Image display device

An image display device of the present disclosure includes an image light generating device, a first, a second, a third, and a fourth optical unit. A first intermediate image is formed between the first and the third optical unit. A pupil is formed between the second and the fourth optical unit. A second intermediate image is formed between the third and the fourth optical unit. An exit pupil is formed at an opposite side of the fourth optical unit from the third optical unit. The image light generating device includes a first, a second, a third light emitting panel, and a color synthesis element. The color synthesis element is constituted of a cross dichroic prism including a first and a second dichroic film that intersect with each other. Each of the first and the second dichroic film does not have a polarization separation characteristic.

The present application is based on, and claims priority from JP Application Serial Number 2018-210560, filed Nov. 8, 2018, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to an image display device.

2. Related Art

A head-mounted display device configured to guide image light to an eye of an observer while reflecting the image light by using a plurality of reflective surfaces is known. JP-A-2012-18414 discloses a head-mounted display device including a frame, an image generating device, a light-guiding plate that guides light emitted from the image generating device to an eye of an observer, and a first deflection means and a second deflection means for reflecting the light incident on the light-guiding plate.

However, in the head-mounted display device in JP-A-2012-18414, the light-guiding plate is used as a means for guiding light emitted from the image generating device to an eye of an observer. For this reason, there is a problem in that the device becomes large and heavy. Thus, JP-A-2017-167181 discloses a display device configured to guide image light to an eye of an observer by using two diffraction elements constituted of a reflection-type hologram. In JP-A-2017-167181, a combination of a laser light source and a scanning optical system, a liquid crystal panel, an organic electroluminescence (EL) panel, and the like are exemplified as an image light generating device.

It can be said that a reflection-type hologram described in JP-A-2017-167181 is an optical system suitable for a see-through image display device configured to superimpose external light on a display for display since the reflection-type hologram reflects only light in a specific wavelength region and transmits light in the other wavelength region. However, a reflective wavelength width is generally very narrow in a reflection-type hologram, and thus a lot of image light emitted from a display is not reflected by the hologram and is transmitted through the hologram. Thus, there is a problem in that light-guiding efficiency is low.

It is conceivable to use, as an image light generation device, an organic EL panel that can achieve higher contrast than that of a liquid crystal panel, for example. The organic EL panel has features such as low profile and light weight, and is expected to be applied to a direct view display, of course, and also a head-mounted display device in combination with the aforementioned reflection-type hologram. However, when the organic EL panel is combined with an optical system having low light-guiding efficiency, such as the reflection-type hologram, there is a problem in that, when panel luminance is increased, a life of an organic EL element is reduced, and brightness deteriorates quickly.

SUMMARY

To solve the above-described problem, an image display device according to one aspect of the present disclosure includes an image light generating device, a first optical unit having positive power, a second optical unit including a first diffraction element and having positive power, a third optical unit having positive power, and a fourth optical unit including a second diffraction element and having positive power, the first to fourth optical units being provided along an optical path of image light emitted from the image light generating device. On the optical path, a first intermediate image of the image light is formed between the first optical unit and the third optical unit, a pupil is formed between the second optical unit and the fourth optical unit, a second intermediate image of the image light is formed between the third optical unit and the fourth optical unit, and an exit pupil is formed at an opposite side of the fourth optical unit from the third optical unit. The image light generating device includes a first light emitting panel configured to emit first image light in a red wavelength region, a second light emitting panel configured to emit second image light in a green wavelength region, a third light emitting panel configured to emit third image light in a blue wavelength region, and a color synthesis element configured to synthesize the first image light, the second image light, and the third image light. The color synthesis element is constituted of a cross dichroic prism including a first dichroic film and a second dichroic film that intersect with each other, and each of the first dichroic film and the second dichroic film does not have a polarization separation characteristic.

In the image display device according to one aspect of the present disclosure, each of the first light emitting panel, the second light emitting panel, and the third light emitting panel may face a light incident surface of the cross dichroic prism, and may be disposed such that a longitudinal direction of an image generation region is parallel to a cross axis of the first dichroic film and the second dichroic film.

In the image display device according to one aspect of the present disclosure, each of the first light emitting panel, the second self-light-emitting panel, and the third light emitting panel may include a pixel including an organic EL element.

In the image display device according to one aspect of the present disclosure, the organic EL element may include an optical resonator.

In the image display device according to one aspect of the present disclosure, each of the first light emitting panel, the second light emitting panel, and the third light emitting panel may include a pixel including an inorganic light-emitting diode element.

