Fiber Optic Glossary

• Damped Least Squares
  An organizational method used in optical design computer programs. The technique produces one number to measure the state of correction...
• Damping
  Continuous conversion of oscillatory energy into heat, relative to time or distance.
• Dark Current
  1. The external current that under specified biasing conditions, flows in a photodetector when there is no incident radiation. 2....
• 
  Dark Fiber
  Unused fiber; fiber that has been installed but is reserved for future use. Carrying no light.
• Dark Mirror
  A multilayer coating that manifests both a low radiant reflectance and radiant absorption.
• Dark Noise
  The noise produced in a photodetector when the photocathode is shielded from all external optical radiation and operating voltages are...
• Dark Operate Mode
  An operate mode in which the sensor is programmed to perform a task such as generating output when the light...
• Data
  The basic elements of information that can be processed or produced by a computer. A representation of facts, concepts, or instructions...
• Data Bus
  A system incorporated into fiber optic data communications characterized by several spatially distributed terminals that are served with the same multiplexed...
• Data Communications
  The movement of encoded information by an electrical transmission system. The transmission of data from one point to another.
• Data Compression
  Storing of digital data with techniques that consume less memory space than basic methods.
• Data Dependent Jitter
  Also called data dependent distortion. Jitter related to the transmitted symbol sequence. DDJ is caused by the limited bandwidth characteristics,...
• Data Frame
  Consists of the Destination Address, Source Address, Length Field, LLC Data, Pad and Check Frame Sequence.
• Data Link
  1. The communication network between nodes of a data transmission system. 2. Transmitter with Modulator, Transmission medium and Demodulator with Receiver...
• Data Link Layer
  Layer 2 of the OSI reference model. This layer takes data from the network layer and passes it on to...
• Data Rate
  1. The maximum number of bits of information which can be transmitted per second, as in a data transmission link; typically...
• Database
  Data stored in computer-readable form, and usually indexed or sorted in a logical order. Users can use the index or logical...
• Datagram
  A particular type of information encapsulation at the network layer of the adapter protocol. No explicit acknowledgment of the information is...
• dBC
  Abbreviation for decibel relative to a carrier level.
• dBμ
  Decibel referenced to a microwatt.
• DBM
  (dBm) A power level compared with 1 milliwatt.
• dBmV
  An abbreviation for decibel millivolt. The level at any point in a system expressed in dB's above or below a 1...
• DBR
  Reflection of light caused by periodic changes in refractive index in a stack of layers of different composition or-equivalently-by a...
• DC
  Abbreviation for direct current. An electric current flowing in one direction only and substantially constant in value.
• DCE
  Abbreviation for data circuit-terminating equipment. 1) In a data station, the equipment that performs functions such as signal conversion and...
• Deblocking
  The removal of optical elements from a block.
• Decentration
  In a single element, any lack of coincidence between the optical and the mechanical axes. In a lens system, any...
• Decentration Aberration
  An aberration occurring in a lens system when one or more of the centers of curvature of the optical surfaces...
• Decibel DB
  A decibel (dB) is a unit of measure of light transmission. It is a logarithmic unit used to compare two...
• Decoding
  Validity checking of received transmission characters and generation of valid data bytes and special codes from those characters.
• Deep
  A concave surface that has too much negative power; i.e., its radius of curvature is too short. This condition can...
• Deeply Depressed Cladding Fiber
  An optical fiber construction, usually a single-mode fiber, that has an outer cladding of approximately the same refractive index as...
• Deflection Circuit
  The circuit that regulates an electron beam's deflection in a cathode-ray tube.
• Deformable Mirror Device
  A spatial light modulator consisting of a metallized polymer film stretched over an array of metal-oxide semiconductor field-effect transistors. Each...
• Degenerate Level
  The condition in which two or more energy states are identical.
• Degradation
  The gradual decrease over time in output signal with constant input light level.
• Delay Distortion
  The distortion created because the different frequencies of a signal have different propagation velocities through a medium.
• Delay Line
  A device used to delay transmission of a signal for functions such as memory loops, sequential processing or built-in testing....
• Delay Time
  The interval between direction of signal to a light-emitting diode and attainment of 10 percent output current in the...
• Delta
  Greatest relative difference in refractive index of core and cladding.
• Demultiplex
  Separation of channels which has been multiplexed in order to share a common transmission medium. With respect to a fiber optic...
• Demultiplexer
  A device that separates a multiplexed signal into its original components; the inverse of a multiplexer.
• Demultiplexing
  Separating two or more signals that have been combined into one signal.
• Demux
  An abbreviation for demultiplexer.
• Dense Wavelength-Division Multiplexing (DWDM)
  Transmitting signals at multiple wavelengths through the same fiber with close spacing. Channel spacing usually is 200GHz or less in...
• Depletion Region
  The region at the PN junction in a semiconductor radiation detector where the potential energies of the two materials create...
• Depolarization Loss
  Losses of optical power in a laser resonator, caused by depolarization in a laser crystal.
• Depolarizer
  A device that obliterates the polarization of a polarized beam by reflecting the beam in all directions at right angles...
• Depth of crimp
  The distance the crimp die indenter penetrates into the wire barrel.
• Destination
  Receiver of data; data sink.
• Destination Address
  That part of a message which indicates for whom the message is intended. Usually a collection of characters or bits. Just...
