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-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.