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Fiber-optic communication

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An optical fiber junction box. The yellow cables are single mode fibers; the orange and blue cables are multi-mode fibers: 62.5/125 µm OM1 and 50/125 µm OM3 fibers respectively.

Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information. First developed in the 1970s, fiber-optic communication systems have revolutionized the telecommunications industry and have played a major role in the advent of the Information Age. Because of its advantages over electrical transmission, optical fibers have largely replaced copper wire communications in core networks in the developed world. Optical fiber is used by many telecommunications companies to transmit telephone signals, Internet communication, and cable television signals. Researchers at Bell Labs have reached internet speeds of over 100 petabits per second using fiber-optic communication.[1]

The process of communicating using fiber-optics involves the following basic steps: Creating the optical signal involving the use of a transmitter, relaying the signal along the fiber, ensuring that the signal does not become too distorted or weak, receiving the optical signal, and converting it into an electrical signal.


1 Applications

2 History

3 Technology

3.1 Transmitters

3.2 Receivers

3.3 Fiber cable types

3.4 Amplifier

3.5 Wavelength-division multiplexing

4 Parameters

4.1 Bandwidth–distance product

4.2 Record speeds

4.3 Dispersion

4.4 Attenuation

4.5 Transmission windows

4.6 Regeneration

4.7 Last mile

5 Comparison with electrical transmission

6 Governing standards

7 See also

8 References

9 Further reading

10 External links


Optical fiber is used by many telecommunications companies to transmit telephone signals, Internet communication, and cable television signals. Due to much lower attenuation and interference, optical fiber has large advantages over existing copper wire in long-distance and high-demand applications. However, infrastructure development within cities was relatively difficult and time-consuming, and fiber-optic systems were complex and expensive to install and operate. Due to these difficulties, fiber-optic communication systems have primarily been installed in long-distance applications, where they can be used to their full transmission capacity, offsetting the increased cost. Since 2000, the prices for fiber-optic communications have dropped considerably. The price for rolling out fiber to the home has currently become more cost-effective than that of rolling out a copper based network. Prices have dropped to $850 per subscriber[citation needed] in the US and lower in countries like The Netherlands, where digging costs are low and housing density is high.

Since 1990, when optical-amplification systems became commercially available, the telecommunications industry has laid a vast network of intercity and transoceanic fiber communication lines. By 2002, an intercontinental network of 250,000 km of submarine communications cable with a capacity of 2.56 Tb/s was completed, and although specific network capacities are privileged information, telecommunications investment reports indicate that network capacity has increased dramatically since 2004.


In 1880 Alexander Graham Bell and his assistant Charles Sumner Tainter created a very early precursor to fiber-optic communications, the Photophone, at Bell's newly established Volta Laboratory in Washington, D.C. Bell considered it his most important invention. The device allowed for the transmission of sound on a beam of light. On June 3, 1880, Bell conducted the world's first wireless telephone transmission between two buildings, some 213 meters apart.[2][3] Due to its use of an atmospheric transmission medium, the Photophone would not prove practical until advances in laser and optical fiber technologies permitted the secure transport of light. The Photophone's first practical use came in military communication systems many decades later.

In 1966 Charles K. Kao and George Hockham proposed optical fibers at STC Laboratories (STL) at Harlow, England, when they showed that the losses of 1000 dB/km in existing glass (compared to 5-10 dB/km in coaxial cable) was due to contaminants, which could potentially be removed.

Optical fiber was successfully developed in 1970 by Corning Glass Works, with attenuation low enough for communication purposes (about 20dB/km), and at the same time GaAs semiconductor lasers were developed that were compact and therefore suitable for transmitting light through fiber optic cables for long distances.

After a period of research starting from 1975, the first commercial fiber-optic communications system was developed, which operated at a wavelength around 0.8 µm and used GaAs semiconductor lasers. This first-generation system operated at a bit rate of 45 Mbps with repeater spacing of up to 10 km. Soon on 22 April 1977, General Telephone and Electronics sent the first live telephone traffic through fiber optics at a 6 Mbit/s throughput in Long Beach, California.

The first wide area network fibre optic cable system in the world seems to have been installed by Rediffusion in Hastings, East Sussex, UK in 1978. The cables were placed in ducting throughout the town, and had over 1000 subscribers. They were used at that time for the transmission of television channels,not available because of local reception problems. The system is still in place, but disused.[citation needed]

The second generation of fiber-optic communication was developed for commercial use in the early 1980s, operated at 1.3 µm, and used InGaAsP semiconductor lasers. These early systems were initially limited by multi mode fiber dispersion, and in 1981 the single-mode fiber was revealed to greatly improve system performance, however practical connectors capable of working with single mode fiber proved difficult to develop. By 1987, these systems were operating at bit rates of up to 1.7 Gb/s with repeater spacing up to 50 km.

The first transatlantic telephone cable to use optical fiber was TAT-8, based on Desurvire optimized laser amplification technology. It went into operation in 1988.

