Abstract-Controllable Terahertz Switch Using Toroidal Dipolar Mode of a Metamaterial

 

Tong Guo, Chen Chen, Fei Yan, Ruoxing Wang,  Li Li, 

https://link.springer.com/article/10.1007/s11468-020-01359-5

We present a controllable terahertz (THz) metamaterial switch by manipulating toroidal dipolar mode in simulation. The metamaterial switch consists of periodically patterned metallic split rings with photosensitive silicon stripes. The excitation of toroidal dipolar resonance is closely dependent on the transition between the dielectric and conductive phases of photosensitive silicon. The toroidal dipolar mode is exploited to modulate the ON/OFF-switching transmission of THz wave under wide incident angles. The operation mechanism and frequency tunability are discussed.

Abstract-Theoretical study on 2.52 terahertz beam shaping and polarization conversion based on the transmissive all-dielectric metasurface

Author links open overlay panelZewen Wang,  Qi Li, Fei Yan



https://www.sciencedirect.com/science/article/abs/pii/S0030401819311320

Based on the physical optics vector diffraction integral formula and the commercial electromagnetic software EastWave, a transmissive all-dielectric square metasurface with a side length of 12.4 mm is designed in this paper. It can simultaneously modulate the phase and polarization of the terahertz wave. The 2.52 terahertz x-polarized normal incident Gaussian beam can be shaped into a radially polarized narrow-width annular Bessel-Gaussian beam (radii of the inner and outer circles are 4.125 mm and 5.5 mm, respectively) at a propagation distance of 23.8 mm away from the metasurface. The metasurface is composed of the poly (4-methyl-1-pentene) substrate and the rectangular silicon resonators with different dimensions and rotation angles (counterclockwise rotation angle of the rectangle long axis as the reference of positive x axis). The relative square error between the amplitude distribution of the shaped beam and the target beam is 7.36%, and the fitting coefficient of them is 96.6%. The diffraction efficiency (defined as the ratio of the total light field energy in the target region to that in the rear plane of the metasurface along the incident beam propagation direction) of the shaped annular region is 75.5%. By focusing the narrow-width annular Bessel-Gaussian beam obtained in this paper, we can get smaller focal spot and longer focal depth, which is of great significance for using terahertz wave in particle acceleration and material processing. In addition, the emergent polarization can be flexibly switched between radially and azimuthally polarized beams by changing the polarization direction of the linearly polarized incident beam.

Abstract-Triple-band tunable perfect terahertz metamaterial absorber with liquid crystal

Ruoxing Wang, Li Li, Jianlong Liu, Fei Yan, Fengjun Tian, Hao Tian, Jianzhong Zhang,  Weimin Sun,

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-26-32280

We report a compact triple-band tunable perfect terahertz metamaterial absorber (TMA) at the subwavelength scale of thickness, which is composed of a planar metallic disk resonator array above a conductive ground plane separated with liquid crystal (LC) mixture. The calculations of terahertz absorption spectra demonstrate triple near-unity absorption bands in the gap plasmonic resonance coupling regime. Three resonance frequencies of the absorber exhibit continuous linear-tunability as changing the refractive index of LC. Remarkably, each peak absorbance of the triple bands maintains at a level of beyond 99% in the whole tuning operation, and the absorbance can remain more than 90% over a wide range of incident angles. Our work suggests that the LC tunable absorber scheme has the potential to overcome the basic difficulty to perform simultaneously multiband spectral tuning and near-unity absorbance with wide angle of incidence and weak polarization dependence. The proposed LC-tunable multiband perfect TMA is promising in the application of biomolecular spectra-selective terahertz imaging and sensing.

