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A/B Switch

A device that accepts inputs (optical or electrical) from a primary path and a secondary path to provide automatic or manual switching in the event that the primary path signal is broken or otherwise disrupted. In optical A/B switches, optical signal power thresholds dictate whether the primary path is functioning and signals a switch to the secondary path until optical power is restored to the primary path.

Access Network

Part of the telecommunication network that connects to individual and corporate users.

Active Device

A device that requires a source of energy for its operation and has an output that is a function of present and past input signals. Examples include controlled power supplies, transistors, LEDs, amplifiers, and transmitters.


An adapter is a mechanical device designed to align fiber-optic connectors. It contains the split sleeve, also known as the interconnect sleeve, that holds the two ferrules together. Adapters can help mate or connect a variety of fiber optic cables together.

Adapter Sleeve

A mechanical fixture within an adapter body that aligns and holds two terminated fiber connectors. Adapter sleeve material is typically phosphor bronze, ceramic or polymer.

Add/Drop Multiplexing

A multiplexing function offered in connection with SONET that allows lower level signals to be added or dropped from a high-speed optical carrier in a wire center. The connection to the add/drop multiplexer is via a channel to a central office port at a specific digital speed (DS3, DS1, etc.)

Add-drop multiplexer

A device that drops and/or add one or more optical channels to a signal.


Abbreviation for add-drop multiplexer. A device which adds or drops signals from a communications network.


Abbreviation for asynchronous digital subscriber line. See DSL.


Abbreviation for automatic gain control. A process or means by which gain is automatically adjusted in a specified manner as a function of input level or another specified parameter.

All-Dieletric Cable

Cable made entirely of dielectric (insulating) materials without any metal conductors, armor, or strength members.


Abbreviation for amplitude modulation. A transmission technique in which the amplitude of the carrier varies in accordance with the signal.


A device, inserted within a transmission path, that boosts the strength of an electronic or optical signal. Amplifiers may be placed just after the transmitter (power booster), at a distance between the transmitter and the receiver (in-line amplifier), or just before the receiver (preamplifier).


A signal that varies continuously (e.g., sound wavers). Analog signals have frequency and bandwidth measured in hertz.

Angle of Incidence

The angle between an incident ray and the normal to a reflecting or refracting surface.

Angular Misalignment

Loss at a connector due to fiber end face angles being misaligned.


Abbreviation for American National Standards Institute. An organization that administers and coordinates the U.S. voluntary standardization and conformity assessment system.

APC (Angled Physical Contact)

Abbreviation for angled physical contact. A style of fiber optic connector with a 5°-15° angle on the connector tip for the minimum possible backreflection.

APD (Avalanche Photodiode)

A photodiode that exhibits internal amplification of photocurrent through avalanche multiplication of carriers in the junction region. AR Coating

AR Coating

Antireflection coating. A thin, dielectric or metallic film applied to an optical surface to reduce its reflectance and thereby increase its transmittance.

Aramid Yarn

Yellow fibers that provide cable tensile strength, support, and additional protection for the optical fiber bundle. Kevlar® is a particular brand of aramid yarn.

Armadillo Loopback

A ruggedized fiber optic test adapter designed to loop a signal from the Tx side of a port to the Rx side, simulating a complete connection.


A protective layer, usually metal, wrapped around a cable.

ASE (Amplified Spontaneous Emission)

A background noise mechanism common to all types of erbium-doped fiber amplifiers (EDFAs). It contributes to the noise figure of the EDFA which causes loss of signal-to-noise ratio (SNR).


Abbreviation for application-specific integrated circuit. A custom-designed integrated circuit.


Abbreviation for American Society for Testing and Materials. An organization that provides a forum for the development and publication of voluntary consensus standards for materials, products, systems, and services that serve as a basis for manufacturing, procurement, and regulatory activities.


Data that is transmitted without an associated clock signal. The time spacing between data characters or blocks may be of arbitrary duration. Opposite of synchronous.

