Curved holographic optical elements and applications for curved see-through displays

Abstract

Holographic optical elements (HOEs) have been used as important tools for implementing augmented reality (AR) and see-through displays because they are transparent and thin. Moreover, as HOEs usually come in the shape of a thin film, they can be bent, used for coating, or attached to curved surfaces. While they can be used to implement curved AR displays, however, the applications of the curved HOE have not been sufficiently studied. In this paper, an analysis method for curved/bent HOEs using the coupled-wave theory and the numerical ray tracing method is introduced. Using this method, the influence of the surface curvature on the optical characteristics of HOEs, including the aberration and diffraction efficiency, was analyzed. Also presented herein is a method of designing the optimal curvature that can reduce the aberration. Curved HOEs can be applied to see-through displays such as head-mounted displays (HMDs), head-up displays (HUDs), or transparent screens. They can be used to expand the field of view (FOV) and to reduce the form factor. The proposed analysis method provides a useful guideline for designing practical curved see-through displays.

Notice of Violation of IEEE Publication Principles: Design and Performance of an Off-Axis Free-Form Mirror for a Rear Mounted Augmented-Reality Head-Up Display System

“…Using this structure, both volume and weight of the system can be reduced. However, the structure still needs to be attached to the windshield glass, which adds complexity and increases cost.Because the holographic optical elements(HOEs) are transparent and thin, K. Bang et al [19] analyzed the influence of the surface curvature of the holographic optical elements on its optical characteristics, designed an optimal curvature method to reduce aberrations, and bends the holographic optical elements and applied it to head-up display.…”

A Multi-Plane Augmented Reality Head-Up Display System Based on Volume Holographic Optical Elements With Large Area

“…Therefore, the reduction of FOV or object size can reduce aberrations of the system. In addition, feasible methods to further correct astigmatism include adding a cylindrical mirror to the recording optical path and fabricating HOEs on a curved glass substrate [20], [21].…”

“…Wayray Corp. has demonstrated a HUD system using a curved HOE on the windshield, effectively reducing the size of the projection module. South Korea's Byoungho Lee et al have proposed an analysis and design method for curved holographic optical elements, mainly analyzing the aberrations of two different recording methods: curved surface HOE and bendable surface HOE [21]. This method can effectively solve the aberration problem of the curved HOE.…”

Design and fabrication of freeform holographic optical elements

“…In this work, we limited our design of freeform volume grating profiles to 2D planes rather than 3D freeform surfaces. For some VR/AR applications, it could be beneficial to create HOEs with physically curved form-factors, for example, for HOEs laminated on curved windshields or glasses [Bang et al 2019;Blanche et al 2019]. We expect our fabrication framework to expand well to such cases, since neither the printer or the diamond turning approaches require the HOE to be flat, and the optimization method of Algorithm 1 could be adapted to intersect rays with a curved surface on step 3.…”