[Timon3]

Imagine a beam of light hitting a prism. What comes out on the other side is a Fourier transform of the incoming light. Did the prism do a computation? If you say no, how about if I place photo detectors on the other side and measure the result - did I build a computer that does not do computations?

[didntreadarticl]

If its doing something with the result of the photon detectors, then yes I guess its processing the input and taking some action as a result. Bonus points if the incoming beam or light actually means something (e.g. perhaps it varies when something gets in the way). Congratulations you imagined a processor