Technical Glossary

Reprinted with permission from The 2008 Photonics Dictionary. Copyright 2008, Laurin Publishing, Pittsfield, MA. For more photonics terms, visit www.PhotonicsDictionary.com .

Acceptance Angle: The maximum angle within which light will be accepted by an element, such as a detector or waveguide. In the latter, it is quantified as half the vertex angle of the cone within which optical power may be coupled into bound modes of a fiber. Also called acceptance cone.
 

Aligned Bundle: An assembly of fibers in which the coordinates of each fiber are the same at the two ends of the bundle. Also called coherent bundle.

All Silica Fiber: Also known as all-glass fiber. A fiber with both a silica core and a silica cladding, regardless of the presence of a polymer overcoat or buffer.

Angle of Convergence: An angle formed by the lines of sight of both eyes when focusing on an object. Also, the rate at which a ray approaches the optical axis.

Angle of Deflection: The angle through which a beam is deflected

Angle of Deviation: The angle through which a ray of light is deviated by a refracting or reflecting surface, or a prism; the angle between an incident ray and the refracted or reflected ray.

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.

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When rays or beams strike a surface and are refracted through the surface they obey Snell's law .

where is the index of refraction of the material the incident ray is traveling through, the index of refraction of the material the refracted ray travels through, is the angle of incidence , and is measured between the ray and a line normal to the surface that intersects the surface at the same point as the ray.

Antireflection (AR) Coating: A th in layer of material applied to a glass surface to reduce the amount of reflected energy. Ideally the index of refraction of that material should be equal to the square root of the product of the indices of the material on either side of the coating, while the ideal thickness for a single-layer coating is one-quarter of the wavelength at which reflectance is to be minimized.

Aperture: An opening or hole through which radiation or matter may pass.

Armor: A protective jacket added to an optical fiber to facilitate use in harsh environments. Armor usually consists of steel or aluminum and is placed between the fiber and its outer jacket.

Array (linear, matrix): Mult iples of light-sensitive elements in cameras, detectors or scanning devices.

Attenuation: The decrease in signal strength along a fiber optic waveguide caused by absorption and scattering. Attenuation is usually expressed in dB/km.

Average Power: In a pulsed laser, the pulse energy in joules times the repetition rate in hertz.

Bandwidth-Limited Operation: The condition in a fiber optic link when bandwidth, rather than received optical power, limits performance. This condition is reached when the signal becomes distorted, principally by dispersion , beyond specified limits.

Beam: A bundle of light rays that may be parallel, converging or diverging. 2. A concentrated, unidirectional stream of particles. 3. A concentrated, unidirectional flow of electromagnetic waves.

Beam Converter: A device used to alter the shape of or energy distribution within a beam of radiation

Beam Diameter: Calculated distance between two exactly opposed points on a beam at a chosen fraction of peak power (typically 1/e 2 ). 2. The diameter of a circular aperture that will pass a specified percentage (usually 90) of the total beam energy.

Beam Divergence: Increase in the diameter of an initially collimated beam, as measured in milliradians (mrad) at specified points; i.e., where irradiance is a given fraction (often 1/e 2 ) of peak irradiance.

Beam Expander: A system of optical components designed to increase the diameter of a radiation beam. Usually an afocal system.

Bend Loss: The loss of optical power in an optical fiber because radiation escapes through its bends. The radiation loss caused by fiber bending is proportional to the bend radius

Bend Radius (BR): The radius of curvature that an optical fiber can bend without breaking.

Bending of Light: That action occurring when light passes through an optical interface at other than normal incidence, i.e., refraction. 2. The curving of a path of light that passes close by a massive object, due to the consideration of the general relativity theory plus the identification of a null-geodesic as possible light ray path. With respect to the sun, the theoretical value is 1.75 s.

Biconic Connector: A type of fiber optic connector consisting of two cone-shaped ferrules aligned by a mating sleeve.

Bifurcated Fiber: A branched fiber optic lightguide that performs both receiving and transmitting functions.

Borescope: A device for the internal inspection of hard-to-get-at mechanical parts, such as rifle barrels, sewer pipes, oil wells, or gas mains. The long narrow tube used contains a telescope system with as many relay lenses as necessary. A lamp located in front illuminates the inside of the bore, and the inclusion of a small 45° mirror often permits detailed examination of the tube wall. Some small borescopes and most types of medical endoscopes are now equipped with a fiber optic bundle, for image and/or illumination transfer.

