In the field of augmented reality (AR), geometric waveguide has become one of the effective solutions of near-eye display due to their thinness and high transmittance. To obtain clearer viewing experiences, the causes of the stray light are analyzed and solved. The improper tilt angle and the difference in parallelism of the partially reflective mirrors array (PRMA)units may cause stray light or overlapping ghost images, and the refractive indices of the glue and the glass also plays an important role as the appearance of several opposite ghost images. The results show that by adjusting the tilt angle of the PRMA, the stray light within the major area of the eye box can be eliminated. Then a 1.8 mm thick waveguide with stray light of less than 1% is designed. The refractive index of the glass is 1.502 and that of the matched glue is 1.500. The FOV of the designed system is 40°, the size of eye box is 10 mm × 10 mm, and the eye relief is 20 mm. The distribution of the stray light on the observed virtual image is simulated. Finally, a proof-of-concept prototype with eliminated stray light is fabricated and demonstrated.
Compared with the traditional panel display, the head-mounted display (HMD) is a new technology. When using an HMD, it occupies a significant portion of the eyes’ natural field of view (FOV). Thus, it is necessary to ensure the imaging quality of an HMD, which requires accurate measurement and evaluation. Based on the measurement of panel display, this paper proposes a kind of luminance and chromaticity measuring equipment for HMD by combining an optical fiber spectrometer with a translation platform. The equipment measures various parameters such as brightness, chromaticity, contrast, color gamut, eyebox, etc. To prove the validity of the equipment, several HMDs with different luminance are used for multiple measurements. The final results show that the brightness stability of the equipment reaches 2%, and the chromaticity stability reaches 0.002, which fully meets the measurement requirements of HMD. This equipment has certain reference value for HMD production and testing.
It has been a challenge to design an automotive head-up display (HUD) that has large eyebox while maintain a compact structure. In this paper, we present a combiner-type HUD design using freeform mirrors. The HUD is an off-axis fourmirror system consisting of 4 mirrors, which are enclosed in a box to achieve a compact form. The tilt angle of the combiner is adjustable, which can be adapted to different heights of exit pupil. We initially propose an off-axis, fourmirror system which only uses spherical surfaces, then we optimize it by replacing with freeform surfaces, which enables us to balance the residual asymmetrical aberrations. Finally, we obtain an HUD system with good imaging performance. The virtual image is projected at 5 meters away from observer, and the eye box is 106 × 66 mm2 .
With the widespread use of AR/VR head-mounted displays, there is an increasing demand for pinhole cameras to test their image quality. However, it has been a challenge to design a pinhole camera with a wide field of view (FOV), high image performance and low distortion while maintaining compact and lightweight. In this paper, a pinhole camera optical system is designed. Based on a 1 in. sensor, the pinhole lens has a FOV of 100° and an entrance pupil diameter of 4mm. In our final design, the distortion is limited within 2.5% and the modulation transfer function values across the entire field are above 0.3 at 161 line pairs/mm (lps/mm). The spherical aberration, color aberration and field curvature are corrected. The design result shows that the optical system of the pinhole camera is compact and meets the requirements of the VR/AR image quality test system.
As an important auxiliary function of head-mounted displays (HMDs), eye tracking has an important role in the field of intelligent human–machine interaction. In this paper, an eye-tracking HMD system (ET–HMD) is designed based on the rotational symmetric system. The tracking principle in this paper is based on pupil–corneal reflection. The ET–HMD system comprises three optical paths for virtual display, infrared illumination, and eye tracking. The display optics is shared by three optical paths and consists of four spherical lenses. For the eye-tracking path, an extra imaging lens is added to match the image sensor and achieve eye tracking. The display optics provides users a 40° diagonal FOV with a ״ 0.61 OLED, the 19 mm eye clearance, and 10 mm exit pupil diameter. The eye-tracking path can capture 15 mm × 15 mm of the users’ eyes. The average MTF is above 0.1 at 26 lp/mm for the display path, and exceeds 0.2 at 46 lp/mm for the eye-tracking path. Eye illumination is simulated using LightTools with an eye model and an 850 nm near-infrared LED (NIR-LED). The results of the simulation show that the illumination of the NIR-LED can cover the area of the eye model with the display optics that is sufficient for eye tracking. The integrated optical system HMDs with eye-tracking feature can help improve the HMD experience of users.
This study introduces a telescope with virtual reality (VR) and augmented reality (AR) functions. In this telescope, information on the micro-display screen is integrated to the reticule of telescope through a beam splitter and is then received by the observer. The design and analysis of telescope optical system with AR and VR ability is accomplished and the opto-mechanical structure is designed. Finally, a proof-of-concept prototype is fabricated and demonstrated. The telescope has an exit pupil diameter of 6 mm at an eye relief of 19 mm, 6° field of view, 5 to 8 times visual magnification , and a 30° field of view of the virtual image.
Nowadays, the waveguide has the advantages of small thickness and light weight so that it attracts more and more attention in the field of near-eye display. However, as a major problem, stray lights generated in the waveguide seriously degrade the display quality. In this paper, a geometrical waveguide with a beam-splitting mirror array (BSMA) is designed by using the non-sequential ray-tracing software LightTools, and great efforts are paid to study the causes and solutions of the stray light. With mass calculation and optimization based on the criterion of stray light/useful light ratio, an optimum design with the least amount of stray lights is found. To further eliminate the stray light, a novel structure that couples the rays into the waveguide is designed. The optimized waveguide has a FOV of 36° in the pupil-expanding direction of the waveguide, with stray light energy reduced to 1% over the useful light, the exit pupil diameter is 11.6mm at an eye relief of 20mm and the thickness is 2.4mm.
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