JP2018109738A - Optical element and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element capable of achieving a display device in which display unevenness is difficult to be visually recognized.SOLUTION: An optical element comprises a plurality of reflection factor variable half mirrors and a translucent member. The plurality of reflection factor variable half mirrors has a plurality of regions having different reflection factors along an inclination direction. The plurality of regions includes at least a low reflection factor region positioned at a farther side from an emission surface and a high reflection factor region positioned at a closer side to the emission surface. An occupancy area of the high reflection factor region of the reflection factor variable half mirrors positioned at a farther side from an incident section is greater than an occupancy area of the high reflection factor region of the reflection factor variable half mirrors positioned at a closer side to the incident section.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an optical element and a display device.

  2. Description of the Related Art In recent years, as one of wearable information devices, an image display device using a method such as a head mounted display that is worn on an observer's head has been provided. There is also known an image display device that can simultaneously view both an image generated by a display element and an image of the outside of the viewer when the viewer wears the image display device, so-called see-through type image display device. .

  For example, in Patent Document 1 below, a light-transmitting substrate, a display light source, optical means for coupling light in the field of view incident on the substrate by internal reflection, and a substrate are provided. An optical device is disclosed that includes a partially reflecting surface disposed obliquely with respect to a main surface. Patent Document 2 below discloses a see-through display device system including an image generation device and a light guide member including an image extraction system including a diffraction grating.

Special table 2007-505353 JP 2004-157520 A

  In the head-mounted display including the optical device of Patent Document 1 and the display device system of Patent Document 2, striped display unevenness is visually recognized due to the pattern of the partial reflection surface provided in front of the observer's eyes. There is a problem. In addition, in these patent documents, there is a description that the uniformity of brightness is improved and display unevenness can be eliminated by providing regions having different reflectivities in one partial reflection surface. It is insufficient.

  One aspect of the present invention is made to solve the above-described problem, and an object of the present invention is to provide a display device that can reduce the visibility of striped display unevenness. Another object of one embodiment of the present invention is to provide an optical element suitable for use in the above display device.

  In order to achieve the above object, the optical element according to one aspect of the present invention is provided so as to be parallel to each other with a gap therebetween, and reflects a part of the image light incident from the incident portion, so that the image light A plurality of reflectivity changing half mirrors that transmit the other part of the mirror, and a translucent member that supports the plurality of reflectivity change half mirrors, wherein the translucent member makes the image light incident thereon. Each of the plurality of reflectivity changing half mirrors is disposed to be inclined with respect to the incident surface and the exit surface, and the plurality of reflections are provided. The rate change half mirror has a plurality of regions having different reflectances along the tilt direction, and each of the plurality of regions of the plurality of reflectivity change half mirrors is located on a side farther from the exit surface in the tilt direction. A low reflectivity region located; A plurality of reflectivity change half mirrors including at least a high reflectivity region positioned closer to the exit surface than the low reflectivity region in the tilt direction and having a reflectivity higher than that of the low reflectivity region Each occupying area of the high reflectivity region of the reflectance change half mirror located on the side far from the incident portion is equal to that of the high reflectivity region of the reflectivity change half mirror located on the side close to the incidence portion. It is characterized by being larger than the occupied area.

  In this type of optical element, the image light traveling to the side farther from the incident part is incident at a nearer perpendicular angle to the half mirror than the image light proceeding to the side closer to the incident part, and a larger number of sheets Change the direction of travel while branching by a half mirror. Therefore, the intensity of the image light traveling to the side farther from the incident part is significantly lower when passing through the half mirror than the image light traveling to the side closer to the incident part.

  Therefore, in the optical element according to one aspect of the present invention, the occupied area of the high reflectivity region in the reflectance change half mirror on the side far from the incident portion is the high reflectivity region in the reflectivity change half mirror on the side close to the entrance portion. Larger than the occupied area. In other words, on the side far from the incident part, the change position of the reflectance in one half mirror is set at a position farther from the exit surface (observer) than the side closer to the incident part. Thereby, the degree of intensity reduction of the image light traveling to the side farther from the incident part can be made closer to the degree of intensity reduction of the image light proceeding to the side closer to the incident part. Thereby, the intensity distribution of the emitted light from the optical element can be made closer to the uniform.

  In the optical element according to one aspect of the present invention, the plurality of reflectivity changing half mirrors have an area occupied by each of the high reflectivity regions from a side closer to the incident portion toward a side farther from the incident portion. May be larger.

  According to this configuration, an optical element having a uniform intensity distribution of emitted light can be manufactured by a simple manufacturing method.

  In the optical element according to one aspect of the present invention, the plurality of reflectance change half mirrors have a linear area occupied by each of the high reflectance regions from a side closer to the incident part toward a side farther from the incident part. May be larger.

  According to this configuration, an optical element having a uniform intensity distribution of emitted light can be manufactured by a simple manufacturing method.

In the optical element of one embodiment of the present invention, the reflectivity of the high reflectivity region and R _1, the reflectance of the low reflectance region and R _2, the reflectance difference parameter Φ in (1) below When defined
Φ = (R ₁ −R ₂ ) / [(R ₁ + R ₂ ) / 2] (1)
The reflectance difference parameter Φ may satisfy 0.1 <Φ <0.7.

  According to this configuration, it is possible to reduce the amplitude of the intensity of the emitted light to such an extent that the observer cannot recognize the intensity unevenness.

  The optical element according to one aspect of the present invention may further include a constant reflectivity half mirror provided in parallel to each of the plurality of reflectivity change half mirrors.

  According to this configuration, the manufacturing cost of the optical element can be reduced. In particular, if the arrangement and the number of half mirrors with constant reflectivity are set appropriately, the manufacturing cost of the optical element can be reduced while suppressing the deterioration of the characteristics of the optical element.

  In the optical element according to one aspect of the present invention, among the plurality of reflectance change half mirrors, the constant reflectance half mirror is between the two reflectance change half mirrors adjacent to each other. May be arranged in parallel with each other.

  According to this configuration, the intensity distribution of the emitted light from the optical element can be made close to uniform.

  In the optical element according to one aspect of the present invention, in the plurality of reflectance change half mirrors, the high reflectance region and the low reflectance region may be gently changed.

  According to this configuration, the intensity distribution of the emitted light from the optical element can be made close to uniform.

  A display device according to one aspect of the present invention includes an image forming device and a light guide device that guides image light generated by the image forming device, and the light guide device causes the image light to enter. An incident portion; a light guide that guides the image light incident from the incident portion; and an emission portion that emits the image light. The emission portion includes the optical element according to one aspect of the present invention. It is characterized by having.

  Since the display device according to one embodiment of the present invention includes an emission portion including an optical element with a more uniform intensity distribution of emitted light, a display device in which striped display unevenness is less visible can be realized.

  In the display device according to one aspect of the present invention, the emission portion may be provided on a surface on the viewing side of the light guide.

  According to this configuration, a display device that is easy to design can be realized.

It is a top view of the display apparatus of a 1st embodiment. It is a back view of a light guide device. It is a figure which shows the optical path of the image light in a light guide device. It is sectional drawing of the optical element of 1st Embodiment. It is sectional drawing of the conventional optical element. It is a graph which shows the relationship between an angle of view and the relative intensity of an emitted light. It is process drawing which shows the 1st manufacturing method of an optical element. FIG. 7B is a continuation of the process diagram of FIG. 7A. FIG. 7B is a continuation of the process diagram of FIG. 7B. It is a continuation of the process diagram of FIG. 7C. It is process drawing which shows the 2nd manufacturing method of an optical element. FIG. 8B is a continuation of the process diagram of FIG. 8A. FIG. 8B is a continuation of the process diagram of FIG. 8B. FIG. 8C is a continuation of the process diagram of FIG. 8C. It is process drawing which shows the 3rd manufacturing method of an optical element. FIG. 9B is a continuation of the process diagram of FIG. 9A. FIG. 9B is a continuation of the process diagram of FIG. 9B. It is a continuation of the process diagram of FIG. 9C. It is sectional drawing of the optical element of 2nd Embodiment. It is a graph which shows the relationship between an angle of view and the relative intensity of an emitted light. It is process drawing which shows the 1st manufacturing method of an optical element. It is a continuation of the process diagram of FIG. 12A. FIG. 12B is a continuation of the process diagram of FIG. 12B. It is process drawing which shows the 2nd manufacturing method of an optical element. FIG. 13B is a continuation of the process diagram of FIG. 13A. FIG. 13B is a continuation of the process diagram of FIG. 13B. It is process drawing which shows the 3rd manufacturing method of an optical element. FIG. 14B is a continuation of the process diagram of FIG. 14A. FIG. 14B is a continuation of the process diagram of FIG. 14B. FIG. 14C is a continuation of the process diagram of FIG. 14C. FIG. 14D is a continuation of the process diagram of FIG. 14D. It is a figure for demonstrating an effect | action of the optical element of this invention. It is a figure for demonstrating the other effect | action of the optical element of this invention. It is a graph which shows the relationship between an angle of view and the relative intensity of an emitted light. It is a graph which shows the relationship between a reflectance difference parameter and the amplitude of an emitted light intensity. It is sectional drawing of the optical element of 3rd Embodiment. It is a graph which shows the relationship between an angle of view and the relative intensity of an emitted light. It is sectional drawing of the optical element of the modification of 3rd Embodiment.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
The display device of the first embodiment is used as a head mounted display, for example.
FIG. 1 is a plan view of the display device according to the first embodiment. FIG. 2 is a rear view of the light guide device. FIG. 3 is a diagram illustrating an optical path of image light in the light guide device.
In the following drawings, in order to make each component easy to see, the scale of the size may be varied depending on the component.

