Organic Photonic Polymer Thin Films: Fundamental and Applications

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Organic Photonic Polymer Thin Films Fundamental
and Applications
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Outline

• Opto-electronic properties and applications of
  conjugated organic molecules and polymers
• Optical poling of azo-dye and DANS polymer thin
  films
• Optically induced anisotropy of third order
  susceptibility in azo-dye and DANS polymer thin
  films
• Polymer photonic crystals
• Conclusions

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• Opto-electronic properties of conjugated organic
  molecules and polymers

• Conjugated an alternation of double and single
  bonds linking a sequence of atoms.

Conjugated molecule
Conjugated polymer
-electrons in conjugated molecules (or
polymers) are delocalized, which makes the
-electron distribution highly deformable in
conjugated molecules (or polymers). That is why
conjugated molecules (or polymers) has large
optical nonlinearities.
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• Nonlinear optical response of noncentrosymmetric
  conjugated molecules

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• Bond alternation and band gap

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Trans-cis photoisomerization effect
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Comparisons between organic and inorganic
materials

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Potential applications

• OLED, PLED
• Laser frequency conversion
• Holography memory
• Electro-optic modulation
• All optical modulation
• Optical data storage
• Polymer photonic crystal devices

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Polymer Light Emitting Diodes (PLED)
Microdisplay with CDT Green Polymers
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Toshiba PLED Full Color Display
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POLYMER LIGHT EMITTING DIODES
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• ITO/PEDOT/MEH-PPV/Ca/Al

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POLYMER LIGHT EMITTING DIODES
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POLYMER LIGHT EMITTING DIODES
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Electric field poling
Use Electric field poling technique to generate
non-centro symmetric distribution of conjugated
dye molecules.
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Optical poling of dye polymer materials
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DR1/PMMA absorption spectrum and molecules
structure
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Polar excitation of molecules
Excitation probability of a 1D molecule by a
linearly polarized light
Under optimized poling conditions
Polar axis(polarization of seeding beams)
Molecular dipole moment
Probability of excitation as function of the
polar angle ? under optimized poling conditions
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Angular hole burning
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The evolution of the molecular angular
distribution (a) before poling (b) after few
minutes of seeding the sample with optical poling
field E?E2? (c) the final distribution after
several hours of the poling .
Molecular angular redistribution
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Real time optical poling experimental setup
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Traditional probe configurations
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Basic concept of our new method
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Polarization properties of ?(2)
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Real-time monitoring of ?(2) buildup
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Photoinduced nonlinear optical phenomena in
DANS-PMMA polymer thin films
In azo-systems, the optical anisotropy caused by
the AHB disappear in few second after the pump
beam is switched off, because of the thermal
relaxation from cis to trans. Stilbene
derivatives (e.g. (DANS)) also experience
trans-cis photoisomerization, but no visible
cis-trans thermal relaxation has been detected.
The irreversible trans-cis in DANS polymers
photoisomerization is attractive for permanent
optical memories.
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Simplified four-level scheme of trans-cis
photoisomerization in DANS
Dynamics of trans population is described by
equation
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Optical poling of DANS-PMMA thin films
Growth of the square root of SH signal in
DR1-PMMA (a) and DANS-PMMA (b) samples (in
arbitrary unites). The experimental data are
fitted to functions f(t)A1(1-exp(-t/?A1))A2(1-ex
p(-t/?A2)) for the DR1-PMMA sample and
f(t)-B((1-B1)exp(-t/?B1)B1)B((1-B2)exp(-t/?B2)
B2) for the DANS-PMMA sample. The following fit
parameters are used A15.4, A22.1 ?A11.7
min,?A219.3 min B9.3, B10.80, B20.91,
?B10.46 min, ?B28.3 min.
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Conclusions

