STUDY ON LOSS CHARACTERISTIC OF POLYMER...

STUDY ON LOSS CHARACTERISTIC OF POLYMER MATERIAL FOR OPTICAL WAVEGUIDE APPLICATION

ANIS SHAHIDA NIZA MOKHTAR

A thesis submitted in fulfilment of the requirements for the award of the Degree of

Master of Engineering (Electrical-Electronic & Telecommunication)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

NOVEMBER 2005

v

ABSTRACT

Communication technologies today are increasingly reliant on the

manipulation of optical signals where previously electronic circuit manipulated those

signals. With photonic technology, devices are no longer limited only to the silicon

wafer because it also not requires broader functionality than can be offered on this

traditional platform. Optical waveguides using polymer materials are attractive for

telecommunication applications due to their low costs and simple processing steps

compared to silica-based materials. Many advantages in term of optical properties

have been proved by the polymer waveguides. Polymer waveguides are potentially

useful for short distance optical interconnections. The most important characteristic

of a waveguide is the attenuation or loss experienced by light wave as it travels

through the waveguide. This dissertation focused on loss measurement of BCB

polymer waveguides. Sample of waveguides with variation thickness have been

fabricated by deposition of the polymer solution onto glass substrate. The

measurement is done by using two types of wavelength that is 630nm and 1550nm.

After analyzed all the coupling method, prism coupler method is considered as one

of the best ways to couple large amount of light in planar optical waveguides.

Furthermore it can be used to determine the loss of polymer waveguide and its

characteristics. Investigation of the polymer waveguides with respect to temperature

and water also done to see its stability.

vi

ABSTRAK

Komunikasi pada hari ini semakin beralih kepada isyarat optik yang mana

sebelum ini di manipulasi oleh litar elektronik. Dengan teknologi fotonik, peralatan

tidak lagi bergantung kepada lapisan silika kerana ia memerlukan fungsi yang lebih

luas daripada yang telah diberikan oleh platform tradisional. Pemandu gelombang

optik menggunakan polimer mempunyai daya tarikan untuk aplikasi telekomunikasi

kerana kos yang rendah dan langkah pemprosesan yang ringkas berbanding dengan

bahan berasaskan silika. Banyak kelebihan di dalam terma ciri-ciri optik yang telah

dibuktikan oleh pandu gelombang polimer. Pandu gelombang polimer berpotensi

berguna untuk sambungan optik jarak dekat. Ciri-ciri yang paling penting di dalam

pandu gelombang adalah pelemahan atau kehilangan cahaya yang merentasi pandu

gelombang polimer. Sampel pandu gelombang dengan ketebalan yang berbeza telah

di fabrikasi dengan menggunakan polimer ke atas substrat kaca. Pengiraan

dilakukan dengan menggunakan dua jenis panjang gelombang iaitu 630nm dan

1550nm. Setelah menganalisis kaedah-kaedah gandingan yang ada, kaedah

pengganding prisma adalah cara terbaik untuk menggandingkan cahaya yang banyak

di dalam pemandu gelombang polimer. Tambahan pula ia boleh digunakan untuk

menentukan kehilangan pemandu gelombang dan sifat-sifatnya. Pemandu gelombang

polimer juga di kaji terhadap kesan suhu dan air untuk melihat stabilitinya.

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITLE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF SYMBOLS xv

LIST OF ABBREVIATIONS xvii

CHAPTER 1 INTRODUCTION

1.1 Introduction 1

1.2 Objectives 3

1.3 Scope Of Research 3

1.4 Methodology 4

1.5 Thesis Outline 5

viii

CHAPTER 2 WAVE THEORY OF OPTICAL WAVEGUIDES

2.1 Introduction 7

2.2 Slab Waveguide structure 8

2.3 Formation of guided modes 10

2.4 Maxwell equation 14

2.5 Cut-off Condition 20

2.6 Losses In Optical Waveguide 20

2.6.1 Scattering Losses 21

2.6.1.1 Surface Scattering Losses 22

2.6.2 Absorption Losses 25

2.6.2.1 Interband Absorption 25

2.6.2.2 Free carrier Absorption 26

2.6.3 Radiation Losses 27

2.6.3.1 Radiation Loss From Planar And Straight Channel 27

Waveguide

2.6.3.2 Radiation Loss From Curved Channel Waveguides 28

2.7 Measurement Of Waveguide Losses 29

2.7.1 End-Fire Coupling To Waveguides of Different Length 29

2.7.2 Fabry-Perot Cavity Measurement Technique 31

2.7.3 Direct Cut Back Method 33

2.7.4 Prism Coupled Loss Measurements 34

2.8 Polymeric Optical Waveguides 36

2.8.1 Polymeric Waveguide Characteristic 36

2.8.2 Polymer Waveguide For Optical Interconnects And 37

Optical Telecommunication Devices.