In the image display device according to one aspect of the present disclosure, the first diffraction element and the second diffraction element each may be constituted of a reflection-type volume hologram.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

In each of the figures below, to illustrate each of layers or each of members at a recognizable size, a scale of each of the layers or each of the members is different from an actual scale and an actual angle.

FIG. 1is an external view illustrating one aspect of an image display device100according to the present exemplary embodiment.FIG. 2is an external view illustrating another aspect of the image display device100.FIG. 3is a schematic diagram illustrating one aspect of an optical system10of the image display device100illustrated inFIG. 1.

InFIGS. 1 to 3, a front-rear direction is a direction along a Z axis, a front direction being one of the front-rear direction is a front side Z1, and a back direction being the other front-rear direction is a rear side Z2. Further, a left-and-right direction is a direction along an X axis, a right direction being one of the left-and-right direction is a right side X1, and a left direction being the other left-and-right direction is a left side X2. Further, an up-and-down direction is a direction along a Y-axis direction, an upper direction being one of the up-and-down direction is an upper side Y1, and a lower direction being the other up-and-down direction is a lower side Y2.

As illustrated inFIG. 1, the image display device100is a head-mounted display device, and includes a right-eye optical system10athat causes image light L0ato be incident on a right eye Ea and a left-eye optical system10bthat causes image light L0bto be incident on a left eye Eb. For example, the image display device100is formed in a shape like glasses.

Specifically, the image display device100includes a frame90that holds the right-eye optical system10aand the left-eye optical system10b. The frame90is mounted on a head of an observer. The frame90has a front portion91that holds a second diffraction element70aof the right-eye optical system10aand a second diffraction element70bof the left-eye optical system10b. A temple92aon a right side of the frame90and a temple92bon a left side respectively hold an image light projecting device of the right-eye optical system10aand an image light projecting device of the left-eye optical system10b.

The right-eye optical system10aand the left-eye optical system10bhave the same basic configuration. Therefore, the right-eye optical system10aand the left-eye optical system10bwill be collectively described as the optical system10without distinction in the description below.

In the image display device100illustrated inFIG. 1, the image light L0travels in the left-and-right direction along the X axis. However, as illustrated inFIG. 2, a configuration in which the image light L0travels from the upper side Y1to the lower side Y2and is emitted to an eye E of an observer, a configuration in which the optical system10is disposed from a head top portion to the front of the eye E, and the like may be applied.

A basic configuration of the optical system10of the image display device100will be described with reference toFIG. 3.

FIG. 3is a schematic diagram illustrating one aspect of the optical system10of the image display device100illustrated inFIG. 1. Note thatFIG. 3illustrates, in addition to light L1(solid line) having a specific wavelength of the image light L0, light L2(dot-and-dash line) on a long wavelength side with respect to the specific wavelength, and light L3(dashed line) on a short wavelength side with respect to the specific wavelength.

As illustrated inFIG. 3, in the optical system10, a first optical unit L10having positive power, a second optical unit L20having positive power, a third optical unit L30having positive power, and a fourth optical unit L40having positive power are disposed along a traveling direction of the image light L0emitted from an image light generating device31.

In the present exemplary embodiment, the first optical unit L10having positive power is constituted of a projection optical system32. The second optical unit L20having positive power is constituted of a first diffraction element50of a reflection type. The third optical unit L30having positive power is constituted of a light-guiding optical system60. The fourth optical unit L40having positive power is constituted of a second diffraction element70of a reflection type. In the present exemplary embodiment, the first diffraction element50and the second diffraction element70are constituted of reflection-type volume holograms85and86that are described later.

In the optical system10, with a focus on the traveling direction of the image light L0, the image light generating device31emits the image light L0toward the projection optical system32, the projection optical system32emits the incident image light L0toward the first diffraction element50, and the first diffraction element50emits the incident image light L0toward the light-guiding optical system60. The light-guiding optical system60emits the incident image light L0toward the second diffraction element70, and the second diffraction element70emits the incident image light L0toward the eye E of the observer.

The image light generating device31generates the image light L0. A detailed configuration of the image light generating device31will be described later.

The projection optical system32projects the image light L0generated by the image light generating device31. The projection optical system32includes a plurality of lenses321. InFIG. 3, an example is given of a case in which the projection optical system32includes three lenses321. However, the number of lenses321is not limited, and the projection optical system32may include four or more lenses321. Further, the projection optical system32may be constituted in a form in which the plurality of lenses321are bonded together. Further, the lens321may be constituted of a free-form lens.

