UNIVERSITI PUTRA MALAYSIA

DESIGN AND EVALUATION OF A DUAL CORE ERBIUM DOPED FIBER AMPLIFIER (DC-EDFA)

ABDULLATIF MOHAMMED ALSHARJABI

FK 2003 30

DESIGN AND EVALUATION OF A DUAL CORE ERBIUM DOPED FIBER AMPLIFIER (DC-EDFA)

By

ABDULLATIF MOHAMMED ALSHARJABI

Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, In Partial fulfillment of the Requirements for the Degree of Master of Science

June 2003

DEDICATION

To all mankind

II

Abstract of thesis presented to the Senate of the Universiti Putra Malaysia in partial fulfillment of the requirement for degree of Master of Science

DESIGN AND EVALUATION OF A DUAL CORE ERBIUM DOPED FIBER AMPLIFIER (DC-EDFA)

By

ABDULLATIF MOHAMMED ALSHARJABI

June 2003

Chairman: Associate Professor Mohamad Khazani Abdullah, Ph.D.

Faculty: Engineering

Traditional erbium doped fiber amplifiers EDFA (unidirectional signaling) can only

amplify signals propagating in a single direction, as some isolators must be installed to

eliminate the reflections from end faces and fusion points. This means the amplifiers

only amplify signal in one direction over a fiber. For long haul transmission, many

amplifiers are placed along each single mode fiber. Total numbers of the amplifiers will

be the number of the amplifier over a fiber multiply by the number of the fibers in the

cable. This means a large number of amplifiers are required thus increasing a high cost.

In order to reduce the system cost, and increase the capacity, many studies have been

done using bi-directional signaling in a single fiber (duplex), through one or two

separate amplifiers.

In this work, a bi-directional signaling technique has been exploited, this in order to

amplify the signals bi-directionally, over two single mode fibers (unidirectional) . This is

111

achieved by using two circulators instead of isolators at the terminals of the EDF A. The

main goal is to reduce the number of amplifiers in the optical communication system,

which results in a decrease in the system cost. The new system is tested by laboratory

experiments. From the results, it is found that the system has the same characterizations

as bi-directional ED FA amplifiers, (i.e. independent amplification, medium gain, low

ASE), as expected. Reflections also occur. The system has high reflection when the

difference in the input powers of the bidirectional signals is high. This causes different

gains and different amplified powers. The reflection of the signal which has higher input

power is associated with the other main signal (over the other fiber) . The system shows

the best performance, when the difference in the input powers (for the two fibers) is

small and is even better when the bidirectional signals have the same input powers.

In conclusion, the project objectives have been achieved, and the system can reduce the

number of the amplifiers to as much as 50% of that in a unidirectional propagating

system, due to the fact that, two fibers can now share one amplifier and results in cost

reduction by almost 50%. Furthermore, the approach is flexible and simple.

iv

Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi sebahagian keperluan untuk Ijazah Master sains

REKABENTUK DAN PENILAIAN PENGUAT FffiER TERDOP ERBIUM DUA TERAS

Oleh

ABDULLATIF MOHAMMED ALSHARJABI

Jun 2003

Pengerusi: Profesor Madya Mohamad Khazani Abdullah, Ph.D.

Fakulti: Kejuruteraan

Secara tradisinya EDFA (Erbium Doped Fiber Amplifier) adalah penguat satu hala yang

mana ia hanya menguatkan isyarat yang merambat didalam satu arah sahaja. Isolator

mestilah dipasang untuk menge1akkan be1akunya balikan dari arah yang bertentangan ke

titik penghantar. Ini bermakna penguat hanya akan menguatkan isyarat di dalam satu

hala sahaja. Bagi penghantaran jarak jauh, penguat di gunakan di beberapa tempat di

sepanjang fiber untuk menguatkan isyarat. Jumlah keseluruhan penguat yang di gunakan

didalam sistem, merupakan jumlah penguat yang di gunakan didalam setiap fiber

didarab dengan jumlah bilangan fiber yang di gunakan. Ini bermakna banyak penguat di

perlukan serta memerlukan kos yang tinggi. Bagi mengurangkan kos serta meningkatkan

kapasiti, banyak kajian telah di jalankan menggunakkan penisyaratan dua hala didalam

satu fiber melalui satu atau dua penguat yang berasingan.

