Scalable Optical Architectures for Electronic Holography
Submitted to the Program in Media Arts and Sciences,
School of Architecture and Planning,
on June 23, 1994
in Partial Fulfillment of the Requirements for the Degree of
Doctor of Philosophy
Holography has long been recognized as an effective way to convey the
information of complex 3-dimensional structures such as those
encountered in medical imaging, computer-aided design and navigation.
However, attempts at implementing a real-time holographic display
device have been hampered by the enormous space-bandwidth products
required by such a task. I present here an approach that alleviates
many of the problems encountered in previous attempts at real-time
computer generated holography.
The basic idea underlying the MIT electronic holography display is the
use of an acousto-optic modulator as a dynamic display medium and the
synthesis of a large aperture by scanning the image of the
modulator. The original implementation of the display is unsuitable
for images larger than a few square centimeters, because the necessary
optical space-bandwidth product become unmanageable by the
electronic and optical subsystems. The goal of this thesis is to
demonstrate that large displays can be implemented with available
technologies if we break the space bandwidth product in small segments
at both the image plane and Fourier plane, i.e. if we take a parallel
In the image plane domain the display space-bandwidth product can be
increased by simultaneously writing multiple acoustic columns on a
single crystal and then optically multiplexing the resulting
holograms. I discuss the proper conditions under which the interline
crosstalk remains acceptable and introduce a scanning geometry that
allows for such a multiple channel operation.
The Fourier domain can also be segmented in small domains, each being
processed by a different scanning element. I describe the behavior of
the image when such a segmentation in implemented and I then derive
the conditions under which it can be effected without incurring
significant image degradation.
I finally describe the implementation of these concepts into a large
scale holographic display which includes the use of an array of 6
galvanometric scanners as the horizontal scanning element, two
18-channel acousto-optic Bragg cells working in tandem, and a bank of
custom-designed high-bandwidth framebuffers. The application of the
concept of parallelism has allowed a six-fold scale-up of the
display, which now produces high quality images 150mm x 75 mm in
frontal dimensions, with a 30 degrees view zone.
Thesis Supervisor: Professor Stephen A. Benton.
Title: Allen Professor of Media Technology, MIT Media Laboratory.
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