ISBN Number: 978-979-8575-05-1
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Yogyakarta, INDONESIA
September 5-7, 2007
Organized by:
The Study Program on
Opto-Electrotechniques and Laser Applications
Dept. of Electrical Engineering, University of Indonesia
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Yogyakarta, INDONESIA
September 5-7, 2007
Organized by:
The Study Program on
Opto-Electrotechniques and Laser Applications
Dept. of Electrical Engineering, University of Indonesia
Indonesia Section
©
PS-OEAL
The Study Program on Opto-Electrotechniques and Laser Applications
Dept. of Electrical Engineering, University of Indonesia
All right reserved. No part of this publication may be reproduced, stored in a
retrieval system, or transmitted in any form or by any means, electronics,
mechanical, photocopying, recording or otherwise, without the prior permission ot
the copyright owner.
PS-OEAL, Dept of Electrical Engineering, University of Indonesia
Jl. Salemba Raya 4, Jakarta Pusat 10430, Indonesia
Preface
Dear the ICOLA 2007 Participants
On behalf of the Committee of International Conference on Optics and Laser Applications, ICOLA’07
allow me to express my gratitude to all of you, who participate in this conference. The Study Program on
Opto-Electrotechniques and Laser Applications, Dept. Electrical Engineering, University of Indonesia
organizes this conference in conjunction with the 30
thanniversary of the study program.
The ICOLA’07 is technically supported by the International Commission for Optics (ICO), International
Society for Optical Engineering (SPIE), and the Abdul Salam International Center for Theoretical
Physics (ICTP), in cooperation with other professional society like: HFI, HAI, IEEE Indonesia Section,
etc. We would like to warmly welcome the participants from
USA, Japan, South Korea, P.R. China,
Taiwan, Thailand, Singapore, Malaysia, Bangladesh, India, Iran, Yemen, Algiers, Moldova, Ukraine, the
Netherlands
, etc., especially the distinguished professors from the well known and recognized
institutions as invited speakers.
The time of conference is remarked by a significant progress in science and technology, especially in
the field opto-electronics and laser applications. Although our country is facing with political and
economical problems, in fact, there are still some researchers, young engineers, students --who are
working in their own fields-- wishing to present their works in this conference.
We received around
81
extended abstracts (invited, overseas, and domestic) but only about 5
5
selected
or reviewed papers will be presented in the conference. These are divided into three categories:
A: Nanotechnology, Biomedical Optics, and Optical Communication
B: General Optics, Holography, and Laser Technology
C: Photonic Devices/Materials, Design, and Applications
We would like to thank to all Committee members, to all organizations and sponsors who have provided
their supports and efforts to make this conference become a success. In addition, thanks also are
forwarded to all individuals for their valuable time and supports to the conference.
Finally, have intensive discussions in the conference and enjoyable stay in Yogyakarta !
Prof. Dr. Sar Sardy
ICOLA2007 Committee Members
Organizer
The Study Program on Opto-electrotechnique and Laser Applications (OEAL) Department of Electrical Engineering, Faculty of Engineering, University of Indonesia
Sponsor (technical)
ICO, SPIE, ICTP, IEEE Indonesia Section, Indonesian Physical Society, Indonesian Astronomical Society
International Program Committee
Prof. Dr. Suganda Jutamulia, Chair, Univ. of Nothern California, USA Prof. Dr. Yashuhiru Suematsu, The Past President Tokyo Institute of Technology
Prof. Dr. Jumpei Tsujiuchi, Prof. Emeritus Tokyo Institute of Technology Prof. Dr. Toshimitsu Asakura, Prof. Emeritus Hokkaido University