v

Didalam kajian ini teknik pengisyaratan dua hala di perkenalkan dalam usaha untuk

menyuatkan isyarat di dalam dua arah bagi dua fiber satu mode. Ini dapat dicapai dengan

menggunakan dua Isolator berbanding satu Isolator pada terminal EDFA. Tujuan utama

adalah untuk mengurangkan bilangan penguat di dalam sistem komunikasi optik yang

mana akan dapat mengurangkan kos keseluruhan sistem. Sistem baru ini telah diuji di

dalam makmal. Bagi membolehkan simulasi sistem dapat di buat, isyarat yang telah di

modulat daripada Penanalisa SDH di biarkan melalui Fiber 1, manakala Sumber Tunable

Laser di laraskan pada lebarjalur yang berlainan untuk menghasi l isyarat pada fiber 2.

Daripada keputusan yang di perolehi, sebagaimana yang telah di anggarkan sistem

tersebut mempuyai ciri-ciri yang sarna dengan penguat EDFA dua hala, yang mana

penguat mempunyai gandaan bebas dan sederhana serta mempunyai rendah ASE

disamping itu balikan juga terjadi. Sistem akan mempunyai balikan yang tinggi apabila

terdapat perbezaan an tara kuasa masukan bagi isyarat duahala yang tinggi. Selalunya

balikan terjadi daripada isyarat yang kuasa masukan yang tinggi. Manakala sistem

mempunyai prestasi yang baik apabila kuasa masukan isyarat dua hala adalah sarna.

Sebagai kesimpulan, objektif projek ini telah di capai, dimana penggunaan penguat

dapat di kurang kan sehingga 50% bagi sistem perambatan satu hala. Ini adalah kerana

dua fiber akan berkongsi satu penguat dan dapat mengurangkan kos sebanyak 50%.

Sistem baru ini adalah fleksible, mudah dan mempunyai cirri-ciri EDFA dua hala.

VI

ACKNOWLEGEMENTS

In the name of Allah, the Most Beneficent, the Most Merciful

I would like to express my sincere gratitude to my thesis supervisor, Associate Professor

Dr. Mohd Khazani Abdullah for his invaluable guidance, enthusiastic encouragements

and support at every stage of this research project. A research project as this entails a lot

of sacrifice in term of time, energy, money etc, not only on my part but also on that of

my supervisor. He introduces me into the field of optical amplifiers and provided me the

resources necessary for the completion of this project. These include writing of surveys,

turning ideas into implementation, and getting through the inevitable research setbacks.

I am also grateful to Professor Dr. Borhanuddin Mohd Ali for his guidance, comments

and advices throughout the entire project.

I also say thank you to Associate Professor Dr. Kaharudinn Dimyati for accepting to be

on my committee.

I am indebted to all the people at the photonics laboratory for creating the conducive and

encouraging atmosphere.

Finally, I want to express my deepest feeling to my family for their constant support and

encouragement during my study period. I also say sorry to them for being far away from

home for too long.

Vll

I certify that an Examination Committee met on 17th June 2003 to conduct the final examination of Abdullatif Mohammed Alsharjabi on his Master of Science thesis entitle "Design and Evaluation of a Dual Core Erbium Doped Fiber Amplifier (DC­EDFA)" in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti Pertanian Malaysia (Higher Degree) Regulations 198 1 The Committee

recommends that the candidates be awarded the relevant degree Members of the Examination Committee are the follows

Sudhanshu Shekhar Jamuar, Ph.D.

