Index-matching material: Difference between revisions

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In [[optics]] and [[fiber optics]], an '''index-matching material''' is a substance, usually a liquid, cement (adhesive), or [[gel]], which has an [[index of refraction]] that closely approximates that of an optical element or [[optical fiber|fiber]], and is used to reduce [[Fresnel reflection]] at the surface of the element.

In fiber optics and [[telecommunications]], an index-matching material may be used in conjunction with pairs of mated connectors, with mechanical splices, or at the ends of fibers. Without the use of an index-matching material, Fresnel reflections will occur at the smooth endfacesend faces of a fiber. These reflections may be as high as -14 [[decibel|dB]] (''i.e.,'' 14 dB below the level of the incident [[SignallingSignaling (telecommunication)|signal]]). When the reflected signal returns to the transmitting end, it is reflected again and returns to the receiving end at a level that is (28 plus twice the fiber loss) dB below the direct signal. The reflected signal will also be delayed by twice the delay time introduced by the fiber. The reflected signal will have no practical effect on [[digital]] systems because of its low level relative to the direct signal; ''i.e.'', it will have no practical effect on the detected signal seen at the decision point of the digital [[optical receiver]]. It may be noticeable in an analog [[baseband]] [[intensity]]-modulated [[video]] signal.

==References==

*[[Federal Standard 1037C]]

==External links==

* [http://www.opticsforkids.org/futurescientists/intermediate/loseglassinglass.html Home experiment based on index matching between glass and paint thinner]

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