Third-generation fiber-optic systems operated at 1.55 µm and had losses of about 0.2 dB/km. This development was spurred by the discovery of Indium gallium arsenide and the development of the Indium Gallium Arsenide photodiode by Pearsall. Engineers overcame earlier difficulties with pulse-spreading at that wavelength using conventional InGaAsP semiconductor lasers. Scientists overcame this difficulty by using dispersion-shifted fibers designed to have minimal dispersion at 1.55 µm or by limiting the laser spectrum to a single longitudinal mode. These developments eventually allowed third-generation systems to operate commercially at 2.5 Gbit/s with repeater spacing in excess of 100 km.

The fourth generation of fiber-optic communication systems used optical amplification to reduce the need for repeaters and wavelength-division multiplexing to increase data capacity. These two improvements caused a revolution that resulted in the doubling of system capacity every 6 months starting in 1992 until a bit rate of 10 Tb/s was reached by 2001. In 2006 a bit-rate of 14 Tbit/s was reached over a single 160 km line using optical amplifiers.[4]

The focus of development for the fifth generation of fiber-optic communications is on extending the wavelength range over which a WDM system can operate. The conventional wavelength window, known as the C band, covers the wavelength range 1.53-1.57 µm, and dry fiber has a low-loss window promising an extension of that range to 1.30-1.65 µm. Other developments include the concept of "optical solitons, " pulses that preserve their shape by counteracting the effects of dispersion with the nonlinear effects of the fiber by using pulses of a specific shape.

In the late 1990s through 2000, industry promoters, and research companies such as KMI, and RHK predicted massive increases in demand for communications bandwidth due to increased use of the Internet, and commercialization of various bandwidth-intensive consumer services, such as video on demand. Internet protocol data traffic was increasing exponentially, at a faster rate than integrated circuit complexity had increased under Moore's Law. From the bust of the dot-com bubble through 2006, however, the main trend in the industry has been consolidation of firms and offshoring of manufacturing to reduce costs. Companies such as Verizon and AT&T have taken advantage of fiber-optic communications to deliver a variety of high-throughput data and broadband services to consumers' homes.


Modern fiber-optic communication systems generally include an optical transmitter to convert an electrical signal into an optical signal to send into the optical fiber, a cable containing bundles of multiple optical fibers that is routed through underground conduits and buildings, multiple kinds of amplifiers, and an optical receiver to recover the signal as an electrical signal. The information transmitted is typically digital information generated by computers, telephone systems, and cable television companies.


A GBIC module (shown here with its cover removed), is an optical and electrical transceiver. The electrical connector is at top right, and the optical connectors are at bottom left

The most commonly used optical transmitters are semiconductor devices such as light-emitting diodes (LEDs) and laser diodes. The difference between LEDs and laser diodes is that LEDs produce incoherent light, while laser diodes produce coherent light. For use in optical communications, semiconductor optical transmitters must be designed to be compact, efficient, and reliable, while operating in an optimal wavelength range, and directly modulated at high frequencies.

In its simplest form, a LED is a forward-biased p-n junction, emitting light through spontaneous emission, a phenomenon referred to as electroluminescence. The emitted light is incoherent with a relatively wide spectral width of 30-60 nm. LED light transmission is also inefficient, with only about 1%[citation needed] of input power, or about 100 microwatts, eventually converted into launched power which has been coupled into the optical fiber. However, due to their relatively simple design, LEDs are very useful for low-cost applications.

Communications LEDs are most commonly made from Indium gallium arsenide phosphide (InGaAsP) or gallium arsenide (GaAs). Because InGaAsP LEDs operate at a longer wavelength than GaAs LEDs (1.3 micrometers vs. 0.81-0.87 micrometers), their output spectrum, while equivalent in energy is wider in wavelength terms by a factor of about 1.7. The large spectrum width of LEDs is subject to higher fiber dispersion, considerably limiting their bit rate-distance product (a common measure of usefulness). LEDs are suitable primarily for local-area-network applications with bit rates of 10-100 Mbit/s and transmission distances of a few kilometers. LEDs have also been developed that use several quantum wells to emit light at different wavelengths over a broad spectrum, and are currently in use for local-area WDM networks.

Today, LEDs have been largely superseded by VCSEL (Vertical Cavity Surface Emitting Laser) devices, which offer improved speed, power and spectral properties, at a similar cost. Common VCSEL devices couple well to multi mode fiber.

A semiconductor laser emits light through stimulated emission rather than spontaneous emission, which results in high output power (~100 mW) as well as other benefits related to the nature of coherent light. The output of a laser is relatively directional, allowing high coupling efficiency (~50 %) into single-mode fiber. The narrow spectral width also allows for high bit rates since it reduces the effect of chromatic dispersion. Furthermore, semiconductor lasers can be modulated directly at high frequencies because of short recombination time.

Commonly used classes of semiconductor laser transmitters used in fiber optics include VCSEL (Vertical Cavity Surface Emitting Laser), Fabry–Pérot and DFB (Distributed Feed Back).