ix

CHAPTER 3 FABRICATION OF SLAB WAVEGUIDE

3.1 Introduction 40

3.2 B-Staged Bisbenzocyclobutene (BCB) from DOW® Chemical 41

3.3 Fabrication Process 43

3.3.1 Surface Preparation 45

3.3.2 Adhesion Promoter 46

3.3.3 BCB Coating 46

3.3.4 Hot Plate Soft Bake 48

3.3.5 Exposure 50

3.3.6 Pre-Develop Bake 51

3.3.7 Puddle Develop 51

3.3.8 Post Develop Bake 51

3.3.9 Curing Process 52

3.4 End Product 52

CHAPTER 4 PRISM COUPLING

4.1 Introduction 55

4.2 Prism coupler principle 56

4.3 Prism Design 57

4.4 Optimum Coupling 59

4.5 Experimental arrangement 59

4.6 Metricon2010 prism coupler 61

4.6.1 Measurement procedure 62

x

CHAPTER 5 RESULT AND ANALYSIS

5.1 Introduction 65

5.2 Result Of Prism Coupling At Wavelength of 630nm 66

5.3 Result Of Prism Coupling At Wavelength of 1550nm 77

5.4 Polishing Waveguide 86

5.4.1 Problems Encountered in Polishing Slab Waveguide 89

5.5 Waveguide Test Towards Thermal 89

5.6 Waveguide Test Towards Water 91

CHAPTER 6 FURTHER WORKS AND CONCLUSIONS

6.1 Further Works 93

6.2 Conclusion 94

REFERENCES 96

APPENDIX 99

xi

LIST OF TABLES

TABLE TITLE PAGE

3.1 Recommended storage temperatures and times 43

3.2 Thickness of film for different speed for Cyclotene 47

4024-40 resins.

3.3 Hot plate soft bake temperatures for pre-develop bake 49

process.

3.4 Cure Profile for convention oven curing 53

4.1 Specification of metricon2010 prism Coupler 62

5.1 Summary of loss measurements at wavelength of 630nm 67

5.2 Summary of loss measurement at wavelength 1550nm 80

5.3 Comparison between data collected in the lab and NTU 85

5.4 Losses for Thermal Stress Effect. 90

xii

LIST OF FIGURES

FIGURE TITLE PAGE

1.1 (a) optical-electric-optical (OEO) and (b) all optical datalink. 2

2.1 A planar slab waveguide 8

2.2 Basic structure and refractive-index profile of the optical 8

waveguide

2.3 Light ray and their phase fronts in the waveguide. 10

2.4 Total internal reflection of a plane wave at dielectric interface. 11

2.5 Formation of modes (a) fundamental modes (b) higher order modes. 13

2.6 Dispersion curves of a slab waveguide 14

2.7 Symmetric diagrams of planar dielectric waveguides. 18

2.8 diagram of ray optic approach to determination of scattering loss. 22

2.9 Diagram illustration the velocity approach to the determination 29

of radiation loss.

2.10 Schematic diagram for measurement of waveguide employing 31

end-fire coupling

2.11 Schematic view of the experiment setup for Fabry-Perot cavity 33

waveguide loss measurements. Inserts shows the detailed cavity

configuration consisting of the waveguide coupled to two

polarization maintaining fibers.

2.12 Schematic diagrams for measurement of waveguide attenuation 35

employing prism coupler

2.13 A prism is located a small distance above the guiding film. A 36

beam is incident in the prism, and under proper conditions can

couple into the waveguide.

2.14 Schematic of board-to-board connection by a polymeric 38

waveguide film with connector

2.15 Schematic of 45o mirror applied as 90o out-of-plane optical 39

deflectors for use as connects between multimode fibers and

VSCEL’s.

