From Wikipedia, the free encyclopedia Single-mode optical fiber
Single-mode optical fiber
In fiber-optic communication, a single-mode optical fiber indices of the core and cladding. The solution of
SMF) monomode fiber,
(SMF (monomode optical fiber single-mode optical Maxwell’s equations for the lowest order bound mode
waveguide, fiber)
waveguide or unimode fiber is an optical fiber designed will permit a pair of orthogonally polarized fields in the
to carry only a single ray of light (mode). Modes are the fiber, and this is the usual case in a communication fiber.
possible solutions of the Helmholtz equation for waves, In step-index guides, single-mode operation occurs
which is obtained by combining Maxwell’s equations and when the normalized frequency, V, is less or equal than
the boundary conditions. These modes define the way 2.405. For power-law profiles, single-mode operation oc-
the wave travels through space, i.e. how the wave is dis- curs for a normalized frequency, V, less than approxi-
tributed in space. Waves can have the same mode but mately
have different frequencies. This is the case in single-
mode fibers, where we can have waves with different fre-
quencies, but of the same mode, which means that they ,
are distributed in space in the same way, and that gives
us a single ray of light. Although the ray travels paral- where g is the profile parameter.
lel to the length of the fiber, it is often called transverse In practice, the orthogonal polarizations may not be
mode since its electromagnetic vibrations occur perpen- associated with degenerate modes.
dicular (transverse) to the length of the fiber. The 2009 Optical fiber connectors are used to join optical fibers
Nobel Prize in Physics was awarded to Charles K. Kao for where a connect/disconnect capability is required. The
his theoretical work on the single-mode optical fiber. [1] basic connector unit is a connector assembly. A connec-
tor assembly consists of an adapter and two connector
Characteristics plugs. Due to the sophisticated polishing and tuning pro-
cedures that may be incorporated into optical connector
Like multi-mode optical fibers, single mode fibers do ex- manufacturing, connectors are generally assembled onto
hibit modal dispersion resulting from multiple spatial optical fiber in a supplier’s manufacturing facility. How-
modes but with narrower modal dispersion. Single mode ever, the assembly and polishing operations involved can
fibers are therefore better at retaining the fidelity of each be performed in the field, for example to make cross-con-
light pulse over longer distances than multi-mode fibers. nect jumpers to size.
For these reasons, single-mode fibers can have a higher Optical fiber connectors are used in telephone com-
bandwidth than multi-mode fibers. Equipment for single pany central offices, at installations on customer premis-
mode fiber is more expensive than equipment for multi- es, and in outside plant applications. Their uses include: -
mode optical fiber, but the single mode fiber itself is usu- Making the connection between equipment and the tele-
ally cheaper in bulk. phone plant in the central office - Connecting fibers to
A typical single mode optical fiber has a core diam- remote and outside plant electronics such as Optical Net-
eter between 8 and 10 µm[2] and a cladding diameter of work Units (ONUs) and Digital Loop Carrier (DLC) sys-
125 µm. There are a number of special types of single- tems - Optical cross connects in the central office - Patch-
mode optical fiber which have been chemically or phys- ing panels in the outside plant to provide architectural
ically altered to give special properties, such as flexibility and to interconnect fibers belonging to dif-
dispersion-shifted fiber and nonzero dispersion-shifted ferent service providers - Connecting couplers, splitters,
fiber. Data rates are limited by polarization mode disper- and Wavelength Division Multiplexers (WDMs) to optical
sion and chromatic dispersion. In 2005, data rates of up to fibers - Connecting optical test equipment to fibers for
10 gigabits per second were possible at distances of over testing and maintenance.
80 km (50 mi) with commercially available transceivers Outside plant applications may involve locating con-
(Xenpak). By using optical amplifiers and dispersion- nectors underground in subsurface enclosures that may
compensating devices, state-of-the-art DWDM optical be subject to flooding, on outdoor walls, or on utility
systems can span thousands of kilometers at 10 Gbit/s, poles. The closures that enclose them may be hermetic,
and several hundred kilometers at 40 Gbit/s. or may be “free-breathing.” Hermetic closures will pre-
The lowest-order bounds mode is ascertained for the vent subjection of the connectors within to temperature
wavelength of interest by solving Maxwell’s equations swings unless they are breached. Free-breathing enclo-
for the boundary conditions imposed by the fiber, which sures will subject them to temperature and humidity
are determined by the core diameter and the refractive swings, and possibly to condensation and biological ac-
1
From Wikipedia, the free encyclopedia Single-mode optical fiber
tion from airborne bacteria, insects, etc. Connectors in Industry requirements for multi-fiber optical connec-
the underground plant may be subjected to groundwater tors are covered in GR-1435, Generic Requirements for
immersion if the closures containing them are breached Multi-Fiber Optical Connectors.
or improperly assembled.
The latest industry requirements for optical fiber
connectors are in Telcordia GR-326, Generic Requirements
See also
for Singlemode Optical Connectors and Jumper Assemblies. • Optical waveguide
A multi-fiber optical connector is designed to simulta- • Multi-mode optical fiber
neously join multiple optical fibers together, with each • Graded-index fiber
optical fiber being joined to only one other optical fiber.
The last part of the definition is included so as not to
confuse multi-fiber connectors with a branching compo-
Notes
nent, such as a coupler. The latter joins one optical fiber [1] Nobel Prize Citation http://nobelprize.org/
to two or more other optical fibers. nobel_prizes/physics/laureates/2009/
Multi-fiber optical connectors are designed to be sciback_phy_09.pdf
used wherever quick and/or repetitive connects and dis- [2] ARC Electronics (2007-10-01). "Fiber Optic Cable
connects of a group of fibers are needed. Applications Tutorial". http://www.arcelect.com/
include telecommunications companies’ Central Offices fibercable.htm.
(COs), installations on customer premises, and Outside
Plant (OSP) applications. References
The multi-fiber optical connector can be used in the
creation of a low-cost switch for use in fiber optical test- • This article incorporates public domain material from
ing. Another application is in cables delivered to a user the General Services Administration document "Federal
with pre-terminated multi-fiber jumpers. This would re- Standard 1037C".
duce the need for field splicing, which could greatly re- • Force, Inc. (2005-14-14). "Types of Optical Fiber".
duce the amount of hours necessary for placing an opti- http://www.fiber-optics.info/articles/fiber-
cal fiber cable in a telecommunications network. This, in types.htm.
turn, would result in savings for the installer of such ca-
ble. External links
• The Basics of Fiber Optic Cable
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Categories:
• Optical fiber
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