Abstract-Dual-regulated broadband terahertz absorber based on vanadium dioxide and graphene

 

Chunyu Zhang, Heng Zhang, Fang Ling, and Bin Zhang

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-60-16-4835

A tunable broadband terahertz (THz) absorber based on vanadium dioxide (VO2${\mathrm{V}\mathrm{O}}_2$) and graphene is proposed. The absorber, consisting of the VO2${\mathrm{V}\mathrm{O}}_2$ square loop, polymethacrylimide (PMI) dielectric layer, and a layer of unpatterned graphene, can achieve absorption over 90% from 1.04 THz to 5.51 THz and relative bandwidth of up to 136.5% under normal incidence. Its absorption bandwidth and absorption peak can be adjusted by changing the conductivity of VO2${\mathrm{V}\mathrm{O}}_2$ or the chemical potential of graphene. The physical mechanism of the absorber is analyzed in detail by the use of the impedance matching theory and the electric field distributions of the VO2${\mathrm{V}\mathrm{O}}_2$ layer and graphene layer. The proposed absorber, with polarization insensitivity and incidence angle of 30° for both TE and TM polarizations, may have potential applications in tunable sensors, modulators, and imaging.

© 2021 Optical Society of America

Abstract-Enhanced on-chip terahertz sensing with hybrid metasurface/lithium niobate structures

Applied Physics Letters

Ride Wang, Qiang Wu, Yaqing Zhang, Xitan Xu, Qi Zhang, Wenjuan Zhao, Bin Zhang, Wei Cai, Jianghong Yao, Jingjun Xu

(a) Schematic of THz detection of an analyte using a microrod array metasurface as an on-chip sensor. A column of y-polarized dipoles located inside the LN waveguide is used to excite THz waves (blue oscillation signal). The thickness of the SiO2 layer is h = 2 μm. The inset shows the detailed design parameters: p, a, l and g are 20, 10, 55, and 15 μm, respectively. (b) Enhanced field confined to the surface of the composite structure. (c) and (d) Distribution of the field components Ey and Ez at f = 0.529 THz.

https://aip.scitation.org/doi/abs/10.1063/1.5087609

Recognizing special molecules is crucial in many biochemical processes, and thus, highly enhanced sensing methods are in high demand. In this work, we designed a microrod array metasurface with a SiO2-loaded subwavelength lithium niobate waveguide as a unique platform for enhanced experimental fingerprint detection of lactose. The metasurface could lead to strong surface wave modes due to the near-field coupling of the spoof localized surface plasmon, which also could provide a stronger interaction length between light and matter. The selectivity was remarkable in the transmission spectrum at an intrinsic characteristic frequency of 0.529 THz with a thin layer of lactose, while it was faint while transmitting terahertz (THz) waves normally through a lactose layer of the same thickness. Together with the ability to freely design the shape of the metasurface and the electromagnetic properties, we believe that this platform can function as an elegant on-chip-scale enhanced THz sensing platform.

Abstract-Mutual Coupling Reduction for Ultra-Dense Multi-Band Plasmonic Nano-Antenna Arrays Using Graphene-Based Frequency Selective Surface

Bin Zhang, Josep Jornet, Ian Akyildiz, Zhi Wu,

https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=8662671

Terahertz (THz) band provides huge bandwidth but the molecular absorptions in these frequencies cause high path losses in long-distance communications. Recently, multi-band ultra-massive MIMO (UM-MIMO) systems based on graphene-based plasmonic nano-antennas have been proposed to overcome the distance problem. In the UM MIMO systems, the mutual coupling effect is a challenging problem because of the ultra-dense integration of the multi-band nano-antenna arrays. In this paper, a graphene-based frequency selective surface (FSS) is proposed to reduce the coupling effects in dense plasmonic nano-antenna arrays for multi-band UM MIMO systems. The performance of the proposed structure is evaluated by full-wave simulation for different cases. The results show that the FSS structure has a wide stopband (−15 dB bandwidth, approximately 43%–50%) from 1.1 to 1.7 THz. By inserting the FSS structure between nano-antennas, a high isolation coefficient of −25 dB with a 15 dB fall and an envelope correlation coefficient of less than 0.01 are achieved. The field distributions and the radiation patterns are also presented to confirm that the proposed FSS structure improves the performance of the array with negligible influence on the antenna itself. Moreover, the receiving mode simulation of the array is performed with the FSS structure. It is also asymptotically shown that the mutual coupling experienced by the nano-antenna with the FSS structure is negligible even in the presence of a very large number of closely integrated elements. Finally, the technological issues are discussed for practical implementations

