Research On The Method Of Enhancing The Viewing Angle Of Holographic Display System

In recent years,with the concept of "metaverse" proposed,the industry urgently needs a three-dimensional(3D)display technology that can provide users with a more immersive experience.Compared to other 3D display technologies,holographic display is based on the principles of interference and diffraction,which can reconstruct the complex information of object light waves to provide real depth cues for 3D scenes.With the visual effect of single-eye focusing,holographic display is considered as one of the most ideal 3D display technologies,and is widely used in fields such as national defense,military,medical health,scientific research and education,culture,and entertainment,which has continuous growth in industry demand and broad market prospects.Computergenerated holographic display is realized based on spatial light modulator(SLM).However,due to the limited spatial bandwidth product of the SLM,the display system has problems such as small viewing angles.In order to obtain a better visual experience,this dissertation conducts relevant theoretical and experimental research on the viewing angle enhancement of holographic 3D display systems based on the light control performance of holographic optical element(HOE).The research content and innovation points of the dissertation are as follows:(1)Binocular holographic 3D display based on angle multiplexing technology of HOEThe viewing angle of traditional holographic display system is small,which can be seen with a single eye for a single person.Hence,the visual experience is poor.Common methods for improving the viewing angle of holographic display system based on SLM multiplexing technology have disadvantages such as high cost and complex system structure.Traditional binocular 3D display systems have the accommodation-vergence conflict and visual fatigue problem.Based on the above two problems,this dissertation researches and designs a binocular holographic 3D display system based on the HOE.In this system,a composite lens with two different focal points is made based on angle multiplexing technology,which completes the design of the light control element HOE.The synthesized phase hologram for the left view and the right view is calculated based on the layered angular spectrum diffraction theory and loaded onto the SLM for display.The reconstructions of the left view and the right view are used as the probe waves.Under the Bragg matched condition,the left-view and the right-view reconstructions are modulated by the HOE and focused on the left and right viewing positions of the observer,respectively.The system is mainly composed of a single SLM and a light control element HOE,which has the advantages of simple structure and low cost.The experimental results show that the designed system achieves binocular holographic augmented reality(AR)display effect without accommodation-vergence conflict.The HOE can increase the viewing angle of each view to 8.7 degrees,and the width of the viewing zone is 2.3 cm at a viewing distance of 25 cm.(2)Dual-view holographic 3D display based on the Braggmismatched focus offset characteristic of HOETo improve the viewing angle of holographic display system and simplify the HOE design process to improve practicality,a dual-view holographic 3D display system based on the Bragg-mismatched focus offset characteristic of HOE is designed and studied.The HOE is completed by interfering a plane wave with a converging spherical wave,and two probe waves different from the reference wave are used for reconstruction.By utilizing the reflection control of HOE,two different 3D reconstructed images with real physical depth are directed to different viewing zones,achieving dual-view holographic display.The advantages of this system are lower cost and simpler manufacturing process of HOE.Experimental results show that this system can achieve dual-view holographic AR display with monocular focus effect and the viewing angle of each viewing zone is 11.2 degrees,which is 2.5 times larger than that of traditional holographic display system.(3)The high-resolution multi-view holographic 3D display system using computer-generated hologram printing technology.In order to further improve the viewing angle,realize the 3D display effect with motion parallax,a high-resolution multi-view holographic display system is designed.To adjust the reconstructed position of each sub-image,ensure the resolution enhancement and no crosstalk reconstruction of the multi-view images,the digital grating is added in the hologram design algorithm based on the layered angular spectrum diffraction theory.The modulation function of HOE is designed based on point cloud algorithm and four lens functions with different focus coordinates are set.The HOE is designed and fabricated based on the computer-generated hologram printing technology.Experimental results show that the designed HOE can redirect four view reconstructions into four different viewing zones,achieving multi-view holographic AR display,and the resolution of each view is 4K,which is higher than that of other multi-view display systems.This dissertation focuses on the problem of small viewing angles in holographic display system and carries out a series of research work.Based on the control characteristic of HOE,three new holographic 3D display systems are designed,and the design goal of 3D display that meets human viewing needs is successfully achieved,laying the foundation for the development of the Metaverse platform.