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93 terms

Photonics Dictionary: D

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digital optical processing

The scanning of photographs or transparencies of images, either by a vidicon camera or flying spot scanner, for the conversion of the images to digital form for storage on magnetic tape.

diode laser -> diode laser

A diode laser is a type of laser that uses a semiconductor diode as the active medium to generate coherent light. Semiconductor diodes are electronic devices that conduct electricity primarily in one...

diode laser

diopter

A unit of optical measurement that expresses the refractive power of a lens or prism. In a lens or lens system, it is the reciprocal of the focal length in meters. For example, if a lens has a focal...

dioptric system

An optical system that uses refraction to form an image.

dioptrics

The branch of optics that deals with the study of the refraction of light, particularly by the transmitting medium of the eye, and by lenses.

direct detection

In a fiber optic transmission system, the conversion of received optical pulses directly to an electrical signal.

direct read after write

A write-once optical disc storage system in which the optical head reads continuously while writing to check the accuracy of the stored data. Data recorded erroneously are then rewritten at another...

direct viewfinder

A viewfinder whose optical system forms a direct image of a subject, as opposed to those systems that use reflectance in the image formation.

dirt hole

A hole filled with dirt such as a polishing abrasive and located in an optical surface. See dig; scratch.

discontinuously reinforced aluminum

A composite derived from aluminum alloy powder and silicon carbide, used as an optical substrate in air- and spacecraft applications. It is as light as aluminum but exhibits greater strength and...

dispersion

Dispersion refers to the phenomenon where different wavelengths (colors) of light travel at different speeds when passing through a medium. This variation in the speed of light for different colors...

dispersion-flattened single-mode fiber

A type of glass optical fiber that provides low pulse dispersion over a broad portion of the light spectrum and as a result can operate at 1300-nm and 1550-nm wavelengths simultaneously.

dispersion-limited operation

Operation in which the dispersion of a pulse limits the distance between repeaters in optical systems. Waveguide and material dispersion can make recognition of a pulse impossible.

dispersion-shifted fiber

A dispersion-shifted fiber (DSF) refers to a type of optical fiber designed to minimize the effects of chromatic dispersion, which is the phenomenon where different wavelengths of light travel at...

dispersive lens -> diverging lens

A diverging lens is a type of lens that causes parallel rays of light to spread out or diverge. It is thinner in the center than at the edges and is commonly referred to as a concave lens. The most...

dissector

In optical character recognition, the mechanical or electronic transducer used to detect the level of illumination present in the various portions of an illuminated sample region.

dissonance

In optics, the production of maxima and minima by the superimposition of two sets of interference fringes from light of two different wavelengths.

distal end

The end of an optical fiber farthest from the source of illumination.

distributed feedback laser

A distributed feedback laser (DFB laser) is a type of semiconductor laser diode designed to emit coherent, narrow-bandwidth light with precise control over the wavelength. It achieves this through a...

divergence

1. In optics, the bending of rays away from each other. 2. In lasers, the spreading of a laser beam with increased distance from the exit aperture. Also called beam spread. 3. In a binocular...

divergent lens -> diverging lens

diverging lens

divided slit scan

A scanning technique in optical character recognition in which an array of photocells is used to scan each character to determine its horizontal and vertical characteristics.

dome -> optical instrument dome

A dome-shaped structure used for some optical instruments in place of a flat window. The transparent material should be of good quality and the hemispherical surfaces should be concentric.

Doppler-spread imaging

An imaging process, similar to specific Doppler mapping radar techniques, that utilizes a laser, an optical imaging system, and a line array of photodetectors and spectrum analyzers. The laser...

DOT

designating optical tracker

dots per inch

A measurement of the spatial resolution of a line or area array in an optical character recognition scanning device.

double refraction

The separation of unpolarized light into two plane-polarized elements by a doubly refracting crystal. When a crystal, such as calcite, is placed between the eye and a pinhole in a card, two bright...

double vision

A defect of a binocular instrument causing two images to be seen separately instead of being fused. It is caused when the optical axes of the two telescopes are not parallel. In minor cases, the eyes...

double-clad fiber

Double-clad fiber (DCF) is a specialized optical fiber that features two concentric cladding layers surrounding a core. The design of double-clad fibers allows them to be used in various...

double-crucible method

A method of fabricating an optical waveguide by melting the core and clad glasses in two suitably joined concentric crucibles and then drawing a fiber from the combined melted glass.

double-window fiber

Optical fiber capable of operating at both a shorter and a longer wavelength.

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...

drive

The hardware for reading (and writing in devices so equipped) an optical mass data storage disk.

dual-window cable -> double-window fiber

Optical fiber capable of operating at both a shorter and a longer wavelength.

duplet lens system

An optical system having two sets of components separated by an air space, while successive lenses in each set are cemented together.

dust extinction

In atmospheric optics, the almost total blocking of light transmission in the atmosphere due to the scattering and absorption of the light by dust particles.

dye-polymer optical disc

A type of erasable data storage device that uses a medium deposited on the disc in two layers, each dyed to absorb a different wavelength of laser light. To record data, the lower layer is heated by...

dynamic fatigue

Stress applied to an optical fiber at a constant rate.

dynamic magneto-optical correlator

An optical correlator incorporating a binary phase-only spatial light modulator made from an iron garnet magneto-optic solid crystal and used in target recognition systems.

dynamic spectroscopy

A spectroscopic technique used to display the intensity of an optical pulse as functions of time and frequency simultaneously.

DYNAMO

dynamic magneto-optical correlator

Photonics DictionaryD