Optical scanning device and image display device

Abstract

An optical scanning device (10) comprises: a light source (11); an optical element (12) which has an angle dependence that exhibits a convergence effect at a reference incident angle, and in which light from the light source (11) is incident at the reference incident angle; a first deflector (13) that rotates a first mirror (131), on which light that has passed through the optical element (12) is incident, to cause the light to scan in a first direction; a second deflector (14) that rotates a second mirror (141), on which the light that has passed through the first deflector (13) is incident, to cause the light to scan in a second direction; and a concave mirror (15) that is disposed between the first deflector (13) and the second deflector (14) and has the function of converging light emitted from a point at the first position to a second position. The first mirror (131) and the second mirror (141) are respectively disposed at the first position and the second position. The optical element (12) and the concave mirror (15) constitute an afocal optical system.

Description

Optical scanning device and image display device

[0001] The present invention relates to an optical scanning device that scans light and an image display device that displays an image using the optical scanning device.

[0002] Conventionally, known image display devices that display images by scanning light include head-mounted displays such as goggles and glasses that realize AR (Augmented Reality) and VR (Virtual Reality). In these devices, for example, light modulated by a video signal and scanned by an optical scanning device is irradiated onto a user's eyes. Known methods for providing images to a user include a light guide plate method that uses a light guide plate to create an image in close proximity to the user's eyes, and a retinal direct imaging method that creates an image by scanning light on the user's retina.

[0003] In both of the above two methods, it is preferable that the beam diameter of the scanned light be somewhat large. For example, in the light guide plate method, if the beam diameter is small, areas where the beam does not reach the scanning lines are generated, which is likely to result in brightness unevenness. In contrast, if the beam diameter is somewhat large, such areas are less likely to occur, thereby suppressing brightness unevenness. Furthermore, in the retinal direct imaging method, the larger the beam diameter of the light incident on the eye lens, the larger the NA (numerical aperture) of the eye lens relative to the light, and the smaller the beam spot of light converged on the retina. This allows the user to view a high-resolution image. Therefore, even in the retinal direct imaging method, it is preferable that the beam diameter of the scanned light be somewhat large.

[0004] Patent Document 1 below describes an optical module capable of expanding the beam diameter of scanned light. This optical module includes a light source, a vertical mirror that scans the light from the light source in the vertical direction, and a vertical mirror that scans the light reflected by the vertical mirror in the horizontal direction. A beam expander is disposed between the light source and the vertical mirror. This expands the beam diameter of the scanned light.

[0005] European Patent Application Publication No. 4001996

[0006] In the configuration of Patent Document 1, the light beam, after being expanded by the beam expander, is incident on the vertical mirror and the horizontal mirror, which results in a large mirror size. In particular, the horizontal mirror at the rear stage must be significantly larger in size in order to properly receive the light deflected by the vertical mirror. The larger mirror size results in a decrease in rotation efficiency and rotation speed.

[0007] In view of these problems, the present invention aims to provide an optical scanning device and an image display device that can easily set the beam diameter of the scanned light to a desired size while keeping the size of the scanning mirror small.

[0008] A first aspect of the present invention relates to an optical scanning device. The optical scanning device according to this aspect includes a light source that emits substantially parallel light; an optical element that has angle dependence and exhibits a converging effect at a predetermined incident angle and is arranged so that the light from the light source is incident at the incident angle; a first deflector that rotates a first mirror onto which the light passing through the optical element is incident to scan the light in a first direction; a second deflector that rotates a second mirror onto which the light passing through the first deflector is incident to scan the light in a second direction different from the first direction; and a concave mirror that is arranged between the first deflector and the second deflector and that converges the light emitted at a point at a first position to a second position. The first mirror and the second mirror are arranged at the first position and the second position, respectively. The optical element and the concave mirror form an afocal optical system with a common focal point.

[0009] In the optical scanning device according to this aspect, the optical element and the concave mirror form an afocal optical system, so that the light reflected by the concave mirror and directed toward the second deflector becomes substantially parallel light. In this case, the beam diameter of the light directed toward the second deflector can be increased as the focal length of the optical element is reduced.

[0010] Here, if the focal length of the optical element is reduced, the optical element will be closer to the first deflector, making it easier for the light reflected by the first mirror to hit the optical element. However, in the above configuration, because the optical element has angular dependency, even if the light reflected by the first mirror hits the optical element, the optical element will not have a converging effect. Therefore, the focal length of the optical element can be reduced, making it easy to set the beam diameter of the light heading toward the second deflector to a desired size.

[0011] Furthermore, since the light being converged by the optical element is incident on the first mirror, the size of the first mirror can be reduced. Furthermore, since the first mirror and the second mirror are respectively positioned at the first and second positions relative to the concave mirror, light deflected by the first deflector at any deflection angle is converged onto the second mirror. Therefore, the size of the second mirror can also be reduced.

[0012] Therefore, with the optical scanning device according to this aspect, the beam diameter of the scanned light can be easily set to a desired size while keeping the size of the scanning mirror small.

[0013] A second aspect of the present invention relates to an image display device, which includes the optical scanning device according to the first aspect and displays an image using the light scanned by the optical scanning device.

[0014] The image display device according to this aspect has the same effects as the first aspect, and since the beam diameter of the scanned light can be set to a desired size, it is possible to provide a high-quality image to the user.

[0015] As described above, according to the present invention, it is possible to provide an optical scanning device and an image display device that can set the beam diameter of the scanned light to a desired size while keeping the size of the mirror for scanning the light small.

[0016] The effects and significance of the present invention will become more apparent from the following description of the embodiments, however, the embodiments shown below are merely examples of how the present invention can be implemented, and the present invention is not limited to the embodiments described below.

[0017] FIG. 1 is a diagram showing the configuration of an optical scanning device according to the first embodiment. FIG. 2 is a side view schematically showing an example configuration of an optical element according to the first embodiment. FIGS. 3A to 3C are diagrams schematically showing another example configuration of an optical element according to the first embodiment. FIG. 3A is a perspective view schematically showing the appearance of an optical element according to another example configuration. FIG. 3B is a plan view schematically showing a method of dividing a pillar structure in an optical element according to another example configuration. FIG. 3C is a side cross-sectional view schematically showing a portion of the pillar structure of an optical element according to another example configuration. FIG. 4 is a diagram schematically showing a method of designing a reflective surface of a concave mirror according to the first embodiment when the reflective surface of the concave mirror is shaped along an ellipsoid of revolution. FIG. 5 is a diagram schematically showing the optical characteristics of an afocal optical system composed of an optical element and a concave mirror according to the first embodiment. FIGS. 6A and 6B are diagrams schematically showing an example of setting the reflective surface of the concave mirror relative to the ellipsoid of revolution according to the first embodiment. FIG. 7A is a diagram schematically illustrating an example of the setting of a reflecting surface relative to an ellipsoid of revolution according to the first embodiment. FIGS. 7B and 7C are diagrams schematically illustrating the scanning states of a beam spot on the reflecting surface when the incident position of light on the reflecting surface is near the center of the first mirror and when the incident position is shifted from the center in the major axis direction of the ellipsoid of revolution, respectively, according to the first embodiment. FIGS. 8A to 8C are diagrams illustrating simulation results according to the first embodiment. FIG. 9 is a diagram illustrating the configuration of an optical scanning device according to the second embodiment. FIG. 10 is a diagram illustrating the configuration of an optical scanning device according to the third embodiment. FIG. 11 is a perspective view illustrating the configuration of AR glasses according to the fourth embodiment. FIG. 12 is a diagram illustrating an example of the configuration of an image display device according to the fourth embodiment. FIG. 13 is a diagram illustrating an example of the configuration of an image display device according to the fifth embodiment. FIG. 14 is a diagram illustrating an example of the configuration of an image display device according to the fifth embodiment.

