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- Front Matter: Volume 8258
- Photonic Materials
- Bio-photonics
- Solar Cell and OLED I
- Solar Cell and OLED II
- Organic Transistors and Lasers
- Miscellaneous
- Electro-Optics
- Nonlinear Optics
- Optical Fiber and Waveguide Devices I
- Optical Fiber and Waveguide Devices II
- Grating Formation
- Poster Session
Front Matter: Volume 8258
Front Matter: Volume 8258
Show abstract
This PDF file contains the front matter associated with SPIE Proceedings Volume 8258, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.
Photonic Materials
Tuning the refractive index of blended polymer films by RIR-MAPLE deposition
Show abstract
Graded index polymer films enable novel optics using rigid or flexible substrates, such as waveguides or anti-reflection
coatings. Previously, such films have been fabricated by nanoimprint lithography or the decomposition of a single
component in polymer blends. Yet, it is desirable to have precise control over the polymer film composition in order to
have the most flexibility in designing refractive index profiles. Resonant-infrared matrix-assisted pulsed laser
evaporation (RIR-MAPLE) is a polymer thin film deposition technique that enables multi-layer structures on a wide
variety of substrate materials, regardless of the solubilities of constituent polymers. In this work, the feasibility of tuning
the refractive index of blended polymer films of polystyrene and poly(methyl methacrylate) deposited by RIR-MAPLE
is demonstrated. Different polymer blend film compositions are deposited using RIR-MAPLE by varying the polymer
target ratio. Transmission electron microscopy and atomic force microscopy are used to characterize the film
morphology.
Bio-photonics
Nanocrystalline cellulose for covert optical encryption
Show abstract
Nanocrystalline cellulose solid films derived from spruce pulp exhibit iridescence when cast from chiral nematic
aqueous phase suspensions of the nanocrystals. Iridescence is a color travel phenomenon that might have potential for
overt encryption as an anti-counterfeiting measure. The iridescent phase also offers an intrinsic level of covert
encryption by virtue of the fact that films of NCC reflect left-circularly polarized light. Addition of TINOPAL, an
optical brightening agent (OBA), adds a third level of (covert) encryption potential since the chromophore exhibits
strong fluorescence when excited at ultra-violet wavelengths. The overall result is a selectively polarizing fluorescent
iridescent film. We study the impact of additions of OBA on NCC iridescence, optical activity, and physical structure
variation with polarized optical microscopy, circular dichroism spectropolarimetry and zeta potential analysis. Increasing
OBA additions increase the chiral nematic pitch of NCC films, and this in turn alters chiral nematic domain structure in
the solid film. Under low concentration conditions defined by our experiments, OBA yields intense UV fluorescence,
without compromising the visible light iridescent properties of the film. The potential security offered by NCC and its
optical responses can be authenticated using a UV light source such as is commonly used for banknote verification, a
circular polarizer in conjunction with an iridescent feature which can be verified by the eye or by chiral spectrometry.
Solar Cell and OLED I
Carrier mobility characterization of DNA-surfactant complexes
Ting-Yu Lin,
Yu-Chueh Hung
Show abstract
Deoxyribonucleic acid (DNA) biopolymer has been emerging as a promising material for photonic applications. As
many optoelectronic devices rely on carrier transportation to achieve desired functionality, carrier mobility is important
for the exploitation of these biopolymer-based materials for practical implementation. In this study, we present the
mobility measurement by employing time-of-flight technique and characterize the current-voltage (I-V) properties based
on DNA-surfactant complexes. An additional NPB layer was introduced in the fabricated structure to serve as a charge
generation layer (CGL). The dependency of hole mobility with respect to the applied electric field was characterized and
a linear correlation was exhibited. Hole transport was found to be dispersive, indicating a high degree energetic disorder
in these DNA-surfactant complexes. The characterization results show promises for the employment of DNA complexes
in the applications of organic light-emitting devices and organic field-effect transistors.
Solar Cell and OLED II
White organic light-emitting diodes with ultra-thin mixed emitting layer
Show abstract
White light can be obtained from Organic Light Emitting Diodes by mixing three primary colors, (i.e.
red, green and blue) or two complementary colors in the emissive layer. In order to improve the
efficiency and stability of the devices, a host-guest system is generally used as an emitting layer.
