Simulation And Analysis Of Membrane Imaging System Based On Vector Diffraction Theory

With the increasing demand of high resolution remote sensing images for highorbit optical information acquisition,space optical loads are urgently needed with the characteristics of super-large aperture,ultra-light weight,rapid fabrication,rapid folding/unfolding and low cost.However,imaging characteristics of diffraction imaging system is complicated: the system Modulation Transfer Function(MTF)and signal-to-noise ratio(SNR)are lower as well as exists serious space-variant characteristic and chromatic aberration.It will lead to the sever image degradation.Aiming at this problem,the imaging characteristic analysis method and image quality degradation model of diffractive membrane optical imaging system are build based on strict electromagnetic theory,and the corresponding experimental verification is carried out.The main research work is as follows.(1)Imaging characteristics analyzing for Diffractive Optical Elements(DOEs)based on scalar diffraction theory.The imaging mechanism of DOEs is analyzed,meanwhile the characterization model of DOE's diffraction efficiency is established.Starting from scalar theory,the relationship between MTF and diffraction efficiency of diffractive optical system is analyzed,and an analysis method of optical transfer function of diffractive optical system with modified diffraction efficiency is proposed.(2)Analysis of imaging characteristics of diffractive optical system based on vector diffraction theory.When the micro-structure size of the primary mirror reaches the sub-wavelength level,the results of scalar diffraction theory analysis will produce large errors.Aiming at this problem,based on strict electromagnetic theory,a method for analyzing imaging characteristics of diffractive optical system based on vector diffraction theory is proposed.The diffraction efficiency is used as the characterization parameter of the imaging characteristics of the diffractive optical system,and the analysis process of the diffraction characteristics is transformed into the calculation process of the energy distribution of the image plane of the diffractive optical system.Based on the finite element difference method in time domain,the computational space construction method of the diffraction efficiency analysis and the method of updating the electromagnetic field components are proposed.The analysis method of diffraction efficiency of diffraction optical system is presented.(3)The fast analysis method for imaging characteristics of diffractive optical systems.Aiming at the problem of large amount of data in vector diffraction theory,the micro-structure distribution of diffractive optical elements is modeled and characterized based on space dimension reduction method,which reduces the dimension of vector theory analysis.Considering the excellent performance of GPU's large-scale highparallel stream processor in parallel operation with large amount of data and the difference of computing speed between different matrix operation modes,a fast analysis method of imaging characteristics of diffractive optical system is proposed by combining vector programming and GPU's acceleration strategy,which provides a reference for the practical application of vector diffraction theory analysis method.Support.(4)In-orbit imaging characteristics of space thin film diffractive optical system are analyzed.Based on the optical remote sensing imaging link,the link elements affecting image quality are studied,which are reduced to image blurring,sampling,transformation and random noise,and the characterization model is established.The thickness distribution function of thin film diffraction primary mirror is constructed to model and characterize the coupling characteristics of in-orbit force,thermal environment and thin film material,and on this basis,the imaging characteristics of the diffraction optical system are combined.A fast analysis method for on-orbit imaging characteristics of space thin film diffractive optical system is established.The imaging simulation experiment of a real space thin film diffractive optical system is carried out to verify the correctness of the model and method for on-orbit imaging characteristics analysis of space membrane diffractive optical system.