The loss of light as it passes through a material, generally due to its conversion to other energy forms (typically heat).
n indicator of a material's internal absorptance. If the unit transmission of the material is t, the absorption coefficient (a) is: a= -log e t
The angle over which the core of an optical fiber accepts incoming light; usually measured from the fiber axis. Related to numerical aperture (NA).
advanced custom WDM. An intermolecular substance that serves to hold materials together. Two types are used in the optical industry: one, which must be transparent and colorless, to cement lenses together; and a general-purpose adhesive for bonding prisms and other glass parts to their metallic supports
add/drop multiplexer (capitalize only when indicating a product name).
A device for connecting two parts (as of different diameters) of an apparatus; an attachment for adapting devices for uses not originally intended.
Cable made entirely of dielectric (insulating) materials without any metal conductors, armor, or strength members.
AM amplitude modulation.
A modulation scheme in which the amplitude of a carrier wave is changed by information signals.
A signal that varies continuously (e.g., sound waves). Analog signals have frequency and bandwidth measured in hertz.
Angle of incidence
The angle formed between a ray of light striking a surface and the normal to that surface at the point of incidence
Angle of reflection
The angle formed between the normal to a surface and the reflected ray. This angle lies in a common plane with the angle of incidence and is equal to it.
Angle of refraction
The angle formed between a refracted ray and the normal to the surface. This angle lies in a common plane with the angle of incidence.
A unit of length, 0.1 nm or 10-10 m, often used to measure wavelength but not part of the Sl system of units. Often written Angstrom because the special symbol is not available.
APC APD avalanche photodiode.
angled physical contact A device that uses avalanche multiplication of photocurrent via hole-electrons created by absorbed photons. When the reverse-bias voltage of a device nears breakdown level, the hole-electron pairs collide with ions, create more hole-electron pairs, and achieve a signal gain.
APON APS AR AR coating
ATM based passive optical network. automatic protection switching. antireflection. antireflective coating. A thin layer of material applied to optical parts to reduce reflections.
amplified spontaneous emission. A protective layer, usually metal, wrapped around a cable.
ATM (Asynchronous Transfer Mode)
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 rate of optical power loss with respect to distance along the fiber, usually measured in dB/km at a specific wavelength. The lower the number, the better the fiber 抯 attenuation will be.
An optical element that reduces the intensity of light passing through it (i.e., attenuates it).
Avalanche Photodiode (APD)
A semiconductor photodetector with integral detection and amplification stages. Electrons generated at a p/n junction are accelerated in a region where they free an avalanche of other electrons. APDs can detect faint signals but require higher voltages than other semiconductor electronics.
The average level of power in a signal that varies with time.
AWG Axis Backbone System
array waveguide filter. The center of an optical fiber. A transmission network that carries high-speed telecommunications between regions (e.g., a nationwide long-distance telephone system). Sometimes used to describe the part of a local area network that carries signals between branching points.
Back Reflection ( or Backreflection)
Back reflection refers to the reflected light as a portion of the input power and is the inverse of return loss, so that high return loss equals loss back reflection.
Scattering of light in the direction opposite to that in which it was originally traveling.
The range of frequencies that will pass through a filter or other device. Synonymous with passband
The highest frequency that can be transmitted in analog operation. Also (especially for digital systems), the information-carrying capacity of a system.
Strictly speaking, the number of signal-level transitions per second in digital data. For some common coding schemes, this equals bits per second, but this is not true for more complex coding, where it is often misused. Telecommunication specialists prefer bits per second, which is less ambiguous.
A device that divides incident light into two separate beams.
A relative measurement, denoting a factor of ten change. Rarely used in practice; most measurements are in decibels (0.1 bel).
See bit-error rate.
Operating in both directions. Bidirectional couplers operate the same way regardless of the direction light passes through them. Bidirectional transmission sends signals in both directions, sometimes through the same fiber.
Having a refractive index that differs for light of different polarizations.
See Broadband-Integrated Services Digital Network.
Optical devices with two stable transmission states.
Bit-Error Rate (BER)
The fraction of bits transmitted incorrectly.
BPON bps Broadband
broadband on passive optical network. bits per second. In general, covering a wide range of frequencies. The broadband label is sometimes used for a network that carries many different services or for video transmission.
Broadband-Integrated Services Digital Network (B-ISDN)
A family of standards for digital telecommunications integrating voice, video, data, and other services. Includes ATM and SONET.
Sending the same signal to many different places, like a television broadcasting station. Broadcast transmission can be over optical fibers if the same signal is delivered to many subscribers.
Bundle (of fibers)
A rigid or flexible group of fibers assembled in a unit. Coherent fiber bundles have fibers arranged in the same way on each end and can transmit images.
bandwidth. A circuit that carries telephone signals from a subscriber to another point without the use of local telephone company circuits.
Eight bits of digital data. (Sometimes parity and check bits are included, so one 揵 yte?may include ten bits, but only eight of them are data.)
central or conventional wavelength; approximately 1525 to 1562 nm
An acronym for cable television, derived from Community Antenna TeleVision.