(Overall configuration of light guide device and display device)
As shown in FIG. 1, the display device 100 includes an image forming device 10 and a light guide device 20. 1 corresponds to the AA cross section of the light guide device 20 shown in FIG.
The display device 100 allows an observer to visually recognize a display image as a virtual image and allows the observer to observe an outside world image with see-through. In the display device 100, the image forming device 10 and the light guide device 20 are provided in pairs corresponding to the right eye and the left eye of the observer. However, since the device for the right eye and the device for the left eye are symmetric, only the device for the left eye is shown here, and the illustration for the device for the right eye is omitted. Note that the display device 100 includes a vine portion (not shown) that an observer puts on his / her ear, and has an appearance like general glasses as a whole.

  The image forming apparatus 10 includes a liquid crystal panel 11 and a projection lens 12. The liquid crystal panel 11 spatially modulates illumination light from the light source 14 to form a moving image or other image light GL to be displayed. The projection lens 12 is a collimating lens that makes the image light GL emitted from each point on the liquid crystal panel 11 substantially parallel. The projection lens 12 is made of glass or plastic, and is not limited to one, but may be composed of a plurality of lenses. The projection lens 12 is not limited to a spherical lens, and may be an aspheric lens, a free-form surface lens, or the like.

  The light guide device 20 includes a flat light transmitting member. The light guide device 20 emits the image light GL formed by the image forming device 10 as virtual image light toward the observer's eye EY, and transmits the external light EL that constitutes the external image to pass through the observer's eye EY. Lead to. The light guide device 20 includes an incident portion 21 that captures image light, a parallel light guide 22 that mainly guides the image light, and an emission portion 23 that extracts the image light GL and the external light EL. The parallel light guide 22 and the incident portion 21 are integrally formed of a resin material having high light transmittance. In the case of the first embodiment, the optical path of the image light GL propagating through the light guide device 20 is composed of one type of optical path that is reflected the same number of times, and a plurality of types of optical paths are not synthesized.

  The parallel light guide 22 is disposed to be inclined with respect to the optical axis AX with the observer's eye EY as a reference. The normal direction Z of the plane 22a of the parallel light guide 22 is inclined by an angle κ with respect to the optical axis AX. Thereby, the parallel light guide 22 can be arrange | positioned along the front surface of a face, and the normal line of the plane 22a of the parallel light guide 22 has an inclination with respect to the optical axis AX. As described above, when the normal line of the plane 22a of the parallel light guide 22 is inclined by the angle κ with respect to the z direction parallel to the optical axis AX, the image light GL0 on and near the optical axis AX emitted from the optical element 30. Forms an angle κ with the normal of the light exit surface OS.

  The incident unit 21 includes a light incident surface IS that captures the image light GL from the image forming apparatus 10 into the incident unit 21, and a reflective surface RS that reflects the captured image light GL and guides the image light GL into the parallel light guide 22. Have. The light incident surface IS is formed from a concave curved surface 21b on the projection lens 12 side. The curved surface 21b also has a function of totally reflecting the image light GL reflected by the reflecting surface RS on the inner surface side.

  The reflecting surface RS is formed from a concave curved surface 21a on the projection lens 12 side. The reflective surface RS is composed of a metal film such as an aluminum film formed on the curved surface 21a by vapor deposition or the like. The reflecting surface RS reflects the image light GL incident from the light incident surface IS and bends the optical path. The curved surface 21b bends the optical path by totally reflecting the image light GL reflected by the reflecting surface RS inside. Thus, the incident part 21 reliably guides the image light GL into the parallel light guide 22 by reflecting the image light GL incident from the light incident surface IS twice and bending the optical path.

  The parallel light guide 22 is a flat light guide member that is parallel to the y axis and inclined with respect to the x axis, and is also referred to as a light guide. The parallel light guide (light guide) 22 is formed of a light transmissive resin material or the like. The parallel light guide 22 has a pair of planes 22a and 22b that are substantially parallel to each other. Since the plane 22a and the plane 22b are parallel planes, enlargement of the external image and focus shift do not occur. The flat surface 22a functions as a total reflection surface that totally reflects the image light from the incident portion 21, and guides the image light GL to the emission portion 23 with a small loss. The flat surface 22a is disposed on the outside side of the parallel light guide 22 and functions as a first total reflection surface, and is also referred to as an outside side surface in this specification.

  The plane 22b is also referred to as an observer side surface in the present specification. The flat surface (observer side surface) 22 b extends to one end of the emitting portion 23. Here, the plane 22b is a boundary surface IF between the parallel light guide 22 and the emitting portion 23 (see FIG. 3).

In the parallel light guide 22, the image light GL reflected by the reflection surface RS or the light incident surface IS of the incident portion 21 is incident on the plane 22 a that is a total reflection surface, is totally reflected by the plane 22 a, and is guided by the light guide device 20. , That is, to the + x side or the + X side where the injection portion 23 is provided. As shown in FIG. 2, the parallel light guide 22 has a termination surface ES as an end surface on the + x side in the outer shape of the light guide device 20. Moreover, the parallel light guide 22 has an upper end surface TP and a lower end surface BP as end surfaces on the ± y side.
As shown in FIG. 3, coordinate axes obtained by rotating a coordinate axis composed of the x-axis, y-axis, and z-axis counterclockwise by an angle κ around the y-axis are referred to as an X-axis, a Y-axis, and a Z-axis, respectively. To do.

  As shown in FIG. 3, the emitting portion 23 is configured in a plate shape along the plane 22 b or the boundary surface IF on the back side (+ x side) of the parallel light guide 22. The emission unit 23 reflects the incident image light GL at a predetermined angle when passing the image light GL totally reflected by the region FR of the plane (total reflection surface) 22a on the outside world side of the parallel light guide 22. And bend to the light exit surface OS side. Here, the image light GL that first enters the emission unit 23 without passing through it is an extraction target as virtual image light. That is, even if there is light reflected by the inner surface of the light emission surface OS in the emission unit 23, this is not used as image light.

  The emission unit 23 includes an optical element 30 in which a plurality of half mirrors 31 having light transmission properties and light reflection properties are arranged. The structure of the optical element 30 will be described in detail later with reference to FIG. The optical element 30 is provided along the plane 22 b on the viewer side of the parallel light guide 22. Thus, the emission part 23 is provided on the surface on the viewing side of the parallel light guide 22.

  Since the light guide device 20 has the above-described structure, the image light GL emitted from the image forming device 10 and incident on the light guide device 20 from the light incident surface IS is bent by reflection at the incident portion 21 a plurality of times. Then, the light is totally reflected in the region FR of the plane 22a of the parallel light guide 22 and travels substantially along the optical axis AX. The image light GL reflected by the region FR of the plane 22a on the + z side is incident on the emission unit 23.

  At this time, the width in the longitudinal direction of the region FR is narrower than the width in the longitudinal direction of the injection portion 23 in the xy plane. In other words, the incident width at which the light bundle of the image light GL enters the emission unit 23 (or the optical element 30) is wider than the incident width at which the light bundle of the image light GL enters the region FR. Thus, by making the incident width of the light beam of the image light GL incident on the region FR relatively narrow, the interference of the optical path is less likely to occur, and the boundary surface IF is not used for light guiding, that is, the boundary It becomes easy to make the image light GL from the region FR directly incident on the emission part 23 (or the optical element 30) without reflecting the image light GL on the surface IF.

  The image light GL incident on the emission part 23 is in a state where it can be taken out by being bent at an appropriate angle in the emission part 23 and finally emitted from the light emission surface OS. The image light GL emitted from the light exit surface OS enters the observer's eye EY as virtual image light. By forming the virtual image light on the retina of the observer, the observer can recognize the virtual image by the image light GL.

  Here, the angle at which the image light GL used for image formation is incident on the emitting portion 23 increases as the distance from the incident portion 21 on the light source side increases. In other words, the image light GL having a large inclination with respect to the Z direction parallel to the external plane 22a or the optical axis AX is incident on the back side of the emission unit 23 and is bent at a relatively large angle. The image light GL having a small inclination with respect to the Z direction or the optical axis AX is incident on the front side of the light and is bent at a relatively small angle.

