Fig. 1. The development history of artificial intelligence

Fig. 2. National strategy overview and hardware implementation of brain-like intelligence^[5-12,15-23]

Fig. 3. Research progress of Xidian University^[32-72]

Fig. 4. Schematic diagram of a 4×4 MRR array

Fig. 5. Research progress in photonic neural networks based on MRR arrays^{[84-85,87-91]}

Fig. 6. 4×4 MZI network. (a) Triangle structure; (b) Rectangular structure

Fig. 7. Research progress in photonic neural networks based on MZI mesh^{[94,96-97,99-101,103]}

Fig. 8. Photonic neural network based on PCM. (a) Principle and experiment of all-optical spiking neurosynaptic network^[108]; (b) Integrated photonic hardware accelerator architecture based on photonic tensor cores^[109]; (c) In-memory photonic–electronic computing platform based on non-volatile electronically reprogrammable PCM memory cells^[110]

Fig. 9. Research progress in diffractive optical neural network^[116-125]

Fig. 10. Photonic neural network based on metasurfaces. (a) The principle and experiment of optical logic operations performed by a diffractive neural network based on a compound Huygens’ metasurface^[132]; (b) Optical convolutional neural network based on the phase-change metasurface mode converter as a photonic computing core^[133]; (c) A programmable diffractive deep neural network based on a multi-layer digital-coding metasurface array^[134]

Fig. 11. Research progress in training optical neural networks^[89,135-144]