Optical wireless communications (OWC) is a form of optical communication in which unguided visible, infrared (IR), or ultraviolet (UV) light is used to carry a signal. It is generally used in short-range communication.
OWC systems operating in the visible band (390–750 nm) are commonly referred to as visible light communication (VLC). VLC systems take advantage of light-emitting diodes (LEDs) which can be pulsed at very high speeds without a noticeable effect on the lighting output and human eye. VLC can be possibly used in a wide range of applications including wireless local area networks, wireless personal area networks and vehicular networks, among others. [1] On the other hand, terrestrial point-to-point OWC systems, also known as the free space optical (FSO) systems, [2] operate at the near IR frequencies (750–1600 nm). These systems typically use laser transmitters and offer a cost-effective protocol-transparent link with high data rates, i.e., 10 Gbit/s per wavelength, and provide a potential solution for the backhaul bottleneck.
There has also been a growing interest in ultraviolet communication (UVC) as a result of recent progress in solid-state optical sources/detectors operating within solar-blind UV spectrum (200–280 nm). In this so-called deep UV band, solar radiation is negligible at the ground level and this makes possible the design of photon-counting detectors with wide field-of-view receivers that increase the received energy with little additional background noise. Such designs are particularly useful for outdoor non-line-of-sight configurations to support low-power short-range UVC such as in wireless sensors and ad-hoc networks.
Wireless communications technologies proliferated and became essential very quickly during the last few decades of the 20th century, and the early 21st century. The wide-scale deployment of radio-frequency technologies was a key factor in the expansion of wireless devices and systems. However, the portion of the electromagnetic spectrum used by wireless systems is limited in capacity, and licenses to use parts of the spectrum are expensive. With the rise in data-heavy wireless communications, the demand for RF spectrum is outstripping supply, causing companies to consider options for using parts of the electromagnetic spectrum other than radio frequencies.
Optical wireless communication (OWC) refers to transmission in unguided propagation media through the use of optical carriers: visible, infrared (IR), and ultraviolet (UV) radiation. Signalling through beacon fires, smoke, ship flags and semaphore telegraph can be considered the historical forms of OWC. [3] Sunlight has also been used for long-distance signaling since very early times. The earliest use of sunlight for communication purposes is attributed to ancient Greeks and Romans who used polished shields to send signals by reflecting sunlight during battles. [4] In 1810, Carl Friedrich Gauss invented the heliograph which uses a pair of mirrors to direct a controlled beam of sunlight to a distant station. Although the original heliograph was designed for the geodetic survey, it was used extensively for military purposes during the late 19th and early 20th century. In 1880, Alexander Graham Bell invented the photophone, the world’s first wireless telephone system.
Military interest in photophones continued after Bell's time. For example, in 1935, the German Army developed a photophone where a tungsten filament lamp with an IR transmitting filter was used as a light source. Also, American and German military laboratories continued the development of high-pressure arc lamps for optical communication until the 1950s. [5] Modern OWC uses either lasers or light-emitting diodes (LEDs) as transmitters. In 1962, MIT Lincoln Labs built an experimental OWC link using a light-emitting GaAs diode and was able to transmit TV signals over a distance of 30 miles. After the invention of the laser, OWC was envisioned to be the main deployment area for lasers and many trials were conducted using different types of lasers and modulation schemes. [6] However, the results were in general disappointing due to the large divergence of laser beams and the inability to cope with atmospheric effects. With the development of low-loss fiber optics in the 1970s, they became the obvious choice for long distance optical transmission and shifted the focus away from OWC systems.
Over the decades, interest in OWC was mainly limited to covert military applications, [7] and space applications including inter-satellite and deep-space links. [8] OWC’s mass market penetration has been so far limited with the exception of IrDA which is a highly successful wireless short-range transmission solution.[ needs update? ]
Variations of OWC can be potentially employed in a diverse range of communication applications ranging from optical interconnects within integrated circuits through outdoor inter-building links to satellite communications.
OWC can be divided into five categories based on the transmission range:
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word laser is an anacronym that originated as an acronym for light amplification by stimulated emission of radiation. The first laser was built in 1960 by Theodore Maiman at Hughes Research Laboratories, based on theoretical work by Charles H. Townes and Arthur Leonard Schawlow.
Free-space optical communication (FSO) is an optical communication technology that uses light propagating in free space to wirelessly transmit data for telecommunications or computer networking. "Free space" means air, outer space, vacuum, or something similar. This contrasts with using solids such as optical fiber cable.
Optoelectronics is the study and application of electronic devices and systems that find, detect and control light, usually considered a sub-field of photonics. In this context, light often includes invisible forms of radiation such as gamma rays, X-rays, ultraviolet and infrared, in addition to visible light. Optoelectronic devices are electrical-to-optical or optical-to-electrical transducers, or instruments that use such devices in their operation.
A laser diode is a semiconductor device similar to a light-emitting diode in which a diode pumped directly with electrical current can create lasing conditions at the diode's junction.
