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1. Fiber Optics Fiber Optics

2. IntroductionIntroduction

You hear about fiber-optic cables whenever You hear about fiber-optic cables whenever
people talk about the people talk about the telephone systemtelephone system, the , the
cable TV systemcable TV system or the Internet. or the Internet.

Fiber-optic lines are strands of optically pure Fiber-optic lines are strands of optically pure
glassglass as thin as a human hair that carry as thin as a human hair that carry
digital information over long distances. digital information over long distances.

They are also used in medical imaging and They are also used in medical imaging and
mechanical engineering inspection. mechanical engineering inspection.

3. What are Fiber Optics? What are Fiber Optics?

Fiber opticsFiber optics (optical fibers) are long, (optical fibers) are long,
thin strands of very pure glass about thin strands of very pure glass about
the diameter of a human hair. the diameter of a human hair.

They are arranged in bundles called They are arranged in bundles called
optical cablesoptical cables and used to transmit and used to transmit
lightlight signals over long distances. signals over long distances.

4. What are Fiber Optics? What are Fiber Optics?

If you look closely at a single optical fiber, If you look closely at a single optical fiber,
you will see that it has the following parts: you will see that it has the following parts:

CoreCore - Thin glass center of the fiber where - Thin glass center of the fiber where
the light travels the light travels

CladdingCladding - Outer optical material - Outer optical material
surrounding the core that reflects the light surrounding the core that reflects the light
back into the core back into the core

Buffer coatingBuffer coating - Plastic coating that protects - Plastic coating that protects
the fiber from damage and moisture the fiber from damage and moisture

5. Fiber OpticsFiber Optics
plastic jacketglass or plastic
cladding
fiber core
TOTAL INTERNAL REFLECTION

6. What are Fiber Optics? What are Fiber Optics?

7. Fiber Optic CablesFiber Optic Cables
SOURCE: SURFNET.NL

8. What are Fiber Optics? What are Fiber Optics?

Single-mode fibersSingle-mode fibers have small cores (about 3.5 x 10-4 have small cores (about 3.5 x 10-4
inches or 9 microns in diameter) and transmit infrared inches or 9 microns in diameter) and transmit infrared
laserlaser light (wavelength = 1,300 to 1,550 nanometers). light (wavelength = 1,300 to 1,550 nanometers).

Multi-mode fibersMulti-mode fibers have larger cores (about 2.5 x 10-3 have larger cores (about 2.5 x 10-3
inches or 62.5 microns in diameter) and transmit inches or 62.5 microns in diameter) and transmit
infrared light (wavelength = 850 to 1,300 nm) from infrared light (wavelength = 850 to 1,300 nm) from
light-emitting diodeslight-emitting diodes (LEDs). (LEDs).

Some optical fibers can be made from Some optical fibers can be made from plasticplastic. These . These
fibers have a large core (0.04 inches or 1 mm diameter) fibers have a large core (0.04 inches or 1 mm diameter)
and transmit visible red light (wavelength = 650 nm) and transmit visible red light (wavelength = 650 nm)
from LEDs. from LEDs.

9. How Does an Optical Fiber How Does an Optical Fiber
Transmit Light? Transmit Light?

Suppose you want to shine a flashlight beam down a Suppose you want to shine a flashlight beam down a
long, straight hallway. long, straight hallway.

Just point the beam straight down the hallway -- light Just point the beam straight down the hallway -- light
travels in straight lines, so it is no problem. What if the travels in straight lines, so it is no problem. What if the
hallway has a bend in it? hallway has a bend in it?

You could place a mirror at the bend to reflect the light You could place a mirror at the bend to reflect the light
beam around the corner. beam around the corner.

What if the hallway is very winding with multiple bends? What if the hallway is very winding with multiple bends?

You might line the walls with mirrors and angle the You might line the walls with mirrors and angle the
beam so that it bounces from side-to-side all along the beam so that it bounces from side-to-side all along the
hallway. This is exactly what happens in an optical fiber. hallway. This is exactly what happens in an optical fiber.

10. How Does an Optical Fiber How Does an Optical Fiber
Transmit Light? Transmit Light?

11. How Does an Optical Fiber How Does an Optical Fiber
Transmit Light? Transmit Light?

The light in a fiber-optic cable travels through the The light in a fiber-optic cable travels through the
core (hallway) by constantly bouncing from the core (hallway) by constantly bouncing from the
cladding (mirror-lined walls), a principle called cladding (mirror-lined walls), a principle called total total
internal reflectioninternal reflection. .

