TABLE OF CONTENTS CHAPTER TITLE PAGE

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1 v ABSTRACT Fabrication of fiber coupler using fusion requires stable torch flame. Stable torch flame is needed to have a good performance of fabrication. A model was required to observe the stable by equilibrium state of silicon dioxide fiber and nitrogen gas used for fabrication of fiber coupler. Continuity equation was applied to show the model of kinetic reaction derived from process of fiber molecule and nitrogen gas. Arrhenius equation form based on temperature variation and integration of kinetic model was examined. Validation of kinetic model towards thermodynamic equilibrium is evaluated by a zero dimensional and time dependence. Nitrogen species density is modelled by a continuity equation and extended form of Arrhenius equation. These equations were used to integrate the change of density over time. The integration was performed to acquire density and the reaction rate of each reaction where temperature and time dependence were imposed. A comparison was made with global model within pressure range of 1-100mTorr and the temperature of electron is set to be higher than other nitrogen species. Results show that the chemical kinetic model agrees only for high pressure because of no power imposition. The global model provides the power in the pressure range for electron and nitrogen at high density by a factor of 3 to 5. This model is plausible for evaluating experimental process in the fabrication of fiber coupler.

2 vi ABSTRAK Fabrikasi pengganding gentian menggunakan kaedah lakuran memerlukan nyalaan api yang stabil. Kestabilan nyalaan api diperlukan dalam menghasilkan fabrikasi yang baik. Sebuah model digunakan untuk melihat kestabilan keseimbangan gentian silicon dioksida dan gas hidrogen yang digunakan dalam proses fabrikasi pengganding gentian. Persamaan kesinambungan diaplikasikan untuk menunjukkan tindak balas kinetik. Bentuk persamaan Arrhenius berdasarkan variasi suhu dan integrasi model kinetik diperiksa. Pengesahan model kinetik terhadap keseimbangan termodinamik dinilai oleh dimensional sifar dan kebergantungan masa. Spesis ketumpatan nitrogen dimodelkan dengan persamaan kesinambungan dan bentuk persamaan Arrhenius lanjutan. Kedua-dua persamaan ini digunakan untuk integrasi perubahan ketumpatan melalui masa. Integrasi ini memerlukan ketumpatan dan kadar tindak balas di mana kebergantungan masa dan ketumpatan dikenakan. Perbandingan dibuat dengan model global dalam julat tekanan 1-100mTorr dan suhu elektron diset lebih tinggi dari spesis nitrogen yang lain. Keputusan menunjukkan model kinetik kimia menepati pada tekanan yang lebih tinggi kerana tiada kuasa yang dikenakan; manakala model global mengambil kira kuasa luar sepanjang julat tekanan. Elektron dan nitrogen memberikan ketumpatan yang tinggi pada faktor 3 hingga 5. Model ini boleh digunakan untuk menilai proses eksperimen dalam fabrikasi pengganding gentian.

3 vii TABLE OF CONTENTS CHAPTER TITLE PAGE DECLARATION DEDICATION ACKNOWLEDGEMENTS ABSTRACT ABSTRAK TABLE OF CONTENTS LIST TABLES LIST OF FIGURES LIST OF SYMBOLS ii iii iv v vi vii x xi xii 1 INTRODUCTION 1.1 Overview Background of study Problem statement Objectives of the study Scope of the study Significance of the study Organization of the study 5

4 viii 2 LITERATURE REVIEW 2.1 Introduction Fabrication of fusion fiber coupling Thermodynamic equilibrium Nitrogen plasma species 12 3 MODELING OF KINETIC COLLISIONS OF FIBER FUSION 3.1 Introduction Chemical kinetic model Global model Simulation and execution of Matlab programming 20 4 RESULTS AND DISCUSSION 4.1 Introduction Integration and application model to low pressure discharge Comparative model Nitrogen species densities for higher atmospheric pressure Integration model for nitrogen gas mixture 35

5 ix 5 CONCLUSIONS 5.1 Conclusions Future works 37 REFERENCES 38 Publications 42 Appendices A-F 43-73

6 x LIST OF TABLES TABLE NO. TITLE PAGE 3.1 Nitrogen reaction composition with Arrhenius parameters 17

7 xi LIST OF FIGURES FIGURE NO. TITLE PAGE 1.1 Fabrication of fused coupler: the basic fuse-pull-taper method The basic structure of a fused biconical tapered (FBT) fiber coupler Experimental setup to fabricate fused fiber coupler Schematic diagram of SMF-28e during fiber fusion Coupled SMF-28e fibers SMF-28e fibers after fusion coupling process Job control for each specified m.file Schematic diagram showing the execution of Matlab m.file for the reaction rate of nitrogen species (a) Simulation flow chart (b) Simulation flow chart (continued) Snapshots of figure generated by output m.file for nitrogen species densities Nitrogen species density for T = 1.8eV to 7eV 28

8 xii 4.3 The electron density and electron temperature in global model measured by Singh and Graves(2000b) as a function of discharge pressure Nitrogen species density where the initial values are taken from the global model The initial species densities is used by global model measured by Singh and Graves(2000b) as a function of discharge pressure The reaction rate of species densities as a function of discharge pressure. 34

9 xiii LIST OF SYMBOLS T e - Temperature of electron (K) T g - Temperature of gas (K) T i - Temperature of ion (K) n i - density ν i - velocity K - Temperature in kelvin

