Fiber Optic Glossary : D


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  • 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...
  • 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...
  • 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...

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