Abstract-One-way edge modes in truncated semiconductor photonic crystal at terahertz frequencies

Lingjuan He, Linfang Shen, Xiaohua Deng, Kai Yuan,

https://iopscience.iop.org/article/10.1088/2040-8986/ab1bcd/pdf

Terahertz one-way edge modes in truncated photonic crystals (PhCs) are investigated theoretically. The PhC consists of a square array of air columns in semiconductor. By applying an external dc magnetic field in the PhC, a band gap is generated by lifting the degeneracy point of the lowest two bands. Based on this band gap, edge mode always exists in the truncated PhC for any boundary cutting, and it may propagate unidirectionally or bidirectionally, closely depending on the PhC boundary shape. It is shown that for one-way edge mode, the PhC boundary cutting has remarkable influence on the propagation length when the semiconductor loss is taken into account. A boundary structure is introduced into the PhC system for weakening the loss effect, and the propagation length of the one-way edge mode can be increased nearly by twice by optimizing the boundary parameters.

Abstract-A terahertz signal propagation model in hypersonic plasma sheath with different flight speed

Physics of Plasmas

Rongxin Tang,  Mingyang Mao,  Kai Yuan,  Yuhao Wang,  Xiaohua Deng

The electron densities (Ne) and the electron collision frequencies (νc) of different flight speeds.

https://aip.scitation.org/doi/abs/10.1063/1.5091676

A hypersonic plasma sheath could shield communication signals, which results in the so-called “blackout.” Hypersonic flights in near space used to suffer from the “blackout.” Terahertz (THz) communication is considered to be a potential solution to the blackout problem. On the other hand, it is still not clear that how the complex flight conditions impact the THz communication channel conditions in the plasma sheath. The relation between the occurrence of communication blackout and the flight conditions is unclear either. In the present study, the relation between the THz signal attenuation in plasma sheaths and the hypersonic flight speed was investigated using the numerical hypersonic hydrodynamic model. According to this study, the thickness of the plasma sheath decreases with the increasing flight speed. The electron density and the electron collision frequency increase with the flight speed. As a result, the THz signal attenuation increases with the flight speed. In addition, a new estimation model, which is able to predict the THz signal attenuation in the plasma sheath for arbitrary flight speed, was developed on the basis of the numerical study. The estimation model, in which the hypersonic hydrodynamics is absent, could help to significantly reduce the time consumption in predicting the THz communication channel conditions as well as the occurrence of the blackout.