Distortions of the virtual image in augmented reality displays based on waveguide holograms: the arising of tangential distortion and magnification chromatism

Subject of study. Waveguide holographic periscopes and virtual image distortions arising in augmented reality display circuits are studied. Aim of study. The main sources of distortion in the virtual image formed by the waveguide holographic periscopic display are determined, and the identified types of distortions are analyzed. Method. First, we use mathematical modeling to analyze the influence of various errors arising in the manufacturing process of waveguide holographic periscopes. The simulation is performed under the geometric optics approximation using the vector diagrams method. We develop a program to simulate virtual images in a head-mounted display based on waveguide holograms generated using the above approach. A specialized ray tracing program designed by the authors is also used. Next, waveguide holographic periscope samples are recorded and analyzed under specific parametrizations. Main results. The variability in the period of waveguide holograms and the wedge shape of the waveguides are found to induce similar distortions that cannot be fully compensated for by the projection system. Errors in the orientation of the waveguide holograms relative to each other and the periods introduce tangential distortion and magnification chromatism. The average output angle (angle of beams after waveguide outcoupling) also changes significantly. Practical significance. We identify the manufacturing errors that lead to specific distortions in virtual images. The estimated requirements for certain types of errors in the manufacturing process of waveguide holographic periscopes are determined. The results of the study can be used in novel augmented reality display designs.