In
fiber-optic communication
Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of infrared light through an optical fiber. The light is a form of carrier wave that is modulated to carry information. Fiber is pref ...
, a single-mode optical fiber (SMF), also known as fundamental- or mono-mode, is an
optical fiber
An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means to ...
designed to carry only a single
mode
Mode ( la, modus meaning "manner, tune, measure, due measure, rhythm, melody") may refer to:
Arts and entertainment
* '' MO''D''E (magazine)'', a defunct U.S. women's fashion magazine
* ''Mode'' magazine, a fictional fashion magazine which is ...
of light - the
transverse mode
A transverse mode of electromagnetic radiation is a particular electromagnetic field pattern of the radiation in the plane perpendicular (i.e., transverse) to the radiation's propagation direction. Transverse modes occur in radio waves and microwav ...
. Modes are the possible solutions of the
Helmholtz equation
In mathematics, the eigenvalue problem for the Laplace operator is known as the Helmholtz equation. It corresponds to the linear partial differential equation
\nabla^2 f = -k^2 f,
where is the Laplace operator (or "Laplacian"), is the eigenv ...
for waves, which is obtained by combining
Maxwell's equations
Maxwell's equations, or Maxwell–Heaviside equations, are a set of coupled partial differential equations that, together with the Lorentz force law, form the foundation of classical electromagnetism, classical optics, and electric circuits.
...
and the boundary conditions. These modes define the way the wave travels through space, i.e. how the wave is distributed in space. Waves can have the same mode but have different frequencies. This is the case in single-mode fibers, where we can have waves with different frequencies, 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 parallel to the length of the fiber, it is often called
transverse mode
A transverse mode of electromagnetic radiation is a particular electromagnetic field pattern of the radiation in the plane perpendicular (i.e., transverse) to the radiation's propagation direction. Transverse modes occur in radio waves and microwav ...
since its
electromagnetic
In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of a ...
oscillations occur perpendicular (transverse) to the length of the fiber. The 2009
Nobel Prize in Physics
)
, image = Nobel Prize.png
, alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then " ...
was awarded to
Charles K. Kao
Sir Charles Kao Kuen [Charles K. Kao was elected in 1990](_blank)
as a memb ...
for his theoretical work on the single-mode optical fiber. The standards
G.652
G.652 is an international standard that describes the geometrical, mechanical, and transmission attributes of a single-mode optical fibre and cable, developed by the Standardization Sector of the International Telecommunication Union (ITU-T) th ...
and
G.657 define the most widely used forms of single-mode optical fiber.
History
In 1961,
Elias Snitzer while working at American Optical published a comprehensive theoretical description of single mode fibers in the
Journal of the Optical Society of America
The ''Journal of the Optical Society of America'' is a peer-reviewed scientific journal of optics, published by Optica. It was established in 1917 and in 1984 was split into two parts, A and B.
''Journal of the Optical Society of America A''
P ...
.
At the Corning Glass Works (now
Corning Inc.), Robert Maurer, Donald Keck and Peter Schultz started with fused silica, a material that can be made extremely pure, but has a high melting point and a low refractive index. They made cylindrical preforms by depositing purified materials from the vapor phase, adding carefully controlled levels of dopants to make the refractive index of the core slightly higher than that of the cladding, without raising attenuation dramatically. In September 1970, they announced they had made single-mode fibers with attenuation at the 633-nanometer helium-neon line below 20 dB/km.
Characteristics
Like
multi-mode optical fiber
Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Multi-mode links can be used for data rates up to 100 Gbit/s. Multi-mode fiber has a fairly large ...
s, single-mode fibers do exhibit
modal dispersion
Modal dispersion is a distortion mechanism occurring in multimode fibers and other waveguides, in which the signal is spread in time because the propagation velocity of the optical signal is not the same for all modes. Other names for this phenom ...
resulting from multiple spatial modes but with narrower modal dispersion. 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
Bandwidth commonly refers to:
* Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range
* Bandwidth (computing), the rate of data transfer, bit rate or thr ...
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.
![Single mode fiber1](https://upload.wikimedia.org/wikipedia/commons/0/03/Single_mode_fiber1.jpg)
A typical single-mode optical fiber has a core diameter between 8 and 10.5
µm 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 fiber and
nonzero dispersion-shifted fiber. Data rates are limited by
polarization mode dispersion
Polarization mode dispersion (PMD) is a form of modal dispersion where two different polarizations of light in a waveguide, which normally travel at the same speed, travel at different speeds due to random imperfections and asymmetries, causing ...
and
chromatic dispersion
In optics, and by analogy other branches of physics dealing with wave propagation, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency; sometimes the term chromatic dispersion is used for specificity to ...
