Abstract-Contribution of terahertz waves to near-field radiative heat transfer between graphene-based hyperbolic metamaterials

Qi-Mei Zhao (赵启梅)1, Tong-Biao Wang (王同标)1, De-Jian Zhang (张德建)1, Wen-Xing Liu (刘文兴)1, Tian-Bao Yu (于天宝)1, Qing-Hua Liao (廖清华)1 and Nian-Hua Liu (刘念华)2



https://www.blogger.com/blogger.g?blogID=124073320791841682#editor/target=post;postID=8698960416063716885


Hyperbolic metamaterials alternately stacked by graphene and silicon (Si) are proposed and theoretically studied to investigate the contribution of terahertz (THz) waves to near-field radiative transfer. The results show that the heat transfer coefficient can be enhanced several times in a certain THz frequency range compared with that between graphene-covered Si bulks because of the presence of a continuum of hyperbolic modes. Moreover, the radiative heat transfer can also be enhanced remarkably for the proposed structure even in the whole THz range. The hyperbolic dispersion of the graphene-based hyperbolic metamaterial can be tuned by varying the chemical potential or the thickness of Si, with the tunability of optical conductivity and the chemical potential of graphene fixed. We also demonstrate that the radiative heat transfer can be actively controlled in the THz frequency range.

Abstract-VO2 as a natural optical metamaterial

Miller Eaton, Alessandra Catellani, Arrigo Calzolari

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-5-5342

VO2 is a unique phase change material with strongly anisotropic electronic properties. Recently, samples have been prepared that present a co-existence of phases and thus form metal-insulator junctions of the same chemical compound. Using first principles calculations, the optical properties of metallic and semiconducting VO2 are here discussed to design self-contained natural optical metamaterials, avoiding coupling with other dielectric media. The analysis of the optical properties complements the experiments in the description of the vast change in reflectance and metallicity for both disordered and planar compounds. The present results also predict the possibility to realize ordered VO2 junctions operating as efficient hyperbolic metamaterials in the THz-visible range, by simply adjusting the ratio between metallic and insulating VO2 content. The possibility to excite propagating volume plasmom polariton across the metamaterial is finally discussed.

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

Abstract-Generation, amplification, frequency conversion, and reversal of propagation of THz photons in nonlinear hyperbolic metamaterial

Alexander K. Popov and Sergey A. Myslivets

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-20-4151&origin=search

We propose metamaterial (MM) that supports a mixture of three or more normal and backward electromagnetic modes with equal co-directed phase velocities and mutually contra-directed energy fluxes. This enables extraordinary three-wave mixing, greatly enhanced optical parametric amplification, and frequency-changing generation of entangled photons in the reflection direction. Proof-of-principle numerical simulation of such processes is presented based on the particular example of the wave-guided terahertz waves contra-propagating in the MM made of carbon nanotubes.

© 2017 Optical Society of America

Abstract-Limits of imaging with multilayer hyperbolic metamaterials

Tengfei Li, Vivek Nagal, David H. Gracias, and Jacob B. Khurgin

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-12-13588

The multilayer hyperbolic metamaterials are known to be capable of imaging with sub-wavelength resolution. In this work performance of these “hyperbolic lenses” is analyzed in depth by employing commonly used transfer matrix method as well as the eigen-mode approach, the latter offering a clear physical insight into the operation of hyperbolic imagers and revealing their fundamental limitations. The resolution of multilayer structures is shown to decrease with the number of layers not only due to increased loss but also because of the severe suppression of large spatial frequencies caused by the cancellation between symmetric and antisymmetric eigen-modes. Additionally, the resolution is strongly affected by the granularity and fill ratio. In the end, hyperbolic metamaterials can create an image with subwavelength resolution only at very close distance to the object and hence limiting their utility.

© 2017 Optical Society of America

Abstract-Ultrabroad terahertz bandpass filter by hyperbolic metamaterial waveguide

Ultrabroad terahertz bandpass filter by hyperbolic metamaterial waveguide Xuetong Zhou, Xiang Yin, Tian Zhang, Lin Chen, and Xun Li  »View Author Affiliations

Optics Express, Vol. 23, Issue 9, pp. 11657-11664 (2015)
http://dx.doi.org/10.1364/OE.23.011657

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http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-23-9-11657

We propose and demonstrate an ultrabroad terahertz (THz) bandpass filter (BPF) by integrating two different-sized tapered hyperbolic metamaterial (HMM) waveguides, each of which has wide but different absorption and transmission bands, into a unit cell. With proper structural design of each HMM waveguide to control the absorption and transmission bands, we numerically demonstrate the designed BPF is capable of operating with a broad passband in the THz domain. A typical TM-polarized HMM BPF has a peak transmission of 37% at 3.3 THz with the passband bandwidth of 2.2 THz ranging from 2.97 to 5.17 THz. The co-designed three-dimensional HMM BPF also shows the capability of operating with independence to the polarization of incident light because of the structural symmetry and has sharp bandedge transitions of 22.6 and 17.6 dB/THz to the stop bands, respectively. The presented results here hold great promise for developing practical THz BPF with various applications in THz field.

© 2015 Optical Society of America

Abstract-Near-perfect absorption in epsilon-near-zero structures with hyperbolic dispersion

Klaus Halterman and J. Merle Elson  »View Author Affiliations

Optics Express, Vol. 22, Issue 6, pp. 7337-7348 (2014)
http://dx.doi.org/10.1364/OE.22.007337

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-22-6-7337

We investigate the interaction of polarized electromagnetic waves with hyperbolic metamaterial structures, whereby the in-plane permittivity component ε_x is opposite in sign to the normal component ε_z. We find that when the thickness of the metamaterial is smaller than the wavelength of the incident wave, hyperbolic metamaterials can absorb significantly higher amounts of electromagnetic energy compared to their conventional counterparts. We also demonstrate that for wavelengths leading to ℜ(ε_z) ≈ 0, near-perfect absorption arises and persists over a range of frequencies and subwavelength structure thicknesses.

© 2014 Optical Society of America

Hyperbolic metamaterials

                                                                                    Examples of hyperbolic metamaterials.
                                            a, Layered metal–dielectric structure; b, hyperlens; c, multilayer fishnet; d, nanorod arrays; e, arrays of metal–dielectric nanopyramids²³; f, graphene metamaterials. Figure e reproduced with permission from ref. 23, © 2012,

• Alexander Poddubny,
• Ivan Iorsh,
• Pavel Belov
• & Yuri Kivshar
• • http://www.nature.com/nphoton/journal/v7/n12/full/nphoton.2013.243.html

Electromagnetic metamaterials, artificial media created by subwavelength structuring, are useful for engineering electromagnetic space and controlling light propagation. Such materials exhibit many unusual properties that are rarely or never observed in nature. They can be employed to realize useful functionalities in emerging metadevices based on light. Here, we review hyperbolic metamaterials — one of the most unusual classes of electromagnetic metamaterials. They display hyperbolic (or indefinite) dispersion, which originates from one of the principal components of their electric or magnetic effective tensor having the opposite sign to the other two principal components. Such anisotropic structured materials exhibit distinctive properties, including strong enhancement of spontaneous emission, diverging density of states, negative refraction and enhanced superlensing effects.