Optical Path

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optical path

[′äp·tə·kəl ′path]
For a ray of light traveling along a path between two points, the optical path is the integral, over elements of length along the path, of the refractive index. Also known as optical distance; optical length.

Optical Path


The optical path between points A and B of a transparent medium is the distance optical radiation, or light, would travel in a vacuum during the time it takes to move from A to B. Since the speed of light in any medium is less than in a vacuum, the optical path is always greater than the distance actually traversed by the light except in the limiting case of a vacuum, where the optical path is equal to the distance traversed.

The trajectory of a light beam in an optical system consisting of ρ homogeneous media is a broken line. In such a system the optical path is equal to [com] Σp/knk, where lk is the distance traveled by the light in the kth medium (k = 1,2,…,p),nk is the refractive index of the medium, and Σ is the summation sign. For one medium (p = 1), the sum is reduced to a single term ln. In an optically inhomogeneous medium with a smoothly changing n, the trajectory of a beam is a curve. The optical path in such a medium is [com] ∫ABn(l) dl, where dl is an infinitely small element of the beam trajectory.

The concept of optical path plays a major role in optics, especially geometrical and crystal optics, because it makes possible comparison of the paths traversed by light in media in which the rate of propagation differs. The locus of points for which the optical paths, reckoned from the same source, are identical is called the surface of the light wave; light oscillations on this surface are in the same phase.


Landsberg, G. S. Optika, 4th ed. Moscow, 1957. (Obshchii kurs fiziki, vol. 3.)
Tudorovskii, A. I. Teoriia opticheskikh priborov, 2nd ed., part 1. Moscow-Leningrad, 1948.
Born, M, and E. Wolf. Osnovy optiki, 2nd ed. Moscow, 1973. (Translated from English.)

line of position (LOP)

line of position (LOP)
Aircraft flying from O to P obtains a bearing of 045° from A. Its position lies anywhere along the line AB.
In air navigation, a line along which an aircraft is known to be traveling and which may be utilized to establish a position or a fix. This line can be straight or curved, depending on the source of information: a true bearing from a mountain peak will be a straight line of positions; the distance from an object will be a circle of radius equal to that distance. Two or more LOPs are required to establish a fix.
line of sight
i. The straight line between two points. This line is in the plane of the great circle but does not follow the contour of the earth. Radar and some forms of radio waves are capable of being received in the line of sight.
ii. The straight line between the eye of an observer and the observed object or point. Also called an optical path.
iii. In radio, a direct propagation path that does not go below the radio horizon.
References in periodicals archive ?
The subject of the fulfillment is the delivery and installation of optical paths, the implementation of the passenger information system at selected passenger transport stops and the equipment of CSAD MHD Kladno vehicles, the supply and connection of electric and related technologies for electronic information signs and electronic information boards located at public transport stops in Kladno.
Moreover, Elastic Lambda Aggregation Network improves the reliability of access-metro networking, which will need to accommodate a huge number of subscribers, by using WSSs to switch optical paths flexibly.
In addition, SiP designs often incorporate multiple parallel optical paths with multiple interacting inputs and outputs, all requiring optimization.
As is shown in Figure 4, SY1 and SY2 are optical generators with three states-the controlled optical paths and main optical paths respectively.
Long optical paths and widely spaced reflective elements mean that small relative displacements will cause large displacements and defocusing.
Treating in turn uniform and non-uniform optical paths, he considers such topics as absorption by isolated lines, exact band models, hybrid and cluster models, the adaptation of uniform band models, and exponent-pressure models.
Optical techniques overcome this limitation, but optical paths can be affected by dirt, moisture and other contaminants compromising accuracy and reliability.
Each of the optical paths has a reflective surface at the end so that some of the light traveling down either path is reflected.
A variety of flow cells and probes with different optical paths and materials of construction are available.
Whether the rays add constructively or destructively depends on the difference in their optical paths.
Elitzur and Lev Vaidman of Tel Aviv University in Ramat Aviv, Israel, developed a scheme in which a partially silvered mirror splits a photon so it travels along two separate optical paths before recombining.
CyberSweep[TM] Path Manager gives operators the unique ability to dynamically control pure optical paths for network monitoring.

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