UNIVERSITI TEKNOLOGI MALAYSIA

OUTPUT POWER AND EFFICIENCY IN LINEAR AND RING

CONFIGURATIONS OF CONTINUOUS WAVE ERBIUM DOPED FIBER

LASER

RABI‟ATUL „ADAWIYAH BINTI MAT YUSOFF

.

OUTPUT POWER AND EFFICIENCY IN LINEAR AND RING

CONFIGURATIONS OF CONTINUOUS WAVE ERBIUM DOPED FIBER

LASER

APRIL 2017

Faculty of Science

Universiti Teknologi Malaysia

A dissertation submitted in fulfillment of the

requirements for the award of the degree of

Master of Science

RABI‟ATUL „ADAWIYAH BINTI MAT YUSOFF

iii

Special dedicated to my parents,

Mat Yusoff Bin Ahmad & Rofiah Binti Jaafar

To my beloved siblings,

Siti Rohayu, Rahimatul Azlina, Siti Rohaiza, Marini, Ismail, Ibrahim

To my special friend,

Amin

And, my beloved Master in Science/Research friends.

Thank you for all your supports, pray, blessing and endless love!

DEDICATION

iv

Alhamdulillah, thank to Almighty Allah, the Most Gracious and Most

Merciful for Him is the source of his success for giving me strength and faith to

complete my dissertation work. Hopefully this thesis will be beneficial for further

research which related to this study.

First and foremost, I am deeply indebted to my supervisor, Dr Nabilah Kasim

for her guidance, patience, and encouragement throughout the process of completion

this thesis. I would like to express my deepest gratitude to Asc. Prof. Dr. Yusof

Munajat for his guidance, support and comments during my dissertation work

I would also like to thank to Che Fackrey, Kak Azie (Fadzilah), Kak Farha,

Kak Fida, Kak Shazliza, Kak Ummu, En.Nasir, Azimah, Syifaa, Shairah Ghafar, and

Ija for giving me the support that I needed in completing this work.

To my family and friends, I am thankful and grateful for your endless love,

support, pray and patience throughout the duration of this thesis.

ACKNOWLEDGEMENT

v

Erbium doped fiber laser plays an important role in 1.5 micron wavelength

region which contributes in many applications for example in communication such as

erbium doped fiber amplifier and spectroscopy in medical fields. A continuous wave

fiber laser operating at 1.5 micron wavelength region was demonstrated utilizing

erbium doped as the gain medium in both linear and ring configurations. The output

power and the efficiency of both linear and ring configurations of Erbium Doped

Fiber (EDF) laser were characterised. The laser threshold and the efficiency of linear

and ring configurations of EDF laser then were compared. In the linear

configuration, the wavelength division multiplexing (WDM) was used and Fiber

Bragg Gratings (FBGs) was inserting at both ends of the laser cavity. In the ring

configuration, WDM and 3 dB output coupler are used to complete the laser cavity.

The slope efficiency for the linear configuration is 0.23 % while for the ring

configuration is 2.12 %. The laser threshold where the lasing occurred for linear

cavity is 88.8 mW and the laser threshold for ring cavity is 40.2 mW. The maximum

output power for both linear and ring configurations are 0.32 mW and 4.13 mW

respectively.

ABSTRACT

vi

Laser gentian terdop erbium yang beroperasi dalam panjang gelobang 1.5

mikron memainkan peranan penting dalam menyumbang pelbagai aplikasi

contohnya dalam komunikasi seperti penguat laser gentian erbium dan spektroskopi

dalam bidang perubatan. Laser gentian gelombang berterusan yang beroperasi dalam

rantau gelombang 1.5 mikron telah didemonstrasi menggunakan terdop erbium

sebagai ruang penggandaan dalam kedua-dua konfigurasi iaitu linear dan lingkaran.

Output kuasa yang dikeluarkan dan efisiensi laser gentian terdop erbium bagi ke dua-

dua konfigurasi linear dan lingkaran dicirikan. Ambang laser dan kecekapan bagi

kedua-dua konfigurasi ini kemudiannya dibandingkan. Bagi konfigurasi linear,

multiplexer pembahagian panjang gelombang dan jalur gentian Bragg telah

disambungkan di kedua-dua hujung rongga linear. Di dalam konfigurasi lingkaran

pula, multiplexer pembahagian panjang dan penghubung output digunakan untuk

melengkapkan rongga laser. Efisiensi kecerunan bagi konfigurasi linear adalah 0.23

% manakala untuk konfigurasi lingkaran adalah 2.12 %. Nilai ambang laser di mana

minimum kuasa input yang diberikan untuk penghasilan laser bagi rongga linear

ialah 88.8 mW manakala nilai bagi ambang laser rongga bulatan adalah 40.2 mW.

