The image is crystal clear, and you feel as if you are really walking through the incredible worlds that your VR glasses are conjuring up around you. Until now, however, these glasses have usually been rather heavy and bulky. That is mainly due to the display, which is the key component in every pair of VR glasses. Commercially available VR glasses generally use displays designed for the smartphone market, which are cheaply available and employ simple optics to provide a wide field of view. Their disadvantage is a pixelated image because of their limited resolution and insufficient pixel density. Modulating LCD and LCOS microdisplays are also used. These are not self-illuminating, however, which means an external light source is necessary. In order to produce VR glasses that are light and ergonomic, now the focus lies on OLED microdisplays. These are based on organic light-emitting diodes, which are integrated onto a silicon chip and are self-illuminating. As a result, they are energy-efficient and yield very high contrast ratios >10 000:1. They can be constructed in a simpler fashion, with fewer optical components. Another advantage is the fast switching speed of OLEDs, which is around a few microseconds as against milliseconds in the case of LCDs. This enables high frame rates as well as to employ special modulation processes to improve the perceived image.
As part of the EU’s LOMID project (large cost-effective OLED microdisplays and their applications) researchers at Fraunhofer FEP have been collaborating with partners from industry to develop innovative OLED microdisplays that significantly outperform others currently on the market. The goal is to develop a new generation of OLED displays that provide outstanding picture quality and make it possible to produce VR glasses in a compact format. This could be achieved by a specially designed OLED microdisplay.
A speciality of the microdisplay is their resolution, which achieves extended full HD (resolution of 1920 × 1200 pixels (WUXGA)). The diagonal screen size is about one inch, and the frame rate is around 120 Hertz, so 120 images are displayed every second, which makes movements in the virtual world seem very fluid indeed.
The microdisplay consists of a silicon chip to control the pixels, and an OLED. This OLED consists of several organic layers, which are monolithically integrated on silicon wafers. The microdisplay’s resolution and frame rate are set by the chip with the help of its integrated circuit. The really innovative feature is the type of circuit that is used and which keeps power consumption to a minimum at the same time. This is possible thanks to a cleverly designed system concept, modern design methodology and a long lasting experience in designing OLED microdisplays. A first prototype is existing and further prototypes are due to follow by the middle of 2018.
The use of OLED microdisplays is by no means limited only to VR glasses even though this may well be the largest market in the medium-term. They are also suitable for other products such as augmented reality (AR) glasses or view finders in cameras. The underlying technology of CMOS-integrated light emitters (and any detectors) also has potential uses in other market segments such as optical metrology and identification, or optogenetics. Especially with regard to microdisplays in consumer-facing augmented reality glasses, the researchers still see some as yet unresolved challenges that they wish to tackle in the future. These challenges include: very high levels of luminance and efficiency (which will necessitate removing the color filters used until now, and replacing these with directly structured emitters); a high yield for a large (chip) area; curved surfaces for more compact optics; circular light panels; irregular pixel matrices at even higher pixel density; integrated eye tracking; and transparent substrates.
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