JP7558841B2 - Image Projection Device - Google Patents

Description

The present invention relates to an image projection device, and in particular to an image projection device that uses a diffraction grating.

Conventionally, dashboards that light up icons have been used as devices for displaying various types of information inside vehicles. As the amount of information to be displayed increases, it has also been proposed to embed an image display device in the dashboard or to configure the entire dashboard with an image display device.

However, because the instrument panel is located below the windshield of the vehicle, the driver must move his or her eyes downward while driving in order to view the information displayed on the instrument panel, which is undesirable. For this reason, a head-up display (hereinafter referred to as HUD) has been proposed that projects an image onto the windshield so that the driver can read the information when viewing the area ahead of the vehicle (see, for example, Patent Document 1). Such a HUD requires an optical device for projecting an image over a wide area of the windshield, and there is a demand for a smaller and lighter optical device.

On the other hand, as an image display device that projects light using a small optical device, a wearable HUD is known in which light is incident from one end of a light guide plate and is extracted in the direction of the viewpoint from the other end (see, for example, Patent Document 2). In a wearable HUD, light emitted from a light source is directly irradiated onto the viewer's eyes, and an image is projected onto the viewer's retina. In such a wearable HUD, a diffraction grating or half mirror is used when irradiating light from the light source to the viewer. Wearable HUDs are worn on the head to project images toward the user's individual viewpoint, and are therefore used in highly immersive virtual reality (VR) and augmented reality (AR), etc.

JP 2019-119262 A JP 2020-144190 A

However, in conventional wearable HUDs, images are projected from a light guide plate in the direction of the viewpoint using a diffraction grating or half mirror, so all images are displayed on a plane that is the same distance from the viewpoint. This makes it difficult to display multiple images at different distances from the viewpoint and overlay them. Furthermore, in order to project multiple images at positions at different distances from the viewpoint, it is necessary to design and individually arrange image projection units and optical system components corresponding to the projection positions, which increases the number of parts and makes it difficult to make the device smaller and lighter.

The present invention has been developed in consideration of the above-mentioned problems with the conventional technology, and aims to provide an image projection device that can project multiple images at positions at different distances from the viewpoint, and can also be made smaller and lighter.

In order to solve the above problem, the image projection device of the present invention comprises a first image irradiation section that irradiates a first light, a first light incident section into which the first light is incident, a light guide section that guides a portion of the first light as guided light while totally reflecting it, a light guide plate section having a first light exit section that emits a portion of the guided light in a viewpoint direction, and a diffraction grating section provided on the first light incident section, wherein the first light exit section comprises a beam splitter provided within the light guide section and a retroreflection section provided at an end of the light guide section , and the light guide plate section comprises a second light exit section that transmits one of the light beams branched by the diffraction grating section and emits it in a direction of an external screen different from the viewpoint direction .

In the image projection device of the present invention, the first light is split by the beam splitter to project an image onto a screen, and the first light is retroreflected by the retroreflecting section at the end of the optical waveguide section and projected in the direction of the viewpoint by the beam splitter to form an aerial image. This makes it possible to project multiple images at positions at different distances from the viewpoint, and further reduce the size and weight of the device.

In one embodiment of the present invention, the viewing direction and the external screen direction are approximately parallel.

In one aspect of the present invention, an optical shutter section that switches between transmitting and blocking light is provided in the first light emitting section or the second light emitting section.

In one aspect of the present invention, a wavelength conversion unit that converts the wavelength of the first light is provided in the first light output unit or the second light output unit.

In one embodiment of the present invention, the retroreflective portion is formed by mixing a specular reflection area that specularly reflects light and a retroreflective area that retroreflects light.

In one aspect of the present invention, a partial reflector that reflects a portion of the guided light and transmits the remainder is provided between the beam splitter and the retroreflector.

In one aspect of the present invention, a second image irradiation unit is provided that irradiates the diffraction grating with a second light, and the angles of incidence of the first light and the second light with respect to the diffraction grating unit are different, and the optical waveguide unit totally reflects a portion of the second light while guiding it as guided light.

In one aspect of the present invention, a selective reflection section that reflects the first wavelength of light and transmits the second wavelength of light is provided between the beam splitter and the retroreflection section.

In one aspect of the present invention, an optical filter that selectively blocks the wavelength of the first light or the wavelength of the second light is provided in the second light output section.

In one aspect of the present invention, the optical waveguide portion has a curved shape.

In one aspect of the present invention, the first image irradiating unit includes a liquid crystal display element or a digital mirror device, and changes the content of the first image contained in the first light over time.

In one aspect of the present invention, two light guide plate sections are provided, and one of the diffraction grating sections is commonly provided at the first light entrance section of each of the light guide plate sections.

In one aspect of the present invention, the diffraction grating portion includes a flat portion that constitutes the light incidence surface and an uneven portion that is integral with the flat portion, and is formed separately from the light guide plate portion.

In one aspect of the present invention, the diffraction grating portion has a holographic grating that diffracts light in at least two directions.

The present invention provides an image projection device that can project multiple images at different distances from a viewpoint and can be made smaller and lighter.

2 is a schematic cross-sectional view showing the structure of a diffraction grating portion 10 in the first embodiment. FIG. 1 is a schematic diagram showing a structure of an image projection device according to a first embodiment. 2 is a schematic cross-sectional view showing an enlarged view of a first light exit portion of the image projection device according to the first embodiment. FIG. The photographs were taken by placing a camera at viewpoint 60 to capture an image EX projected onto an external screen 30 and an aerial image A1 formed in the air. In FIG. 4(a), the camera was focused on the external screen 30, and in FIG. 4(b), the camera was focused on the position where the aerial image A1 was formed. 10 is a schematic cross-sectional view showing an enlarged view of a first light exit portion of an image projection device according to a second embodiment. FIG. The photographs were taken by placing a camera at viewpoint 60 to capture images EX and V1 projected onto external screen 30, and an aerial image A1 formed in the air. In FIG. 6(a), the camera was focused on external screen 30, and in FIG. 6(b), the camera was focused on the position where aerial image A1 was formed. FIG. 13 is a schematic diagram showing a structure of an image projection device according to a third embodiment. FIG. 11 is a schematic cross-sectional view showing an enlarged view of a first light exit portion of an image projection device according to a third embodiment. The photographs were taken by placing a camera at viewpoint 60 to capture images EX and V1 projected onto external screen 30, and aerial images A1 and A2 formed in the air. In Figure 9(a), the camera was focused on the position where aerial image A1 is formed, in Figure 9(b), the camera was focused on the position where aerial image A2 is formed, and in Figure 9(c), the camera was focused on external screen 30. 10A and 10B show the beam profiles of aerial images A1 and A2, where FIG. 10A is a photograph focused from viewpoint 60, FIGS. 10B and 10C show the three-dimensional luminance profile at the imaging position, FIG. 10D is the luminance profile in the x direction, and FIG. 10E is the luminance profile in the y direction. FIG. 13 is a schematic diagram showing a structure of an image projection device according to a fourth embodiment. FIG. 13 is a schematic diagram showing a structure of an image projection device according to a modified example of the fourth embodiment. FIG. 13 is a schematic diagram showing a structure of an image projection device according to a fifth embodiment. FIG. 13 is a schematic diagram showing a structure of an image projection device according to a modified example of the fifth embodiment. 13A to 13C are schematic diagrams illustrating an example of the structure of a retroreflective portion 24 in a sixth embodiment.