3.1 Synthesis of benzocyclobutene 42

3.2 Process flows for Cyclotene 4024. 44

3.3 Ultrasonic cleaner used in cleaning process 45

3.4 Spin coater used in coating process 48

3.5 Oven used in softbake, pre-develop and cure process 50

3.6 Slab waveguide. 53

3.7 Fabricated samples of BCB polymer waveguides 54

4.1 Prism coupling into a planar waveguide with rutile half prism 57

4.2 Prism coupling with a symmetrical prism 57

4.3 Prism coupler used in the experiment 58

4.4 Actual set-up using prism coupling method 60

4.5 Coupling the light into prism. 61

5.1 Graph of Spin Speed against Thickness 67

5.2 Graph of Spin Speed versus loss of waveguide 68

5.3 Refractive index profile hard cure for 4024 Cyclotene given by 69

manufacturer

5.4 Modes in waveguide with spin speed 1500 rpm, TE polarization 70

and wavelength of 630nm

5.5 Modes in waveguide with spin speed 1500 rpm, TM polarization 71

at wavelength of 630nm

5.6 Modes in waveguide with spin speed 3000rpm, TE polarization 72


5.7 Modes in waveguide with spin speed 3000rpm, TM polarization 73


5.8 Modes in waveguide with spin speed 5000rpm, TE polarization 74


5.9 Modes in waveguide with spin speed 5000rpm, TM polarization 75


xiv

5.10 Result of cut-off thickness calculation for wavelength of 630nm 76

5.11 Loss for 3000rpm sample waveguide 78




5.15 Graph of Spin Speed against Loss Waveguide. 80

5.16 Modes found in waveguide with spin speed 3000rpm, TE 81

polarization at wavelength 1550nm

5.17 Modes found in waveguide with spin speed 3000rpm, TM 82


5.18 Modes found in waveguide with spin speed 5000rpm, TE 83


5.19 Modes found in waveguide with spin speed 5000rpm, TM 84


5.20 Result of cut-off thickness calculation for wavelength of 1550nm 85

5.21 Waveguide before polishing process 87

5.22 Grinding machine 87

5.23 Waveguide after grinding process. 88

5.24 Waveguide after etching process. 88

5.25 Graph of Losses towards Re-Heated Waveguide. 91

5.26 Waveguide soaked in water 92

5.27 BCB coated was peeled off from substrate. 92

xv

LIST OF SYMBOLS

maxθ - Maximum Light Acceptance Angle

vρ - Current Density.

D - Electric Field Density,

φ - Propagation Angle

E - Electric Field Intensity

B - Magnetic Field Density

H - Magnetic Field Intensity

Ima x - Maximum Transmitted Intensity

Imin - Minimum Transmitted Intensity

m. - Mode Number

n1 - Refractive Index of Cladding Region

n2, nf - Refractive Index of The Thin Film

n3, ns - Refractive Index of Substrate Layer

na - Refractive Index of Air

np - Refractive Index of The Prism

r - Reflection Coefficient.

T - Transmission Reflection Coefficients

α - Attenuation Coefficient

β - Propagation Constant

ε - Permittivity of a Medium

η - Coupling Efficiency

θc - Critical Angle of Total Internal Reflection

θi - Incident Angle,

θm - Incident on The Prism Face At An Angle

xvi

κ - Coupling Coefficient.

λ - Wavelength

λc - Cutoff (free space) Wavelength

µ - Permeability of a Medium

σ2 - Variances

Ф - Phase Shift

xvii

LIST OF ABBREVIATIONS

AWG - Arrayed Waveguide Grating

AWG - Arrayed-Waveguide Grating

BCB - B-Staged Bisbenzocyclotene

NA - Numerical Aperture.

OADM - Optical Add/Drop Filter/Multiplexer

OEO - Optical-Electrical-Optical

OIC’s - Optical Integrated Circuits

PIC’s - Photonic Integrated Circuits

TDM - Time Division Multiplexing

TE - Transverse Electric

TEM - Transverse Electromagnetic Mode

TLS - Tunable Laser Source

TM - Transverse Magnetic

VCSEL’s - Vertical-Cavity Surface-Emitting-Laser

VLSI - Very Large-Scale Integrated

VOA - Variable Optical Attenuator

CHAPTER 1

INTRODUCTION

1.1 Introduction

There is a great interest in creating optical integrated circuits (OIC’s) or

photonic integrated circuits (PIC’s) that are capable of switching optical rather than

electrical signal. The fundamental difference between existing optical networks and

future all-optical networks is illustrated in Figure 1. 1. Current data networks

typically handle several signal formats by transmitting optical signals over long

distances via single-mode fibers and performing data manipulation, such as

switching and filtering, on electrical signals. Therefore, current networks require an

optical-electrical-optical (OEO) signal conversion step, one that is costly in terms of

network speed, bandwidth, power consumption, hardware complexity, and signal

integrity (noise). All-optical switching refers to the direct manipulation and routing

of optical signals without the need for an intermediate conversion to electrical signals

before switching takes place.

