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A01Electromagnetic (Microwave & THz wave) metamaterials
Group AFundamentals and Applications of Periodic Microwave Metamaterials
Group director: Atsushi Sanada (Yamaguchi University)
The group explores novel phenomena, theory, characterizations, implementations, and applications of the periodic non-resonant composite right/left-handed (CRLH) metamaterials that can exhibit left-handed properties potentially with lower losses and broader band operations compared with those of resonant types. The research area covers the CRLH theory, design and modeling, finite-difference time-domain (FDTD) based large-scale material simulations and characterizations, a fast and precise experimental material parameter retrieval methods and techniques, and their applications to devices, circuits and systems in wireless, radar and sensor systems at microwave frequencies, including diverse topics of polarization independent isotropic 3-dimensional left-handed metamaterials, multi-layer CRLH implementations and their ultra-compact microwave filter applications based on the low-temperature co-fired ceramics technology, non-reciprocal metamaterials and their novel antenna and circuit device applications using magnetic materials, and the like.
The group plays another important role of exporting and exchanging the concept and techniques of the broadband and low-loss microwave CRLH metamaterials to terahertz and optical regions collaborating with other groups, especially with Groups B, D, and F, to accelerate the program in the interdisciplinary areas.
Group BFabrication and functions of terahertz metamaterials using structural resonance
Group director: Masanori Hangyo (Osaka University)
In the terahertz region, it is easy to fabricate metamaterials compared to the optical region, and therefore there is more freedom of structures for metamaterials. Further, it is possible to use various parent materials such as metals, dielectrics, and semiconductors for fabricating metamaterials. Based on high terahertz technologies (emission, detection, spectroscopy, imaging) of our group, we fabricate and characterize metamaterials in the terahertz region. We also clarify the characteristics of low-dimensional propagation modes in metamaterials and apply them to developping terahertz devices.
We design resonant-type metamaterials made of metals, dielectrics, and semiconductors and fabricate them using various methods such as a lithography, super-fine ink-jet printing technology, ceramic process, laser fabrication, etc. Planar, stereo, and 3-dimensional metamaterials will be fabricated. Active metamaterials for controlling terahertz waves will be also developed. Novel phenomena such as nonlinear optics in metamaterials will be investigated using high-electric-field terahertz waves.
The novel metamaterials developed in the terahertz region will be applied to the microwave and optical regions with cooperation of other groups.
Group CControl of polarization and propagation using resonant metamaterial in microwave region
Group director: Masao Kitano (Kyoto University)
This research group focuses on peculiar characteristics of polarization and propagation in metamaterials in microwave region. Based on the prediction by Prof. Kitano, we experimentally investigate no reflection phenomenon for circularly polarized wave for any incident angle at interface between a vacuum and magneto-electric coupled metamaterial (chiral metamaterial), collaborating with Prof. Hangyo's group. For the design of meta-atoms, Prof. Deguchi introduces genetic algorithm to optimize the characteristics of the metamaterial, collaborating with Dr. Tanaka's group. Prof. Nakanishi fabricates electromagnetically-induced-transparency-like (EIT-like) metamaterial to realize slow electromagnetic propagation and experimentally investigates efficient harmonic generation in metamaterials with nonlinear elements by utilizing enhancement effect of electric fields at resonance, collaborating with Prof. Sakoda's group. Prof. Hisakado establishes theoretical frameworks by introducing circuit models for understanding fundamental aspects of wave propagation in metamaterials, collaborating with Prof. Sanada's group. Prof. Sakai studies dynamical control of metamaterial using gaseous plasma. By introducing gaseous plasma into (a part of) meta-atoms and controlling creation or annihilation of the plasma, or the plasma frequency or collision frequency, the effective permittivity or permeability of the metamaterial can be dynamically controlled. Prof. Sakai also demonstrates self-formation of negative refractive index medium by intense microwave incidence; this phenomena can be applicable to novel switching device.=
 
A02Optical metamaterials
Group DFabrication and physics of periodic metamaterials in optical regime.
