Preface

To fulfill the ever increasing demands of internet based communication network, the speed of computing as well as the speed of data processing should be high enough with the transmission medium of enormous potential bandwidth having the vast amount of information handling capabilities. On the other hand, conventional electronic technology has already reached its ultimate speed limit (40 Gb/s) through the limitations of miniaturization of chips and bandwidth limitation, and obviously it will create data traffic jam in future internet based networking services. Therefore, a drastic solution of the acute problem is needed and the scientists and technologists promote their thinking to a totally different track from the conventional electronic system so that the computer performance and data signal processing can be further improved with potential communicating medium to such an extent that we would be well prepared to accept the present and future challenges of data traffic.

Optical computing and optical signal processing are strongly believed to be the most feasible technology that can provide the way out of the extreme limitations imposed on the speed and the complexity of present days computation and communication by conventional electronics. Optics provides higher bandwidth than electronics, which enables more information to be carried simultaneously and data to be processed in parallel with impressive increase in speed by several orders of magnitude over that of the electronic signals. If the parallelism of optics be associated with fast switching speed of optical devices, it would result in the surprising computational speed and processing of data.

Considering the present scenario of speed and band width limitation of electronic computing, signal processing and future problem of data traffic, the scientists, technologists and researchers are working in the field of optical computing and optical signal processing in telecommunication network. The role of optical amplifier is indispensable in optical computation and optical data communication network. Over the past two decades, optical amplifiers such as Erbium doped fiber amplifier (EDFA), Raman Amplifier, Semiconductor Optical Amplifier (SOA) are the prime candidates as optical network functional components and have many functional applications such as wavelength conversion, regeneration, wavelength selection, booster, in-line amplification, in-node optical pre-amplification, and mid-span spectral inversion etc.

The selected topics in this book covers the roles of semiconductor optical amplifier (SOA) as the building blocks of the next generation of optical access network, high speed all-optical cascaded switches, frequency encoded all-optical logic processors; key element of optical packet switching architectures, multifunctional elements in microwave photonic system and use of it to generate tunable high power narrowspectrum diode laser system for performing different advance functionalities in present scenario of optical communication network. Technology of upgrading the gain and noise figure of erbium doped fiber amplifier (EDFA) in shorter wavelength side and, the study of the variation of material gain of quantum dot (QD) structure over the long wavelength ranges are also included in this book

Preface IX

amplifiers in present scenario and I believe that this book will be of great value not only to the researchers in the field of optical computing and data processing, optical telecommunications, but also to the component suppliers, postgraduate students, academics and anyone seeking to understand the trends of optical amplifiers in present scenario and the consequent changes in optical amplifier design and

Without the unstinting support from so many persons, it would not have been possible for me to edit this book. Therefore, it is a great pleasure for me to take this opportunity to express my gratitude to all of them. First of all I would like to express my indebtedness to Aleksandar Lazinica, CEO of InTech Publisher for appointing me the Editor of this book. I am also grateful to all the writers for contributing their valuable research works in this book. Again I am indebted to Ms. Maja Bozicevic, Publishing Process Manager for her incessant help in numerous aspects to enable me to do the editorial work. I wish to convey my thanks to Technical Editorial staff and all other staff members of the InTech publisher. I am grateful to my respected teacher, Prof. Sourangshu Mukhopadhyay, University of Burdwan, India for his constant encouragement and valuable suggestions. Finally. I would like to extend my sincere

We shall deem our effort amply rewarded if the book wins the appreciation of the

**Dr. Sisir Kumar Garai** Assistant Professor

West Bengal,

India

M.U.C. Women's College, Burdwan

thanks to all my colleagues for their incessant encouragement.

technology.

users.

