Reflective display comprising coupling lightguides folded at different fold angles
In some aspects, a display comprises a reflective spatial light modulator, a light source, and a film-based lightguide having an array of coupling lightguides in a form of strips of the film extending from and continuous with a lightguide region of the film. The coupling lightguides are folded and stacked behind the reflective spatial light modulator along fold lines oriented at different orientation angles. In some embodiments, the coupling lightguides comprise lateral edges with curved portions. In some embodiments, the coupling lightguides are tapered. In some embodiments, the reflective spatial light modulator comprises an active area in a shape of a polygon with more than four sides or an active area defined by a boundary with a circular, semi-circular, or arcuate portion.
1. A display comprising:
a reflective spatial light modulator comprising a front viewing side and a back side opposite the front viewing side;
a lightguide formed from a film having opposing surfaces with a thickness not greater than 0.5 millimeters therebetween, the lightguide positioned on the front viewing side of the reflective spatial light modulator and comprising a lightguide region, a light emitting region, and a plurality of coupling lightguides in a form of strips of the film extending from and continuous with the lightguide region, and each coupling lightguide of the plurality of coupling lightguides terminates in a bounding edge;
a light source positioned to emit light into the bounding edges, the light propagating within the plurality of coupling lightguides to the lightguide region; and
a plurality of light extraction features arranged within the light emitting region, the plurality of light extraction features frustrate totally internally reflected light from the light source propagating in the lightguide region such that light exits the lightguide in the light emitting region and propagates to the reflective spatial light modulator,
wherein the plurality of coupling lightguides are folded along linear fold lines behind the reflective spatial light modulator such that the plurality of coupling lightguides are stacked on the back side of the reflective spatial light modulator with the bounding edges positioned to receive the light from the light source, and the linear fold lines of the plurality of coupling lightguides are oriented at different fold angles such that a difference between fold angles of adjacent coupling lightguides of the plurality of coupling lightguides is greater than 5 degrees.
2. The display of claim 1 wherein each fold angle of the fold angles directs the bounding edge toward a center of the light emitting region in a width direction orthogonal to a thickness direction of the film.
3. The display of claim 1 wherein the plurality of coupling lightguides comprise linear lateral edge sections proximate the linear fold lines that are substantially parallel to each other and perpendicular to the linear fold lines.
4. The display of claim 1 wherein the reflective spatial light modulator comprises a designed illumination angle for ambient light illumination of the reflective spatial light modulator and a primary axis of illumination defined as an in-plane component of the designed illumination angle in a plane perpendicular to a thickness direction of the reflective spatial light modulator, and optical axes of light from the plurality of coupling lightguides are within 10 degrees of the primary axis of illumination when entering the light emitting region.
5. The display of claim 4 where the primary axis of illumination is a downward vertical direction when viewing the display.
6. The display of claim 1 wherein the reflective spatial light modulator comprises a designed illumination angle for ambient light illumination of the reflective spatial light modulator and a primary axis of illumination defined as an in-plane component of the designed illumination angle in a plane perpendicular to a thickness direction of the reflective spatial light modulator, the plurality of coupling lightguides comprise lateral edges, and the lateral edges join the lightguide region at an angle less than 10 degrees from the primary axis of illumination.
7. The display of claim 1 wherein the reflective spatial light modulator comprises a designed illumination angle for ambient light illumination of the reflective spatial light modulator and a primary axis of illumination defined as an in-plane component of the designed illumination angle in a plane perpendicular to a thickness direction of the reflective spatial light modulator, the plurality of coupling lightguides comprises a central coupling lightguide with a fold angle of 90 degrees from the primary axis of illumination.
8. The display of claim 7 wherein the plurality of coupling lightguides comprises coupling lightguides on opposite sides of the central coupling lightguide with fold angles at a same magnitude but opposite in sign.
9. The display of claim 1 wherein the reflective spatial light modulator comprises an active area defined by a boundary with a circular, semi-circular, or arcuate portion.
10. The display of claim 1 wherein the reflective spatial light modulator comprises an active area in a shape of a polygon with more than four sides.
11. The display of claim 10 wherein the linear fold lines are substantially parallel to two or more sides of the more than four sides.
12. The display of claim 1 wherein the plurality of coupling lightguides comprise lateral edges that are asymmetric in a width direction orthogonal to a thickness direction of the film.