Professor, Department of Electrical and Electronic Engineering, Faculty of engineering, Universiti Putra Malaysia (Chairman)

Mohd Khazani Abdullah, Ph.D.

Associate Professor, Department of Computer and Communication Systems Engineering, Faculty of engineering, Universiti Putra Malaysia (Member)

Borhanuddin Mohd Ali, Ph.D.

Professor, Department of Computer and Communication Systems Engineering, Faculty of engineering Universiti Putra Malaysia (Member)

KAHARUDDIN DIMYATI, Ph.D.

Associate Professor, Department of Electrical Engineering, F acuIty of engineering, Universiti Malaya (Member)

ProfessorlDepu ean, School of G uate Studies, Universiti Putra Malaysia

Date 2 1 JUL 2003

VIII

This thesis submitted to the Senate ofUnivrsiti Pura Malaysia has been accepted as fulfillment of the requirement for the degree of Master of Science.

Mohd Khazani Abdullah, Ph.D.

Associate Professor, Department of Computer and Communication Systems Engineering, F acuIty Of Engineering

Universiti Putra Malaysia (Member)

Borhanuddin Mohd Ali, Ph.D.

Professor, Department of Computer and Communication Systems Engineering, F acuIty of Engineering, Universiti Putra Malaysia (Member)

KAHARUDDIN DIMYATI, Ph.D.

Associate Professor, Department of Electrical Engineering, Faculty of Engineering, Universiti Malaya (Member)

AINI IDERIS, Ph.D.

PofesssorlDean, School of Graduate Studies, Universiti Putra Malaysia

Date r1 5 AUG 2003

IX

DECLARATION

I hereby declare that the thesis is based on my original work except for quotations and citations, which have been duly acknowledged. I also declare that it has not been previously or concurrently submitted for any other degree at UPM or other institution.

ABDULLATIF ALSHARJABI

Date: 30 I � I 20 .. )

TABLE OF CONTENTS

DEDICATION ABSTRACT

Page 11 III

ABSTRAK ACKNOWLEDGEMENTS APPRO V AL SHEETS DECLARATION FORM LIST OF TABLES

V Vii Viii X Xiv Xv Xiv

LIST OF FIGURES LIST OF ABBREVIATIONS

CHAPTER

I INTRODUCTION 1 . 1 The Importance of Fiber Optics Communication 1 .2 The Need for Optical Amplifiers

1 .2. 1 Loss in the System 1 .2. 1 . 1 Absorption 1 .2. 1 .2 Scattering Losses 1 .2. 1 .3 Bending Losses 1 .2. 1 .4 Reflection Losses

1 .3 Literature Review on Amplifier Systems in Optical Communications

1 .3 . 1 The Traditional Amplifier and Repeaters 1 .3 .2 Optical Amplifiers

1 .3 .2 . 1 Semiconductors Optical Amplifiers (SOAs) 1 .3 .2.2 Doped Fiber Amplifier (DFA): 1 .3 .2.3 EDFA Background

1 .4 Problem Statement 1 .5 Objective 1 .6 Scope of Work 1 .7 Methodology 1 .8 Thesis Organization

1 . 1 1 .3 1 . 3 1 .5 1 .6 1 .6 1 .7 1 .8

1 .8 1 .9 1 . 1 1 1 . 1 2 1 . 1 3 1 . 1 6 1 . 1 8 1 . 1 8 1. 1 9 1 .20

II WORKING PRINCIPLE OF EDFA 2. 1 Working principle of EDFA 2. 1

2. 1 . 1 Energy Level 2.3 2. 1 .2 Characteristics of EDFAs 2.5

2. 1 .2. 1 Gain: 2.6 2. 1 .2.2 ASE 2.9 2. 1 .2.3 Noise Figure (NF) 2. 1 1 2. 1 .2.4 EDFA Power-Conversion Efficiency and 2. 1 2

