- Single-mode optical fiber
fiber-optic communication, a single-mode optical fiber (SMF) is an optical fiberdesigned to carry only a single ray of light (mode). This ray of light often contains a variety of different wavelengths. Although the ray travels parallel to the length of the fiber, it is often called the transverse modesince its electromagnetic vibrations occur perpendicular (transverse) to the length of the fiber. Single-mode optical fibers are also called monomode optical fibers, single-mode optical waveguides, or unimode fibers.
multi-mode optical fibers, single mode fibers do not exhibit modal dispersion resulting from multiple spatial modes. Single mode fibers are therefore better at retaining the fidelity of each light pulse over long distances than are multi-mode fibers. For these reasons, single-mode fibers can have a higher bandwidth than multi-mode fibers. Equipment for single mode fiber is more expensive than equipment for multi-mode optical fiber, but the single mode fiber itself is usually cheaper in bulk.
A typical single mode optical fiber has a core diameter between 8 and 10
µmcite web | title = Fiber Optic Cable Tutorial | url = http://www.arcelect.com/fibercable.htm | author = ARC Electronics | date=2007-10-01 ] and a cladding diameter of 125 µm. There are a number of special types of single-mode optical fiber which have been chemically or physically altered to give special properties, such as dispersion-shifted fiberand nonzero dispersion-shifted fiber. Data rates are limited by polarization mode dispersionand chromatic dispersion. In 2005, data rates of up to 10 gigabits per second were possible at distances of over 60 km with commercially available transceivers ( Xenpak). By using optical amplifiers and dispersion-compensating devices, state-of-the-art DWDMoptical systems can span thousands of kilometers at 10 Gb/s, and several hundred kilometers at 40 Gb/s.
The lowest-order bound mode is ascertained for the wavelength of interest by solving
Maxwell's equationsfor the boundary conditions imposed by the fiber, which are determined by the core diameter 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.
Multi-mode optical fiber
Federal Standard 1037C
* [http://www.arcelect.com/fibercable.htm The Basics of Fiber Optic Cable]
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