Optical Fiber Cables
1. Definition
and Construction
The construction of an
optical fiber cable has been shown in figure.It 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. Light is launched into the fiber using a light
source such as a light emitting diode (LED) or Laser.It is detected on the
other side using a photo detector such as a phototransistor. The optical fiber
cables are costlier than the other two types but they have several advantages
over the other two types*.
2. Special
Characteristics
The characteristics of optical fiber cables may be listed as
under:
(i) Higher bandwidth therefore can operate at higher data rates
(ii) Reduced losses as the signal attenuation is low
(iii) Distortion is reduced hence better quality is assured.
(iv) They are immune to electromagnetic interferences.
(v) Small size and light weight
(vi) Used for point-to-point communication
3. Applications
(i) 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.
(ii) The installation
cost of ontical fibers is higher than that for the co-axial or twisted wire
cables.
(iii) Optical fibers
are now used in the telephone systems.
(iv) In the local area
networks (LANS).
4. Advantages of Optical Fibers
Some of the advantages
of fiber optic communication over the conventional means of
communication may be
listed as under:
(i)Small Size and
Light Weight: The size (diameter) of the optical fibers is very small (it is comparable
to the diameter of human hair). Therefore, a large number of optical fibers can
fit into a cable of small diameter.
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(ii) Easy
availability and low cost: The material used for the manufacturing of optical
fibers is silica glass. This material is easily available. Hence, the optical
fibers cost lower than the cables with metallic conductors.
(iii) 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 interference.
(iv) Large
bandwidth: As the light rays have a very high frequency in the GHz range
bandwidth of the optical fiber extremely large. This allows transmission of
more number of channel Therefore, the information carrying capacity of an
optical fiber is much higher than that of a ge
axial cable.
(v) Other
advantages: In addition to the advantages discussed earlier, the optical
fiber communication has the following other advantages:
(i) No crosstalk
inside the optical fiber cable
(ii) Signal can be
transmitted upto 100 times faster
(iii) Intermediate
amplifier are not required as the transmission losses in the fiber are low
(iv) Ground loops
are absent
(v) Installation is
easy as the fiber optic cables are flexible
(vi) These cables
are not affected by the drastic environmental conditions
Because of all these
advantages the optical fiber cable is replacing the conventional metallic
conductor cable rapidly in many areas.
5. Drawback of Optical Fiber
Some of the
drawbacks of optical communication system may be listed as under:
(i) Sophisticated
plants are required for manufacturing optical fibers
(ii) The initial
cost incurred is high
(iii) Joining the
optical fibers is a difficult job.
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