Prototype full-color, three-dimensional (3-D) imaging using liquid-crystal-display (LCD) cells and grating cells has been developed by researcher Susumu Takahashi of Toppan Printing (Tsukuba, Japan). The operating principle of Takahashi’s display is somewhat similar to that used by MicroDisplay (Berkeley, CA) in its two-dimensional color LCD display (see Laser Focus World, Feb. 1996, p. 25).
The MicroDisplay method first diffracts the white light with grating elements into colors that are shuttered by the LCDs to form a two-dimensional color image. In the Toppan system, however, parallax images are used to generate a 3-D effect (see photos on p. 40). White light is first passed through color filters to be modulated by LCD cells and is then diffracted through curved grating cells behind each LCD element. The modulated rays are directed by the gratings into the left and right eyes.
The curvature of the grating lines governs image direction with red-green-blue color sensitivity depending on line separation (pitch). Each image pixel will have nine parallax images, a 3 × 3 array giving vertical as well as horizontal parallax, for each of the three primary colors. This results in a 27-grating "cell" for each image pixel.
Takahashi says that the simplicity of the grating cells offers the prospect of brighter and clearer 3-D images than current holograms. The grating array is made using electron-beam lithography and can be replicated onto plastic plates. Thus, production of the grating array could be done together with the LCD panel for easy fabrication. He adds, "Because the input data consist only of parallax images, the volume of data is very small compared with holographic video systems. Therefore, the system is easily realized at low cost and energy by using current technology."
The prototype, demonstrated at Photonics West in January, uses a thin-film transistor LCD panel (640 × 480 pixel) and driver from a Sharp video projector. The grating array panel is 40 × 40 mm. Takahashi says that larger displays are just a matter of "money and time."
Rick DeMeis | Associate Editor, Technology
Rick DeMeis was Associate Editor, Technology for Laser Focus World from March 1995 through March 1997.