ATM (Asynchronous Transfer Mode)

A digital transmission switching format, with cells containing 5 bytes of header information followed by 48 data types. A transmission standard widely used by the telecom industry. A digital transmission switching format with cells containing 5 bytes of header information followed by 48 data bytes. Part of the B-ISDN standard.


Reduction of signal magnitude, or loss, normally measured in decibels. Fiber attenuation is normally measured per unit length in decibels per kilometer. The decrease in signal strength along a fiber optic waveguide caused by absorption and scattering. Attenuation is usually expressed in dB/km.

Attenuation Meter

A device used to measure power loss in fiber optic connectors, cables, or systems.

Attenuation-Limited Operation

The condition in a fiber optic link when operation is limited by the power of the received signal (rather than by bandwidth or distortion).


1) In electrical systems, a usually passive network for reducing the amplitude of a signal without appreciably distorting the waveform.

2) In optical systems, a passive device for reducing the amplitude of a signal without appreciably distorting the waveform.

Category Cable

Twisted pair cabling is a form of wiring in which two conductors are wound together for the purposes of canceling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and crosstalk between neighboring pairs.

CATV Amplifier

A RF power amplifier is a type of electronic amplifier used to convert a low-power radio-frequency signal into a larger signal of significant power, typically for driving the antenna of a transmitter. It is usually optimized to have high efficiency, high P1dB compression, good return loss on the input and output, good gain, and good heat dissipation.

CATV Television

Cable television is a system of distributing television programs to subscribers via radio frequency (RF) signals transmitted through coaxial cables or light pulses through fiber-optic cables. This contrasts with traditional broadcast television (terrestrial television) in which the television signal is transmitted over the air by radio waves and received by a television antenna attached to the television. FM radio programming, high-speed Internet, telephone service, and similar non-television services may also be provided through these cables.

Coaxial Cable

Coaxial cable is an electrical cable consisting of an inner conductor or several uninsulated conductors tightly twisted together, often surrounded by an insulating spacer, surrounded by an outer cylindrical conducting shield (sheath), and usually surrounded by a final insulating layer (jacket). The term coaxial comes from the inner conductor and the outer shield sharing ("co-") the same axis. It is often used as a high-frequency transmission line to carry a high-frequency or broadband signal but may also be used for frequencies as low as audio frequency.


DVB, short for Digital Video Broadcasting, is a suite of internationally accepted open standards for digital television. DVB standards are maintained by the DVB Project, an industry consortium with more than 270 members, and they are published by a Joint Technical Committee (JTC) of European Telecommunications Standards Institute (ETSI), European Committee for Electrotechnical Standardization (CENELEC) and European Broadcasting Union (EBU). The interaction of the DVB sub-standards is described in the DVB Cookbook (DVB-Cook).


EDFA is the abbreviation of erbium-doped fiber amplifier. It is a kind of laser amplifier and it is the most deployed fiber amplifier as its amplification window coincides with the third transmission window of silica-based optical fiber. EDFAs have two commonly-used pumping bands - 980 nm and 1480 nm. The 980 nm band has a higher absorption cross-section and is generally used where low-noise performance is required. The absorption band is relatively narrow and so wavelength stabilized laser sources are typically needed. The 1480 nm band has a lower, but broader, absorption cross-section and is generally used for higher power amplifiers. A combination of 980 nm and 1480 nm pumping is generally utilized in amplifiers.

Ethernet Switch

A switch is a mechanical device used to connect and disconnect a circuit at will. Switches cover a wide range of types, from subminiature up to industrial plant switching megawatts of power on high voltage distribution lines.

Fiber Optic Adaptor

An adaptor is a device used to connect the same or different type connectors, so that a connection may be made between them.

Fiber Optic Cable

An fiber optic cable is a cable containing one or more optical fibers. The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed.

Fiber Optic Closure

Fiber optic closure, include horizontal and vertical type, is a device that is used to splice and jointing for optical fiber cables. They are commonly used in fiber optic communication system.

Fiber Optic Patch Cord

A patch cord is an optical cable, used to connect optical device to another for signal routing. Each end of the cable is attached to a connector, so the cord may be plugged in.