International Consultative Commission on Telephone and Telegraph, an arm of the International Telecommunications Union, which sets standards.
an assembly of optical fiber and other materials providing mechanical and environmental protection of the optical fiber.
code division multiple access. Blocks of data transmitted in Asynchronous Transfer Mode.
A telephone company facility for switching signals among local telephone circuits; connects to subscriber telephones. Also called a switching office.
A centerpiece is the subassembly of an optical device consisting of two Selfoc lenses and an optical element (or elements) that has no focusing function. For example, a WDM centerpiece is constructed so that the first lens is used to collimate the light from the transmitting fiber(s). The collimated light beam then passes through the optical element (typically a wavelength selective filter or beam splitting coating). Finally, a second lens focuses the light passing through onto the reception fiber(s).
The number of channels per unit bandwidth handled by a single optical fiber.
Pulse spreading arising from differences in the speed that light of different wavelengths travels through materials. Measured in picoseconds (of dispersion) per kilometer (of fiber length) per nanometer (of source bandwidth), it is the sum of waveguide and material dispersion.
Circularly polarized light
A light beam whose electric vectors can be broken into two perpendicular elements that have equal amplitudes and that differ in phase by l/4 wavelength.
The layer of glass or other transparent material surrounding the light-carrying core of an optical fiber. It has a lower refractive index than the core, and thus confines light in the core. Coatings may be applied over the cladding.
complementary metal oxide semiconductor.
configurable optical add/drop multiplexer.
Coherent Bundle (of fibers)
Fibers packaged together in a bundle so they retain a fixed arrangement at the two ends and can transmit an image.
In fiber optics, a communication system where the output of a local laser oscillator is mixed with the received signal, and the difference frequency is detected and amplified.
Reducing the number of bits needed to encode a digital signal, typically by eliminating long strings of identical bits or bits that do not change in successive sampling intervals (e.g., video frames).
A device mounted on the end of a fiber-optic cable, light source, receiver, or housing that mates to a similar device to couple light into and out of optical fibers. A connector joins two fiber ends or one fiber end and a light source or detector.
Energy loss encountered at connectors in optical fiber transmission systems. The major contributors are mutual core displacement and fiber axis tilt. It is observed in both permanent splices and optical connectors.
The central part of an optical fiber that carries light.
A 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.
Transfer of light into or out of an optical fiber. (Note that coupling does not require a coupler.)
CPAM Critical Angle
compact passive amplifier module. The angle at which light undergoes total internal reflection.
The measurable leakage of optical energy from one optical conductor to another. Also known as optical coupling
Crystal quartz (used in thin film/AR coating)
The naturally occurring crystalline form of silicon dioxide. It is slightly birefringent and exhibits rotary dispersion of light rays transmitted along the crystal axis, both right-hand and left-hand forms being known. Quartz transmits light from about 1800 A to 4.5 祄 in the infrared. It is very hard and takes a high polish, and has a low thermal expansion coefficient.
CSA CTR CW Cut-Back Measurements
Canadian Standards Association. current transfer ratio. continuous wave, clockwise. Measurement of optical loss made by cutting a fiber to compare loss of a short segment with loss of a longer one.
The longest wavelength at which a single-mode fiber can transmit two modes, or (equivalently) the shortest wavelength at which a single-mode fiber carries only one mode.
Cycles per Second
The frequency of a wave, or number of oscillations it makes per second. One cycle per second equals one hertz.
The noise current generated by a photodiode in the dark.
A fiber-optic transmitter, cable, and receiver that transmit digital data between two points.
decibel. Decibels below 1 mW.
Decibels below 1 礧. dispersion compensation filter/fiber; do not use abbreviation DCF without proper definition, as this would violate trademark
A logarithmic comparison of power levels, defined as ten times the base ten logarithm of the ratio of the two power levels. One-tenth of a bel.
The distortion created because the different frequencies of a signal have different propagation velocities through a medium.
demultiplexer A device that separates a multiplexed signal into its original components; the inverse of a multiplexer.
A device that generates an electrical signal when illuminated by light. The most common in fiber optics are photodiodes.
distributed feedback. A DFB laser uses feedback to cause oscillation of certain modes in the resonator.
DIF Dielectric Digital
dichroic interference filter. Nonconductive. Encoded as a signal in discrete levels, typically binary 1s and 0s.
An electronic device that lets current flow in only one direction. Semiconductor diodes used in fiber optics contain a junction between regions of different doping. They include light emitters (LEDs and laser diodes) and detectors (photodiodes).
A semiconductor diode in which the injection of current carriers produces laser light by amplifying photons produced when holes and electrons recombine at the junction between p- and n-doped regions.
A coupler in which light is transmitted differently when it goes in different directions.
The spreading out of light pulses as they travel in an optical fiber, proportional to length. The two major types are: Modal Dispersion caused by a differential optical path lengths in a mulit-mode fiber, and Chromatic Dispersion caused by differential delay of various wavelengths of light passing through a fiber.
