The present application is based on, and claims priority from JP Application Serial Number 2019-139499, filed Jul. 30, 2019, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to an image display device.

2. Related Art

In recent years, a wearable image display device such as a head-mounted display has been focused on. As such an image display device, there is a technique that includes an incident side diffraction element and an exit side diffraction element formed at a front surface of a light-guiding plate, and a virtual image is displayed by propagating imaging light captured into the light-guiding plate from the incident side diffraction element and extracting the imaging light outward from the exit side diffraction element (see, for example, JP-A-2016-85426).

In the image display device described above, diffraction efficiency of the exit side diffraction element varies depending on magnitude of a propagation angle of the light propagating within the light-guiding plate, and thus there has been a problem in that brightness of the imaging light exited from the exit side diffraction element is uneven.

SUMMARY

In order to solve the problem described above, an image display device according to a first aspect of the present disclosure includes, an imaging light generation part configured to generate imaging light having a single color, a light-guiding plate, an incident side diffraction element provided at a light incident part of the light-guiding plate, and configured to cause the imaging light to enter the light-guiding plate, an exit side diffraction element provided at a light emitting part of the light-guiding plate, and configured to cause the imaging light propagating within the light-guiding plate to exit, and an angle dependent reflective film provided between the light-guiding plate and the exit side diffraction element, and having reflectance varying depending on magnitude of a propagation angle of the imaging light propagating within the light-guiding plate, wherein reflectance of the angle dependent reflective film for the imaging light propagating at a relatively small propagation angle is larger than reflectance of the angle dependent reflective film for the imaging light propagating at a relatively large propagation angle.

An image display device according to a second aspect of the present disclosure includes, an imaging light generation part configured to generate imaging light including first colored light, second colored light, and third colored light, a first light-guiding plate, a first incident side diffraction element provided at a first light incident part of the first light-guiding plate, and on which the first colored light is incident, a first exit side diffraction element provided at a first light emitting part of the first light-guiding plate, and configured to cause the first colored light propagating within the first light-guiding plate to exit, a first angle dependent reflective film provided between the first light-guiding plate and the first exit side diffraction element, and having reflectance varying depending on magnitude of a propagation angle of the first colored light propagating within the first light-guiding plate, a second light-guiding plate, a second incident side diffraction element provided at a second light incident part of the second light-guiding plate, and on which the second colored light is incident, a second exit side diffraction element provided at a second light emitting part of the second light-guiding plate, and configured to cause the second colored light propagating within the second light-guiding plate to exit, a second angle dependent reflective film provided between the second light-guiding plate and the second exit side diffraction element, and having reflectance varying depending on magnitude of a propagation angle of the second colored light propagating within the second light-guiding plate, a third light-guiding plate, a third incident side diffraction element provided at a third light incident part of the third light-guiding plate, and on which the third colored light is incident, a third exit side diffraction element provided at a third light emitting part of the third light-guiding plate, and configured to cause the third colored light propagating within the third light-guiding plate to exit, and a third angle dependent reflective film provided between the third light-guiding plate and the third exit side diffraction element, and having reflectance varying depending on magnitude of a propagation angle of the third colored light propagating within the third light-guiding plate, wherein reflectance of the first angle dependent reflective film for the first colored light propagating within the first light-guiding plate at a relatively small propagation angle is larger than reflectance of the first angle dependent reflective film for the first colored light propagating within the first light-guiding plate at a relatively large propagation angle, reflectance of the second angle dependent reflective film for the second colored light propagating within the second light-guiding plate at a relatively small propagation angle is larger than reflectance of the second angle dependent reflective film for the second colored light propagating within the second light-guiding plate at a relatively large propagation angle, and reflectance of the third angle dependent reflective film for the third colored light propagating within the third light-guiding plate at a relatively small propagation angle is larger than reflectance of the third angle dependent reflective film for the third colored light propagating within the third light-guiding plate at a relatively large propagation angle.

In the above first aspect, at least one of the incident side diffraction element and the exit side diffraction element may be a surface relief type diffraction grating.

In the above first aspect, at least one of the incident side diffraction element and the exit side diffraction element may be a volume hologram.

In the second aspect, at least one of the first incident side diffraction element, the second incident side diffraction element, the third incident side diffraction element, the first exit side diffraction element, the second exit side diffraction element, and the third exit side diffraction element may be a surface relief type diffraction grating.

In the second aspect, at least one of the first incident side diffraction element, the second incident side diffraction element, the third incident side diffraction element, the first exit side diffraction element, the second exit side diffraction element, and the third exit side diffraction element may be a volume hologram.

In the first aspect or the second aspect, a light source for the imaging light may be laser light.

