Abstract-Deeply Subwavelength Metasurface Resonators for Terahertz Wavefront Manipulation

Mingkai Liu,  Quanlong Yang,  Ahmmed A. Rifat,   Vidur Raj,   Andrei Komar,   Jiaguang Han,   Mohsen Rahmani,   Haroldo T. Hattori,   Dragomir Neshev,   David A. Powell,   Ilya V. Shadrivov,

https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201900736?af=R

Metasurfaces offer a highly flexible platform for controlling the propagation and localization of electromagnetic waves. Due to the relatively large size of commonly used resonators, various undesirable effects including spatial dispersion and spurious diffraction occur, thus limiting the metasurface performance. To overcome these problems, one straightforward approach is to utilize deeply subwavelength metaunits. In contrast to conventional approaches that minimize the resonator size by reshaping the metallic patches, the capacitive gaps are reshaped, an approach which is more robust to material loss, minimizing the problem of overdamping. As an example, a novel design based on interdigital capacitors (meander gap) is introduced with extremely subwavelength gaps for use in the terahertz frequency range. The size of the new resonator can be reduced to below λ/30 in a reflective‐type terahertz metasurface, while maintaining the 2 𝜋$\pi$ phase shift required for full wavefront control. Using an advanced electron‐beam lithography technique, a proof‐of‐concept experiment is performed and a 5 mm × 5 mm beam deflector is fabricated, with the capacitive gaps as small as 300 nm (≈λ/1130). The device performance is characterized using angle‐resolved time‐domain spectroscopy. The study provides useful insight for ultracompact metadevices based on deeply subwavelength metaunits working at terahertz frequencies and beyond.

Abstract-Enhanced terahertz magnetic dipole response by subwavelength fiber

Shaghik Atakaramians,  Ilya V. Shadrivov, Andrey E. Miroshnichenko,   Alessio Stefani, Heike Ebendorff-Heidepriem, Tanya M. Monro, Shahraam Afshar,

http://aip.scitation.org/doi/10.1063/1.5010348

Dielectric sub-wavelength particles have opened up a new platform for realization of magnetic light. Recently, we have demonstrated that a dipole emitter by a sub-wavelength fiber leads to an enhanced magnetic response. Here, we experimentally demonstrate an enhanced magnetic dipole source in the terahertz frequency range. By placing the fiber next to the hole in a metal screen, we find that the radiation power can be enhanced more than one order of magnitude. The enhancement is due to the excitation of the Mie-type resonances in the fiber. We demonstrate that such a system is equivalent to a double-fiber system excited by a magnetic source. This coupled magnetic dipole and optical fiber system can be considered a unit cell of metasurfaces for manipulation of terahertz radiation and is a proof-of-concept of a possibility to achieve enhanced radiation of a dipole source in proximity of a sub-wavelength fiber. It can also be scaled down to optical frequencies opening up promising avenues for developing integrated nanophotonic devices such as nanoantennas or lasers on fibers.

Abstract-A Terahertz Controlled-NOT Gate Based on Asymmetric Rotation of Polarization in Chiral Metamaterials

Wei-Zong Xu, Ya-Ting Shi, Jiandong Ye, Fang-Fang Ren, Ilya V. Shadrivov, Hai Lu, Lanju Liang, Xiaopeng Hu, Biaobing Jin, Rong Zhang, Youdou Zheng, Hark Hoe Tan, Chennupati Jagadish

http://onlinelibrary.wiley.com/doi/10.1002/adom.201700108/abstract

Logical operation based on polarization encoding of light is important for future data transmission and information processing. However, in the terahertz (THz) region, chiral materials with large optical activity are not available in nature, and the effective manipulation of polarization states remains challenging. Here, the authors demonstrate a double-layer bi-anisotropic metamaterial that consists of planar spiral and cut-wire layers separated by a polyimide film. Strong asymmetric polarization rotation of two orthogonal linear polarizations can be observed around 0.53 THz. By investigating the correlation between two linear polarization states before and after the spiral-wire metamaterial at this frequency, a controlled-NOT (CNOT) gate operating on two linear-polarization-based qubits is further exploited. The processing mechanism of the asymmetric rotation and CNOT gate is attributed to the scattering of dipole momentum based on classical multipole theory. This polarization processor's architecture is promising for robust and energy-efficient THz polarization control, and also provides an effective path for the development of future optical supercomputing technology.