. , data rates of up to 10 gigabits per second were possible at distances of over with commercially available transceivers (
Xenpak XENPAK is a multisource agreement (MSA), instigated by Agilent Technologies and Agere Systems, that defines a fiber-optic or wired transceiver module which conforms to the 10 Gigabit Ethernet (10GbE) standard of the Institute of Electrical and Elec ...
). By using
optical amplifier
An optical amplifier is a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal. An optical amplifier may be thought of as a laser without an optical cavity, or one in which feedback fr ...
s and dispersion-compensating devices, state-of-the-art
DWDM
In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e., colors) of laser light. This techni ...
optical systems can span thousands of kilometers at 10 Gbit/s, and several hundred kilometers at 40 Gbit/s.
The lowest-order bounds mode is ascertained for the wavelength of interest by solving
Maxwell's equations
Maxwell's equations, or Maxwell–Heaviside equations, are a set of coupled partial differential equations that, together with the Lorentz force law, form the foundation of classical electromagnetism, classical optics, and electric circuits.
...
for the boundary conditions imposed by the fiber, which are determined by the
core
Core or cores may refer to:
Science and technology
* Core (anatomy), everything except the appendages
* Core (manufacturing), used in casting and molding
* Core (optical fiber), the signal-carrying portion of an optical fiber
* Core, the centra ...
diameter and the refractive indices of the core and
cladding
Cladding is an outer layer of material covering another. It may refer to the following:
*Cladding (boiler), the layer of insulation and outer wrapping around a boiler shell
*Cladding (construction), materials applied to the exterior of buildings
...
. 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
Communication (from la, communicare, meaning "to share" or "to be in relation with") is usually defined as the transmission of information. The term may also refer to the message communicated through such transmissions or the field of inquir ...
fiber.
In step-index guides, single-mode operation occurs when the
normalized frequency, ''V'', is less than or equal to 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.
OS1 and OS2 are standard single-mode optical fiber used with wavelengths 1310 nm and 1550 nm (size 9/125 µm) with a maximum attenuation of 1 dB/km (OS1) and 0.4 dB/km (OS2). OS1 is defined in
ISO/IEC 11801
International standard ISO/IEC 11801 ''Information technology — Generic cabling for customer premises'' specifies general-purpose telecommunication cabling systems (structured cabling) that are suitable for a wide range of applications (analog an ...
, and OS2 is defined in ISO/IEC 24702.
Connectors
Optical fiber connector
An optical fiber connector joins optical fibers, and enables quicker connection and disconnection than splicing. The connectors mechanically couple and align the cores of fibers so light can pass. Better connectors lose very little light due ...
s are used to join optical fibers where a connect/disconnect capability is required. The basic connector unit is a connector assembly. A connector assembly consists of an adapter and two connector plugs.
Due to the sophisticated polishing and tuning procedures that may be incorporated into optical connector manufacturing, connectors are generally assembled onto optical fiber in a supplier's manufacturing facility. However, the assembly and
polishing operations involved can be performed in the field, for example to make cross-connect jumpers to size.
Optical fiber connectors are used in telephone company central offices, at installations on customer premises, and in outside plant applications. Their uses include:
* Making the connection between equipment and the telephone plant in the central office
* Connecting fibers to remote and outside plant electronics such as Optical Network Units (ONUs) and Digital Loop Carrier (DLC) systems
* Optical cross connects in the central office
* Patching panels in the outside plant to provide architectural flexibility and to interconnect fibers belonging to different service providers
* Connecting couplers, splitters, and Wavelength Division Multiplexers (WDMs) to optical fibers
* Connecting optical test equipment to fibers for testing and maintenance.
Outside plant applications may involve locating connectors underground in subsurface enclosures that may be subject to flooding, on outdoor walls, or on utility poles. The closures that enclose them may be hermetic, or may be “free-breathing.” Hermetic closures will prevent the connectors within being subjected to temperature swings unless they are breached. Free-breathing enclosures will subject them to temperature and humidity swings, and possibly to condensation and biological action from airborne bacteria, insects, etc. Connectors in the underground plant may be subjected to groundwater immersion if the closures containing them are breached or improperly assembled.
The latest industry requirements for optical fiber connectors are in
Telcordia
iconectiv is a supplier of network planning and network management services to telecommunications providers. Known as Bellcore after its establishment in the United States in 1983 as part of the break-up of the Bell System, the company's name ...
br>
GR-326 ''Generic Requirements for Singlemode Optical Connectors and Jumper Assemblies''.