However, the color balance to obtain white light is difficult to control and optimize because the
spectrum is very sensitive to doping concentration (especially when a small amount of material is
used). We use here an ultra-thin mixed emitting layer (UML) deposited by thermal evaporation to
fabricate white organic light emitting diodes (WOLEDs) without co-evaporation. The UML was
inserted in the hole-transporting layer consisting of 4, 4'-bis[N-(1-naphtyl)-N-phenylamino]biphenyl
(α-NPB) instead of using a conventional doping process. The UML was formed from a single
evaporation boat containing a mixture of two dipolar starbust triarylamine molecules (fvin and fcho)
presenting very similar structures and thermal properties and emitting in complementary spectral
regions (orange and blue respectively) and mixed according to their weight ratio. The composition of
the UML specifically allows for fine tuning of the emission color despite its very thin thickness
down to 1 nm. Competitive energy transfer processes from fcho and the host interface toward fvin
are key parameters to control the relative intensity between red and blue emission. White light with
very good CIE 1931 color coordinate (0.34, 0.34) was obtained by simply adjusting the UML film
composition.
Organic Transistors and Lasers
Waveguide exciton polaritons in polymer optical waveguides doped with J-aggregating dyes: generation, emission and control
Show abstract
We show that the optical modes of thin polymer slabs doped with J-aggregating dye molecules are strongly coupled
exciton - waveguide photon modes. The hybridization appears as splitting in the dispersion relation of the fundamental
transverse electric (TE) and transverse magnetic (TM) modes of the system. It is shown that these modes can be
controlled by changing the thickness of the optical waveguide and by changing the concentration of the dye molecules.
Leaky conical emission from the strongly coupled modes with radial and azimuthl polarizations is captured.
Reconfigurable visible quantum dot microlasers integrated on a silicon chip
Show abstract
Developing on-chip, dynamically reconfigurable visible lasers that can be integrated with additional optical and
electronic components will enable adaptive optical components. In the present work, we demonstrate a reconfigurable
quantum dot laser based on an integrated silica ultra high-Q microcavity. By attaching the quantum dot using a
reversible, non-destructive bioconjugation process, the ability to remove and replace it with an alternative quantum dot
without damaging the underlying microcavity device has been demonstrated. As a result of the absorption/emission
characteristics of quantum dots, the same laser source can be used to excite quantum dots with distinct emission
wavelengths.
Towards polarization controlled organic micro-lasers
Show abstract
In this work we study optically pumped polymer-based lasers doped by various organic dyes in two different
configurations, namely plane cavities of various shapes and vertical external cavities ("VECSOL"). The intrinsic
fluorescence anisotropy of specific dye molecule together with the polarization state of the pump beam defines the basic
emission properties of such dye-doped polymer system. The nonlinear enhancement of amplified spontaneous emission
(ASE) and lasing results in the forcing of the emission properties and particularly of their polarization features. However,
we demonstrate experimentally that it is possible to release this constraint and to obtain laser emission with a
polarization state different from that of the pump.
Miscellaneous
Photonic applications of photochromic molecules
Show abstract
We present results of studies of the systems containing photochromic molecules, for all-optical switching and amplified
spontaneous emission applications. The systems consisted of: a) deoxyribonucleic acid doped with different
photochromic molecules like Disperse Orange 3 or spiropyranes, and b) photochromic molecules of 4-heptyl-4'-
methoxyazobenzene showing nematic liquid crystalline properties close to the room temperature (above T = 34° C).
Experiments of dynamic birefringence switching were done in Optical Kerr Effect set-up, where for the sample
excitation chopped cw or picosecond pulsed lasers were used. An excellent switching times and reversibility of the
studied processes have been observed. The amplified spontaneous emission in luminescent dye doped biopolymeric
system was achieved under the sample excitation by UV light pulses (355 nm) coming from pulsed Nd:YAG laser.
Reversible multi-color electrofluorescence switching
Show abstract
The color of the electrofluorescence switching device was tuned to white by adding extra electroactive
fluorophores with different emission colors. The reversible electrochemistry of fluorophores between neutral
and anion radical was accompanied by fluorescence on and off, respectively, allowing fluorescence switching.
