With the advent of high brightness microdisplay, augmented reality head mounted display (AR-HMD) has rapidly developed and applied. Various optical schemes emerge one after another. However, it is still a huge challenge to realize large field of view (FOV), high resolution and keep the compact form of head mounted display. We propose a novel free-form prism tiling optical system, which can simultaneously realize large field of view, high resolution and compact optical see-through augmented reality HMD. It can overcome the FOV/resolution invariant and solves the problem that the optical axes of the display channels don’t coincide with the visual axis of the human eye. The optical system consists of two microdisplays, two free-form prisms and a compensation lens which are attached together. The prisms are partially overlapped to provide the same field of view and reduce the seam at the transition region of adjacent FOV. The optical see-through system we designed achieves large FOV of 52.8°×52.8° (70° diagonally) and resolution of 33.7 pixels/degree, and has good optical performance. We emulated the system with distortion and illuminance pre-conditioning and discussed the remaining problems and future work.
Virtual image distance (VID) is a key parameter in augmented reality (AR) or virtual reality (VR) systems and has a great influence on product performance and user experience. Therefore, it is very necessary to measure the VID accurately and efficiently. In this paper, we develop a VID measurement system which needs no mechanical scanning in the measurement process. The VID can be measured in a short period of time based on one single image generated by the AR/VR system. An image-telecentric lens is designed which is used to capture the virtual image. A diaphragm with two pinholes is placed at the entrance pupil plane of the imaging lens. When the imaging lens is not focused on the virtual image, the captured image contains two copies of the virtual image with a certain interval which is proportional to the VID in units of diopters. By calculating the interval, we can obtain the VID. A simulation is performed in LightTools to verify the effectiveness of the measurement system, and the result indicates that the measurement error is 5 mm when the virtual image is at 3 m.
This study proposes an optical-see-through light-field near-eye display (OST LF-NED) based on integral imaging (InI) using a discrete lenslet array (DLA). A light-field image is used as the image source. A special microdisplay array built on a transparent substrate is used as the screen. A DLA is used as a spatial light modulator (SLM) to generate dense light field of the 3-D scene inside the eyebox of the system and provide correct focus cues to the user. The key to realize the OST capacity is that the microdisplays and the lenslets are both discretely-arranged so that the light from the real world passes directly through the gaps among the microdisplays on the transparent substrate and then the flat portion on the DLA panel, providing a clear view of the real world as well as the virtual information. The stray light can be totally eliminated in the region of the eyebox in ideal situations. In practical situations, take the limitation of the F-number into consideration, a trade-off between the size of eyebox and the stray light is made. Analysis and simulation of the stray light are conducted in detail. A ring-shaped aperture on each lenslet is added to reduce the stray light significantly by blocking the screen light that passes by the outer edge of each lenslet. The simulation shows that the proposed method is capable of providing an OST view in LF displays.
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