The 8-9 micron fiber corresponds to which mode?

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Multiple Choice

The 8-9 micron fiber corresponds to which mode?

A small-core fiber around 8–9 micrometers defines singlemode operation. When the core diameter is this small (and the wavelength is in the telecom region), only the fundamental transverse mode can propagate; higher-order modes cannot form because the core is too tight to support them. This is captured by the V-number criterion (V = 2πa/λ × NA): for a core about 8–9 μm at typical wavelengths, V stays below the single-mode threshold of about 2.405, so only one mode exists. In contrast, multimode fibers have much larger cores (like 50 μm or more) and support many modes; graded-index multimode is a multimode fiber with a refractive-index profile to reduce modal dispersion; plastic fiber typically has even larger cores. So the 8–9 μm core is characteristic of singlemode fiber.

A small-core fiber around 8–9 micrometers defines singlemode operation. When the core diameter is this small (and the wavelength is in the telecom region), only the fundamental transverse mode can propagate; higher-order modes cannot form because the core is too tight to support them. This is captured by the V-number criterion (V = 2πa/λ × NA): for a core about 8–9 μm at typical wavelengths, V stays below the single-mode threshold of about 2.405, so only one mode exists. In contrast, multimode fibers have much larger cores (like 50 μm or more) and support many modes; graded-index multimode is a multimode fiber with a refractive-index profile to reduce modal dispersion; plastic fiber typically has even larger cores. So the 8–9 μm core is characteristic of singlemode fiber.

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