Display device and optical unit

Abstract

To prevent contaminations of an optical element located in a front stage of a see-through mirror or an optical element behind the optical element in the front stage, with dust.SOLUTION: A display device 100 includes: a picture element 11; a prism mirror 22 for causing an image light ML emitted from a picture element 11 to enter a light entrance surface, be reflected by an internal reflection surface, and exit a light exit surface 22c; and a see-through mirror 23 for reflecting the image light ML emitted from the prism mirror 22 to be reflected to a pupil position pp. The prism mirror 22 emits the image light ML entering from the front so that the light will go back to a direction inclined to the front. The light exit side of a picture source 10 including the picture element 11 and the prism mirror 22 is covered with a translucent window 153 for blocking dust.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a see-through type display device and optical unit that enable the observation of a virtual image, and more particularly to a display device and optical unit of the type in which image light from an image source is incident on a see-through mirror and the reflected light from the see-through mirror is observed. [Background technology]

[0002] As a see-through type display device, there exists a type in which a zigzag optical path is formed by two oblique incidence type mirrors, and image light from a display element is made incident on a user's eyes via the zigzag optical path (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-34722 A Summary of the Invention [Problem to be solved by the invention]

[0004] In see-through display devices such as those in Patent Document 1 mentioned above, the arrangement of optical components is limited because it is necessary to secure an area for viewing the outside world. In particular, the see-through mirror that covers the eyes is positioned separately from the optical elements in front of it and is exposed, so it is necessary to prevent the optical elements in the front and the optical elements behind it from becoming contaminated with dirt and dust. [Means for solving the problem]

[0005] A display device in one aspect of the present invention comprises an image element, a prism mirror that allows image light emitted from the image element to enter through a light entrance surface, reflects it off an internal reflective surface, and emits it from a light exit surface, and a see-through mirror that reflects the image light emitted from the prism mirror toward a pupil position, the prism mirror emits the image light by folding it back in a direction inclined to the direction of incidence, and the light exit side of the image source including the image element and the prism mirror is covered with a translucent window that blocks dust. [Brief description of the drawings]

[0006] [Figure 1] FIG. 2 is an external perspective view illustrating a mounting state of the display device according to the first embodiment. [Diagram 2] FIG. 2 is a side cross-sectional view illustrating the internal structure of the display device. [Figure 3A] 10 is a partially enlarged cross-sectional view illustrating a method for fixing the light transmitting member to the case. FIG. [Figure 3B] 13 is a partially enlarged cross-sectional view illustrating a fixing method according to a modified example. FIG. [Figure 3C] FIG. 11 is a partially enlarged cross-sectional view illustrating a fixing method of another modified example. [Figure 4] 1A and 1B are a side cross-sectional view and a partially cross-sectional plan view of a display device. [Diagram 5] 1A and 1B are diagrams illustrating forced distortion of a display image formed on an image element. [Figure 6] FIG. 11 is a side cross-sectional view illustrating the structure of a display device according to a second embodiment. [Figure 7] FIG. 11 is a side cross-sectional view illustrating the structure of a display device according to a third embodiment. [Figure 8] FIG. 13 is a side cross-sectional view illustrating the structure of a display device according to a fourth embodiment. [Figure 9] FIG. 13 is a side cross-sectional view illustrating the structure of a display device according to a fifth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] [First embodiment] Hereinafter, a display device according to a first embodiment of the present invention and an optical unit incorporated therein will be described with reference to FIGS. 1 to 3 and so on.

[0008] Fig. 1 is a diagram for explaining a wearing state of a head mounted display (hereinafter also referred to as HMD) 200, and the HMD 200 allows an observer or wearer US wearing the HMD 200 to recognize an image as a virtual image. In Fig. 1 and the like, X, Y, and Z are an orthogonal coordinate system, and the +X direction corresponds to the lateral direction in which the eyes EY of the observer or wearer US wearing the HMD 200 or the display device 100 are aligned, the +Y direction corresponds to the upward direction perpendicular to the lateral direction in which the eyes EY are aligned for the wearer US, and the +Z direction corresponds to the forward direction or front direction for the wearer US. The ±Y directions are parallel to the vertical axis or vertical direction.

[0009] The HMD 200 includes a first display device 100A for the right eye, a second display device 100B for the left eye, and a pair of temple-shaped support devices 100C that support the display devices 100A and 100B. The first display device 100A is composed of a display driver 102 arranged at the top and an exterior member 103 that is shaped like a pair of glasses and covers the front of the eyes. Similarly, the second display device 100B is composed of a display driver 102 arranged at the top and an exterior member 103 that is shaped like a pair of glasses and covers the front of the eyes. In the first display device 100A and the second display device 100B, the display driver 102 is the main part that forms an image, and the display driver 102 is also called the image source 10. The support device 100C supports the upper end side of the exterior member 103 via the display driver 102. The first display device 100A and the second display device 100B are optically reversed left and right, and hereinafter, the first display device 100A for the right eye will be described as the representative display device 100.

[0010] 2 is a side cross-sectional view illustrating the optical structure of the display device 100. As shown in the figure, the display device 100 includes an image element 11, an imaging optical system 12, and a display control circuit 13. However, in this specification, the display device 100 excluding the display control circuit 13 is also called the display device 100 from the viewpoint of achieving optical functions. The image element 11 and the display control circuit 13 are supported in a case 51 which is an outer frame of the display drive unit 102 shown in FIG. 1, and a part of the imaging optical system 12 is also supported in the case 51 of the display drive unit 102.

[0011] The image element 11 is a self-luminous display device. The image element 11 is, for example, a micro LED display, and forms a color still image or video on a two-dimensional display surface 11a. The image element 11 is arranged along an xy plane that is slightly rotated and tilted around the X axis with respect to the XY plane. The image element 11 is driven by a display control circuit 13 to perform a display operation. The image element 11 is not limited to a micro LED display, and can be replaced with a display device using an organic EL (organic electroluminescence), inorganic EL, organic LED, laser array, quantum dot light-emitting element, or the like. The image element 11 is not limited to a self-luminous image light generating device, and may be composed of an LCD or other light modulation element, and may form an image by illuminating the light modulation element with a light source such as a backlight. Instead of an LCD, LCOS (Liquid crystal on silicon, LCoS is a registered trademark), a digital micromirror device, or the like can be used as the image element 11.

[0012] The imaging optical system 12 includes a projection lens 21, a prism mirror 22, and a see-through mirror 23. In this embodiment, the optical path from the image element 11 to the prism mirror 22 is disposed above the upper end of the see-through mirror 23, but may be disposed at a position partially lower than the upper end of the see-through mirror 23 as long as it does not block the optical path of the image light ML incident on the eye EY. In other words, the image element 11, the projection lens 21, and the prism mirror 22 can be disposed at a position partially lower than the upper end of the see-through mirror 23 as long as it does not block the optical path of the image light ML incident on the eye EY.