Abstract-Strong broadband terahertz optical activity through control of the Blaschke phase with chiral metasurfaces

Michael A. Cole, Wen-chen Chen, Mingkai Liu, Sergey S. Kruk, Willie J. Padilla, Ilya V. Shadrivov, David A. Powell


https://journals.aps.org/prapplied/accepted/6e07eAb0N761870c20e140b145fd23b6eadac6cd4

We demonstrate terahertz chiral metamaterials that achieve resonant transmission and strong optical activity. This response is realized in a metasurface coupled to its Babinet complement, with additional twist. Uniquely, the optical activity achieved in this type of metamaterial is weakly dispersive around the resonant transmission maxima, but can be highly dispersive around the transmission minima. It has recently been shown that this unique optical activity response is closely related to zeros in the transmission spectra of circular polarizations through the Kramers-Kronig relations and strong resonant features in the optical activity spectrum corresponding to the Blaschke phase terms. Here we demonstrate how modifying the meta-atom geometry greatly affects the location and magnitude of these Blaschke phase terms. We study three different meta-atoms, which are variations on the simple cross structure. Their responses are measured using terahertz time-domain spectroscopy, and analyzed via numerical simulations.

Abstract-Experimental realization of a terahertz all-dielectric metasurface absorber

Xinyu Liu, Kebin Fan, Ilya V. Shadrivov, and Willie J. Padilla

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-1-191

Metamaterial absorbers consisting of metal, metal-dielectric, or dielectric materials have been realized across much of the electromagnetic spectrum and have demonstrated novel properties and applications. However, most absorbers utilize metals and thus are limited in applicability due to their low melting point, high Ohmic loss and high thermal conductivity. Other approaches rely on large dielectric structures and / or a supporting dielectric substrate as a loss mechanism, thereby realizing large absorption volumes. Here we present a terahertz (THz) all dielectric metasurface absorber based on hybrid dielectric waveguide resonances. We tune the metasurface geometry in order to overlap electric and magnetic dipole resonances at the same frequency, thus achieving an experimental absorption of 97.5%. A simulated dielectric metasurface achieves a total absorption coefficient enhancement factor of FT=140, with a small absorption volume. Our experimental results are well described by theory and simulations and not limited to the THz range, but may be extended to microwave, infrared and optical frequencies. The concept of an all-dielectric metasurface absorber offers a new route for control of the emission and absorption of electromagnetic radiation from surfaces with potential applications in energy harvesting, imaging, and sensing.

© 2017 Optical Society of America

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Abstract-Terahertz focusing of multiple wavelengths by graphene metasurfaces

Liming Liu^1,2,a), Yair Zarate¹, Haroldo T. Hattori², Dragomir N. Neshev^1,3, Ilya V. Shadrivov¹ and David A. Powell^1,3
 HIDE AFFILIATIONS
1 Nonlinear Physics Centre, Research School of Physics and Engineering, Australian National University, Canberra, ACT 2601, Australia
2 School of Engineering and Information Technology, University of New South Wales, Canberra, ACT 2612, Australia
3 Centre for Ultrahigh Bandwidth Devices for Optical Systems (CUDOS), Australian National University, Canberra, ACT 2601, Australia
a) Author to whom correspondence should be addressed. Electronic mail:liming.liu@student.adfa.edu.au
Appl. Phys. Lett. 108, 031106 (2016); http://dx.doi.org/10.1063/1.4940231

http://scitation.aip.org/content/aip/journal/apl/108/3/10.1063/1.4940231?TRACK=RSS

Metasurfaces can achieve nearly arbitrary wavefront control based on manipulation of the wavephase profile. We propose a metasurface based on double graphene cut-wire resonatorswhich can cover the complete 2π phase region with high reflection efficiency. This full phase coverage is essential for efficient wavefront manipulation, without reflecting energy into unwanted channels. A mirror capable of focusing multiple wavelengths is demonstrated numerically based on the proposed structure. The mirror can effectively focus terahertz (THz)waves from 1.2 to 1.9 THz to the same focal point by changing the Fermi level of eachgrapheneresonator separately. The presented metasurface could provide a powerful platform for controlling THz waves, including focusing, beam steering, beam shaping, and holograph