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.
Sleaford (historically known as New Sleaford) is a market town and civil parish in Lincolnshire, England. Since 1973, the parish boundaries have included Quarrington to the south-west, Holdingham to the north and Old Sleaford to the east – contiguous settlements and former civil parishes which, with New Sleaford, had formed an Urban District. The town is on the edge of the fertile Fenlands, about 11 miles (18 kilometres) north-east of Grantham, 16 mi (26 km) west of Boston, and 17 mi (27 km) south of Lincoln. With a population of 17,671 at the 2011 Census, the town is the largest settlement in the North Kesteven district. Bypassed by the A17 and the A15, it is connected to Lincoln, Newark, Peterborough and King's Lynn. Sleaford railway station is on the Nottingham to Skegness (via Grantham) and Peterborough to Lincoln Lines.
The first settlement formed in the Iron Age where a prehistoric track crossed the River Slea. It was a tribal centre and home to a mint for the Corieltauvi in the 1st centuries BC and AD. Evidence of Roman and Anglo-Saxon settlement has been uncovered. In the medieval period, records differentiate between Old and New Sleaford, the latter emerging by the 12th century around the present-day market place and St Denys' Church; Sleaford Castle was also built at that time for the Bishops of Lincoln, who owned the manor. Granted the right to hold a market in the mid-12th century, New Sleaford developed into a market town and became locally important in the wool trade, while Old Sleaford declined.
From the 16th century, the landowners were the Carre family, who operated tight control over the town, and it grew little in the early modern period. The manor passed from the Carre family to the Hervey family by the marriage of Isabella Carre to John Hervey, 1st Earl of Bristol, in 1688. The town's common land and fields were legally enclosed by 1794, giving ownership mostly to the Hervey family; this coincided with the Slea's canalisation; the Sleaford Navigation brought economic growth until it was superseded by the railways in the mid-1850s. In the 20th century, the sale of farmland around Sleaford by Bristol Estates led to the development of large housing estates. The subsequent availability of affordable housing combined with the town's educational facilities and low crime rates made it an attractive destination for home-buyers. As a result, the town's population underwent the fastest growth of any town in the county in the 1990s.
Sleaford was primarily an agricultural town until the 20th century, supporting a cattle market, with seed companies, such as Hubbard and Phillips, and Sharpes International Seeds, being established in the late 19th century. The arrival of the railway made the town favourable for malting. Industry has declined, and in 2011 the most common occupations are in wholesale and retail trade, health and social care, public administration and defence and manufacturing. Regeneration of the town centre has led to the redevelopment of the old industrial areas, including the construction of the National Centre for Craft & Design on an old wharf.