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Glossary

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Term Main definition
Diameter mismatch loss
The loss of power that occurs when one fiber transmits to another and the transmitting fiber has a diameter greater than the receiving fiber. It can occur at any type of coupling where the fiber/coupling sizes are mismatched: fiber-to-fiber, fiber-to-device, fiber-to-detector, or sourceto- fiber. Fiber-optic cables and connectors should closely match the size of fiber required by the equipment.
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Diamond Network / Programme

MBNL Network improvement / consolidation programme.

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Dichroic filter
Selectively transmits or reflects light according to selected wavelengths. Also referred to as dichromatic mirror.
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Die Cast

(see Shielded hood)

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Dielectric
Material that does not conduct electricity, such as nonmetallic materials that are used for cable insulation and jackets. Optical fiber cables are made of dielectric material.
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Dielectric constant
The property of a dielectric material that determines the amount of electrostatic energy that can be stored by the material when a given voltage is applied to it. The ratio of the capacitance of a capacitor using the dielectric to the capacitance of an identical capacitor using a vacuum as a dielectric. Also called permittivity.
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Dielectric loss
The power dissipated in a dielectric material as the result of the friction produced by molecular motion when an alternating electric field is applied.
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Dielectric nonmetallic
Refers to materials used within a fiber-optic cable.
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Differential group delay (DGD)
The total difference in travel time between the two polarization states of light traveling through an optical fiber. This time is usually measured in picoseconds, and can differ depending on specific conditions within an optical fiber and the polarization state of the light passing through it.
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Differential modal dispersion (DMD)
The test method used to determine the variation in arrival time of modes in a pulse of light in an optical fiber (typically for multimode fiber).
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Differential mode attenuation
A variation in attenuation in and among modes carried in an optical fiber.
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Diffraction
The deviation of a wave front from the path predicted by geometric optics when a wave front is restricted by an edge or an opening of an object. Diffraction is most significant when the aperture is equal to the order of the wavelength.
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Diffraction grating
An array of fine, parallel, equally spaced reflecting or transmitting lines that mutually enhance the effects of diffraction to concentrate the diffracted light in a few directions determined by the spacing of the lines and by the wavelength of the light.
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Diffuse infrared
It enables the use of infrared optical emissions without the need for line-of-sight between the transmitting and receiving communication entities.
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Digital
Refers to transmission, processing, and storage of data by representing the data in binary values (two states: on or off). On is represented by the number 1 and off by the number 0. Data transmitted or stored with digital technology is expressed as a string of 0s and 1s. Digital signals are used to communicate information between computers or computer-controlled hardware.
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