Optical fiber refers to the medium and the technology associated with the transmission of information as light pulses along a glass or plastic strand or fiber. Optical fiber carries much more information than conventional copper wire and is in general not subject to electromagnetic interference and the need to retransmit signals. Most telephone company long-distance lines are now made of optical fiber. Transmission over an optical fiber cable requires repeaters at distance intervals, and because the installation of any new cabling is labor-intensive, for these reasons, few communities have installed optical fiber cables from the phone company’s branch office to local customers (known as local loops). A type of fiber known as single mode fiber is used for longer distances; multimode fiber is used for shorter distances.
Suppose you want to shine a flashlight beam down a long, straight hallway. Just point the beam straight down the hallway — light travels in straight lines, so it is no problem. What if the hallway has a bend in it? You could place a mirror at the bend to reflect the light beam around the corner. What if the hallway is very winding with multiple bends? You might line the walls with mirrors and angle the beam so that it bounces from side-to-side all along the hallway. This is exactly what happens in an optical fiber.
The light in a fiber-optic cable travels through the core (hallway) by constantly bouncing from the cladding (mirror-lined walls), a principle called total external inflection. Because the cladding does not absorb any light from the core, the light wave can travel great distances.
Why are fiber-optic systems revolutionizing telecommunications? Compared to conventional metal wire (copper wire), optical fibers are:
- Less expensive – Several miles of optical cable can be made cheaper than equivalent lengths of copper wire. This saves your provider (cable TV, Internet) and you money.
- Thinner – Optical fibers can be drawn to smaller diameters than copper wire.
- Higher carrying capacity – Because optical fibers are thinner than copper wires, more fibers can be bundled into a given-diameter cable than copper wires. This allows more phone lines to go over the same cable or more channels to come through the cable into your cable TV box.
- Less signal degradation – The loss of signal in optical fiber is less than in copper wire.
- Light signals – Unlike electrical signals in copper wires, light signals from one fiber do not interfere with those of other fibers in the same cable. This means clearer phone conversations or TV reception.
- Low power – Because signals in optical fibers degrade less, lower-power transmitters can be used instead of the high-voltage electrical transmitters needed for copper wires. Again, this saves your provider and you money.
- Digital signals – Optical fibers are ideally suited for carrying digital information, which is especially useful in computer networks.
- Non-flammable – Because no electricity is passed through optical fibers, there is no fire hazard.
- Lightweight – An optical cable weighs less than a comparable copper wire cable. Fiber-optic cables take up less space in the ground.
Because of these advantages, you see fiber optics in many industries, most notably telecommunications and computer networks. For example, if you telephone Europe from the United States (or vice versa) and the signal is bounced off a communications satellite, you often hear an echo on the line. But with transatlantic fiber-optic cables, you have a direct connection with no echoes.