• Destructive Interference
  Any interference that decreases the desired signal. For example, two light waves that are equal in amplitude and frequency, and...
• Detector
  A photodiode that converts optical signals to electrical signals.
• Detector Noise Limited Operation
  In optical communication systems, operations in which the amplitude of the pulses, as opposed to their width, determines the distance...
• Detem
  A device in which the functions of optical detector and emitter are combined.
• Dextrogyrate
  Able to rotate the plane of polarization of a transmitted, plane-polarized light beam clockwise as seen by a viewer looking...
• DFB
  Feedback arising from reflection distributed through a structure.
• Diameter Divergence Product
  Product of the diameter (at a beam waist) and the divergence angle of a laser beam.
• Diameter Mismatch Loss
  The loss of power at a joint that occurs when the transmitting half has a diameter greater than the diameter of...
• Dichroic Filter
  An optical filter that transmits light selectively according to wavelength.
• Dichroic Mirrors
  Mirrors with significantly different reflection or transmission properties at two different wavelengths.
• Die closure
  The distance between the crimp die indenters when the crimp tool handle is at full closure. This is usually checked...
• Dielectric
  A material such as a glass fiber, which is not metallic and is not conductive.
• Dielectric Coatings
  Thin film coatings made of transparent dielectric materials for laser mirrors or anti-reflection coatings.
• Dielectric Filter
  An optical fiber that selectively transmits one wavelength and reflects others based on interference effects inside the structure. Also called...
• Dielectric Mirrors
  Mirrors consisting of multiple thin layers of different transparent optical materials.
• Dielectric Waveguide
  A waveguide that consists of a dielectric material surrounded by another dielectric material, such as air, glass, or plastic, with...
• Differential Efficiency
  See slope efficiency.
• Differential Gain (DG)
  A type of distortion in a video signal that causes the brightness information to be distorted.
• Differential Mode Attenuation
  The variation in attenuation among the propagating modes of an optical fiber.
• Differential Mode Delay
  A variation in propagation delay caused by differences in group velocity among modes of an optical fiber. Also called multimode...
• Differential Phase (DP)
  A type of distortion in a video signal that causes the color information t be distorted.
• Differential Quantum Efficiency
  In an optical source or detector, the slope of the curve relating output quanta to input quanta.
• Diffraction
  As a wavefront of light passes by an opaque edge or through an opening, secondary weaker wavefronts are generated, apparently originating...
• Diffraction Angle
  The angle that lies between the direction of an incident light beam and any resulting diffracted beam.
• Diffraction Grating
  An array of fine, parallel, equally spaced reflecting or transmitting lines that mutually enhance the effects of diffraction to concentrate the...
• Diffraction Limited Beams
  Beams with a minimum possible beam divergence for a given waist radius.
• Dig
  A cosmetic defect on the surface of an optical element. A dig is nearly equal in terms of its length...
• Digital
  Signals encoded into discrete bits.
• Digital Compression
  An engineering technique for converting a cable television signal into a digital format (in which it can easily be stored...
• Digital Subscriber Line (DSL)
  A service that transmits digital signals to homes at speeds of hundreds of kilobits to tens of metabits per second...
• Diode
  An electronic device that lets current flow in only one direction. Semiconductor diodes used in fiber optics contain a junction...
• Diode Bars
  A type of semiconductor laser containing a one-dimensional array of broad-area emitters.
• Diode Laser
  A semiconductor diode that generates laser light. A current flowing through the diode causes electrons and holes to recombine at...
• Diode Pumped Lasers
  Solid-state lasers which are pumped with laser diodes.
• Diode Stacks
  Arrangements of multiple diode bars delivering very high output power.
• DIP
  Abbreviation for dual in-line package. An electronic package with a rectangular housing and a row of pins along each of...
• Diplexer
  A device that combines two or more types of signals into a single output. Usually incorporates a multiplexer at the...
• Direct Detection
  In a fiber optic transmission system, the conversion of received optical pulses directly to an electrical signal.
• Direct Modulation Laser
  Laser directly modulated by the electrical voltage and current.
• Direct Ray
  A ray that travels from one point to another without being reflected or refracted.
• Directed Energy Weapon
  A weapon employing laser light, x-rays or particle beams as proposed for ballistic missile defense systems.
• Directional Coupler
  A coupler in which light is transmitted differently when it goes in different directions.
• Directivity
  This is also referred to as near end crosstalk. It is the amount of power observed at a given input...
• Directories and Naming
  Facilities for storing location information for different files, databases, tables or objects. Distributed-data technology requires using names for data structures that...
• Dirt Hole
  A hole filled with dirt such as a polishing abrasive and located in an optical surface.
• Disc Laser
  A laser having a rod that is a stacked array of discs immersed in a transparent flowing coolant fluid. In...
• Discriminator
  A circuit incorporated into counter systems that records only pulses that have amplitudes between two preselected limits.
• Dispersion
  The temporal spreading of a pulse in an optical waveguide. May be caused by modal or chromatic effects.
• Dispersion Compensating Module DCM
  This module has the opposite dispersion of the fiber being used in a transmission system. It is used to nullify...

Suggestions?
The Timbercon Fiber Optic Glossary continues to expand and improve. If you have suggestions for improvement, we would enjoy hearing from you. Please contact the webmaster here.