【正文】 images, thus allowing viewing in confined spaces. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers. Optical fibers typically include a transparent core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by total internal reflection. This causes the fiber to act as a waveguide. Fibers that support many propagation paths or transverse modes are called multimode fibers (MMF), while those that only support a single mode are called singlemode fibers (SMF). Multimode fibers generally have a wider core diameter, and are used for shortdistance munication links and for applications where high power must be transmitted. Singlemode fibers are used for most munication links longer than 1050 meters (3440ft). Joining lengths of optical fiber is more plex than joining electrical wire or cable. The ends of the fibers must be carefully cleaved, and then spliced together, either mechanically or by fusing them with heat. Special optical fiber connectors for removable connections are also available. History Fiber optics, though used extensively in the modern world, is a fairly simple, and relatively old, technology. Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon and Jacques Babi in Paris in the early 1840s. John Tyndall included a demonstration of it in his public lectures in London, 12 years later.[3] Tyndall also wrote about the property of total internal reflection in an introductory book about the nature of light in applications, such as close internal illumination during dentistry, appeared early in the twentieth century. Image transmission through tubes was demonstrated independently by the radio experimenter Clarence Hansell and the television pioneer John Logie Baird in the 1920s. The principle was first used for internal medical examinations by Heinrich Lamm in the following decade. Modern optical fibers, where the glass fiber is coated with a transparent cladding to offer a more suitable refractive index, appeared later in the decade.[3] Development then focused on fiber bundles for image transmission. Harold Hopkins and Narinder Singh Kapany at Imperial College in London achieved lowloss light transmission through a 75 cm long bundle which bined several thousand fibers. Their article titled A flexible fibrescope, using static scanning was published in the journal Nature in 1954.[78] The first fiber optic semiflexible gastroscope was patented by Basil Hirschowitz,C. Wilbur Peters, and Lawrence E. Curtiss, researchers at the University of Michigan, in 1956. In the process of developing the gastroscope, Curtiss produced the first glassclad fibers。Photophone39。rner at Telefunken Research Labs in Ulm in 1965, which was followed by the first patent application for this technology in 1966.[1415] Charles K. Kao and Gee A. Hockham of the British pany Standard Telephones and Cables were the first to promote the idea that the attenuation in optical fibers could be reduced below 20 decibels per kilometer, making fibers a practical munication medium. They proposed that the attenuation in fibers available at the time was caused by impurities that could be removed, rather than by fundamental physical effects such as scattering. They correctly and systematically theorized the lightloss properties for optical fiber, and pointed out the right material to use for such fibers — silica glass with high purity. This discovery earned Kao the Nobel Prize in Physics in 2022. NASA used fiber optics in the television cameras that were sent to the moon. At the time, the use in the cameras was classified confidential, and only those with the right security clearance or those acpanied by someone with the right security clearance were permitted to handle the crucial attenuation limit of 20 dB/km was first achieved in 1970, by researchers Robert D. Maurer, Donald Keck, working for American glass maker Corning Glass Works, now Corning Incorporated. They demonstrated a fiber with 17 dB/km attenuation by doping silica glass with titanium. A few years later they produced a fiber with only 4 dB/km attenuation using germanium dioxide as the core dopant. Such low attenuation ushered in optical fiber telemunication. In 1981, General Electric produced fused quartz ingots that could be drawn into fiber optic strands 40km long. Attenuation in modern optical cables is far less than in electrical copper cables, leading to longhaul fiber connections with repeater distances of 70–150 kilometers. The erbiumdoped fiber amplifier, which reduced the cost of longdistance fiber systems by reducing or eliminating opticalelectricaloptical repeaters, was codeveloped by teams led by David N. Payne of the University of Southampton and Emmanuel Desurvire at Bell Labs in 1986. Robust modern optical fiber uses glass for both core and sheath, and is therefore less prone to aging. The emerging field of photonic crystals led to the development in 1991 of photoniccrystal fiber, which guides light by diffraction from a periodic structure, rather than by total internal reflection. The first photonic crystal fibers became mercially available in crystal fibers can carry higher power than conventional fibers and their wavelengthdependent properties can be manipulated to improve performance. Optical fiber munication Optical fiber can be used as a medium for telemunication and puter working because it is flexible and can be bundled as cables. It is especially advantageous for longdistance munications, because light propagates through the fiber with little attenuation pared to electrical cables. This allows long distances to be spanned with few repeaters. Additionally, the perchanne