Fig. 1

Illustration of the hybrid processor for OAM spectrum measurement. The incident structured light with certain OAM distribution is firstly processed by the diffractive optical neural network, whereby the OAM information is transformed into high-dimensional sparse feature in the photoelectric detector plane. For this model, the optical-diffraction-based processing part can ‘split’ the input beam into two main lobes that are related to positive and negative topological charges respectively. Once the complex optical field is turned into real-numbered intensity patterns, the shallow fully connected layer can recover the OAM spectrum in a regressive manner (see detailed model in Methods)