| With the wave of augmented reality(AR)products for near eye display devices and the continuous development and progress of display technology,AR products for near eye display devices have gradually penetrated into fields such as entertainment,education,and healthcare,and are widely used.Among them,near-eye display devices based on waveguide display technology have the advantages of a large field of view,a lightweight waveguide shape,and a size closer to ordinary glasses,making them one of the mainstream development solutions for current display systems.In order to provide users with a better viewing experience and a more comfortable wearing experience,the demand for high-resolution and lightweight waveguide based near eye display devices is becoming increasingly urgent.Waveguide based near eye display devices are mainly composed of waveguide plates and micro projection systems.The performance of micro projection systems directly affects the overall performance of near eye display devices.Therefore,studying how to achieve high resolution and lightweight of micro projection systems is of great significance.The traditional micro projection system based on spherical lens design has a large number of lenses and a large volume,which is difficult to meet application requirements.With the development and progress of technology,aspheric lenses and diffractive optical elements(DOE)are increasingly used in optical systems.Aspheric lenses and diffractive optical elements have more design parameters of freedom than spherical lenses,and diffractive optical elements also have the characteristics of light weight and negative dispersion,which is very conducive to the miniaturization of optical systems.This article combines the unique advantages of aspherical lenses and diffractive optical elements to study the key technologies of micro projection systems based on waveguide displays.Firstly,in response to the complex and bulky nature of traditional lighting optical systems,optical rods and DOE are respectively used for beam shaping in the lighting optical path of micro projection systems;Secondly,based on the requirements of a large field of view and highquality projection,while pursuing miniaturization and lightweight of the system structure in existing processes,aspheric and diffractive optical elements were used for the projection optical system of the micro projection system.Finally,a high-resolution small-scale micro projection system consisting of DOE illumination optical system and five pieces of aspheric projection optical system was designed and prepared,Simultaneously completed the design of a refractive diffractive projection system based on double diffraction and aspheric structure.Firstly,this article analyzes and designs the illumination system,including the design of illumination system based on aspherical surfaces,light rods,and DOE.The illumination system design based on aspherical lenses is relatively complex,requiring a total of 7 optical components,with an average energy utilization rate of 22.6%and an average illumination uniformity of 87%;The illumination system based on light rods uses light rods as uniform devices,requiring only 4 optical elements,with an average energy utilization rate of 26.6%and an average illumination uniformity of 92%.In order to improve energy utilization,a DOE based illumination illumination system was designed,specifically a multi wavelength beam shaping DOE element based on multi color light emitting diodes(LEDs)was designed.Weak phase deviation was used as negative feedback optimization,and combined with the advantages of particle swarm optimization algorithm global search,the multi wavelength DOE of multi color LEDs was optimized.During the optimization process,to ensure the same illumination uniformity for different colors,By adding dynamic weighted average adaptive weights to adjust the optimization direction,the design results show an average energy utilization rate of 80.5%and an average illumination uniformity of 91.5%.This provides a reference for solving the problem of traditional illumination system that cannot simultaneously balance small volume,high energy utilization rate,and high illumination uniformity.Secondly,for the projection system,four spherical projection optical systems with a system size of 34.78 mm × 12.7 mm × 12.7 mm were first designed,its modulation transfer function is higher than 0.28 in the full field of view at 50 Ip/mm,and the distortion is less than 5%.The system size is too large to meet the application requirements.Subsequently,aspheric surfaces were added to the optical system,and five aspheric and four aspheric projection systems were designed,respectively.Among them,the size of the five aspheric projection systems was 20.59 mm× 10 mm × 10 mm,its modulation transfer function is above 0.5 in the full field of view at 50 lp/mm,and the distortion is less than 3%;Four piece aspheric projection system size 21 mm × 9 mm × 9 mm,its modulation transfer function is higher than 0.37 in the full field of view at 50 lp/mm,and the distortion is less than 1%.In order to further reduce the volume size of the system,double-layer diffractive optical elements were used in the optical system,and the double-layer refractive diffractive hybrid projection optical system was designed and optimized,with a system size of 17.76 mm × 8.5 mm × 8.5 mm.The modulation transfer function is higher than 0.24 in the full field of view at 50 lp/mm,and the distortion is less than 1%.From this,it can be seen that adding aspherical and diffractive optical elements to the optical system can achieve miniaturization of the system structure while satisfying high-quality projection effects.Finally,tolerance analysis was carried out for each part of the designed micro projection system,and five aspheric projection optical paths based on liquid crystal on silicon(LCoS),as well as beam shaping DOE elements and light rod illumination optical system for illumination were processed.An experimental platform was built to test the performance and analyze the data of the integrated micro projection system,The feasibility and advantages of using aspherical and diffractive optical elements in micro projection systems have been demonstrated. |
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