Single-mode optical fiber
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In telecommunication, a single-mode optical fiber is an optical fiber in which only the lowest order bound mode can propagate at the wavelength of interest. Single mode fibers are best at retaining the fidelity of each light pulse over longer distances and exhibit no dispersion caused by multiple modes; thus more information can be transmitted per unit time giving single mode fibers a higher bandwidth in comparison with multi-mode fibers. A typical single mode optical fiber has a core radius of 5-10 micrometers and a cladding radius of 120 micrometers. Currently, data rates of up to 1 Gigabits/second are possible at distances of 60 km and over 6 Gigabits/second at distances of up to 10km.
The lowest order bound mode is ascertained for the wavelength of interest by solving Maxwell's equations for the boundary conditions imposed by the fiber, e.g., core (spot) size and the refractive indices of the core and cladding.
The solution of Maxwell's equations for the lowest order bound mode will permit a pair of orthogonally polarized fields in the fiber, and this is the usual case in a communication fiber.
In step-index guides, single-mode operation occurs when the normalized frequency, V, is less than 2.405. For power-law profiles, single-mode operation occurs for a normalized frequency, V, less than approximately where g is the profile parameter.
In practice, the orthogonal polarizations may not be associated with degenerate modes.
Single mode fiber is more expensive for both the fiber and equipment than Multi-mode optical fiber.
- Synonyms: monomode optical fiber, single-mode fiber, single-mode optical waveguide, unimode fiber
Source: from Federal Standard 1037C