Multi-level Optical Diffraction Holographic Grating Neural Network Interconnection

The optical system, with its massive interconnection and parallel processing capabilities, is particularly suitable for megalo-capacity data processing and computation. The neural network is a large-scale information processing system which consists of a great many simple processing units and those processing units are connected parallelly to perform a computation function collectively. The high density interconnections in the neural networks are more suitable for the optical implementation. So, in recent years attention has been paid to problems concerning the optical implementation.of neural networksThe simple model for neural network proposed by Hopfield has attracted much attention in the field of optical information processing. A lot of researches have been done with regard to the optical implementation of the neural networks. In all optical neural networks developed, the optical interconnection is a fundamental problem to be solved. Several methods have been proposed for the sake of yielding the matrix-vector product of an interconnection weigh matrix(IWM) and an input state.On the other hand, as a splitter beam instrument , grating still plays an important role in spectrum measure, optical computation, and optical information processing. In this paper, the author makes a new grating──holographic grating with multiorder diffraction, based on the traditional optical holographic method, used to implement matrix vector optical interconnection.The work is divided into three parts. In the first part, optical interconnection and the principle of perfect shuffle in optical interconnection networks are presented in detail as a first step. Then the principle of the neural network and optical implementation, Hopfield model and its optical systems and the main difficulty of implementation of the optical neural networks are also presented.In the second part, a new concept of object spatial modulationis introduced to lenses imaging system, into which is then theoretically researched, and its mathematical formula is given. It is thus proved that PS (perfect shuffle) and FPS (Folded PS) is an application example of the specific object spatial modulation.In the third part, the method of holographic grating with multiorder diffraction made by using Mach-Zehnder inter ferometer in two stepped is presented, the principle of this method is interpreted in detail. The Fourier spectrum of this grating sample and the experiment result of image multiplication by using multiorder diffraction grating are also given.Then, in the two-lens optical system, input information as object function is placed in the front focal plane, Holographic grating with multiorder diffraction as filter is placed in the back focal plane, and its multiorder diffraction effect can be used for optical interconnection form one to many points, so 1-D optical inter connects is implemented, then, 2-D optical interconnect of neural network is implemented through the normal contract of two 1-D grating.The experiment results show that the method used in this projetct is feasible, simple in structure and easily operational. What remain to be improved are the effect of the general noise in grating-making on the output quality and the imbalance of diffraction order intensity.