(Light path of image light)
Hereinafter, the optical path of the image light GL will be described in detail.
As shown in FIG. 3, among the image lights emitted from the emission surface 11a of the liquid crystal panel 11, the component emitted from the central portion of the emission surface 11a indicated by the broken line is defined as the image light GL0 and indicated by a one-dot chain line. The component emitted from the left side (−x and + z side) of the drawing surface 11a in the periphery of the emission surface 11a is the image light GL1, and the right side (+ x and −z side) of the drawing surface 11a indicated by the two-dot chain line. Let the component emitted from the image light GL2. Of these, the optical path of the image light GL0 is assumed to extend along the optical axis AX.

  The image lights GL0, GL1, and GL2 that have passed through the projection lens 12 are respectively incident from the light incident surface IS of the light guide device 20, and then pass through the parallel light guide 22 through the incident portion 21 to reach the emission portion 23. Specifically, among the image lights GL0, GL1, and GL2, the image light GL0 emitted from the central portion of the emission surface 11a is bent at the incident portion 21 and coupled into the parallel light guide 22 and then standardized. The light enters the region FR of one plane 22a at the reflection angle θ0 and is totally reflected, passes through the boundary surface IF without being reflected by the boundary surface IF between the parallel light guide 22 and the emitting portion 23 (or the optical element 30). Then, the light directly enters the central portion 23k of the emitting portion 23. The image light GL0 is reflected at a predetermined angle at the portion 23k, and is parallel to the optical axis AX direction (direction of angle κ with respect to the Z direction) inclined from the light exit surface OS to the XY plane including the light exit surface OS. It is emitted as a light beam.

  The image light GL1 emitted from one end side (−x side) of the emission surface 11a is bent at the incident portion 21 and coupled into the parallel light guide 22 and then into the region FR of the plane 22a at the maximum reflection angle θ1. The incident light is totally reflected and passes through the boundary surface IF without being reflected by the boundary surface IF between the parallel light guide 22 and the emitting portion 23 (or the optical element 30). ) At a predetermined angle and is emitted as a parallel light flux from the light exit surface OS toward the predetermined angle direction. At this time, the exit angle γ1 is relatively large in the angle returned to the incident portion 21 side.

  On the other hand, the image light GL2 emitted from the other end side (+ x side) of the emission surface 11a is bent at the incident portion 21 and coupled into the parallel light guide 22, and then the region of the plane 22a at the minimum reflection angle θ2. The light enters the FR, is totally reflected, passes through the boundary surface IF without being reflected by the boundary surface IF between the parallel light guide 22 and the emission unit 23 (or the optical element 30), and enters the entrance side ( The light is reflected at a predetermined angle at the portion 23m on the −x side, and is emitted as a parallel light flux from the light exit surface OS toward the predetermined angle direction. In this case, the exit angle γ2 is relatively small in the angle returned to the incident portion 21 side.

  Note that the image light GL0, GL1, and GL2 have been described as representative of a part of the entire light beam of the image light GL, but the light beam components constituting the other image light GL are also similar to the image light GL0 and the like. It is guided and emitted from the light exit surface OS. Therefore, illustration and description of these are omitted.

  Here, as an example of the value of the refractive index n of the transparent resin material used for the incident portion 21 and the parallel light guide 22, when n = 1.4, the value of the critical angle θc is θc≈45.6 °. . Of the reflection angles θ0, θ1, and θ2 of the image lights GL0, GL1, and GL2, the minimum reflection angle θ2 is set to a value larger than the critical angle θc, thereby satisfying the total reflection condition for the necessary image light. be able to.

  The image light GL0 directed toward the center is incident on the portion 23k of the emission unit 23 at an elevation angle φ0 (= 90 ° −θ0). The image light GL1 for the periphery is incident on the portion 23h of the emission unit 23 at an elevation angle φ1 (= 90 ° −θ1). The image light GL2 for the periphery enters the portion 23m of the emission unit 23 at an elevation angle φ2 (= 90 ° −θ2). Here, the relationship of φ2> φ0> φ1 is established between the elevation angles φ0, φ1, and φ2, reflecting the magnitude relationship of the reflection angles θ0, θ1, and θ2. That is, the incident angle ι (see FIG. 4) of the optical element 30 to the half mirror 31 is gradually reduced in the order of the portion 23m corresponding to the elevation angle φ2, the portion 23k corresponding to the elevation angle φ0, and the portion 23h corresponding to the elevation angle φ1. Become. In other words, the incident angle ι to the half mirror 31 or the reflection angle ε at the half mirror 31 decreases as the distance from the incident portion 21 increases.

The overall behavior of the light bundle of the image light GL that is reflected by the external plane 22a of the parallel light guide 22 and travels toward the exit 23 will be described.
As shown in FIG. 3, the light bundle of the image light GL has a width in one of the front and rear straight light paths P <b> 1 and P <b> 2 reflected by the external region FR of the parallel light guide 22 in the cross section including the optical axis AX. Is squeezed. Specifically, the beam bundle of the image light GL has a width as a whole at a position in the cross section including the optical axis AX, in the vicinity of the region FR, that is, near the boundary between the straight light paths P1 and P2 and straddling the straight light paths P1 and P2. The beam width is narrowed down. As a result, the light bundle of the image light GL is narrowed in front of the emission unit 23, and it becomes easy to make the viewing angle in the horizontal direction relatively wide.
In the illustrated example, the beam width is narrowed and the beam width is narrowed at a position where the light beam of the image light GL straddles the straight light paths P1 and P2, but only on one side of the straight light paths P1 and P2. The beam width may be narrowed by narrowing the width.

(Configuration of optical element)
Hereinafter, with reference to FIG. 3 and FIG. 4, the structure of the optical element 30 which comprises the injection | emission part 23 is demonstrated.
As shown in FIG. 3, the emitting portion 23 is configured by an optical element 30 provided on the viewing side surface of the parallel light guide 22. Therefore, similarly to the parallel light guide 22, the emission portion 23 is provided along the XY plane inclined by the angle κ with respect to the optical axis AX.

  The optical element 30 includes a plurality of half mirrors 31 and a plurality of translucent members 32. The optical element 30 has a configuration in which a plurality of translucent members 32 sandwich a half mirror 31 between two adjacent translucent members 32. In other words, the optical element 30 has a configuration in which the half mirrors 31 and the translucent members 32 are alternately arranged.

  At least a part of the plurality of half mirrors 31 includes a plurality of reflectance change half mirrors. The reflectivity changing half mirror has a plurality of regions having different reflectivities along the tilt direction. In the present embodiment, all the half mirrors 31 are constituted by reflectance change half mirrors. However, all the half mirrors 31 may not be configured with reflectance change half mirrors, and half mirrors with a constant reflectance may be mixed. In the present embodiment, it is not necessary to distinguish between the reflectivity changing half mirror and the constant reflectivity half mirror. Therefore, in the following description, the reflectivity changing half mirror is simply referred to as a half mirror.

  As shown in FIG. 4, the translucent member 32 is a columnar member whose cross-sectional shape perpendicular to the longitudinal direction is a parallelogram. Therefore, the translucent member 32 has two sets of a pair of planes extending in parallel to the longitudinal direction and parallel to each other. Of these two pairs of planes, one plane of one set is an incident surface 32a on which the image light GL and the external light EL are incident, and the other plane of one set is the image light GL and the external light EL. It is the injection surface 32b to inject. A half mirror 31 having two regions 31A and 31B having different film thicknesses is provided on one plane of the other set. The translucent member 32 is made of, for example, glass or transparent resin.

  The plurality of translucent members 32 are all configured to have the same shape and the same dimensions. Therefore, when a plurality of pairs of a pair of translucent members 32 and half mirrors 31 are bonded together, the plurality of half mirrors 31 are arranged in parallel with each other at an equal pitch. Although not shown in FIG. 4, an adhesive layer is provided between one surface of the half mirror 31 and the adjacent translucent member 32. Thereby, the optical element 30 becomes a rectangular plate-like member as a whole. When the optical element 30 is viewed from the normal direction of the incident surface 32a or the exit surface 32b of the translucent member 32, a plurality of thin strip-shaped half mirrors 31 are arranged in a stripe shape. That is, the optical element 30 has a configuration in which a plurality of rectangular half mirrors 31 are arranged at a predetermined interval (pitch PT) in the direction in which the parallel light guide 22 extends, that is, in the X direction.

  In addition, as shown in FIG. 4, since one surface of the half mirror 31 is a flat surface and the other surface is a surface having a step difference in film thickness difference, strictly speaking, adjacent half mirrors 31 are adjacent to each other. Are not said to be parallel to each other. However, in the present invention, when a plane passing through the center of the film thickness direction of the half mirror 31 or at least one surface of the half mirror 31 is parallel, the plurality of half mirrors 31 are considered to be parallel to each other. Since the half mirror 31 is formed of a thin film and has a slight film thickness difference, if the film thickness difference is ignored, it can be said that the plurality of half mirrors 31 are parallel to each other.