[0018] However, the drawings are for illustrative purposes only and do not limit the scope of the present invention.

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. For convenience, each drawing is labeled with mutually orthogonal X, Y, and Z axes. The positive X-axis direction is the light emission direction of the light source 11, and the positive Y-axis direction is the light emission direction of the semiconductor lasers 111a to 111c.

[0020] First Embodiment FIG. 1 is a diagram showing the configuration of an optical scanning device 10 according to a first embodiment.

[0021] In the first embodiment, the direction in which light is scanned in a direction parallel to the Z axis is the horizontal scanning direction, and the direction in which light is scanned in a direction perpendicular to the Z axis is the vertical scanning direction. The horizontal scanning is performed by the first deflector 13, and the vertical scanning is performed by the second deflector 14.

[0022] The optical scanning device 10 includes a light source 11 , an optical element 12 , a first deflector 13 , a second deflector 14 , and a concave mirror 15 .

[0023] The light source 11 emits light beams L1, L2, and L3 of three different wavelengths in the positive direction of the X axis. The three light beams L1, L2, and L3 are substantially parallel beams. The three wavelengths are in the range of 440 nm to 780 nm. For example, the central wavelength of light L1 is in the red wavelength band (approximately 650 nm to 780 nm), the central wavelength of light L2 is in the green wavelength band (approximately 500 to 550 nm), and the central wavelength of light L3 is in the blue wavelength band (approximately 440 to 500 nm).

[0024] The light source 11 includes semiconductor lasers 111a to 111c, collimator lenses 112a to 112c, apertures 113a to 113c, a total reflection mirror 114a, and dichroic mirrors 114b and 114c.

[0025] The semiconductor lasers 111a, 111b, and 111c emit the three light beams L1, L2, and L3, respectively. The collimator lenses 112a, 112b, and 112c collimate the light beams L1, L2, and L3 emitted from the semiconductor lasers 111a, 111b, and 111c, respectively. The apertures 113a, 113b, and 113c shape the collimated light beams L1, L2, and L3 into substantially circular beams.

[0026] The light beams L1, L2, and L3 that pass through apertures 113a, 113b, and 113c are aligned with one another by an alignment optical system consisting of total reflection mirror 114a and dichroic mirrors 114b and 114c, and are each reflected in the positive direction of the X-axis. Dichroic mirror 114b selectively reflects light in the wavelength band emitted by semiconductor laser 111b, and dichroic mirror 114c selectively reflects light in the wavelength band emitted by semiconductor laser 111c.

[0027] The light source 11 is not limited to the configuration shown in FIG. 1 and may have other configurations. For example, the light source 11 does not necessarily have to emit light in three wavelength bands, and may be configured to emit light in two or one wavelength bands. In the configuration shown in FIG. 1, the light source 11 is configured to emit light of three wavelengths L1, L2, and L3 because it is assumed that the optical scanning device 10 is used to display a color image. When the optical scanning device 10 is used to display a monochromatic image, the light source 11 may be configured to emit light of one or two wavelengths. The configuration of the light source 11 may be changed as appropriate to another configuration capable of emitting substantially parallel light.

[0028] The optical element 12 converges the light beams L1, L2, and L3 to a single focal point FP0. In this embodiment, the optical element 12 is a transmissive optical element that imparts a converging effect to light passing through it. The optical element 12 has angle dependency, which causes the converging effect to occur at a predetermined angle of incidence (hereinafter referred to as the "reference angle of incidence"). The optical element 12 is positioned so that light from the light source 11 is incident at the reference angle of incidence.

[0029] The first deflector 13 includes a first mirror 131 on which the light beams L1, L2, and L3 that have passed through the optical element 12 are incident, and the first mirror 131 is rotated about a rotation axis 132 to cause the light beams L1, L2, and L3 to scan in the horizontal direction (a direction parallel to the Z axis). The rotation axis 132 is parallel to the XY plane. The first deflector 13 is formed, for example, by a MEMS (Micro Electro Mechanical Systems) mirror.

[0030] The second deflector 14 includes a second mirror 141 on which the light beams L1, L2, and L3 that have passed through the first deflector 13 are incident, and the second mirror 141 is rotated about a rotation axis 142 to cause the light beams L1, L2, and L3 to scan in the vertical direction (a direction perpendicular to the Z axis). The rotation axis 142 is parallel to the Z axis. The second deflector 14 is formed, for example, by a MEMS mirror.

[0031] The concave mirror 15 is disposed between the first deflector 13 and the second deflector 14. The concave mirror 15 collimates the light beams L1, L2, and L3 that have been converged by the optical element 12 and scanned by the first deflector 13, and guides the parallel light beams to the second mirror 141 of the second deflector 14. The optical element 12 and the concave mirror 15 form an afocal optical system that shares a focal point FP0.

[0032] The reflecting surface 151 of the concave mirror 15 has a shape that collimates the light beams L1, L2, and L3 and directs them toward the second mirror 141, regardless of which scanning position the light beams L1, L2, and L3 are scanned to by the first deflector 13. The reflecting surface 15 has the function of converging point-emitted light emitted at the position (first position) of the first mirror 131 to the position (second position) of the second mirror 141. The reflecting surface 151 has a shape that follows a spheroid of revolution, for example. The reflecting surface 151 may also be designed based on other shapes, such as a paraboloid. A design method for the reflecting surface 151 when the reflecting surface 151 has a shape that follows a spheroid of revolution will be described later with reference to FIG. 4.

[0033] 1 is used to display a color image, the first mirror 131 and the second mirror 141 are each driven repeatedly at separate cycles so that horizontal scanning lines for one frame are formed on the image surface S1. At this time, the semiconductor lasers 111a to 111c are each driven so that light beams L1 to L3 are modulated by video signals corresponding to the respective horizontal scanning lines. As a result, a color frame image based on the video signals is displayed on the image surface S1 at a predetermined cycle.

[0034] FIG. 2 is a side view schematically showing an example of the configuration of the optical element 12. As shown in FIG.

[0035] 1 is configured by superimposing three wavelength-selective volume holograms (HOEs: holographic optical elements) 121, 122, and 123. The volume hologram 121 converges parallel light having the wavelength of light L1 onto a focal point FP0, the volume hologram 122 converges parallel light having the wavelength of light L2 onto a focal point FP0, and the volume hologram 123 converges parallel light having the wavelength of light L3 onto a focal point FP0.

[0036] Holograms that impart a converging effect to the light beams L1, L2, and L3 incident at a reference incident angle are formed inside the volume holograms 121, 122, and 123. Therefore, when the light beams L1, L2, and L3 are incident at an incident angle deviating from the reference incident angle, the volume holograms 121, 122, and 123 do not impart a converging effect to the light beams L1, L2, and L3.