It is expected that future networks will avoid the OEO signal conversion step

by performing all data manipulation directly on optical signals, thereby greatly

increasing network performance. The field that will enable all-optical data

2

manipulation is referred to as integrated optics. It is envisioned that integrated optical

circuits will eventually reach a complexity similar to that of very large-scale

integrated (VLSI) electronic circuits where this electronic circuits will be replaced by

photonic circuits. With photonic technology, devices are no longer limited only to

the silicon wafer and often require broader functionality than can be offered on this

traditional platform. Recently, polymeric optical waveguide are becoming

increasingly important because of the functionality and complexity that can be

fabricated reliably at low cost with high manufacturing output.

This project discusses the fabrication and loss characterization of polymer

based optical waveguide. Slab waveguides were fabricated by deposition of polymer

onto substrate to form a film layer and spinning the substrate on the spinner to spread

the layer evenly. Different thicknesses of slab waveguide are realized by using

different spin speed. Photo BCB is used as a polymer material and the loss was

measured by using prism coupler technique. The behaviours of these polymer

waveguides are then investigated with respect to temperature and water to see its

stability. The next section in this chapter presents the objectives, scopes and research

methodology of this thesis. Description of thesis outline is presented at the end of

this section.

(a) (b)

Figure 1.1: (a) optical-electric-optical (OEO) and (b) all optical datalink.

3

1.2 Objectives

i. To fabricate polymer slab waveguide and acquire the experience on the

fabrication process

ii. To setup measurement system in order to determine the attenuation of polymer

based optical waveguide

iii. To identify possible polymer material for the purpose of developing a polymer

based optical waveguide

1.3 Scope of research

i. To understand fundamentals of related areas including optical waveguide and

optical measurement technique.

ii. To study properties of cyclotene 4024-40 photo polymer from the given

specifications.

iii. To understand and practice in house fabrication process of slab waveguide.

iv. To setup a measurement system.

v. To measure loss of the fabricated slab waveguides using setup system.

vi. To test the waveguides stability towards thermal and water

vii. To analyze measured results.

4

1.4 Methodology

Two main stages are employed in order to fulfill the objectives of this project.

The first stage is to acquire the basic knowledge about optical waveguides. Journals

and papers will be referred to enhance the understanding and to get the overview of

the projects. The second stage is to concentrate in exploring the important

characteristic in designing optical devices. In order to design an optical device, there

are many criteria that need to be considered such as the material that we want to use,

the application of the optical devices and how much cost is needed to design it. This

is followed by understanding the actual fabrication process of a polymer based

optical waveguide. There are many important properties to determine the quality of a

waveguide such as its attenuation, refractive index, birefringence, thermo optics

coefficient and thickness. This project is focused on the attenuation of polymer based

slab waveguides. Therefore simple measurement system based on the prism

coupling technique is developed. All results are collected and analyzed, and the

performances of these waveguides are then evaluated. Lastly, a report will be written

which composed of all findings, results and conclusion.

5

1.5 Thesis Outline

This thesis is organized into 6 chapters. Chapter 1 discusses the general

explanation of polymer based optical waveguide, coupling method and the

application of this polymer waveguides in the industry. The objectives that need to

Collecting Data and Analyzing

Report Writing

Setup measurement system

Validation of finding

Literature Review

Fabrication of Slab Waveguide

Meet the quality?

Yes

No

6

be achieved, the scope of research and the methodology used in this project are also

described in this chapter. In chapter 2, the theory of planar slab waveguides is

reviewed. These includes the derivation of mode in slab waveguides, the losses that

encountered in the optical waveguides and some of the measurement methods that

are used to measure loss of optical waveguides. At the end of this chapter, it will

discuss the polymeric optical waveguides, its material characteristic and the

applications. The fabrication process of slab waveguide is explained in chapter 3.

Details of every stage are clarified here. Prism coupler which is the method used in

this project is described in chapter 4. In chapter 5 the results from the measured data

are presented and analyzed. Finally the conclusions of the research will be drawn and

some suggestions for further work will be recommended in Chapter 6.

96

REFERENCES

1. Claire Piyois and Anders Hult. Absorption And Scattering In Low Loss

Polymer Optical Waveguides. J.OptSoc.Am. July 2001Vol. 18, No.7.