First Embodiment
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The same or equivalent components, members, and processes shown in each drawing are given the same reference numerals, and duplicated descriptions are omitted as appropriate. FIG. 1 is a schematic cross-sectional view showing the structure of a diffraction grating section 10 in this embodiment. As shown in FIG. 1, the diffraction grating section 10 includes a flat plate-like portion 11, a convex portion 12, and a concave portion 13. Here, the convex portion 12 and the concave portion 13 are portions that constitute a periodic repetition of refractive index in the in-plane direction in the diffraction grating section 10, and correspond to the concave-convex portion in the present invention. The flat plate-like portion 11 and the convex portion 12 are integrally formed of the same material. Note that FIG. 1 is a schematic diagram showing the structure of the diffraction grating section 10, and the dimensions and angles in the figure do not indicate the actual dimensions of the diffraction grating section 10.

In the example shown in FIG. 1, the convex portions 12 and concave portions of the diffraction grating portion 10 are formed in stripes extending in the depth direction of the paper. The convex portions 12 are formed at a predetermined angle φ with respect to the main surface of the flat plate portion 11, forming a slanted grating. The convex portions 12 and concave portions 13 are covered with a covering portion made of a material having a refractive index different from that of the flat plate portion 11. The material constituting the diffraction grating portion 10 is not limited, but as an example, the material constituting the flat plate portion 11 and the convex portions 12 is a dielectric material having a refractive index of about 2.5 and mainly composed of TiO ₂ , and the covering portion covering the convex portions 12 and concave portions 13 is a glass or polymer mainly composed of SiO ₂ .

The uneven portion of the diffraction grating portion 10 can be formed by a known method, such as photolithography, nanoimprinting, or EBL (Electron Beam Lithography). In addition, the covering portion can be held in an inclined state and the protrusions 12 and recesses 13 can be formed at an angle φ by using a reactive ion etching (RIE) method or the like. In this case, the inclination angle φ of the protrusions 12 and recesses 13 is the angle between the line connecting the center of the upper end and the lower end of the protrusion 12 and the main surface of the diffraction grating portion 10. In FIG. 1, a slanted grating in which the protrusions 12 and recesses 13 are inclined is shown as the uneven portion of the diffraction grating portion 10, but a pillared grating perpendicular to the main surface may also be used.

Next, the optical path in the diffraction grating section 10 will be described with reference to FIG. 1. Note that FIG. 1 uses arrows to show the progression of light in the diffraction grating section 10, but does not reflect the exact position of incidence, progression path, or exit position of the light. Laser light is irradiated toward the diffraction grating section 10 from a light source section (not shown). Here, the laser light is coherent light with a uniform phase, and is irradiated as collimated light by a collimating lens or the like. The incident light irradiated from the light source section enters the inside of the flat plate-shaped section 11 from the interface of the diffraction grating section 10 at a predetermined inclination angle.

Here, the polarization direction of the incident light is parallel to the stripes of the convex portions 12. In FIG. 1, an example is shown in which the inclination angle of the incident light and the inclination direction φ of the convex portions 12 and the concave portions 13 in the diffraction grating portion 10 are the same direction, but they may be opposite directions. A portion of the light incident on the diffraction grating portion 10 travels toward the outside at a predetermined angle as diffracted light due to the periodic refractive index difference between the convex portions 12 and the concave portions 13, and a portion of the light propagates as leaky propagating light within the plane of the flat portion 11 as propagating light. The leaky propagating light propagating within the flat portion 11 is reflected at the interface with the air and reaches the concave portions again, where it is diffracted by the convex portions 12 and the concave portions 13.

In the example shown in FIG. 1, of the light diffracted by the diffraction grating section 10, the zeroth order light T1 passes through the coating and is irradiated to the outside. In addition, the primary light (-1st order light T2) diffracted in the direction in which the convex section 12 is tilted also passes through the coating and is irradiated to the outside. This is because the zeroth order light T1 and -1st order light T2 are diffracted at an angle close to perpendicular to the main surface of the diffraction grating section 10, and therefore do not satisfy the condition for total reflection at the interface between the coating and the air layer.

The primary light (+1st order light I1) diffracted in the opposite direction to the inclination of the convex portion 12 is totally reflected by the interface between the coating portion and the air layer and propagates within the coating portion. Similarly, the secondary light (-2nd order light I2) diffracted in the inclination direction of the convex portion 12 is totally reflected by the interface between the coating portion and the air layer and propagates within the coating portion. The total reflection condition at the interface between the coating portion and the air layer is determined by the refractive index of the material that constitutes the coating portion. The +1st order light I1 and -2nd order light I2 that are totally reflected and propagate within the coating portion are irradiated to the outside from the end of the coating portion. At this time, the 0th order light T1, -1st order light T2, +1st order light I1, and -2nd order light I2 are diffracted by the convex portion 12 and the concave portion 13, so the light diameter slightly expands as they proceed.

Figure 2 is a schematic diagram showing the structure of the image projection device according to this embodiment. As shown in Figure 2, the image projection device includes a diffraction grating section 10, a light guide plate section 20, an external screen 30, and image projection sections 40 and 50. A viewer wearing the image projection device visually recognizes the direction of the light guide plate section 20 and the external screen 30 from the position of a viewpoint 60. As shown in Figure 1, the diffraction grating section 10 is an optical element including a flat plate-shaped portion 11, a convex portion 12, a concave portion 13, and a covering portion, and is formed separately from the light guide plate section 20. The light guide plate section 20 is a plate-shaped member made of a light-transmitting material, and includes a light guide section 21, a light entrance section 22, a beam splitter 23, and a retroreflection section 24.

The optical waveguide 21 is a flat plate-shaped member made of a light-transmitting material, and guides light from one end to the other end by repeating total reflection at the interface with air. In addition, since light is transmitted from one surface of the optical waveguide 21 to the other surface, it is possible to view the direction of the external screen 30 through the optical waveguide 21 from the viewpoint 60. At one end of the optical waveguide 21, a light entrance section 22 that is a surface inclined with respect to the main surface is formed, and a diffraction grating section 10 is arranged. At the other end of the optical waveguide 21, an end face is formed and a retroreflection section 24 is provided. Although a flat plate-shaped optical waveguide 21 is shown in FIG. 1, it may be a curved shape as long as light can be propagated by total reflection inside.

The light entrance section 22 is an inclined surface formed at one end of the optical waveguide section 21, and is adjacent to the diffraction grating section 10, which corresponds to the first light entrance section in the present invention. The light entrance section 22 may be provided with an anti-reflection film or a refractive index adjustment section to increase the optical coupling rate with the diffraction grating section 10.

The beam splitter 23 is an optical element that reflects a portion of the light incident on one side and transmits the remainder. In the example shown in FIG. 1, it is formed as a flat surface inclined with respect to the main surface inside the optical waveguide section 21. The specific configuration of the beam splitter 23 is not limited, and known structures and design methods can be used.

