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  Nanospheres
which all equal in size will be self-organized from a suspension into
orderly, hexagonally packed crystalline lattices in two or three dimensions,
called colloidal crystals (see Figure 1). These lattices can show
unusual optical insulating behavior against light wave in certain
range of wavelengths (Photonic Band Gaps, PBG) like semiconductors
in electronic microcircuit, which are called 'photonic
bandgap materials.' Such behavior of photonic bandgap
materials arises from cooperation of periodic scatterers in every
lattice point (multiple light scattering).
 According
to theories, optical properties of such photonic crystals could be
significantly influenced by characteristics of each scatterer including
size, shape and refractive index distribution. Due to practical limitation
thus far, monodisperse nanospheres of isotropic scattering points
have been used for demonstration of colloidal opal structures or their
inverse structures as three dimensional photonic crystals (see Figure
2). However, it is still challenging to create practically useful
structures for photonic crystals application in spite of a few successful
experimental fabrication of 3D photonic crystals of spherical building
blocks. This is because such dielectric crystals of spherical lattices
do not exhibit a complete but just pseudo PBG behavior and their inverse
structure have also shown narrow photonic band gaps, which may be
practically meaningless for highly integrated photonic chips. Therefore,
it is necessary to produce more complex building blocks and novel
fabrication route for their assembly, which is promising for photonic
crystals of practical significance.
During last a few years, we have conducted research on the fabrication
of such novel building blocks and their assemblies and developed a
number of clever approaches including soft-microfluidics, electrospraying
or aerosol generation, micropipette injection, etc. (Figure 3,4)
 
Our collaboration groups are as follows.
 MRL
in UCSB
CSEM
in Caltech
Nanolaser
group in KAIST
LAMP
in KAIST
LaSIE
in Osaka University
Applied
Mechanics Group in Harvard University
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Research
Overview
