https://en.wikipedia.org/wiki/Charles_K._Kao "In 1965,[44][47]b[›] Kao with Hockham concluded that the fundamental limitation for glass light attenuation is below 20 dB/km (decibels per kilometer, is a measure of the attenuation of a signal over a distance), which is a key threshold value for optical communications.[48] However, at the time of this determination, optical fibres commonly exhibited light loss as high as 1,000 dB/km and even more. This conclusion opened the intense race to find low-loss materials and suitable fibres for reaching such criteria.[citation needed] Kao, together with his new team (members including T. W. Davies, M. W. Jones, and C. R. Wright), pursued this goal by testing various materials. They precisely measured the attenuation of light with different wavelengths in glasses and other materials. During this period, Kao pointed out that the high purity of fused silica (SiO2) made it an ideal candidate for optical communication. Kao also stated that the impurity of glass material is the main cause for the dramatic decay of light transmission inside glass fibre, rather than fundamental physical effects such as scattering as many physicists thought at that time, and such impurity could be removed. This led to a worldwide study and production of high-purity glass fibres.  When Kao first proposed that such glass fibre could be used for long-distance information transfer and could replace copper wires which were used for telecommunication during that era, his ideas were widely disbelieved; later people realized that Kao's ideas revolutionized the whole communication technology and industry.[50] He also played a leading role in the early stage of engineering and commercial realization of optical communication.[51] In spring 1966, Kao traveled to the U.S. but failed to interest Bell Labs, which was a competitor of STL in communication technology at that time.[52] He subsequently traveled to Japan and gained support.[52] Kao visited many glass and polymer factories, discussed with various people including engineers, scientists, businessmen about the techniques and improvement of glass fiber manufacture. In 1969, Kao with M. W. Jones measured the intrinsic loss of bulk-fused silica at 4 dB/km, which is the first evidence of ultra-transparent glass. Bell Labs started considering fibre optics seriously.[52][end of quote] Of course, neither Kao nor any of his industry recognized what I eventually did:  that even after modern-purified fused-silica was produced, there were still a few more sources of impurity in that, and that included Si-29 and Ge-73 isotopes.  I fully expect that when these 'spin'-containing isotopic sources are removed, the silica single-mode fiber loss will drop to 0.001 dB/kilometer, about 150x lower than it currently is.                       Jim Bell