The retroreflective section 24 is an optical element that reflects incident light while maintaining its focusing ability in the direction of incidence, and can be a retroreflective section with a structure in which tiny glass beads are spread on the surface side of a reflective film or a structure using prisms. When light that has propagated through the optical waveguide section 21 is incident on the retroreflective section 24, the light is reflected in the direction in which it was incident, so that light that travels with an expanding light diameter is reflected as light with a shrinking light diameter.

As described below, the area in the optical waveguide 21 between the area where the beam splitter 23 is provided and the end where the retroreflecting section 24 is provided is an area where the light propagating through the optical waveguide 21 is irradiated to the outside, and constitutes the first light emitting section in the present invention.

The external screen 30 is a part on which light irradiated from the light guide plate unit 20 is projected to display an image, as described below. The material constituting the external screen 30 is not limited, and a light-transmitting material that transmits light may be used, or a white material that blocks and reflects light may be used. When a light-transmitting material is used, superimposed images can be projected with the external environment of the image projection device as the background. In the example shown in FIG. 1, the external screen 30 and the arm portion are integrally formed, and the arm portion is fixed to the light guide plate unit 20, thereby maintaining the relative positional relationship between the external screen 30 and the light guide plate unit 20, but the external screen 30 may be provided separately from the image projection device.

The image irradiation unit 40 is a device that irradiates the diffraction grating unit 10 with the first light for projecting the first image, and corresponds to the first image irradiation unit in the present invention. The specific configuration of the image irradiation unit 40 is not limited, but in the example shown in FIG. 1, the image irradiation unit 40 includes a light source unit 41, a half-wave plate 42, and polarizers 43 and 44. The image irradiation unit 40 irradiates the diffraction grating unit 10 with light via mirrors 45, 46, and 47 and a bandpass filter 48. The light source unit 41 preferably uses a laser light source, and the laser light irradiated from the light source unit 41 is irradiated to an image forming unit (not shown) to include the first image in the first light. The image forming unit may be a known one such as a liquid crystal display element or a digital mirror device, and may be provided inside the image irradiation unit 40 or may be disposed on the optical path to the diffraction grating unit 10. By equipping the image projection unit 40 with a liquid crystal display element or digital mirror device as the image forming unit, it is also possible to change the content of the first image contained in the first light over time and project a moving image.

The image irradiation unit 50 is a device that irradiates the diffraction grating unit 10 with the second light for projecting the second image, and corresponds to the second image irradiation unit in the present invention. The image irradiation unit 50 is provided separately from the image irradiation unit 40, and the angle of incidence of the second light on the diffraction grating unit 10 is different from the angle of incidence of the first light irradiated by the image irradiation unit 40. The specific configuration of the image irradiation unit 50 is not limited, and a configuration similar to that of the image irradiation unit 40 can be used, but the wavelengths of the first light and the second light are different.

Next, image projection in the image projection device of this embodiment will be described with reference to Figures 2 and 3. Figure 3 is a schematic cross-sectional view showing an enlarged view of the first light output section of the image projection device of this embodiment. The solid and dashed arrows in the figure show schematic diagrams of the path of light.

The first light irradiated from the image irradiation unit 40 is reflected by mirrors 45, 46, and 47 and reaches the diffraction grating unit 10 via the bandpass filter 48. In the diffraction grating unit 10, the zeroth order light T1 and the +1st order light I1 are extracted as diffracted light according to the incident angle of the first light, and are incident on the light incident unit 22. The first light incident on the light incident unit 22 from the diffraction grating unit 10 is totally reflected within the optical waveguide unit 21 and propagates as guided light. Here, the angle of incidence of the first light incident on the light incident unit 22 from the diffraction grating unit 10 to the light incident unit 22 is determined by the diffraction condition, so the inclination angle of the light incident unit 22 is set so that any one of the zeroth order light T1, -1st order light T2, +1st order light I1, and -2nd order light I2 satisfies the total reflection condition on both sides of the optical waveguide unit 21.

The first light propagates as guided light while being totally reflected within the optical waveguide 21, and part of it is reflected by one surface of the beam splitter 23, while the remainder is transmitted through the beam splitter 23. The guided light reflected by the beam splitter 23 is extracted as the illumination light LE in the direction of the external screen 30, and the image EX is projected onto the external screen 30. Here, by designing the reflectance of one surface of the beam splitter 23 to be low, it is also possible to suppress the intensity of the illumination light LE and make the image EX invisible.

The guided light that passes through the beam splitter 23 is again totally reflected by the optical waveguide 21 and reaches the retroreflection section 24 where it is retroreflected. The guided light retroreflected by the retroreflection section 24 travels in the opposite direction within the optical waveguide 21, is totally reflected, reaches the beam splitter 23 where it is reflected, and is extracted as imaging light L1 in the direction of the viewpoint 60. At this time, the optical diameter of the guided light that has propagated through the optical waveguide 21 is enlarged, but the optical diameter of the guided light reflected by the retroreflection section 24 is reduced as it travels. In the example shown in Figures 2 and 3, the reflective surface of the retroreflection section 24 is concave, so the optical diameter is further reduced as it reaches the beam splitter 23.

Therefore, the imaging light L1 reflected by the beam splitter 23 and traveling in the direction of the viewpoint 60 is focused at a predetermined position, and an aerial image A1 is formed in the air. If the retroreflecting section 24 is formed with a flat surface, the optical path length from the diffraction grating section 10 to the retroreflecting section 24 and the optical path length from the retroreflecting section 24 to the aerial image A1 will be the same. After forming the aerial image A1, the imaging light L1 enters the viewpoint 60 while expanding its light diameter. As a result, by looking in the direction of the optical waveguide section 21 and the external screen 30 from the viewpoint 60, the viewer can simultaneously view the aerial image A1 formed in the air and the image EX projected on the external screen 30.

2 and 3 show that the other end of the optical waveguide 21 is formed in a convex shape and the retroreflective section 24 is formed in a concave shape, but the other end may be formed in a flat or concave shape and the retroreflective section 24 may be formed in a flat or convex shape. By appropriately designing the shape and curvature of the retroreflective section 24, it is possible to adjust the reduction rate of the light diameter after retroreflection by the retroreflective section 24, and to fine-tune the position where the aerial image A1 is formed after reflection by the beam splitter 23.

In addition, the guided light propagating through the optical waveguide 21 must be totally reflected at the interface with air at least once before reaching the retroreflecting portion 24 from the beam splitter 23. It is preferable to select either an even number or an odd number of total reflections at the interface depending on the optical design. By ensuring a distance between the beam splitter 23 and the retroreflecting portion 24 that allows light to be totally reflected between them, it is possible to prevent the retroreflecting portion 24 from being located near the center of the field of view when the direction of the external screen 30 is viewed from the viewpoint 60 through the beam splitter 23. In addition, since the retroreflecting portion 24 does not transmit light and is visible, it is not preferable for the retroreflecting portion 24 to be located in the center of the field of view because this reduces the visibility of the aerial image A1.

Furthermore, of the first light diffracted and branched by the diffraction grating section 10, that which does not satisfy the condition for total reflection on both sides of the optical waveguide section 21 is extracted as irradiation light LV to the outside from the surface of the optical waveguide section 21 facing the external screen 30. Here, the region of the optical waveguide section 21 from which the irradiation light LV is extracted corresponds to the second light output section in the present invention. The irradiation light LV extracted from the second light output section reaches the external screen 30 and projects an image V1 (not shown).