[0013] The projection lens 21 focuses the image light ML emitted from the image element 11 into a state close to a parallel light beam. The projection lens 21 is a single lens and has an entrance surface 21a and an exit surface 21b. The prism mirror 22 has a light entrance surface 22a, an internal reflection surface 22b, and a light exit surface 22c. The image light ML emitted from the projection lens 21 is incident on the light entrance surface 22a, totally reflected by the internal reflection surface 22b, and emitted from the light exit surface 22c. At this time, the prism mirror 22 emits the image light ML incident from the front so as to bend it back in a direction inclined with respect to the incident direction (the direction of the light source as seen from the prism mirror 22). In the case of an optical system decentered in the vertical direction as in this embodiment, the front with respect to the optical path includes a direction within a range of about 45° above and below the +Z direction, and the direction inclined with respect to the incident direction includes a direction within a range of about 45° above and below the intermediate direction that forms 45° with respect to the +Z direction and the -Y direction. The see-through mirror 23 reflects the image light ML emitted from the prism mirror 22 toward the pupil position PP. The pupil position PP is a position where the image light ML from each point on the display surface 11a is incident in a predetermined divergent or parallel state so as to be superimposed from an angular direction corresponding to the position of each point on the display surface 11a. The FOV (field of view) of the display device 100 including the illustrated imaging optical system 12 is, for example, 44°. The display area of ​​the virtual image by the display device 100 is rectangular, and the above 44° is the diagonal direction.

[0014] The projection lens 21 and the prism mirror 22 are housed in a case 51 together with the image element 11. The combination of the image element 11, the projection lens 21, and the prism mirror 22, including the case 51, is referred to as an optical unit 15 in this specification. The case 51 is formed of a light-shielding material, and in this embodiment, a display control circuit 13 that operates the image element 11 is built in. The main body of the case 51 is an airtight frame 52, which is formed of a metal material or a resin material. In the case of a resin material, a black light-shielding material can be applied to the inner surface. The frame 52 supports the image element 11, the projection lens 21, and the prism mirror 22 by a member (not shown) that protrudes inward. When the image element 11 and the prism mirror 22 are supported by the airtight frame 52, it is possible to prevent the optical surface of the prism mirror 22 and the display surface of the image element 11 from being contaminated by dirt, dust, and the like. Here, the frame 52 has an opening 52a near the prism mirror 22, and emits the image light ML outside the display drive unit 102 or outside the image source 10. The image light ML emitted to the outside of the display drive unit 102 through the opening 52a is incident on the inside of the see-through mirror 23. The opening 52a is sealed by a rigid, flat, light-transmitting member 53. In other words, the case 51 blocks the interior IS from dust, water droplets, and even the outside air, and seals the optical path space OS from the image element 11 to the prism mirror 22 airtight or liquid-tight.

[0015] The light-transmitting member 53 functions as a light-transmitting window 153 that transmits the image light ML while covering the light-emitting side of the display drive unit 102 or the image source 10. The light-transmitting window 153 blocks dirt and dust from the inside of the case 51. When the light-transmitting window 153 or the case 51 blocks dust, it can include a case where the light-transmitting window 153 or the like seals the optical path space OS from the image element 11 to the prism mirror 22 airtightly or liquid-tightly as in this embodiment. The light-transmitting member 53 as the light-transmitting window 153 has rigidity, which makes it easy to prevent the light-transmitting member 53, i.e., the light-transmitting window 153, from being damaged, and the light-transmitting member 53 being flat plate-shaped can ensure light weight while avoiding any influence on the optical performance. The light-transmitting member 53 is disposed on the light-emitting side of the prism mirror 22, and as a result, is disposed between the prism mirror 22 and the see-through mirror 23. By disposing the light transmitting member 53 or the light transmitting window 153 between the prism mirror 22 and the see-through mirror 23, the optical surface of the prism mirror 22 is protected.

[0016] As described above, the optical unit 15 has a structure in which the image element 11, prism mirror 22, etc. are built in by the case 51 having a shielding structure or sealing structure with a transparent window 153, and the prism mirror 22, etc. are protected from dirt and dust. However, the see-through mirror 22, while supported by the optical unit 15, is exposed to the outside of the optical unit 15.

[0017] The light transmitting member 53 is a parallel plate having a thickness of about 0.5 to 2 mm. That is, the entrance surface 53a and the exit surface 53b are planar optical surfaces. By making the thickness of the light transmitting member 53 0.5 mm or more, the strength of the light transmitting member 53 can be ensured, and the occurrence of interference fringes due to the light transmitting member 53 can be prevented. Furthermore, by making the thickness of the light transmitting member 53 2 mm or less, the weight of the light transmitting member 53 can be prevented from increasing, and the weight of the display drive unit 102 can be reduced. The light transmitting member 53 can be formed of a resin plate having rigidity, but may also be formed of dustproof glass. When the light transmitting member 53 is formed of a resin plate, it is easy to reduce the weight and the possibility of breakage can be reduced. A high-performance optical surface can be formed on the dustproof glass, and the optical performance of the display device 100 can be easily maintained. It is desirable that the light transmitting member 53 has a low refractive index whether it is formed of resin or glass. When the light transmitting member 53 is formed of a resin plate, an anti-reflection film AL is formed on the incident surface 53a, and a hard coat layer HL and an anti-reflection film AL are formed on the exit surface 53b. Such an anti-reflection film AL can suppress the occurrence of ghosts. The hard coat layer HL formed on the exit surface 53b prevents the light transmitting window from being damaged by external forces and suppresses deterioration of optical performance due to use. By imparting water repellency to the surface of the coat formed on the exit surface 53b, anti-soiling properties can be exhibited. Note that when the light transmitting member 53 is formed of dustproof glass, an anti-reflection film AL is formed on the incident surface 53a and the exit surface 53b, but a hard coat layer HL is not formed.

[0018] Covering the opening 52a of the case 51 with the light-transmitting member 53 can prevent the optical surfaces of the optical elements built into the display driver 102, such as the prism mirror 22, from being contaminated with dirt and dust. The light-transmitting member 53 has not only a dustproof function, but also a drip-proof and moisture-proof function that prevents moisture from entering, and also plays a role in preventing fingers and other objects from touching the optical surfaces.

[0019] The light transmitting member 53 is a parallel plate and therefore has substantially no optical power, and passes the image light ML without affecting the image formation and without attenuating the light. The light transmitting member 53 is not limited to a parallel plate, and may be a plate-like body having a wedge angle. The light transmitting member 53 may have an entrance surface 53a and an exit surface 53b that are optical surfaces such as spherical surfaces, aspherical surfaces, or free-form surfaces.

[0020] In the illustrated example, display control circuit 13 is disposed inside case 51, but display control circuit 13 may also be disposed outside case 51. Image element 11 does not need to be disposed inside case 51 either, and an opening for image element 11 may be provided in case 51, and image element 11 may be fixed to case 51 so that display surface 11a faces interior IS of case 51 through this opening.

[0021] The frame 52 of the case 51 supports the see-through mirror 23 via the support plate 61. In this case, the see-through mirror 23 is stably supported relative to the prism mirror 22 and the like via the frame 52. The see-through mirror 23 and the support plate 61 correspond to the exterior member 103 shown in FIG. 1. That is, the see-through mirror 23 is a part of the exterior member 103. The exterior member 103 can also function as a shade. When the exterior member 103 functions as a shade, a see-through area that allows the observation of an external image can be formed in the support plate 61. The see-through area of ​​the support plate 61 and the outside thereof can be provided with light-reducing properties and light-blocking properties. In this case, the see-through mirror 23 functions as a part of the shade, and continuity can be provided in terms of the transmission of external light, etc., in the boundary area between the see-through mirror 23 and the support plate 61.

