Glossary of Terms
APC: Angled Physical Contact is a terminus end-face finish profile that is angled 8° from a plane normal to the axis of the fiber.
Absorption: That portion of fiber optic attenuation resulting from the conversion of optical power to heat.
Analog: Signals that are continually changing, as opposed to being digitally encoded.
Attenuation: A general term indicating a decrease in power from one point to another. In optical fiber, it is the decrease in optical power as it passes along a fiber caused by absorption and scattering, usually expressed in decibels (dB).
Attenuation Coefficient: Characteristic of the attenuation of an optical fiber per unit length, in dB/km.
Back reflection, optical return loss: Light reflected from the cleaved or polished end of a fiber caused by the difference of refractive indices of air and glass. Expressed in dB relative to incident power.
Backscattering: The return of a portion of scattered light to the input end of a fiber; the scattering of light in the direction opposite to its original propagation.
Bandwidth: The range of signal frequencies or bit rate for a fiber optic component, link or network will operate.
Bend Radius: Radius of curvature that a fiber can be bent without losing light signal or breaking.
Bending loss, microbending loss: Loss in fiber caused by stress on the fiber bent around a restrictive radius.
Bit Error Rate (BER): The fraction of data bits transmitted that are received in error.
Buffer: A protective coating applied directly on the fiber.
Cable Assembly: A cable that has connectors installed on one or both ends.
Chromatic dispersion: The temporal spreading of a pulse in an optical waveguide caused by different wavelengths of light traveling at different speeds down the optical fiber. Chromatic dispersion occurs because the speed at which an optical pulse travels depends on its wavelength, a property inherent to all optical fiber.
Cladding: Material that surrounds the core of an optical fiber. Its lower index of refraction, compared to that of the core, causes the transmitted light to travel down the core.
Cleave: The process of separating an optical fiber by a controlled fracture of the glass, for the purpose of obtaining a fiber end, which is flat, smooth and perpendicular to the fiber axis.
Coating: A material put on a fiber during the drawing process to protect it from the environment.
Conduit: Pipe or tubing through which cables can be pulled or housed.
Connector: A mechanical device used to align and join two fibers together to provide a means for attaching and decoupling it to a transmitter, receiver, or another fiber.
Core: The light-conducting central portion of an optical fiber composed of material with a higher index of refraction than the cladding.
Core Eccentricity: A measure of the displacement of the center of the core relative to the cladding core.
Coupler: A passive optical device that distributes optical power among two or more ports; commonly called a splitter.
Coupling Loss: The power loss suffered when coupling light from one optical device to another.
dBm: Decibel referenced to a milliwatt. 1mW=0dBm.
Decibel (dB): A unit of measurement of optical power which indicates relative power on a logarithmic scale. The decibel (dB) =10log(P2/P1).
Dispersion: The temporal spreading of a light signal in an optical waveguide caused by light signals traveling at different speeds through a fiber either due to modal or chromatic effects.
Duplex Cable: A two-fiber channel cable.
Duplex Transmission: Transmission in both directions, either one direction at a time (half duplex) or both directions simultaneously (full duplex).
Electromagnetic Interference (EMI): Any electrical or electromagnetic interference that causes undesirable response, degradation, or failure in electronic equipment. Optical fibers neither emit nor receive EMI.
End finish: The quality of the end surface of a fiber prepared for splicing or terminated in a connector.
Equilibrium modal distribution (EMD): The steady modal state of a multimode fiber in which the relative power distribution among modes is independent of fiber length.
Expanded Beam: A type of non-contact interface that terminates optical fibers to the back of a lens. The lens collimates the light beam and increases its diameter.
Ferrule: A precision rigid tube that confines or holds a fiber as part of a connector assembly. The ferrule is usually a part of an assembly called a terminus (termini – plural)
Fiber Optics: Light transmission through optical fibers for communication or signaling.
Fiber Optic Cable: A cable containing one or more optical fibers.
Fusion Splicing: A permanent joint accomplished by application of localized heat sufficient to fuse or melt the ends of the optical fiber forming a continuous single fiber.
Gap Loss: Loss resulting from the end separation of two axially aligned fibers.
Graded-index: An optical fiber whose core has a non-uniform index of refraction. The core is composed of glass whose refractive index decreases from the center axis with a predetermined profile. The purpose is to reduce modal dispersion and thereby increase fiber bandwidth.
Index Of Refraction: An optical characteristic of a material, referencing the speed of light in that material to a vacuum.
Index profile: The refractive index of a fiber as a function of cross section.
Insertion Loss: The attenuation caused by the insertion of an optical component; in other words, a connector or coupler in an optical transmission system.
Jacket: The protective outer coating of the cable.
Jumper Cable: A short single fiber cable with connectors on both ends used for interconnecting other cables or testing.
