CrystalEyes may turn out to be one of the most important products of the last few decades. It’s self-serving to say so because I am the primary inventor of CrystalEyes and shuttering eyewear that may be the basis for 3D TV image selection. The basic concept of shuttering eyewear for viewing stereoscopic images isn’t mine. You can find mentions of it in the literature before my work began. Missing from the early work were the elegant electro-optical shutters that we now have and a good communications link between the display and the eyewear. When CrystalEyes was designed in the mid-1980s infrared links were advanced and a good way to communicate between the video source and the eyewear. Today you might also consider using Bluetooth or some other form of radio.
As I studied the requirements for viewing stereoscopic images on a CRT monitor (they are, quite incredibly, all but gone now) I realized that there were two ways that selection could be done. One would be with an onscreen modulator that could produce alternate characteristics of polarized light at video field rate, which could then be analyzed by polarizing eyewear; and the other is selection by means of shuttering eyewear.
I have to back up and say that one key ingredient is to have a high enough field rate so that the field-sequential image (left-right-left-right…) doesn’t flicker. I was the first person to make that happen in 1980, working with an engineer named Jim Stewart who goosed a monochrome video camera and a Conrac monitor to run at 120 Hz.
I founded StereoGraphics Corporation in 1980 for the specific purpose of developing stereoscopic technology and offering products to industry. All of these products were to be based on selection devices using CRT monitors, which was the dominant form of electronic display. In my earliest research I had hoped that I could find the solution for stereoscopic movies, and based on my research I wrote the book, Foundations of the Stereoscopic Cinema (you can download it free from my site). It took more than three decades but I eventually did it (I had a lot of help). The DLP stereoscopic cinema is a direct outgrowth of the work I did based on a high field rate and both modulator and shuttering eyewear selection. Same thing is true of the new generations of 3D TVs that will use shuttering eyewear and versions of my side-by-side digital multiplexing.
The initial StereoGraphics products used tethered or wired eyewear for viewing a CRT monitor. We needed to modify the monitors to run at a high field rate. That was the work of Lhary Meyer (yes – with an “h”), who was the first employee of StereoGraphics Corporation. Lhary was a self-taught electronics designer who had worked at ABC and ILM, and Lhary was my inventing partner for many years until he died of leukemia. We wound up making motherboards that were introduced into monitors to goose them into running at 120 fields per second. We took the sync pulse from the video signal and used that to tell our tethered eyewear when to shutter. We used lead-lanthanum-zirconate-titanate (PLZT) electro-optical shutters provided by Motorola and mounted them in headband visors. These visors are made for craftsmen who need to see magnified images of things like watches. (This morning I visited my comedian-dermatologist, the amazing Dr. Rish, who, looking like The Mastermind of Mars, was wearing one of those visors.) We took the magnifying lenses out of them and added the PLZT electro-optical shutters. The result was a decent stereoscopic image, but the shutters used pretty high voltage (200-300 volts), had low transmission, had parallel electrodes running through them and made an odd buzzing sound that wasn’t exactly comforting close to your eyeballs. And there was one other disagreeable aspect that I have forgotten.
The major trick was to substitute a different kind of electro-optical shutter that had superior transmission and used lower power. The answer was just about at hand: liquid crystal shutters. In the early 1980s I had spoken to Jim Fergason, who is one of the fathers of modern liquid crystal technology. When I first spoke to him he lived in Ohio, but right after that he moved to California. Jim was supportive and helpful, and suggested that we use a kind of liquid crystal cell that he invented, the pi-cell. “Pi-cell” is what Tektronix and some workers in the field called it. Fergason himself called it the surface mode device (SMD).
Let me tell you a little something about liquid crystal cells, because it’s important in today’s stereoscopic cinema universe. It is the basis for Real D’s ZScreen, which I invented along with my colleagues at StereoGraphics, and it’s also the basis for the ExpanD shuttering eyewear – and shuttering eyewear are the subject of this little story.
Take two parallel pieces of glass spaced apart by a few microns and fill the gap with something called liquid crystal. On the outside surfaces of the glass you have linear sheet polarizers (axes crossed). The liquid crystal material can be thought of as being made up of directors, which are rod-like clumps of molecules. These molecules provide order to the liquid – the kind of order that is found in solid crystals; hence the name “liquid crystal.” When an electric field is applied to the liquid crystal material the direction of the directors can be changed. That’s the key to the electro-optical effect that makes liquid crystal devices work. In many kinds of liquid crystal devices the electro-optical effect is based on the bulk or all of the material between the plates.
In the surface mode device, or the pi-cell, the directors that make the device work are the ones that are immediately adjacent to the glass plates that make up the walls of the cell itself. Actually these directors are touching coatings of indium tin oxide (ITO) a more or less transparent conductive layer. Another caveat – the directors are in fact in contact with the director alignment layer that is coated on the ITO. Since only the surface directors, not the bulk, move when the electric field is applied, the pi-cell can be fast – maybe 30 or 40 percent faster than the other type of frequently used liquid crystal in which the entire bulk moves, called the twisted nematic. (“Nematic” comes from the Greek, and means “hair” or “hair-like.”)
The pi-cell is phase shifting device or variable retarder (see my earlier articles on polarized light). When an electric field is applied the directors line up with their axes parallel to the field lines or perpendicular to the plane of the glass. Hence the material is isotropic. That is to say, there is no phase shift of the incoming polarized light. When the field is turned off the directors relax into the pi-state and the device becomes anisotropic, or a retarder, and the phase of the incoming polarized light is shifted by a half-wave so that resultant almost exiting light’s polarization axis is toggled by ninety degrees. Thus the exiting polarizer analyzes the phase shifted polarized light and it is more or less extinguished. (There is a third state in which the device has been unenergized for a long time in which the parts are green-blue, and that’s why I know the Xpand eyewear use pi-cells.)
We obtained some pi-cells and tried to get them to work properly, but no go – because the dynamic range was terrible. That is, the leakage of the light from the unwanted eye was so severe that you saw a double image. We doubled up the cells and built what we called a “low-order multiplicative cell” in which, although the transmission was slightly reduced, by having a proper arrangement of polarizers with two pi-cells in series, the dynamic range was greatly increased. This allowed us to put a double stack of pi-cells and associated polarizers in our headband visor, and for the first time we got what was a decent image with high transmission, high dynamic range, and it used low voltage.