[0022] FIG. 3A is a partially enlarged cross-sectional view for explaining a method of fixing the light transmitting member 53 to the case 51. The light transmitting member 53 is supported by a seat 51c provided around the opening 52a of the case 51 or the frame body 52. ​​The light transmitting member 53 is fixed to the seat 51c of the case 51 with sufficient strength by an adhesive 55 on the entrance surface 53a side of the outer edge portion 53p. The opening 52a is oval or rectangular, and the seat 51c extends in an annular shape in accordance with the opening 52a. The adhesive 55 is also provided in an annular shape along the outer edge portion 53p. This blocks and separates the inside and outside of the light transmitting member 53, and prevents external dust, moisture, steam, etc. from entering the inside IS. The opening 52a needs to be wider than the optical path of the image light ML, but the size is set to the minimum necessary from the viewpoint of suppressing the passage of light that causes stray light. When the opening 52a is wider than the optical path of the image light ML, a light shielding portion SS can be provided on the outer periphery side of the light transmitting member 53. The light shielding portion SS is formed by applying a black light shielding material or attaching a black light shielding sheet. The light shielding portion SS can also be formed in one step by two-color molding of the light transmitting member 53. The light shielding portion SS can prevent the occurrence of stray light and can prevent unwanted light rays from entering the eye ring ER.

[0023] The adhesive 55 that fixes the light transmitting member 53 can be elastic even after curing. When the adhesive 55 has elasticity even after curing, it is possible to prevent distortion from occurring in the light transmitting member 53. As the elastic adhesive 55, for example, a silicon-based adhesive can be used.

[0024] Fig. 3B shows a modified example of the fixing method shown in Fig. 3A. In this case, an annular step 53s is provided on the outer edge 53p of the light transmitting member 53, and the light transmitting member 53 is fitted into the seat 51c of the case 51. Although not shown in the figure, the light transmitting member 53 can be fixed reliably by interposing an adhesive between the surface of the step 53s and the lower surface of the seat 51c. Although not described in detail, a step can be provided on the seat 51c of the case 51, and the outer edge 53p of the light transmitting member 53 can be fitted into the step.

[0025] 3C shows another modified example of the fixing method shown in FIG. 3A. In this case, an annular protrusion 53r is provided on the outer edge 53p of the light transmitting member 53, an annular groove 51g is provided on the seat 51c of the case 51, and the protrusion 53r of the light transmitting member 53 is fitted into the groove 51g of the case 51. Although not shown, the light transmitting member 53 can be fixed reliably by interposing an adhesive between the protrusion 53r and the groove 51g. Although not described in detail, a protrusion can be provided on the seat 51c of the case 51 and a groove can be provided on the outer edge 53p of the light transmitting member 53, and the protrusion of the case 51 can be fitted into the groove of the light transmitting member 53.

[0026] 3A to 3C, a sealing member made of a material such as rubber can be attached to the joint between the case 51 and the light transmitting member 53 and its periphery. In this case, reliable sealing can be achieved even if the adhesive is not provided seamlessly along the outer edge 53p of the light transmitting member 53.

[0027] Returning to FIG. 2, the imaging optical system 12 is an off-axis optical system 112 due to the see-through mirror 23 being a concave mirror. In this embodiment, the projection lens 21, the prism mirror 22, and the see-through mirror 23 are arranged non-axisymmetrically and have non-axisymmetric optical surfaces. The imaging optical system 12 being the off-axis optical system 112 means that the optical path is bent before and after the light ray is incident on at least one reflecting surface or refracting surface in the optical elements 21, 22, and 23 constituting the imaging optical system 12. In this imaging optical system 12, i.e., the off-axis optical system 112, the optical axis AX is bent so that the optical axis AX extends along an off-axis surface (a surface parallel to the YZ plane) corresponding to the paper surface. In this imaging optical system 12, the optical axis AX is bent within the off-axis surface parallel to the YZ plane, so that the optical elements 21, 22, and 23 are arranged along the off-axis surface. The imaging optical system 12 includes optical axis portions AX1, AX2, and AX3 that are arranged along an off-axis plane (a plane parallel to the YZ plane) that is a predetermined reference plane and are inclined to each other in front of and behind the reflecting surface. The optical axis AX as a whole extends along the optical path of the chief ray emitted from the center of the image element 11 and passes through the eye ring ER or the center of the pupil that corresponds to the eye point. When viewed in a cross section, the optical axis AX includes multiple optical axis portions AX1, AX2, and AX3 and is arranged in a Z-shape. That is, on the off-axis plane parallel to the YZ plane, the optical path P1 from the projection lens 21 to the internal reflecting surface 22b, the optical path P2 from the internal reflecting surface 22b to the see-through mirror 23, and the optical path P3 from the see-through mirror 23 to the pupil position PP are arranged to be folded back in two stages in a Z-shape. The imaging optical system 12 is arranged vertically. That is, the off-axis plane (a plane parallel to the YZ plane) that is a predetermined reference plane extends in the vertical Y direction. In this case, the optical elements 21, 22, and 23 constituting the display device 100 are arranged at different height positions in the vertical direction, so that an increase in the width of the display device 100 can be prevented.

[0028] In the imaging optical system 12, the optical path P1 from the projection lens 21 to the internal reflection surface 22b is nearly parallel to the Z direction. That is, in the optical path P1, the optical axis portion AX1 extends substantially parallel to the Z direction or the front direction. As a result, the projection lens 21 is disposed between the prism mirror 22 and the imaging element 11 with respect to the Z direction or the front direction. It is desirable that the optical axis portion AX1 in the optical path P1 is within a range of about -30° to +30° on average, with the downward direction being negative, toward the Z direction. By making the optical axis portion AX1 of the optical path P1 downward at -30° or more toward the Z direction, it is possible to prevent the projection lens 21 and the imaging element 11 from interfering with the see-through mirror 23. In addition, by making the optical axis portion AX1 of the optical path P1 upward at +30° or less toward the Z direction, it is possible to prevent the projection lens 21 and the imaging element 11 from protruding upward and becoming conspicuous in appearance. In the optical path P2 from the inner reflection surface 22b to the see-through mirror 23, the optical axis portion AX2 is preferably within a range of about -70° to -45° on average, with the downward direction being negative, toward the Z direction. By making the optical axis portion AX2 of the optical path P2 downward at -70° or more toward the Z direction, it is possible to prevent the overall inclination of the see-through mirror 23 from becoming excessively large, and it is easy to secure a space for arranging an inner lens inside the see-through mirror 23. In addition, by making the optical axis portion AX2 of the optical path P2 downward at -45° or less toward the Z direction, it is possible to prevent the prism mirror 22 from being disposed so as to protrude significantly in the -Z direction or toward the back surface relative to the see-through mirror 23, and it is possible to prevent the thickness of the imaging optical system 12 from increasing. The optical path P3 from the see-through mirror 23 to the pupil position PP is nearly parallel to the Z direction, but in the illustrated example, the optical axis portion AX3 is approximately -10°, with the downward direction being negative, toward the Z direction. In other words, the exit optical axis EX, which is an extension of the optical axis portion AX3, extends at an angle of about 10° downward with respect to the forward +Z direction. This is because the human line of sight is stable when the eye is slightly downcast, tilted about 10° downward from the horizontal.The central axis HX extending horizontally with respect to the pupil position PP is assumed to be a case in which the wearer US wearing the display device 100 is in an upright position, relaxed, facing forward, and gazing at the horizontal direction or the horizon. The shape and posture of the head, including the arrangement of the eyes and ears, of each wearer US wearing the display device 100 are various, but by assuming an average head shape or head posture of the wearer US, an average central axis HX can be set for the display device 100 of interest. As a result, the reflection angle of the light ray along the optical axis AX on the inner reflection surface 22b of the prism mirror 22 is about 10° to 60°. Also, the reflection angle of the light ray along the optical axis AX on the see-through mirror 23 is about 20° to 45°.

