| Both observation range and detect efficiency of optical remote sensor can be enhanced by wide field optical imaging system.For the design of two-dimensional large field of view off-axis free-form surface system,when the field-of-view(FOV)of the system is continuously increased,especially in the meridional direction,more decentration and/or tilt need to be introduced to eliminate the occlusion,and the asymmetric higher level aberration related to field increases dramatically.In addition,the image field continuity requirement will be more prominent because the imaging surface is larger.Therefore,this paper focuses on the optimization design of the freeform optical system based on bicubic B-spline surface fitting,which integrates two surfaces into one optical element.A two-dimensional(2-D)freeform optical system with large field of view is designed,which increases the meridional field angle of the off-axis optical system with large field of view and reduces the difficulty of installation and adjustment.The main research contents of this paper can be summarized as follows:(1)The mathematical representation forms of optical freeform surfaces are summarized and the characteristics of each representation method are analyzed.Based on the vector aberration theory,the evaluation method of off-axis system based on real ray tracing is studied,and the aberration characteristics of off-axis optical system with large field of view are analyzed.(2)A design method of optical system with 2-D large FOV based on decomposition surface is proposed.Based on the initial structure of a typical optical system,the meridional field of view angle is discards into two sub-field units,and the specific surface of the optical system is decomposed into two sub-surfaces.In the process of system optimization,the two sub-surfaces are designed simultaneously with multiple structural functions,and the surface parameters and structural parameters are changed independently.The custom constraint function is constructed,and the constraint conditions of structure contour and surface shape are proposed to constrain the external dimension of the system and optimize the structural form.Based on this design method,an off-axis reflective freeform surfaces optical system was designed,which realized the2-D large-field imaging of 40°×16°,the focal length of 1000 mm,and the F-number of10.(3)In this paper,a transitional discrete surface is constructed between the surfaces of two optical elements,and the co-body discrete surface is established.Through bicubic B-spline surface fitting,the co-body discrete surface is characterized as a Bspline surface with continuous curvature,and the double-surface on co-body of optical system is realized.The main mirror surface 1 and surface 2 as well as the second mirror surface and the fourth mirror surface of the freeform off-axis optical system designed in this paper are respectively characterized as bicubic B-spline surfaces of the co-body.In the effective region,the root mean square value of B-spline surface fitting error is no more than 1E-7mm,and the PV value is no more than 1E-5mm.The number of optical surfaces in this design system is reduced from five to three by the method of doublesurface on common body optical element,which significantly reduces the difficulty of system installation and adjustment. |