Laser diodes are often directly modulated, that is the light output is controlled by a current applied directly to the device. For very high data rates or very long distance links, a laser source may be operated continuous wave, and the light modulated by an external device such as an electro-absorption modulator or Mach–Zehnder interferometer. External modulation increases the achievable link distance by eliminating laser chirp, which broadens the linewidth of directly modulated lasers, increasing the chromatic dispersion in the fiber.

A transceiver is a device combining a transmitter and a receiver in a single housing (see picture on right).


The main component of an optical receiver is a photodetector, which converts light into electricity using the photoelectric effect. The primary photodetectors for telecommunications are made from Indium gallium arsenide The photodetector is typically a semiconductor-based photodiode. Several types of photodiodes include p-n photodiodes, p-i-n photodiodes, and avalanche photodiodes. Metal-semiconductor-metal (MSM) photodetectors are also used due to their suitability for circuit integration in regenerators and wavelength-division multiplexers.

Optical-electrical converters are typically coupled with a transimpedance amplifier and a limiting amplifier to produce a digital signal in the electrical domain from the incoming optical signal, which may be attenuated and distorted while passing through the channel. Further signal processing such as clock recovery from data (CDR) performed by a phase-locked loop may also be applied before the data is passed on.

Fiber cable types

A cable reel trailer with conduit that can carry optical fiber

Single-mode optical fiber in an underground service pit

Main articles: Optical fiber and Optical fiber cable

An optical fiber cable consists of a core, cladding, and a buffer (a protective outer coating), in which the cladding guides the light along the core by using the method of total internal reflection. The core and the cladding (which has a lower-refractive-index) are usually made of high-quality silica glass, although they can both be made of plastic as well. Connecting two optical fibers is done by fusion splicing or mechanical splicing and requires special skills and interconnection technology due to the microscopic precision required to align the fiber cores.[5]

Two main types of optical fiber used in optic communications include multi-mode optical fibers and single-mode optical fibers. A multi-mode optical fiber has a larger core (≥ 50 micrometers), allowing less precise, cheaper transmitters and receivers to connect to it as well as cheaper connectors. However, a multi-mode fiber introduces multimode distortion, which often limits the bandwidth and length of the link. Furthermore, because of its higher dopant content, multi-mode fibers are usually expensive and exhibit higher attenuation. The core of a single-mode fiber is smaller (<10 micrometers) and requires more expensive components and interconnection methods, but allows much longer, higher-performance links.

In order to package fiber into a commercially viable product, it typically is protectively coated by using ultraviolet (UV), light-cured acrylate polymers, then terminated with optical fiber connectors, and finally assembled into a cable. After that, it can be laid in the ground and then run through the walls of a building and deployed aerially in a manner similar to copper cables. These fibers require less maintenance than common twisted pair wires, once they are deployed.[6]

Specialized cables are used for long distance subsea data transmission, e.g. transatlantic communications cable. New (2011–2013) cables operated by commercial enterprises (Emerald Atlantis, Hibernia Atlantic) typically have four strands of fiber and cross the Atlantic (NYC-London) in 60-70ms. Cost of each such cable was about $300M in 2011. source: The Chronicle Herald.

Another common practice is to bundle many fiber optic strands within long-distance power transmission cable. This exploits power transmission rights of way effectively, ensures a power company can own and control the fiber required to monitor its own devices and lines, is effectively immune to tampering, and simplifies the deployment of smart grid technology.


Main article: Optical amplifier

The transmission distance of a fiber-optic communication system has traditionally been limited by fiber attenuation and by fiber distortion. By using opto-electronic repeaters, these problems have been eliminated. These repeaters convert the signal into an electrical signal, and then use a transmitter to send the signal again at a higher intensity than it was before. Because of the high complexity with modern wavelength-division multiplexed signals (including the fact that they had to be installed about once every 20 km), the cost of these repeaters is very high.

An alternative approach is to use an optical amplifier, which amplifies the optical signal directly without having to convert the signal into the electrical domain. It is made by doping a length of fiber with the rare-earth mineral erbium, and pumping it with light from a laser with a shorter wavelength than the communications signal (typically 980 nm). Amplifiers have largely replaced repeaters in new installations.

Wavelength-division multiplexing

Main article: Wavelength-division multiplexing

Wavelength-division multiplexing (WDM) is the practice of multiplying the available capacity of optical fibers through use of parallel channels, each channel on a dedicated wavelength of light. This requires a wavelength division multiplexer in the transmitting equipment and a demultiplexer (essentially a spectrometer) in the receiving equipment. Arrayed waveguide gratings are commonly used for multiplexing and demultiplexing in WDM. Using WDM technology now commercially available, the bandwidth of a fiber can be divided into as many as 160 channels[7] to support a combined bit rate in the range of 1.6 Tbit/s.