Borosilicate Glass: A strong, heat-resistant glass that contains a minimum of 5 percent boric oxide.

Bragg Grating: A filter that separates light into many colors via Bragg's law. Generally refers to a fiber Bragg grating used in optical communications to separate wavelengths.

Breakout Cable: A type of fiber optic cable containing several fibers, each with its own jacket and all of them surrounded by one common jacket. Breakout cables are designed for convenient installation of fiber optic connectors but tend to have high transmission losses due to bends in the fibers.

Buffer: In fiber optics, a protective material applied as an optical fiber cover that has no optical function. 2. In image processing, a peripheral that stores data between two active processing stages.

Cable: See Fiber Optic Cable .

Chalcogenide Glass: An infrared-transmitting material used in optical fibers for applications in the wavelength region from 2 to 11 µm.

Chromatic Dispersion: The separation of a beam into its various wavelength components. In an optical fiber, dispersion occurs because the differing wavelengths propagate at differing speeds.
 

Cladding: The low-refractive-index material that surrounds the core of an optical fiber to contain core light while protecting against surface contaminant scattering. In all-glass fibers, the cladding is glass. In plastic-clad silica fibers, the plastic cladding also may serve as the coating.

Cladding Glass: In fiber optics, the glass that is found around the glass core of the fiber, and that has a lower refractive index than the fiber.

Cladding Mode: A mode that is confined by virtue of a lower-index medium surrounding the cladding. Cladding modes, in the terminology of mode descriptors, are equivalent to cladding rays in the terminology of geometric optics.

Cladding Mode Stripper: A mechanism or device, especially a coating with a refractive index equal to or slightly greater than that of an optical fiber's cladding, that removes modes propagating through the cladding by allowing them to radiate out of the fiber.

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.

Coefficient of Thermal Expansion: A numerical representation of the rate at which a material will exhibit dimensional changes as a direct result of changes in temperature

Coherent Bundle: See Aligned Bundle .

Collimator: An optical instrument consisting of a well-corrected objective lens with an illuminated slit or reticle at its focal plane. Collimators are used in lens testing to determine focal lengths, and in other metrological applications where a distant object at a known location is required.
 

Combiner: A semitransparent mirror in an optical system that combines two or more output beams into a single coaxial beam.

Connector: Hardware installed on fiber cable ends to provide cable attachment to a transmitter, receiver or other cable. Usually a device that can be connected and disconnected repeatedly.
 

Connector Loss: 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.

Convergent Angle: See Angle of Convergence .

Core: The light-conducting portion of an optical fiber, defined by the region of high refractive index.

Critical Angle: The least angle of incidence at which total internal reflection takes place. The angle of incidence in a denser medium, at an interface between the denser and less dense medium, at which the light is refracted along the interface. When the critical angle is exceeded, the light is totally reflected back into the denser medium. The critical angle varies with the indices of refraction of the two media with the relationship:

where I c is the critical angle; n´ the refractive index of the less dense medium; and n the refractive index of the denser medium.
 

Data Link: The communications network between nodes of a data transmission system

Decibel: The standard unit used to express gain or loss and relative power levels. The decibel (dB) = 10 log (P 2 /P 1 ).

Depth of Focus: The range of image distances that corresponds to the range of object distances covered by the depth of field.
 

Diameter Mismatch Loss: The loss of power at a joint that occurs when the transmitting fiber has a diameter greater than the diameter of the receiving fiber. The loss occurs when coupling light from a source to fiber, from fiber to fiber, or from fiber to detector .

Dielectric: Exhibiting the characteristic of materials that are electrical insulators or in which an electric field can be sustained with a minimum dispersion of power. They exhibit nonlinear properties, such as anisotropy of conductivity or polarization, or saturation phenomena.

Diffraction: As a wavefront of light passes by an opaque edge or through an opening, secondary weaker wavefronts are generated, apparently originating at that edge. These secondary wavefronts will interfere with the primary wavefront as well as with each other to form various diffraction patterns.
 

Diffraction Angle: The angle that lies between the direction of an incident light beam and any resulting diffracted beam.

Diode Laser: See Semiconductor Laser .

