Basics of
Fiber Optics
Mark Curran/Brian Shirk
Fiber
optics, which is the science of light transmission through very fine glass or
plastic fibers, continues to be used in more and more applications due to its
inherent advantages over copper conductors. The purpose of this article is to
provide the non-technical reader with an overview of these advantages, as well
as the properties and applications of fiber optics.
I.
Advantages
Fiber
optics has many advantages over copper wire (see Table 1) including:
Increased bandwidth: The high signal bandwidth of optical fibers provides
significantly greater information carrying capacity. Typical bandwidths for
multimode (MM) fibers are between 200 and 600MHz-km and >10GHz-km for single
mode (SM) fibers. Typical values for electrical conductors are 10 to 25MHz-km.
Electromagnetic/Radio Frequency
Interference Immunity: Optical fibers
are immune to electromagnetic interference and emit no radiation.
Decreased cost, size and weight: Compared to copper conductors of equivalent signal
carrying capacity, fiber optic cables are easier to install, require less duct
space, weigh 10 to 15 times less and cost less than copper.
Lower loss: Optical fiber has lower attenuation (loss of signal
intensity) than copper conductors, allowing longer cable runs and fewer
repeaters.
No sparks or shorts: Fiber optics do not emit sparks or cause short
circuits, which is important in explosive gas or flammable environments.
Security: Since fiber optic systems do not emit RF signals, they
are difficult to tap into without being detected.
Grounding: Fiber optic cables do not have any metal conductors;
consequently, they do not pose the shock hazards inherent in copper cables.
Electrical Isolation: Fiber optics allow transmission between two points
without regard to the electrical potential between them.
Coaxial Cable
|
Fiber Optic Cable (MM)
|
Fiber Optic Cable (SM)
|
|||
Representative distance
bandwidth products
|
100
MHz km
|
500
MHz km
|
100,000+
MHz km
|
||
Attenuation/km @ 1 GHz
|
>45 dB
|
1 dB
|
0.2 dB
|
||
Cable cost ($/m)
|
$$$$$$$$$
|
$
|
$
|
||
Cable diameter (in.)
|
1
|
1/8
|
1/8
|
||
Data security
|
Low
|
Excellent
|
Excellent
|
||
EMI immunity
|
OK
|
Excellent
|
Excellent
|
||
Table 1: Advantages of Fiber Optics over Copper
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