02 Nov 2016
Technology to benefit manufacturers of economical 2D/3D convertible mini-screens for mobile applications.
Convertible video displays that offer both 2D and 3D imaging without the need of any eyewear will mean greater convenience for users who would otherwise have to always carry another accessory. Such autostereoscopic displays have already reached the TV market, but existing technology shows its limitations when close viewing distances are needed. Viewers typically must view these displays from at least 1 meter – eliminating any practical applicability to the smaller screens of mobile devices.
Now, researchers at Seoul National University (SNU), South Korea, have developed a new method of making such convertible displays that not only achieve near-viewing capabilities, but are also simplified with a “shrunken technology architecture”. In a newly-published paper in the journal Optics Express, the researchers describe their novel design.
For such eyewear-free displays, the only action takes place behind the screen where pixels and optics are layered together to produce the stereoscopic effect. The two primary ways of producing these optically illusive effects are by using either an array of micro-lenses, called lenticular lenses, or an array of micro-filters, called parallax barriers, in front of the image to make its appearance depend on the angle at which it is being seen.
The simplest example of this effect is found on a movie poster (or similar) whose image appears to change as a viewer passes by. Two (or more) images can be interlaced and printed behind a plastic layer with grooves to match the interlaced pattern. The grooves act as distinct, interlaced arrays of lenses or filters, revealing one image as the viewer approaches such a poster and another as the viewer passes, then seeing the same poster but from a different angle.
In the case of 2D/3D convertible screens, these layers are active, meaning they can be electronically switched on or off. The gap distance between the image layer and the barrier layer is a key determinant of the viewing distance. Closer stacking of these layers together allows for a closer viewing distance.
In the paper, Sin-Doo Lee, a professor of electrical engineering at SNU, and his colleagues describe a monolithic structure that effectively combines the active parallax barrier, a polarizing sheet and an image layer into a single panel. Instead of two separate image and barrier panels, they use a polarizing interlayer with the image layer in direct contact with one side of the interlayer, while the active parallax barrier of a liquid crystal layer is formed on the other side as an array of periodically patterned indium-tin-oxide electrodes.
The use of this interlayer allows the minimum separation of the image and barrier layers, thus providing the short viewing distance required for the smaller screens of mobile devices.
"The polarizing interlayer approach here will allow high resolution together with design flexibility of the displays, and will be applicable for fabricating other types of displays such as viewing-angle switchable devices,” Lee commented. “Our technology will definitely benefit display companies in manufacturing low cost and light weight 2D/3D convertible displays for mobile applications. Under mobile environments, the weight is one of the important factors.”
This concept not only applies to LC-based 2D/3D displays, but also to OLED-based 2D/3D displays, offering application to a broad range of present and future device designs.
The Optics Express paper concludes: “We have demonstrated a new concept of 2D/3D convertible autostereoscopic LCD based on the LPI for near-viewing applications. The viewing distance of our device was decreased with decreasing the pixel-barrier separation by the introduction of the LPI between the image cell and the switching cell. This approach provides more flexible design in the viewing distance in 3D displays, particularly for mobile applications. The concept of the LPI and similar interlayers will be useful for more sophisticated autostereoscopic display systems.”