Fiber-optic communication

[6][better source needed] First developed in the 1970s, fiber-optics have revolutionized the telecommunications industry and have played a major role in the advent of the Information Age.

[7] Because of its advantages over electrical transmission, optical fibers have largely replaced copper wire communications in backbone networks in the developed world.

In addition to serving the purposes of telecommunications, it is used as light guides, for imaging tools, lasers, hydrophones for seismic waves, SONAR, and as sensors to measure pressure and temperature.

Due to lower attenuation and interference, optical fiber has advantages over copper wire in long-distance, high-bandwidth applications.

Due to these difficulties, early fiber-optic communication systems were primarily installed in long-distance applications, where they can be used to their full transmission capacity, offsetting the increased cost.

[citation needed] Since 1990, when optical-amplification systems became commercially available, the telecommunications industry has laid a vast network of intercity and transoceanic fiber communication lines.

[13][14] 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.

[18][19] In 1966 Charles K. Kao and George Hockham at Standard Telecommunication Laboratories showed that the losses of 1,000 dB/km in existing glass (compared to 5–10 dB/km in coaxial cable) were due to contaminants which could potentially be removed.

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.

[21] After a period of research starting from 1975, the first commercial fiber-optic telecommunications system was developed which operated at a wavelength around 0.8 μm and used GaAs semiconductor lasers.

Canadian service provider SaskTel had completed construction of what was then the world's longest commercial fiber optic network, which covered 3,268 km (2,031 mi) and linked 52 communities.

The fourth generation of fiber-optic communication systems used optical amplification to reduce the need for repeaters and wavelength-division multiplexing (WDM) to increase data capacity.

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.

[a] 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 have been largely superseded by vertical-cavity surface-emitting laser (VCSEL) devices, which offer improved speed, power and spectral properties, at a similar cost.

"Dual-polarization quadrature phase shift keying is a modulation format that effectively sends four times as much information as traditional optical transmissions of the same speed.

Coherent receivers use a local oscillator laser in combination with a pair of hybrid couplers and four photodetectors per polarization, followed by high-speed ADCs and digital signal processing to recover data modulated with QPSK, QAM, or OFDM.

[citation needed] An optical communication system transmitter consists of a digital-to-analog converter (DAC), a driver amplifier and a Mach–Zehnder modulator.

Digital predistortion counteracts the degrading effects and enables Baud rates up to 56 GBd and modulation formats like 64-QAM and 128-QAM with the commercially available components.

The core of a single-mode fiber is smaller (< 10 micrometers) and requires more expensive components and interconnection methods, but allows much longer and higher-performance links.

In order to package fiber into a commercially viable product, it typically is protectively coated by using ultraviolet cured acrylate polymers[citation needed] and assembled into a cable.

These are made by doping a length of fiber with the rare-earth mineral erbium and laser pumping it with light with a shorter wavelength than the communications signal (typically 980 nm).

[37] Using WDM technology now commercially available, the bandwidth of a fiber can be divided into as many as 160 channels[38] to support a combined bit rate in the range of 1.6 Tbit/s.

Research conducted by the RMIT University, Melbourne, Australia, have developed a nanophotonic device that carries data on light waves that have been twisted into a spiral form and achieved a 100-fold increase in current attainable fiber optic speeds.

Although fiber-optic systems excel in high-bandwidth applications, the last mile problem remains unsolved as fiber to the premises has experienced slow uptake.

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.

[needs update] In the US, Verizon Communications provides a FTTH service called FiOS to selected high-average-revenue-per-user markets within its existing territory.

The other major surviving incumbent local exchange carrier, AT&T, uses a fiber to the node (FTTN) service called U-verse with twisted-pair to the home.

Optical fiber is generally chosen for systems requiring higher bandwidth, operating in harsh environments or spanning longer distances than electrical cabling can accommodate.

The main benefits of fiber are its exceptionally low loss (allowing long distances between 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.