Nilai kuasa output bagi konfigurasi linear dan lingkaran, masing-masing ialah 0.32

mW dan 4.13 mW.

ABSTRAK

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF ABBREVIATIONS xiv

LIST OF SYMBOLS xv

LIST OF APPENDICES xvi

1 INTRODUCTION 1

1.1 Background 1

1.2 Problem Statement 2

1.3 Objectives 3

1.4 Scope 3

1.5 Dissertation Layout 3

2 LITERATURE REVIEW 5

2.1 Introduction 5

2.2 Fundamental of Optical Fiber 6

2.3 Fundamental of Fiber Laser 9

viii

2.4 Working Principles of Fiber Laser 12

2.5 Erbium Fiber Laser 14

2.5.1 Erbium Doped Glass Laser 15

2.6 Fiber Bragg Grating (FBG) 17

2.7 Laser Threshold and Output Power 19

2.8 Slope Efficiency 19

2.9 Previous study of CW Erbium Doped Fiber for

Linear and Ring Configurations

20

3 METHODOLOGY 25

3.1 Introduction 25

3.2 Laser Configurations 25

3.3 Research Outlines 27

3.4 Experimental Instruments 28

3.4.1 Laser Diode Pump 28

3.4.2 Wavelength Division Multiplexing (WDM) 29

3.4.3 Optical Fiber Connector 30

3.4.4 Output Coupler 31

3.4.5 Fiber Bragg Grating (FBG) 32

3.4.6 Erbium Doped Fiber Laser 33

3.5 Splicing Equipments 33

3.5.1 Optical Fiber Cleaver 33

3.5.2 Fusion Splicing 34

3.6 Measuring Equipments 36

3.6.1 Optical Power Meter (OPM) 36

3.6.2 Optical Spectrum Analyser (OSA) 37

4 DATA COLLECTIONS AND ANALYSIS 38

4.1 Introduction 38

4.2 Calibration of Pumping Source 38

4.3 Linear Cavity CW Erbium Doped Fiber Laser 40

4.4 Ring Cavity CW Erbium Doped Fiber Laser 45

ix

5 CONCLUSIONS 49

5.1 Introduction 49

5.2 Suggestions and Recommendations 50

5.3 Future Works 51

RFERENCES 52

Appendices A - E 54-62

x

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Common laser active ions, host glasses and the relevant

emission wavelengths [6,12,14,15].

11

4.1 Pump laser output power and EDF laser output power as

a function of injection current for linear configuration.

44

4.2 Pump laser output power and EDF laser output power as

a function of injection current for ring configuration.

48

xi

LIST OF FIGURES

FIGURES NO. TITLE PAGE

2.1 Basic structure of optical fiber and its refractive

index profile. [6]

6

2.2 Condition for optical confinement. 7

2.3 Propagation of light ray through optical fiber. 8

2.4 Essential elements of laser oscillator. 10

2.5 “Normal Population” compared to “Population

Inversion”.

12

2.6 (a)Absorption (b)Spontaneous emission

(c)Stimulated emission

13

2.7 Laser transition of pump wavelength 980 nm. 15

2.8 Energy diagram of for ion in the glass fiber 17

2.9 Fiber Bragg grating (FBG). 18

2.10 (a) Schematic of linear cavity laser configuration

using FBGs (b) Schematic diagram of ring cavity

laser configuration.

21

2.11 Experimental setup of SWNT-based passively mode-

locked fiber laser using ring configurations.

22

2.12 Schematic linear configurations of fiber laser with

CNT-SA.

22

2.13 Setup of ring cavity of Q-switched thulium doped

fiber laser with graphene oxide based saturable

absorber.

23

2.14 Setup of random fiber laser with ring configurations. 24

xii

2.15 Linear configuration of the proposed tunable thulium

doped fiber laser.

24

3.1 Linear configuration of EDF laser. 26

3.2 Ring configuration of EDF laser. 27

3.3 Research outline. 28

3.4 Compact laser diode controller. 29

3.5 980/1550 nm wavelength division multiplexing

(WDM).

30

3.6 HPC-FC connector. 31

3.7 50/50 output coupler. 32

3.8 Fiber Bragg grating (FBG). 32

3.9 Erbium doped fiber (EDF). 33

3.10 Optical fiber cleaver. 34

3.11 Electric arc fusion. 35

3.12 Fujikura arc fusion splicer, FSM-17S. 35

3.13 Optical power meter. 36

3.14 Optical spectrum analyser. 37

4.1 The output spectrum of the EDF at 1550 nm and the

pump wavelength of laser diode at 980 nm.

39

4.2 The input current (mA) versus output power (mW) of

the laser diode at 25 ºC.

40

4.3 Transmission spectrum of 95.78 % FBG. 41

4.4 Experimental set-up for linear configuration of EDF

without FBGs.