Bandwidth–distance product

Because the effect of dispersion increases with the length of the fiber, a fiber transmission system is often characterized by its bandwidth–distance product, usually expressed in units of MHz•km. This value is a product of bandwidth and distance because there is a trade off between the bandwidth of the signal and the distance it can be carried. For example, a common multi-mode fiber with bandwidth–distance product of 500 MHz•km could carry a 500 MHz signal for 1 km or a 1000 MHz signal for 0.5 km.

Engineers are always looking at current limitations in order to improve fiber-optic communication, and several of these restrictions are currently being researched.

Record speeds

Each fiber can carry many independent channels, each using a different wavelength of light (wavelength-division multiplexing). The net data rate (data rate without overhead bytes) per fiber is the per-channel data rate reduced by the FEC overhead, multiplied by the number of channels (usually up to eighty in commercial dense WDM systems as of 2008).

Year Organization Effective speed WDM channels Per channel speed Distance

2009 Alcatel-Lucent[8] 15 Tbit/s 155 100 Gbit/s 90 km

2010 NTT[9] 69.1 Tbit/s 432 171 Gbit/s 240 km

2011 KIT[10] 26 Tbit/s 1 26 Tbit/s 50 km

2011 NEC[11] 101 Tbit/s 370 273 Gbit/s 165 km

2012 NEC, Corning[12] 1.05 Petabit/s 12 core fiber 52.4 km

While the physical limitations of electrical cable prevent speeds in excess of 10 Gigabits per second, the physical limitations of fiber optics have not yet been reached.[citation needed]

In 2013, New Scientist reported that a team at the University of Southampton had achieved a throughput of 73.7 Tbit per second, with the signal traveling at 99.7% the speed of light through a hollow-core photonic crystal fiber.[13]


For modern glass optical fiber, the maximum transmission distance is limited not by direct material absorption but by several types of dispersion, or spreading of optical pulses as they travel along the fiber. Dispersion in optical fibers is caused by a variety of factors. Intermodal dispersion, caused by the different axial speeds of different transverse modes, limits the performance of multi-mode fiber. Because single-mode fiber supports only one transverse mode, intermodal dispersion is eliminated.

In single-mode fiber performance is primarily limited by chromatic dispersion (also called group velocity dispersion), which occurs because the index of the glass varies slightly depending on the wavelength of the light, and light from real optical transmitters necessarily has nonzero spectral width (due to modulation). Polarization mode dispersion, another source of limitation, occurs because although the single-mode fiber can sustain only one transverse mode, it can carry this mode with two different polarizations, and slight imperfections or distortions in a fiber can alter the propagation velocities for the two polarizations. This phenomenon is called fiber birefringence and can be counteracted by polarization-maintaining optical fiber. Dispersion limits the bandwidth of the fiber because the spreading optical pulse limits the rate that pulses can follow one another on the fiber and still be distinguishable at the receiver.

Some dispersion, notably chromatic dispersion, can be removed by a 'dispersion compensator'. This works by using a specially prepared length of fiber that has the opposite dispersion to that induced by the transmission fiber, and this sharpens the pulse so that it can be correctly decoded by the electronics.


Fiber attenuation, which necessitates the use of amplification systems, is caused by a combination of material absorption, Rayleigh scattering, Mie scattering, and connection losses. Although material absorption for pure silica is only around 0.03 dB/km (modern fiber has attenuation around 0.3 dB/km), impurities in the original optical fibers caused attenuation of about 1000 dB/km. Other forms of attenuation are caused by physical stresses to the fiber, microscopic fluctuations in density, and imperfect splicing techniques.

Transmission windows

Each effect that contributes to attenuation and dispersion depends on the optical wavelength. The wavelength bands (or windows) that exist where these effects are weakest are the most favorable for transmission. These windows have been standardized, and the currently defined bands are the following:[14]

Band Description Wavelength Range

O band original 1260 to 1360 nm

E band extended 1360 to 1460 nm

S band short wavelengths 1460 to 1530 nm

C band conventional ("erbium window") 1530 to 1565 nm

L band long wavelengths 1565 to 1625 nm

U band ultralong wavelengths 1625 to 1675 nm

Note that this table shows that current technology has managed to bridge the second and third windows that were originally disjoint.

Historically, there was a window used below the O band, called the first window, at 800-900 nm; however, losses are high in this region so this window is used primarily for short-distance communications. The current lower windows (O and E) around 1300 nm have much lower losses. This region has zero dispersion. The middle windows (S and C) around 1500 nm are the most widely used. This region has the lowest attenuation losses and achieves the longest range. It does have some dispersion, so dispersion compensator devices are used to remove this.


When a communications link must span a larger distance than existing fiber-optic technology is capable of, the signal must be regenerated at intermediate points in the link by optical communications repeaters. Repeaters add substantial cost to a communication system, and so system designers attempt to minimize their use.