2, the viewing direction, which is the traveling direction of the imaging light L1, and the external screen direction, which is the traveling direction of the irradiation light LV, are approximately parallel. As a result, even if the distance between the external screen 30 and the optical waveguide unit 21 is changed, the projection position of the image V1 on the external screen 30 does not change. Therefore, when the viewer views the external screen 30 direction from the viewing point 60, the position where the aerial image A1 is formed and the position where the image V1 is projected do not overlap, and it becomes possible to view the aerial image A1 and the image V1 side by side within the same field of view. Here, an example is shown in which the viewing direction and the external screen direction are parallel, but they may be directions in which they intersect at a predetermined angle. By appropriately setting the distance between the external screen 30 and the optical waveguide unit 21, the projection position of the image V1 on the external screen 30 can be adjusted, so that the positional relationship between the aerial image A1 and the image V1 can be adjusted and viewed at the viewing point 60.

The second light irradiated from the image irradiation unit 50 can also project the image EX and form the aerial image A1 in the same manner as the first light, by a part of the light diffracted by the diffraction grating unit 10 satisfying the total reflection condition in the optical waveguide unit 21. In addition, the image V1 can be projected by the second light diffracted by the diffraction grating unit 10 that does not satisfy the total reflection condition in the optical waveguide unit 21. In addition, the second light diffracted by the diffraction grating unit 10 may not all satisfy the total reflection condition in the optical waveguide unit 21, and only the image V1 may be projected on the external screen 30 with the second light. In addition, the second light irradiated from the image irradiation unit 50 may not be incident on the diffraction grating unit 10, but may be incident on the surface of the optical waveguide unit 21 facing the viewpoint 60, and the image V1 may be directly projected on the external screen 30. In this case, the area through which the irradiation light LV for projecting the image V1 passes corresponds to the second light emission unit in the optical waveguide unit 21.

Figure 4 shows photographs taken by a camera installed at viewpoint 60, capturing image EX projected on external screen 30 and aerial image A1 formed in the air. In Figure 4(a), the camera is focused on external screen 30, and in Figure 4(b), the camera is focused on the position where aerial image A1 is formed. In Figures 4(a) and 4(b), the left photograph shows how the images are viewed in a bright state with the interior light turned on, and the right photograph shows how the images are viewed in a dark state with the interior light turned off. Image EX and aerial image A1 are captured at the positions indicated by white ellipses in the photographs. As shown in Figure 4(a), image EX is difficult to view in a bright environment, but is viewable in a dark environment. Also, as shown in Figure 4(b), aerial image A1 is viewable in both a bright environment and a dark environment. Also, aerial image A1 and image EX are viewable close to each other in the same field of view, and the viewer can select the object to view simply by adjusting the focal length of the view.

As described above, in the image projection device of this embodiment, the first light is split by the beam splitter 23 to project the image EX onto the external screen 30, and the first light is retroreflected by the retroreflection section 24 at the end of the optical waveguide section 21, and the beam splitter 23 reflects the first light in the direction of the viewpoint to form an aerial image A1. This makes it possible to project and visually recognize multiple images at positions with different distances from the viewpoint. In addition, since the diffraction grating section 10 is provided in the light entrance section 22 of the light guide plate section 20, and the beam splitter 23 and the retroreflection section 24 are provided to form the first light exit section, complex optical design and an increase in the number of parts are not required, making it possible to achieve a smaller size and lighter weight.

Second Embodiment
Next, a second embodiment of the present invention will be described with reference to FIG. 5 and FIG. 6. The description of the contents overlapping with the first embodiment will be omitted. FIG. 5 is a schematic cross-sectional view showing an enlarged first light emitting section of the image projection device according to this embodiment. The solid line arrow and the dashed line arrow shown in the figure show the path of light. The area hatched with diagonal lines in the figure shows the area where the irradiation light LV is irradiated. The image projection device of this embodiment differs from the first embodiment only in the projection position of the image V1, and the other configurations are the same as those described in the first embodiment with reference to FIG. 1. In this embodiment, the second light irradiated from the image irradiation unit 50 is set as the irradiation light LV, and the external screen direction, which is the traveling direction of the irradiation light LV, is crossed with the viewing direction to project the image EX and the image V1 onto the same area.

As shown in FIG. 5, the light propagating through the optical waveguide 21 after total reflection is split by the beam splitter 23 and projected as irradiation light LE onto the external screen 30 as an image EX. The light transmitted through the beam splitter 23 is again totally reflected by the optical waveguide 21 and reaches the retroreflection section 24, where it is retroreflected and then reflected by the beam splitter 23 to form an aerial image A1 as imaging light L1.

The direction of travel of the illumination light LV projected from the second light emitting unit onto the external screen 30 intersects with the viewing direction, which is the direction of travel of the imaging light L1. In the example shown in FIG. 5, the second light irradiated from the image irradiating unit 50 is not incident on the diffraction grating unit 10, but is directly irradiated as illumination light LV to the external screen 30 via the optical waveguide unit 21, and the image V1 is projected onto the external screen 30.

Figure 6 shows photographs taken with a camera placed at viewpoint 60, capturing images EX and V1 projected onto external screen 30, and an aerial image A1 focused in the air; in Figure 6(a) the camera is focused on external screen 30, and in Figure 6(b) the camera is focused on the position where aerial image A1 is focused. Image EX and aerial image A1 are captured at the positions indicated by white ellipses in the photographs, and image V1 is captured over a larger area than image EX. As shown in Figure 6(a), image EX is displayed superimposed on image V1, making it possible to view both at the same time. Furthermore, the viewer can select the object to view simply by adjusting the focal length of their vision.

In this embodiment, image V1 is projected over a wide area of the external screen 30 using the second light as the irradiation light LV, so that image projection can be performed in which image V1 is used as a background image and is superimposed on aerial image A1. In addition, by projecting image EX onto the external screen 30, the projection positions of image V1, which is the background image, and image EX are at the same distance from viewpoint 60, and the viewer can simultaneously view two different images V1, A1, and image EX.

Third Embodiment
Next, a third embodiment of the present invention will be described with reference to Fig. 7 to Fig. 10. Description of the contents overlapping with the first embodiment will be omitted. This embodiment differs from the first embodiment in that a partial reflection section that reflects a part of the guided light with a predetermined reflectance and transmits the rest is provided between the beam splitter 23 and the retroreflection section 24 that constitute the first light output section. Fig. 7 is a schematic diagram showing the structure of an image projection device according to this embodiment.

As shown in FIG. 7, the image projection device includes a diffraction grating section 10, a light guide plate section 20, an external screen 30, and image projection sections 40 and 50. A viewer wearing the image projection device views the light guide plate section 20 and the external screen 30 from a viewpoint 60. As shown in FIG. 1, the diffraction grating section 10 is an optical element including a flat plate-like portion 11, a convex portion 12, a concave portion 13, and a covering portion, and is formed separately from the light guide plate section 20. The light guide plate section 20 is a plate-like member made of a light-transmitting material, and includes a light guide section 21, a light entrance section 22, a beam splitter 23, a retroreflection section 24, and a partial reflection section 25.

