Grating Light Valve GLV

Silicon Light MachinesTM and Grating Light ValveTM are trademarks of Silicon Light Machines. Silicon Light Machines (SLMTM) has developed silicon chip based display architecture that can be used for many imaging applications including high-definition televisions, movie projection and high-performance desktop display systems. SLM™ was formed to commercialise a broad range of products based on patented Grating Light Valve (GLVTM) technology. GLVTM, an optical MEMS device built onto silicon wafers, defines itself as a tiny silicon machine, and is capable of modulating the light. After initially developing GLVTM-based technology it was licensed to Sony for high-end display applications. Cypress Semiconductor acquired SLMTM in 2000.

SLM™ also focuses on components for optical communications. For instance, GLVTM devices have been used as a solution for switching, attenuating and modulating laser light. Additionally, the product includes computer-to-plate (CTP) printing equipment. When used in CTP products, this device diffracts high power laser beams to provide a high-speed, ultra-precise method of transferring digital images directly onto a printing plate. With an extremely fast switching speed and accurate diffraction control, the GLVTM device generates a writing beam on the surface of the plate enabling CTP technology to appear as products that can offer faster plate making performance and incredible image quality.

Like DMDTM, GLVTM is also considered to be a digital technology. Here it is a reflective cum refractive technology in which ribbon like mirrors are physically moved to alter the path of light on the chip's surface. The difference with respect to DMD™ is that in GLV™ the pixels reflect light only in their OFF state. With regards to construction, a pixel in a GLVTM array consists of a number of aluminium-coated ribbons. The aluminium coating acts as the mirror. The dimension of the ribbon-structured mirror is about 100 ^m long, 100nm thick and about 3 ^m wide as shown in Fig. 2.12.

Structurally, GLVTM consists of pairs of fixed and movable ribbons located approximately a quarter wavelength above a silicon dioxide layer. The ribbons are suspended over a thin air gap. Each ribbon is pulled down a controlled distance into the air gap by means of an electrostatic voltage, called the driving voltage. The ribbons representing a pixel reflect light away from the projector's optical path. When an appropriate driving voltage is applied to alternate ribbons in a pixel, the corresponding mirror-ribbons are pulled down, forming a square-well diffraction grating. Each well is comparable with the wavelength of incident light. Light waves reflecting off adjacent up and down ribbons are now out of phase with each other. This interaction (formation of grating) causes the waves to build up in such a manner that each frequency of light will radiate at a different angle of radiation. By deliberately varying the width, separation and the amount of depth (well) of the ribbons in each pixel, in accordance with the modulating signal, the angle at which certain frequencies of the light are to be radiated can be controlled. This is turn implies that a single colour of light can be directed into the optical path. The switching between two states of a GLVtm ribbon takes about 20 nanoseconds. Each pixel in the linear GLVTM array is capable of reproducing precise grayscale values (Fig. 2.13) at the rate of millions of times per second, which is thousand times faster than any other light modulator technology.

Kodak Laser Projector Technology
(a)
Grating Light Valve

Fig. 2.12. A GLV Valve consists of pairs of fixed and movable ribbons; (b) GLV uses reflection and diffraction to create dark and bright image areas (Courtesy: Silicon Light Machines, Author: Bloom; Apte, 1994)

Fig. 2.12. A GLV Valve consists of pairs of fixed and movable ribbons; (b) GLV uses reflection and diffraction to create dark and bright image areas (Courtesy: Silicon Light Machines, Author: Bloom; Apte, 1994)

It has been reported that the response time of SLM™ is faster than a DMD™'s mirror switches state. In an GLV™ projector, each column of the picture is displayed sequentially, from left to right across the screen. This is done so quickly, that the device has time to display the same image three or four times during a conventional video frame. So visual resolution can be increased. The scanned GLVTM architecture, which can cost-effectively create very high-resolution images, has been successfully demonstrated in a front-projection display system (http://www.siliconlight.com/htmlpgs/masterframeset/pressreleasepgs/pressrelease 3.html).

Fig. 2.13. Schematic of Grating Light Valve technology (Courtesy: Meko Ltd.)

Fig. 2.13. Schematic of Grating Light Valve technology (Courtesy: Meko Ltd.)

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