In the last several years, holographic elements have been introduced into a wide array of display applications. Holographic Reflectors are incorporated with liquid crystal displays to shift optimum viewing angle away form specular glare and raise brightness by concentrating light at a convenient viewing angle. Reflectors can be produced in blue, green, gold, red, or white colors. Denso GlassVision projection screens incorporate transmission holograms to efficiently direct projected light to the viewer in a screen that reverts to clear glass When the projection image is turned off. JVC has introduce da large-screen HDTV that uses a holographic color filter to separate blue, green, and red light from the illumination beam, and direct the sorted colors to the appropriate color pixel, raising brightness with a passive component. Most recently, HOE prototypes have been produced to improve the efficiency of portable liquid crystal color display. Front diffuser are affixed to the face of reflective color LCDs and direct output light from the LCD to the viewer at a convenient viewing angle in a concentrated view cone. Reflective Colors Filters are pixelated diffuse reflectors internal to the LCD structure and aligned to the LCD matrix. These reflective filters provide higher brightness, larger color gamut, and better color saturation including a holographic grating are under development to provide wider view angle in direct-view LCDs.
Holographic reflectors with high brightness and excellent environmental stability have been produced using DuPont holographic films. The center wavelength, color bandwidth and viewing cone are defined for the optimal viewing performance. Measurement methods used to quantify holographically enhanced reflective LCD performance are presented. The test results show that holographic reflectors based on the DuPont OmniDex film experienced less than 1 percent brightness degradation under 70 degrees and 95 percent relative humidity for 200 hours, with no measurable color shift. Two examples of how this technology can be extended to enhance color LCDs are also presented.
A technique is described for determining three-color exposure energies to achieve a specific color balance in multicolor holographic recordings. The technique relies on the application of multivariable analysis to a series of exposures in which the intensity of the three recording colors is varied. Modeling required for the technique is discussed, followed by examples of three-color holographic mirrors exposed simultaneously in experimental full-color photopolymer film.
DuPont has developed holographic photopolymer films capable of producing high diffraction efficiency in full-color volume holograms and holographic optical elements. The properties of these films allows for a greater range of applications than has been considered feasible for color holograms. The recording mechanism and methods for holographic color recording in these materials is considered. Methods for full-color mastering and copying to achieve optimal performance in three-color recording are discussed. Examples of full-color holograms are presented.
Independent characterization of changes in film thickness and refractive index is necessary for accurate prediction of the Bragg playback conditions of volume holograms after processing. We have developed a method which uses weak holographic mirrors to characterize processing- induced swelling or shrinkage and index change in volume holographic films, and have applied this method to DuPont OmniDex<SUP>TM</SUP> holographic recording films. Results of these measurements are presented.
DuPont holographic photopolymers have been used to fabricate high quality holographic optical elements. The wide spectral sensitivity possible in these materials allows imaging near the desired HOE playback conditions. Multicolor imaging with ion and dye lasers using these materials is discussed. Mastering materials and methods are described for reflection and transmission HOE replication. HOE performance is compared to performance predicted by coupled- wave theory and HOE applications using these materials are described.