The Business of Technology



Display System

Video projector technologies are commonly limited in the brightness or resolution of the image.  Although laser image projectors have frequently been tried, and are used in theme parks for vector-displays, there is a difficulty in producing an information-dense raster-scanned display.  If mirror scanners are used, impractically high mirror speeds are necessary to fulfill the line-rate requirements of typically 16kHz.  If acousto-optic scanning is used, rather low scan angles are feasible and efficiency can be badly compromised.

The system developed made use of a combination of technologies which enabled a compact, high efficiency, high brightness and high resolution video display.

In this system, a copper vapour laser produces a pulsed beam of light.  The pulsing rate is synchronised with the video line rate.  The beam is optically configured to illuminate the aperture of a Tellurium Dioxide modulator, operating in slow shear mode.  This is critical, since a slow-shear modulator of this type has both an anomalously low propagation speed for the sound wave, and a very high diffraction efficiency.  In this way, a complete video line can be pre-loaded into the modulator between laser pulses.  The laser acts like a sophisticated flashlight, taking a snapshot of the information in the cell.

Downstream optics produces a line focus of the light onto the screen, and the line is scanned vertically using a galvanometer mirror scanner operating at either 50Hz or 60Hz, synchronised to the video frame rate.

This system has been adopted for use in the BAe Microdome training simulator, where a single laser is used to generate four independent images on the inner surface of a dome.  Many of these systems are now in use worldwide.

This system was developed when Dr Sawyers worked with PA Technology and Scientific Generics.