  In addition, when light having the same angle is incident on the plurality of half mirrors 31, the plurality of half mirrors 31 are only required if the difference in angle between the lights reflected from the half mirrors 31 is invisible to the observer. Consider parallel to each other. As an example, when the visual acuity of the observer is 1.0, the observer has a resolution of 1/60 degrees, so that the angle difference between the lights reflected from the respective half mirrors 31 is half of that. If the angle is 1/120 degrees, the observer cannot visually recognize the difference, and the plurality of half mirrors 31 are considered to be parallel to each other. As another example, if the angle difference between the lights reflected from the respective half mirrors 31 is an angle difference equal to or less than half of the pixels of the image forming apparatus 10, the observer cannot visually recognize the difference. The plurality of half mirrors 31 are considered to be parallel to each other. For example, when the left and right angle of view of the image light GL is 30 degrees and the number of left and right pixels is 1280 pixels, the angle of the half pixel is 30 ÷ 1280 ÷ 2 = 0.012, so the half angle Are regarded as parallel to each other.

  The half mirror 31 is composed of a reflective film sandwiched between the translucent members 32. As the reflection film, for example, a metal film having a high reflectance such as aluminum is used. Since the thickness of the reflective film is sufficiently thin, the half mirror 31 reflects a part of the image light GL and the external light EL that are incident on the optical element 30, and the other part of the image light GL and the external light EL. Make it transparent. As the reflective film, a dielectric multilayer film in which a plurality of dielectric thin films having different refractive indexes are alternately laminated in addition to a metal film may be used.

  The half mirror 31 is provided such that the short side of the half mirror 31 is inclined with respect to the entrance surface 32a and the exit surface 32b of the translucent member. More specifically, the half mirror 31 is inclined so that the reflecting surface 31r faces the incident portion 21 side toward the outside of the parallel light guide 22. In other words, the half mirror 31 is inclined in the direction in which the upper end (+ Z side) rotates counterclockwise with the long side (Y direction) of the half mirror 31 as an axis and the YZ plane orthogonal to the planes 22a and 22b as a reference. ing.

  Hereinafter, the angle formed by the reflection surface 31r of the half mirror 31 and the emission surface 32b of the translucent member 32 is defined as the inclination angle δ of the half mirror 31. In the present embodiment, the inclination angle δ of the half mirror 31 is 45 ° or more and less than 90 °. In this embodiment, the refractive index of the translucent member 32 and the refractive index of the parallel light guide 22 are equal, but these refractive indexes may be different. When the refractive indexes are different, it is necessary to change the inclination angle δ of the half mirror 31 with respect to the case where the refractive indexes are equal.

  The half mirror 31 has a plurality of regions 31A and 31B having different reflectances along the tilt direction. In the example of FIG. 4, a metal film is used as the reflective film, and the half mirror 31 is formed of a metal film having a plurality of regions having different film thicknesses along the tilt direction. The film thicknesses of the metal films in the regions 31A and 31B are, for example, 10 nm and 20 nm, respectively. In this example, the half mirror 31 includes two regions 31A and 31B having different reflectivities, but the number of regions having different reflectivities is not limited to two, and the number of regions may be three or more. Further, the half mirror 31 does not have a region where the reflectivity is changed stepwise, but the reflectivity may be continuously different. Even when the reflectances are continuously different, the half mirror 31 is included in the concept of having a plurality of regions having different film thicknesses.

  As described above, when a metal film is used as the reflective film, the reflectance can be varied by varying the film thickness depending on the region. Further, the material of the metal film may be different depending on the region. Further, when a dielectric multilayer film is used as the reflective film, the reflectance is varied by changing at least one layer thickness, the number of layers, or the dielectric material of the dielectric multilayer film depending on the region. Is possible.

  In the half mirror 31, two regions having different reflectivities are located on the side closer to the exit surface 32b in the tilt direction, and the high reflectivity region 31B having a relatively high reflectivity and the high reflectivity region 31B in the tilt direction. And a low reflectance region 31A that is located farther from the exit surface 32b and has a reflectance lower than that of the high reflectance region 31B. That is, the high reflectance region 31B corresponds to a region where the metal film is thick, and the low reflectance region 31A corresponds to a region where the metal film is thin.

  In the plurality of half mirrors 31, the occupied area of the high reflectance region 31 </ b> B in each half mirror 31 on the side far from the incident portion 21 is larger than the occupied area of the high reflectance region 31 </ b> B in each half mirror 31 on the side closer to the incident portion 21. Is also provided to be larger.

  Specifically, in the case of the present embodiment, the plurality of half mirrors 31 include a first half mirror group 34 </ b> A composed of a plurality of half mirrors 31 on the side close to the incident part 21, and a plurality of half mirrors 31 on the side far from the incident part 21. A second half mirror group 34B composed of the half mirror 31 is divided into two. In the first half mirror group 34A, the plurality of half mirrors 31 have a constant occupation area of the high reflectivity region 31B. In the second half mirror group 34B, the plurality of half mirrors 31 have a constant occupation area of the high reflectance region 31B.

  That is, in the present embodiment, the area occupied by the high reflectivity region 31B in the plurality of half mirrors 31 increases stepwise from the side closer to the incident part 21 toward the side farther from the incident part 21. In other words, on the side far from the incident part 21, the boundary (reflectance change position) between the high reflectance region 31B and the low reflectance region 31A of one half mirror 31 is closer to the exit surface 32b than the side closer to the incident part 21. It is set at a position away from (observer). Therefore, the boundary line (shown by a broken line) between the high reflectivity region 31B and the low reflectivity region 31A is bent in a step shape across the plurality of half mirrors 31. “Occupied area of the high reflectivity region 31B in the plurality of half mirrors 31 increases stepwise” means that “a plurality of half mirrors that are adjacent to each other and have the same reflectance change position exist”.

(Operation of optical element)
As shown in FIGS. 3 and 4, the plurality of half mirrors 31 have an inclination angle δ of about 48 ° to 70 °, for example, and specifically have an inclination angle δ of 60 °, for example. . Here, it is assumed that the elevation angle φ0 of the image light GL0 is set to, for example, 30 °, the elevation angle φ1 of the image light GL1 is set to, for example, 22 °, and the elevation angle φ2 of the image light GL2 is set to, for example, 38 °. In this case, the image light GL1 and the image light GL2 enter the observer's eye EY at an angle γ1 = γ2≈12.5 ° with the optical axis AX as a reference. Note that the sum of the angle γ1 and the angle γ2 is referred to as an angle of view.

  Thereby, a component having a relatively large total reflection angle (image light GL1) in the image light GL is mainly incident on the −x side portion 23h side of the optical element 30, and a component having a relatively small total reflection angle ( When the image light GL2) is mainly incident on the + x side portion 23m side of the emitting portion 23, the image light GL can be efficiently extracted at an angle that collects the image light GL as a whole in the observer's eye EY. Since the optical element 30 is configured to take out the image light GL with such an angle relationship, the light guide device 20 allows the image light GL to pass through the optical element 30 only once rather than through the optical element 30 in principle. it can. Therefore, the optical element 30 can extract the image light GL as virtual image light with little loss.

  It should be noted that a small portion of the image light GL passes through the half mirror 31 a plurality of times (specifically, one reflection and one or more times) in the central side and back side portions 23k and 23h of the optical element 30. Passing through, including transmission). In this case, although the number of times of passing through the half mirror 31 is plural, the reflected light from the plurality of half mirrors 31 respectively enters the observer's eye EY as the image light GL, and thus the loss of light quantity does not become so great.

  Further, in the central and rear portions 23k and 23h of the optical element 30, the back side of the parallel light guide 22 or the viewer side (that is, the light exit surface OS, the boundary surface IF, etc.) of the image light GL. Reflected components may also occur. However, such image light GL is guided out of the optical path as unused light GX reflected by the half mirror 31 (see FIG. 4), and is prevented from entering the observer's eye EY. Note that the unused light that passes through the half mirror 31 may be incident on the plane 22a on the outside world again. However, in the case of total reflection here, most of the light can be incident on the back side portion 23h of the optical element 30 or further outside the effective area on the heel side, and the possibility of entering the eye EY is reduced.

(Effect of this embodiment)
Hereinafter, specific effects of the optical element 30 of the present embodiment will be described.
FIG. 5 is a cross-sectional view of a conventional optical element 300.
As shown in FIG. 5, in the conventional optical element 300, each of the plurality of half mirrors 301 has a constant in-plane reflectance of one half mirror 301. In this case, since the image light GLa is continuously transmitted through the plurality of half mirrors 301, the intensity Ia′n of the image light GLa decreases as it proceeds to the observer side. That is, Ia′1>Ia′2> Ia′3. Due to the intensity reduction of the branched image light, the image display state becomes non-uniform. The same applies to the image light GLc, and Ic′1>Ic′2>Ic′3>Ic′4> Ic′5.

