Head-mounted projection display using reflective microdisplays
The present invention relates generally to a head-mounted projection display, and more particularly, but not exclusively to a polarized head-mounted projection display including a light engine and a compact, high-performance projection lens for use with reflective microdisplays.
1. An optical illumination system for use with a reflective microdisplay of a headmounted display, comprising:
a light emissive panel having a 2-dimensional surface, with a width x and length y, from which surface a light distribution is emitted;
a reflective microdisplay; and
a reflector having a reflector focal length associated therewith and disposed one focal length away from the surface of the panel at a location to receive the light emitted by the surface of the panel and disposed one reflector focal length away from the microdisplay to reflect light received from the panel onto the microdisplay, the reflector structured such that the light distribution on the microdisplay is the Fourier transform of the light distribution of the light emissive panel.
2. The optical illumination system according to claim 1 , wherein the light emissive panel is an LED panel.
3. The optical illumination system according to claim 1 , wherein the reflector comprises a concave spherical surface.
4. The optical illumination system according to claim 1 , wherein light distribution on the microdisplay is
E
display
(
x
,
y
)
=
L
*
Ω
=
L
LED
(
arctan
(
x
2
+
y
2
f
)
)
*
S
LED
f
2
,
where E display (x,y) is the illuminance at (x,y) on the display assuming the center of the microdisplay is at the origin, L LED (θ) is the luminance of LED light emissive panel as a function of angle, S LED is the area of the light emissive panel and f is the focal length of the reflector.
5. The optical illumination system according to claim 1 , wherein the ratio of the luminance at the center of the microdisplay to that at the edge is
L
LED
(
0
°
)
/
L
LED
(
arctan
(
D
2
f
)
)
where D is the diagonal size of the microdisplay, L LED (θ) is the luminance of LED light emissive panel as a function of angle, and f is the focal length of the reflector.
6. The optical illumination system according to claim 1 , wherein ratio of the maximum luminance to the minimum luminance on the microdisplay is 1:0.8.
7. The optical illumination system according to claim 1 , comprising a tapered light pipe disposed proximate the light emissive panel.
8. The optical illumination system according to claim 7 , wherein the light pipe comprises a plurality of mirrors oriented in the shape of a truncated pyramid.
9. The optical illumination system according to claim 1 , comprising a reverse telephoto projection lens, telecentric in image space, disposed in optical communication with the microdisplay, the microdisplay located at a back focal length of the projection lens.
10. The head-mounted projection display system according to claim 9 , wherein the overall length of the projection lens is no more than 85% larger than the effective focal length of the projection lens.
11. The head-mounted projection display system according to claim 9 , wherein the back focal length of the projection lens is 40% larger than the effective focal length of the projection lens.
12. The head-mounted projection display system according to claim 9 , wherein the projection lens comprises a diffractive optical element.
13. The head-mounted projection display system according to claim 9 , wherein the projection lens comprises a final lens element disposed closest to the image plane, the final lens element comprising a diffractive optical element disposed thereon.
14. The head-mounted projection display system according to claim 13 , wherein the final lens element includes an aspheric surface.
15. The head-mounted projection display system according to claim 14 , wherein the diffractive optical element is disposed on the aspheric surface.
16. The head-mounted projection display system according to claim 9 , wherein the projection lens comprises a plurality of optical elements, and at least two-thirds of the optical elements comprise plastic.
17. The head-mounted projection display system according to claim 9 , wherein the projection lens comprises a lens group disposed on the object side of the stop of the projection lens, the lens group having an effective focal length two orders of magnitude larger than the effective focal length of the projection lens.
18. The head-mounted projection display system according to claim 9 , wherein the projection lens comprises a plurality of lens elements configured to have an overall length that is no more than two times the effective focal length of the projection lens.