A three dimensional volumetric display system utilizing a rotating helical surface is described. The rotating helix system permits images to be displayed in a three-dimensional format that can be observed without the use of special glasses. Its rotating helical screen sweeps out a cylindrical envelope, providing a volumetric display medium through which scanned laser pulses are projected. The light scatters from the surface of the helix so that each voxel appears to emanate from specific points in space. Each point has x-y-coordinates determined by the laser scanner and a z-coordinate determined by the intersection of the laser beam and the helix surface. Display images are created by synchronizing the interaction of the laser pulses and the moving screen to address a full three-dimensional volume that gives the viewer true depth cues (binocular parallax, accommodation, convergence) without the need for any special viewing aids. We describe recent work on the development of mechanical, optical, electronic, and software engineering for a display system based on a 36-inch diameter helix using high speed, multichannel, random access laser scanners. Color images are created using red, green and blue laser sources. The system is capable of displaying 800,000 voxels per second, per color. A portable, 12-inch diameter, translucent helix system is also presented.

NR aD, the RDT&E Division of the Naval Command, Control and Ocean Surveillance Center (NCCOSC), has developed its second generation device for displaying data, information and scenes in a three‐dimensional volume of image space. The device incorporates a 36‐inch diameter double helix that spins at approximately 10 revolutions per second, providing a means to address a cylindrical volume. Under computer control, a laser beam is directed to illuminate certain discrete volume points (voxels) on the helix needed to create a scene. The laser light scatters from the surface of the helix, so, to the observer, each voxel appears to emanate from specific points in space. Each point has x‐y coordinates determined by the position of the laser beam, and a z coordinate determined by the height of the point on the helical surface. Any point within the cylindrical image volume can be computer‐addressed to appropriately synchronize the laser eam, the Acousto‐Optic (AO) Scanner and the phase of the helix, as shown in figures 1 and 8. Using a novel Acousto‐Optic (AO) Random‐Access Scanner, up to 40 thousand laser‐generated voxels refreshed at 20 Hz per color are projected onto the reflective surface of the rotating helix. (This is about 10 times more than the current state of the art.) The higher resolution allows improved color images, updated in real time, for group viewing with the naked eye (see the optical head in figure 8).

A novel type of electro-optic diffractive element is presented which can satisfy the requirements for a high space-time bandwidth deflector while providing for two-dimensional random access beam steering control. The basic device consists of a multichannel array of phase modulators fabricated using Lanthanum-modified Lead Zirconate Titanate (PLZT) operating as a programmable diffractive optical element. Two-dimensional deflection control can be readily obtained by crossing two one-dimensional arrays. This device is useful for wavelengths in the Visible to Mid-JR range and is based on PLZT ceramic materials which can be readily mass-produced. It possesses the versatility and multifunctionality of liquid crystal based optical phased array systems while allowing for very fast switching speeds with good thermal stability. We present a brief comparison of this novel deflector with other scanning technologies and outline the benefits and trade-offs of the PLZT-based device. Experiments on 16-and 32-channel arrays with fullwave voltages less than 400 volts demonstrate continuous lateral beam steering control of a HeNe laser beam. We also demonstrate full deflection control with a minimum number of control lines using a modified deflector arrangement. And we present measurements showing sub-microsecond switching speeds from such PLZT-based phase modulators. Mature versions of this type of scanner will find use in a wide variety of applications including 2-D and 3-D laser displays, laser communications, and LIDAR systems.

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