Eyeball-projection display apparatus

1. An eyeball-projection display apparatus comprising:

an image display device for showing an image, and

a virtual image projection optical system in which an image shown by the image display device is optically guided into the eyeball of a viewer for projection of a virtual image, wherein:

the virtual image projection optical system includes an eyepiece optical system having an eyepiece optical element including an eyepiece transmitting surface and an eyepiece reflecting surface for reflecting off a light ray incident from the eyepiece transmitting surface and again guiding the light ray back into the same the eyepiece transmitting surface, having a medium filled in between the eyepiece transmitting surface and the eyepiece reflecting surface, the medium having a refractive index of greater than 1, and further including a back-surface reflecting mirror capable of only one reflection in an effective optical path and having a positive power;

a relay optical system having a positive power, and including a prism optical element having a curved, internal-reflecting surface that is decentered with respect to a center chief ray, being filled in with a medium having a refractive index of greater than 1 and being capable of plural internal reflections, and receiving light from the image display device for projection of an intermediate image of an image onto an exit side of the display apparatus; and

a reflecting element that is positioned in an optical path between the eyepiece optical system and the relay optical system and includes an intermediate reflecting surface to reflect a light beam incident obliquely from a side of the display apparatus, on which the relay optical system is located, toward a side of the display apparatus, on which the eyepiece optical system is located, thereby deflecting an optical path.

2. The eyeball-projection display apparatus according to claim 1 ,

wherein the eyepiece transmitting surface and the eyepiece reflecting surface are each decentered with respect to the center chief ray.

3. The eyeball-projection display apparatus according to claim 1 ,

wherein the reflecting element includes only one intermediate reflecting surface capable of only one reflection thereby deflecting the optical path.

4. The eyeball-projection display apparatus according to claim 3 ,

wherein the reflecting surface is a front surface mirror.

5. The eyeball-projection display apparatus according to claim 1 ,

assuming that the Z-axis is defined by an axis that is along the center chief ray exiting out from the virtual image projection optical system, and that the YZ plane is defined by a plane including the Z-axis and the center chief ray that is incident on and reflected off the eyepiece reflecting surface of the eyepiece optical system,

wherein a center of the image shown on the image display device is positioned between a plane vertical to the Z-axis passing through the outermost position of an effective area of the eyepiece reflecting surface of the eyepiece optical system in the YZ plane and in the Z-axis direction and a plane vertical to the Z-axis passing through the position nearest to the viewer side of an effective area of the intermediate reflecting surface of the reflecting element in the YZ plane and in the Z-axis direction.

6. The eyeball-projection display apparatus according to claim 1 ,

assuming that that the Z-axis is defined by an axis that is along the center chief ray exiting out from the virtual image projection optical system, and that the YZ plane is defined by a plane including the Z-axis and the center chief ray that is incident on and reflected off the eyepiece reflecting surface of the eyepiece optical system,

wherein an intermediate image of the center of the image shown on the image display device is positioned between a plane vertical to the Z-axis passing through the outermost position of an effective area of the intermediate reflecting surface of the eyepiece optical system in the YZ plane and in the Z-axis direction and a plane vertical to the Z-axis passing through the position nearest to the viewer side of an effective area of the intermediate reflecting surface of the reflecting element in the YZ plane and in the Z-axis direction.

7. The eyeball-projection display apparatus according to claim 5 ,

wherein an intermediate image at the center of the image shown on the display device is formed in a space between the reflecting element and the eyepiece optical system.

8. The eyeball-projection display apparatus according to claim 1 ,

wherein the reflecting element is located outside a range through which an effective light beam exiting out from the eyepiece optical system passes.

