Index-matching material
Encyclopedia
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 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 end faces of a fiber. These reflections may be as high as -14 dB
(i.e., 14 dB below the level of the incident 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.
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
and fiber optics, an index-matching material is a substance, usually a liquid, cement (adhesive), or gel
Gel
A gel is a solid, jelly-like material that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state...
, which has an index of refraction that closely approximates that of an optical element or fiber
Optical fiber
An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...
, 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 end faces of a fiber. These reflections may be as high as -14 dB
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
(i.e., 14 dB below the level of the incident 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
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
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
Baseband
In telecommunications and signal processing, baseband is an adjective that describes signals and systems whose range of frequencies is measured from close to 0 hertz to a cut-off frequency, a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies...
intensity-modulated video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
signal.