Fiber-optic cabling uses either glass or plastic fibers to guide light impulses from source to destination. The bits are encoded on the fiber as light impulses . Optical fiber cabling is capable of very large raw data bandwidth rates. Most current transmission standards have yet to approach the potential bandwidth of this media.
Fiber Compared to Copper Cabling
Given that the fibers used in fiber-optic media are not electrical conductors, the media is immune to electromagnetic interference and will not conduct unwanted electrical currents due to grounding issues. Because optical fibers are thin and have relatively low signal loss, they can be operated at much greater lengths than copper media, without the need for signal regeneration. Some optical fiber Physical layer specifications allow lengths that can reach multiple kilometers.
Optical fiber media implementation issues include:
More expensive (usually) than copper media over the same distance (but for a higher capacity)
Different skills and equipment required to terminate and splice the cable infrastructure
More careful handling than copper media
At present, in most enterprise environments, optical fiber is primarily used as backbone cabling for high-traffic point-to-point connections between data distribution facilities and for the interconnection of buildings in multi-building campuses. Because optical fiber does not conducts electricity and has low signal loss, it is well suited for these uses.
Optical fiber cables consist of a PVC jacket and a series of strengthening materials that surround the optical fiber and its cladding. The cladding surrounds the actual glass or plastic fiber and is designed to prevent light loss from the fiber. Because light can only travel in one direction over optical fiber, two fibers are required to support full duplex operation. Fiber-optic patch cables bundle together two optical fiber cables and terminate them with a pair of standard single fiber connectors. Some fiber connectors accept both the transmitting and receiving fibers in a single connector.
Generating and Detecting the Optical Signal
Either lasers or light emitting diodes (LEDs) generate the light pulses that are used to represent the transmitted data as bits on the media. Electronic semi-conductor devices called photodiodes detect the light pulses and convert them to voltages that can then be reconstructed into data frames.
Note: The laser light transmitted over fiber-optic cabling can damage the human eye. Care must be taken to avoid looking into the end of an active optical fiber.
Single-mode and Multimode Fiber
Fiber optic cables can be broadly classified into two types: single-mode and multimode.
Single-mode optical fiber carries a single ray of light, usually emitted from a laser. Because the laser light is uni-directional and travels down the center of the fiber, this type of fiber can transmit optical pulses for very long distances.
Multimode fiber typically uses LED emitters that do not create a single coherent light wave. Instead, light from an LED enters the multimode fiber at different angles. Because light entering the fiber at different angles takes different amounts of time to travel down the fiber, long fiber runs may result in the pulses becoming blurred on reception at the receiving end. This effect, known as modal dispersion, limits the length of multimode fiber segments.
Multimode fiber, and the LED light source used with it, are cheaper than single-mode fiber and its laser-based emitter technology.