Dispersion Compensation The use of fiber segments with different dispersions to reduce total dispersion. Dispersion-Shifted Fiber Optical fiber designed to have its nominal zero-dispersion point at 1550 nm rather than the 1300 nm in step-index single-mode fiber. A type of single-mode optical fiber designed by Corning Glass Works for use in high-bit-rate, long-distance telecommunications systems. The silica-clad fiber has a segmented core that lowers the slope of the dispersion curve at 1550 nm, the wavelength at which silica-based glasses reach their lowest attenuation. DLC DML DOE digital loop carrier. directly modulated laser. diffractive optical element.
A slow variation over time in the performance of an instrument. In contrast to degradation, the instrument can continue to operate within its performance specifications.
A transmission rate in the North American Digital Telephone hierarchy. Also called T carrier.
DSF DSP DUT Duplex
dispersion shifted fiber. digital signal processing. device under test. A duplex cable contains two fibers; a duplex connector links two pairs of fibers.
dense wavelength division multiplexing/er.
A measure of the ability to see low-level signals that are very close in wavelength to a stronger signal.
ECL EDFA Edge-Emitting Diode
emitter-coupled logic. erbium doped fiber amplifier. An LED that emits light from its edge, producing more directional output than LEDs that emit from their top surface.
edge-emitting light emitting diode. See edge-emitting diode.
Electromagnetic Interference (EMI)
Noise generated when stray electromagnetic fields induce currents in electrical conductors.
Electromagnetic Radiation Waves made up of oscillating electrical and magnetic fields perpendicular to one another and traveling at the speed of light. Can also be viewed as photons or quanta of energy. Electromagnetic radiation includes radio waves, microwaves, infrared, visible light, ultraviolet radiation, X rays, and gamma rays. Elliptically polarized light A light beam whose electric vectors are broken into two elements of unlike amplitudes that are perpendicular to each other and that differ in phase by values other than 1, 3/4, 1/2, 1/4, etc., wavelengths. EMC EMI Endoscope electromagnetic compatibility. See electromagnetic interference. A fiber-optic bundle used for imaging and viewing inside the human body. Epoxy Common name for a variety of adhesives used for lens bonding, fiber optic splicing and other photonics applications. The term is actually a prefix denoting the presence of an epoxide group in a molecule. Erbium-Doped Fiber Amplifier Optical fibers doped with the rare earth element erbium, which can amplify light in the 1550 nm region when pumped by an external light source. Error Deviation from the true or nominal value. Different types of errors include offset, linearity, random, retrace, reversal, scale, systematic, and transfer. Evanescent Wave Light guided in the inner part of an optical fiber's cladding rather than in the core.
Loss of a passive coupler above that inherent in dividing light among the output ports.
Modulation of a light source by an external device.
The ratio of the power of a plane-polarized beam that is transmitted through a polarizer placed in its path with its polarizing axis parallel to the beam's plane, as compared with the transmitted power when the polarizer's axis is perpendicular to the beam's plane.
Splice losses arising from the splicing process itself.
A pattern displayed when an oscilloscope is driven by a receiver output and triggered by the signal source that drove the transmitter. The more open the eye, the better the signal quality.
A rigid array of short fibers fused together to direct light onto a traffic signal or imaging tube.
In a birefringent material, the index of refraction varies with the direction of vibration of a light wave. That direction having a low refractive index is the fast axis; at right angles to it is the slow axis, with a high index of refraction.
FBG FDDI FDM FDMA Ferrule
fiber Bragg grating. See Fiber Distributed Data Interface. frequency division multiplexing/er. frequency division multiple access. A tube within a connector with a central hole that contains and aligns a fiber.
far end cross talk.
Thin filaments of glass capable of carrying information in the form of light. The solid piece of glass consists of a core (inner region), cladding (outer region), and an acrylic coating.
Fiber Distributed Data Interface (FDDI) Fiber Grating
A standard for a 100 Mbit/s fiber-optic local area network. An optical fiber in which the refractive index of the core varies periodically along its length, scattering light in a way similar to a diffraction grating, and transmitting or reflecting certain wavelengths selectively. Fiber gratings are sensitive to outside effects, making them good sensors.
light transmission through optical fibers for communications or signalling.
A coil of optical fiber that can detect rotation about its axis.
Fiber To The Curb (FTTC)
Fiber-optic service to a node that is connected by wires to several nearby homes, typically on a block.
With respect to radiation, a device used to attenuate particular wavelengths or frequencies while passing others with relatively no change.
FITL Fluoride Glasses
Fiber In The Loop. Materials that have the amorphous structure of glass but are made of fluoride compounds (e.g., zirconium fluoride) rather than oxide compounds (e.g., silica).
frequency modulation. A modulation scheme in which frequency of a carrier is changed according to information signals.
Fiber-Optic Guided Missile.
Fiber optics test procedures as defined as TIA/EIA publication series 455. These test procedures are recognized standards and used across the optical fiber industry.
