Abstract-Tunable terahertz band-stop filter based on self-gated graphene monolayers with antidot arrays

Wei Wang, Dongxiao Yang, Zhenhai Qian, Chuanshan Xu, Chang Wang,

https://www.sciencedirect.com/science/article/pii/S0030401818305066

An electrically tunable terahertz band-stop filter, which is composed of self-gated graphene monolayers with antidot arrays, is proposed and numerically investigated in this letter. Simulation results show that a pronounced resonance trough caused by graphene surface plasmons (0, 1) mode is obtained, which can be used to realize terahertz band-stop filtering efficiently. Center frequency of the resonance trough can be dynamically controlled over a broad frequency range from 6.6 to 8.6 terahertz through changing the voltage from 8.5 to 24.9 volt. Besides, the proposed filter is independent on the polarization state of incident terahertz wave as a result of its high azimuthal symmetry. The influences of structural parameters, substrate properties and misalignment of the two perforated graphene monolayers are also taken into account in further investigations for better understanding characteristics of the terahertz filter. Specifically, the proposed filter can be applied for refractive index sensing as well with a high sensitivity larger than 8.2 μ$\mathrm{}$m/RIU, which is potentially valuable for gas detection and so on.

Abstract-Surface plasmons based terahertz modulator consisting of silicon–air–metal–dielectric–metal layers

Wei Wang, Dongxiao Yang, Zhenhai Qian

https://www.sciencedirect.com/science/article/pii/S0030401817310192

An optically controlled modulator of the terahertz wave, which is composed of a metal–dielectric–metal structure etched with circular loop arrays on both the metal layers and a photoexcited silicon wafer separated by an air layer, is proposed. Simulation results based on experimentally measured complex permittivities predict that modification of complex permittivity of the silicon wafer through excitation laser leads to a significant tuning of transmission characteristics of the modulator, forming the modulation depths of 59.62% and 96.64% based on localized surface plasmon peak and propagating surface plasmon peak, respectively. The influences of the complex permittivity of the silicon wafer and the thicknesses of both the air layer and the silicon wafer are numerically studied for better understanding the modulation mechanism. This study proposes a feasible methodology to design an optically controlled terahertz modulator with large modulation depth, high speed and suitable insertion loss, which is useful for terahertz applications in the future.

Abstract-Terahertz modulation based on surface plasmon resonance by self-gated graphene

Zhenhai Qian, Dongxiao Yang, Wei Wang

https://www.sciencedirect.com/science/article/pii/S0030401817311604

We theoretically and numerically investigate the extraordinary optical transmission through a terahertz metamaterial composed of metallic ring aperture arrays. The physical mechanism of different transmission peaks is elucidated to be magnetic polaritons or propagation surface plasmons with the help of surface current and electromagnetic field distributions at respective resonance frequencies. Then, we propose a high performance terahertz modulator based on the unique PSP resonance and combined with the metallic ring aperture arrays and a self-gated parallel-plate graphene capacitor. Because, to date, few researches have exhibited gate-controlled graphene modulation in terahertz region with low insertion losses, high modulation depth and low control voltage at room temperature. Here, we propose a 96% amplitude modulation with 0.7 dB insertion losses and ∼$$5.5 V gate voltage. Besides, we further study the absorption spectra of the modulator. When the transmission of modulator is very low, a 91% absorption can be achieved for avoiding damaging the source devices.

Abstract-Design of terahertz narrowband filter based on surface plasmon polaritons of metal–dielectric–metal structure with circular loop arrays

Xiang Liu, Wei Wang, Yinlong Zhao

Zhejiang University, College of Information Science and Electronic Engineering, Hangzhou, Zhejiang 310027, China

Dongxiao Yang

Zhejiang University, College of Information Science and Electronic Engineering, Hangzhou, Zhejiang 310027, China

Zhejiang University, Research Center for Terahertz Technology, Hangzhou, Zhejiang 310027, China

Opt. Eng. 54(12), 127107 (Dec 29, 2015). doi:10.1117/1.OE.54.12.127107

http://opticalengineering.spiedigitallibrary.org/article.aspx?articleid=2480140

Abstract.  A narrowband terahertz (THz) filter based on metal–dielectric–metal structure with a circular loop array patterned on metallic films was proposed. The transmission properties in the THz range of the structure were experimentally and theoretically analyzed. The structure’s transmission spectrum has two narrow bands of which band 1 in the lower frequency range was dominated by the transmission mode due to localized plasmon polaritons and band 2 in the higher frequency range was dominated by propagated plasmon polaritons mode and guided mode. Both band 1 and band 2 have high Q$Q$-factors. By designing an asymmetry periodic constant in orthogonal directions, band 2 exhibits potentials as a narrowband polarizer. Furthermore, the transmittance of band 2 can be promoted to 100% by laterally shifting the metallic arrays.

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Abstract-Applications of Terahertz Wave Technology in Smart Textiles

• Dongxiao Yang

http://link.springer.com/referenceworkentry/10.1007/978-981-4451-68-0_41-2

The terahertz radiation bridges the gap between microwave and infrared light, which consists of electromagnetic waves with frequencies ranging from 100 GHz to 1,000 GHz. There are approximately one-half of the total luminosity and most of the photons emitted since the Big Bang fall into the terahertz frequency region. Terahertz spectroscopy and imaging are two important techniques for the applications to textiles, which are described in this chapter. Some terahertz spectroscopy experimental systems were presented, such as time-domain spectroscopy-based terahertz pulsed system and backward-wave oscillator-based continuous-wave terahertz system. Several applications of the terahertz spectroscopy technique were reviewed to textile identification and sensing, such as textile fibers, textile materials, and wool textiles. Terahertz imaging of object behind textile barriers was demonstrated and the images were segmented for target detection. Terahertz imaging applications to textiles were also reviewed, such as measuring textile water content, detecting target behind textile barriers, and testing composites nondestructively.

Abstract-High speed optical modulation of terahertz waves using annealed silicon wafer

Tao Li   Dongxiao Yang   Jian Wang 
http://www.opticsjournal.net/abstract.htm?id=OJ140723000031C0FbIe

Modulation properties of terahertz waves going through a light excited high resistivity silicon wafer are analyzed and measured. Free carrier lifetime of the silicon wafer affects the modulation depth and speed of the terahertz wave. The lifetime is reduced to less than 1 μs by thermal processing for high speed modulation. Experimental results show that the response time and modulation depth of the proposed modulating structure are close to 1 μs and 51%, respectively.

Abstract-Role of surface plasmon resonant modes in anomalous terahertz transmission through double-layer metal loop arrays

Song Xia, Dongxiao Yang, Tao Li, Xiang Liu, and Jian Wang  »View Author Affiliations

Optics Letters, Vol. 39, Issue 5, pp. 1270-1273 (2014)
http://dx.doi.org/10.1364/OL.39.001270

A three-layer construction was proposed to induce anomalous transmission response for a normal incidence of terahertz (THz) wave. This structure was composed of a dielectric layer of quartz and two metallic layers, which were deposited on the two surfaces of quartz and patterned the same periodic arrays of subwavelength air circular loop. Based on comparative analyses of dispersion relations of both the structure and its partial structures, propagating surface plasmon and localized surface plasmon principally dominated the lower and higher resonant peaks appearing in the calculated transmittance spectrum, respectively. A sample was fabricated by laser technology for experiment and the measured THz transmission showed a good agreement with simulation, providing reference for potential applications.

© 2014 Optical Society of America