Abstract-Quasibound states in the continuum in terahertz free-standing metal complementary periodic cross-shaped resonators

Dejun Liu, Feng Wu, Lin Chen, Feng Liu

https://arxiv.org/abs/2007.08104

We numerically and experimentally achieve quasi-bound states in the continuums (BICs) with high-Q factors in the free-standing metal complementary periodic cross-shaped resonators (CPCRs) at terahertz (THz) frequencies. Such induced quasi-BICs arises from the breaking of the mirror symmetry of CPCRs. By properly tuning the asymmetric factor, the measured Q factor of quasi-BIC can reach 102, which is lower than the simulated Q factor of 166 due to the limited system resolutions. We also simulate the electric field magnitude and vector distributions at the quasi-BICs, where the out-phase alignment between the electric dipoles is found. The sharp quasi-BICs realized in this thin free-standing metal structure may immediately boost the performance of filters and sensors in terahertz wave manipulation or biomolecular sensing.

Abstract-Terahertz composite plasmonic slabs based on double-layer metallic gratings

Dejun Liu, Lin Chen, Xiaohu Wu, and Feng Liu

Sketch of the composite plasmonic slab (CPS). The slab consists of double-layer metal gratings and a dielectric film. (a) The side view of the CPS. (b) The 3D model of the CPS. (c) The image of the experimental sample of a single-layer metal (copper) grating.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-12-18212

One composite plasmonic slab with a broad bandgap (40%) is experimentally and numerically demonstrated in the terahertz (THz) region. The composite slab consists of double-layer metallic gratings and a dielectric film, which supports two resonant modes. Electric field vectors and charge distributions proved that the low-frequency resonant mode originates from the symmetric plasmonic mode, while the high-frequency resonant mode is induced by the hybrid mode of plasmonic and dielectric modes. Compared with the double-layer metallic grating, the inserted dielectric film significantly enhances the transmission of the transverse magnetic (TM) waves and induces Fano resonances. The near-field coupling between metal gratings and dielectric film can be manipulated by changing the thickness and the refractive index of dielectric films. We further demonstrated that the plasmonic bandgap can be manipulated by tuning the grating width. These results suggest that this composite plasmonic slab is promising in terahertz integrated components development such as a filter, polarizer, or sensor.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz composite plasmonic slabs based on double-layer metallic gratings

Dejun Liu, Lin Chen, Feng Liu

https://arxiv.org/abs/2003.04113

A composite plasmonic slab based on double-layer metallic gratings and a dielectric film is experimentally and numerically demonstrated in terahertz (THz) regions, which can support two resonance modes and then form a broad bandgap (40%). As compared to the double-layer metal grating, the dielectric film in composite THz slabs significantly enhances the transmission of the transverse magnetic (TM) mode. Electric field vector proved that the low-frequency resonance mode originates from the symmetric plasmonic mode and the high-frequency resonance mode is induced by the hybrid mode of plasmonic and dielectric modes. The inherently near field coupling between metal gratings and dielectric film has been analyzed by changing the structural parameters. We further demonstrate that by tuning the metallic grating width, the plasmonic bandgap can be manipulated. These results suggest that this composite plasmonic slab has great potential for use as a filter, polarizer, and sensor in THz regions.

Abstract-Tunable terahertz hybrid graphene-metal patterns metamaterials

Chenyuyi Shi, Xiaoyong He, Jun Peng, Guina Xiao, Feng Liu, Fangting Lin, Hao Zhang,



https://www.sciencedirect.com/science/article/pii/S0030399218317250

Based on the hybrid metal-graphene structures, we investigated the tunable Fano resonances in the terahertz region, including the effects of graphene Fermi levels, structural parameters, and operation frequencies. The results reveal that an obvious Fano resonance can be observed, the maximum peak value of Fano resonance can reach 0.9711, and its Q-quality factor is more about 20. With the help of the graphene layer, the resonant curves of the proposed structures can be effectively modulated, the frequency modulation depth can reach 60% as the Fermi level changes in the range of 0.1–1.0 eV. In addition, by varying the length of graphene bar in the scope of 10–60 μm, the amplitude modulation depths are about 21.0%. The results are helpful for designing novel graphene-based tunable terahertz devices with high Q factor, e.g. modulators, sensors and antenna.

Abstract-Meander Line Nanoantenna Absorber for Subwavelength Terahertz Detection

Yuyao Chen,  Haoran Zhou, Xiaochao Tan, Shun Jiang,  Ao Yang, Junyu Li, Mingming Hou,  Qiushi Guo, Shao-Wei Wang,  Feng Liu, Huan Liu, Fei Yi

https://ieeexplore.ieee.org/document/8370898/

The detection of terahertz electromagnetic waves is crucial for emerging applications within this frequency band, such as spectroscopy, imaging and communication. Extending the well-developed uncooled infrared focal plane array technology to terahertz frequency regime would be very attractive, but high absorption in the terahertz region with a subwavelength pixel is necessary. In this paper, we proposed a meander line nanoantenna(MLNA) absorber with a metal-insulator-metal structure for sub-wavelength terahertz absorption. 89% absorption is achieved at the wavelength of 155 μm with a 10 μm pitch size. The MLNA absorber is polarization insensitive and can maintain a high absorption when the incident angle is within 40 degrees. We expect that the proposed MLNA absorber can be integrated with the small pixels of uncooled infrared focal plane array for terahertz detection.

