Geometrical waveguide illuminator and display based thereon
An illuminator for illuminating a display panel includes a lightguide with an array of buried slanted bulk reflectors that out-couple portions of the light beam propagating in the lightguide through one of the lightguide surfaces. Polarization beam-splitting slanted surfaces may be used to provide polarized output. Such an illuminator may be used with a reflective display panel operating by polarization. The beam-splitting slanted surfaces operate as a polarizer, providing polarized illuminating light. The light reflected by the reflective panel may propagate back through the illuminator, and the polarization beam-splitting slanted surfaces may operate also as analyzer.
1. An illuminator for a display panel, the illuminator comprising:
a lightguide configured to propagate a light beam along a length dimension of the lightguide by a series of internal reflections from first and second opposed outer surfaces of the lightguide, wherein the first and second surfaces are separated by a lightguide thickness dimension perpendicular to the length dimension; a first plurality of slanted partial bulk reflectors inside the lightguide configured to out-couple portions of the light beam along the length dimension of the lightguide through the first surface, the out-coupled light beam portions forming an output light beam for illuminating the display panel; and
a diffuser upstream of the lightguide and configured to scatter the light beam within a pre-defined light cone having an apex angle no greater than four degrees.
2. The illuminator of claim 1 , wherein the slanted partial reflectors of the first plurality comprise polarization-selective reflectors configured to reflect light at a first polarization and transmit light at a second, orthogonal polarization.
3. The illuminator of claim 2 , further comprising a linear transmission polarizer disposed proximate the second surface of the lightguide and configured to transmit light at the second polarization.
4. The illuminator of claim 1 , wherein the slanted partial bulk reflectors extend from the first surface to the second surface of the lightguide.
5. The illuminator of claim 1 , further comprising a partial reflector buried in the lightguide and disposed at a distance from and parallel to the first and second opposed outer surfaces in an optical path upstream of the first plurality of slanted partial bulk reflectors, wherein the partial reflector is configured to split the light beam to increase a spatial density of the light beam portions out-coupled by the first plurality of slanted partial bulk reflectors from the lightguide.
6. The illuminator of claim 1 , further comprising a second plurality of slanted partial bulk reflectors disposed inside the lightguide upstream of the first plurality of slanted partial bulk reflectors, wherein the second plurality of slanted partial bulk reflectors is configured to expand the light beam along a width dimension of the lightguide to obtain an expanded light beam and to direct the expanded light beam towards the first plurality of slanted partial bulk reflectors.
7. The illuminator of claim 1 , further comprising a tiltable reflector in an optical path upstream of the lightguide, wherein the tiltable reflector is configured to vary an angle of incidence of the light beam onto the lightguide.
8. The illuminator of claim 1 , wherein
a reflectivity of at least some of the slanted partial bulk reflectors of the first plurality is greater than 50%.
9. The illuminator of claim 1 , wherein the slanted partial bulk reflectors of the first plurality are parallel to one another to within 0.5 degrees, and wherein at least some of the slanted partial bulk reflectors of the first plurality are angled with respect to each other by at least 0.2 degrees.
10. The illuminator of claim 1 , wherein the lightguide thickness is less than 0.5 mm.
11. The illuminator of claim 1 , wherein a width of the slanted partial bulk reflectors of the first plurality between the first and second opposed outer surfaces of the lightguide is less than 0.7 mm.
12. A display device comprising:
a display panel comprising a substrate and a pixel array supported by the substrate;
a lightguide configured to illuminate the pixel array of the display panel, the lightguide comprising opposed first and second outer surfaces for guiding a light beam in the lightguide and a plurality of slanted partial bulk reflectors extending between the first and second surfaces at an acute angle thereto and configured to reflect, portions of the light beam out of the lightguide to impinge onto the pixel array of the display panel; and
a focusing element configured to form, downstream of the focusing element, an array of light spots from the portions of the light beam reflected out of the lightguide, such that in operation, an array of optical power density peaks is formed at the pixel array due to Talbot effect.
13. The display device of claim 12 , further comprising an ocular lens downstream of the pixel array, wherein the ocular lens is configured to convert an image in spatial domain displayed by the display panel into an image in angular domain downstream of the ocular lens, for observation by a user's eye downstream of the ocular lens.
14. The display device of claim 13 , wherein:
the pixel array is a reflective pixel array; and
the lightguide is disposed between the display panel and the ocular lens;
wherein in operation, the light beam portions reflected by the plurality of slanted partial bulk reflectors impinge onto the reflective pixel array, get reflected thereby, propagate back through the lightguide, and impinge onto the ocular lens.
15. The display device of claim 14 , wherein:
the reflective pixel array is configured to controllably tune polarization of the impinging light beam portions from a first polarization state to a second, orthogonal polarization state; and
the slanted reflectors are polarization-selective and configured to reflect light in the first polarization state and to transmit light in the second polarization state.
16. The display device of claim 14 , further comprising a linear transmission polarizer between the lightguide and the ocular lens.
17. The display device of claim 13 , wherein:
the pixel array comprises a transmissive pixel array; and
the display panel is disposed between the lightguide and the ocular lens;
wherein in operation, the light beam portions reflected by the plurality of slanted partial bulk reflectors propagate through the substrate, through the transmissive pixel array, and impinge onto the ocular lens.
18. The display device of claim 12 , wherein at least one of:
a thickness of the lightguide is less than 0.5 mm; or
a width of the slanted partial bulk reflectors between the opposed first and second outer surfaces of the lightguide is less than 0.7 mm.
19. A method for illuminating a display panel, the method comprising:
propagating a light beam in a lightguide along a length dimension by a series of internal reflections from first and second opposed outer surfaces of the lightguide;
out-coupling portions of the light beam along the length dimension of the lightguide through the first surface using a plurality of slanted partial bulk reflectors inside the lightguide; and
forming an output light beam from the out-coupled light beam portions for illuminating the display panel,
wherein at least one of:
a thickness of the lightguide is less than 0.5 mm; or
a width of the slanted partial bulk reflectors between the opposed first and second outer surfaces of the lightguide is less than 0.7 mm.
20. The method of claim 19 , wherein the display panel is a reflective display panel, the method further comprising:
reflecting the output light beam by the reflective display panel; and
propagating the output light beam reflected by the reflective display panel through the lightguide.