Aside from the actual fiber itself: literally your entire computer. No part of a modern consumer computing device has 1Tb/s bandwidth - RAM, SSDs, networking cards, PCI, the front-side bus, and everything else, with the possible exception of the L1 cache[1], have maximum bandwidths well below 1Tb/s (= 125 GiB/s).

[1] https://electronics.stackexchange.com/questions/329789/how-c...