Abstract- Optically tuneable broadband terahertz metamaterials using photosensitive semiconductor material

Qinglong Meng, Yan Zhang, Zheqiang Zhong, Bin Zhang

https://www.tandfonline.com/doi/abs/10.1080/09500340.2018.1496288?journalCode=tmop20

We present optically tuneable broadband terahertz metamaterials consisting of photosensitive semiconductor material. The characteristics of semiconductor materials are very important for terahertz functional devices, which is strongly dependent on the photoexcited carriers in semiconductor materials. Based on the model of the generation of the carriers in semiconductor materials, the tuneability of the resonance frequency and resonance strength in terahertz metamaterials under the femtosecond laser pulse has been analysed. The experimental results of the transmissivities of several bare semiconductor materials show that GaAs semiconductor could be a potential candidate for broadband terahertz functional devices design. Moreover, the simulation results of the resonance frequency increase with the increase of the laser fluence, whereas the resonance strength near the resonance frequency is significantly weakened with the increase of the laser fluence. Meanwhile, the modulation depth can be reached approximately 90% at 1.24 THz. Our proposed broadband tuneable terahertz metamaterials have numerous potential applications, including terahertz modulator, absorber and switches.

Abstract-A broadband tunable terahertz negative refractive index metamaterial

Fang Ling, Zheqiang Zhong, Renshuai Huang,  Bin Zhang

https://www.nature.com/articles/s41598-018-28221-3

A strategy to greatly broaden negative refractive index (NRI) band, reduce loss and ease bi-anisotropy of NRI metamaterials (MMs) has been proposed at terahertz frequencies. Due to the symmetric structure of the MM, the transmission and refractive index are independent to polarizations of incident radiations, and a broadband NRI is obtainable for the range of the incident angle from 0° to 26°. In addition, THz MMs’ properties such as transmission, phase and negative refraction exhibit a real-time response by controlling the temperature. The results indicate that the maximum bands of the negative and double-negative refraction are 1.66 THz and 1.37 THz for the temperature of 40 °C and 63 °C, respectively. The figure of merit of the MMs exceeds 10 (that is, low loss) as the frequency increases from 2.44 THz to 2.56 THz in the working temperature range, and the maximum figure of merit is 83.77 at 2.01 THz where the refractive index is −2.81 for a given temperature of 40 °C. Furthermore, the negative refraction of the MMs at the low loss band is verified by the classical method of the wedge, and the symmetric slab waveguide based on the proposed MM has many unique properties.

Abstract-Thermally tunable broadband terahertz metamaterials with negative refractive index

