Optically coupled toroidal lens:hemi-bead brightness enhancer for total internal reflection modulated image displays
View Patent ↗A brightness enhancing structure for a reflective display. A plurality of transparent hemi-beads form a film substantially covering and protruding inwardly from the structure's inward surface. A corresponding plurality of microstructured toroidal lenses are provided on the structure's outward side. Each lens is optically coupled to an adjacent one of the hemi-beads to redirect incident light rays toward the adjacent hemi-bead, such that the redirected light is totally internally reflected by the hemi-bead and reflected back in a direction approximately opposite that of the incident rays. This substantially reduces undesirable dark, non-reflective circular regions of each hemi-bead which would otherwise exist in the absence of this invention.
1. A brightness enhancing structure for a reflective display, the structure comprising a transparent sheet having a transparent hemi-bead monolayer array on an inward side of the sheet and a transparent microstructured surface on an outward side of the sheet, the hemi-bead monolayer array further comprising a plurality of approximately hemispherical transparent hemi-beads substantially covering and protruding inwardly from the inward surface of the sheet, the microstructured surface further comprising, for substantially each one of the hemi-beads, an adjacent structure for redirecting incident light toward the one of the hemi-beads such that the redirected light is totally internally reflected by the one of the hemi-beads.
2. A brightness enhancing structure as defined in claim 1 , each one of the adjacent structures further comprising a lens structure having:
an annular light focusing zone substantially coincident with an annular light reflecting region of the one of the hemi-beads, and
a perpendicular axis of symmetry substantially coincident with a perpendicular axis of symmetry of the one of the hemi-beads.
3. A brightness enhancing structure as defined in claim 2 , the lens structure further comprising a substantially toroidal lens having a minor radius r t .
4. A brightness enhancing structure as defined in claim 2 , the lens structure further comprising a conical approximation of a toroidal lens having a minor radius r t .
5. A brightness enhancing structure as defined in claim 3 , further comprising a transparent central portion having a thickness d optically coupled between the hemi-bead monolayer array and the microstructured surface.
6. A brightness enhancing structure as defined in claim 4 , further comprising a transparent central portion having a thickness d optically coupled between the hemi-bead monolayer array and the microstructured surface.
7. A brightness enhancing structure as defined in claim 5 , wherein:
r
t
=
r
o
=
r
1
+
r
2
2
where r 1 is the radius of the one of the hemi-beads and r 2 is the radius of a non light-reflecting region of the one of the hemi-beads which would exist in the absence of the toroidal lens.
8. A brightness enhancing structure as defined in claim 6 , wherein:
r
t
=
r
o
=
r
1
+
r
2
2
where r 1 is the radius of the one of the hemi-beads and r 2 is the radius of a non light-reflecting region of the one of the hemi-beads which would exist in the absence of the conical approximation of the toroidal lens.
9. A brightness enhancing structure as defined in claim 7 , wherein d has a value d 0 :
d
o
=
(
η
o
η
1
-
η
o
)
r
0
where η 0 is the refractive index of a medium on the outward side of the sheet and η 1 is the refractive index of the one of the hemi-beads.
10. A brightness enhancing structure as defined in claim 8 , wherein d has a value d 0 :
d
o
=
(
η
o
η
1
-
η
o
)
r
0
where η 0 is the refractive index of a medium on the outward side of the sheet and η 1 is the refractive index of the one of the hemi-beads.
11. A brightness enhancing structure as defined in claim 5 , wherein the toroidal lens is sized and positioned, relative to the one of the hemi-beads, to align a focal ring of the toroidal lens substantially coplanar with and substantially centered with respect to an outward surface of the one of the hemi-beads.
12. A brightness enhancing structure as defined in claim 11 , wherein the toroidal lens is further sized and positioned, relative to the one of the hemi-beads, so that the focal ring of the toroidal lens is substantially coextensive with a non light-reflecting region of the one of the hemi-beads which would exist in the absence of the toroidal lens.
13. A brightness enhancing structure as defined in claim 6 , wherein the conical approximation of the toroidal lens is sized and positioned, relative to the one of the hemi-beads, to align a focal ring of the conical approximation of the toroidal lens substantially coplanar with and substantially centered with respect to an outward surface of the one of the hemi-beads.
14. A brightness enhancing structure as defined in claim 13 , wherein the conical approximation of the toroidal lens is further sized and positioned, relative to the one of the hemi-beads, so that the focal ring of the conical approximation of the toroidal lens is substantially coextensive with a non light-reflecting region of the one of the hemi-beads which would exist in the absence of the conical approximation of the toroidal lens.
15. A brightness enhancing structure as defined in claim 9 , wherein d has a value d=0.5d 0 .
16. A brightness enhancing structure as defined in claim 10 , wherein d has a value d=0.5d 0 .
17. A brightness enhancing structure as defined in claim 7 , wherein r t has a value r t =0.8r 0 .
18. A brightness enhancing structure as defined in claim 8 , wherein r t has a value r t =0.8r 0 .
19. A brightness enhancing structure as defined in claim 9 , wherein d has a value d=0.5d 0 and r t has a value r t =0.8r 0 .
20. A brightness enhancing structure as defined in claim 10 , wherein d has a value d=0.5d 0 and r t has a value r t =0.8r 0 .
21. A reflective display having a brightness enhancing structure as defined in claim 1 .
22. A reflective display having a brightness enhancing structure as defined in claim 2 .
23. A reflective display having a brightness enhancing structure as defined in claim 3 .
24. A reflective display having a brightness enhancing structure as defined in claim 4 .
25. A reflective display having a brightness enhancing structure as defined in claim 5 .
26. A reflective display having a brightness enhancing structure as defined in claim 6 .
27. A reflective display having a brightness enhancing structure as defined in claim 7 .
28. A reflective display having a brightness enhancing structure as defined in claim 8 .
29. A reflective display having a brightness enhancing structure as defined in claim 9 .
30. A reflective display having a brightness enhancing structure as defined in claim 10 .
31. A reflective display having a brightness enhancing structure as defined in claim 11 .
32. A reflective display having a brightness enhancing structure as defined in claim 12 .
33. A reflective display having a brightness enhancing structure as defined in claim 13 .
34. A reflective display having a brightness enhancing structure as defined in claim 14 .
35. A method of enhancing the brightness of a reflective display, the method comprising:
(a) providing a transparent sheet having an inward surface and an outward surface;
(b) substantially covering the inward surface of the sheet with a plurality of inwardly protruding, approximately hemispherical, transparent hemi-beads; and
(c) redirecting incident light through the sheet toward each one of the hemi-beads, such that the redirected light is totally internally reflected by the hemi-beads.
36. A method as defined in claim 35 , wherein the redirecting incident light further comprises providing a plurality of substantially toroidal lenses on the outward side of the sheet.
37. A method as defined in claim 36 , further comprising sizing and positioning each toroidal lens, relative to an adjacent one of the hemi-beads, to align a focal ring of the toroidal lens substantially coplanar with and substantially centered with respect to an outward surface of the adjacent one of the hemi-beads.
38. A method as defined in claim 37 , further comprising sizing and positioning each toroidal lens, relative to an adjacent one of the hemi-beads, to align the focal ring substantially coextensively with a non light-reflecting region of the one of the hemi-beads which would exist in the absence of the toroidal lens.