A combination of nano- and optical
technologies is breathing new life into glass. Prof. Hirao
is the originator of nanoglass, which is created through
nano-scale manipulations of glass structures. He now focuses
on commercializing nanoglass products with novel functions
which ordinary glass does not have.
In 1970, Prof. Hirao majored in ceramics at a university
and was most fascinated by glass. He says, "Glass
is transparent and very beautiful.
It can easily be molded into any shape, is highly resistant
to scratches, and any element can be dissolved into it." Initially,
he studied the strength and structure of glass. Meanwhile,
glass became the key material for optical fibers and began
to attract attention as a material for optical communications
devices. Under the circumstances, Prof. Hirao strengthened
his determination to add more value to glass because of
its excellent properties.
Prof. Hirao says, "Since people are usually encouraged
to do things by external stimuli, I expected external stimulation
would also make glass show new functions." Based on
his idea, the Japan Science and Technology Organization
(now called the Japan Science and Technology Agency, JST)
started the Hirao Active Glass Project in 1994. In the
project, Prof. Hirao first concentrated on analyzing glass
structures through computer simulations in which he always
focused on the thermal vibrations of constituent atoms
of glass. He thought that interesting results might come
out by applying a laser with a pulse width shorter than
the atomic vibration periods to the atoms to prevent the
exposed laser energy from being converted into heat. He
used a femtosecond laser with a pulse width of 10^-13 seconds,
which is shorter than a thermal vibration period of atoms,
10^-12 seconds. Since a femtosecond laser emits very highly
condensed energy for a very short period of time, it can
irradiate a very small spot of transparent glass with a
very powerful laser light. When glass was exposed to the
femtosecond laser, it did not crack and the structure around
the glass's focal point changed. As a result, the refractive
index for light at the area drastically changed. He found
that an optical fiber can be formed inside glass by moving
the focal point of the laser. The laser through a polarized
lens can also precipitate very tiny crystals at the focal
point in glass and draw a circuit pattern with 10 nm-wide
lines. This level of line width is much finer than the
diffraction limit of light.
These developments have been creating a great sensation
among researchers worldwide. Various fine crystals such
as silicon, carbon, metal and metal oxide can be precipitated
inside glass, which depends on elements dissolved into
the glass. Prof. Hirao's team has been studying the development
of both three-dimensional light guides and electrical
circuits with the processing technology based on the
femtosecond laser. The new devices could transmit a
much larger volume of information much faster than
the present semiconductor-based devices.
Prof. Hirao is the leader of the Nanoglass Project of
the New Energy and Industrial Technology Development Organization
(NEDO) and the Photon Craft Project of the Japan Science
and Technology Agency (JST).
In the Nanoglass Project, a 50 to 70 nm-thick nanoglass
film with uniformly dispersed nanocrystals of Co3O4 is
formed on an optical disc through a sputtering method.
Its refractive index changes depending on the strength
of the blue laser beam, and the glass film works like a
converging lens. This technology halves the diameter of
the laser beam so that the disc's data recording density
quadruples. Prof. Hirao's Nanoglass Project team aims to
record 350 GB of data onto a 12 cm- diameter optical disc,
which is as large as current CDs and DVDs, by utilizing
the technology. The team has also developed the so-called "Super
Prism," of which wavelength resolution is 10 times
as fine as those of ordinary prisms presently used in optical
communications. To develop the super prism, the team first
formed glass film through the CVD and then fabricated a
structure with a period almost as long as light wavelengths
on the glass film using semiconductor lithography technology.
In the Photon Craft Project, which is a joint research
with Chinese researchers, Prof. Hirao's team is developing
high- performance light-emitting devices, optical switches
and optical modulators by making use of the femtosecond
laser processing technology.
Prof. Hirao says, "Basic research on nanoglass is
undoubtedly important. However, now is the time for commercializing
nanoglass products. We need to develop various excellent
products not only through cooperation with researchers
around the world but also through competition with them." He
adds that many small and mid-size companies are working
hard to develop nanoglass products as well as large companies. "Now
is a great time for researchers to create new things in
this area, due partly to the slumping IT sector, for which
many people once had high expectations. Researchers can
have big dreams in the nanoglass area and the age of optical
technology is sure to arrive,"he says. The era in
which glass will replace semiconductors is just around
the corner.
(Interviewer: Naoko Nishimura, Cosmopia Inc.)
For more information,
http://www.nanonet.go.jp/english/mailmag/2005/050a.html
