Glossary of Fiber Optic Terms
Active components: devices based on semiconductor laser technology that provide the light in a fiber optic network. They require the integration of electronics and wiring into a package using traditional assembly technologies. Receivers, transmitters, modulators, amplifiers and switches are examples of active components. These devices are generally easier to assemble than passive components.
Attenuation: the loss of optical energy a signal experiences as it travels through optical fiber. It determines the spacing of repeaters needed to maintain acceptable signal levels. Attenuation is one of the key factors that determine the cost of a fiber optic telecommunication network.
Bandwidth: a measure of the information-carrying capacity of an optical fiber.
Buffering: a protective material extruded directly on the fiber coating to protect it from harsh environments.
Cladding: the material surrounding the core of an optical waveguide. The cladding must have a lower index of refraction to keep the light in the core.
Connector: a component used to align and join two optical fibers together.
Core: the central region of an optical fiber through which light is transmitted. The typical core is 0.005 inch in diameter.
Dense wavelength division multiplexing (DWDM): a technology that increases the number of wavelengths on a single beam of light. Using DWDM, more than 75 separate wavelengths can be multiplexed into a lightwave transmitted on a single optical fiber.
Ferrule: a mechanical fixture, such as a rigid metallic tube, used to confine, protect and align an optical fiber being attached to a connector or other component.
Gob drop: the process used to manufacture optical fiber, which is very similar to a dripping piece of taffy. A large preform rod of highly purified glass is mounted vertically in a furnace and heated to more than 1,200 C. The bottom tip, known as the gob, melts, separates from the cylinder and falls down a 4-story drawing tower, pulling behind it a thin strand of glass fiber. As it is exposed to air, the hot glass thread emerging from the furnace solidifies almost instantly. A protective coating and cladding is applied and the fiber is wound onto a large spool.
Micrometer: a unit of measurement used to determine the geometric dimension of optical fiber. One micrometer is equal to one millionth of a meter or 10-6 meter. One micrometer equals 0.00003937 inch. Also called a micron.
Multiplexer: a device that combines two or more signals into a single output.
Nanometer: a unit of measurement used to determine wavelengths. One nanometer is equal to one billionth of a meter or 10-9 meter. One nanometer equals 0.00000003937 inch.
Nanopositioning: a process involving precise motion and positioning with the accuracy of a fraction of a micrometer that is used to assemble fiber optic components.
Passive components: devices that filter, divide or combine the light signals traveling through optical fiber. They require no input power to operate on an optical signal. Couplers, isolators and wavelength division multiplexers are examples of passive components. These devices are much more labor intensive and costly to manufacture than active components.
Photonic: a term coined for devices that work using photons or light. It is analogous to "electronic" for devices that work with electrons.
Pigtailing: the process of attaching an optical fiber to a component. A small length of fiber is grabbed and its tip is encapsulated in a ferrule, which provides a housing necessary for rigidity and bonding purposes. Once optimum coupling efficiency is achieved with the help of nanopositioning devices, such as machine vision systems, linear motors and piezo stages, the component is attached with adhesive, laser welding or solder.
Pump laser: a semiconductor laser that provides the light that excites atoms in a fiber amplifier, putting them in the right state to amplify light.
Receiver: a device that converts optical signals to electrical signals.
Repeater: a receiver-transmitter pair that detects and amplifies a weak signal for retransmission through another length of optical fiber.
Scattering: a property of glass that causes light to deflect from optical fiber. It contributes to attenuation.
Transmitter: a device that converts electrical signals to optical signals. The transmitter is usually a pump laser.
Waveguide: a structure that guides electromagnetic waves along its length. An optical fiber is an optical waveguide.
Wavelength: the distance between two successive points of an electromagnetic waveform, usually measured in nanometers.