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Fibre

​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.[1] 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.[2] 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.[3] Specially designed fibers are also used for a variety of other applications, some of them being fiber optic sensors and fiber lasers.[4]

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.[5] 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).[6] Multi-mode fibers generally have a wider core diameter[7] and are used for short-distance communication links and for applications where high power must be transmitted.[8] Single-mode fibers are used for most communication links longer than 1,000 meters (3,300 ft).[citation needed]

Being able to join optical fibers with low loss is important in fiber optic communication.[9] 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.[10]

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.[11]

​Lichfield (/ˈlɪtʃfiːld/) is a cathedral city and civil parish[2] in Staffordshire, England. Lichfield is situated roughly 16 mi (26 km) north of Birmingham, 8.1 miles (13.0 km) from Rugeley, 9 miles (14 km) from Walsall, 7.9 miles (12.7 km) from Tamworth and 13 miles (21 km) from Burton Upon Trent. At the time of the 2011 Census the population was estimated at 32,219 and the wider Lichfield District at 100,700.[3]

Notable for its three-spired medieval cathedral, Lichfield was the birthplace of Samuel Johnson, the writer of the first authoritative Dictionary of the English Language. The city's recorded history began when Chad of Mercia arrived to establish his Bishopric in 669 AD and the settlement grew as the ecclesiastical centre of Mercia. In 2009, the Staffordshire Hoard, the largest hoard of Anglo-Saxon gold and silver metalwork, was found 5.9 km (3.7 mi) south-west of Lichfield.

The development of the city was consolidated in the 12th century under Roger de Clinton, who fortified the Cathedral Close and also laid out the town with the ladder-shaped street pattern that survives to this day. Lichfield's heyday was in the 18th century, when it developed into a thriving coaching city. This was a period of great intellectual activity, the city being the home of many famous people including Samuel Johnson, David Garrick, Erasmus Darwin and Anna Seward, and prompted Johnson's remark that Lichfield was "a city of philosophers".

Today, the city still retains its old importance as an ecclesiastical centre, and its industrial and commercial development has been limited. The centre of the city has over 230 listed buildings (including many examples of Georgian architecture), and preserves much of its historic character.

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