Current augmented reality (AR) waveguide display technology faces a challenging trade-off between essential factors such as eyebox, efficiency, and image uniformity. Surface relief grating has been a commonly used exit pupil expander (EPE) in waveguides, but it exhibits limitations in efficiency and uniformity. To overcome these shortcomings, polarized volume grating (PVG) with ultra-wide angular bandwidth and high efficiency has been employed as an EPE to enhance efficiency and uniformity. However, the challenge arises when attempting to achieve high uniformity within the eyebox using nematic liquid crystal for controlling each expansion, as the polarization changes of diffracted light contribute to varying diffraction efficiencies, which affects the maintenance of uniformity across the entire field of view. This article introduces an innovative approach by incorporating high-low cover-layers on top of PVG to effectively control the path difference between light rays at various angles. This design modification mitigates unnecessary out-coupling and ensures a remarkably high level of uniformity in the entire AR system, providing a more efficient and uniform expanded eyebox.
A diffractive waveguide-based optical combiner is one of the most commonly used elements to construct head mount AR displays. This paper proposes a design method for a compact and wide field-of-view layout for an AR-applicable diffractive waveguide. The layout design utilizes multiplexed 1D gratings as both the exit pupil expander (EPE) and the out-coupler, combined with minimum-sized 2D grating to improve image uniformity and deliver a better user experience. The design outcome is optimized and simulated in LightTools and RSoft. The result has indicated the feasibility of a compact and 60 degrees FOV design of a diffractive waveguide AR display with a 12 mm × 10 mm eye box.
For a diffractive waveguide-based augmented reality display, we demonstrate a rapid and straightforward method to define the most compact layout of an exit pupil expander (EPE) from an analysis of diffractive optical elements in kspace. The idea is to consider all k-vectors coming from in-coupling to out-coupling areas according to the grating theory, and with the geometrical tracing of the EPE region to find the optimal layout. For a working wavelength of 532 nm, 40 degrees field of view display, our method is able to fit the layout into a circular shaped area with a minimal radius or to optimize for the minimal EPE area. Furthermore, a web-based interactive application demonstrating the EPE layout calculation is provided as a layout design tool.
Diffractive gratings, one of the most promising near-eye display designs, has been challenging to satisfy the essential features without making sacrifices in output efficiency or the direction of incidence due to the low diffraction efficiency of higher modes at normal incidence. Here, we propose dielectric metagratings that support light deflect to a larger angle with high efficiency within the field of view of 54 degrees. In this paper, through the proposed model of the eye-imaging system, we present optimal designs of metagratings for diffractive total internal reflection combiner or diffractive exit pupil expanders.
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