Weili Li, Qinglong Meng, Renshuai Huang, Zheqiang Zhong, Bin Zhang

https://www.sciencedirect.com/science/article/pii/S0030401817310945

A thermally tunable broadband metamaterials with negative refractive index (NRI) is investigated in terahertz (THz) region theoretically. The metamaterials is designed by fabricating two stand-up opposite L shape metallic structures on fused quartz substrate, and the indium antimonide (InSb) is filled in the bottom gap of the two L shape structures. The tunability is attributed to the InSb because the InSb can changes the capacitance of the gap area by adjusting the temperature. The transmission characteristics and the retrieved electromagnetic parameters of the metamaterials are analyzed. Results indicate that the resonant frequency and amplitude modulation of the metamaterials can be tuned continuously in broadband range (about 0.62 THz), and the phase modulation from −2$\mathrm{}$ to 3 rad is also achieved within broadband range (about 0.8 THz). In addition, the metamaterials shows dual-band NRI behaviors at 0.4$\mathrm{}\mathrm{}$–0.9$\mathrm{}\mathrm{}$ THz and 1.06$\mathrm{}\mathrm{}$–1.15$\mathrm{}\mathrm{}$THz when the temperature increases to 400 K. The wedge-shaped prism simulations are implemented to verify the NRI characteristics and indicate that the NRI of the metamaterials can be achieved.

Abstract-Study on thermally control terahertz narrow bandpass filter

Fang Ling; Renshuai Huang; Qinglong Meng; Weili Li; Bin Zhang;

In general, the terahertz metamaterial filter based on the complementary structure mainly has the fixed resonant frequency and asymmetric resonant frequency edges. In this paper, a thermally control terahertz narrow bandpass filter consisting of a periodic array of complementary wires embedded with thermosensitive semiconductor indium antimonide (InSb) has been proposed. Due to the structure of the filter is relatively simple, it can be more easily fabricated by lithograph technology compared with traditional terahertz metamaterial filter structure. Furthermore, its performance has also been analyzed based on the effective medium theory and the Drude model. The results show that the resonant frequency shifts from 1.16THz to 2.11THz with the increasing of the temperature from 160K to 360K, and the blueshift of resonance frequency as large as 81% can be implemented. Meanwhile, the reflectivity at the resonant frequency almost tends to be zero and the transmissivity spectrum at the resonant frequency exhibits sharp and symmetric edges. The filter can be applied to THz imaging system, and can effectively improve the imaging quality as a result of well characteristics of dynamic tuned filer and relatively simple structure.

© (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Research on output frequency characteristics of optically pumped THz gas laser

Xiaoyang Guo; Renshuai Huang; Qinglong Meng; Bin Zhang

http://spie.org/Publications/Proceedings/Paper/10.1117/12.2186980


Considering the two-photon light shift (TPLS) effect and the Doppler shift effect, the model of the output frequency of the optically pumped THz gas laser has been built up. The influence of the TPLS and the Doppler shift effects on THz output frequency stability has been analyzed theoretically and numerically. Results indicate that, increasing the pump laser power may degrade the THz output frequency stability to some extent. When only considering the TPLS, with certain pump laser power, the THz frequency shift increases first and then decreases with the increasing of the pump laser frequency offset. In addition, the THz frequency shift tends to decrease gradually with the increasing of the gas pressure and the operating temperature. However, further considering the influence of the Doppler shift effect simultaneously, the THz frequency shift tends to increase nearly linearly with the pump frequency offset. The results provide reference to improve output frequency stability of the optically pumped THz gas laser.

Abstract-Trajectory-based analysis of low-energy electrons and photocurrents generated in strong-field ionization

Jinlei Liu, Wenbo Chen, Bin Zhang, Jing Zhao, Jianhua Wu, Jianmin Yuan, and Zengxiu Zhao

https://journals.aps.org/pra/abstract/10.1103/PhysRevA.90.063420

The three-dimensional classical-trajectory Monte Carlo method is employed to investigate low-energy photoelectron spectra in above-threshold ionization by strong laser fields. By connecting the tunneling coordinates with the final momentum-energy spectra, we identify the effects of the Coulomb potential on electron trajectories and the final energy spectra. In addition, we verify that the photoelectron spectra, depending on the energy region, can be controlled with a two-color laser pulse by varying the phase delay. The modulations of the electron spectra and yields as well as the generated photocurrents reveal the connections among them, which support our previous work [Phys. Rev. Lett. 109, 243002 (2012)] on terahertz wave generation from two-color laser pulses.

DOI: http://dx.doi.org/10.1103/PhysRevA.90.063420

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• Published 17 December 2014
• Received 11 November 2014

©2014 American Physical Society