Image projector with polarizing catadioptric collimator
An image projector for injecting a collimated image into an entrance aperture of a lightguide employs collimating optics including a polarizing catadioptric arrangement to provide enhanced proximity of the principal plane of the collimating optics to the entrance aperture of the lightguide, thereby reducing the size of the optics or allowing an enlarged field of view for optics of a given size. Disclosed embodiments employ a front-lit polarization-modifying spatial light modulator (SLM) illuminated via a polarizing beam splitter (PBS) prism with a 30-degree or 45-degree PBS angle, laser scanning illumination arrangements, with or without an SLM, and active-matrix image generators combined via a dichroic combiner cube.
1. An image projector for injecting a collimated image into an entrance aperture of a lightguide, the image projector comprising:
(a) a polarization-modifying spatial light modulator (SLM) deployed for modifying a polarization of illumination according to image data supplied to said SLM;
(b) an illumination arrangement for illuminating said SLM with polarized illumination;
(c) a polarization-selective element deployed to select light from said SLM corresponding to an image; and
(d) collimating optics for collimating the light corresponding to the image so as to provide the collimated image at the entrance aperture of the lightguide, wherein said collimating optics includes a polarizing catadioptric arrangement comprising, sequentially:
(i) a first quarter-wave plate;
(ii) a first optical surface implemented as a partial reflector;
(iii) a second quarter-wave plate; and
(iv) a second optical surface implemented as a polarization-selective reflector,
wherein at least one of said first and second optical surfaces is implemented as a non-planar surface with optical power which acts twice on the light, once as a refractive lens surface and once as a reflective lens.
2. The image projector of claim 1 , wherein said polarization-selective element is a polarizing beam splitter (PBS) integrated into a prism, and wherein said illumination arrangement directs illumination so as to reflect from said PBS towards said SLM.
3. The image projector of claim 2 , wherein said PBS is inclined at an angle of 30 degrees to a surface of said SLM, the image projector further comprising an angularly-selective reflector deployed parallel to said SLM between said SLM and said PBS, said illumination arrangement directing illumination so as to reflect from said angularly-selective reflector towards said PBS, and to reflect from said PBS towards said SLM, said angularly-selective reflector being reflective for visible light incident at an angle of incidence of 60 degrees and substantially transparent to visible light incident at an angle of incidence less than 30 degrees.
4. The image projector of claim 2 , wherein said PBS is inclined at an angle of 45 degrees to a surface of said SLM, the image projector further comprising a quarter-wave plate and an illumination-optics reflective lens associated with a face of said prism for directing illumination that has passed through said PBS back towards said PBS to be reflected at said PBS towards said SLM.
5. The image projector of claim 4 , wherein said illumination arrangement further comprises a light source associated with an illumination aperture from which light propagates through said prism towards said illumination-optics reflective lens, and wherein said illumination-optics reflective lens and said collimating optics are configured to image said illumination aperture to the entrance aperture of the lightguide.
6. The image projector of claim 4 , wherein said illumination arrangement further comprises a scanning mirror for scanning a beam of illumination through a range of angles about at least one tilt axis, said scanning mirror being deployed to direct the beam of illumination through said prism towards said illumination-optics reflective lens, and wherein said illumination-optics reflective lens and said collimating optics are configured to image said scanning mirror to the entrance aperture of the lightguide.
7. The image projector of claim 2 , wherein said second optical surface is a planar surface that is bonded to an image input surface of the lightguide.
8. The image projector of claim 2 , wherein said first optical surface is a planar surface that is bonded to an output surface of said prism.
9. The image projector of claim 2 , wherein said first optical surface is a non-planar surface that is bonded to a corresponding non-planar output surface of said prism.
10. The image projector of claim 1 , wherein said illumination arrangement comprises a lightguide having a pair of mutually-parallel major surfaces for supporting propagation of illumination by internal reflection at said major surfaces, and a plurality of mutually-parallel partially-reflecting coupling-out surfaces internal to said lightguide and oriented obliquely to said major surfaces so as to couple out illumination towards said SLM.
11. An image projector for injecting a collimated image into an entrance aperture of a lightguide, the image projector comprising:
(a) a beam splitter integrated into a prism;
(b) an image generator configured for generating an image at an image plane associated with a third face of said prism; and
(c) collimating optics for collimating light of the image so as to provide a collimated image at the entrance aperture of the lightguide, wherein said collimating optics includes a polarizing catadioptric arrangement comprising, sequentially:
(i) a first quarter-wave plate;
(ii) a first optical surface implemented as a partial reflector;
(iii) a second quarter-wave plate; and
(iv) a second optical surface implemented as a polarization-selective reflector,
wherein at least one of said first and second optical surfaces is implemented as a non-planar surface with optical power which acts twice on the light, once as a refractive lens surface and once as a reflective lens.
12. The image projector of claim 11 , wherein said beam splitter is a polarizing beam splitter (PBS), the image projector further comprising:
(a) an illumination arrangement comprising at least one light source for generating a modulated intensity beam of light and a scanning mirror for scanning the beam of light through a range of angles about at least one tilt axis, said scanning mirror being deployed to direct the beam of light into a first face of said prism;
(b) an illumination-optics reflective lens and a first quarter-wave plate associated with a second face of said prism for directing light that has passed through said prism back towards said PBS;
(c) a beam-spreading reflector and a second quarter-wave plate associated with the third face of said prism; and
(d) a controller for synchronously modulating an intensity of said light source and controlling said scanning mirror so as to generate a time-averaged intensity distribution of light at said beam-spreading reflector corresponding to an image.
13. The image projector of claim 11 , wherein said beam splitter is a dichroic mirror, and wherein said image generator is a first active-matrix image generator generating an image emitted as light of at least a first wavelength that is reflected by said dichroic mirror, the image projector further comprising a second active-matrix image generator associated with a second face of said prism, said second active-matrix image generator generating an image emitted as light of at least a second wavelength that is transmitted by said dichroic mirror so as to be combined with the light of said first wavelength on reaching said collimating optics.
14. The image projector of claim 13 , further comprising a second dichroic mirror deployed within said prism non-parallel to said dichroic mirror, said second dichroic mirror being transparent to light of said first and second wavelengths and reflective to light of a third wavelength, the image projector further comprising a third active-matrix image generator associated with a first face of said prism, said third active-matrix image generator generating an image emitted as light of at least the third wavelength that is reflected by said second dichroic mirror so as to be combined with the light of said first and second wavelengths on reaching said collimating optics.
15. The image projector of claim 11 , wherein said second optical surface is a planar surface that is bonded to an image input surface of the lightguide.
16. The image projector of claim 11 , wherein said first optical surface is a planar surface that is bonded to an output surface of said prism.
17. The image projector of claim 11 , wherein said first optical surface is a non-planar surface that is bonded to a corresponding non-planar output surface of said prism.