ABSTRACT
Augmented reality (AR) displays are gaining attention as next-generation intelligent display technologies. Diffractive waveguide technologies are progressively becoming the AR display industry's preferred option. Gradient period polarization volume holographic gratings (PVGs), which are considered to have the potential to expand the field of view (FOV) of waveguide display systems due to their wide bandwidth diffraction characteristics, have been proposed as coupling elements for diffraction waveguide systems in recent years. Here, what we believe to be a novel modeling method for gradient period PVGs is proposed by incorporating grating stacking and scattering analysis utilizing rigorous coupled-wave analysis (RCWA) theory. The diffraction efficiency and polarization response were extensively explored using this simulation model. In addition, a dual-layer full-color diffractive waveguide imaging simulation using proposed gradient period PVGs is accomplished in Zemax software using a self-compiled dynamic link library (DLL), achieving a 53° diagonal FOV at a 16:9 aspect ratio. This work furthers the development of PVGs by providing unique ideas for the field of view design of AR display.
ABSTRACT
This work proposes a green light-sensitive acrylate-based photopolymer. The effects of the preparation conditions for the waveguide applied volume holographic gratings (VHGs) were experimentally investigated. The optimum preparation conditions for holographic recording were revealed. After optimization, the peak of VHG diffraction efficiency reached 99%, the diffractive wavelength bandwidth increased from 13 nm to 22 nm, and the corresponding RIM was 0.06. To prove the wide application prospect of the acrylate-based photopolymer in head-mounted augmented reality (AR) displays, green monochromatic volume holographic waveguides were fabricated. The display results showed that the prototype was able to achieve a 28° diagonal FOV and possessed a system luminance of 300 cd/m2.
ABSTRACT
A ray-tracing model is developed based on coupled wave theory for a volume holographic grating, which is the most important element of the holographic waveguide display but not accessibly integrated in current optical design software. The model fully and faithfully represents the angular selectivity, wavelength selectivity, polarization, and other properties for the in-coupling, out-coupling, and expansion gratings. It is especially important that the model is compatible with the current optical design software. In this paper, combining with other mature optical simulation functions of Zemax, integrated models are built for typical holographic waveguide display configurations, including image source, collimation element, gratings, waveguide plates, and approximate eye. It could provide the retina image at different viewing positions, based on which the main performance characteristics of a holographic waveguide display, such as field of view, color uniformity, eye box, and light efficiency, could be easily derived. Consequently, it provides a valuable guiding approach for the design and optimization of holographic waveguide displays.
ABSTRACT
In this Letter, we demonstrate polarization volume grating (PVG)-based couplers for a double-layer waveguide display to realize a full-color near-eye display. The polarized interference exposure with photo-alignment methods was employed to generate a birefringent spiral configuration with two-dimensional periodicity in a chiral-dopant reactive mesogen material. Such a structure presents a unique highly efficient single-order Bragg diffraction with polarized selectivity. The prepared PVG couplers exhibited over 80% diffraction efficiency with large diffraction angles at spectra of blue (457 nm), green (532 nm), and red (630 nm). The demonstrated waveguide prototype showed a full-color display with a diagonal field of view of around 35°. The overall optical efficiency was measured as high as 118.3 cd/m2 per lumen with a transparency of 72% for ambient light.
