Waveguide-dispersion definitions

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A type of dispersion caused by the different refractive indexes of the core and cladding of an optical fiber. Regardless of the nature of the light source and optical fiber, some light travels in the cladding, as well as the core. Assuming a step-index fiber, the core is of one highly consistent index of refraction (IOR), and the cladding is of another, although sometimes the cladding is of several layers of glass, each with a sharp step in IOR. As the IOR of glass varies as the wavelength varies, with longer wavelengths propagating at higher velocities, as no light pulse has a perfectly narrow spectral width, and as multiple layers of glass of different properties make up the core and cladding, different wavelengths of light propagate at different velocities in the different layers. So, the optical pulse can disperse, or spread, over a distance, which clearly can confuse the light detector at the far end of the fiber.Waveguide dispersion is one factor contributing to chromatic dispersion, both of which are issues in long haul fiber optic transmission systems (FOTS) employing single-mode fiber (SMF) of step-index construction. Multimode graded-index fibers suffer so much from modal dispersion over short distances that material dispersion and chromatic dispersion never become factors. See also chromatic dispersion, dispersion, IOR, SMF, spectral width, step-index fiber, and waveguide dispersion.
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A type of dispersion attributable to the relationship of the physical dimensions of the waveguide and the optical signal, specifically, the diameter of the fiber in cross-section and the length of the optical wave, i.e., the wavelength of the signal. The closer the relationship is to 1:1, the less the waveguide dispersion.As the waveguide increases in size from 50 microns to 62.5 microns, for example, waveguide dispersion increases at a given wavelength, such as 1300 nm.The diameter of the waveguide determines the number of modes, or physical paths, along which the signals are allowed to propagate. As the wavelength decreases from 1300 nm to 850 nm, for example, waveguide dispersion increases in fiber of a given core diameter, such as 62.5 microns.This is due to the increased frequency of the signal and, therefore, the increased opportunity for the signal to interact with the waveguide.This type of waveguide dispersion affects only multimode fiber (MMF) as single-mode fiber (SMF) supports only a single mode. See also MMF, mode, propagate, SMF, and wavelength.
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