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.

Abstract-Broadband one-way propagation and rainbow trapping of terahertz radiations

Jie Xu, Sanshui Xiao, Chiaho Wu, Hang Zhang, Xiaohua Deng, and Linfang Shen

Fig. 1 Schematics of the metal-semiconductor-dielectric-metal (a) and related semiconductordielectric-metal (b) structures for sustaining one-way SMPs. An external dc magnetic field is applied along the −y direction in the two structures.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-8-10659

Surface magnetoplasmon (SMP) supported at an interface between magnetized plasmonic and dielectric materials has been widely explored; however, it suffers with narrow bandwidth for one-way propagation. Here we propose a novel metal-semiconductor-dielectricmetal (MSDM) structure showing the large bandwidth for the complete one-way propagation (COWP). Because of the compression of the zone for two-way propagating modes in the semiconductor layer by reducing semiconductor thickness, the bandwidth is significantly increased by several times. More importantly, in such MSDM structure, the SMP dispersion can be engineered by controlling the semiconductor thickness, and based on this, slowing wave and trapping rainbow can be realized in a tapered system at terahertz frequencies.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz planar lenses based on plasmonic metasurfaces

Chang Yang, Yun Shen, Yanqiang Xie, Qi Zhou, Xiaohua Deng, Juncheng Cao,


https://www.sciencedirect.com/science/article/abs/pii/S037596011831185X


Plasmonic planar lenses on silicon substrate are designed to realize terahertz (THz) wave focusing. Super-unit-cells containing eight different resonant units are presented to construct eight concentric rings on the silicon substrate. By controlling of the position distribution of the resonant units, it is shown that focusing at 4.3 THz can be achieved. Moreover, due to that the eight units can steer THz wave and keep phase gradient in frequency range of 4.2 to 4.5 THz, the metalenses can realize broadband THz focusing. The results imply the potential applications in THz wave control devices of light collection and multi-channel optical communication.

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

Lingjuan He, Qian Shen, Jie Xu, Yun You, Tianbao Yu, Linfang Shen, Xiaohua Deng,

https://www.nature.com/articles/s41598-018-26395-4

Electromagnetic edge mode in a photonic crystal (PhC), which is a square array of semiconductor rods in air, is theoretically investigated for terahertz frequencies. In the PhC, gyroelectric anisotropy is introduced in the semiconductor rods by applying an external magnetic field and consequently, a degeneracy point, at which two dispersion surfaces intersect, is lifted and a new band gap is created. The edge mode sustained by the PhC possesses the character of one-way propagation, and it even can be immune to backscattering at large defect on the wavelength scale and 90° sharp bend. The properties of the one-way mode are closely dependent on the cladding layer structure of the PhC.

Abstract-Terahertz unidirectional invisibility in grating-based structures

Tao Wang, Liner Zou, Yun Shen, Miao Yi, Xiaohua Deng

http://www.tandfonline.com/doi/abs/10.1080/09500340.2017.1330973?journalCode=tmop20

A grating-based structure is proposed to realize unidirectional invisibility in the terahertz range. We show that the strict demand on refractive index for unidirectional invisibility can be flexibly satisfied in such proposed structure due to the tunable effective refractive index property of the grating layer by adjusting its geometric parameters. All these behaviours are demonstrated in the example of GaAs grating-based structure illuminated around 40 μm. Our results may lead to the development of a variety of novel terahertz devices for photonic integrated circuits.

Abstract-Stopping terahertz radiation without backscattering over a broad band

Stopping terahertz radiation without backscattering over a broad band Linfang Shen, Xiaodong Zheng, and Xiaohua Deng  »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-23-9-11790

Optics Express, Vol. 23, Issue 9, pp. 11790-11798 (2015)
http://dx.doi.org/10.1364/OE.23.011790

View Full Text Article

Enhanced HTML    Acrobat PDF (1154 )

We present an approach to completely stop terahertz radiation in an optical system with a gyroelectric semiconductor. This system is composed of guiding and stopping parts formed by the semiconductor with different cladding structures. Because the dispersion properties of surface magnetoplasmons (SMPs) in the semiconductor closely depend on its cladding structure, robust one-way SMPs sustained by the guiding part are prohibited in the stopping part, thereby stopping terahertz radiation without any backscattering. For incident continuous waves, trapped spots with strongly enhanced fields occur on a subwavelength scale. For incident pulses, the wave packets can be completely trapped and simultaneously compressed to subwavelength sizes.

© 2015 Optical Society of America

Abstract-Backscattering-immune one-way surface magnetoplasmons at terahertz frequencies

Backscattering-immune one-way surface magnetoplasmons at terahertz frequencies Linfang Shen, Yun You, Zhuoyuan Wang, and Xiaohua Deng  »View Author Affiliations

Optics Express, Vol. 23, Issue 2, pp. 950-962 (2015)
http://dx.doi.org/10.1364/OE.23.000950

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-23-2-950

View Full Text Article

Enhanced HTML    Acrobat PDF (1002 KB)

Surface magnetoplasmons (SMPs) in a basic physical model for the terahertz regime, which consists of a semi-infinite magnetized semiconductor with dielectric cladding terminated by a metal slab, are theoretically investigated. The dispersion properties of such SMPs are analyzed and examined in detail. It is shown that SMPs may follow three different kinds of dispersion diagrams, depending on the applied dc magnetic field intensity. Complete one-way propagation that operates within the band gap of the semiconductor is available for SMPs, and the one-way bandwidth reaches a maximum at a certain magnetic field intensity. Regular modes guided by the dielectric layer are also analyzed. These modes may cause the (complete) SMP one-way region to be compressed or even removed, but they can be suppressed by reducing the dielectric layer thickness. Owing to the mirror effect of the metal slab, one-way propagating and backscattering-immune basic SMPs can exhibit a larger propagation length than those sustained by a single dielectric–semiconductor interface.

© 2015 Optical Society of America