DEVELOPMENT OF AN OPTICAL PULSING BY USING POCKELS EFFECT
THIAN LEE ENG
UNIVERSITI TEKNOLOGI MALAYSIA
PSZ 19:16(Pind. 1/97)
UNIVERSITI TEKNOLOGI MALAYSIA
BORANG PENGESAHAN STATUS TESIS
JUDUL : DEVELOPMENT OF AN OPTICAL PULSING BY USING
POCKELS EFFECT
SESI PENGAJIAN : 2005/2006
Saya : THIAN LEE ENG
(HURUF BESAR)
mengaku membenarkan tesis (PSM/ Sarjana/ Doktor Falsafah)* ini disimpan di Perpustakaan
Universiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut :
1.
2.
Tesis adalah hakmilik Universiti Teknologi Malaysia.
Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk tujuan
pengajian sahaja.
Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara
institusi pengajian tinggi.
** Sila tandakan (9 )
3.
4.
¥
SULIT
(Mengandungi maklumat yang berdarjah keselamatan atau
kepentingan Malaysia seperti yang termaktub di dalam AKTA
RAHSIA RASMI 1972)
TERHAD
(Mengandungi maklumat TERHAD yang telah ditentukan oleh
organisasi/ badan di mana penyelidikan dijalankan)
TIDAK TERHAD
Disahkan oleh
(TANDATANGAN PENULIS)
Alamat Tetap :
59, JALAN KELAPA BALI,
TAMAN SOGA,
83000 BATU PAHAT,
JOHOR.
Tarikh :
3-8-2005
(TANDATANGAN PENYELIA)
PM. DR. NORIAH BIDIN
NAMA PENYELIA
Tarikh :
3-8-2005
CATATAN : * Potong yang tidak berkenaan.
** Jika Tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/
organisasi berkenaan dengan menyatakan sekali tempoh tesis ini perlu dikelaskan
sebagai SULIT atau TERHAD.
i Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah dan Sarjana
secara penyelidikan, atau disertai bagi pengajian secara kerja kursus atau penyelidikan,
atau Laporan Projek Sarjana Muda (PSM).
“We hereby declare that we have read this thesis and in our
opinion this thesis is sufficient in terms of scope and quality for the
award of the degree of Master of Science (Physics)”
Signature
: …………………………….
Name of Supervisor I
: ASSOC. PROF. DR. NORIAH BIDIN
Date
3-8-2005
: …………………………….
Signature
: …………………………….
Name of Supervisor II
: DR. YACOOB MAT DAUD
Date
3-8-2005
: …………………………….
DEV
ELOPMENT OF AN OPTICAL PU
LSIN
G BY S
UING POCKELS EFFECT
THIAN LEE ENG
A thesis submitted in fulfilment of the
requirements for the award of the degree of
Master of Science (Physics)
Faculty of Science
U
niversiti Teknologi Malaysia
AU
GS
UT, 2005
ii
I declare that this thesis entitled “Development of An Optical Pulsing By Using Pockels
Effect” is the result of my own research except as cited in the references. The thesis has
not been accepted for any degree and is not concurrently submitted in candidature of any
other degree.
Signature
: ………………………….
Name
: THIAN LEE ENG
Date
3-8-2005
: ………………………….
iii
To my beloved parents,
brother and sisters
iv
ACKNOWLEDGEMENTS
Although it is beyond my ability to adequately thank people who have helped me
in completing this project, I can at least mention some names of those whose help I
consider above and beyond the call of duty without which I could have never completed
my work. My supervisor, Associate Professor Dr. Noriah Binti Bidin, deserves my
special thanks for being my advisor and for giving me invaluable guidance in this work.
I would also like to extend my gratitude to my co-supervisor, Dr. Yaacob Bin Mat Daud
for giving me unending patience in directing my work. My gratitude also goes to other
collaborators and classmates including Mr. Nyan, Hadi, Kua, Hazimin, Izi, Fairus, Naza,
Ejant, Fatin and Aizi for their help and support. They were always ready to provide help
whenever needed, their friendship will never be forgotten. Finally, I must thank to my
parents, and my family including my brother Hua Guey, my sisters Lee Nak and Lee
Chuang for their love, faithful support and encouragements in these years.
v
ABSTRACT
Laser produced from active medium is normally in continuous mode. The beam
can be modulated by inserting switching mechanism. An electro-optic mechanism is one
of the techniques used to alter the operation of laser beam from continuous into pulse
mode. Hence, the objective of this project is to develop an optical switch system by
using Pockels effect. Helium-Neon (He-Ne) laser was used as continuous light source in
the project. Calcite and quartz crystals were employed as natural birefringent materials.
While a synthetic birefringent material, lithium niobate was used as a Pockels cell. The
lithium niobate crystal can become birefringent only through the application of electric
field. Therefore, several pulse generators were developed and used to trigger an electrooptic driver to electrify the lithium niobate crystal. A Pockels cell house was designed
and fabricated by using perspex. The Pockels cell house was completed with electrodes.
The performance of the fabricated Pockels cell was compared to the commercial Pockels
cell.
Both of the Pockels cells exhibited similar characteristic, whereby the linear
polarization state of laser light was turned into circular state when it entered the
electrified Pockels cells with a : b ratio of 1.0 : 1.0 (2 kV and 3 kV voltage applied) and
1.1 : 1.0 (4 kV voltage applied). This converts the continuous He-Ne beam into pulse
mode. The generation of the laser pulse can be operated either in a single or repetitive
mode.
It depends on the frequency of the pulse generator.
The amplitude of the
produced laser pulse was increased by increasing the voltage supplied to electrify the
lithium niobate crystal. The amplitude of the produced laser pulse by using transverse
Pockels cell was 500 mV, 700 mV and 1000 mV at 2 kV, 3 kV and 4 kV applied voltage.
While the result obtained by using commercial Pockels cell was 700 mV, 900mV and
1200 mV.
vi
ABSTRAK
Laser yang dihasilkan daripada medium aktif biasanya diperoleh dalam bentuk
selanjar.
Alur ini boleh dimodulasi dengan memasukkan mekanisma pensuisan.
Mekanisma elektro-optik adalah salah satu teknik yang digunakan dalam pensuisan laser
selanjar kepada denyut.
Tujuan projek ini adalah untuk menghasilkan satu sistem
pensuisan cahaya dengan menggunakan kesan Pockels. Laser Helium-Neon (He-Ne)
digunakan sebagai sumber cahaya selanjar dalam projek ini. Hablur kalsit dan kuartz
digunakan sebagai bahan dwibiasan semulajadi.
Manakala lithium niobate (bahan
dwibiasan buatan) digunakan sebagai sel Pockels. Lithium niobate hanya akan menjadi
bahan dwibiasan apabila dikenakan medan elektrik. Beberapa penjana denyut dibina dan
digunakan untuk membekalkan medan elektrik kepada lithium niobate.
Pockels direka dan dibina dengan menggunakan perspek.
Rumah sel
Rumah ini dilengkapkan
dengan elektrod. Prestasi sel Pockels yang dibina dibandingkan dengan sel Pockels
komersial.
Kedua-dua sel Pockels menunjukkan sifat sama dengan menukarkan
pengutuban linear cahaya laser kepada bulat dengan a : b 1.0 : 1.0 (bekalan elektrik 2 kV
dan 3 kV) dan 1.1 : 1.0 (bekalan elektrik 4 kV) apabila laser dilintaskan melalui sel
Pockels yang dikenakan elektrik. Keadaan ini menyebabkan operasi He-Ne laser selanjar
bertukar kepada denyut. Laser denyut yang dijanakan boleh dalam bentuk tunggal atau
berulang-ulang. Penjanaan laser denyut bergantung kepada frekuensi penjana denyut.
Amplitud laser denyut yang dihasilkan bertambah dengan penambahan bekalan elektrik
pada lithium niobate. Amplitud laser denyut yang dihasilkan (sel Pockels yang dibina)
adalah 500 mV, 700 mV dan 1000 mV pada bekalan elektrik 2 kV, 3 kV dan 4 kV.
Manakala untuk sel Pockels kommersial adalah 700 mV, 900 mV dan 1200 mV.
vii
TABLE OF CONTENTS
CHAPTER
1
TITLE
PAGE
TITLE
i
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
xvii
LIST OF APPENDICES
xix
INTRODUCTION
1.1
Light Modulation
1
1.2
The History Of Electro-optic
2
1.3
Research Background
3
1.4
Comparison Between Different Techniques Of
Beam Modulation
6
1.5
Research Objectives
8
1.6
Scopes Of Research
8
1.7
Organization Of Thesis
9
viii
2
3
THEORY
2.1
Introduction
10
2.2
Polarization
10
2.3
Malus’ Law
12
2.4
Birefringence (Double Refraction)
14
2.5
Analysis Of Elliptically Polarized Light
15
2.6
Optics Of Uniaxial Crystal
16
2.7
The Pockels (Linear Electro-optic) Effect
18
METHODOLOGY
3.1
Introduction
21
3.2
BPX65 Photodetector
22
3.3
Equipments
23
3.3.1
Helium-Neon (He-Ne) Laser
24
3.3.2
Polarizer and Analyzer
25
3.3.3
Quartz Crystal
26
3.3.4
Calcite Crystal
27
3.3.5
Lithium Niobate Crystal (LiNbO3)
28
3.3.6
Pockels Cell
29
3.3.7 TDS 210 Digitizing Real-Time Oscilloscope
3.3.8
3.3.9
3.4
4
30
Long Scale Galvanometer And Photoelectric
Detector
31
High Voltage Probe
33
Demonstration Of The Birefringence Phenomenon
34
DEVELOPMENT OF PULSE GENERATORS
4.1
Introduction
38
4.2
Electro-optic Driver
39
4.3
CD4528BCN Dual Monostable Multivibrator
39
4.4
Pulse Generators
41
ix
4.4.1 Repetitive Mode With Frequency Range Less
5
Than 300 Hz
42
4.4.2
Single Pulse
44
4.4.3
Repetitive Mode With Frequency Of 1 Hz
46
4.5
Calibration Of Pulse Generators
50
4.6
Triggering Of An Electro-optic Driver
56
4.7
Summary
59
DETERMINATION OF THE POLARIZATION
STATE OF HE-NE LIGHT OUT OF NATURAL
BIREFRINGENT MATERIALS
5.1
Introduction
60
5.2
Polarization State Of He-Ne Light
61
5.3
Polarization State Of He-Ne Light Out Of
Quartz Crystal
5.4
5.5
6
65
Polarization State Of He-Ne Light Out Of
Calcite Crystal
71
Summary
76
DEVELOPMENT OF TRANSVERSE POCKELS
CELL
6.1
Introduction
77
6.2
Designing Of Pockels Cell House
78
6.3
Fabrication Of Transverse Pockels Cell
78
6.4
Electrifying The Transverse Pockels Cell
79
6.5
Experiment Of He-Ne Polarization By Using
Pockels Cell
6.6
Characterization Of He-Ne Polarization State
Through Transverse Pockels Cell
6.7
80
83
Characterization Of He-Ne Polarization State
Through Commercial Pockels Cell
92
x
6.8
6.9
7
Comparison Between The Output Intensity Of The
Commercial and Transverse Pockels Cell
99
Summary
101
OPTICAL SWITCH
7.1
Introduction
102
7.2
Optical Switching Operation
102
7.3
He-Ne Switching By Using Transverse
Pockels Cell
7.4
He-Ne Switching By Using Commercial
Pockels Cell
7.5
105
109
Comparison Between The Switching of He-Ne By
Using The Transverse Pockels Cell And The
7.6
8
Commercial Pockels Cell
111
Summary
113
CONCLUSIONS AND SUGGESTIONS
8.1
Conclusion
114
8.2
Problems
116
8.3
Suggestions
117
REFERENCES
APPENDICES A – O
PRESENTATION
118
124-140
141
xi
LIST OF TABLES
TABLE NO.
TITLE
PAGE
1.1
Comparison between different modulation techniques
7
2.1
Some negative and positive uniaxial crystals
18
4.1
The truth table of CD4528BCN dual monostable multivibrator
48
4.2
Calibration result obtained from various pulse generators
56
5.1
Data obtained from the experiment of the He-Ne light
polarization
63
5.2
Polarization of He-Ne light out of Q
67
5.3
Polarization state of He-Ne out of calcite
73
6.1
Determination of He-Ne polarization state out of the
transverse Pockels cell
6.2
90
Determination of He-Ne polarization state out of the commercial
Pockels cell
99
7.1
Light switching by using transverse Pockels cell
108
7.2
Light switching by using commercial Pockels cell
111
xii
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE
1.1
Lumped modulator and its electric circuit
4
1.2
Traveling-wave modulator using two-plate structure
4
1.3
Zigzag modulator
5
1.4
Optical waveguide modulator
5
2.1
An electromagnetic wave
11
2.2
Light wave passing through a polarizer
11
2.3
Resolution of the amplitude of the transmitted light, Ao
into two components, A1 and A2
2.4
The crystal resolves polarized light into ordinary, O
and extraordinary, EO beams
2.5
14
Resolution of the amplitude of transmitted polarized light
into two components, a and b
2.6
13
16
Principal plane of the crystal (kz) and
(a) ordinary beam and
(b) extraordinary beams
17
2.7
Transverse Pockels effect
19
2.8
Longitudinal Pockels effect
20
3.1
Schematic diagram of BPX65 photodetector
22
3.2
Typical spectral response of BPX65 photodiode
23
3.3
He-Ne laser with 1 mW output power
24
3.4
He-Ne laser with 4 mW output power
25
xiii
3.5
Polarizer
26
3.6
Quartz crystal
27
3.7
Calcite crystal
28
3.8
Cubic lithium niobate crystal
29
3.9
Laser light enters a Pockels cell through the window beside
the insulator housing
30
3.10
LT PYRKAL CJSC Pockels cell
30
3.11
TDS 210 Digitizing Real Time Oscilloscope
31
3.12
Schematic diagram of detector system
32
3.13
Long scale galvanometer
32
3.14
Photoelectric detector
33
3.15
Tektronix high voltage probe
34
3.16
Demonstration setup of birefringence
35
3.17
Ordinary, O and extraordinary, EO beams out of the calcite.
