Illumination apparatus having an array of micro-LEDs and a plurality of catadioptric optical elements configured to output light from the array of micro-LEDs

1. An illumination apparatus comprising:

a plurality of LEDs arranged in an LED array, wherein the plurality of LEDs are micro-LEDs or mini-LEDs, each of the plurality of LEDs being arranged to output light having a respective light output distribution; and

a plurality of catadioptric optical elements arranged in a catadioptric optical array, each catadioptric optical element comprising a reflective surface and a transmissive surface facing the reflective surface, wherein:

for each catadioptric optical element, the reflective surface is arranged to receive light output from one or more of the LEDs through the transmissive surface and to reflect the received light back through the transmissive surface, thereby to provide re-directed light having a respective light output distribution,

wherein the light output distribution of the re-directed light provided by each catadioptric optical element has a luminous intensity half maximum solid angle that is smaller than the luminous intensity half maximum solid angle of the light output distribution of the light output by each of the plurality of LEDs.

2. An illumination apparatus according to claim 1 wherein at least some of the light from the plurality of LEDs is guided, at least in part via total internal reflection, within the catadioptric optical array.

3. An illumination apparatus according to claim 1 wherein each of the plurality of LEDs is arranged on a first surface of at least one transmissive LED support substrate; and a transmissive output surface is provided by a second surface of the transmissive LED support substrate; wherein the second surface of the transmissive LED support substrate faces the first surface of the transmissive LED support substrate.

4. An illumination apparatus according to claim 3 wherein the reflective surface of each catadioptric optical element is arranged on a first surface of an input substrate, and a second surface of the input substrate facing the reflective surface comprises a transmissive input surface;

wherein the first surface of the transmissive LED support substrate faces the transmissive input surface.

5. An illumination apparatus according to claim 4 wherein at least some of the light from the plurality of LEDs is guided, at least in part via total internal reflection, within the catadioptric optical array, and wherein the light from the plurality of LEDs that is guided within the catadioptric optical array is guided, at least in part via total internal reflection, between the reflective surface and the transmissive input surface.

6. An illumination apparatus according to claim 3 , wherein a transparent material is provided between the first surface of the transmissive LED support substrate and the transmissive surface of the catadioptric optical element; and the light from the plurality of LEDs that is guided within the catadioptric optical array is guided between the reflective surface and the second surface of the transmissive LED support substrate.

7. An illumination apparatus according to claim 6 , wherein the transparent material is air.

8. An illumination apparatus according to claim 4 , wherein a transparent material with a lower refractive index than a material from which the input substrate is made is arranged between the plurality of LEDs and the transmissive surfaces of the catadioptric optical elements.

9. An illumination apparatus according to claim 3 , further comprising diffuser structures arranged on at least one surface of the transmissive LED support substrate.

10. An illumination apparatus according to claim 4 , wherein for each catadioptric optical element the transmissive surface of the input substrate further comprises a refractive light input structure aligned in correspondence with a respective optical axis of the catadioptric optical element; wherein each refractive light input structure is arranged between the transmissive input surface and the reflective surface of the input substrate.

11. An illumination apparatus according to claim 10 wherein in at least one catadioptric cross-sectional plane through its optical axis the refractive light input structure comprises a plurality of pairs of oppositely inclined refractive input facets.

12. An illumination apparatus according to claim 11 wherein in at least one catadioptric cross-sectional plane the plurality of pairs of inclined input facets are inclined at equal and opposite inclination angles;

and in the plane of the catadioptric optical array the plurality of pairs of inclined refractive input facets are circularly or elliptically symmetric.

13. An illumination apparatus according to claim 10 , wherein the transmissive surface of the input substrate comprises planar regions between the refractive light input structures.

14. An illumination apparatus according to claim 1 , wherein each catadioptric optical element comprises an optical axis.

15. An illumination apparatus according to claim 14 wherein each optical axis is aligned in correspondence with a respective one or more of the LEDs, and each of the LEDs is aligned in correspondence with the optical axis of only one of the catadioptric optical elements.

16. An illumination apparatus according to claim 15 further comprising a further plurality of LEDs arranged in an LED array, wherein the further plurality of LEDs are micro-LEDs or mini-LEDs, and each optical axis is offset from one or more of the LEDs of the further plurality of LEDs, and each of the LEDs of the further plurality of LEDs is offset from the optical axis of at least one of the catadioptric optical elements.