Abstract-Graphene patterns supported terahertz tunable plasmon induced transparency

Xiaoyong He, Feng Liu, Fangting Lin, and Wangzhou Shi

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-8-9931

The tunable plasmonic induced transparency has been theoretically investigated based on graphene patterns/SiO2/Si/polymer multilayer structure in the terahertz regime, including the effects of graphene Fermi level, structural parameters and operation frequency. The results manifest that obvious Fano peak can be observed and efficiently modulated because of the strong coupling between incident light and graphene pattern structures. As Fermi level increases, the peak amplitude of Fano resonance increases, and the resonant peak position shifts to high frequency. The amplitude modulation depth of Fano curves is about 40% on condition that the Fermi level changes in the scope of 0.2-1.0 eV. With the distance between cut wire and double semi-circular patterns increases, the peak amplitude and figure of merit increases. The results are very helpful to develop novel graphene plasmonic devices (e.g.sensors, modulators, and antenna) and find potential applications in the fields of biomedical sensing and wireless communications.

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

Abstract-Investigation of graphene-supported tunable asymmetric terahertz metamaterials

Chenyuyi Shi, Xiaoyong He, Feng Liu, Fangting Lin, and Hao Zhang

https://www.osapublishing.org/josab/abstract.cfm?uri=josab-35-3-575

By integrating a graphene layer with asymmetric split-ring metamaterial (MM) metal resonators, we investigated tunable propagation properties in the terahertz regime, including the effects of graphene Fermi levels, structural parameters, and operation frequencies. The results reveal that a sharp inductor-capacitor (LC) resonance can be observed at low frequency for the asymmetric MM structure, and its 𝑄$Q$ factor can reach more than 17.5. With the help of a graphene layer, the optical response is modulated efficiently. For instance, if the Fermi level changes in the range of 0.01–0.3 eV, for the semiconductor MM structure, the modulation depths (MDs) of amplitude and frequency are 27.0% and 43.4%, respectively. In addition, the resonant curves of indium antimonide (InSb) MMs can be modulated by changing the temperature; the amplitude MD is 56.2% as the temperature changes in the range of 350–800 K. The 𝑄$Q$ factor of the InSb MM structure is about 44.6. The results are helpful for designing novel graphene-based tunable terahertz devices, e.g., filters and modulators.

© 2018 Optical Society of America

Abstract-Spectral interference of terahertz pulses from two laser filaments in air

Yanping Chen^1,2,a), Zhelin Zhang^1,2, Zhen Zhang^1,2, Xiaohui Yuan^1,2, Feng Liu^1,2, Min Chen^1,2, Jianqiu Xu^1,2, Jin Yu^1,3, Zhengming Sheng^1,2,4,b) and Jie Zhang^1,2
 VIEW AFFILIATIONS
a) Electronic mail: yanping.chen@sjtu.edu.cn
b) Electronic mail: zmsheng@sjtu.edu.cn
Appl. Phys. Lett. 106, 221105 (2015); http://dx.doi.org/10.1063/1.4922143

Spectral interference is experimentally demonstrated by two terahertz pulses emitting from filaments induced by two successive femtosecond laser pulses in air. Here, a leading pulse is set to be weaker than a trailing pulse and their temporal separation is larger than the pulse duration of the terahertz pulses. When the leading pulse is stronger than the trailing pulse, thefrequency modulation within the whole terahertz envelope is greatly deteriorated due tononlinear effects applying on the trailing pulse through the plasmas generated by the leading pulses. Such unique terahertz spectrum may find applications in terahertz spectroscopy.

Abstract-Dual-frequency terahertz emission from splitting filaments induced by lens tilting in air

Zhelin Zhang¹, Yanping Chen^1,a), Liu Yang¹, Xiaohui Yuan¹, Feng Liu¹, Min Chen¹, Jianqiu Xu¹, Zhengming Sheng^1,2 and Jie Zhang¹
http://scitation.aip.org/content/aip/journal/apl/105/10/10.1063/1.4895720
1 Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
2 Department of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG, United Kingdom
a) Author to whom correspondence should be addressed. Electronic mail: yanping.chen@sjtu.edu.cn
Appl. Phys. Lett. 105, 101110 (2014); http://dx.doi.org/10.1063/1.4895720

Dual-frequency terahertz radiation from air-plasma filaments produced with two-color lasers in air has been demonstrated experimentally. When a focusing lens is tilted for a few degrees, it is shown that the laser filament evolves from a single one to two sub-filaments. Two independent terahertz sources emitted from the sub-filaments with different frequencies and polarizations are identified, where the frequency of terahertz waves from the trailing sub-filament is higher than that from the leading sub-filament.