[0029] The display driver 102 will be described in detail with reference to Fig. 4. In Fig. 4, area AR1 shows a side cross-sectional view of the imaging optical system 12, etc., and area AR2 shows a plan view of the imaging optical system 12, etc. In area AR2, the optical surfaces 21a and 21b of the projection lens 21, the optical surfaces 22a, 22b, and 22c of the prism mirror 22, and the reflecting surface 23a of the see-through mirror 23 are shown projected onto the XZ plane through the optical axis AX.

[0030] The lateral end 11e of the image element 11 constituting the display drive unit 102, i.e., the optical unit 15, is held by a pair of support members 41 protruding inside the case 51 shown by a dashed line. These support members 41 achieve alignment of the image element 11 within the case 51. The lateral end 21e of the projection lens 21 constituting the optical unit 15 is held by a pair of support members 42 protruding inside the case 51. These support members 42 achieve alignment of the projection lens 21 with respect to the case 51. The lateral end 22e of the prism mirror 22 constituting the optical unit 15 is also held by a pair of support members 43 protruding inside the case 51. These support members 43 achieve alignment of the prism mirror 22 with respect to the case 51. In the illustrated example, the end 21e of the projection lens 21 is disposed inside the case 51, but the end 21e may be exposed to the outside at the side wall of the case 51. Similarly, it is not necessary to dispose end 22e of prism mirror 22 inside case 51, and end 21e can be exposed to the outside at a side wall of case 51. Note that frame body 52 of case 51 can be formed by combining frame members divided in half, for example, by a plane parallel to the YZ plane, and when these frame members are joined, image element 11, projection lens 21, etc. can be assembled inside while being aligned. Case 51 is not limited to being made up of two parts, but can be made up of three or more parts.

[0031] The projection lens 21 is a single lens, and the entrance surface 21a and the exit surface 21b, which are optical surfaces constituting the projection lens 21, are asymmetric about the optical axis AX in first vertical directions D11, D12 that are parallel to the YZ plane and intersect with the optical axis AX, and are symmetric about the optical axis AX in a second horizontal direction D02 or the X direction that is perpendicular to the first directions D11, D12. The first vertical direction D11 with respect to the entrance surface 21a and the second vertical direction D12 with respect to the exit surface 21b form a predetermined angle.

[0032] The projection lens 21 is formed of, for example, resin, but may also be made of glass. The entrance surface 21a and the exit surface 21b of the projection lens 21 are, for example, free-form surfaces. The entrance surface 21a and the exit surface 21b are not limited to free-form surfaces, but may also be aspheric surfaces. In the projection lens 21, by making the entrance surface 21a and the exit surface 21b free-form or aspheric, aberration can be reduced. In particular, when a free-form surface is used, it becomes easy to improve the optical performance of the decentering system, so that it becomes easy to reduce the aberration of the imaging optical system 12, which is a non-coaxial off-axis optical system 112. Note that a free-form surface is a surface that does not have an axis of rotational symmetry, and various polynomials can be used as the surface function of the free-form surface. Also, an aspheric surface is a surface that has an axis of rotational symmetry and is expressed by a polynomial, but is a surface other than a parabolic surface or a spherical surface. Although detailed illustration is omitted, an anti-reflection film is formed on the entrance surface 21a and the exit surface 21b.

[0033] Prism mirror 22 is a refracting / reflecting optical member having a function of combining a mirror and a lens, and reflects while refracting image light ML from projection lens 21. More specifically, in prism mirror 22, image light ML enters the inside through light entrance surface 22a, which is a refracting surface, is totally reflected in a non-front direction by inner reflecting surface 22b, which is a reflective surface, and is emitted to the outside through light exit surface 22c, which is a refracting surface. Light entrance surface 22a and light exit surface 22c are optical surfaces made of curved surfaces, and contribute to improving resolution compared to the case where only the reflecting surfaces are present or the case where these are flat surfaces. The light entrance surface 22a, the internal reflection surface 22b, and the light exit surface 22c, which are the optical surfaces that constitute the prism mirror 22, are asymmetric about the optical axis AX in a first vertical direction D21, D22, D23 that is parallel to the YZ plane and intersects the optical axis AX, and are symmetric about the optical axis AX in a second horizontal direction D02 or the X direction that is perpendicular to the first directions D21, D22, D23.

[0034] Prism mirror 22 is made of, for example, resin, but can also be made of glass. The refractive index of the body of prism mirror 22 is set to a value that achieves total reflection on the inner surface, taking into consideration the reflection angle of image light ML. It is desirable to set the refractive index and Abbe number of the body of prism mirror 22 in consideration of its relationship with projection lens 21. In particular, by increasing the Abbe numbers of prism mirror 22 and projection lens 21, the remaining color dispersion as a whole can be reduced.

[0035] The optical surfaces of the prism mirror 22, that is, the light entrance surface 22a, the inner reflection surface 22b, and the light exit surface 22c, are, for example, free-form surfaces. The light entrance surface 22a, the inner reflection surface 22b, and the light exit surface 22c are not limited to free-form surfaces, but may be aspheric surfaces. In the prism mirror 22, by making the optical surfaces 22a, 22b, and 22c free-form or aspheric, it is possible to reduce aberrations, and in particular, when free-form surfaces are used, it is easy to improve the optical performance of the decentering system. In other words, it is easy to reduce the aberrations of the imaging optical system 12, which is the non-coaxial off-axis optical system 112, and it is possible to improve the resolution. The inner reflection surface 22b is not limited to a surface that reflects the image light ML by total reflection, but may be a reflection surface made of a metal film or a dielectric multilayer film. In this case, a reflection film made of a single layer film or a multilayer film made of a metal such as Al or Ag is formed on the inner reflection surface 22b by deposition or the like, or a sheet-like reflection film made of a metal is attached. Although not shown in detail, an anti-reflection film is formed on the light incident surface 22a and the light exit surface 22c.