(a) The existence of the two He-Ne beams out of calcite and
(b) The two projected beams of He-Ne
3.18
36
Occurrence of double images of object when viewed through
the calcite
37
4.1
Electro-optic driver
39
4.2
Schematic diagram of CD4528BCN dual monostable
multivibrator
40
4.3
CD4528BCN dual monostable multivibrator
41
4.4
Schematic diagram of the pulse generator (f < 300 Hz)
42
4.5
The whole block circuit diagram of the pulse generator
(f < 300 Hz)
43
4.6
Schematic diagram of single pulse generator
45
4.7
The block circuit diagram of single pulse generator
45
4.8
Schematic diagram of the pulse generator with frequency of
1 Hz
4.9
47
The block diagram of the pulse generator with the frequency
of 1 Hz
47
xiv
4.10
The oscillograms of the input at label of (a) A, (b) B, (c) Clear and
the output (d) Q of Figure 4.9
4.11
The circuit of 1 Hz pulse generator mounted in a black
plastic box
4.12
49
50
(a) Frequency versus resistance graph and
(b) Frequency versus 1/R graph for pulse generator with
f < 300 Hz (Vin = 10V and 12V)
4.13
51
(a) Frequency versus resistance graph and
(b) Frequency versus 1/R graph
for pulse generator with 1 Hz (Vin = 10V and 12V)
4.14
52
Pulse width versus resistance graph for pulse generator
with f < 300 Hz
54
4.15
Pulse width versus resistance graph for the single pulse generator 54
4.16
Pulse width versus resistance graph for the pulse generator
(f = 1 Hz)
4.17
55
The output of the electro-optic driver when triggered by
(a) pulse generator with frequency of 100 Hz, and
(b) single pulse generator
4.18
The pulse width of (a) 1Ps, (b) 2Ps, (c) 3Ps and (d) 4Ps
produced by the pulse generators
5.1
58
Schematic diagram of the experiment to determine the
polarization of He-Ne light
5.2
57
61
Experimental arrangement for measuring polarization state of
He-Ne laser
62
5.3
Current ratio, i/io versus cos2 T graph
63
5.4
Schematic diagram of the experiment to determine the polarization state
of He-Ne out of quartz crystal, Q
5.5
65
Experiment setup for determination of the polarization state
of He-Ne out of quartz crystal, Q
66
5.6
Oscillation of He-Ne light out of quartz crystal
68
5.7
Graph of current, i versus cos2 T out of quartz crystal, Q
69
xv
5.8
Schematic diagram of the experiment to determine the
polarization state of He-Ne light out of calcite crystal
5.9
71
Experimental setup for the determination of the polarization state
of He-Ne light out of calcite
72
5.10
Current, i versus cos2 T out of calcite graph
74
6.1
Fabricated Pockels cell house
78
6.2
The setup of the transverse Pockels cell
79
6.3
Ensemble of optical switch
80
6.4
Schematic diagram of the experiment by using fabricated
transverse Pockels cell
6.5
Experimental arrangement by using fabricated
transverse Pockels cell
6.6
81
82
Schematic diagram of the experiment by using commercial
Pockels cell
82
6.7
Experimental arrangement by using commercial Pockels cell
83
6.8
Graph of power, P versus T at 2 kV out of transverse Pockels
cell
6.9
Graph of power, P versus T at 3 kV out of transverse Pockels
cell
6.10
84
84
Graph of power, P versus T at 4 kV out of transverse Pockels
cell
85
6.11
P versus cos2 T at 2 kV (f = 100 Hz)
86
6.12
P versus cos2 T at 2 kV (f = 200 Hz)
87
6.13
P versus cos2 T at 3 kV (f = 100 Hz)
87
6.14
P versus cos2 T at 3 kV (f = 200 Hz)
88
6.15
P versus cos2 T at 4 kV (f = 100 Hz)
88
6.16
P versus cos2 T at 4 kV (f = 200 Hz)
89
6.17
P versus T graph at f = 100 Hz (V = 2 kV, 3 kV and 4 kV)
91
6.18
P versus T graph at f = 200 Hz (V = 2 kV, 3 kV and 4 kV)
91
6.19
Graph of power, P versus T at 2 kV out of commercial
xvi
Pockels cell
6.20
Graph of power, P versus T at 3 kV out of commercial
Pockels cell
6.21
93
93
Graph of power, P versus T at 4 kV out of commercial
Pockels cell
94
6.22
P versus T at f = 100 Hz (V = 2 kV, 3 kV and 4 kV)
95
6.23
P versus T at f = 200 Hz (V = 2 kV, 3 kV and 4 kV)
95
6.24
P versus cos2 T at 2 kV (f = 100 Hz)
96
6.25
P versus cos2 T at 2 kV (f = 200 Hz)
96
6.26
P versus cos2 T at 3 kV (f = 100 Hz)
97
6.27
P versus cos2 T at 3 kV (f = 200 Hz)
97
6.28
P versus cos2 T at 4 kV (f = 100 Hz)
98
6.29
P versus cos2 T at 4 kV (f = 200 Hz)
98
6.30
P versus T (f = 100 Hz and V = 4 kV)
100
7.1
Schematic diagram of light switching experiment by
using transverse Pockels cell
103
7.2
Light switching experiment by using transverse Pockels cell
103
7.3
Schematic diagram of light switching experiment by
using commercial Pockels cell
104
7.4
Light switching experiment by using commercial Pockels cell
104
7.5
Output He-Ne light signal (V = 2 kV; f = 55 Hz)
105
7.6
Output He-Ne light signal (V = 3 kV; f = 55 Hz)
106
7.7
Output He-Ne light signal (V = 4 kV; f = 55 Hz)
106
7.8
Output He-Ne light signal (V = 2 kV; f = 100 Hz)
109
7.9
Output He-Ne light signal (V = 3 kV; f = 100 Hz)
110
7.10
Output He-Ne light signal (V = 4 kV; f = 100 Hz)
110
7.11
Variation of the laser pulse amplitude to the applied voltage
112
xvii
LIST OF SYMBOLS
a
-
Amplitude of the light component A1
Ao
-
Amplitude of the transmitted light
A1
-
Amplitude of the light component
A2
-
Amplitude of the light component
As
-
Total amplitude of the light
B
-
Pulse width
C
-
Capacitance
b
-
Amplitude of the light component A2
d
-
Width of the crystal
E
-
Electric vector
EO
-
Extraordinary beam
f
-
Frequency
F
-
Focal length
H
-
Magnetic vector
I
-
Intensity of the transmitted electromagnetic or mechanical waves
I
-
Intensity of the He-Ne light
Io
-
Intensity of the incident light
i
-
Current
k
-
Multiple factor
k
-
Wave vector of the light wave
KPD
-
Responsivity of the photodiode
l
-
Length of the crystal
ne
-
Refraction index of the extraordinary beam
xviii
no
-
Refraction index of the ordinary beam
'n
-
Birefringence or double refraction
M
-
Slope of the graph
O
-
Ordinary beam
P
-
Light power
P1
-
Polarizer
P2
-
Analyzer
Q
-
Quartz crystal
r
-
Electro-optic coefficient
R
-
Resistance
t
-
Period
V
-
Applied voltage
Va
-
Average voltage
Vin
-
Supplied voltage
z
-
Optical axis
O
-
Wavelength of the light
T
-
Angle of the analyzer
'I
-
Phase retardation
xix
LIST OF APPENDICES
APPENDIX NO
TITLE
PAGE
A
Technical specifications of the electro-optic driver
124
B
Optical properties of lithium niobate
125
C
CD4528BCN Dual Monostable Multivibrator
126
D
Data obtained from the experiment by using
transverse Pockels cell (f = 200 Hz and V = 2 kV)
E
Data obtained from the experiment by using
transverse Pockels cell (f = 100 Hz and V = 2 kV)
F
135
Data obtained from the experiment by using
commercial Pockels cell (f = 100 Hz and V = 2 kV)
L
134
Data obtained from the experiment by using
commercial Pockels cell (f = 200 Hz and V = 2 kV)
K
133
Data obtained from the experiment by using
transverse Pockels cell (f = 100 Hz and V = 4 kV)
J
132
Data obtained from the experiment by using
transverse Pockels cell (f = 200 Hz and V = 4 kV)
I
131
Data obtained from the experiment by using
transverse Pockels cell (f = 100 Hz and V = 3 kV)
H
130
Data obtained from the experiment by using
transverse Pockels cell (f = 200 Hz and V = 3 kV)
G
129
136
Data obtained from the experiment by using
commercial Pockels cell (f = 200 Hz and V = 3 kV)
137
xx
M
Data obtained from the experiment by using
commercial Pockels cell (f = 100 Hz and V = 3 kV)
N
Data obtained from the experiment by using
commercial Pockels cell (f = 200 Hz and V = 4 kV)
O
138
139
Data obtained from the experiment by using
commercial Pockels cell (f = 100 Hz and V = 4 kV)
140
CHAPTER 1
INTRODUCTION
1.1
Light Modulation
Applications of laser light always require the modulation of some properties
of the laser light wave. The modulation of light wave is to control variation of some
detectable properties of the light wave, such as its intensity (amplitude), phase,
wavelength (frequency) or polarization (direction of the beam propagation)
(Schawlow, 1969; Hammer, 1975). A modulator is a device that alters a detectable
property of a light wave corresponding to an applied electric signal (Hammer, 1975).
Actually there are a number of methods which can be used to modulate laser
light such as mechanical, electro-optic, magneto-optic and acousto-optic. Most
mechanical methods such as rotating mirror and mechanical shutter or chopper used
for laser-beam modulation are slow, unreliable and have much inertia to allow the
faster light modulation (Kaminow and Turner, 1966; Schawlow, 1969). Thus, the
mechanical methods are seldom used in modern modulation equipment. Hence, the
interaction between laser wave and electric, magnetic or acoustic fields acting
through the electro-optic, magneto-optic and acousto-optic effect are used to
modulate laser-beam (Kaminow and Turner, 1966; Chen, 1970). Modulation of
2
laser-beam by using these effects is faster and more reliable than the mechanical
methods. Among these three interactions, electro-optic effect has received most
attention and is widely used for light modulation as it provides the fastest modulation
(Schawlow, 1969; Booth and Hill, 1998). For electro-optic effect, the application of
an electric field across certain crystal is used to result in change of refraction index of
the crystal. The crystal becomes birefringent under the influence of the applied
electric field (O’Konski, 1978; Noriah Bidin, 2003). These crystals include,
potassium dihydrogen phosphate (KDP), potassium dideuterium phosphate (KD*P),
lithium niobate (LiNbO3), lithium tantalite (LiTaO3) and cesium dihydrogen arsenate
(CDA) (Kuhn, 1998).
The electro-optic effect can be used to control the intensity or phase of the
propagating light (Yariv, 1997). The modulation by using electro-optic effect is the
basic operation concept for the optical modulator, optical switch, Q-switch, and
deflector (Zajac, 1982; Laud, 1985; Chuang, 1996).
1.2
The History Of Electro-optic
In 1875, Kerr observed that certain dielectric medium become doubly
refractive when placed in a strong electric field (Schawlow, 1969; Kaminow, 1974).
This effect was consequently named as Kerr effect, or quadratic electro-optic effect.
He also discovered this effect in liquids such as carbon disulphide (Kaminow and
Turner, 1966; Camatini, 1973; Kaminow, 1974). The Kerr effect can be observed in
any crystal (Schawlow, 1969).
The linear electro-optic effect was introduced by Pockels in 1893 (Jenkins,
and White, 1976). The linear electro-optic effect is always called as Pockels effect to
distinguish it from Kerr effect. This effect can occur only in crystals that lack of a
3
center of symmetry (Schawlow, 1969). During the nineteenth century, Pockels
examined the Pockels effect in quartz, tourmaline, sodium chlorate and K-Na tartrate
salt (Rochelle salt) (Kaminow and Turner, 1966).
1.3
Research Background
The first useful Pockels cell was made of potassium dihydrogen phosphate
(KDP) by Billings in 1949. However, this device was not capable to be used for
high-frequency operation. In 1961, Schawlow, developed a high frequency laser
modulator made of KDP crystal based on the Pockels effect. But, the power required
was too high for practical use. This stimulated interest of many researchers in
searching other feasible crystals (Kaminow, 1974).
Since then, lithium niobate (LiNbO3), lithium tantalite (LiTaO3) and
ammonium dihydrogen phosphate (ADP) are a few more capable materials used for
light modulation (Schawlow, 1969). In 1967, Kaminow and his group constructed
light intensity modulators by using LiTaO3 and LiNbO3. The performance of the
LiNbO3 intensity modulator has of slight advantage compared to the LiTaO3 due to
the larger electro-optic coefficient of LiNbO3. Light modulation by using Pockels
effect on LiNbO3, KDP and ADP was well established (White and Chin, 1972;
Salvestrini et al., 2004).
A few forms of modulator have been developed by using Pockels effect.
They are lumped, traveling wave, zigzag, and optical waveguide modulator. The
configuration of each type of modulator has been described by Chen (1970). The
physical construction of each modulator is illustrated in Figure 1.1, 1.2, 1.3 and 1.4
(Chen, 1970). Among them, lumped modulator is most suitable to be used for
4
modulation of frequency < 1 GHz and with the crystal length about 1 cm. Travelingwave and zigzag modulator are used for modulation of frequencies greater than
1 GHz (Denton et al, 1967). The type of modulator chosen depends on the required
driving power and crystal length (Chen, 1970).
Figure 1.1: Lumped modulator and its electric circuit (Chen, 1970)
Figure 1.2: Traveling-wave modulator using two-plate structure (Chen, 1970)
5
Figure 1.3: Zigzag modulator (Chen, 1970)
Figure 1.4: Optical waveguide modulator (Hammer, 1975)
A lumped electro-optic optical modulator has been developed by using single
crystal LiTaO3 which is in a cylinder form. A transistor driver-amplifier with a 0.2
W output power is used to drive the LiTaO3 at a light wavelength of 632.8 nm In
order to reduce the voltage for modulation, the modulator is configured in the
transverse mode. The modulator provides 40% intensity of modulation (Kaminow
and Sharpless, 1967).
6
The accurate and direct determination of the phase retardation due to the
birefringence of certain materials can be done by using a technique based on the
linear variation of the transmitted intensity with the applied electric field to an
amplitude modulator (O’Shea, 1985).
1.4
Comparison Between Different Techniques Of Beam Modulation
Besides the Pockels (linear electro-optic) effect, other techniques like
magneto-optic, acousto-optic and Kerr effects can also be used to change the
refraction index of an optical medium through the application of an external field.
However the Pockels (linear electro-optic) effect is chosen because of some
advantages. The comparison between different techniques of laser beam modulation
is listed in Table 1.1.
7
Table 1.1: Comparison between different modulation techniques
Techniques
Advantages
Disadvantages
1. Pockels (linear electro-
- Fastest modulation
- Expensive.
optic) effect
speed (Schawlow, 1969;
- Only occur in the 21
Booth and Hill, 1998;
types of crystal classes
O’Shea, 1985).
(Bessley, 1976; Noriah
- Easy electric field
Bidin, 2003).
generation (Booth and
- Required large voltage.
Hill, 1998).
- To get good result need
- Precise timing.
high quality polarizer
(Booth and Hill, 1998).
2. Kerr effect
- Occur in all the 32 types
- Kerr coefficient of most
of crystal classes (Bessley, crystals is small.
1976).
- Nitrobenzene with high
Kerr coefficient is toxic
and unstable (Bessley,
1976).
- Required higher voltage
than Pockels effect
(Lothian, 1975).
3. Acoustic effect
4. Magneto effect
- Simple radio frequency
- Slow opening times
circuit.
(Booth and Hill, 1998)
- Applied to gases, liquids - Slow opening times.
and solids (Bessley,
- Hard to generate require
1976).
magnetic strength
(Bessley, 1976).
There are many techniques that can be used to modulate the laser beam by
changing the refraction index of an optical medium. But electro-optic promises a
better offer than the rest. It can be used either as an internal or external modulator
(Bessley, 1976).
8
In this project, Pockels effect has been applied to produce an optical switch.
It is an important element in the construction of a Q-switched Nd:YAG laser for
medical purpose.
1.5
Research Objectives
The objectives of this research are listed as followed:
1. To diagnose birefringence characteristic,
2. To design a trigger system,
3. To develop a Pockels cell and
4. To characterize the output of an optical switch.
1.6
Scopes of Research
In this research, the polarization of He-Ne light was analyzed by using
Malus’ Law. Natural birefringent materials, like quartz and calcite crystal were used
as specimen.
A transverse Pockels cell was developed by applying electric field across the
lithium niobate crystal. High voltage was supplied to Pockels cell. A pulse
generator was designed to trigger the switch in single mode and repetitive mode.
9
1.7
Organization of Thesis
This thesis consists of seven chapters. The introduction, research
background, objectives and scopes of research are briefly mentioned in Chapter 1.
Chapter 2 describes some important theories that are related to optical switch.
Chapter 3 discusses about the optical and electrical equipments used to accomplish
the project. The development of the pulse generator used to trigger the electro-optic
driver is discussed in Chapter 4. Chapter 5 describes about the preliminary works on
natural birefringent materials. The development of a transverse Pockels cell and it
diagnostic will be discussed in Chapter 6. The application of Pockels cell as an
optical switch is elaborated in Chapter 7. Finally, the conclusions of this research,
research problems and suggestions are in Chapter 8.
CHAPTER 2
THEORY
2.1
Introduction
The operation of optical switch is based on birefringence phenomenon.
Therefore, it is very important to understand the birefringence characteristic. The
optical properties of birefringent material can only be manipulated by applying polarized
light. Hence, the fundamental concept of the polarization state of light needs to be
understood prior to optical switch development.
2.2
Polarization
Laser emits coherent electromagnetic radiation field (Yariv and Yeh, 1984). An
electromagnetic field in free space can be described by its electric, E and magnetic, H
vectors, that vibrate perpendicularly to each other as shown in Figure 2.1 (Setian, 2002).
11
The interaction between a light (electromagnetic wave) and a matter involves
redistribution of the charges on its molecules. It is predominantly influenced by the
electric vector rather than the magnetic vector (Jenkins and White, 1976; Klinger et al.,
1990). Therefore, further discussion will emphasize more on the electric vector.
E
Z
H
Figure 2.1: An electromagnetic wave (Klinger et al., 1990)
Light wave can be polarized by using polarizer (Tenquist et al., 1970; Clarke and
Grainger, 1971; Rahim Sahar, 1996) as illustrated in Figure 2.2. When an unpolarized
light is directed to a polarizer, only the light with its vibration parallel to the axis of the
polarizer is allowed to pass through, while the others will be absorbed. Thus, the light
emitted from the analyzer is linearly polarized. If a second polarizer with perpendicular
axis is placed, no light (electric field) will be passing through the second polarizer
(Tenquist et al., 1970). The second polarizer is known as an analyzer (O’Shea, 1985).
x
Ex
Ex
E
no E field
z
Ey
y
Axis of polarizer
Figure 2.2: Light wave passing through a polarizer (Setian, 2002)
12
The polarization of the light beam can be diagnosed by using Malus’ Law.
2.3
Malus’ Law
Malus’ law explains how the intensity of the polarized light transmitted by the
analyzer varies with the angle between the axis of the polarizer and analyzer (Tenquist et
al., 1970). Thus, Malus’ law can be adopted in controlling the brightness of a polarized
light (Kallard, 1977).