The book comprises eight chapters. The functionalities of SOA are spanned from chapter 1 to chapter 6. In chapter 1, the authors have presented the role of reflecting semiconductor optical amplifier in next generation of optical access network. Chapter 2 deals with a review work on successive development of SOA based optical switches regarding their speed limitation, signal to noise ratio and clearly mentioned the role of the turbo switch to overcome these limitation and finally illustrate the importance of cascaded- SOA based optical switches in optical signal processing. In chapter-3, the author has presented a method of developing all-optical frequency encoded logic processor exploiting the state of polarization rotation (SOP) character of the probe beam in nonlinear SOA. Here the author at first mentions the advantages of frequency encoded data over other conventional data encoding and then successively presents the method of generating frequency data, different logic gates and all-optical memory unit and finally mentions the way out of developing multivalued logic processors and application of the scheme in optical computing and WDM telecommunication network. The authors have presented the SOA based optical packet switching architectures in chapter-4. Here they have mentioned different switching paradigms and the superiority of SOA in optical packet switching and have established some optical packet architectures and illustrate their realization using SOA in elegant ways. The effectiveness of SOA in reducing the power consumption is also analyzed. The multi-functional capability of SOA in microwave photonic communication systems such as optical amplification with modulation, gating, photo-detection, dispersion compensation, linearization, etc. have been demonstrated in chapter-5. The chapter also describes the applications of SOA-modulator, SOA-detector and SOA-dispersion compensator in microwave photonic communication systems. Based on the performance of tapered semiconductor optical amplifier, the generation of three red tunable high-power narrow-spectrum diode laser systems is demonstrated in chapter-6 which has so many applications in optical communication network, like as pump source of different optical and optoelectronic devices. The chapter-7 covers the improvement of gain and noise figure of EDFA in shorter wavelength side using different macro-bending approaches and varying fibre parameters such as length, radius, etc. The knowledge of material gain of a medium is very important to design an optical amplifier. Therefore, study of the variation of material gain of quantum dot (QD) structure for p-type and n-type doping over the long wavelength (800-2300 nm) is included in chapter-8.

All the selected topics of this book are very interesting, well organized and the presentation is also very lucid. This book covers the emerging applications of optical amplifiers in present scenario and I believe that this book will be of great value not only to the researchers in the field of optical computing and data processing, optical telecommunications, but also to the component suppliers, postgraduate students, academics and anyone seeking to understand the trends of optical amplifiers in present scenario and the consequent changes in optical amplifier design and technology.

VIII Preface

speed all-optical cascaded switches, frequency encoded all-optical logic processors; key element of optical packet switching architectures, multifunctional elements in microwave photonic system and use of it to generate tunable high power narrowspectrum diode laser system for performing different advance functionalities in present scenario of optical communication network. Technology of upgrading the gain and noise figure of erbium doped fiber amplifier (EDFA) in shorter wavelength side and, the study of the variation of material gain of quantum dot (QD) structure over the

The book comprises eight chapters. The functionalities of SOA are spanned from chapter 1 to chapter 6. In chapter 1, the authors have presented the role of reflecting semiconductor optical amplifier in next generation of optical access network. Chapter 2 deals with a review work on successive development of SOA based optical switches regarding their speed limitation, signal to noise ratio and clearly mentioned the role of the turbo switch to overcome these limitation and finally illustrate the importance of cascaded- SOA based optical switches in optical signal processing. In chapter-3, the author has presented a method of developing all-optical frequency encoded logic processor exploiting the state of polarization rotation (SOP) character of the probe beam in nonlinear SOA. Here the author at first mentions the advantages of frequency encoded data over other conventional data encoding and then successively presents the method of generating frequency data, different logic gates and all-optical memory unit and finally mentions the way out of developing multivalued logic processors and application of the scheme in optical computing and WDM telecommunication network. The authors have presented the SOA based optical packet switching architectures in chapter-4. Here they have mentioned different switching paradigms and the superiority of SOA in optical packet switching and have established some optical packet architectures and illustrate their realization using SOA in elegant ways. The effectiveness of SOA in reducing the power consumption is also analyzed. The multi-functional capability of SOA in microwave photonic communication systems such as optical amplification with modulation, gating, photo-detection, dispersion compensation, linearization, etc. have been demonstrated in chapter-5. The chapter also describes the applications of SOA-modulator, SOA-detector and SOA-dispersion compensator in microwave photonic communication systems. Based on the performance of tapered semiconductor optical amplifier, the generation of three red tunable high-power narrow-spectrum diode laser systems is demonstrated in chapter-6 which has so many applications in optical communication network, like as pump source of different optical and optoelectronic devices. The chapter-7 covers the improvement of gain and noise figure of EDFA in shorter wavelength side using different macro-bending approaches and varying fibre parameters such as length, radius, etc. The knowledge of material gain of a medium is very important to design an optical amplifier. Therefore, study of the variation of material gain of quantum dot (QD) structure for p-type and n-type doping over the long wavelength (800-2300 nm)

