「様式３」P-43

Development of Infrared sensor based on 3D photonic crystal[1] Organization

still a challenging task, and in this project we aim atrealizing artificial 3D photonic crystal structures capableof such “wavelength conversion” mechanism using a
rapid prototyping technique called Direct Laser Write(DLW). The principle of DLW fabrication in photoresist isexplained in Fig. 2.
The main research focus during this year was realizationof the structural color phenomenon in the fabricatedphotonic crystals, because structural color is the mainprerequisite to realization of the IR sensing mechanism
described above. In this report we describe our efforts intheoretical and experimental studies of the structural color
phenomenon.

Leader：Prof. Junko Morikawa（Tokyo Institute of Technology）
Representative：Prof. Vygantas Mizeikis
Research Institute of Electronics, Shizuoka
University, Japan）
Participants：
Prof. Kestutis Staliunas(Universitat Politecnica de Catalunya (UPC),
Fisica i Enginyeria Nuclear, Barcelona, Spain)
Dr. Mangirdas Malinauskas (VilniusUniversity,)Department of Quantum Electronics[3] Results
Prof. Saulius Juodkazis (Centre of Microphotonics,Swinburne University of Technology, Melbourne,
Australia)(3-1) Research results
Prof. Kamen Kanev (Department of Computer
Science, Faculty of Informatics, Shizuoka
Practical realization of devices based on the above
University, Japan)
principles requires coordinated studies in several areas ofresearch, such as nanophotonics, micro-/nano-fabrication,
thermal imaging, and polymer science, represented by the[2] Research progress
participants of this project and their respective resereachgroups. To promote collaboration, a mini workshop
This joint research project pursues development ofinfrared (IR) sensor capable of high-sensitivity uncooled
operation, all-optical remote readout, and integration into
micro-scale systems. The sensing mechanism is based on
3D photonic crystal structure, whose resonant reflectanceband is tuned to visible spectral range, and can bemodified by infrared irradiation absorbed by the photonic
crystal lattice thus allowing to perform infrared sensing bymonitoring visible reflectivity of the sensor. Suchsensitivity was discovered first in some naturally existing
PhC structures, such as blue scales covering wings ofMorpho butterflies, whose resonant reflectance band atvisible wavelengths (λ ≈ 450nm) becomes modified in
the presence of IR radiation. The principle of IR sensitivity
is illustrated schematically in Fig. 1.
However, since naturally existing biological systems can
not be easily integrated into practical devices, artificial
structures exhibiting similar IR sensitivity must beprepared. However, fabrication of 3D PhC structures isFig. 1. IR sensitivity mechanism in natural and artificial
in PhCs: (a) in natural Morpho butterfly wing, (b) inartificial 3D PhC structure, (c) modification of visible
optical reflectivity of the PhC due to IR irradiation.

entitled “Applications of Infrared, Visible, and X-ray
Beams for Fabrication and Imaging ” was organized onFebruary 1, 2016 at the Research Institute of Electronics,
Shizuoka University. The workshop was attended byparticipating researchers, as well as interested guests andstudents.
Presentations and discussions during the workshop were
centered on the following topics:
A. Fundamental studies of structural color phenomenon
The biomimetic new materials based on the Morpho
butterfly, which produce highly reflective blue coloration.
The brilliant blue color of the Morpho butterfly has been aphysical mystery, which has a single color in too wideangular range (> ± 40° from the normal) despite theinterference effect. The key to solve the Morpho-blue's
mystery having both interference and a single color inwide angular range is a peculiar optical nanostructure on
their scales. This principle is based on a skillfulcombination of two opposed characters, the ordered anddisordered nanostructures.
After proven the principle of the mystery by emulating thespecific nanostructures of their scales by extracting theoptical essence, we found the reproduced Morpho-color toserve wide applications, because it can produce a
conspicuous single color in wide angular range with highreflectance without any chemical pigment, which is alsoFig. 2. Optical setup for DLW fabrication of PhC
structures in photoresist.

