The VRD uses a scanned, modulated light beam and treats the retina as a projection screen, creating a "laser light show." To create an image with the VRD a photon source such as a laser diode (or three such sources in the case of a color display) is used to generate a coherent beam of light. The light beam's intensity is modulated to match the intensity of the image being rendered. The resulting modulated beam is then scanned to place each image point, or pixel, at the proper position on the retina. In order to allow the VRD to be driven by standard video source, a raster method of image scanning is used, much like in standard computer monitors or television. A horizontal scanner moves the beam to draw a row of pixels; a vertical scanner then moves the beam to the next line where another row of pixels is drawn.
After scanning, the optical beam must be properly projected into the eye. The exit pupil of the VRD needs to be coplanar with the entrance pupil of the eye. The lens and cornea of the eye will then focus the beam on the retina, forming a spot. The position on the retina where the eye focuses the spot is determined by the angle at which light enters the eye. This angle is determined by the scanners and is continually varying in a raster pattern. The brightness of the focused spot is determined by the intensity modulation of the light beam.
The drive electronics synchronize the scanners and intensity modulator with the incoming video signal in such a manner that a stable image is formed.
All components in the VRD are small and light, making them ideal for use in a portable hand-held or head-mounted display. Prototypes of this system were developed at The Human Interface Technology Laboratory (HITL) of the University of Washington. The work is funded by MicroVision, Inc., Seattle, which holds an exclusive license to manufacture and distribute the VRD.
There are several challenges yet to be overcome, however, to make this a commercially viable technology -- these are discussed later in the Over-"Seeing" the Development section.
A block diagram of the VRD is shown in the figure below.
For more details on the technology, see HITL publications P-95-1, P-95-5, R-95-5, P-95-12, and Michael Tidwell's Master Thesis.