Since the fluorophores have different emission color and also different redox potential, emission color could
be further modified by quenching of the particular emission with precise voltage control. A reversible multicolor
switching device was prepared by packing electroactive fluorophores blend of polymer electrolyte
between ITO electrodes, and its emission color was examined with various fluorophore contents and
potentials.
Organic nanofibers from squarylium dyes: local morphology, optical, and electrical properties
Show abstract
Environmentally stable, non-toxic squarylium dyes with strong absorption maxima in the red and near infrared
spectral region are known for almost fifty years. Despite the fact that their optoelectronic properties distinguish
them as promising materials for organics based photovoltaic cells, they have regained attention only very
recently. For their application in heterojunction solar cells knowledge of their nanoscopic morphology as well
as nanoscopic electrical properties is paramount. In this paper thin films from two different squarylium dyes,
from squarylium (SQ) and from hydroxy-squarylium (SQOH) are investigated. The thin films are either solution
casted or vacuum sublimed onto substrates such as muscovite mica, which are known to promote self-assembly
into oriented, crystalline nanostructures such as nanofibers. Local characterization is performed via (polarized)
optical microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and Kelvin probe
force microscopy (KPFM).
All printed touchless human-machine interface based on only five functional materials
Show abstract
We demonstrate the printing of a complex smart integrated system using only five functional inks: the fluoropolymer
P(VDF:TrFE) (Poly(vinylidene fluoride trifluoroethylene) sensor ink, the conductive polymer PEDOT:PSS (poly(3,4
ethylenedioxythiophene):poly(styrene sulfonic acid) ink, a conductive carbon paste, a polymeric electrolyte and SU8 for
separation. The result is a touchless human-machine interface, including piezo- and pyroelectric sensor pixels (sensitive
to pressure changes and impinging infrared light), transistors for impedance matching and signal conditioning, and an
electrochromic display. Applications may not only emerge in human-machine interfaces, but also in transient
temperature or pressure sensing used in safety technology, in artificial skins and in disposable sensor labels.
Electro-Optics
Fabry-Perot resonant switch using electro-optic polymer
Show abstract
An electro-optic (EO) switch based on a Fabry-Perot resonator design was fabricated and tested. The switch is comprised
of two high index glass substrates with indium tin oxide (ITO) coated Bragg mirrors, surrounding an electro-optic
polymer layer. The ITO top layers were patterned, the electro-optic polymer, SEO100 (Soluxra Inc.), was spun coat onto
each of the two Bragg substrates, and the two samples were wafer bonded. The sandwich device was then electric field
poled using a field between 80 and 90 V/μm in order to induce a second-order nonlinear optical activity in the electrooptic
polymer. The experimental results done at 1.31 micron laser wavelength with a drive voltage of ±200 volts yielded
a modulation depth of around 86% and 80% for frequencies of 1kHz and 10kHz, respectively.
Solution phase-assisted reorientation of chromophores
Show abstract
Organic electro-optic materials, or "EO polymers," offer much higher nonlinearities than traditional crystalline
materials, making these materials ideal for next generation electro-optic modulators. These materials require an
additional processing step known as poling, which reorients the chromophores through the application of a high electric
field. This effort will focus on corona poling, where a gas is ionized and the electric field across the sample is applied
through the relocation of charged ions. The proposed technique avoids the need to raise the temperature of the material
by applying the electric field while the material is deposited in solution phase. This process can overcome the thermal
stability tradeoff in many organic electro-optic materials, and preliminary results indicate this process results in an
enhancement in the electro-optic activity of the material.
Nonlinear Optics
Nonlinear absorption and nonlinear refraction: maximizing the merit factors
Show abstract
Both nonlinear absorption and nonlinear refraction are effects that are potentially useful for a plethora of applications in
photonics, nanophotonics and biophotonics. Despite substantial attention given to these phenomena by researchers
studying the merits of disparate systems such as organic materials, hybrid materials, metal-containing molecules and
nanostructures, it is virtually impossible to compare the results obtained on different materials when varying parameters
of the light beams and different techniques are employed. We have attempted to address the problem by studying the
properties of various systems in a systematic way, within a wide range of wavelengths, and including the regions of onephoton,
two-photon and three-photon absorption.