Because the cladding does not absorb any light from Because the cladding does not absorb any light from
the core, the light wave can travel great distances. the core, the light wave can travel great distances.

However, some of the light signal However, some of the light signal degradesdegrades within within
the fiber, mostly due to impurities in the glass. The the fiber, mostly due to impurities in the glass. The
extent that the signal degrades depends on the extent that the signal degrades depends on the
purity of the glass and the wavelength of the purity of the glass and the wavelength of the
transmitted light transmitted light

12. Dense Wave-Division Dense Wave-Division
Multiplexing (DWDM)Multiplexing (DWDM)
-
-
-
1
2
3
N
-
-
-
Multiple colors (frequencies) sent
through the fiber at the same time,
more than 100
Each color carries a separate signal
Allows huge bandwidth

13. Advantages of Fiber OpticsAdvantages of Fiber Optics

Less expensiveLess expensive . .

ThinnerThinner

Higher carrying capacityHigher carrying capacity

Less signal degradationLess signal degradation Light signalsLight signals Low powerLow power
Digital signalsDigital signals Non-flammableNon-flammable

LightweightLightweight

FlexibleFlexible Medical imagingMedical imaging

- in bronchoscopes, endoscopes, laparoscopes - in bronchoscopes, endoscopes, laparoscopes

Mechanical imagingMechanical imaging - inspecting mechanical welds in pipes - inspecting mechanical welds in pipes
and engines (in airplanes, rockets, space shuttles, cars) and engines (in airplanes, rockets, space shuttles, cars)

PlumbingPlumbing - to inspect sewer lines - to inspect sewer lines

14. How Are Optical Fibers Made?How Are Optical Fibers Made?

Now that we know how fiber-optic systems work and Now that we know how fiber-optic systems work and
why they are useful -- how do they make them? why they are useful -- how do they make them?
Optical fibers are made of extremely pure Optical fibers are made of extremely pure optical optical
glassglass. .

We think of a glass window as transparent, but the We think of a glass window as transparent, but the
thicker the glass gets, the less transparent it thicker the glass gets, the less transparent it
becomes due to impurities in the glass. becomes due to impurities in the glass.

However, the glass in an optical fiber has far fewer However, the glass in an optical fiber has far fewer
impurities than window-pane glass. impurities than window-pane glass.

One company's description of the quality of glass is as One company's description of the quality of glass is as
follows: If you were on top of an ocean that is miles of solid follows: If you were on top of an ocean that is miles of solid
core optical fiber glass, you could see the bottom clearly. core optical fiber glass, you could see the bottom clearly.

15. How Are Optical Fibers Made?How Are Optical Fibers Made?

Making optical fibers requires the Making optical fibers requires the
following steps: following steps:

Making a preform glass cylinderMaking a preform glass cylinder

Drawing the fibers from the preformDrawing the fibers from the preform

Testing the fibersTesting the fibers

16. Making the Preform Blank Making the Preform Blank

The glass for the The glass for the
preform is made by preform is made by
a process called a process called
modified chemical modified chemical
vapor depositionvapor deposition
(MCVD). (MCVD).

17. Making the Preform Blank Making the Preform Blank

In MCVD, oxygen is bubbled through solutions of In MCVD, oxygen is bubbled through solutions of
silicon chloride (SiCl4), germanium chloride silicon chloride (SiCl4), germanium chloride
(GeCl4) and/or other chemicals. (GeCl4) and/or other chemicals.

The precise mixture governs the various physical The precise mixture governs the various physical
and optical properties (index of refraction, and optical properties (index of refraction,
coefficient of expansion, melting point, etc.). coefficient of expansion, melting point, etc.).

The gas vapors are then conducted to the inside The gas vapors are then conducted to the inside
of a of a synthetic silicasynthetic silica or or quartz tubequartz tube (cladding) in (cladding) in
a special a special lathelathe. As the lathe turns, a torch is . As the lathe turns, a torch is
moved up and down the outside of the tube. moved up and down the outside of the tube.

18. Making the Preform Blank Making the Preform Blank

The extreme heat from the torch causes The extreme heat from the torch causes
two things to happen: two things to happen:

The silicon and germanium react with The silicon and germanium react with
oxygen, forming silicon dioxide (SiO2) and oxygen, forming silicon dioxide (SiO2) and
germanium dioxide (GeO2). germanium dioxide (GeO2).

The silicon dioxide and germanium dioxide The silicon dioxide and germanium dioxide
deposit on the inside of the tube and fuse deposit on the inside of the tube and fuse
together to form glass together to form glass

19. Making the Preform Blank Making the Preform Blank

The lathe turns continuously to The lathe turns continuously to
make an even coating and make an even coating and
consistent blank. consistent blank.