Dispersion: The separation of a beam into its various wavelength components. In an optical fiber, dispersion occurs because the differing wavelengths propagate at differing speeds. Also called chromatic dispersion.

Double Clad Fiber: Optical fiber that exhibits wide transmission bandwidth and low bending loss to reduction of guided modes as a result of the high-refractive index external cladding and the tight confinement within the core regions.

Drawing Tower: A system for fabricating optical fiber, consisting of a furnace that heats the materials, a polymer coating stage, a capstan-pulling apparatus that free-draws the preform into a fiber and a drum on which the finished product is wound.

Duplex Cable: A two-fiber cable suitable for duplex transmission

Effective Aperture:  That portion of the aperture that functions to collect energy and deliver it to the final system detector. 2. For an obscured or noncircular aperture, the equivalent nonobscured, circular aperture.

Effective Numerical Aperture (N.A.): The real numerical aperture (NA) of a fiber when the computed NA is not valid because of change in the glass indices during drawing and fusion.

Endoscope: A medical instrument used to view inside the human body by inserting the instrument into a natural or created aperture. The endoscope may use a coherent fiber optic bundle or conventional optics to relay the image to the eye or a television camera. Illumination is provided by a concentric bundle of noncoherent fiber optics.
 

Entrance Slit: A thin slit in an opaque screen by which light enters a spectrometer. The spectrum thus formed is the image of this slit in each wavelength of light present. Since the slit must be narrow enough for good resolution and yet wide enough to allow a suitable amount of radiation to enter, the slit width must be carefully calculated

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.

Excimer Laser: A rare-gas halide or rare-gas metal vapor laser emitting in the ultraviolet (126 to 558 nm) that operates on electronic transitions of molecules, up to that point diatomic, whose ground state is essentially repulsive. Excitation may be by E-beam or electric discharge. Lasing gases include ArCl, ArF, KrCl, KrF, XeCl and XeF.

Exit Angle: The angle between a light ray emerging from an optical system and the optical axis of that system.

Extrinsic Fiber Loss: A type of optical fiber loss resulting from the misalignment of fibers in a splice or connector.

F Number: The expression denoting the ratio of the equivalent focal length of a lens to the diameter of its entrance pupil.

Ferrule: A mechanical fixture, generally a rigid tube, used to confine the stripped end of a fiber or a fiber bundle.

Fiber: See Optical Fiber .

Fiber Axis: The mechanical centerline through the core of an optical fiber.

Fiber Bandwidth: The lowest frequency at which the magnitude of the fiber transfer function decreases to a specified fraction of the zero frequency value. Often, the specified value is one-half the optical power at zero frequency.

Fiber Bundle: A ri gid or flexible, concentrated assembly of glass or plastic fibers used to transmit optical images or light. See Aligned Bundle ; Incoherent Bundle .

Fiber Laser: A laser in which the lasing medium is an optical fiber doped with low levels of rare-earth halides to make it capable of amplifying light. Output is tunable over a broad range and can be broadband. Laser diodes can be used for pumping because of the fiber laser's low threshold power, eliminating the need for cooling.

Fiber Optic Cable: A package for an optical fiber or fibers that may include cladding, buffering, strength members and an outer jacket

Fiber Optic Cable Assembly: A length of fiber optic cable that has been terminated with a connector, pigtail or other component.

Fiber Optic Connector: See Connector .

Fiber Optic Lightguide: A bundle of optical fibers arranged randomly for the purpose of transmitting energy, not an image.

Fiber Optic Probe: A flexible single or multifiber cable having a bundle of glass fibers arranged to transmit an image.

Fiber Optic Ribbon: A coherent optical fiber bundle in which the configuration is flat rather than round, giving an output in a line.

Fiber Optic Taper: A coherent fiber optic bundle made from fibers whose diameter changes gradually along its length. Used to magnify or reduce the input image.

Fiber Optics: The branch of optical technology concerned with the transmission of radiant power through fibers made of transparent materials such as glass, fused silica or plastic. See also Optical Fiber .

Fiber Undercut: The distance between the surface of a ferrule and the surface of a fiber end, provided that the ferrule extends above the fiber end. If the fiber end extends above the ferrule surface, the difference in height is called protrusion.

Fluorescence: The emission of light or other electromagnetic radiation of longer wavelengths by a substance as a result of the absorption of some other radiation of shorter wavelengths, provided the emission continues only as long as the stimulus producing it is maintained. In other words, fluorescence is the luminescence that persists for less than about 10 -8 s after excitation.

