Another Dimension For Virtual Reality

When you put on a virtual reality (VR) headset, you are connecting visually to another place—real or imagined. Most people connect VR with gaming, but increasingly business, industry and government users are finding new applications for the evolving technology. These applications, and many more to come, will help drive the adoption of VR and the devices used to access virtual environments.

Today, the ubiquitous smartphone is typically the engine of a VR headset, encouraging mass adoption. As VR technologies advance, however, several display requirements must be met to achieve a desirable state of presence and improve the user experience: low image “persistence” and high screen-refresh rate; a high frame rate to avoid latency effects; high screen resolution; and a large field of view (FOV). All of these take advantage of the tricks the mind uses to perceive depth of field and focus, and to create 3D vision.

Persistence
Image persistence and screen refresh rate are closely linked—and in both cases, faster is better when it comes to replicating reality. Persistence is the time it takes for a new image to replace the current one. The lower the persistence, the sharper the image appears. If persistence is high or “full,” the image will seem blurry.

Screen refresh rate is the number of times the image on a display screen can be refreshed per second. The faster the refresh, the lower persistence will be. Every millisecond is critical.

OLED displays respond more than 1000 times faster than LCD displays, eliminating motion blur and jitter and meeting requirements for image quality, power efficiency and smaller form factors. They are therefore the industry standard for smartphone VR.

Latency
A truly realistic VR experience requires low latency, which is the time from when you move your head to when you see the correctly rendered view. In the real world, your head’s actual movement and the image of motion you perceive are in sync between the eye and the inner ear. By contrast, in VR there is a delay between moving your head and the movement of the image in the VR headset. If the delay is too long, the VR immersion will feel unnatural. To achieve a smooth and natural VR experience, the latency must be less than 20 milliseconds.

Field of View
FOV is the extent of the observable environment at a given moment. It is one of the more important aspects of VR: the wider the FOV, the more likely the user will feel present in the experience. FOV comprises both monocular and binocular vision that work in tandem to determine depth of focus and 3D vision.

Full human eye FOV is 170° horizontal x 130° vertical. But in VR, the limiting factor is the lenses in the headset. To get a better FOV, you must either move closer to the lenses or increase their size.

Fig. 1: Field of view depends on both monocular and binocular vision. Source: vr-lens-lab.com

Resolution
Screen resolution, as measured in pixels per inch (ppi), is another important aspect of VR systems. Because smartphone displays are placed fairly close to the eye in VR headsets and are magnified by lenses, individual pixels are sometimes seen. Higher-density OLED screens eliminate this problem.

Fig. 2: In smartphone-based VR systems, screen resolution must be ≥800 ppi to eliminate pixilation.

Vergence
Smartphone-based VR systems must accommodate our eyes’ vergence, which is the simultaneous turning of the pupils toward or away from one another as we focus on something. The closer an object is, the more our eyes will converge to keep it in the center of the FOV. When something is farther away, our eyes will diverge to keep it centered.

Vergence gives the brain the geometric data to triangulate and calculate the distance from us to the object: two angles (one from each eye) and our position. Most VR displays show a separate image to each eye to take advantage of these depth cues. If the images are properly synced with each other and with the motion of the head, this generates a tolerably convincing illusion of depth.

Fig. 3: Human eyes use both binocular and monocular cues to focus, create depth perception and perceive distance.

OLED Displays

Applied Materials’ technology is used to fabricate OLED displays. Our tools build high-performance thin-film transistors (TFTs) that offer high electron mobility, highly reliable backplane performance and OLED performance stability. In the future, with the growing requirements for higher screen resolution and smaller pixels, our materials engineering solutions will become even more important—as discussed in a recent blog by my colleague Tony Chao, who also considers the role Light Field Technology and digital light processing could potentially play in creating convincing VR.

Even if you’re not a VR user, the advances in display technology that will make VR a reality will affect you: as a smartphone user, you’ll benefit from better picture quality, OLED displays for stunning color and small form factors.