Virtual-image display device and optical unit
A virtual-image display device includes a display panel configured to output image light, a projection optical system configured to collimate the image light from the display panel, and a light-guiding member including a light-guiding plate configured to guide the image light, an input diffraction optical element configured to cause the image light to enter the light-guiding plate, and an output diffraction optical element configured to cause the image light to be outputted from the light-guiding plate. A diffraction region of the input diffraction optical element covers an incident region of the image light at the light-guiding member, and the diffraction region is set at a region in which the image light diffracted at the input diffraction optical element is reflected on an opposing surface of the light-guiding plate, and enters an outside of the input diffraction optical element.
1 . A virtual-image display device comprising:
a display panel configured to output image light;
a projection optical system configured to collimate the image light from the display panel; and
a light-guiding member including
a light-guiding plate configured to guide the image light,
an input diffraction optical element configured to cause the image light to enter the light-guiding plate, and
an output diffraction optical element configured to cause the image light to be outputted from the light-guiding plate, wherein
a diffraction region of the input diffraction optical element covers an incident region of the image light at the light-guiding member, and
the diffraction region is set in a region in which the image light diffracted at the input diffraction optical element is reflected on an opposing surface of the light-guiding plate, and enters an outside of the input diffraction optical element,
wherein the region in which the image light enters the outside of the input diffraction optical element is defined by an external incidence structure in which a size of the incident region is set such that a size of the diffraction region is less than or equal to a width until a light beam turns back in a light-guiding direction, the width until the light beam turns back being defined as two times a thickness of the light-guiding plate multiplied by a tangent value of a critical angle of the light beam.
2 . The virtual-image display device according to claim 1 , further comprising:
a region restricting member configured to restrict the incident region.
3 . The virtual-image display device according to claim 1 , wherein
the diffraction region is configured such that an expansion size is small at a light guiding side relative to the incident region.
4 . The virtual-image display device according to claim 1 , wherein
the diffraction region and the incident region are substantially equal.
5 . The virtual-image display device according to claim 1 , wherein
the input diffraction optical element is disposed at a position of an exit pupil of the projection optical system.
6 . The virtual-image display device according to claim 1 , wherein
a cover member is provided either between the projection optical system and the light-guiding member or at an outside relative to the light-guiding member.
7 . The virtual-image display device according to claim 1 , further comprising:
a first display panel serving as a display panel configured to output first image light of the image light;
a second display panel configured to output second image light having a wavelength region differing from the first image light;
a third display panel configured to output third image light having a wavelength region differing from the first image light and the second image light; and
a cross dichroic prism configured to synthesize the first image light, the second image light, and the third image light.
8 . The virtual-image display device according to claim 1 , further comprising:
a first light-guiding member serving as the light-guiding member; and
a second light-guiding member configured to diffract the image light having a wavelength region differing from the first light-guiding member.
9 . The virtual-image display device according to claim 1 , wherein
the diffraction region has a circular shape.
10 . An optical unit comprising:
a display panel configured to output image light;
a projection optical system configured to collimate the image light from the display panel; and
a light-guiding member including
a light-guiding plate configured to guide the image light,
an input diffraction optical element configured to cause the image light to enter the light-guiding plate, and
an output diffraction optical element configured to cause the image light to be outputted from the light-guiding plate, wherein
a diffraction region of the input diffraction optical element covers an incident region of the image light at the light-guiding member, and
the diffraction region is set at a region in which the image light diffracted at the input diffraction optical element is reflected on an opposing surface of the light-guiding plate, and enters an outside of the input diffraction optical element,
wherein the region in which the image light enters the outside of the input diffraction optical element is defined by an external incidence structure in which a size of the incident region is set such that a size of the diffraction region is less than or equal to a width until a light beam turns back in a light-guiding direction, the width until the light beam turns back being defined as two times a thickness of the light-guiding plate multiplied by a tangent value of a critical angle of the light beam.