Grating Light Valve

The GLV is a specific Microsystems application working as a dynamic tunable grating to change precisely the quantity of diffracted or reflected laser light. The GLV is made of many tapes on the surface of a silicon plate (see the picture below). These tapes can move upwards or downwards on very small distances by adjusting the electrostatic forces between the tapes and substrate. Due to the positioning of the tapes, each element can reflect and diffract light, so that a well positioned matrix can make the level of reflected light on the plate vary. The light control can be analogical (variable control of the light level) or digital (on/off switching). As the GLV devices use the diffraction principle to switch, dim and modulate light, they are very precise, are easy to produce and can possibly manipulate relatively high power beams. However, as the projected light is obtained by diffraction instead by a direct reflection, there are obviously some losses towards incident power.

Each GLV component is made up of 6 parallel tapes are suspended at both ends and made on silicon nitride covered with a reflective metal layer. This superior layer also acts as an electrode to create an attractor electric field strength with the inferior electrode shared by every tape. It takes 20ns, which is much more faster than with the current pivoting mirrors. The current devices are said to have a diffraction efficiency near to the 81% theoretical maximum, a 95% filling factor and a 91% superior electrode reflective ratio, with an overall efficiency of devices of about 70%, corresponding to insertion losses to the order of 1.5dB.

Large size projection displays were the first applications affected by GLV technologies. We showed that a projection display, in order to show a high definition TV image of 1920 x 1080 pixels, could be made by the scanning of a 1080 pixel linear GLV matrix. But because of the commercial competition between DLP and LCD devices and the price war that followed, the additional costs of the scanning system and the speckle effect due to the laser beam led to a postponement of GLV screen marketing. But the GLV digital accordability allowed to use with success many reconfigurable optical devices such as tunable filters, dynamic gain equalizing filters and GLV printers.