Prof. Dr. Guoguang Mu, Nankai University, China Prof. Dr. Lambertus Hesselink, Stanford Univ. USA Prof. Dr. Mohammad S. Alam, Univ. of South Alabama, USA
Prof. Dr. Francis Yu, Pennsylvania State University, USA Prof. Dr. Cardinal Warde, Massachusetts Inst. Tech. USA Prof. Dr. Pochi Yeh, Univ. of California Santa Barbara, USA Prof. Dr. Alexander Sawchuck, SIPI, Univ. of Southern California, USA
Prof. Dr. Kehar Singh, Indian Inst. Tech. Delhi, India Prof. Dr. Rene Dandliker, President SATW, Switzerland
Prof. Dr. Gallieno Denardo, ICTP, Trieste, Italy Prof. Dr. Min Gu, Swinburne Univ. of Technology, Australia
Prof. Dr. Arthur Chiou, National Yang Ming Univ., Taiwan Prof. Dr. Joewono Widjaja, Suranaree Univ. of Technology, Thailand Prof. Dr. Anand Krishna Asundi, Nanyang Technological Univ. Singapore Prof. Dr. Yoshizumi Yasuda, Tokyo University for Information Science, Japan
Prof. Dr. Yoshihisa Aizu, Muroran Inst. Tech. Japan
Prof. Dr. Byoung Yoon Kim, Novera Optics, KT Second Research Center, South Korea Prof. Dr. Feijun Song, China Daiheng Coorp., P.R. China
Prof. Dr. Kazuhiko Ohnuma, Chiba University, Japan Prof. Dr. A.N. Chumakov, National Academy of Science, Belarus
Dr. Yoshiji Suzuki, Hamamatsu Photonics KK, Japan
Advisory Committee
Prof. Dr. Rinaldy Dalimi, Chair, Dean Fac. of Engineering, University of Indonesia Prof. Dr. Eko Tjipto Rahardjo, University of Indonesia
Prof. Dr. Bambang Hidayat, Chairman Indonesian Academy of Science Prof. Dr. Zuhal, President Indonesian Al-Azhar University Prof. Dr. Budi Santoso, Indonesian Atomic Energy Agency
Prof. Dr. Tjia May On, Bandung Institute of Technology
General Chairman
Sar Sardy, Professor, Head of OEAL-FTUI, Univ. of Indonesia
Technical Program Committee
Prof. Dr. Anung Kusnowo, Indonesian Institute of Science Dr. Ary Syahriar, Indonesian Al-Azhar University Dr. Henri Putra Uranus, University of Twente, the Netherlands
Dr. Ir. Sekartedjo, Sepuluh Nopember Institute of Technology Dr. Hendrik Kurniawan, University of Indonesia Prof. Dr. Masbach R. Siregar, Indonesian Physical Society
Dr. Hakim L. Malasan, Indonesian Astronomical Society
Local Organizing Committe
Dr. Ir. Purnomo Sidi Priambodo, MSEE, Chair, University of Indonesia Dr. Ir. Dodi Sudiana, MEng, University of Indonesia
Dr. Ir. Retno Wigajatri MEng, University of Indonesia Dr. Abdul Muis, ST. MEng, University of Indonesia Dr. Ir. Feri Yusivar, MEng, University of Indonesia Fitri Yuli Zulkifli, ST. MSc, University of Indonesia Arief Udhiarto, ST. MT, University of Indonesia Budi Sudiarto, ST. MT, University of Indonesia Muhammad Suryanegara, ST. MSc, University of Indonesia
CONTENT
Invited-Planery Papers
Scientists and Their Society: Between Advocacy and Arbitration
Bambang Hidayat
1
Angular Division Multiplexing in Pulsed Digital Holography for
Recordings of High Resolution
Hongchen Zhai, Xiaolei Wang, CaojinYuan and Guoguang Mu
7
Design and analysis for laser beaming devices using surface plasmon
resonance
Byoungho Lee, Hwi Kim, and Seyoon Kim
12
Phase Singularity Distribution of Fractal Speckles
Jun Uozumi
17
Laser Aided Golf Trainer – Product and Business Development
Suganda Jutamulia
22
Quality of Images Reconstructed from In-Line Fresnel Holograms
Joewono Widjaja and Phacharawadee Raweng
25
Three-dimensional computer-generated holographic display of
biological tissue
Toyohiko Yatagai, Yusuke Sando , Ken-ichi Miuraand Masahide Itoh
30
Application of VIS-NIR Spectral Imaging to Skin Tissue
Measurements
Yoshihisa Aizu, Takaaki Maeda, and Izumi Nishidate
34
On-demand optical tweezers by time-division multiplexing of
computer-generated holograms
Toshiaki IWAI and Johtaro YAMAMOTO
39
Digital holography a new paradigm for imaging, microscopy
and measurement
Anand Asundi and Vijay Raj Singh
43
