File 17
Terahertz Wave Wireless Communication Pioneered by
Organic Electro-optic Polymers
Q&As● Biography
1981
2009

2009

KAJI Takahiro
Senior Researcher, Nano-Scale
Functional Assembly ICT Laboratory, Kobe Frontier ResearchCenter, Advanced ICT ResearchInstitute, Ph.D. (Engineering).

2015

Born in Kyoto prefecture.
Completed graduate school’s
doctoral course (latter period) inMaterials Engineering Science,
Engineering Science, OsakaUniversity.
After serving as speciallyappointed assistant professor
for Global COE (Core Researchand Engineering of Advanced
Materials-Interdisciplinary
Education Center for MaterialsScience) in Engineering Science,joined NICT.
Current position.

● Research Activities

He is jointly conducting Research andDevelopment for Expansion of Radio
Wave Resources, which newly started in
FY2021.

n order to attain ultra-high-speed,large-capacity wireless communication in Beyond 5G, radio-over-fiber (RoF)
technology is attracting attention. Thistransmits signal waveforms of terahertz
waves (0.1–10 THz), which have higher
frequencies than radio waves, as opticalsignals by using optical fibers. A RoF signal
converter converts between optical andradio signals at each remote antenna. As
terahertz waves have higher directionality
than radio waves, the range covered by one
remote antenna is limited and so a huge
number of remote antennas are required.
For this reason, high-performance, small,
low-cost remote antenna transceivers need
to be developed.
Existing remote antenna receivers using
electronic technologies convert from terahertz to electrical signals, and then fromelectrical to optical signals by using an optical modulator. However, those receivers
have problems such as complicated mechanisms, large device size, and high cost. We
are focusing on organic electro-optic (EO)
polymers that enable highly efficient opti-I

12NICT NEWS 2021 No.5

Q What are you currently interested inoutside of your research?

A Iplay Japanese traditional music(“honkyoku”) with a five-holed bamboo
Japanese flute (“shakuhachi”). My
teacher encourages me to play in acertain style that is not written in themusic scores, and I greatly enjoy it.

Q What advice would you like to pass onto people aspiring to be researchers?

A It is important to take an interest in awide variety of research fields and tobroaden your horizons. You should also
try to challenge yourself by opening up untapped areas beyond
existing research fields.

Q How do you spend your time on holidays?

A I enjoy taking my baby daughter, who was born in March, aroundthe neighborhood. It is an immense pleasure to watch her
growing each day.

cal modulation at ultra-high speeds above
several hundred gigahertz. Our researchaims to develop a radio-to-optical signal
conversion device that can directly convert
from terahertz to optical signals, without
conversion to electrical signals.
To create such a device, we have developed
our own technology for transferring EOpolymer films on which poling (a processfor aligning the directions of EO molecules)
has been conducted in advance, and haveused it to fabricate a device that combines

EO polymers with terahertz wave low absorption loss materials, which would be difficult to fabricate by any existing method.
With the fabricated device, we have succeeded in observing direct optical modulation by irradiating electromagnetic waves
in the 100 GHz band.
We will continue improving the structure of
the device in order to increase the radio frequency and optical modulation efficiency,
and then work on its practical application.

Figure S chematic diagram of radio-to-optical signal conversion device using EO polymer
waveguides and Au antenna arrays, and a prototype 100 GHz-band device