Gain

XI

3 .3 EDFA Configuration 2. 1 6 3 .3 . 1 EDFA Co- and Counter Directional Pumping 2 . 1 6 3 .3 .2 EDFA Bidirectional Pump 2. 1 6

3 .5 Applications of EDFA 2. 1 9 3 .5 . 1 Post-Amplifier 2 . 1 9 3 .5 .2 In-Line amplifiers 2. 1 9 3 .5 .3 Preamplifiers 2.20

Conclusion 2 .21

ill DESIGN OF DUAL CORE OPTICAL AMPLIFIER (DC-EDFA) 3 . 1 Requirement and Advantages of DC-EDFA 3 . 1 3 .2 Components of DC-EDFA 3 . 1

3 .2 . 1 Optical Circulators 3 .2 3 .2 .2 Pump Laser 3 .4 3 .2 .3 WDM Couplers 3 .4 4.2.4 Erbium Doped Fiber 3 .5

3 .4 Design And Performance Parameters 3 .6 3 .4 . 1 Design Parameters 3 .6

3 .4. 1 . 1 Data Rate 3 .6 3 .4. l .2 Wavelengths 3 .6 3 .4. 1 .3 Input Power signal 3 .7 3 .4. 1 .4 Pumping Power 3 .7

3 .4.2 Performance Parameters 3 .7 3 .4.2. 1 Output Power 3 .8 3 .4.2.2 Gain 3 .8 3 .4.2.3 Crosstalk 3 .8 3 .4 .2.4 Bit Error Rate BER 3 .9 3 .4.2.5 Eye Pattern 3 .9

IV RESULTS AND DISCUSSIONS 4. 1 Components Characterizations 4. 1

4. 1 . 1 Wave Division Multiplexer WDM coupler 4. 1 4 . 1 .2 Circulator 4.4

4.2 Amplifier Experimental Results 4.5 4.2. 1 Gain 4.6 4.2.2 Output Power 4. 12 4.2 .3 ASE LEVEL 4. 1 7 4.2.4 Noise Figure NF 4.23

4.3 Optimizing the system 4.28 4.4 System Level Measurement 4.3 1

4.4. 1 BER 4.32 4.4.2 Eye Pattern 4.34

V CONCLUSION AND FUTURE STUDY 5 . 1 Conclusion 5 . 1 5 .2 Future Study 5 .3

XJl

REFERENCES APPENDICES

Appendix A Appendix B Appendix C Appendix D

BIODATA of the AUTHOR

R. 1

A. 1 A.8 A.39 A.46 B . 1

Xlll

Table

1 . 1

2. 1

LIST OF TABLE

Typical Attenuation Values for Wavelength 1 550nm

EDFA Characteristics

Page

1 .8

2.5

XIV

Figure

1 . 1

1 .2

1 .3

1 .4

1 .5

1 .6

2. 1

2.2

2.3

2.4

2 .5

2.6

2.7

2.8

2.9

2. 1 0

2. 1 1

3 . 1

LIST OF FIGURES

The Basic Attenuation vs. Wavelength

Scattering Loss

Reflection Losses

Basic Operation of Generic Optical Amplifier

Current System and Proposed System Design DC-EDFA

The Project Model

The Basic Working Principle of the EDF A

Energy Level States of Erbium

Output Power as a Function of Wavelengths at Different Input Power

Gain Dependence on Input Signal Power

Gain vs. Output Signal Power with Increasing Input Power Signal at Different Constant Pumping Power

The Output Power of Signal ( 1 540 nm) After Amplified Associated with Amplified Spontaneous Emission (ASE)

ASE Noise Power vs. Pump Power

Erbium's Length, Input Power and Signal Wavelengths Vs. Gain and Noise Figure

EDF A Gain vs. Doped Fiber Length for Pump Power

Three Possible Configuration of an EDFA: (a) Co-directional Pumping, (B) Counter-Directional Pumping, (C) Dual Pumping

Functional Type of the Amplifiers a) Post-amplifier; b) In- line amplifier; c) Preamplifier.