Assume that Ao represents the amplitude of the light that is transmitted by the
polarizer (Figure 2.3). When the light strikes the analyzer with an angle lj, it resolves
into A1 and A2. Of these two lights, only the light with its vibration parallel to the axis
of the analyzer is allowed to pass through. Assume that A1 is the amplitude of the light
that passes through the analyzer, it can be determined as:
$ 0 cos T
$1
(2.1)
And its intensity, I is
,
Therefore,
$1
2
(2.2)
13
2
$ 0 cos 2 T
,
(2.3)
As the intensity, I of the electromagnetic wave is proportional to the square of the
amplitude, A2, the intensity of the polarized light that enters the analyzer, Io is equal to
Ao2. Therefore, Equation (2.3) can be written as (Jenkins and White, 1976):
,
, 0 cos 2 T
(2.4)
Axis of polarizer, P1
Axis of analyzer, P2
Ao
T
A2 = Ao sin T
A1 = Ao cos T
Figure 2.3: Resolution of the amplitude of the transmitted light, Ao into two
components, A1 and A2 (Jenkins and White, 1976)
14
2.4
Birefringence (Double Refraction)
When a polarized light enters a quartz or calcite crystal (natural birefringence
materials), the light will split into two beams (ordinary, O and extraordinary, EO beams)
which travel in different directions (Figure 2.4). This phenomenon is called
birefringence or double refraction (Andrews, 1960; Waldman, 1983; Setian, 2002).
O
EO
Polarized light
Figure 2.4: The crystal resolves polarized light into ordinary, O and extraordinary, EO
beams (Andrews, 1960)
Many crystalline materials exhibit birefringence naturally, such as quartz,
tourmaline, cellophane and calcite crystal (Billings, 1993). There are also numbers of
crystals that are not birefringent naturally but the birefringence can be induced through
the application of an external voltage. Examples of such crystals are ammonium
dihydrogen phosphate (ADP), potassium dihydrogen phosphate (KDP) and lithium
niobate (LiNbO3) (Dmitriev et al., 1991).
15
2.5
Analysis Of Elliptically Polarized Light
The characteristics of the polarized light can be determined by using a
combination of an analyzer with optical element like quartz crystal or some form of
compensator (Jenkins and White, 1976).
When a polarized light enters a polarizer, it will become linearly polarized light.
The electric field of the linearly polarized light oscillates in the plane parallel to the axis
of the polarizer. The linearly polarized light can be represented by its vertical, A1 and
horizontal, A2 components (section 2.3), which are in phase. The two components travel
in different velocities when they pass through a quartz crystal or an electro-optic
medium. Gradually, they become out of phase and appear as elliptically polarized light
(Schawlow, 1969). In this case, the amplitude of the component A1 is not the same as
the amplitude of the component A2. Assume that the amplitude of the A1 and A2 are
equal to b and a. T is the angle between the axis of the analyzer and the axis of the
ellipse (elliptically polarized light). The amplitudes of A1 and A2 that are allowed to
pass through the analyzer are b sin T and a cos T. The total amplitude, $ s allowed to
pass through the analyzer is (b sin T + a cos T ), the intensity of the transmitted light, I
through the analyzer is proportional to the square of the total amplitude, $ 2s . Therefore,
intensity of the transmitted light, I, can be written as Equation (2.5) below.
$ 2s
,
a 2 cos 2 T b 2 sin 2 T
= a 2 cos 2 T b 2 1 cos 2 T
= a 2 b 2 cos 2 T b 2
(2.5)
16
A1= b
T
A2=a
Axis of
analyzer
Figure 2.5: Resolution of the amplitude of transmitted polarized light into two
components, a and b
2.6
Optics Of Uniaxial Crystal
Uniaxial crystals have optical axis, z (Andrew, 1960; Lothian, 1975). The plane
which contains the optical axis and the wave vector of the light wave, k is defined as the
principal plane. The light beam with its polarization (direction of the vector E
oscillations) normal to the principal plane is known as ordinary beam, O. While, the
beam polarized in the principal plane is the extraordinary beam, EO (Figure 2.6)
(Dmitriev el at., 1991). The direction of light propagation does not influence the
refraction index of ordinary beam, but that of the extraordinary beam (Clarke and
Grainger, 1971).
17
(a)
(b)
Figure 2.6: Principal plane of the crystal (kz) and (a) ordinary and (b) extraordinary
beams (Dmitriev et al., 1991)
The difference between the refraction index of the ordinary beam, no and
extraordinary beam, ne is known as the birefringence or double refraction, 'n (Dmitriev
et al., 1991). The value of 'n is zero along the optic axis. If no > ne, the crystal is
negative uniaxial crystal and if no < ne, the crystal is positive uniaxial crystal (Fredericq
and Houssier, 1973). Some negative and positive uniaxial crystals are listed in Table 2.1.
18
Table 2.1: Some negative and positive uniaxial crystals (Dmitriev et al., 1991)
Negative Uniaxial Crystal
Positive Uniaxial Crystal
Calcite (CaCO3)
Quartz (SiO2)
Potassium dihydrogen phosphate (KDP)
Selenium (Se)
Ammonium dihydrogen phosphate (ADP)
Tellurium (Te)
Lithium niobate (LiNbO3)
Cadmium Selenide (CdSe)
2.7
The Pockels (Linear Electro-optic) Effect
The refraction index of certain crystal can be changed by using electro-optic
effect (Lothian, 1975). Electro-optic effect is the change of refraction index of a crystal
that is induced through the application of an electric field (Enami, 2003). The change of
the refraction index is proportional to the strength of the applied electric field. This is
named as Pockels (linear electro-optic) effect (Schawlow, 1969; Camatini, 1973; Robert,
2003).
There are two types of Pockels effect. They are transverse Pockels effect and
longitudinal Pockels effect, which are named according to the orientation of the applied
electric field (Noriah Bidin, 2002). In the transverse Pockels effect, the propagation
direction of the incident polarized light is perpendicular to the direction of the applied
electric field (Figure 2.7) (Lothian, 1975; Bessly, 1976). The phase retardation, 'I
induced by the transverse Pockels effect is
'I
S rlVn
Od
3
o
radian
(2.6)
19
where l is the length of the crystal, d is the width of the crystal, no is the refraction index
of the ordinary ray, r is the electro-optic coefficient, V is the applied voltage and O is the
wavelength of the light.
For longitudinal Pockels effect, the propagation direction of the incident
polarized light is parallel to the direction of the applied electric field (Figure 2.8). The
optical path of the light, l is same as the width of the crystal, d. The phase retardation,
'I induced by the longitudinal Pockels effect is given as:
'I
2Sno3 rV
O
(2.7)
radian
where no is the refraction index of the ordinary ray, r is the electro-optic coefficient, V is
the applied voltage and O is the light wavelength.
d
l
V-
V+
Direction of light
propagation
Figure 2.7: Transverse Pockels effect (Noriah Bidin, 2002)
20
d
l
V-
Direction of light
propagation
V+
Figure 2.8: Longitudinal Pockels effect (Noriah Bidin, 2002)
CHAPTER 3
METHODOLOGY
3.1
Introduction
In this chapter, all the elements used in the experimental works and signal
detection will be discussed. The discussion will start from the development and
fabrication of a BPX
65 photode tector. Other equipments required for the preliminary
works and the setup of an electro-optic modulator system consist of He-Ne lasers (1 mW
and 4 mW), polarizer and analyzer, quartz crystal, calcite crystal, Pockels cell, lithium
niobate crystal, TDS 210 Digitizing Real Time Oscilloscope, long scale galvanometer,
high voltage probe and electro-optic driver.
At the end of this chapter, the demonstration of the birefringence phenomenon
was carried out by using calcite crystal. While the triggering part of the electro-optic
driver by using fabricated pulse generators will be discussed in Chapter 4.
22
3.2
BPX65 Photodetector
A photodetector was fabricated by using a BPX
65 photodiode w ith the rise time
of 0.5 ns. BPX
65 photodiode has been used because of its high responsivity to high
speed pulse. The BPX
65 photodiode wa s connected as in Figure 3.1.
A 9V battery was used as a power source to drive the circuit. The BPX
65
photodiode was connected with a 560 : fixed resistor in series. The current flowing
through the resistor was connected to TDS 210 Digital Real Time Oscilloscope.
BPX
65
Photodiode
560 ȍ
Oscilloscope
9V
Figure 3.1: Schematic diagram of BPX
65 photodetector (Noriah Bidin, 1995)
The total light power (in Watt) illuminating the BPX
65 phot odiode is
proportional to the current flowing through the photodiode. Therefore, a simple
relationship between the photodiode current, i and the light power, P is given as
i = KPD P
(3.1)
23
65 photodiode
where KPD is the responsivity of the photodiode. The responsivity of BPX
is obtained from Figure 3.2.
Typical Spectral Response
0.7
Responsivity (A/W)
0.6
0.5
0.4
0.3
0.2
0.1
0
300
400
500
600
700
800
900
1000
1100
Wavelength (nm)
Figure 3.2: Typical spectral response of BPX
65 photodiode (RS Data Sheet, 1997)
3.3
Equipments
All equipments required in this research will be discussed in detail in this
following section.
24
3.3.1 Helium-Neon (He-Ne) Laser
Two Melles Griot model continuous wave (CW) Helium-Neon (He-Ne) lasers
with the wavelength of 632.8 nm and power of 1 mW and 4 mW were employed as light
sources. The light beam produced by 632.8 nm He-Ne is a red, monochromatic and
coherent light. The 1 mW and 4 mW lasers are class II and III lasers, respectively.
They are dangerous and any direct exposure of the laser light to eye must be avoided.
He-Ne laser exhibits several desirable characteristics such as low output noise, small
size and low cost. Therefore it was chosen as the light source. The sources are shown in
Figure 3.3 and 3.4.
In this project, a higher power laser (4 mW) was employed to study the
polarization state of the light out of calcite crystal, quartz crystal and Pockels cells.
While the 1 mW He-Ne laser was only used in the experiment of the He-Ne polarization.
Figure 3.3: He-Ne laser with 1 mW output power
25
Figure 3.4: He-Ne laser with 4 mW output power
3.3.2
Polarizer and Analyzer
Two Melles Griot polarizers were used in the experiment. The polarizer was
used to ensure that the incident laser light was linearly polarized. The analyzer was
always aligned to the polarizer. The optical axes of polarizer and analyzer can be
rotated from 0q to 360q. When the optical axis of the analyzer was orientated
perpendicularly to the optical axis of the polarizer, it can be used to prevent transmission
of light. Figure 3.5 shows a typical polarizer.
26
Figure 3.5: Polarizer
3.3.3
Quartz Crystal
Figure 3.6 shows a quartz crystal produced by CASTECH. The circular quartz
crystal is 1.00 mm thick with diameter of 1.00 cm. It can be used as a quarter wave
plate to alter the polarization state of light.
27
Figure 3.6: Quartz crystal
3.3.4
Calcite Crystal
Calcite crystal is another type of natural birefringent material (Figure 3.7). Its
scientific name is calcium carbonate, CaCO3. The crystal is rhombic in shape with
dimension of 1.5 cm u 1.5 cm u 4.5 cm. It is an uniaxial crystal as it has only one
optical axis. It can be obtained naturally form earth. Therefore there are many defects
in it. Before using the calcite, two main section of the crystal had been polished by
using agent diamond compound with the size 6 micron to reduce the light scattering and
absorption during light propagation.
28
Figure 3.7: Calcite crystal
3.3.5
Lithium Niobate Crystal (LiNbO3)
Lithium niobate is a synthetic birefringent material (Figure 3.8). Thus, it is not
naturally obtainable like other crystals such as calcite and quartz. In this project, a CASI
X(10 mm x 10 mm x 10 mm) uncoated cubic lithium niobate crystal was used as an
electro-optic material. Two opposite faces (x-y cut) are been polished. Lithium niobate
crystal was chosen for this particular experiment due to its large electro-optic coefficient,
good transmission, high optical quality and high damage threshold (Turner, 1966;
Salvestrini et al., 2004). The optical properties of lithium niobate crystal are listed in
Appendix A.
29
Figure 3.8: Cubic lithium niobate crystal
3.3.6
Pockels Cell
In this project, a 8 mm x 8 mm x 20 mm LiNbO3 crystal coated with Silicon and
Z
inc Oxide was m ounted at the center of a cylinder insulator housing to be employed as
a Pockels cell (electro-optic modulator). The Pockels cell was provided with a cathode
and anode. Laser light entered the Pockels cell through the window beside the house
(see Figure 3.9). This Pockels cell is manufactured by LT PYRKAL CJSC. Figure 3.10
shows the Pockels cell used in this experiment.
30
Laser
Pockels cell
Photodetector
Figure 3.9: Laser light enters a Pockels cell through the window beside the insulator
housing
Figure 3.10: LT PYRKAL CJSC Pockels cell
3.3.7 TDS 210 Digitizing Real-Time Oscilloscope
A TDS 210 Digitizing Real Time Oscilloscope is shown in Figure 3.11. TDS
210 Digitizing Real Time Oscilloscope is a two channels oscilloscope. It is small and
lightweight. It is manufactured by Tektronix. The light signals of the laser light from
the electro-optic modulator system were detected by a BPX
65 photodetector, and
subsequently measured and displayed on the oscilloscope.
31
Figure 3.11: TDS 210 Digitizing Real Time Oscilloscope
3.3.8
Long Scale Galvanometer And Photoelectric Detector
In the preliminary tests, a long scale galvanometer was used to measure the total
intensity of the illuminating laser light that fell onto the surface of the photoelectric
detector. The photoelectric detector was connected to the galvanometer by using 2
cables and a switch (Figure 3.12). Figure 3.13 and 3.14 show the long scale
galvanometer and the photoelectric detector respectively.
32
Photoelectric detector
Long scale Galvanometer
Switch
Figure 3.12: Schematic diagram of detector system
Figure 3.13: Long scale galvanometer
33
Figure 3.14: Photoelectric detector
3.3.9
High Voltage Probe
Tektronix P6015 (1000 x 3 pF, 100 Mȍ) high voltage probe was used to measure
the high voltage produced by the electro-optic driver and to display it by using the TDS
210 Real Time Oscilloscope. Maximum rating voltage of this probe with dielectric fluid
is 40 kV peak and 20 kV for direct current. While without dielectric fluid the maximum
rating voltage is 18 kV peak or 13 kV for direct current. Figure 3.15 shows the
Tektronix P6015 high voltage probe.
34
Figure 3.15: Tektronix high voltage probe
3.4
Demonstration Of The Birefringence Phenomenon
The schematic diagram of the birefringence phenomenon setup is illustrated in
Figure 3.16. In this experiment, a 4 mW He-Ne laser was used as a light source. An
upright white paper was used as a screen. A calcite crystal was mounted on a holder and
illuminated with He-Ne laser beam. The birefringence phenomenon is illustrated by the
existence of two lines that are named ordinary, O and extraordinary, EO beams
respectively. The O beam is in axis with the original beam. The EO beam is off axis
with the original beam.
35
EO
He-Ne Laser (4mW)
O
Calcite
Screen
Figure 3.16: Demonstration setup of birefringence
The result of the demonstration is shown in Figure 3.17. Figure 3.17(a) shows
the two existing beams of He-Ne out of the calcite. From Figure 3.17(b), it is clearly
shown that there were two He-Ne light lines projected on the screen.
Birefringence phenomenon can also be demonstrated without using light. In this
case, the calcite crystal was placed over a word “laser”(F igure 3.18). Through the
crystal, the “s”and “e”characters were view
ed as gray letters. The double images were
due to the birefringent effect. This result was in good agreement with the result by
Setian (2002) and Billings (1993).
36
(a)
Extraordinary
beam, EO
Ordinary
beam, O
(b)
Figure 3.17: Ordinary, O and extraordinary, EO beams out of the calcite. (a) The
existence of the two He-Ne beams out of calcite and (b) The two projected He-Ne beams
37
Figure 3.18: Occurrence of double images of object when viewed through the calcite
As conclusion, calcite crystal was proven to be a natural birefringent material
that shows birefringence phenomenon.
CHAPTER 4
DEVELOPMENT OF PULSE GENERATORS
4.1
Introduction
Pulse generators are used for research and development purposes in a wide range
of applications. Basically, pulse-forming circuits can be categorized into three groups
according to the type of multivibrator used (Swearer, 1970). Each generator has
particular characteristic and operational advantages and disadvantages depending on its
application. In this project, pulse generator was designed and fabricated by using
CD4528BCN dual monostable multivibrator, to trigger an electro-optic driver to
mobilize its output voltage within microseconds. The following sections describe the
development of the pulse generators. Normally, the energy requirement, voltage rise
time, duration of the waveform, amplitude of the signals, output waveform, the pulse
repetition rate and cost, are the governing factors in choosing generator (White, 1966).
