Image display apparatus and head-mounted display

Abstract

Variation of the wavelength of the light emitted from a light source is reduced by a wavelength variation reduction mechanism. Hence, wavelength deviation of the intensity peak of the light emitted from the light source from the diffraction-efficiency peak of a hologram optical element is reduced. Thus, even when a high-brightness light source is used, the light emitted therefrom can be diffracted with the hologram optical element efficiently. Moreover, the heat generated by the light source is efficiently rejected through the surface of a land portion of a flexible printed circuit, is then, via an insulating layer of the flexible printed circuit, efficiently absorbed through the surface of a heat absorbing member, and is then, via a shield conductor, led out of a casing, so as to be thereby expelled.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will be apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view showing, as one embodiment of the present invention, an outline of the construction of an image display apparatus used in a head-mounted display;

FIG. 2A is a plan view showing an outline of the construction of the above head-mounted display;

FIG. 2B is a side view of the above head-mounted display;

FIG. 2C is a front view of the above head-mounted display;

FIG. 3A is a plan view showing an outline of the construction of another head-mounted display;

FIG. 3B is a side view of the above head-mounted display;

FIG. 3C is a front view of the above head-mounted display;

FIG. 4 is a diagram illustrating the optical paths in the above image display apparatus, as optically unfolded in one direction;

FIG. 5 is a cross-sectional view showing, in simplified form, an outline of the structure of the display element provided in the above image display apparatus;

FIG. 6 is a diagram illustrating the wavelength dependence of the diffraction efficiency of the hologram optical element provided in the above image display apparatus;

FIG. 7 is a diagram illustrating the wavelength dependence of the transmissivity of the color filters provided in the above display element;

FIG. 8 is a diagram illustrating the spectral intensity characteristics of the light source provided in the above image display apparatus;

FIG. 9 is a diagram illustrating the color reproduction region of the virtual image, as represented using XY chromaticity coordinates in an XYZ color representation system;

FIG. 10 is a diagram schematically illustrating how the wavelengths of the emitted RGB light vary with the duration of use of the above light source;

FIG. 11A is a cross-sectional view showing an example of the structure of transmitting means serving as wavelength variation reducing means provided in the above image display apparatus;

FIG. 11B is a cross-sectional view showing another example of the structure of the above transmitting means;

FIG. 11C is a cross-sectional view showing still another example of the structure of the above transmitting means;

FIG. 12A is a graph showing one of various examples of how the supply of electric currents to individual light-emitting portions is controlled by a control portion servings as the wavelength variation reducing means provided in the above image display apparatus;

FIG. 12B is a graph showing another of the above various examples;

FIG. 12C is a graph showing still another of the above various examples;

FIG. 12D is a graph showing how the RGB light-emitting portions for illuminating the above display element are generally controlled in an image display apparatus employing a display element of the type that is driven on a time-division basis;

FIG. 13 is a diagram illustrating the relationship between the pupil position in the optical pupil and a principal diffraction wavelength;

FIG. 14 is a diagram illustrating the optical paths in an image display apparatus as another embodiment of the present invention, as optically unfolded in one direction;

FIG. 15 is a plan view of the light source provided in the above image display apparatus, as seen from the display element side;

FIG. 16 is a diagram illustrating the relationship between the pupil position in the optical pupil in the X direction and light intensity;

FIG. 17 is a diagram showing another example of the structure of the above light source, the diagram being a plan view of the above light source as seen from the display element side;

FIG. 18 is a cross-sectional view showing an outline of the construction of an image display apparatus as still another embodiment of the present invention;

FIG. 19 is a diagram illustrating the optical paths in the above image display apparatus, as optically unfolded in one direction;

FIG. 20 is a diagram illustrating the relationship between the pupil position in the optical pupil and a principal diffraction wavelength;

FIG. 21 is a perspective view showing an outline of the construction of an HMD as a further embodiment of the present invention;

FIG. 22 is a diagram schematically illustrating the construction inside the casing of the image display apparatus provided in the above HMD;

FIG. 23 is a cross-sectional view of the cable provided in the above image display apparatus;

FIG. 24 is a cross-sectional view schematically showing the connecting portion between the light source of the above image display apparatus and a flexible printed circuit;

FIG. 25 is a perspective view showing another example of the construction of the above HMD;

FIG. 26 is a diagram illustrating the detailed construction inside the casing of the above HMD; and

FIG. 27 is a diagram illustrating another example of the construction inside the casing of the above HMD.

