Optical: systems and elements – Light interference – Produced by coating or lamina
Reexamination Certificate
1999-05-14
2002-06-18
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Light interference
Produced by coating or lamina
C359S589000, C428S212000
Reexamination Certificate
active
06407862
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electronic projection systems with specularly reflective optical components. More particularly, the present invention relates to front or rear screen electronic projection systems with specularly reflective optical components made of a multilayered polymeric film. Compared to conventional specularly reflective optical components, the enhanced reflectivity of the multilayered polymeric film over a wide wavelength range improves the optical performance of a projection system by increasing brightness, improving color gamut, increasing contrast, reducing color shift, and reducing power consumption.
BACKGROUND OF THE INVENTION
In an electronic projection system an image is projected onto an image surface of a screen component. The optical train in a conventional electronic projection system uses many optical components, including, for example, mirrors, beam splitters, polarizers, and the like. In designing the optical train the effect of each of these components on the image to be displayed must be considered. Each time the image to be displayed encounters an optical component in the optical train, the integrity of the original optical signal may be compromised. For example, reflection at the surface of a specular mirror may cause a color shift as some wavelengths of light in the incident image signal are absorbed by the reflective surface of the mirror. This color shift reduces the quality of the image projected to the screen for viewing by an observer.
The specularly reflective optical components used in electronic projection systems are metal coated glass plates, referred to as second surface “silvered” mirrors. These metal coated mirrors are glass plates coated on a back surface with a metallic layer, typically silver or other highly reflective metal. Metal coated mirrors reflect a wide range of wavelengths of incident visible light, but the reflectivity of wavelengths in the blue (about 400 nm to about 450 nm) and the red (about 600 nm to about 700 nm) regions of the spectrum are reflected much less strongly than the wavelengths in the green (about 450 nm to about 600 nm) portions of the spectrum. These variations in reflectivity cause color shifts in the light reflected from the metallic surfaces and cause color imperfections in the projected image of an electronic projection system. These variations become more pronounced as the number of reflective optical components in the optical train increase, and result in corresponding color defects in the projected image.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides an electronic projection system that includes specularly reflective optical components made of a multilayered polymeric material described in U.S. Pat. No. 5,882,774 and WO 97 01774. Compared to conventional metal coated mirrors, optical components made of the multilayered polymeric reflective components described in the '774 patent and '774 publication have greater and more uniform reflectivity over the entire portion of the visible spectrum from about 400 nm to about 700 nm. This broad range of reflectivity may be used to advantage in any optical train, but it provides specific benefits in electronic projection display systems. If a conventional optical component in the optical train of a projection display system is replaced with an optical component made of the multilayered polymeric film described in the '774 patent, the light reflected from these components has less color shift (greater color uniformity) over the entire region of visible spectrum. This reduced color shift provides a projected image with increased brightness, enhanced color gamut, and increased contrast.
The optical components in the optical engines of conventional projection systems absorb in the blue region of the spectrum, so enhanced reflectivity in the blue region is particularly important in projection display applications. Therefore, in a second aspect, the present invention is a method for enhancing the optical quality of the projected image in a projection display device. Specifically, the present invention is a method of enhancing the optical quality of the projected image in a projection display device by reducing the color shift caused by reflections from the specularly reflective optical components in the optical train of the device. The optical quality is enhanced by incorporating at least one specular mirror component in the optical train of the device, wherein the specular mirror component comprises a multilayered optical film with a reflectivity of at least 96% from about 400 nm to about 700 nm.
The enhanced reflectivity and reduced color shift caused by the specularly reflective optical components of the present invention in the blue and red regions of the spectrum also provides a method for improving the color gamut of the projected image in a projection display device. If more blue and red light is reflected from the surfaces of the specularly reflective optical components in the optical train of the device, a richer and more varied palate of colors may be produced in the reflected image and projected on the screen to the viewer.
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3M Innovative Properties Company
Assaf Fayez
Hohenshell Jeffrey J.
Miller William D.
Schuberg Darren
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