  Further, the image light GLa and the image light GLc having different angles of view are compared. The position where the image light GLa is incident on the optical element 300 is close to the incident portion of the light guide, and the position where the image light GLc is incident on the optical element 300 is far from the incident portion of the light guide. Therefore, the image light GLc enters the half mirror 301 at an angle closer to the vertical than the image light GLa, and is deflected while being branched by a larger number of half mirrors 301. Therefore, the intensity of the image light GLc is greatly reduced as compared with the intensity of the image light GLa. As a result, the conventional optical element 300 has a problem in that striped display unevenness is visually recognized.

  On the other hand, in the optical element 30 of the present embodiment, one half mirror 31 has a high reflectivity region 31B on the viewer side and a low reflectivity region 31A on the outside side. When the reflectance of the reflectance region 31B is higher than the reflectance of the conventional half mirror 301, the intensity Ia ″ 3 of the image light reflected by the high reflectance region 31B is the image light reflected by the conventional half mirror 301. It becomes higher than the intensity Ia′3. In this way, it is possible to suppress a decrease in the intensity of the image light branched by the half mirror 31.

  Further, on the side far from the incident portion 21, the boundary (reflectance change position) between the high reflectance region 31B and the low reflectance region 31A in one half mirror 31 is located away from the observer. For this reason, the intensity reduction (Ic′1> Ic′2> Ic ″ 3) of the image light GLc traveling to the side farther from the incident part 21 is set to the intensity decrease (Ia) of the image light GLa proceeding closer to the incident part 21. It is possible to approach the degree of '1> Ia'2> Ia ″ 3). As a result, it is possible to suppress both fluctuations in the image light intensity between the individual half mirrors 31 and fluctuations in the image light intensity on the side closer to and far from the incident portion 21, thereby reducing striped display unevenness. It can be difficult to see.

  Here, in order to verify the effect of the optical element 30 of the present embodiment, the inventor performed the following optical simulation. As an optical simulation, an angle profile of an image at the center of the exit pupil (φ = 0.5 mm) was obtained for the following three types of optical elements. The diameter of the light receiver was set to 0.5 mm, which is smaller than the pitch of the half mirror (0.9 mm).

As the optical element of the example, the reflectance of the high reflectance region 31B of the half mirror 31 is 25%, the reflectance of the low reflectance region 31A is 15%, and the height t of the half mirror 31 shown in FIG. An optical element 30 is assumed in which the ratio d / t of the difference d in height between the reflectance boundaries in the two half mirror groups 34A and 34B is 0.1.
As an optical element of the comparative example, an optical element in which the reflectance of the high reflectance region of the half mirror is 25%, the reflectance of the low reflectance region is 15%, and the height of the reflectance boundary is constant is assumed. .
As a conventional optical element, a uniform optical element with a half mirror reflectance of 20% was assumed.

FIG. 6 is a graph showing the relationship between the angle of view and the relative intensity of the emitted light. The horizontal axis of the graph is the angle of view [degree], and the vertical axis is the relative intensity of the emitted light [a. u. ]. Note that the negative angle of view is the angle of view closer to the entrance with respect to the central axis of the exit pupil, and the positive angle of view is the angle of view farther from the entrance with respect to the center axis of the exit pupil. The relative intensity is defined as the intensity of the emitted light for each angle of view when the intensity of the image light incident on the optical element is 1.
The graph indicated by the solid line SA is the data of the optical element of the example, the graph indicated by the two-dot chain line SB is the data of the optical element of the comparative example, and the graph indicated by the broken line SC is the data of the optical element of the conventional example.

  When observing the optical element of the conventional example, display unevenness is not visually recognized in the region close to the incident part (region where the angle of view is negative), and striped display unevenness is observed in a region far from the incident part (region where the angle of view is positive). It was visually recognized. Therefore, as shown by the broken line SC in FIG. 6, a good image is observed if the intensity change of the emitted light is about 20% under this observation condition, but the intensity change of the emitted light is about 50%. It was found that display unevenness was visually recognized.

  On the other hand, by providing the half mirror with regions having different reflectivities as in the optical element of the comparative example, the intensity change of the emitted light is reduced over the entire angle of view as indicated by a two-dot chain line SB in FIG. It was. Further, as shown in the solid line SA in FIG. 6, the optical element of the comparative example is separated from the observer by separating the boundary of the region (change position of the reflectance) from the observer on the side far from the incident portion as in the optical element of the example. In comparison with, the intensity change of the emitted light could be further reduced. When the optical element of the example was actually observed, it was confirmed that striped display unevenness was not visually recognized even in a region far from the incident part.

(Optical element manufacturing method)
Hereinafter, with reference to FIG. 7A to FIG. 7D, FIG. 8A to FIG. 8D, and FIG. 9A to FIG. 9D, three examples of the optical element manufacturing method of the present embodiment will be described.

(First manufacturing method)
First, as shown in FIG. 7A, a plurality of transparent substrates 51 on which a relatively thin reflective film, for example, a first reflective film 53A having a thickness of 10 nm, which will later become a low reflectance region, is laminated. Then, the first stacked body 54A is produced. Similarly, a plurality of transparent substrates 51 each having a relatively thick reflective film, for example, a second reflective film 53B having a film thickness of 20 nm, which later becomes a high reflectivity region, are stacked to form a second stacked body. 54B is produced.

  Next, as shown in FIG. 7B, one half mirror in which each first reflective film 53A of the first multilayer body 54A and each second reflective film 53B of the second multilayer body 54B are continuous. In this manner, the first stacked body 54A and the second stacked body 54B are overlapped and bonded to produce a plurality of bonded bodies 55.

  Next, as illustrated in FIG. 7C, among the plurality of bonded bodies 55, a part of the bonded bodies 55 has a thick second film so that the first reflective film 53 </ b> A having a small thickness remains. The side on which the reflective film 53B is formed is removed by polishing to produce the first joined body 56A. On the other hand, with respect to the other part of the joined bodies 55, the side on which the first reflective film 53A having a small thickness is formed so that a large amount of the second reflective film 53B having a large thickness remains. A large amount is removed by polishing to produce the second bonded body 56B.

Next, as shown in FIG. 7D, the first joined body 56A and the second joined body 56B are joined.
The optical element 30 of this embodiment is completed through the above steps.

(Second manufacturing method)
First, as shown in FIG. 8A, a plurality of transparent substrates 51 on which a first reflective film 53A having a relatively thin film thickness, which later becomes a low reflectance region, is laminated, and a first laminated body 54A is laminated. Is made. Similarly, a plurality of transparent substrates 51 on which a second reflective film 53B having a relatively thick film thickness, which will later become a high reflectance region, is laminated to produce a second laminated body 54B.

  Next, as shown in FIG. 8B, one half mirror in which each first reflective film 53A of the first stacked body 54A and each second reflective film 53B of the second stacked body 54B are continuous. In this manner, the first stacked body 54A and the second stacked body 54B are overlapped and bonded to produce a plurality of bonded bodies 55.

  Next, as shown in FIG. 8C, the bonding position of the first reflective film 53 </ b> A and the second reflective film 53 </ b> B in one bonded body 55, and the first reflective film 53 </ b> A and the second reflective film 53 in the other bonded body 55. It arrange | positions so that the joining position of the reflecting film 53B may shift | deviate, and these two joined bodies 55 are joined.

Next, as shown in FIG. 8D, part of the two bonded bodies 55 is removed by polishing until the mutually displaced surfaces of the two bonded bodies 55 become flat surfaces, whereby the optical element 30 is obtained.
The optical element 30 of this embodiment is completed through the above steps.

(Third production method)
First, as shown in FIG. 9A, as a first film forming process, a metal film such as aluminum is formed on one surface of the transparent substrate 51 with a film thickness of 20 nm, for example, by vapor deposition using a mask 52, sputtering, or the like. The second reflective film 53B is formed.

  Next, as shown in FIG. 9B, as the second film formation step, the mask 52 is moved above the region where the second reflective film 53B is formed in the first film formation step, so that the same surface as the transparent substrate 51 is formed. A metal film of material is formed with a film thickness of 20 nm, for example, to form the first reflective film 53A. In this manner, the transparent substrate 51 including the half mirror 31 having the low reflectance region and the high reflectance region is manufactured.

  Next, as illustrated in FIG. 9C, a plurality of transparent substrates 51 provided with the half mirror 31 are stacked to produce a stacked body 57. At this time, the plurality of transparent substrates 51 are laminated and bonded together so that the boundary position between the first reflective film 53A and the second reflective film 53B is shifted stepwise.

Next, as shown in FIG. 9D, a part of the plurality of transparent substrates 51 is removed by polishing until the plurality of shifted surfaces of the plurality of transparent substrates 51 become flat surfaces as a whole, whereby the optical element 30 is obtained. .
The optical element 30 of this embodiment is completed through the above steps.

  As described above, the optical element 30 of the present embodiment having a uniform intensity distribution of the emitted light can be manufactured by a simple manufacturing method.

