Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
1999-06-04
2001-02-20
Ben, Loha (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S618000, C359S629000, C353S031000, C349S005000, C349S008000, C348S762000, C348S756000
Reexamination Certificate
active
06191893
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention was made with United States Government support under Award 70NANB5H1070, entitled “High Information Content Display Technology”, awarded by the Department of Commerce through its National Institute of Science and Technology (NIST).
This invention relates to color projection display systems employing one or more electro-optic light modulators, and more particularly relates to such a system which employs a white light illumination source, and dichroic filters to separate the white light into primary color components, and to recombine these components.
Most color projection display systems employing one or more electro-optic light modulators, also employ a single white light illumination source, a first set of dichroic filters arranged to separate the white light from the source into primary (red, blue and green) color components, and a second set of dichroic filters to recombine the components after modulation.
The design of such systems dictates that the dichroic filters be inclined at an angle to the paths of the light beams, usually 45 degrees. These inclined surfaces in the optical paths break what would otherwise be a symmetrical arrangement of light rays with respect to the top and bottom (or left and right, depending on the layout) of modulator panel(s), and corresponding asymmetry of light rays in the projected image.
This asymmetry, and the well-known sensitivity of the transmission characteristics of such filters to the incident angles of the light rays striking their surfaces, results in a variation of cut-off wavelength of the filters, and a consequent variation in hue of the primary colors across the display image, the direction of variation (width or height) depending on the direction of tilt of the dichroic filters in the lightpath.
In co-pending U.S. patent application Ser. No. 09/100,829 filed Jun. 19, 1998, now U.S. Pat. No. 5,999,321, the specification of which is incorporated herein by reference, dichroic filters with reduced angle sensitivity and sharper cut-off wavelengths are described. While use of such improved filters in a color projection display system reduces hue variation, appreciable hue variation can still occur.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to provide a color projection display system employing dichroic filters for color separation and recombination, in which the display exhibits improved hue variation.
According to the invention, in a color projection display system having a source of white light, an electro-optic light modulator for modulating the light in accordance with a display signal, a projection lens, and dichroic filters for separating the white light into color components prior to modulation, and for recombining the modulated color components prior to projection, the hue variation of the display is improved by designing the filters to have different cut-off wavelengths of separation and recombination for at least one of the color components.
A color projection display system of the invention comprises: a white light illumination source, at least one electro-optic light modulator, and a projection lens, the system also comprising a first set of dichroic filters to separate the white light into color components, each of the filters of the a first set having at least one cut-off wavelength for separating at least one color component, and a second set of dichroic filters to recombine these components, each of the dichroic filters of the second set having at least one cut-off wavelength for recombining at least one color component, characterized in that the cut-off wavelength for separation of at least one color component is different from the cut-off wavelength for recombination of that color component.
In the preferred embodiments, the color projection display system employs two dichroic filters in the first set for separating the white light into red (R), blue (B) and green (G) components, and two dichroic filters in the second set for recombining the color components, and the cut-off wavelengths for separation and recombination of each color component are different. These differences can range from 5 to 20 nanometers.
As used herein, the term “cut-off wavelength” of a dichroic filter means the wavelength at which the filter is 50% transmissive and 50% reflective at the design angle of incidence of the filter.
There are six different orders in which the light can be separated prior to modulation in such a three-color system. For each of these orders, there is a preferred relationship between the cut-off wavelengths of the separation and recombination filters.
For the order of separation, blue, green, red, designated herein BGR, a first filter of the first set (Filter I) separates blue light from green and red light, a second filter of the first set (Filter II) separates green light from red light, a first filter of the second set (Filter III) recombines green light and blue light, and a second filter of the second set (Filter IV) recombines red light with green and blue light; the cut-off wavelength Ic of Filter I is less than the cut-off wavelength IIIc of Filter III, and the cut-off wavelength IIc of Filter II is greater than the cut-off wavelength IVc of Filter IV.
For the order of separation RGB, a first filter of the first set (Filter I) separates red light from green and blue light, a second filter of the first set (Filter II) separates green light from blue light, a first filter of the second set (Filter III) recombines red light and green light, and a second filter of the second set (Filter IV) recombines blue light with green and red light; the cut-off wavelength Ic of Filter I is less than the cut-off wavelength IIIc of Filter III, and the cut-off wavelength IIc of Filter II is greater than the cut-off wavelength IVc of Filter IV.
For the order of separation BRG, a first filter of the first set (Filter A) separates blue light from green and red light, a second filter of the first set (Filter B) separates red light from green light, a first filter of the second set (Filter C) recombines blue light and red light, and a second filter of the second set (Filter D) recombines blue and red light with green light; and the cut-off wavelength Ac of Filter A is less than the cut-off wavelength Dc of Filter D, and the cut-off wavelength Bc of Filter B is greater than the cut-off wavelength Dc of Filter D.
For the order of separation GRB, a first filter of the first set (Filter A) separates green light from blue and red light, a second filter of the first set (Filter B) separates red light from blue light, a first filter of the second set (Filter C) recombines green light and red light, and a second filter of the second set (Filter D) recombines green and red light with blue light; and the cut-off wavelength Ac of Filter A is less than the cut-off wavelength Bc of Filter B, and the cut-off wavelength Ac of Filter A is greater than the cut-off wavelength Cc of Filter C.
For the order of separation RBG, a first filter of the first set (Filter A) separates red light from green and blue light, a second filter of the first set (Filter B) separates blue light from green light, a first filter of the second set (Filter C) recombines red light and blue light, and a second filter of the second set (Filter D) recombines blue and red light with green light; and the cut-off wavelength Bc of Filter B is less than the cut-off wavelength Dc of Filter D, and the cut-off wavelength Ac of Filter A is greater than the cut-off wavelength Dc of Filter D.
For the order of separation GBR, a first filter of the first set (Filter A) separates green light from blue and red light, a second filter of the first set (Filter B) separates blue light from red light, a first filter of the second set (Filter C) recombines green light with blue light, and a second filter of the second set (Filter D) recombines red light with blue and green light; and the cut-off wavelength Ac of Filter A is less than the cut-off wavelength Cc of Filter C, and the cut-off wavelength Ac of Filter A is less than
Ben Loha
Fox John C.
Philips Electronics North America Corporation
LandOfFree
Color projection display system with improved hue variation does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Color projection display system with improved hue variation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Color projection display system with improved hue variation will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2561847