According to our Special Topics analysis on photonic
crystals, the work of Professor Susumu Noda ranks at #5,
with 89 papers cited a total of 2,293 times. InEssential
Science IndicatorsSMfrom
Thomson
Reuters, Professor Noda's citation record includes 453
papers, mostly classified in the fields of Physics and
Materials Science, cited a total of 7,515 times between
January 1, 1998 and August 31, 2008.
Professor Noda hails from Kyoto University, where he heads up the
Quantum Optoelectronics Laboratory and is a leader in the program on
"Photonics and Electronics Science and Engineering."
In the interview
below, ScienceWatch.com talks with Professor Noda
about his work in photonic crystals.
Please tell us a little about your research
and educational background.
I received B.S., M.S., and Ph.D. degrees from Kyoto University, Kyoto,
Japan, in 1982, 1984, and 1991, respectively, all in electronics. From 1984
to 1988, I was with the Mitsubishi Electric Corporation, where I studied
semiconductor lasers called distributed feedback (DFB) lasers with one
dimensional (1D) periodic refractive index distribution, and also crystal
growth technology (molecular beam epitaxy).
In 1988, I joined Kyoto University as an assistant professor and became a
full professor in 2000. I am currently serving also as a leader of Kyoto
University Global Center of Excellence (GCOE) program on "Photonics and
Electronics Science and Engineering." After joining Kyoto University in
1988, I extended my research areas to more general photonics and
optoelectronics including ultrafast nonlinear optical phenomena and
optoelectronic materials and devices. In particular, in the early 1990s, I
started research on photonic crystals with 2D and 3D periodic refractive
distribution by extending my previous work on DFB lasers with 1D periodic
refractive index distribution.
"Compact light sources with a range
of beam patterns are important for progress
in several areas, including optical tweezers,
micro-fluidics, ultrahigh-density optical
memories, and related
photonics."
I have been fortunate to receive several awards, including the OSA Joseph
Fraunhofer Award/Robert M. Burley Prize (2006), an honorary degree from
Gent University, Gent, Belgium (2006), IEEE Distinguished Lecturer awards
(2005), IEEE Fellow awards (2007), the Japan Society of Applied Physics
Achievement Award on Quantum Electronics (2005), and the IBM Science Award
(2000).
What prompted you to study photonic
crystals?
Photonic crystals are a kind of nanostructures for light with a periodic
refractive index distribution described above. A photonic bandgap, which
blocks photons in certain wavelengths, is formed as an analogy of
solid-state crystals. By controlling the photonic crystal structures, novel
manipulations of photons in all aspects of optical phenomena including
photon emission, propagation, amplification, storage, and interaction with
other materials are expected to be realized. The existence of the photonic
bandgap itself in a periodic refractive index distribution was discovered
about 120 years ago. The importance of 3D periodicity was then pointed out
in 1987 for light emission control. However, the realization of 3D photonic
crystals had been very difficult in optical regime because the optical
wavelength size nanotechnology is required. Thus, the developed crystals at
the initial stage of the photonic crystal research had been limited to the
"microwave" regime, even though the word "photonic" was used. In other
words, the photonic crystals had been a kind of "a pie in the sky."
Therefore, the most important and urgent issue was to realize photonic
crystals at optical regime.
This fact strongly prompted me to study photonic crystals, especially to
realize true "photonic" crystals. My experience on the study of the DFB
laser with 1D periodic refractive index distribution also pushed me in that
direction. In 1999, after various trials and errors, we succeeded in
developing 3D crystals with a complete bandgap by stacking GaAs stripes
with the period of 700nm with the accuracy of <50nm based on our own
nanotechnology. The crystals showed unprecedented optical rejection of
–40dB and were proved to possess complete bandgap at 1.55µm
region. The result was published in Science in 2000, and was
highlighted as the realization of the world's foremost crystals.
After this success, we have extended and deepened the works on photonic
crystals in all aspects and found various interesting phenomena and new
concepts, which include spontaneous emission control (Science 305:
227-229, 2004; Science 308: 1296-1298, 2005), photonic
nanostructure devices (Nature 407: 608-610, 2000; Science
300: 1537, 2003), high-Q photonic nanocavities (Nature 425:
944-947, 2003; Nature Materials 4: 207-210, 2005; and Nature
Photonics 1: 449-458, 2007), and novel photonic crystal lasers
(APL 75: 316-318, 1999; Science 293: 1123-1125, 2001;
Nature 441: 946, 2006; and Science 319: 445-447, 2008).