All the selected topics of this book are very interesting, well organized and the presentation is also very lucid. This book covers the emerging applications of optical

long wavelength ranges are also included in this book

is included in chapter-8.

Without the unstinting support from so many persons, it would not have been possible for me to edit this book. Therefore, it is a great pleasure for me to take this opportunity to express my gratitude to all of them. First of all I would like to express my indebtedness to Aleksandar Lazinica, CEO of InTech Publisher for appointing me the Editor of this book. I am also grateful to all the writers for contributing their valuable research works in this book. Again I am indebted to Ms. Maja Bozicevic, Publishing Process Manager for her incessant help in numerous aspects to enable me to do the editorial work. I wish to convey my thanks to Technical Editorial staff and all other staff members of the InTech publisher. I am grateful to my respected teacher, Prof. Sourangshu Mukhopadhyay, University of Burdwan, India for his constant encouragement and valuable suggestions. Finally. I would like to extend my sincere thanks to all my colleagues for their incessant encouragement.

We shall deem our effort amply rewarded if the book wins the appreciation of the users.

**Dr. Sisir Kumar Garai** Assistant Professor M.U.C. Women's College, Burdwan West Bengal, India

**1**

*France* 

**Next Generation of Optical**

*Alcatel-Lucent Bell Labs France, Route de Villejust, Nozay,* 

Guilhem de Valicourt

**Access Network Based on Reflective-SOA** 

Communication networks have evolved in order to fulfil the growing demand of our bandwidth-hungry world. First, the coaxial cable has replaced the copper cable since 1950 for long- and medium-range communication networks. The Bit rate-distance product (BL) is commonly used as figure of merit for communication systems, where the B is the bit rate (bit/sec) and L is the repeater spacing (km). A suitable medium for transmission needed to be available and optical fibres were selected as the best option to guide the light (Kao & Hockham, 1966). A radical change occurred, the information was transmitted using pulses of light. Thus further increase in the BL product was possible using this new transmission medium because the physical mechanisms of the frequency-dependent losses are different for copper and optical fibres. The bit-rate was increased in the core network by the introduction of a new technique: Wavelength-Division Multiplexing (WDM). The use of WDM revolutionized the system capacity since 1992 and in 1996, they were used in the

While WDM techniques were mostly used in long-haul systems employing EDFA for online amplification, access networks were using more and more bandwidth. Access network includes the infrastructures used to connect the end users (Optical Network Unit - ONU) to one central office (CO). The CO is connected to the metropolitan or core network. The distance between the two network units is up to 20 km. The evolution of access network was very different from in the core network. High bit-rate transmissions are a recent need. At the beginning, it provided a maximum bandwidth of 3 kHz (digitised at 64 kbit/s) for voice transmission and was based on copper cable. Today, a wide range of services need to be carried by our access network and new technologies are introduced which allow flexible and high bandwidth connection. The access network evolution is obvious in Europe with the rapid growth of xDSL technologies (DSL: Digital Subscriber Loop). They enable a broadband connection over a copper cable and allow maintaining the telephone service for that user. In 2000, the maximum bit rate was around 512 kbit/s while today it is around 12 Mbit/s. However since 2005, new applications as video-on-demand need even more bandwidth and the xDSL technologies have reached their limits. The introduction of broadband access network based on FTTx (Fiber To The x) technology is necessary to answer to the recent explosive growth of the internet. Today, Internet service providers propose 100 Mbit/s using optical fibre. The experience from the core network evolution is a great benefit to access network. The use of WDM mature technology in access and

Atlantic and Pacific fibre optic cables (Otani et al., 1995).

**1. Introduction** 
