Mandrel-wrapping meaning

A technique used in multimode fiber (MMF) optics to modify the modal distribution of an optical signal. The wrapping of the MMF around a mandrel results in intentional macrobends and forces modes into higher orders, i.e., away from direct paths through the core and towards the core/cladding interface. If the MMF is fully filled by the source, mandrel wrapping forces the higher-order modes into the cladding, where they are attenuated and lost. If the MMF is underfilled, mandrel wrapping forces some low-order modes into higher-order modes, which redistribution results in modal equilibrium, i.e., equal distribution of power across modes propagating in the core. Mandrel wrapping sometimes is used in jumper cables to intentionally attenuate high-power optical signals in order to prevent damage to optical receivers. Mandrel wrapping also is used in launch cables to achieve modal equilibrium for testing purposes. The diameter of the mandrel and the number of wraps or turns around it are sensitive to the fiber characteristics and the desired modal distribution. See also attenuation, cladding, core, high-order mode, jumper, launch cable, low-order mode, mandrel, MMF, mode, and signal.
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