Problems with pure optical computing
There have been fundamental problems with photonic computing for a long time.
One is heat dissipation, when an optical gate is off it effectively goes black so just generates heat. Transistors don't do this.
Secondly, light is quite large. Chips are already have feature massively smaller than optical wavelength, lithography requiring ultraviolet light these days. So any optical chip will have to be larger (features wise) than an equivalent electronic chip.
So basically for bulk across board/CPU maybe high bandwidth comms is the likely immediate and perhaps only possible use for photonics in the immediate future.
Surface plasmons are probably a more likely path for actual computation.
One other thing is that optical fibres have a pretty slow propagation rate has a VF (Velocity Factor) of about 0.6-0.7 (of the speed of light in a vacuum), decent coax can do 0.8-0.9. This higher bandwidth of fibre usually makes this much more preferable but for certain in computer functions this maybe a limiting factor (memory buses perhaps). I just mention this as hardly anyone seems to know this.