Research Of Aberration Correction Technology For Optical System With Aspheric Dome

As the technique as radar detection and precision anti-missile developmentrapidly, the requirement of aerodynamic performance for the aircraft becomes higherand higher. In order to realize the optimial aerodymanic outer shape, the traditionalhemispheric shape is frequently replaced by the streamline aspheric shape in thedesign of the optical dome on aircraft. The optical system with an aspheric dome(hereinafter referred to as aspheric dome optical system) usually uses the pitch-yawgimbal to scan and image, when the scaning angle is not zero, the aspheric dome willshow serious asymmetrical performance, and induce a mass of aberration for theoptical system, and the amount of the aberration acutely changes as the scaningangle. Due to the serious decenter and tilt performance of the aspheric dome opticalsystem, the classical optical aberration theory and wavefront aberration theorycannot be used in the analysis of this system, and traditional optical structures arefailed to correct the dynamic aberrations of this system, which brings a greatchallenge for the optical design.This thesis concentrated on the analysis of aberration characteristics and theresearch of aberration correcting theory for the aspheric dome optical system. Themain innovate productions are: focus on the ellipsoidal dome, which is the maindevelopment direction of the seeker dome, two novel aberration correcting theory and method are proposed. And two novel aspheric dome shapes which have goodaerodyamnic performance and induce less aberration are bringed forward. Thedominating work and results in this paper are as follows:1. At first, the geometrical performance and third-order aberration characteristicsfor the aspheric optical dome are analyzed: The transformation between geometricalparameters of an aspheric dome and the input of optical design software isestablished. Zernike polynomials aberration theory and vector wavefront aberrationtheory are combined to establish the aberration evaluation model for the asphericdome optical system. Based on the displacement property of the vector aberrationfield center, the design idea of using a decentered corrector to balance the comainduced by the tilt of the dome is proposed. On the base of above work, the contactof geometrical characteristics and aberration performance for the aspheric domeoptical system is deeply discussed, and the fundamental causes of the production oflarge aberration are pointed out: Firstly, there is a dramatic difference betweentangential and sagittal radius of curvatures of the aspheric dome; secondly, when theray fan pass through the aspheric dome, the line of sight deviation and asymmetricalpupil distribution present themselves.2. Based on the structure and aberration characteristics of the aspheric opticaldome, a few complex surfaces, including the dioptric Wassermann-Wolf surfaces, theplane symmetric surface and the Gaussian radial basis function surface, are selected.These surface types are fit for being used in aberration correcting for the asphericdome. The optical characteristics of them which are beneficial to aberrationcorrecting for the aspheric dome are discussed. These optical characteristics are rootin the mathsmatic models of these surfaces. The discussion provides a theoreticfoundation for the application of these surface types in the design of aberrationcorrectors below.3. To solve the problem that a reasonable intial structure of the aspheric domeoptical system is difficult to established, a design theory based on reflectiveWassermann-Wolf (W-W) equations is proposed. On the basis of reflection law and light path caculation method, a pair of Wassermann-Wolf (W-W) equations relatingto designs of highly non-rotationally symmetric reflective systems are derived forthe first time. Combined this way with the least square fitting method, we can get anintial structure of a two-mirror aberration corrector concerned theaberration-corrected need of every field-of-regard(FOR) point. Based on theplane-symmetric vector aberration theory, the aberration properties of thisplane-symmetric reflective system is analyzed, and the design scheme of tiltingmirrors to compensate the residual dynamical aberration in different FOR. Finally,the integrated aspheric dome optical system design example is finished, and theimaging quality of this system approaches to the diffraction limit.4. To overcome the problem that the searching FORs of existing aspheric domeoptical systems are relatively narrow, an aberration compensating method for theaspheric dome optical system based on the combination of an arch corrector and adynamic corrector is proposed. The arch corrector is designed in plane-symmetricsurfaces to satify different aberration-corrected needs in tangential and sagittaldirections. The surface shape of the dynamic corrector is represented by Gaussianradial basis function, and the feasibility of this represented method is proved. Theaccurate simulation of the optical properities of the deformable mirror is achieved.Through a design example the validity of this aberration compensating method isproved, and the design result indicates that this method reaches the requirements ofsuper wide FOR and high imaging quality at the same time.5. To radically solve the problem that the existing correcting methods areexcessively complex, two novel aspheric dome, sphere-cone (SC) andsphere-cone-polynomial (SCP) domes, are designed. The mathematic models of SCand SCP surfaces are established. The smoothness and continuity of these twosurfaces are proved. The equations used to decide geometrical parameters of domeswith these shapes are deduced. Through the simulations, it is proved that these twodomes have not only good aerodynamic performance, but also introduce the minimalamount of aberration in±75°super scanning field. So the correcting system structure is significantly simplified, which reduces the weight and cost and enhances thereliability of the system.