UNIVERSITI PUTRA MALAYSIA

MOHAMMED AJIYA

FK 2010 13

MULTIPLE WAVELENGTH LASER UTILIZING HYBRID ERBUIM AND BRILLOUIN GAINS IN DISPERSION COMPENSATING FIBER

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MULTIPLE WAVELENGTH LASER UTILIZING HYBRID ERBUIM AND

BRILLOUIN GAINS IN DISPERSION COMPENSATING FIBER

By

MOHAMMED AJIYA

Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in

Fulfilment of the Requirements for the Degree of Doctor of Philosophy

January 2010

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DEDICATION

This work is dedicated to the loving memory of my late parents. May Allah (SWA)

grant them Al-Jannat Firdaus, Amen.

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Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment of

the requirement for the degree of Doctor of Philosophy

MULTIPLE WAVELENGTH LASER UTILIZING HYBRID ERBUIM AND

BRILLOUIN GAINS IN DISPERSION COMPENSATING FIBER

By

MOHAMMED AJIYA

January 2010

Chair: Mohd Adzir Bin Mahdi, PhD

Faculty: Engineering

This dissertation presents experimental design and development of multiwavelength

fiber laser sources utilizing hybrid erbium and Brillouin gains in dispersion

compensating fiber. Four laser designs have been successfully demonstrated. Also

presented is a simple method of stimulated Brillouin scattering threshold (SBS)

reduction.

Highly stable multiwavelength Brillouin/erbium fiber laser (MWBEFL) in which the

cavity is formed by a virtual mirror, where the oscillating modes are reflected back into

the laser cavity by SBS effect rather than by a physical reflector is demonstrated. The

issue of low tuning range associated with such laser configurations was successfully

resolved. Tuning range of 39 nm from 1527 to 1566 nm, which is only limited by the

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amplification bandwidth of the erbium gain was successfully achieved. At maximum

pumping powers, four channels that are rigidly separated by 0.08 nm (10 GHz) and

where each has power above 0 dBm has been demonstrated.

Simple method of SBS threshold reduction was demonstrated. The BP signal was

recycled back into the fiber thereby increasing the total gain in the fiber and thus SBS

threshold was reduced. In a 5 km long fiber, the proposed method reduced SBS

threshold by over 48%, from 16.5 mW to 8.5 mW of the input signal. The Brillouin

Stokes generated in the 5 km fiber has a peak power of 9.2 dBm against 4.3 dBm

measured using the conventional technique. Similarly, the results obtained from the

various lengths of tested fibers, proved that the proposed technique significantly reduced

the SBS threshold value and improved the level of the Brillouin Stokes signal power.

Two structures of MWBEFL incorporating the SBS threshold reduction technique were

also proposed. In one structure, unidirectional propagation of both the Brillouin Stokes

and the Brillouin pump signals was allowed through the erbium amplifier while in the

other, bidirectional propagation of the two signals are forced through the erbium gain.

The unidirectional amplifier configuration provides greater tuning range of 46.8 nm,

against 23 nm provided by the bidirectional configuration at the same pumping powers.

On the other hand, the bidirectional amplifier configuration provides 13 output channels

against only 6 output channels obtained from the unidirectional amplifier configuration

under maximum pumping powers. The channels output power however remained lower

than 0 dBm in both cases.

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An enhanced structure of MWBEFL that provided flawless tuning range and high

channels power was also demonstrated. At maximum pumping powers, up to seven

output channels that can broadly be tuned over 35 nm, are demonstrated. Wavelength

tunability is also limited by the amplification bandwidth of the erbium amplifier

employed. Each of the initial four channels has peak power above 1.6 dBm with the first

and seventh channels having a peak power of 8.19 dBm and -8.30 dBm respectively.

After an observation period of one hour, the average power fluctuations by all the seven

channels is only 1.47 dB with average wavelength shifts of 0.007 nm.

