Grating Light Valve Display Technology

The Cathode Ray Tube TV set has ruled the consumer electronics world for decades. Now a days every one wants big screens for their entertainment rooms. But bigger a CRT screen, the glass tube will be deeper and the set becomes impossibly heavy and unwieldy when the diagonal measurement of the screen goes beyond about 36 inches. Thus the CRT is destined for a slow but sure decline giving way to many new technologies.

All of us must have noted the red colour of the hero's suit in the movie 'spiderman', the blues of the sky and water scenes were captivating. The dark horse technology behind this is GRATING LIGHT VALVE TECHNOLOGY (GLV).

The original GLV device concepts were developed at Stanford University. Later Silicon Light Machines was found in 1994 to develop and commercialize a range of products based on this technology.

The GLV device is a type of optical micro electromechanical system or MEMS essentially a movable, light reflecting surface created directly on a silicon wafer, utilizing standard semiconductor processes and equipment.

FUNDAMENTAL CONCEPT

A Grating Light Value (GLV) device consists of parallel rows of reflective ribbons. Alternate rows of ribbons can be pulled down approximately one-quarter wavelength to create diffraction effects on incident light (see figure 1). When all the ribbons are in the same plane, incident light is reflected from their surfaces. By blocking light that returns along the same path as the incident light, this state of the ribbons produces a dark spot in a viewing system. When the (alternate) movable ribbons are pulled down, however, diffraction produces light at an angle that is different from that of the incident light. Unblocked, this light produces a bright spot in a viewing system.

The Grating Light Valve uses reflection and diffraction to create dark
and bright image areas.

If an array of such GLV elements is built, and subdivided into separately controllable picture elements, or pixels, 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 producing greater image brightness. If the up and down ribbon switching state can be made fast enough, then modulation of the diffraction can produce many gradations of gray and\or colors.

There are several means for displaying color images using GLV devices. These include color filters with multiples light valves, field sequential color, and sub-pixel color using "turned" diffraction gratings.