Research On Head-mounted Display Based On Planar Optical Waveguide

With the rapid development of information society, head-mounted display (HMD) has shown great values and development potential in many fields. The see-through display system has been the focus of the study in HMD. Imaging based on goggles is the main technology of see-through HMD. However, its optical system is bulky and occupies much space inside the helmet. In order to meet the trends and requirements of lightweight and small size, display based on planar holographic waveguide and planar transparent-filmed waveguide are proposed as new methods for HMD. Due to immature technology, only low-resolution quasi-monochromatic image can be acquired in display based on planar holographic waveguide. Although planar transparent-filmed waveguide can achieve color display, the traditional structure will cause ghost images.In-depth research on the technology and principles of display based on planar holographic waveguide is conducted in the paper. Firstly, correlation of grating's spatial frequency, FOV, wavelength, waveguide's size and other parameters are analyzed. Secondly, considering exit-pupil diameter, exit-pupil distance, working distance, MTF, spot diagram, field curvature, distortion and so on, optical system is optimized. Lastly, a set of holographic HMD's system is designed with 640nm and 532nm LDs as light source. The system can achieve 20.2°horizontal FOV and 15.2°vertical FOV. It also has a large eye box and over 25mm eye relief. Limited by the experimental conditions, only partial experiment is carried out to verify the theoretical analysis.Through computational analysis, there will be serious ghost images in traditional structure of display based on planar transparent-filmed waveguide. Improved program is proposed to eliminate ghosts. A set of system with tri-layer planar transparent-filmed waveguide is designed. The system can achieve 16°horizontal FOV and 12°vertical FOV, and a large eye box. With the system parameters, an experimental platform has been built. Due to reasonable reflectivity of transparent films, a high-transmittance background and color conformity are gained. Meanwhile, experimental results show that the improved structure can avoid ghost images caused by traditional structure of planar transparent-filmed waveguide.