Abstract-Excitation of graphene magneto-plasmons in terahertz range and giant Kerr rotation

Journal of Applied Physics

Jun Guo,  Xiaoyu Dai, Yuanjiang Xiang, Dingyuan Tang

Schematic diagram of the proposed (a) Otto, (b) KR, and (c) grating configurations to excite graphene MPs.

https://aip.scitation.org/doi/abs/10.1063/1.5057372

We propose three classical coupling methods (Otto, Kretschmann, and grating configurations) to excite graphene magneto-plasmons (MPs). After MP excitation, extraordinary Kerr rotations are obtained. As a demonstration, we discuss the Otto configuration in detail, but the other two methods have similar mechanisms and are only given limited descriptions. The dispersion relations of the MPs are discussed and found to well match previous predictions. It is found that the MP excitation and critical coupling are directly responsible for the large Kerr rotations. Combining the graphene MPs and critical coupling, much larger Kerr rotations (easily above 20°) away from the cyclotron resonance are achieved, as compared to previously described Faraday rotations (below 10°) using graphene MPs. By optimizing the graphene properties and structure parameters, the Kerr rotations are further enhanced. Moreover, using the grating coupling method, we easily find the largest Kerr rotation over 50° at 3 THz. The results are calculated using the anisotropic scattering-matrix method, and the finite element method is used as a comparison. The calculation methods are discussed in detail as a basis for future studies. These results are helpful not only to better understand graphene MPs but also for their potential terahertz applications.

Abstract-Terahertz imaging sensor based on the strong coupling of surface plasmon polaritons between PVDF and graphene

Jiaqi Zhu, Banxian Ruan, Qi You, Jun Guo,  Xiaoyu Dai, Yuanjiang Xiang

https://www.sciencedirect.com/science/article/pii/S0925400518304696
Surface plasmon polaritons (SPPs) of metal materials such as gold and silver are excited in the visible and near-infrared band, while the graphene SPPs exist from mid-infrared to terahertz (THz) ranges. Hence it is difficult to realize the coupling of SPPs of metals and graphene. In this paper, we realize coupling of two SPPs modes based on graphene and polyvinylidene fluoride (PVDF) in THz range, which is vital for the research of new sensors in terahertz spectrum. Based on the dispersion relation, it is demonstrated that the two different THz SPP modes in the hybrid configuration can be coupled together. We apply our design to the imaging sensor, and the highest imaging sensitivity as high as 730RIU⁻¹ is realized in the proposed sensors (which can be used in gas detection). Our results suggest that the strong coupling of two SPPs modes is an efficient method to achieve high sensing properties for the devices.

Abstract- Tunable terahertz/infrared coherent perfect absorption in a monolayer black phosphorus

Xi Wang, Qian Ma, Leiming Wu, Jun Guo, Shunbin Lu, Xiaoyu Dai, and Yuanjiang Xiang

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-5-5488

Black phosphorus (BP), a promising new two-dimensional (2D) material, has drawn a lot of attentions in academia and industry due to its extraordinary physical and chemical properties. In this paper, we theoretically demonstrate a monolayer BP that achieves coherent perfect absorption (CPA) at the THz/infrared band. It is found that quasi-CPA point does exist at the THz/infrared band. The CPA, which has a relative bandwidth of 141.3% and a coherent absorptivity of more than 90%, can be implemented at the quasi-CPA wavelength through a proper phase modulation. Moreover, the coherent absorptivity can be modulated with a high modulation depth by means of the phase difference between the two coherent counter-propagating beams. The angular selectivity of the monolayer BP is also investigated. The CPA wavelength is divided into two wavelength branches for TE and TM polarization at oblique incidence. In addition, the CPA wavelength can be tuned from THz to infrared band by adjusting the electron doping of the BP while maintaining the modulation depth of 104. Hence, our results may be potentially used for coherent modulations in terahertz/infrared detections and signal processing with 2D materials.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Highly Sensitive Terahertz Gas Sensor Based on Surface Plasmon Resonance With Graphene

Yuanjiang Xiang,   Jiaqi Zhu, Leiming Wu,  Qi You,  Banxian Ruan, Xiaoyu Da

One of the most important applications of THz frequencies is biomedical sensing. However, in a THz range, surface plasmon waves on flat metals are not confined and therefore cannot be used for subwavelength sensing. But, it has been shown that graphene can support surface waves at THz frequencies, which has similar properties as plasmonic waves in an optical range. In this paper, a highly sensitive gas sensor in the terahertz frequencies by exciting surface plasmon resonance (SPR) of graphene is proposed. The results show that the proposed SPR gas sensor has high stability and high sensitivity (S), and the highest Smax (∼147°/RIU) has been obtained by optimizing the Fermi energy, the thickness of the dielectric layer, and the incident light frequency. Moreover, the S of the proposed THz sensor for different refractive index (RI) of gas sensing medium (n1) is also discussed.

