Novel light-valve technology promises smaller, higher-resolution displays
In the area of projection display and instrumentation systems, many investigations are underway to reduce the power and weight of standard displays. One company, Texas Instruments (TI; Dallas, TX), has developed a microelectromechanical device known as a Digital Micromirror Device (DMD). When combined with image processing, memory, a light source, and optics, this device can be used to build imaging systems that are capable of projecting large, bright, seamless, color images (see Fig. 1).
Another company, start-up Silicon Light Machines (SLM; Sunnyvale, CA), has designed a different type of microelectromechanical device that uses reflective ribbons instead of micromirrors to develop an imaging device. Claimed to be 1000 times faster than TI`s micromirror light valve, the SLM grating light valve (GLV) is fabricated by forming movable ribbon structures on the surface of a silicon wafer using traditional semiconductor manufacturing techniques (see Fig. 2). In response to electrical signals, these structures can be turned on and off, thereby controlling the reflective properties of the chip`s surface.
"If an array of GLV elements is built and subdivided into separately controllable picture elements," says David Bloom, SLM chairman and chief executive officer, "then a white light source can be selectively diffracted to produce an image of monochrome bright and dark pixels."
By making the ribbons small enough, pixels can be built with multiple ribbons that produce brighter images. If the up and down ribbon switching state can be made fast enough, then modulation of the diffracted light can produce gray-scale images. Because GLV switching occurs in 20 ns, about 1000 times faster than TI`s DMD, image buffers are not needed to match the speeds of electronic devices and the GLV elements.
Similar to the TI device, the GLV elements require optics and light sources to display images. One way of producing color images is to use different ribbon pitches to create an red-green-blue triad. In such systems, white light would be introduced at an off-axis angle to the GLV elements. The red area, having the widest pitch, would then refract light normal to the GLV plane, whereas the green and blue areas would refract light at other angles.
