VOLUMETRIC 3D DISPLAY TECHNIQUES

U.S.Patent 5684621 by Downing

     Solid-state Up-Conversion

One of the fundamental requirements for a volumetric 3D display system is to have entire display volume filled with materials that can be selectively excited at any desired locations. To achieve this goal, one can have two independently controlled radiation beams which activate a voxel only when they intersect.   called two photon Up-conversion   

                                                   Gas Medium Up-Conversion

Another 3D display based on the up-conversion concept employs the intersection of two laser beams in an atomic vapor, and subsequent omnidirectional florescence from the intersection point (U.S. Patent 4 881 068 by Korevaar, 1989).
                                                    Rotating LEDs Array 

It consists of a rotating electroluminenscent panel with embedded high-speed light emitter array. By controlling the timing of - addressing of the light emitter array and the rotation of the panel, 3D images can be formed within the volume swept by the rotating panel.

                                                   Cathode-Ray Sphere

The voxels are created by addressing a rapidly rotating phosphor-coated target screen in vacuum by electron beams synchronized to the screen’s rotation. The view of this rotating multi-planar surface depends on the clarity of the glass enclosure and the translucency of the rotating screen. Another image quality issue is the interaction between the phosphor decay ray and the speed of the rotation of the screen.
                               Varifocal Mirror and High Speed Monitor

The varifocal mirror system consists of a vibrating circular mirror along with a high-speed monitor. The monitor is connected to a woofer such that the woofer can be synchronized to the monitor. A flexible, circular mirror is attached to the front of the woofer,and the monitor is pointed toward the mirror. With the vibrations
from the woofer, the mirror changes focal length and the different points being displayed on the monitor seem to appear at different physical locations in space, giving the appearance of different depths to different objects in the scene being displayed. Variable mirror based 3D display systems are primarily limited by the size of the mirror and updating rate of images, since this mirror has to vibrate.
                       Laser Scanning Rotating Helix 3D Display

Lasers scanning 3D displays operate by deflecting a beam of coherent light generated by a laser to a rotating helical surface. Timing modulation of the laser beam controls the height of the light spot that is produced
by the laser on the rotating surface. The deflectors include devices such as polygonal mirrors, galvanometer, acousto- optics modulated deflectors, and micro-deformable mirrors. There are several problems with this 3D display mechanism that have prevented it from becoming commercially feasible.
The most serious problem is the limitation on the maximum number of voxels that can be displayed. Due to the nature of sequential (non-parallel) laser scanning, only one spot of light can be displayed at any given moment. All the activated image voxels have to be addressed, one by one, by the scanning of single laser beam in time-multiplex fashion. The time needed for steering the laser beam and to stay on the voxel position to
produce sufficient brightness poses an upper limit to how many voxels it can display. To increase the number of voxels, multiple channel lasers and scanners could be used. However, many attempts to increase the spatial resolution have hampered with high cost and bulky hardware design.