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Optical Fibers

ITU Standard Fiber Categories

ITU has categorized single mode fibers to assist suppliers and their customers to meet specific telecom applications. This is under ITU-T Study Group 15. Note: Many fiber properties are actually specified in cable, since that is usually the way fiber is used. Also many fiber properties can change once the fiber has been cabled. Some other statistically based properties are specified on a link basis. ITU standards are developed that sometimes prefers weakening requirements in order to gain broad consensus. They should be viewed as necessary but not sufficient conditions for an optical fiber to enable a particular application. Optical fiber...

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Graded-index Fibers Calculation

This article discusses the wave propagation in graded-index fibers. We will calculate the number of propagable waves and the optimal shape of the refractive index profile. Single Mode Fibers Single mode fibers have a high bandwidth, but due to the generally small fiber parameter V, they either have a small core diameter or a small numerical aperture (N.A.). This makes the coupling between fibers and devices hard. Step-Index Multi-Mode Fibers On the other hand, multi-mode step-index fibers (high V) the eigenmodes have in general different propagation delays, resulting in a pulse broadening calculated below: N1 is the group index in...

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Graded-Index Fibers

The refractive index of the core in graded-index fibers is not constant but decreases gradually from its maximum value n1 at the core center to its minimum value n2 at the core-cladding interface. As shown in the following picture. Most graded-index fibers are designed to have a nearly quadratic decrease and are analyzed by using α-profile, given by where ρ is the radial position, a is the core radius, α is the profile parameter, and Δ represents the relative refractive number difference The parameter α determines the index profile. A step-index profile is approached in the limit of large α. A parabolic-index fiber corresponds to α =...

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