resistant to fading caused by chemical change for longtime.
Thus, we have developed various technologies forpractical applications of the specific color, such as
mass-production processes, large-area fast fabrication,
production of RGB colors, control (both in the reflective
angles and in spectra) and simulation of their opticalproperties.
One of the remaining key issues is to produce thesubstrate-free color materials such as micro-powders,
because all processes have long been accompanied withthe thick substrate designed with a specific nanostructure,
which has fatally limited the variety of applications. We
developed a simple process to fabricate the color powders.
This process will extend effectively the applications of theMorpho-color, which enables the coloring without any
limit of shape.
Another remaining problem is how to complete thelarge-area fabrication process. The key point is how toFig. 3. Control of the structural color in 3D woodpilephotonic crystals, (a) optical microscopy images of 3D
woodpile PhC structures with different lattice periods
fabricated at different exposure levels exhibit different
colors in reflectance, (b) visible reflectivity spectra ofthese structures exhibit the corresponding spectral
variations.

produce the nanopatterns in large area, easily and quickly.
One of the candidate processes is the laser ablation,
whereas some difficulties have been found inreproducibility. We discussed about how to solve thisproblem using our own possible facilities by limited
man-powers and time. Our collaboration will be apotential good solution for this problem.
The last issue is how to realize the FDTD simulations in
3D by use of standard personal comupters (PC). Certainly,
we have succeeded in revealing the specific optical role ofthe nano-disorder in the Morpho-nanopatterns, whereas
we need still more realistic 3D simulations, which requires
unrealistic long time for our present PCs. We discussed
about the potential countermeasures to overcome thisdifficulties.
In future, a variety of applications are relevant to thestructural color: cosmetics, decorations, textures, paints,security (such as hologram), etc. Especially, in case of theMorpho-type color, it realizes both of wide reflective angle
and high reflectivity that are usually not compatible witheach other. These characters are fit well to the use ofposters or displays.
B. Practical realization of PhC structures exhibiting
structural color by DLW technique in photoresist.
3D architecture woodpile photonic crystals werefabricated by femtosecond DLW lithography inphotoresist, and their optical properties were characterisedby micro-reflectance spectroscopy at visible and nearinfrared wavelengths. The results are summarized in Fig. 3.
The fabricated structures were found to exhibit resonant
optical reflectance at wavelengths corresponding tohigh-frequency photonic bands, where opening ofphotonic stop gaps is not expected. The visible reflectanceleads to structural color that can be controlled
experimentally via photonic crystal lattice period anddielectric filling ratio. According to theoretical analysis andnumerical simulations of sample reflectance spectra andphotonic band diagrams, resonant reflectance and visible
coloration of the samples can be associated with coupling
losses which occur when plane waves incident fromoutside become converted to strongly dispersive, lowgroup velocity Bloch modes of the photonic crystal. Thisphenomenonis useful from the practical viewpoint, since it
occurs at high frequency/short wavelength, and allows
realisation of stuctural color in samples with relatively
large lattice periods a ≈ 1 μm. Consequently, requirement
for high resolution of 3D fabrication becomes somewhat
relaxed, and fabrication time becomes shortened. Discrete
photonic crystals exhibiting structural color may be usefulin photonic crystal-based environmental and imagingsensors.
(3-2) Ripple effects and further developments
Exchange of scientific expertise between the participants
was very helpful for coordination of experimental andtheoretical work towards the goal of this project. Also, it
has contributed to strengthening of domestic andinternational collaboration at Research Institute ofElectronics.
It must be also stressed that joint work of all participants
during the mini-workshop and informal discussions
have broadened the scope of existing domestic andinternational research collaborations at RIE, as well as
opened new venues for collaboration in the future.
[4] Achievements
Scientific articles:(1) M. Malinauskas,A. Zukauskas,Y. Hasegawa,V.
Hayasaki,V. Mizeikis, R. Buividas, S. Juodkazis,“Ultrafast laser processing of materials: from science toindustry”, Light: Science & Applications , accepted(2016).

Travelling report
Name:
Affiliation:
Period of time:
Destination:
Purpose:Name of receiver:Prof. Saulius Juodkazis
Centre of Microphotonics, Swinburne University of Technology, Melbourne, Australia
2016.01.31-02.04
Shizuoka University, JapanTo carry out a joint research, plan the future collaboration, participate at the mini-workshop andreport previously obtained results.
Prof. Vygantas Mizeikis