If you look at some of the earliest Synthetic Aperture Radar (SAR) systems, you'll find that they used exposed film (i.e. light) to perform some serious fourier

If you look at some of the earliest Synthetic Aperture Radar (SAR) systems, you'll find that they used exposed film (i.e. light) to perform some serious fourier-style computations using diffractive optics. I.e. you can use physical processes to perform useful computations. It's not entirely out of the realm of possibility... it's just that silicon & Moore's law generated a lot of deterministic, general-purpose compute capability -- whether CPU or GPU. it's kind of akin to certain compute jobs using quantum effects: There are a class of algorithms that can benefit from that kind of co-processor. Off the cuff, I don't know of any compute jobs where optical "computers" give you major speedups compared to standard digital processes. But it's not altogether crazy.