[0037] When the optical scanning device 10 scans only with light of a single wavelength, only one volume hologram is arranged to impart a converging effect to the light of this wavelength. When the optical scanning device 10 scans with light of two different wavelengths, two volume holograms are arranged to impart a converging effect to the light of these wavelengths, respectively.

[0038] 2, the diameters of the light beams L1, L2, and L3 incident on the volume holograms 121, 122, and 123 are slightly different so that the NA (numerical apertures) of the light beams L1, L2, and L3 converged by the volume holograms 121, 122, and 123, respectively, are substantially equal. This adjustment can be performed, for example, by adjusting the diameters of the apertures 113a, 113b, and 113c in FIG. 1. By making the NAs of the light beams L1, L2, and L3 equal, the beam diameters of the light beams L1, L2, and L3 reflected by the concave mirror 15 can be made equal to one another by the afocal optical system described above.

[0039] However, since the thicknesses of the volume holograms 121, 122, and 123 are significantly smaller than their focal lengths (distances to the focal point FP0), even if the diameters of the light beams L1, L2, and L3 incident on the volume holograms 121, 122, and 123 are the same, it can be said that the NAs of the light beams L1, L2, and L3 converged by the volume holograms 121, 122, and 123 are substantially equal. Therefore, the light beams L1, L2, and L3 may be incident on the volume holograms 121, 122, and 123 with the same beam diameter.

[0040] 3A to 3C are diagrams schematically showing other configuration examples of the optical element 12. In FIG.

[0041] Fig. 3(a) is a perspective view schematically showing the appearance of the optical element 12, and Fig. 3(b) is a plan view schematically showing a method of dividing the pillar structures 12b in the optical element 12. Fig. 3(c) is a side cross-sectional view schematically showing the configuration of a portion of the pillar structures 12b of the optical element 12.

[0042] In this configuration example, the optical element 12 is configured as a metalens. As shown in Fig. 3(a), the optical element 12 has a transparent substrate 12a and a pillar structure 12b formed on the upper surface of the substrate 12a. The pillar structure 12b is disposed in a region through which the light beams L1, L2, and L3 pass.

[0043] As shown in FIG. 3( c), the pillar structure 12 b is composed of multiple cylindrical pillars 12 b 1. The pillar structure 12 b includes multiple types of pillars 12 b 1, each with a different diameter D 1 . The diameter D 1 of the pillars 12 b 1 is smaller than the wavelength of the light beams L 1 , L 2 , and L 3 . By adjusting the spacing G 1 between the pillars 12 b 1, the distribution of the pillars 12 b 1, and the height H 1 , it is possible to selectively impart a converging effect to light incident at a predetermined angle of incidence. Furthermore, by setting the refractive index of the pillars 12 b 1 to a high value, it is possible to impart a similar converging effect to the wavelength band of visible light, and also to the light beams L 1 , L 2 , and L 3 .

[0044] As shown in FIG. 3B, the area where the pillar structures 12b are arranged is divided into multiple areas A1-An at predetermined diameters from the center toward the periphery. The configuration and distribution of the pillars 12b1 in the areas A1-An are adjusted so that the converging action at the reference incident angle in these areas A1-An is the converging action that converges the light beams L1, L2, and L3 to a focal point FP0. As a result, the converging action is imparted to the light beams L1, L2, and L3 that are incident on the optical element 12 at the reference incident angle, but the converging action is not imparted to the light beams L1, L2, and L3 that are incident on the optical element 12 at an incident angle deviating from the reference incident angle.

[0045] FIG. 4 is a diagram showing a schematic diagram of a design method for the reflecting surface 151 of the concave mirror 15 when the reflecting surface 151 has a shape conforming to an ellipsoid of revolution.

[0046] In Figure 4, the spheroid of revolution E0 is an elliptical spherical surface formed by rotating an ellipse having a major axis AX1 and a minor axis AX2 about the major axis AX1. The major axis AX1 and the minor axis AX2 intersect at the center P0 of the elliptical sphere having the spheroid of revolution E0 as its surface. The center P0 is located at the midpoint of both the major axis AX1 and the minor axis AX2. For convenience, the center P0 will be referred to below as the "center P0 of the spheroid of revolution."

[0047] If the inside of this spheroid E0 is a reflective surface, light (diffused light) L0 emitted from a point at a predetermined first position P1 on the major axis AX1 will converge at a predetermined second position P2 on the major axis AX1. Therefore, if the reflective surface 151 of the concave mirror 15 is formed along this spheroid E0, light incident on the reflective surface 151 from the first position P1 will be guided to the second position P2. In this way, the reflective surface 151 of the concave mirror 15 is formed into a shape that follows the spheroid E0.

[0048] 1 is disposed at a first position P1, and the second mirror 141 is disposed at a second position P2. Therefore, the light beams L1, L2, and L3 reflected by the first mirror 131 and incident on the reflecting surface 151 of the concave mirror 15 are guided to the second mirror 141 regardless of the scanning position of the first mirror 131, i.e., the incident position with respect to the reflecting surface 151. For this reason, the size of the second mirror 141 only needs to be large enough to cover the size of the beam spot of the incident light beams L1, L2, and L3.

[0049] As shown in Figure 4, the reflective surface 151 of the concave mirror 15 converges the diffused light L0 emitted from the first position P1 to the second position P2, so the distance FD1 from the first position P1 to the reflective surface 151 is longer than the focal length of the reflective surface 151 in the direction of the first position P1, and the distance FD2 from the second position P2 to the reflective surface 151 is longer than the focal length of the reflective surface 151 in the direction of the second position P2.

[0050] FIG. 5 is a diagram showing the optical characteristics of an afocal optical system formed by the optical element 12 and the concave mirror 15. As shown in FIG.

[0051] 5 shows the optical paths of the light beams L1, L2, and L3 as linearly expanded from just before they enter the optical element 12 to just after they are reflected by the second mirror 141. Here, the focal length f1 of the optical element 12 is set to be greater than the focal length f2 of the concave mirror 15 on the upstream side of the optical path. As described above, the distance FD1 is greater than the focal length f2.

[0052] As shown in Figure 5, when an afocal optical system is configured from optical element 12 and concave mirror 15 and shares a focal point FP0, the following relationship holds between the beam diameter D11 of light L1, L2, and L3 incident on optical element 12 and the beam diameter D12 of light L1, L2, and L3 reflected by concave mirror 15 and converted into parallel light.

[0053] D12=(f2 / f1)・D11...(1)

[0054] Therefore, the beam diameter D12 of the light beams L1, L2, and L3 reflected by the concave mirror 15 can be increased by decreasing the distance α between the optical element 12 and the first mirror 131 and decreasing the focal length f1 of the optical element 12. When the optical scanning device 10 is used to display an image, as described above, it is preferable that the beam diameters of the light beams L1, L2, and L3 after passing through the second mirror 141 be relatively large. For this reason, it is preferable that there is as much freedom as possible in adjusting the distance α and the focal length f1.

[0055] However, when the distance α is reduced to bring the optical element 12 and the first mirror 131 closer to each other, as shown in Fig. 1, the light beams L1, L2, and L3 reflected by the first mirror 131 are more likely to strike the optical element 12. Furthermore, when the angle θ in Fig. 1 is reduced in order to make the configuration of the optical scanning device 10 more compact in the Y-axis direction, the light beams L1, L2, and L3 reflected by the first mirror 131 are even more likely to strike the optical element 12.