The Proposed EDFA System to Support Two Fibers Simultaneously

Page

1 .4

1 .6

1 .7

1 . 1 1

1 . 1 7

1 . 1 9

2.2

2.3

2.7

2.8

2.9

2. 1 0

2. 1 0

2. 1 2

2. 1 5

2. 1 8

2.20

3 .2

xv

3 .2

3 .3

3 .4

4. 1

4 .2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

4. 1 0

4. 1 1

4. 1 2

4. 1 3

Circulators working principle a) Three-Port Circulator B ) Four­Port Circulator

WDM Multiplexers / Demultiplexers (A) Function of a WDM Multiplexer; (b) Function of a WDM Demultiplexer; (c) Function of a WDM Multiplexer in EDFA System

Eye diagram

Input power Versus a) Insertion loss 980nm of WDM Coupler

b) directivity Loss at

wavelengths Versus a) insertion loss at 980nm b) isolation loss at 1 550nm of WDM coupler

Wavelengths Versus a) Insertion loss from port 1 to port 2 b) Directivity Loss from 1 to 3

Wavelengths Versus a) Insertion Loss from Port 2-3 2) Isolation Loss from 2- 1

Gain measurements of the Unmodulated Signals at Port 3 of Circulator A with Pump Laser fixed of 95 mW

Figure 4.6: Gain Measurements of Unmodulated Signals in the presence of 1 554nm, from Port 3 of Circulator A

Gain of 1 554nm Modulated Signal Versus Unmodulated Signals wavelengths

Figure 4.8 : Gain Measurements of 1 554nm (modulated signal) V s. Pumping Power

Gain of Unmodulated Signals Versus Input Power of Modulated Signal

Gain of the Modulated Signal at Versus Input Power

Measurements the Output Power Versus Wavelengths at Pump Power 95 m W from Circulator a at port 3

Output Power Measurements of the Unmodulated Signals Getting out from Port 3 of Circulator A

The Output Power of 1 554nm in the Presence of Different Unmodulated Signals at Maximum Pump Powers of 95mW

3.3

3 .5

3 . 1 0

4.3

4.3

4.4

4.5

4.6

4.7

4.8

4.9

4. 1 1

4. 1 1

4. 1 2

4. 1 3

4. 14

XVI

4. 1 4

4. 1 5

4. 1 6

4. 1 7

4. 1 8

4. 1 9

4.20

4.2 1

4.22

4.23

4 .24

4.25

4.26

4.27

4.28

4.29

4.30

4.3 1

Output Power Measurements of 1 554nm Vs. Pumping Power

Output Power of Unmodulateds Signal vs. Tuning Input Power of The Modulated Signal

The Modulated S ignal Output Power Vs Input Power

ASE Measurements as a Function of Wavelength at 95 m W Fixed Pumping Powers

ASE of the Unmodulated Signals as a Function of Pump Power

ASE of the 1 554nm (modulated signal) versus Unmodulated Wavelengths

ASE Measurements of the Modulated Signal ( 1 554nm) versus Pumping Power

ASE level of the Unmodulated S ignal Vs. Input Power of the Modulated Signal

ASE Level of the Modulated Signal Vs. Input Power

Noise Figure Measurement of Unmodulated Signal from Port 3 of Circulator A at Pumping Power of 95mw

Noise Figure Measurement of unmodulated signal wavelength as a Function of Pump Power

Noise Figure of 1 554nm (modulated) as Function of Wavelength at Pump power of 95m W

Noise Figure Measurement of 1 554nm Modulated Signal as a Function of Pump Power taken From Port 3 of Circulator B

Noise Figure of Ur.modulated S ignal Wavelengths as a function of Input Power of 1 554nm the modulated signal