39
4.2
Electro-optic Driver
In designing a pulse generator, some technical specifications of the electro-optic
driver were obeyed to avoid damage. The technical specifications of the electro-optic
driver are listed in Appendix A (LT PYRKAL CJSC Technologies Armenia, 2003). The
electro-optic driver was the product of LT PYRKAL CJSC. It was used as a power
supply to electrify the Pockels cell. As a safety precaution, it was earthed to avoid
electrical shock. Photograph of the electro-optic driver is shown in Figure 4.1.
Figure 4.1: Electro-optic driver
4.3
CD4528BCN Dual Monostable Multivibrator
CD4528BCN dual monostable multivibratior is also known as one-shot or
single-short multivibrator (Bozic, 1975). It can be used to produce a single square
output pulse (Green, 1995). Monostable multivibrator has two permissible output states
40
(High and Low), but only one of them is stable (Carr, 1999). Figure 4.2 shows the pin
out of the CD4528BCN dual monostable multivibrator. Photograph of CD4528BCN
dual monostable mltivibrator is shown in Figure 4.3. The features of this multivibrator
are listed in Appendix B.
Figure 4.2: Schematic diagram of CD4528BCN dual monostable multivibrator
(National Semiconductor Inc., 1988).
41
Figure 4.3: CD4528BCN dual monostable multivibrator.
4.4
Pulse Generators
A pulse generator was fabricated to trigger the electro-optic driver. It can
operate in single mode and repetitive mode. In the latter mode, two ranges of frequency
were set up. One generator was designed with only 1 Hz frequency. The other was with
a set of frequency less than 300 Hz. The pulse width of the pulse was found in the range
of 1 µs to 4 µs, which was appropriate with the requirement of the electro-optic driver.
The details of the pulse generator circuits are discussed in sections 4.4.1, 4.4.2 and 4.4.3.
42
4.4.1 Repetitive Mode With Frequency Range Less Than 300 Hz
A simplified schematic diagram of the pulse generator with frequency, f < 300
Hz is shown in Figure 4.4. For this pulse generator, the minimum frequency was about
25 Hz. A zener diode (15 V, 1W) was connected between the supplied voltage, Vin and
ground to avoid damage to monostable multivibrator by the over voltage (> 18 V). The
frequency of the resulted pulse was controlled by using external timing components - a
50 kȍ resettable resistor, 4.7 k: resistor and a 1 µF capacitor, while the pulse width of
the pulse was controlled by a 50 kƺ resettable resistor and a 0.1 µF capacitor (external
timing components). In order to limit the frequency to 300 Hz, a 4.7 kȍ resistor was
connected to the 50 kȍ resettable resistor in series, while a 100 ȍ fixed resistor was
connected to a 0.1 PF capacitor to delay a transition from Low to High at pin 4
(AAINPUT). The whole block circuit diagram of this generator is shown in Figure 4.5.
CD4528BC
9
Figure 4.4: Schematic diagram of the pulse generator (f <300Hz).
43
External
timing
components
A
Q
B
External
timing
components
B
Q
B
Figure 4.5: The whole block circuit diagram of the pulse generator (f < 300 Hz).
The operation of this circuit with reference to Figure 4.5 is, the input of ABINPUT
and BBINPUT were always High (1). Initially, the input AAINPUT was zero. The resultant
QAOUT was Low (0) and QAOUT to High (1). The QAOUT was redirected to charge the
0.1 PF capacitor. When the capacitor was fully charged, AAINPUT transition from Low to
High (n) occurred. The transition at AAINPUT produced a high QAOUT and a pulse was
obtained. Meanwhile, Low QAOUT was obtained and the capacitor started to discharge.
When the capacitor was fully discharged, the input AAINPUT was back to low again.
Consequently, Low QAOUT and High QAOUT were obtained. The charging and
discharging of capacitor took place simultaneously, resulting in a repetitive pulse mode
of Low and High QAOUT.
44
The pulse mode QAOUT then triggered the second part of the multivibrator as the
input AAINPUT. As BBINPUT was always High (1), the QBOUT would follow the trend of
input BAINPUT. Therefore, a pulse mode QBOUT was obtained.
The pulse width of the QAOUT was alterable by adjusting the external timing
components (54.7 kȍ resistor and a 1 µF capacitor). Likewise, a 50 kƺ resettable
resistor and a 0.1 µF capacitor (external timing components) were tuned to manipulate
the pulse width from QBOUT.
4.4.2 Single Pulse
Figure 4.6 shows the schematic diagram of a single pulse generator. A zener
diode was also connected between the supplied voltage (Vin) and ground to avoid
damage of the monostable multivibrator caused by the over-supplement of voltage (> 18
V). The pulse width was controlled by using a 200 kȍ resettable resistor and a 1 µF
capacitor. A single pulse produced when the switch connected between the supplied
voltage (Vin) and pin 12 was pressed. While, a 0.47 PF capacitor was connected to a 100
k: resistor to allow the charging and discharging process of the capacitor in order to
produce a transition from Low to High at pin 12 (BAINPUT). The whole block circuit
diagram of single pulse generator is shown in Figure 4.7.
45
CD4528BC
9
Figure 4.6: Schematic diagram of single pulse generator.
B
Q
Figure 4.7: The block circuit diagram of single pulse generator.
46
With reference to Figure 4.7, the BBINPUT was always High (1). Initially, the
BAINPUT was nil. The resultant QBOUT was Low (0). When the switch connected
between the supplied voltage (Vin) and BAINPUT was pressed, the 0.47 PF capacitor was
charged. When the capacitor was full, BAINPUT transition from Low to High (n) occurred.
When the transition occurred, High QBOUT obtained and pulse was produced.
Meanwhile, Low QBOUT was obtained and the capacitor started to discharge. When the
capacitor was fully discharged, the BAINPUT was back to low again. Consequently, Low
QBOUT and High QBOUT were obtained. Therefore, a pulse mode QBOUT was obtained
when the switch was pressed. The pulse width of the QBOUT was adjusted by using a
capacitor of 1 PF and a 200 k: resettable resistor (external timing components).
4.4.3 Repetitive Mode With Frequency Of 1 Hz
The schematic diagram of the pulse generator with 1 Hz frequency is shown in
Figure 4.8. Similar to the two previous generators, a zener diode was connected
between the supplied voltage, Vin and ground to avoid damage to monostable
multivibrator caused by the over voltage (> 18 V). The frequency of the pulse was
controlled through 10 µF capacitor, 100 k: and 120 k: fixed resistors, and also a 200
kŸ resettable resistor (external timing components). The pulse width of the produced
pulse was controlled through a 200 kŸ resettable resistor and a 1 µF capacitor. To limit
the maximum frequency to 1.2 Hz, the 100 kŸ and 120 kŸ fixed resistor was connected
to the 200 kŸ resettable resistor in series. Meanwhile a 100 Ÿ resistor was connected to
a 0.47 uF capacitor to delay a transition from Low to High at pin 4 through the charging
and discharging of the capacitor. The block circuit diagram of this generator is shown in
Figure 4.9.
47
CD4528BC
9
Figure 4.8: Schematic diagram of the pulse generator with frequency of 1 Hz.
A
Q
B
B
Q
Figure 4.9: The block diagram of the pulse generator with the frequency of 1 Hz.
48
The operation of the circuit shown in Figure 4.9 was almost the same as the pulse
generator with frequency of 300 Hz except that the 0.1 PF capacitor was replaced by a
0.47 PF capacitor. The replacement of 0.47 PF capacitor slows down the production of
the pulse by lengthening the charging time of the capacitor. The pulse width of the
output QAOUT was adjusted by the 420 k: resistor and 10 PF capacitor. The pulse width
of the output QBOUT was adjusted with the 200 k: resettable resistor and 1 PF capacitor
Basically, to ensure a continuous production of pulse from all generators, the
inputs of Clear and B were set to High level (1) while the inputs of the A were set to a
transition from Low to High (n). The input and output characteristics used in the
development of the pulse generators by using CD4528BCN dual monostable
multivibrator are shown and marked in Table 4.1. Figure 4.10 shows the osillosgrams of
the input of A, B, Clear and the output at Q of Figure 4.9, respectively.
Table 4.1: The truth table of CD4528BCN dual monostable multivibrator (National
Semiconductor Inc., 1988).
49
(a)
(c)
(b)
(d)
Figure 4.10: The oscillograms of the input at label of (a) A, (b) B, (c) Clear and the
output (d) Q of Figure 4.9.
In this project, all the circuits of the pulse generators were packed in a black
plastic box (Figure 4.11) for safety reason.
50
Figure 4.11: The circuit of 1 Hz pulse generator mounted in a black plastic box.
4.5
Calibration Of Pulse Generators
In this project, all the frequencies and pulse widths of the pulse produced from
the generators were controlled by external timing components (Duncan, 1985).
Frequency of the pulse was controlled by the first part of the block circuit diagram of
CD4528BCN dual monostable multivibrator while the second part controlled the pulse
width of the pulse. All the pulse widths and frequencies of the pulse could be changed
by adjusting the resistance of the resettable resistor. The generators were calibrated in
order to determine the relationship between the resistance of the resistor with the
frequencies and the pulse widths of the produced pulse when 10 V and 12 V were
supplied to the generators, respectively.
The relationship between the frequency of the produced pulse and resistance of
the resistor for the pulse generators (a generator with frequency less than 300 Hz and a
generator with frequency of 1 Hz) is showed in Figure 4.12 (a) and 4.13 (a).
51
(a)
350
Frequency, f (Hz)
300
250
200
10V
12V
150
100
50
0
0
10
20
30
40
50
60
Resistance, R ( kŸ )
(b)
y = 1.3598x + 0.0097
350
y = 1.2668x + 0.0056
Frequency, f (Hz)
300
250
200
10V
12V
150
100
50
0
0
50
100
150
-1
200
250
-1
1/Resistance, R ( µŸ )
Figure 4.12: (a) Frequency versus resistance graph and (b) Frequency versus 1/R graph
for pulse generator with f < 300 Hz (Vin= 10V and 12 V).
52
(a)
1.5
Frequency, f (Hz)
1.25
1
10V
0.75
12V
0.5
0.25
0
0
100
200
Resistance, R (k:)
(b)
y = 1.2894 - 0.5806
1.4
y = 1.2300 – 0.5687
Frequency, f (Hz)
1.2
1
0.8
10V
12V
0.6
0.4
0.2
0
0
5
10
15
20
25
30
35
-1
1/Resistance, R ( P:
-1-1))
Figure 4.13: (a) Frequency versus resistance graph and (b) Frequency versus 1/R graph
for pulse generator with 1 Hz (Vin = 10V and 12V).
53
All these figures show that the frequencies of the pulse generators decreased
exponentially with the increase in resistance. In order to confirm the exponential
relationship, the frequency is plotted against the inverse of the resistance as shown in
Figure 4.12 (b) and 4.13 (b). Linear graphs are obtained, proving that the frequencies of
the pulse generators decrease with the resistance of the resistor.
Figure 4.12 and 4.13 show that the frequency of the pulse generators was almost
the same at two different supplying voltages. The frequency of the pulse generators
depend on the period of the external timing components, t = kRC and f = 1/t, where k is
the multiple factor of CD4528BCN dual monostable multivibrator, R is the resistance of
the resistor, C is the capacitance of the external timing capacitor, f is the frequency of
the pulse and t is the period (Carr, 1999). An increase in resistance led to the increasing
in period, t and consequently reduces the frequency of the pulse generator. The
frequency of the pulse generators was not influenced by the applied voltage.
The relationship between the pulse widths and the resistance of the generators
are shown in Figure 4.14, 4.15 and 4.16.
54
y = 0.7825x - 0.0055
180
y = 0.7656x - 0.0034
Pulse width, B ( µs)
160
140
120
100
10V
12V
80
60
40
20
0
0
50
100
150
200
250
Resistance, R ( kŸ )
Figure 4.14: Pulse width versus resistance graph for pulse generator with f < 300 Hz
y = 0.7625x - 0.0045
180
y = 0.7456x - 0.0034
Pulse width, B ( µs)
160
140
120
100
10V
12V
80
60
40
20
0
0
50
100
150
200
250
Resistance, R ( kŸ )
Figure 4.15: Pulse width versus resistance graph for single pulse generator
55
y = 0.6684x + 0.0087
40
y = 0.6475x + 0.0095
Pulse width,B ( µs )
35
30
25
10V
12V
20
15
10
5
0
0
10
20
30
40
50
60
Resistance, R ( kŸ )
Figure 4.16: Pulse width versus resistance graph for pulse generator (f = 1 Hz)
These figures show a linear correlation between the pulse width and the
resistance of the pulse generator. The graphs also show that the pulse width increased
with the increase of the resistance of the pulse generators, and the results are similar for
input voltages of either 10V or 12V. This was because the pulse width of the produced
pulse depended on the period, t. Therefore, the increase of the resistance led to the
increase of the pulse width. The results obtained from the pulse generators are
summarized as listed in Table. 4.2.
56
Table 4.2: Calibration result obtained from various pulse generators.
Type of Pulse
Generator
f < 300 Hz
f = 1 Hz
Single Pulse
4.6
Applied
Voltage, V
10
12
10
12
10
12
Frequency, f Versus
Inverse Resistance, 1/R
y = 1.3598x + 0.0097
y = 1.2668x + 0.0056
y = 1.2894x – 0.5806
y = 1.2300x – 0.5687
Pulse Width, B Versus
Resistance, R
y = 0.7825x – 0.0055
y = 0.7656x – 0.0034
y = 0.7625x – 0.0045
y = 0.7456x – 0.0034
y = 0.6684x 0.0087
y = 0.6475x 0.0095
Triggering Of An Electro-optic Driver
The pulse signal was used to trigger the output voltage of the electro-optic driver
in this experiment instead of the square wave because of the technical specification of
the electro-optic driver (as mentioned in Appendix B). Thus, the output voltage of the
driver can only be interrupted by using the pulse signal instead of using the square wave.
The pulse generators could be used to trigger the electro-optic driver to mobilize
its output within microseconds. Figure 4.17 shows the mobilization of the voltage of the
electro-optic driver when triggered by using the pulse generator.
57
(a)
(b)
Figure 4.17: The output of the electro-optic driver when triggered by (a) pulse
generator with frequency of 100 Hz, and (b) single pulse generator
The upper signal of Figure 4.17 indicates the signal of the pulse generator and
the lower signal is the output voltage of the electro-optic driver. When the electro-optic
driver was externally triggered by the pulse generator, the voltage of the electro-optic
driver dropped. Without triggering the electro-optic driver by using the pulse generator,
the voltage of the driver will remain constant. Thus, the negative signal like indicated at
Figure 4.17 was obtained when the electro-optic driver was triggered by the pulse
generator. The output voltage of the electro-optic driver can be controlled according to
the frequency of the pulse generator. The output voltage of the electro-optic driver can
also be mobilized either in single or repetitive mode depending on the frequency of the
pulse generator.
58
The pulse width of the pulse produced by the pulse generators could be adjusted
from 1 Ps to the higher depending on the value of the resistance. However, the pulse
width used to trigger the electro-optic driver was limited in the range of 1 µs to 4 µs.
The allowable pulse width (1 µs to 4 µs) of the pulse generators are shown in Figure
4.18. This result is the same for all type of pulse generators (pulse generator with single
pulse, f =1 Hz and less than 300 Hz).
(a)
(c)
(b)
(d)
Figure 4.18: The pulse width of (a) 1 Ps, (b) 2Ps, (c) 3 Ps and d) 4 Ps produced by the
pulse generators
59
4.7
Summary
Pulse generators were successfully developed by using CD4528BCN dual
monostable multivibrator to trigger the electro-optic driver. The pulse width of the pulse
produced was in the range of 1 µs to 4 µs. The maximum frequency of the repetition
mode was limited to 300 Hz. This generator was successfully developed to be used
within the safety level of the electro-optic driver.
CHAPTER 5
DETERMINATION OF THE POLARIZATION STATE OF HE-NE LIGHT
OUT OF NATURAL BIREFRINGENT MATERIALS
5.1
Introduction
One way to analyze an optical switch is by testing the polarization state of laser
through it. Prior to examining the real system, preliminary works were carried out to
study:
a. the polarization of He-Ne light,
b. the polarization state of He-Ne light out of quartz and
c. the polarization state of He-Ne light out of calcite (Calcium Carbonate).
In all the preliminary works, we assumed that the intensity of the illuminating
He-Ne light, I detected by photoelectric detector is proportional to the current, i that
flows through the photodetector. The intensity of the He-Ne light was measured by the
long scale galvanometer. Hence, the data of these experimental works were recorded in
current reading. The methodology and result of the preliminary works will be discussed
in the following sections.