[0036] The see-through mirror 23 is a plate-shaped optical member that functions as a concave surface mirror and reflects the image light ML from the prism mirror 22. That is, the see-through mirror 23 reflects the image light ML from the emission area of ​​the image source 10 toward the pupil position PP. The see-through mirror 23 covers the pupil position PP where the eye EY or pupil is located, has a concave shape toward the pupil position PP, and has a convex shape toward the outside world. The see-through mirror 23 is a concave transmissive mirror that covers the entire effective area of ​​the screen in the field of view. The see-through mirror 23 is a collimator with a converging function, and converges the chief ray of the image light ML emitted from each point on the display surface 11a and once spreads due to imaging near the emission area of ​​the image source 10 to the pupil position PP. The see-through mirror 23 is a mirror plate having a structure in which a mirror film 23c is formed on the front or back surface of a plate-shaped body 23b. The reflecting surface 23a of the see-through mirror 23 has transparency. The see-through mirror 23 and the reflecting surface 23a are asymmetric about the optical axis AX in a first vertical direction D31 that is parallel to the YZ plane and intersects the optical axis AX, and are symmetric about the optical axis AX in a second horizontal direction D02 or the X direction that is perpendicular to the first direction D31.

[0037] The reflecting surface 23a of the see-through mirror 23 is, for example, a free-form surface. The reflecting surface 23a is not limited to a free-form surface, but can also be an aspheric surface. By making the see-through mirror 23 a free-form surface or an aspheric surface, aberration can be reduced, and in particular, when a free-form surface is used, it becomes easier to reduce aberration in the imaging optical system 12, which is an off-axis optical system or a non-coaxial optical system. Regardless of whether the reflecting surface 23a of the see-through mirror 23 is a free-form surface or an aspheric surface, the see-through mirror 23 has a shape in which the origin of the curved surface formula is shifted toward the projection lens 21 side or the image element 11 side from the effective area of ​​the see-through mirror 23. In this case, the inclined surface of the see-through mirror that realizes a Z-shaped optical path can be set without placing an excessive burden on the design of the optical system.

[0038] The see-through mirror 23 is a transmissive reflecting element that transmits a portion of light when reflected, and the mirror film 23c of the see-through mirror 23 is formed of a semi-transparent reflecting layer. As a result, the outside light OL passes through the see-through mirror 23, making it possible to see through the outside world, and a virtual image can be superimposed on the outside world image. In this case, if the plate-like body 23b is thin, such as a few mm or less, the magnification change of the outside world image can be kept small. The reflectance of the mirror film 23c to the image light ML and the outside world light OL is set to 10% or more and 50% or less in the assumed range of the incidence angle of the image light ML, from the viewpoint of ensuring the brightness of the image light ML and facilitating the observation of the outside world image by the see-through. The plate-like body 23b, which is the base material of the see-through mirror 23, is formed of, for example, resin, but can also be made of glass. The plate-like body 23b is formed of the same material as the support plate 61 that supports it from the periphery, and has the same thickness as the support plate 61. The mirror film 23c is formed of, for example, a dielectric multilayer film consisting of a plurality of dielectric layers whose thicknesses are adjusted. The mirror film 23c may be a single layer film or a multilayer film of a metal such as Al or Ag whose thicknesses are adjusted. The mirror film 23c can be formed by laminating, but can also be formed by attaching a sheet-like reflective film. An anti-reflection film is formed on the outer surface 23o of the plate-like body 23b.

[0039] In this imaging optical system 12, an intermediate pupil IP is disposed between the projection lens 21 and the internal reflection surface 22b of the prism mirror 22, and closer to the light entrance surface 22a of the prism mirror 22 than the projection lens 21 and the internal reflection surface 22b. More specifically, the intermediate pupil IP is disposed at or near the light entrance surface 22a of the prism mirror 22. The intermediate pupil IP refers to the location where the image lights from each point on the display surface 11a spread most widely and overlap with each other, and is disposed at the conjugate point of the eye ring ER or the pupil position PP. It is desirable to dispose an aperture stop at or near the intermediate pupil IP.

[0040] The intermediate image IM is formed between the prism mirror 22 and the see-through mirror 23. The intermediate image IM is formed closer to the prism mirror 22 than the see-through mirror 23. In this way, by forming the intermediate image IM closer to the prism mirror 22 than the see-through mirror 23, the burden of magnification by the see-through mirror 23 can be reduced and the aberration of the observed virtual image can be suppressed. The intermediate image IM is a real image formed in a position upstream of the eye ring ER in the optical path and conjugate with the display surface 11a, and has a pattern corresponding to the display image on the display surface 11a, but does not need to be a sharp image and may exhibit various aberrations such as field curvature and distortion aberration.

[0041] Regarding the optical path, the image light ML from the image element 11 enters the projection lens 21 and is emitted in a substantially collimated state. The image light ML that passes through the projection lens 21 enters the prism mirror 22 and passes through the light entrance surface 22a while being refracted, is reflected by the inner reflection surface 22b with a high reflectance rate close to 100%, and is refracted again by the light exit surface 22c. The image light ML from the prism mirror 22 enters the see-through mirror 23 and is reflected by the reflection surface 23a with a reflectance rate of about 50% or less. The image light ML reflected by the see-through mirror 23 enters the pupil position PP where the eye EY or pupil of the wearer US is located. The external light OL that passes through the see-through mirror 23 and the support plate 61 around it also enters the pupil position PP. In other words, the wearer US wearing the display device 100 can observe a virtual image by the image light ML superimposed on the external image.

[0042] As is clear from a comparison of the areas AR1 and AR2 in Fig. 4, the FOV of the imaging optical system 12 has a horizontal viewing angle α2 larger than a vertical viewing angle α1. This corresponds to the fact that the display image formed on the display surface 11a of the image element 11 is long in the horizontal direction. The horizontal to vertical aspect ratio is set to a value such as 4:3 or 16:9.

[0043] As shown in FIG. 5, the original projected image IG0 showing the image formed by the imaging optical system 12 has a relatively large distortion. Since the imaging optical system 12 is an off-axis optical system 112, it is not easy to completely remove distortion such as keystone distortion. Therefore, even if distortion remains in the imaging optical system 12, when the original display image is DA0, the display image formed on the display surface 11a is a corrected image DA1 that has a distortion such as keystone distortion in advance. In other words, by making the image displayed on the imaging element 11 have an inverse distortion that cancels out the distortion formed by the projection lens 21, the prism mirror 22, and the see-through mirror 23, the pixel arrangement of the projected image IG1 of the virtual image observed at the pupil position PP through the imaging optical system 12 can be a lattice pattern corresponding to the original display image DA0, and the outline can be made rectangular. As a result, it is possible to suppress aberration as a whole including the imaging element 11 while allowing distortion aberration generated by the see-through mirror 23, etc. As a result, the degree of freedom in the arrangement and size of optical elements such as the prism mirror 22 is increased, and the optical performance of the display device 100 can be easily ensured while achieving a compact size of the display device 100.

[0044] In the above embodiment, the image element 11, the projection lens 21, etc. are aligned by the case 51, but the present invention is not limited to this. For example, a lens barrel may be provided separately from the case 51, the projection lens 21 and the prism mirror 22 may be attached to this lens barrel, and the lens barrel to which the projection lens 21, etc. are attached may be fixed inside the case 51.

