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.
Birmingham (/ˈbɜːrmɪŋəm/ (About this soundlisten) BUR-ming-əm) is a city and metropolitan borough in the West Midlands, England. It is the second-largest city, urban area and metropolitan area in England and the United Kingdom,[b] with roughly 1.1 million inhabitants within the city area, 2.9 million inhabitants within the urban area and 4.3 million inhabitants within the metropolitan area and lies within the most populated English district. Birmingham is commonly referred to as the second city of the United Kingdom.
Located in the West Midlands county and region in England, approximately 100 miles (160 km) from Central London, Birmingham, as one of the United Kingdom's major cities, is considered to be the social, cultural, financial, and commercial centre of both the East and West Midlands. Distinctively, Birmingham only has small rivers flowing through it, mainly the River Tame and its tributaries River Rea and River Cole – one of the closest main rivers is the Severn, approximately 20 miles (32 km) west of the city centre.
A market town of Warwickshire in the medieval period, Birmingham grew in the 18th-century Midlands Enlightenment and subsequent Industrial Revolution, which saw advances in science, technology, and economic development, producing a series of innovations that laid many of the foundations of modern industrial society. By 1791, it was being hailed as "the first manufacturing town in the world". Birmingham's distinctive economic profile, with thousands of small workshops practising a wide variety of specialised and highly skilled trades, encouraged exceptional levels of creativity and innovation and provided an economic base for prosperity that was to last into the final quarter of the 20th century. The Watt steam engine was invented in Birmingham.
The resulting high level of social mobility also fostered a culture of political radicalism which, under leaders from Thomas Attwood to Joseph Chamberlain, was to give it a political influence unparalleled in Britain outside London, and a pivotal role in the development of British democracy. From the summer of 1940 to the spring of 1943, Birmingham was bombed heavily by the German Luftwaffe in what is known as the Birmingham Blitz. The damage done to the city's infrastructure, in addition to a deliberate policy of demolition and new building by planners, led to extensive urban regeneration in subsequent decades.
Birmingham's economy is now dominated by the service sector. The city is a major international commercial centre and an important transport, retail, events and conference hub. Its metropolitan economy is the second largest in the United Kingdom with a GDP of $121.1bn (2014), and its six universities make it the largest centre of higher education in the country outside London. Birmingham's major cultural institutions – the City of Birmingham Symphony Orchestra, the Birmingham Royal Ballet, the Birmingham Repertory Theatre, the Library of Birmingham and the Barber Institute of Fine Arts – enjoy international reputations, and the city has vibrant and influential grassroots art, music, literary and culinary scenes. The city will host the 2022 Commonwealth Games. Birmingham is the fourth-most visited city in the UK by foreign visitors.