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Fig. 1: Throughout history, each technological age has been successively shorter, but each has presented exponential increases in knowledge. The Information Age is not likely to be any different.

miniature CRT with an LC shutter can present a very adequate, full-color display at low- ambient-light levels.

It's Not a Light Bulb
An accountant friend of mine asks, "How are those light bulbs you are working on coming?" Clearly, he does not have a good understanding of the challenges associated with designing image sources for an HMD.

Making miniature projection CRTs involves many design minimums and maximums:

The Honeywell IHADSS used in the Apache helicopter was a major program that moved the use of miniature projection CRTs in HMDs from experimental to operational status.

Additional improvements came slowly, but a developmental program initiated by the Armstrong Laboratory at Wright-Patterson Air Force Base (AAMRL-WPAFB) in 1986 produced a tube with significantly improved performance over the tube used in the IHADSS and provided the first hope that it was possible to use a CRT for daylight opera tion in the cockpit of a modem fighter aircraft.

This development incorporated major design and construction changes that allowed the light output to be essentially doubled while cutting the pixel size in half - all at the same drive levels (Fig. 2). In addition to the new design and construction, the new H1426 employed a YAG phosphor (P53) with the same 545-nm peak wavelength excitation as the P43 used in the H1380 but with superior phosphor-saturation characteristics.

Today, the challenge is to exceed this performance while reducing the weight and vol ume and increasing the reliability and life of the miniature image source. A new program to accomplish this is incorporated in the Visually Coupled Acquisitioning Target System (VCATS) program. Initially, the overall AAMRL-WPAFB program is aimed at incorporating an HMD in the F-15 aircraft. This will be the first full HMD in a fixed-wing aircraft in the United States.

Electron Optics
CRTs can be classified by type of deflection and method of focus - either electromagnetic or electrostatic. Modem deflection coils are superior to electrostatic deflection plates in their ability to precisely position the electron beam. The deflection circuit allows the linearity, pattern correction, and sensitivity to be tailored so that each pixel in the display can be located precisely. Even with its added cost and weight, magnetic deflection is the preferred choice for the miniature CRTs in new HMDs.

The focusing of the electron beam at the image plane can be accomplished electrostatically or magnetically. Although the magnetic focus lens can give superior spot size and density, it does have drawbacks, especially in regard to volume and weight. The potentially superior performance of magnetic focus stems