Fluoride Glass: Optical glass containing zirconium fluoride that results in special characteristics such as improved transmission.

Fresnel Loss: Reflection losses at the ends of fibers caused by differences in the refractive index between glass and air. The maximum reflection caused by a perpendicular air-glass interface is about 4% or about -17 dB.

Fused Silica: Glass consisting of almost pure silicon dioxide (SiO 2 ). Also called vitreous silica. Frequently used in optical fibers and windows.

Gap Loss: The optical power loss caused by a space between axially aligned fibers.

Graded Index (GI): Descriptive of an optical fiber having a core refractive index that decreases almost parabolically and radially outward toward the cladding. This type of fiber combines high bandwidth with moderately high coupling efficiency. Sometimes called graduated-index.

Hard Clad Silica Fiber: A type of optical fiber in which a silica core is surrounded by a hard polymer or similar material much stronger than the customary cladding material.

Helium Neon (HeNe) Laser: The most commonly used gas laser. The HeNe laser has an emission that is determined by neon atoms by virtue of a resonant transfer of excitation of helium. It operates continuously in the red, infrared and far-infrared regions and emits highly monochromatic radiation.

High-Loss Fiber: Optical fiber in which the attenuation exceeds the normally acceptable level for long-haul or data communications use.

Hydroxyl Ion (OH) Absorption: An optical fiber's absorption of electromagnetic waves due to hydroxyl ions remaining after manufacture of glass.
 

Incoherent Bundle: See Non-Coherent Bundle

Index of Refraction: The ratio of the velocity of light in a vacuum to the velocity of light in a refractive material for a given wavelength.

n = C/V

Where:
c = The speed of light in a vacuum.
v = The speed of the same wavelength in the fiber material.

Index Profile: In an optical waveguide, the refractive index as a function of radius.

Infrared (IR): The invisible portion of the electromagnetic spectrum that lies between about 0.75 and 1000 µm. Radiation in the near-infrared produces a sensation of heat.

Insertion Loss: The total optical power loss caused by the insertion of an optical component such as a connector, splice or coupler into a fiber optic system. See Attenuation .

Jacket: The outer material that surrounds and protects the buffered and unbuffered fibers in an optical cable.

Kevlar: E.I. duPont's trade name for an aramid yarn used as a strength member in the jacket of fiber optic cable.

Large Core Fiber: Optical fiber with a large core, often a step-index fiber; "large'' is at times defined as greater than 85 µm.

Launch Numerical Aperture (N.A.): The numerical aperture of an optical system used to couple (launch) power into an optical waveguide.

Lightguide: See Fiber Optic Lightguide .

Liquid Lightguide: An optical fiber with a hollow core filled with a liquid material that has a higher refractive index than the solid surrounding it.

Loose Tube Buffer: In f iber optic cable, containment of the fiber or fibers within an outer protective tube in which they can move to some extent. The interstices usually are filled with an insulating material. See Tight Buffer .

Low-Loss Fiber: Optical fiber that transmits a greater percentage of input light than does high-loss step-index fiber. Low-loss fiber requires higher purity materials and a more sophisticated drawing process and thus is more expensive; it is used primarily in data communications.

Macrobend Loss: 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 .

Matrix Array: Image sensors in a two-dimensional configuration of rows or columns

Meter: The basic unit of length in the metric system, equal to 39.37 in. or 3.28 ft. 2 . Any device or instrument used for measuring. The term often appears in conjunction with the quantity it measures, as in voltmeter, radiometer, wattmeter, etc.

Microbending: Mechanical stress on a fiber that introduces local discontinuities,  which results in light leaking from the core to the cladding by a process called mode coupling .

Microbend Loss: Transmission loss in optical fibers caused by packaging processes; it is considered a power-coupling effect from the guided modes to the radiation modes.

Micron (?m): A unit of length in the metric system equal to one millionth of a meter (10 -6 m). Also called micrometer.

Millimeter (mm): A unit of metric measurement, equal to 0.001 m. 25.4 mm equal 1 inch.

Mode: The characteristic of the propagation of light through a waveguide that can be designated by a radiation pattern in a plane transverse to the direction of travel. 2 . The state of an oscillating system such as a laser that corresponds to a particular field pattern and one of the possible resonant frequencies of the system.