Some of them are described more in detail here in later answers.
A key paper in your publications is the 2000
Nature paper, "Trapping and emission of photons by a single
defect in a photonic bandgap structure," (407 [6804]: 608-10, 5
October 2000)." Would you sum up the major points of this paper for
our readers?
This paper concerns 2D photonic crystals. In this case, one of the most
important issues was how to confine light for the vertical direction. We
found that quasi-3D confinement of light becomes possible by using a slab
structure with appropriate thickness, refractive index contrast, and
designed lattice structures from the knowledge obtained through work on 3D
photonic crystals. We then demonstrated a very unique phenomenon of
"trapping and emission" of photons by a point-defect nanocavity formed at
the vicinity of a line-defect waveguide. This phenomenon indicates that
photons can be introduced and/or extracted through a tiny nanocavity. This
is the achievement discussed in this paper.
This work was highlighted as "Defects boost optical communication" (Physics
Web). In addition, we further introduced a new concept of "In-plane
Heterostructure" in 2D photonic crystals and succeeded in developing
photonic nanostructure devices (Science 300: 1537, 2003) with a
function of multiple wavelength channel add/drop function. I believe that
these works became an important step for the realization of a full
photonic-crystal network with waveguides, nanocavities, etc., and is one of
the holy grails in nano-optics.
Your most-cited paper in our analysis is the 2003
Nature paper, "High-Q photonic nanocavity in a
two-dimensional photonic crystal," (425 [6961]: 944-7, 30 October
2003). Would you talk a little bit about this paper and its
significance for the field?
In the photonic crystal nanocavity described in the answer to question #3,
the cavity Q was limited to around several hundreds. If the Q factor of
nanocavities can be increased significantly while keeping their very small
modal volume V, it should have a significant impact in broad areas of
physics and engineering, including coherent electron-photon interactions,
ultra-low threshold nanolasers, photonic chips, nonlinear optics, and
quantum information processing. This is because Q/V determines the strength
of various cavity interactions; an ultra-small cavity enables large-scale
integration and single-mode operation for a broad range of wavelengths.
However, a high-Q nanocavity of optical wavelength size had been difficult
to build, since radiation loss increases in inverse proportion to cavity
size.
In the 2003 Nature paper, we reported an important concept that
"light should be confined gently to be confined strongly." More precisely,
the form of the cavity electric field distribution should vary slowly,
ideally as described by a Gaussian function, in order to suppress
out-of-slab photon leakage. Based on this concept, we demonstrated a
nanocavity with Q=45,000 and V=7.0x10-14cm3, or Q/V=6.4x1017cm-3, a factor
10 to 100 times larger than in previous studies. Currently, the Q of
nanocavities has been increased up to 2,500,000 by extending this concept
(also see our paper, Nature Materials 4: 207-210, 2005; Nature
Photonics 1: 449-458, 2007; and Optics Express 15:
17206-17213, 2007). Fortunately, these works have had significant impact to
the aforementioned various fields, and many researchers are currently using
our cavities.
One of your more recent papers is the 2006
Nature paper, "Lasers producing tailored beams," (441: 946,
June 22, 2006). Would you discuss the findings of this work?
In the answer to question #4, I have explained that photonic crystals are
very useful for confining photons in an ultra-small volume of wavelength
size. The photonic crystals can also manipulate photons nicely in a broad
area. The 2006 Nature paper describes such a broad-area control of
photons. More concretely, this paper reports on an unprecedented type of
lasers that can produce a tailored beam on demand while keeping stable
single longitudinal and lateral mode.
Compact light sources with a range of beam patterns are important for
progress in several areas, including optical tweezers, micro-fluidics,
ultrahigh-density optical memories, and related photonics. For example,
lasers with single- or multiple-doughnut beams are important for the
manipulation of both transparent and non-transparent materials. Lasers
possessing a single-doughnut beam having radial polarization are important
for light sources with super-resolution, which can be focused to a size
much less than the wavelength. In addition, lasers with a circular
single-lobed beam have useful applications in many existing optical
systems.