Encrypted Content-addressable Holographic Memories
Kehar Singh, Renu John, and Joby Joseph
Three-Dimensional Microscopic Imaging
Colin J.R. Sheppard
53
Contributed Papers : Overseas
Enhancing the Performance of Integrated Optical Sensor by
Slow-light: Theoretical Study on Ring-Resonator Based Structures
Henri P. Uranus, and Hugo J. W. M. Hoekstra
56
Electro-Optical Studies Of Chemically Deposited Zn
x
cd
1-X
Nanocrystalline Films
Shashi Bhushanand Ayush Khare
61
Compact Optical Sensor for Soil Nutrients Analysis by using LEDs
Masayuki Yokota
66
Precision Dynamic Force Measurement Using Mass Levitation and
Optical Interferometer
Yusaku FUJII
70
Optical properties of vanadium doped ZnTe thin cermet films for
selective surface applications
M. S. Hossain, R. Islam and K. A. Khan
74
Improved 90° Bend Transmission Defined in a Triangular Lattice
Photo nic Crystals
Leila DEKKICHE, and Rafah NAOUM
79
Dual Ball Lenses for Relaxed Alignment Tolerances in Pigtailing of a
Laser Diode Transmitter
Mohamed Fadhali, Saktioto,Jasman Zainal, Yusof Munajat, Jalil Ali and Rosly Abdul Rahman
83
Normalized Frequency Gradient of Coupled Fibers as a Function of
Coupling Ratio
Saktioto, Jalil Ali, Jasman Zainal, Mohamed Fadhali
88
Experimental studies on the short wave transmission characteristics of
a laser protection filter coating used in the laser optical systems
Nimmagadda Rama Murthy, and A.S. Murthy
93
Two-Photon Lasing Controlled by Resonator Losses
Vitalie Eremeev, Marina Turcan, Nicolae Enaki
98
Incoherent Light Depolarization by Multiple Reflections
Yaroslav Aulin
Influence of Filters on Recognition of Noisy Objects
Seyed Mohsen Mirsadri, Hosein Bolandi, Farhad Fani Saberi
107
Design and Development of Holographic Sighting System used for
small arm weapons in Close Quarter Battle situations
Nimmagadda Rama Murthy, P.Rajesh Kumar, and N. Raghavender
113
Contributed Papers : Domestic
The Effects of Substitution on the Optical Properties of
poly(
p
-phenylenevinylene) Derivatives
A. Bahtiarand C. Bubeck
117
Possible use of formaldehyde as fluorescence tracer to examine the
state of mixture formation in Spark Ignited (SI) engines
A.M.T Nasution1, V. Beushausen, R. Mueller
122
The Parameter Modeling of Grating Reflector for External Cavity
Tunable Lasers as light sources in DWDM System
Supriyanto
127
Surface Roughness Measurement by Electronics Speckle Pattern
Interferometry (ESPI) Method
A.S. Pramono, Rakiman, D. Ardiansyah, H. Setijono
131
Generalized Linear Dispersion Relation for Symmetrical
Directional-coupler of Five-layer Waveguide
Sekartedjo, and Ali Yunus Rohedi
135
Design of Multimode Interference Structure for 1x2 Optical
Waveguide Filter for 1.3 and 1.55
µ
m
Sekartedjo, and Agus Muhamad Hatta
140
Phase Unwrapping Applied to Digital Holography
D. Ardiansyahand Sekartedjo
143
Introducing Stable Modulation Technique for Solving an
Inhomogeneous Bernoulli Differential Equation
Ali Yunus Rohedi
147
High Temperature Annealing effects on Silica based Optical
Waveguides
Ary Syahriar
Simple Model of Design 1.55
μ
m and 1.31
μ
m VCSEL’s for High Speed
Modulation Optical Interconnections
Gunawan Witjaksono, Ucuk Darusalam, Gunady Haryanto, Arum Setyowati
158
Simulation GaInAsP/InP Surface Emitting Distributed Feedback
Laser for Radio Over Fiber Application
Gunawan Witjaksono, Irma Saraswati
163
Optical Waveguide Directional Fiber Coupler Design Method Based
on Numerical Analysis
Ucuk Darusalam, Gunady H., Arum Setyowati, Purnomo Sidi Priambodo, V. Vekky R. R
167
Gain Characteristics Analysis of Distributed Raman Amplifier on
CWDM Band Based on Numerical Simulation
V. Vekky R. Repi, Ucuk Darusalam, Purnomo Sidi Priambodo
172
Design of Multimode Interference (MMI) Couplers Using Method of
Lines
Helmi Adam, Ary Syahriar
177
Design of Three Parallel Waveguide Using Coupled Mode Theory and
Method of Lines
