computers are not necessarily built on EMF principles. optical, fluid, gear driven and other mechanisms can be used to implement compuutation, and not just binary discrete math, but there are analog computers, for example, the soviet bloc was running their train networks and other infrastructure control systems using a computer that works entirely using water pressure and counts using volumes of water.
also, the new memory tech that Google has been developing, Systolic Array Memory, is likely something that lends itself very well to implementation in optical circuitry. that field is still very young, also. in 2001 a housemate at a sharehouse i lived at, was an engineer working for a company developing pure optical switch systems. the backbone of the internet is actually powered by light.