The objects of our studies have been typical nonlinear chromophores, such as π-conjugated molecules, oligomers and
polymers, organometallics and coordination complexes containing transition metals, organometallic dendrimers, small
metal-containing clusters, and nanoparticles of various kinds, including semiconductor quantum dots, plasmonic
particles and rare-earth doped nanocrystals. We discuss herein procedures to quantify the nonlinear response of all of
these systems, by defining and comparing the merit factors relevant for various applications.
Poly (cyanophenylene sulfide) as new host materials of second order nonlinear optical polymers
Show abstract
Here, we will propose poly (cyano phenylene sulfide) as novel host materials of nonlinear optical (NLO) polymers. Our
experimental results proved that NLO chromophore-doped PCPS thin films deposited on the metal layers exhibited
second order NLO susceptibilities just by annealing at the temperatures higher than a glass transition point even without
conventional poling procedures. We determined the optimized annealing temperatures and the film thickness for the
nonelectrical poling procedure. The nonelectrical poling procedure was applicable for the films as thick as a few μm.
The second order nonlinear coefficient of was 0.5 pm/V for the PCPS doped with 10w% of 4-[Ethyl(2-
hydroxyethyl)amino]-4'-nitroazobenzene. Taking advantage of the unique polarization self-organization procedure, we
may prepare one- or two-dimensionally periodically poled structures in these materials for the second-order NLO active
photonic crystals pretty easily.
Optical Fiber and Waveguide Devices I
EO-polymer waveguide based high dynamic range EM wave sensors
Show abstract
In this paper, we present the design and experimental demonstration of a high dynamic range electric field sensor based
on electro-optic (EO) polymer directional coupler waveguides that offers the strong and ultra-fast EO response of EO
polymer. As compared to conventional photonic electric field sensors, our directional coupler waveguide design offers
several advantages such as bias-free operation, highly linear measurement response up to 70dB, and a wide electric field
detection range from 16.7V/m to 750kV/m at a frequency of 1GHz.
Optical Fiber and Waveguide Devices II
Photopolymer-based three-dimensional optical waveguide devices
Show abstract
Photopolymer based three-dimensional (3D) waveguide devices are very attractive in low-cost optical system
integration. Especially, Light-Induced Self-Written (LISW) technology is suitable for this application, and the
technology enables low-loss 3D optical circuitry formation from an optical fiber tip which soaked in photopolymer
solution by employing its photo-polymerization due to own irradiation from the fiber tip. This technology is expected
drastic mounting cost reduction in fields of micro-optic and hybrid integration devices assembly. The principle of the
LISW optical waveguides is self-trapping effect of the irradiation flux into the self-organized waveguide, where, used
wavelength can be chosen to fit photopolymer's reactivity from visible to infrared. Furthermore, this effect also makes
possible grating formation and "optical solder" interconnection. Actually fabricated self-written grating shows well
defined deep periodic index contrast and excellent optical property for the wavelength selectivity. And the "optical
solder" interconnection realizes a passive optical interconnection between two faceted fibers or devices by the LISW
waveguide even if there is a certain amount of gap and a small degree of misalignment exist. The LISW waveguides
grow towards each other from both sides to a central point where the opposing beams overlap and are then combined into
one waveguide. This distinctive effect is confirmed in all kind optical fibers, such as from a singlemode to 1-mm-corediameter
multimode optical fiber. For example of complicated WDM optical transceiver module, mounted a branchedwaveguide
and filter elements, effectiveness of LISW technology is outstanding. In assembling and packaging process,
neither dicing nor polishing is needed. In this paper, we introduce LISW technology principles and potential application
to integrated WDM optical transceiver devices for both of singlemode and multimode system developed in our research
group.
Critical angle in fluorescent polymer optical fibers
Show abstract
The aim of this work is to analyze the propagation of the emitted light in fluorescent POFs by using the side-illumination
technique. In particular, we have studied the angular distribution of the emitted light as a function of the launching angle
and of the height of the incident beam. A theoretical model has been developed in order to explain the experimental
measurements. A good agreement between the theoretical and the experimental results has been obtained both
qualitatively and quantitatively. It is shown that both the theoretical and the experimental critical angles are appreciably
higher than the meridional one corresponding to the maximum acceptance angle for a single source placed at the fiber
axis. This increase changes the value of several important parameters in the performance of active fibers. The analysis
has been performed in polymer optical fibers doped with a conjugated polymer.
