Download 29 - BSNL Durg SSA(Connecting India)

CONTENTS
1.INTRODUCTION
2.OPTICAL FIBER CABLE
3.CONSTRUCTION
4.PRINCIPLE OF OPERATION
5.MULTIMODE FIBER
6.SINGLE MODE FIBER
7.SPECIAL PURPOSE FIBER
8.SPLICING OF FIBER CABLE
9.OPTICAL FIBER COMMUNICATION
10.FIBER OPTIC SENSOR
11.PROTECTION
12.APPLICATIONS OF OPTICAL FIBER CABLE
13.ADVANTAGE OF FIBER CABLES
14.DISADVANTAGES OF FIBER CABLE
An optical fiber is a flexible, transparent fiber made of very
pure glass (silica) not much wider than a human hair that
acts as a waveguide, or "light pipe", to transmit light
between the two ends of the fiber.
Optical fibers are widely used in fiber-optic communications,
which permits transmission over longer distances and at
higher bandwidths (data rates) than other forms of
communication. Fibers are used instead of metal wires
because signals travel along them with less loss.
OPTICAL FIBRE CABLE ::
Optical fiber is the latest underground
cable that is being used extensively in
all the networks including long
distance trunks, junction circuits and
even the local subscriber loops to
enhance the data transmission.
An optical fiber is a flexible,
transparent fiber made of very pure
glass (silica).
CONSTRUCTION
The construction of an optical fiber cable consists of an inner
glass core surrounded by a glass cladding which has a lower
refractive index. Digital signals are transmitted in the form of
intensity-modulated light signal which is trapped in the glass
core.
Principle of operation
An optical fiber is a cylindrical dielectric waveguide
(nonconducting waveguide) that transmits light along its axis,
by the process of total internal reflection. The fiber consists of
a core surrounded by a cladding layer, both of which are made
of dielectric materials. To confine the optical signal in the core,
the refractive index of the core must be greater than that of
the cladding. The boundary between the core and cladding
may either be abrupt, in step-index fiber, or gradual, in
graded-index fiber.
Fiber with large core diameter (greater than
10 micrometers) may be analyzed by geometrical optics.
Such fiber is called multi-mode fiber, from the
electromagnetic analysis
The structure of a typical singlemode fiber.
1. Core: 8 µm diameter
2. Cladding: 125 µm dia.
3. Buffer: 250 µm dia.
4. Jacket: 400 µm dia.
Fiber supporting only one mode is called single-mode or
mono-mode fiber.
SPECIAL PURPOSE FIBER
Some special-purpose optical fiber is constructed
with a non-cylindrical core and/or cladding layer,
usually with an elliptical or rectangular crosssection.
Such fiber uses diffraction effects instead of or in
addition to total internal reflection, to confine light
to the fiber's core
SPLICING OF OPTICAL FIBER
Optical fibers may be connected to each other by
connectors or by splicing, that is, joining two fibers
together to form a continuous optical waveguide.
The generally accepted splicing method is arc fusion
splicing, which melts the fiber ends together with an
electric arc. For quicker fastening jobs, a
"mechanical splice" is used.
Fusion splicing is done with a specialized instrument
1.Fusion Splicing- Fusion splicing is done with a
specialized instrument.
2. Mechanical Splicing – For more fastening
mechanical splicing is used.
Optical Fiber Communication
Optical fiber can be used as a medium for
telecommunication and networking because it is
flexible and can be bundled as cables. It is especially
advantageous for long-distance communications,
because light propagates through the fiber with little
attenuation compared to electrical cables.
A single fiber can carry much more data than electrical
cables such as standard category 5 Ethernet cabling,
which typically runs at 1 Gbit/s .
Fiber Optic Sensors
Fibers have many uses in remote sensing. In some
applications, the sensor is itself an optical fiber. In
other cases, fiber is used to connect a non-fiberoptic
sensor to a measurement system. Depending on the
application, fiber may be used because of its small
size,
Optical fibers can be used as sensors to measure
strain, temperature, pressure and other quantities by
modifying a fiber so that the property to measure
modulates the intensity, phase, polarization,
wavelength, or transit time of light in the fiber.
PROTECTION
Fiber cables require Protection:1.from probable mechanical damages.
2. from water and chemicals or soil conditions.
3. from Induction due to Electrical lines.
4. from diggings by different agencies.
5. from damages while handling.
APPLICATIONS OF OPTICAL FIBER CABLE
1. Optical fiber transmission systems are widely
used in the backbone of networks. Current
optical fiber systems provide transmission
rates from 45 Mb/s to 9.6 Gb/s using the single
wavelength transmission.
2. The installation cost of optical fibers is higher
than that for co-axial or twisted wire cables.
3. Optical fiber are now used in the telephone
systems.
4. In the local area networks (LANs).
5. 8 MB MUX for 120 channels.
6. 34 MB for 480 channels.
7. 140 MB for 1920 channels.
ADVANTAGES OF OPTICAL FIBERS
1. Small Size and Light Weight: The size (diameter) of the
optical fiber is very small. Therefore, a large number of optical
fibers can fit into a cable of small diameter.
2. Easy availability and low cost: The material used for the
manufacturing of optical fibers is silica glass. The material is
easily available. Hence , the optical fibers cost lower than the
cables with metallic conductors.
3. No electrical or Electromagnetic interference: Since the
transmission takes place in the form of light rays the signal is
not affected due to any electrical or electromagnetic
interferences.
4. Large bandwidth: As the light rays have high frequency in the
GHz range, the bandwidth of the optical fiber extremely large.
5. Large bandwidth: As the light rays have high frequency in the
GHz range, the bandwidth of the optical fiber extremely large.
DISADVANTAGES OF FIBER CABELS
1. Sophisticated plants are required for
manufacturing optical fiber.
2. The initial cost incurred is high.
3. Joining the optical fiber is a difficult job.