The partial reflection section 25 is an optical element that reflects a portion of light at a predetermined reflectance and transmits the remaining light, and is provided on the optical path between the beam splitter 23 and the retroreflection section 24. In the example shown in FIG. 7, the partial reflection section 25 is formed between the end of the optical waveguide section 21 and the retroreflection section 24. Also, FIG. 7 shows an example in which the end of the optical waveguide section 21, the retroreflection section 24, and the partial reflection section 25 are flat, but as in the first embodiment, they may be a convex shape and a concave mirror, or a concave shape and a convex mirror. They may also be a combination of three-dimensional parabolic concave and convex shapes.

Figure 8 is a schematic cross-sectional view showing an enlarged view of the first light output section of the image projection device according to this embodiment. The solid and dashed arrows in the figure show the path of light. The hatched area in the figure shows the area where the irradiation light LV is irradiated. As in the first embodiment, the first light irradiated from the image irradiation section 40 or the second light irradiated from the image irradiation section 50 enters the optical waveguide section 21 from the light entrance section 22 and is guided as guided light while being totally reflected by the optical waveguide section 21. The guided light reflected by the beam splitter 23 is extracted as irradiation light LE for the external screen 30, and projects the image EX onto the external screen 30.

The guided light that passes through the beam splitter 23 is reflected by the partial reflection section 25 and the retroreflection section 24, then re-enters the beam splitter 23 and is reflected, and is extracted as imaging light L1, L2 in the direction of the viewpoint 60. At this time, since the light reflected by the partial reflection section 25 is specular reflection, the guided light that has been propagating within the optical waveguide section 21 while expanding in diameter continues to expand in diameter until it is reflected by the beam splitter 23 and reaches the viewpoint 60. As a result, at the viewpoint 60, it is visually recognized that an aerial image A2 is formed in the space between the optical waveguide section 21 and the external screen 30.

The light that has passed through the partial reflection section 25 enters the retroreflection section 24, where the guided light is retroreflected and reflected by the beam splitter 23, traveling with its light diameter shrinking until it reaches the viewpoint 60. As a result, at the viewpoint 60, an aerial image A1 appears to be formed in the space between the optical waveguide section 21 and the viewpoint 60. The traveling direction of the illumination light LV projected from the second light emission section onto the external screen 30 intersects with the viewing direction, which is the traveling direction of the imaging light L1 and L2, and the image V1 is projected onto the external screen 30.

Figure 9 shows photographs taken with a camera placed at viewpoint 60, capturing images EX and V1 projected onto external screen 30, and aerial images A1 and A2 focused in the air; in Figure 9(a) the camera was focused on the position where aerial image A1 is focused, in Figure 9(b) the camera was focused on the position where aerial image A2 is focused, and in Figure 9(c) the camera was focused on external screen 30. Aerial images A1, A2 and image EX are captured at the positions indicated by white ellipses in the photographs, and image V1 is captured over a larger area than image EX.

As shown in FIG. 9(a), by focusing on the viewpoint 60 side of the optical waveguide 21, aerial image A1 can be clearly projected. Also, as shown in FIG. 9(b), by focusing between the optical waveguide 21 and the external screen 30, aerial image A2 can be clearly projected. Also, as shown in FIG. 9(c), by focusing on the external screen 30, images EX and V1 can be clearly projected. Also, aerial images A1, A2 and images EX and V1 can be viewed closely in the same field of view, and the viewer can select the object to view simply by adjusting the visual focal length.

Figure 10 shows the beam profiles of aerial images A1 and A2, where Fig. 10(a) is a photograph focused from viewpoint 60, Figs. 10(b) and (c) show the three-dimensional luminance profile at the imaging position, Fig. 10(d) is the luminance profile in the x direction, and Fig. 10(e) is the luminance profile in the y direction. Figs. 10(a) and (b) show enlarged views of the areas surrounded by white lines in Figs. 9(a) and (b), respectively. Figs. 10(c) to 10(e) show the measurement results of the luminance at the imaging positions of aerial images A1 and A2, respectively. The "x direction" and "y direction" shown in Fig. 10 refer to the x-axis and y-axis directions shown in Fig. 9(c).

As shown in Figures 10(a) to 10(c), aerial image A1 is formed as an ellipse elongated in the x-axis direction, and aerial image A2 is formed as an ellipse elongated in the y-axis direction. Also, as shown in Figures 10(d) and 10(e), the half-width of aerial image A1 in the x-axis direction is about 31 pixels, and the half-width in the y-axis direction is about 10 pixels. Also, the half-width of aerial image A2 in the x-axis direction is about 20 pixels, and the half-width in the y-axis direction is about 25 pixels. Therefore, aerial images A1 and A2 are formed in different shapes, and the shapes perceived by the viewer when they change the focal length of their vision will change between aerial images A1 and A2.

As described above, in the image projection device of this embodiment, an aerial image A2 is formed by the guided light specularly reflected by the partial reflection section 25 at the end of the light guide section 21, and an aerial image A1 is formed by the guided light retroreflected by the retroreflection section 24. In addition, an image EX and an image V1 are projected onto an external screen 30. This makes it possible to project and visually recognize multiple images at positions at different distances from the viewpoint. In addition, a diffraction grating section 10 is provided at the light entrance section 22 of the light guide plate section 20, and the first light exit section is configured by providing a beam splitter 23, a partial reflection section 25, and a retroreflection section 24, so that a complex optical design or an increase in the number of parts is not necessary, and it is possible to achieve a smaller size and lighter weight.

Fourth Embodiment
Next, a fourth embodiment of the present invention will be described with reference to Fig. 11. Description of the contents overlapping with the first embodiment will be omitted. Fig. 11 is a schematic diagram showing the structure of an image projection device according to this embodiment. In this embodiment, two light guide plate sections 20 are provided, and a common diffraction grating section 10 is arranged opposite the light entrance section 22 provided in each light guide plate section 20.

As shown in FIG. 11, the image projection device includes one diffraction grating section 10, two light guide plate sections 20, an external screen 30, and image projection sections 40, 50. A viewer wearing the image projection device views the light guide plate section 20 and the external screen 30 with both eyes from two viewpoints 60. As shown in FIG. 1, the diffraction grating section 10 is an optical element that includes a flat plate-like portion 11, a convex portion 12, a concave portion 13, and a covering portion, and is formed separately from the light guide plate section 20. The light guide plate section 20 is a plate-like member made of a light-transmitting material, and includes a light guide section 21, a light entrance section 22, a beam splitter 23, and a retroreflection section 24.

The two light guide plate sections 20 are arranged so that their light entrance sections 22 are adjacent to each other, and a common diffraction grating section 10 is arranged facing each other across the two light entrance sections 22. In addition, a first light is incident on the diffraction grating section 10 from one image irradiation section 40, and the first light diffracted by the diffraction grating section 10 is incident on the light guide section 21 from the light entrance section 22 of each light guide plate section 20. The two light guide plate sections 20 are each flat and arranged in a V shape.

As shown in FIG. 1, in the diffraction grating section 10, the first light is diffracted by the uneven portion formed by the convex portions 12 and concave portions 13, and the zeroth order light T1 and the +1st order light I1 travel to the right in the figure, and the -1st order light T2 and the -2nd order light I2 travel to the left in the figure. Therefore, the zeroth order light T1 and the +1st order light I1 are incident on the optical waveguide section 21 arranged opposite the right half of the diffraction grating section 10, and the -1st order light T2 and the -2nd order light I2 are incident on the optical waveguide section 21 arranged opposite the left half of the diffraction grating section 10.

