Grating Light Valve (GLV) Technology
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INTRODUCTION
The objective of this paper is to detail the Grating Light Valve technology and demonstrate its flexibility in attaining high performance in a variety of optical systems and applications, concentrating particularly on its application toward projection display systems. The GLV technology represents a unique approach to light modulation and offers remarkable performance in terms of contrast, efficiency, switching speed, and cost. The electro-mechanical response of the
GLV device can be tuned through various design and operational modes to deliver desired performance for a given application. The design and fabrication of a linear array module of 1,088 GLV pixels is described. This module enables a
Scanned Linear GLV Architecture for HDTV projection products. The flexibility of the GLV technology and the Scanned Linear GLV Architecture can support line sequential and frame sequential color, as well as 3-valve color systems.
Fundamental concepts
A Grating Light Valve (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.
Building the GLV device
The following describes the materials, dimensions and packaging of a GLV device capable of implementing a high-resolution display. The entire GLV device is designed to be built using mainstream IC fabrication technology (e.g. photolithographic masking, deposition, etching, metalization, etc.) to create the
micro electromechanical systems (MEMS) that make up the GLV device. The GLV ribbons are built using silicon nitride, then coated with a very thin layer of aluminum (see figure 2). By making the aluminum layer very thin, one avoids some of the surface roughness that otherwise scatters the light reducing the contrast ratio.
Controlling the GLV device
To control a GLV-based device, one simply directs the up and down ribbon movement of this two-state technology. As mentioned previously, the ribbons will naturally assume the up state. To pull them down, one must apply a voltage difference (e.g. the switch-down voltage, V2) between the movable ribbons and
bottom electrodes. Interestingly, the ribbons maintain their down state even as the voltage differential is reduced. Thus, one can pull the ribbon down with a switch-down voltage (V2), and maintain that state with bias voltage, Vb, such that V1<Vb<V2 volts (see figure 5), where V1 is the switch-up voltage at which the
ribbon returns to its up state.
THE LINEAR GLV ARRAY
Several of the unique features of the GLV device described above, particularly its fast switching time, high power handling capability, and analog addressability, enable a novel display architecture that offers significant advantages compared to other projection display architectures. A linear GLV array can be used to modulate a single column of image data, while a mechanical scan mirror is used to sweep that column across the field of view. Updating the video data appropriately during
the scan can effectively render a full two-dimensional image. The Scanned Linear GLV Architecture was introduced previously . A more complete description of the linear GLV array module and its associated electronic drivers is given
here.
Conclution
The Grating Light Valve technology offers unique performance among spatial light modulator technologies. Particularly compelling are its extremely fast switching speed, its ability to be addressed in an analog fashion, and its ability to withstand
very high optical power densities. These attributes can be exploited to achieve a novel projection display architecture, which in turn offers a number of system cost and performance advantages over conventional projection display systems that are
based on either 2-D spatial light modulators or scanned point systems.