A04 KAWANO, Yukio |Proposed Research Projects (2016-2017)

Paper | Original Paper


Takaaki Iguchi, Takeyoshi Sugaya, and *Yukio Kawano,
Silicon-immersed terahertz plasmonic structures,
Applied Physics Letters 110, 151105-1-4 (2017).

[Summary] A Bull’s eye (BE) plasmonic structure exhibits a powerful property of highly enhanced light transmission through a sub-wavelength aperture. However, the BE structure in the terahertz (THz) region exhibits the problems of a relatively low THz-field enhancement factor and a large area with an increasing groove number. Here, we report on a design of a THz BE structure that utilizes a solid immersion method based on the high refractive index of a silicon (Si) material. By fabricating a deep-etched Si template covered with a gold film, we achieved a greatly enhanced THz transmission with an enhancement factor of up to 10^8 and also miniaturized the structure size by the factor of 11. These features demonstrate that the BE performance can be further improved by engineering dielectric materials.


Daichi Suzuki, Shunri Oda and *Yukio Kawano,
A flexible and wearable terahertz scanner,
Nature Photonics 10, 809-814 (2016).

[Summary] Imaging technologies based on terahertz (THz) waves have great potential for use in powerful non-invasive inspection methods. However, most real objects have various three-dimensional curvatures, and existing THz technologies often encounter difficulties in imaging such configurations, which limits the useful range of THz imaging applications. Here, we report the development of a flexible and wearable THz scanner based on carbon nanotubes (CNTs). We achieved room-temperature THz detection over a broad frequency band ranging from 0.14 THz to 39 THz and developed a portable THz scanner. Using this scanner, we performed THz imaging of samples concealed behind opaque objects, breakages and metal impurities inspection of a bent film, and multi-view scan of a syringe. Also we demonstrated a passive biometric THz scan of a human hand. Our results are expected to have considerable implications for non-destructive and non-contact inspections, such as medical examinations for the continuous monitoring of health conditions.

Xiangying Deng, Shunri Oda, and *Yukio Kawano,
Frequency Selective, High Transmission Spiral Terahertz Plasmonic Antennas,
Journal of Modeling and Simulation of Antennas and Propagation​​ 2, 1-6 (2016).

[Summary] Terahertz is long been studied and has potential in various applications. However, lack of efficient and sensitive detector is still an obstacle in the development of terahertz technology. The utilization of antennas can largely enhance sensitivity of terahertz detector. A bull’s eye plasmonic antenna has a great potential to sub-wavelength terahertz technologies because of its unique property of local electric-field concentration. However, a conventional bull’s eye antenna has a problem of a narrow band, limiting its ability for multi-frequency detection. Here we propose two terahertz plasmonic antennas for enabling arbitrary frequency selection: the split-joint bull’s eye structure and the spiral bull’s eye structure. We show that both of the two antennas can achieve wide-band transmission without large sacrifice on overall transmission. The frequency band can be arbitrarily tuned either by varying excitation directions or by adjusting structure parameters. These advantageous features will open up a door to frequency-selective terahertz antennas and their applications to multi-frequency investigations.

Paper | Review


*Yukio Kawano,
Chip-Based Near-Field Terahertz Microscopy,
IEEE Transactions on Terahertz Science and Technology 6, 356-364 (2016).

[Summary] Near-field terahertz (THz) imaging is vital to investigations in sub-wavelength regions down to the micro/nanometer scale. This technology is particularly useful for examining objects such as nanomaterials, polymers, cells, and biomolecules. The first part of this article briefly explains two types of near-field THz imaging technologies: aperture type and apertureless type. The second part explains our chip-based near-field imaging technology. We perform collection-mode near-field THz imaging by scanning an evanescently coupled THz detector closely across a sample surface. The implementation of a magnetically tunable THz detection method further enables us to obtain frequency-selective, near-field THz images. As an application of this technology, cryogenic THz-emission imaging is presented, wherein THz radiation associated with electron injection into a semiconductor device is imaged with no THz pump source. This technique provides direct information about the spatial distribution of electrons injected from an electrode into a semiconductor channel.

International Conferences


Oral (contributed)

Toshio Sugaya, Takashi Iguchi, and Yukio kawano,
Resonant Frequency Tuning and Transmission Enhancement of Terahertz Plasmonic Antenna by Dielectric Engineering,
42nd International Conference on Infrared, Millimeter and Terahertz Waves (Aug. 27 – Sep. 1, 2017), Cancún, México.


*Xiangying Deng, Shunri Oda, and Yukio Kawano,
Spiral Bull’s Eye Structure for Multi-frequency High-transmission Plasmonic Antenna,
5th Advanced Electromagnetics Symposium (Jul. 26-28, 2017), Incheon, Korea.



*Yukio Kawano,
Nanoscale Terahertz Sensing and Imaging with Graphene and Arrayed Carbon Nanotubes,
4th Advanced Electromagnetics Symposium (Jul. 26-28, 2016), Malaga, Spain.

*Yukio Kawano,
Near-field frequency-selective terahertz imaging utilizing graphene and carbon nanotubes,
SPIE DCS (Apr. 17-21, 2016), Baltimore, MD, USA.

Grant-in-Aid for Scientific Research (KAKENHI) on Innovative Areas, MEXT, Japan
Synergy of Fluctuation and Structure : Quest for Universal Laws in Non-Equilibrium Systems