On-chip sensing of volatile organic compounds in water by hybrid polymer and silicon photonic-crystal slot-waveguide devices
Show abstract
Lab-on-chip integrated infrared spectroscopy and sensing with hybrid polymer and silicon photonic crystal slot
waveguides is demonstrated for the specific and selective identification of volatile organic compounds, xylene and
toluene, in water. A 300 micron long photonic crystal slot waveguide was demonstrated that enabled the detection of
100ppb xylene in water by near-infrared absorption signatures, with five times higher sensitivity on an order of
magnitude smaller length scale. The on-chip absorption spectroscopy, determined by Beer-Lambert absorption law, is
enabled by the combined effects of slow light and high electric field intensity enhancement in photonic crystal slot
waveguides.
Grating Formation
Quickly updatable hologram images with high performance photorefractive polymer composites
Show abstract
We present here quickly updatable hologram images using high performance photorefractive (PR) polymer composite
based on poly(N-vinyl carbazole) (PVCz). PVCz is one of the pioneer materials for photoconductive polymer. PVCz/7-
DCST/CzEPA/TNF (44/35/20/1 by wt) gives high diffraction efficiency of 68 % at E = 45 V/μm with fast response
speed. Response speed of optical diffraction is the key parameter for real-time 3D holographic display. Key parameter
for obtaining quickly updatable hologram images is to control the glass transition temperature lower enough to enhance
chromophore orientation. Object image of the reflected coin surface recorded with reference beam at 532 nm (green
beam) in the PR polymer composite is simultaneously reconstructed using a red probe beam at 642 nm. Instead of using
coin object, object image produced by a computer was displayed on a spatial light modulator (SLM) is used as an object
for hologram. Reflected object beam from a SLM interfered with reference beam on PR polymer composite to record a
hologram and simultaneously reconstructed by a red probe beam. Movie produced in a computer was recorded as a realtime
hologram in the PR polymer composite and simultaneously clearly reconstructed with a video rate.
Grating couplers in polymer with a thin Si3N4 layer embedded
Linghua Wang,
Yanlu Li,
Marco Garcia Porcel,
et al.
Show abstract
Polymer has been considered to be an ideal material option for integrated photonics devices. To measure these devices,
normally the route of horizontal coupling is chosen to couple the light into or out of the polymer waveguide. Due to the
relatively low refractive index, implementing the surface grating coupler in this material system remains to be a
challenge. In this paper, we present a polymer based surface grating coupler. Rather than expensive CMOS fabrication,
the device is fabricated through a simple and fast UV based soft imprint technique utilizing self-developed low loss
polymer material. The coupling efficiency is enhanced by embedding a thin Si3N4 layer between the waveguide core and
under cladding layer. Around -19.8dB insertion loss from single-mode fiber (SMF) to single-mode fiber is obtained for a
straight waveguide with grating coupler at each end. If collected with multi-mode fiber (MMF), it can be reduced to
around -17.3dB. The 3dB bandwidth is 32nm centered at 1550nm. The proposed surface grating coupler and its easy
fabrication method would be attractive for practical applications.
Poster Session
Picosecond polarization spectroscopy of fluorescein attached to different molecular volume polymer influenced by rotational motion
Show abstract
Time-resolved fluorescence polarization spectroscopy of various molecular volume fluorescein dye-labeled polymers
influenced by the molecular rotation motion was investigated by picosecond dynamics measurements. The time-resolved
picosecond polarization spectroscopy was modeled using a system of first-order linear differential equations containing
two main parameters: the decay rate of emission and the rate of one orthogonal emission component transferring to
another. Both experimental observation and theoretical calculation indicate that the fluorescent molecular rotation is the
cause of the depolarization. The dipole's rotational time was extracted and shows increasing with the molecular volume
obeying the Einstein-Stokes relation.
