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-A High-Resolution Terahertz Electric Field Sensor Using a Corrugated Liquid Crystal Waveguide

Lan-Lan Xu, Yi Gong, Ya-Xian Fan,  Zhi-Yong Tao

https://www.mdpi.com/2073-4352/9/6/302

Liquid crystals (LCs) can always reflect variable optical properties in a broad terahertz (THz) band under external electric or magnetic fields. Based on the measurements of these varying properties, we can realize electric and magnetic field sensing with very high sensitivity. Here, we theoretically and numerically demonstrate a type of electric field sensor in the THz frequency range based on the defect mode arising in a periodically corrugated waveguide with liquid crystals. The Bragg defect structure consisting of periodically corrugated metallic walls and a defect in the middle can provide a narrow transmitted peak with controllable bandwidth, which can be used for external field sensing when it is filled with LCs. The molecular orientation of nematic LCs (E7) is not only very sensitive to the applied DC electric field but also very crucial to the effective refractive index of E7. Changing the effective index can efficiently shift the frequency of the transmitted peak in the THz spectrum. The simulated results show that the sensitivity can reach as high as 9.164 MHz/(V/m) and the smallest resolution is 0.1115 V/m. The proposed sensor and its significant performance could benefit electric field sensing and extend the applications of THz technology

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.

Abstract-Thermally Tunable Narrow Band Filter Achieved by Connecting Two Opaque Terahertz Waveguides

Lan-Lan Xu,  Zhi-Yong Tao,  Tang-Qing Sang , Dan Xu,  Peng-Fei Wang, Ya-Xian Fan,

http://ieeexplore.ieee.org/document/7896525/


We propose a thermally tunable terahertz narrow band filter by combining two different periodic waveguides. When the terahertz tube wall is corrugated periodically, the transparent spectrum presents a very complex structure as various pass and stopbands emerging. The terahertz wave cannot propagate through the waveguide when its frequency falls into the stopbands. When we connected two tubes with different types of stopbands, it is very intriguing that we have found an unexpected ultra-narrow-band transparency in the frequency gap. Our findings provide a more feasible and effective terahertz waveguide filter beyond these existing ones. By using the finite-element method, we have obtained the filtering characteristics of the proposed structures. The filter bandwidth could be narrowed from 2.3 GHz to 0.29 MHz by increasing the number of waveguide segments and the highest Q -factor achieved is about 3.5×106 . Moreover, the tunability on temperature is obtained in a waveguide device of Au based on the combination of opaque structures.