Optical fibres come in two types: Single-mode fibres and Multi-mode fibres. Single-mode fibres have small cores (about 3.5 x 10-4 inches or 9 microns in diameter) and transmit infrared laser light (wavelength = 1,300 to 1,550 nanometers). Multi-mode fibres have larger cores (about 2.5 x 10-3 inches or 62.5 microns in diameter) and transmit infrared light (wavelength = 850 to 1,300 nm) from light-emitting diodes (LEDs). Some optical fibres can be made from plastic. These fibres have a large core (0.04 inches or 1 mm diameter) and transmit visible red light (wavelength = 650 nm) from LEDs.

The light in a fibre-optic cable travels through the core by constantly bouncing from the cladding (like mirror-lined walls), a principle called total internal reflection. However, the cladding does not absorb any light from the core, so the light wave can travel great distances. Yet some of the light signal degrades within the fibre, mostly due to impurities in the glass. The extent that the signal degrades depends on the purity of the glass and the wavelength of the transmitted light (for example, 850 nm = 60 to 75 percent/km; 1,300 nm = 50 to 60 percent/km; 1,550 nm is greater than 50 percent/km). Some premium optical fibres show much less signal degradation -- less than 10 percent/km at 1,550 nm.

As mentioned above, some signal loss occurs when the light is transmitted through the fibre, especially over long distances (more than a half mile, or about 1 km) such as with undersea cables. Therefore, one or more optical regenerators is spliced along the cable to boost the degraded light signals. An optical regenerator consists of optical fibres with a special coating (doping). The doped portion is "pumped" with a laser. When the degraded signal comes into the doped coating, the energy from the laser allows the doped molecules to become lasers themselves. The doped molecules then emit a new, stronger light signal with the same characteristics as the incoming weak light signal.

The optical receiver is like the sailor on the deck of the receiving ship. It takes the incoming digital light signals, decodes them and sends the electrical signal to the other user's computer, TV or telephone (receiving ship's captain). The receiver uses a photocell or photodiode to detect the light. Compared to conventional metal wire (copper wire), optical fibres 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 fibres can be drawn to smaller diameters than copper wire. Higher carrying capacity - Because optical fibres are thinner than copper wires, more fibres 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 fibre is less than in copper wire. Light signals - Unlike electrical signals in copper wires, light signals from one fibre do not interfere with those of other fibres in the same cable. This means clearer phone conversations or TV reception.
Low power - Because signals in optical fibres 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 fibres are ideally suited for carrying digital information, which is especially useful in computer networks.
Non-flammable - Because no electricity is passed through optical fibres, there is no fire hazard.
Lightweight - An optical cable weighs less than a comparable copper wire cable. fibre-optic cables take up less space in the ground.
Flexible - Because fibre optics are so flexible and can transmit and receive light, they are used in many flexible digital cameras including uses such as Medical imaging - in bronchoscopes, endoscopes, laparoscopes, Mechanical imaging - inspecting mechanical welds in pipes and engines (in airplanes, cars, space shuttles, etc) and in Plumbing - to inspect sewer lines.

Because of these advantages, you see fibre optics used in many of Professional Cabling Services projects and installations, most notably telecommunications and computer networks. This technology is employed by professionals and is commonly used throughout the world. For example, if you telephone Asia from Australia (or vice versa) and the signal is bounced off a communications satellite, you often hear an echo on the line. But with trans-oceanic fibre optic cables, you have a direct connection with no echoes.