Recent advances in fiber and optical communications technology have reduced signal degradation so far that regeneration of the optical signal is only needed over distances of hundreds of kilometers. This has greatly reduced the cost of optical networking, particularly over undersea spans where the cost and reliability of repeaters is one of the key factors determining the performance of the whole cable system. The main advances contributing to these performance improvements are dispersion management, which seeks to balance the effects of dispersion against non-linearity; and solitons, which use nonlinear effects in the fiber to enable dispersion-free propagation over long distances.

Last mile

Main article: Last mile

See also: National Broadband Network

Although fiber-optic systems excel in high-bandwidth applications, optical fiber has been slow to achieve its goal of fiber to the premises or to solve the last mile problem. However, as bandwidth demand increases, more and more progress towards this goal can be observed. In Japan, for instance EPON has largely replaced DSL as a broadband Internet source. South Korea’s KT also provides a service called FTTH (Fiber To The Home), which provides fiber-optic connections to the subscriber’s home. The largest FTTH deployments are in Japan, South Korea, and China. Singapore started implementation of their all-fiber Next Generation Nationwide Broadband Network (Next Gen NBN), which is slated for completion in 2012 and is being installed by OpenNet. Since they began rolling out services in September 2010, Network coverage in Singapore has reached 85% nationwide.

In the US, Verizon Communications provides a FTTH service called FiOS to select high-ARPU (Average Revenue Per User) markets within its existing territory. The other major surviving ILEC (or Incumbent Local Exchange Carrier), AT&T, uses a FTTN (Fiber To The Node) service called U-verse with twisted-pair to the home. Their MSO competitors employ FTTN with coax using HFC. All of the major access networks use fiber for the bulk of the distance from the service provider's network to the customer.

Also in the US, Wilson Utilities located in Wilson, North Carolina, have implemented FTTH and have successfully achieved 1 gigabit fiber to the home. This was implemented in late 2013. Wilson Utilities first rolled out their FTTN (Fiber to the Home) in 2012 with speeds offerings of 20/40/60/100 megabits per second. Their service is referred to as GreenLight.

The globally dominant access network technology is EPON (Ethernet Passive Optical Network). In Europe, and among telcos in the United States, BPON (ATM-based Broadband PON) and GPON (Gigabit PON) had roots in the FSAN (Full Service Access Network) and ITU-T standards organizations under their control.

Comparison with electrical transmission

A mobile fiber optic splice lab used to access and splice underground cables

An underground fiber optic splice enclosure opened up

The choice between optical fiber and electrical (or copper) transmission for a particular system is made based on a number of trade-offs. Optical fiber is generally chosen for systems requiring higher bandwidth or spanning longer distances than electrical cabling can accommodate.

The main benefits of fiber are its exceptionally low loss (allowing long distances between amplifiers/repeaters), its absence of ground currents and other parasite signal and power issues common to long parallel electric conductor runs (due to its reliance on light rather than electricity for transmission, and the dielectric nature of fiber optic), and its inherently high data-carrying capacity. Thousands of electrical links would be required to replace a single high bandwidth fiber cable. Another benefit of fibers is that even when run alongside each other for long distances, fiber cables experience effectively no crosstalk, in contrast to some types of electrical transmission lines. Fiber can be installed in areas with high electromagnetic interference (EMI), such as alongside utility lines, power lines, and railroad tracks. Nonmetallic all-dielectric cables are also ideal for areas of high lightning-strike incidence.

For comparison, while single-line, voice-grade copper systems longer than a couple of kilometers require in-line signal repeaters for satisfactory performance; it is not unusual for optical systems to go over 100 kilometers (62 mi), with no active or passive processing. Single-mode fiber cables are commonly available in 12 km lengths, minimizing the number of splices required over a long cable run. Multi-mode fiber is available in lengths up to 4 km, although industrial standards only mandate 2 km unbroken runs.

In short distance and relatively low bandwidth applications, electrical transmission is often preferred because of its

Lower material cost, where large quantities are not required

Lower cost of transmitters and receivers

Capability to carry electrical power as well as signals (in appropriately designed cables)

Ease of operating transducers in linear mode.

Crosstalk from nearby cables and other parasitical unwanted signals increase profits from replacement and mitigation devices.

Optical fibers are more difficult and expensive to splice than electrical conductors. And at higher powers, optical fibers are susceptible to fiber fuse, resulting in catastrophic destruction of the fiber core and damage to transmission components.[15]

Because of these benefits of electrical transmission, optical communication is not common in short box-to-box, backplane, or chip-to-chip applications; however, optical systems on those scales have been demonstrated in the laboratory.

In certain situations fiber may be used even for short distance or low bandwidth applications, due to other important features:

Immunity to electromagnetic interference, including nuclear electromagnetic pulses (although fiber can be damaged by alpha and beta radiation).

High electrical resistance, making it safe to use near high-voltage equipment or between areas with different earth potentials.

Lighter weight—important, for example, in aircraft.

No sparks—important in flammable or explosive gas environments.

Not electromagnetically radiating, and difficult to tap without disrupting the signal—important in high-security environments.