The light-guiding optical system60includes a lens system61on which the image light L0emitted from the first diffraction element50is incident and a mirror62that emits the image light L0emitted from the lens system61in a direction inclined diagonally. The lens system61is constituted of a plurality of lenses611arranged in the front-rear direction along the Z axis. The mirror62includes a reflective surface620inclined diagonally to the front-rear direction. In the present exemplary embodiment, the mirror62is constituted of a total reflection mirror. However, the mirror62may be a half mirror, and in this case, a range in which the external light is visually recognizable can be widened.

A detailed configuration of the first diffraction element50and the second diffraction element70will be described below.

In the present exemplary embodiment, the first diffraction element50and the second diffraction element70have the same basic configuration. Hereinafter, a configuration of the second diffraction element70will be described as an example.

FIG. 4Ais a schematic diagram of interference fringes751of the second diffraction element70illustrated inFIG. 3.

As illustrated inFIG. 4A, the second diffraction element70includes the reflection-type volume hologram85. The reflection-type volume hologram85is a partially reflection diffraction optical element. Thus, the second diffraction element70constitutes a partial transmissive reflective combiner. Therefore, external light is also incident on the eye E via the second diffraction element70, and thus the observer can recognize an image in which the image light L0formed by the image light generating device31and the external light (background) are superimposed on each other.

The second diffraction element70faces the eye E of the observer. The incident surface71of the second diffraction element70on which the image light L0is incident has a concave surface being recessed in a direction away from the eye E. In other words, the incident surface71has a shape having a central portion recessed and curved with respect to a peripheral portion in the incident direction of the image light L0. Thus, the image light L0can be efficiently condensed toward the eye E of the observer.

The second diffraction element70includes interference fringes751R,751G, and751B having a pitch corresponding to a specific wavelength. The interference fringes751R,751G, and751B are recorded as a difference in refractive index and the like in a hologram photosensitive layer. The interference fringes751R,751G, and751B are inclined in one direction with respect to the incident surface71of the second diffraction element70so as to correspond to a specific incident angle. Therefore, the second diffraction element70diffracts and then deflects the image light L0in a predetermined direction. The specific wavelength and the specific incident angle respectively correspond to a wavelength and an incident angle of the image light L0. The interference fringes751R,751G, and751B can be formed by performing interference exposure on the holographic photosensitive layer by using reference light Lr and object light Ls.

In the present exemplary embodiment, the image light L0is image light for color display. Thus, the second diffraction element70includes the interference fringes751R,751G, and751B having a pitch corresponding to the specific wavelength. For example, the interference fringes751R are formed at a pitch corresponding to red light LR having a wavelength of 615 nm, for example, in a wavelength range from 580 nm to 700 nm. The interference fringes751G are formed at a pitch corresponding to green light LG having a wavelength of 535 nm, for example, in a wavelength range from 500 nm to 580 nm. The interference fringes751B are formed at a pitch corresponding to blue light LB having a wavelength of 460 nm, for example, in a wavelength range from 400 nm to 500 nm. The interference fringes751R,751G, and751B of this kind are formed by forming a holographic photosensitive layer having sensitivity corresponding to the respective wavelengths, and performing interference exposure on the holographic photosensitive layer by using reference light LrR, LrG, and LrB and object light LsR, LsG, and LsB having the respective wavelengths.

Note that a photosensitive material having sensitivity corresponding to the respective wavelengths may be dispersed in the holographic photosensitive layer, and then interference exposure may be performed on the holographic photosensitive layer by using the reference light LrR, LrG, and LrB and the object light LsR, LsG, and LsB having the respective wavelengths. In this way, as illustrated inFIG. 4B, the interference fringes751in which the interference fringes751R,751G, and751B are superimposed on one layer may be formed. Further, light having a spherical wave may be used as the reference light LrR, LrG, and LrB and the object light LsR, LsG, and LsB.

The first diffraction element50having the same basic configuration as the second diffraction element70includes the reflection-type volume hologram86. An incident surface51of the first diffraction element50on which the image light L0is incident has a concave surface being recessed. In other words, the incident surface51has a shape having a central portion recessed and curved with respect to a peripheral portion in the incident direction of the image light L0. Thus, the image light L0can be efficiently deflected toward the light-guiding optical system60.

FIG. 5is a schematic diagram illustrating a diffraction characteristic of the first diffraction element50and the second diffraction element70illustrated inFIG. 3.FIG. 5illustrates a difference in diffraction angle between a specific wavelength and a peripheral wavelength when a light beam is incident on one point on the volume hologram. InFIG. 5, when assuming that a specific wavelength is 531 nm, a deviation in diffraction angle of light having a peripheral wavelength of 526 nm is indicated by a solid line L526, and a deviation in diffraction angle of light having a peripheral wavelength of 536 nm is indicated by a dashed line L536.

