Abstract-High extinction ratio terahertz broadband polarizer based on the aligned Ni nanowire arrays

Wenfeng Xiang, Xiaowei Huang, Dong Li, Qingli Zhou, Haizhong Guo, and Junjian Li

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-45-7-1978

We present a broadband terahertz (THz) polarizer based on the stacks of aligned Ni nanowire (NW) arrays. We demonstrated that the polarizer has an extinction ratio of 58.8 dB and an average extinction ratio of 46.6 dB throughout a frequency range of 0.3–2.3 THz. Compared to carbon-nanotube and metallic wire-grid polarizers, our Ni-NW polarizers with rapid, reliable, low-cost fabrication processes are ideal candidates for emerging THz technologies.

© 2020 Optical Society of America

Abstract-Effect of the broken symmetry on the electromagnetic properties in the terahertz ring resonators

Lan Shi, Qingli Zhou, Wanlin Liang, GeLi, Jianhai Sun, Cunlin Zhang



https://www.sciencedirect.com/science/article/abs/pii/S0030401819303086

We experimentally and numerically demonstrate resonant behaviors of terahertz metamaterials can be tuned significantly by their asymmetry. For the ring structure cut symmetrically, transmission spectra are nearly the same as those of their individual single-ring resonators. However, three resonant dips appear in the spectra due to the broken symmetry in single-ring resonator cut asymmetrically from the top. For the asymmetrically-cut double-ring structures, the mutual coupling between four arcs results in multi-resonance dips, especially a low-frequency Fano-like resonance accompanied with a sharp peak. Our asymmetric structures could offer potential applications in terahertz frequency selectors and bio-sensors.

Abstract-Resonance coupling and optical modulation properties in terahertz asymmetric double-wire structures

Ge Li, Qingli Zhou, Wanlin Liang, Cunlin Zhang,

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10826/108261P/Resonance-coupling-and-optical-modulation-properties-in-terahertz-asymmetric-double/10.1117/12.2502510.short

The spectral characteristics of the asymmetric double-wire structures have been investigated in the terahertz (THz) range. Based on the THz time-domain spectroscopy system, the spectral of the samples has been measured. It is shown that a transparent peak appears in the transmission spectrum which indicate that a resonance coupling exist between the two metal bars. Furthermore, we study the optical modulation properties when the pump light irradiates on the sample by using optical pump-terahertz probe technique (OPTP). The measured results indicate that the pump light can realize an optical switch effect to modulate the transmittance of THz wave. When adjusting the time delay between the optical pump and the terahertz probe pulses, the transmittance of THz wave varies, indicating the photoexcited carriers in the substrate have great influence on the resonance characteristics of the structure. Our obtained results indicate optical modulation method could provide the functionally potential applications in the terahertz modulators and filters.

© (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Study on asymmetric terahertz metamaterials for biosensing

Wanlin Liang, Qingli Zhou, Ge Li, Cunlin Zhang

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10826/108261Q/Study-on-asymmetric-terahertz-metamaterials-for-biosensing/10.1117/12.2502511.short

Recently, the terahertz biosensors based on metamaterials have attracted much attention due to the fact that metamaterials are sensitive to the local enhancement of electromagnetic field and the changes of the surrounding dielectric environment. In order to obtain the resonances with the high quality factor for biosensing, here we designed, simulated, and fabricated the metamaterial structures composed of a series of the asymmetric “double” circular arc (DASR) structures. The experimental data show there are three sharp resonance dips named Fano resonance in the terahertz transmission spectra. In the previous study of asymmetric double rings, we studied the effect of different cutting widths on the transmission characteristics of terahertz when the samples were placed at 0 degrees. Here, the spectral characteristics and polarization conversion characteristics of the samples after 90 degrees were studied. We found that when the sample rotated by 90 degrees only two resonance dips exist in the transmission spectrum. As the separation of asymmetric arcs gradually increases, two resonance frequencies also show blue-shift. To further analyze the reasons for the changes in the transmission spectrum at different angles of sample placement, we present the surface currents and the electromagnetic field distributions in those structures. Our obtained results indicate the terahertz metamaterial has great potential in application of biosensing field.

© (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Studies on the trapped-mode resonant properties in asymmetric terahertz metamaterial

Wei Chen,  Qingli Zhou,  Chenyu Li, Lan Shi,  Changxiang Liu, Cunlin Zhang

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10459/104590D/Studies-on-the-trapped-mode-resonant-properties-in-asymmetric-terahertz/10.1117/12.2284323.pdf

Artificial metamaterials with appropriate design can exhibit unique electromagnetic phenomena which do not exist in natural materials. Some studies have shown that the method of breaking the geometric symmetry is capable to modify the electromagnetic responses. Here, we simulated and measured the transmission spectra of period arrays of subwavelength double-bar structure. The obtained results show the trapped-mode resonance with Fano-shaped spectrum can be induced in terahertz metamaterial with asymmetric double-bar structure, accompanied with a metamaterial induced transparency window between two resonant dips. And the bar spacing and lattice constant have great impact on the coupling strength concerned with the transparency position and spectral lineshape. We attribute there are two mechanisms together determine the coupling pattern between the bar array and the terahetz wave, the coupling between the bars of the same unit cell and the coupling between the bars of the neighbouring cells. Our obtained results indicate that such metamaterial with very simple configuration could also provide the potential application in the field of terahertz slow-light devices, amplitude and phase modulators.

