So fibre can carry hundreds of signals / streams at once. More signals = more throughput. But so can electrical - just look at your cable tv connection - 200+ channels, and all sent over the one wire. It's the same principle - different frequencies on the radio dial. Fibre uses the same principle, and can carry 100+ channels, but the frequencies are represented by different colours, split and combined using a prism - though you cant see these colours as they're deep into the infra-red (like how you cant see the light from your TV IR remote). The main difference is that electrical has a limit to how much total combined speed it can carry...
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