Research On Key Technology Of Ultra-short-focus Projection Objective System Based On Freeform Surfaces

With the rapid development of science and technology and the improvement of the quality of life of the whole society,people hope that the projection system can occupy a smaller space while pursuing the large screen projection display.Therefore,the projection system gradually develops towards the direction of large screen,low throw ratio,ultra-short focal length,large field-of-view angle,high resolution,high definition and low cost.The traditional projection display system can not meet these strict requirements gradually.Ultra-short-focus projection system can achieve large screen projection at very short projection distance,which can break through the limitation of space environment.It has gradually aroused people’s interest and become the mainstream development direction of projection display field and the research hotspot at home and abroad.Ultra-short-focus projection objective,as a key component of ultra-short-focus projection system,can determine the key performance parameters such as throw ratio,image quality of projection screen and system volume.Therefore,it is necessary to design a new type of ultra-short-focus projection objective to further reduce the throw ratio of the system and broaden the application market in the field of projection display.However,as the throw ratio decreases and the field of view angle increases,the projection system becomes more and more complex,and aberration correction becomes more and more difficult.Freeform surface is gradually introduced into the optical design of ultra-short-focus projection objectives because of its high degree of freedom.Therefore,the technical difficulties that need to be solved in ultra-short-focus projection objective system mainly include: firstly,how to optimize the initial surface shape of freeform surface in ultra-short-focus projection system by using effective methods;secondly,how to reduce the throw ratio of ultra-short-focus projection objective and design the ultra-short-focus projection objective for engineering application;thirdly,how to establish a prototype of the ultra-short-focus projection system.Based on the above research background and technical difficulties,this paper focuses on the optical design method of freeform surface to facilitate the design of freeform surface in ultra-short-focus projection system.At the same time,combining with the design method of freeform surface,the optical design of ultra-short-focus projection objective with low throw ratio is studied.Finally,combining with the designed ultra-short-focus projection objective,the development of the principle prototype is advanced.A study was carried out.The main research contents include:1.Research on the optical design method of freeform surface.According to the application requirement of freeform surface in imaging system,based on the construction-iteration method,a direct iteration optimization design method is proposed,and the method is verified by designing freeform surface reflector and refractive lens containing freeform surface respectively.The design results show that the RMS spot can converge to the diffraction limit quickly.In order to further study the freeform surface design method suitable for ultra-short-focus projection objective system and improve it,a multi-field weighted optimization iteration design method is proposed,and an ultra-short-focus projection objective system is designed.The simulation results show that the proposed method can obtain the initial surface of freeform surface which can be used to optimize,and can effectively correct the system distortion.2.Optical design of ultra-short-focus projection objective based on freeform surface.Combining with freeform surface optical design method,the theoretical basis of optical design of ultra-short-focus projection objective,the principle and advantages and disadvantages of various optical path structures of ultra-short-focus projection objective are analyzed.On this basis,a kind of ultra-short-focus projection objective with high-order aspheric surface and low throw ratio is designed.Its throw ratio reaches 0.18,and the imaging quality of the system is analyzed.In order to further reduce the throw ratio of ultra-short-focus projection objective,the design of ultra-short-focus projection objective was studied by using freeform surface,and an ultra-short-focus projection objective with throw ratio of 0.11 was designed.Finally,the design results of the system are compared with those of the traditional refractive projection lens,which proves the superiority of the designed system.3.Verification of Ultra-short-focal projection system.Combined with the designed ultra-short-focus projection objective system based on freeform surface,the optical engine,the designed ultra-short-focus projection objective and the projection screen are combined,the appropriate structure scheme is selected,the principle prototype is built,and the performance of the principle prototype is tested and analyzed.