vii
TABLE OF CONTENT
CHAPTER
1
TITLE
PAGE
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
xi
LIST OF FIGURES
xii
LIST OF SYMBOLS
xvi
LIST OF ABBREVIATIONS
xviii
LIST OF APPENDICES
xix
INTRODUCTION
1
1.1 Introduction
1
1.2 Background of the Study
2
1.3 Statement of the Problem
3
1.4 Objective of the Study
4
1.5 Scope of the Study
4
1.6 Significant of the Study
5
viii
2
LITERATURE REVIEW
6
2.1 Introduction
6
2.2 Relationship of Refractive Index with Temperature,
Concentration and Wavelength
7
2.3 Basic of Optical Fiber
9
2.4 Fiber Optic Sensor Technology
10
2.5 Optical Modulation Mechanism
12
2.5.1 Intensity Modulated Fiber Optic Sensor
12
2.6 Fresnel’s Law of Reflection
13
2.7 Fiber Optic Coupler Technology
16
2.7.1 Coupling Ratio
18
2.7.2 Characteristic of Fiber Coupler
18
2.8 Light Source
20
2.9 Optical Detector
21
2.10 Works relating Fiber Optics and Refractive Index
Measurement
3
23
RESEARCH METHODOLOGY
28
3.1 Introduction
28
3.2 Fabrication of Fiber Optic Coupler
29
3.3 Characterization of Sensor System
30
3.3.1 Fiber Ends Preparation of the Single Mode
Fiber Coupler
30
3.3.2 Characteristics of the selected Fiber couplers
31
3.3.3 Liquid Samples Preparation
33
ix
3.3.4 Relation between Power of the Light Source
and Reflected Light Intensity
34
3.3.5 Determination the Depth of Immersion
35
3.3.6 Checking the Sensor Sensitivity
35
3.4 The Measurement System
36
3.4.1 Sensor Set up
36
3.4.1.1 Power meter as a detector
37
3.4.1.2 Photodiode as a detector
37
3.5 Method of Data Measurement
38
3.5.1 Variation of Refractive Index of Solution with
Wavelength of Incident Light
40
3.5.2 Variation of Refractive Index of Solution with
Concentration
40
3.5.3 Variation of Refractive Index of Solution with
Temperature of Solute
3.6 Calibration Curve
42
42
3.6.1 The Measurement of the Refractive Index
using Refractormeter
42
3.7 Measurement of Liquid Refractive Index using
44
OTDR
4
RESULT AND DISCUSSION
46
4.1 Introduction
46
4.2 Results of Sensor Characterization
47
4.2.1 Sensing Performance of Different Ratio of
Fiber Coupler
47
x
4.2.2 Depth of Immersion
48
4.2.3 Relation between Power of the Light Source
and Reflected Light Intensity
4.2.4 Sensitivity of the Sensor System
49
51
4.3 Measurement of Refractive Index with Reflected
Intensity
53
4.3.1 Concentration Relation
54
4.3.2 Temperature Relation
59
4.3.3 Wavelength Relation
62
4.4 Measurement of Liquid Refractive Index using
OTDR
65
4.5 Performance of Fiber-Couplers for Refractive Index
Measurement
5
68
4.6 Calibration Curve for the Sensor
72
CONCLUSION AND RECOMMENDATION
80
5.1 Conclusion
80
5.2 Recommendation
82
REFERENCES
83
Appendices A- F
87-95
xi
LIST OF TABLES
TABLE NO.
TITLE
PAGE
3.1
Concentration of the liquid sample
34
3.2
Configuration between two probes
36
4.1
The outputs of the two ports using
powermeter as a detector
47
The outputs of two port using photodiode as
a detector
47
Reflected Intensity in different media
52
4.2
4.3
xii
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE
2.1
Graph of RI (solid lines) and group index (dotted lines)
of silica against wavelength
9
Fiber optic structures
10
2.3(a)
Extrinsic optical fiber sensor
11
2.3(b)
Intrinsic fiber optic sensor
11
2.4(a)
Reflection type
13
2.4(b)
Transmission type
13
2.5
Fresnel’s Law at medium interface
14
2.6
Graph of reflectivity relation to the angle of incidence
between two medium interfaces
16
Directional coupler consisting of two fibers whose
core is brought close to each other
17
2.8
Characteristics of coupler
19
2.9
Graph of optical output power versus input drive
current
for laser diode
21
2.10
Photodiode model
22
2.11
Graph of RI of sucrose versus a variation of
concentration
24
Schematic demonstration of the light paths at the end of
a fiber
25
2.2
2.7
2.12
xiii
Temporal response showing the sensors performance as
a function of refractive index
26
Graph of the comparison of theoretical and measured
reflectance for various refractive index of media
27
3.1
Flow chart of the fabrication of fiber-based coupler
29
3.2
Twisting and pulling the fiber
29
3.3
Photograph of cleaved glass fiber(x50)
31
3.4
Fiber based coupler
31
3.5
The experiment set up for measuring output power P1
32
3.6
The experiment set up for measuring output power P2
33
3.7
Schematic experimental set up for reflected light
intensity measurement using fiber coupler
37
Schematic experimental set up for reflected light
intensity measurement using fiber coupler
37
3.9
The experimental set up of the sensor system
38
3.10
Reflected light intensity from powermeter under 5 time
measurements or distilled water at room temperature
39
3.11
Reflected light pulse display on oscilloscope
41
3.12
Graph of refractive index versus concentration for salt
solution
43
Schematic experimental set up for reflectance
measurement using OTDR
44
3.14
Reflectance measurements from OTDR trace
45
4.1
Graph of output power of reflected light intensity
versus depth of fiber end immersed in liquid
49
Graph of reflected output power of light intensity
versus input power for 50:50,70:30 and 90:10 coupling
ratio
50
Graph of output voltage of reflected light intensity
versus injection current for 50:50, 70:30 and 90:10
coupling ratio
50
2.13
2.14
3.8
3.13
4.2
4.3
xiv
4.4
4.5
4.6
4.7
4.8
4.9
4.10
4.11
4.12
4.13
4.14
4.15
4.16
4.17
4.18(a)
Sensor responses for 50:50 coupler at different
temperature of salt solution
55
Sensor responses for 70:30 coupler at different
temperature of salt solution
55
Sensor responses for 90:10 coupler at different
temperature of salt solution
56
Graph of normalized intensity versus concentration of
sucrose
58
Graph of normalized intensity versus concentration of
ethanol
58
Sensor responses for 50:50 coupler at different
concentration of salt solution
59
Sensor respond for 70:30 coupler at different
concentration of salt solution
60
Sensor respond for 90:10 coupler at different
concentration of salt solution
60
Graph of output power of reflected light intensity
versus concentration for different operating wavelength
at room temperature (22.9 ± 0.1°C) for salt solution for
50:50 coupling ratio
62
Graph of output power versus temperature at different
operating wavelength for distilled water (0% mass of
solvent) for 50:50 coupling ratio
63
Represent the measured refractive index versus
temperature of distilled water at wavelength 1310 nm
and 1551 nm
64
OTDR trace for salt solution in range 3%-15%
(zoom=14x)
65
Graph of reflectance versus concentration of salt
solution for temperature in range 30ºC-90ºC
66
Graph of reflectance versus temperature of salt solution
for concentration in range 3%-24%
67
Graph of output power of reflected light intensity
versus temperature for different coupling ratio of fiber
coupler for distilled water using power meter
68
xv
4.18(b)
Graph of output voltage of reflected light intensity
versus temperature for different coupling ratio of fiber
coupler for distilled water using photodiode
69
Graph output power of reflected light intensity versus
concentration for different coupling ratio at room
temperature using power meter
71
Graph of output voltage of reflected light intensity
versus concentration for different coupling ratio at
room temperature using photodiode
71
Graph of output power of reflected light intensity
versus refractive index for 50:50 coupling ratio at room
temperature using power meter as a detector
73
Graph of output voltage of intensity versus refractive
index for 50:50 coupling ratio at room temperature
using photodiode as a detector
73
Graph of refractive index versus temperature of
solution for distilled water
74
Graph of refractive index versus the temperature for
NaCl–H2O solutions with different concentrations,
which ranged from 20 to 70 °C
75
Graph refractive index of tap water versus the
temperature at the wavelength of 1550nm
76
4.25
Graph of refractive index versus temperature of water
77
4.26
Graph of refractive index versus concentration for
sugar solution at room temperature using 50:50
coupling ratio of fiber coupler
78
Graph for the variation of refractive index with
concentration of sugar solution
79
4.19(a)
4.19(b)
4.20
4.21
4.22
4.23
4.24
4.27
xvi
LIST OF SYMBOLS
n
-
Refractive index
c
-
Speed of light in vacuum
v
-
Speed of light in medium
I
-
Incident ray
θi
-
Angle of incident
θr
-
Angle of reflection
θt
-
Angle of refraction
n1
-
Refractive index of medium 1
n2
-
Refractive index of medium 2
R
-
Reflectance
T
-
Transmission
RS
-
s-polarized light
RP
-
p-polarized light
μ
-
Permeability
μo
-
Vacuum permeability
Pout
-
Output power
Pin
-
Power input
L
-
Length oh the interaction region