[0056] In contrast, in this embodiment, the optical element 12 has angle dependency as described above. Therefore, even if the light beams L1, L2, and L3 reflected by the first mirror 131 are incident on the optical element 12, the angles at which the light beams L1, L2, and L3 are incident on the optical element 12 deviate from the reference angle of incidence, thereby substantially preventing the converging action of the optical element 12 from affecting the light beams L1, L2, and L3. Therefore, according to this embodiment, the degree of freedom in adjusting the distance α and the focal length f1 can be increased, and the beam diameters of the light beams L1, L2, and L3 after passing through the second mirror 141 can be smoothly adjusted to the desired size.

[0057] <Study> The inventors have studied which range of the ellipsoid of revolution E0 shown in FIG. 4 is preferably used for scanning with the light beams L1, L2, and L3.

[0058] 6A and 6B are diagrams showing schematic examples of setting the incident positions of the light beams L1, L2, and L3 on the ellipsoid of revolution E0.

[0059] For convenience, Figures 6(a) and 6(b) are labeled with mutually orthogonal x, y, and z axes. The x-axis coincides with the major axis AX1 (see Figure 4) of the spheroid E0, and the y-z plane includes the minor axis AX2 (see Figure 4) of the spheroid E0. Therefore, the first position P1 and the second position P2 in Figure 4 exist on the x-axis. P0 is the center of the spheroid E0 (spheroid). Light beams L1, L2, and L3 are scanned parallel to the y-z plane by the first deflector 13 positioned at the first position P1. In Figures 6(a) and 6(b), the optical paths of light beams L1, L2, and L3 when the first mirror 131 of the first deflector 13 is in the neutral position are indicated by dashed arrows.

[0060] In the example of Fig. 6(a), the light beams L1, L2, and L3 are scanned along a range near the spheroid E0 that includes the center P0 of the spheroid E0 and intersects with a central plane C0 perpendicular to the major axis AX1. In the example of Fig. 6(b), the light beams L1, L2, and L3 are scanned along a range near the spheroid E0 that includes a position on the x-axis shifted to the negative x-axis side from the center P0 and intersects with a plane C1 perpendicular to the axis AX1.

[0061] As shown in Figures 6(a) and 6(b), the radius of curvature of the spheroid E0 around the x-axis decreases as the distance from the center P0 increases in the x-axis direction, and the degree of decrease in the radius of curvature increases the further away from the center P0. Therefore, comparing the examples of Figures 6(a) and 6(b), the degree of decrease in the radius of curvature of the reflecting surface 151 is greater in the example of Figure 6(b) than in the example of Figure 6(a). Therefore, in the example of Figure 6(b), when the light beams L1, L2, and L3 scan the reflecting surface 151 parallel to the y-z plane, some of the light beams L1, L2, and L3 tend to deviate from the reflecting surface 151, which makes it more likely that the beam spots of the light beams L1, L2, and L3 reflected by the reflecting surface 151 will be chipped.

[0062] 7A is a diagram schematically illustrating an example of the setting of the reflecting surface 151 relative to the ellipsoid of revolution E0. Figures 7B and 7C are diagrams schematically illustrating the scanning states of the beam spots on the reflecting surface 151 when the incident positions of the light beams L1, L2, and L3 on the reflecting surface 151 are near the center C10 of the first mirror 151 and when the incident positions are shifted from the center C10 in the major axis direction of the ellipsoid of revolution E0, respectively.

[0063] 7A, the reflecting surface 151 is set to be an ellipsoid of revolution E0 so as to have an elliptical shape in a plan view. The center C10 of the reflecting surface 151 coincides with the center P0 of the ellipsoid of revolution E0, and the major axis and minor axis of the reflecting surface 151 coincide with the major axis AX1 (x-axis) and minor axis AX2 (y-axis) of the ellipsoid of revolution E0.

[0064] 7A, two types of dashed arrows indicate the optical paths of the light beams L1, L2, and L3 when the first mirror 131 disposed at the first position P1 is in the neutral position. Here, the arrows indicate a case where the light beams L1, L2, and L3 are incident on the reflecting surface 151 near the center C10 (long dashed arrows), and a case where the light beams L1, L2, and L3 are incident on the reflecting surface 151 at a position shifted from the center C10 to the negative side of the x-axis (short dashed arrows).

[0065] 7B shows the scanning state of light beams L1, L2, and L3 when they are incident on the reflecting surface 151 near the center C10. The width DA1 of the reflecting surface 151 in the major axis direction and the width DA2 of the minor axis direction are set so that the shape of the reflecting surface 151 is elliptical in a planar view. To reduce the size of the reflecting surface 151 and the concave mirror 15, the width DA2 of the reflecting surface 151 in the minor axis direction is set slightly larger than the scanning range of light beams L1, L2, and L3 indicated by the dashed arrows, and the width DA1 of the major axis direction is set slightly larger than the width DA2. In the state shown in FIG. 7B, the beam spots of light beams L1, L2, and L3 scan the reflecting surface 151 without straying from the reflecting surface 151.

[0066] 7C shows the scanning state of light beams L1, L2, and L3 when they are incident on reflecting surface 151 at a position shifted toward the negative side of the x-axis from center C10. In this case, if the size (widths DA1 and DA2) of reflecting surface 151 is the same as in FIG. 7A, the beam spots of light beams L1, L2, and L3 will deviate from reflecting surface 151 near the ends of the scanning ranges of light beams L1, L2, and L3. To avoid this, it is necessary to enlarge reflecting surface 151, but doing so would increase the size of concave mirror 15 and lead to an increase in the size of optical scanning device 10.

[0067] Figures 8(a) to (c) are diagrams showing the simulation results of the state of the beam spot BS of light L1, L2, and L3 incident on the second mirror 141 when the incident positions of light L1, L2, and L3 are shifted in the long axis direction relative to the center C10 of the reflecting surface 151 when the reflecting surface 151 is set as shown in Figures 7(a) to (c).

[0068] The upper rows of Figures 8(a) to (c) schematically show the incident positions of light L1, L2, and L3 in each simulation. In Figure 8(a), as in Figure 7(b), light L1, L2, and L3 are scanned near the center C10 of the reflecting surface 151. In Figures 8(b) and (c), as in Figure 7(c), light L1, L2, and L3 are scanned at positions shifted in the major axis direction from the center C10 of the reflecting surface 151.

[0069] 8(b) and 8(c), the shift amount of the incident position relative to the center C10 is shown by the angle formed between the line connecting the incident positions of the light beams L1, L2, and L3 on the reflecting surface 151 when the first mirror 131 is in the neutral position and the center P0 of the ellipsoid E0, and the central plane C0 shown in FIG. 6(a). In FIG. 8(b), the angle is 15°, and in FIG. 8(c), the angle is 35°. In FIG. 8(a), the angle is 0°.

[0070] 8(a) to 8(c) show, in the lower part thereof, the state (simulation result) of the beam spot BS on the second mirror 141 of the light beams L1, L2, and L3 that are reflected by the reflecting surface 151 and incident on the second mirror 141 when the shift amount (angle) is set as shown in the upper part thereof. Here, the state of the beam spot BS when the light beams L1, L2, and L3 are positioned near the end of the scanning range on the reflecting surface 151 is shown as a simulation result.

