Abstract-Reconfigurable Terahertz Quarter-Wave Plate for Helicity Switching Based on Babinet Inversion of an Anisotropic Checkerboard Metasurface

Yosuke Nakata, Kai Fukawa, Toshihiro Nakanishi, Yoshiro Urade, Kunio Okimura, and Fumiaki Miyamaru

https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.11.044008

Dynamic helicity switching by utilizing metasurfaces is challenging because it requires deep modulation of polarization states. To realize such helicity switching, this paper proposes a dynamic metasurface functioning as a switchable quarter-wave plate, the fast axis of which can be dynamically rotated by ${90}^{\circ }$. The device is based on the critical transition of an anisotropic metallic checkerboard, which realizes the deep modulation and simultaneous design of the switchable states. After verifying the functionality of the ideally designed device in a simulation, we tune its structural parameters to realize practical experiments in the terahertz frequency range. By evaluating the fabricated sample with vanadium dioxide, the conductivity of which can be controlled by temperature, its dynamic helicity switching function is demonstrated.

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Abstract-Reconfigurable terahertz quarter-wave plate for helicity switching based on Babinet inversion of anisotropic checkerboard metasurface

Yosuke Nakata, Kai Fukawa, Toshihiro Nakanishi, Yoshiro Urade, Kunio Okimura, Fumiaki Miyamaru

https://arxiv.org/abs/1805.10034

Dynamic helicity switching by utilizing metasurfaces is challenging because it requires deep modulation of polarization states. To realize such helicity switching, this paper proposes a dynamic metasurface functioning as a switchable quarter-wave plate, the fast axis of which can be dynamically rotated by 90∘. The device is based on the critical transition of an anisotropic metallic checkerboard, which realizes the deep modulation and simultaneous design of the switchable states. After verifying the functionality of the ideally designed device in a simulation, we tune its structural parameters to realize practical experiments in the terahertz frequency range. By evaluating the fabricated sample with vanadium dioxide, the conductivity of which can be controlled by temperature, its dynamic helicity switching function is demonstrated.

Abstract-Energy loss of terahertz electromagnetic waves by nano-sized connections in near-self-complementary metallic checkerboard patterns

Keisuke Takano, Yoku Tanaka, Gabriel Moreno, Abdallah Chahadih, Abbas Ghaddar, Xiang-Lei Han, François Vaurette, Yosuke Nakata, Fumiaki Miyamaru, Makoto Nakajima, Masanori Hangyo,Tahsin Akalin

https://arxiv.org/abs/1708.03107

The design of a self-complementary metallic checkerboard pattern achieves broadband, dispersion-less, and maximized absorption, concentrating in the deep subwavelength resistive connections between squares, without any theoretical limitation on the energy absorbing area. Here, we experimentally and numerically investigate the electromagnetic response in the limit of extremely small connections. We show that finite conductivity and randomness in a near-self-complementary checkerboard pattern plays a crucial role in producing a frequency-independent energy loss in the terahertz frequency region. Here metals behave like an almost perfect conductor. When the checkerboard pattern approaches the perfect self-complementary pattern, the perfect conductor approximation spontaneously breaks down, owing to the finite conductivity at the nano- scale connection, leading to broadband absorption. It is also shown that the random connections between metallic squares also lead to broadband and maximized energy loss through scattering loss, similar to finite conductivity.

Abstract-Freestanding transparent terahertz half-wave plate using subwavelength cut-wire pairs

Yosuke Nakata, Yudai Taira, Toshihiro Nakanishi, and Fumiaki Miyamaru

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-3-2107

We designed a cut-wire-pair metasurface that works as a transparent terahertz half-wave plate, by matching the electric and magnetic resonances of the structure. Due to the impedance matching nature of the resonances, a large transmission phase shift between the orthogonal polarizations was achieved, while permitting a high transmission. The electric and magnetic responses of the proposed structure were confirmed by evaluating the electric admittance and magnetic impedance. The structure was fabricated on a flexible film and its helicity-conversion function in the terahertz frequency range was experimentally demonstrated. The thickness of the device is less than 1/10 of the working vacuum wavelength, and a high amplitude helicity conversion rate over 80 % was achieved. Finally, using simulations, we demonstrate the feasibility of the gradually rotating cut-wire-pair array in terahertz wave-front control.

© 2017 Optical Society of America

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Abstract-Observation of Fano resonance using a coupled resonator metamaterial composed of meta-atoms arranged by double periodicity

Tsubasa Nishida, Yosuke Nakata, Fumiaki Miyamaru, Toshihiro Nakanishi, Mitsuo W. Takeda

(Submitted on 12 Dec 2016)

https://arxiv.org/abs/1612.03552

We studied the transmission characteristics of a planar metamaterial consisting of an array of electric split-ring resonators (eSRRs) with double periodicity. Because of coupling between different resonant modes induced by different lattice periods in metamaterials with double periodicity, the appearance of Fano resonance can be expected in the same manner as that in the case of coupled classical oscillators. We fabricated complementary eSRRs and verified that a Fano-like spectral shape appeared in the transmission spectra of eSRRs with double periodicity in the terahertz region.

