Head-mounted projection display using reflective microdisplays

1. A telecentric optical illumination system for use with a reflective microdisplay, comprising:

a source of optical radiation having a first polarization state;

a polarized beamsplitter disposed at a location to receive optical radiation from the optical radiation source and oriented relative to the source of optical radiation to reflect the received optical radiation;

an optical retarder disposed at a location relative to the beamsplitter to receive optical radiation reflected by the beamsplitter and oriented to convert the polarization state of the received optical radiation to be circularly polarized; and

a reflector having optical power disposed at a location to receive the circularly polarized optical radiation from the optical retarder and to reflect the received optical radiation back through the retarder and beamsplitter,

wherein the pupil of the illumination system is disposed at the source of optical radiation to provide an optical illumination system that is telecentric in image space.

2. The optical illumination system according to claim 1 , wherein the reflector is disposed one reflector focal length away from the source of optical radiation.

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 the retarder comprises a quarter-wave retarder placed between the reflector and beamsplitter with the fast axis of the retarder oriented at about 45 degrees to the polarization direction of the first polarization state.

5. The optical illumination system according to claim 1 , wherein source of optical radiation comprises a LED.

6. The optical illumination system according to claim 1 , comprising a tapered light pipe disposed proximate the source of optical radiation.

7. The optical illumination system according to claim 6 , wherein the light pipe comprises a plurality of mirrors oriented in the shape of a truncated pyramid.

8. A head-mounted projection display system, comprising:

the optical illumination system according to claim 1 ;

a microdisplay disposed one reflector focal length away from the reflector for receiving optical radiation from the reflector; and

a projection lens, telecentric in image space, located so that the image plane is disposed proximate the microdisplay.

9. The head-mounted projection display system according to claim 8 , comprising:

a polarized projection beamsplitter disposed at about a 45 degree angle relative to the optical axis and disposed at a location to receive optical radiation transmitted by the projection lens;

a projection system quarter-wave retarder disposed at a location to receive optical radiation reflected by the projection beamsplitter; and

a projection screen disposed at a location to receive optical radiation from the projection system quarter-wave retarder.

10. The head-mounted projection display system according to claim 8 , wherein the overall length of the projection lens is no more than about 85% larger than the effective focal length of the projection lens.

11. The head-mounted projection display system according to claim 8 , wherein the back focal length of the projection lens is about 40% larger than the effective focal length of the projection lens.

12. The head-mounted projection display system according to claim 8 , wherein the projection lens comprises a diffractive optical element.

13. The head-mounted projection display system according to claim 8 , 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 8 , 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 8 , wherein the ratio of the weight of the projection lens to the square of the F-number of the projection lens is less than about 2 to 1.

18. The head-mounted projection display system according to claim 8 , 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.

19. The head-mounted projection display system according to claim 8 , wherein the projection lens comprises a plurality of lens elements configured to have an overall length that is no more than about two times the effective focal length of the projection lens and configured so that the projection lens is telecentric in image space.