Reflective spatial light modulator display with stacked light guides and method
A reflective display includes a reflective spatial light modulator and a front light having a lightguide formed by an array of film-based lightguides coupled into a lightguide region of the lightguide. One or more light sources emit light into the array of lightguides, with light extraction features frustrating totally internally reflect light within the lightguide region such that the light exits the lightguide through a cladding region toward a light redirecting optical element that redirects the light toward a reflective spatial light modulator.
1. A display comprising:
a. a reflective spatial light modulator comprising a reflective surface;
b. a lightguide formed from a film having opposing faces with a thickness not greater than about 0.5 millimeters therebetween, the lightguide having an array of coupling lightguides continuous with a lightguide region of the lightguide, wherein:
i). each coupling lightguide of the array of coupling lightguides terminates in a bounding edge; and
ii). each coupling lightguide is folded in a fold region such that the bounding edges of the array of coupling lightguides are stacked;
c. a light source disposed to emit light into the stacked bounding edges, the light propagating within the array of coupling lightguides to the lightguide region, with light from each coupling lightguide combining and totally internally reflecting within the lightguide region;
d. a cladding region having a first side optically coupled to the lightguide and an opposing second side;
e. a light redirecting optical element optically coupled to the second side of the cladding region; and
f. a plurality of light extraction features arranged in a pattern that varies spatially in a light emitting region of the lightguide, each of the plurality of light extraction features to frustrate totally internally reflected light within the lightguide region such that frustrated totally internally reflected light exits the lightguide in the light emitting region into the cladding region with a first angle of peak luminous intensity in the cladding region and a first angular full-width at half-maximum intensity in a first output plane in the cladding region,
wherein the light redirecting optical element redirects the frustrated totally internally reflected light exiting the lightguide toward the reflective spatial light modulator such that the frustrated totally internally reflected light after redirection has a second angle of peak luminous intensity different from the first angle of peak luminous intensity and the second angle of peak luminous intensity is within an angular range from 0 to 30 degrees from a direction perpendicular to the reflective surface of the reflective spatial light modulator.
2. The display of claim 1 wherein the first angular full-width at half-maximum intensity is less than 10 degrees.
3. The display of claim 1 wherein the cladding region comprises an adhesive layer.
4. The display of claim 1 wherein the reflective spatial light modulator is positioned between the lightguide and the light source.
5. The display of claim 1 wherein the light emitting region of the lightguide has a haze less than 3%.
6. The display of claim 1 wherein the plurality of light extraction features comprises a plurality of volumetric light scattering features.
7. The display of claim 1 wherein the first angular full-width at half-maximum intensity is less than 20 degrees.
8. The display of claim 7 wherein light from the lightguide exiting the reflective spatial light modulator has a second angular full-width at half maximum intensity in the first output plane larger than the first angular full-width at half maximum intensity due at least in part to the light redirecting optical element.
9. The display of claim 1 wherein the light redirecting optical element comprises one or more linear light redirecting features.
10. The display of claim 9 wherein the light redirecting optical element comprises a one-dimensional array of linear light redirecting features.
11. The display of claim 9 wherein the one or more linear light redirecting features redirect light based at least partially on total internal reflection.
12. The display of claim 11 wherein the lightguide is positioned between the light redirecting optical element and the reflective spatial light modulator.
13. A display comprising:
a. a reflective spatial light modulator comprising a reflective surface;
b. a lightguide having opposing faces with a thickness not greater than about 0.5 millimeters therebetween wherein light propagates by total internal reflection between the opposing faces, the lightguide comprising:
i). a core layer;
ii). a cladding layer having a first side optically coupled to the core layer and an opposing second side;
iii). a light redirecting optical element optically coupled to the second side of the cladding layer;
iv). an array of coupling lightguides continuous with a lightguide region of the lightguide, each coupling lightguide of the array of coupling lightguides terminates in a bounding edge, and each coupling lightguide is folded in a fold region such that the bounding edges of the array of coupling lightguides are stacked; and
v). a light emitting region comprising a plurality of light extraction features arranged in a pattern that varies spatially in the light emitting region, each of the plurality of light extraction features to frustrate totally internally reflected light propagating within the core layer such that light exits the core layer in the light emitting region into the cladding layer with an angular full-width at half-maximum intensity in an output plane in the cladding layer,
wherein the lightguide has an average thickness in the light emitting region, the light emitting region has a largest dimension in a plane of the light emitting region, and the largest dimension of the light emitting region divided by the average thickness of the lightguide in the light emitting region is greater than 100; and
c. a light source disposed to emit light into the stacked bounding edges, the light propagating within the array of coupling lightguides to the lightguide region, with light from each coupling lightguide combining and totally internally reflecting within the lightguide region,
wherein the light redirecting optical element redirects frustrated totally internally reflected light toward the reflective spatial light modulator such that the frustrated totally internally reflected light after redirection has an angle of peak luminous intensity within an angular range from 0 to 30 degrees from a direction perpendicular to the reflective surface of the reflective spatial light modulator.
14. The display of claim 13 wherein the angular full-width at half-maximum intensity is less than 20 degrees.
15. The display of claim 13 wherein the angular full-width at half-maximum intensity is less than 10 degrees.
16. The display of claim 13 wherein the core layer is positioned between the light redirecting optical element and the reflective spatial light modulator.
17. The display of claim 13 wherein the light emitting region comprises a light emitting surface, the plurality of light extraction features each have a largest dimension in a plane parallel to the light emitting surface, and an average of the largest dimensions of the plurality of light extracting features is less than 0.050 millimeters.
18. The display of claim 17 wherein the largest dimension of the light emitting region divided by the average thickness of the lightguide in the light emitting region is greater than 500.
19. A method of producing a display, the method comprising:
a. forming a lightguide from a film having opposing faces with a thickness not greater than about 0.5 millimeters therebetween, the lightguide having an array of coupling lightguides continuous with a lightguide region of the lightguide, each coupling lightguide of the array of coupling lightguides terminating at a bounding edge;
b. folding each coupling lightguide in a fold region such that the bounding edges of the array of coupling lightguides are stacked;
c. positioning at least one light source to emit light into the stacked bounding edges, the light propagating within the array of coupling lightguides to the lightguide region of the lightguide, with light from each coupling lightguide combining and totally internally reflecting within the lightguide region;
d. optically coupling a first side of a cladding region to the lightguide;
e. optically coupling a light redirecting element to a second side of the cladding region opposite the first side;
f. forming a plurality of light extraction features in a pattern that varies spatially in a light emitting region of the lightguide, the plurality of light extraction features to frustrate totally internally reflected light within the lightguide region such that frustrated totally internally reflected light exits the lightguide in the light emitting region into the cladding region with an angular full-width at half-maximum intensity in an output plane in the cladding region such that the light redirecting optical element redirects the frustrated totally internally reflected light exiting the lightguide toward the reflective spatial light modulator, the frustrated totally internally reflected light after redirection has a an angle of peak luminous intensity within an angular range from 0 to 30 degrees from a direction perpendicular to the reflective surface of the reflective spatial light modulator; and
g. optically coupling a reflective spatial light modulator to the lightguide.
20. The method of claim 19 wherein the angular full-width at half-maximum intensity is less than 20 degrees.
21. The method of claim 19 wherein optically coupling a reflective spatial light modulator to the lightguide comprises positioning the lightguide between the light redirecting optical element and the reflective spatial light modulator.
22. The method of claim 19 wherein the cladding region comprises a first adhesive layer and optically coupling a reflective spatial light modulator to the lightguide comprises adhering the reflective spatial light modulator to the lightguide in the light emitting region using a second adhesive layer.