[0045] The case 51 does not have to be completely sealed, and may have a ventilation hole in a part of it. The ventilation hole may be equipped with a valve or a filter. The filter may be, for example, one that allows air to pass through but blocks dirt and dust.

[0046] In the display device 100 of the first embodiment described above, the light emission side of the image source 10 is covered with a light-transmitting window 153 that blocks dust, so that the optical surfaces (e.g., light emission surface 22c) of one or more optical elements constituting the image source 10 can be prevented from being contaminated by dust or debris that has entered from the outside, and deterioration of optical performance due to use can be suppressed.

[0047] Second Embodiment Hereinafter, a display device according to a second embodiment of the present invention will be described. Note that the display device according to the second embodiment is a partial modification of the display device according to the first embodiment, and a description of common parts will be omitted.

[0048] A display device according to a second embodiment will be described with reference to FIG. 6. In the display device 100 according to this embodiment, the projection lens 21 includes two lens elements 221a and 221b. The four optical surfaces constituting the two lens elements 221a and 221b are asymmetrical about the optical axis AX in a vertical direction parallel to the YZ plane and intersecting the optical axis AX, and are symmetrical about the optical axis AX in a horizontal direction parallel to the X direction. The projection lens 21 may include three or more lens elements. When the projection lens 21 includes a plurality of lens elements 221a, 221b, ..., the optical performance can be easily improved by the plurality of optical surfaces of the plurality of lens elements 221a, 221b, ....

[0049] Third Embodiment Hereinafter, a display device according to a third embodiment of the present invention will be described. Note that the display device according to the third embodiment is a partial modification of the display device according to the first embodiment, and a description of common parts will be omitted.

[0050] A display device of the third embodiment will be described with reference to Fig. 7. In the display device 100 of this embodiment, the image element 11, the projection lens 21, and the prism mirror 22 are fixed in the case 51. However, in the opening 52a of the case 51, the light exit surface 22c of the prism mirror 22 is exposed to the outside air. In other words, the light exit portion 22p, which is a surface portion including the light exit surface 22c of the prism mirror 22, functions as a light-transmitting window 153. The light-transmitting window 153 is fixed to the bottom plate 52f of the case 51 at the periphery of the opening 52a formed in the bottom plate 52f as a part of the prism mirror 22.

[0051] In the case of the display device 100 shown in FIG. 7, the light exit portion 22p, which is a surface portion including the light exit surface 22c of the prism mirror 22, functions as the light-transmitting window 153. That is, the light exit portion 22p includes the optical surface of the prism mirror 22 and is a portion for extracting the image light ML to the outside of the image source 10 or the optical unit 15. In this case, the image element 11, the projection lens 21, etc. are built into the case 51, and the light entrance surface 22a and the internal reflection surface 22b of the prism mirror 22 are also arranged in the case 51. The prism mirror 22 is formed of a material having optical transparency, and an anti-reflection film is formed on the light exit surface 22c, so that the light exit portion 22p passes the image light ML with almost no loss. The light exit portion 22p, which is the light-transmitting window 153, is supported by the case 51 while being sealed at its outer edge via a shielding structure or a sealing structure. The light exit portion 22p and the like spatially blocks or separates the light exit surface 22c of the prism mirror 22 from other surfaces while enabling the image light ML to be emitted outside the case 51, and prevents dust, moisture, steam, and the like from the outside of the case 51 from entering the inside IS of the case 51. This prevents the optical surfaces such as the light entrance surface 22a of the prism mirror 22 from being contaminated with dirt or dust, or from becoming cloudy. In other words, the light-transmitting member 53 not only provides a dustproof effect, but also provides a drip-proof and moisture-proof effect. When the light-transmitting window 153 is a light exit portion including the light exit surface 22c of the prism mirror 22, there is no need to separately incorporate a light-transmitting member, making it easier to achieve a reduction in weight and size of the display device 100.

[0052] An anti-reflection film 22q is formed on the light exit surface 22c of the prism mirror 22. When the prism mirror 22 is made of a resin material, it is preferable that a hard coat layer HL is formed as a base for the anti-reflection film. A coating layer having antifouling properties can also be provided on the light exit surface 22c.

[0053] [Fourth embodiment] Hereinafter, a display device according to a fourth embodiment of the present invention will be described. Note that the display device according to the fourth embodiment is a partial modification of the display device according to the first embodiment, and a description of common parts will be omitted.

[0054] A display device according to a fourth embodiment will be described with reference to Fig. 8. In a display device 100 according to this embodiment, an imaging optical system 12 includes a reflecting mirror 421, a prism mirror 22, and a see-through mirror .

[0055] The reflection mirror 421 is provided in place of the projection lens 21 in the first embodiment. The reflection mirror 421 is a third mirror that reflects the image light ML emitted from the image element 11 before the image light ML enters the prism mirror 22. The reflection mirror 421 increases the number of times the optical path is bent compared to the first embodiment. The reflection mirror 421 has a positive power that collects the image light ML emitted from the image element 11 when reflecting it. The reflection mirror 421 has asymmetrical properties with respect to the optical axis AX in the vertical direction that is parallel to the YZ plane and intersects with the optical axis AX, similar to the projection lens 21, and has symmetry with respect to the optical axis AX in the horizontal direction that is parallel to the X direction. The reflection mirror 421 is a back-surface reflection type element and has a reflection surface 21r on the back side of the plate-shaped body 21j, but a reflection surface may be provided on the front side. When the reflection surface 21r is provided on the back side as shown in the figure, it is desirable to form an anti-reflection film on the front side surface 21k. The prism mirror 22 has a light entrance surface 22a, an inner reflection surface 22b, and a light exit surface 22c, as in the first embodiment, and the image light ML exiting from the reflection mirror 421 is incident on the light entrance surface 22a, totally reflected by the inner reflection surface 22b, and exits from the light exit surface 22c. The see-through mirror 23 reflects the image light ML exiting from the prism mirror 22 toward the pupil position PP. The see-through mirror 23 is a back-reflection type element, and has a reflection surface 23a on the back side of the plate-shaped body 23b. An anti-reflection film is formed on the inner surface 23i of the plate-shaped body 23b. The reflection surface 23a of the see-through mirror 23 is formed by a semi-transparent reflection layer. The reflection mirror 421, the prism mirror 22, and the see-through mirror 23 constitute the off-axis optical system 112, as in the first embodiment.

[0056] In the optical unit 15 or the image source 10, the image element 11, the reflection mirror 421, and the prism mirror 22 are housed in a case 451. The case 451 includes a support structure 75, a first cover member 71, a second cover member 72, and a third cover member 73. The support structure 75 supports the reflection mirror 421 and also supports the first cover member 71 and the second cover member 72. The first cover member 71 covers the upper, rear, and side of the optical unit 15, the second cover member 72 covers the front of the optical unit 15, and the third cover member 73 covers the lower part of the optical unit 15. The first cover member 71 supports the image element 11 and the prism mirror 22 in an aligned state in the case 451. The second cover member 72 is a part of the support plate 61, and indirectly supports the see-through mirror 23. The first cover member 72 and the second cover member 73 are formed of a light-shielding metal material or resin material. When the first cover member 72 and the like are formed of a resin material, a black light-shielding material can be applied to the inner surface side of the resin base material. The third cover member 73 has a light-transmitting member 53 in a local area corresponding to the optical path of the image light ML. The light-transmitting member 53 is a light-transmitting window 153 that covers the light-emitting side of the image source 10 including the prism mirror 22. The third cover member 73 is fixed airtight to the first cover member 71 and the second cover member 72 using, for example, an adhesive 55. The first cover member 71 and the second cover member 72 are also airtightly joined together using an adhesive or a seal member (not shown).

