Research On Holographic Optical Elements In Laser Augmented Reality System

Augmented Reality(AR)is a display technology that integrates virtual information with the real world.It applies computer-generated text and images to the real world to achieve "enhancement" of the real world.Due to its advantages such as interactive virtuality and strong immersion,AR is widely regarded as the nextgeneration display terminal platform after smartphones.It will revolutionize the way humans obtain information.Currently,the software and hardware technologies of AR are gradually maturing.Both domestical and international AR industry are gathering momentum.Full-color laser optical engines have advantages of a wide color gamut,high brightness,good directional performance,and long lifespan.When applied to AR systems,they can reproduce more realistic and higher-quality images and ensure sufficient image brightness.Holographic optical elements(HOE)are attracting widespread attention in AR optical hardware due to their advantages such as lightness,stability,and low production costs,which can guarantee high-quality imaging effects and compactness systems.In addition,the combination of narrow-bandwidth laser spectrum and holographic optical elements with wavelength selectivity can achieve high transmittance and high luminous efficiency,which can prevent virtual images from being drowned out by ambient light.Therefore,the laser AR system based on the holographic optical elements are a promising technological path.Supported by the National Key R&D Program and Huawei’s project,this article studies the theory and experiment of holographic optical elements in laser AR systems to explore solutions to achieve better display effects and help the AR display industry achieve a breakthrough as soon as possible.The main research work and achievements of this paper are as follows:1.The chromatic aberration of holographic lenses was studied through simulation and the constraint conditions are proposed for the wavelength of the holographic lens imaging system.The imaging equation of the off-axis HOE lens is theoretically given,and the accurate prediction of the object point is achieved,providing a theoretical basis for the design of the holographic lens imaging system.Through this modified imaging equation,the wavefront condition of holographic recording can be inversely deduced.It lays a theoretical foundation for the design of freeform HOE.2.A naked-eye 3D display system based on dual-wavelength illuminated HOE lenses is proposed and designed.It can add resolution-preserving naked-eye 3D functionality to a laser AR display system.The effectiveness of this principle is verified through experiments.It provides a novel idea for the application of nakedeye 3D in AR displays.3.A highly efficient and compact laser white light module is designed and implemented.High coupling efficiency output with green light efficiency greater than 95%,red light efficiency greater than 90%and blue light efficiency greater than 80%is achieved.And it can achieve the separable function of light source and optical system.A laser pico-projector with a brightness of 1210 lm and a volume of 4.8 L was built through the design of the white laser module,power module and optical machine.4.We have established an HOE fabrication platform and achieved the production of green light monochromatic HOEs with a peak diffraction efficiency of 96.6%.We studied the parameters of the exposure process of full-color HOE and achieved the fabrication of full-color HOE with high peak diffraction efficiency and uniformity.Its average peak diffraction efficiency is 73.4%and the standard deviation of 7.9%.By combining a laser pico-projector with a full-color HOE,a compact full-color laser AR display system was built.Good display effect of laser AR system is achieved.5.We proposed a method for designing the initial structure of a freeform HOE and a recording method for the HOE fabrication.By using such methods,we can solve the problems such as aberrations,distortion,and image misalignment between RGB channels and eliminate the pain points of the traditional freeform element fabrication processes.Highlights of the dissertation are as follows:1.The chromatic aberration of holographic lenses was studied through simulation and the constraint conditions are proposed for the wavelength of the holographic lens imaging system.The imaging equation of off-axis HOE lenses has been theoretically established,allowing for precise prediction of the image points.Based on this equation,a method to calculate the initial structure of a freeform HOE(holographic optical element)has been proposed,as well as a method for preparing a segmented-recorded freeform HOE.This design method can not only eliminate problems such as image aberration,distortion and RGB image misalignment in traditional HOE lens imaging systems,but also solve the pain points of difficult traditional fabrication processes for reflective and refractive freeform elements.2.By utilizing the wavelength and angle selection characteristics of HOEs,a dualwavelength illumination HOE lens display system has been proposed and designed.It can add resolution-preserving naked-eye 3D functionality to a laser AR display system.This provides a novel approach for the application of naked-eye 3D in AR displays.3.A highly efficient and compact laser white light module is designed and implemented.It can achieve the separable function of the light source and optical mechanical system.A laser pico-projector with a brightness of 1210 lm and a volume of 4.8 L was built through the design of the white laser module,power module and optical machine.We studied the parameters of the exposure process of full-color HOE and achieved the fabrication of full-color HOE with high peak diffraction efficiency and uniformity.Its average peak diffraction efficiency is 73.4%and the standard deviation of 7.9%.By combining a laser pico-projector with a full-color HOE,a compact full-color laser AR display system was built.Good display effect of laser AR system is achieved.