2. Christos Themistos, B.M Azizur Rahman,Angelos Hadjicharalambous, and

Kenneth Thomas Victor Grattan. Loss/Gain Characterization of Optical

Waveguides. IEEE J. Quantum Electron, 1995. pp.1760-1675,

3. Shee Yu Gang, Norazan Mohd. Kassim, Abu Bakar Mohammad,and Mohd

Haniff Ibrahim. Fabrication of Polymeric Optical Waveguides by B-staged

Bisbenzocyclobutene(BCB). ICSE2004. Kuala Lumpur, Malaysia, 2004

4. Shacklette, R.Blomquist,J.Deng,P.Ferm, M. Maxfield, J. Mato, P.Jiang,

K.Kilian, K.Beeson, and H.Zou. Polymer Waveguide and Device

Applications. OFC2003. Vol. 1, 2003

5. Tatsuya Yamashita, Manabu Kagami, and Hiroshilto. Waveguide shape

control and loss properties of light-induced self written (LISW) optical

waveguides, Journal of lightwave technology.2002. Vol 20

6. John. M. Senior Optical Fiber Communications, Principal And Practice.

pp.84-96, p 347-349, Prentice Hall, 1992

7. Aydin Yeniay, Renyuan Gao, Kazuka Takayama, Renfeng Gao, and Anthony

F. Garito. Ultra Low Loss Polymer Waveguides. Journal Lightwave

Technology. Vol. 22, no 1, p.154-158 ,2004

8. William H. Steier, S-S Lee, S. Gamer, A.Chen, H.Zhang, and Larry R.

Dalton. Applications Of Polymers To Integrated Optics.

9. S Monneret, P Huguet-Chantome and F Flory. M-line technique: prism

coupling measurement and discussion of accuracy for homogeneous

waveguides, j.Opt A: pure Appl. Opt 2 , p. 185-195, 2000

97

10. S. Agan F.Ay, A.Kocabas, A.Aydinli. Stress Effect In Prism Coupling

Measurement of Thin Polymer Films. Appl.Phys A.80 p 341-345, 2005.

11. Casey F. Kane and Robert R Krchnavek. Benzocyclobutene optical

waveguides IEEE Photonics Technology letters, Vol 7. 5 May 2005.

12. Polymers for encapsulation: material Processes and Reliability.

13. Aydin Yeniay, Renyuan Gao, Kazuya Takayama, Renfeng Gao and Anthony

F. Garito. ‘Ultra-Low-Loss Polymer Waveguides’, Journal of Lightwave

Technology, Vol.22, No.1, January 2004, pp.154-158.

14. Tien P.K., Ulrich R. and Martin R. J Modes of propagating Light waves in

thin deposited semiconductor films. Applied Physics Leters, 1969. 14:291-

294

15. Myung-Hyun Lee, Jung Jin Ju,Suntak, Jung Yun Do and Seong Koo Park.

Polymer-based Devices for Optical Communications ETRI Journal, Vol.

24,Number 4, pp. 259-304, August 2004

16. Dow Chemical Company. Processing Procedures for cyclotene 4000 Series

Photo BCB Resins.1999

17. Michael E. Clarke. Introducing Low-k Dielectrics into Semiconductor

Processing.2001

18. D. Navarro-Urrios et. Al .Pump-probe experiments on low loss silica

waveguides containing Si nanocrystals Mater. Res. Soc. Symp. Proc. Vol.

832. 2005

19. Edwin Y B Pun, W H Wong,.Polymeric waveguides and devices for

integrated optics applications

20. John H. Lupnski and Robert S. Moore, Silicone Gels and Coatings for

Integrated-Circuit Packaging. In polymeric material foe electronics

Packaging and Interconnection. USA:Americal Chemical Society. pp 268-

274;1989

21. M.S.Sodha and A.K.Ghatak, Inhomogeneous Optical Waveguides. New

York: Plenum Press.1977

22. Thomas Feuchter and Carsten Thirstrup. High Precision Planar Waveguide

Propagation Loss Measurement Technique Using Fabry-Perot Cavity: IEEE

Photonics Technology Letter.Vol6. Oct 1994

23. H.P. Weber, F.A. DUM and W.N. Leibolt. Appt. Optics 12 (1973) 755.

24. Y.H. Won, P.C. Janss and G.H. Chattier. Appl. Phys. Lett. 37 (1980) 269.

98

25. E.A. Aruhmyan and S.K. Galoyan, Optics Comm. 57 (1986)391.

26. Makoto Hikita, Koji Enbutsu, et.al. Polymeric Optical Waveguide Films For

Short Distance Optical Interconnects. IEEE Journal Vol. 5. No 5. Oct 1999.

STUDY ON LOSS CHARACTERISTIC OF POLYMER...

Documents

Transcript of STUDY ON LOSS CHARACTERISTIC OF POLYMER...