[Second Embodiment]
Hereinafter, a second embodiment of the present invention will be described with reference to FIGS. 10 to 14C.
The basic configuration of the display device of the second embodiment is the same as that of the first embodiment, and the configuration of the optical elements is different from that of the first embodiment. Therefore, description of the entire display device is omitted, and only the optical element is described.
FIG. 10 is a cross-sectional view of the optical element according to the second embodiment. FIG. 10 corresponds to FIG. 4 in the first embodiment.
In FIG. 10, the same components as those in FIG.

(Configuration of optical element)
As shown in FIG. 10, the optical element 60 of the second embodiment includes a plurality of half mirrors 61 and a plurality of translucent members 62. In the optical element 60 of the second embodiment, the half mirror 61 includes a high reflectance region 61B located on the side closer to the exit surface 62b in the tilt direction, and a low reflectivity region located on the side far from the exit surface 62b in the tilt direction. 61A. Further, in the plurality of half mirrors 61, the occupied area of the high reflectance region 61B in the half mirror 61 far from the incident portion 21 is larger than the occupied area of the high reflectance region 61B in the half mirror 61 near the incident portion 21. Is also provided to be larger.

In the present embodiment, in the plurality of half mirrors 61, the occupied area of the high reflectivity region 61B is sequentially increased at a constant rate from the side closer to the incident part 21 toward the side farther from the incident part 21. That is, in the first embodiment, the occupied area of the high reflectance region 31B in the plurality of half mirrors 31 is increased stepwise from the side closer to the incident part 21 toward the side farther from the incident part 21. On the other hand, in this embodiment, the area occupied by the high reflectivity region 61B in the plurality of half mirrors 61 increases linearly from the side closer to the incident part 21 toward the side farther from the incident part 21. “Occupied area of the high reflectivity region 61B in the plurality of half mirrors 61 increases linearly” means that “a plurality of half mirrors adjacent to each other and having the same reflectivity change position do not exist and are adjacent to each other. The reflectance change position of the mirror is different.
Other configurations are the same as those of the first embodiment.

  Also in the present embodiment, the first variation in which fluctuations in image light intensity on the side closer to and far from the incident portion 21 in the optical element 60 can be suppressed, and the striped display unevenness can be made difficult to visually recognize. The same effect as the embodiment can be obtained.

  The present inventor also performed an optical simulation for demonstrating the effect of this embodiment. As an optical simulation, an angle profile of an image at the center of the exit pupil (φ = 0.5 mm) was obtained for the following three types of optical elements. The diameter of the light receiver was set to 0.5 mm, which is smaller than the pitch of the half mirror (0.9 mm).

As an optical element of the example, the reflectance of the high reflectance region of the half mirror is 25%, the reflectance of the low reflectance region is 15%, and the high reflectance region of each half mirror shown in FIG. An optical element was assumed in which the inclination angle α formed by the straight line connecting the boundary (reflectance change position) with the reflectance region and the exit surface is 2.5 degrees.
As an optical element of the comparative example, an optical element in which the reflectance of the high reflectance region of the half mirror is 25%, the reflectance of the low reflectance region is 15%, and the height of the reflectance boundary is constant is assumed. .
As a conventional optical element, a uniform optical element with a half mirror reflectance of 20% was assumed.

FIG. 11 is a graph showing the relationship between the angle of view and the relative intensity of the emitted light. The horizontal axis of the graph is the angle of view [degree], and the vertical axis is the relative intensity of the emitted light [a. u. ]. Note that the negative angle of view is the angle of view closer to the entrance with respect to the central axis of the exit pupil, and the positive angle of view is the angle of view farther from the entrance with respect to the center axis of the exit pupil.
The graph indicated by the solid line SD is the data of the optical element of the example, the graph indicated by the two-dot chain line SE is the data of the optical element of the comparative example, and the graph indicated by the broken line SF is the data of the optical element of the conventional example.

  As shown in FIG. 11, in the optical element of the conventional example indicated by the broken line SF, the fluctuation of the relative intensity of the emitted light is particularly large in a region far from the incident part. When the optical element of the conventional example is actually observed, display unevenness is not visually recognized in the area close to the incident part (area where the angle of view is negative), and the display is striped in the area far from the incident part (area where the angle of view is positive). Unevenness was visible.

  On the other hand, the intensity change of the emitted light became small over the entire field angle by providing the half mirror with regions having different reflectivities as in the optical element of the comparative example indicated by the two-dot chain line SE. Further, as in the optical element of the example shown by the solid line SD, by moving away from the observer as the region boundary (reflectance change position) goes farther from the incident part, compared with the optical element of the comparative example, The intensity change of the emitted light could be further reduced. When the optical element of the example was actually observed, striped display unevenness was not visually recognized even in a region far from the incident part.

(Optical element manufacturing method)
Hereinafter, with reference to FIGS. 12A to 12C, FIGS. 13A to 13C, and FIGS. 14A to 14E, three examples of the manufacturing method of the optical element of the present embodiment will be described.

(First manufacturing method)
First, as shown in FIG. 12A, a plurality of transparent substrates 51 on which a relatively thin reflective film, for example, a first reflective film 53A with a film thickness of 10 nm, which later becomes a low reflectance region, is laminated. Then, the first stacked body 54A is produced. Similarly, a plurality of transparent substrates 51 each having a relatively thick reflective film, for example, a second reflective film 53B having a film thickness of 20 nm, which later becomes a high reflectivity region, are stacked to form a second stacked body. 54B is produced.

  Next, as shown in FIG. 12B, each of the first stacked body 54A and the second stacked body 54B is polished obliquely so that two surfaces facing each other are non-parallel.

Next, as illustrated in FIG. 12C, the first stacked body 54 </ b> A and the second stacked body 54 </ b> B are overlapped and bonded in the direction in which the inclined surfaces face each other, thereby forming the optical element 60.
The optical element of this embodiment is completed through the above steps.

(Second manufacturing method)
First, as shown in FIG. 13A, a plurality of transparent substrates 51 each having a relatively thin first reflective film 53A, which later becomes a low reflectivity region, are stacked, and a first stacked body 54A is formed. Is made. Similarly, a plurality of transparent substrates 51 on which a second reflective film 53B having a relatively thick film thickness, which will later become a high reflectance region, is laminated to produce a second laminated body 54B.

  Next, as shown in FIG. 13B, one half mirror 61 in which each first reflective film 53A of the first multilayer body 54A and each second reflective film 53B of the second multilayer body 54B are continuous. Thus, the first stacked body 54A and the second stacked body 54B are overlapped and joined to produce a joined body.

Next, as shown in FIG. 13C, the two surfaces facing each other are polished so that the boundary surface 53AB between the first reflective film 53A and the second reflective film 53B is non-parallel to the polished surface. The optical element 60 is used.
The optical element 60 of this embodiment is completed by the above process.

(Third production method)
First, as shown in FIG. 14A, a metal film 59a such as aluminum is formed with a predetermined film thickness on one surface of the transparent substrate 51 by vapor deposition using a mask 52, sputtering, or the like as a first film forming step. Film.

  Next, as shown in FIG. 14B, as the second film formation step, the mask 52 is moved away from the region where the metal film 59 a is formed in the first film formation step, and then the same as one surface of the transparent substrate 51. A metal film 59b of material is formed with a predetermined film thickness. At this time, since the metal film 59b in the second film formation step is also formed on the metal film 59a formed in the first film formation step, the metal film in the metal film formation region in the first film formation step is It becomes thicker than the metal film in the metal film formation region in the second film formation step.

  Similarly, as shown in FIG. 14C, as the third film formation step, the mask 52 is moved in a direction away from the region where the metal film 59b is newly formed in the second film formation step, and then one surface of the transparent substrate 51 is formed. A metal film 59c of the same material is formed with a predetermined film thickness. As a result, a half mirror having a stepped upper surface is formed.

  Note that the number of film forming steps is not limited to three and may be increased. By increasing the number of film forming steps to reduce the film thickness step, a half mirror with a more gradual step can be formed. Further, instead of the method of forming a film after moving the mask, the film may be formed while moving the mask. According to this method, a half mirror having an inclined surface without a step can be formed.

  Next, as illustrated in FIG. 14D, a plurality of transparent substrates 51 each provided with a half mirror 65 are stacked and bonded to form a stacked body 66. Here, it is illustrated as a half mirror 65 having an inclined surface without a step.

Next, as illustrated in FIG. 14E, the multilayer body 66 is obliquely polished so that portions where the thicknesses of the plurality of half mirrors 65 are different from each other in the thickness direction of the multilayer body 66 are exposed to the polishing surface 51 k, thereby 60.
The optical element 60 of this embodiment is completed by the above process.

