2. OBJECTIVES
• Define optical communications
• Present an overview of the history of optical fiber
• Compare the advantages and disadvantages of
optical fibers over metallic cables
• Describe several types of optical fiber construction
• Describe how light waves propagate through an
optical fiber cable.
• Define modes of propagation and index profile
• Describe the three types of optical fiber
configurations
3. W H E R E IT STARTED?
1854
John Tyndall demonstrated to the
Royal Society that light could be
conducted through a curved stream of
water, proving that a light signal could
be bent.
4. TYNDALL’S H I S T O R I C A L E X P E R I M E N T
What was expected
to happen?
What actually
happened?
5. The tank of water had a
horizontal pipe extending out
one side which allowed water
to flow out in an arc to a
collection pan on
the floor
.
A bright light was directed into
the pipe and the light rays
traveled within
the water until they were
broken up by the
turbulence of the water hitting
the collection pan.
6. L I G H T G U I D I N G A P P L I C A T I O N S
• Road Signs
• Endoscopes
• HazardousAreas
• All at Sea
• Communications
7. C O M M U N I C A T I O N S
1880
Alexander Graham Bell invented his
"Photophone," which transmitted a
voice signal on abeam of light.Bell
focused sunlight with amirror and
then talkedinto amechanism that
vibrated the mirror.
At the receiving end,adetector picked
up the vibrating beam and decoded it
back into avoice the same way a
phone did with electrical signals.
However, many things — acloudy day
,
for instance — could interfere with the
Photophone, causing Bell to stop any
further research with this invention.
8. P H O T O P H O N E
• Uses light for the transmission of speech.
• It was atube with aflexible mirror atits end.
• He spoke down the tube and the sound vibrated the
mirror.
• The modulated light was detected by aphotocell
placed atadistance of two hundred meters or so.
• The result was certainly not hi-fi but the speech
could atleast be understood.
9. C O M M U N I C A T I O N S
Kao co-authored aproposal that
would revolutionize global
communications and laythe
groundwork for the internet we
know today
.
Along with collaborator George
Hockham, Kao proposed using
thin glass fibers to transmit data
across long distances, replacing
the bulky copper wires then in
use in telecommunications
10. FIBER O P T I C S T E C H N O L O G Y
• Optic Fiber is the transparent material, along which
we can transmit light.
• Fiber Optics is the system, or branch of
engineering concerned with using the optic fibers.
Optic fiber is therefore used in afiber optic system.
• Fiber is afriendly abbreviation for either
,so we
could say that fiber is used in afiber system.
11. FATHER OF O P T I C A L FIBER
Dr. Narinder Singh Kapany
Coined the term “Fiber Optics in 1956”
12. F IBER S C O PE
• Heel, Hopkins and Kapany- In
1950’sthey experimented with
light transmission through bundles
of fibers. It led to the development
of the flexible fiberscope.
• A fiberscope is a flexible fiber
optic bundle with an eyepiece at
one end, and a lens at the other.
• It is used for inspection work, often
to examine small components in
tightly packed equipment, when the
inspector cannot easily access the
part requiring inspection.
13. PR IN C IPL E OF O P E R AT I O N
• The system is basically very simple: asignal is used to
vary
,or modulate, the light output of asuitablesource
— usually alaser or an LED (light emittingdiode).
• The flashes of light travel along the fiber and,atthe
far end,are converted to an electrical signal by means
of aphoto-electriccell.
• Thus the original input signal is recovered
A simple fiber
optic system
14. B L O C K D I A G R A M
Voltage-to-
Current
Converter
Light Source
Source-to-
fiber
Interface
Signal
Regenerator
Fiber-to-light
detector
Interface
Light
Detector
Current-to-
Voltage
Converter
Source
Destination
15. A D VA N TA G E S OF
O P T I C A L FIBER C A B L E S
1. Wider bandwidth and greater information capacity
2. Immunity to crosstalk
3. Immunity to static interference
4. Environmental immunity
5. Safety and convenience
6. Lower transmission loss
7. Security
8. Durability and reliability
9. Economics
16. D I S A D VA N TA G E S OF
O P T I C A L FIBER C A B L E S
1. Interfacing cost
2. Strength
3. Remote electrical power
4. Susceptible to losses introduced by bending
the cable
5. Specialized tools, equipment and training.
17. E L E C T R O M A G N E T I C S P E C T R U M
Fiber optics used visible light and infrared
18. G E N E R A L S U B D I V I S I O N
• Light is an electromagnetic wave having a
very high oscillation frequency and very
short wavelength.
a.Infrared – Band of light wavelengths that
are too long to be seen by the human eye.
(770 nm to 100,000 nm)
b.Visible Light – Band of lightwavelengths
to which the human eye respond 390 nm
to 770 nm)
c.Ultraviolet – Band of lightwavelengths
that are too short to be seen by the
human eye (10 nm to 390 nm)
19. A N G S T R O M & M I C R O N S
• When dealing with light frequencies, it is common to
use units of wavelength rather than frequency.
• Wavelength is often stated in microns where 1
micron = 10-6 meter (1um) or in nanometers
1nm=10-9.
• When describing the optical spectrum, the unit
angstrom is sometimes used to expressed wavelength
where 1 angstrom = 10-10 meters, or 0.001 micron.
20. N A T U R E OF L I G H T
• Albert Einstein & MaxPlanck
– showed that when light is
emitted or absorbed, it behaves
like an electromagnetic wave and
also like aparticle, called aphoton,
which possess energy
proportional to its frequency.
• Planck’s Law – “whenvisiblelight
orhighfrequencyelectromagnetic
radiationilluminatesa metallic
surface,electronsareemitted”
21. P L A N C K ’ S L A W
Ep= energy of the photon (joules)
h= Planck’s constant= 6.625 x 10-34 J-s
f= frequency of light (photon) emitted (Hertz)
22. O P T I C A L P O W E R
• Photometry – is the science of measuring only light
waves that are visible to the human eye.
• Radiometry – measures light throughout the entire
electromagnetic spectrum
• Optical Power – measures the rate atwhich the
electromagnetic waves transfer light energy.It is
described as the flow of light energy past agiven
point in aspecified time. “Radiant Flux”(J/s)
23. V E L O C I T Y OF P R O P A G A T I O N
• Electromagnetic energy (light waves) travels at
approximately 300,000,000 m/s(186,000 mi/s).
• In free space, velocity of propagation is the same for
alllight frequencies.
• EMW travels slower in material more dense than
free space and that alllight frequencies do not
propagate atthe same velocity.
24. R EF RACTIVE I N D E X
Where:
n = refractive index (unitless)
c = speed of light
v = speed of light in a given
material (m/s)
25. I N D E X OF R E F R A C T I O N
SUBSTANCE Refractive Index
Vacuum 1.0000
Air 1.0003
Ice 1.309
Water 1.33
Ethyl Alcohol 1.36
Magnesium Fluoride 1.38
Glass (fused quarts) 1.46
Glass (crown) 1.52
Sodium Chloride 1.54
Diamond 2.42
27. C R I T I C A L A N G L E
• Minimum angle of incidence atwhich alight ray may
stike the interface of two media and result in an
angle of refraction of 90 degrees or greater
.
