 26.5 meV and 19 meV are determined for the GSP-BPLSP hybridization along armchair and zigzag direction, respectively. We also find that the coupling strength can be strongly affected by the distance between graphene sheet and black phosphorus nanoribbons. Our work may provide the building blocks to construct future highly compact anisotropic plasmonics devices based on two-dimensional materials at infrared and terahertz frequencies.

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

Abstract-Surface plasmons based terahertz modulator consisting of silicon–air–metal–dielectric–metal layers

Wei Wang, Dongxiao Yang, Zhenhai Qian

https://www.sciencedirect.com/science/article/pii/S0030401817310192

An optically controlled modulator of the terahertz wave, which is composed of a metal–dielectric–metal structure etched with circular loop arrays on both the metal layers and a photoexcited silicon wafer separated by an air layer, is proposed. Simulation results based on experimentally measured complex permittivities predict that modification of complex permittivity of the silicon wafer through excitation laser leads to a significant tuning of transmission characteristics of the modulator, forming the modulation depths of 59.62% and 96.64% based on localized surface plasmon peak and propagating surface plasmon peak, respectively. The influences of the complex permittivity of the silicon wafer and the thicknesses of both the air layer and the silicon wafer are numerically studied for better understanding the modulation mechanism. This study proposes a feasible methodology to design an optically controlled terahertz modulator with large modulation depth, high speed and suitable insertion loss, which is useful for terahertz applications in the future.

Abstract-Terahertz modulation based on surface plasmon resonance by self-gated graphene

Zhenhai Qian, Dongxiao Yang, Wei Wang

https://www.sciencedirect.com/science/article/pii/S0030401817311604

We theoretically and numerically investigate the extraordinary optical transmission through a terahertz metamaterial composed of metallic ring aperture arrays. The physical mechanism of different transmission peaks is elucidated to be magnetic polaritons or propagation surface plasmons with the help of surface current and electromagnetic field distributions at respective resonance frequencies. Then, we propose a high performance terahertz modulator based on the unique PSP resonance and combined with the metallic ring aperture arrays and a self-gated parallel-plate graphene capacitor. Because, to date, few researches have exhibited gate-controlled graphene modulation in terahertz region with low insertion losses, high modulation depth and low control voltage at room temperature. Here, we propose a 96% amplitude modulation with 0.7 dB insertion losses and ∼$$5.5 V gate voltage. Besides, we further study the absorption spectra of the modulator. When the transmission of modulator is very low, a 91% absorption can be achieved for avoiding damaging the source devices.

Abstract-Simultaneous measurement of refractive index and conductivity based on metamaterial absorber

Wei Wang1, Fengping Yan2.  Siyu Tan3, Luna Zhang4, Zhuoya Bai5, Dan Cheng6, Hong Zhou7 and Yafei Hou

http://iopscience.iop.org/article/10.1088/2040-8986/aa8fc1

An algorithm for the metamaterial sensors to simultaneously measure the refractive index and conductivity of the analyte is introduced. To verify the algorithm, a square ring metamaterial absorber is numerically calculated as a specific example in the terahertz frequency. Firstly, the sensing performances of the absorber on the refractive index (RI) and conductivity are evaluated separately. Then the relationship expressions between dual variables (frequency shift (FS) and amplitude modulation (AM)) and two arguments (RI and conductivity) can be obtained through mathematical fitting process. By reversely solving this equations set, the conductivity and RI of the analyte can be expressed as another equations set that can be solved easily. The proposed algorithm offers an effective method to determine RI and conductivity of the analyte by measuring the AM and FS of the reflection dip of the absorber sensor. To validate the effectiveness and accuracy of the algorithm, the FS and AM obtained from the simulations are plugged into the reverse equations set. Then the calculated n and σ are compared to their responding original values. The maximum percentage error between them are both less than 0.83%, which are small enough to illustrate the rightness of the proposed method.