10 xiv LIST OF APPENDICES APPENDIX TITLE PAGE A Kinetic parameters applied to NOx model 43 B equilbnox.m 44 C Coding for kinetic parameters of nitrogen species (n2data.m) 46 D Coding for run the equilibrium densities of nitrogen species (equilb.m) 48 E Coding for calculating the reaction rates of nitrogen species (rrates.m) 52 F Set of data generated by Matlab for each pressure range from 1 to 3 atm 53

11 CHAPTER 1 INTRODUCTION 1.1 Overview The technological process in single mode optical fiber fabrication has stimulated significant interest in a variety of scientific fields. Single mode fiber now widely is used in communication systems, because of its ability in handling highcapacity data. Their unique properties also make them particularly interesting for a broad range of applications, such as interferometers, optical sensors, and optical signal processors (Ramaswani, 2002). The widespread use of fiber couplers in a variety of systems has become quite commonplace. Major market segments include telecommunications and cable television, instrumentation and sensors. Of these, telecommunication sectors have the largest market share today and still have the greatest potential for growth (Yadlowsky, et al., 1997). In addition, fused couplers are important passive components in fiber communication systems which perform such functions as light branching and splitting in passive networks, light wavelength multiplexing/demultiplexing, light filtering, light polarization selective splitting and wavelength independent light splitting (Shaafsma et al,. 1997). As is well known, the basic technique of fabrication of fused fiber coupler involves lateral flame fusion and simultaneous stretching of a pair of unjacketed single-mode fibers over a short length in a high temperature micro flame as shown in Figure 1.1. The fused region transforms into a biconical-tapered junction and hence

12 2 it is also called "fused biconical tapered" coupler shown in Figure 1.2. Because the input and output ends are identical, thus either side may be used as an input end, or hence these components are also referred to as bidirectional couplers. During the process of "fusion and elongation," light is launched into one of the input ports and output light from the two exit fibers ports is constantly monitored. Figure 1.1: Fabrication of fused coupler: the basic "fuse-pull-taper" method (Bisnu et al., 2006). Figure 1.2: The basic structure of a fused biconical tapered (FBT) fiber coupler (Bisnu et al., 2006). Because of the smallness of the fiber dimensions, the process of fabrication requires a high degree of precision and control by appropriate parameters, and even a minute perturbation in any of the process variables from the designed ones may significantly affect the performance characteristics of the device (Bisnu et al., 2006). Most development in the fabrication of fused fiber coupler is focused in achieving loss excess loss fused fiber coupler (Bilodeau et al., 1988; Hsieh et al., 2001), novel optical fiber (Chen et al., 2004; Chuai Ci-jun et al., 2006), fusion

13 3 elongation method (Wong et al., 1997; Mc Atamney et al., 2005; Itaru Yokohama et al., 1987) and other mechanical process. But rarely any review discussing the process occurs during the fused fiber coupler fabrication. However, for some unknown reason achieving the efficiency of coupling are not obvious. It is not only the complicated system where the optical parameter involved when fusion coupling, the mechanical process tends to reach output of result by ignoring other parameter. This can be seen where the input and output port of the machine can be controlled readily, while it is not possible for the process. 1.2 Background of the study Fabrication of 1x2 coupled fiber type SMF28e has been experimentally conducted using AcuPler 2000 machine (Saktioto et al., 2007). This system has a slightly stable fire torch with temperature range of 800 o C-1300 o C measured using a thermocouple. The fire torch is injected by hydrogen gas flowing at pressure of 1 bar. Fusion fiber by flame is affected by environment and flame itself. The heat source normally employed for this purpose is a gas such as a mixture of hydrogen, nitrogen and oxygen flame. It is intended to investigate the reaction occurred and achieved during the fabrication of fused fiber coupler.

14 4 1.3 Problem statement During the fabrication of fused fiber coupler, two fiber lengths with their jackets stripped off over a short section, are placed side by side on the manufacturing stage, heated, fused together and pulled. The flame torch was applied to heat the two fibers. Fabrications of fused couplers are affected by temperature, coupling mechanism and optical parameters. The efficiency of the fabricated couplers is affected by theses parameters. The reaction of fiber compound with nitrogen flame to achieve equilibrium is a subject of interest. 1.4 Objectives of the study The aim of this research is to investigate the equilibrium state of reaction process for fiber compound with nitrogen gas during the fabrication of fused fiber coupler. 1.5 Scope of the study The scope of this study will focus on the fabrication of fused fiber coupler by flame torch with temperature at 800 C to melting point of fiber using nitrogen gas at atmospheric pressure. In this study, various factors affecting the reaction during fabrication of fused fiber coupler will be investigated. The dominant factors affecting the processes will then be identified.

15 5 1.6 Significance of the study In a common fabrication process of fiber couplers, only a certain short length of the fibers corresponding to the centre region of the coupler is heated with torch flame, and the fibers are pulled outward from the flame. Research done mostly focused on the mechanical process in order to upgrade the performance of fused fiber coupler. But then, the equilibrium of chemical reaction occurs during the fabrication is remain unclear. This study will provide much clear picture of the reaction process and what can be done to improve the fabrication of fused fiber coupler. 1.7 Organization of the study This thesis consists of five main chapter beginning with a brief introduction of the overall review of this research background and works under taken in Chapter 1, which includes statements of problem, aims and objectives, scope of the study, as well as significance of the study. Depth explanation of literature review on fabrication of fused fiber coupler, the thermodynamic equilibrium and review on nitrogen plasma species was included in Chapter 2. Chapter 3 basically elaborate the methodology of this research. Chapter 4 consists of integration and application of model to low pressure discharge, comparative global model and profiles of nitrogen species densities at higher atmospheric pressure. Lastly, Chapter 5 contains summary and conclusion for this research as well as recommendation for improving this research.