Abstract-Multifunctional and dynamically tunable terahertz metamaterials based on TiNi shape memory alloy films with a simple design

 

Changlong Tan. Juan Liu. Xiaohua Tian, Jiachen Zhu, Kun Zhang, 

https://www.sciencedirect.com/science/article/pii/S2211379721003144

In the terahertz (THz) fields, a crucial point of restricting its development and application is the lack of dynamic and multifunctional materials. In this work, NiTi films are innovatively introduced into the design, and multifunctional and dynamically tunable terahertz metamaterials are proposed. The influence and mechanism of the shape deformation and conductivity changes before and after martensitic transformation on the electromagnetic response are systematically investigated and revealed. Based on the novel NiTi metamaterials, inductance-capacitance (LC) resonance and dipole resonance are used simultaneously for the terahertz filter, and an excellent dual-band filter is obtained. The frequencies of both LC and dipolar resonances can be dynamically tuned to the desired operating frequencies by driving the martensitic transformation. And the resonant frequency of the band-stop filter achieves a dynamic modulation range up to 0.56 THz. Furthermore, the results also show that when martensitic transformation occurs, the terahertz wave transmission can be tuned from 0.78 to 0.04 at 0.47 THz. Moreover, as an excellent switch, the ON state transmittance is one order of magnitude higher than the OFF-state transmittance. In brief, this study provides a new perspective and ideas for developing a tunable dual-band terahertz filter and thermal-induced terahertz switch.

Abstract-Actively tunable bi-functional metamirror in a terahertz band

 

Kun Zhang, Yan Liu, Shixia Li, Feng Xia, Weijin Kong, 

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-46-3-464

In this work, we have proposed an actively tunable bi-functional metamirror based on a bi-layer graphene structure. The metamirror acts as a spin-selective absorber under circularly polarized incidence, which behaves as nearly perfect absorption and reflection for right and left circularly polarized waves, respectively, leading to giant circular dichroism. On the other hand, it is a polarization converter under linearly polarized incidence, which reflects the linearly polarized wave into a left circularly polarized wave. Both the spin-selective absorber and the polarization converter can be actively switched between ON and OFF states, with the working frequency controlled by the voltages applied to graphene. Moreover, the metamirror is insensitive to the incidence angle, which contributes to its application as a stable single-mode spin-selective absorber and polarization converter. This bi-layer graphene structure offers a method to construct actively tunable bi-functional metamirrors, which may achieve potential applications in integrated devices, such as active spin detectors, absorbers, and quarter-wave plates for terahertz waves.

© 2021 Optical Society of America

Abstract-Broadband polarization beam splitter based on subwavelength grating in Terahertz

Yelan Zhang,  Yuyang Cheng,  Kun Zhang, Caiyu Li,  Weijin Kong

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11064/110640J/Broadband-polarization-beam-splitter-based-on-subwavelength-grating-in-Terahertz/10.1117/12.2535633.short?SSO=1

We design a broadband polarization beam splitter (PBS) operating in the terahertz (THz) communication band 0.1THz-1.2THz. The transmittance of the TM mode is larger than 95%, in the meanwhile, the extinction ratio can even reach 49dB. Considering the unavoidable deformation in grating fabrication, we also check the performance of the PBS based on trapeziform grating. Results show that increasing the duty cycle while the slope angle diminishing can effectively increase the TM mode transmittance and the extinction ratio, which can compensate the affection induced by the geometric deformation. This design may achieve some potential applications in THz manipulation system.

© (2019) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Terahertz Superconducting Radiometric Spectrometer in Tibet for Atmospheric Science

