Screen for image light projection and display system

1. An image light projection screen comprising:

a plurality of aperiodic lens array units on a main surface of the image light projection screen, the aperiodic lens array units being arrayed two-dimensionally regularly and without any gap at least within an image display region; wherein:

each of the aperiodic lens array units includes at least four apexes of micro-lenses each having a curved surface shape and arranged without any gap and non-periodically, and has symmetry keeping continuity of the curved surface shapes of the micro-lenses located in a boundary portion.

2. The image light projection screen according to claim 1 , wherein:

the image display region is filled with a repeating structure of a single kind of aperiodic lens array unit whose outer edge shape is quadrangular or hexagonal.

3. The image light projection screen according to claim 1 , wherein:

in each of the aperiodic lens array units, each Dn (n=1 to a number of apexes of micro-lenses) satisfies 0.9×D ave ≦Dn≦1.1×D ave , when Dn designate closest distances between the apexes of the micro-lenses belonging to the aperiodic lens array unit, and D ave designates an average of the closest distances Dn of the micro-lenses.

4. The image light projection screen according to claim 2 , wherein:

in each of the aperiodic lens array units, each Dn (n=1 to a number of apexes of micro-lenses) satisfies 0.9×D ave ≦Dn≦1.1×D ave , when Dn designate closest distances between the apexes of the micro-lenses belonging to the aperiodic lens array unit, and D ave designates an average of the closest distances Dn of the micro-lenses.

5. The image light projection screen according to claim 1 , wherein:

each of the aperiodic lens array units includes micro-lenses different in apex height, which is a distance in a height direction between a reference plane and an apex of a curved surface of each of the micro-lenses; and

in each of the aperiodic lens array units, an optical path length of a maximum difference Δh max among differences in height between the apexes of the micro-lenses is not smaller than λ, which is at least one of target wavelengths.

6. The image light projection screen according to claim 2 , wherein:

each of the aperiodic lens array units includes micro-lenses different in apex height, which is a distance in a height direction between a reference plane and an apex of a curved surface of each of the micro-lenses; and

in each of the aperiodic lens array units, an optical path length of a maximum difference Δh max among differences in height between the apexes of the micro-lenses is not smaller than λ, which is at least one of target wavelengths.

7. The image light projection screen according to claim 3 , wherein:

each of the aperiodic lens array units includes micro-lenses different in apex height, which is a distance in a height direction between a reference plane and an apex of a curved surface of each of the micro-lenses; and

in each of the aperiodic lens array units, an optical path length of a maximum difference Δh max among differences in height between the apexes of the micro-lenses is not smaller than λ, which is at least one of target wavelengths.

8. The image light projection screen according to claim 4 , wherein:

each of the aperiodic lens array units includes micro-lenses different in apex height, which is a distance in a height direction between a reference plane and an apex of a curved surface of each of the micro-lenses; and

in each of the aperiodic lens array units, an optical path length of a maximum difference Δh max among differences in height between the apexes of the micro-lenses is not smaller than λ, which is at least one of target wavelengths.

9. The image light projection screen according to claim 1 , wherein:

each of the micro-lenses has a concave shape.

10. The image light projection screen according to claim 1 , wherein:

each of the micro-lenses has a convex shape.

11. The image light projection screen according to claim 1 , wherein:

in each of the aperiodic lens array units, each Rn (n=1 to a number of apexes of micro-lenses) satisfies 0.8×R ave ≦Rn≦1.2×R ave , when Rn designate curvature radii of the micro-lenses belonging to the aperiodic lens array unit, and R ave designates an average of the curvature radii Rn.

12. The image light projection screen according to claim 1 , wherein:

in each of the aperiodic lens array units, a maximum difference Δh max among differences in height between the apexes of the micro-lenses satisfies 0.1×R ave ≧Δh max , when R ave designates an average of curvature radii of the micro-lenses belonging to the aperiodic lens array unit.

13. The image light projection screen according to claim 1 , wherein:

D ave is twice or less of length of a diagonal line of a display pixel when D ave designates an average of closest distances between apexes of micro-lenses belonging to the aperiodic lens array unit.

14. The image light projection screen according to claim 1 , wherein:

a first standard pitch Pu and a second standard pitch Pv are twice or less of corresponding axial lengths of a display pixel when the first standard pitch Pu and the second standard pitch Pv are Lu/M and Lv/J, where Lu and Lv designate any two lengths in axial directions crossing each other in the aperiodic lens array unit, M designates a number of apexes of micro-lenses arrayed in a first axial direction, which is the axial direction of the length Lu in a region measuring the length Lu, and J designates a number of apexes of micro-lenses arrayed in a second axial direction, which is the axial direction of the length Lv in a region measuring the length Lv.

15. The image light projection screen according to claim 1 , wherein:

each of the aperiodic lens array units satisfies R ave /D ave ≧0.9 when D ave designates an average of closest distances between apexes of micro-lenses belonging to the aperiodic lens array unit, and R ave designates an average of curvature radii of the micro-lenses.

16. The image light projection screen according to claim 1 , wherein:

a period of the aperiodic lens array units is 10 times or less of a diagonal length of a display pixel.

17. The image light projection screen according to claim 1 , wherein:

a scattering angle ranges from 10° to 40°.

18. A display system comprising:

an image projection apparatus including a light source that emits coherent light, an image light forming unit that modulates a beam of the light emitted from the light source in accordance with image information so as to form image light, and a projection optical system that enlarges and projects the image light toward a predetermined screen surface; and

an image light projection screen including a plurality of aperiodic lens array units on a main surface of the image light projection screen, the aperiodic lens array units being arrayed two-dimensionally regularly and without any gap at least within an image display region; wherein:

the image light projection screen is a transmission type screen; and

each of the aperiodic lens array units includes at least four apexes of micro-lenses each having a curved surface shape and arranged without any gap and non-periodically, and has symmetry keeping continuity of the curved surface shapes of the micro-lenses located in a boundary portion.

19. The display system according to claim 18 , wherein:

the display system is a head-up display;

the display system further comprises a box-like exterior housing that receives the image projection apparatus;

an opening portion is formed on a front surface side of the exterior housing; and

the transmission type screen is disposed in an optical path including the opening portion so that the image light projected from a back side of the transmission type screen can be projected toward a front side thereof.