ISBN Number: 978-979-8575-05-1

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IICCOOLLAA’’0077

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

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IICCOOLLAA’’0077

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

ISBN Number: 978-979-8575-05-1

i

© 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

Phone (62) 21 330188, Fax. (62) 21 391115, Email: spsopto@bit.net.id http://opto.eng.ui.ac.id

ii

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 30th anniversary 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 55 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 General Chairman of ICOLA2007

iii

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

Dr. Gunawan Witjaksono, Chair, University of Indonesia Prof. Dr. Dadang Gunawan, IEEE-Indonesia Section

iv

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 F. Ashta Ekadiyanto, ST. MSc, University of Indonesia

Aji Nur Widyanto, ST, University of Indonesia

v

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 Miura�� and 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

48

vi

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 Znxcd1-X Nanocrystalline Films

Shashi Bhushan and 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

103

vii

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. Bahtiar and 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 μm

Sekartedjo, and Agus Muhamad Hatta

140

Phase Unwrapping Applied to Digital Holography D. Ardiansyah and 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

152

viii

Simple Model of Design 1.55μm and 1.31μm 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

Helmi Adam, Dwi Astharini, Ary Syahriar

181

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 Gani and 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

202

ix

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 Wahab

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

245

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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: ayibahtiar@yahoo.com

†Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany Tel. ++49-6131-379122, Fax. ++49-6131-379100, email: bubeck@mpip-mainz.mpg.de

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-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 system have 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-1,2-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 Figure 1.

T

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Proc. of the 2nd International Conf. on Optics and Laser Applications ICOLA’07, September 5-7, Yogyakarta, Indonesia

O

O

CH3

nCH=CH

CH CH

OCH3

CH3O

O

CH3On

CH CH

MEH-PPV M3EH-PPV

CH CH CHCH

CH3O

O

CH3O

O

0.5nCH CH CH

CH3O

O

CH3O

OCH3

0.5nCH

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(

maxχ [10-11 esu]

αgw (TE0) [dB/cm]

αgw (TM0) [dB/cm]

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 6000

5

10

15

20

25

M3EH-PPV

MEH-M3EH-PPV

MEH-PPV

α [1

04 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.

In addition to reflection spectroscopy, we used prism coupling technique to measure the refractive index of slab waveguides at several wavelengths between 633 nm and 1064 nm. The typical thicknesses of waveguides were in the range of 400 - 800 nm. The results are displayed in Figure 3 together

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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

2,2Closed 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 the prism. The coupling angle was adjusted until the

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:YAGλ = 1064 nm

PCSi-Diode array

S

L2

SubstrateFilm

P

L1ACw Nd:YAG

λ = 1064 nm

PCSi-Diode array

S

L2

SubstrateFilm

P

L1A

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-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-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 index are correlated to each other; both quantities can show significant anisotropy in thin films. The electronic π-π* transition at λmax and the electric polarizability which is related

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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-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

Rat

io o

f nTE

/nTM

Wavelength [nm]

Figure 5. Ratio of nTE and nTM of MEH-PPV, MEH-M3EH-PPV and 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

8MEH-PPV

300 400 500 600

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5

10

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20 MEH-M3EH-PPV

0

2

4

6

8

10

300 400 500 600

0

5

10

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25M3EH-PPV

χ(3) [1

0-11 e

su]

χ(3) [1

0-11 e

su]

χ(3) [1

0-11 e

su]

α [1

04 cm

-1]

α [1

04 cm

-1]

α [1

04 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-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) value.

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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 MEH-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

Inte

nsity

[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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[2]. F. Kajzar, and J.D. Swalen, Eds.; Organic Thin Films for Waveguiding Nonlinear Optics; Gordon and Breach Publ.: Amsterdam, 1996.

[3]. A. Mathy, K. Ueberhofen, R. Schenk, H. Gregorius, R. Garay, K. Müllen, and C. Bubeck, “Third-harmonic-generation spectroscopy of poly(p-phenylenevinylene): A comparison with oligomers and scaling laws for conjugated polymers”, Phys. Rev. B Vol. 53, pp. 4367-4376, 1996.

[4]. M.A. Bader, G. Marowsky, A. Bahtiar, K. Koynov, C. Bubeck, H. Tillmann, H.-H. Hörhold, and S. Pereira, “Poly(p-phenylenevinylene) derivatives: new promising materials for nonlinear all-optical waveguide switching”, J. Opt. Soc. Am. B Vol. 19, pp. 2250-2262, 2002.

[5]. R.H. Friend, R.W. Gymer, A.B. Holmes, J.H. Burroughes, R.N. Marks, C. Taliani, D.D.C. Bradley, D.A. Dos Santos, J.L. Bredas, M. Logdlund, and W.R. Salaneck, “Electroluminescence in conjugated polymers”, Nature Vol. 397, pp. 121-128, 1999.

[6]. M.D. McGehee, and A.J. Heeger, “Semiconducting (conjugated) polymers as materials for solid-state lasers”, Adv. Mater. Vol. 12, pp. 1655-1668, 2000.

[7]. J. Zaumseil, R.H. Friend, and H. Sirringhaus, “Spatial control of the recombination zone in an ambipolar light-emitting organic transistor”, Nature. Mater. Vol. 5, pp. 69-74, 2006.

[8]. K. Koynov, A. Bahtiar, T. Ahn, R.M. Cordeiro, H.-H. Hörhold, and C. Bubeck, “Molecular weight dependence of chain orientation and optical constants of thin films of the conjugated polymer MEH-PPV”, Macromolecules Vol. 39, pp. 8692-8698, 2006.

[9]. A. Bahtiar, K. Koynov, T. Ahn, and C Bubeck,” The effect of molecular weight on the third-order nonlinear optical susceptibility in thin MEH-PPV films” 2006, submitted.

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