13. The display of claim 1 wherein the plurality of coupling lightguides comprise tapered lateral edges that reduce widths of each coupling lightguide of the plurality of coupling lightguides from the lightguide region to the bounding edge.
14. The display of claim 1 wherein the plurality of coupling lightguides comprise tapered lateral edges that reduce widths of each coupling lightguide of the plurality of coupling lightguides from the lightguide region to the bounding edge, and the tapered lateral edges comprise portions curved in a plane orthogonal to a thickness direction of the film.
15. The display of claim 1 wherein each coupling lightguide of the plurality of coupling lightguides comprises lateral edges with portions curved in a plane orthogonal to a thickness direction of the coupling lightguide.
16. The display of claim 15 wherein one or more coupling lightguides of the plurality of coupling lightguides comprise:
a first lateral edge of the one or more coupling lightguides with a radius of curvature r 1 along a section of the first lateral edge;
a second lateral edge of the one or more coupling lightguides opposite the first lateral edge with a radius of curvature r 2 along a section of the second lateral edge; and
a width, w, at a bounding edge in a direction orthogonal to an optical axis of the light source and orthogonal to the thickness direction of the coupling lightguide, and an average radius-to-width ratio, (r 1 +r 2 )/2w, of the one or more coupling lightguides is greater than 6.
17. A display comprising:
a reflective spatial light modulator comprising a front viewing side and a back side opposite the front viewing side;
a lightguide formed from a film having opposing surfaces with a thickness not greater than 0.5 millimeters therebetween, the lightguide positioned on the front viewing side of the reflective spatial light modulator and comprising a lightguide region, a light emitting region, and a plurality of coupling lightguides in a form of strips of the film extending from and continuous with the lightguide region, and each coupling lightguide of the plurality of coupling lightguides terminates in a bounding edge;
a light source positioned to emit light into the bounding edges, the light propagating within the plurality of coupling lightguides to the lightguide region; and
a plurality of light extraction features arranged within the light emitting region, the plurality of light extraction features frustrate totally internally reflected light from the light source propagating in the lightguide region such that light exits the lightguide in the light emitting region and propagates to the reflective spatial light modulator,
wherein the plurality of coupling lightguides are folded along linear fold lines behind the reflective spatial light modulator such that the plurality of coupling lightguides are stacked on the back side of the reflective spatial light modulator with the bounding edges positioned to receive the light from the light source, the linear fold lines of the plurality of coupling lightguides are oriented at different fold angles, and the plurality of coupling lightguides comprise lateral edges with curved portions.
18. The display of claim 17 wherein the plurality of coupling lightguides comprise tapered lateral edges that reduce widths of each coupling lightguide of the plurality of coupling lightguides from the lightguide region to the bounding edge.
19. The display of claim 17 wherein the lateral edges of each coupling lightguide of the plurality of coupling lightguides comprise linear portions proximate the linear fold lines that are substantially parallel to each other.
20. A display comprising:
a reflective spatial light modulator comprising a front viewing side and a back side opposite the front viewing side;
a lightguide formed from a film having opposing surfaces with a thickness not greater than 0.5 millimeters therebetween, the lightguide positioned on the front viewing side of the reflective spatial light modulator and comprising a lightguide region, a light emitting region, and a plurality of coupling lightguides in a form of strips of the film extending from and continuous with the lightguide region, and each coupling lightguide of the plurality of coupling lightguides terminates in a bounding edge;
a light source positioned to emit light into the bounding edges, the light propagating within the plurality of coupling lightguides to the lightguide region; and
a plurality of light extraction features arranged within the light emitting region, the plurality of light extraction features frustrate totally internally reflected light from the light source propagating in the lightguide region such that light exits the lightguide in the light emitting region and propagates to the reflective spatial light modulator,
wherein the reflective spatial light modulator comprises an active area defined by a boundary with a circular, semi-circular, or arcuate portion, or an active area in a shape of a polygon with more than four sides, the plurality of coupling lightguides are folded along linear fold lines behind the reflective spatial light modulator such that the plurality of coupling lightguides are stacked on the back side of the reflective spatial light modulator with the bounding edges positioned to receive the light from the light source, and the linear fold lines of the plurality of coupling lightguides are oriented at different fold angles.