fundamentals of fibre optics for I year engineering students

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fiber optics.
 Optical fibers are widely used in fiber-
optic communications, which permits
transmission over longer distances and
at higher bandwidths .
Fibers are used instead of metal wires
because signals travel along them with
less loss .
They are also immune to
electromagnetic interference.
Fibers are also used for illumination.
Fibers are wrapped in bundles so that
they may be used to carry images, thus
allowing viewing in confined spaces.
Specially designed fibers are used for a
variety of other applications, including
sensors and fiber lasers.

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OPTICAL FIBER
• An optical fiber is a glass
or plastic fiber that carries
light along its length.
• Light is kept in the "core" of
the optical fiber by total
internal reflection.
One type of Optic fibre

3. WHAT ARE OPTICAL FIBERS ?
Optical Fibers are thins long strands of ultra
pure glass (silica) or plastic that can transmit
light from one end to another without much
attenuation or loss.
Optical fibers are widely used in fiber-optic
communications, which permits transmission
over longer distances higher bandwidths (data
rates)
Fibers are used instead of metal wires
because signals travel along them with
less loss and are also immune
to electromagnetic interference. Fibers are
also used for illumination, and are wrapped in
bundles so that they may be used to carry
images, thus allowing viewing in confined
spaces. Specially designed fibers are used for
a variety of other applications, 3

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Fiber Optic Layers
• consists of three concentric sections
• The core, and the lower-refractive-
index cladding, are typically made of
high-quality silica glass, though they
can both be made of plastic as well.
• Core – higher refractive index
• Cladding – lower refractive index
• Buffer coating – mechanical protection

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OPTICAL FIBER CONSTRUCTION
Core – thin glass center of the
fiber where light travels.
Cladding – outer optical
material surrounding the core
Buffer Coating – plastic
coating that protects the
fiber.

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Practical optic fibers

8. As man’s need for communication increased, the amount
of bandwidth required increased exponentially.
It was not until Optical Fibers came on the scene that large
amount of communication bandwidth became
economically and easily available to everyone.
As an example, 50,000 voice / data circuit copper cable is
massive in size and very expensive, while a single Optical
Fiber, the diameter of human hair, can carry 5,00,000
circuits of voice and data. This capacity is increasing day
by day as supporting electronics is developing. In itself the
capacity of Optical Fibers is limitless.
Why Optical Fibers ?
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Advantages of fiber optics
 Much Higher Bandwidth (Gbps) - Thousands of channels
can be multiplexed together over one strand of fiber
 Immunity to Noise - Immune to electromagnetic interference
(EMI).
 Safety - Doesn’t transmit electrical signals, making it safe in
environments like a gas pipeline.
 High Security - Impossible to “tap into.”
 Less Loss - Repeaters can be spaced 75 miles apart (fibers
can be made to have only 0.2 dB/km of attenuation)
 Reliability - More resilient than copper in extreme
environmental conditions.
 Size - Lighter and more compact than copper.
 Flexibility - Unlike impure, brittle glass, fiber is physically
very flexible.

10. 1. VERY HIGH INFORMATION CARRING CAPACITY.
2. LESS ATTENUATION (order of 0.2 db/km)
3. SMALL IN DIAMETER AND SIZE & LIGHT WEIGHT
4. LOW COST AS COMPARED TO COPPER (as glass is made
from sand..the raw material used to make OF is free….)
5. GREATER SAFETY AND IMMUNE TO EMI & RFI,
MOISTURE & COROSSION
6. FLEXIBLE AND EASY TO INSTALL IN TIGHT CONDUICTS
7. ZERO RESALE VALUE (so theft is less)
8. IS DILECTRIC IN NATURE SO CAN BE LAID IN
ELECTICALLY SENSITIVE SURROUNDINGS
9. DIFFICULT TO TAP FIBERS, SO SECURE
10. NO CROSS TALK AND DISTURBANCES
ADVANTAGES OF OPTICAL FIBERS
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12. 1. The terminating equipment is still costly as compared to copper
equipment.
2. Of is delicate so has to be handled carefully.
3. Last mile is still not totally fiberised due to costly subscriber
premises equipment.
4. Communication is not totally in optical domain, so repeated
electric –optical – electrical conversion is needed.
5. Optical amplifiers, splitters, MUX-DEMUX are still in
development stages.
6. Tapping is not possible. Specialized equipment is needed to tap
a fiber.
7. Optical fiber splicing is a specialized technique and needs
expertly trained manpower.
8. The splicing and testing equipments are very expensive as
compared to copper equipments.
DISADVANTAGES OF OPTICAL FIBERS…
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Total internal reflection

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Acceptance angle /cone half-angle
• The maximum angle in which external light rays
may strike the air/glass interface and still
propagate down the fiber.

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MODE OF PROPAGATION
• Two main categories of
optical fiber used in fiber
optic communications are
multi-mode optical fiber
and single-mode optical
fiber.