[0071] In the simulation, the widths DA1 and DA2 shown in FIG. 7B were set to 12 mm and 10 mm, respectively. The major axis AX1 and minor axis AX2 of the ellipsoid of revolution E0 were set to 20 mm and 10 mm, respectively. In the simulation of FIG. 8A, the angle θ in FIG. 1 was set to 15°, and the distance between the first position P1 and the second position P2 in FIG. 4 was set to 5 mm. The scanning angle of the first deflector 13 (the rotation angle of the first mirror 131) was set to ±10°, and the focal length f1 of the optical element 12 was set to 10 mm. The beam diameter D11 in FIG. 5 was set to 0.8 mm.

[0072] As shown in the lower part of Figure 8(a), when the above-mentioned angle is 0°, the beam spot BS on the second mirror 141 is not chipped, and a substantially circular beam spot BS is obtained. In contrast, as shown in the lower part of Figure 8(b), when the above-mentioned angle is 15°, chipping occurs in the beam spot BS, and the beam spot BS becomes distorted from a circular shape. Furthermore, as shown in the lower part of Figure 8(c), when the above-mentioned angle is 35°, chipping occurs in the beam spot BS, and the beam spot BS becomes distorted from a circular shape, and further, deviations occur in the positions of the beam spots BS of the light beams L1, L2, and L3.

[0073] From these simulation results, it is preferable to set the above-mentioned angle (shift amount) to near 0° in order to cause the light beams L1, L2, and L3 to be incident on the second mirror 141 in a circular beam shape without any missing parts. Further simulations by the inventors have confirmed that by setting the above-mentioned angle (shift amount) in the range of ±5°, the light beams L1, L2, and L3 can be incident on the second mirror 141 in a circular beam shape without any missing parts. From these study results, it can be said that under the above simulation conditions, it is preferable to cause the light beams L1, L2, and L3 to scan in the minor axis direction on the reflecting surface 151 when the angle (shift amount from the center C10) is in the range of ±5°.

[0074] <Effects of First Embodiment> According to the first embodiment, the following effects are achieved.

[0075] As shown in FIGS. 1 and 4, the optical scanning device 10 includes a light source 11 that emits substantially parallel light, an optical element 12 that has angle dependency that exhibits a converging effect at a predetermined incident angle (reference incident angle) and is arranged so that light beams L1, L2, and L3 from the light source 11 are incident at the reference incident angle, and a first mirror 131 that rotates to receive the light beams L1, L2, and L3 that have passed through the optical element 12 and are incident thereon, thereby flattening the light beams L1, L2, and L3 along the Z axis. The optical element 12 includes a first deflector 13 that scans the light beams L1, L2, and L3 in a direction perpendicular to the Z axis (first direction), a second deflector 14 that rotates a second mirror 141 onto which the light beams L1, L2, and L3 that have passed through the first deflector 13 are incident, and scans the light beams L1, L2, and L3 in a direction perpendicular to the Z axis (second direction), and a concave mirror 15 that is disposed between the first deflector 13 and the second deflector 14 and has the function of converging light emitted as a point at a first position P1 to a second position P2. The first mirror 131 and the second mirror 141 are disposed at the first position P1 and the second position P2, respectively. As shown in FIG. 5 , the optical element 12 and the concave mirror 15 form an afocal optical system that shares a focal point FP0.

[0076] In the optical scanning device according to this aspect, an afocal optical system is formed by the optical element 12 and the concave mirror 15, so that the light beams L1, L2, and L3 reflected by the concave mirror 15 and directed toward the second deflector 14 become substantially parallel light beams. In this case, the beam diameter of the light beams L1, L2, and L3 directed toward the second deflector 14 can be increased as the focal length f1 of the optical element 12 is reduced.

[0077] Here, if the focal length f1 of the optical element 12 is reduced, the optical element 12 will be closer to the first deflector 13, and the light beams L1, L2, and L3 reflected by the first mirror 131 will more easily fall on the optical element 12. However, in the above configuration, the optical element 12 has angle dependency, and therefore, even if the light beams L1, L2, and L3 reflected by the first mirror 131 fall on the optical element 12, the converging action of the optical element 12 will not be imparted to the light beams L1, L2, and L3. Therefore, the focal length f1 of the optical element 12 can be reduced, and the beam diameter of the light beams L1, L2, and L3 directed toward the second deflector 14 can be easily set to a desired size.

[0078] Furthermore, since light being converged by optical element 12 is incident on first mirror 131, the size of first mirror 131 can be reduced. Furthermore, since first mirror 131 and second mirror 141 are respectively disposed at first position P1 and second position P2 relative to concave mirror 15, the light beams L1, L2, and L3 at any deflection angle swung by first deflector 13 are converged onto second mirror 141. Therefore, the size of second mirror 141 can also be reduced.

[0079] Therefore, according to the optical scanning device 10 of this embodiment, the beam diameter of the scanned light L1, L2, and L3 can be easily set to the desired size while keeping the size of the first mirror 131 and the second mirror 141 (scanning mirrors) small.

[0080] According to the method shown in FIG. 4, the reflecting surface 151 of the concave mirror 15 has a shape that follows the ellipsoid of revolution E0.

[0081] According to this configuration, the shape of the reflecting surface 151 of the concave mirror 15 can be set so that the first position P1 and the second position P2 are set on the major axis AX1 of the spheroid of revolution E0.

[0082] 7A, the reflecting surface 151 may have an elliptical shape that is long in the major axis direction of the ellipsoid of revolution E0 in a plan view. In this case, as described with reference to FIGS. 7B, 7C, and 8A to 8C, it is preferable that the light beams L1, L2, and L3 are scanned near the center C10 of the reflecting surface 151.

[0083] According to this configuration, the concave mirror 15 can be made smaller, and the light beams L1, L2, and L3 can be guided to the second mirror 141 in a circular beam shape without any missing parts.

[0084] As shown in FIG. 5, the focal length f1 of the optical element 12 can be set to be equal to or greater than the focal length f2 of the concave mirror 15.

[0085] According to this configuration, the beam diameter D12 of the light L1, L2, and L3 reflected by the concave mirror 15 can be reduced from the beam diameter D11 of the light emitted from the light source 11 and set to a desired size.

[0086] As shown in FIG. 2, the optical element 12 can be composed of volume holograms 121, 122, and 123.

[0087] According to this configuration, by forming an angle-dependent hologram inside the volume holograms 121, 122, and 123, a converging effect can be imparted to the light L1, L2, and L3 that is incident on the volume holograms 121, 122, and 123 from the light source 11 at a predetermined angle of incidence (reference angle of incidence), and even if the light L1, L2, and L3 reflected by the first mirror 131 is incident on the volume holograms 121, 122, and 123 at an angle of incidence other than the reference angle of incidence, the converging effect on this light L1, L2, and L3 can be prevented.

[0088] Alternatively, as shown in Figures 3(a)-(c), the optical element 12 may be a metalens.

