Optical fibre is a long
cylindrical wire that consists of an inner core and a cladding layer on top of
inner core. The inner core is made of a glass of higher refractive index as
compared to the cladding core. The diameter of the inner core of a fibre is
approximately 100 micro meters. The outer part of cladding is coated with a polymer. It protects fibre from breaking. Multiple fibres are put inside a protective sheathing in a cable. One fibre is used for communication in each direction. So cables have pairs of cables.
In 1985-90 the fibre cables came in to a wide use. A cable was laid in 1990 between USA and England under the Atlantic ocean.
An electrical signal is converted into an
optical signal by use of (transducer) optical LEDs. They glow at the
frequency of the incoming signal. The LED is kept at one end of the fibre.
When a light wave is incident on the
circular cross section of the fibre at one end, it is refracted on entering
inner core and it is incident on the interface between inner core and the
cladding. The angle is arranged to be more than the critical angle and so the
light wave is reflected totally. into the inner core. The light wave travels
along the fibre cable with innumerable number of total internal
When the light wave reaches the other side
(receiver), the optical-diodes sense the light and convert the signal into
electrical pulses. These pulses are given for digital processing.
Silica glass Optical fibres can transmit with
very small loss of energy over kilometres. The fibres are flexible inside the
covering material. Many fibres are packed together in to a cable. Each
fibre has a very large optical bandwidth and high response time. It is suitable
for super fast transmission systems and for computer networking and for
on board connections too. One fibre can be used to transmit waves of many
One advantage of optical fibre is that they are
electrically and magnetically not affected by any external
interference unlike copper wires. Multiple grades of the fiber is
fabricated suitable for different applications.
These cables are some what expensive, but the
advantages are many fold. So they are used in telecommunications. They are
also used as table top decorative (colorful) lighting articles (fountain) made
of plastic (cheap) fibre. Their top ends
are illuminated in bright colors. These cables are used to illuminate internal
organs like esophagus, stomach and intestines.