FIBER OPTICS
FIBER OPTICS AND ITS ADVANTAGES
SECTION A
-7-
The obvious questions concerning fiber optics are
these: Why go through all the trouble of converting
the signal to light and back? Why not just use wire?
The answers lie in the following advantages of fiber
optics.
a) Wide bandwidth
b) Low loss
c) Electromagnetic immunity
d) Light weight
e) Small size
f ) Safety
g) Security
Of all the above mentioned advantages, wide
bandwidth, low loss and electromagnetic immunity
are probably the most important features.
Bandwidth is an effective indication of the rate at
which information can be sent.
Potential
information-carrying capacity increases with the
bandwidth of the transmission medium. From the
earliest days of radio,
useful transmission
frequencies have pushed upward five orders of
magnitude, from about 100kHz (100 x 10
3
Hz) to
about 10GHz (10 x 10
9
Hz). Optical fibers have a
potential useful range to about 1THz (1 x 10
12
Hz).
The information-carrying possibilities of fiber optics
have only begun to be exploited, whereas the same
potentials of copper cable are pushing their limits.
To give perspective to the incredible capacity that
fibers are moving toward, a 10GHz (10 x 10
9
) signal
has ability to transmit any of the following per
second.
a) 1,000 books
b) 130,000 voice channels
Loss indicates how far the information can be sent.
As a signal travels along a transmission path, be it
copper or fiber, the signal loses strength. The loss
of strength is called attenuation. In a copper cable,
attenuation increases with frequency. The higher
the frequency of the information signal, the greater
the loss. In an optical fiber, attenuation is flat. Loss
is the same at any signaling frequency up until a
very high frequency.
The combination of high
bandwidth and low loss has made the telephone
industry probably the heaviest user of fiber optics.
Unlike copper cables, optical fibers do not radiate or
pick-up electromagnetic radiation.
Any copper
conductor acts like an antenna, either transmitting
or receiving energy.
One piece of electronic
equipment can emit electromagnetic interference
(EMI) that disrupts other equipment.
Among
reported problems resulting from EMI are the
following:
• An electronic cash register interfered with
aeronautical transmissions at 113MHz.
• Coin-operated video games interfered with police
radio transmissions in the 42MHz band.
• Some personal computers tested by the Federal
Communications Commission (FCC) in 1979
emitted enough radiation to disrupt television
reception several hundred feet away.
Since fibers do not radiate or receive
electromagnetic energy, they make an ideal
transmission medium when EMI is a concern.
Furthermore, signals do not become distorted by
EMI in fiber.
As a result, fiber offers very high
standards in error-free transmission.
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4
The above paragraphs are reproduced by permission TECHNICIAN’S GUIDE TO FIBER OPTICS 2E (PAGES 24-29)
By Donald J Sterling, Jr. - DELMAR PUBLISHERS, INC., Albany, New York, Copyright 1993