H
elmi Adam, Dwi Astharini, Ary Syahriar181
Laser Micromachining of Silicon and Its Application for the
Fabrication of Micro Gas Sensor Device
Goib Wiranto,Gandi Sugandi, I Dewa P. Hermida, and Edy Supriyanto
185
Edge-element based finite element analysis of leaky modes of photonic
crystal microcavities
Ardhasena Sopaheluwakan
189
Measurement of the nonlinear susceptibility of the third order
dielectric materials by means of Z-scan technique
Freddy Susanto Tan
193
Optical Fibre Biosensor Based on Enzymatically Doped Sol-Gel
Glasses for Monitoring of Pesticides in Flow System
Bambang Kuswandi, Chulaifah Indah Fikriyah, Agus Abdul Ganiand Anak Agung Istri
Ratnadewi
197
Simulations of rib waveguide structure with trapezoidal cross-section
using Finite Difference Method
Suwasti Broto, N. Mohd Kassim, M.H. Ibrahim
Achieving gain flatness in C-band Erbium Doped Fiber
Amplifiers
Sholeh Hadi Pramono, Sar Sardy, Ary Syahriar, Irwan R.Hc, Sasono R
207
Design and Implementation of Knowledge-Based Expert Systems GIS
for Fishing Ground Prediction Models:
a preliminary results
Muhamad Sadly, and Yoke Faisal
210
The Assessment of Fish Abundance by using Modis Satellite Data of
SSC and SST (Case Study : In the South Kalimantan)
Suhendar I Sachoemar, Muhamad Sadly and Fanny Meliani
214
Fitting of Linear Transducer Characteristic using Genetic Algorithm
and Segmented by Golden Ratio
Purwowibowo, Sar Sardy, and Wahidin Waha
b
219
Visible to Near Infrared Spectrum
Reflectance Ratios in Cancer Detection
Hamdani Zain, Anwar S. Ibrahim, Aryo Tedjo and Kusmardi
224
Speech Recognition for Controlling Movement of the Wheelchair
Thiang
227
A Comparison of Discrete Cosine Transform and Discrete Wavelet
Transform Techniques in Audio Compression
Endra
232
Face Identification with Multi-resolution Method
Indra Riyanto, and Wihartini
235
Splice Loss: Estimated Value Versus OTDR Measurement
Dwi Bayuwati, Tomi Budi Waluyo, Imam Mulyanto
238
The Spectral Reflectance Characteristic of Coral and Its Relation to
The Optic Properties of Waters
Nurjannah Nurdin, Muhamad Sadly, Indra Jaya, Vincentius Siregar
242
Introducing “OPTO”: Portal for Optical Communities in Indonesia
Tomi Budi Waluyo and Laksana Tri Handoko
Proc. of the 2nd International Conf. on Optics and Laser Applications ICOLA’07, September 5-7, Yogyakarta, Indonesia
The Effects of Substitution on the Optical Properties of
poly(
p
-phenylenevinylene) Derivatives
A. Bahtiar
*and C. Bubeck
†*
Department of Physics, University of Padjadjaran Bandung, Jl. Jatinangor km. 21 Sumedang, 45363, Indonesia. Tel. ++62-22-7796014, Fax. ++62-22-7792435, email: [email protected]
†
Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany Tel. ++49-6131-379122, Fax. ++49-6131-379100, email: [email protected]
Abstract - We have studied the optical linear, optical nonlinear and waveguide properties of thin films of newly synthesized poly(phenylenevinylene) (PPV) derivatives: MEH-PPV, M3EH-PPV and copolymer MEH-M3EH-PPV by means of reflectrometry, prism coupling, third harmonic generation spectroscopy and waveguide propagation loss. Anisotropic refractive index measurements by means of waveguide prism coupling and reflectometry were used to analyse the polymer chain orientation in the films. We observed that the absorption coefficient, refractive index, birefringence and third order susceptibility and waveguide loss coefficient are increased in going from MEH-PPV, MEH-M3EH-PPV and finally to M3EH-MEH-M3EH-PPV, which indicates that the thin film of M3EH-PPV have the most polymer chain segments oriented parallel to the film plane. For all-optical switching applications, the thin film of MEH-PPV is the most appropriate candidate, since it exhibit a good combination of large value of cubic nonlinearity and small waveguide propagation loss coefficient.
