We analyze the light efficiency of a virtual reality (VR) system from display panel to eyebox, and brightness non uniformity caused by the imaging process of the VR lens. Two types of light engines: OLED and LCD are evaluated. For an OLED panel, we optimize the microcavity structure to suppress the image non-uniformity, while keeping a high optical efficiency. For LCD, we propose a 2D patterned prism film to locally modulate the radiation pattern for optimizing the light collection efficiency while minimizing the vignetting effect. The proposed optimization method provides valuable guidelines for designing next-generation display devices for VR headsets.
Virtual reality (VR) systems bring fantastic immersive experiences to users in multiple fields. However, the performance of VR displays is still troubled by several factors, including inadequate resolution, noticeable chromatic aberration, and low optical efficiency. Pancharatnam-Berry phase optical element (PBOE) exhibits several advantages, such as high efficiency, simple fabrication process, compact, and lightweight, which is an excellent candidate for VR systems. We have demonstrated that by using three kinds of PBOEs, the above-mentioned problems can be solved satisfactorily. The first PBOE is PB grating/deflector (PBD), which can deflect the left-handed and the right-handed circularly polarized beams to two opposite directions. Therefore, if we insert a PBD to the VR system and carefully design the deflection angle, it can optically separate each display pixel into two virtual pixels and superimpose them to obtain a higher pixel density. In this way, the pixel per inch (PPI) of the original display can be doubled. The second PBOE is PB lens (PBL). As one kind of diffractive optical lenses, it has an opposite chromatic dispersion to that of a refractive lens. When a PBL with an appropriate focal length is hybridized with a refractive Fresnel lens, the system’s chromatic aberration can be significantly reduced. The third PBOE is multi-domain PB lens. The effective focal length of each domain can be customized independently. This multi-domain PBL can function as a diffractive deflection film in the VR system. If such a diffractive deflection film is cooperated with a directional backlight, the etendue wasting can be reduced prominently, and more than doubled optical efficiency can be achieved in both Fresnel and “Pancake” VR systems. These ultrathin PBOEs will find promising applications in future VR systems
KEYWORDS: Light emitting diodes, LED displays, RGB color model, Reflectivity, Light sources and illumination, Televisions, Optical properties, Mobile devices, LED lighting, Display technology
Micro-light-emitting-diode (μLED) displays with low power consumption are highly desirable for the mobile devices powered by batteries. However, since the smaller LED chip size corresponds to lower optical efficiency, this advantage is compromised. In this paper, we develop a model to evaluate the power consumption of micro-LED displays based on ambient contrast ratio. Then, the optimal μLED chip sizes to achieve the lowest power consumption for smartphones, laptop computers, and TVs, are obtained. Furthermore, we propose to employ different RGB chip sizes in μLED displays. In comparison with the optimal results with uniform LED chip size, our new design offers an additional 12% average power saving for real image contents.
Micro-scale light emitting diode (micro-LED) with a chip size less than 100 μm has improved light extraction efficiency due to increased sidewall emission. However, it causes mismatched angular distributions between AlGaInP-based red micro-LED and InGaN-based blue/green counterparts because of the epitaxial material difference. As a result, color shift of RGB micro-LED displays may become visually noticeable. To address this issue, the angular distributions of RGB micro-LEDs are analyzed theoretically and experimentally. In addition, a device structure with top black matrix and taper angle in micro-LEDs is proposed, which greatly suppresses the color shift while keeping a reasonably high light extraction efficiency.
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