Fiber Optic Pigtail

A pigtail is a cable with one connector. Types of connectors may vary widely, FC, SC, ST, and etc.

Fiber optic splitter

The Fiber Optic Splitter, also named beam splitter, is based on a quartz substrate of integrated waveguide optical power distribution device, the same as coaxial cable transmission system, The optical network system also needs to be an optical signal coupled to the branch distribution, which requires the fiber optic splitter, Is one of the most important passive devices in the optical fiber link, is optical fiber tandem device with many input terminals and many output terminals, Especially applicable to a passive optical network (EPON, GPON, BPON, FTTX, FTTH etc.) to connect the MDF and the terminal equipment and to achieve the branching of the optical signal.

Fiber Optic Termination Box

Fiber optic termination box is used to terminate and connect optical fibers by splices and connectors. The boxes are wall mounted, or installed in the cabinet. They can be used with any type of connectors.


Fiber to the x (FTTX) including FTTH, FTTB, FTTC and FTTN, is a generic term for any network architecture that uses optical fiber to replace all or part of the usual copper local loop used for telecommunications. FTTx is delivered using active Ethernet and various passive optical network (PON) technologies. The passive FTTx approach utilizes equipment that does not require power, and splits or divides the bandwidth between users.


A passive optical network (PON) is a point-to-multipoint, fiber to the premises network architecture in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises, typically 16-128. A PON consists of an optical line terminal (OLT) at the service provider's central office and a number of optical network units (ONUs) near end users. A PON reduces the amount of fiber and central office equipment required compared with point-to-point architectures. A passive optical network is a form of fiber-optic access network.

Downstream signals are broadcast to all premises sharing multiple fibers. Encryption can prevent eavesdropping.

Upstream signals are combined using a multiple access protocol, usually time division multiple access (TDMA). The OLTs "range" the ONUs in order to provide time slot assignments for upstream communication.

Insertion Loss

Insertion loss is the loss of signal power resulting from the insertion of a device in a transmission line or optical fiber and is usually expressed in dBs. The total Optical Power Loss caused by the insertion of a component such as a Splice or Connector in an optical Fiber system. Insertion loss from Absorption Insertion loss from misalignment- either from mismatched Core diameters or from lateral misalignment Insertion loss from an air gap. This occurs from no physical contact. The degree of loss is not as severe, however, with loss typically less than 0.5dB. Insertion loss from contamination. Contamination is the mostcommon cause of insertion loss, such as dirt, scratches, or chips. See Attenuation. See Optical Loss. See Intrinsic Loss. See Gap Loss.


Local Area Network (LAN) is a computer network covering a small geographic area, like a home, office, or group of buildings e.g. a school. The defining characteristics of LANs, in contrast to wide-area networks (WANs), include their much higher data-transfer rates, smaller geographic range, and lack of a need for leased telecommunication lines.


A fiber laser is a laser in which the active gain medium is an optical fiber doped with rare-earth elements such as erbium, ytterbium, neodymium, dysprosium, praseodymium, and thulium. They are related to doped fiber amplifiers, which provide light amplification without lasing. Fiber nonlinearities, such as stimulated Raman scattering or four-wave mixing can also provide gain and thus serve as gain media for a fiber laser.

Optical Attenuator

An optical attenuator is a device used to reduce the power level of an optical signal, either in free space or in an optical fiber. They are commonly used in fiber optic communications. The basic types of optical attenuators are fixed, step-wise variable, and continuously variable.

Optical Coupler

Optical coupler is passive optical device that connects three or more fiber ends, dividing one input between two or more outputs, or combining two or more inputs into one output. Optical coupler is generally deployed in passive optical network.

Optical Receiver

The main component of an optical receiver is a photodetector that converts light into electricity through the photoelectric effect. The photodetector is typically a semiconductor-based photodiode, such as a p-n photodiode, a p-i-n photodiode, or an avalanche photodiode. Metal-semiconductor-metal (MSM) photodetectors are also used due to their suitability for circuit integration in regenerators and wavelength-division multiplexers.

