Many years ago, the navy lab in SD, as well as the physics dept at SDSU, had active optical signal processing groups. They were using optics to perform convolution, and were able to apply the convolution to various matched filters including Fourier transforms. The bottle neck in the various systems was the transducers that converted electrical signals to light and then the light back to electrical signals. The dynamic range of the processing system was always limited by the granularity (quantization) of the input and output transducers. Every time the optics folks mad a significant improvement in the transducers, the dsp area made a more significant improvement. It was a matter of one discipline being overtaken by technology in another. It was still fun to work with folks in the optical signal processing groups.