Research On Retinal Projection Technology On Human Visual Characteristics

Near-Eye Displays(NEDs)are considered the next generation display platform,demonstrating immense application potential in fields such as communication,education,healthcare,and military.Retinal projection display,as an important NED technology,has attracted widespread attention due to its advantages of large depth of field,wide viewing angle,and simple structure.Traditional retinal projection display systems use glass lenses to focus light waves carrying image information at the pupil position of the human eye.After receiving these light waves and the human eye directly generates a clear image on the retina after.This technology avoids the blurring of monocular focusing and alleviates the issue of vergence-accommodation conflict(VAC)to some extent.However,this system has some problems,such as large volume,limited exit pupil area,and inability to trigger monocular focusing responses.To this end,various retinal projection display technologies based on holographic optical elements(HOE)have been proposed.By using portable,efficient and maneuverable HOE,these technologies simplify the structure of retinal projection display.However,HOE is an optical element based on diffraction principles,and such systems usually require lasers as light sources.Laser is expensive and has speckle problems,which also pose potential safety hazards to the eyes.The combination of HOE and super-multi-viewpoint retinal projection technology can provide monocular focusing information and a natural viewing effect without obvious VAC issues.However,this technology has problems such as large image computation and low rendering efficiency.To address these issues,this article proposed a 3D retinal projection display technology based on dual holographic optical element(HOE).The performance of traditional retinal projection display systems is simplified and improved through the use of inexpensive and safe LED light sources and HOE which is lightweight and transparent.An optical combiner composed of a reflective volume holographic grating and a reflective volume holographic lens is used to compensate for HOE dispersion,thereby reducing image blur and enhancing the clarity of the display system.By combining the resolution characteristics of the human eye in the depth direction,a rendering algorithm based on discrete depth planes was proposed and validated,which optimized the rendering process of 3D retinal projection images,improved rendering speed,and achieved good results.The main research content is as follows:(1)The principle of the HOE-based retinal projection display system is analyzed.The imaging laws of holographic optical elements including holographic gratings and holographic lenses and their application in retinal projection display technology are explained.The dispersion blur of diffraction elements under incoherent light illumination conditions is described,and dispersion blur size as well as the methods and principles of dispersion compensation are discussed.(2)The principle of 3D retinal projection display is explained,and the relationship between the depth of the 3D image and system parameters is derived,and the formulas for viewpoint offset and viewpoint spacing are analyzed.A 3D retinal projection display system based on multi-viewpoint technology is designed using a dual HOE structure,and optimized parameters ranges are given.The manufacturing process of holographic optical elements is optimized and improved to obtain high-performance holographic optical elements.Furthermore,reflective volume holographic gratings and reflective volume holographic lenses are designed and fabricated with diffraction efficiencies of61% and 58%,respectively.(3)A 3D retinal projection display based on a dual HOE structure has been constructed.The dispersion problem coming from HOE under incoherent light source illumination conditions is solved using the dual HOE structure.The use of HOE is expanded to avoid speckle noise and safety hazards of laser sources in near-eye display systems.The dense viewpoint retinal projection display is achieved using time-division multiplexing and angle-multiplexing techniques.The exit pupil of the system is effectively expanded,and the exit pupil area reaches 7 mm x 7 mm.True 3D display with monocular focusing depth information is achieved with the 3D refresh rate of100 Hz,which effectively solving the visual accommodation conflict problem and improving the visual experience of near-eye display systems.Using HOE instead of glass lenses and LED instead of laser sources,this display system possess good application prospects with a compact structure,controllable cost,high integration.(4)The visual characteristics of the human eye in the depth direction are analyzed,and a rendering algorithm for multi-viewpoint images used for 3D retinal projection is simplified using these characteristics.Based on this algorithm,a nearly continuous 3D display effect can be achieved by rending multiple discrete planes with the same diopter distance in the depth direction.This multi-viewpoint rendering algorithm that combines human visual characteristics can effectively reduces redundant calculations and improves rendering efficiency.