Group director: Teruya Ishihara (Tohoku University)
By appropriately designing sub-wavelength periodic structure, we investigate physics in novel phenomena in metamaterials and explore application possibilities of their functionalities. One of the main research targets is the optical rectification effect based on the second order optical nonlinearity in artificial metallic structures. This effect can be utilized as a new probe for novel electromagnetic states including negative index of refraction as well as the elementary technology bridging electronics and nano-optics. Because surface roughness on the metal can contribute additional loss, it is a real challenge to fabricate high-precision metal-dielectric multilayers combined with state-of-the-art nano-fabrication technique in order to establish excellent figure of merit for a negative refractive index structure. As metamaterials can provide various novel circumstances in electromagnetic field, we expect that it will be fruitful to find electromagnetic analogy for intriguing electronic states in various Hall effects and other new phenomena in multiferroics. New magneto-optical effects in metamaterials will be investigated under static magnetic field. The concept of Berry phase will be helpful to build a general perspective of various phenomena in metamaterials. Another important target is a development of the novel nanolithography technique utilizing high-wavenumber states of surface plasmons for fabrication of periodic metamaterials. In many of research activities in this group, novel electromagnetic field calculation techniques based on fast multipole boundary element method will be utilized to enjoy its benefit.
Group EFabrication and characterization of three-dimensional resonant metamaterials working at visible light region
Group director: Takuo Tanaka (RIKEN)
In this research team, we aim to accomplish millimeter to centimeter size three-dimensional metamaterials that work at visible light region. The group leader, Dr. Tanaka, provides the following techniques as the basis of this research subject; structural design of resonators for optical metamaterials, direct laser writing as top-down nanofabrication, measurement and analysis on optical property, application for optical devise. The group members offer skills on bottom-up nanofabrication techniques that are advantageous to large-area fabrications.
Metamaterials are composed of integrated three-dimensional structures of nanometer-scale metallic resonators. To fabricate these structures with high Q-value, it is essential to combine top-down and bottom-up techniques for arranging numerous metallic nanostructures with high precision. Based on the protocol for structural designs of metamaterials developed by Dr. Tanaka, we investigate optimal high-Q structures prepared using bottom-up techniques, considering the fluctuations arising from the nature of self-assembled structures. Dr. Tanaka improves his two-photon-reduction method to realize a high-throughput fabrication and establishes a fundamental technology for fabrication of three-dimensional metallic resonators in nanoscale. Prof. Iyoda utilizes the self-assembled nanostructures of diblock copolymers and natural life forms as templates for fabrication of metamaterials. Prof. Fujikawa applies his nanocoating lithography to fabrication processes for metamaterials and develops a large-area scaffold for metallic resonators. Assembly of chemically synthesized metallic nanoparticles is also investigated by Dr. Tanaka’s group. We place importance on coalitions between the group members and achieve an yet-undiscovered three-dimensional optical metamaterials in millimeter to centimeter size. The collaborations between the other teams promise efficient progresses on the realization of new functional metamaterials.
Group FDevelopment of the fabrication technology for metamaterial surfaces with plasmonic resonances
Group director: Kazuaki Sakoda (National Institute for Materials Science)
In this project, we develop the fabrication technology for metamaterials that function in the optical range from visible to near infrared frequencies by fully utilizing nano-growth and nano-fabrication technologies of Nanotechnology Innovation Station and Photonic Materials Unit of National Institute for Materials Science. In addition to currently available fabrication technologies, we will newly introduce a nano-imprinting technology that can be applied to the production of large-area specimens. The first target of this project is the fabrication of meta-surfaces consisting of two-dimensional arrays of metal/dielectric/metal resonators of the trench type, for which we have demonstrated quite a large enhancement effect of the local electric field. The second target is the design of specimens by first-principle calculations such as FDTD and FEM for achieving the negative refractive index that enables extraordinary wave propagations. We will also develop semi-analytical methods based on the electromagnetic resonances in unit structures, which are either plasmonic or structural, to investigate the enhancement of linear (absorption, emission, Raman scattering, etc.) and non-linear (harmonic generation, two-photon absorption, etc.) optical phenomena that are caused by the increase in the local photon density of states and/or the decrease in the group velocity of photons. The third target is the characterization of meta-surfaces by reflection and transmission spectroscopy, second-harmonic generation, etc. We will demonstrate the negative refractive index, the selective enhancement of magnetic-dipole transitions, and all-optical switching by means of the electric-field enhancement. We will also try to demonstrate optical phenomena peculiar to meta-surfaces like s-polarized magnetic surface polaritons and the perfect absorption of light by means of the impedance matching between the meta-surfaces and free space.
 
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