Abstract-Terahertz mode selector based on multimode resonances in corrugated waveguides

 

Lan-Lan Xu, Ting Liu, Ya-Xian Fan, Huan Liu, and Zhi-Yong Tao

https://www.osapublishing.org/josab/abstract.cfm?uri=josab-38-8-2323

We propose a magnetically switchable terahertz (THz) mode selector based on four transverse mode resonances in corrugated waveguides. The theoretical and numerical results show that two passbands can be obtained in the transmission spectra around the resonance points. The passband of 0.9611–1.0006 THz outputs a single second-order transverse mode with the highest ratio of 99.03% while the passband of 0.8712–0.9111 THz contains the multiple transverse mode output with the first two modes. A tunable THz mode selector with frequency band of 0.5572–0.5926 THz is realized by filling the waveguide core with a liquid crystal (E7). The widest working frequency range of the mode selector reaches 28.4 GHz when the molecular steering angle 𝜃$\theta$ lies between 71.22° and 90°.

© 2021 Optical Society of America

Abstract-An efficient terahertz metamaterial linear polarization converter

Meng-Qiang Zou,  Huan Liu,  Yi Gong,  Ya-Xian Fan,  Zhi-Yong Tao,

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11196/111960L/An-efficient-terahertz-metamaterial-linear-polarization-converter/10.1117/12.2538629.short

An efficient terahertz (THz) metamaterial linear polarization converter is proposed. The structure consists of three layers of metal-dielectric-metal, including an anisotropic super-surface based on bimetallic arc structure as the top layer and a dielectric layer and a metal plate as middle layer and bottom layer, separately. The numerical analysis results show that broadband polarization conversion of a linearly polarized wave in the terahertz band is realized using the structure proposed. The polarization conversion ratio of the linearly polarized wave is more than 90% across a wide frequency range from 1.21 THz to 2.82 THz. The ratio of bandwidth to central frequency can reach 80%. The mechanism of high polarization conversion rate and broadband is analyzed. At the same time, the dependence of the polarization conversion rate of the structure on the incident angle is studied. The results show that the structure has good polarization conversion performance in the incident angle range of 0-60°. Compared with previous designs, the polarization converter has not only simple structure, but also wide bandwidth. It has potential application value in polarization modulation of terahertz wave.

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

Abstract-Vanadium dioxide-assisted broadband tunable terahertz metamaterial absorber

Huan Liu, Zhi-Hang Wang, Lin Li, Ya-Xian Fan,  Zhi-Yong Tao

https://www.nature.com/articles/s41598-019-42293-9

Tunable terahertz (THz) functional devices have exhibited superior performances due to the use of active materials, such as liquid crystals, graphene, and semiconductors. However, the tunable range of constitutive parameters of materials is still limited, which leads to the low modulation depth of THz devices. Here, we demonstrate a broadband tunable THz absorber based on hybrid vanadium dioxide (VO2) metamaterials. Unlike other phase change materials, VO2 exhibits an insulator-to-metal transition characteristic and the conductivity can be increased by 4–5 orders of magnitude under external stimulus including electric fields, optical, and thermal pumps. Based on the unique transition character of VO2, the maximum tunable range of the proposed absorber can be realized from 5% to 100% by an external thermal excitation. Meanwhile, an absorption greater than 80% in a continuous range with a bandwidth about 2.0  THz can be obtained when VO2 is in its metal phase at high temperature. Furthermore, the absorber is insensitive to the incident angle up to 50° and such a broadband THz absorber can be used in applications including imaging, modulating, cloaking, and so on.

Abstract-Self-adaptive terahertz spectroscopy from atmospheric vapor based on Hilbert-Huang transform

Huan Liu, Ya-Xian Fan, Lin Li, Hong-Ge Chen, Peng-Fei Wang, and Zhi-Yong Tao

           Fig. 1 Schematic diagram of the optical fiber integrated THz-TDS in transmission mode.
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-21-27279

Absorption lines of atmospheric vapor commonly appear in terahertz (THz) spectra measured in a humid air environment. However, these effects are generally undesirable because they may mask critical spectroscopic information. Here, a self-adaptive method is demonstrated for effectively identifying and eliminating atmospheric vapor noise from THz spectra of an all-fiber THz system with the Hilbert-Huang transform. The THz signal was decomposed into eight components in different time scales called the intrinsic mode functions and the interference of atmospheric vapor was accurately isolated. A series of experiments confirmed the effectiveness and strong self-adaptiveness of the proposed system in vapor noise elimination.

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

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-Analysis of fluoroquinolones antibiotic residue in feed matrices using terahertz spectroscopy

Yuan Long, Bin Li, Huan Liu,

http://65.202.222.105/ao/abstract.cfm?uri=ao-57-3-544

As antibiotic residue becomes more and more serious all over the world, a rapid and effective detection method is needed to evaluate the antibiotic residue in feed matrices to ensure food safety for consumers. In this study, three different kinds of fluoroquinolones (norfloxacin, enrofloxacin, and ofloxacin) in feed matrices were analyzed using terahertz (THz) spectroscopy, respectively. Meanwhile, pure fluoroquinolones and pure feed matrices were also measured in the same way. Then, the absorption spectra of all of the samples were extracted in the transmission mode. Pure norfloxacin has two absorption peaks at 0.825 and 1.187 THz, and they could still be observed when mixing norfloxacin with feed matrices. Also, there was an obvious and strong absorption peak for ofloxacin at 1.044 THz. However, no obvious absorption peak for enrofloxacin was observed, and only a weak absorption peak was located at 0.8 THz. Then, the different models were established with different chemometrics to identify the fluoroquinolones in feed matrices and determined the fluoroquinolones content in the feed matrices. The least squares support vector machines, Naive Bayes, Mahalanobis distance, and back propagation neural network (BPNN) were used to build the identification model with a Savitzky–Golay filter and standardized normal variate pretreatments. The results show that the excellent classification model was acquired with the BPNN combined with no pretreatment. The optimal classification accuracy was 80.56% in the testing set. After that, multiple linear regression and stepwise regression were used to establish the quantitative detection model for different kinds of fluoroquinolones in feed matrices. The optimal correlation coefficients for norfloxacin, enrofloxacin, and ofloxacin in the prediction set were obtained with multiple linear regression that combined absorption peaks with wavelengths selected by stepwise regression, which were 0.867, 0.828, and 0.964, respectively. Overall, this research explored the potential of identifying the fluoroquinolones in feed matrices using THz spectroscopy without a complex pretreatment process and then quantitatively detecting the fluoroquinolones content in feed matrices. The results demonstrate that THz spectra could be used to identify fluoroquinolones in feed matrices and also detect their content quantitatively, which has great significance for the food safety industry.

© 2018 Optical Society of America

Abstract-Hypersensitive and tunable terahertz wave switch based on non-Bragg structures filled with liquid crystals

Lu Zhang,  Ya-Xian Fan, Huan Liu,  Lan-Lan Xu,  Jiu-Ling Xue,  Zhi-Yong Tao

http://ieeexplore.ieee.org/document/7933180/

We investigated a hypersensitive and tunable terahertz (THz) wave switch based on liquid-crystal-filled non-Bragg structures. Non-Bragg structures, which consist of periodically corrugated metallic tube walls, provide spectra with very sharp rising edges, making them usable for sensitive switching. Tunability can be achieved by dynamically shifting the rising edge of a THz spectrum by using an externally applied magnetic field to change the orientations of the nematic liquid crystal (E7) molecules. The simulated results revealed that the switch effects are hypersensitive and tunable in the THz frequency range and that such switches could be applicable in future THz systems.