Fabry-Perot four photon mixing. The non linear polarisation in optical fibers generates new optical waves at pusations. These new optical waves copropogate with the initial wave and grow at their expense. In quantum mechanical terms, four photon mixing can be viewed as the anhilation of photons from some waves and the creation of new photons at different frequencies so that the total energy and momentum are conserved during the process. In multiwavelength systems with equally spaced channels the additional waves appear as undesireable crosstalk. Significant FPM occurs only if the phase matching condition is satisfied. Because of dispersion in single-mode fibers, the four-wave mixing efficiency decreases with increasing channel spacing. Consequently, FPM sets a limit on the minimum channel spacing in order to keep the crosstalk below a certain level.
Blocks of data transmitted in the SONET format; also individual images shown in sequence on video screens. (One video frame has the full number of lines for a standard format.)
Frequency Division Multiplexing
Combining analog signals by assigning each a different carrier frequency and merging them in a single signal with a broad range of frequencies.
Free Spectral Range.
A bundle of fibers fused together so they maintain a fixed alignment with respect to each other in a rigid rod.
A splice accomplished by the application of localized heat sufficient to fuse or melt the ends of two lengths of optical fiber, forming a continuous single fiber.
FWHM FWM GaAlAs GaAs Gain
full width at half maximum. four-wave mixing. See Gallium aluminum arsenide. See Gallium arsenide. Also known as amplification. 1. The increase in a signal that is transmitted from one point to another through an amplifier. A material that exhibits gain rather than absorption, at certain frequencies for a signal passing through it, is known as an active medium. 2. With reference to optical properties, the term may be defined in two ways: a. the relative brightness of a rear projection screen as compared with a perfect Lambertian reflective diffuser; b. the ratio of brightness in foot lamberts to incident illumination in foot-candles. 3. In a photo detector, the ratio of electron-hole pairs generated per incident photon.
Gallium Aluminum Arsenide (GaAlAs) Gallium Arsenide (GaAs)
A semiconductor compound used in LEDs, diode lasers, and certain detectors. A semiconductor compound used in LEDs, diode lasers, detectors, and electronic components.
The optical power loss caused by a space between axially aligned fibers.
A fiber in which the refractive index changes gradually with distance from the fiber axis, rather than abruptly at the core-cladding interface.
Graded-Index Fiber Lens
A short segment of graded-index fiber that focuses light passing along it.
gradient index, graded index. GRIN lens, graded-index lens. Note: Selfoc is a trademark of Nippon Sheet Glass Co., Ltd. referring to their line of graded-index lens products - it is not a general term for graded-index lenses.
Hard-Clad Silica Fiber
A fiber with a hard plastic cladding surrounding a step-index silica core. (Other plastic-clad silica fibers have a soft plastic cladding.)
Full width of the band pass at half-power or half of peak transmittance points, specified in either wavelength units or in percent of center wavelength.
High-definition (or high-resolution) television; television with about double the resolution of present systems.
The central facility where signals are combined and distributed in a cable television system.
A series of flanges or other conducting surfaces, usually metal, attached to an electronic device to transmit and dissipate heat that might damage internal circuitry.
Frequency in cycles per second. A set of transmission speeds arranged to multiplex successively higher numbers of circuits.
high performance physical contact. high reflection, high resolution.
Increases in fiber attenuation that occur when hydrogen diffuses into the glass matrix and absorbs some light.
Index of Refraction
The ratio of the speed of light in a vacuum to the speed of light in a material, usually abbreviated n.
A gel or fluid with refractive index close to glass that reduces refractive-index discontinuities that can cause reflective losses.
Indium Gallium Arsenide (InGaAs) Indium Gallium Arsenide Phosphide (InGaAsP) Infrared
A semiconductor material used in lasers, LEDs, and detectors. A semiconductor material used in lasers, LEDs, and detectors. Wavelengths longer than 700 nm and shorter than about 1 mm. We cannot see infrared radiation but can feel it as heat. Transmission of glass optical fibers is best in the infrared at wavelengths of 1100-1600 nm.
Colloquially, optical fibers with best transmission at wavelengths of 2mm or longer, made of materials other than silica glass.
See Indium gallium arsenide. See Indiurn gallium arsenide phosphide. Properties depend on composition.
Another name for a semiconductor or diode laser.
The loss of power that results from inserting a component, such as a connector or splice, into previously continuous path.
Optical devices that perform two or more functions and are integrated on a single substrate; analogous to integrated electronic circuits.
Integrated Services Digital Network (ISDN)
A digital standard calling for 144 kbit/s transmission, corresponding to two 64 kbit/s digital voice channels and one 16 kbit/s data channel.
Intensity Interferometric Sensors
Power per unit solid angle. Fiber-optic sensors that rely on interferometric detection.
Splice losses arising from differences in the fibers being spliced.
Power per unit area. A device intended to prevent return reflections along a transmission path.
ISO ISDN Jacket
International Organization for Standardization. See Integrated Services Digital Network. The outer material that surrounds and protects the buffered and unbuffered fibers in an optical cable.
A device to hold and locate a work piece as it guides, controls or limits a cutting tool.
Junction Laser KB Kevlar
A semiconductor diode laser. kilobyte. A strong synthetic material used in cable strength members; Kevlar is a trademark of Dupont (E.I. du Pont de Nemours and Company).
long wavelength; approximately 1575 to 1610 nm.