[0057] By covering the light exit portion of the case 51 with the light transmitting member 53 of the third cover member 73, the inside and outside of the light transmitting member 53 are spatially blocked or separated while enabling the image light ML to be emitted, and it is possible to prevent dust, moisture, steam, etc. from the outside of the case 51 from entering the inside IS. This makes it possible to prevent the optical surfaces of the optical elements built into the optical unit 15, such as the prism mirror 22, from being contaminated with dirt or dust, or from becoming cloudy on the optical surfaces. In other words, the light transmitting member 53 not only provides a dustproof effect, but also provides a drip-proof and moisture-proof effect. The third cover member 73 is a parallel flat plate having a thickness of about 0.5 to 2 mm. In other words, the entrance surface 53a and the exit surface 53b of the light transmitting member 53 formed in a partial region of the third cover member 73 are flat surfaces that have little effect on the image formation by the image light ML. The third cover member 73 including the light transmitting member 53 can be formed of a resin plate having rigidity, but may also be formed of dustproof glass. When the light transmitting member 53 is made of a resin plate, an anti-reflection film AL is formed on the incident surface 53a, and a hard coat layer HL and an anti-reflection film AL are formed on the exit surface 53b. When the light transmitting member 53 is made of dust-proof glass, an anti-reflection film AL is formed on the incident surface 53a and the exit surface 53b, but a hard coat layer HL is not formed. A light shielding portion SS is formed in a peripheral region 73b of the third cover member 73 excluding the light transmitting member 53, to prevent the occurrence of stray light. The light shielding portion SS is formed by applying a black light shielding material or attaching a black light shielding sheet.

[0058] In the above description, the support structure 75, the first cover member 71, and the second cover member 72 are formed separately, but they may be formed integrally. Also, the light transmitting member 53 and the peripheral region 73b constituting the third cover member 73 may be formed separately, and the light transmitting member 53 may be joined to the peripheral region 73b, etc.

[0059] The reflecting mirror 421 can be replaced by a prism mirror having one or more refracting surfaces.

[0060] Fifth embodiment Hereinafter, a display device according to a fifth embodiment of the present invention will be described. Note that the display device according to the fifth embodiment is a partial modification of the display device according to the fourth embodiment, and a description of the common parts will be omitted.

[0061] A display device of the fifth embodiment will be described with reference to FIG. 9. In the display device 100 of this embodiment, the image element 11, the reflecting mirror 421, and the prism mirror 22 are fixed in the case 51. However, the light exit surface 22c of the prism mirror 22 is exposed to the outside air through the opening 52a provided in the bottom plate 52f of the case 51. In other words, the light exit portion 22p, which is a surface portion including the light exit surface 22c of the prism mirror 22, functions as the light-transmitting window 153. The light-transmitting window 153 is fixed to the bottom plate 52f at the periphery of the opening 52a formed in the bottom plate 52f of the case 51 as a part of the prism mirror 22. The second cover member 72 of the case 51 is separate from the support plate 61, and supports the upper end of the support plate 61 by bonding or the like.

[0062] In the case of the display device 100 shown in FIG. 9, the light exit portion 22p of the prism mirror 22 functions as a light-transmitting window 153. That is, the light exit portion 22p includes the optical surface of the prism mirror 22, and is a portion for extracting the image light ML to the outside of the image source 10 or the optical unit 15. In this case, the image element 11, the projection lens 21, etc. are built into the case 51, and the light entrance surface 22a and the inner reflection surface 22b of the prism mirror 22 are also arranged in the case 51. The prism mirror 22 is formed of a material having optical transparency, and an anti-reflection film is formed on the light exit surface 22c, so that the light exit portion 22p passes the image light ML with almost no loss. The light exit portion 22p, which is the light-transmitting window 153, is supported by the case 51, which is sealed at its outer edge via a shielding structure or a sealing structure. Light exit portion 22p etc. spatially blocks or separates light exit surface 22c of prism mirror 22 from other surfaces while enabling image light ML to be emitted outside case 51, and prevents dust, moisture, steam, etc. from outside case 51 from entering interior IS of case 51. This makes it possible to prevent optical surfaces such as light entrance surface 22a of prism mirror 22 from being contaminated with dirt or dust, or from becoming cloudy on such optical surfaces. In other words, light transmitting member 53 not only provides a dustproof effect, but also provides a drip-proof and moisture-proof effect.

[0063] An anti-reflection film 22q is formed on the light exit surface 22c of the prism mirror 22. When the prism mirror 22 is made of a resin material, for example, it is preferable that a hard coat layer HL is formed as a base for the anti-reflection film. A coating layer having antifouling properties can also be provided on the light exit surface 22c.

[0064] [Variations and Others] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments and can be embodied in various forms without departing from the spirit of the present invention. For example, the following modifications are also possible.

[0065] In the display device 100 of the above embodiment, a self-luminous display device such as an organic EL element, an LCD, or other light modulation elements are used as the image element 11, but instead of this, a configuration using a laser scanner combining a laser light source and a scanner such as a polygon mirror is also possible. In other words, the present invention can also be applied to a laser retinal projection type head mounted display.

[0066] A dimming device that adjusts light by limiting the light transmitted through the see-through mirror 23 can be attached to the outside world side of the see-through mirror 23. The dimming device adjusts the transmittance electrically, for example. As the dimming device, a mirror liquid crystal, an electronic shade, etc. can be used. The dimming device may adjust the transmittance according to the illuminance of outside light.

[0067] In the above description, it is assumed that the display device 100 is used by being mounted on the head, but the display device 100 can also be used as a handheld display that is not mounted on the head and is peered at like binoculars. In other words, in the present invention, the head mounted display also includes a handheld display.

[0068] In the above embodiment, the image source 10 is a combination of an image element 11, a projection lens 21, and a prism mirror 22, or a combination of an image element 11, a reflection mirror 421, and a prism mirror 22, but the image source 10 may also be a combination of an image element 11 and a prism mirror 22, or a combination of an image element 11 and a projection lens 21.

[0069] In a specific embodiment, the display device comprises an image element, a prism mirror that allows image light emitted from the image element to enter through a light entrance surface, reflects it off an internal reflection surface, and emits it from a light exit surface, and a see-through mirror that reflects the image light emitted from the prism mirror toward a pupil position, the prism mirror emits the light so as to bend it back in a direction inclined relative to the direction of incidence, and the light exit side of the image source including the image element and the prism mirror is covered with a translucent window that blocks dust.