Key: A feature of a terminus that keep the terminus from rotating when it is installed in a connector. This ensures proper alignment of tuned termini and termini that use an APC polish.
Lateral Displacement Loss
The loss of power that results from lateral displacement from optimum alignment between two fibers or between a fiber and an active device.
Link: A fiber optic cable with connectors attached to a transmitter (source) and receiver (detector). The link may pass analog or digital information.
Link Budget: The minimum transmitted optical power required to maintain a data link between transmitter and receiver – a combination of channel insertion loss and optical power penalties.
Loose Structure Cable: A fiber optic cable structure that allows limited movement of the fiber with respect to the outer jacket and strength member.
Loss: Attenuation of optical signal, normally measured in decibels.
Macrobending: In a fiber, all macroscopic deviations of the fiber’s axis from a straight line, that will cause light to leak out of the fiber, causing signal attenuation.
Microbending: Curvatures of the fiber which involve axial displacements of a few micrometers and spatial wavelengths of a few millimeters. Microbends cause loss of light and consequently increase the attenuation of the fiber.
Modal dispersion: The temporal spreading of a pulse due to multiple light rays traveling different distances and speeds through an optical fiber.
Mode: A term used to describe a light path through a fiber, as in multimode or single-mode.
Multimode fiber: An optical waveguide in which light travels in multiple modes. The core/cladding sizes are measured in microns and the typical multimode fiber cable core/cladding sizes are 50/125, 62.5/125, and 100/140.
Multiplex: The combination of several signals onto a single communications channel.
Multiplexing: The process by which two or more signals are transmitted over a single communications channel – examples include time-division multiplexing and wavelength-division multiplexing.
Numerical aperture (NA): A numerical value that expresses the light gathering ability of a fiber. The imaginary cone which defines the acceptance area for the fiber core to accept rays of light.
Optical fiber: An optical waveguide comprised of a light carrying core and cladding which traps light in the core.
Optical loss test set (OLTS): A measurement instrument for optical loss that includes both a meter and source.
Optical power: The amount of radiant energy per unit time, expressed in linear units of Watts or on a logarithmic scale, in dBm (0 dB = 1 mW) or dB* (0 dB* =1 microwatt).
Optical return loss, back reflection: Light reflected from the cleaved or polished end of a fiber caused by the difference of refractive indices of air and glass. Expressed in dB relative to incident power.
Optical Time Domain Reflectometer (OTDR): A method for characterizing a fiber wherein an optical pulse is transmitted through the fiber and the resulting backscatter and reflections to the input are measured as a function of time. Useful in estimating attenuation coefficient as a function of distance and identifying defects and other localized losses.
PC: Physical Contact, a specific ferrule end finish profile in which a plane that is tangent to the end face at the center of the fiber core is normal to the axis of the fiber.
Pigtail: A short length of fiber attached to a fiber optic component such as a laser or coupler.
Primary Buffer: The plastic coating applied directly to the cladding surface of the fiber during manufacture to preserve the integrity of the surface.
Silica Fiber: An optical fiber having a glass core and plastic cladding.
Power meter, fiber optic: An instrument that measures optical power emanating form the end of a fiber.
Scattering: A property of glass which causes light to deflect from the fiber and contributes to losses.
Secondary Buffer: The protective coating over the optical fiber which is typically 900um in diameter.
Simplex Cable: A term used for a single fiber cable.
Simplex Transmission: Transmission in one direction only.
Singlemode fiber: A fiber with a small core, only a few times the wavelength of light transmitted, that only allows one mode of light to propagate. Commonly used with laser sources for high speed, long distance links.
Splice: A device that provides for a connection between two fibers.
Step-Index: Fiber Optical fiber which has an abrupt ("step") change in its refractive index, due to a core and cladding that have different indices or refraction. Typically used for single mode
Strength Member: The part of a fiber optic cable composed of Kevlar aramid yarn, steel strands, or fiberglass filaments that increase the tensile strength of the cable.
Terminus: Plural for termini
Test cable: A short single fiber jumper cable with connectors on both ends used for testing.
Tight Buffer: Type of cable construction whereby each glass fiber is tightly buffered by a protective thermoplastic coating to a diameter of 900um.
Tight Structure Cable: A fiber optic cable structure that allows no movement of the fiber with respect to the outer jacket.
Total internal reflection: Total reflection of light back into a material when it strikes the interface of a material having a lower index at an angle below the critical angle.
Transmission Loss: Total loss encountered in transmission through a system.
Visual fault locator: A device that couples visible light into the fiber to allow visual tracing and testing of continuity.
Wavelength: A measure of the color of light, usually expressed in nanometers (nm) or microns (*m).
Wavelength division multiplexing (WDM): Simultaneous transmission of several signals in an optical waveguide at differing wavelengths. The process of using multiple wavelengths to carry multiple signals on a single fiber.