Fraunhofer FEP Scientists Showcase Small OLED-display-based VR Headset Prototype

During during the awe Europe 2018, Scientists from Fraunhofer FEP presented a LOMID headset prototype. The new prototype uses four OLED display panels in a 3D printed device. Fraunhofer scientists designed the device to begin to overcome motion sickness, a common issue among VR users. According to Fraunhofer, the motion sickness results from a combination of flickering images, low frame rates, and an inappropriate field of view.

Fraunhofer FEP developed an OLED-display-based VR headset prototype.

OLED displays can inherently overcome issues of low frame rates and flickering images, and the positioning of the displays is also intended to show an appropriate field of view. The Fraunhofer scientists intend to use their latest research results from the LOMID (Large cost-effective OLED microdisplays and their applications) project to solve these issues.

The scientists also want to make such devices less bulky. The researchers says that the OLED microdisplays, combined with advanced free-form optics offer an ergonomic and lightweight solution for the VR glasses.

OLED Microdisplays Developed for Project

As part of the project, the Fraunhofer FEP scientists have developed new one inch OLED microdisplays with a resolution of 1920×1200 pixels (WUXGA, 2300ppi) and framerates of 120Hz, about four times the frame rate of a conventional movie.

Project partner LIMBAK designed two display chips per eye that are seamlessly combined, making a total of four in the headset. The headset also features two WUXGA microdisplays per eye, providing a total resolution of 4800×1920 pixels, which is near 5k. The researchers point out that this design supports very high effective display resolutions and a wide field of view of greater than 100°.

Additionally, the optics scientists of LIMBAK were able to reduce the display-to-eye distance required in the headset. They lowered it to just 37mm (compared to 60-75mm in most conventional headsets). This compact optical design reduces the headset size to about a quarter of the volume and half the weight of a conventional headset, the researchers assert. At the same time, the device maintains the field of view of a conventional headset.

Fraunhofer FEP developed an OLED-display-based VR headset prototype-picture of the insides of the prototype with four optics and four OLED microdisplays.

Design Strategy to Reduce Motion Sickness

Judith Baumgarten, a scientist in the IC and System Design department at Fraunhofer FEP, described the design strategy taken to achieve high framerates and thus reduce motion sickness effects and flickering for VR applications. “To offer such high framerates of 120Hz and thus high data rates, we have extended the parallel interface of the OLED microdisplays. The display mode can be configured flexible from hold-type to impulse-type.”

She pointed out that the impulse-type hold allows the elimination of motion artifacts and flicker with a unique rolling emission mode, and the chip uses special look-up-tables for gamma correction. Therefore, each channel including red, green, blue, and white can be calibrated individually.

“We achieved a superior image quality with a very high contrast ratio of >100’000:1 at extraordinary low power consumption. We are very pleased about these positive results of our displays in combination with the ultra-compact optic design of LIMBAK, which enable really compact VR devices,” Baumgarten said.

OLED-on-Silicon Microdisplays Allow Smaller Form Factor

The researchers noted that the tiling of multiple OLED-on-silicon microdisplays inside the system helped to shrink its form factor and reduce its weight while increasing resolution to a level not easily achieved using conventional TFT-based AMOLED displays in VR headsets due to their typical pixel density limits. The scientists also contend that this approach supports keeping costs in a reasonable range.

Partner X-FAB reportedly developed economical processes at the CMOS silicon foundry that pay specially account for the interface between the top metal electrode of the CMOS backplane and the following OLED layers.
Additionally, partner Microoled S.A.S. fabricated each the entire OLED microdisplays using those CMOS backplane wafers.

While the resulting performance of the device was impressive, according to attendees at the event, the device still showed significant distortion. The researchers intend to reduce this distortion with proper image calculations.F

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