Abstract
The representation of three-dimensional volumetric pixels, voxels, is an important issue for the near-to-eye displays (NEDs) to solve the vergence-accommodation conflict problem. Although the holographic waveguides using holographic optical element (HOE) couplers are promising technologies for NEDs with the ultra-thin structure and high transparency, most of them have presented only a single and fixed depth plane. In this paper, we analyze the imaging characteristics of holographic waveguides, particularly to represent the arbitrary voxels and investigate the voxel duplication problem arising from the non-collimated light from the voxels. In order to prevent the image crosstalk arising from the voxel duplication, we propose an adjustment method for the emission angle profile of voxels by using the integral imaging technique. In the proposed method, the sub-regions of elemental images, which correspond to the duplicated voxels, are masked in order to optimize the emission angle of integrated voxels. In the experimental verification, a see-through integral imaging system, based on the organic light-emitting diode display and a holographic waveguide with the thickness of 5 mm, was constructed. The fabricated HOE in the waveguide showed high diffraction efficiency of 72.8 %, 76.6%, and 72.5 % for 460 nm, 532 nm, and 640 nm lasers, respectively. By applying the masked elemental images, the proposed method resulted in a reduced crosstalk in the observed voxels by 2.35 times. The full-color experimental results of see-through holographic waveguide with integral imaging are provided, whereby the observed 3D images are presented clearly without the ghost images due to the voxel duplication problem.
Highlights
See-through near-to-eye displays (NEDs), which are core components of the augmented reality (AR) headsets, have been given considerable attention recently [1,2]
If we mask a pixel in the elemental images (EIs) under the i-th lenslet in Figure 5a, the emission angle of integrated voxel (θ e,integral imaging (InIm) ) decreases by the amount of θ i,ub –θ i,lb
This alters the upper bound of the emission angle of the voxel from θ i,ub to θ i+1,ub (=θ i,lb ), and prohibits the emitted light by exceeding the effective angular range (EAR)
Summary
See-through near-to-eye displays (NEDs), which are core components of the augmented reality (AR) headsets, have been given considerable attention recently [1,2]. Various optical technologies have been actively studied for the see-through AR NEDs, such as the free-form optics [3], the direct retinal projection optics [4,5], and the waveguide optics [6,7,8,9,10,11,12,13,14,15]. Among these technologies, the waveguide optics provide the best way to minimize the size of NEDs, which is crucial for the comfort and compactness of the AR headsets. Such a selective functionality of HOEs allows users to view a real-world scene more clearly without severe light attenuation or degradation
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