Abstract: Recently,artificial intelligence,particularly deep learning,has developed rapidly，which deeply empowers traditional industries and leads the realization of a new round of industrial technology revolution.However,the size of transistors on electronic chips is gradually approaching the physical limit,resulting in the inability of traditional electronic neural networks to meet the exponential increasing demand for computing power.Benefiting from the unique advantages of photon,optical computing technology merges optoelectronic technology with neural network models,which has the advantages of parallelization,high speed,low power consumption and multi-dimensional processing.The research progress of optical neural networks is reviewed,concentrating on the computational architecture of optical diffractive neural networks.The challenges facing the practical implementation of large-scale optical diffractive neural networks are analysed and summarized，and the future development trend is prospected.

Key words: Optical information processing, Optical computing, Optical neural network