Fibre-optic communication uses glass or plastic fibers to transmit data as light. A fiber-optic cable contains a core that carries the light, surrounded by cladding with a lower refractive index. Total internal reflection within the core allows light to propagate long distances with little attenuation. Fiber-optic cables have several advantages over electrical cables including higher bandwidth, lower losses, lighter weight, and immunity to electromagnetic interference. Common applications include telephone networks, cable television, computer networking, and industrial sensors.

2. Fibre-0ptic Communication
 The communication medium in most electronic
communication systems is either a wire conductor cable or
free space. But now, a new medium is growing in popularity,
the Fiber-optic cable.
 A fiber-optic cable is essentially a light pipe that is
used to carry a light beam from one place to another. Light is
an electromagnetic signal like a radio wave.
 It can be modulated by information and sent over
the fiber-optic cable. Because the frequency of light is
extremely high, it can accommodate very wide bandwidths of
information and/or extremely high data rates can be
achieved with excellent reliability.

3.  An optical fiber is a dielectric waveguide capable of carrying
light energy
 Optical Fiber operates from 800 nm to 2550 nm. Specially at
1300 and 1550 nm .(Optical frequency lie in 1012-1016 Hz.
 With the Advancement in the field of fiber optic technology,
optical electronics has changed the world into global
information village.
 Apart from network communication fiber optics is useful in
industrial applications, Medical research etc.
INTRODUCTION

4. Construction of Fiber-Optical Cables
Core
Cladding
Jacket
The portion of a Fiber-optic cable that
carries the light is made from whether
glass or plastic, another name for glass
is silica. The glass or plastic is melted
and pulled through a form to produce a
fine threadlike Fiber. Glass has superior
optical characteristics over plastic.
Glass is costly but the attenuation is
negligible, Plastic is cheep but the
attenuation is more. The glass Fiber is
used for long distance communication.
Core is used to carry the light, usually surrounded by a protective
cladding. Cladding is made of glass or plastic but has a lower refractive index
and adds strength. A plastic jacket is used to protect the fiber-optic.

5. Theory of fiber optics
How optical fiber works
 The principle of operation of optical fiber lies in the
behavior of light. It is a widely held view that light
always travels in straight line and at constant speed.
 The propagation of light within an optical fiber it is
necessary to take into account refractive index of the
dielectric medium
 Refractive index of the dielectric medium is defined as
the ratio of velocity of light in vacuum to velocity of
light in medium
 Refractive index = velocity of light in vacuum
velocity of light in medium

6. 2
1
Incident ray
Exit ray
Partial internal
reflection
Low index n2
air
High index n1
glass
The velocity of light in any solid, transparent material is less
than in vacuum the refractive index of such material I s always
greater than 1.
When a ray is incident on the interface between two
dielectrics of differing refractive indices, refraction occurs.

7. 

At angles of incidence greater than the critical angle the
light is reflected back into the originating dielectric medium.
This behavior of light is termed as “Total internal
reflection”. Here, angle of incidence = angle of reflection
Total internal reflection

8. This is the mechanism by which light may be considered
the propagate down to an optical fiber with low loss. Fig.
below illustrates the transmission of a light ray in an optical
fiber via a series of total internal reflection at the interface o
the silica core and slightly lower refractive index silica
cladding.
Low index cladding
High index cladding
The light ray shown in figure is known as meridian ray
as it passes through the axis of the fiber core. It is generally
used when illustrating the fundamental transmission
properties of optical fiber.

9. Characteristics and classification
• Characteristics depends on following
factors
 Composition of the fiber
 Amount and type of light into the fiber
 Diameter and length of fiber

10. Modes of operation
 Characteristics , which depends on its size, is
its mode of operation
 Mode refers to mathematical and physical
descriptions of the propagation of energy
through a medium
 The number of modes supported by a single
fiber can be as low as 1 or as high 100,00
 From this characteristics come the term
single mode and multi mode

11. Relationship between the multiple indices
 Light changes speeds when it passes from
one medium to another
 There are two major indices in this
relationship
 Step index
 Graded index

12. Types of Fiber-Optic Cable
Core
Cladding
Refractive
index
Refractive
index
Step-Index Graded-Index
Cross-Section diagram
1. Step-Index In this
type of cable the
refractive index is
constant of the core
from centre to the
interface of core and
clad.
2. Graded-Index In
this type of cable the
refractive index of
core is varies, at the
centre of the core is
max and gradually
decrease towards the
clad.