Much smaller cable size—important where pathway is limited, such as networking an existing building, where smaller channels can be drilled and space can be saved in existing cable ducts and trays.

Resistance to corrosion due to non-metallic transmission medium

Optical fiber cables can be installed in buildings with the same equipment that is used to install copper and coaxial cables, with some modifications due to the small size and limited pull tension and bend radius of optical cables. Optical cables can typically be installed in duct systems in spans of 6000 meters or more depending on the duct's condition, layout of the duct system, and installation technique. Longer cables can be coiled at an intermediate point and pulled farther into the duct system as necessary.

Governing standards

In order for various manufacturers to be able to develop components that function compatibly in fiber optic communication systems, a number of standards have been developed. The International Telecommunications Union publishes several standards related to the characteristics and performance of fibers themselves, including

ITU-T G.651, "Characteristics of a 50/125 µm multimode graded index optical fibre cable"

ITU-T G.652, "Characteristics of a single-mode optical fibre cable"

Other standards specify performance criteria for fiber, transmitters, and receivers to be used together in conforming systems. Some of these standards are:

100 Gigabit Ethernet

10 Gigabit Ethernet

Fibre Channel

Gigabit Ethernet


Synchronous Digital Hierarchy

Synchronous Optical Networking

Optical Transport Network (OTN)

TOSLINK is the most common format for digital audio cable using plastic optical fiber to connect digital sources to digital receivers.

See also

Dark fiber

Google Fiber

Fiber to the x

Free-space optical communication

Information theory

Passive optical network


Bell Labs breaks optical transmission record, 100 Petabit per second kilometer barrier,, 29 September 2009

Mary Kay Carson (2007). Alexander Graham Bell: Giving Voice To The World. Sterling Biographies. New York: Sterling Publishing. pp. 76–78. ISBN 978-1-4027-3230-0.

Alexander Graham Bell (October 1880). "On the Production and Reproduction of Sound by Light". American Journal of Science, Third Series XX (118): 305–324. also published as "Selenium and the Photophone" in Nature, September 1880.

"14 Tbit/s over a single optical fiber: successful demonstration of world's largest capacity". News release (NTT). September 29, 2006. Retrieved June 17, 2011.

An optical fiber will break if it is bent too sharply. Alwayn, Vivek (2004-04-23). "Splicing". Fiber-Optic Technologies. Cisco Systems. Retrieved 2006-12-31.


Infinera Introduces New Line System Infinera Corp press release, Retrieved 2009-08-26

"Alcatel-Lucent Bell Labs announces new optical transmission record and breaks 100 Petabit per second kilometer barrier" (Press release). Alcatel-Lucent. 2009-10-28.

"World Record 69-Terabit Capacity for Optical Transmission over a Single Optical Fiber" (Press release). NTT. 2010-03-25. Retrieved 2010-04-03.

"Laser puts record data rate through fibre". BBC. 2011-05-22.

"Ultrafast fibre optics set new speed record". New Scientist. 2011-04-29. Retrieved 2012-02-26.

"NEC and Corning achieve petabit optical transmission". 2013-01-22. Retrieved 2013-01-23.

"Big data, now at the speed of light", New Scientist, March 30, 2013, p. 14. See "Information superhighway approaches light speed".

Encyclopedia of Laser Physics and Technology

Lee, M. M.; J. M. Roth; T. G. Ulmer; C. V. Cryan (2006). "The Fiber Fuse Phenomenon in Polarization-Maintaining Fibers at 1.55 μm" (PDF). Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies. paper JWB66 (Optical Society of America). Retrieved March 14, 2010.

Encyclopedia of Laser Physics and Technology

Fiber-Optic Technologies by Vivek Alwayn

Agrawal, Govind P. (2002). Fiber-optic communication systems. New York: John Wiley & Sons. ISBN 0-471-21571-6.

Fiber termination's most critical step: Polishing to perfection

by Manho Chung

Courtesy of Cabling Installation & Maintenance Magazine

How proper optical-fiber polishing techniques can improve network performance.

No matter how you splice it, a networking system is only as good as its weakest link. Chances are the weakest link in an optical-fiber system is a connector. If your network fails due to poor connector termination, the cost to find the problem and rework it can become significant.

With today’s increasing bandwidths demanding lower loss budgets, it is essential that fiber terminations do not impact the system’s performance. Well designed connectors, good termination practices, and installer skill become invaluable.

Popular optical-fiber connectors like the SC (top) and LC (bottom) are available in field-polish versions, meaning whoever installs them must have the right tools, and skills, to properly terminate and polish.

Many installers fear connectorizing optical-fiber cable, mainly due to the delicate techniques of polishing and lapping. Additionally, since the optical connector is a high-precision device with tolerances on the order of microns, it is crucial that the fiber not only be formed perfectly to align with a mating connector, but that it be free of any dust or dirt. Failing to do so can cause high insertion loss and high reflection, and can contaminate the equipment to which the connectors and patch cords will be connected.

