optics, scientific study of light. Physical optics is concerned with the genesis, nature, and properties of light; physiological optics with the part light plays in vision; and geometrical optics with the reflection and refraction of light as encountered in the study of the mirror and the lens.

fiber optics, transmission of digitized messages or information by light pulses along hair-thin glass fibers. Each fiber is surrounded by a cladding having a high index of refractance so that the light is internally reflected and travels the length of the fiber without escaping. Cables of optical fibers can be made smaller and lighter than conventional cables using copper wires or coaxial tubes, yet they can carry much more information, making them useful for transmitting large amounts of data between computers and for carrying data-intensive television pictures or many simultaneous phone conversations. Optical fibers are immune to electromagnetic interference (from lightning, nearby electric motors, and similar sources) and to crosstalk from adjoining wires, and tapping into them is more easily detected. To keep a signal from deteriorating, optical fibers require fewer repeaters over a given distance than does copper wire. In addition to communications, optical fibers are beginning to be used in medical procedures, automobiles, and aircraft and are expected to have many other applications.

Science concerned with the production and propagation of light, the changes it undergoes and produces, and closely related phenomena. Physical optics deals with the nature and properties of light; geometric optics deals with the formation of images by mirrors, lenses, and other devices that use light. Optical data processing involves manipulation of the information content of an image formed by coherent (one-wavelength) optical systems. The study of optics has led to the development of devices such as eyeglasses and contact lenses, telescopes, microscopes, cameras, binoculars, lasers, and optical fibres (see fibre optics).

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Thin transparent fibres of glass or plastic that transmit light through their length by internal reflections, used for transmitting data, voice, and images. Fibre-optic technology has virtually replaced copper wire in long-distance telephone lines and is used to link computers in local area networks, with digitized light pulses replacing the electric current formerly used for the signal. Telecommunication using fibre optics is usually conducted with infrared light. Fibre optics uses light in the visible wavelengths to transmit images directly, in various technical devices such as those developed for endoscopy.

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