Design And Experimental Research Of Continuous Surface Diffractive Optical Element

In recent years,the optoelectronic industry has developed in the direction of miniaturization,integration,and intelligence.Diffractive optical element(Diffractive Optical Element,DOE)has unique performance advantages,so it is widely used in modern optical systems.The traditional diffractive optical element generally has two steps,and its processing technology is relatively mature,but the diffraction efficiency is low.Theoretically,the diffraction efficiency of two steps,four steps,eight steps,and sixteen steps are 40.5%,81%,94.9%,and 98.6%,respectively.In order to improve the diffraction efficiency,it is necessary to perform multi-step registration.Although multiple engravings can improve the diffraction efficiency,the simultaneous engraving alignment errors will seriously reduce the quality of the output light field.In addition,more and more application scenarios require large-angle diffractive devices,and the feature size of the corresponding diffractive element will be reduced to the order of hundreds of nanometers,making multi-step overprinting impossible.In order to solve the problem of low diffractive efficiency in current diffractive optical elements,this paper proposes to use continuous-surface diffractive elements to improve the diffractive efficiency.Starting from the application requirements of two typical diffractive elements,laser beam splitting and beam shaping,continuous-surface diffractive optics are developed.Element design algorithm and manufacturing process research,the basic idea is to improve the design method of diffractive optical element,in order to obtain the continuous surface diffractive element phase distribution,and then use the moving mask technology for the continuous surface micro-nano structure forming After preparation,a diffraction device with high diffraction efficiency is finally obtained.The main work of the paper is as follows:(1)Research on design algorithm and processing technology of continuous surface beam splitter.Aiming at the problem of low diffraction efficiency of the current beam splitter,on the basis of the traditional Gerchberg-Saxton(GS)algorithm,the initial phase selection and the amplitude limitation of the output surface are improved.The beam splitter was designed using this algorithm and the traditional algorithm respectively,and the design results were compared.Lab-based moving mask technology has prepared continuous-surface beam splitters and beam splitters.After actual measurement,their diffraction efficiency and uniformity are better than traditional beam splitters.The influence of the profile error of the beam splitter on its performance is briefly analyzed.(2)Design algorithm and processing technology of continuous surface beam shaping device.Aiming at the problem of serious speckle noise in the beam shaping system,a design algorithm for continuous surface beam shaping device is proposed.Based on the traditional GS algorithm,a special phase is selected as the initial phase.The output spot reduces speckle noise while ensuring high diffraction efficiency.Using this algorithm and the traditional GS algorithm,rectangular flat-top beam shaping devices were designed,and the design results were compared.The influence of the parameters in the processing process on the continuous surface structure on the thick rubber surface is analyzed,and the moving surface mask technology is used to prepare the continuous surface linear and rectangular beam shaping device.Using this algorithm,a ring-shaped flat-top beam is designed,and a spatial light modulator(Spatial Light Modulator,SLM)is used to build the experimental light path.The experimental results of the ring beam designed by the algorithm in this chapter and the GS algorithm are compared,and some experimental phenomena are analyzed.