I guess as long as you have any sort of device that can do basic Boolean logic (aka logic operations) then you're good to go.
Take Minecraft for example: many people have already built their own CPU/computer which can do simple calculus and even run some games ! Nothing more than blocks were needed.
As long as you can do execute/process the very same operations as modern processors do with a given system or material, then you're just on your way to another type of processor. Since light physics can be used to make this 1 and 0 states "happen", we can have optical processors.
Now the thing is, how do you make RAM ? (or equivalent) Will it be optical memory ? Or will there be some sort of classical RAM bridge to the optical components ? And what about the graphics cards, hard disks, etc ?
Time will tell. For now, calculus only.