[0089] According to this configuration, by forming angle-dependent pillars 12b1 on the metalens, a converging effect can be imparted to light L1, L2, and L3 that is incident on the metalens from light source 11 at a predetermined angle of incidence (reference angle of incidence), and even if light L1, L2, and L3 reflected by first mirror 131 is incident on the metalens at an angle of incidence other than the reference angle of incidence, the converging effect can be prevented from being imparted to this light L1, L2, and L3.

[0090] As shown in FIG. 1, the light source 11 emits light of three wavelengths in the range of 440 nm to 780 nm.

[0091] According to this configuration, by controlling the light source 11 and modulating the light of each wavelength with a video signal, a color image can be displayed on the image surface S1.

[0092] As shown in Figure 2, the optical scanning device 10 is arranged with three wavelength-dependent optical elements 121, 122, and 123 that impart a converging effect to the light beams L1, L2, and L3 of the respective wavelengths, and the three optical elements 121, 122, and 123 cause the light beams L1, L2, and L3 of the respective wavelengths to form a common focal point FP0.

[0093] With this configuration, the focal point FP0 of the light L1, L2, and L3 of each wavelength converged by the three optical elements 121, 122, and 123 can be aligned with the focal point of the concave mirror 15, and the beam diameter of the light L1, L2, and L3 of each wavelength reflected by the concave mirror 15 can be set to a desired size.

[0094] As shown in Figures 3(a) to (c), the optical scanning device 10 is provided with one optical element 12 that imparts a converging effect to the light beams L1, L2, and L3 of each wavelength, causing the light beams of each wavelength to form a common focal point FP0.

[0095] According to this configuration, by placing one optical element 12, the focal point FP0 of each wavelength of light L1, L2, L2 can be aligned with the focal point of the concave mirror 15, and the beam diameter of the light of each wavelength band reflected by the concave mirror 15 can be set to a desired size.

[0096] Second Embodiment In the first embodiment, a transmissive optical element 12 is used as shown in Fig. 1. In contrast, in the second embodiment, a reflective optical element is used.

[0097] FIG. 9 is a diagram showing the configuration of an optical scanning device 10 according to the second embodiment.

[0098] 9 , in the second embodiment, a reflective optical element 16 is disposed between the light source 11 and the first deflector 13. The optical element 16 has angle dependency that provides reflection and convergence to the light beams L1, L2, and L3 incident at a reference incident angle. The optical element 16 is disposed so that the light beams L1, L2, and L3 from the light source 11 are incident at the reference incident angle.

[0099] 2, the optical element 16 can be configured by superimposing three wavelength-selective volume holograms that respectively reflect and converge the wavelengths of the light beams L1, L2, and L3. A hologram is formed inside each volume hologram, which reflects the corresponding light beam and converges it to a focal point FP0 when the corresponding light beam is incident at a reference angle of incidence. Therefore, even if a portion of the light beams L1, L2, and L3 reflected by the first mirror 131 of the first deflector 13 is incident on the optical element 16 as shown in FIG. 9, this portion of the light beams L1, L2, and L3 will pass through the optical element 16 without being reflected or converged by the respective volume holograms.

[0100] As in the above-described first embodiment, the optical element 16 and the concave mirror 15 form an afocal optical system that shares a focal point FP0. The configurations, arrangements, and operations of the light source 11, the first deflector 13, the second deflector 14, and the concave mirror 15 are the same as those in the above-described first embodiment. A metalens having angle dependency may be used as the optical element 16.

[0101] <Effects of Second Embodiment> The configuration of the second embodiment can also achieve the same effects as those of the first embodiment.

[0102] In the second embodiment, as in the first embodiment, the beam diameters of the light beams L1, L2, and L3 incident on the second mirror 141 can be adjusted by adjusting the focal lengths f1 and f2 of the optical element 16 and the concave mirror 15 that constitute the afocal optical system and the distance between the optical element 16 and the first mirror 131. Also, in the configuration of the second embodiment, as in the simulations shown in Figures 6(a) and 6(b) and 8(a) to 8(c), by setting the angle between the light beams L1, L2, and L3 to within the range of ±5°, the light beams L1, L2, and L3 can be guided to the second deflector 14 in a circular beam shape without any missing parts.

[0103] Third Embodiment FIG. 10 is a diagram showing the configuration of an optical scanning device 10 according to a third embodiment.

[0104] In comparison with Embodiment 1, in Embodiment 3, the scanning directions of the first deflector 13 and the second deflector 14 are reversed. That is, horizontal scanning (scanning of the light beams L1, L2, and L3 in a direction parallel to the Z axis) is performed by the second deflector 14, and vertical scanning (scanning of the light beams L1, L2, and L3 in a direction perpendicular to the Z axis) is performed by the first deflector 13. Therefore, the rotation axis 132 of the first deflector 13 is parallel to the Z axis, and the rotation axis 142 of the second deflector 14 is parallel to the X-Y plane.

[0105] As in the first embodiment, the optical element 16 and the concave mirror 15 form an afocal optical system that shares a focal point FP0. The configurations, arrangements, and functions of the light source 11 and the optical element 12 may be the same as those in the first embodiment.

[0106] <Effects of Third Embodiment> The configuration of the third embodiment can also achieve the same effects as those of the first embodiment.

[0107] Fourth Embodiment In a fourth embodiment, a configuration example is disclosed in which the optical scanning device 10 configured as described above is applied to a light guide plate type image display device. Here, an image display device using the optical scanning device 10 is mounted on AR glasses. The image display device is not limited to AR glasses, and may be mounted on other types of head-mounted displays, such as AR goggles, VR glasses, or VR goggles. Furthermore, the image display device to which the optical scanning device 10 configured as described above is applied may be mounted on a head-up display for vehicle use, not limited to a head-mounted display.

[0108] FIG. 11 is a perspective view showing the configuration of AR glasses 1 according to the fourth embodiment.

[0109] The AR glasses 1 include a frame 2, a pair of image display devices 3, and a pair of light guide plates 4. The AR glasses 1 are worn on the user's head, similar to ordinary eyeglasses.

[0110] The frame 2 holds a pair of image display devices 3 and a pair of light guide plates 4. The frame 2 is composed of a front portion 2a and a pair of support portions 2b. The pair of support portions 2b extend rearward from the right and left ends of the front portion 2a. When the frame 2 is worn by a user, the front portion 2a is positioned in front of a pair of eyes E of the user. The frame 2 is made of a transparent material.

[0111] The pair of image display devices 3 are symmetrical with respect to the YZ plane that passes through the center of the AR glasses 1. The image display devices 3 generate and display an image in front of the eyes E of a user who wears the AR glasses 1 on their head. The image display devices 3 include a transparent light guide plate 4 and the optical scanning device 10 configured as described above.

[0112] Light beams L1, L2, and L3 emitted from the optical scanning device 10 are captured by the light guide plate 4. These light beams L1, L2, and L3 propagate through the light guide plate 4 and are emitted from a diffraction region positioned in front of the eye E. The light beams L1, L2, and L3 are scanned horizontally and vertically in the diffraction region by the scanning of the optical scanning device 10. As a result, one frame of image is constructed in the diffraction region. The diffraction region functions as a screen. For example, information for the current day on a calendar stored in the control circuit of the optical scanning device 10 is displayed in the diffraction region. The user can see the image displayed in the diffraction region superimposed on the scenery in front of them.

[0113] FIG. 12 is a diagram showing an example of the configuration of an image display device 3 according to the fourth embodiment.