Optical Transmitter

The most commonly-used optical transmitters are semiconductor devices such as light-emitting diodes (LEDs) and laser diodes. The difference between LEDs and laser diodes is that LEDs produce incoherent light, while laser diodes produce coherent light. For use in optical communications, semiconductor optical transmitters must be designed to be compact, efficient, and reliable, while operating in an optimal wavelength range, and directly modulated at high frequencies.


An OTDR injects a series of optical pulses into the fiber under test. It also extracts, from the same end of the fiber, light that is scattered back and reflected back from points in the fiber where the index of refraction changes. (This is equivalent to the way that an electronic TDR measures reflections caused by changes in the impedance of the cable under test.) The intensity of the return pulses is measured and integrated as a function of time, and is plotted as a function of fiber length. An OTDR may be used for estimating the fiber's length and overall attenuation, including splice and mated-connector losses. It may also be used to locate faults, such as breaks.


Plesiochronous Digital Hierarchy (PDH) is a technology used in telecommunications networks to transport large quantities of data over digital transport equipment such as fiber optic and microwave radio systems.

Power Meter

Optical power meter is a device used to measure the energy in an optical signal. A typical device consists of a display unit and a calibrated sensor. Power meters are calibrated using a traceable calibration standard such as an NIST standard.


Router, including broadband and wireless router, is a device whose software and hardware are usually tailored to the tasks of routing and forwarding information. It is used to connect two or more logical subnets, which do not necessarily map one-to-one to the physical interfaces of the router.


Synchronous digital hierarchy (SDH) and synchronous optical network (SONET) based on circuit mode communication, meaning that each connection achieves a constant bit rate and delay refer to a group of fiber-optic transmission rates that can transport digital signals with different capacities.


Telecommunications, also called telecommunication, is the exchange of information over significant distances by electronic means. A complete, single telecommunications circuit consists of two stations, each equipped with a transmitter and a receiver. The transmitter and receiver at any station may be combined into a single device called a transceiver. The medium of signal transmission can be electrical wire or cable (also known as "copper"), optical fiber or electromagnetic fields. The free-space transmission and reception of data by means of electromagntetic fields is called wireless.

The simplest form of telecommunications takes place between two stations. However, it is common for multiple transmitting and receiving stations to exchange data among themselves. Such an arrangement is called a telecommunications network. The Internet is the largest example. On a smaller scale, examples include:

     Corporate and academic wide-area networks (WANs)

     Telephone networks

     Police and fire communications systems

     Taxicab dispatch networks

     Groups of amateur radio operators

Data is conveyed in a telecommunications circuit by means of an electrical signal called the carrier or carrier wave. In order for a carrier to convey information, some form of modulation is required. The mode of modulation can be broadly categorized as either analog or digital. In analog modulation, some aspect of the carrier is varied in a continuous fashion. The oldest form of analog modulation is amplitude modulation (AM), still used in radio broadcasting at some frequencies. Digital modulation actually predates analog modulation; the earliest form was Morse code. During the 1900s, dozens of new forms of modulation were developed and deployed, particularly during the so-called "digital revolution" when the use of computers among ordinary citizens became widespread.

In some contexts, a broadcast network, consisting of a single transmitting station and multiple receive-only stations, is considered a form of telecommunications. Radio and television broadcasting are the most common examples.

Telecommunications and broadcasting worldwide are overseen by the International Telecommunication Union (ITU), an agency of the United Nations (UN) with headquarters in Geneva, Switzerland. Most countries have their own agencies that enforce telecommunications regulations formulated by their governments. In the United States, that agency is the Federal Communications Commission (FCC).


Wavelength-division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths of laser light to carry different signals. This allows for a multiplication in capacity, in addition to enabling bidirectional communications over one fiber.


A wireless LAN( WLAN) is a wireless local area network, which is the linking of two or more computers without using wires. WLAN utilizes spread-spectrum or OFDM modulation technology based on radio waves to enable communication between devices in a limited area, also known as the basic service set. This gives users the mobility to move around within a broad coverage area and still be connected to the network.

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