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Bigger screens, smaller bills

You could get plasma quality for a lot less

The days of large, expensive LCD (liquid crystal display) screens for public displays could be numbered thanks to a light diffraction technology developed by a Californian company and licensed to Sony.

Conventional LCDs use a mesh of active transistors — three for each pixel — to switch on or off red, green or blue light. The bigger the screen, the more likely there is to be a dud transistor or 'dead pixel'. A screen can't be used with more than a few percent of dead pixels, so if it isn't made near-perfect, it has to be scrapped, which keeps costs high.

But large-scale high-definition displays can now be made using laser light diffracted through a grating light valve array, or GLV.

The GLV comprises tiny strips of silicon nitride, coated on the upper surface with reflective aluminium and mounted on a substrate. Laser light beamed onto the strips is normally reflected straight back. But when a current is passed through the strips they bend, diffracting the light off at an angle. The amount of diffraction can be varied by the amount of current passing through the strips.

GLVs can be assembled in arrays, for example 1,088 of them to create a 1,920x1,088 screen scanned horizontally at 60 frames a second. With such a module operating all 1,088 channels at 8 bits, at a line rate of 250Hz, the array can process visual images at over 2Gbps (gigabits per second).

The result is high-contrast, high-colour images that can be scaled up without loss of definition.

The GLV was born of research conducted at Stanford University in California and developed by Silicon Light Machines, a 1994 Silicon Valley start-up recently acquired by semiconductor giant Cypress Technologies.

It is also finding application in laser image setters which expose aluminium plates used in magazine printing, as well as in optical communications switching to equalise the amplitude of varying wavelengths of light from fibreoptic networks.

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