"By controlling the photonic crystal
structures, novel manipulations of photons in
all aspects of optical phenomena including
photon emission, propagation, amplification,
storage, and interaction with other materials
are expected to be
realized."
The 2006 Nature paper describes that such very unique and
important lasers can be actually produced: A range of beam
patterns—including doughnut, twin-doughnut, quadruplet-doughnut,
shifted-doughnut, and circular single-lobed beams—were successfully
produced while maintaining stable single-mode oscillation. The principle of
the lasers is based on "band edge effects in 2D photonic crystals, where a
2D broad area cavity mode is constructed" and "design of unit cell
structures and lattice phases." These findings suggest a new direction for
semiconductor lasers, and could allow the realization of compact lasers
capable of producing diverse beam patterns as required. In addition, due to
the capability of broad area coherent oscillation, ultrahigh power stable
single-mode lasers could be realized by extending these results.
What are the practical applications (or hoped-for
applications) for photonic crystals? And, where do you see this field
going in 10 years?
The photonic crystal lasers described in the answer to question #5 are one
of the most important candidates for practical applications. These lasers
have unprecedented features as described above: first, perfect, single
longitudinal, and lateral mode oscillation can be achieved even when the
lasing area becomes very large; and second, the polarization mode and the
beam patterns can be controlled while keeping single mode oscillation by
appropriate design of the unit cell and/or lattice phase in the photonic
crystal; and thirdly the output can be emitted to the direction normal to
the device surface (namely, the device has a surface-emitting function) and
2D arrays are straightforward. Very recently, we have succeeded in lasing
oscillation in blue-violet wavelength region (Science 319:
445-447, 2008).
This would open the door to a much broader range of applications. For
example, super-high-resolution light sources that could be focused to a
spot smaller than blue-violet wavelengths could be made available by the
use of doughnut beams. This would lead to the realization of post-blue
lasers, as well as optical tweezers for ultra-fine manipulation.
Furthermore, blue-violet surface emitting lasers could find uses in a
variety of new areas, including micro-operation to nano-operation in
biological and/or medical fields.
The ability of photonic crystals in light emission control is also very
important for practical applications. Right now, solid lighting is one of
the most important research fields, and the efficiency of light-emitting
diodes should be as high as possible. The photonic crystal technology will
definitely contribute to increase such light-emission efficiency.
It is expected that, over the next 10 years, nano-processing technology
will further advance, and that more reliable and precise devices will
continue to be developed. In the case of 2D photonic crystal slabs, there
is the promise of remarkable advances in Si-based systems, together with
progress in integration with electronic circuits. Further advances can be
expected in combined optical and electronic circuits equipped with features
such as optical switching, tuning, and delay functionality. It is expected
that the main components of such circuits will be optical, and
optical/electronic chips will be developed. There is no doubt that the size
and power consumption of such devices will be more than hundreds of times
smaller than they are now.
Advances in a large number of applications can also be expected, where
ultra-high Q nanocavity would be utilized for one of the most important key
elements for stopping light, quantum communications and informatics.
Actually, currently, the studies on the combination of nanocavities and
quantum dots are becoming the very active research fields. Dynamic control
of photonic crystal nanocavity has also started to be achieved in very fast
time range (see our paper Nature Materials 6: 862-865, 2007).
It is expected that the technology available for the fabrication of 3D
photonic crystals, which are considered to be more difficult to fabricate
than 2D crystals at the present time, will also advance over the coming
decade, and that 3D crystals will witness completely new levels of light
control that will also enable intricate 'complete control of
fields."
Professor Susumu Noda
Quantum Optoelectronics Laboratory
Department of Electronic Science and Engineering
Graduate School of Engineering
Kyoto University
Nishikyo-ku, Kyoto, Japan
Noda S; Chutinan A; Imada M, "Trapping and emission of
photons by a single defect in a photonic bandgap
structure," Nature 407(6804): 608-10, 5 October
2000. Source:
Essential Science Indicators from
Thomson
Reuters.