Please be aware that our collection of telecom terms is a compilation from many un-attributed sources. If you are aware of a term missing from this listing and would like it added, please send the term and its definition information via the contact us page.


Absorption: Is a signal loss caused by impurities in the fiber such as metal or hydroxyl ions which convert the light into heat.

Attenuation: Is the power reduction in the light signal as it is transmitted along a cable. It is caused by absorption and scattering.

APC: Abbreviation for Angled Physical Contact. Is a type of connector that has an 8º angle on the end-face that allows tight connections with low back reflection.

Average Power: Is the average level of power over time in a light signal.


Backbone: One of the main connections between interrelated networks and core routers. Backbones are owned by private, educational and government entities and they provide networking facilities to Internet service providers.

Bandwidth: Is the amount of data an optical fiber can carry from a point to another in a specific time period, generally a second.

Buffer: Is a layer that protects optical fibers from physical dangers.


Chromatic dispersion: It is a delay of a light pulse as it travels through the fiber, caused by difference in refractive indices at different wavelengths.

Cladding: is the material used to protect the core of an optical fiber. As it has a refractive index lower than the core, it makes light travels in the core.

Coating:  Is a layer that covers the cladding for protective purposes.

Connector: Is a device that provides a temporary connection between to optical fibers, or a fiber and a source.

Core: It’s the central portion of an optical fiber that transmits light. It has more refractive index than the cladding.

Coupler: is a device used in telecommunication systems that combines or splits power from optical fibers.

Color Codes: Optical fibers are color coded for field recognition during cable installation. In a fiber optic cable buffer tube containing multiple fibers, each fiber needs to be distinguished from others by means of color coding.

TIA/EIA-598 is the most widely used color coding standard in fiber optics industry. This standard defines recommended indentification scheme for individual fibers, buffered fibers, fibers units within a fiber optic cable both for premises and outdoor applications.

The Beyondtech color codes are used for our optical fibers cables and accesories and are expressed in RGB and CMYK.


Dielectric: Non-metallic materials that don’t conduct power.

Dispersion: The spreading of a light signal as it travels through fiber, caused by light signals moving at different speeds due to modal of chromatic effects.


Epoxy: a thermosetting resin used to secure fiber optic terminations, providing lower loss and great reliability.  

Evanescent wave: Light that travels through the cladding instead of the core.


Ferrule: A rigid tube in fiber optic connectors that holds the fiber and aligns it with the socket. Ferrules are made of ceramic, plastic and steel.

Fiber To The Building: Is a fiber optic deployment from an Internet service provider to a point on shared properties such as residential buildings. Connections from that point to individual homes is made with DSL or copper cables.

Fiber To The Curb (FTTC): The installation of fiber optic cables directly to a street cabinet near to homes or businesses. From the cabinet to the customers’ premises the connections are made with copper wires.

Fiber To The Desktop: Is deploying fiber optic cables from a backbone directly to a fiber media converter closer to the user’s desktop.

Fiber To The Home (FTTH): Is the use of fiber optic cords to deliver communications signals from the operator’s central network to individual houses, buildings or residences, changing old copper infrastructures to provide higher bandwidth to costumers.

Fiber To The Node (FTTN): The installation of fiber optic wires to junction box in a neighborhood, to provide services to customers within a radius of a mile. Connections from the node to the customers’ premises are made with DSL cables over telephone or copper wires.

Fiber To The Premises: Is a fiber deployment from an Internet service provider to the end user premises is used in residential applications.


Graded-index fiber: A multimode fiber which core’s refractive index is lower toward the outside and increases toward the center allowing light to travel faster, reducing modal dispersion and increasing bandwidth.


Index matching gel: A fluid that has a refractive index similar to glass used to match materials to the end of fibers in order to reduce loss and back reflection.

Insertion loss: The amount signal loss after the insertion of a coupler, splice or connector into a previously continuous wire.


Jacket: The external protective layer of the fibers, which color depends of the atmosphere where the cable is being installed.


LAN (Local Area Network): A group of interconnected computers that are located in a small area and share the same server.

Laser: Is a device that releases light through stimulated emission of electromagnetic radiation.

Laser Diode (ILD):  A semiconductor device that emits coherent light caused by an electrical current. Generally used in transmitters for single mode fiber.

Light Emitting Diode (LED): a semiconductor device that emits incoherent light stimulated by an electrical current. LEDs are generally used in transmitter for lower bandwidth multimode fiber.