LAN LD LEC LED Large-Core Fiber
See local area network. laser diode. local exchange carrier, liquid exchange crystal. See light-emitting diode Usually, a fiber with a core of 200 mm or more.
From Light Amplification by Stimulated Emission of Radiation, one of the wide range of devices that generates light by that principle. Laser light is directional, covers a narrow range of wavelengths, and is more coherent than ordinary light. Semiconductor diode lasers are the standard light sources in fiber-optic systems.
A device used in a transmitter to convert information from electrical to optical form.
A transparent optical component consisting of one or more pieces of optical glass with surfaces so curved (usually spherical) that they serve to converge or diverge the transmitted rays from an object, thus forming a real or virtual image of that object.
Strictly speaking, electromagnetic radiation visible to the human eye at 400 to 700 nm. Commonly, the term is applied to electromagnetic radiation with properties similar to visible light, including the invisible near-infrared radiation in most fiber-optic communication systems.
Light Piping Light-Emitting Diode (LED)
Use of optical fibers to illuminate. A semiconductor diode that emits incoherent light at the junction between p- and n- doped materials.
An optical fiber or fiber bundle. As an adjective, a synonym for optical; often (but not always) meaning fiber-optic.
A telecommunications circuit or channel between any two telecommunication devices, not including the equipment connector.
The relationship between two variables such that a change in the first quantity is directly proportional to a change in the second quantity.
Liquid crystal display (LCD)
An alphanumeric display formed by a layer of liquid crystal material sandwiched between two sheets of glass; a transparent conductive coating on the glass is etched to form the character segments. An applied voltage causes the appropriate segments to darken as the molecules in the liquid crystal change their arrangement.
Local Area Network (LAN) A network that transmits data among many nodes in a small area (e.g., a building or campus). Local Loop The part of the telephone network extending from the central (switching) office to the subscriber. Longitudinal Modes Oscillation modes of a laser along the length of its cavity. Each longitudinal mode contains only a very narrow range of wavelengths, so a laser emitting a single longitudinal mode has a very narrow bandwidth. Distinct from transverse modes. Loose Tube A protective tube loosely surrounding a cabled fiber, often filled with gel. Loss Attenuation of optical signal, normally measured in decibels. Loss Budget LPG Margin An accounting of overall attenuation in a system. long period grating. Allowance for attenuation in addition to that explicitly accounted for in system design. Mass Splicing Material Dispersion Simultaneous splicing of many fibers in a cable. Pulse dispersion caused by variation of a material 抯 refractive index with wavelength. MB Mbit/s Mechanical Splice megabyte. Megabits (million bits) per second. A splice in which fibers are joined mechanically (e.g., glued or crimped in place) but not fused together.
A unit of frequency that is equal to one million cycles per second.
mode field diameter. A measure of the spot size or beam width of light in a single-mode fiber. MFD is a function of wavelength, core diamater, and fiber refractive index profile.
One millionth of a meter. Typically used to express the geometric dimension of fibers.
Tiny bends in a fiber that allow light to leak out and increase loss.
Micrometer MiniVOAT Modal Dispersion
One-millionth of a meter, abbreviated 祄. mini variable optical attenuator. Dispersion arising from differences in the times that different modes take to travel through multimode fiber.
An electromagnetic field distribution that satisfies theoretical requirements for propagation in a waveguide or oscillation in a cavity (e.g., a laser). Light has modes in a fiber or laser.
Mode Field Diameter
The diameter of the one mode of light propagating in a single-mode fiber, typically slightly larger than core diameter.
A device that removes high-order modes in a multimode fiber to give standard measurement conditions.
In general, changes in one wave train caused by another wave, such as amplitude or frequency modulation in radio. In optics the term generally is used as a synonym for contrast, particularly when applied to a series of parallel lines and spaces imaged by a lens.
MM MTBF Multimode
See multimode. mean time between failure. Transmits or emits multiple modes of light.
an optical fiber in which light travels in multiple modes. Typical core/cladding sizes (measured in micrometers) are 50/125 and 62.5/125.
Combining two or more signals into a single bit of stream that can be individually recovered.
multiplex/er. A device that combines two or more signals into a single output.
A semiconductor doped to have an excess of electrons as current carriers.
NA NBWDM Nanometer
See numerical aperture. narrow band wavelength division multiplexing/er. A unit of length, 10-9 m. It is part of the Sl system and has largely replaced the non-SI Angstrom (0.1 nm) in technical literature.
Nanosecond National Electrical Code
One-billionth of a second, 10-9 second. A wiring code that specifies safety standards for copper and fiber-optic cable.
Nd:YAG NEXT Near Infrared
neodymium:yttrium aluminum garnet. near end cross talk. The part of the infrared near the visible spectrum, typically 700 to 1500 or 2000 nm; it is not rigidly defined.
A system of cables or other connections that links many terminals, all of which can communicate with each other through the system.
