summary of my talk:
Photonic nanostructures, i.e. photonic crystals (PCs) and high index
contrast structures (HICs), have attracted attention in this decade.
They strongly control light emission and propagation, and so allow novel
phenomena and applications. Recently, they are particularly discussed
with other topics such as nanolaser, slow light, negative refraction,
and Si photonics. My presentation reviewed our research activities on
The PC nanolaser has been expected as a high-efficiency and high-speed
light source in a photonic chip. Two key issues are the small modal
volume and high Q. We employed a point-shift nanocavity consisting of
only the shift of two neighboring holes in a PC slab. Its cavity mode
has an extremely small volume of 0.2 times the cubic wavelength, which
is close to the optical diffraction limit. We fabricated it into 1.55-mm-GaInAsP
QW slab and obtained the room temperature cw lasing by photopumping
with an effective threshold power of nearly 1 micro-watts. For this
cavity, we also observed the spontaneous emission enhancement due to
the Purcell effect and the nearly thresholdless operation. In the photonic
chip, such nanolasers must be integrated with passive components. We
integrated them with 1.30-mm-GaInAsP passive PC waveguides using MOVPE
buttjoint regrowth process, and obtained a practical value of external
quantum efficiency of 8%.
Slow light in the PC waveguide is of great interest due to its potential
for optical buffering and enhancement of the light-matter interaction.
However, a narrow bandwidth and large group velocity dispersion are
serious problems that disturb its practical use. We have proposed some
modified PC waveguides for wideband and dispersion-free operation. For
example, dispersion-compensated slow light with a group index (= slowdown
factor) of 35 - 40 in a wide wavelength range of 35 nm was obtained
a directional coupler of chirped PC waveguides with opposite dispersions.
The zero-dispersion slowlight was also demonstrated by some minute control
of waveguide structure.
Negative refractive optics has become a hot topic with metamaterials.
However, those based on PCs are advantageous for lightwaves as they
are free from absorption loss. We successfully observed superprism and
superlens effects of negative refractive optics in a SOI PC slab by
optimizing I/O interfaces for low reflection and diffraction losses.
The superlens is unique because it focuses light at the flat surface,
and forms a real image inside the PC. This means that the focusing characteristics
are independent of the input position of light. A compact wavelength
demultiplexer and parallel optical coupler were demonstrated as applications
of this lens.
In parallel with PCs, the Si photonics is increasing importance for
intra-chip optical interconnects and low-cost and compact photonic lightwave
circuits. The HIC Si wire waveguide allows sharp bends and micro-optic
components due to the strong optical confinement. In addition to these
components, we have demonstrated a very compact H-tree optical signal
distribution circuit and AWG demultiplexer whose footprint was less
than 100 micron square. By carefully optimizing the connection between
elements, the sidelobe level and device loss were reduced to less than
-20 dB and 1.5 dB, respectively, and the polarization-insensitive characteristics
were also obtained. It will be a practical device for course WDM.
Short summary of my travel:
I visited all the LEOS chapters that invited me, as long as their meeting
plan fit to my schedule. The following summarizes the date, chapter,
city, place of meeting, organizer of meeting, special note of my trips.
(1) 08/09/06, Japan, Tokyo, Kozai Kaikan, Y. Yoshikuni, I started my
year term from Japan with other two DL lecturers Prof. M. Selim Ünlü
and Dr. M. Notomi.
(2) 13/10/06, Ottawa, Ottawa, National Research Council, K. Liu, It
was just after OSA annual meeting at Rochester. The audience showed
particular interest on Si photonics.
(3) 08/11/06, Ukraine, Guanajuato (Mexico), Guanajuato University, I.
Sukhoivanov, My talk was scheduled as a formal opening lecture of Multiconference
on Electronics and Photonics.
(4) 13/11/06, Italy, Turin, Avago Technology, T. Tambosso, I was impressed
by the steadiness of their research on semiconductor devices, while
surprised at hearing the low percentage of students in the science and
engineering majors in Italy.
(5) 15/11/06, Italy, Rome, Universitate degli Studi di Roma, A. d’Alessandro,
I gave a lecture in a special class of the university.
(6) 15/03/07, Poland, Lodz, Technical Institute of Lodz, W. Nakwaski,
I also met Prof. M. Marciniak who invited me to International Conference
on Transparent Optical Network on June.
(7) 19/03/07, Hampton Roads, Norfork, Old Dominion University, A. Dharamsi,
I gave a lecture for undergraduate and younger graduate students of
(8) 20/03/07, Washington/Northern VA, Washington DC., University of
Merryland, M. Dagenais, I enjoyed seeing some research activities on
bio-sensing and cavity QED of the University.
(9) 21/03/07, Rochester, Corning, Corning Research Center, S. Garner,
I saw the history of Corning and recent research on bio-sensing applications.
(10) 14/05/07, Albuquerque, Albuquerque, University of New Mexico, Y.
D. Sharma, An image sensor in the wavelength range from 3 to 10 microns
and auto-tracking system of laser beam were demonstrated at the visit.
(11) 16/05/07, Central New England, Boston, Boston University, M. Cabodi,
A one day symposium on nanophotonics was held, and I and Dr. M. Notomi