Fibre optics

In the mid-1960s light could already be trapped inside a thin glass thread, but the glass was hopeless: after only 20 metres, just 1 percent of the light was left. Nobody serious thought it could replace copper for telephone lines.

In January 1966 Charles Kao, working with George Hockham at Standard Telecommunication Laboratories in England, presented a different diagnosis. The problem, he argued, was not the fibre itself but impurities in the glass. Purify it enough and at least 1 percent of the light would survive a full kilometre, enough for telecommunications. He suggested fused silica, an extremely pure form of quartz.