Scalable Optical Architectures for Electronic Holography

Pierre St.-Hilaire

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 approach.

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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