Noise Figure of the Modulated Signal as function of Input Power

The 1 554nm Output Associated with Reflection from 1 550nm ( 1 554nm i/p- 1 5dBm, 1 550 nm i/pOdB)

The 1 550nm Output Associated with Reflection from 1 554nm ( 1 550 nm i/pOdB, 1 554nm i/p- 1 5dBm)

Crosstalk as a Function of Wavelength

4. 1 5

4. 1 6

4. 1 6

4. 1 7

4. 1 9

4.20

4.2 1

4.22

4.23

4.23

4.24

4.25

4.26

4.27

4.28

4.29

4.30

4.3 1

XVII

4.32

4.33

4.34

4.35

BER vs. Pumping Power m W at the presence of I 530nm

BER vs. Input Power (dBm) at Fixed Pump Power of 2.4mW

Eye pattern of signal 1 554nm at rate 622m1s after amplifier (7 m EDF) at lip -5 . 1 1 and pump power off

Eye pattern of signal 1 554nm at rate 622m1s in the presence of unmodulated signal at same wavelength ( 1 554nm)and input power (lip -5 . 1 1 ) and pump power 90m W

4.33

4.34

4.35

4.35

XVl\l

l R

2R

3R

ASE

BEDFA

BER

o

dB

dBm

DC-EDFA

DP

EDF

EDFA

G

I

ilP

IL

InGaAs

InGaAsP:

IR

MCVD

LIST OF ABBREVIATIONS

Repeaters Perform Reampl ification the S ignal

Repeaters Perform Reamplification and Reshaping

Repeaters Provide Regenerators and Reshaping And Retiming

Amplified Spontaneous Emission

Bidirectional Erbium Doped Fiber Amplifier

Bit Error Rate

Directivity

A Unit of Measurement Indicating Relative Power on a Logarithmic Scale

Abbreviation for Decibel Relative to Milliwatt.

Dual Core Fiber EDFA

Design Parameters

Erbium Doped Fiber

Erbium Doped Fiber Amplifier

Gain

Isolation

Input Power

Insertion Loss

Abbreviation For Indium Gallium Arsenide.

Abbreviation For Indium Gall ium Arsenide Phosphide.

Infrared

Modified Chemical Vapor Deposition Method

X.IX.

MUXl DEMUX

NF

OIP

OA

OC- 12

OC- 1 92

OSA

OSI

PP

SDH

SM

SMF

SOAs

SONET

STM

STM- l

STM-4

TAT- 1 2, 1 3

TLS

TPC-5

UEDFA

WDM

Multiplexer I Demultiplexr

Noise Figure

Output Power

Optical Amplifier

Standard For Optical Carrier Level at 622.08 Mbps In Sonnet

Standard For Optical Carrier Level at 1 0 Gbps

Optical Spectrum Analyzer

Open System Interconnection

Performance Parameters

Synchronous Digital Hierarchy

Single Mode

Single Mode Fiber

Semiconductors Optical Amplifiers

Synchronous Optical Network

Synchronous Transport Modules

Standard for Optical Carrier Level at 1 55 Mbps in SDH

Standard for Optical Carrier Level at 622 Mbps in SDH

Transatlantic cable system

Tunable Laser Source

Transpacific cable system

Unidirectional Erbium Doped Fiber Amplifier

Wave Division Multiplexer

xx

CHAPTER I

INTRODUCTION

Light has been used for thousands of years for communications, a feat which man being

an intellectual creature needs. This need has created a myriad of astonishing devices

employed in communication systems used for sending messages from one point to

another at a distant place.

Many forms of communication systems have appeared over the years. The basic

motivation behind each new form is to improve the transmission fidelity, increase the

data rate so that more information can be sent, and increase the distance between the

relay stations. Fiber optic communication systems could overcome almost all

shortcoming and problems found in conventional communication systems.

1. 1 The Importance of Fiber Optics Communication

The major characteristic of a telecommunication system is unquestionably its

information- carrying capacity; capacity is the most prized feature that most users need.

