vii
TABLE OF CONTENTS
CHAPTER
1
TITLE
PAGE
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENTS
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLE
x
LIST OF FIGURES
xi
LIST OF ABBREVIATIONS
xii
LIST OF SYMBOLS
xiv
INTRODUCTION
1.1
Background of Study
1
1.2
Statement of Problem
2
1.3
Objective of the Study
3
1.4
Scope of the Study
3
1.5
Significance of the Study
4
1.6
Thesis Plan
4
viii
2
3
LITERATURE REVIEW
2.1
Introduction
6
2.2
Optical Fiber
8
2.3
Principle of Laser
11
2.3.1
Stimulated Emission
11
2.3.2
Optical Amplification
12
2.3.3
Optical feedback
14
2.4
Brief introduction of fiber laser
15
2.5
Double clad fiber
18
2.6
Double clad fiber designs
20
2.7
Ytterbium doped fiber laser
22
2.8
Fiber Bragg Grating
25
2.9
Simplified analytic solution
27
2.10 Rate Equation of Yb-doped fiber laser
32
2.11 Simulation Software
34
RESEARCH METHODOLOGY
3.1
Introduction
35
3.2
Liekki Application Designer (LAD) software
35
3.3
Numerical experimental setup
38
3.3.1
Multimode Ytterbium doped fiberdouble Cladding
41
3.3.2
Pump Power
41
3.3.3
Splice
42
3.3.4
Multimode pump coupler (MPC)
43
3.3.5
Grating
44
3.4
Simulation system
46
3.4.1 System with difference pumping
configuration
47
ix
3.5 Simulation Design
4
48
RESULT AND DISCUSSION
4.1
Introduction
50
4.2
Effective Pump Wavelength
51
4.3
Output power at different pumping scheme
52
4.4
Optimum value for length in difference
54
pumping configuration
4.5
Optimum fiber length as a function of dopant
56
configuration
4.6
Optimum fiber length as a function of pump
power
58
4.7
Optimum fiber length as a function of output
59
reflectivity, R2
5
CONCLUSION AND FUTURE WORK
5.1
Introduction
61
5.2
Conclusion
61
5.3
Future Work
65
REFERENCES
66
Appendices A-E
73
x
LIST OF TABLES
TABLE NO.
TITLE
PAGE
3.1
Specification of Yb-DCF
40
3.2
Typical device specification for multimode ytterbium
41
doped double clad fiber
3.3
Parameter value of MPC in this simulation
45
xi
LIST OF FIGURES
FIGURE NO
TITLE
PAGE
2.1
Ray bouncing inside an optical fiber
8
2.2
Fiber Layer
9
2.3
Two level laser
13
2.4
A three level laser
13
2.5
Schematic of laser cavity
15
2.6
Schematic of fiber resonator for cw fiber laser:
17
2.7
Double clad concept for high power fiber laser
18
2.8
Various designs of double-clad fibers
20
2.9
Model calculation for the absorbtion of difference
21
cladding-pumped structure in dependence of fiber
length
2.10
Absorption and emission cross sections of ytterbium
23
in fused silica
2.11
Energy levels of Yb3+ ions in Yb:YAG
24
2.12
Principle of FBG
25
2.13
Schematic diagram of the double-clad fiber laser
28
with forward pumping configuration
2.14
Schematic diagram of the double-clad fiber laser
30
with backward pumping configuration.
3.1
Flow chart of simulation procedure
38
3.2
Ytterbium doped double clad fiber laser system.
39
3.3
Pump Power
42
3.4
Splice
43
3.5
Multimode Pump Coupler
45
xii
3.6
Grating
46
3.7
Schematic representation of FBG as a mirror
46
3.8
Experimental setup for Ytterbium doped fiber
47
amplifier in difference pumping scheme. (a) forward
(b) backward
3.9
Flow chart of simulation design
49
4.1
Output power as a function of pump power in
51
difference pump wavelength
4.2
Output power as a function of pump power
51
4.3
Output power versus fiber length
55
4.4
Output power profile for difference dopant
56
concentration
4.5
Output power for difference pump power.
59
4.6
Output power in difference output reflectivity, R2
60
xiii
LIST OF ABBREVIATIONS
DCF
-
Double Clad Fiber
DFL
-
Doped Fiber Laser
EDFL
-
Erbium doped fiber Laser
ASE
-
Amplified Spontaneous Emission
FBG
-
Fiber Bragg Grating
WDM
-
Wavelength division multiplexing
MPC
-
Multimode pump Coupler
xiv
LIST OF SYMBOLS
Yb
-
Ytterbium
Er
-
Erbium
Nd
-
Neodynium
N
-
Dopant concentration
λB
-
Bragg wavelength
Pp
-
Pump Power
P+(z)
-
Forward Signal Power
P-(z)
-
Backward Signal Power
αa
-
Absorption Coefficient
αs
-
Scattering Loss Coefficient
λp
-
Pump Wavelength
λs
-
Signal Wavelength
τf
-
Spontaneous Lifetime
σs
-
Stimulated Emission Cross-Section
Af
-
Saturation Signal Output Power
ms
-
Millisecond
m
-
Meter
dB
-
Decibel
nm
-
Nanometer
kW
-
Kilowatt