Claims

1. An image display apparatus, comprising: a light source that emits light having intensity peaks at predetermined wavelengths corresponding to three primary colors;a display element that produces an image by modulating the light emitted from the light source, the display element having color filters corresponding to the three primary colors;an eyepiece optical system that directs image light from the display element to an observer's eye, the eyepiece optical system having a volume-phase-type reflective hologram optical element that diffracts the light from the display element, the hologram optical element having diffraction-efficiency peaks at wavelengths corresponding to the peak-intensity wavelengths of the light emitted from the light source; anda wavelength variation reduction mechanism that reduces variation of wavelengths of the light emitted from the light source.

2. The image display apparatus according to claim 1, wherein, let any of the peak-intensity wavelengths of the light emitted from the light source be λL (nm), and let a corresponding one of the peak-diffraction-efficiency wavelengths of the hologram optical element be λH (nm), then the following formula is fulfilled: λH−10 nm≦λL≦λH+10 nm.

3. The image display apparatus according to claim 2, wherein a half-peak wavelength width of any of the diffraction-efficiency peaks of the hologram optical element is 20 nm or less.

4. The image display apparatus according to claim 2, wherein the following formula is fulfilled: λH−5 nm≦λL≦λH+5 nm.

5. The image display apparatus according to claim 4, wherein a half-peak wavelength width of any of the peak-diffraction-efficiency wavelengths of the hologram optical element is 10 nm or less.

6. The image display apparatus according to claim 1, wherein the light source includes a light-emitting diode.

7. The image display apparatus according to claim 1, wherein the wavelength variation reduction mechanism includes a heat conducting member that conducts heat generated by the light source to outside.

8. The image display apparatus according to claim 7, wherein the heat conducting member has a thermal conductivity of 100 Wm−1K−1 or more.

9. The image display apparatus according to claim 8, wherein the heat conducting member is formed of metal.

10. The image display apparatus according to claim 1, further comprising: a flexible printed circuit on which the light source is mounted,wherein the wavelength variation reduction mechanism includes a heat absorbing member that is arranged on a side of the flexible printed circuit opposite from a side thereof on which the light source is mounted, the heat absorbing member absorbing heat from the light source, anda heat conducting member that leads the heat absorbed by the heat absorbing member to outside a casing.

11. The image display apparatus according to claim 10, further comprising: a cable across which electric power is supplied,wherein a shield conductor of the cable serves as the heat conducting member.

12. The image display apparatus according to claim 1, wherein the light source has three light-emitting chips corresponding to R, G, and B, andwherein the wavelength variation reduction mechanism includes a control circuit that controls driving of the individual light-emitting chips so that light emission periods during which the three light-emitting chips emit light simultaneously alternate with heat rejection periods during which the three light-emitting chips cease to emit light for heat rejection andso that the light emission periods are longer than the heat rejection periods.

13. The image display apparatus according to claim 1, wherein the light source has three light-emitting chips corresponding to R, G, and B, andwherein the wavelength variation reduction mechanism includes a control circuit that controls driving of the individual light-emitting chips so that periods during which the three light-emitting chips respectively emit light are shifted from one another so that at least one of the three light-emitting chips does not emit light at any time.

14. The image display apparatus according to claim 1, wherein the light source has three light-emitting chips corresponding to R, G, and B, andwherein the wavelength variation reduction mechanism includes a control circuit that controls driving of the individual light-emitting chips so that periods during which the three light-emitting chips respectively emit light do not overlap with one another.

15. The image display apparatus according to claim 1, wherein the hologram optical element has an axis-asymmetric positive optical power.

16. The image display apparatus according to claim 15, wherein an optical pupil formed by the eyepiece optical system is larger in a direction perpendicular to a plane of incidence along which an optical axis runs onto the hologram optical element than in a direction parallel to the plane of incidence.

17. The image display apparatus according to claim 16, wherein the light source and the optical pupil are substantially conjugate with each other in a direction parallel to the plane of incidence.