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SINGLE-MODE FIBERS
• single mode fiber
• An optical fiber with a core
diameter of less than 10
microns. Used for high-speed
transmission over long
distances, it provides greater
bandwidth than multimode,
but its smaller core makes it
more difficult to couple the
light source. Increasingly,
single mode fiber is used for
shorter distances. When
single mode fiber is used in
shorter distances, such as a
campus or metropolitan area
network
A typical single-mode
optical fiber. Germanium
oxide is a dopant of the core
silica (Item 1).
1. Core 8 µm
2. Cladding 125 µm
3. Buffer 250 µm
4. Jacket 400 µm

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SINGLE-MODE FIBERS
• Single-mode fibers – used to transmit
one signal per fiber (used in telephone
and cable TV). They have small cores(9
microns in diameter) and transmit infra-
red light from laser.
• Single-mode fiber’s smaller core (<10
micrometers) necessitates more
expensive components and
interconnection methods, but allows
much longer, higher-performance links.

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MULTI-MODE FIBERS
• Multi-mode fibers –
used to transmit many
signals per fiber (used
in computer networks).
They have larger
cores(62.5 microns in
diameter) and transmit
infra-red light from LED.

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Fiber-Optic Cable
 Single-mode fiber
 Carries light pulses
along single path
 Multimode fiber
 Many pulses of
light generated
by LED travel at
different angles

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Fiber Optic Types- based of refractive index
• multimode step-index fiber
– the reflective walls of the fiber move the
light pulses to the receiver
• multimode graded-index fiber
– acts to refract the light toward the center
of the fiber by variations in the density
• single mode fiber
– the light is guided down the center of an
extremely narrow core

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STEP-INDEX
Step-index fibers have a uniform core
with one index of refraction, and a
uniform cladding with a smaller index of
refraction.
(Air serves as the cladding in the simple
glass tube example.)
When plotted on a graph as a function of
distance from the center of the fiber, the
index of refraction resembles a step-
function.
The figure to the left illustrates how the
index of refraction varies with location in
a cross-section of a step-index fiber.

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GRADED-INDEX
• In graded-index fiber, the
index of refraction in the core
decreases continuously
between the axis and the
cladding. This causes light
rays to bend smoothly as
they approach the cladding,
rather than reflecting abruptly
from the core-cladding
boundary.

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INDEX PROFILE
The boundary
between the core and
cladding may either
be abrupt, in step-
index fiber, or
gradual, in graded-
index fiber

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Fiber Optic Signals
fiber optic multimode
step-index
fiber optic multimode
graded-index
fiber optic single mode

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Acceptance angle /cone half-angle
• The maximum angle in which external light rays may
strike the air/glass interface and still propagate down
the fiber.

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Numerical Aperture (NA)
• Used to describe the light-gathering or light-collecting
ability of an optical fiber.
• In optics, the numerical aperture (NA) of an optical
system is a dimensionless number that characterizes the
range of angles over which the system can accept or
emit light

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Numerical Aperture (NA)
The numerical aperture
in respect to a point P
depends on the half-
angle θ of the maximum
cone of light that can
enter or exit the lens.

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Numerical Aperture (NA)

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Fiber-Optic Cable
 Single-mode fiber
 Carries light
pulses along
single path
 Multimode fiber
 Many pulses of
light generated
by LED travel
at different
angles

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MULTI-MODE FIBERS
 Multimode fiber has a
larger core (≥ 50
micrometres), allowing
less precise, cheaper
transmitters and
receivers to connect to it
as well as cheaper
connectors.

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MULTI-MODE FIBERS
• However, multi-mode fiber introduces
multimode distortion which often limits the
bandwidth and length of the link. Furthermore,
because of its higher dopant content,
multimode fiber is usually more expensive and
exhibits higher attenuation.

37. The step-index optical fibre consists of a core surrounded by a
cladding glass of lower refractivity.
A light source coupled to the optical fibre emits a cone of light into
the core of the fibre.
Only rays such as the blue and the magenta ones which meet the the
requirement for total internal reflection will be guided in the fibre
along a zig-zag path.
However, other rays such as the red one will be refracted in the
cladding.
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Fiber-optic communication
1. is a method of transmitting information from one place
to another by sending light through an optical fiber.
2. The light forms an electromagnetic carrier wave that is
modulated to carry information.

48. APPLICATIONS OF OPTICAL FIBERS…
1. LONG DISTANCE COMMUNICATION BACKBONES
2. INTER-EXCHANGE JUNCTIONS
3. VIDEO TRANSMISSION
4. BROADBAND SERVICES
5. COMPUTER DATA COMMUNICATION (LAN, WAN etc..)
6. HIGHT EMI AREAS
7. MILITARY APPLICATION
8. NON-COMMUNICATION APPLICATIONS (sensors etc…)
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Fiber-optic communication
The process of communicating using fiber-optics involves
the following basic steps:
• Creating the optical signal using a transmitter,
• relaying the signal along the fiber, ensuring that the
signal does not become too distorted or weak,
• and receiving the optical signal and converting it into an
electrical signal.

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57. Thank You
Thank You57