Fiber-optic communication

 ( 20th-century Inventions ) 

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 process of communicating digital information using fiber optics involves the following basic steps:

1. create the optical signal, usually by using an optical transmitter to convert electrical signals into optical ones
2. relay the signal along optical fiber cables, possibly with help from optical amplifiers
3. receive the optical signal and convert it into an electrical signal

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 Terabit/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.

 
Mary Kay Carson (2026). 9781402732300, Sterling Publishing. . ISBN 9781402732300

  also published as "Selenium and the Photophone" in ''Nature'', September 1880.
     

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.

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 .

In 1988, the first transatlantic telephone cable to use optical fiber was TAT-8, based on Desurvire optimized laser amplification technology.

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 optics 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.

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 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.

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 (up to ~50%) into single-mode fiber. Common VCSEL devices also couple well to multimode fiber. The narrow spectral width also allows for high bit rates (54 Gb/s, NRZ) since it reduces the effect of chromatic dispersion. Furthermore, semiconductor lasers can be modulated directly at high frequencies (>28 Ghz) because of their short recombination time.

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

To recover data modulated with QPSK, QAM, or OFDM, receivers use a local oscillator laser in combination with a pair of hybrid (active and passive component) couplers and four photodetectors (one for each polarization), followed by high-speed ADCs and digital signal processing.

Older digital predistortion methods only addressed linear effects. Recent publications also consider non-linear distortions. Berenguer et al models the Mach–Zehnder modulator as an independent Wiener series and the DAC and the driver amplifier are modeled by a truncated, time-invariant Volterra series. Khanna et al use a memory polynomial to model the transmitter components jointly. In both approaches, the Volterra series or the memory polynomial coefficients are found using an indirect-learning architecture. Duthel et al records, for each branch of the Mach-Zehnder modulator, several signals at different polarities and phases. The signals are used to calculate the optical field. Cross-correlating in-phase and quadrature fields identifies the timing skew. The frequency response and the non-linear effects are determined by the indirect-learning architecture.

Two main types of optical fiber used in optical communications include multi-mode optical fibers and single-mode optical fibers. A multi-mode optical fiber has a larger core (≥50 micrometre), allowing less precise, less expensive 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 their 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 and higher-performance links. Both single- and multi-mode fibers are offered in different grades.

When packaging fiber into a commercially viable product, fiber is typically protectively coated by using ultraviolet-cured acrylate polymers, Polyimide, or Silicone to improve resistance to environmental factors and mechanical damage. The coated fiber is then assembled into a cable. After cable construction, the cable can be laid in the ground, or run through the walls of a building, or deployed aerially in a manner similar to copper cables. Optical fibers can require less maintenance than common twisted pair wires once they are deployed.

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

Another common practice is to bundle many fiber optic strands within long-distance power transmission cable using, for instance, an optical ground wire. 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.

Current optical fibers for long-distance communication are based on silica. Plastics and other types of glass exhibit much higher optical attenuation and are unsuitable for this application. Yasuhiro Koike developed an advanced perfluorinated polymer with a minimum attenuation of at 650 nm. Using this new material as a basis, he developed the graded-index polymer optical fiber (GIPOF). Transmission at a speed of over 100 m has been demonstrated with GIPOF. This is sufficient for applications in buildings and data centers. Unlike silica fibers, polymer fibers remain flexible even at larger diameters. This larger diameter is a significant advantage for interconnection. GIPOF typically has a core diameter of between 50 and 120 microns.

An alternative approach is to use optical amplifiers, which amplify the optical signal directly without having to convert the signal to the electrical domain. One common type of optical amplifier is an erbium-doped fiber amplifier (EDFA). 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 nanometer). EDFAs provide gain in the ITU C band at 1550 nm. For the same band, semiconductor optical amplifiers (SOA) can be used.

Praseodymium-doped optical fiber amplifiers (PDFA) are suitable for the 1280–1350 nm wavelength range. In an experiment involving eight 100 Gbit/s signals, more than 30 dB of gain was demonstrated across all channels. Semiconductor optical amplifiers (SOA) have been used in a record experiment for the wavelength range around 1300 nm.

Optical amplifiers have several significant advantages over electrical repeaters. First, an optical amplifier can amplify a very wide band at once, which can include hundreds of multiplexed channels, eliminating the need to demultiplex signals at each amplifier. Second, optical amplifiers operate independently of the data rate and modulation format, enabling multiple data rates and modulation formats to co-exist and enabling upgrading of the data rate of a system without having to replace all of the repeaters. Third, optical amplifiers are much simpler than a repeater with the same capabilities and are therefore significantly more reliable. Optical amplifiers have largely replaced repeaters in new installations, although electronic repeaters are still widely used when signal conditioning beyond amplification is required.

Research conducted by RMIT University, Melbourne, Australia, has 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. The technique is known as orbital angular momentum (OAM). The nanophotonic device uses ultra-thin sheets to measure a fraction of a millimeter of twisted light. A nano-electronic device is embedded within a connector smaller than the size of a USB connector and may be fitted at the end of an optical fiber cable.

Intermodal dispersion, caused by the different axial speeds of different , 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, which occurs because the index of the glass varies slightly depending on the wavelength of the light, and, due to modulation, light from optical transmitters necessarily occupies a (narrow) range of wavelengths. 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 birefringence and can be counteracted by polarization-maintaining optical fiber.

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.

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

Historically, there was a window of wavelengths shorter than 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 address this.

Recent advances in fiber and optical communications technology have reduced signal degradation to the point 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.

In the US, Verizon Communications provides an 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. Their MSO competitors employ FTTN with coax using hybrid fiber-coaxial networks. All of the major access networks use fiber for the bulk of the distance from the service provider's network to the customer.

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

The main benefits of fiber are its exceptionally low loss (allowing long distances between repeaters), its absence of ground currents and other parasitic signals 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 , 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 , with no active or passive processing.

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.

In short-distance and relatively low-bandwidth applications, electrical transmission is often preferred because of its lower cost. Optical communication is not common in short box-to-box, backplane, or chip-to-chip applications.

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.
• 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 potential for arcing—important in flammable or explosive gas environments.
  (2026). 9781118019542, John Wiley & Sons. ISBN 9781118019542
• Not electromagnetically radiating, and difficult to tap without disrupting the signal—important in high-security environments.
• Much smaller cable size—important where the 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 using the same equipment that is used to install copper and coaxial cables, with some modifications due to the small size and limited allowable pull tension and bend radius of optical cables.

• 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
• HIPPI
• 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. Polymer optical fibers are described in the IEC (International Electrotechnical Commission) standard 6073-2-40.

• Free-space optical communication

• Encyclopedia of Laser Physics and Technology
• Fiber-Optic Technologies by Vivek Alwayn
• (2026). 9780471215714, John Wiley & Sons. ISBN 9780471215714

• Keiser, Gerd. (2011). Optical fiber communications, 4th ed. New York: McGraw-Hill,
• Senior, John. (2008). Optical Fiber Communications: Principles and Practice, 3rd ed. Prentice Hall.
• Koike, Yasuhiro. (2014). Fundamentals of Plastic Optical Fibers, Wiley,
• Willner, Alan. (2019). Optical Fiber Telecommunications VII, Academic Press,
• Agrawal, Govind. (2021). Fiber-Optic Communication Systems, Wiley,

• "Understanding Optical Communications" An IBM redbook