61
5.2
Polarization Of He-Ne Light
The polarization of He-Ne light was studied by using Malus’ Law. A 1 mW HeNe laser was used as the light source in this experiment. A polarizer P1, analyzer P2 and
photoelectric detector S were aligned in the direction of the He-Ne light propagation.
The angle of P2 was set to zero and P1 was removed from the system. Initially, the
reading of long scale galvanometer was set to zero. The galvanometer was used to
measured the current, i. After that, P1 was reinstalled into the system and P2 was rotated
to obtain a maximum galvanometer reading. At this condition, the axis of the P1 was
parallel to the axis of P2 (T = 0q). Galvanometer reading was recorded when the angle of
P1 was adjusted between T = 0q to 180q. The value of i was measured at every 10q of the
rotation of P1 until 180q. The experimental arrangement for measuring the polarization
of He-Ne light is shown in Figure 5.1, while the photograph of the arrangement of the
experiment is shown in Figure 5.2.
Photoelectric
Detector
He-Ne Laser
(1mW)
Polarizer
Analyzer
Long Scale
Galvanomete
Power Line
Figure 5.1: Schematic diagram of the experiment to determine the polarization of HeNe light
62
Analyzer, P2
Long Scale
Galvanometer
He-Ne Laser (1 mW)
Polarizer, P1
Photoelectric
Detector, S
Figure 5.2: Experimental arrangement for measuring polarization of He-Ne laser
Data obtained from the experimental work are listed in Table 5.1. Ten readings
of current were taken at each angle of rotation. The averaged current was subsequently
calculated.
Assume that the intensity of the transmitted He-Ne, I through the P2 is
proportional to the current, i measured by galvanometer (Equation 5.1). The ratio of
current, i/io is plotted against the square of cosine of the angle between the axis of the P1
to the P2, cos2 T (Figure 5.3).
IDi
(5.1)
63
Table 5.1: Data obtained from the experiment of the He-Ne Light polarization.
Angle
i
(r0.05mA) cos 2 T
Current, i (r0.05 mA)
T
(r0.5q)
i1
i2
i3
i4
i5
i6
i7
i8
i9
i/i0
i10
0
0.60 0.70 0.70 0.60 0.70 0.70 0.60 0.60
0.60 0.60
0.70
1.0000
1.0
10
0.60 0.60 0.70 0.70 0.70 0.70 0.60 0.60
0.60 0.60
0.60
0.9698
0.9
20
0.60 0.60 0.60 0.70 0.60 0.70 0.60 0.60
0.60 0.60
0.60
0.8830
0.9
30
0.50 0.60 0.60 0.60 0.60 0.50 0.50 0.50
0.50 0.50
0.50
0.7500
0.7
40
0.50 0.40 0.40 0.50 0.50 0.50 0.50 0.50
0.50 0.50
0.50
0.5868
0.7
50
0.30 0.40 0.30 0.30 0.30 0.40 0.40 0.30
0.30 0.30
0.40
0.4132
0.6
60
0.30 0.40 0.30 0.40 0.30 0.20 0.30 0.30
0.20 0.30
0.30
0.2500
0.4
70
0.30 0.10 0.20 0.30 0.30 0.20 0.30 0.30
0.20 0.20
0.30
0.1170
0.4
80
0.30 0.20 0.20 0.20 0.20 0.20 0.30 0.20
0.20 0.20
0.20
0.0302
0.3
90
0.20 0.10 0.10 0.10 0.10 0.10 0.20 0.10
0.10 0.10
0.10
0.0000
0.1
1.2
Current ratio,i/io
1
0.8
0.6
0.4
0.2
0
0
0.2
0.4
0.6
0.8
2
Cos T
Figure 5.3: Current ratio, i/io versus cos2 T graph
1
1.2
64
Figure 5.3 shows a linear graph, indicating that the intensity of the He-Ne light is
proportional to the square of the cosine of the angle. The minimum transmission of HeNe light was obtained when cos2T = 0. It means that when T = 90q, the intensity of the
transmitted He-Ne light was very low compared to the intensity of the transmitted HeNe light when T = 0q. The amount of current produced by transmitted He-Ne light
through P1 was apparently zero compared to the current produced by the He-Ne light
when T = 0q. At T = 90q, the axis of P1 was perpendicular to the axis of P2.
Consequently, the linearly polarized He-Ne light from P1 was blocked by P2.
Theoretically, the ratio of minimum transmission should be zero. However, the
zero transmission was not obtained from the experiment. This was due to the polarizer
and analyzer used was not completely opaque to the light polarized in the orthogonal
direction to their transmission plane. This reason lead to the transmission of He-Ne light
from P2 when the transmission axis of P2 was rotated 90q to the transmission axis of the
P1.
The maximum transmission of He-Ne light occurred when the ș was 0º and 180q.
At these angles, the transmission axis of P2 was parallel to the transmission axis of P1.
This allowed almost all of the linearly polarized He-Ne light that penetrated through the
P1 penetrates through P2. However the maximum transmission of the light that occurred
at T = 180q (cos2T = 1) was not the same as the transmission at T = 0q (cos2T = 0q). This
might due to the absorption or scattering of He-Ne light during light propagation. The
linear graph (Figure 5.3) proves that the transmitted He-Ne light through the P2 versus T
obeyed Malus’ law.
65
5.3
Polarization State Out Of Quartz Crystal
A polarizer P1, analyzer P2 and photoelectric detector S were arranged similarly
as in experiment in section 5.2, except for a quartz crystal, Q was added between P1 and
P2. Firstly, Q and P1 were removed from the system and the angle of P2 was set to zero.
After that, P1 was reinstalled into the system and the angle of P2 was rotated to obtain a
maximum galvanometer reading. At this condition, the optical axis of P1was parallel to
the optical axis of P2. Q was then added between P1and P2. A galvanometer was used to
record the current. The current was measured at every 15 q of the rotation of P2 until
360q. The schematic diagram and photograph of this experiment are shown in Figure
5.4 and 5.5. The data obtained from this study are listed in Table 5.2. The average
current, i was calculated.
Polarizer
He-Ne Laser
(4mW)
Analyzer
Photoelectric
Detector
Quartz
Crystal
Long Scale
Galvanometer
Power Line
Figure 5.4: Schematic diagram of the experiment to determine the polarization state of
He-Ne out of quartz crystal, Q
66
Photoelecric Detector
Quarter Wave
Plate, Q
He-Ne Laser (4 mW)
Analyzer
Long Scale
Galvanometer
Polarizer
Figure 5.5: Experiment setup for determination of the polarization state of He-Ne out
of quartz crystal
By using the data obtained, the i versus T graph was plotted as shown in Figure
5.6.
67
Table 5.2: Polarization of He-Ne light out of Q
Angle, ș
(r0.5°)
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
315
330
345
360
i
Current, i (r0.05 mA)
i1
0.70
0.60
0.50
0.30
0.30
0.20
0.10
0.20
0.20
0.30
0.50
0.70
0.70
0.60
0.50
0.40
0.30
0.10
0.10
0.20
0.20
0.50
0.50
0.60
0.70
i2
0.7
0.5
0.5
0.4
0.20
0.20
0.20
0.10
0.30
0.40
0.40
0.50
0.60
0.60
0.50
0.40
0.20
0.20
0.20
0.20
0.40
0.40
0.40
0.60
0.70
i3
0.80
0.60
0.50
0.40
0.20
0.20
0.20
0.20
0.30
0.50
0.50
0.60
0.80
0.60
0.60
0.40
0.30
0.20
0.20
0.20
0.30
0.30
0.50
0.60
0.70
i4
0.60
0.60
0.60
0.30
0.30
0.20
0.10
0.20
0.30
0.50
0.50
0.60
0.60
0.60
0.60
0.40
0.30
0.20
0.10
0.20
0.40
0.40
0.40
0.50
0.60
i5
0.60
0.60
0.50
0.40
0.30
0.10
0.10
0.20
0.20
0.50
0.50
0.60
0.60
0.50
0.50
0.40
0.30
0.20
0.10
0.20
0.30
0.40
0.50
0.50
0.60
(r0.05m A)
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.20
0.30
0.40
0.50
0.60
0.70
cos2 ș
1.0000
0.9330
0.7500
0.5000
0.2500
0.0670
0.0000
0.0670
0.2500
0.5000
0.7500
0.9330
1.0000
0.9330
0.7500
0.5000
0.2500
0.0670
0.000
0.0670
0.2500
0.5000
0.7500
0.9330
1.0000
68
0.8
0.7
Current, i (mA)
0.6
0.5
0.4
0.3
0.2
0.1
0
0
100
200
300
400
Angle, T (q)
Figure 5.6: Oscillation of He-Ne light out of quartz crystal
From Figure 5.6, it is clearly shown that the minimum transmission of the HeNe light occurred at T = 90q and 270q, while the maximum transmission of the He-Ne
light occurred at T = 0q, 180q and 360q. It was theoretically correct as proven by Kallard
(1977). The transmission of He-Ne light decreased from maximum to minimum. The
same reading of the transmission was repeated at each interval of 90q. This was because
at T = 0q, 180q and 360q the polarized light transmitted through the Q was in the plane
parallel to the transmission plane of the P2. The minimum transmission occurred at T =
90q and 270q when the transmission axis of P2 is perpendicular to the plane of the
polarized He-Ne light transmitted through by the Q. From the experiment, the minimum
transmission was not zero, due to the possible reasons discussed in previous section.
69
The i versus cos2 T graph was plotted (Figure 5.7). Figure 5.7 shows a linear
correlation between the i after passing through Q and cos2 T. This obeys Malus’ law.
The polarization state of the He-Ne light out of Q can be determined by using Equation
(2.5).
y = 0.4705x + 0.224
0.7
Current, i (mA)
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.2
0.4
0.6
0.8
1
1.2
2
Cos T
Figure 5.7: Graph of current, i versus cos2 T out of quartz crystal, Q
The value of the interception of the graph in Figure 5.7 is written as:
b2
0.224 u 10 3 A
b 0.0146
While the slope of the graph is found as:
A
70
M = 0.4705u10-3 A
Here, the slope of Figure 5.8, M is equal to ( a 2 b 2 ) .
a
with b 2
2
b2
0.4705 u 10 3 A
0.224 u 10 3 $ ,
a2
(0.4705 u 10 3 $) (0.224 u 10 3 $)
a=0.0264
A
Therefore the a to b ratio is 0.0264: 0.0146
a
b
0.0264 A
0.0146 A
=
1.8
1
As conclusion, when a linearly polarized He-Ne light entered the quarter
wave plate, an elliptically polarized light was produced with a to b ratio was 1.8:1.
71
5.4
Polarization State Of He-Ne Light Out Of Calcite Crystal
The schematic diagram of the experimental setup for the polarization state of HeNe by using calcite crystal is shown in Figure 5.8. The components were arranged
similar to the previous experiment, with a calcite crystal added between polarizer, P1 and
analyzer, P2. Figure 5.9 shows the photograph of the experiment setup. Calcite is a
natural birefringent material. There is a lot of defect inside the crystal. To study the
polarization of beam out of such natural calcite, a He-Ne laser of higher power was used.
In this study, a 4 mW laser was employed. Due to the defect inside the crystal,
illumination beam became scatter after passing through the crystal. The beam was
focused by using a short focal length convergent lens (F = 50 mm). The laser beam was
brought to focus at the photoelectric detector.
Polarizer
He-Ne Laser
(4mW)
Analyzer
Photoelectric
Detector
Calcite Convergent Lens
(F= 50mm)
Long Scale
Galvanomete
Power Line
Figure 5.8: Schematic diagram of the experiment to determine the polarization state of
He-Ne light out of calcite crystal.
72
Photoelectric Convergent Lens
Detector
(F = 50 mm)
He-Ne Laser (4 mW)
Long Scale
Galvanometer
Analyzer
Calcite
Polarizer
Figure 5.9: Experimental setup for the determination of the polarization state of He-Ne
light out of calcite
The results obtained from the experiment by using a calcite crystal are listed in
Table 5.3. Similar procedures were followed whereby; six readings of current, i were
taken at each corresponding angle of rotation, T. The average was then calculated. The
i versus T graph was plotted in Figure 5.10.
73
Table 5.3: Polarization state of He-Ne out of calcite
Angle, T
(r0.5q)
0
i1
0.30
Current, i (r0.05mA)
i2
i3
i4
i5
0.30
0.30
0.30
0.30
i6
0.30
15
0.30
0.30
0.20
0.30
0.30
0.30
0.30
0.9330
30
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.7500
45
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.5000
60
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.2500
75
0.20
0.20
0.10
0.20
0.20
0.20
0.20
0.06700
90
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.0000
105
0.10
0.20
0.20
0.10
0.10
0.10
0.20
0.06700
120
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.2500
135
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.5000
150
0.30
0.30
0.20
0.20
0.30
0.30
0.30
0.7500
165
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.9330
180
0.30
0.30
0.30
0.30
0.30
0.30
0.30
1.0000
195
0.30
0.20
0.30
0.30
0.20
0.20
0.30
0.9330
210
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.7500
225
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.5000
240
0.20
0.10
0.20
0.20
0.10
0.10
0.20
0.2500
255
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.0670
270
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.0000
285
0.2
0.20
0.20
0.20
0.20
0.20
0.20
0.0670
300
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.2500
315
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.5000
330
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.7500
345
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.9330
360
0.30
0.30
0.30
0.30
0.30
0.30
0.30
1.0000
i
cos2 ș
(r0.05mA)
0.30
1.0000
74
In order to determine the polarization state of He-Ne light out of calcite, the i
versus cos2 T graph was plotted as in Figure 5.10.
y = 0.1583x + 0.1543
0.35
Current, i (mA)
0.3
0.25
0.2
0.15
0.1
0.05
0
0
0.5
1
1.5
2
Cos T
Figure 5.10: Current, i versus cos2 T graph
Figure 5.10 shows a linear correlation between the current, i and cos2 T. This
correlation obeyed Malus’ law. The determination of the polarization state of He-Ne
after passing through calcite is shown as below:
The equation obtained from Figure 5.10 indicates that the interception of the graph is
b2
0.1543 u 10 3 $
b 0.0124
A
75
While the slope of the graph is:
M = 0.1583u10-3 A
Since the slope, M is equal to ( a 2 b 2 ) ,
(a 2 b 2 )
with b 2
0.1583 u 10 3 $
0.1583 u 10 3 $ ,
a2
(0.1583 u 10 3 $) (0.1543 u 10 3 $)
a
0.0177 A
a
b
0.0177 A
Therefore the a to b ratio is
0.0124 A
1 .4
1
76
When a linearly polarized He-Ne laser entered the calcite crystal, its polarization
state was converted into elliptical form with an a to b ratio of 1.4:1
5.5
Summary
From the study of polarization of He-Ne light, it can be concluded that the
transmission of He-Ne light obeyed Malus’ law. The intensity of the light was
proportional to the cosine square of the angle between the polarizer and the analyzer.
The output light that was transmitted through the analyzer was linearly polarized. After
passing through the quartz crystal, the linearly polarized He-Ne light was converted into
an elliptically polarized light with a to b ratio was is1.8:1.0. From the study of the
polarization of He-Ne out of calcite crystal, the linearly polarized He-Ne light was
converted into an elliptically polarized light with an a to b ratio of 1.4:1.0.
The comparison study between the change of He-Ne polarization through natural
and synthetic birefringent crystals was done by electrifying a synthetic lithium niobate
crystal in Chapter 6.
CHAPTER 6
DEVELOPMENT OF TRANSVERSE POCKELS CELL
6.1
Introduction
In this chapter, the development of a transverse Pockels cell by using a cubic
uncoated lithium niobate crystal through the application of an external voltage will be
discussed. The development of the transverse Pockels cell was started and focused on
the designing of a Pockels cell house and the connection between the pulse generator,
power supplies and electro-optic driver that was used to electrify the lithium niobate
crystal. The change of polarization state of He-Ne light after passing through the
fabricated transverse Pockels cell was determined. The performance of transverse
Pockels cell in transmitting He-Ne light was compared to the result of He-Ne light
transmission through the commercial Pockels cell. In order to display the change of the
transmitted He-Ne light intensity with respect to the variation angle between polarizer,
P1 and analyzer, P2 and the signal of the pulse generator, all the experimental work in
Chapter 6 were carried out by using BPX65 photodetector and oscilloscope instead of
using the long scale galvanometer and photoelectric detector like in the previous
experimental works.
78
6.2
Designing Of Pockels Cell House
Prior to the development of the transverse Pockels cell, a Pockels cell housing
was designed and fabricated by using Perspex. A lithium niobate crystal was put into
the Pockels cell housing for isolation when the experiment was being conducted. The
dimension of this housing is 6 cm u 10 cm u 13 cm. Two holes were made at both sides
of the housing to facilitate the connection of the high voltage cable to the electrodes.
The fabricated Pockels cell house is shown in Figure 6.1.
