Ultra-thin image projection system
View Patent ↗An ultra-thin rear projection display system (RPDS) is disclosed. The system uses a small flat mirror, a small non-rotationally symmetric mirror and a larger non-rotationally symmetric mirror to achieve a D-to-d ratio of around 11:1 while rendering a significantly distortion free image on the screen. The first two mirrors are significantly smaller than the size of the screen, while the third mirror is significantly larger than the first two mirrors but smaller than the screen. In one embodiment, the lens and light engine are positioned horizontally to one side and, in another example, the lens and light engine are positioned vertically, projecting downwards. In one example, an image processor is used to correct for the remaining distortions. In another example, the system is adapted such that the light rays forming the projected image are within a certain range of angles such that a TIR Fresnel lens could be used to collimate the image.
1. A rear projection display system comprising:
a) a housing having a thickness;
b) a screen, having a screen diagonal and a screen normal direction, positioned at a front side of the housing;
c) a light engine placed inside the housing, having an illumination stage adapted to create a beam of light, at least one display panel adapted to modulate the beam of light to create an image, and a lens system having a focal length and adapted to project the created image forming a projected image consisting of light rays;
d) a non-rotationally symmetric first mirror placed inside the housing and in the optical path of said projected image, having dimensions significantly smaller than said screen diagonal, and having a horizontally convex curvature, and having a vertical curvature which is a function of the focal length of said lens system, such that for shorter focal length it is more concave and less convex, and for longer focal length, it is less concave and more convex, said first mirror adapted to reflect the projected image which is projected from said lens system; and
e) a non-rotationally symmetric second mirror, placed inside the housing and in the optical path of said projected image, having dimensions significantly larger than said first mirror and smaller than said screen diagonal and having a vertical curvature which is a function of the size of the image in the absence of said second mirror relative to the size of the screen, such that for smaller image size it is convex and for larger image size it is concave, said second mirror adapted to reflect the projected image, which is reflected off of the first mirror, onto the screen to form a viewable image.
2. The system of claim 1 , further including a Fresnel lens positioned parallel to and in front of the screen, adapted to collimate light rays forming the projected image onto the screen normal direction.
3. The system of claim 2 , wherein the system is configured such that the rays forming the projected image, when impinging on the Fresnel lens, have a pre-determined angular range with respect to the screen normal to allow collimation via total internal reflection, and wherein the Fresnel lens is a total-internal-reflection (TIR) Fresnel lens.
4. The system of claim 1 , wherein said second mirror is significantly parallel to said screen.
5. The system of claim 1 , wherein the ratio of the screen diagonal to the housing thickness is at least 10:1.
6. The system of claim 1 , further wherein the light engine is a compact light engine to further reduce the housing thickness.
7. The system of claim 1 , wherein the illumination stage is an LED light illumination system.
8. The system of claim 1 , wherein the illumination stage is a laser light illumination system.
9. The system of claim 1 , wherein the screen is on top of a chin portion in front of the housing, and wherein the chin portion has a height less than 15% of the screen diagonal.
10. The system of claim 1 , wherein the second mirror has a horizontally oriented surface with a convex curvature on an upper surface that smoothly transitions by varying its degree of convex curvature to a lower surface, thereby reducing spatial distortion of the final image displayed on the screen.
11. The system of claim 10 , wherein the second mirror has a small degree of horizontal convex curvature on an upper portion and a larger degree of horizontal convex curvature on a lower portion for reducing spatial distortion of the final image displayed on the screen.
12. The system of claim 1 , wherein said first mirror has a horizontal curvature profile that is more convex at its bottom region and smoothly transitions to less convex at its top region.
13. The system of claim 1 , wherein the lens system includes a rotationally non-symmetric lens element being shaped to compensate for defocusing caused by at least one of the first mirror and the second mirror.
14. The system of claim 1 , wherein the lens assembly consists of only spherical lens elements.
15. The system of claim 1 , wherein the system further comprises an image processor connected to the light engine, the image processor being adapted to correct for geometric and optical distortions in the final image.
16. The system of claim 15 , wherein the image processor is adapted to correct luminance and chrominance non-uniformity in the final image.
17. The system of claim 16 , wherein the image processor is adapted to perform optical distortion correction for each color component separately to eliminate lateral color distortions and misconvergence in the final image.
18. The system of claim 1 , wherein the light engine is positioned generally on a top portion of the housing.
19. The system of claim 1 , wherein the light engine is positioned generally on the bottom portion of the housing.
20. The system of claim 1 , further including a flat mirror disposed before the first mirror, said flat mirror being adapted to rotate the image and thereby prevent the protrusion of the lens system from the housing.