-
Coupling coefficient
xvii
dB
-
Decibel
Pexcess
-
Excess loss
Si
-
Silicon
Ge
-
Germanium
InGaAs
-
Indium Gallium Arsenide
C
-
Concentration
T
-
Temperature

-
Wavelength
Vg
-
Group velocity

-
Propagation constant

-
Radian optical frequency
nf
-
Effective index
ng
-
Group index

-
Optical dispersion
mV
-
Milivolt
xviii
LIST OF ABBREVIATIONS
EMI
-
Electromagnetic interference
CR
-
Coupling ratio
IL
-
Insertion loss
D
-
Directivity
RL
-
Return loss
FBT
-
Fused biconical taper
LED
-
Light emitting diode
SLD
-
Superluminescent diode
OPM
-
Optical power meter
NIST
-
National Institute of Standards and Technology
FBG
-
Fiber brag grating
RI
-
Refractive index
IMG
-
Index matching gel
xix
LIST OF APPENDICES
APPENDIX NO:
TITLE
A
Data sheet for each fiber coupler used
B
The specification of InGaAs Photodiode used
PAGE
87
followed by the basic of photodiode circuit,
amplified detector and spectral response by
DET01CFC
C
90
The value of output power value for Port 1 and
Port 2 for 50:50, 70:30 and 90:10 coupling ratio
at 1300nm
D
Performance characterizations and related
formula for CORNING SM28e fiber used
E
92
93
The specification of Digital Handheld
Refractometer from Reichert Technologies
used
F
94
The value of refractive index measured by
refractometer and fiber coupler system.
95