Abstract-Tunable absorption enhancement in periodic elliptical hollow graphene arrays

Chunlian Cen, Lin Liu, Yubin Zhang, Xifang Chen, Zigang Zhou, Zao Yi, Xin Ye, Yongjian Tang, Yougen Yi, and Shuyuan Xiao

Fig. 1 The structural representation and geometric parameters of periodic elliptical hollow graphene arrays deposited on SiO2, and the geometric parameters are marked as shown in the figure. The electric field direction is parallel to X direction.

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-9-2-706&origin=search

In this contribution, a tunable plasmonic absorber consisting of periodical elliptical hollow graphene arrays deposited on SiO2 substrate is proposed in the far infrared and terahertz (THz). The simulation calculation results show that the structure supports a variety of effective tuning methods, such as changing the period, geometry parameters, Fermi level, relaxation time, incident angle, to achieve active and passive tuning. When the incident angle is set to 60°, the maximum absorption value (0.31) in our work can be achieved. Meanwhile, the red shift caused by period variations and blue shift phenomenon made of geometry parameters provides an exercisable way to select the resonance range. Therefore, these outcomes undoubtedly offer a unique source of inspiration for the diversity of graphene array shapes and the design and fabrication of absorption-related devices, such as filters, spatial light modulators, and sensors.

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

Abstract-Tunable Graphene-based Plasmonic Perfect Metamaterial Absorber in the THz Region

Zao Yi, , Jiajia Chen,  Chunlian Cen, Xifang Chen,  Zigang Zhou, Yongjian Tang, Xin Ye,  Shuyuan Xiao, Wei Lu,  Pinghui Wu,

file:///C:/Users/Randy/Downloads/micromachines-10-00194.pdf

The optical performance of a periodically tunable plasma perfect metamaterial absorber based on a square-square-circle array we propose in the terahertz region is analyzed in this work by the finite difference time domain (FDTD) method. We not only discuss the impact of various parameters such as period a, length L, radius R, and incident angle θ under transverse magnetic (TM)- and transverse electric (TE)-polarization on the absorption spectra of the absorber but also study the effect of the Fermi energy EF and relaxation time τ. Finally, we simulate the spectra as the surrounding refractive index n changes to better evaluate the sensing performance of the structure, producing a sensitivity S of the structure of up to 15006 nm/RIU. On account of this research, we find that the absorber is beneficial to sensors and detectors in the terahertz region.

Abstract-Actively tunable slow light in a terahertz hybrid metal-graphene metamaterial

Tingting Liu, Chaobiao Zhou, Le Cheng, Xiaoyun Jiang, Guangzhao Wang, Chen Xu, Shuyuan Xiao

https://arxiv.org/abs/1806.06600

We theoretically and numerically demonstrate an actively tunable slow light in a hybrid metal-graphene metamaterial in the terahertz (THz) regime. In the unit cell, the near field coupling between the metallic elements including the bright cut wire resonator and the dark double split-ring resonator gives rises to a pronounced transmission peak. By positioning a monolayer graphene under the dark mode resonator, an active modulation of the near field coupling is achieved via shifting the Fermi level of graphene. The physical origin can be attributed to the variation in the damping rate of the dark mode resonator arising from the conductive effect of graphene. Accompanied with the actively tunable near filed coupling effect is the dynamically controllable phase dispersion, allowing for the highly tunable slow light effect. This work offers an alternative way to design compact slow light devices in the THz regime for future optical signal processing applications.

Abstract-Plasmonic absorption characteristics based on dumbbell-shaped graphene metamaterial arrays

Chunlian Cen, Jiajia Chen, Hang Lin, Cuiping Liang, Jing Huang, Xifang Chen, Yongjian Tang, Zao Yi, Xibin Xu, Shuyuan Xiao

https://arxiv.org/abs/1802.10285

In this paper, we proposed a theoretical model in the far-infrared and terahertz (THz) bands, which is a dumbbell-shaped graphene metamaterial arrays with a combination of graphene nanorod and two semisphere-suspended heads. We report a detailed theoretical investigation on how to enhance localized electric field and the absorption in the dumbbell-shaped graphene metamaterial arrays. The simulation results show that by changing the geometrical parameters of the structure and the Fermi level of graphene, we can change the absorption characteristics. Furthermore, we have discovered that the resonant wavelength is insensitive to TM polarization. In addition, we also find that the double-layer graphene arrays have better absorption characteristics than single-layer graphene arrays. This work allows us to achieve tunable terahertz absorber, and may also provide potential applications in optical filter and biochemical sensing.

Abstract-Active modulation of electromagnetically induced transparency analogue in terahertz hybrid metal-graphene metamaterials

Shuyuan Xiao, Tao Wang, Tingting Liu, Xicheng Yan, Zhong Li, Chen Xu

(Submitted on 25 May 2017)

      https://arxiv.org/abs/1705.09082

Metamaterial analogues of electromagnetically induced transparency (EIT) have been intensively studied and widely employed for slow light and enhanced nonlinear effects. In particular, the active modulation of the EIT analogue and well-controlled group delay in metamaterials have shown great prospects in optical communication networks. Previous studies have focused on the optical control of the EIT analogue by integrating the photoactive materials into the unit cell, however, the response time is limited by the recovery time of the excited carriers in these bulk materials. Graphene has recently emerged as an exceptional optoelectronic material. It shows an ultrafast relaxation time on the order of picosecond and its conductivity can be tuned via manipulating the Fermi energy. Here we integrate a monolayer graphene into metal-based terahertz (THz) metamaterials, and realize a complete modulation in the resonance strength of the EIT analogue at the accessible Fermi energy. The physical mechanism lies in the active tuning the damping rate of the dark mode resonator through the recombination effect of the conductive graphene. Note that the monolayer morphology in our work is easier to fabricate and manipulate than isolated fashion. This work presents a novel modulation strategy of the EIT analogue in the hybrid metamaterials, and pave the way towards designing very compact slow light devices to meet future demand of ultrafast optical signal processing.

Abstract-Strong interaction between graphene layer and Fano resonance in terahertz metamaterials

Shuyuan Xiao1, Tao Wang1, Xiaoyun Jiang1, Xicheng Yan1, Le Cheng1, Boyun Wang2 and Chen Xu3

Published 13 April 2017 • © 2017 IOP Publishing Ltd 

http://iopscience.iop.org/article/10.1088/1361-6463/aa69b1/pdf

Graphene has emerged as a promising building block in modern optics and optoelectronics due to its novel optical and electrical properties. In the mid-infrared and terahertz (THz) regime, graphene behaves like metals and supports surface plasmon resonances (SPRs). Moreover, the continuously tunable conductivity of graphene enables active SPRs and gives rise to a range of active applications. However, the interaction between graphene and metal-based resonant metamaterials has not been fully understood. In this work, a simulation investigation on the interaction between the graphene layer and THz resonances supported by the two-gap split ring metamaterials is systematically conducted. The simulation results show that the graphene layer can substantially reduce the Fano resonance and even switch it off, while leaving the dipole resonance nearly unaffected, which is well explained with the high conductivity of graphene. With the manipulation of graphene conductivity via altering its Fermi energy or layer number, the amplitude of the Fano resonance can be modulated. The tunable Fano resonance here together with the underlying physical mechanism can be strategically important in designing active metal-graphene hybrid metamaterials. In addition, the 'sensitivity' to the graphene layer of the Fano resonance is also highly appreciated in the field of ultrasensitive sensing, where the novel physical mechanism can be employed in sensing other graphene-like two-dimensional materials or biomolecules with the high conductivity.