Fiber-optic communication is a form of optical communication for transmitting information from one place to another by sending pulses of infrared or visible light through an optical fiber. The light is a form of carrier wave that is modulated to carry information. Optical fiber can carry voice, video, and data through local area networks or across long distances. Fiber is preferred over electrical cabling when high bandwidth, long distance, low power consumption, or immunity to electromagnetic interference is required.
Background First developed in the 1970s, fiber-optics have revolutionized the telecommunications industry and played a major role in the advent of the Information Age. Because of advantages over electrical transmission, optical fibers have largely replaced copper wire communications in backbone networks in the developed world.
The process of communicating digital information using fiber optics involves the following basic steps: create the optical signal, usually by using an optical transmitter to convert electrical signals into optical ones relay the signal along optical fiber cables, possibly with help from optical amplifiers receive the optical signal and convert it into an electrical signal
Applications Optical fiber is used by telecommunications companies to transmit telephone signals, internet communication and cable television signals. It is also used in other industries, including medical, defense, government, industrial and commercial. 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. However, infrastructure development within cities is relatively difficult and time-consuming, and fiber-optic systems can be complex and expensive to install and operate. 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. The prices of fiber-optic communications have dropped considerably since 2000.
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. As of 2020, over 5 billion kilometers of fiber-optic cable have been deployed around the globe.
, rolling out fiber to the home can be more cost-effective than rolling out a copper-based network when all costs: instllation, opex, etc. and "drop" prices are considered. The total cost has dropped below $850 per subscriber in the US and lower in countries like the Netherlands, where digging costs are low and housing density high.
History
In 1880, Alexander Graham Bell and his assistant Charles Sumner Tainter created a very early precursor to fiber-optic communications, the photophone, a device that transmits sound over air using beams of light, at Bell's newly established Volta Laboratory in Washington, D.C.. On June 3, 1880, Bell conducted the world's first wireless telephone transmission between two buildings, some 213 meters apart. also published as "Selenium and the Photophone" in Nature, September 1880. While Bell was extremely proud of it, the photophone never caught on and was soon superseded by radio.
In 1954, Harold Hopkins and Narinder Singh Kapany showed that bundles of glass fibers could be used to transmit an image. In 1963, Jun-ichi Nishizawa, a Japanese scientist at Tohoku University, proposed the use of optical fibers for communication.
In 1966, Charles K. Kao and George Hockham at Standard Telecommunication Laboratories showed that the losses of in existing optical fiber glass (compared to in coaxial cable) were due to contaminants which could potentially be removed.
In 1970, optical fiber with attenuation low enough for practical communication purposes (about ) was developed by Corning Glass Works. Simultaneously, GaAs semiconductor lasers were developed that were compact and powerful enough to transmit light through fiber-optic cables over long distances. InGaAsP lasers were subsequently developed, which operate at a wavelength of , where attenuation in optical fiber is lowest.
First generation In 1973, Optelecom, Inc., co-founded by the inventor of the laser, Gordon Gould, received a contract from ARPA for one of the first optical communication systems. Developed for defense purposes by Army Missile Command in Huntsville, Alabama, the system was intended to allow a short-range missile with video processing to communicate by laser to the ground by means of a five-kilometer-long optical fiber that unspooled from the missile as it flew. Next, Optelecom delivered the first commercial optical communications system to Chevron.
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. This first-generation system operated at a bit rate of with repeater spacing of up to . Soon after, on 22 April 1977, General Telephone and Electronics sent the first live telephone traffic through fiber optics at a throughput in Long Beach, California.
In October 1973, Corning Glass signed a development contract with CSELT and Pirelli aimed to test fiber optics in an urban environment: in September 1977, the second cable in this test series, named COS-2, was experimentally deployed in two lines over in Turin, for the first time in a big city, at a speed of .
Second generation In the early 1980s, the second generation of fiber-optic communication was developed for commercial use, operated at using InGaAsP semiconductor lasers. These early systems were initially limited by multi-mode fiber dispersion, and in 1981 the single-mode fiber was revealed to improve system performance greatly; however, practical connectors capable of working with single-mode fiber proved difficult to develop. Canadian service provider SaskTel had completed construction of what was then the world's longest commercial fiber optic network, which covered and linked 52 communities. By 1987, these systems were operating at bit rates of up to with repeater spacing up to .
In 1988, the first transatlantic telephone cable to use optical fiber was TAT-8, based on Desurvire optimized laser amplification technology.
Third generation In the ealy 1990s, third-generation fiber-optic systems operated at and had losses of about . 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 pulse-spreading difficulties using conventional InGaAsP semiconductor lasers at by using dispersion-shifted fibers designed to have minimal dispersion at and limiting the laser spectrum to a single longitudinal mode. These developments eventually allowed third-generation systems to operate commercially at with increased repeater spacing in excess of .
Fourth generation In the late 1990s, 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. The introduction of WDM was the start of optical networking, as WDM became the technology of choice for fiber-optic bandwidth expansion. The first to market with a dense WDM system was Ciena Corp., in June 1996. The introduction of optical amplifiers and WDM caused system capacity to double every six months from 1992 until a bit rate of was reached by 2001. In 2006, a bit-rate of was reached over a single line using optical amplifiers. In 2021, Japanese scientists transmitted 319 terabits per second over 3,000 kilometers with four-core fiber cables the same diameter as a standard single-core cable.
Fifth generation 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 began to take advantage of fiber-optic communications to deliver a variety of high-throughput data and broadband services to consumers' homes.
In the early 2000s, the fifth generation of fiber-optic communication systems extended the wavelength range (bandwidth) over which a WDM system can operate. The standard band is the C band (1525–1565 nm). Dry fiber is used to provide an addtional low-loss window in the L-band, 1565–1625 nm. 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 2009, researchers at Bell Labs reached a record bandwidth–distance product of over kilometers per second.
Sixth generation In the 2020s, the sixth generation of fiber-optic communication systems will use space-division multiplexing (SDM),
Technology Transmitters
The most commonly used optical transmitters are semiconductor devices such as light-emitting diodes (LEDs), laser diodes, and vertical-cavity surface-emitting lasers (VCSELs). The difference between LEDs and laser diodes is that LEDs produce incoherent light, while laser diodes produce coherent light. VCSELs can produce both coherent and incoherent light. For use in optical communications, semiconductor optical transmitters are designed to be compact, efficient and reliable, while operating in an optimal wavelength range and directly modulated at high frequencies.
LEDs In its simplest form, an LED emits 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. 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– and transmission distances of a few kilometers.
LED light transmission is inefficient, with only about 1% of input power, or about 100 microwatts, eventually converted into launched power coupled into the optical fiber.
LEDs have 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 wavelength-division multiplexing (WDM) applications.
To improve upon the size and power requirements of LEDs in optical communications, microLED transmitters have been developed, which pack several hundred small LEDs into a dense array. Each MicroLED transmits at a lower bit rate of 3 Gbps while the whole array transfers data at over 1 Tbps. The power consumption is lower than VCSELs at switching fabric distances of up to 7 m.
VCSELs