A photo-aligned self-assembled monolayer for polymer transistors
Show abstract
There is a continuing interest in improving electrical characteristics of an organic thin-film transistor (OTFT). One can
accomplish this by controlling molecular orientations of semiconductor materials in the vicinities of an insulating layer
as well as an electrode material. First, it is widely known that a self-assembled monolayer (SAM) is effective for this
purpose. Second, a thin structured layer underneath an organic semiconductor material is effective for aligning the
organic molecules in a specific direction. Irradiating azobenzene compounds with ultraviolet light converts trans isomers
into cis-forms. When exposed to linearly-polarized ultraviolet light, the difference in the absorbance between the two
isomers leads to a state where the azobenzene molecules are aligned perpendicular to the polarization direction of the
ultraviolet light. Such a photo-alignment layer results in anisotropic charge transport in an OTFT and the current flow
along the channel direction is enhanced. In principle, we expect that combination of these two technologies (SAM and
photo-alignment) would further improve the current flow in OTFTs. In experiment, we synthesized a compound 4-(3-
(trichlorosilyl)propoxy)azobenzene (Azo-SAM) and used this material to align an organic semiconductor poly(3-
hexylthiophene) (P3HT). We formed the Azo-SAM on a glass substrate, spin-coated a P3HT/1, 2, 4-trichlorobenzene
solution, annealed in nitrogen atmosphere and exposed it to linearly-polarized ultraviolet light. Absorbance spectroscopy
in the visible range revealed anisotropy in the two samples exposed to the two polarization directions orthogonal to each
other. Fabrication of organic transistors with this photo-alignment SAM is under way.
Vibration-induced mobility enhancement for a polymer transistor
Show abstract
Charge transport in an organic thin-film transistor (OTFT) is controlled by many factors such as molecular packing in the
semiconductor material and the contact property at the source/drain electrode. One approach utilizes an alignment layer
to influence the molecular packing. Charge transport becomes anisotropic. However, additional processes are required
to form such a structured layer. Solution processes offer more pathways in influencing the molecular packing. These
include the use of solvent mixtures for adjusting the evaporation-induced flows, the temperature gradient in molten
materials, drop-casting on tilted substrates, and other flow-induced processes. Common to these approaches is the fact
that some forms of forces introduce directionality in semiconductor materials. Here, we propose to agitate organic
molecules in a solution by applying ultrasound vibrations during the solvent evaporation. The vibration would translate
and rotate the molecules and this might introduce ordering in the organic layer when the solvent evaporation is
completed. In experiment, we fabricated bottom-contact polymer transistors by dispensing a poly(3-
hexylthiophene)/1,2,4-trichlorobenzene solution on a substrate and subsequently drying it in a container immersed in an
ultrasound bath. The average field effect mobility of the transistors prepared from a 0.1wt% solution with 30-min
ultrasound vibration was 2.5 times higher than that of the control devices prepared without the vibration. We attribute
this result to enhanced ordering of the P3HT molecules in the vibrated solution. Atomic-force microscope observation
revealed longer polymer chains for the samples prepared with the vibration. We attribute this mobility enhancement to
changes in molecular packing during the solvent evaporation.
Ultrafast nonlinear optical studies of 3,8,13,18-Tetrachloro-2,7,12,17-tetramethoxyporphyrin and its derivatives
Debasis Swain,
Anup Rana,
Pradeepta K. Panda,
et al.
Show abstract
Recently we synthesized 3,8,13,18-tetrachloro-2,7,12,17-tetramethoxyporphyrin and its metallo-derivatives [1]. The
free-base molecule is unique owing to the presence of an electron donating methoxy group and electron withdrawing
chloro group on the adjacent β- positions of each pyrrole moiety. We could synthesize these molecules through two
different routes; the first route provided pure isomer, albeit in low yield, whereas the second route provided mixture of
isomers with higher yield [1]. Herein we report the third-order nonlinear optical properties of these porphyrins obtained
from Z-scan measurements using ~40 fs, 800 nm pulses. Open aperture data confirmed the presence of saturable
absorption whereas the closed aperture data indicated a positive nonlinearity. We have compared the data of the pure
isomer with that of the mixture of isomers.
Femtosecond and picosecond nonlinear optical studies of Corroles
Syed Hamad,
G. Krishna Podagatlapalli,
L. Giribabu,
et al.