[Effect of providing a plurality of reflectance regions]
As in the optical elements of the first and second embodiments, since the half mirror has a plurality of regions having different reflectivities, an effect that the display becomes bright can be obtained.
FIG. 15 is a diagram for explaining the operation of the optical element 200 of the present invention.
For ease of description, the relative intensity I _A of the image light GL1 reaching the viewer is reflected once by the half mirror 201, the observer is reflected in the next half mirror 202 after passing through the half mirror 201 once and relative intensity _{I B} of the image light GL2 reaching, consider the sum S of.

When the reflectance of the half mirror is uniform in the surface as in the conventional optical element, the sum S of relative intensities is expressed by the following equation (2), where p is the reflectance.
S = p + p (1−p) = 2p−p ² (2)

On the other hand, as shown in FIG. 15, when the half mirrors 201 and 202 have two regions having different reflectances (high reflectance regions 201B and 202B and low reflectance regions 201A and 202A), the average reflectance of the two regions P ′, the reflectance of the high reflectance region on the viewer side is (p ′ + q), the reflectance of the low reflectance region on the back side of the viewer is (p′−q), and the image light is low in the half mirror. Assuming that the light is transmitted through the reflectance region and then reflected by the high reflectance region of the next half mirror, the sum S of relative intensities is expressed by the following equation (3).
S ′ = (p′−q) + [1− (p′−q)] (p ′ + q) = 2p−p ′ ² + q ² (3)

From the formulas (2) and (3), by providing the half mirror with two regions having different reflectivities (high reflectivity region and low reflectivity region), the relative intensity of the image light is increased by q ² , and display is performed. It turns out that becomes brighter.

Furthermore, since the half mirror has a plurality of regions having different reflectivities, an effect of reducing ghost of an external image (see-through image) can be obtained.
FIG. 16 is a diagram for explaining another function of the optical element of the present invention.

As shown in FIG. 16, the ghost of the external image is observed by the external light EL1 transmitted through the half mirror 201 once and reaching the observer, and reflected once by the half mirror 201 and reflected by the next half mirror 202. This is because there is external light EL2 that reaches the person. When the reflectance of the half mirror is uniform in the plane as in the conventional optical element, when the reflectance is p, the relative intensity G of the light causing the ghost is expressed by the following equation (4). Is done.
G = p ² (4)

On the other hand, when the half mirrors 201 and 202 have two regions having different reflectances (high reflectance regions 201B and 202B and low reflectance regions 201A and 202A), the average reflectance of the two regions is p ′, and the observer side Where the reflectance of the high reflectance region is (p ′ + q) and the reflectance of the low reflectance region on the back side of the observer is (p′−q), the relative intensity G ′ of the external light EL2 that causes ghosting. Is represented by the following equation (5).
G ′ = (p′−q) (p ′ + q) = p ′ ² −q ² (5)

(4) from the equation and (5), by providing two areas of different reflectance half mirror (the high reflectance region and the low reflectance region), the relative intensity of light causing the ghost only q ² It can be seen that the ghost is less visible.

  By the way, the difference in reflectance between the high reflectance region and the low reflectance region does not have to be large. If the reflectance difference becomes too large, display unevenness may increase.

FIG. 17 is a graph showing the relationship between the angle of view and the relative intensity of the emitted light when the average reflectance is set to 20% and the reflectance difference between the high reflectance region and the low reflectance region is changed. .
The horizontal axis of the graph is the angle of view [degree], and the vertical axis is the relative intensity of the emitted light [a. u. ]. Note that the negative angle of view is the angle of view closer to the entrance with respect to the central axis of the exit pupil, and the positive angle of view is the angle of view farther from the entrance with respect to the center axis of the exit pupil.
The graph indicated by the solid line SG is data when the reflectance in the high reflectance region is 25%, the reflectance in the low reflectance region is 15%, and the reflectance difference is 10%.
The graph indicated by a two-dot chain line SH is data when the reflectance in the high reflectance region is 29%, the reflectance in the low reflectance region is 11%, and the reflectance difference is 14%.
The graph indicated by the broken line SJ is data when the reflectance is constant in the half mirror plane.

  As shown in FIG. 17, in the optical element of the embodiment having two regions having different reflectivities in the half mirror surface, compared with the conventional optical element having a constant reflectivity in the half mirror surface, It was found that the increase / decrease in the intensity was reduced and the striped display unevenness was improved. It was also found that when the difference in reflectance between the high reflectance region and the low reflectance region is changed, the amplitude of the relative intensity changes accordingly.

  Therefore, the present inventor changed the reflectance difference to various values and obtained the relative intensity amplitude corresponding to each reflectance difference. At this time, the amplitude was obtained from the intensity profile data as shown in FIG. 17 by a sinusoidal fitting method. The result is shown in FIG.

FIG. 18 is a graph showing the relationship between the reflectance difference parameter Φ and the amplitude of the emitted light intensity. The horizontal axis of the graph is the reflectance difference parameter Φ [−], and the vertical axis is the amplitude [a. u. ]. When the reflectance in the high reflectance region is R ₁ and the reflectance in the low reflectance region is R ₂ , the reflectance difference parameter Φ is defined by the following equation (6).
Φ = (R ₁ −R ₂ ) / [(R ₁ + R ₂ ) / 2] (6)

  In the case of a conventional optical element having a constant reflectance in the half mirror plane, the reflectance difference parameter Φ is Φ = 0. Therefore, in the optical element of the present embodiment, the reflectivity of the high reflectivity region and the low reflectivity region are set so that the amplitude of the relative intensity of the emitted light is smaller than the amplitude (approximately 0.00035) when Φ = 0. The reflectivity of each must be set. In this examination example, from FIG. 18, it is necessary to set each reflectance so that the reflectance difference parameter Φ satisfies Φ <0.75.

  According to the inventor's experience, in an optical element having a constant reflectance of the half mirror (Φ = 0), it is understood that display unevenness may be visually recognized depending on conditions such as individual differences and image brightness. ing. Therefore, as a range in which the amplitude of the relative intensity of the emitted light is smaller than the amplitude when Φ = 0, the high reflectance region and the low reflectance are set so that the reflectance difference parameter Φ satisfies 0.1 <Φ <0.7. It is desirable to set the reflectance of the reflectance region.

[Third Embodiment]
Hereinafter, a third embodiment of the present invention will be described with reference to FIGS.
The basic configuration of the display device of the third embodiment is the same as that of the first embodiment, and the configuration of the optical element is different from that of the first embodiment. Therefore, description of the entire display device is omitted, and only the optical element is described.
FIG. 19 is a cross-sectional view of the optical element according to the third embodiment. FIG. 20 is a graph showing the relationship between the angle of view and the relative intensity of the emitted light. FIG. 21 is a cross-sectional view of an optical element according to a modification of the third embodiment.
19 and 21 correspond to FIG. 4 of the first embodiment. In FIG. 19 and FIG. 21, the same components as those in FIG.

  As shown in FIG. 19, the optical element 35 of the present embodiment includes a plurality of reflectivity changing half mirrors 31, a plurality of constant reflectivity half mirrors 33, and a plurality of translucent members 62. Each of the plurality of constant reflectivity half mirrors 33 is provided in parallel to each of the plurality of reflectivity change half mirrors 31 and is closer to the incident portion 21 (see FIG. 1) of the plurality of reflectivity change half mirrors 31. Is arranged. That is, the optical element 35 of the present embodiment further includes a constant reflectance half mirror 33 provided in parallel to each of the plurality of reflectance change half mirrors 31.

  In FIG. 19, four constant reflectance half mirrors 33 are provided on the side close to the incident portion 21 of the plurality of reflectance change half mirrors 31, but the number of constant reflectance half mirrors 33 is not particularly limited. Multiple sheets or one sheet may be used. Further, the constant reflectivity half mirror 33 may be provided on the side far from the incident part 21 of the plurality of reflectivity changing half mirrors 31, or near the incident part 21 of the plurality of reflectivity changing half mirrors 31, or What is necessary is just to be provided in at least one of the side far from the incident part 21. FIG.

  As for the plurality of reflectance change half mirrors 31, as in the first embodiment, the occupied area of the high reflectance region 31 </ b> B in the plurality of reflectance change half mirrors 31 is from the entrance portion 21 from the side close to the entrance portion 21. It gradually increases toward the far side. Instead of this configuration, as in the second embodiment, the occupied area of the high reflectance region 31B in the plurality of reflectance change half mirrors 31 is directed from the side closer to the incident part 21 to the side farther from the incident part 21. May be larger in a straight line.

  Also in the present embodiment, the first variation in which fluctuations in image light intensity on the side close to and far from the incident portion 21 in the optical element 35 can be suppressed, and stripe-like display unevenness can be made difficult to visually recognize. The same effect as the embodiment can be obtained.

  Further, according to the configuration of the present embodiment, the manufacturing cost of the optical element 35 can be reduced by using not only the reflectivity changing half mirror 31 but also the constant reflectivity half mirror 33. In particular, by appropriately setting the arrangement and the number of the half mirrors 33 with constant reflectivity, it is possible to reduce the manufacturing cost of the optical element 35 while sufficiently suppressing the deterioration of the characteristics of the optical element 35.