Optical communication, also known as optical telecommunication, is communication at a distance using light to carry information. It can be performed visually or by using electronic devices. The earliest basic forms of optical communication date back several millennia, while the earliest electrical device created to do so was the photophone, invented in 1880.
Photonics is a branch of optics that involves the application of generation, detection, and manipulation of light in form of photons through emission, transmission, modulation, signal processing, switching, amplification, and sensing. Photonics is closely related to quantum electronics, where quantum electronics deals with the theoretical part of it while photonics deal with its engineering applications. Though covering all light's technical applications over the whole spectrum, most photonic applications are in the range of visible and near-infrared light. The term photonics developed as an outgrowth of the first practical semiconductor light emitters invented in the early 1960s and optical fibers developed in the 1970s.
Wireless communication is the transfer of information (telecommunication) between two or more points without the use of an electrical conductor, optical fiber or other continuous guided medium for the transfer. The most common wireless technologies use radio waves. With radio waves, intended distances can be short, such as a few meters for Bluetooth or as far as millions of kilometers for deep-space radio communications. It encompasses various types of fixed, mobile, and portable applications, including two-way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples of applications of radio wireless technology include GPS units, garage door openers, wireless computer mouse, keyboards and headsets, headphones, radio receivers, satellite television, broadcast television and cordless telephones. Somewhat less common methods of achieving wireless communications involve other electromagnetic phenomena, such as light and magnetic or electric fields, or the use of sound.
Terahertz radiation – also known as submillimeter radiation, terahertz waves, tremendously high frequency (THF), T-rays, T-waves, T-light, T-lux or THz – consists of electromagnetic waves within the ITU-designated band of frequencies from 0.3 to 3 terahertz (THz), although the upper boundary is somewhat arbitrary and is considered by some sources as 30 THz. One terahertz is 1012 Hz or 1000 GHz. Wavelengths of radiation in the terahertz band correspondingly range from 1 mm to 0.1 mm = 100 µm. Because terahertz radiation begins at a wavelength of around 1 millimeter and proceeds into shorter wavelengths, it is sometimes known as the submillimeter band, and its radiation as submillimeter waves, especially in astronomy. This band of electromagnetic radiation lies within the transition region between microwave and far infrared, and can be regarded as either.
RONJA is a free-space optical communication system originating in the Czech Republic, developed by Karel Kulhavý of Twibright Labs and released in 2001. It transmits data wirelessly using beams of light. Ronja can be used to create a 10 Mbit/s full of duplex Ethernet point-to-point link. It has been estimated that 1000 to 2000 links have been built worldwide.
A tunable laser is a laser whose wavelength of operation can be altered in a controlled manner. While all laser gain media allow small shifts in output wavelength, only a few types of lasers allow continuous tuning over a significant wavelength range.
A vertical-external-cavity surface-emitting-laser (VECSEL) is a small semiconductor laser similar to a vertical-cavity surface-emitting laser (VCSEL). VECSELs are used primarily as near infrared devices in laser cooling and spectroscopy, but have also been explored for applications such as telecommunications.
An optical neural network (ONN) is a physical implementation of an artificial neural network with optical components.
Yttrium aluminium garnet (YAG, Y3Al5O12) is a synthetic crystalline material of the garnet group. It is a cubic yttrium aluminium oxide phase, with other examples being YAlO3 (YAP) in a hexagonal or an orthorhombic, perovskite-like form, and the monoclinic Y4Al2O9 (YAM).
A blue laser emits electromagnetic radiation with a wavelength between 400 and 500 nanometers, which the human eye sees in the visible spectrum as blue or violet.
In telecommunications, visible light communication (VLC) is the use of visible light as a transmission medium. VLC is a subset of optical wireless communications technologies.
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 800 Gbit/s. Multi-mode fiber has a fairly large core diameter that enables multiple light modes to be propagated and limits the maximum length of a transmission link because of modal dispersion. The standard G.651.1 defines the most widely used forms of multi-mode optical fiber.
Aluminium gallium indium phosphide is a semiconductor material that provides a platform for the development of multi-junction photovoltaics and optoelectronic devices. It spans a direct bandgap ranging from ultraviolet to infrared photon energies.
Fiber-optic communication is a method of 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. Fiber is preferred over electrical cabling when high bandwidth, long distance, or immunity to electromagnetic interference is required. This type of communication can transmit voice, video, and telemetry through local area networks or across long distances.
Li-Fi is a wireless communication technology which utilizes light to transmit data and position between devices. The term was first introduced by Harald Haas during a 2011 TEDGlobal talk in Edinburgh.
Shlomi Arnon, is a professor in the Department of Electrical and Computer Engineering at Ben Gurion University of the Negev (BGU), Israel. In addition to his role as a professor, he serves as the director of both the Center for Quantum Science and Technology (BGU-QST) and the Satellite and Wireless Communication Laboratory at the university. For his contributions to the field of optics and photonics, he has been recognized as a fellow of the International Society for Optics and Photonics (SPIE).
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