Studies On Design Theory And Application Of Multi-layer Diffractive Optics

As an important part of micro-optics,diffractive optical element(DOE)is a frontier subject in modern optical engineering.It has formed a new type of refractive-diffractive hybrid imaging optical system.DOE can deal with some challenging applications in optical systems.In recent years,great progresses have been made in the design theory and manufacturing technology of multi-layer diffractive optical element(MLDOE).However,in the wide-band range and oblique incidence,the DOE also has a problem that the diffraction efficiency is seriously degraded,resulting in a decrease in the imaging quality of the hybrid optical systems.At present,there is no theory or method for designing a MLDOE based on incident angle range.In addition,manufacturing errors and surface roughness can also affect the imaging quality of the optical system.Main contents of this paper are: the comprehensive consideration of the on-axis beam and the surface of DOE in the incident angle range are mainly taken into account.The concept of angle width-polychromatic integral diffraction efficiency(AWPIDE)and the establishment of the corresponding mathematical analysis model are given.The optimal design method and evaluation basis of AWPIDE are studied.Effects of manufacturing errors and surface roughness on the diffraction efficiency of DOE are further studied.Diffraction efficiency and AWPIDE are obtained under different working indexes.The variation law of diffraction efficiency such as BIADE and AWPIDE are given;based on the special dispersion properties of DOE,a hybrid monitoring lenses with high diffraction efficiency in a wide band is designed.Researches in this paper have realized a complete route of a DOE from design to manufacturing and application.Firstly,based on scalar diffraction theory of light wave,the diffraction efficiency of different types of DOE is systematically studied.By discussing the diffraction efficiency of multi-level grating,the diffraction efficiency of single-layer diffractive optical elements(SLDOE)and MLDOE with continuous surface is analyzed.The design wavelength selection method of DOE is provided.Different design methods for improving diffraction efficiency are discussed.The relationship between design wavelength and diffraction efficiency and polychromatic integral diffraction efficiency is revealed.The special imaging properties such as dispersion,temperature and tertiary aberration are analyzed.At the same time,the extended scalar diffraction theory is utilized to optimize the structure of DOE.To solve the problem of rapid diffraction efficiency decreasing of DOE in certain operating waveband and incidence angle,the concept of AWPIDE is first proposed,and alternative design method of SLDOE is given.The optimal design method of MLDOE has been investigated.The effects of working band and incident angle range on the diffraction characteristics of SLDOE and MLDOE.The mathematical model and mathematical expressions of the diffraction efficiency of the SLDOE and MLDOE.Under this effect are established,and the examples are analyzed.The result shows that this method solves the problem of diffraction efficiency reducing in the wide waveband and large incident angle range.The optimum design method can realize high diffraction efficiency of DOE in wide waveband and large incident angle,which has more practical value in the application of optical system.The effects of manufacturing errors on AWPIDE is studied.Based on the phase delay expression and the basic theory of the AWPIDE,a mathematical model of the effect of manufacturing errors SLDOE and MLDOE is established,and the corresponding expression is given.The influence of manufacturing errors on the AWPIDE of DOE during vertical and oblique incidences analyzed.It shows that the AWPIDE under different manufacturing errors can be used to analyze the manufacturing errors of the DOEs in the refractive-diffractive hybrid optical system.Effects on diffraction efficiency of surface roughness of DOE are studied.The micro-structural phase changes caused by surface roughness can reduce the diffraction efficiency of the design wavelength,thus affecting the imaging quality of the optical system.By establishing a mathematical model of the diffraction characteristics for SLDOE and MLDOE with surface roughness,the expressions of diffraction efficiency and polychromatic integral diffraction efficiency are derived.The effects of surface roughness on diffraction efficiency and AWPIDE are studied.This method can be used to quantitatively analyze the problem of image quality declination in the actual manufacturing of the refractive-diffractive hybrid optical system,which has theoretical guidance for the processing of DOE.Taking the monitoring lenses into the hybrid optical system as the example,the MLDOE can be optimized by the AWPIDE maximization method,and the effects on image quality caused by manufacturing errors and surface roughness are quantitatively analyzed.