Editing Single-mode optical fiber (section)

==Characteristics==
Unlike [[multi-mode optical fiber]], single-mode fiber does not exhibit [[modal dispersion]]. This is due to the fiber having such a small cross section that only the first mode is transported. Single-mode fibers are therefore better at retaining the fidelity of each light pulse over longer distances than multi-mode fibers. For these reasons, single-mode fibers can have a higher [[Bandwidth (computing)|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. {{Citation needed|date=June 2013}}
[[File:Single mode fiber1.jpg|thumb|Cross section of a single-mode optical fiber patch cord end, taken with a [[fiberscope]]. The outermost circle is the cladding, {{val|125|ul=μm}} in diameter. Debris is visible as a streak on the cross-section, and glows due to the illumination.]]
A typical single-mode optical fiber has a core diameter between 8 and 10.5 [[μm]]<ref name="arcelect">{{cite web | title = Fiber Optic Cable Tutorial | url = http://www.arcelect.com/fibercable.htm | author = ARC Electronics | date = 2007-10-01 | access-date = 2007-07-25 | archive-url = https://web.archive.org/web/20181023040952/https://arcelect.com/fibercable.htm | archive-date = 2018-10-23 | url-status = dead }}</ref> and a cladding diameter of 125&nbsp;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 fiber]] and [[nonzero dispersion-shifted fiber]]. Data rates are limited by [[polarization mode dispersion]] and [[chromatic dispersion]]. {{asof|2005}}, data rates of up to 10 gigabits per second were possible at distances of over {{convert|80|km|0|abbr=on}} with commercially available transceivers ([[Xenpak]]). By using [[optical amplifier]]s and dispersion-compensating devices, state-of-the-art [[DWDM]] optical systems can span thousands of kilometers at 10 Gbit/s, and several hundred kilometers at 40 Gbit/s.{{fact|date=May 2025}}

The lowest-order bounds mode is ascertained for the wavelength of interest by solving [[Maxwell's equations]] for the boundary conditions imposed by the fiber, which are determined by the [[Fiber optics#Principle of operation|core]] diameter and the refractive indices of the core and [[Cladding (fiber optics)|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 [[telecommunications|communication]] fiber.

In step-index guides, single-mode operation occurs when the [[Normalized frequency (fiber optics)|normalized frequency]], ''V'', is less than or equal to 2.405. For [[Power law|power-law]] profiles, single-mode operation occurs for a normalized frequency, ''V'', less than approximately 
:<math>2.405 \sqrt{\frac{g+2}{g}}</math>, 
where ''g'' is the profile parameter.

In practice, the orthogonal polarizations may not be associated with degenerate modes.

OS1 and OS2 are standard single-mode optical fiber used with wavelengths 1310&nbsp;nm and 1550&nbsp;nm (size 9/125&nbsp;μm) with  a maximum attenuation of 1&nbsp;dB/km (OS1) and 0.4&nbsp;dB/km (OS2). OS1 is defined in [[ISO/IEC 11801]],<ref>{{Cite web|url=https://www.iso.org/cms/render/live/en/sites/isoorg/contents/data/standard/03/64/36491.html|title=ISO/IEC 11801:2002|website=ISO}}</ref> and OS2 is defined in ISO/IEC 24702.<ref>{{Cite web|url=https://www.iso.org/cms/render/live/en/sites/isoorg/contents/data/standard/03/88/38812.html|title=ISO/IEC 24702:2006|website=ISO}}</ref>