17. An illumination apparatus according to claim 16 , wherein:

for each catadioptric optical element, the reflective surface is arranged to receive light output from one or more of the further plurality of LEDs through the transmissive surface and to reflect the received light back through the transmissive surface, thereby to provide re-directed light having a respective light output distribution, and

the light output distribution of the re-directed light provided by each catadioptric optical element using light output from the further plurality of LEDs has a luminous intensity half maximum solid angle that is greater than the luminous intensity half maximum solid angle of the re-directed light provided by each catadioptric optical element using light output from the plurality of LEDs.

18. An illumination apparatus according to claim 14 , wherein for each catadioptric optical element of the catadioptric optical array, the transmissive surface comprises at least one refractive light output structure arranged on the transmissive surface and aligned in correspondence with the optical axis of the catadioptric optical element.

19. An illumination apparatus according to claim 14 , wherein the input substrate is formed as an integrated body that extends between the optical axes of the plurality of catadioptric optical elements.

20. An illumination apparatus according to claim 14 , wherein the LED support substrate is formed as an integrated body that extends between the optical axes of the plurality of catadioptric optical elements.

21. An illumination apparatus according to claim 1 , wherein the reflective surface of the catadioptric optical array comprises a reflective layer formed on the reflective surface.

22. An illumination apparatus according to claim 21 wherein the reflective layer comprises a metal material.

23. An illumination apparatus according to claim 21 wherein the reflective layer extends to cover the reflective surface of the catadioptric optical array.

24. An illumination apparatus according to claim 1 , wherein the reflective surface of each catadioptric optical element comprises a plurality of light reflecting facets.

25. An illumination apparatus according to claim 1 , wherein the reflective surface of each catadioptric optical element comprises a reflective light input structure that is arranged between the reflective surface and the transmissive input surface of the input substrate;

wherein in at least one catadioptric cross-sectional plane through its optical axis the reflective light input structure comprises a first inner surface and a second inner surface facing the first inner surface;

wherein for each catadioptric optical element of the catadioptric optical array, the refractive light input structure and reflective light input structure are arranged to direct at least some light from the respective aligned at least one LED to be the light that is guided within the catadioptric optical array.

26. An illumination apparatus according to claim 25 wherein in at least one catadioptric cross-sectional plane through its optical axis the first and second inner surfaces comprise curved reflective surfaces.

27. An illumination apparatus according to claim 1 , wherein in at least one catadioptric cross-sectional plane through its optical axis the light reflecting facets of the reflective surface are provided by pairs of inclined facets that are inclined with opposing inclination angles.

28. An illumination apparatus according to claim 1 , wherein the reflective surface comprises reflective planar regions between at least some of the light reflecting facets of the reflective surface.

29. An illumination apparatus according to claim 1 , wherein some of the light reflecting facets of the reflective surface are arranged to direct at least some light through the transmissive output surface of the catadioptric optical element in a direction substantially normal to the transmissive output surface.

30. An illumination apparatus according to claim 1 , wherein in the plane of the catadioptric array the light reflecting facets are circularly or elliptically symmetric about the optical axis of each catadioptric optical element.

31. An illumination apparatus according to claim 1 , wherein the plurality of light reflecting facets of each catadioptric optical element are concentric with the optical axis of said catadioptric optical element.

32. An illumination apparatus according to claim 1 , wherein in at least one catadioptric cross-sectional plane through its optical axis the light reflecting facets of a catadioptric optical element are arranged with a separation that decreases with distance from the optical axis of the catadioptric element.

33. An illumination apparatus according to claim 1 , wherein for each catadioptric optical element the length of the light reflecting facets increases with distance from the optical axis of the respective catadioptric optical element.

34. An illumination apparatus according to claim 1 , wherein for each catadioptric optical element the total area of the light reflecting facets increases with the distance from the optical axis of the respective catadioptric optical element.

35. An illumination apparatus according to claim 1 , wherein for each catadioptric optical element, the total area of the at least one light reflecting facet at a distance, r from the optical axis is proportional to the distance, r.