• Simultaneous writing and probing photoinduced
  second order susceptibility ?(2) in azo-dye
  polymer thin film is demonstrated. This technique
  allows to monitor the ?(2) value in real time
  excluding completely unwanted meddling into the
  optical poling process and to retain the simple
  and effective poling setup with co-propagating
  fundamental and seeding beams.
• The real time optical poling technique is based
  on properties of ?(2) response providing
  different planes of polarization for seeding and
  signal second harmonics.
• The optical encoding of macroscopic ?(2) in
  DANS-PMMA thin films has been demonstrated and
  physical interpretation based on the AHB model is
  given.
• The dynamics of photoinduced second order
  nonlinearity in the DANS-PMMA thin film is
  well-explained by the influence of reverse
  cis-trans photoisomerization of HCCH bond.

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5. The photoinduced second order nonlinearity in
DANS-PMMA has exhibited the better dark stability
than that in azo-polymers because of the absence
of thermal cis-trans relaxation.

• V. M. Churikov, M. F. Hung, and C. C. Hsu, 2000.
  Real time monitoring all optical poling of
  azo-dye polymer thin film. Optics Lett. 25, 960.

• V. M. Churikov, M. F. Hung, C. C. Hsu, C. W.
  Shiau, and T. Y. Luh, 2000. Encoding of
  macroscopic second order nonlinearity via
  all-optical polar alignment in substituted
  norbornene polymer thin films Chem. Phys. Lett.
  332, 19.

• V. M. Churikov, and C. C. Hsu, 2001 Dynamics
  of photoinduced second order nonlinearity in
  dimethylamino-nitrostilbene polymer thin films,
  Optics Comm, 190, 367.

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Optically induced anisotropy of third order
susceptibility in polymers
UV filter
?
3?
PMT
?
DR1-PMMA
2?
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Primary experiment
UV filter
3?
PMT
3?
DR1-PMMA
2?
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Experimental setup
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Angular hole burning without rotation
Original isotropic distribution
Molecular reorientation
The arrows represent dipole moments of trans
molecules. Excitation probability is proportional
to cos2 ?
Some trans molecules with angles ? close to 0 or
180o (gray arrows) are missed (transformed to
cis) and no longer contribute to ?(3)
The number of trans molecules remains the same,
but some molecules are reoriented to the
position with lower excitation probability
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Model of photoinduced anisotropy of ?(3)
susceptibility in azo-polymers
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DR1-PMMA (guest-host system)
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DR1-PMMA (side-chain system)
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Experimental results
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TH intensity as a function of time in the sample
pumped by a cw He-Cd laser. The sample was probed
by the fundamental co-polarized () and
perpendicularly polarized (?) with the pumping
beam.
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TH intensity as a function of time in the sample
pumped by a SH of NdYAG laser. The sample was
probed by the fundamental co-polarized () and
perpendicularly polarized (?) with the pumping
beam. The curves for - and ?-cases are
normalized to the same initial level and
represent a relative change of the TH generation
level.
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TH intensity as a function of polarization angle
? of the probing beam before pumping (first
column from the left), after 8 min of pumping
with the 532 nm and 442 nm light of 0.3 W/cm2
average intensity (a,b) and 442 nm light of 3
W/cm2 intensity (c) (second column), after 1 min
of dark relaxation (third column) and after
following 15 min of dark relaxation (fourth
column). The zero angle corresponds to the plane
of polarization of a pump.
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Homopolymer absorption spectrum and molecules
structure
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Homopolymer
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Homopolymer
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DR1-PMMA
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Photoinduced THG decay and recovery in DANS-PMMA
thin films at room temperature
Pumped at 1064 nm
Pumped at 532 nm
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THG recovery in DANS-PMMA thin films at high
temperature
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Conclusions

• One- and two-photon induced molecular
  conformation change and reorientation effects
  produce large reversible anisotropic THG
  variation in azo polymer thin filmss.
• The observed THG anisotropy agrees qualitatively
  with the prediction of theoretical model.
• The effect can have potential applications in
  multi-photon hole-burning holographic storage
  devices.
• Temperature dependent photoinduced change of THG
  in polyurethane homopolymer and DR1-PMMA thin
  films has been compared.
• Photoinduced THG variations in both samples are
  smaller at high temperature because of the
  decrease of cis states lifetime and population
  and large orientational diffusion constant.