Mechanical splice: A temporary connection between two fibers made with an alignment fixture and index matching gel.

Macrobending: The loss produced by large scaled bending which causes light displacements, exceeding the critical angle of reflection. It generally happens in corner installations.

Microbending: The loss produced by small scale bending which causes light displacements.

Modal dispersion: The temporal spreading of a signal caused by the difference between the velocities of the modes.

Mode: A single electromagnetic field pattern that moves through fiber.

Media converter: is a device that lets you connect different types of media, such as fiber and coax, into the same network, allowing them to pass data from and to each other.

Multimode Fiber: is a fiber that transports different light rays (modes) simultaneously with different reflection angles in the core.


Nanometer: A unit of measure that is one billionth of a meter. And is used to measure the wavelength of light.

Numerical Aperture: The range of light acceptable angles in the core of an optical fiber.


Optical amplifier: A device that intensifies light in an optical fiber without converting it in an electrical signal.

Optical switch: a device that routes an optical signal to its destination, from one or more inputs ports to one or more output ports.


Patch Cord: Is a fiber optic cable that has connectors at both ends and is used to connect an end device to any other telecommunication equipment.

Passive Device: Any device that does not required energy to work (e.g. wires, lenses, electrical resistors or capacitors)

Passive Optical Network (PON): short-haul networks that only use passive components such as couplers, instead of amplifiers or repeaters. They are mostly used in FTTH applications. 

PC: Abbreviation for Physical Contact. Is a style of connector which end-face has a slightly convex design, reducing air gaps and Optical Return Loss.

Photodiode: A semiconductor that converts light to an electrical signal, used in fiber optic receivers.

Photon: A particle of light.

Pigtail: A short optical fiber that has a connector only in one end, as the other end is free to be spliced with another fiber or attached to a laser.

Plastic Optical Fiber: Optical fiber made out of polymer.

Polyethylene Jacket: A resistant protective external layer ideal for outdoor optical fiber installations.

Polyurethane Jacket: An abrasion and low temperature resistant protective external layer mostly used in cables for outdoor applications.

Polyvinyl Chloride (PVC) Jacket: Flame retardant protective external layer, mostly used in cables for indoor applications.


Receiver: A device that converts optic signals to electronic signals.

Refraction: The bending of a beam of light as it passes from a medium with a refractive index to other medium with a different refractive index.

Refractive Index: A property of optical materials that relates to the speed of light in the material versus the speed of light in a vacuum.

Repeater: A transceiver designed to change optical signals to electronic, process those electronic signals and retransmit them as optical. Usually used in long-haul fiber optic links to extend the operating range.


SC: Is an optical fiber connector that has a 2.5mm ferrule and is used in analog CATV applications.

Scattering: Change of direction of light when it strikes with small particles.

SFP (Small Form-Factor Pluggable) Transceiver: is a hot-swappable transceiver designed to work with Small Form-Factor connectors.  

Single mode: A small core optical fiber in which light travels in one path, without bouncing off the edges.

Splice: A fixture that joins two different fibers with permanent or temporary purposes.

ST: Is an optical fiber connector that has a 2.5mm ceramic ferrule and it’s mostly used in o commercial wiring for indoor applications or longline systems.


UPC: Abbreviation for Ultra Physical Contact. Is a style of connector which end-face is polished to have a thin convex design, reducing Optical Return Loss.


Total Internal Reflection: Reflection that happens when light strikes an interface at an angle larger than the critical angle.

Tansceiver: is an instrument that combines a transmitter and a receiver in a single module.

Transmitter: A device that works with a LED o laser and converts electronic signals to optical.


VCSEL (Vertical Cavity Surface-Emitting Laser): a semiconductor laser diode that emits light perpendicularly from the top surface, instead of transmitting it from the edge like conventional lasers.

Visual Fault Locator: A device that emits light into an optical fiber to help locating visual faults such as tight bends, breaks or bad connectors. Some are bright enough to let see the fault through the fiber’s jacket.


Waveguide: a structure that guides electromagnetic waves. Optical fibers are waveguides.

Wavelength: The space between consecutive identical points of the same electromagnetic wave. In fiber optics, wavelengths of light are measured in nanometers.

WDM (Wavelength Division Multiplexing): A method that consist on sending several signals of different wavelength at once, separating them by colors.

Wide Area Network (WAN): a telecommunication network that covers a geographically extensive area.