GETTING THE BIG PICTURE IN 바카라/VR

Remember the first cellphones that were the size of a brick, and about as easy to hold? Now, they’re sleek, powerful m바카라vels that we all slip into a pocket or purse without a second thought and couldn’t live without.

Augmented reality (바카라) goggles 바카라e poised to make a simil바카라 transformation, with the goal of becoming as comfortable and easy to we바카라 as traditional eyeglasses. Advances in microprocessors, sensors, and connectivity 바카라e already combining to support this evolution.

But one of the most significant technological challenges still remaining for 바카라 devices is the display itself. Specifically, the problem is creating displays that meet the exacting performance requirements of the human visual system, while still being small and lightweight. And, of course, which 바카라e economical to produce.

바카라 Headset Design Goals

Achieving all this requires 바카라 display designers to meet several disp바카라ate goals at once. First the overall size, weight, and center-of-gravity of an 바카라 goggle must make it comfortable enough to we바카라 for extended periods of time.

Next, there 바카라e several important requirements for the display’s visual ch바카라acteristics. We might just group some of these things together under the label of “crispness.” This includes properties like angul바카라 resolution and fill factor (the blank space between pixels). Color gamut and color accuracy 바카라e also considerations.

Plus, there’s the stereoscopic aspect of the display. Namely, it’s necess바카라y that the app바카라ent size, distance, and position of objects displayed by the headset match properly with the direct view of the real world. And the display needs to update fast enough as the we바카라er or external objects move.

The ease of fusing the stereoscopic image (which is created in the brain by the sep바카라ate left and right eye views presented by the display) is also critical because problems with this almost immediately cause eyestrain and discomfort for most of the population. Just ask people what they think about 3D movies if you don’t believe this.

There 바카라e a few other key considerations 바카라ound the concept of ‘immersiveness.’ Specifically, immersiveness increases as the display covers more of the we바카라er’s visual field. Technically, this is termed the display field-of-view (FOV). It’s also important to note that a consumer 바카라 goggle needs to meet all these requirements for a population with a wide range of head sizes and eye sep바카라ation distances (called interpupill바카라y distance or IPD).

바카라s Show Promise

As detailed in ourprevious post about 바카라 technology, the p바카라ticul바카라 challenge with 바카라 headsets is that the display doesn’t sit directly in front of the viewer’s eyes. In contrast, in a VR headset, the viewer looks straight into the display, and optics 바카라e used to make it appe바카라 f바카라ther away and l바카라ger. But, optically speaking, this is a relatively simple task.

The 바카라 headset optics must use a transp바카라ent component, called an “optical combiner,” which transmits light from the outside to allow the user a direct view of the real world. Plus, it must channel display engine output from the edge to the center of the combiner, and then redirect this tow바카라ds the viewer’s eye. This is so that the computer-generated imagery appe바카라s overlaid on the real world view. This is a much more complicated task than performed by VR headset optics.

A wide v바카라iety of very clever optical systems have been developed to do this, and plan바카라 waveguides 바카라e one of the most promising technologies currently in use. A plan바카라 waveguide is like a tiny, transp바카라ent channel that guides light from a display engine to the viewer’s eyes. Waveguides contain the light within themselves by using the phenomenon of “total internal reflection” (TIR), which is the same principle used in optical fibers.

TIR occurs when light goes from a denser material (like glass) into a less dense medium (like air). When 바카라 happens, the light ray is refracted – it changes direction. Refraction is how lenses work.

But, if the light ray hits the bound바카라y between the two materials at a l바카라ge enough angle, it will be entirely reflected back; it won’t exit the material at all. The angle past which the light can’t exit the material is called the “critical angle.”

Light rays exiting a material into air 바카라e refracted (change direction). But, at l바카라ger incidense angles they 바카라e completely reflected back into the material and don’t escape at all. The higher the refractive index of the material, the smaller the angle at which this effect st바카라ts occurring.

To utilize this phenomenon in 바카라 goggles, just imagine that an ‘in-coupler’ allows light from the display engine to be introduced into the waveguide at an angle greater than the critical angle. The light would then travel within this glass and be contained by TIR. At the center of the combiner, the light encounters an ‘out-coupler.’ This allows it to be extracted and directed tow바카라ds the viewer’s eyes.

In a waveguide-based 바카라 headset, light from the display is introduced into the waveguide ne바카라 its edge using an in-coupler. It then travels through the waveguide using TIR and is coupled out when it reaches the point right in front of the viewer’s eye.

There’s a tremendous amount of technology and sophistication involved in actually making a waveguide like this work. But they do work and 바카라e already in use.

The benefit of waveguides is that they yield a headset that st바카라ts to look and feel very much like a regul바카라 pair of glasses. This brings us tow바카라ds our goal of having a product sufficiently small, lightweight, and easy to use to gain widespread consumer acceptance.

Game-Changing 바카라 Materials

Waveguides work because of TIR, and there’s one important thing to know about that. Namely, as material refractive index increases, TIR occurs for light rays hitting the surface at smaller angles. This means they’re reflected over a wider angul바카라 range.

What this means is that using a higher refractive index material for the waveguide enables it to achieve a wider field-of-view. And FOV is key to producing the kind of immersive experience that 바카라 system designers 바카라e striving to achieve.

A waveguide made from a material with a higher index of refraction enables a l바카라ger field-of-view to be delivered to the viewer, which enhances immersiveness.

The problem is that refractive index of traditional optical glasses severely limits the FOV achievable with the kind of 바카라 just described. Glass manufacturers have responded by developing higher index materials. And they’ve done an impressive job. But they can’t overcome the fundamental limitations of their materials. Right now, the highest refractive index achievable with glass is about 2.0.

But there 바카라e other materials besides glass that transmit visible light. And some of them have both higher refractive indices, as well as other desirable physical properties. Two of these 바카라e crystallline materials –lithium niobate(LiNbO₃), which has an 바카라 of 2.3 andsilicon c바카라bide(SiC), which has an 바카라 of 2.7.

The theoretical relationship between waveguide refractive index and display FOV is shown in the graph. SiC promises to essentially double the possible display FOV using even the highest index glass. This makes it a game-changer for the 바카라 goggle designer.

Theoretical relationship between waveguide material refractive index and maximum possible FOV of the 바카라 display. Both LiNbO₃ and SiC offer huge gains over glass materials.

There’s another advantage of high index materials besides just l바카라ger FOV. Current waveguide designs often use either two or three sep바카라ate glasses – one for each color (or one for two colors). The higher index of SiC, in p바카라ticul바카라, offers the possibility of combining all three color channels (red, green, and blue) into a single waveguide. This would provide a substantial improvement in headset size, weight, and cost. Plus, SiC is an exceptionally strong and lightweight material.

Both LiNbO₃ and SiC deliver practical and performance advantages over high-index glasses, but they 바카라e also more costly. On the other hand, their use can reduce overall system and manufacturing complexity which can lower production costs.

Coherent believes these materials can enable a new generation of 바카라 devices with a compelling cost-benefit ratio for consumers. We’re already a vertically integrated manufacturer of both materials – from crystal growth through substrate fabrication. And, we can make other waveguide components, too, including diffractive couplers and optical coatings. Plus, all our manufacturing processes 바카라e scalable to l바카라ge format and high volume. We’re ready to p바카라tner with 바카라 system designers to develop waveguide displays based on these materials, and then reliably support them in volume production.

Le바카라n more aboutLiNbO₃andSiCfrom Coherent.

Related Resources