Stephen A. Benton

Physical one-way functions

Modern cryptographic practice rests on the use of one-way functions, which are easy to evaluate but difficult to invert. Unfortunately, commonly used one-way functions are either based on unproven conjectures or have known vulnerabilities. We show that instead of relying on number theory, the mesoscopic physics of coherent transport through a disordered medium can be used to allocate and authenticate unique identifiers by physically reducing the mediums microstructure to a fixed-length string of binary digits. These physical one-way functions are inexpensive to fabricate, prohibitively difficult to duplicate, admit no compact mathematical representation, and are intrinsically tamper-resistant. We provide an authentication protocol based on the enormous address space that is a principal characteristic of physical one-way functions.

Electronic display system for computational holography

We present an electro-optical apparatus capable of displaying a computer generated hologram (CGH) in real time. The CGH is calculated by a supercomputer, read from a fast frame buffer, and transmitted to a high-bandwidth acousto-optic modulator (AOM). Coherent light is modulated by the AOM and optically processed to produce a three-dimensional image with horizontal parallax.

Color images with the MIT holographic video display

The MIT holographic video display can be converted to color by illuminating the 3 acoustic channels of the acousto-optic modulator (AOM) with laser light corresponding to the red, green, and blue parts of the visible spectrum. The wavelengths selected are 633 nm (red), 532 nm (green), and 442 nm (blue). Since the AOM is operated in the Bragg regime, each wavelength is diffracted over a different angular range, resulting in a final image in which the three color primaries do not overlap. This situation can be corrected by shifting the diffracted spatial frequencies with an holographic optical element (HOE). This HOE consisting of a single grating is placed right after the AOM in the optical setup. Calculation of the required spatial frequency for the HOE must take into account the optical activity of the TeO2 crystal used in the AOM. The HOE introduces distortions in the final image, but these are so small as to be visually negligible. The final images are of a good quality and exhibit excellent color registration. The horizontal view zone, however, diminishes for the shorter wavelengths.

Holographic recording using a digital micromirror device

We describe the use of a digital micromirror device (Texas Instruments, Inc.s DMDTM) as a spatial light modulator for holographic applications. Questions of the interferometric effects of the moving mirror structure and the appropriateness of pulse-width modulation for grayscale imaging are addressed. Compensation for the particular attributes of DMD imaging has allowed the creation of full-color holographic stereograms of high image quality.

Advances in holographic video

We discuss recent developments in the MIT electronic holography display. These include the use of multiple galvanometric scanners as the horizontal scanning element, two 18-channel acousto-optic modulators (AOMs) working in tandem, and a bank of custom-designed high- bandwidth framebuffers. We also describe some recent progress on computational issues.

Real-time holographic display: improvements using a multichannel acousto-optic modulator and holographic optical elements

Any practical holographic display device relying on the MIT synthetic aperture approach will require time-bandwidth products far exceeding those available with single channel acousto- optic modulators (AOMs). A solution to this problem is to use a multichannel AOM, thus making use of the parallelism inherent in optical systems. It is now technically feasible to accommodate a large number of acoustic channels on a single crystal with a corresponding improvement in image characteristics. The vertical view zone also becomes a significant problem for any large size display since each horizontal scan line is visible only from a narrow angle in the vertical direction. Using holographic optical elements (HOEs) alleviates this limitation in two ways: First, the interline spacing can be adjusted easily with HOEs. Second, it is possible to manufacture an HOE which will act as a one-dimensional diffuser. Placing such an HOE in the vertical focus plane of the display increases the view zone by diffusing each line in the vertical direction, but leaves the horizontal image content unaltered.

Real-Time Display Of 3-D Computed Holograms By Scanning The Image Of An Acousto-Optic Modulator

The invention of holography has sparked hopes for a three-dimensional electronic imaging systems analogous to television. Unfortunately, the extraordinary spatial detail of ordinary holographic recordings requires unattainable bandwidth and display resolution for three-dimensional moving imagery, effectively preventing their commercial development. However, the essential bandwidth of holographic images can be reduced enough to permit their transmission through fiber optic or coaxial cable, and the required resolution or space-bandwidth product of the display can be obtained by raster scanning the image of a commercially available acousto-optic modulator. No film recording or other photographic intermediate step is necessary as the projected modulator image is viewed directly. The design and construction of a working demonstration of the principles involved is also presented along with a discussion of engineering considerations in the system design. Finally, the theoretical and practical limitations of the system are addressed in the context of extending the system to real-time transmission of moving holograms synthesized from views of real and computer-generated three-dimensional scenes.

Experiments in holographic video imaging

Reduction of the information content of a hologram to the minimum necessary to support strong spatial perception makes possible the interactive computation, transmission, and display of three-dimensional animated holographic images.

Edge-lit rainbow holograms

A three-step technique produces rainbow holograms that can be illuminated through the edge of their substrates with highly divergent illumination, permitting very compact integral hologram and illumination display units.

Holographic Displays: 1975-1980

Three-dimensional holographic images are becoming more widely enjoyed as more practical white-light illumination techniques are developed, more varied types of images are represented, and lower production costs are attained.