Study On The Mechanism Of Conformal Optical Dynamic Aberration Correction

With the progress of the times and technology,the aircraft requires higher speeds currently.When the aircraft is flying,the traditional hemispherical dome will suffer a lot of air resistance,which is difficult to meet the aerodynamic requirements of the high-speed aircraft,and greatly limits the speed of the aircraft.Therefore,it is necessary to streamline the dome design,so the conformal optical technology was born.Conformal optical technology uses streamlined conformal dome instead of traditional hemispherical dome to reduce air drag and increase aircraft speed.However,the aspheric dome will introduce dynamic aberrations that fluctuating with the change of scanning field-of-view(FOV),which becomes the key issue of the development of optoelectronic imaging systems for high-speed aircraft.In this thesis,the aberration correction of conformal optical systems is studied based on the above problems.Firstly,the shape of the dome of the conformal optical system is analyzed,and the shape of the dome of the conformal optical system in this thesis is determined as ellipsoid.The geometric characteristics of the ellipsoid dome are analyzed and the dome parameters are determined.In the optical design software,the dome was modeled,and Zernike aberration theory was used to analyze the types and sizes of aberrations introduced by the dome,so that subsequent aberrations could be corrected in a targeted way.The method of aberration correction for conformal optical system used in this thesis is a large scan field of view aberration correction method combining static correction and adaptive optics of wavefront-free detector.The static fixed corrector and dynamic aberration corrector of the conformal optical system are analyzed respectively,and the structure of the system is designed based on the analysis.The conformal optical system with scanning field of view of ±60° is designed,which is working within medium wave infrared waveband,F number is 1.5,pupil diameter is 30 mm.In the initial optical structure design,the types of system aberration are reduced and the fifth-order Zernike aberration is eliminated during initial aberration correction,thus,the number of the subsequent adaptive optimization control variables is reduced.Reduce the number of subsequent variables from the first sixteen terms of Zernike polynomial coefficients to the first nine terms.Next,the optimization algorithm based on Zernike model coefficient minimization is constructed.Firstly,the principle and flow of the algorithm used in this thesis are introduced.Then the various parameters of the algorithm are determined,and the Strehl ratio is used as the fitness function of the algorithm,and the Strehl ratio is equal to 0.7 as the stopping condition of the algorithm.The optimized variable of the algorithm is the voltage of the deformable mirror driver.In order to use the first nine Zernike polynomial coefficients as the optimization variables of the algorithm,a conversion matrix between the Zernike polynomial coefficients and the deformable mirror driver voltage is constructed,and the optimization variables are reduced from 140 driver voltages to the first nine Zernike polynomial coefficients.Finally,a simulation experiment is carried out to verify the superiority and feasibility of the aberration correction method of the conformal optical system in this thesis.Genetic algorithm based on Zernike model was used to control the deformable mirror shape and correct the residual aberration of conformal optical system.The simulation results show that the optimization speed of each typical scanning field of view point of the system is increased by more than 95%,and the optical image quality is close to the diffraction limit.And experimental verification was carried out.The spatial light modulator is used to modulate the wavefront to introduce the wavefront aberration,the residual aberration of the system is simulated,and the algorithm based on the Zernike model is used to optimize the deformed mirror shape to correct the aberration.Experimental results show that the optimization method can successfully eliminate the introduced wavefront aberration.Therefore,the aberration correction method of conformal optical system based on Zernike polynomial coefficients designed in this thesis is feasible.