The Mark-II Holographic Video Display

The Mark-II Holographic Video Display: A Scaled up Design

The design strategy for the Mark-II holovideo display was to exploit parallelism

wherever possible, both optically and electronically, such that the approach would

be extensible to arbitrarily large image sized displays. To acheive the goal of a

150x75x75mm image, two 18-channel Acousto-Optic Modulators (AOM) were used,

with each channel of a single AOM modulating beams of red light in parallel. Six tiled

horizontal mirrors scan across matched to the speed of the signal in the AOM, such

that it appears the diffraction pattern in the AOM is stationary. As the mirrors scan

from left to right, one AOM provides 18 lines of rastered image. When the mirrors

return from right to left, the second crossfired AOM provides the next 18 lines of

rastered image. A vertical scanner images each 18-line pass below the previous

one, with 8 horizontal scans in all, providing 18x8=144 vertical scan lines.

The resulting image is horizontal parallax only (HPO), with video resolution in the
vertical direction, and holographic resolution in the horizontal direction. To match
the shear-mode active bandwidth of the tellurium dioxide crystal, we need to produce
a signal with a ~50Mhz bandwidth. To provide the output sampling at above the
Nyquist rate, we use a pixel clock of 110Mhz. Each horizontal line of the display is
256-thousand pixels of holographic fringe pattern translating to 36Mbytes of
information per frame, fed at a total data rate of 2Gpixels/sec into the display
from the frame buffers.

To drive this display, we needed an 18-channel frame buffer with each channel
configured to provide 8 vertical lines of 256K pixels. While no known off the shelf
frame buffer is capable of this, we were able to adapt the Cheops Imaging
System to the task. Cheops is a data-flow architecture digital video platform
developed at the MIT Media Laboratory. The Holovideo Cheops system provides
six synchronized frame buffers to drive our 256Kx144 display as well as a high
speed interface to host processors and a local data-flow processing card for
decoding of encoded or compressed image formats.

Holovideo Images