THE FRONT LINE: JUNE 23, 2005
SAY, ISN’T THAT ELVIS?
The Grating Light Valve emerges from hiding in Salt Lake City
Hidden in the seemingly endless stream of wanna-be HDTV display technologies, the grating light valve (GLV) hasn’t gotten much media attention these days. First introduced in a white paper at the Society for Information Display show in 1998, it has remained more a rumor than a working technology since then.
The GLV is a clever device that is constructed from super-thin, flexible metal bands mounted over a CMOS substrate. The bands flex in and out in response to control voltages from the substrate. Viewed from a side, they resemble a metal grate. (Viewed from the top, they resemble a tabletop finger harp!)
Each “pixel” in a GLV array consists of a number of aluminum-coated bands, each about 100µm long, 100nm thick and typically about 3µm wide, suspended over a thin air gap. They are arranged in vertical rows, which gives them a native pixel resolution in that plane only. Since the bands are continuous and can bend in extremely small areas, they have essentially unlimited horizontal resolution. Given the device size, that resolution spec number is realistically 4,000 to 8,000 pixels.
Figure 1. This diagram shows how a GLV projection system works. (Artwork from Sony)
The GLV was first developed at Stanford University, and a start-up company, Silicon Light Machines, took it to the next level. Their efforts were not unnoticed, and a few years back Sony signed an agreement with SLM to commercialize the GLV into a laser projector for large venues (can you say “digital cinema?”)
Sony had also been involved in the development of efficient red, green, and blue lasers through their investment in Portsmouth, NH-based COLOR, Inc. Why lasers? Because diffused red, green, and blue light derived with filters from short-arc lamps wouldn’t work with the GLV. A much more intense illumination source with an extremely small spot size would be required – hence, the use of lasers.
GLVs are as sophisticated mechanically as Texas Instruments’ Digital Micromirror Devices (DMDs). Both are microelectromechanical systems (MEMs) and both are 100% digital. But the GLV is capable of switching back and forth at much higher speeds than a DMD, according to Silicon Light Machines. SLM’s claims are that the latest GLV can easily handle a 100 Hz refresh rate, which is fast enough for any standard HD application and also active stereoscopic projection.
All well and good. So, what happened to the forthcoming Sony GLV large venue projector?
With the introduction of Sony’s 10,000-lumens SRX-R110 front LCoS projector with 4K native resolution last year, the GLV seems to have dropped off their radar completely. Given that Sony can now produce 4K (4096x2160 pixel) LCoS devices on their own and use conventional xenon arc lamps with them, perhaps their ardor for the “not invented here” GLV has cooled. Even the market demand for 4K imaging is still insignificant.
Figure 2. Sony’s SRX-R110 4K LCoS front projector.
But weep not for the GLV; it has found a new home in Utah. Evans and Sutherland have developed a new laser-powered projection system for use in domes and planetariums. It’s known as the DigiStar 3 and is basically the same product that Sony had planned to develop before their success with 4K LCoS sidetracked them.
Evans and Sutherland claim their GLV projector, for which they apparently have an exclusive license to use in domed theaters and simulators, can crank out images with 4000x4000 pixel resolution and 2,000 lumens of brightness per projector, using a 60 Hz refresh rate. By stacking a second projector, system resolution is claimed to be 8K x 8K.
Figure 3. Evens and Sutherland’s DigiStar 3 large venue projector
for domed theaters and simulators employs GLV technology.
(Photo from Evans and Southerland)
Hmmm … 2,000 lumens @ 4K resolution with the GLV, versus 10,000 lumens @ 4K resolution for the SRX-R110. Looks like those “safe”, diffuse RGB lasers E&S uses in the DigiStar 3 don’t produce nearly as much horsepower as Sony’s xenon lamp system. And 2,000 lumens of image brightness isn’t difficult at all to achieve with LCoS.
Don’t you get the feeling that another contender for the large venue and digital cinema HD display championship just got “kayoed?”