© 2017 Optical Society of America under the terms of the OSA Open Access Publishing 

Abstract-Investigate the effects of EG doping PEDOT/PSS on transmission and anti-reflection properties using terahertz pulsed spectroscopy

Yiwen Sun, Shengxin Yang, Pengju Du, Fei Yan, Junle Qu, Zexuan Zhu, Jian Zuo, and Cunlin Zhang

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-3-1723&origin=search

The conductivity of poly(3,4-ethylene dioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) is significantly enhanced on adding some organic solvent such as ethylene glycol (EG). In this paper, the optoelectronic properties of EG doped PEDOT/PSS on transmission and anti-reflection effects are investigated in detail by terahertz time domain spectroscopy (THz-TDS). The transmission line circuit theory gives us an insight into the THz transmission mechanisms of the main and second pulses. In particular, we show that the conductivities of 10% EG doped PEDOT/PSS are nearly frequency independent from 0.3 to 1.5 THz. To demonstrate applications of this property, we design and fabricate broadband terahertz neutral density filters and anti-reflection coatings based on 10% EG doped PEDOT/PSS thin films with varying thickness. Our measurements highlight the capability of THz-TDS to characterize the conductivity of EG doped PEDOT/PSS, which is essential for broadband optoelectronic devices in THz region.

© 2017 Optical Society of America

Abstract-Low-cost and broadband terahertz antireflection coatings based on DMSO-doped PEDOT/PSS

Fei Yan, Edward P. J. Parrott, Xu Dong Liu, and Emma Pickwell-MacPherson
https://www.osapublishing.org/ol/abstract.cfm?uri=ol-40-12-2886

We report the potential application of 6% dimethylsulfoxide (DMSO)-doped poly (3, 4-ethylenedioxythiophene)/poly (4-styrenesulfonate) (PEDOT/PSS) as a low cost and broadband terahertz (THz) antireflection coating based on the impedance matching effect. The reflected pulses from the quartz and silicon substrates are observed to change with the thickness of the PEDOT/PSS layer. Theoretical analysis based on an equivalent transmission line circuit model and FDTD computational simulations have been used to understand the experimental results. Excellent impedance matching is achieved by a ∼39-nm-thick 6% DMSO-doped PEDOT/PSS layer on quartz, and a ∼101-nm-thick 6% DMSO-doped PEDOT/PSS layer on silicon due to the almost-frequency-independent conductivity of the thin film between 0.3 and 2.5 THz. In the critical conditions, the normalized main pulse transmission remains as high as 74% and 64%, for the quartz and silicon substrates, respectively, significantly higher than the existing state of the art THz antireflection coatings.

© 2015 Optical Society of America

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Abstract-Solvent Doping of PEDOT/PSS: Effect on Terahertz Optoelectronic Properties and Utilization in Terahertz Devices

Fei Yan , Edward P. J. Parrott , Benjamin S. Y. Ung , and Emma Pickwell-MacPherson

J. Phys. Chem. C, Just Accepted Manuscript

DOI: 10.1021/acs.jpcc.5b00465

Publication Date (Web): March 9, 2015

Copyright © 2015 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.5b00465

Poly (3, 4-ethylenedioxythiophene)/poly (4-styrenesulfonate) (PEDOT/PSS) is a conducting polymer and is a promising material for use in optoelectronic devices. Adding dopants to PEDOT/PSS significantly affects its optoelectronic properties: in this paper we use terahertz time domain spectroscopy (THz-TDS) to probe the effects of dopants dimethylsulfoxide (DMSO) and ethylene glycol. The carrier density, mobility and conductivity are calculated from the THz measurements by fitting the dielectric permittivity to the Drude-Smith model. This gives us an insight into the conductivity enhancement mechanisms and we find evidence to suggest that both carrier delocalization and charge screening play a role, although the relative importance of these two mechanisms depends upon both dopant polarity and concentration. To demonstrate an application of this finding, we design and fabricate broadband terahertz neutral density filters based upon 6% DMSO doped PEDOT/PSS thin films of varying thickness, and demonstrate optical densities between 0.14 and 0.53 from 0.5-2.2 THz with a comparable frequency variation to commercially available optical frequency ND filters.