Abstract-Dynamically Babinet-invertible metasurface: a capacitive-inductive reconfigurable filter for terahertz waves using vanadium-dioxide metal-insulator transition

Yoshiro Urade, Yosuke Nakata, Kunio Okimura, Toshihiro Nakanishi, Fumiaki Miyamaru, Mitsuo W. Takeda, Masao Kitano

(Submitted on 24 Feb 2016)

https://www.blogger.com/blogger.g?blogID=124073320791841682&pli=1#editor/target=post;postID=2197810776175091966

This paper proposes a reconfigurable planar metamaterial that can be switched between capacitive and inductive responses using local changes in the electrical conductivity of its constituent material. The proposed device is based on Babinet's principle and exploits the singular electromagnetic responses of metallic checkerboard structures, which are dependent on the local electrical conductivity. Utilizing the heating-induced metal-insulator transition of vanadium dioxide (VO2), the proposed metamaterial is designed to compensate for the effect of the substrate and is experimentally characterized in the terahertz regime. This reconfigurable metamaterial can be utilized as a switchable filter and as a switchable phase shifter for terahertz waves.

Abstract-Dynamically Babinet-invertible metasurface: a capacitive-inductive reconfigurable filter for terahertz waves using vanadium-dioxide metal-insulator transition

Yoshiro Urade, Yosuke Nakata, Kunio Okimura, Toshihiro Nakanishi, Fumiaki Miyamaru, Mitsuo W. Takeda, and Masao Kitano

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-5-4405

This paper proposes a reconfigurable planar metamaterial that can be switched between capacitive and inductive responses using local changes in the electrical conductivity of its constituent material. The proposed device is based on Babinet’s principle and exploits the singular electromagnetic responses of metallic checkerboard structures, which are dependent on the local electrical conductivity. Utilizing the heating-induced metal-insulator transition of vanadium dioxide (VO2), the proposed meta-material is designed to compensate for the effect of the substrate and is experimentally characterized in the terahertz regime. This reconfigurable metamaterial can be utilized as a switchable filter and as a switchable phase shifter for terahertz waves.

© 2016 Optical Society of America

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Abstract-Trapping waves with terahertz metamaterial absorber based on isotropic Mie resonators

Riad Yahiaoui, Kenichiro Hanai, Keisuke Takano, Tsubasa Nishida, Fumiaki Miyamaru, Makoto Nakajima, and Masanori Hangyo
https://www.osapublishing.org/ol/abstract.cfm?uri=ol-40-13-3197

Quasi-monodisperse dielectric particles organized in a periodic hexagonal network on an aluminum surface are exploited numerically and experimentally as a single-layered near-perfect absorber in the terahertz regime. Of particular interest are titanium dioxide (TiO2) microspheres because of their large dielectric permittivity and isotropic shape leading to Mie resonances with insensitive polarization. Absorption higher than 80% at normal incidence covering two distinct ranges of frequencies is demonstrated experimentally. Furthermore, the performance of the metamaterial absorber is kept over a wide range of incident angles.

© 2015 Optical Society of America

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Abstract-Fast-Scan Terahertz Time Domain Spectrometer Based on Laser Repetition Frequency Modulation

Takashi Furuya1, Elmer S. Estacio1, Kazuki Horita1, Christopher T. Que1, Kohji Yamamoto1, Fumiaki Miyamaru2, Seizi Nishizawa2,3 and Masahiko Tani1

1 Research Center for Development of Far-Infra Red Region, University of Fukui, Fukui 910-8507, Japan
2 Shinshu University, Matsumoto, Nagano 390-8621, Japan
3 Advanced Infrared Spectroscopy Co., Ltd., Hachioji, Tokyo 193-0835, Japan 

http://iopscience.iop.org/1347-4065/52/2R/022401/

We propose a high-speed scanning terahertz (THz) time-domain spectrometer (TDS) based on optical sampling by repetition frequency modulation (OSREFM) using a repetition-frequency-tunable femtosecond fiber laser. Repetition frequency modulation is controlled by a highly stabilized external sweep generator. The fast scan of the time-delay between the pump and probe pulses is similar to an optical sampling with cavity tuning (OSCAT) THz-TDS system. However, the advantage of this technique is that it does not require physically moving components and uses only one laser system having an electronically modulated repetition rate. The time window and scanning time of this system depend on the modulation frequency range and the sweeping speed of the laser. In this study, we demonstrate the acquisition of a ~300 ps-window THz time waveform within 3 ms at a scan rate of 333 Hz.