Mode Field Diameter (MFD): For a single-mode fiber, the measurement of the irradiance at the fiber's end face.

Monocoil Sheathing: A type of tubing used to protect optical fiber cables, consisting of a wire spiral of aluminum, galvanized steel or stainless steel, encased in a polyvinyl chloride or silicon rubber coating.

Multifiber Cable: Fiber optic cable bearing many fibers independently sheathed and capable of carrying unrelated signals. They often surround a central strength member, and can be either loose- or tight-buffered. One standard configuration is a 12-fiber cable.

Multifibers: An array of optically distinct fibers that are fused into one strand. They are used to keep the resolution efficiency of the smaller, single fibers and eliminate difficulty in handling. Their specific usage is determined by their flexibility or rigidity.

Multileg Lightguide: A fiber optic bundle split along its length with the ends of the fibers extending separately to illuminate different points with a single light source.
 

Multimode Optical Fiber: An optical fiber that will allow more than one bound mode to propagate

Multiple Slits: The series of equally spaced parallel slits that make up a scanning aperture in place of a single slit, in the scanning of a repetitive pattern.

N, n: A symbol used to represent the refractive index. It is commonly used with a subscript to represent the wavelength of light.

Nd:YAG: Literally, neodymium:yttrium-aluminum-garnet. A cylindrical rod of yttrium-aluminum-garnet doped with neodymium that is the active medium of the Nd:YAG laser, a highly serviceable solid-state device.

Nanometer (nm): A unit of length in the metric system equal to 10 -9 meters. It formerly was called a millimicron.

Near Infrared (NIR): The shortest wavelengths of the infrared region, nominally 0.75 to 3 µm.

Near Ultraviolet (NUV): The longest wavelengths of the ultraviolet region, nominally 300 to 400 nm.  

Non-Coherent Bundle: A bundle of filaments of optical glass or other transparent materials that transmit only light, not optical images. The arrangement of the individual fibers in the bundle is not sufficiently regular to transmit optical images.

Numerical Aperture (N.A.): The light-gathering ability of a fiber ; the maximum angle to the fiber axis at which light will be accepted and propagated through the fiber. NA = sin a , where a is the acceptance angle . NA also describes the angular spread of light from a central axis, as in exiting a fiber, emitting from a source , or entering a detector .

Optical Cable Assembly: An optical cable that is connector terminated. Generally, an optical cable that has been terminated by a manufacturer and is ready for installation

Optical Combiner: A passive device in which power from several output fibers is distributed among a smaller number (one or more) of input fibers.

Optical Fiber: A thin filament of drawn or extruded glass or plastic having a central core and a cladding of lower index material to promote internal reflection. It may be used singly to transmit pulsed optical signals (communications fiber) or in bundles to transmit light or images.
 

Packing Fraction: The ratio of the active core area of a fiber bundle to the total area at its light-emitting or receiving end.

Patch Cord: A short fiber optic cable with connectors on both ends.

Pigtail: A short length of optical fiber permanently fixed to a component and used to couple power between it and the transmission fiber

Pistoning: Motion of a fiber into and out of the ferrule. This effect is often caused by changes in temperature.

Pixel: Contraction of "picture element." A small element of a scene, the smallest resolvable area, in which an average brightness value is determined and used to represent that portion of the scene. Pixels are arranged in a rectangular array to form a complete image.

Plastic Fiber: Fiber in which both core and cladding are made of plastic.
 

Plastic Cladding: The direct cladding used for fused silica cores to create large numerical aperture fibers and used as overcoats to glass-clad fibers to reduce microbend loss and increase mechanical protection.

Plastic Clad Silica (PCS) Fiber: An optical waveguide having a silica core and a plastic cladding

Polarization Maintaining (PM) Fiber: Single-mode fiber that preserves the plane of polarization of the light launched into it as the beam propagates through its length. Also called polarization-maintaining fiber. The polarization is maintained by introducing asymmetry in the fiber structure, either in its shape (geometrical birefringence) or in its internal stresses (stress-induced birefringence). Because of this asymmetry, the two perpendicularly polarized modes transmitted by the fiber have different propagation constants, reducing cross-coupling between them as compared with conventional single-mode fiber.
 