Figure 6.1: Fabricated Pockels cell housing
6.3
Fabrication Of Transverse Pockels Cell
To develop a transverse Pockels cell, it must be arranged so that the direction of
the incident light beam propagates perpendicularly to the direction of the applied electric
field. The setup of the transverse Pockels cell is shown in Figure 6.2.
79
Figure 6.2 shows that a 10 mm x 10 mm x 10 mm uncoated cubic lithium niobate
crystal was placed inside the fabricated perspex Pockels cell house in between two
copper plates. The two 2 cm u 1 cm copper plates were used as the anode and cathode
to conduct voltage from the electro-optic driver to the lithium niobate crystal.
High Voltage
Cable
Anode
(copper plate)
LiNbO3 crystal
Cathode (copper plate)
Pespex
V+
Screw
V-
Figure 6.2: The setup of the transverse Pockels cell
6.4
Electrifying The Transverse Pockels Cell
Pulse generator was designed and fabricated by using CD4528BCN dual
monostable multivibrator (mentioned in Chapter 4) to trigger an electro-optic driver
within microseconds. The electro-optic driver will stop electrifying the lithium niobate
crystal whenever triggered by the pulse from the pulse generator. The schematic
diagram of the connection between the pulse generator, power supplies, and electrooptic driver used to electrify the transverse Pockels cell is shown in Figure 6.3. In this
connection, two high voltage cables were used to conduct the high voltage from the
electro-optic driver to the electrodes of the Pockels cell house. The electro-optic driver
and pulse generator were powered with 15 V and 10 V.
80
Transverse
Pockels Cell
High voltage
Cable
Electro-optic
Driver
Power
Supply
Pulse Generator
Power
Supply
Figure 6.3: Ensemble of optical switch
6.5
Experiment Of He-Ne Polarization By Using Pockels Cell
The performance of the developed transverse Pockels cell was tested by
determining the change of the polarization state of the He-Ne light after passing through
the Pockels cell.
A 4 mW He-Ne laser was used as a light source in this study. A polarizer P1,
analyzer P2 and BPX65 photodetector were aligned in the direction of the propagation of
He-Ne light. The axis of P1 was set parallel to the incident light propagation in order to
produce linearly polarized light was then incident onto a transverse Pockels cell. By
rotating P2, the intensity of the He-Ne light that passed through the fabricated transverse
Pockels cell was adjusted. This caused the voltage flowing through the photodetector
change. Gradually the change of the flowing current caused the voltage change. The
change was displayed on an oscilloscope and was recorded at every 15q of the rotation
81
of P2 until 360q. The amount of light that passed through the crossed polarizer in this
experiment could be altered by changing the orientation of the analyzer (Klinger, 1990).
The experiment was carried out with the frequency of 100 Hz and 200 Hz. And the
voltage applied to electrify the transverse Pockels cells was 2 kV, 3 kV and 4 kV. The
experiment was carried out in dark room to avoid other light source from being detected
by the BPX 65 photodetector. The schematic diagram and the photograph of this
experiment are shown in Figure 6.4 and 6.5, respectively. The same experiment was
then repeated by using a commercial Pockels cell. Each experiment was repeated three
times. The schematic diagram and the photograph of the experiment by using the
commercial Pockels cell are shown in Figure 6.6 and 6.7.
V-
He-Ne Laser
(4mW)
Transverse Pockels Cell (LiNbO3)
BPX65
Photodiode
V+
Polarizer
Electro-optic
Driver
Oscilloscope
Analyzer
Pulse Generator
Figure 6.4:
Pockels cell
Schematic diagram of the experiment by using fabricated transverse
82
Oscilloscope
Power Supply
Power Supply
Electro-optic Driver
BPX65
Photodetector
Analyzer
Transverse
Pockels Cell
Pulse Generator
Polarizer
He-Ne Laser
(4 mW)
Figure 6.5: Experimental arrangement by using fabricated transverse Pockels cell
Commercial Pockels Cell (LiNbO3)
He-Ne Laser
(4mW) Polarizer
BPX65
Photodiode
Electro-optic
Driver
Oscilloscope
Analyzer
Pulse Generator
Figure 6.6: Schematic diagram of the experiment by using commercial Pockels cell
83
Oscilloscope
Power Supply
Power Supply
Electro-optic Driver
Pulse Generator
Analyzer
Commercial
Pockels Cell
He-Ne Laser
(4 mW)
Figure 6.7: Experimental arrangement by using commercial Pockels cell.
6.6
Characterization Of He-Ne Polarization State Through Transverse Pockels
Cell
The intensity of the He-Ne light transmitted through the transverse Pockels cell
was changed into the unit of power, P by using Equation (3.1). The data obtained from
this experimental works are listed at Appendix D, E, F, G, I and J. Figures 6.8, 6.9 and
6.10 show the variation of the intensity of the He-Ne light transmitted through the
transverse Pockels cell with respect to the relative angle between P1 and P2, when 2 kV,
3 kV and 4 kV of voltages were applied to the Pockels cell.
84
0.003
Power,P (W)
0.0025
0.002
f=200 Hz
0.0015
f=100 Hz
0.001
0.0005
0
0
100
200
300
400
Angle,T ( q )
Figure 6.8: Graph of power, P versus T at 2kV out of transverse Pockels cell
0.003
Power,P (W)
0.0025
0.002
f=200 Hz
f=100 Hz
0.0015
0.001
0.0005
0
0
100
200
300
400
Angle,T ( q )
Figure 6.9: Graph of power, P versus T at 3kV out of transverse Pockels cell
85
0.004
Power,P (W)
0.003
f=200 Hz
f=!00 Hz
0.002
0.001
0
0
100
200
300
400
Angle,T ( q )
Figure 6.10: Graph of power, P versus T at 4kV out of transverse Pockels cell
All these three figures show graphs of similar waveform. Starting from the
maximum, the intensity of the transmitted He-Ne light decreases to the minimum,
and reversely, at every 45q of the angle, ș. The oscillation of the He-Ne light through P2
for this study was twice more rapid than in the experiment with natural birefringent
materials (see Chapter 5). This was because the homogeneity and clearness of the
lithium niobate is better than the calcite and quartz crystal. Thus, the transmitted light is
more easily transmit through the lithium niobate than calcite and quartz crystal.
These figures clearly show that the frequency of the pulse generator was not of
significant influence to the intensity of the transmitted He-Ne light through the Pockels
cell. This was because the intensity of the transmitted He-Ne light was almost similar at
100 Hz and 200 Hz of the pulse generator frequency. The intensity measured depends
on the amount of photons that passed through the Pockels cell and received by the
86
photodetector. Hence, the intensity of the transmitted He-Ne light does not depend on
the frequency of the pulse generator.
The results obtained from the experiments were not good and consistent
compared to the result obtained by using natural birefringent materials. The instability
of the mobilization of the applied voltage could be the possible reason to cause the
inconsistency of the intensity of the transmitted He-Ne light through the Pockels cell.
The P versus cos2 T graphs for f = 100 Hz and 200 Hz at 2 kV, 3 kV and 4 kV
applied voltage are plotted respectively in Figure 6.11, 6.12, 6.13, 6.14, 6.15 and 6.16.
All the graphs show linear correlation between P and cos2 T. This indicates that the
intensity of the transmitted He-Ne light that passed through the Pockels cell was
proportional to the cosine square of the rotated angle between P1 and P2 at f = 100 Hz
and 200 Hz. The polarization state of the He-Ne light out of the Pockels cell was
determined by using Equation (2.5) and the collected data are listed in Table 6.1.
y = 0.0002x + 0.002
0.003
Power, P (W)
0.0025
0.002
0.0015
0.001
0.0005
0
0
0.2
0.4
0.6
0.8
1
2
cos T
Figure 6.11: P versus cos2 T at 2 kV (f=100 Hz)
1.2
87
y = 0.0001x + 0.0021
0.003
Power, P (W)
0.0025
0.002
0.0015
0.001
0.0005
0
0
0.2
0.4
0.6
0.8
1
1.2
2
cos T
Figure 6.12: P versus cos2 T at 2 kV (f = 200 Hz)
y = 0.0001x + 0.0023
0.0035
Power, P (W)
0.003
0.0025
0.002
0.0015
0.001
0.0005
0
0
0.2
0.4
0.6
0.8
1
1.2
2
cos T
Figure 6.13: P versus cos2 T at 3 kV (f = 100 Hz)
88
y = 0.0002x + 0.0022
0.0035
Power, P (W)
0.003
0.0025
0.002
0.0015
0.001
0.0005
0
0
0.2
0.4
0.6
0.8
1
1.2
2
cos T
Figure 6.14: P versus cos2 T at 3 kV (f = 200 Hz)
y = 0.0007x + 0.0023
0.0035
Power, P (W)
0.003
0.0025
0.002
0.0015
0.001
0.0005
0
0
0.2
0.4
0.6
0.8
2
cos T
Figure 6.15: P versus cos2 T at 4 kV (f = 100 Hz)
1
89
y = 0.0005x + 0.0024
0.0035
Power, P (W)
0.003
0.0025
0.002
0.0015
0.001
0.0005
0
0
0.2
0.4
0.6
0.8
1
1.2
2
cos T
Figure 6.16: P versus cos2 T at 4 kV (f = 200 Hz)
Figure 6.11 was analyzed by using Equation (2.5) to determine the polarization
state of He-Ne light out of the Pockels cell at 2 kV applied voltage (f = 100 Hz). The
linear equation obtained from Figure 6.11 indicates that the interception of the graph is
b2
b
0.0020 W
0.0447
W
With the slope, M is equal to (a2 b2), the value of a is,
a2 b2
a2
0.0002
0.0002 + 0.0020
a2
0.0022
90
a = 0.0469 W
Therefore, a to b ratio is 0.0469 : 0.0447 or
a
b
0.0469 W
0.0447 W
=
1.0
1.0
The polarization of He-Ne light (under different test conditions) was determined
similarly for Figure 6.11, 6.12, 6.13, 6.14, 6.15 and 6.16. The results are listed in Table
6.1.
Table 6.1: Determination of He-Ne polarization state out of the transverse Pockels cell
Applied
Frequency
Voltage
Reference
a( W )b( W )
f (Hz)
V ( r 0.1 kV)
Fig. 6.11
100
0.0469 0.0447
2
Fig. 6.12
200
0.0470 0.0458
Fig. 6.13
100
0.0490 0.0480
3
Fig. 6.14
200
0.0490 0.0469
Fig. 6.15
100
0.0548 0.0480
4
Fig. 6.16
200
0.0539 0.0490
a:b
Polarization
State
1.0 : 1.0
Circular
1.0 : 1.0
Circular
1.0 : 1.0
Circular
1.0 : 1.0
Circular
1.1 : 1.0
Circular
1.1 : 1.0
Circular
When a linearly polarized He-Ne light entered the transverse Pockels cell, a
circularly polarized light was produced with a : b ratio of 1.0 : 1.0 (2 kV and 3 kV
voltage applied) and 1.1 : 1.0 (4 kV voltage applied).
91
The intensities of the He-Ne light transmitted through the transverse Pockels cell
at various applied voltages are shown in Figure 6.17 and 6.18, respectively.
0.0035
Power,P (W)
0.003
0.0025
V=4kV
V=3kV
V=2kV
0.002
0.0015
0.001
0.0005
0
0
100
200
300
400
Angle,T (q )
Figure 6.17: P versus T at f=100 Hz (V = 2 kV, 3 kV and 4 kV)
0.0035
Power,P (W)
0.003
0.0025
V=4kV
0.002
V=3kV
0.0015
V=2KV
0.001
0.0005
0
0
100
200
300
400
Angle,T( q )
Figure 6.18: P versus T at f = 200 Hz (V = 2 kV, 3 kV and 4 kV)
92
From theses two figures, the power of the transmitted He-Ne (at the 4 kV, 3 kV
and 2 kV applied voltage) for f = 100 Hz was 3.2 mW, 2.8 mW and 2.4 mW. While, for
f = 200 Hz (V = 4 kV, 3kV and 2 kV) was 3.2 mW, 2.8 mW and 2.4 mW. Therefore, it
is proven that the intensity of the transmitted He-Ne light can be manipulated by
adjusting the voltage applied to the Pockels cell. The higher the applied voltage is, the
higher the intensity of He-Ne light will be. This was because, by applying voltage to the
transverse Pockels cell, the polarization state of the transmitted He-Ne through the
Pockels cell will become more or less elliptical. Hence, the intensity of the transmitted
He-Ne light through the transverse Pockels cell changes accordingly to the change of
polarization of the He-Ne light caused by the application of voltage (Schawlow, 1969).
6.7
Characterization Of He-Ne Polarization State Through Commercial Pockels
Cell
The intensity of the He-Ne light transmitted through the commercial Pockels cell
was changed into the unit of power, P by using Equation (3.1). The data obtained from
this experiment are listed at Appendix I, J, K, L, N and M.
Figure 6.19, 6.20 and 6.21 show the variation of the intensity of the He-Ne light
transmitted through the commercial Pockels cell with respect to the angle between P1
and P2, when 2 kV, 3 kV and 4 kV of voltage was applied to the Pockels cell.
93
0.004
Power,P (W)
0.003
f=200 Hz
0.002
f=100 Hz
0.001
0
0
100
200
300
400
Angle,Tq)
Figure 6.19: Graph of power, P versus T at 2kV out of commercial Pockels cell
0.0035
Power,P (W)
0.003
0.0025
0.002
f=200 Hz
0.0015
f=100 Hz
0.001
0.0005
0
0
100
200
300
400
Angle,Tq )
Figure 6.20: Graph of power, P versus T at 3kV out of commercial Pockels cell
94
0.004
Power,P (W)
0.003
f=200 Hz
0.002
f=100 Hz
0.001
0
0
100
200
300
400
Angle,Tq)
Figure 6.21: Graph of power, P versus T at 4kV out of commercial Pockels cell
The relationship between P and T shown in these three graphs are the same with
the relationship established from the previous experiments by using transverse Pockels
cell. This was because the type of crystal, voltage applied and frequency of the pulse
generator used in both Pockels cells were the same. Therefore, the transverse and
commercial Pockels cell exhibited same characteristics and functions in the modulation
of He-Ne light.
The effect of the frequency of the pulse generator frequency to the intensity of
He-Ne light was negligible. The intensity of the transmitted light was correlated to the
voltage applied to the commercial Pockels cell. This is indicated in the graphs of P
versus T shown in Figures 6.22 and 6.23, respectively.
95
0.004
0.0035
Power,P (W)
0.003
0.0025
0.002
V
= 4kV
V
= 3kV
0.0015
V
= 2kV
0.001
0.0005
0
0
100
200
300
400
Angle,T (q )
Figure 6.22: P versus T at f=100 Hz (V = 2 kV, 3 kV and 4 kV)
0.004
0.0035
Power,P (W)
0.003
0.0025
V
= 4kV
0.002
V
= 3kV
V
= 2kV
0.0015
0.001
0.0005
0
0
100
200
300
400
Angle,T ( q )
Figure 6.23: P versus T at f = 200 Hz (V = 2 kV, 3 kV and 4 kV)
96
Figures 6.24, 6.25, 6.26, 6.27, 6.28 and 6.29 are plotted to analyze the
polarization state of He-Ne light out of the Pockels cell under different test conditions.
The polarization state of He-Ne was determined by analyzing the figures through
Equation (2.5), as discussed in previous section. The results are listed in Table 6.2.
y = 0.0002x + 0.0022
0.0035
0.003
Power, P (W)
0.0025
0.002
0.0015
0.001
0.0005
0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
2
cos T
Figure 6.24: P versus cos2 T at 2 kV (f = 100 Hz)
y = 0.0002x + 0.0023
0.003
Power, P (W)
0.0025
0.002
0.0015
0.001
0.0005
0
0.0
0.2
0.4
0.6
0.8
2
cos T
Figure 6.25: P versus cos2T at 2 kV (f = 200 Hz)
1.0
97
y = 0.0005x + 0.0024
0.004
0.003
Power, P (W)
0.003
0.002
0.002
0.001
0.001
0.000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
2
cos T
Figure 6.26: P versus cos2 T at 3 kV (f = 100 Hz)
y = 0.0001x + 0.0027
0.0035
Power, P (W)
0.003
0.0025
0.002
0.0015
0.001
0.0005
0
0.0
0.2
0.4
0.6
0.8
1.0
2
cos T
Figure 6.27: P versus cos2 T at 3 kV (f = 200 Hz)
1.2
98
y = 0.0005x + 0.0027
0.0045
0.004
Power, P (W)
0.0035
0.003
0.0025
0.002
0.0015
0.001
0.0005
0
0
0.2
0.4
0.6
0.8
1
1.2
2
cos T
Figure 6.28: P versus cos2 T at 4 kV (f = 100 Hz)
y = 0.0005x + 0.0028
0.004
0.0035
Power, P (W)
0.003
0.0025
0.002
0.0015
0.001
0.0005
0
0.0
0.2
0.4
0.6
0.8
1.0
2
cos T
Figure 6.29: P versus cos2 T at 4 kV (f = 200 Hz)
1.2
99
Table 6.2: Determination of He-Ne polarization out of the commercial Pockels cell
Reference
Fig. 6.24
Fig. 6.25
Fig. 6.26
Fig. 6.27
Fig. 6.28
Fig. 6.29
6.8
Applied
Frequency
Voltage
a (W)
f (Hz)
V (r 0.1 kV)
2
3
4
b (W)
a:b
Polarization
State
100
0.0490 0.0469 1.0 : 1.0
Circular
200
0.0500 0.0480 1.0 : 1.0
Circular
100
0.0556 0.0490 1.0 : 1.0
Circular
200
0.0529 0.0520 1.0 : 1.0
Circular
100
0.0566 0.0520 1.1 : 1.0
Circular
200
0.0574 0.0529 1.1 : 1.0
Circular
Comparison Between The Output Intensity Of The Commercial And
Transverse Pockels Cell
The power, P versus angle, T graph (f = 100 Hz and V = 4 kV) is shown in
Figure 6.30.