Nm No Return to Zero (NRZ)
See namometer. A digital code in which the signal level is low for a 0 bit and high for a 1 bit, and does not return to 0 between successive 1 bits.
The unwanted and unpredictable fluctuations that distort a received signal and hence tend to obscure the desired message. Noise disturbances, which may be generated in the devices of a communications system or which may enter the system from the outside, limit the range of the system and place requirements on the signal power necessary to ensure good reception.
Noise Equivalent Power (NEP)
The optical input power to a detector needed to generate an electrical signal equal to the inherent electrical noise.
Normal (angle) NRZ NTSC
Perpendicular to a surface. See no return to zero. The analog video broadcast standard used in North America, set by the National Television System Committee.
Numerical Aperture (NA)
The sine of half the angle over which a fiber can accept light. Strictly speaking, this is multiplied by the refractive index of the medium containing the light, but that equals 1 for air, the normal medium from which NA is measured.
OC-12, STM-4 >OC-3, STM-1 OC-48, STM-16 OADM OCX OC-x
622.08 Mbit/s 155.52 Mbit/s 248.32 Mbit/s or 2.5 Gbit/s optical add/drop multiplexer. optical crossconnect. Optical Carrier, a carrier rate specified in the SONET standard.
A device that amplifies an input optical signal without converting it into electrical form. The best developed are optical fibers doped with the rare earth erbium.
Optical Loss Test Set
An optical power meter and light source calibrated for use together.
Optical Time-Domain Reflectometer (OTDR)
An instrument that measures transmission characteristics by sending a short pulse of light down a fiber and observing backscattered light.
Technically, any structure that can guide light. Sometimes used as a synonym for optical fiber, it can also apply to planar light waveguides.
OS OSA OSC OTDM O/E p Region
optical switch. optical spectrum analyser. optical supervisory channel. optical time division multiplexing/er. optical to electrical. Part of a semiconductor doped with electron acceptors in which holes (vacancies in the valence electron level) are the dominant current carriers.
The fraction of the surface area of a fiber-optic bundle that is fiber core.
PC PCB PCM PCSFiber PD PDL Phase Photodetector Photodiode
physical contact. printed circuit board. pulse code modulation, phase-conjugate mirror. See plastic-clad silica fiber. photodiode, or perfect diffuser. See Polarization Dependant Loss The position of a wave in its oscillation cycle. A light detector. A diode that can produce an electrical signal proportional to light falling upon it.
A term coined for devices that work using photons, analogous to 揺 lectronic?for devices working with electrons.
Quanta of electromagnetic radiation. Light can be viewed as either a wave or a series of photons.
A short length of optical fiber permanently fixed to a component and used to couple power between it and the transmission fiber.
A semiconductor detector with an intrinsic (i) region separating the p- and n-doped regions. It has fast linear response and is used in fiber-optic receivers.
Plasma (used in thin film/AR coatings) PLC Planar Waveguide
A gas made up of electrons and ions.
planar lightwave circuit. A waveguide fabricated in a flat material such as a thin film.
Plastic-Clad Silica (PCS) Fiber
A step-index multimode fiber in which a silica core is surrounded by a lower-index plastic cladding.
Cable made of fire-retardant material that meets electrical code requirements (UL 910) for low smoke generation and installation in air spaces.
Phase modulation. A modulation scheme in which the phase of a carrier is changed according to information signals.
polarization mode dispersion. The maximum difference in transmission time over all polarization states. PMD causes pulse broadening. PMD is typically found in fiber and devices that split polarizations and recombine them (for example, isolators and circulators).
polarization maintaining fiber. A reference sphere used to represent all possible states of polarization. All linear polarizations will lie on the equator and circular polarizations will correspond with the poles. Named for the French mathematician Henri Poincare.
PON Point-to-point Transmission
passive optical network. Carrying a signal between two end points, without branching to other points.
Alignment of the electric and magnetic fields that make up an electromagnetic wave; normally refers to the electric field. If all light waves have the same alignment, the light is polarized.
Polarization Dependant Loss (PDL)
The difference between the maximum and the minimum insertion loss in the fiber. It is the maximum difference in transmission between one Polarization State and another measured in dB.
Polarization-Maintaining Fiber Precision
Fiber that maintains the polarization of light that enters it. The degree of consistency and agreement among independent measurements of a quantity under the same conditions. The coherence or closeness of one result to all of the measurement results.
A cylindrical rod of specially prepared and purified glass from which an optical fiber is drawn.
A transparent optical element having at least two polished plane faces inclined relative to each other, from which light is reflected or through which light is refracted.
The spreading out of pulses as they travel along an optical fiber.
p/p or pp QAM Quantum Efficiency
peak-to-peak. quadrature amplitude modulation. The fraction of photons that strike a detector which produce electron-hole pairs in the output current.
A semiconductor compound made of four elements (e.g., InGaAsP).
Radiation-Hardened Insensitive to the effects of nuclear radiation, usually for military applications. Radiometer An instrument, distinct from a photometer, to measure power (watts) of electromagnetic radiation.
Straight lines that represent the path taken by light. A device that detects an optical signal and converts it into an electrical form usable by other devices.