Polishing the fiber is the last and most critical step in the connectorization process. Polishing finalizes the connector endface and cleans the surface, which has a direct impact on such optical performance parameters as insertion loss, return loss, and bit-error-rate for overall network performance. Reliable polishing processes rely on proper training and a well-equipped termination toolkit.

Time versus money

Several connectivity options are available, including patch cords (preconnectorized or preterminated cables), field connectorization, and one-end termination pigtails that require fusion splicing. Each method and its success depend on the connector termination process and installer expertise.

Preterminated cables, patch cords, or connectorized interconnect assemblies eliminate time-consuming field-termination processes and provide a factory-tested and certified endface, but can also have downfalls. Prepolished connectorized fibers can cost much more than epoxy-style field-polish connectors, and need to be precisely measured. If they are too short, you will have to install a replacement. If they are too long, you will have outlaid additional expense and still have to deal with installation issues associated with managing the extra cable length.

This optical-fiber termination kit includes the necessary items for polishing, such as a microscope, distilled water, and polishing and lapping film.

Epoxy/polish connectors, in which fiber is glued to the connector with heat-cured epoxy, provide a reliable connection with losses less than 0.5 dB per mated pair, but can be time-consuming because they need to set or “cure.” Anaerobic adhesive is a quick-setting adhesive that is rapidly replacing epoxy because it provides a simple installation process that does not require power. Additionally, anaerobic adhesive connectors will typically have less than a 0.3 dB insertion loss per mated pair, which is better than the TIA/EIA-568-B.3 standard-specified maximum of 0.75 dB per mated pair.

Connectors themselves vary greatly in design and style. TIA/EIA-604 outlines intermateability specifications, known as FOCIS (Fiber Optic Connector Intermateability Standard) documents. These specifications ensure that connectors by varying manufacturers are intermateable with those of other manufacturers. The FOCIS documents include specifics for the most widely used connectors, including SC, LC, FJ, MPO, ST, FC, and MT-RJ.

In the premises market, the SC, LC, FJ, and ST are the most predominant for both singlemode and multimode field installations. The SC offers low cost, simplicity, and durability, as well as accurate alignment with its ceramic ferrule and “push-pull” connection. The LC, designed for high density applications, features a small, 1.25-mm ferrule (half the size of its predecessors), which requires a more-precise polishing operation. Although the method for attaching optical-fiber connectors to optical fibers varies among connector types, the basic steps of termination and polishing are common.

Tools of the trade

Automated polishing equipment can provide higher first-pass yields and a more consistent product quality, but manual polishing techniques are common field practices for some connectivity types. Controlling the procedures in the field through emulating automated lab procedures or an assembly house will provide comparably high yields.

Most field connector manufacturers offer field termination kits and extensive training. Intermateability standards, such as TIA/EIA-604-3 for SC connectors, define tolerances and geometry of all mating parameters.

It would be ideal if connector termination kits would work across the board, but often, they do not because of different tooling and variances in consumable items. A kit from one manufacturer may not be capable of terminating another manufacturer’s connector, even though they are the same-style connector. So, you should be equipped with the appropriate toolkit, current editions of the manufacturers’ termination instructions, and the training to achieve the desired quality and performance levels.

The field termination kit should include distilled water (as a lubricant and flushing agent between each polishing process), anaerobic adhesive (to bond the fiber inside the ferrule), a cleaving tool (to cut off the fiber to the desired height above the ferrule), a portable microscope (200? minimum), and a polishing kit that includes a polishing puck, pads, and an assortment of films.

Become familiar with the many different materials available within these kits. Polishing pucks, which hold the connector in place during the polishing procedure, are made from high-abrasion resistant metal or plastic. Manufacturers, such as Panduit, offer a precision, case-hardened puck with tolerances for the ferrule to fit easily in the puck and allow free rotation. Polishing pads come in different materials, such as rubber or hard plastic, based on the manufacturer’s recommendation.

True grit

The most important element in a polishing kit is the polishing and lapping film, which consist of materials with abrasive particulate on a Mylar substrate in different grit sizes. The rate of fiber erosion within each polishing step is dictated by the film’s defined grade and erosion rate.

This magnified image shows a fiber endface after rough polishing with 5-µm Al2O3 dry polishing paper.

A coarse polishing film also removes excess adhesive, while a finer film yields a more exact surface finish for the final geometry of the connector’s endface. For multiple polishing steps, Panduit recommends that you keep a stock of requisite polishing film that should include diamond, aluminum oxide (Al2O3) and silica (SiO2).

Rough polishing with 1-ìm diamond film yields this fiber endface, a visibly noticeable improvement over the rough polishing pictured earlier.

Diamond is the hardest polishing material, cutting the ferrule and endface the fastest. But if caution is not taken, diamond film can cause the most subsurface damage. Any loose particulate can then potentially cause damage to the mating interface. Aluminum oxide, one of the most common films, is also hard and long-lasting, but has little effect on the ceramic ferrule. Silica works for both glass (fiber) and ceramic (ferrule), and is used in the final finishing.

