Abstract
In a waveguide-type display for augmented reality, the image is injected in the waveguide and extracted in front of the eye appearing superimposed on the real-world scene. An elegant and compact way of coupling these images in and out is by using blazed gratings, which can achieve high diffraction efficiencies. We report the design of blazed gratings for green light (λ = 543 nm) and a diffraction angle of 43°. The blazed gratings with a pitch of 508 nm and a fill factor of 0.66 are fabricated using grayscale electron beam lithography. We outline the subsequent replication in a polymer waveguide material with ultraviolet nanoimprint lithography and confirm a throughput efficiency of 17.4%. We finally show the in- and outcoupling of an image through two blazed gratings appearing sharp and non-distorted in the environment.
Highlights
With the virtual reality (VR) and augmented reality (AR) application’s boom, head-mounted displays (HMDs) are gaining a lot of attention
Holographic lithography, on the other hand, is mostly used for symmetric structures and should be combined with ion milling [11] or anisotropic KOH etching [12] to achieve asymmetric structures. As these combined processes are expensive and time consuming, we focus on grayscale electron beam lithography in this paper
To investigate the blazed grating profiles, cross sections are made with focused ion beam (FIB) scanning electron microscope (SEM) (Nova 600 NanoLab, FEI Company, Hillsboro, OR, USA)
Summary
With the virtual reality (VR) and augmented reality (AR) application’s boom, head-mounted displays (HMDs) are gaining a lot of attention. The waveguide approach is of particular interest because the HMD can be made small and light-weighted [1,2,3,4]. Various waveguide based techniques are used in modern HMDs such as reflective optics, polarized optics, diffraction optics and holographic optics. These are briefly discussed below [5]. Virtual image appears here in the field of view of the user
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