Research On Wavefront Reconstruction Method For Diffraction Optical System Based On Phase Diversity

Compared with the traditional catadioptric optical system,the membrane optical diffraction system,which embodies large aperture,light weight and low cost,is an important development direction for ultra-high resolution spatial optical loads in the future.However,subject to the special mechanism of diffractive imaging,diffraction optical imaging shows more severe imaging degradation characteristics such as energy loss,complex PSF spatial variation,coupled with the effects of atmospheric turbulence and thermal environment in the orbital force,the imaging results of membrane diffraction optical system may not meet the requirements for image interpretation applications.The wavefront information is a direct reflection of the degradation characteristics of the optical link full-link image quality.The accurate detection of the wavefront can provide a priori and input for image quality enhancement and restoration.Research on wavefront reconstruction methods for diffraction optical systems is still vacant at present.Based on the imaging mechanism of the diffraction optical system,the wavefront reconstruction method of the membrane diffraction optical system based on the phase diversity method is studied.The main research contents are as follows:?1?Diffraction optical imaging characteristics and characterization model.Different from the traditional catadioptric optical system,the imaging process of the diffraction optical system is affected by the diffraction efficiency and the space-variant characteristics of the PSF.The imaging degradation mechanism is more complex,and the imaging results show that the imaging energy of the focal plane is low,and the MTF of the fringe field is seriously degraded.Based on the scalar diffraction theory,the image degradation characteristics of the diffraction optical system are analyzed,and the diffraction imaging characterization model of multi-imaging parameters such as diffraction efficiency,field of view?FOV?and wavefront phase is established,which provides a theoretical basis for the phase diversity method of the diffractive optical system.?2?Phase diversity wavefront reconstruction method based on diffraction imaging characterization model.In order to solve the problem that the traditional phase diversity method does not take the diffraction efficiency and the space-variant imaging characteristics of PSF into account,the imaging characterization model of the diffractive optical system is incorporated into the cost function of the phase diversity method.Combined with the idea of isoplanatic region block,the reconstruction method of full-field wavefront for the diffraction optical system is proposed.Aiming at the non-convex optimization problem of the objective function of phase diversity,a particle swarm optimization algorithm based on simulated annealing is proposed to realize the global efficient solution of wavefront information.?3?Adaptability and error analysis of phase diversity method.Firstly,based on the principle of wavefront reconstruction algorithm of diffraction optical system,the physical factors affecting the accuracy of wavefront reconstruction are mainly divided into two categories:image quality degradation factor and input error factor.Secondly,the adaptive analysis of phase diversity method is carried out for the factors of image quality degradation;Aiming at the input error factors,the error theoretical analysis model is established,and the wavefront inversion synthetic error analysis method is proposed based on the error theory.Finally,numerical simulation experiments on a membrane diffraction optical system are carried out to verify the error analysis model and method.?4?Experimental verification and analysis.Taking a membrane diffraction optical system as an example,the space-variant degraded image is simulated,and the full-field diffraction wavefront information is reconstructed with the idea of isoplanatic region block.The adaptability of the full field of view wavefront inversion method is analyzed.The experimental results show that the average wavefront RMSE in full field of view can reach2.5×10^-4?when the diffraction efficiency is better than 0.65 and the variance of Gauss noise is better than 0.001.The modified phase diversity wavefront reconstruction method proposed in this paper can accurately reconstruct the wavefront information,and provide more accurate input for the inverse enhancement and restoration of diffraction degraded image,laying the foundation for the future space application of ultra-large aperture membrane diffraction optical system.