9. The eyeball-projection display apparatus according to claim 1 ,

satisfying the following condition (1):

1°<θ1min<θ1max<30°  (1)

where, assuming that the Z-axis is defined by an axis along the center chief ray exiting out from the virtual image projection optical system and the YZ plane is defined by a plane including the Z-axis and the center chief ray incident on and reflected off the eyepiece reflecting surface of the eyepiece optical system θ1min and θ1max stand for the minimum and maximum values of the angle of incidence of the chief ray on the YZ plane at the eyepiece reflecting surface of the eyepiece optical system, respectively.

10. The eyeball-projection display apparatus according to claim 1 ,

satisfying the following condition (2):

0.7< LYM 1/ LM 0<5  (2)

where, assuming that the Z-axis is defined by an axis along the center chief ray exiting out from the virtual image projection optical system, the YZ plane is defined by a plane including the Z-axis and the center chief ray incident on and reflected off the eyepiece reflecting surface of the eyepiece optical system, and the Y-axis direction is defined by a direction vertical to the Z-axis at the YZ plane LYM1 stands for a length of an effective reflecting surface, as measured in the Y-axis direction, of the eyepiece reflecting surface of the eyepiece optical system at the YZ plane, and LM0 stands for a separation distance between the reflecting element and the eyepiece optical system as measured along the Y-axis direction.

11. The eyeball-projection display apparatus according to claim 1 ,

wherein the intermediate reflecting surface of the reflecting element has a planar shape.

12. The eyeball-projection display apparatus according to claim 1 ,

wherein the intermediate reflecting surface of the reflecting element has a curved shape.

13. The eyeball-projection display apparatus according to claim 12 ,

wherein the intermediate reflecting surface of the reflecting element has an aspheric curved shape.

14. The eyeball-projection display apparatus according to claim 13 ,

wherein the intermediate reflecting surface of the reflecting element has a non-rotationally symmetric aspheric shape having a total of two symmetric surfaces at most.

15. The eyeball-projection display apparatus according to claim 1 ,

wherein the reflecting surface includes a diffracting surface.

16. The eyeball-projection display apparatus according to claim 1 ,

wherein the intermediate reflecting surface of the reflecting element satisfies the following condition (3):

−30°<θ<10°  (3)

where, assuming that the Z-axis is defined by an axis along the center chief ray exiting out from the virtual image projection optical system, θ is an angle between a tangent plane in a position of passage of the center chief ray at the intermediate reflecting surface of the reflecting element and a plane vertical to the Z-axis, with a negative sign in the case where the tangent plane tilts in a direction coming closer to the viewer side as it is spaced further away from the Z-axis.

17. The eyeball-projection display apparatus according to claim 1 ,

wherein the prism optical system of the relay optical system includes at least three optical surfaces decentered with respect to one another, wherein:

any one of the optical surfaces is an incident surface having transmission in a normal optical path, and there is a non-rotationally symmetric concave reflecting surface located in opposition to the incident surface, there is a non-rotationally symmetric convex reflecting surface located in opposition to the concave reflecting surface, the incident surface and the concave reflecting surface are decentered with respect to each other, and there is a transmitting surface positioned on a side of the prism optical element on which a distance between the incident surface and the concave reflecting surface grows long.

18. The eyeball-projection display apparatus according to claim 17 ,

wherein any one of the optical surfaces of the prism optical element of the relay optical system is a combined reflecting and transmitting surface in a normal optical path.

19. The eyeball-projection display apparatus according to claim 1 ,

satisfying the following condition (4):

5°<θ2min<θ2max<80°  (4)

where, assuming that the Z-axis is defined by an axis along the center chief ray exiting out from the virtual image projection optical system and the YZ plane is defined by a plane including the Z-axis and the center chief ray incident on and reflected off the eyepiece reflecting surface of the eyepiece optical system, θ2min and θ2max stand for the minimum and maximum values of the angle of incidence of the center chief ray on the YZ plane at the reflecting surface of the reflecting element, respectively.

20. The eyeball-projection display apparatus according to claim 19 ,

satisfying the following condition (5):

35°<θ2max−θ2min<70°  (5)