In the example shown in FIG. 11, the inclination angle of the light incident portion 22 and the shape of the light guiding portion 21 are designed so that the +1st order light I1 satisfies the total reflection condition of the light guiding portion 21 located on the right side, so that the +1st order light I1 is guided as guided light. Similarly, the inclination angle of the light incident portion 22 and the shape of the light guiding portion 21 are designed so that the -2nd order light I2 satisfies the total reflection condition of the light guiding portion 21 located on the left side, so that the -2nd order light I2 is guided as guided light.

The first light (guided light) guided through the two light guide plate sections 20 is reflected by the beam splitter 23 and the retroreflecting section 24 provided on the other end side, extracted in the direction of the viewpoint 60, and forms an aerial image A1. Although not shown in FIG. 11, if a partial reflecting section 25 is provided between the retroreflecting section 24 and the beam splitter 23 as in the third embodiment, an aerial image A2 can also be formed between the light guide section 21 and the external screen 30.

The image projection unit 50 can project the image V1 over a wide area on the external screen 30 by projecting the projection light LV directly onto the external screen 30 via the light guide plate unit 20. In FIG. 11, the projection light LV projected from the image projection unit 50 onto the left half of the external screen 30 is shown, but by using a separate optical member such as a lens, the projection light LV can be projected onto the entire area of the external screen 30, so that the image V1 is projected onto the entire area of the external screen 30, covering the entire field of view.

As described above, in the image projection device of this embodiment, a common diffraction grating section 10 is provided on the two light guide plate sections 20, so that the image formation of aerial images A1 and A2 can be visually recognized by both eyes of the viewer. In addition, by projecting image V1, which is a background image, onto the external screen 30 with irradiation light LV irradiated by the image irradiation section 50, aerial images A1 and A2 can be projected superimposed on image V1. Furthermore, the image projection device of this embodiment does not require complicated optical design or an increase in the number of parts, making it possible to achieve a smaller size and lighter weight.

(Modification of the fourth embodiment)
Next, a modified example of the fourth embodiment of the present invention will be described with reference to Fig. 12. Description of the contents overlapping with the first embodiment will be omitted. Fig. 12 is a schematic diagram showing the structure of an image projection device according to a modified example of the fourth embodiment. This modified example differs from the fourth embodiment in that the light guide plate section 20 has a curved shape.

In the example shown in FIG. 12, the inclination angle of the light entrance section 22 and the shape of the light guide section 21 are designed so that the zero-order light T1 satisfies the total reflection condition of the light guide section 21 arranged on the right side, and thus the zero-order light T1 is guided as guided light. Similarly, the inclination angle of the light entrance section 22 and the shape of the light guide section 21 are designed so that the -1-order light T2 satisfies the total reflection condition of the light guide section 21 arranged on the left side, and thus the -1-order light T2 is guided as guided light. In this modified example, as in the fourth embodiment, the aerial images A1 and A2 formed in the air from two viewpoints 60 and the image V1 projected on the external screen 30 can be viewed.

In the example shown in FIG. 12, the two light guide plate sections 20 have a curved shape along the direction of the viewpoint 60, but since the angle of incidence of the first light from the diffraction grating section 10 to the light entrance section 22 is determined by the diffraction conditions, it is possible to design the light guide plate section 20 so that total reflection is repeated along the curved surface. In addition, in FIG. 12, the left and right light guide plate sections 20 are drawn in a shape close to line symmetry, but the inclination angle of the light entrance section 22 on the left and right may be made different depending on which light of the first light diffracted by the diffraction grating section 10 is to be guided light.

In this modified example, the optical waveguide section 21 has a curved shape, which increases the design freedom of the image projection device, improving its design and comfort when worn.

Fifth Embodiment
Next, a fifth embodiment of the present invention will be described with reference to Figs. 13 and 14. Description of the contents overlapping with the first embodiment will be omitted. Fig. 13 is a schematic diagram showing the structure of an image projection device according to this embodiment. As shown in Fig. 13, the image projection device includes a diffraction grating unit 10, a light guide plate unit 20, an external screen 30, and image projection units 40 and 50. A viewer wearing the image projection device visually recognizes the direction of the light guide plate unit 20 and the external screen 30 from the position of a viewpoint 60.

As shown in FIG. 1, the diffraction grating section 10 is an optical element having a flat portion 11, a convex portion 12, a concave portion 13, and a covering portion, and is formed separately from the light guide plate section 20. The light guide plate section 20 is a plate-shaped member made of a light-transmitting material, and includes a light guide section 21, a light entrance section 22, a beam splitter 23, a retroreflection section 24, a partial reflection section 25, and an optical filter 26. In addition, an optical filter 61, an optical shutter section 62, and a projection lens 63 are provided in the second light exit section from which the second light from the image irradiation section 50 is extracted.

The optical filters 26 and 61 are optical components that transmit light in a predetermined wavelength range and block light of other wavelengths. In this embodiment, a bandpass filter or an equivalent optical filter that blocks the wavelength of the second light and transmits the wavelength of the first light is used as the optical filter 26, and a bandpass filter or an equivalent optical filter that blocks the wavelength of the first light and transmits the wavelength of the second light is used as the optical filter 61. As an example, the first light irradiated by the image irradiation unit 40 is red light, and the second light irradiated by the image irradiation unit 50 is green light. Therefore, the optical filter 26 may be a longpass filter, and the optical filter 61 may be a shortpass filter.

The optical shutter unit 62 is an optical element that is driven and controlled by a control unit (not shown) to switch between transmitting and blocking light. The specific configuration of the optical shutter unit 62 is not limited, and a known liquid crystal shutter or the like can be used. The projection lens 63 is an optical element that expands the light diameter of the irradiation light LV extracted from the second light emitting unit and projects it onto the external screen 30. Although one lens is shown as the projection lens 63 in FIG. 13, the projection lens 63 may be formed by combining multiple lenses.

A portion of the first light irradiated from the image irradiation unit 40 is diffracted by the diffraction grating unit 10 and enters the light entrance unit 22, where it is totally reflected within the optical waveguide unit 21 and guided as guided light. The guided light of the first light reaches the beam splitter 23 while being totally reflected, and a portion of it is reflected to project the image EX onto the external screen 30. Of the guided light of the first light, the light that passes through the beam splitter 23 is totally reflected again and reaches the end of the optical waveguide unit 21.

The guided light of the first light that reaches the end of the optical waveguide 21 passes through the optical filter 26 and enters the partial reflection section 25, where a portion is specularly reflected and the remainder is transmitted and reaches the retroreflection section 24. The guided light is retroreflected in the retroreflection section 24. The first light that is retroreflected in the retroreflection section 24 is focused as an aerial image A1 in the air between the viewpoint 60 and the optical waveguide 21, as described in the first embodiment. The light that is specularly reflected in the partial reflection section 25 is focused as an aerial image A2 in the air between the optical waveguide 21 and the external screen 30.

The first light that does not satisfy the total reflection condition in the optical waveguide section 21 is extracted from the second light output section toward the external screen 30. However, since the second light output section is provided with an optical filter 61, the first light is blocked by the optical filter 61 and is not projected onto the external screen 30.

