An optical fiber (or fibre in British English) is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means to transmit light[a] between the two ends of the fiber and find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths (data transfer rates) than electrical cables. Fibers are used instead of metal wires because signals travel along them with less loss; in addition, fibers are immune to electromagnetic interference, a problem from which metal wires suffer. Fibers are also used for illumination and imaging, and are often wrapped in bundles so they may be used to carry light into, or images out of confined spaces, as in the case of a fiberscope. Specially designed fibers are also used for a variety of other applications, some of them being fiber optic sensors and fiber lasers.
Optical fibers typically include a core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by the phenomenon of total internal reflection which causes the fiber to act as a waveguide. Fibers that support many propagation paths or transverse modes are called multi-mode fibers, while those that support a single mode are called single-mode fibers (SMF). Multi-mode fibers generally have a wider core diameter and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibers are used for most communication links longer than 1,000 meters (3,300 ft).
Being able to join optical fibers with low loss is important in fiber optic communication. This is more complex than joining electrical wire or cable and involves careful cleaving of the fibers, precise alignment of the fiber cores, and the coupling of these aligned cores. For applications that demand a permanent connection a fusion splice is common. In this technique, an electric arc is used to melt the ends of the fibers together. Another common technique is a mechanical splice, where the ends of the fibers are held in contact by mechanical force. Temporary or semi-permanent connections are made by means of specialized optical fiber connectors.
The field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics. The term was coined by Indian-American physicist Narinder Singh Kapany, who is widely acknowledged as the father of fiber optics.
Bristol (/ˈbrɪstəl/ (About this soundlisten)) is a city, ceremonial county and unitary authority in England. Situated on the River Avon, it is bordered by the ceremonial counties of Gloucestershire, to the north; and Somerset, to the south. Bristol is the most populous city in South West England. The wider Bristol Built-up Area is the eleventh most populous urban area in the United Kingdom.
Iron Age hill forts and Roman villas were built near the confluence of the rivers Frome and Avon, and around the beginning of the 11th century, the settlement was known as Brycgstow (Old English "the place at the bridge"). Bristol received a royal charter in 1155 and was historically divided between Gloucestershire and Somerset until 1373 when it became a county of itself. From the 13th to the 18th century, Bristol was among the top three English cities, after London, in tax receipts; however, it was surpassed by the rapid rise of Birmingham, Manchester and Liverpool in the Industrial Revolution.
Bristol was a starting place for early voyages of exploration to the New World. On a ship out of Bristol in 1497 John Cabot, a Venetian, became the first European to land on mainland North America. In 1499 William Weston, a Bristol merchant, was the first Englishman to lead an exploration to North America. At the height of the Bristol slave trade, from 1700 to 1807, more than 2,000 slave ships carried an estimated 500,000 people from Africa to slavery in the Americas. The Port of Bristol has since moved from Bristol Harbour in the city centre to the Severn Estuary at Avonmouth and Royal Portbury Dock.
Bristol's modern economy is built on the creative media, electronics and aerospace industries, and the city-centre docks have been redeveloped as centres of heritage and culture. The city has the largest circulating community currency in the UK; the Bristol pound, which is pegged to the Pound sterling. The city has two universities, the University of Bristol and the University of the West of England, and a variety of artistic and sporting organisations and venues including the Royal West of England Academy, the Arnolfini, Spike Island, Ashton Gate and the Memorial Stadium. It is connected to London and other major UK cities by road and rail, and to the world by sea and air: road, by the M5 and M4 (which connect to the city centre by the Portway and M32); rail, via Bristol Temple Meads and Bristol Parkway mainline rail stations; and Bristol Airport.
One of the UK's most popular tourist destinations, Bristol was named the best city in Britain in which to live in 2014 and 2017, and won the European Green Capital Award in 2015.