Uniform speckle reduced laser projection using spatial and temporal mixing
View Patent ↗A digital image projector includes a light assembly configured to project light along a light path from at least one laser array light source, the projected light having an overlapping far field illumination in a far field illumination portion of the light path; a temporally varying optical phase shifting device configured to be in the light path; an optical integrator configured to be in the light path; a spatial light modulator located downstream of the temporally varying optical phase shifting device and the optical integrator in the light path, the spatial light modulator configured to be located in the far field illumination portion of the light path; and projection optics located downstream of the spatial light modulator in the light path, the projection optics configured to direct substantially speckle free light from the spatial light modulator toward a display surface.
1. A digital image projector comprising:
a) a light assembly for a particular color channel configured to project light along a light path from at least one laser array light source including multiple lasers, the projected light from the multiple lasers overlapping in a far field illumination portion of the light path to form a combined light beam, the far field illumination portion of the light path being a portion beyond a far field distance wherein a laser intensity pattern from an individual laser satisfies a far field criterion such that only the size of the laser intensity pattern varies and the structure of the laser intensity pattern does not vary;
b) a temporally varying optical phase shifting device configured to be in the light path downstream from the far field distance;
c) an optical integrator downstream of the temporally varying optical phase shifting device;
d) a spatial light modulator located downstream of the optical integrator in the light path, the spatial light modulator; and
e) projection optics located downstream of the spatial light modulator in the light path, the projection optics configured to direct speckle reduced light from the spatial light modulator toward a display surface.
2. The digital image projector of claim 1 , wherein the spatial light modulator comprises a micromirror device or a liquid crystal display based device.
3. The digital image projector of claim 1 , wherein at least one of the laser array light sources comprises at least one vertical cavity laser.
4. The digital image projector of claim 1 , wherein the temporally varying phase shifting device comprises a rotating element that (a) is optically wedged, (b) is aberrated, (c) has a diffusive surface, or (d) has combinations thereof.
5. The digital image projector of claim 1 , wherein the temporally varying phase shifting device comprises a spatially tilted or displaced optical element.
6. The digital image projector of claim 1 , wherein the laser array light source is or the laser array light sources are configured to cause the projected light to have a common polarization axis, and wherein the optical integrator is a polarization maintaining optical integrator.
7. The digital image projector of claim 6 , wherein the spatial light modulator comprises a micromirror device or a liquid crystal display based device.
8. The digital image projector of claim 6 , wherein at least one of the laser array light sources comprises at least one vertical cavity laser.
9. The digital image projector of claim 6 , wherein the temporally varying phase shifting device comprises a rotating element that (a) is optically wedged, (b) is aberrated, (c) has a diffusive surface, or (d) has combinations thereof.
10. The digital image projector of claim 6 , wherein the temporally varying phase shifting device comprises a spatially tilted or displaced optical element.
11. A stereoscopic digital image projector comprising:
a) a light assembly configured to project polarized light having a common first polarization state along a light path from at least one laser array light source, the projected polarized light having an overlapping far field illumination in a far field illumination portion of the light path;
b) a polarization rotator configured to be in the light path of the projected polarized light and actuable to controllably rotate the polarization state of the projected polarized light from the first polarization state to a second polarization state;
c) a temporally varying optical phase shifting device configured to be in the light path;
d) a polarization maintaining optical integrator configured to be in the far field portion of the light path;
e) a micro-electromechanical spatial light modulator located in the light path downstream of the polarization rotator, temporally varying optical phase shifting device, and the optical integrator, the spatial light modulator configured to form a first modulated light from light of the first polarization state and to form a second modulated light from light of the second polarization state;
f) a synchronizing device configured to synchronize the polarization rotator with image data; and
g) projection optics located downstream of the spatial light modulator in the light path, the projection optics configured to direct substantially speckle free light from the spatial light modulator toward a display surface.
12. The stereoscopic digital image projector of claim 11 , wherein the spatial light modulator is a micromirror device.
13. The stereoscopic digital image projector of claim 11 , wherein the polarization rotator is a segmented disk with at least one reflective segment and at least one transmissive segment.
14. The stereoscopic digital image projector of claim 13 , wherein the polarization rotator is the temporally varying phase shifting device.
15. The stereoscopic digital image projector of claim 11 , wherein the temporally varying phase shifting device has an optical wedged, aberrated, diffusive surfaced element, or combinations thereof.
16. A digital image projector comprising:
a) a light assembly for a particular color channel configured to project light along a light path from at least one laser array light source including multiple lasers, the projected light from the multiple lasers overlapping in a far field illumination portion of the light path, the far field illumination portion of the light path being a portion beyond a far field distance wherein a laser intensity pattern from an individual laser satisfies a far field criterion such that only the size of the laser intensity pattern varies and the structure of the laser intensity pattern does not vary;
b) a temporally varying optical etendue shifting device configured to be in the light path downstream from the far field distance;
c) an optical integrator downstream of the temporally varying optical phase shifting device;
d) a spatial light modulator located downstream of the the optical integrator in the light path, the spatial light modulator; and
e) projection optics located downstream of the spatial light modulator in the light path, the projection optics configured to direct speckle reduced light from the spatial light modulator toward a display surface.
17. The digital image projector of claim 16 , wherein the temporally varying optical etendue shifting device is configured to change an angular position, an angular size, or both the angular position and the angular size of the projected light.
18. The digital image projector of claim 16 , wherein the temporally varying optical etendue shifting device is configured to change an angular or spatial position, an angular or spatial size, or any combination thereof.
19. The digital image projector of claim 16 , wherein the optical integrator is configured to substantially maintain a polarization state of the projected light.
20. A method of reducing laser speckle in a laser displayed image, the method comprising:
a) projecting light from a laser array light source including multiple lasers in a particular color channel along a light path, the projected light from the multiple lasers overlapping in a far field illumination portion of the light path, the far field illumination portion of the light path being a portion beyond a far field distance wherein a laser intensity pattern from an individual laser satisfies a far field criterion such that only the size of the laser intensity pattern varies and the structure of the laser intensity pattern does not vary;
b) temporally varying the projected light using a temporally varying optical phase shifting device or a temporally varying optical etendue shifting device configured to be in the light path downstream from the far field distance;
c) optically integrating the projected light subsequently to temporally varying the projected light;
d) spatially modulating the projected light subsequently to optically integrating the projected light; and
e) optically projecting speckle reduced light toward a display surface subsequently to spatially modulating the projected light.