Fig. 1. Part of the spectrum data in dataset

Fig. 2. Network structure diagram

Fig. 3. Data preprocessing

Fig. 4. Detection area in the result image and identification area of different labels

Fig. 5. Structure diagram of optical diffractive neural network classification system

Fig. 6. Structure diagram of grating group

Fig. 7. Grating height discretization

Fig. 8. Two etching to achieve four steps

Fig. 9. Partial diagram of diffraction grating model

Fig. 10. Accuracy and error curve of train set

Fig. 11. Accuracy curve of train set and test set

Fig. 12. Confusion matrix of test results

Fig. 13. Height distribution of each layer of grating and the output image of each layer of grating after training. (a1)-(a6) Gratings; (b1)-(b6) Output of gratings; (c1)-(c3) Recognition