[0114] In this configuration example, the optical scanning device 10 according to the first embodiment is used. However, the configuration of the optical scanning device 10 used in the image display device 3 may be the configuration of either the second or third embodiment.

[0115] 11 is composed of a first light guide plate 41, a second light guide plate 42, wavelength-selective polarizing beam splitter (PBS) films 43 and 44, and a quarter-wave plate 45. The first light guide plate 41 propagates red wavelength light L1 and green wavelength light L2 to the diffraction region 41a, and the second light guide plate 42 propagates blue wavelength light L3 to the diffraction region 42a. The PBS film 43 acts on the red wavelength light L1 and the green wavelength light L2, and the PBS film 44 acts on the blue wavelength light L3. The second deflector 14 is disposed behind the light guide plate 4.

[0116] The optical scanning device 10 is positioned so that the linearly polarized light beams L1, L2, and L3 reflected by the concave mirror 15 are incident on the PBS films 43 and 44 as P-polarized light. Therefore, the light beams L1, L2, and L3 reflected by the concave mirror 15 are transmitted through the PBS films 43 and 44 and converted into circularly polarized light by the quarter-wave plate 45. The light beams L1, L2, and L3 are then reflected by the second mirror 141 of the second deflector 14 and transmitted through the quarter-wave plate 45. As a result, the light beams L1, L2, and L3 become S-polarized light with respect to the PBS films 43 and 44. Therefore, the light beams L1 and L2 are reflected by the PBS film 43 and introduced into the first light guide plate 41. Furthermore, the light beam L3 is reflected by the PBS film 44 and introduced into the second light guide plate 42.

[0117] The light beams L1, L2, and L3 are then repeatedly totally reflected by the inner surfaces of the first light guide plate 41 and the second light guide plate 42, and propagate to the diffraction regions 41a and 42a for drawing images. At this time, the inner surfaces of the first light guide plate 41 and the second light guide plate 42 may be formed with diffraction regions for changing the traveling direction of the light beams L1, L2, and L3 or diffraction regions for expanding the scanning range. Thus, the light beams L1 and L2 are scanned across the diffraction region 41a and emitted from the diffraction region 41a toward the eye E, and the light beam L3 is scanned across the diffraction region 42a and emitted from the diffraction region 42a toward the eye E. This allows the user to view a composite image of the images drawn in the diffraction regions 41a and 42a.

[0118] <Effects of Embodiment 4> According to the image display device 3 of Embodiment 4, since the optical scanning device 10 of Embodiment 1 is used, the same effects as those of Embodiment 1 are achieved. Furthermore, as described in Embodiment 1, the beam diameters of the scanned light beams L1, L2, and L3 can be set to a desired size, so that gaps between the scanning lines in the diffraction regions 41 a and 42 a, which would otherwise cause uneven brightness, can be suppressed. Therefore, a high-quality image can be provided to the user.

[0119] Fifth Embodiment In a fifth embodiment, a configuration example is disclosed in which the optical scanning device 10 having the above configuration is applied to a retinal direct imaging type image display device. Here, the image display device using the optical scanning device 10 is mounted on VR glasses.

[0120] FIG. 13 is a diagram showing an example of the configuration of an image display device 3 according to the fifth embodiment.

[0121] In the fifth embodiment, an image display device 3 is mounted on a frame 2 having the same configuration as in the fourth embodiment. However, in the fifth embodiment, the frame 2 is opaque. A pair of cameras 6 is disposed on the front surface of the frame 2. The pair of cameras 6 capture images in front of the frame 2 and transmit video signals based on the captured images to a control circuit of the optical scanning device 10. The control circuit displays the captured images on the image display device 3 based on the received video signals.

[0122] FIG. 14 is a diagram showing an example of the configuration of an image display device 3 according to the fifth embodiment.

[0123] In this configuration example, the optical scanning device 10 according to the first embodiment is used. However, the configuration of the optical scanning device 10 used in the image display device 3 may be the configuration of either the second or third embodiment.

[0124] The image display device 3 includes a mirror 5 and an optical scanning device 10. The mirror 5 reflects the light beams L1, L2, and L3 emitted from the optical scanning device 10 and makes them incident on the eye lens E1 of the eye E. The light beams L1, L2, and L3 are imaged on the retina E2 of the eye E by the eye lens E1. The light beams L1, L2, and L3 are scanned horizontally and vertically on the retina E2 by scanning with the optical scanning device 10. This generates one frame of image on the retina E2. This allows the user to see an image of the scenery ahead.

[0125] <Effects of Embodiment 5> According to the image display device 3 of Embodiment 5, the optical scanning device 10 of Embodiment 1 is used, and therefore the same effects as those of Embodiment 1 are achieved. Furthermore, as described in Embodiment 1, the beam diameter of the scanned light L1, L2, and L3 can be set to a desired size, and therefore the NA of the light L1, L2, and L3 incident on the eyeball lens E1 can be increased to a desired size. This makes it possible to reduce the beam spot of the light L1, L2, and L3 that is imaged on the retina E2, and to show a high-definition image to the user.

[0126] 2, the three volume holograms 121, 122, and 123 are arranged in a stacked manner, but the three volume holograms 121, 122, and 123 may also be arranged spaced apart in the thickness direction. However, if the beam diameters of the light beams L1, L2, and L3 incident on the volume holograms 121, 122, and 123 are the same, the greater the distance between the volume holograms 121, 122, and 123, the greater the difference between the NAs of the light beams L1, L2, and L3 converging at the same focal point FP0. Therefore, in order to suppress this difference and properly configure the above-described afocal optical system for the light beams L1, L2, and L3, it is preferable to arrange the volume holograms 121, 122, and 123 in a stacked manner, as shown in FIG. 2.

[0127] The configuration and layout of the optical system of the optical scanning device 10 are not limited to those shown in FIGS. 1, 9, and 10 according to the first to third embodiments. For example, the optical system may be configured so that the angle θ is smaller than in the configuration of FIG. 1. Furthermore, the tilt angle of the second mirror 141 when the second mirror 141 is in the neutral position may be different from that shown in FIG. 1. Furthermore, the light source of the light source 11 is not limited to the semiconductor lasers 111a to 111c, and may be another light source such as a light-emitting diode.

[0128] Furthermore, the image display device to which the optical scanning device 10 is applied is not limited to the head-mounted displays and in-vehicle head-up displays described in the fourth and fifth embodiments, and the optical scanning device of the present invention may be used in, for example, an optical scanning projector. Furthermore, the device to which the optical scanning device of the present invention is applied is not limited to an image display device, and may be another type of device that scans light in two directions. For example, the optical scanning device of the present invention may be applied to a laser radar that detects objects present in a scanning range based on reflected light when light is scanned in two dimensions.

[0129] The embodiments of the present invention can be modified in various ways as appropriate within the scope of the technical idea defined in the claims.

[0130] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0131] (Technology 1) An optical scanning device comprising: a light source that emits substantially parallel light; an optical element that has angle dependency to exhibit a converging effect at a predetermined incident angle and is arranged so that light from the light source is incident at the incident angle; a first deflector that rotates a first mirror onto which the light that has passed through the optical element is incident, thereby scanning the light in a first direction; a second deflector that rotates a second mirror onto which the light that has passed through the first deflector is incident, thereby scanning the light in a second direction different from the first direction; and a concave mirror that is arranged between the first deflector and the second deflector, and has the effect of converging light that is point-emitted at a first position onto a second position, wherein the first mirror and the second mirror are arranged at the first position and the second position, respectively; and wherein the optical element and the concave mirror form an afocal optical system that shares a common focal point.

