Research On Optical Coupling Technologys Applied For Full-color Waveguide Displays

As a hot topic in the field of information display,the HMD-AR(Head Mounted DisplayAugmented Reality)devices represent a good vision for a future method of information interaction.As a widely recognized solution for HMD-AR technology,optical waveguides have significant advantages in terms of volume,weight,exit pupil size,and see-through ability.As an essential component,the performance of waveguide coupler directly determines the optical efficiency,exit pupil,color performance,sharpness and imaging quality of optical waveguide display systems.Among the current mainstream waveguide coupling technology,VHG(Volume Holographic Grating)has received extensive attention due to its low fabrication difficulty and high optical coupling efficiency.However,the current VHG waveguide display technology suffers a small field of view(FOV)and poor color performance.At the same time,there is currently no effective simulation or analysis method for the VHG waveguide system since it involves both physical and geometric optics.In order to solve these problems,this thesis focuses on VHG waveguide display application,establishes a rigorous mathematical simulation model of VHG waveguide coupler to study and analyze the diffraction characteristics of VHG.The key grating parameters that affect the FOV and color performance is extracted,which reveals the correlation between VHG diffraction characteristics and imaging performance of the waveguide display system.In addition,a double-layer grating waveguide structure is proposed,which effectively improves the FOV and chromatic performance of the VHG waveguide display system.For the first time,we combine the mechanisms of Bragg diffraction with the Pancharatnam-Berry(PB)phase modulation and develops a novel polarization volume grating(PVG)by using photo-alignment technology and self-assembly characteristics of liquid crystal.The proposed PVG features as high diffraction efficiency with a large diffractive angle,which is same as of the VHG.At the same time,the angular bandwidth of the PVG is nearly 2.5 times higher than that of conventional photopolymer VHG and the wavelength bandwidth of the PVG is increased by 4 times compared with that of the VHG.In addition,PVG's unique PB polarization sensitivity not only ensure a high see-through ability of the AR waveguide system but also provide a new design and optimization dimension for the waveguide system.In this thesis,a rigorous PVG mathematical simulation model is established,and the diffraction and parameter characteristics of the PVG are studied comprehensively.We also proposed the detailed fabrication process of the PVG,and a double-layer PVG color waveguide structure is also proposed and prepared.The prepared PVG-couplers exhibit over 80% peak efficiency in the red,green and blue spectra,which satisfies the requirements of waveguide coupling.In this paper,an experimental prototype of PVG-based full-color waveguide system is also demonstrated.The display results show that the waveguide system can achieve a clear display of full-color images with a diagonal FOV of about 35°.The total optical efficiency of the waveguide system is as high as 118.3 nit/lm,and the transmittance of ambient light is around 72%,which further proves the practicability of PVGs as couplers in waveguide coupling applications.In summary,we establishe a rigorous mathematical model and design method for volume holographic optical waveguide display system.A series of optimization designs and methods are proposed for solving the existing problems.In particular,the proposed PVG-coupler provides a new promising candidate for optical waveguide coupling technology,which strongly promotes the realization of high-quality AR waveguide display applications in the future.