Fiber Optics in Phone Systems

Fiber Optics in Phone Systems

The invention of fiber optics, photodetectors, and solid state lasers has brought light into the field of telecommunications and made it the preferred method for long-distance transmissions.

Basic Operations

The idea of using light to pass information along isn’t new. Flashing signals with a lantern or a mirror reflecting sunlight goes back centuries. Fiber optic cables use light instead of electricity and function very differently from copper wiring.

In order for a fiber optics cable to efficiently carry a light signal, the light must be traveling in a single direction. Scattered light won’t travel through the cable very far. For this reason, lasers are used to create a beam with energy moving in parallel so it’ll cover great distances.

Unlike electrical signals that fluctuate in frequency, fiber optic systems transmit messages by flashing laser light in code at extremely high rates. The optical cable relies on the fact that when light encounters the divide between two clear materials of different densities at a shallow angle, it is reflected at an equal angle. Thus, a beam of light traveling down an unprotected glass fiber that’s much denser than the surrounding air will bounce off its outer surface and continue through it so long as the fiber isn’t bent into too much of a curve. At the other end of the cable, a photodetector receives the pulsing laser beam and turns it back into electrical pulses.


The physical qualities of fiber optic cables and the fact they rely on light for signals give them several advantages over electrical wires.

  • Thinner: Optical fibers are strands of glass or plastic, each only slightly thicker than a single human hair.
  • Lighter: Fiber optic cables are made of lighter materials than copper wiring. In addition, there’s no need to add more strands to handle more signals because light has no mass. Multiple light beams can occupy the same space simultaneously.
  • Safer: With no electricity passing through the cables, there’s no risk of fire, shock or electrocution.
  • Non-corrosive: Unlike copper cabling, fiber optic cables made of glass or plastic have almost no risk of being damaged by water and chemicals.
  • Non-conductive: When magnetic fields pass through conductive wiring, electricity is produced. In copper wiring, unwanted fields create static. If it’s strong enough, it can generate high voltage and short out equipment or even melt the wiring. This is not a problem for fiber optic cables.
  • More security: When electricity passes through wiring, it creates a magnetic field that can be intercepted and listened to. It’s much harder to eavesdrop on optical phone lines.


The fact that fiber optic cables can’t be bent too sharply limits their use in individual devices and tight spaces. At this level, the higher costs of transmitting and receiving components comes into play. Fiber optic services are only available to 25 percent of the country. New infrastructure is a large expenditure many companies aren’t willing to take on, yet.