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Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai

memenuhi keperluan untuk ijazah Doktor Falsafah

LASER PELBAGAI JARAK GELOMBANG MENGGUNAKAN GANDAAN –

GANDAAN HIBRID ERBIUM DAN BRILLOUIN DI DALAM GENTIAN OPTIK

PAMPASAN PENYEBARAN

Oleh

MOHAMMED AJIYA

Januari 2010

Pengerusi: Mohd Adzir Bin Mahdi, PhD

Fakulti: Kejuruteraan

Disertasi ini membentangkan reka bentuk eksperimen dan perkembangan punca laser

gentian pelbagai jarak gelombang menggunakan gabungan perolehan erbium dan

Brillouin dalam gentian pemampas penyebaran. empat reka bentuk laser telah berjaya

didemonstrasikan. Juga dibentangkan adalah kaedah mudah pengurangan ambang

penyerakan Brillouin terangsang.

Laser gentian pelbagai jarak gelombang Brillouin/Erbium (MWBEFL) yang sangat

stabil ditunjukkan di mana rongganya dibentuk oleh cermin maya, yang mana mod-mod

berayun adalah dipantulkan kembali ke dalam rongga laser oleh kesan SBS dan

bukannya oleh pemantul fizikal telah ditunjukkan. Julat penalaan rendah yang dikaitkan

dengan konfigurasi laser telah dapat diselesaikan dengan jayanya. Julat penalaan sebesar

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39 nm bermula dari 1527 nm ke 1566 nm, yang hanya dihadkan oleh lebar jalur

pembesaran dari gandaan erbium telah berjaya dicapai. Pengepaman maksimum, empat

saluran yang terpisah secara tegar pada 0.08 nm (10 GHz) dan diaman setiapnya

berkuasa melebihi 0 dBm telah didemonstrasikan.

Kaedah mudah untuk mengurangkan ambang SBS telah dipamerkan. Isyarat BP dikitar

semula ke dalam gentian lalu meninggikan jumlah perolehan di dalam gentian dan

mengurangkan ambang SBS. Pada fiber kepanjangan 5 km, kaedah tercadang

mengurangkan ambang SBS sebanyak 48% daripada 16.5 mW ke 5 mW dari signal

input. Kuasa Brillouin Stokes tertinggi yang diukur adalah sebanyak 9.2 dBm

berbanding 4.3 dBm yang diperolehi melalui teknik konvensional. Kelebihan ini turut

didapati pada kepanjangan fiber yang berlainan lalu membuktikan teknik yang diusulkan

ini jelas mengurangkan nilai ambang SBS dan turut memperbaiki kuasa isyarat Brillouin

Stokes.

Dua struktur MWBEFL yang meggunakan kaedah pengurangan ambang SBS turut

diusulkan. Dalam satu struktur propagasi searah membenarkan Brillouin Stokes dan

isyarat pam Brillouin bergerak sehala di dalam pengganda erbium manakala satu

struktur lagi membenarkan kedua-dua isyarat itu untuk bergerak dua hala di dalam

pengganda erbium. Konfigurasi pengganda sehala memberikan julat penalaan yang lebih

besar iaitu sebanyak 46.8 nm manakala pada kuasa pam yang sama, julat penalaan bagi

konfigurasi pengganda dua hala hanyalah sebesar 23 nm. Namun begitu, pada kuasa

pam maksimum, 13 saluran dapat diperolehi melalui konfigurasi pengganda dua hala

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berbanding 6 saluran sahaja yang didapati dari konfigurasi penaik sehala. Kuasa saluran

adalah lebih rendah dari 0 dBm dalam kedua-dua konfigurasi.

Satu strukur MWBEFL yang telah diperbaiki bagi memberikan julat penalaan yang

sempurna berserta kuasa saluran yang tinggi turut dibentangkan. Tujuh saluran yang

mampu ditala pada julat sebesar 35 nm diperolehi pada kuasa pam maksimum. Julat

penalaan ini dihadkan oleh lebar jalur perolehan pengganda erbium yang digunakan. 4

saluran awal diukur mempunyai kuasa tertinggi melebihi 1.6 dBm dengan saluran

pertama dan ketujuh masing-masing berkuasa 8.19 dBm dan -8.30 dBm. Berdasarkan

pemerhatian selama satu jam, purata ketidakstabilan kuasa ketujuh-tujuh saluran

hanyalah 1.47 dB manakala purata pergerakan jarak gelombang didapati sebanyak 0.007

nm.