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• 6. THG recovery experiment show that the
  photoinduced THG change in the polyurethane
  homopolymer sample is more stable than that in
  the DR1-PMMA sample, consistent with its large
  molecular weight and small free volume.
• Photoinduced THG decay in DANS-PMMA thin films is
  irreversible when the samples are pumped at 1064
  nm or 532 nm in air environment. The permanent
  THG decay is likely due to the phtoinduced
  oxidation of DANS molecules in the films.
• Photoinduced THG decay in DANS-PMMA thin films
  can be fully recovered at room temperature when
  the samples are pumped at 1064 nm in nitrogen
  environment.
• The THG signal is only partially recovered when
  the samples are pumped at 532 nm in nitrogen
  environment. However, the THG decay signal can be
  fully recovered when the samples are heated up at
  high temperature.

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• V. M. Churikov, and C. C. Hsu, 2000. Optical
  control of third-harmonic generation in azo-doped
  polymethacrylate thin films Appl. Phys. Lett.
  77, 2095.

• V. M. Churikov, and C. C. Hsu, 2001. Optically
  induced anisotropy of third- order susceptibility
  in azo-dye polymers JOSA B 18, 1772.

• V. M. Churikov, J. T. Lin, H. H. Wu, J. H. Lin,
  T. H. Huang, and C. C. Hsu, 2002 One- and
  two-photon induced molecular conformation change
  and reorientation and related third-order
  nonlinearities in phenylamine azo-dye polymer
  thin films, Optics Comm. 209, 451.

• C. C. Hsu, J. H. Lin, T. H. Huang, K. Harada,
  2003. Temperature dependent photoiduced third
  harmonic generation variation in azo homopolymer
  and azo-doped polymer thin films Appl. Phys.
  Lett.

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• V. M. Churikov, and C. C. Hsu, 2002.
  Photoinduced third order nonlinear optical
  phenomena in azo-dye polymer in Photoreactive
  organic polymer thin films edited by Z. Sekkat
  and W. Knoll, Academic Press, San Diego, P366-392.

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Polymer Photonic Crystals

• Photonic crystals (PC) are optical materials
  with periodic variation of refractive index.
  Analogous to a semiconductor crystal a periodic
  refractive index distribution can produce a
  photonic bandgap that blocks a range of optical
  frequencies of light propagating inside a PC.

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Defect in photonic crystals

• If local disorders such as variations of
  refractive index or geometry are introduced into
  a PC, we may obtain localized defect modes whose
  eigenfunctions are strongly localized around the
  disorder.

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Transmission spectra of 9 x 18 array of
cylinders. The incident wave comes along (a) the
1,0 , (b) the 2,1 , and (c) the 1,1
direction of the regular crystal without the
defect. In (d) , the orientation of the incident
wave is the same as in (a) , but a single
cylinder located at the center of the array is
removed. Note the sharp extra peak in the gap
located at 11.2 GHz signifyinga localized defect
mode.
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http//www.tu-harburg.de/et7/forschung/crystal/cry
stal_e.html
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http//www.tu-harburg.de/et7/forschung/crystal/cry
stal_e.html
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http//www.tu-harburg.de/et7/forschung/crystal/cry
stal_e.html
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Self assembly polymer PC
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CS2-PS(1-wt),100rpm,TE-CoolingRoom
Temp. ?????100C CS2-PS(1-wt)??
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CS2-PS(1-wt) 300rpm TE COOLINGRoom Temp.
Top View
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Two-photon polymerization experimental setup
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ms,????700 nm
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ms,????234 nm
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????????,?????750nm,??2.4um,??????36mW
/cm2,?????10.4µm /s????????
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