Combination of an electron and a hole in a semiconductor that releases energy, sometimes leading to light emission.
The bending of light as it passes between materials of different refractive index.
Ratio of the speed of light in a vacuum to the speed of light in a material; abbreviated n.
Refractive-Index Gradient Regenerator
The change in refractive index with distance from the axis of an optical fiber. A receiver-transmitter pair that detects a weak signal, cleans it up, then sends the regenerated signal through another length of fiber.
The ability of an instrument to perform as specified without premature failure.
The smallest change in quantity that can be detected or provided by an instrument.
A measure of the ability to resolve displayed signal in wavelength. For example, if two signals are 0.5 nm apart in wavelength, the optical spectrum analyzer (OSA) is set at 1 nm Res. BW, the OSA display would show only one combined signal.
Often a receiver-transmitter pair that detects, cleans up, and amplifies a weak signal for retransmission through another length of optical fiber. Sometimes a repeater contains multiple regenerators, one for each fiber in a cable.
The ratio of detector output to input, usually measured in units of amperes per watt (or microamperes per microwatt).
The ratio of input optical power to the optical power, which comes back along the input fiber after reflecting or scattering from an optical component. When two fibers are separated by an air gap, optical energy will be reflected back at the source. Accounts for "backscattering" (Raylaigh scattering - distributed reflection) and is a more inclusive term that describes the function of most of our instruments as they measure both distributed reflection and discrete reflection. To be used when describing anything other than the performance of a connector.
Return to Zero (RZ) A digital coding scheme where signal level is low for a 0 bit and high for a 1 bit during the first half of a bit interval, then in either case returns to zero for the second half of the bit interval. RFTS RI RIN Ribbon Cables remote fiber test system. See refractive index. relative intensity noise. Cables in which many fibers are embedded in a plastic material in parallel, forming a flat ribbon-like structure. Ring Architecture A network scheme in which a transmission line forms a complete ring. If the ring is broken, signals can still be sent among the terminals. Rise Time The time it takes output to rise from low levels to peak value. Typically measured as the time to rise from 10% to 90% of maximum output. RZ S-band Scattering See return to zero. short wavelength; approximately 1440 to 1500 nm. Change of the spatial distribution of a beam of radiation when it interacts with a surface or a heterogeneous medium, in which process there is no change of wavelength of the radiation. SDH Selfoc Lens See Synchronous Digital Hierarchy. A trade name used by the Nippon Sheet Glass Company for a graded-index fiber lens; a segment of graded-index fiber made to serve as a lens.
A laser in which injection of current into a semiconductor diode produces light by recombination of holes and electrons at the junction between p- and n-doped regions.
The degree of response of a measuring device to the change in input quantity.
Sheath Sl Units Signal-to-Noise Ratio Silica Glass
An outer protective layer of a fiber-optic cable. The standard international system of metric units. The ratio of signal to noise, measured in decibels; an indication of signal quality in analog systems. Glass made mostly of silicon dioxide, SiO 2 used in conventional optical fibers.
Single element (e.g., a simplex connector is a single-fiber connector).
Single-Frequency Laser Single Mode
A laser that emits a range of wavelengths small enough to be considered a single frequency. Containing only one mode. When dealing with lasers, beware of ambiguities because of the difference between transverse and longitudinal modes. A laser operating in a single transverse mode typically does not operate in a single longitudinal mode.
an optical wavelength (or fiber) in which the signal travels in one mode. The fiber has a small core diameter.
Single-Polarization Fibers Smart Structures (or Smart Skins) SM SMF SNR SOA
Optical fibers capable of carrying light in only one polarization. Materials containing sensors (fiber-optic or other types) to measure their properties during fabrication and use. See single-mode. See single-mode fiber. signal-to-noise ratio. semiconductor optical amplifier.
An optical pulse that regenerates original shape at certain points as it travels along an optical fiber. Solutions can be combined with optical amplifiers to carry signals very long distances.
SONET Network) SOP
A standard for fiber-optic transmission that is part of
(Synchronous Optical B-ISDN.
state of polarization
Spectrophotometer An instrument for measuring spectral transmittance or reflectance. Spectrum analyzer A scanning device used to cyclically tune through a given frequency range to determine the amplitude-frequency distribution of the signals present, usually by displaying output on a chart or cathode-ray tube. Splice Splitting Ratio A permanent junction between two fiber ends. The ratio of power emerging from two output ports of a coupler. SPM Self phase modulation. The self-induced phase shift experienced by an optical field during its propagation in optical fibers. Sputtering (used in thin film/AR coating) A vacuum deposition method in which the coating material (target) is removed from the surface of the coating source (cathode) by ion bombardment and deposited upon the substrates. SS Stability solid-state. The ability of an instrument to have a response or output that is consistent over time. Star Coupler Step-Index Multimode Fiber Step-Index Single-Mode Fiber Submarine Cable A coupler with more than three ports. A step-index fiber with a core large enough to carry light in multiple modes. A step-index fiber with a small core capable of carrying light in only one mode. A cable designed to be laid underwater.
