Image projector
An image projector includes a spatial light modulator (SLM) with a two dimensional array of pixel elements controllable to modulate a property of light transmitted or reflected by the pixel elements. An illumination arrangement delivers illumination to the SLM. A collimating arrangement collimates illumination from the SLM to generate a collimated image directed to an exit stop. The illumination arrangement is configured to sequentially illuminate regions of the SLM, each corresponding to a multiple pixel elements. A controller synchronously controls the pixel elements and the illumination arrangement so as to project a collimated image with pixel intensities corresponding to a digital image.
1. An image projector for projecting a collimated image via an exit stop, said collimated image being a representation of a digital image, the image projector comprising:
(a) a spatial light modulator providing a two dimensional array of pixel elements, each of said pixel elements being controllable to modulate a property of light transmitted or reflected by said pixel element;
(b) an illumination arrangement delivering illumination to said spatial light modulator;
(c) a controller in electronic connection with said spatial light modulator and said illumination arrangement; and
(d) a collimating arrangement of at least one optical element configured to collimate illumination from said spatial light modulator to generate a collimated image directed to said exit stop,
wherein said illumination arrangement is configured to sequentially illuminate a plurality of regions of said spatial light modulator, each region containing a plurality of said pixel elements, and wherein said controller is configured to synchronously control said pixel elements and vary an illumination level of said illumination arrangement so as to illuminate the plurality of regions of said spatial light modulator with differing levels of illumination and to control said pixel elements according to the differing levels of illumination so as to project a collimated image with pixel intensities corresponding to the digital image.
2. The image projector of claim 1 , wherein said illumination arrangement includes a scanning arrangement deployed to scan a beam of illumination across said two-dimensional array of said spatial light modulator.
3. The image projector of claim 2 , wherein said beam of illumination spans one dimension of said two-dimension array, and wherein said scanning arrangement scans said beam of illumination in a one-dimensional scanning pattern.
4. The image projector of claim 2 , wherein said controller updates pixel elements of said two-dimensional array in a sequence of rows sweeping across said two-dimensional array, and wherein said scanning arrangement is synchronized to follow behind said sequence of rows, illuminating part of an updated image before completion of said update across said two-dimensional array.
5. The image projector of claim 4 , wherein said illumination arrangement is configured to generate at least two simultaneous beams of at least two different colors in different angular positions, and wherein said controller updates pixel elements of said two-dimensional array between passing of a first of said beams and a second of said beams.
6. The image projector of claim 2 , wherein said scanning arrangement scans said beam of illumination in a two-dimensional scanning pattern.
7. The image projector of claim 2 , wherein said scanning arrangement includes a tip of an optic fiber and an actuator deployed for displacing said tip of said optic fiber.
8. The image projector of claim 1 , wherein said illumination arrangement includes a plurality of independently switchable illumination sources for illuminating said plurality of regions.
9. The image projector of claim 1 , wherein said controller is configured to:
(a) determine a maximum required intensity of a pixel of the digital image in a part of the digital image corresponding to each of said regions of the two-dimensional array;
(b) determine a reduced illumination level for at least one of said regions sufficient to generate the corresponding maximum required intensity within said regions;
(c) generate a modified pixel intensity map for pixels within said at least one region for generating a required projected image intensity based on said reduced illumination level; and
(d) actuate said illumination arrangement to illuminate at least one region with said reduced illumination level while said pixel elements within said at least one region are actuated according to said modified pixel intensity map.
10. The image projector of claim 1 , wherein said illumination arrangement delivers said illumination from an illumination stop, the image projector further comprising illumination optics deployed in an optical path between said illumination stop and said spatial light modulator, wherein said illumination optics and said collimating arrangement are configured such that an image of said illumination stop falls substantially on the exit stop.
11. The image projector of claim 10 , wherein said illumination optics and said collimating arrangement are implemented using reflective optical components, and wherein an optical path from said illumination optics to said exit stop is implemented without an air gap.
12. The image projector of claim 10 , further comprising a diffuser deployed at said illumination stop.
13. The image projector of claim 12 , wherein said diffuser has a substantially linear intensity distribution.
14. The image projector of claim 12 , wherein said diffuser has a rectangular intensity distribution.
15. The image projector of claim 10 , further comprising a scanning arrangement deployed to generate a beam of illumination scanning a range of angles at said illumination stop.
16. The image projector of claim 10 , wherein said spatial light modulator is a reflective spatial light modulator, and wherein illumination is directed towards said spatial light modulator by internal reflection at a surface parallel to a plane of said spatial light modulator followed by reflection at a beam splitter oriented at an angle of substantially 30 degrees to said plane of said spatial light modulator.
17. The image projector of claim 10 , further comprising a light guide formed as a block of transparent material having at least one pair of parallel faces for supporting propagation of a projected image by internal reflection, wherein the exit stop is an entrance to said light guide.
18. The image projector of claim 1 , wherein said controller updates pixel elements of said plurality of regions of said two-dimensional array synchronously with the sequential illumination of said plurality of regions such that pixel values in at least one of said plurality of regions are updated during a period of illumination of another of said plurality of regions.
19. The image projector of claim 1 , wherein said controller updates pixel elements of said plurality of regions of said two-dimensional array synchronously with the sequential illumination of said plurality of regions such that pixel values in a first of said plurality of regions are updated during a period of illumination of a second of said plurality of regions with a first color and of a third of said plurality of regions with a second color.
20. The image projector of claim 1 , wherein said illumination arrangement is configured to generate at least two simultaneous beams of at least two different colors in different angular positions, said at least two simultaneous beams being generated by a side-by-side arrangement of laser light sources of different colors.