Design And Manufacture Of Achromatic Multi-Order Diffractive Lens

With the increasing demand for the comprehensive performance of optical systems in the market,optical systems are developing in the direction of lightweight,simple structure and excellent optical performance.Among them,achromatic diffractive lenses with good optical performance,thermal stability and flat image field are increasingly used in aerospace,medical,military and other fields.It can not only provide more parameter choices for optical systems,but also show advantages in terms of image quality,volume and weight.Based on the scalar diffraction theory,this paper proposes the design of achromatic multi-order diffraction element combination system,and analyzes the system composed of multi-order diffractive element,refractive element and diffractive Fresnel element.The specific research contents are as follows:Firstly,the research progress of diffractive optical elements is briefly introduced.The achromatic status of refractive-diffractive hybrid lens,multi-order diffractive lens and multi-layer diffractive elements is explored.The development of processing technology of diffractive optical elements is investigated.The achromatic and apochromatic theories of wide spectrum optical system are expounded,and the derivation of positional chromatic aberration and secondary spectrum are given.The preliminary selection of glass materials and the distribution of the initial structure of the system are guided.Secondly,the imaging properties and dispersion characteristics of diffractive optical elements are described.The third-order aberration theory of thin lens is applied to the design of the combined system of multi-order diffractive element,refractive element and Fresnel element,and the third-order aberration formula of the combined system is derived.Again,the designed system is achromatic and apochromatic,and the spherical aberration is corrected.Then,the surface shape of the combined system is analyzed.The results show that the imaging quality of the whole system is better and the achromatic effect is more obvious when the system is spherical and aspherical compared with the planar surface type.In the case of aspheric surface,at the cut-off frequency of 50 lp/mm,the MTF value of the system is much higher than that of the system under the spherical surface,and the diffractive encircled energy is higher.Then,based on the scalar diffraction theory,the expressions of the diffraction efficiency of the multi-order diffractive elements are derived by calculating the diffraction efficiency of different types of diffractive optical elements.Based on this,the mathematical expressions of the diffraction efficiency of the combined system designed in this paper is derived.When the diffractive element materials are PMMA and PC respectively,the diffraction efficiency of the system in the visible light band reaches above 94.82%,which promotes the work of the hybrid achromatic system.Finally,the experiment of single point diamond turning multi-order diffractive elements is carried out.A PMMA multi-order diffractive element with a diffraction microstructure height of 16.4983 μm and a diameter of 5 mm is fabricated.The PV value of the element is 0.1015 μm and the surface roughness is 2.48 nm,which provides a technical guidance for the engineering application of single point diamond turning multi-order diffractive elements.This topic has theoretical guidance for the design and manufacture of achromatic multi-order diffractive elements.