1. Field of the Invention
The present invention relates generally to displays and more particularly to a system and a method for two-dimensional transparent displays utilizing special laser induced fluorescence media.
2. Background Art
Image display and associated technologies are a fundamental necessity of today's society. Application areas include communication, entertainment, military, medical and health. Traditionally, a display system consists of a source beam, beam masks or deflectors, and a projection screen. Although the basic concept of a display system served us well in the past, new technologies have been developed steadily. As demonstrated in FIG. 1, a prior art light beam based display system consists of a collimated light source 110, a light masking or deflecting unit 130, and the modified light beam (150) strikes a display screen 180. Typical example of this type of displays are: movie and film display systems, liquid crystal based display, MEMs and liquid crystal based reflective light projection systems for TV and computer. In these light based systems, the image can be viewed on the same side of the projection system as in the case of a movie display, or on the opposite side of the projection system, as in the case of back illuminated large screen projection TV. A common element in these light based display system is that the displaying screen does not change the color (or wavelength) of the illumination light. The screen preferably be opaque to increase scattering of the illuminated light to the viewers. Also the intensity of a particular color component is modulated, and/or the beam position is scanned. In FIG. 2, a prior art electron beam based display system is illustrated. These systems are used in Cathode Ray Tube (CRT) based displays for TV and computers and are gradually being replaced by liquid crystal based flat panel displays. A typical CRT display consists of an electron gun 210, horizontal and vertical beam deflecting conductive plates 230 and 240, and a conductive screen 280. A well-collimated electron beam is deflected by periodically changed electrical fields and strikes certain location of the screen at a specified time. The conductive screen is coated with phosphor particles that convert absorbed electrons into photons of a particular color. The intensity of the electron beam is controlled to regulate intensity patterns displayed on the CRT screen. The CRT screen is normally grounded or maintained at certain electrical potential to avoid charge build up. In order to operate properly, these CRT systems are evacuated and sealed in a glass vacuum tube (not shown). In both situations, the display screens are opaque and people can only see the information on the display surface but cannot see through the screens.
Recently, several research groups have studied the potential of using light conversion as a mean to two- and three-dimensional displays. Of particular interests are the work by E. Downing et. al, as described in an article entitled: “A three-color, Solid-state, Three-dimensional Display” published in Science, vol. 273, pp. 1185–89, 1996. The work described in the Science article formed basis for several US patents granted. See for example, U.S. Pat. Nos. 5,684,621; 5,764,403; 5,914,807; 5,943,160; and U.S. Pat. No. 5,956,172 all to Downing. M. Bass and co-workers, at the University at Central Florida, carried out other related research works. Several related US patents were issued. See for example, U.S. Pat. Nos. 6,327,074; 6,501,590; and 6,654,161; to Bass and co-inventors. These patents and article are thereby included herein by ways of reference.
The research work of Downing et. al, and M. Bass and co-inventors all employed a two color excitation scheme called up-conversion. In an up-conversion process, an absorption center must absorb at least two longer wavelength photons to emit one photon with a shorter wavelength. While Downing et. al, used a solid display material (fluoride ZBLAN glass) doped with rare earth cations, M. Bass and co-workers investigated the use of both dye doped plastics micron sized particles as well as rare earth cation containing fluoride micron particles (NaYF4) as display medium. The major difference is that the former uses solid glass layers whereas the latter uses solid particle sizes from 0.5 μm to 50 μm. The major drawback for both methods is the use of multiple lasers as the excitation sources. The use of multiple lasers is normally required for the up-conversion process due to the inefficiency of the process. The use of very intense, infrared lasers substantially limits the practical applicability of the research works and may introduce safety hazards for the viewers. For each displaying color, two laser beams with specified laser wavelengths need to be used to generate a particular color. Therefore, in order to realize a three-color display, a three-layered display solid structure doped with three color-specific emitters (rare earth cations, or dyes) together with six excitation lasers have to be used.
There are several areas that can be improved on these prior art two- and three-dimensional displays. For instance, it is desirable to use a single excitation laser to generate all three colors. Also desirable is methods using one laser for each color instead of the two lasers per color methods used in these prior art displays. Even more desirable is the use of regular dark light sources (e.g. Light emitting diodes or arc lamps of UV-blue emission) and fluorescent “down-conversion” materials for a 2-D display with transparent screen. Inexpensive manufacturing processes are also the key to a practical display technology. There is a need therefore to have improvements to these prior arts such that inexpensive displays with reduced number of laser sources can be made.