Originally, a device known as the 'photophone' was used to transmit sound. This replaced Thomas .A. Edison's 'phonograph. Since the development of optical fibres 'photo phones' and 'phonographs' are no longer used or needed. Optical fibres have many advantages; they enable the sound messages to carry for 50km without any need for a repeater unlike other optical communication systems, which need repeaters at 1km intervals. Optical fibres have replaced other methods of communication for many …showed first 75 words of 533 total…

…showed last 75 words of 533 total…to relay messages is not a new one. It has been used since the early 1960's. Because the electrical information is carried by light, it can be exchanged from one place to another very quickly (199,861,639 m/sec). Optical fibres are used throughout the world, in telephones, cable TV, security systems, computers and other communication devices. They are particularly useful because computers on the other side of the world can communicate in a matter of seconds.