basic concepts of optical fiber communications

1. OPTICAL FIBRES
Submitted by
K.Vishnu prasanna

2. introduction
 An optical fiber or optical fibre is a flexible, transparent fiber
made by drawing glass (silica) or plastic to a diameter slightly
thicker than that of a human hair.
 Optical fiber is a type of cabling technology that uses light to
carry voice and data communications (telecommunications)
over distances both great and small.
 This presentation will provide a definition of optical fiber,
explore the different types and explain how the different types
are used.

3. Optical fiber
core
 inner part where wave
propagates
cladding
 outer part used to keep wave
in core
buffer
 protective coating
jacket
 outer protective shield

4. Types of optical fibers
Single mode
 only one signal can be transmitted only
one signal can be transmitted
 use of single frequency use of single
frequency
Multi mode Multi mode
 Several signals can be transmitted
 Several frequencies used to modulate the
signal

6. Construction
A hair-thin Fiber consist of two concentric
layers of high-purity silica glass the core
and the cladding, which are enclosed by a
protective sheath as shown in Fig. 2. Core
and cladding have different refractive
indices, with the core having a refractive
index, n1, which is slightly higher than that
of the cladding, n2. It is this difference in
refractive indices that enables the Fiber to
guide the light. Because of this guiding
property, the Fiber is also referred to as an
“optical waveguide.”
Principle of operation

7. Principle of operation
The optical Fiber has two concentric layers
called the core and the cladding. The inner
core is the light carrying part. The
surrounding cladding provides the difference
refractive index that allows total internal
reflection of light through the core. The index
of the cladding is less than 1%, lower than
that of the core. Light injected into the Fiber
and striking core to cladding interface at
greater than the critical angle, reflects back
into core, since the angle of incidence and
reflection are equal, the reflected light will
again be reflected. The light will continue
zigzagging down the length of the Fiber.
Light striking the interface at less than the
critical angle passes into the cladding, where
it is lost over distance.

8. Uses of optical fiber
 Communication
Optical fiber can be used as a medium for telecommunication
and computer networking because it is flexible and can be bundled
as cables.
1.Broad bandwidth
A single optical fiber can carry over 3,000,000 full-
duplex voice calls or 90,000 TV channels.
2.Electrical insulator
Optical fibers do not conduct electricity, preventing
problems with ground loops and conduction of lightning.

9.  Sensors
Fibers have many uses in remote sensing. In some applications,
the sensor is itself an optical fiber.
Depending on the application, fiber may be used because of its small
size, or the fact that no electrical power is needed at the remote
location, or because many sensors can be multiplexed along the
length of a fiber by using different wavelengths of light for each
sensor, or by sensing the time delay as light passes along the fiber
through each sensor.

10.  Power transmission
Optical fiber can be used to transmit power using a photovoltaic cell to
convert the light into electricity.
While this method of power transmission is not as efficient as
conventional ones, it is especially useful in situations where it is
desirable not to have a metallic conductor as in the case of use near
MRI machines, which produce strong magnetic fields.
 Other uses
Medical sciences, imaging optics,microscopes etc..,

11. Advantages of optical Fibres
 Can carry much more information
 Much higher data rates Much higher data rates
 Much longer distances than co-axial Much longer distances than co-
axial cables cables
 Immune to electromagnetic noise Immune to electromagnetic noise
 Light in weight Light in weight
 Unaffected by atmospheric agents Unaffected by atmospheric
agents

12. Disadvantages of optical fiber
 High investment cost
 Need for more expensive optical transmitters
and receivers
 More difficult and expensive to splice than
wires
 Price
 Fragility
 Affected by chemicals
 Opaqueness
 Requires special skills

13. Characteristics
1)Wider bandwidth: The optical carrier frequency is in the
range 10^13 Hz to 10^15Hz.
2)Low transmission loss: The fibers having a transmission
loss of 0.002dB/km.
3)Dielectric waveguide: Optical fibers are made from silica
which is an electrical insulator. Therefore they do not pickup
any electromagnetic wave or any high current lightning.
4)Signal security: The transmitted signal through the fibers
does not radiate. Further the signal cannot be tapped from a
Fiber in an easy manner.
5)Small size and weight: Fiber optic cables are developed
with small radii, and they are flexible, compact and
lightweight. The fiber cables can be bent or twisted without
damage.

14. Conclusions
 We are currently in the middle of a rapid increase in the
demand for data bandwidth across the Earth.
 For most applications optical fibers are the primary solution
to this problem.
 They have potentially a very high bandwidth, with many of
the bandwidth limitations now being at the transceivers rather
than being an intrinsic property of the fiber allowing easy
upgrading of systems without relaying cable.

15. Thank you