42

4.5 ASE spectra from EDF laser. 42

4.6 Laser threshold and slope efficiency of linear

configuration EDF laser at pump wavelength of 980

nm.

43

4.7 Lasing spectrum for laser threshold of EDF for linear

configuration.

44

4.8 Lasing spectrum for different pump from EDF for

linear configuration.

45

xiii

4.9 Laser threshold and slope efficiency of ring

configurations EDF laser at pump wavelength of 980

nm.

47

4.10 Lasing spectrum for laser threshold of EDF for ring

configuration.

47

4.11 Lasing spectrum for different pump from EDF for

ring configuration.

48

xiv

LIST OF ABBREVIATION

ASE - Amplified Spontaneous Emission

CW - Continuous wave

EDF - Erbium doped fiber

FBG - Fiber Bragg grating

NA - Numerical Aperture

OPM - Optical power meter

OSA - Optical spectrum analyser

WDM - Wave division multiplexing

xv

LIST OF SYMBOLS

n - Refractive index

- Refractive index of air

- Refractive index of core

- Refractive index of cladding

- Effective refractive index

- Reflected angle

- Transmitted angle

- Incident angle

- Critical angle

- Acceptance angle

Δ - Refractive index

R - Reflectivity

E - Energy level

- Bragg wavelength

xvi

LIST OF APPENDICES

APPENDIX. TITLE PAGE

A Raw Data for Calibration of Laser Diode. 54

B Raw Data for Laser Threshold of EDF for

Linear Configuration.

56

C Raw Data for Laser Threshold of EDF for

Ring Configuration.

58

D Spectrum from OSA. 60

E Picture of Splicing Work. 62

CHAPTER 1

INTRODUCTION

1.1 Background

Optical fiber technology has been revolutionized the communication over the

past decades, especially with the rapidly growth of the internet and the increasingly

high demand in bit rate. In addition optical fiber also has been used in medicine

technologies because of the properties of the fiber optics have allowed medical

personnel to see places in the human body with greater ease and also comfort to the

patient. Fiber lasers have gained many great interest since they possess a number of

physical attributes that distinguish them from other classes of lasers and that

differentiate them in terms of functionality [1], performance and practically.

Fiber laser firstly invented by Elias Snitzerin in 1963 [2,3,4] and in late 1980s

fiber laser devices appeared in market. The output laser was emitted a few tens

milliwatts with large gain medium because the used of single mode laser diode as a

pumping source in the fiber laser system.

The revolution of fiber laser was continued with the variation rare earth

elements such as erbium, ytterbium, thulium and neodymium. These rare earth

elements also known as gain medium which is provides the energy levels in the laser

2

system. Erbium is one of the rare earth elements that have attracted many

researchers to explore the characterization of this fiber laser gerating at 1.5 micron

meter.

In this dissertation work, the rare earth of Erbium is chosen to study the

lasing properties at 1.5 micron meter region. This topic was chosen we want to

research about the optimization of output power fiber laser based on linear and ring

configuration.

1.2 Problem Statement

Continuous wave, single frequency lasers are required in a wide range

communication, medical technologies, sensor and spectroscopic applications. In

addition, with the system integration and miniaturization is being emphasized. The

study about the device compatibility with fiber and optical waveguide is essential.

The miniature devices, diode pump, single frequency (wavelength), narrow line

width, solid state lasers are currently being commercially manufactured in varied

configurations. In order to design fiber laser compatible with size and performance

which is highly demand in market, studies and researches about fiber laser

configurations are crucially needed. In this dissertation work, erbium doped fiber

laser (EDF) is used to generate linear and ring laser cavity. This fiber configurations

designs are adjusted by increasing the pump power. Hence, the efficiency and output

power are measured.

3

1.3 Objectives

This study aims to achieve the objectives as listed below:

1. To characterise the output power and the efficiency of both linear and ring

configurations of Erbium doped fiber laser.

2. To compare the performance of linear and ring configurations of erbium

doped fiber laser.

1.4 Scope

The focus of this study is to compare the performance of linear and ring

configuration of erbium doped fiber laser. The preparation of the erbium doped fiber

for linear and ring configuration is one of the scopes of the study. Next, the fiber is

tested using Optical Spectrum Analyzer. The output result from the experiment for

both ring and linear configurations are analysed in order to compare the performance

of different configurations erbium doped fiber laser.

1.5 Dissertation Layout

The dissertation consists of five chapters. Chapter one consists of a brief

introduction of the laser and erbium doped fiber laser, problem statement, objectives

of the study and the scope of the study. Chapter two briefs the theoretical and the

literature review related to this study.

4

Chapter three reveals and explains the instrumentation used and the

methodology conducted in this study. Chapter four contains the results, analysis and

the discussion of the results. Then, chapter five concludes the experiment has

successfully fulfilled the objectives of the study together with brief recommendations

and suggestions for future work.

52

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