Design Of Infrared Dual-band Optical System With Diffractive Optics

Infrared optical system has obvious advantages in acquiring object information and tracking multiple targets.With the complexity of the application environment and the continuous improvement of detection and camouflage technology,infrared dual-band,three-band and other multi-band detection has gradually become the focus of research in the optical field.Due to the wide band,there are few infrared materials available and the temperature coefficient is large,which leads to the complex structure of the optical system.Therefore,diffraction optical elements are introduced.The multilayer diffractive optical elements(MLDOEs)not only has the imaging characteristics of the traditional single-layer diffractive optical element,but also overcomes the defect that the diffraction efficiency of the single-layer diffractive optical element decreases dramatically when it deviates from the central wavelength.It can not only correct chromatic aberration and realize thermalization of refractive and diffractive hybrid optical system,but also simplify the system structure and reduce the weight of the system,which can solve the problems that are difficult to be solved in traditional imaging optical system.Based on the integrated diffraction efficiency of multi-color light,this paper designed a double-layer diffraction optical element suitable for infrared dual-band,explored the influence of shielding effect brought by single-point diamond turning tool on its diffraction efficiency,and applied it to infrared dual-band thermalization optical system.The specific research contents are as follows:First of all,this paper briefly introduces the background of diffraction optical and infrared dual band optical systems,and the current situation of the development of the research,explores the diffraction efficiency of diffraction optical element,imaging properties and design methods,again without from infrared thermalized optical materials,the types of infrared detectors and other aspects of understanding infrared design principle and method of thermalization,The structures of several infrared dual-band optical systems are compared.Secondly,when diffractive optical elements are processed based on single diamond turning technology,the shielding effect caused by the cutting tool will affect the diffraction efficiency of diffractive optical elements.To solve this problem,based on the effective area method of MLDOEs,the mathematical model of MLDOEs diffraction efficiency and multicolor integrated diffraction efficiency under the influence of shielding effect is proposed in this paper.The application of double-layer diffractive optical element with substrate materials of zinc sulfide and zinc selenide in medium long wave infrared is taken as an example.The effect of shielding effect on diffraction efficiency of double layer diffractive optical element is studied.Finally,the requirement of allweather measurement for optical system is highlighted on temperature change,that is,infrared optical system is required to maintain good image quality and image surface stability in a large temperature range.In this paper,the passive thermal desorption method is used to design the infrared dual-band(3.7～4.8μm,8～12μm)asthermic optical system with F# 1.1 and focal length of 75 mm by combining different optical materials.The dual-color detector is 640×512 and 17μm uncooled detector.The double-layer diffractive optical element is used in the system.The optical system can image clearly in a wide temperature range without focusing,and realize no thermalization.Besides,it has a simple structure,small size and light weight,and has a good application prospect in photoelectric detection and other fields.