18. The image display apparatus according to claim 16, wherein the light source has three light-emitting portions corresponding to the three primary colors, andwherein the three light-emitting portions are arranged in a direction perpendicular to the plane of incidence.

19. The image display apparatus according to claim 1, wherein the light source has an even number of sets of three light-emitting portions corresponding to the three primary colors, andwherein order in which the light-emitting portions are arranged within each set in a direction perpendicular to a plane of incidence along which an optical axis runs onto the hologram optical element is reversed between adjacent sets.

20. The image display apparatus according to claim 1, wherein the light source has an even number of sets of three light-emitting portions corresponding to the three primary colors,wherein the light-emitting portions are arranged plane-symmetrically with respect to a plane of incidence along which an optical axis runs onto the hologram optical element, andwherein light-emitting portions located on opposite sides of and at an equal distance from the plane of incidence correspond to a same color.

21. The image display apparatus according to claim 20, wherein the light-emitting portions are so arranged that wavelengths of light emitted therefrom are increasingly short in a direction perpendicular to and running away from the plane of incidence.

22. The image display apparatus according to claim 1, wherein the hologram optical element is a combiner that directs the image light from the display element and outside light simultaneously to the observer's eye.

23. The image display apparatus according to claim 1, wherein the eyepiece optical system includes a first transparent substrate that, by internal total reflection, reflects and thereby directs the image light from the display element through the hologram optical element to the observer's eye and that simultaneously transmits and thereby directs outside light to the observer's eye.

24. The image display apparatus according to claim 23, wherein the eyepiece optical system includes a second transparent substrate that cancels refraction of the outside light by the first transparent substrate.

25. A head-mounted display, comprising: the image display apparatus according to claim 1, anda supporting member that supports the image display apparatus in front of the observer's eye.

26. An image display apparatus, comprising: a light source including a light-emitting diode, the light-emitting diode being mounted on a circuit board;a display element that produces an image by modulating light emitted from the light source;an eyepiece optical system that directs image light from the display element to an observer's eye;a heat absorbing member that is arranged on a side of the circuit board opposite from a side thereof on which the light-emitting diode is mounted, the heat absorbing member absorbing heat generated by the light-emitting diode; anda heat conducting member that conducts the heat absorbed by the heat absorbing member to outside a casing.

27. The image display apparatus according to claim 26, wherein the circuit board is a flexible printed circuit, andwherein the light-emitting diode is solder-mounted in a land portion of the flexible printed circuit.

28. The image display apparatus according to claim 27, wherein the heat absorbing member is arranged opposite the land portion of the flexible printed circuit so as to cover the entire land portion.

29. The image display apparatus according to claim 27, wherein the land portion is formed of a metal material having a thermal conductivity of 100 Wm−1K−1 or more.

30. The image display apparatus according to claim 29, wherein the land portion is formed of rolled copper foil.

31. The image display apparatus according to claim 26, wherein the heat absorbing member is formed of a metal material having a thermal conductivity of 100 Wm−1K−1 or more.

32. The image display apparatus according to claim 26, wherein the heat conducting member is formed of a metal material having a thermal conductivity of 100 Wm−1K−1 or more.

33. The image display apparatus according to claim 26, further comprising: a circuit unit that supplies driving electric power to the light source and/or the display element across a cable, the circuit unit being arranged outside the casing,wherein a shield conductor of the cable serves as the heat conducting member.

34. The image display apparatus according to claim 26, wherein at least part of the casing is formed of a metal material having a thermal conductivity of 100 Wm−1K−1 or more, andwherein the heat conducting member links together the heat absorbing member and part of the casing.

35. The image display apparatus according to claim 26, wherein the eyepiece optical system includes a volume-phase-type reflective hologram optical element, andwherein the hologram optical element diffracts and thereby directs the light from the display element to the observer's eye.

36. The image display apparatus according to claim 35, wherein the hologram optical element is a combiner that directs the image light from the display element and outside light simultaneously to the observer's eye.

37. The image display apparatus according to claim 35, wherein a half-peak wavelength width of a diffraction-efficiency peak of the hologram optical element is 5 nm or more but 10 nm or less.