13. Classification of fibers
 From the above terms three classifications
of fibers are
1. Multimode step index fiber
2. Multimode graded index fiber
3. Single-mode step index fiber

14. Multimode step index fiber
 Core diameter from 100 to 970 m
 With this large core diameter there are many paths, which
light can travel( multi mode)
 The difference in the length of time it takes the various
light rays to exist the fiber is called model dispersion
 Model dispersion is a form of a signal distortion which
limits the bandwidth of the fiber
Dispersion
A Multi-mode Step-Index Cable

15. Multimode graded index fiber
 It is an improvement on the multimode step index fiber
because light travel faster through the lower index of
refraction, the light at the fiber core travels more slowly
than the light nearer the surface.
 Therefore both light rays arrive at the exit point at
almost same time
 Thus reduces model dispersion
 Core diameter ranges from 50 to 85 m
 Cladding diameter of 125 m
A Multi-mode Graded-Index Cable

16. Single mode step index
 Most widely used in wide band communication
arena
 Light rays travel on only one path
 Model dispersion is zero
 Core diameter ranges from 5 m to 10 m
 Cladding diameter is 125 m
A Single-mode Step-Index Cable

17. Specification of a single-mode fiber
 Bandwidth from 50 to 100 GHz/km
 More than 100,000 voice channels are
available
 Higher frequency capabilities

18. Coder or
Converter
Light
Source
Transmitter
Shaper Decoder
Original
voice or
video
Data to Computer
Data from Computer
Information
Voice or
Video
The components of a typical fiber-optic communication system are
illustrated in the fig. The communication is done in several steps.
A Fiber-Optic System
Fibre-Optic
cable

19. Fiber losses
 Light scattering
 Absorption of light energy
 Micro bend loss
 Macro bend loss
 Attenuation

20. Applications of Fibre-Optic cables
1. Local and long distance telephone systems.
2. TV studio-to-transmitter interconnection, eliminating
microwave radio link.
3. Closed Circuit TV systems used in building for security.
4. Secure communications systems at military bases.
5. Computer networks, wide area network (WAN) and local
area network (LAN).
6. Shipboard communications.
7. Aircraft controls.
8. Interconnection of measuring monitoring instruments in
plants and laboratories.
9. Data acquisition and control signal communication in
industrial process control systems.
10. Nuclear plant instrumentation

21.  HIGH BANDWIDTH AND HIGH SPEED
 THIN, LIGHT WEIGHT & FLEXIBLE
 NOT AFFECTED BY E M I
 EXCELLENT SECURITY
 LOW ATTENUATION - ABILITY TO SUPPORT LARGE
NUMBER OF STATIONS
 NO CROSS TALK
IMPORTANCE OF FIBER OPTICS

22. Advantages of Fibre-Optic cables
over Conventional electric cable
1. Wider bandwidth: Fibre-Optic cable have higher information
carrying capability.
2. Lower Loss : With Fibre-Optic cables, there is less signal
attenuation over long distances.
3. Lightweight : Glass or Plastic cables are much lighter than
copper cables.
4. Small in Size: Practical Fibre-Optic cables are much smaller
than in diameter than electrical cables.
5. Security: Fibre-Optic cables cannot be “tapped” as easily as
electrical cables, and they do not radiate signals.
6. Greater safety: Fibre-Optic cables do not carry electricity.
Therefore there is no shock hazard.
7. Interference immunity: Neither these type of cables interfere to
other cables nor immune to pickup of interference from other.

23. Disadvantages of Fibre-Optic cables
1. Due to small size and brittleness make it difficult to
work with.
2. Special expensive tools and techniques are required.
3. Now its cost is so high due to difficulty of
manufacturing.
4. At a joint the attenuation is more.
5. The losses are occurred when the cable is bend.
6. During transmission the dispersion is occurred.