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Chapter 4: Optical fibers and their parameters
Graphic representation of three different types of how the refractive index change in the core of an optical fiber.
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Modes
Graph of the Bessel function.
LP01 mode - the fundamental mode and cut-off
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Numerical aperture
The acceptance cone of a fiber.
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Group refractive index
Refractive index profile for a primary coated fiber including the refractive index for the acrylate. Diagram shows the refractive index and group refractive index versus wavelenght used.
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Dispersion
Intermodal dispersion
Because the different modes follow different paths through the fiber, a light pulse is broadened in proportion to the length of the fiber.
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Intramodal dispersion or chromatic dispersion
The chromatic dispersion is the sum of material- and waveguide dispersion.
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Intramodal dispersion or chromatic dispersion
Pulse broadening through dispersion. In single-mode fiber, intramodal and PMD dispersion occurs; in multi-mode fiber, modal dispersion causes the greatest amount of pulse broadening.
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Polarization mode dispersion, PMD
Pulse broadening through polarization mode dispersion, PMD.
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Nonlinear effects
Because of the three evenly spaced wavelengths (channels) λ1, λ2 and λ3 in this example, some of the newly
generated signals occur at the original wavelengths.
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Multimode fiber with rectangular index profile
Energy path in a step index, multimode fiber. Note that the angle (90 - α) < β.
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Multimode fiber with graded index profile
Ray path in a graded index multimode fiber.
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Standard single-mode fiber with rectangular indexprofile
Energy path in an ideal single-mode fiber.
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Chromatic dispersion in a standard single-mode fiber for the interval 1150 – 1600 nm.
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Dispersion shifted fibers
Standard dispersion shifted fiber
Chromatic dispersion for a dispersion shifted fiber and the refractive index profile.
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Non-zero dispersion shifted fiber
Graph showing the different types of non-zero dispersion fibers compared with a dispersion shifted fiber (red), included is also the refractive index profile.
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Graph showing the chromatic dispersion in a non-zero dispersion shifted fiber and a dispersion shifted fiber. New techniques have opened two new windows, (4 and 5) for WDM. Window 3 is traditionally used for DWDM.
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Fiber with a continuous usable bandspectrum from 1285 nm to 1625 (1700) nm.
Attenuation versus wavelength for the fiber with reduced “water peak”. The fiber may be used continuously for 1285–1625 nm.
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Dispersion-compensating fiber
The dispersion compensating modules can be used at the beginning, in the middle or at the end of a transmission link. They can preferable be combined with en EDFA.
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The evolution of the optical fiber.