  The present inventor also performed an optical simulation for demonstrating the effect of this embodiment. As an optical simulation, an angle profile of an image at the center of the exit pupil (φ = 0.5 mm) was obtained for the following four types of optical elements. The diameter of the light receiver was set to 0.5 mm, which is smaller than the pitch of the half mirror (0.9 mm).

As an optical element of Example 1, an optical element provided with a single constant reflectivity half mirror on the side close to the incident part of a plurality of reflectivity changing half mirrors among the half mirrors related to the light rays entering the eyes of the observer Assumed. The reflectance of the high reflectance region of the reflectance change half mirror was 25%, the reflectance of the low reflectance region was 15%, and the reflectance of the constant reflectance half mirror was 20%.
As an optical element of Example 2, an optical element provided with two constant reflectance half mirrors on the side close to the incident part of a plurality of reflectance change half mirrors among the half mirrors related to the light rays entering the eyes of the observer Assumed. The configuration of each half mirror is the same as that of the first embodiment.
As an optical element of the comparative example, an optical element in which only a plurality of reflectance change half mirrors were provided without assuming a constant reflectance half mirror was assumed. The configuration of the plurality of reflectance change half mirrors is the same as that of the optical element of the embodiment whose data is shown in FIG.
As a conventional optical element, a uniform optical element with a half mirror reflectance of 20% was assumed.

FIG. 20 is a graph showing the relationship between the angle of view and the relative intensity of the emitted light. The horizontal axis of the graph is the angle of view [degree], and the vertical axis is the relative intensity of the emitted light [a. u. ]. Note that the negative angle of view is the angle of view closer to the entrance with respect to the central axis of the exit pupil, and the positive angle of view is the angle of view farther from the entrance with respect to the center axis of the exit pupil. The relative intensity is defined as the intensity of the emitted light for each angle of view when the intensity of the image light incident on the optical element is 1.
The graph indicated by symbol SA1 is data of the optical element of Example 1, the graph indicated by symbol SA2 is data of the optical element of Example 2, and the graph indicated by symbol SA is data of the optical element of Comparative Example. The graph indicated by the symbol SC is the data of the conventional optical element.

  As shown in FIG. 20, in the optical elements of Examples 1 and 2, the relative intensity slightly decreases in the region where the angle of view is −10 to −15 degrees, but the whole is substantially the same as the optical element of the comparative example. It was found that characteristics were obtained. Therefore, it was confirmed that display unevenness can be reduced even when a constant reflectance half mirror is used as a part of the plurality of reflectance change half mirrors.

  As shown in FIG. 21, in the optical element 36 of the modified example, the occupied area of the high reflectance region 31 </ b> B in the plurality of reflectance change half mirrors 31 is incident from the side closer to the incident portion 21, as in the first embodiment. It gradually increases toward the side far from the part 21. Further, the constant reflectivity half mirror 33 is provided between the first half mirror group 34A and the second half mirror group 34B, which are the boundaries of the reflectivity change positions.

  In FIG. 20, one constant reflectivity half mirror 33 is provided, but the number of constant reflectivity half mirrors 33 is not particularly limited, and may be plural. When a plurality of constant reflectivity half mirrors 33 are provided, the plurality of constant reflectivity half mirrors 33 may be arranged together or separately. In addition, the position where the constant reflectivity half mirror 33 is provided may not necessarily be between the first half mirror group 34A and the second half mirror group 34B which are the boundary of the reflectivity change position. The half mirror group 34A and the second half mirror group 34B may be disposed between the plurality of reflectance change half mirrors 31 constituting each of the half mirror group 34A and the second half mirror group 34B.

  Further, instead of the above configuration, as in the second embodiment, the occupied area of the high reflectivity region 31B in the plurality of reflectivity changing half mirrors 31 is directed from the side closer to the incident portion 21 to the side farther from the incident portion 21. May be larger in a straight line. Between such a plurality of reflectance change half mirrors 31, a constant reflectance half mirror 33 may be provided.

The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, in the optical element of the above embodiment, an example in which two regions of a high reflectance region and a low reflectance region are provided as a plurality of regions having different reflectances, but the number of reflectance regions is two. Not exclusively. Three or more regions having different reflectances may be provided. The more the types of reflectance, the more uniform the image.

  Further, the reflectance value of each region can be freely set by the designer from a value close to 0% to a value close to 100% depending on the application. When the reflectance is increased, there is a drawback that the external image (see-through image) becomes dark, but the display image becomes bright and clear. The reflectivity may be appropriately selected depending on whether the display image or the external image is to be presented to the observer preferentially.

  All the half mirrors included in the optical element do not necessarily have a plurality of reflectance regions. For example, even if the half mirrors at both ends of the optical element are not provided with regions having different reflectivities and have a constant reflectivity, there is no problem in display. Alternatively, among the plurality of reflectivity changing half mirrors, a half mirror having a constant reflectivity is arranged between two adjacent reflectivity changing half mirrors in parallel with the plurality of reflectivity changing half mirrors. Also good.

  Moreover, the area | region where the boundary (reflectance change position) of the high reflectance area | region of a half mirror which has several reflectance area | regions and a low reflectance area | region (reflectance change position) is changing may be mixed. . Further, the boundary (reflectance change position) between the high reflectivity region and the low reflectivity region may not be clearly separated, and the reflectivity may change gently.

  In addition, the specific configuration of each part such as the number, shape, material, and the like of each component included in the optical element and the display device is not limited to the above embodiment, and can be changed as appropriate. For example, as the image forming apparatus, in addition to the liquid crystal display device described above, an organic EL device, a combination of a laser light source and a MEMS scanner, or the like may be used.

  DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus, 20 ... Light guide device, 21 ... Incident part, 22 ... Parallel light guide (light guide), 23 ... Ejection part, 30, 35, 36, 60, 200 ... Optical element 31, 61 , 65, 201, 202 ... half mirror (reflectance changing half mirror), 33 ... constant reflectance half mirror, 31A, 61A ... low reflectance region, 31B, 61B ... high reflectance region, 32, 62 ... translucency Member, 32a ... incidence surface, 32b, 62b ... emission surface, 100 ... display device.

Claims (9)

A plurality of reflectance change half mirrors provided so as to be parallel to each other at an interval, reflecting a part of the image light incident from the incident portion and transmitting the other part of the image light;
A translucent member that supports the plurality of reflectance change half mirrors,
The translucent member has an incident surface on which the image light is incident and an emission surface on which the image light is emitted,
Each of the plurality of reflectance change half mirrors is disposed to be inclined with respect to the entrance surface and the exit surface,
The plurality of reflectance change half mirrors have a plurality of regions having different reflectances along the tilt direction,
Each of the plurality of regions of the plurality of reflectance change half mirrors includes a low reflectance region located on a side farther from the exit surface in the tilt direction, and the exit surface than the low reflectivity region in the tilt direction. At least a high reflectance region having a reflectance higher than that of the low reflectance region,
Each of the plurality of reflectance change half mirrors includes a reflectance change half in which the area occupied by the high reflectance region of the reflectance change half mirror located on the side far from the incident portion is located on the side closer to the incidence portion. An optical element characterized by being larger than the area occupied by the high reflectivity region of a mirror.   The plurality of reflectance change half mirrors are characterized in that the area occupied by each of the high reflectance regions increases stepwise from a side closer to the incident part toward a side farther from the incident part. The optical element according to claim 1.   In the plurality of reflectance change half mirrors, the area occupied by each of the high reflectance regions increases linearly from a side closer to the incident portion toward a side farther from the incident portion. The optical element according to claim 1. When the reflectivity of the high reflectivity region and R _1, and the reflectance of the low reflectance region and R _2, defines a reflectance difference parameter Φ in (1) below,
Φ = (R ₁ −R ₂ ) / [(R ₁ + R ₂ ) / 2] (1)
The optical element according to any one of claims 1 to 3, wherein the reflectance difference parameter Φ satisfies 0.1 <Φ <0.7.   The optical element according to claim 1, further comprising a constant reflectivity half mirror provided in parallel to each of the plurality of reflectivity change half mirrors. .   Of the plurality of reflectance change half mirrors, the constant reflectance half mirror is disposed between two adjacent reflectance change half mirrors so as to be parallel to the plurality of reflectance change half mirrors. The optical element according to claim 5.   7. The plurality of reflectivity changing half mirrors, wherein the high reflectivity region and the low reflectivity region are gently changed. Optical element. An image forming apparatus;
A light guide device for guiding image light generated by the image forming apparatus,
The light guide device includes an incident portion that makes the image light incident thereon, a light guide that guides the image light incident from the incident portion, and an emission portion that emits the image light,
The display unit comprising the optical element according to any one of claims 1 to 7, wherein the emission section includes the optical element according to any one of claims 1 to 7.   The display device according to claim 8, wherein the emission unit is provided on a surface on the viewing side of the light guide.

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