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ACKNOWLEDGEMENTS

All praises are due to Allah (SWA), the almighty, Lord of the worlds, the most

beneficent, the most merciful. I thank Him for help, support and allowing us to see to

this stage of my quest for knowledge.

I would like to profoundly thank my supervisor, Prof. Dr. Mohd Adzir Bin Mahdi,

without whose help and support, this dissertation may not be a reality. A distinguished

gentleman, Prof. Adzir accorded us, the liberty to consult with him at any time, be it in

his office, on the road or in the lab without prior appointment. He is always available to

us despite his tight schedule as an administrator, a researcher, a lecturer and a wonderful

head of a family. He always listens and offer prompt solutions to whatever problem we

confronted him with. He continually supported us, in the lab, academically and morally.

To Prof. Adzir, I say thank you. May Allah (SWA) guide, support and pour his blessings

upon you and your family.

I would also wish to express my deepest gratitude and appreciation to another

gentleman, Assoc. Prof. Dr. Mohammed Hayder Al-Mansoori. A member of my

supervisory committee, Dr Mansoori contributed immensely to the success of this

dissertation. I benefitted tremendously from his wide and vast knowledge in the field of

not only fiber laser but other aspects of general knowledge. May Allah help and reward

him abundantly.

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I also deeply appreciate the contributions, guidance and support of my other supervisory

committee members, Dr. Salasiah bt. Hitam and Dr. Makhfudzah bt. Mokhtar.

I appreciate the help and assistance of my colleagues in our research group, Nor Azura

Malini Ahmad Bin Hambali, Yu Gang Shee, Muhammad Hafiz Abu Bakar, Yeo Kwok

Shien, Nelidya Md Yusuf, Hafizah Mohammed, Shafiqul Islam and the components

manager, Zubaidah Abd Rahman. I cherish the brotherhood with which we stayed. I

would also want to thank all staffs and other students of the photonic and fiber optic

system laboratory, for their help and support. Equally, I would like to thank all the other

staffs of the computer and communication systems engineering department.

I would also want to thank members of the Nigeria community in UPM, particularly Dr.

Abdulkareem Sabo Mohammed who ensured that I had a smooth settlement in Malaysia

and Dr. Mustapha Bala Abubakar, my close confidant and a housemate.

I would want to express my deepest gratitude to my elder brother, Alhaji Danjuma

Mohammed for not only taking care of my family while I am here in Malaysia, but also

for his strong encouragement, moral and financial support.

Finally to my family who suffered long period of deprivation while I am pursuing the

PhD degree, I say thank you for understanding. May Allah bless you all, amen.

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This thesis was submitted to the Senate of Universiti Putra Malaysia and has been

accepted as fulfillment of the requirement for the degree of Doctor of Philosophy. The

members of the Supervisory Committee were as follows:

Mohd Adzir bin Mahdi, PhD

Professor

Faculty of Engineering

Universiti Putra Malaysia

(Chairman)

Salasiah bt. Hitam, PhD

Faculty of Engineering

Universiti Putra Malaysia

(Member)

Makhfudzah bt. Mokhtar, PhD

Faculty of Engineering

Universiti Putra Malaysia

(Member)

Mohammed H. Al-Mansoori, PhD

Associate Professor,

Faculty of Engineering

Universiti Tenaga Nasional

(External Member)

HASSANAH MOHD GHAZALI, PhD

Professor and Dean

School of Graduate Studies

Universiti Putra Malaysia

Date: 17th March 2010

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DECLARATION

I declare that the thesis is my original work except for quotations and citations which

have been duly acknowledged. I also declare that it has not been previously, and is not

concurrently, submitted for any other degree at Universiti Putra Malaysia or at any other

institution.