Polyethylene: A material used to jacket fiber optic cables. It is chemical- and moisture-resistant, but not fire-resistant.

Primary Coating: In a fiber, the material in intimate contact with the cladding surface, applied to preserve the integrity of that surface.

Proof Strength: The minimum amount of strength characteristic of an optical fiber, as determined by proof stressing; expressed in thousands of pounds at tensile strength.

Proof-of-Concept System: An assembly of prototype instruments, equipment and/or software designed to perform all the functions of a concept or idea which, when operated as a system, produce evidence, results or data demonstrating that the underlying scientific, engineering or programming principles and theories are feasible or valid.

Pulsed Laser: A laser that emits energy in a series of short bursts or pulses and that remains inactive between each burst or pulse. The frequency of the pulses is termed the pulse-repetition frequency.

Radiation Hard Fiber: An optical fiber made with core and cladding materials that are designed to recover their intrinsic value of attenuation coefficient, within an acceptable time period, after exposure to a radiation pulse.

Randomized Fiber Optic Cable: Fiber optic cable in which the arrangement of fibers within the bundle has been made random so that output light will be uniformly distributed and not relay the image of the light source at the input end.

Refractive Index: See Index of Refraction .

Refractive Index Profile (RIP): The description of the refractive index along a fiber diameter.

Semiconductor Laser: A light-emitting diode designed to use stimulated emission to form a coherent light output. Synonymous with laser diode and diode laser.
 

Sheathing: See Jacket .

Silica Glass: Glass made mostly of silicon dioxide, SiO 2 , used in conventional optical fibers .

Simplex Cable: A term sometimes used for a single fiber cable

Single Mode Fiber: An optical fiber in which only the lowest order bound mode, which may consist of a pair of orthogonally polarized fields, can propagate at the wavelength of interest.

Slit: An aperture, usually rectangular in shape, with a large length-to-width ratio, and a fixed or adjustable shape through which radiation enters or leaves an instrument. The aperture is generally small as compared to the light source

Solarization: 1. The reduction in the developable density of a photographic emulsion that has been extremely overexposed. 2 . In a laser system, damage resulting from ultraviolet radiation that degrades the lasing crystal and results in increased overall absorption

Splitter: A passive fiber optic coupler that divides light from a single fiber into two or more fiber channels.

Spot-to-Line Converter: An arrangement of optical fibers in a bundle whereby the geometric configuration of the input end differs from that of the output end without changing the total area; for example, a circular bundle can be fanned out to form a rectangular output.

Step Index Fiber: An optical fiber in which the core is of uniform refractive index.

Step Index Profile: A profile of an optical component, usually a fiber, in which the core is of uniform refractive index and the cladding or surrounding optical surface of a different, usually lower, index.

Strength Member: A strand of aramid yarn, steel or fiberglass in an optical cable intended to prevent bending or stretching that would damage the transport medium.

Tight Buffer: Protective material surrounding the cladding of an optical fiber that allows the fiber no play within it.

Total Internal Reflection (TIR): The reflection that occurs within a substance because the angle of incidence of light striking the boundary surface is in excess of the critical angle.

Transmission Loss: The decrease in power that occurs when an optical beam or signal is transmitted through a system.

Ultraviolet (UV): That invisible region of the spectrum just beyond the violet end of the visible region. Wavelengths range from 10nm to 400 nm.

Ultraviolet A: The region of the electromagnetic spectrum from 320 to 400 nm.

Ultraviolet B: The region of the electromagnetic spectrum from 280 to 320 nm.

V-Groove: A V-shaped channel pressed or etched into a substrate, in which, for example, optical fibers may be placed to create an integrated optical component.

Visible (VIS): That term pertaining to the spectral region that can be perceived by the eye.   It extends from about 400 to 750 nm in wavelength.

Watt (W): The power that gives rise to the production of energy at the rate of 1 joule per second.

Wavelength: Electromagnetic energy is transmitted in the form of a sinusoidal wave. The wavelength is the physical distance covered by one cycle of this wave; it is inversely proportional to frequency.

Wavelength Division Multiplexing (WDM): A system that allows the transmission of more than one signal over a common path, by assigning each signal a different frequency band. Also known as frequency division multiplexing.

YAG Laser: A solid-state laser using yttrium aluminum garnet as the matrix material, doped with neodymium (Nd:YAG).