Research On Optical Zoom System Based On Lateral Shift Of Free-form Lenses

Optical freeform surfaces have high degree of freedom and strong aberration correction ability,which has attracted extensive attention.In the field of deep space exploration,considering the adaptability of the environment and the requirements of the detection target resolution,the optical system with fixed focal length gradually fails to meet the detection requirements.For the consideration of light miniaturization and small displacement of optical imaging system,this paper realizes the adjustment/zoom function of the optical imaging system through the use of the freeform lenses with lateral shift.This method has great potential in aerospace,deep space exploration and other fields.In this paper,the expressions of focal length function and aberration function are derived based on the method of paraxial optics.The main parameters of the focal length function include freeform surface structure,lateral offset and offset direction.The quadratic phase function is the essence of focal length function.Through the analysis in this paper,it is found that the surface forms that generate the quadratic phase function mainly appear in the expressions of high-order odd terms,and there are correlation equations between the components of high-order odd terms.The paraxial aberration function has the characteristics of non-rotational symmetry.By introducing field of view information variables,an aberration function containing field of view information is derived to facilitate the classification and optimization of aberration types.The method of ray tracing is also introduced to solve the aberration function.Secondly,the freeform lens is optimized by combining the focal length function and aberration function.For a single group of freeform surface lens,the optimization strategy is to improve the zoom efficiency of components,and optimize the combination mode of freeform surface structure and offset direction.After analysis,the migration direction in the typical combination mode is along the x-axis and y-axis direction respectively.The optimization scheme for multiple groups of freeform surface lenses is to reduce the contribution rate of aberration and optimize the distribution ratio of optical power of multiple groups of freeform surface lenses.The optimization scheme of uniform distribution of optical power is obtained,and the structure of multiple components in the same direction and different direction is studied in depth.Then,according to the application of the focusing optical system,imaging drift compensation is realized by using the feature of free-form surface lateral movement to realize,a mathematical model of focusing is established,and a set of focusing optical system has designed witch focuses from infinity to 2m.The initial structure of the rotating symmetric optical system is solved by Delano graphic method,and the evaluation functions of aberration,system length and deflection Angle are constructed.The freeform lenses are added as focusing group to improve the optical system and further optimized in optical software.In this paper,an optical system is taken as an example to achieve clear imaging under the conditions of an object distance from infinity to 2m and complex space environment.The focal length is 100 mm,the relative aperture is 1/5.6,the field of view of 12°,and the total length of the system is 115 mm.The results show that the modulation transfer function of the optical system is greater than 0.3 at the Nyquist frequency,and the maximum lateral offset of the freeform surface is 0.5mm.Finally,according to the application requirements of the zoom optical system,a variable focal length is achieved by using the feature of free-form surface lateral movement,a zoom mathematical model is established,and a set of zoom optical system has designed witch has 4x zoom.On the basis of focusing research,the evaluation functions such as optical power compensation and zoom ratio are reconstructed.In this paper,a four times zoom optical system is taken as an example.The focal length changes from 26.7 mm to 107.4 mm,the relative aperture is 1 / 5,and the total length of the system is 185 mm.The zoom system has a compact structure,and the freeform lens can achieve a four times zoom function with a maximum lateral offset of4.5mm.