Show abstract
We present our results of nonlinear optical properties of Tritolyl Corrole (TTC) and Triphenyl Corrole (TPC) studied in
the form of solution using Z-scan technique with 660 nm, ~2 picosecond (ps) pulses and 800 nm, ~40 femtosecond (fs)
pulses excitation. Picosecond open-aperture Z-scan data revealed these molecules exhibited strong saturable absorption.
These molecules possessed negative nonlinear refractive index (n2). The estimated value of n2 was 6×10-15 cm2/W and
8×10-15 cm2/W for TPC and TTC, respectively. We have recently reported NLO properties of Corroles with 800 nm
excitation where they exhibited strong two-photon absorption (2PA) at higher intensities and effective two-photon
absorption at lower intensities in the ps regime. Femtosecond open aperture Z-scan studies indicated the presence of
strong saturable absorption with effective nonlinear absorption coefficients (β) of ~0.8×10-13 cm/W and ~2.7×10-13
cm/W for TPC and TTC, respectively. We have also estimated the sign and magnitude of real part of third order
nonlinearity through the closed aperture scans. We discuss the nonlinear optical performance of these organic molecules.
Influence of the polymer processing conditions on the performance of bulk heterojunction solar cells
Show abstract
We performed a systematic study of the effect of processing conditions on the performance of P3HT:PCBM solar
cells. We have investigated the influence of the source material, solution preparation (stirring vs. sonication),
additives (such as 1,8-octanedithiol), pre-formation of P3HT nanowires, and annealing on the device performance
and/or morphology and phase separation in the active layer. Furthermore, the influence of spin-coating PCBM on
top of P3HT and PCBM on top of the P3HT:PCBM layer has been investigated. We found that all of these factors
affect the performance of the solar cells, although there are several alternative methods which can result in similar
improvements of the performance. We found that the improvement trends for various procedures (additives, PCBM
top layer, P3HT nanowires, etc.) are similar and also strongly dependent on the different source materials. The main
factor determining in the obtainable efficiency is the solution preparation and the source materials. Obtained results
and the implications on further improvement of solar cell performance are discussed in detail.
Multi high-order anisotropic self-diffraction in Cerium doped BaTiO3 crystal
Show abstract
Higher-order anisotropic self-diffraction up to third orders have been observed in Cerium doped barium titanate by using
red beam at 633 nm from He-Ne laser. In our experiment, the third orders and second orders have been observed
simultaneously for the first time from our knowledge. From our observation, the phase conjugate beam has not been
generated before and after the appearance of higher orders as observing when the green beam from the Argon-ion laser at
514.5 nm has been used. The diffraction efficiency and the decay rate of the grating have been measured as well in the
red light case.
Efficient configuration transition in a new azobenzene-LC polymer for red light holographic recording
Show abstract
We demonstrate cis-to-trans transition based red light holographic recording in an azobenzene-liquid crystal (LC)
polymer material following efficient crucial transition of trans-to-cis, which is prepared by selected wavelength light
pre-illumination. The presence and orientation of soft liquid crystal impregnating the polymer backbone allows the
cis intermediate states to hold for the stable red hologram recording and non-destructive readout. Using a 50 nm
bandwidth light source at the center wavelength of 575 nm, we have efficient pre-illumination on the material. The
diffraction efficiency of up to 2% can be achieved by a HeNe laser at 632.8 nm wavelength, and two-dimensional
holograms of USAF resolution target are successfully recorded.
Development of fibre Bragg grating based strain/temperature sensing system
Show abstract
We have characterised a strain and temperature sensing system being developed by Southern Photonics that uses a new
Optical Interrogator and fibre Bragg gratings. We have determined the key strain and temperature coefficients, and
shown that strain and temperature can be measured simultaneously. The experimental uncertainty is 5.2 pm when using
the 1540 nm fibre Bragg grating, which corresponds to an experimental uncertainty in measuring the temperature of 0.54
ºC and in measuring the strain of 3.4 με. Simulations predict that a Bragg reflection of more than 90% can be achieved
for Bragg Gratings in polymer thin films containing chromophores for grating lengths as small as 200 μm. A small Bragg
grating length means that it should be possible to create waveguides and four Bragg gratings for strain tensor and
temperature measurements within an area as small as 5×5 mm2.