The second light irradiated from the image irradiation unit 50 is diffracted by the diffraction grating unit 10 and enters the light entrance unit 22, where a portion of the light is totally reflected within the optical waveguide unit 21 and guided as guided light. At this time, the angle of incidence of the second light on the diffraction grating unit 10 can be set to be different from the angle of incidence of the first light, and an angle of incidence that provides appropriate diffraction conditions can be selected, so that the angles of incidence of the first light and the second light on the optical waveguide unit 21 can be set to be the same. In addition, if the positions of incidence of the first light and the second light on the diffraction grating unit 10 are also the same, the paths of the first light and the second light that are totally reflected and guided within the optical waveguide unit 21 can be made the same.

The guided light of the second light also reaches the beam splitter 23 while being totally reflected, and a portion of it is reflected and image EX is projected onto the external screen 30. Of the guided light of the second light, the light that passes through the beam splitter 23 is totally reflected again and reaches the end of the optical waveguide section 21. The guided light of the second light that reaches the end of the optical waveguide section 21 is blocked by the optical filter 26 and does not reach the partial reflection section 25 or the retroreflection section 24. Therefore, there is no second light that is reflected back to the beam splitter 23, and aerial images A1 and A2 are not formed by the second light.

The second light that does not satisfy the total reflection condition in the optical waveguide section 21 is extracted from the second light exit section toward the external screen 30, and when the optical shutter section 62 is in a transmitting state, the irradiated light LV is irradiated onto the external screen 30 via the projection lens 63, and the image V1 is projected. When the optical shutter section 62 is in a blocking state, the irradiated light LV of the second light is blocked, and the image V1 is not projected.

As described above, in this embodiment, the optical filter 26 is provided between the beam splitter 23 and the retroreflection section 24, so that the aerial images A1 and A2 can be formed using only the first light. Furthermore, the optical filter 61 is provided in the second light emission section, so that the image V1 can be projected onto the external screen 30 using only the second light. Therefore, by differentiating the contents of the aerial images A1 and A2 formed using the first light irradiated from the image irradiation section 40 from the contents of the image V1 projected using the second light irradiated from the image irradiation section 50, a variety of image projections can be realized.

In addition, the image projection unit 40 can include a lens optical unit with a variable focal length to adjust the spread angle of the first light incident on the diffraction grating unit 10, thereby changing the imaging efficiency of the aerial images A1 and A2.

(Modification of the fifth embodiment)
Next, a modified example of the fifth embodiment of the present invention will be described with reference to FIG. 14. Descriptions of contents overlapping with the first embodiment will be omitted. FIG. 14 is a schematic diagram showing the structure of an image projection device according to a modified example of the fifth embodiment. As shown in FIG. 14, the image projection device includes a diffraction grating unit 10, a light guide plate unit 20, an external screen 30, and image projection units 40a, 40b, and 50.

In this modified example, the image irradiation unit 40a irradiates a first light of a first wavelength including a first image, the image irradiation unit 40b irradiates a second light of a second wavelength including a second image, and the image irradiation unit 50 irradiates a third light of a third wavelength including a third image. As an example, the first wavelength is red light, the second wavelength is blue light, and the third wavelength is green light. In this modified example, a notch filter that blocks the third wavelength and transmits the first and second wavelengths is used as the optical filter 26, and a bandpass filter that blocks the first and second wavelengths and transmits the third wavelength is used as the optical filter 61. In this modified example, a dichroic mirror (selective reflection unit) that reflects the first wavelength and transmits the second wavelength is used as the partial reflection unit 25.

The angles of incidence of the first light, second light, and third light irradiated from the image irradiation units 40a, 40b, and 50 to the diffraction grating unit 10 are selected to satisfy appropriate diffraction conditions, and the light incident on the optical waveguide unit 21 from the diffraction grating unit 10 is totally reflected along the same path and propagates within the optical waveguide unit 21.

Of the first and second lights irradiated from the image irradiation units 40a and 40b, a portion of the light diffracted by the diffraction grating unit 10 enters the light entrance unit 22 and is totally reflected within the optical waveguide unit 21 and guided as guided light. The guided light of the first and second lights reaches the beam splitter 23 while being totally reflected, and a portion of it is reflected to project the image EX onto the external screen 30. Of the guided light of the first and second lights, the light that passes through the beam splitter 23 is totally reflected again and reaches the end of the optical waveguide unit 21.

The guided light of the first light that reaches the end of the optical waveguide 21 passes through the optical filter 26, enters the partial reflector 25, and is specularly reflected. The first light specularly reflected by the partial reflector 25 is focused as an aerial image A2 in the air between the optical waveguide 21 and the external screen 30. The guided light of the second light that reaches the end of the optical waveguide 21 passes through the optical filter 26 and the partial reflector 25, enters the retroreflector 24, and is retroreflected. The second light retroreflected by the retroreflector 24 is focused as an aerial image A1 in the air between the viewpoint 60 and the optical waveguide 21, as described in the first embodiment.

The first light and the second light that do not satisfy the total reflection condition in the optical waveguide section 21 are extracted from the second light output section toward the external screen 30. However, since the second light output section is provided with an optical filter 61, the first light and the second light are blocked by the optical filter 61 and are not projected onto the external screen 30.

Of the third light irradiated from the image irradiation unit 50, a portion of the light diffracted by the diffraction grating unit 10 enters the light entrance unit 22 and is totally reflected within the optical waveguide unit 21 and guided as guided light. The guided light of the third light also undergoes total reflection as it reaches the beam splitter 23, where a portion of it is reflected and the image EX is projected onto the external screen 30. Of the guided light of the third light, the light that passes through the beam splitter 23 is totally reflected again and reaches the end of the optical waveguide unit 21.

The guided third light that reaches the end of the optical waveguide 21 is blocked by the optical filter 26 and does not reach the partial reflection section 25 or the retroreflection section 24. Therefore, there is no third light that is reflected back to the beam splitter 23, and the aerial images A1 and A2 are not formed by the third light.

The third light that does not satisfy the total reflection condition in the optical waveguide section 21 is extracted from the second light output section toward the external screen 30, and when the optical shutter section 62 is in a transmitting state, the irradiated light LV is irradiated onto the external screen 30 via the projection lens 63, and the image V1 is projected. When the optical shutter section 62 is in a blocking state, the irradiated light LV of the second light is blocked, and the image V1 is not projected.

As described above, in this embodiment, the optical filter 26 is provided between the beam splitter 23 and the retroreflection section 24, so that the aerial images A1 and A2 can be formed using the first light and the second light, respectively. In addition, the optical filter 61 is provided in the second light output section, so that the image V1 can be projected onto the external screen 30 using only the third light. Therefore, by differentiating the contents of the aerial images A1 and A2 formed using the first light and the second light irradiated from the image irradiation section 40 from the contents of the image V1 projected using the third light irradiated from the image irradiation section 50, a variety of image projections can be realized.

Sixth Embodiment
Next, a sixth embodiment of the present invention will be described with reference to Fig. 15. Descriptions of contents overlapping with the first embodiment will be omitted. Fig. 15 is a schematic diagram showing a structural example of the retroreflective portion 24 in this embodiment. As shown in Fig. 15, the retroreflective portion 24 has microbeads selectively formed on a sheet portion 24a, and is formed by mixing a retroreflective region 24b where the microbeads are formed and a regular reflection region 24c where the sheet portion 24a is exposed.