100
0.004
0.0035
Power,P (W)
0.003
0.0025
Transverse Pockels cell
0.002
Commercial Pockels Cell
0.0015
0.001
0.0005
0
0
100
200
300
400
Angle,T ( q )
Figure 6.30: P versus T (f = 100 Hz and V=4 kV)
Figure 6.30 shows that the intensity of the He-Ne light transmitted out of the
commercial Pockels cell was higher than that of the transverse Pockels cell. The
electrodes in the transverse Pockels cell might not have perfect contact with the surface
of the crystal. This might reduce the amount of voltage across to the crystal in order to
generate birefringence. The materials and the size of the electrodes such as its thickness
was not appropriate to produce a strong electric field to the lithium niobate crystal.
Consequently, the transmission of the He-Ne light through the transverse Pockels cell
was affected.
101
6.9
Summary
As conclusion, the intensity of the He-Ne light transmitted through both
transverse and commercial Pockels cell was independent to the frequency of the pulse
generator. This result was in good agreement with the result obtained by Mohd.
Hazimin (2004). The intensity of the transmitted He-Ne through the transverse Pockels
cell and commercial Pockels cell depended on the voltage applied across the Pockels
cells (Schawlow, 1969). The transverse Pockels cell performed similar function as the
commercial Pockels cell. When a linearly polarized He-Ne light entered the Pockels cell
(commercial or transverse Pockels cell), a circularly polarized light was produced
(Kuhn, 1998).
CHAPTER 7
OPTICAL SWITCHING
7.1
Introduction
The discussion of this chapter will focus on the application of Pockels cell as
an optical switch to change the transmitted He-Ne light from continuous to pulse
mode.
7.2.
Optical Switching Operation
The experimental arrangement for this study was similar to the previous
experiment (see Chapter 5), except for the transmission axis of the analyzer P2 was
perpendicular to the transmission axis of the polarizer P1 (Schawlow, 1969; Lothian,
1975). The output signal from P2 was detected by a BPX 65 photodetector and
displayed on oscilloscope. The signal display on the oscilloscope was then captured
by using a digital camera. The experiment was carried out with the frequency of
pulse generator set at single pulse, 1 Hz, 55 Hz and 100 Hz, and with the voltage
103
ranged from 2 kV to 4 kV to electrify the transverse Pockels cell. The schematic
diagram and photograph of the experimental setup are shown in Figure 7.1 and
Figure 7.2, respectively. This experiment was then repeated by replacing the
transverse Pockels cell with the commercial Pockels cell. The schematic diagram
and photograph of the experimental setup arrangement by using the commercial
Pockels cell is shown in Figure 7.3 and 7.4, respectively.
V-
Transverse Pockels Cell (LiNbO3)
BPX65
Photodiode
He-Ne (4mW)
V+
Polarizer
Oscilloscope
Analyzer
Electrooptic Driver
Pulse
Generator
Figure 7.1: Schematic diagram of light switching experiment by using transverse
Pockels cell
Oscilloscope
Power Supply
Power Supply
Electro-optic Driver
BPX65
Photodetector
Analyzer
Transverse
Pockels Cell
Pulse Generator
Polarizer
He-Ne Laser
(4 mW)
Figure 7.2: Light switching experiment by using transverse Pockels cell
104
Commercial Pockels Cell (LiNbO3)
BPX65
Photodiode
He-Ne (4mW)
Polarizer
Oscilloscope
Analyzer
Electro-optic
Driver
Pulse
Generator
Figure 7.3: Schematic diagram of light switching experiment by using commercial
Pockels cell
Oscilloscope
Power Supply
Power Supply
BPX65
Photodetector
Analyzer
Commercial
Pockels Cell
Electro-optic Driver
Pulse Generator
Polarizer
He-Ne
Laser
(4 mW)
Figure 7.4: Light switching experimental by using commercial Pockels cell
105
7.3
He-Ne Switching By Using Transverse Pockels Cell
The typical result obtained from the switching studied is shown in Figure 7.5,
7.6, and 7.7. Each figure was conducted with different voltages supplied by the
electro-optic driver, but operated at the same frequency of the pulse generator. There
are two signals in each of the oscillogram, the upper signal indicates the pulse
produced from the pulse generator. The lower signal indicates the light switching.
The difference between these two signals is that, the amplitudes of the pulse
generator are constant at 10 V, whereas the amplitude of the laser pulse changes
corresponding to the voltage supplied by the electro-optic driver. In this case, the
higher the voltage supplied, the lower the laser pulse are detected. In this particular
study of switching, the reference line of the laser pulse is the horizontal line (lower
signal).
Figure 7.5: Output He –Ne light signal (V = 2 kV; f = 55 Hz)
106
Figure 7.6: Output He-Ne light signal (V = 3 kV; f = 55 Hz)
Figure 7.7: Output He-Ne light signal (V = 4 kV; f = 55 Hz)
Figure 7.5, 7.6, and 7.7 show that the He-Ne light was switched to ON
(horizontal line) and OFF state (drop line) depending on the frequency of the pulse
107
generator. The pulse from the pulse generator was generated to trigger the electrooptic driver. When triggered, no voltage was applied to electrify the transverse
Pockels cell. Hence, no birefringence occurred within the lithium niobate crystal.
The polarization state of the He-Ne remained the same after passing through the
transverse Pockels cell. The analyzer, P2 with a perpendicular axis, then blocked the
linearly polarized light. Therefore, minimum intensity of the transmitted He-Ne light
was detected when the triggering pulse was generated. The laser pulse duration was
found within 1 Ps to 4 Ps which is similar with the pulse width of pulse generator.
The laser pulse rose again as the generator stopped triggering.
Contrary, when the Pockels cell was electrified (no pulse generated),
birefringence phenomenon occurred within the crystal. It changed the transmitted
He-Ne light into a circularly polarized light, which was allowed to pass through P2
and detected by the photodetector. This signal was indicated by the horizontal line of
the lower signal. The signal was alternatively changed corresponding to the
frequency of the pulse generator. Obviously, the continuous He-Ne laser was
successfully converted into pulse laser.
The operation of laser pulse was also tested by applying higher voltage to the
transverse Pockels cell. The typical results are exhibited in Figure 7.6 and 7.7. The
voltage supplied was 3 kV and 4 kV. The result obtained by increasing the voltage
was that the laser pulse amplitude was also increased. Physically, this was due to the
Pockels (linear electro-optic) effect, which is that, when more power supplied to the
transverse Pockels cell, the more energy it received and the higher birefringence
characteristic can be resulted. As a result, this phenomenon induced higher laser
pulse amplitude, when the pulse generator triggered the Pockels cell.
However, the voltage was given to the transverse Pockels cell only and not
involving He-Ne laser. Meaning that, the intensity of He-Ne laser will remain the
same, regardless of the voltage supplied.
108
The laser pulse was measured based on the amplitude. The obtainable results
are listed in Table 7.1. The measurement were made upon various voltages of
electro-optic driver and triggered at different frequencies of the pulse generator. The
voltage varied in the range of 2 kV to 4 kV. The pulse generator was operated at a
single pulse mode and repetitive mode (1 Hz, 55 Hz and 100 Hz).
Table 7.1: Light Switching by using transverse Pockels cell
Applied Voltage
V ( ± 0.1 kV)
2
Transverse
Pockels
Cell
3
4
Frequency
f (Hz)
Single pulse
1
55
100
Single pulse
1
55
100
Single pulse
1
55
100
Light beam
attenuated,
V ( ± 50mV)
500
500
500
500
700
700
700
700
1000
1000
1000
1000
As seen from the Table 7.1, the amplitude of the laser pulse was found to be
constant at 500 mV at the applied voltage of 2 kV, independent to the frequency of
the pulse generator. Either with single mode, lower or higher frequency in repetitive
mode, the laser pulse remained the same. This also occurred at other higher orders of
voltage namely 3 kV and 4 kV, which produced laser pulse of 700 mV and 1000 mV,
respectively.
Generally, the amplitude of the laser pulse was higher when the supplied
voltage increased. Meanwhile, the amplitude of the laser pulse was independent to
the pulse generator frequency. Hence, the transverse Pockels cell was proven to be
109
usable as an optical switch. The Pockels cell was able to switch the light from
continuous to pulse mode.
7.4
He-Ne Switching By Using Commercial Pockels Cell
The typical result of light switching by using a commercial Pockels cell is
shown in Figure 7.8, 7.9 and 7.10. Again, the voltages supplied were still in the
range of 2 kV to 4 kV. The frequency of the pulse generator was at single mode, 1
Hz, 55 Hz and 100 Hz.
Figure 7.8: Output He-Ne signal (V = 2 kV; f = 100 Hz)
110
Figure 7.9: Output He-Ne signal (V = 3 kV; f = 100 Hz)
Figure 7.10: Output He-Ne signal (V = 4 kV; f = 100 Hz)
111
Table 7.2: Light switching by using commercial Pockels cell
Applied Voltage
V ( ± 0.1 kV)
2
Commercial
Pockels Cell
3
4
Frequency f
(Hz)
Single pulse
1
55
100
Single pulse
1
55
100
Single pulse
1
55
100
Light Beam
Attenuating
V ( ± 50 mV)
700
700
700
700
900
900
900
900
1200
1200
1200
1200
The light switching obtained by using this commercial Pockels cell was still
the same as tested by using the transverse Pockels cell. The measurements of laser
pulses through the commercial Pockels cell are listed in Table 7.2. The voltage and
pulse frequency were the same as the one used in the transverse Pockels cell.
7.5
Comparison Between The Switching Of He-Ne By Using The Transverse
Pockels Cell And The Commercial Pockels Cell
From the previous sections, it is found that both the transverse and
commercial Pockels cell possess similar functions in light switching.
The frequency of the pulse from the pulse generator influences the frequency
of the stoppage of the He-Ne transmission. However, it did not influence the
amplitude of the laser pulse produced.
112
Laser Pulse Amplitude, A (mV)
1400
1200
1000
800
Transverse Pockels Cell
Commercial Pockels Cell
600
400
200
0
0
1
2
3
4
5
Applied Voltage, V (kV)
Figure 7.11: Variation of the laser pulse amplitude to the applied voltage
From Figure 7.11, it is clearly shown that by applying a higher voltage to the
Pockels cell (both transverse and commercial), the amplitude of the laser pulse was
also increased. The commercial Pockels cell was found to be more effective in
switching the He-Ne than the transverse Pockels cell.
Clearly, the result of laser pulse obtained from the commercial Pockels cell
was higher than that with the transverse Pockels cell. In particular, when the
commercial Pockels cell was powered at 2 kV, the laser pulse produced was with
amplitude of 700 mV which was 200 mV higher than the fabricated Pockels cell.
The differences were the same for 3 kV and 4 kV.
113
The difference was because of several factors. The lithium niobate crystal in
the cylinder house (the commercial Pockels cell) was in good contact with the
electrodes. This produced uniform electric filed across the crystal. Consequently,
this provided very good birefringent characteristic. In addition, the lithium niobate
was also properly coated at both ends. Therefore, the incident beam was antireflected and its transmission was high. The size of the crystal used in both Pockels
cell was also different which also contributed to different effects on the birefringent
characteristic. This is because the strength of the birefringent phenomenon on a
synthetic birefrigent crystal is influenced by the size of the crystal.
The imperfect contact between the electrodes and the lithium niobate crystal
in the transverse Pockels cell might have reduced the effect of electric field in the
crystal. The type of the electrodes used to electrify the crystal can also affected the
light switching. The lithium niobate used in the transverse Pockels cell was also
uncoated. This would have caused the loss of energy in the transmission beam. As a
result, the production of laser pulse was affected.
We note that the electro-optic driver was difficult to be regulated. It is very
dangerous because of its high voltage. As the result, in this experiment the voltage
of the driver was properly set to 2 kV, 3 kV and 4 kV.
7.6
Summary
As conclusion, both the transverse and commercial Pockels cells could be
used as an optical switch. The efficiency of light switching was found to be linearly
proportional to the voltage used to electrify the Pockels cell. The frequency of the
triggering pulse did not influence the amplitude of the laser pulse, but determine
when the transmission of the light may be stopped.
CHAPTER 8
CONCLUSIONS AND SUGGESTIONS
8.1
Conclusion
From this project, three pulse generators with frequency of 1 Hz, 300 Hz and
single pulse were successfully developed by using CD4528BCN dual monostable
multivibrator. They were used to trigger the electro-optic driver within its safety level.
The voltage of the electro-optic driver could be cut off within 1 to 4 microseconds when
the driver was triggered by the pulse generator. The output voltage of the electro-optic
driver was modulated into the frequency the same as the frequency set for the pulse
generator. Thus, by using single pulse or repetitive pulse generators, the output voltage
of the electro-optic driver can be modulated into single or repetitive mode.
The polarization of He-Ne light was successfully determined by using Malus’
Law. The study of the polarization of He-Ne light proved that the intensity of the He-Ne
light transmitted through the analyzer is proportional to the cosine square of the angle
between the polarizer and analyzer. The He-Ne light that passed through the analyzer
was linearly polarized. Meanwhile, in the study of He-Ne out of natural birefringent
115
materials (quartz and calcite crystal), the linearly polarized He-Ne light was converted
into an elliptically polarized light with a : b ratio of 1.8 : 1.0 and 1.4 : 1.0, respectively.
Thus, the quartz and calcite crystal could be used as quarter wave plate to produce
elliptically polarized light. The intensity of the He-Ne out of the quartz and calcite
crystal that was transmitted through the analyzer subsequently was also proportional to
the cosine square of the angle between the polarizer and analyzer. Therefore, the
polarization of He-Ne light out of birefringent materials obeys the Malus’ law.
In this research, a transverse Pockels cell was developed. The polarization of HeNe light through the developed transverse Pockels cell and a commercial Pockels cell was
studied. When a linearly polarized He-Ne light entered the Pockels cell, a circularly
polarized light was produced. Besides that, the intensity of the transmitted He-Ne light
through both the Pockels cell depended on the voltage applied to electrify the cells and
was independent to the frequency of the pulse generator used to trigger the electro-optic
driver. The transverse Pockels cell was similar in properties as the commercial Pockels
cell.
The transverse and commercial Pockels cell could be used as an optical switch as
both of them could change the He-Ne light continuous wave into pulse mode. The
amplitude of the produced laser pulse was found to be higher when higher voltage applied
to electrify the Pockels cells. Meanwhile, the frequency of the pulse generator used to
trigger the electro-optic driver did not influence the amplitude of the produced laser
pulse.
116
8.2
Problems
Many problems arose during the project. All of these problems could affect the
result of the experiment if not prevented. Some of the problems were faced when dealing
with the equipment and others were caused by the light source from the surrounding and
the design of the electrodes connection in transverse Pockels cell.
The electro-optic driver effected the detection of light signal. The electric field
induced by the driver introduced noise in the BPX65 photodetector. This noise disturbed
the light signal detected by the photodetector. Hence, to prevent this disturbance, the
electro-optic driver was placed under the table to keep it far away from the BPX65
photodetector during the experiment.
The Polaroid polarizers used were not completely opaque. Therefore, when the
axis of the polarizer and of the analyzer was set perpendicular to each others, the linearly
polarized light could still be detected by the BPX65 photodetector.
All the experiments were carried out in a dark room to avoid other light source
from the surrounding from being detected by the BPX65 photodetector. The developed
photodetector was capable in detecting a wide range of spectrum. Thus, any light source
from the surrounding could be detected by the photodetector. This posed problems in
getting accurate results.
The imperfect contact between the designed electrodes in the transverse Pockels
cell and the surface of the lithium niobate crystal affected the obtainable results. The
117
dimension and the material of the electrodes in the transverse Pockels cell were not
suitable to produce a strong electric field to the crystal.
