Research On Wide Waveband Optical System For Diffractive Computational Imaging System

The unique optical properties of diffractive optical elements(DOEs)used in imaging optical systems can simplify the structure while improve the imaging quality.It has been widely used in the military and commercial imaging.Single-layer diffractive optical elements(SLDOEs)have simpler structure,smaller thickness and lower cost.However,the diffraction efficiency decreases sharply with wavelength deviating from the center wavelength.The low diffraction efficiency will seriously affect the imaging quality,making it impossible to apply to a wide waveband imaging system.In recent years,computational imaging technology has been developing rapidly.This technology can solve problems that cannot be solved by traditional optical methods,and at the same time,it is easy to achieve system miniaturization.This paper proposes a wide waveband optical system for diffractive computational imaging,which reduces the influence of low diffraction efficiency on imaging by optical-digital joint design.Aiming at the applicable range of medium-and long waveband,the design method of dual waveband infrared optical system for diffractive computational imaging is studied.Then the influence of temperature and angle on the dual waveband infrared optical system for diffractive computational imaging is studied further.This method provides a new idea and method to solve the problem caused by the low diffraction efficiency of SLDOEs.It is of great significance to realize the wide waveband application of SLDOEs and the miniaturization and lightweight of wide waveband imaging system.This paper first studies the theoretical basis of diffractive computational imaging,discusses the diffraction efficiency characteristics of SLDOEs,and analyses its unique dispersion characteristics,thermal characteristics and primary aberration characteristics.Based on image degradation models,a variety of common image restoration methods are discussed,and common fast iterative algorithms are analyzed.The subjective evaluation methods in image evaluation methods and several objective evaluation methods are discussed.Based on joint analysis of diffraction characteristics and restoration characteristics,this paper proposes the design method of dual waveband infrared optical system for diffractive computational imaging.In this method,the central wavelength of the SLDOE is designed at the medium waveband to ensure the imaging quality of the medium waveband,and a point spread function(PSF)affected by the diffraction efficiency is constructed in this paper to restore the image of long waveband.Dual wavebands can be imaged with high quality.A cooled medium-and long-wave dual waveband infrared system with SLDOE is designed.The focal length of the system is 200 mm,the F number is 2,and the field of view is 3.6°.The image of long waveband is restored and the results are evaluated.The results show that the design method can improve the image blur caused by low diffraction efficiency and expand the applicable waveband range of SLDOEs.The change of temperature will affect the dual waveband infrared optical system for diffractive computational imaging.This paper studies the design method of SLDOE that maximizes the temperature–polychromatic integral average diffraction efficiency and brings temperature integral average diffraction efficiency into the PSF model.Based on infrared radiation characteristics,it is proposed to bring the corrected temperature wavelength weight into the PSF model.Then a cooled medium-and long-wave dual waveband infrared-40?+60°C athermalization with SLDOE is designed with a focal length of 200 mm,a F number of 2,a field of view of 3.6°.In this paper,the image recovery and evaluation are carried out and we compare it with traditional athermalization design method.The results show that this method can reduce the influence of temperature on the dual waveband infrared optical system for diffractive computational imaging,and simplifies the athermalization structure of the dual waveband infrared optical system.The change of incident angle and field angle will affect the dual waveband infrared optical system for diffractive computational imaging.This paper studies the design method of SLDOE that maximizes the incident angle–polychromatic integral average diffraction efficiency and brings the incident angle integral average diffraction efficiency into the PSF model.The influence of field angle on the PSF model is deducted and a diffraction multi-level weight optimization method is proposed.The method simplifies the problem of spatial variation recovery to the spatial invariation recovery.A cooled medium-and long-wave dual waveband infrared system with SLDOE is designed with a focal length of50 mm,a F number of 2,and a field of view of 14.4°.The image recovery and evaluation are carried out,then we compare it with the traditional design methods.The results show that this method can reduce the influence of incident angle and field of view angle on the diffractive computational imaging dual waveband infrared optical system,and expand the applicable angle range of diffractive computational imaging dual waveband infrared optical system.