The purity of the glass is The purity of the glass is
maintained by using corrosion-maintained by using corrosion-
resistant plastic in the gas resistant plastic in the gas
delivery system (valve blocks, delivery system (valve blocks,
pipes, seals) and by precisely pipes, seals) and by precisely
controlling the flow and controlling the flow and
composition of the mixture. composition of the mixture.

The process of making the The process of making the
preform blank is highly preform blank is highly
automated and takes several automated and takes several
hours. After the preform blank hours. After the preform blank
cools, it is tested for quality cools, it is tested for quality
control.control.

20. Drawing Fibers from the Preform Drawing Fibers from the Preform
Blank Blank

Once the preform blank has Once the preform blank has
been tested, it gets loaded been tested, it gets loaded
into a into a fiber drawing towerfiber drawing tower. .

Diagram of a fiber drawing Diagram of a fiber drawing
tower used to draw optical tower used to draw optical
glass fibers from a preform glass fibers from a preform
blank.blank.

The blank gets lowered into a The blank gets lowered into a
graphite furnace (3,452 to graphite furnace (3,452 to
3,992 degrees Fahrenheit or 3,992 degrees Fahrenheit or
1,900 to 2,200 degrees 1,900 to 2,200 degrees
Celsius) and the tip gets Celsius) and the tip gets
melted until a molten glob melted until a molten glob
falls down by gravity. As it falls down by gravity. As it
drops, it cools and forms a drops, it cools and forms a
thread. thread.

21. Drawing Fibers from the Preform Drawing Fibers from the Preform
Blank Blank

The operator threads the strand The operator threads the strand
through a series of coating cups through a series of coating cups
(buffer coatings) and ultraviolet (buffer coatings) and ultraviolet
light curing ovens onto a tractor-light curing ovens onto a tractor-
controlled spool. controlled spool.

The tractor mechanism slowly The tractor mechanism slowly
pulls the fiber from the heated pulls the fiber from the heated
preform blank and is precisely preform blank and is precisely
controlled by using a controlled by using a laser laser
micrometermicrometer to measure the to measure the
diameter of the fiber and feed the diameter of the fiber and feed the
information back to the tractor information back to the tractor
mechanism.mechanism.

Fibers are pulled from the blank Fibers are pulled from the blank
at a rate of 33 to 66 ft/s (10 to 20 at a rate of 33 to 66 ft/s (10 to 20
m/s) and the finished product is m/s) and the finished product is
wound onto the spool. It is not wound onto the spool. It is not
uncommon for spools to contain uncommon for spools to contain
more than 1.4 miles (2.2 km) of more than 1.4 miles (2.2 km) of
optical fiber. optical fiber.

22. Testing the Finished Optical FiberTesting the Finished Optical Fiber

The finished optical fiber is The finished optical fiber is
tested for the following: tested for the following:

Tensile strengthTensile strength

Refractive index profileRefractive index profile Fiber Fiber
geometrygeometry

AttenuationAttenuation

Information carrying capacityInformation carrying capacity
(bandwidth) (bandwidth)

Chromatic dispersionChromatic dispersion ) )

Operating Operating
temperature/humidity rangetemperature/humidity range

Temperature dependence of Temperature dependence of
attenuationattenuation

Ability to conduct light Ability to conduct light
underwaterunderwater

23. Optical Fiber Capacity Growth Optical Fiber Capacity Growth
1983-20021983-2002
0
1
9
8
3
1
9
8
4
1
9
8
5
1
9
8
6
1
9
8
7
1
9
8
8
1
9
8
9
1
9
9
0
1
9
9
1
1
9
9
2
1
9
9
3
1
9
9
4
1
9
9
5
1
9
9
6
1
9
9
7
1
9
9
8
1
9
9
9
200
400
600
800
1,000
1,200
1,400
OC-48
OC-192
OC-192, 2
OC-48, 40
OC-192, 16
OC-48, 96
OC-192, 32
OC-192, 48
OC-192, 80
OC-192, 128
1.7 Gb565Mb
135Mb
Single
Fiber
Capacity
(Gigabits/sec)
1 Terabit =
World record ~ 16 terabits per second

24. Fiber Optic Lines in Central Fiber Optic Lines in Central
PhiladelphiaPhiladelphia
SOURCE: CYBERGEOGRAPHY.ORG
TELECOM HOTEL

25. SOURCE: ALCATEL

26. Submarine Cables in North East Submarine Cables in North East
AsiaAsia