App Notes

Basic advantages of a fiber optic transmission system

The main advantages of fiber are;

  • Isolation from noise, high voltage, and ground loops.
  • High information bandwidth
  • Minimal signal attenuation compared to wire transmission.

All fiber optic transmission systems use modulated light to convey information from a transmitter to a companion receiver as shown in figure 1.

 Basic Fiber Optic System

You will notice from the diagram that the only interconnection between the two units is by means of a fiber optic cable which, as we will ultimately see is really the heart of the system. This cable contains a hair-thin fiber, made of ultra-pure glass that is the actual conductor of the modulated light. There are no other electrical or metallic signal carrying conductors in the cable. As a result, fiber optic cables are normally composed of totally non-conductive materials. This leads to one of the most important advantages of this form of transmission, a fiber optic cable will not be affected by any extraneous electrical pickup. While a long copper wire (even shielded coax) can easily act as an antenna picking up all kinds of interference, an optical fiber can only respond to light which is many magnitudes in frequency above even the highest microwave frequencies commonly used. This means that radio frequency fields, sparking motors and other electromechanical devices not to mention nearby lightning strikes have no effect on the signal at all. In fact so immune is the fiber optic cable to electrical and electromagnetic interference that only an actual break in the fiber will interfere with the signal.

The non-conductive cable also has other advantages. Short circuits and the detrimental effects of water and explosive atmospheres are virtually non existent. The fact that each end of the fiber optic link is not electrically connected to the other eliminates the possibility of ground-loops, a significant problem in video transmission and in fact each end of the link can even be at widely different potentials such as in a high voltage isolation system.

Light is electromagnetic radiation at frequencies in the THz region.  Since light is the carrier of information, the bandwidth of an optical fiber is potentially thousands of times wider than that of any form of metallic based cable. This allows the transmission of huge amounts of information on a tiny, hair-thin conductor enclosed in a cable that is smaller and lighter in weight than any other type of conductor.

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