The sheet portion 24a is a thin plate-like member whose surface is formed as a reflective surface. The sheet portion 24a is preferably flexible, and by being flexible, it can take the shape of a flat plate as shown in FIG. 15(a), a concave mirror as shown in FIG. 15(b), or a convex mirror as shown in FIG. 15(c).

The retroreflective area 24b is an area where microbeads are formed on the surface of the sheet portion 24a, and light that is incident on the retroreflective area 24b is reflected within the microbeads and is retroreflected in the direction from which it was incident. No microbeads are formed in the specular reflection area 24c, and the reflective surface of the sheet portion 24a is exposed, so that light that is incident on the specular reflection area 24c is specularly reflected by the reflective surface of the sheet portion 24a.

The retroreflective portion 24 in this embodiment can be formed by a method such as forming a mask on the regular reflection region 24c of the sheet portion 24a using photolithography technology, and depositing microbeads in the areas where the mask is not formed to form the retroreflective region 24b. After depositing the microbeads, the mask layer is removed to expose the reflective surface of the sheet portion 24a in the regular reflection region 24c.

As shown in Figures 15(a) to 15(c), a portion of the light that enters the retroreflective portion 24 while its light diameter is expanding is retroreflected in the retroreflective region 24b as imaging light L1, and is reflected with a reduced light diameter. In addition, in the regular reflection region 24c, the light is retroreflected as imaging light L2, and is reflected with an expanded light diameter. Here, as shown in Figures 15(a) to 15(c), it is possible to adjust the expansion and reduction rates of the light diameters of the imaging light L1 and L2 depending on whether the retroreflective portion 24 is a flat plate, a concave mirror, or a convex mirror.

By using the retroreflection section 24 of this embodiment, the guided light that reaches the end of the optical waveguide section 21 is partially reflected again and the remainder is specularly reflected, so that aerial images A1 and A2 can be formed in the same manner as in the third embodiment shown in FIG. 8. The difference from the third embodiment is that the sheet section 24a is a thin plate-like member and has flexibility, as described above. In addition, the retroreflection efficiency can be designed by adjusting the arrangement and purity of the microbeads on the surface of the sheet section 24a. In addition, a reflective retroreflection element or a retroreflection type optical filter that combines reflection and retroreflection can be configured by evaporating a thin metal film on the surface of the sheet section 24a. By using these structures in the sheet section 24a, the degree of freedom of optical design and the design can be improved.

Seventh Embodiment
Next, a seventh embodiment of the present invention will be described. Descriptions of contents overlapping with the first embodiment will be omitted. In the first to sixth embodiments, the first light irradiated from the image irradiating unit 40 is used for projecting the image EX and the image V1 and for forming the aerial images A1 and A2 with its original wavelength. However, by providing a wavelength conversion member that converts the wavelength of the first light in the first light emitting unit or the second light emitting unit, the image EX and the image V1 may be projected and the aerial images A1 and A2 may be formed with a color different from that of the light irradiated from the image irradiating unit 40.

Eighth embodiment
Next, an eighth embodiment of the present invention will be described. The description of the contents overlapping with the first embodiment will be omitted. In the first to seventh embodiments, a grating having periodic unevenness is used as the diffraction grating section 10. However, the unevenness of the diffraction grating section 10 does not need to have a periodic structure, and may have a holographic grating structure as long as it can diffract light in at least two directions. In addition, although an example in which the diffraction grating section 10 is formed separately from the light guide plate section 20 has been shown, the diffraction grating section 10 may be formed inside the light guide section 21 or on the surface of the light entrance section 22.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in different embodiments.

10... Diffraction grating section 20... Light guide plate section 30... External screen 40, 40a, 40b, 50... Image irradiation section 60... Viewpoint 11... Flat plate-like section 12... Convex section 13... Concave section 21... Light guide section 22... Light entrance section 23... Beam splitter 24... Retroreflection section 24a... Sheet section 24b... Retroreflection area 24c... Regular reflection area 25... Partial reflection section 26... Optical filter 41... Light source section 42... Half-wave plate 43... Polarizer 45, 46, 47... Mirror 48... Bandpass filter 61... Optical filter 62... Optical shutter section 63... Projection lens A1, A2... Aerial image V1, EX... Image

Claims (14)

a first image irradiating unit that irradiates a first light;
a light guide plate having a first light incident portion to which the first light is incident, a light guide portion that guides a portion of the first light as guided light while totally reflecting the first light, and a first light exit portion that exits the portion of the guided light in a viewing direction;
a diffraction grating portion provided on the first light incident portion,
The first light output portion includes a beam splitter provided in the optical waveguide portion and a retroreflection portion provided at an end of the optical waveguide portion ,
The light guide plate section includes a second light exit section that transmits one of the beams branched by the diffraction grating section and outputs the beam in a direction toward an external screen different from the viewpoint direction . 2. The image projection device according to claim 1 ,
13. An image projection device, comprising: a projection unit for projecting an image from a projection screen onto a surface of the projection screen; 3. The image projection device according to claim 1 ,
An image projection device, comprising: an optical shutter section that switches between transmitting and blocking light, the first light exit section or the second light exit section. 4. The image projection device according to claim 1 ,
An image projection device, comprising: a wavelength conversion unit that converts a wavelength of the first light, the wavelength conversion unit being provided in the first light output unit or the second light output unit. 5. The image projection device according to claim 1 ,
The image projection device, wherein the retroreflective portion is formed by mixing a specular reflection area that specularly reflects light and a retroreflective area that retroreflects light. 5. The image projection device according to claim 1 ,
an optical fiber having a first reflector and a second reflector arranged to reflect a portion of the guided light and transmit the remainder of the guided light; 7. The image projection device according to claim 1 ,
a second image irradiating unit that irradiates the diffraction grating unit with a second light,
the first light and the second light have different angles of incidence with respect to the diffraction grating portion,
The image projection device, wherein the optical waveguide portion guides a part of the second light as guided light while totally reflecting the part. 8. The image projection device according to claim 7 ,
an optical fiber having a first wavelength and a second wavelength, the first wavelength being reflected by the first reflector and the second wavelength being transmitted through the first selective reflector; 9. The image projection device according to claim 7 ,
an optical filter that selectively blocks the first light wavelength or the second light wavelength is provided in the second light output portion; 10. The image projection device according to claim 1 ,
The light guide plate includes two light guide plate portions,
an optical fiber having a first light input portion and a second light input portion, the first light input portion being provided with a first diffraction grating portion; 11. The image projection device according to claim 1 ,
The image projection device, wherein the optical waveguide portion has a curved surface shape. 12. The image projection device according to claim 1 ,
An image projection device, characterized in that the first image irradiation unit is equipped with a liquid crystal display element or a digital mirror device, and changes the content of the first image contained in the first light over time. 13. The image projection device according to claim 1 ,
An image projection device characterized in that the diffraction grating portion has a flat portion that constitutes a light incident surface and a concave-convex portion that is integral with the flat portion, and is formed separately from the light guide plate portion. 13. The image projection device according to claim 1 ,
The image projection device, wherein the diffraction grating portion has a holographic grating that diffracts light in at least two directions.