Implementation And Optimization Of Holographic Waveguide Coupling Element Used In AR Display System

In this dissertation,the working principle,optical structure,and manufacturing method of holographic waveguide coupling elements,which are the key elements in AR display systems,are studied.The purpose is to provide a holographic waveguide coupling element with a simple structure and suitable for AR head mounted display device.The holographic waveguide coupling element is the key optical element of the augmented reality display system.The beam is incident perpendicular to the holographic waveguide plate,and the beam propagation direction is changed by the input-coupling element.The waveguide phenomenon is formed in the waveguide plate and transmitted to the output-coupling element,and the transmission direction is changed again by the outgoing coupling element.The light beam propagation direction is changed again by the output-coupling element,and exits from the holographic waveguide plate to the human eye.When the input-coupling element and the output-coupling element are either transmissive or reflective coupling elements,the angle values of changing the beam propagation direction twice are equal.Therefore,based on the imaging principle of the holographic waveguide optical system,this paper makes a thorough research on the holographic waveguide coupling element.The main research contents and conclusions are as follows:Firstly,based on the imaging principle of holographic waveguides,combined with the k vector circle theory and holographic optical recording principles,a symmetrical periodic structure of the holographic wave introduction coupling element and the holographic wave export coupling element is designed.The MATLAB software was used to simulate the interference light intensity model of the holographic waveguide coupling element during recording,which coincided with the periodic structure data of the designed coupling element.The COMSOL software is used to simulate the change process of the beam propagation angle of the holographic waveguide coupling element,which is consistent with the theoretical change of the beam propagation direction.It is proved that the two holographic waveguide coupling elements are arranged in the holographic waveguide optical system in a mutually symmetrical structure,which can meet the requirements of the holographic waveguide optical system for the beam propagation direction.Secondly,dichromate gelatin was selected as the holographic recording material,and a transmissive holographic waveguide coupling element was fabricated using holographic interference exposure technology.A holographic interference exposure experimental system with a working wavelength of 633 nm was designed.Based on this system,the optical path of the holographic interference exposure experimental system was optimized using the variablewavelength reproduction principle.The manufacturing process of the holographic waveguide coupling element was determined,and the key parameters and processing conditions of preparation,exposure and post-processing were studied.Finally,a reproduction experiment was performed on the holographic waveguide coupling element.The working wavelength of the experimental system was 633 nm.The first order diffraction of the input-coupling element and the output-coupling element met the design requirements.The influence of the thickness of the grating,the wavelength shift,the angular shift and the preparation process parameters on the experimental results are analyzed,which has certain reference value for subsequent experimental research.