Keywords- Conjugated polymers, Chain Orientation, Third-order susceptibility, Waveguide propagation loss
I. INTRODUCTION
he control and processing of fast optical signals is of increasing importance in integrated optics. Various concepts for integrated devices based on materials with high third-order nonlinearities and fast response times have been suggested [1]. The demonstration of all-optical switching in planar waveguides would become the breakthrough in integrated nonlinear optics. The bottleneck for the realization of such devices is still the problem of identifying the material that have multifunctional properties like high third-order nonlinearity with fast response times, low absorption
losses, high photostability and easy fabrication of slab waveguides [1].
Conjugated polymers that posses a delocalized π-electron systemhave been considered to be the most promising organic material candidates for all-optical switching applications because of their high cubic nonlinearity and fast response times in the order of picoseconds or less, and relative ease of waveguide preparation [2]. In particular, poly(p -phenylenevinylene) (PPV) was identified as a promising material for nonlinear optical applications because of large cubic nonlinearities with fast response times and high damage thresholds [3]. Recently, its derivatives have incurred much more interest due to their good combination of large third-order nonlinearity and superior waveguide properties [3,4]. Moreover, they are also attractive for electroluminescence devices [5], plastic laser [6] and transistor [7].
In this paper, we present comparative studies of the linear and nonlinear optical properties as well as waveguide properties of newly synthesized of several solution processable PPV by means of reflectrometry, prism coupling, third harmonic generation spectroscopy and waveguide propagation loss. The aim is to study their suitability for application in a nonlinear all-optical switching planar waveguides. It will be shown that the conjugated polymer MEH-PPV is the best suited material for all-optical switching applications due to its good combination of large value of cubic nonlinearity and ultimately low waveguide propagation losses.
II. MATERIALS AND EXPERIMENTAL METHODS 2.1. Materials
The chemical structures of three PPV derivatives: Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV); Poly[2,5-dimethoxy-1,4-phenylene-1,ethenylene, 2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] (M3EH-PPV) and their copolymer Poly[2-methoxy-5-(2- ethylhexyloxy)-1,4-phenylene-vinylene-2,5-dimethoxy-1,4- phenylene-vinylene-2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-M3EH-PPV) are displayed in
Proc. of the 2nd International Conf. on Optics and Laser Applications ICOLA’07, September 5-7, Yogyakarta, Indonesia
O O
CH3
n
CH=CH CH CH
OCH3
CH3O
O
CH3O
n CH CH
MEH-PPV M3EH-PPV
CH CH CH
CH
CH3O
O
CH3O O
0.5n
CH CH CH
CH3O
O
CH3O OCH3
0.5n CH
MEH-M3EH-PPV
Figure 1. Chemical structure of MEH-PPV, MEH-M3EH-PPV and M3EH-PPV
They were synthesized via the polycondensation route by the use of the Horner-carbonylolefination that yields well-defined conjugated polymers with excellent solubility in organic solvents. The weight-average molecular weight (Mw) and number-average molecular
weight (Mn) of all PPVs were determined with gel
permeation chromatography (GPC) using polystyrene standards and tetrahydofuran (THF) as eluent. Their values are displayed in Table 1.
Table 1. Properties of MEH-PPV, MEH-M3EH-PPV and M3EH-PPV
Polymer Mw [kg/mol] Mn [kg/mol] λmax [nm] αmax
[104 cm-1]
MEH-PPV 40.3 14.1 489 12.3
MEH- M3EH-PPV
32.3 11.4 485 16.1
M3EH-PPV 44.0 12.0 486 18.8
Polymer ) 3 ( max χ
[10-11 esu] α[dB/cm]gw (TE0) α[dB/cm] gw (TM0) MEH-PPV 6.50 ± 0.7 0.5 ± 0.3 0.5 ± 0.3
MEH-M3EH-PPV 9.65 ± 1.0 12.4 ± 1.4 5.3 ± 1.0 M3EH-PPV 13.8 ± 1.4 > 20 9.4 ± 1.5
Two common organic solvents like toluene and chlorobenzene were used to dissolve the polymers. The polymers MEH-PPV and MEH-M3EH-PPV were dissolved in toluene. The polymer M3EH-PPV, however, was dissolved in chlorobenzene and the solution was heated at approximately 1000C while stirred for 1 hour in order to obtain complete solubility. Thin films of MEH-PPV and MEH-M3EH-PPV were prepared by spin coating from freshly prepared and filtered (0.5 or 1 µm syringe filters) solutions at ambient atmosphere under a laminar flow. Whereas, thin films of M3EH-PPV were spin coated at high temperature (~ 1000C). We varied the concentration by weight (1 - 5 %) and spinning speed (500 – 9000 rpm) to control the film thickness. The films were placed subsequently in a vacuum oven at elevated temperatures (T ≈ 50 0C) for about 6 hours. The thickness d
and the average surface roughness of the films were measured with a Tencor Model P10 profilometer.