After final finish polishing with 0.05-µm SiO2 film, the fiber endface is ready to transport optical signals.

Other film materials used in the field include silicon carbide (SiC) and cerium oxide (CeO2). Silicon carbide’s hardness is between diamond and aluminum oxide and can be used for removing adhesive, but not for the final finishing. Cerium oxide is softer and used only for final polishing.

Step by step

The polishing process can begin once the anaerobic adhesive is cured and after the fiber is cleaved. For best cleaving results, Panduit recommends a carbide cleaving tool with a 30-degree tip. The cleaved fiber tip should then be smoothed through air polishing-a freehand operation aimed at quick removal of excess fiber protruding from the end of the connector. Air polishing reduces pressure on the fiber when contracting the polishing film.

A recommended aluminum oxide film, with a grit size between 5 and 12 microns (µm), should be used in circular “figure 8” paths until no film scratching is visible. Optimum fiber height is 100 µm above the ferrule.

In each stage, take care not to over-polish, which can create fiber undercutting resulting in expensive rework and product replacement. And because particles from the grit can cause defects in the glass, it is critical that you clean the fiber with distilled water between each step.

The next step, rough polishing, also removes excess anaerobic adhesive from the fiber. Panduit recommends a 5-µm aluminum oxide polishing paper on the polishing pad. Other films can potentially make pits on the fiber surface. Using the polishing puck and backing pad, make the requisite number of “figure 8” passes as recommended by the manufacturer.

The next step is fine polishing, using a finer grade of grit, such as 1-µm or less diamond film. Although diamond film is more expensive, it can be reused more often than other films. During this process, apply distilled water to keep the film wet.

After fine polishing, inspect the fiber with a powerful microscope (200? minimum) to precisely view any scratches, pits, or damage. At this point, the fiber can be checked with a light source, such as a visual fault locator. Typical insertion loss for such connector styles as SC-to-SC or LC-to-LC can be 0.25 dB per mated pair; the manufacturer’s recommendation is 0.5 dB per mated pair.

Return loss, which is caused by the reflection at the mated joint of two connectors, is affected by the fine polishing methods and can achieve above 35 dB with diamond polishing. An additional, final finishing procedure is recommended to achieve return loss values greater than 55 dB. This is especially critical for today’s high-speed singlemode, laser-based systems.

Final finishing requires a grit size of 0.3-µm or less. Silica, aluminum oxide, and cerium oxide are preferred, again with distilled water in a wet process. The film, pad, pressure, number of “figure 8s,” together with the track and travel distance will determine the final endface shape.

More than a pretty endface

The reliability and integrity of optical-fiber connectivity depends on the degree of control taken during the polishing procedures-a significant contributor to optimal endface geometry. Too small a curvature radius and the fiber could prematurely fracture. Too large a radius introduces the possibility of reflections, which will result in high reflectivity; thus, a lower return-loss performance.

Telcordia standard GR-326-Core, Issue 3, Section defines the shape of the connector endface, specifying the metrics of apex offset (AO), radius of curvature (ROC), and spherical fiber height (SpH).

Telcordia specification GR-326-Core, Issue 3, Section defines the shape of the connector and endface. The three metrics are apex offset (AO), radius of curvature (ROC), and the spherical fiber height (SpH). Apex offset occurs whenever the polished ferrule’s geometric peak does not correspond with the center of the fiber core. Up to 50 µm is allowable. The ferrule’s radius of curvature should be no more than 25 mm, since physical contact of the fiber endfaces could be affected. The standard specifies the fiber height to be less than 50 nm.

Because using sophisticated and cumbersome lab equipment in the field is impractical, it is difficult to check detailed endface geometry. Proper polishing techniques, therefore, become essential. Proven methods, previously mentioned, have been tested in the lab and implemented in the field. These methods should be replicated in the field for consistent high quality and desired loss margins.

Alternatives to field polishing

Successful optical-fiber connector field polishing can be achieved, provided the required tools, consumable products, appropriate manufacturers’ guidelines, and the necessary operator skill sets are used. But field polishing is just one termination style for optical-fiber connectors. Prepolished optical-fiber connectors, which can also be terminated in the field, feature a factory pre-polished fiber-stub endface. The pre-polished fiber stub in the ferrule offers comparable performance with the added benefit of eliminating time-consuming field polishing, thereby reducing installation time and cost.

Pre-polished connectors, such as Panduit’s OptiCam brand, provide a quick termination alternative to field-polish connectors. Pre-polished devices have a factory-polished endface that meets the critical geometry requirements referenced earlier, eliminating field polishing. The connectors also allow field terminating in less than half the time of field-polish connectors. With retermination capability, they also provide yield rates approaching 100%.

MANHO CHUNG is a product development engineer for Panduit. (Additional information on field polishing is available at:

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