36. An illumination apparatus according to claim 1 , wherein some of the light reflecting facets arranged on the reflective surface of the catadioptric optical element are arranged to direct light that has not guided within the catadioptric optical array.

37. An illumination apparatus according to claim 36 , wherein the angular light output distribution of light from the refractive light output structure is substantially the same as the angular light output distribution of light from the plurality of reflective light reflecting facets that is transmitted through regions of the transmissive output substrate that do not comprise a refractive light output structure.

38. An illumination apparatus according to claim 1 , comprising a plurality of opaque mask regions wherein the first surface of the transmissive LED support substrate for each catadioptric optical element comprises an opaque mask region that is aligned with an optical axis of the catadioptric optical element;

wherein a respective one or more of the LEDs of the plurality of LEDs is arranged between the mask region and the reflective surface; and

wherein the opaque mask region is provided between the refractive light output structure and the respective one or more of the LEDs of the plurality of LEDs.

39. An illumination apparatus according to claim 38 wherein the plurality of opaque mask regions is provided by LED addressing electrodes.

40. An illumination apparatus according to claim 1 , wherein some light reflecting facets of the reflective surface of the respective catadioptric optical element are arranged to direct light to the refractive light output structure.

41. An illumination apparatus according to claim 1 , wherein in at least one catadioptric cross-sectional plane through its optical axis the refractive light output structure comprises a concave refractive surface arranged to provide negative optical power.

42. An illumination apparatus according to claim 1 , wherein in at least one catadioptric cross-sectional plane the refractive light output structure comprises a plurality of pairs of oppositely inclined transmissive light deflecting facets.

43. An illumination apparatus according to claim 42 wherein for each catadioptric optical element the plurality of pairs of oppositely inclined transmissive light deflecting facets are circularly or elliptically symmetric in the plane of the transmissive output surface about the optical axis of the catadioptric optical element.

44. An illumination apparatus according to claim 1 , further comprising a reflective polariser arranged to provide polarisation recirculation of light reflected from the reflective surface of the catadioptric optical element.

45. An illumination apparatus according to claim 1 , wherein the ratio of luminous intensity half maximum solid angle of the output light cone to the luminous intensity half maximum solid angle of a Lambertian light source is less than 1, preferably less than 50%, more preferably less than 25% and most preferably less than 10%.

46. An illumination apparatus according to claim 1 , further comprising a wavelength conversion layer.

47. An illumination apparatus according to claim 46 wherein the wavelength conversion layer is arranged between the LEDs of the plurality of LEDs and the reflective surface of each catadioptric optical element.

48. An illumination apparatus according to claim 46 wherein the wavelength conversion layer is arranged to receive light from the catadioptric optical array.

49. An illumination apparatus according to claim 1 , wherein the electrodes of each of the LEDs of the plurality LEDs are respectively connected to one column addressing electrode and one row addressing electrode.

50. An illumination apparatus according to claim 1 , further comprising an integrated circuit controlling one or more LEDs and located within the LED array.

51. An illumination apparatus according to claim 50 wherein the integrated circuit comprises a storage or memory or latching function.

52. An illumination apparatus according to claim 1 , wherein the LEDs of the plurality of LEDs are from a monolithic wafer arranged in an array with their original monolithic wafer positions and orientations relative to each other preserved; and

wherein in at least one direction, for at least one pair of the plurality of LEDs in the at least one direction, for each respective pair there was at least one respective LED in the monolithic wafer that was positioned in the monolithic wafer between the pair of LEDs in the at least one direction and that is not positioned between them in the array of LEDs.

53. An illumination apparatus according to claim 1 , wherein the LEDs of the plurality of LEDs are micro-LEDs of width or diameter less than 300 micrometres, preferably less than 200 micrometres and more preferably less than 100 micrometres.

54. An illumination apparatus according to claim 1 , wherein in the at least one catadioptric cross-sectional plane the distance between the transmissive output surface and reflective surface is less than 750 micrometres, preferably less than 500 micrometres and more preferably less than 250 micrometres.

55. A display apparatus comprising the illumination apparatus of claim 1 and a transmissive spatial light modulator arranged to receive light that has transmitted through the transmissive LED support substrate.

56. A backlight apparatus for a liquid crystal display comprising the illumination apparatus of claim 1 .