[0070] In the above-mentioned display device, the light emission side of the image source is covered with a translucent window that blocks dust, so that the optical surfaces of one or more optical elements that make up the image source can be prevented from becoming contaminated by dust or debris that has entered from the outside, and deterioration of optical performance due to use can be suppressed.

[0071] In a specific aspect, the light-transmitting window is disposed between the prism mirror and the see-through mirror, in which case the optical surface of the prism mirror is protected.

[0072] In another aspect, the light-transmitting window is a light-transmitting member having a rigid plate shape. When the light-transmitting member has rigidity, it is easy to prevent the light-transmitting window from being damaged, and when the light-transmitting member has a plate shape, it is possible to ensure light weight while avoiding any adverse effect on optical performance.

[0073] In another aspect, the light-transmitting window is dust-proof glass. A high-performance optical surface can be formed on the dust-proof glass, making it easier to maintain the optical performance of the display device.

[0074] In another aspect, the light-transmitting window is a resin plate, and a hard coat layer is formed on the exit surface. The hard coat layer prevents the light-transmitting window from being damaged by external forces and suppresses deterioration of optical performance due to use.

[0075] In another aspect, an anti-reflection film is formed on the entrance surface and the exit surface of the light-transmitting window. The anti-reflection film can suppress the occurrence of ghosts.

[0076] In another aspect, the light-transmitting window is a light exit portion including a light exit surface of a prism mirror. In this case, it is not necessary to incorporate a member such as a light-transmitting member, and it is easy to achieve a reduction in weight and size of the display device.

[0077] In another aspect, the image element and the prism mirror are supported by an airtight frame body. The frame body makes it possible to prevent the inner surface of the prism mirror and the display surface of the image element from being contaminated by dirt, dust, and the like.

[0078] In another aspect, the frame constitutes a case that seals the optical path space from the image element to the prism mirror.

[0079] In another aspect, the light exit portion including the light exit surface of the prism mirror functions as a light-transmitting window.

[0080] In another aspect, the frame has a light-shielding portion formed along an outer edge of the light-transmitting window. The light-shielding portion can prevent unwanted light rays from entering the pupil.

[0081] In another aspect, the frame supports the see-through mirror. In this case, the see-through mirror is stably supported with respect to the prism mirror or the like via the frame.

[0082] In another aspect, the light entrance surface, the internal reflection surface, and the light exit surface of the prism mirror are free-form surfaces. When the prism mirror includes a free-form surface, it becomes easy to improve the optical performance of the decentered system.

[0083] In another aspect, the image source has a projection lens through which the image light emitted from the image element passes before entering the prism mirror.

[0084] In another aspect, the projection lens includes multiple lens elements. Multiple optical surfaces of the multiple lens elements facilitate improved optical performance.

[0085] In another aspect, the image source has a third mirror that reflects the image light emitted from the image element before the image light is incident on the prism mirror.

[0086] In another aspect, the image source is an off-axis optical system that includes optical axis portions disposed along a predetermined reference plane and inclined relative to each other before and after the reflecting surface.

[0087] In another aspect, the predetermined reference plane extends in the vertical direction. In this case, the optical elements constituting the display device are arranged in the vertical direction, and an increase in the horizontal width of the display device can be prevented.

[0088] In another aspect, the optical system including the prism mirror and the see-through mirror generates distortion, and the image element corrects the distortion. In this case, the degree of freedom in the arrangement and size of the optical elements such as the prism mirror is increased, and it is possible to easily ensure the optical performance of the display device while achieving a compact display device.

[0089] In a specific embodiment, the optical unit comprises an image element and a prism mirror that allows image light emitted from the image element to enter through a light entrance surface, reflects it off an internal reflection surface, and emits it from a light exit surface, the prism mirror emits the image light incident from the front so as to bend it back in a direction inclined relative to the front, and the light exit side of the image source including the image element and the prism mirror is covered with a translucent window that blocks dust. [Explanation of symbols]

[0090] 10...image source, 11...image element, 11a...display surface, 12...imaging optical system, 13...display control circuit, 15...optical unit, 21...projection lens, 21a...entrance surface, 21b...exit surface, 22...prism mirror, 22a...light entrance surface, 22b...internal reflection surface, 22c...light exit surface, 23...see-through mirror, 23a...reflection surface, 41, 42, 43...support member, 51, 451...case, 52...frame, 52a...opening, 53, 153... Light-transmitting member, 55...adhesive, 61...support plate, 100, 100A, 100B...display device, 100C...support device, 102...display drive unit, 103...exterior member, 112...off-axis optical system, AX...optical axis, AX1, AX2, AX3...optical axis portion, ER...eye ring, EY...eye, IG0, IG1...projected image, IS...inside, ML...image light, OL...external light, OS...optical path space, P1, P2, P3...optical path, PP...pupil position, US...wearer

Claims

1. An imaging element; a prism mirror that allows the image light emitted from the image element to enter through a light incident surface, reflects the image light on an internal reflection surface, and emits the image light from a light exit surface; a see-through mirror that reflects the image light emitted from the prism mirror toward a pupil position, the prism mirror emits the image light so as to bend the image light in a direction inclined with respect to a direction of incidence, a light exit side of the image source including the image element and the prism mirror is covered with a light-transmitting window that blocks dust; The display device, wherein the light-transmitting window is a light exit portion including a light exit surface of the prism mirror.

2. The display device according to claim 1 , wherein an anti-reflection film is formed on the entrance surface and the exit surface of said light-transmitting window.

3. 3. The display device according to claim 1, wherein the image element and the prism mirror are supported by an airtight frame.

4. The display device according to claim 3 , wherein the frame constitutes a case that seals an optical path space from the image element to the prism mirror.

5. The display device according to claim 3 , wherein the frame has a light-shielding portion formed along an outer edge of the light-transmitting window.

6. 6. The display device according to claim 3, wherein the frame supports the see-through mirror.

7. 7. The display device according to claim 1, wherein the light entrance surface, the internal reflection surface, and the light exit surface of the prism mirror are free-form surfaces.

8. 8. The display device according to claim 1, wherein the image source has a projection lens through which the image light emitted from the image element passes before being incident on the prism mirror.

9. The display device of claim 8 , wherein the projection lens comprises a plurality of lens elements.

10. 10. The display device according to claim 1, wherein the image source has a third mirror that reflects the image light emitted from the image element before the image light is incident on the prism mirror.

11. The display device according to any one of claims 1 to 10, wherein an imaging optical system including the prism mirror and the see-through mirror is an off-axis optical system that is arranged along a predetermined reference plane and includes optical axis portions that are inclined relative to each other before and after the reflective surface.

12. 12. The display device according to claim 1, wherein an optical system including the prism mirror and the see-through mirror produces a distortion, and the image element corrects the distortion.

13. An imaging element; a prism mirror that causes the image light emitted from the image element to enter from a light incident surface, reflects the image light on an internal reflection surface, and emits the image light from a light exit surface; the prism mirror outputs the image light incident from the front so as to bend the image light in a direction inclined with respect to the front; a light exit side of the image source including the image element and the prism mirror is covered with a light-transmitting window that blocks dust; the light-transmitting window is a light exit portion including a light exit surface of the prism mirror;

Images