Fibre optics on the 1969 Moon cameras were a classified secret
When NASA sent television cameras to the Moon, their use of optical fibres was classified, and anyone handling the cameras had to be watched by someone with security clearance. Just three years earlier, a German physicist had demonstrated the first working system for sending data through glass fibres.
An optical fibre is a thin strand of glass or plastic with a core surrounded by cladding that bends light less strongly. Light striking the boundary at a shallow enough angle cannot escape and bounces along the core by total internal reflection, even around curves. Compared with copper cables, fibres carry more data over longer distances with less loss, and electromagnetic interference does not affect them. Thick-cored multi-mode fibre suits short links, while thin single-mode fibre handles most links longer than about a kilometre.
The underlying effect was shown in Paris in the early 1840s by Daniel Colladon and Jacques Babinet, and John Tyndall later demonstrated it in public lectures in London. In 1870 Tyndall noted that light leaving water at more than about 48 degrees from the perpendicular is trapped completely, and that the critical angle is smaller for flint glass and smaller still for diamond. Late in the nineteenth century Viennese doctors used bent glass rods to light up body cavities, and dentists later adopted similar tricks.
Sending pictures proved harder. Heinrich Lamm passed images through a bundle of bare fibres in the 1930s for medical examinations, but his work was forgotten. In 1953 the Dutch scientist Bram van Heel added transparent cladding, and in London that year Harold Hopkins and Narinder Singh Kapany built bundles of over 10,000 fibres. Researchers at the University of Michigan patented a flexible fibre-optic gastroscope in 1956, and one of them, Lawrence Curtiss, made the first glass-clad fibres; earlier versions had relied on air, oils or waxes.
Kapany popularised the phrase fibre optics in a 1960 Scientific American article and wrote the first book on the field. Manfred Börner demonstrated fibre data transmission at Telefunken in Ulm in 1965. Joining fibres remains delicate work, often done by fusing the ends with an electric arc.
Source: Optical fiber