Sheng Li, Qijun Yao, Dong Liu, Wenying Duan, Kun Zhang, Junda Jin, Zhenhui Lin, Feng Wu, Jinping Yang, Wei Miao, Shengcai Shi

https://link.springer.com/article/10.1007/s10762-018-0557-4

Terahertz superconducting radiometric spectrometer (TSRS), as one of seven instruments of the atmospheric profiling synthetic observation system (APSOS) project, was completed in the middle of 2017 after 5 years of development. It is a dual-band heterodyne receiver system based on high sensitive superconductor-insulator-superconductor (SIS) mixers which cover the frequency range of 180 to 380 GHz. With fast Fourier transform spectrometer (FFTS) of each band, real-time observation of 2 GHz bandwidth of high spectral resolution atmospheric molecular emission lines has been demonstrated. TSRS has been deployed at Yangbajing site, which stands on the Qinghai-Tibet Plateau at an altitude of 4300 m in southwestern China, since October 2017. It has been worked in a preliminary observation phase along with other active observation equipment of APSOS. Since then, ozone emission lines around 236 GHz and 358 GHz have been monitored simultaneously. Achieved data will be used to retrieve the in situ vertical distribution of ozone and its movement among different layers of the atmosphere

Abstract-Wide Band Terahertz Switch of Undulated Waveguide with VO2 Film Coated Inner Wall

Kun Zhang, Lu Zhang, Di Duan, Ya-Xian Fan, Zhi-Yong Tao

https://ieeexplore.ieee.org/document/8417923/


We propose a wide band terahertz (THz) switch of undulated waveguide with vanadium dioxide ( 
VO2 ) film coated inner wall. The forbidden bands formed by periodically undulated walls effectively restrain THz transmission when VO2 is in the insulator phase. An unexpected wide band appears in the transmission spectrum, connecting two forbidden bands, where metal phase VO2 covers the undulations and eliminates band gaps. Simulations confirm that the switch could be realized by varying the temperature in the frequency range of 0.71-1.07 THz, and hence such a switch could be applied in THz systems.

Abstract-All-dielectric metalens for terahertz wave imaging

Xue Jiang, Hao Chen, Zeyu Li, Hongkuan Yuan, Luyao Cao, Zhenfei Luo, Kun Zhang, Zhihai Zhang, Zhongquan Wen, Li-guo Zhu, Xun Zhou, Gaofeng Liang, Desheng Ruan, Lianghui Du, Lingfang Wang, Gang Chen,

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-11-14132

Terahertz wave imaging offers promising properties for non-destructive testing applications in the areas of homeland security, medicine, and industrial inspection. However, conventional optical lenses are heavy and bulky and difficult to integrate. An all-dielectric metasurface provides an attractive way to realize a planar lens of light weight that is ultrathin and offers ease of integration. Terahertz lenses based on various metasurfaces have been studied, especially for the application of wave focusing, while there are few experimental demonstrations of terahertz wave imaging lenses based on an all-dielectric metasurface. In the present work, we propose a metalens based on an all-dielectric metasurface with a sub-wavelength unit size of 0.39λ for terahertz wave imaging and experimentally demonstrate its performance in focusing and imaging. A large numerical aperture metalens was fabricated with a focal length of 300λ, radius of 300λ, and numerical aperture of 0.707. The experimental results show that the lens can focus THz waves with an incident angle up to 48°. More importantly, clear terahertz wave images of different objects were obtained for both different cases of forward- and inverse-incident directions, which demonstrate the reversibility of the metalens for imaging. Such a metalens provides a way for realization of all-planar-lens THz imaging system, and might find application in terahertz wave imaging, information processing, microscopy, and others.

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

Abstract-Dual-mode electromagnetically induced transparency and slow light in a terahertz metamaterial

Kun Zhang, Cheng Wang, Ling Qin, Ru-Wen Peng, Di-Hu Xu, Xiang Xiong, and Mu Wang  »View Author Affiliations
http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-12-3539

Optics Letters, Vol. 39, Issue 12, pp. 3539-3542 (2014)
http://dx.doi.org/10.1364/OL.39.003539

In this Letter, we construct a metamaterial with dual-mode electromagnetically induced transparency (EIT)-like behavior by introducing “bright atoms,” “quasi-dark atoms,” and “dark atoms” simultaneously. The dual-mode EIT-like behavior has been demonstrated both experimentally and theoretically in terahertz (THz) regime. At two EIT-like modes, slow light is also observed as two time-delayed wave packets, and the effective group refractive index can reach 102. Furthermore, stable dual-mode EIT-like behavior is verified in this metamaterial for a wide range of oblique incident angles. Our work provides a design approach to mimic dual-mode EIT, and such an approach may achieve potential applications on miniaturized and versatile THz devices.

© 2014 Optical Society of America