The CD4528BCN dual monostable multivibrator used was very sensitive. The
operation of single and repetitive mode pulse generator could not be combined.
Therefore, two types of pulse generator were developed.
8.3
Suggestions
The project should be continued for further studies by packaging or combining all
the separate components like pulse generator, power supply, electro-optic driver and
Pockels cell to become a complete optical switch system.
In order to use this system as a Q-switch system for high power laser, the Pockels
cell should be provided with a temperature controller to avoid overheating, which will
damage the crystal during switching.
It is also suggested that an interlocking system should be installed in this system
to avoid any accident, by switching off the system immediately whenever overheating
occurs.
Further studies can also be carried out to determine the most suitable material,
dimension and method to produce a better electrode.
118
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124
APPENDIX A
TECHNICAL SPECIFICATIONS OF THE ELECTRO-OPTIC DRIVER (LT
PYRKAL CJSC Technologies Armenia, 2003)
a. Maximum output voltage, kV
4.5 (on load 10 pF)
b. Limits of smooth installation output voltage, kV
2.0…4.5 (on load 10 pF)
c. Duration of high voltage drop on load 10 pF,
15
nsecond, not more
measure between levels 0.9
and 0.1
d. Duration of a high voltage rise after interruption,
Psecond, not more
200
measure between levels 0.1
and 0.9
e. Maximum frequency of the interruption of high voltage
on load 10 pF, Hz
f. Mode of interruption
300
external
g. Interruption Pulse Parameters:
- Amplitude, V
9…13
- Current, mA, not more than
5
- Duration, Psecond
1, 0…4, 0
h. The power supply of the driver is carried out from a
source of a constant voltage with output voltage, V
15 r 0,5
i. Consumed power, W, not more than
4
j. Overall dimension of the driver, mm3
35 u 108 u 82
k. Weight, kg, not more
0.44
125
APPENDIX B
OPTICAL PROPERTIES OF LITHIUM NIOBATE (Dmitriev et al., 1991)
126
APPENDIX C
127
128
129
APPENDIX D
Transverse Pockels cell
Applied voltage, V = 2 kV
Frequency of the Pulse Generator,f =200 Hz
Angle, T
( r 0.5q)
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
315
330
345
360
cos2 T
V1 ( r50 mV)
V2 ( r50 Mv)
V3 ( r50 mV)
Va ( r50 mV)
P (W)
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
600
550
550
200
450
600
650
600
350
150
550
500
650
450
150
550
350
500
600
650
450
250
500
500
600
700
550
350
250
550
650
450
550
250
250
150
500
600
450
450
350
350
550
650
550
250
150
150
500
600
500
550
450
150
350
400
700
550
300
200
650
500
550
450
300
450
350
450
550
150
350
200
400
500
600
600
550
450
200
450
550
600
500
300
200
450
500
600
450
300
450
350
500
600
450
350
200
350
500
600
0.00240
0.00220
0.00180
0.00080
0.00180
0.00220
0.00240
0.00200
0.00110
0.00080
0.00180
0.00200
0.00240
0.00180
0.00110
0.00080
0.00150
0.00200
0.00240
0.00180
0.00150
0.00080
0.00150
0.00200
0.00240
130
APPENDIX E
Transverse Pockels cell
Applied Voltage, V = 2 kV
Frequency of the Pulse Generator, f=100 Hz
Angle, T
( r 0.5q)
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
315
330
345
360
cos2 T
V1 ( r50 mV)
V2 ( r50 Mv)
V3 ( r50 mV)
Va ( r50 mV)
P (W)
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
650
550
500
200
400
500
600
600
600
250
650
750
650
500
400
150
350
350
650
500
350
200
300
600
650
600
500
500
300
550
500
650
600
450
150
550
400
600
500
400
250
350
550
800
650
350
300
350
550
450
550
600
500
250
400
500
550
450
300
200
150
500
550
500
250
200
350
450
350
500
350
250
400
550
750
600
550
500
250
450
500
600
550
450
200
450
550
600
500
350
200
350
450
600
550
350
250
350
500
600
0.00240
0.00220
0.00200
0.00100
0.00180
0.00200
0.00240
0.00220
0.00180
0.00080
0.00180
0.00232
0.00240
0.00200
0.00140
0.00080
0.00150
0.00180
0.00240
0.00220
0.00140
0.00100
0.00140
0.00200
0.00240
131
APPENDIX F
Transverse Pockels cell
Applied Voltage, V = 3 kV
Frequency of the Pulse Generator, f =200Hz
Angle, T
( r 0.5q)
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
315
330
345
360
cos2 T
V1 ( r50 mV)
V2 ( r50 Mv)
V3 ( r50 mV)
Va ( r50 mV)
P (W)
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
700
550
450
250
550
500
700
650
350
300
250
500
750
550
500
300
400
550
750
650
450
250
450
550
950
750
600
450
250
400
550
750
650
500
400
400
300
750
550
300
450
400
500
700
650
650
400
350
550
500
800
650
450
400
400
700
800
650
650
350
400
700
750
700
550
150
550
600
800
650
400
250
550
550
800
750
600
450
300
450
600
750
650
500
300
350
500
750
600
450
300
450
550
750
650
500
300
450
550
750
0.00280
0.00240
0.00180
0.00120
0.00180
0.00230
0.00280
0.00260
0.00200
0.00120
0.00140
0.00200
0.00280
0.00240
0.00180
0.00120
0.00180
0.00220
0.00280
0.00260
0.00200
0.00120
0.00180
0.00220
0.00280
132
APPENDIX G
Transverse Pockels cell
Applied Voltage, V = 3 kV
Frequency of the Pulse Generator, f=100 Hz
Angle, T
rq
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
315
330
345
360
cos2 T
V1 ( r50 mV)
V2 ( r50 mV)
V3 ( r50 mV)
Va ( r50 mV)
P (W)
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
500
600
400
350
550
450
650
300
500
400
500
350
650
650
500
300
350
850
650
600
500
350
400
550
650
850
500
650
350
350
600
750
700
500
250
200
650
750
650
500
250
500
400
850
550
500
300
250
500
800
900
700
450
350
450
900
850
800
350
250
600
800
850
650
500
500
500
700
750
650
500
250
400
450
800
750
600
500
350
450
650
750
600
450
300
400
600
750
650
500
350
450
650
750
600
500
300
350
500
750
0.00280
0.00240
0.00200
0.00140
0.00180
0.00260
0.00280
0.00240
0.00180
0.00120
0.00160
0.00240
0.00280
0.00260
0.00200
0.00140
0.00180
0.00260
0.00280
0.00240
0.00200
0.00120
0.00140
0.00200
0.00280
133
APPENDIX H
Transverse Pockels cell
Applied voltage, V = 4 kV
Frequency of the Pulse Generator, f=200Hz
Angle, T
( r 0.5q)
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
315
330
345
360
cos2 T
V1 ( r50 mV)
V2 ( r50 Mv)
V3 ( r50 mV)
Va ( r50 mV)
P (W)
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
900
800
600
200
450
550
700
500
500
300
500
700
800
500
500
200
550
850
850
600
150
300
450
600
800
900
750
550
350
450
600
950
600
500
300
500
600
800
750
550
250
500
800
850
600
650
150
400
750
800
900
700
650
200
450
650
900
850
500
150
500
800
950
400
450
300
600
750
850
600
550
300
650
750
800
900
750
600
250
450
600
850
650
500
250
500
700
850
550
500
250
550
800
850
600
450
250
500
700
800
0.00320
0.00280
0.00240
0.00100
0.00180
0.00240
0.00310
0.00260
0.00200
0.00100
0.00200
0.00270
0.00310
0.00220
0.00200
0.00100
0.00220
0.00300
0.00310
0.00240
0.00180
0.00100
0.00200
0.00270
0.00300
134
APPENDIX I
Transverse Pockels cell
Applied Voltage, V = 4 kV
Frequency of the Pulse Generator, f=100Hz
Angle, T
( r 0.5q)
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
315
330
345
360
cos2 T
V1 ( r 50 mV)
V2 ( r 50 mV)
V3 ( r50 mV)
Va ( r50 mV)
P (W)
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
900
800
500
200
350
550
800
850
450
400
550
600
900
550
450
300
400
650
800
650
450
250
500
750
750
950
850
650
100
500
550
900
500
450
200
600
450
900
550
350
150
450
850
950
650
450
250
400
750
900
850
750
500
450
500
550
850
900
450
150
550
750
750
550
550
300
650
750
950
650
600
250
750
900
900
900
800
550
250
450
550
850
750
450
250
500
600
850
550
450
250
500
750
900
650
500
250
550
800
850
0.0320
0.0030
0.0022
0.0010
0.0018
0.0022
0.0031
0.0028
0.0018
0.0010
0.0200
0.0024
0.0031
0.0022
0.0018
0.0010
0.0020
0.0028
0.0032
0.0026
0.0020
0.0010
0.0022
0.0030
0.0031
135
APPENDIX J
Pockels Cell
Applied Voltage, V = 2 kV
Frequency of the Pulse Generator, f = 200 Hz
Angle, T
( r 0.5q)
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
315
330
345
360
cos2 T
V1 ( r50 mV)
V2 ( r50 mV)
V3 ( r50 mV)
Va (r50 mV)
P (W)
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
800
650
400
50
400
600
650
200
350
50
300
550
650
600
250
50
400
550
800
550
300
50
450
550
750
700
550
400
50
350
600
900
500
350
50
600
750
800
300
250
50
300
550
800
400
400
50
550
700
850
900
600
550
50
600
600
800
600
350
50
750
650
950
450
550
50
500
700
800
700
350
50
350
550
800
800
600
450
50
450
600
800
400
350
50
550
650
800
450
350
50
400
600
800
550
350
50
450
600
800
0.00290
0.00240
0.00180
0.00030
0.00180
0.00240
0.00290
0.00160
0.00140
0.00030
0.00220
0.00260
0.00290
0.00180
0.00140
0.00028
0.00160
0.00240
0.00290
0.00230
0.00140
0.00030
0.00180
0.00240
0.00290
136
APPENDIX K
Pockels Cell
Applied Voltage, V = 2 kV
Frequency of the Pulse Generator, f = 100 Hz
Angle, T
( r 0.5q)
0
15
30
45
cos2 T
V1 ( r50 mV)
V2 ( r50 Mv)
V3 ( r50 mV)
Va ( r50 mV)
P (W)
1.0000
0.8705
0.5625
0.2500
700
850
250
850
800
550
450
800
750
400
500
600
750
600
400
750
0.00280
0.00245
0.00160
0.00028
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
315
330
345
360
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
450
600
700
400
400
50
500
500
700
600
300
50
200
600
800
550
350
50
300
450
900
450
450
800
550
400
50
500
700
700
600
350
50
250
700
650
600
500
50
500
600
900
450
600
750
400
250
50
500
750
800
600
550
50
500
650
800
650
350
50
700
600
750
450
550
750
450
350
50
500
650
750
600
400
50
350
650
750
600
400
50
500
550
800
0.00180
0.00220
0.00280
0.00180
0.00140
0.00029
0.00200
0.00260
0.00290
0.00240
0.00160
0.00028
0.00140
0.00260
0.00280
0.00240
0.00160
0.00029
0.00200
0.00230
0.00290
137
APPENDIX L
Pockels cell
Applied Voltage, V =3 kV
Frequency of the Pulse Generator, f = 200 Hz
Angle, T
( r 0.5q)
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
315
330
345
360
cos2 T
V1 ( r50 mV)
V2 ( r50 mV)
V3 ( r50 mV)
Va ( r50 mV)
P (W)
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
900
750
550
150
550
700
850
650
450
100
350
600
900
700
300
100
350
600
850
750
550
150
350
400
850
850
800
600
200
650
800
850
650
450
100
350
700
850
750
250
100
350
600
850
800
600
150
250
750
800
800
700
500
100
600
750
850
650
450
100
300
650
850
800
350
100
350
600
850
700
550
150
300
500
800
850
750
550
150
600
750
850
650
450
100
350
650
900
750
300
100
350
600
850
750
600
150
300
550
850
0.00320
0.00280
0.00220
0.00036
0.00240
0.00280
0.00320
0.00260
0.00180
0.00039
0.00130
0.00260
0.00320
0.00280
0.00110
0.00039
0.00140
0.00240
0.00320
0.00280
0.00240
0.00036
0.00120
0.00230
0.00320
138
APPENDIX M
Pockels cell
Applied Voltage, V =3 kV
Frequency of the Pulse Generator, f =100 Hz
Angle, T
( r 0.5q)
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
315
330
345
360
cos2 T
V1 ( r50 mV)
V2 ( r50 Mv)
V3 ( r50 mV)
Va ( r50 mV)
P (W)
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
850
800
650
150
550
650
900
650
250
100
500
450
900
600
300
100
450
650
900
650
250
50
450
600
800
750
750
650
100
400
550
900
600
350
100
500
650
900
600
350
100
450
550
850
650
300
100
450
500
800
800
700
650
50
250
600
900
550
300
100
500
550
900
600
250
100
450
450
950
650
350
150
450
550
800
800
750
650
100
400
600
900
600
300
100
500
550
900
600
300
100
450
550
900
650
300
100
450
550
800
0.00300
0.00280
0.00260
0.00039
0.00160
0.00240
0.00320
0.00240
0.00110
0.00039
0.00200
0.00230
0.00320
0.00240
0.00110
0.00039
0.00190
0.00230
0.00320
0.00260
0.00110
0.00039
0.00190
0.00230
0.00300
139
APPENDIX N
Pockels cell
Applied voltage, V = 4 kV
Frequency of the Pulse Generator, f=200 Hz
Angle, T
( r 0.5q)
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
315
330
345
360
cos2 T
V1 ( r50 mV)
V2 ( r50 Mv)
V3 ( r50 mV)
Va ( r50 mV)
P (W)
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
950
850
550
50
550
700
950
900
400
750
500
950
950
800
400
50
500
400
950
850
550
800
400
900
950
950
850
600
50
550
750
950
900
350
750
500
900
950
950
400
50
500
850
950
800
700
850
700
800
950
950
850
650
50
550
800
950
750
600
750
650
850
950
850
550
50
200
700
950
900
550
750
550
850
950
950
850
600
50
550
750
950
850
450
750
550
900
950
850
450
50
400
650
950
850
600
800
550
850
950
0.00360
0.00320
0.00240
0.00029
0.00220
0.00280
0.00360
0.00320
0.00190
0.00028
0.00220
0.00340
0.00360
0.00330
0.00190
0.00029
0.00160
0.00260
0.00360
0.00330
0.00240
0.00030
0.00220
0.00330
0.00360
140
APPENDIX O
Pockels cell
Applied Volatge, V = 4 kV
Frequency of the Pulse Generator, f=100 Hz
Angle, T
( r 0.5q)
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
315
330
345
360
cos2 T
V1 ( r50 mV)
V2 ( r50 Mv)
V3 ( r50 mV)
Va ( r50 mV)
P (W)
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
0.8705
0.5625
0.2500
0.0625
0.0045
0.0000
0.0045
0.0625
0.2500
0.5625
0.8705
1.0000
950
650
500
50
500
650
900
650
450
50
450
650
950
650
200
50
500
600
900
950
400
50
350
500
950
950
850
500
50
750
650
950
650
550
50
450
600
800
650
600
50
500
650
900
900
350
50
300
600
950
950
900
500
50
400
650
800
650
300
50
450
700
900
650
500
50
350
700
900
850
450
50
550
550
950
950
800
500
50
550
650
900
650
450
50
450
650
900
650
400
50
450
650
900
900
400
50
400
550
950
0.00380
0.00300
0.00200
0.00028
0.00220
0.00260
0.00360
0.00260
0.00180
0.00029
0.00190
0.00260
0.00360
0.00260
0.00160
0.00029
0.00190
0.00260
0.00380
0.00360
0.00160
0.00028
0.00160
0.00220
0.00380
PRESENTATION
1. Thian Lee Eng, Yacoob Mat Daud and Noriah Bidin. Development of a Microsecond
Pulse Generator Using CD4528BCN Dual Monostable Multivibrator. Paper presented at
Annual Fundamental Science Seminar 2004 (AFSS 2004). 14-15 June 2004, Johor Bahru.
2. Thian Lee Eng, Yacoob Mat Daud and Noriah Bidin. Modulation of Beam
Polarization by Using Pockels Effect. Poster presented at Malaysian Science and
Technology Conference (MSTC). 4-7 October 2004, Kuala Lumpur.
3. Thian Lee Eng, Yacoob Mat Daud and Noriah Bidin. Light Switching by an Electrooptic Technique. Paper presented at The XXI Regional Conference and Workshop on
Solid State Science& Technology (RCWSST 2004). 10-13 October 2004, Sabah