The part of the telephone network from a central office to individual subscribers.
A cable that carries several video channels between facilities of a cable television company.
An LED that emits light from its flat surface rather than its side. Simple and inexpensive, with emission spread over a wide angle.
A network that routes signals to their destinations by switching circuits.
Synchronous Digital Hierarchy (SDH) Synchronous Optical Network Target (used in thin film/AR coating)
The international version of SONET, the Synchronous Optical Network standard. The biggest difference is in the names of the transmission rates. See SONET.
1.The anode or anticathode of an x-ray tube that emits x-rays when bombarded by electrons. 2. The screen in a television imaging tube that is scanned by an electron beam to determine the charge-density stored on it.
TCP TDL T Carrier
transmission control protocol. tunable diode laser. A system operating at one of the standard levels in the North American Digital Hierarchy.
T Coupler TDM TDMA Ternary
A coupler with three ports. See time-division multiplexing. time division multiple access. A semiconductor compound made of three elements (e.g., GaAlAs).
III-V (3-5) Semiconductor
A semiconductor compound made of one or more elements from the IIIA column of the periodic table (Al, Ga, and In) and one or more elements from the VA column (N, P, As, or Sb). Used in LEDs, diode lasers, and detectors.
total harmonic distortion.
A solid-state semi conducting structure (basically one of the bolo meters) that changes electrical resistance with temperature. Materially, some kind of ceramic composition is used. A thermistor has much higher electrical resistance than metallic bolometers and hence requires much higher voltages to become useful.
A thin layer of a substance deposited on an insulating base in a vacuum by a microelectronic process. Thin films are most commonly used for antireflection, achromatic beam splitters, color filters, narrow pass band filters, semitransparent mirrors, heat control filters, high reflectivity mirrors, polarizers and reflection filters.
TIA Threshold Current
Transimpedance amplifier. The minimum current needed to sustain laser action in a diode laser.
A material tightly surrounding a fiber in a cable, holding it rigidly in place.
Time-Division Multiplexing (TDM)
Digital multiplexing by taking one pulse at a time from separate signals and combining them in a single bit stream.
Total Internal Reflection
Total reflection of light back into a material when it strikes the interface with a material having a lower refractive index at an angle below a critical value.
A characteristic of a calibration, analogous to a pedigree. A traceable calibration is achieved when each instrument and standard, in a hierarchy stretching back to the national standard, was calibrated, and the results were documented. The documentation provides the information that shows every calibration in the chain of calibrations was properly performed.
A combination of transmitter and receiver providing
both output and input interfaces with a device. Transverse Modes Modes across the width of a waveguide (e.g., a fiber or laser). Distinct from longitudinal modes, which are along the length. Tree A network architecture in which transmission routes branch out from a central point. Trunk Line UCA Ultraviolet A transmission line running between telephone universal connector adapter. Electromagnetic waves invisible to the human eye, with wavelengths about 10-400 nm. Unpolarized Behaving as though characterized by a series of waves having planes of vibration oriented at all possible azimuths. V Videoconferencing volt; V AC or V DC Conducting conferences via a video telecommunications system. Videophone Visible Light A telephone-like service with a picture as well as sound. Electromagnetic radiation visible to the human eye at wavelengths of 400-700 nm. VOA Voice Circuit variable optical attenuator. A circuit capable of carrying one telephone conversation or its equivalent; the standard subunit in which telecommunication capacity is counted. The U.S. analog equivalent is 4 kHz. The digital equivalent is 56 kbit/s in North America and 64 kbit/s in Europe. W or mW Waveguide watt or milliwatt. A structure that guides electromagnetic waves along its length. An optical fiber is an optical waveguide. Waveguide Couplers Waveguide Dispersion A coupler in which light is transferred between planar waveguides. The part of chromatic dispersion arising from the different speeds light travels in the core and cladding of a single-mode fiber (i.e., from the fiber 抯 waveguide structure).
The distance an electromagnetic wave travels in the time it takes to oscillate through a complete cycle. Wavelengths of light are measured in nanometers (10-9 m) or micrometers (10-6 m).
Wavelength-Division Multiplexing of signals by transmitting them at different Multiplexing (WDM) WDM WDMA WDM/AC XPM wavelengths through the same fiber. wavelength division multiplexing/er. wavelength division multiple access. WDM/access coupler. Cross phase modulation. When more than one optical wave propogates inside a fiber (e.g., WDM systems), the refractive index seen by a particular wave depends not only on the intensity of that wave, but also on the intensity of the other copropogating waves. This effect is important in coherent systems because coherent detection is a phase sensitive technique and since the phase of the signal in a given channel is shifted randomly through XPM due to power fluctuations in all other channels, the signal-to-noise ratio at the fiber output is reduced. YAG Y Coupler Yttrium aluminum garnet. A variation on the T coupler in which input light is split between two channels (typically planar waveguide) that branch out like a Y from the input.
Wavelength at which net chromatic dispersion of an optical fiber is nominally zero. Arises when waveguide dispersion cancels out material dispersion.