2.2. Linear Optical Constants
Transmission and reflection spectra of thin films (d ≈ 50 nm) were measured by using a UV-Vis-NIR spectrophotometer with electrical field vector oriented parallel to the film plane (TE-polarization). The dispersions of the intrinsic absorption coefficient α(λ) and the refractive index n(λ) of thin films were evaluated from the transmission and reflection spectra. The absorption spectra and the dispersions of linear refractive index of thin films of the conjugated polymers are displayed in Figure 2. Their maxima of absorption αmax and the maximum wavelengths λmax are shown
in Table 1. The data of λmax have an estimated uncertainty of ±
2 nm because of broad absorption bands.
200 300 400 500 600
0 5 10 15 20 25 M3EH-PPV MEH-M3EH-PPV MEH-PPV α [10
4 cm -1 ]
λ [nm]
Figure 2. Spectra of the absorption coefficient after correction of reflection losses of thin films of PPV derivatives at transverse electric
(TE) polarization.
Proc. of the 2nd International Conf. on Optics and Laser Applications ICOLA’07, September 5-7, Yogyakarta, Indonesia
with the results of transmission-reflection measurements. We have also measured the refractive index at TM polarization, nTM of several slab waveguides of PPVs.
The results are displayed in Figure 3 with open symbols. The values of nTM for these polymers are nearly identical.
600 700 800 900 1000 1100
1,6 1,8 2,0 2,2
Closed symbol : TE (prism coupler) Open symbol : TM (prism coupler) Lines : TE (reflectrometry)
M3EH-PPV MEH-M3EH-PPV MEH-PPV
n
Wavelength [nm]
Figure 3. Dispersions of refractive indices of MEH-PPV, MEH-M3EH-PPV and M3EH-PPV.
2.3. Third Harmonic Generation Spectroscopy
Third-harmonic generation (THG) of thin films of MEH-PPV was measured with a similar setup as described earlier [3]. We have used a Nd:YAG laser, the second harmonic output of which pumped an optical parametric generator, which gave laser pulses with a duration of 20 ps, repetition rate 10 Hz, and a wavelength tuning range between 680 nm and 2000 nm. The laser beam was focused on the sample, which was placed in an evacuated chamber and mounted on a rotation stage. The Maker fringes were evaluated taking into account the measured data of the sample (thickness, refractive index, and absorption coefficients at the fundamental and harmonic wavelengths), the free and bound harmonic waves and their reflections at the interfaces as described earlier [3]. The only fitting parameters were modulus
⎪χ(3)⎪
and phase angle ϕ of the complex value of χ(3)
:
χ(3)
= |χ(3)
| exp(iϕ). The values of the modulus of ⎪χ(3)⎪
at TE polarization were determined with respect to the reference value 3.11 10-14 esu for the fused silica substrate for all laser wavelengths [3].
2.4. Waveguide Loss Propagation
Waveguide loss experiments were performed by the prism coupling technique as shown in Figure 4. A cw-Nd:YAG (1064 nm) laser was used as light source. The laser beams were coupled into waveguide using a high refractive index glass prism LaSF18. The film was clamped onto the half-cut prism mounted on a precision rotation table. The lens L1 with focal length of 30 cm was used to focus the laser beam at the coupling edge of
guided mode was launched in the waveguide. The scattered light from the waveguide was imaged by a lens L2 (focal length = 50 mm) onto a diode array. Attenuation loss coefficients αgw were determined from the scattered light
intensity as function of distance from the coupling prism. The detection limit of this method is in the order of αgw ≈ 0.5
dB/cm.
Cw Nd:YAG
λ= 1064 nm
PC Si-Diode array S L2 Substrate Film P L1 A Cw Nd:YAG
λ= 1064 nm
PC Si-Diode array S L2 Substrate Film P L1 A
Figure 4. Setup for waveguide propagation loss measurement.
