Liquid crystal displays have been around for more than 30 years. And yet, the ability of scientists and engineers to innovate and develop new display technologies based on the LCD continues unabated. The latest examples are two new and intriguing prototype displays demonstrated by Toshiba at the recent SID Conference.

Art Berman
Insight Media Consultant

The first was an autostereoscopic display in which it was possible to convert a portion of the image into 3D. Apparently based on an "integral imaging method," the 3D image was created by placing a special LCD panel in front of a conventional LCD. The special LCD panel acted as a GRadient INdex or GRIN lens using an electric field to change the orientations of the liquid crystal molecules and, thus, the distribution of the indices of refraction of the liquid crystal within the layer. This essentially replicates the optical effect of a lenticular lens.

When the voltage of the GRIN lens panel was off, the distribution of the refractive indices allows light to pass unaltered through the GRIN lens panel thus revealing the 2D image produced by the underlying LCD. When the voltage was on, the liquid crystal molecules realigned in a radial pattern, parallel to the electrodes, whichare arranged in vertical stripes. In this state, the light rays are diverted as if a physical lenticular array was in place, thus creating an autostereoscopic 3D image.

There was, however, a problem. The thickness of the liquid crystal layer in the GRIN lens panel is about 150 microns, which is very thick andhas a switching speed that is much slower than that of the LCD. Since this is unacceptable, Toshiba decide to not switch the GRIN lens and to just leave it switched on.

Switching between the 3D and 2D modes was then accomplished by adding a third LCD panel to the optical stack, between the LCD and the GRIN lens panel. It had a conventional LCD layer thickness and switched at least as fast as the LCD. The third LCD panel was used to switch the polarization of light by 90 degrees. The optics were such that the third panel enabled the system to switch between 2D and 3D images at an acceptably high speed.

The good news is that the addition of the third panel reduces device transmission by only a modest 10%. The bad news is that it must also add to the thickness of the display…..and to the cost.

Some specifications reported for the prototype display are that the 12-inch screen produces nine viewpoints. The resolution in the 2D mode is 1400 x 1050 while in the 3D mode the resolution is reduced to 466 x 350.

The second technology demonstrated by Toshiba was an LCD in which the user could zoom in and out on an image with an uncommonly intuitive means: by physically bending the display.

A video demonstrating the functionality of the bendable LCD technology can be found here.

To achieve a flexible device, the glass substrates used to fabricate the LCD had a thickness of 0.1 mm. The backlight consisted of a light guide that was 0.4 mm thick. LEDs were used as edge lights. In addition, bend sensors were applied at the edges of the display. The resistance of each sensor changes when bent, allowing software to monitor this and adjust the image in accordance with the change in the resistance of the bend sensors.

The prototype bendable display had a screen size of 8.4-inches and a resolution of 800 x 600. Apparently, the display could be bent into a curve that has a radius of about 50 mm.

The viability of the new technologies would seem uncertain. In any case, commercialization plans are currently unknown. What is more certain and of more interest is that Toshiba and those elsewhere in the industry engaged in LCD R&D seem quite capable of teaching this old dog a seemingly endless string of new tricks. -Arthur Berman