Optical Design Of Compact Large Aperture And Wide-angle Automotive Lens

More and more cars are equipped with different automotive visual systems with the popularization of smart cars,ADAS and driverless technology in recent years.As eyes of smart cars to obtain external information,the requirements and quality of automotive lens are further improved,for instance,the optical system has the characteristics of wide field of view angle,bright and clear imaging quality and so on.Automotive lens not only takes convenience to everyone’s daily life,but also prevents safety hazards in the road and records traffic accidents.Therefore,a large aperture and wide field of view angle compact automotive lens with simple structure and low cost is worth studying.The purpose of this paper is to design an automotive lens for rear-view system according to the market requirements.The specifications of final design are as follows: FOV 177°,working F#1.5,EFFL 2.59 mm,total optical length 15.53 mm,back focal length 15.53 mm,F-theta distortion-10.3%,CRA is over 0.35 in the max field of view.The lens can be used for 1/2.5inch sensor.The single-pixel of the sensor is 2.2μm with a diagonal of 7.13 mm.The main research contents of this paper are as follows:1)According to the expected specifications,this paper selects the appropriate initial structure and improves the structure with related theories such as geometric optics and optical design aberration theory.Then,the improved structure is optimizing in ZEMAX.After that,the results of optical design are evaluated in the light of the structural requirements of the special occasions of the automotive lens and the imaging quality evaluation standards of the existing automotive lens in the market.The MTF value is closed to 0.7 at 125lp/mm in the central field of view,furthermore,the value is over 0.25 and closed to 0.3 in the marginal field of view,and the value is over 0.3 in the other fields.2)This paper describes the athermal design project,which can divide into two parts.First part is focused on theory that built an ideal model to analyses each lens material about its effect for optical structure.The second part is simulation of imaging based on lens machining process and assembling.In other words,mechanical thermal expansion should be considering.After athermal design,the optical system can operate in-30～+80℃,and the focal shift value between flange distance and back focal length are 0.0032 mm and 0.0029 mm in the extreme temperature（-30℃,+80℃）.The depth of focusing is over focal shift value in working temperature area.This paper provides a useful reference to lens athermal design,and this project can be systematized for improving efficiency.3)In order to have a highly reliable analysis result for the large aperture and wide field of view optical system,the projects of stray light analysis and control are showed in this paper.The final analysis results show that the stray light in each field of view is satisfied with the standard of the ratio of stray light energy to normal light energy.This paper provides a useful reference to optical system with stray light and control,and the projects can be systematized for improving efficiency.4)Tolerance analysis and improvement projects are showed at the end of optical design.According to the existing manufacturing and assembly accuracy,the tolerance is analyzed with sensitivity and Monte Carlo analysis.In addition to the regular lens sensitivity analysis,the tolerance analyzes the items which are related to aspheric surface.Then,the optical system is improved or the sensitive tolerance item is appropriately tightened in light of the results.Finally,this paper provides a risk report about sensitive tolerance items.The Monte Carlo analysis results show that the MTF value at 113lp/mm is over 0.17 in 90 percent for all field of view,and the average MTF of all fields of view is over 0.25,which can be satisfied with the imaging requirements of automotive lens.The high specification automotive lens could be widely used in vehicle rear view system and surround view system.The characteristic of small size can be applied to more complex and diverse situation;The large aperture can meet the high-definition imaging at night,and infrared and visible light switches are no longer used,which can effectively reduce the system cost;Wide field of view can reduce the number of lenses,in other words,a single lens could operate for wide scale monitoring.