38. The image display apparatus according to claim 35, wherein the eyepiece optical system includes a first transparent substrate that, by internal total reflection, reflects and thereby directs the image light from the display element through the hologram optical element to the observer's eye and that simultaneously transmits and thereby directs outside light to the observer's eye.

39. The image display apparatus according to claim 38, wherein the eyepiece optical system includes a second transparent substrate that cancels refraction of the outside light by the first transparent substrate.

40. The image display apparatus according to claim 26, wherein the light source has a plurality of light-emitting portions having light-emission-intensity peaks at wavelengths different from one another.

41. The image display apparatus according to claim 40, wherein the light source has an even number of sets of three light-emitting portions corresponding to three primary colors, andwherein order in which the light-emitting portions are arranged within each set in a direction perpendicular to a plane of incidence along which an optical axis runs onto the hologram optical element is reversed between adjacent sets.

42. A head-mounted display, comprising: the image display apparatus according to claim 26, anda supporting member that supports the image display apparatus in front of the observer's eye.

43. An image display apparatus, comprising: a light source including a light-emitting diode mounted on a circuit board, said light source emitting light having intensity peaks at predetermined wavelengths corresponding to three primary colors;a display element that produces an image by modulating light emitted from the light source;an eyepiece optical system that directs image light from the display element to an observer's eye, the eyepiece optical system having a volume-phase-type reflective hologram optical element that diffracts the light from the display element, the hologram optical element having diffraction-efficiency peaks at wavelengths corresponding to the peak-intensity wavelengths of the light emitted from the light source;a heat absorbing member that is arranged on the circuit board to absorb heat generated by the light-emitting diode; anda heat conducting member that conducts the heat absorbed by the heat absorbing member to outside a casing.

44. The image display apparatus according to claim 43, wherein the circuit board is a flexible printed circuit, andwherein the light-emitting diode is solder-mounted in a land portion of the flexible printed circuit.

45. The image display apparatus according to claim 44, wherein the heat absorbing member is arranged opposite the land portion of the flexible printed circuit so as to cover the entire land portion.

46. The image display apparatus according to claim 44, wherein the land portion is formed of a metal material having a thermal conductivity of 100 Wm−1K−1 or more.

47. The image display apparatus according to claim 46, wherein the land portion is formed of rolled copper foil.

48. The image display apparatus according to claim 43, wherein the heat absorbing member is formed of a metal material having a thermal conductivity of 100 Wm−1K−1 or more.

49. The image display apparatus according to claim 43, wherein the heat conducting member is formed of a metal material having a thermal conductivity of 100 Wm−1K−1 or more.

50. The image display apparatus according to claim 43, further comprising: a circuit unit that supplies driving electric power to the light source and/or the display element across a cable, the circuit unit being arranged outside the casing,wherein a shield conductor of the cable serves as the heat conducting member.

51. The image display apparatus according to claim 43, wherein at least part of the casing is formed of a metal material having a thermal conductivity of 100 Wm−1K−1 or more, andwherein the heat conducting member links together the heat absorbing member and part of the casing.

52. The image display apparatus according to claim 43, wherein the hologram optical element is a combiner that directs the image light from the display element and outside light simultaneously to the observer's eye.

53. The image display apparatus according to claim 43, wherein a half-peak wavelength width of a diffraction-efficiency peak of the hologram optical element is 5 nm or more but 10 nm or less.

54. The image display apparatus according to claim 43, wherein the eyepiece optical system includes a first transparent substrate that, by internal total reflection, reflects and thereby directs the image light from the display element through the hologram optical element to the observer's eye and that simultaneously transmits and thereby directs outside light to the observer's eye.

55. The image display apparatus according to claim 54, wherein the eyepiece optical system includes a second transparent substrate that cancels refraction of the outside light by the first transparent substrate.

56. The image display apparatus according to claim 43, wherein the light source has an even number of sets of three light-emitting portions corresponding to three primary colors, andwherein order in which the light-emitting portions are arranged within each set in a direction perpendicular to a plane of incidence along which an optical axis runs onto the hologram optical element is reversed between adjacent sets.

57. A head-mounted display, comprising: the image display apparatus according to claim 43; anda supporting member that supports the image display apparatus in front of the observer's eye.