Photodetection

Photodetection supplies the main nonlinearity by measuring intensity as a quadratic operation in field amplitude. Class scores are computed by integrating optical energy over disjoint detector regions assigned to classes. The predicted class is selected by taking the argmax over region-integrated energies. Correct classifications arise when learned phase structures create constructive interference in the correct detector region and destructive interference elsewhere. Detection noise is not modeled, although shot noise and read noise may matter in low-power or miniaturized systems.