Abstract-Tunable terahertz optical properties of graphene in dc electric fields

H.M.Dong, F.Huang, W.Xu


https://www.sciencedirect.com/science/article/pii/S1386947717312031

We develop a simple theoretical approach to investigate terahertz (THz) optical properties of monolayer graphene in the presence of an external dc electric field. The analytical results for optical coefficients such as the absorptance and reflectivity are obtained self-consistently on the basis of a diagrammatic self-consistent field theory and a Boltzmann equilibrium equation. It is found that the optical refractive index, reflectivity and conductivity can be effectively tuned by not only a gate voltage but also a driving dc electric field. This study is relevant to the applications of graphene as advanced THz optoelectronic devices.

Abstract-Electrically tunable terahertz polarization converter based on overcoupled metal-isolator-metal metamaterials infiltrated with liquid crystals

Borislav Vasić1, Dimitrios C Zografopoulos2, Goran Isić1, Romeo Beccherelli2  Radoš Gajić1

Published 21 February 2017 • © 2017 IOP Publishing Ltd 

http://iopscience.iop.org/article/10.1088/1361-6528/aa5bbd

Large birefringence and its electrical modulation by means of Fréedericksz transition makes nematic liquid crystals (LCs) a promising platform for tunable terahertz (THz) devices. The thickness of standard LC cells is in the order of the wavelength, requiring high driving voltages and allowing only a very slow modulation at THz frequencies. Here, we first present the concept of overcoupled metal-isolator-metal (MIM) cavities that allow for achieving simultaneously both very high phase difference between orthogonal electric field components and large reflectance. We then apply this concept to LC-infiltrated MIM-based metamaterials aiming at the design of electrically tunable THz polarization converters. The optimal operation in the overcoupled regime is provided by properly selecting the thickness of the LC cell. Instead of the LC natural birefringence, the polarization-dependent functionality stems from the optical anisotropy of ultrathin and deeply subwavelength MIM structures. The dynamic electro-optic control of the LC refractive index enables the spectral shift of the resonant mode and, consequently, the tuning of the phase difference between the two orthogonal field components. This tunability is further enhanced by the large confinement of the resonant electromagnetic fields within the MIM cavity. We show that for an appropriately chosen linearly polarized incident field, the polarization state of the reflected field at the target operation frequency can be continuously swept between the north and south pole of the Poincaré sphere. Using a rigorous Q-tensor model to simulate the LC electro-optic switching, we demonstrate that the enhanced light–matter interaction in the MIM resonant cavity allows the polarization converter to operate at driving voltages below 10 Volt and with millisecond switching times.

Abstract-Graphene based tunable terahertz sensor with double Fano resonances

Yuping Zhang,   Tongtong Li,   Beibei Zeng,   Huiyun Zhang,  Huanhuan Lv,   Xiaoyan Huang,   Weili Zhang and   Abul Azad  

Nanoscale, 2015, Accepted Manuscript

DOI: 10.1039/C5NR03044G
Received 09 May 2015, Accepted 20 Jun 2015
First published online 24 Jun 2015
http://pubs.rsc.org/en/content/articlelanding/2015/nr/c5nr03044g#!divAbstract

We propose an ultrasensitive terahertz (THz) sensor consisting of a subwavelength graphene disk and an annular gold ring within a unit cell. The interference between the resonances arising from the graphene disk and the gold ring gives rise to Fano type resonances and enables ultrasensitive sensing. Our full wave electromagnetic simulations show frequency sensitivity as high as 1.9082THz/refractive index unit (RIU) and a figure of merit (FOM) of 6.5662. Furthermore, the sensing range can be actively tuned by adjusting the Fermi level of graphene.

Abstract-Tunable terahertz Kerr switching based on nonlinear polarization rotation in silicon waveguide

Miaoli Mou, Hongjun Liu, Nan Huang, Qibing Sun, and Zhaolu Wang  »View Author Affiliations

Applied Optics, Vol. 53, Issue 12, pp. 2741-2747 (2014)
http://dx.doi.org/10.1364/AO.53.002741

A compact and widely tunable terahertz (THz) all-optical Kerr switching using nonlinear polarization rotation generated by cross-phase modulation in a silicon waveguide is theoretically proposed. A switching efficiency of 83% is obtained when a π-phase shift difference between the TE and TM polarization components of the continuous-wave THz signal is achieved. Moreover, the tuning range of the THz switching is from 7.69 to 10 THz through changing the pump power. This THz all-optical switching has potential applications in THz communications and other THz switchable devices.

© 2014 Optical Society of America