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