UNIVERSITI PUTRA MALAYSIA MULTIPLE WAVELENGTH LASER UTILIZING HYBRID ERBUIM AND BRILLOUIN GAINS IN DISPERSION COMPENSATING FIBER MOHAMMED AJIYA FK 2010 13
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. iii
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 Chair: Mohd Adzir Bin Mahdi, PhD Faculty: Engineering By MOHAMMED AJIYA January 2010 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 iv
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. v
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. vi
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 Pengerusi: Mohd Adzir Bin Mahdi, PhD Fakulti: Kejuruteraan MOHAMMED AJIYA Januari 2010 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 vii
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 viii
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. ix
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. x
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. xi
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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: 17 th March 2010 xiii
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: 26 th January 2010 xiv
TABLE OF CONTENTS DEDICATION ABSTRACT ABSTRAK ACKNOWLEDGEMENTS APPROVAL SHEET 1 APPROVAL SHEET 2 DECLARATION SHEET TABLE OF CONTENTS LIST OF FIGURES LIST OF ABBREVIATIONS Page iii iv vii x xii xiii xiv xv xviii 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 xv
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 xvi
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 xvii