Display device and light-guiding device
A display device includes a first diffraction element that deflects image light and causes the image light to be incident on an eye of an observer, and a second diffraction element disposed between an image light projecting device and the first diffraction element. A diffraction direction of the first diffraction element and the second diffraction element is set depending on whether a sum of the number of reflections of light and the number of times of generating intermediate image between the second diffraction element and the first diffraction element is an even number or an odd number. For example, when the sum is an even number, a direction in which light incident on a first incident surface is diffracted at the highest diffraction efficiency is the same direction as a direction in which light incident on a second incident surface is diffracted at the highest diffraction efficiency.
1. A display device comprising:
an image light generating device configured to emit image light;
a first diffraction element of a reflection type configured to deflect the image light incident on a first incident surface toward an eye of an observer; and
a transmission-type second diffraction element disposed in an optical path between the image light generating device and the first diffraction element and configured to deflect the image light incident on a second incident surface toward the first diffraction element, wherein
the first diffraction element and the second diffraction element are disposed in such a way that,
when a sum of the number of reflections of light and the number of times of generating intermediate image between the second diffraction element and the first diffraction element is an even number, a direction in which light incident on the first incident surface is diffracted at the highest diffraction efficiency is the same direction as a direction in which light incident on the second incident surface is diffracted at the highest diffraction efficiency when seen from a normal direction of a virtual surface including a normal direction of the first incident surface and a normal direction of the second incident surface, and
when a sum of the number of reflections of light and the number of times of generating intermediate image between the second diffraction element and the first diffraction element is an odd number, a direction in which light incident on the first incident surface is diffracted at the highest diffraction efficiency is a direction different from a direction in which light incident on the second incident surface is diffracted at the highest diffraction efficiency when seen from the normal direction of the virtual surface.
2. The display device according to claim 1 , wherein
the first diffraction element is an element in which light incident from the normal direction of the first incident surface has the highest diffraction efficiency in a first direction,
the second diffraction element is an element in which light incident from the normal direction of the second incident surface has the highest diffraction efficiency in a second direction,
when a sum of the number of reflections of light and the number of times of generating intermediate image between the second diffraction element and the first diffraction element is an even number and the first direction and the second direction are directions different from each other when seen from the normal direction of the virtual surface including the normal direction of the first incident surface and the normal direction of the second incident surface, an angle which the normal direction of the second incident surface forms with an incident direction of light with respect to the second incident surface is greater than an angle which the normal direction of the second incident surface forms with a direction in which the light is emitted from an emitting surface of the second diffraction element at the highest diffraction efficiency, and
when a sum of the number of reflections of light and the number of times of generating intermediate image between the second diffraction element and the first diffraction element is an even number and the first direction and the second direction are the same direction when seen from the normal direction of the virtual surface including the normal direction of the first incident surface and the normal direction of the second incident surface, an angle which the normal direction of the second incident surface forms with an incident direction of light with respect to the second incident surface is smaller than an angle which the normal direction of the emitting surface forms with the direction in which the light is emitted from the emitting surface at the highest diffraction efficiency.
3. The display device according to claim 1 , wherein
the first diffraction element is an element in which light incident from the normal direction of the first incident surface has the highest diffraction efficiency in a first direction,
the second diffraction element is an element in which light incident from the normal direction of the second incident surface has the highest diffraction efficiency in a second direction,
when a sum of the number of reflections of light and the number of times of generating intermediate image between the second diffraction element and the first diffraction element is an odd number and the first direction and the second direction are directions different from each other when seen from the normal direction of the virtual surface including the normal direction of the first incident surface and the normal direction of the second incident surface, an angle which the normal direction of the second incident surface forms with an incident direction of light with respect to the second incident surface is smaller than an angle which the normal direction of the second incident surface forms with a direction in which the light is emitted from an emitting surface of the second diffraction element at the highest diffraction efficiency, and
when a sum of the number of reflections of light and the number of times of generating intermediate image between the second diffraction element and the first diffraction element is an odd number and the first direction and the second direction are the same direction when seen from the normal direction of the virtual surface including the normal direction of the first incident surface and the normal direction of the second incident surface, an angle which the normal direction of the second incident surface forms with an incident direction of light with respect to the second incident surface is greater than an angle which the normal direction of the emitting surface forms with the direction in which the light is emitted from the emitting surface at the highest diffraction efficiency.
4. The display device according to claim 1 , wherein
the first diffraction element is a reflection-type volume holographic element, and
the second diffraction element is a transmission-type volume holographic element.
5. The display device according to claim 4 , wherein
the first diffraction element and the second diffraction element are each provided with interference fringes of a plurality of kinds having different pitches.
6. The display device according to claim 1 , wherein
the first diffraction element has a curved shape being recessed with respect to a peripheral portion.
7. The display device according to claim 1 , wherein
the image light generating device includes an organic electroluminescent display device.
8. The display device according to claim 1 , wherein
the image light generating device includes a liquid crystal device and an illumination light source.
9. A light-guiding device comprising:
a first diffraction element of a reflection type configured to deflect light incident on a first incident surface from a light source; and
a second diffraction element of a transmission type disposed in an optical path between the light source and the first diffraction element and configured to deflect the light incident on a second incident surface toward the first diffraction element, wherein
the first diffraction element and the second diffraction element are disposed in such a way that,
when a sum of the number of reflections of light and the number of times of generating intermediate image between the second diffraction element and the first diffraction element is an even number, a direction in which light incident on the first incident surface is diffracted at the highest diffraction efficiency is the same direction as a direction in which light incident on the second incident surface is diffracted at the highest diffraction efficiency when seen from a normal direction of a virtual surface including a normal direction of the first incident surface and a normal direction of the second incident surface, and
when a sum of the number of reflections of light and the number of times of generating intermediate image between the second diffraction element and the first diffraction element is an odd number, a direction in which light incident on the first incident surface is diffracted at the highest diffraction efficiency is a direction different from a direction in which light incident on the second incident surface is diffracted at the highest diffraction efficiency when seen from the normal direction of the virtual surface.