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 reasons, some listed below.
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