[0132] According to this technology, an afocal optical system is formed by the optical element and the concave mirror, so that the light reflected by the concave mirror and directed toward the second deflector becomes substantially parallel light. In this case, the beam diameter of the light directed toward the second deflector can be increased as the focal length of the optical element is reduced.

[0133] Here, if the focal length of the optical element is reduced, the optical element will be closer to the first deflector, making it easier for the light reflected by the first mirror to hit the optical element. However, in the above configuration, because the optical element has angular dependency, even if the light reflected by the first mirror hits the optical element, the optical element will not have a converging effect. Therefore, the focal length of the optical element can be reduced, making it easy to set the beam diameter of the light heading toward the second deflector to a desired size.

[0134] Furthermore, since the light being converged by the optical element is incident on the first mirror, the size of the first mirror can be reduced. Furthermore, since the first mirror and the second mirror are respectively positioned at the first and second positions relative to the concave mirror, light deflected by the first deflector at any deflection angle is converged onto the second mirror. Therefore, the size of the second mirror can also be reduced.

[0135] Therefore, with the optical scanning device according to this aspect, the beam diameter of the scanned light can be easily set to a desired size while keeping the size of the scanning mirror small.

[0136] (Technology 2) In the optical scanning device according to Technology 1, the reflecting surface of the concave mirror has a shape that conforms to an ellipsoid of revolution.

[0137] According to this technique, the shape of the reflecting surface of the concave mirror can be set so that the first position and the second position are set on the major axis of the spheroid of revolution.

[0138] (Technology 3) In the optical scanning device described in Technology 2, the reflecting surface has an elliptical shape that is long in the major axis direction of the ellipsoid of revolution in a plan view, and the light is scanned near the center of the reflecting surface.

[0139] This technique makes it possible to reduce the size of the concave mirror while guiding light to the second mirror in a circular beam shape without any missing parts.

[0140] (Technology 4) The optical scanning device according to any one of technologies 1 to 3, wherein the focal length of the optical element is equal to or greater than the focal length of the concave mirror.

[0141] According to this technique, the beam diameter of the light reflected by the concave mirror can be reduced from the beam diameter of the light emitted from the light source and set to a desired size.

[0142] (Technology 5) The optical scanning device according to any one of technologies 1 to 4, characterized in that the optical element is a volume hologram.

[0143] According to this technology, by forming an angle-dependent hologram inside a volume hologram, it is possible to impart a converging effect to light incident on the volume hologram from a light source at a predetermined angle of incidence, and even if light reflected by the first mirror enters the volume hologram at an angle of incidence other than the predetermined angle of incidence, it is possible to prevent the converging effect from being imparted to this light.

[0144] (Technology 5) The optical scanning device according to any one of technologies 1 to 4, wherein the optical element is a metalens.

[0145] According to this technique, by forming angle-dependent pillars in the metalens, it is possible to impart a converging effect to light that is incident on the metalens from a light source at a predetermined angle of incidence, and even if light reflected by the first mirror is incident on the metalens at an angle of incidence other than the predetermined angle of incidence, it is possible to prevent the converging effect from being imparted to this light.

[0146] (Technology 7) The optical scanning device according to any one of Technologies 1 to 6, wherein the light source emits light of three wavelengths included in the range of 440 nm to 780 nm.

[0147] According to this technology, a color image can be displayed by controlling a light source and modulating light of each wavelength with a video signal.

[0148] (Technology 8) In the optical scanning device described in Technology 7, three wavelength-dependent optical elements are arranged to impart a converging effect to the light of each of the wavelengths, and the three optical elements cause the light of each of the wavelengths to form a common focus.

[0149] This technology allows the focal points of the light of each wavelength converged by the three optical elements to be aligned with the focal point of the concave mirror, and the beam diameter of the light of each wavelength reflected by the concave mirror can be set to a desired size.

[0150] (Technology 9) In the optical scanning device described in Technology 7, one optical element is disposed that imparts a converging effect to the light of each of the wavelengths, causing the light of each of the wavelengths to form a common focus.

[0151] According to this technology, by placing one optical element, the focus of light of each wavelength can be aligned with the focus of the concave mirror, and the beam diameter of light of each wavelength reflected by the concave mirror can be set to a desired size.

[0152] (Technology 10) An image display device comprising the optical scanning device according to any one of technologies 1 to 9, and displaying an image using the light scanned by the optical scanning device.

[0153] This technique provides the same effects as the first aspect, and also allows the beam diameter of the scanned light to be set to a desired size, making it possible to provide a high-quality image to the user.

[0154] 3 Image display device 10 Optical scanning device 11 Light source 12 Optical element 13 First deflector 131 First mirror 14 Second deflector 15 Concave mirror 121, 122, 123 Volume hologram 141 Second mirror 151 Reflecting surface AX1 Major axis C0 Plane E0 Ellipsoid of revolution FP0 Focus L1, L2, L3 Light P0 Center (intermediate position) P1 First position P2 Second position

Claims

1. An optical scanning device comprising: a light source that emits substantially parallel light; an optical element that has angle dependency to exhibit a converging effect at a predetermined incident angle and is positioned so that light from said light source is incident at said incident angle; a first deflector that rotates a first mirror onto which the light that has passed through said optical element is incident, thereby scanning the light in a first direction; a second deflector that rotates a second mirror onto which the light that has passed through said first deflector is incident, thereby scanning the light in a second direction different from the first direction; and a concave mirror that is positioned between said first deflector and said second deflector, and has the effect of converging light that is point-emitted at a first position onto a second position, wherein said first mirror and second mirror are positioned at said first position and said second position, respectively; and wherein said optical element and said concave mirror form an afocal optical system that shares a common focal point.

2. An optical scanning device according to claim 1, wherein the reflecting surface of the concave mirror has a shape that conforms to an ellipsoid of revolution.

3. An optical scanning device according to claim 2, wherein the reflecting surface has an elliptical shape that is long in the direction of the major axis of the ellipsoid of revolution in a plan view, and the light is scanned near the center of the reflecting surface.

4. An optical scanning device according to claim 1, wherein the focal length of said optical element is equal to or greater than the focal length of said concave mirror.

5. An optical scanning device according to claim 1, wherein the optical element is a volume hologram.

6. An optical scanning device according to claim 1, wherein the optical element is a metalens.

7. An optical scanning device according to claim 1, wherein the light source emits light of three wavelengths within the range of 440 nm to 780 nm.

8. An optical scanning device according to claim 7, characterized in that three wavelength-dependent optical elements are arranged to impart a converging effect to the light of each of the wavelengths, and the three optical elements cause the light of each of the wavelengths to form a common focus.

9. An optical scanning device according to claim 7, characterized in that one optical element is disposed to impart a converging effect to the light of each of the wavelengths, causing the light of each of the wavelengths to form a common focus.

10. An image display device comprising the optical scanning device according to any one of claims 1 to 9, and displaying an image using the light scanned by said optical scanning device.

Images