Design Of Wide-band Imaging Optical System

The visible light-near-infrared-short-wave infrared system mainly uses the reflection characteristics of objects for imaging,in which the visible light system needs sufficient lighting conditions when working;the illuminance emitted by the atmospheric glow phenomenon of sky radiance at night increases rapidly in the short wave infrared region,The radiance peaks in the1.5?m?1.7?m spectral range,which is stronger than the full moon light,Therefore,combining the imaging advantages of visible light and atmospheric glow can achieve all-weather,high-resolution imaging of the same observation target,and can also improve target detection and identification capabilities.Traditional broadband optical imaging systems generally use multiple sets of optical paths to match different focal plane detectors to achieve the function of multi-spectral detection of targets,resulting in a large system and complex equipment structure,and it is difficult to achieve spatial consistency when detecting with different apertures.With the development of uncooled visible-near-infrared-short-wave infrared wide-spectrum focal plane detector technology,new requirements are put forward for the design of optical systems,and the technical scheme of wide-band common optical path confocal plane has become the focus of research.At present,the traditional optical structure of a broad-band common optical path confocal surface based on a refractive lens is difficult to simultaneously eliminate the inter-band chromatic aberration and maintain the design goals of miniaturization and light weight of the system structure.Therefore,it is of great significance for studying and designing a new broadband imaging system that meets the above design requirements.The main research contents of this paper are as follows:In order to deal with the difficulty of chromatic aberration correction in refractive broadband optical systems,a method based on refractive-diffractive hybrid achromatic is proposed.The relationship between the diffraction efficiency of three different types of diffractive optical elements in the 0.4?2.5?m wavelength band was studied respectively.Aiming at the problem that the average diffraction efficiency of the bandwidth integral decreases when the light enters the substrate material at a certain incident angle,a selection method of the combination of the incident angle and the substrate material is proposed.Firstly,a mathematical model for calculating the average diffraction efficiency of the incident angle-bandwidth integral was established.In the incident angle(0?5°),the diffraction efficiencies of Ba F₂-AL₂O₃,Ca F₂-AL₂O₃ and Mg F₂-AL₂O₃ were studied with variation of temperature and wavelength respectively.When the ambient temperature changes,the height of the surface microstructure and the refractive index of the base material affect the diffraction efficiency of the system,and a selection method for the combination of temperature and base material is proposed.The influence of the change in ambient temperature on the height of the diffractive microstructure is analyzed,and the mathematical model of the temperature-bandwidth integral average diffraction efficiency is established.Under the condition that the design temperature is 20?,the relationship between the diffraction efficiency and the wavelength of the Ba F₂-AL₂O₃ base material in the ambient temperature range(-40??60?)is studied.Aiming at the influence of the selection of the design wavelength on the diffraction efficiency of the system,an optimal selection method of the design wavelength is proposed.Firstly,the calculation formula of the height of the diffractive surface microstructure with respect to the design wavelength is deduced,the mathematical model of the bandwidth integral average diffraction efficiency with respect to the design wavelength is established,and its relationship with the wavelength is studied.Two design schemes of the broadband optical system are determined:Scheme 1 completes the design of a traditional refractive optical imaging system;Scheme 2 introduces a double-layer diffractive optical element to complete the design of a refractive-diffractive hybrid optical imaging system.Both of them correct the chromatic aberration in the wide-band range,and use the optical passive athermalization technology to complete the processing of the thermal difference of the system,and the image quality meets the design requirements.The results show that compared with the traditional refractive optical system,the refractive-diffractive hybrid system achieves fewer lenses,compresses the total length of the system,reduces the weight of the system,and achieves the design goals of miniaturization and light weight.