| Augmented reality(AR)is a display technology that merges virtual scenes with real three-dimensional(3D)environments,resulting in interactive and informative interfaces.To achieve this,AR systems must create virtual images that have realistic depth cues and can seamlessly blend into the real scene.Holographic displays offer a solution to this challenge by providing all the necessary depth cues for the human eye without any focal-distance conflicts.This paper proposes two AR holographic display methods that utilize holographic optical element(HOE)to enhance the system’s resolution and depth of field.Both methods create two viewing areas for two viewer to watch at the same time.The main research content and innovation of this paper include the following two parts:1)High-resolution dual-view AR display method based on the holographic optical elementDue to the overlarge pixel pitch of the current available spatial light modulator(SLM),the Angle of view of the holographic reconstruction is too small to realize dual-view holographic 3D display.Meanwhile,the resolution of holographic image reconstruction is limited by the resolution of SLM.In this paper,a high-resolution dual-view AR display method based on holographic optics is proposed.The images of two viewpoints are divided into multiple sub-images with the same resolution as SLM.The phase holograms of each sub-image are calculated using the theory of tomographic angular spectrum diffraction.A digital grating is introduced to adjust the position of the sub-images,and they are seamlessly spliced at the predetermined imaging position to achieve high-resolution image reconstruction.The HOE printed by Computer-Generated Holograms(CGH)was utilized as guide light elements to direct two 3D images reconstructed by SLM to two distinct observation areas simultaneously.In optical experiments,it was observed that a holographic reconstruction image with 4K resolution could be viewed in two separate areas at the same time,with a 45° angle between them.This was achieved under the condition of a 2K resolution SLM and can satisfy two individuals watching at once.The system can realize the high-resolution dual-viewing AR holographic 3D display function at a low cost.2)Large depth of field dual-view AR display method based on the holographic optical elementIn an AR system,virtual information must seamlessly integrate with the real world.Research has shown that the human eye has a limited ability to perceive depth information beyond 7 meters(m).By integrating AR information with the surrounding environment,viewers can experience a natural fusion of the real world and virtual information,while reducing the vergence-accommodation conflict.The virtual image viewing distance(VID)in the AR system needs to be greater than 7 m for this method to work.To increase the VID range,it is essential to enhance the depth of field in the 3D scene displayed in AR.In this paper,we propose a dual-view AR display method with a large depth of field ranging from 0.15 m to 8.28 m.Firstly,SLM is used to reproduce the holographic reconstruction image with depth.Secondly,the grating vector of HOE is designed on the basis of volume holographic grating,and the multi-beam interference system is built to complete the production of dual-lens HOE.According to the optical imaging properties of HOE,the depth of field of the holographic reconstruction image is expanded and the VID range is expanded.Meanwhile,the 3D scene displayed is directed into two viewing areas by HOE for two people to watch simultaneously.The optical experiment results show that the system can satisfy two people watching the same 3D scene at the same time,and the depth range of the two viewing areas can present the three-dimensional scene is 0.15-8.28m.The VID control error of AR display content is less than 5%. |
PDF Full Text Request