A ''multi-fiber'' optical connector is designed to simultaneously join multiple optical fibers together, with each 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 component, such as a coupler. The latter joins one optical fiber to two or more other optical fibers.
Multi-fiber optical connectors are designed to be used wherever quick and/or repetitive connects and disconnects of a group of fibers are needed. Applications include telecommunications companies’ Central Offices (COs), installations on customer premises, and Outside Plant (OSP) applications.
The multi-fiber optical connector can be used in the creation of a low-cost switch for use in fiber optical testing. Another application is in cables delivered to a user with pre-terminated multi-fiber jumpers. This would reduce the need for field splicing, which could greatly reduce the number of hours necessary for placing an
optical fiber cable
A fiber-optic cable, also known as an optical-fiber cable, is an assembly similar to an electrical cable, but containing one or more optical fibers that are used to carry light. The optical fiber elements are typically individually coated with ...
in a telecommunications network. This, in turn, would result in savings for the installer of such cable.
Industry requirements for multi-fiber optical connectors are covered i
GR-1435 ''Generic Requirements for Multi-Fiber Optical Connectors''.
Fiber optic switches
An
optical switch An optical transistor, also known as an optical switch or a light valve, is a device that switches or amplifies optical signals. Light occurring on an optical transistor's input changes the intensity of light emitted from the transistor's output ...
is a component with two or more ports that selectively transmits, redirects, or blocks an optical signal in a transmission medium. According to
Telcordia
iconectiv is a supplier of network planning and network management services to telecommunications providers. Known as Bellcore after its establishment in the United States in 1983 as part of the break-up of the Bell System, the company's name ...
br>
GR-1073 an optical switch must be actuated to select or change between states. The actuating signal (also referred to as the control signal) is usually electrical, but in principle, could be optical or mechanical. (The control signal format may be Boolean and may be an independent signal; or, in the case of optical actuation, the control signal may be encoded in the input data signal. Switch performance is generally intended to be independent of wavelength within the component passband.)
Quadruply clad fiber
In
fiber optics
An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means to ...
, a quadruply clad fiber is a single-mode optical fiber that has four claddings.
Each
cladding
Cladding is an outer layer of material covering another. It may refer to the following:
*Cladding (boiler), the layer of insulation and outer wrapping around a boiler shell
*Cladding (construction), materials applied to the exterior of buildings
...
has a
refractive index
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.
The refractive index determines how much the path of light is bent, or ...
lower than that of the
core
Core or cores may refer to:
Science and technology
* Core (anatomy), everything except the appendages
* Core (manufacturing), used in casting and molding
* Core (optical fiber), the signal-carrying portion of an optical fiber
* Core, the centra ...
. With respect to one another, their relative refractive indices are, in order of distance from the core: lowest, highest, lower, higher.
A quadruply clad fiber has the advantage of very low macrobending losses. It also has two zero-
dispersion
Dispersion may refer to:
Economics and finance
*Dispersion (finance), a measure for the statistical distribution of portfolio returns
*Price dispersion, a variation in prices across sellers of the same item
*Wage dispersion, the amount of variatio ...
points, and moderately low dispersion over a wider
wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...
range than a singly clad fiber or a
doubly clad fiber
Double-clad fiber (DCF) is a class of optical fiber with a structure consisting of three layers of optical material instead of the usual two. The inner-most layer is called the ''core''. It is surrounded by the ''inner cladding'', which is surro ...
.
Advantages
* No degradation of signal
* Low dispersion
* Well suited for long distance communication
Disadvantages
* Manufacturing and handling is more difficult
* Higher price
* Coupling light into the fiber is difficult
See also
*
Graded-index fiber
A graded-index or gradient-index fiber is an optical fiber whose core has a refractive index that decreases with increasing radial distance from the optical axis of the fiber.
Because parts of the core closer to the fiber axis have a higher ref ...
*
Multi-mode optical fiber
Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Multi-mode links can be used for data rates up to 100 Gbit/s. Multi-mode fiber has a fairly large ...
*
Optical waveguide
An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum. Common types of optical waveguides include optical fiber waveguides, transparent dielectric waveguides made of plastic and glass, liquid light ...
References
Citations
Sources
*
* {{cite web , url = http://www.fiber-optics.info/articles/types_of_optical_fiber , title = Types of Optical Fiber , access-date = 2013-11-08 , archive-url = https://web.archive.org/web/20180621154027/http://www.fiber-optics.info/articles/types_of_optical_fiber , archive-date = 2018-06-21 , url-status = dead
External links
Optics: Single mode fiber , MIT Video Demonstrations in Lasers and OpticsOptics: Multi-mode fiber , MIT Video Demonstrations in Lasers and Optics
Optical fiber