MOHAMMED AJIYA

Date: 26th January 2010

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TABLE OF CONTENTS

Page

DEDICATION iii

ABSTRACT iv

ABSTRAK vii

ACKNOWLEDGEMENTS x

APPROVAL SHEET 1 xii

APPROVAL SHEET 2 xiii

DECLARATION SHEET xiv

TABLE OF CONTENTS xv

LIST OF FIGURES xviii

LIST OF ABBREVIATIONS xx

CHAPTER

1 INTRODUCTION 1

1.1 Background 1

1.2 Motivation 3

1.3 Problem Statement 4

1.4 Research Objectives 5

1.5 Scope of Work 6

1.6 Thesis organization 7

2 LITERATURE REVIEW 9

2.1 Introduction 9

2.2 Fiber Nonlinearities 10

2.2.1 Nonlinear Refraction 11

2.2.2 Light Scattering 12

2.2.3 Classification of Light Scattering 14

2.3 Stimulated Brillouin Scattering (SBS) 15

2.3.1 Basic Concept of SBS 15

2.3.2 SBS in Optical Fibers 16

2.3.3 Applications of SBS 19

2.4 Lasers 19

2.4.1 Principles of Laser 20

2.4.2 Types of Lasers 24

2.5 Fiber Laser 25

2.5.1 Single wavelength Brillouin/erbium Fiber Laser 26

2.5.2 Multiple wavelengths Brillouin/erbium Fiber Laser 29

2.5.3 Other Multiple wavelength Fiber Laser technologies 33

2.6 Theory of multiple wavelengths Brillouin/erbium Fiber

Laser

37

2.7 Critical review 45

2.8 Summary 46

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3 METHODOLOGY 47

3.1 Introduction 47

3.2 Research Design 47

3.3 Virtual mirror cavity configured MWBEFL 50

3.4 SBS threshold reduction 52

3.5 Amplification scheme 53

3.6 Enhanced structure to produce high channel power 56

3.7 Summary 57

4 SEAMLESS TUNING RANGE BASED-ON AVAILABLE

GAIN BANDWIDTH IN MULTIWAVELENGTH

BRILLOUIN FIBER LASER

(Opt. Express Vol. 17, No. 8, pp 5944 – 5952, 2009)

58

Article 1 58

Copyright permission 77

5 REDUCTION OF STIMULATED BRILLOUIN

SCATTERING THRESHOLD THROUGH PUMP

RECYCLING TECHNIQUE

(Laser Phys. Lett., Vol. 6, No. 7, pp 535 – 538, 2009)

78

Article 2 78

Copyright permission 90

6 DIRECTIVITY INFLUENCE OF SIGNALS

PROPAGATION THROUGH EDFA GAIN MEDIUM OF

BRILLOUIN-ERBIUM FIBER LASER

(Opt. Commun. In press DOI:10.1016/j.optcom.2009.07.032)

92

Article 3 92

Acceptance letter 109

7 BROADLY TUNABLE MULTIPLE WAVELENGTH

BRILLOUIN FIBER LASER EXPLOITING ERBIUM

AMPLIFICATION

(J. Opt. Soc. Am. B, Vol. 26, No. 9, pp. 1789 – 1794, 2009)

110

Article 4 110

Copyright permission 127

8 ADDITIONAL DISCUSSION AND COMPARISON OF

RESULTS

128

8.1 Introduction 128

8.2 Choice of Brillouin gain medium 128

8.3 Tuning range improvement 130

8.4 Brillouin threshold reduction 131

8.5 Overall comparison of results 132

8.6 Summary 133

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9 CONCLUSION AND RECOMMENDATION FOR FUTURE

WORK

135

9.1 Conclusion 135

9.2 Recommendation for future work 139

REFERENCES/BIBLIOGRAPHY 140

BIODATA OF STUDENT 151