Though optical CPUs are still only theoretical, optical fibers are being used everywhere else in computing and communications.
From a speed standpoint (not a cost one), does it make sense to run internal computer wiring between components (the buses between CPU, video processor, etc.) as optical fiber? Or do the converters that translate the electrical signals into light pulses and back again introduce too much of a time lag to make it worthwhile to switch over for such short runs?
As someone who designed fiber optic data interfaces for a living, I can say that there is no benefit with current technology to using fiber optics for data buses inside a computer. Fiber optics communication is useful not so much for speed, but the ability to transmit high bandwith data over small fibers with little degradation over long distances. For the short runs (less than a foot) between components inside a computer, the size, power consumption, and bandwith limitations of the fiber optic transmitters and recievers would far overwhelm any gains in speed from using fiber optics.
Now, once we have technology to do data processing and switching entierly with light at densities comparable to what we can currently do with electrons, that may change. Or if your computer needs to be spread out over a large space for some reason, it might make sense to transmit the data buses with fiber optics to reduce RF noise problems.