III. RESULTS AND DISCUSSIONS
Thin film of M3EH-PPV has the strongest absorption maximum αmax. It can be understood from the chemical
structures that M3EH-PPV has long alkyl substituents at only every second phenyl-ring, whereas MEH-PPV contains alkyl-chains at every phenyl-ring. Meanwhile, the copolymer MEH-M3EH-PPV has three alkyl-chains in every four phenyl-rings. Thus, the reduced amount of alkyl-chains leads to an increase of the number π-electrons per unit volume and consequently
αmax increases. The dispersions of nTE of these polymers are
shown with solid lines in Figure 3. Similar to the intrinsic absorption coefficient, nTE increases in the sequence from thin
films of MEH-PPV, MEH-M3EH-PPV to M3EH-PPV. The dispersions of nTE and nTM of all polymers are shown with
symbols in Figure 3. The results of prism coupling and reflectometry agree very well which indicates that nTE is not
depending significantly on the film thickness, at least for d = 70 nm and 800 nm. Again, we observe a very pronounced increase of nTE in the sequence from MEH-PPV,
MEH-M3EH-PPV to M3EH-MEH-M3EH-PPV. However, we observe nearly identical values of nTM for all polymers.
In order to study the effect of polymer chain orientation, we plot the ratio of refractive indices in TE-polarization (in-plane) and TM-polarization (out-of-(in-plane) for all polymers studied in Figure 5. Clearly, the ratio of nTE/nTM is increased in
going from MEH-PPV to MEH-M3EH-PPV and finally to M3EH-PPV in all spectra region. Since, αmax and refractive
Proc. of the 2nd International Conf. on Optics and Laser Applications ICOLA’07, September 5-7, Yogyakarta, Indonesia
to n, are both highly polarized and have their main components in the chain direction of PPV. Consequently,
αmax and n are largest if the electric field of incident light
is parallel to the chain direction. If the PPV chains become increasingly aligned parallel to the substrate plane, it is evident that αmax which is measured at E
parallel to the film plane, and nTE will increase. This
behavior strongly indicates that amount of PPV chain segments aligned parallel to the substrate plane in thin film is increased in going from MEH-PPV, MEH-M3EH-PPV and finally to M3EH-MEH-M3EH-PPV. Recently, we observed this effect in thin films of MEH-PPV, which were prepared from different molecular weight, Mw. The chain
segments show an increased tendency to align parallel to the layer plane with increasing Mw [8].
600 700 800 900 1000 1100 1,00 1,05 1,10 1,15 1,20 MEH-PPV MEH-M3EH-PPV M3EH-PPV Ra
tio of n
TE
/nTM
Wavelength [nm]
Figure 5. Ratio of nTE and nTM of MEH-PPV,
MEH-M3EH-PPV and M3EH-MEH-M3EH-PPV films.
The dispersions of the modulus of χ(3)
at 1/3 of the fundamental wavelength compared with linear absorption spectra for all PPVs studied are displayed in Figure 6. The χ(3)
values exhibit a strong spectral dependence on the laser wavelength λL because of three-photon
resonances with electronic states of the polymers. The spectrum of the χ(3)
resembles the linear absorption coefficient: it has a maximum, denoted χ(3)
max, at the
laser wavelength λL≈ 3λmax of the absorption coefficient.
The strong maximum of χ(3)
max is ascribed to a
three-photon resonance with states located at the top of the valence band and the exciton state. It occurs at wavelength λL(χ(3)max) ≈ 3λmax of linear absorption
coefficient. The values of χ(3)
max of all PPVs studied are
given in Table 1. The peaks of χ(3)
spectra of all-PPVs are red shifted as compared to their λmax. These shifts are explained as a
consequence of the statistical distribution on the effective
π-conjugation length. As the second order molecular hyperpolarizability, which is responsible for the process of THG increases strongly with the conjugation length,
the chain segments with longer conjugation exhibit much larger molecular hyperpolarizabilities than those with shorter conjugation. As a result, the relative contribution of the long chain segments dominates in the THG process as compared to the linear absorption. This dominance leads to a red shift of the |χ(3)
| spectra.
