Every time we get on the Internet or make an overseas phone call, we tap into the underwater web. This vast flow of communication is made possible by a vast new network of fiber-optic technology. For this reason, you can send more signals by light than by electric currents, radio, or microwaves. By the year 2000, the vast majority of intercontinental Internet traffic was being carried by underwater fiber-optic cables. This early amplifier changed the optical signal into an electrical one, amplified it, and converted it back to optical.
Later versions use a technique that amplifies optical signals directly.