A copper wire can carry a signal up to 1 MHz over a short distance. A coaxial cable can

propagate a signal up to 1 00MHz. Radio frequencies are in the range of 500MHz to

l OOMHz. Microwaves, including satellite channels; operate up to l OOGHz [ 1 ] . Fiber

1 . 1

optic communication system uses l ight as the signal carrier; light frequency is between

1 00 and 1 000THz. The explosive growth of Internet traffic, deregulation and the

increasing demands of users forced the telecommunications companies (Telco's) to

increase the capacity of their networks. Only optical networks could deliver the required

capacity as the bandwidth on demand is now synonymous with wavelength on demand.

Beside the large capacity of optical communications bandwidth, there is still a number of

extremely attractive features of optical systems such as weightlsize of the fibers, signal

security, low transmission loss, flexibility and the reliability. System reliability is

generally enhanced in comparison with conventional electrical conductor systems.

Furthermore, the reliability of the optical components is no longer a problem with

predicted l ifetimes of 20 to 30 years [2] . All these factors also tend to reduce the

maintenance time and costs.

The telecommunications industry's insatiable appetite for capacity, the bandwidth of

commercial systems has increased more than a hundredfold, the potential information

that can be carried by a single fiber optic channel is estimated at 50 terabits a second

(Tbitls) . However from a practical standpoint, commercial l inks have transmitted far

fewer than 1 00 Gb/s, already an astonishing amount of data in itself that cannot be

achieved with any other transmission medium. Researchers and engineers are working to

develop new techniques that approach the potential capacity l imit. Two recent major

technological advances; Wavelength Division Multiplexing (WDM) and Erbium Doped

Fiber Amplifier (EDFA), have boosted the capacity of existing systems. They have

brought significant improvements in the capacity of the system now in development;

1 .2

WDM is fast becoming the technology of choice in achieving smooth, manageable

capacity expansion.

1.2 The Need for Optical Amplifiers

The essential elements for telecommunication networks are a transmitter, a transmission

medium and a receiver, and in an optical system these devices are represented by a

semiconductor laser, an optical fiber, and a photodiode, respectively. However, a look

back over the history of telecommunications also reveals how amplifiers have played a

vitally important role in the field. Without amplifiers, the present boom in

communications system would have been impossible, let alone prospects of amplifying

extremely weak signals from deep space probes. In this sense, the realization of optical

amplification technology involving the direct amplification of light signals has long been

a dream of many people who are working in fiber optic communication field. Optical

amplification technology has a wide range of possible uses. Not only it is applicable to

trunk transmission l ines to compensate the loss; it is also used in the optical networking

to compensate for the signal splitting losses in the access networks.

1.2.1 Loss in the System

Every transmission l ine introduces some loss in the signal power. In general all losses in

optical fiber can be classified into two general categories: intrinsic and extrinsic. Intrinsic

losses are those associated with a given fiber material and cannot be removed by any

1 .3

improvements in the fabrication and operation processes. Extrinsic losses are those

associated with fabrication, cabling, and installation process, and theoretically, can be

eliminated under ideal conditions.

Loss which is also known as attenuation is the decrease in light power during the propa-

gation of light along an optical fiber. Attenuation plays a major role in the design of an

optical system because it determining the maximum transmission distance between the

transmitter and the receiver or on inline amplifier system. The attenuation takes place in

a fiber due to absorption, scattering and radiative losses of optical energy [3].

c o .... i c: Q ... ... (

to

Optical fibers 8S0nrn

700 900

lJlOnm 1550 run

1100 1300 1500 \\' avelcn�th �nm'

Figure 1 . 1 : The Basic Attenuation vs. Wavelength

Th

e

bas

ic

atte

nua

tio 1700

n

ver

sus

wavelengths characteristics is shown Figure!.!. Losses are mainly contributed by

absorption, scattering and bending.

1 .4