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

Abstract-Resonance coupling and polarization conversion in terahertz metasurfaces with twisted split-ring resonator pairs

Chenyu Li, Chun-Chieh Chang, Qingli Zhou, Cunlin Zhang, and Hou-Tong Chen

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-21-25842

We investigate edge-coupling of twisted split-ring resonator (SRR) pairs in the terahertz (THz) frequency range. Using a simple coupled-resonator model we show that such a system exhibits resonance splitting and cross-polarization conversion. Numerical simulations and experimental measurements agree well with theoretical calculations, verifying the resonance splitting as a function of the coupling strength given by the SRR separation. We further show that a metal ground plane can be integrated to significantly enhance the resonance coupling, which enables the effective control of resonance splitting and the efficiency and bandwidth of the cross-polarization conversion. Our findings improve the fundamental understanding of metamaterials with a view of accomplishing metamaterial functionalities with enhanced performance, which is of great interest in realizing THz functional devices required in a variety of applications.

© 2017 Optical Society of America

Abstract-The birefringence of two liquid crystals in terahertz band

Huijuan Sun, Lingqin Kong, Yuejin Zhao

Beijing Institute of Technology (China)

Qingli Zhou, Chenyu Li, Cunlin Zhang

Capital Normal Univ. (China)

Proc. SPIE 10030, Infrared, Millimeter-Wave, and Terahertz Technologies IV, 100302D (December 8, 2016); doi:10.1117/12.2246343

http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2593079


Compared with the wide application of liquid crystals (LCs) in the visible frequency band, their properties in the terahertz band have not been investigated extensively yet. In this paper, we have investigated the optical anisotropy of LCs TEB30A and 9023 at room temperature using terahertz time-domain spectroscopy (THz-TDS). The extraordinary and ordinary refraction indices of LC TEB30A are ne≈1.84 and no≈1.65, or a birefringence of 0.19 from 0.5 to 2.2 THz. The extraordinary and ordinary refraction indices of LC 9023 are ne≈1.83 and no≈1.62, or a birefringence of 0.21 from 0.5 to 2.2 THz. LC 9023 exhibits a little larger terahertz birefringence than that of LC TEB30A.
 © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Study of asymmetric U-shaped resonator at terahertz frequencies

• Zhou Yang
• Qingli Zhou
• Wen Long
• Chenyu Li
• Yulei Shi
• Ani Wu
• Jianfeng Liu
• Cunlin Zhang

http://www.sciencedirect.com/science/article/pii/S0030401816300906

We demonstrate the asymmetric U-shaped array exhibits different spectral patterns in response to incident terahertz wave with horizontal and vertical polarizations. In the horizontal incident polarization, where terahertz electric-field E_in is in parallel with the bottom bar of U-shaped structure, the two-absorption-dip transmission spectrum is similar to that of a typical split-ring resonator. When E_in is perpendicular to bottom bar, an interesting phenomenon comes up with three dips. This differs from the split-ring resonator which only has one dip in the transmission spectrum. The bottom-bar length also has significant impacts on frequency-shift and absorptive depth related to this resonant phenomenon.

Abstract-Transmitted spectral modulation of double-ring resonator using liquid crystals in terahertz range

Huijuan Sun

Beijing Institute of Technology (China)

Qingli Zhou, Chenyu Li, Ani Wu, Cunlin Zhang

Capital Normal Univ. (China)

Xiumin Wang

Beijing Univ. of Civil Engineering and Architecture (China)

http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1811722

Proc. SPIE 9042, 2013 International Conference on Optical Instruments and Technology: Optical Systems and Modern Optoelectronic Instruments, 90421E (December 31, 2013); doi:10.1117/12.2038128

Metamaterials with subwavelength structural features show unique electromagnetic responses that are unattainable with natural materials. Recent research on these artificial materials has been pushed forward to the terahertz region because of potential applications in biological fingerprinting, security imaging, remote sensing, and high frequency magnetic and electric resonant devices. Active control of their properties could further facilitate and open up new applications in terms of modulation and switching. Liquid crystals, which have been the subject of research for more than a century, have the unique properties for the development of many other optical components such as light valves, tunable filters and tunable lenses. In this paper, we investigated the transmitted spectral modulation in terahertz range by using liquid crystals (5CB and TEB300) covering on the fabricated double-ring resonators to realize the shift of the resonance frequency. Our obtained results indicate the low frequency resonance shows the obvious blue-shift, while the location of high frequency resonance is nearly unchanged. We believe this phenomenon is related to not only the refractive index of the covering liquid crystals but also the resonant mechanism of both resonances. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Study of L-shaped resonators at terahertz frequencies

Jianfeng Liu^1,2, Qingli Zhou^1,a), Yulei Shi¹, Xu Zhao¹ and Cunlin Zhang¹

1 Beijing Key Laboratory for Terahertz Spectroscopy and Imaging, Key Laboratory for Terahertz Optoelectronics, Ministry of Education, Department of Physics, Capital Normal University, Beijing 100048, China
2 Beijing NO. 55 Middle School, Beijing 100027, China
a) Author to whom correspondence should be addressed. Electronic mail: qlzhou@cnu.edu.cn.
Appl. Phys. Lett. 103, 241911 (2013); http://dx.doi.org/10.1063/1.4847295

In experimental and theoretical studies of terahertz subwavelength “L”-shaped structure, we proposed an unusual-mode current resonance responsible for low-frequency characteristic dip in transmission spectra. Comparing spectral properties of our designed simplified structures with that of split-ring resonators, we attribute this unusual mode to the resonance coupling and splitting under the broken symmetry of the structure. Furthermore, it is found that this phenomenon is also related to not only the spacing between horizontal and vertical sides but also their relative position in “L” structure, showing the weakened coupling and spectral splitting with the increased distance and structure symmetry.

© 2013 AIP Publishing LLC