300 400 500 600
0 5 10 15 20 0 2 4 6 8 MEH-PPV
300 400 500 600
0 5 10 15 20 MEH-M3EH-PPV 0 2 4 6 8 10
300 400 500 600
0 5 10 15 20 25 M3EH-PPV χ (3
) [10
-1
1 esu
]
χ
(3
) [1
0
-1
1 es
u]
χ
(3
) [1
0
-1
1 es
u]
α
[10
4 cm -1]
α
[10
4 cm -1]
α
[10
4 cm -1]
λ, λL/3 [nm]
0 5 10 15
Figure 6. Spectra of the modulus of χ(3)
at λL/3 in comparison with
linear absorption spectra of thin films of MEH-PPV, MEH-M3EH-PPV and M3EH-MEH-M3EH-PPV.
As can be seen in Table 1, the χ(3)
values is increased in going from MEH-PPV, MEH-M3EH-PPV and M3EH-PPV which might be indicated that a more ordered and planar arrangement of the polymer chains was promoted in spin cast film M3EH-PPV as discussed above. A planar arrangement of the polymer chains is expected to enhance the nonlinear optical response in force of the reduced dimensionality of the
π-electron delocalisation. This hypothesis of in-plane ordering was also supported by the anisotropy as displayed in Figure 5. Thin film prepared from M3EH-PPV showed the larger refractive index and birefringence that that of MEH-PPV and its copolymer, what is an indication of an increased ordering. Our recent study shows that the third order susceptibility χ(3)
of thin films of MEH-PPV is increased with the orientation of polymer chains parallel to the substrate [9]. The density of polymer might be another factor that influence the χ(3)
Proc. of the 2nd International Conf. on Optics and Laser Applications ICOLA’07, September 5-7, Yogyakarta, Indonesia
The waveguide propagation loss was determined by measuring the stray light of TE modes as a function of distance from the coupling prism. Figure 7 shows the stray light at the diode array for PPV and MEH-M3EH-PPV slab waveguides.
0,0 0,5 1,0 1,5 2,0
102 103
MEH-M3EH-PPV MEH-PPV TE0 at 1064 nm
Intensity [a.u.]
x [cm]
Figure 7. Intensity of the light scattered from TE0 modes of
waveguides of MEH-PPV and MEH-M3EH-PPV versus distance from the prism at λ = 1064 nm.
The slopes of the lines fitted to the experimental data yield the loss coefficients of the guided waves αgw. The
values of αgw of all PPVs both in TE- and
TM-polarizations are presented in Table 1. They contain the contributions of intrinsic absorption and the scattering losses, which depend on the surface roughness of the waveguide. Although the values of the relative surface roughness (Ra/d) of all PPVs are comparable (0.5 –
1.2 %), they exhibit different values of αgw. This might
be related to aggregate formation caused by a different solubility of the polymers. The substitution with the branched 2-ethylhexyloxy group causes very good solubility of the PPVs. We observed that the solubility is reduced in going from MEH-PPV to MEH-M3EH-PPV and finally to M3EH-PPV due to the decrease of the relative number of this “solubility providing” substituent (Figure 1). Consequently, an increased tendency of aggregate formation is imaginable which would cause an increase of light scattering in the sequence of these three PPVs. As a consequence, αgw in both TE and TM
polarizations increases. Another factor might be related to the different morphology of the films. Our recent study of thin films MEH-PPV shows that the large changes of
αgw can be caused by different morphology of thin films,
in particular on the arrangement of polymer chains in the films [8].
IV. CONCLUSIONS
We have performed comparative studies of three polymer films of PPV derivatives by means of reflectrometry, prism coupler, third harmonic generation spectroscopy and waveguide propagation loss. We have shown that the length of alkyl side chains affects both the linear and nonlinear optical properties as well as waveguide properties. The reduced amount of alkyl-chains leads to an increase of the number π -electrons per unit volume, therefore, more polymer chain segments are oriented parallel to the layer plane. As consequences, the αmax, nTE , and χ(3) increase in the sequence
from MEH-PPV, MEH-M3EH-PPV to M3EH-PPV. However, the reduced of alkyl-chains substitution reduce of solubility which leads to the gel formation. Therefore, both αgw (TE0)
and αgw (TM0) are increased. We have concluded that thin
films of the conjugated polymers MEH-PPV is the most appropriate candidate for all-optical switching applications, because it exhibit good combination of large value of cubic nonlinearity and ultimately low waveguide propagation loss coefficient.
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