Abstract-THz Photonics in Two Dimensional Materials and Metamaterials: Properties, Devices and Prospects

Jinhui Shi,  Zhongjun Li,  David K. Sang,  Yuanjiang Xiang,  Jianqing Li,  Shuang Zhang,  Han Zhang

http://pubs.rsc.org/en/content/articlelanding/2018/tc/c7tc05460b#!divAbstract

Terahertz radiation refers to a broad electromagnetic spectrum range between microwave and infrared waves, which is also known as terahertz gap due to inadequate materials and technologies for its generation and manipulation. Atomically thin two dimensional (2D) materials such as graphene, black phosphorus (BP) and transition metal dichalcogenides (TMDs) provide a powerful platform for manipulating the propagation and detection of terahertz waves. Furthermore, hybrid meta-materials that feature the combination of artificially engineered meta-materials and 2D materials greatly facilitate dynamic modulation or manipulation of THz radiation towards novel terahertz applications. Herein, we review recent progress on 2D materials in the terahertz domain and hybrid metamaterials with engineered functionalities through the incorporation of graphene, TMDs and BPs. The emerging THz devices based on the modulation, nonlinearity, filtering, and Plasmonics of 2D Materials and Metamaterials will be highlighted, and a brief discussion with perspectives and the remaining challenges will be concluded.

Abstract-Three Dimensional Photonic Dirac Points in Metamaterials

Qinghua Guo, Biao Yang, Lingbo Xia, Wenlong Gao, Hongchao Liu, Jing Chen, Yuanjiang Xiang, and Shuang Zhang

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.213901

Topological semimetals, representing a new topological phase that lacks a full band gap in bulk states and exhibiting nontrivial topological orders, recently have been extended to photonic systems, predominantly in photonic crystals and to a lesser extent metamaterials. Photonic crystal realizations of Dirac degeneracies are protected by various space symmetries, where Bloch modes span the spin and orbital subspaces. Here, we theoretically show that Dirac points can also be realized in effective media through the intrinsic degrees of freedom in electromagnetism under electromagnetic duality. A pair of spin-polarized Fermi-arc-like surface states is observed at the interface between air and the Dirac metamaterials. Furthermore, eigenreflection fields show the decoupling process from a Dirac point to two Weyl points. We also find the topological correlation between a Dirac point and vortex or vector beams in classical photonics. The experimental feasibility of our scheme is demonstrated by designing a realistic metamaterial structure. The theoretical proposal of the photonic Dirac point lays the foundation for unveiling the connection between intrinsic physics and global topology in electromagnetism.

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Abstract-Tunable and multichannel terahertz perfect absorber due to Tamm surface plasmons with graphene

Xi Wang, Xing Jiang, Qi You, Jun Guo, Xiaoyu Dai, and Yuanjiang Xiang

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-5-6-536

In this paper, we have shown that perfect absorption at terahertz frequencies can be achieved by using a composite structure where graphene is coated on one-dimensional photonic crystal (1DPC) separated by a dielectric. Due to the excitation of optical Tamm states (OTSs) at the interface between the graphene and 1DPC, a strong absorption phenomenon occurs induced by the coupling of the incident light and OTSs. Although the perfect absorption produced by a metal–distributed Bragg reflector structure has been researched extensively, it is generally at a fixed frequency and not tunable. Here, we show that the perfect absorption at terahertz frequency not only can be tuned to different frequencies but also exhibits a high absorption over a wide angle range. In addition, the absorption of the proposed structure is insensitive to the polarization, and multichannel absorption can be realized by controlling the thickness of the top layer.

© 2017 Chinese Laser Press

Abstract-Ultrasensitive Terahertz Biosensors Based on Fano Resonance of a Graphene/Waveguide Hybrid Structure

Banxian Ruan, Jun Guo, Leiming Wu, Jiaqi Zhu, Qi You, Xiaoyu Dai, Yuanjiang Xiang,

http://www.mdpi.com/1424-8220/17/8/1924

Graphene terahertz (THz) surface plasmons provide hope for developing functional devices in the THz frequency. By coupling graphene surface plasmon polaritons (SPPs) and a planar waveguide (PWG) mode, Fano resonances are demonstrated to realize an ultrasensitive terahertz biosensor. By analyzing the dispersion relation of graphene SPPs and PWG, the tunable Fano resonances in the terahertz frequency are discussed. It is found that the asymmetric lineshape of Fano resonances can be manipulated by changing the Fermi level of graphene, and the influence of the thickness of coupling layer and air layer in sandwich structure on the Fano resonances is also discussed in detail. We then apply the proposed Fano resonance to realize the ultrasensitive terahertz biosensors, it is shown that the highest sensitivities of 3260 RIU−1 are realized. Our result is two orders of a conventional surface plasmon resonance sensor. Furthermore, we find that when sensing medium is in the vicinity of water in THz, the sensitivity increases with increasing refractive index of the sensing medium.

Abstract-Manipulating the optical bistability at terahertz frequency in the Fabry-Perot cavity with graphene

Leyong Jiang, Jun Guo, Leiming Wu, Xiaoyu Dai, and Yuanjiang Xiang
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-24-31181

We investigate theoretically the optical bistability from a Fabry-Perot cavity with graphene in the terahertz (THz) frequency. It is demonstrated that the optical bistablility in this cavity can be realized due to the electric field enhancement and the giant third-order nonlinear conductivity of graphene. The optical bistable behavior is strongly dependent on the transmission amplitude of the mirror and the position of the graphene in the cavity. It is especially important that the hysterical behaviors of the transmitted light rely on the optical conductivity of graphene, making the Fabry-Perot cavity to be a good candidate for dynamic tunable optical bistable device in the THz frequencies, owing to the possibility of high tunability of graphene conductivity by means of external electrostatic or magnetostatic field.

© 2015 Optical Society of America

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