As illustrated inFIG. 5, even when a light beam is incident on the same interference fringes recorded in the hologram, the light beam having a longer wavelength is more diffracted, and the light beam having a shorter wavelength is less diffracted. Thus, when two diffraction elements, namely, the first diffraction element50and the second diffraction element70are used as in the present exemplary embodiment, wavelength compensation cannot be appropriately performed unless light having a long wavelength and light having a short wavelength are each incident in consideration of light beam angles of the light having a long wavelength and the light having a short wavelength with respect to a specific wavelength. In other words, a color aberration generated by the second diffraction element70cannot be canceled unless the light is incident in consideration of the light beam angle for each wavelength. Further, diffraction angles vary depending on the number of interference fringes, and thus the interference fringes need to be considered.

In the optical system10illustrated inFIG. 3, an incident direction and the like to the second diffraction element70are made appropriate according to whether a sum of the number of times of formation of an intermediate image between the first diffraction element50and the second diffraction element70and the number of times of reflections by the mirror62is odd or even. Thus, wavelength compensation, namely, a color aberration can be canceled.

Specifically, as illustrated inFIG. 3, the image light L0incident on the first diffraction element50is diffracted and deflected by the first diffraction element50. At this time, the light L2on the long wavelength side with respect to the specific wavelength has a diffraction angle θ2greater than a diffraction angle θ1of the light L1having the specific wavelength. Further, the light L3on the short wavelength side with respect to the specific wavelength has a diffraction angle θ3smaller than the diffraction angle θ1of the light L1having the specific wavelength. Therefore, the image light L0emitted from the first diffraction element50is deflected and dispersed at each wavelength.

The image light L0emitted from the first diffraction element50is incident on the second diffraction element70via the light-guiding optical system60and is diffracted and then deflected by the second diffraction element70. At this time, on the optical path from the first diffraction element50to the second diffraction element70, an intermediate image is formed once, and reflection by the mirror62is performed once.

Therefore, when assuming that an angle between the image light L0and a normal line of the incident surface of the second diffraction element70is an incident angle, the light L2on the long wavelength side with respect to the specific wavelength has an incident angle θ12greater than an incident angle θ11of the light L1having the specific wavelength while the light L3on the short wavelength side with respect to the specific wavelength has an incident angle θ13smaller than the incident angle θ11of the light L1having the specific wavelength. Further, as described above, the light L2on the long wavelength side with respect to the specific wavelength has the diffraction angle θ2greater than the diffraction angle θ1of the light L1having the specific wavelength. The light L3on the short wavelength side with respect to the specific wavelength has the diffraction angle θ3smaller than the diffraction angle θ1of the light L1having the specific wavelength.

Therefore, the light L2on the long wavelength side with respect to the specific wavelength is incident on the first diffraction element50at the incident angle greater than the incident angle of the light L1having the specific wavelength. However, the light L2on the long wavelength side with respect to the specific wavelength has the diffraction angle greater than the diffraction angle of the light L1having the specific wavelength, and thus, as a result, the light L2on the long wavelength side with respect to the specific wavelength and the light L1having the specific wavelength are substantially parallel light when being emitted from the second diffraction element70. In contrast, the light L3on the short wavelength side with respect to the specific wavelength is incident on the first diffraction element50at the incident angle smaller than the incident angle of the light L1having the specific wavelength. However, the light L3on the short wavelength side with respect to the specific wavelength has the diffraction angle smaller than the diffraction angle of the light L1having the specific wavelength, and thus, as a result, the light L3on the short wavelength side with respect to the specific wavelength and the light L1having the specific wavelength are substantially parallel light when being emitted from the second diffraction element70. In this way, as illustrated inFIG. 3, since the image light L0emitted from the second diffraction element70is incident as the substantially parallel light on the eye E of the observer, misalignment of image formation in a retina E0at each wavelength can be suppressed. Therefore, a color aberration generated by the second diffraction element70can be canceled.

A conjugated relationship between the first diffraction element50and the second diffraction element70will be described below.

FIG. 6Ais a schematic diagram of a case in which the first diffraction element50and the second diffraction element70are in the conjugated relationship.FIGS. 6B and 6Care schematic diagrams of a case in which the first diffraction element50and the second diffraction element70are not in the conjugated relationship.FIGS. 7A and 7Bare schematic diagrams illustrating a tolerances for a deviation from the conjugated relationship between the first diffraction element50and the second diffraction element70illustrated inFIGS. 6B and 6C.

InFIGS. 7A and 7B, light having a specific wavelength is indicated by a solid line Le, light having a specific wavelength of −10 nm is indicated by a dot-and-dash line Lf, and light having a specific wavelength of +10 nm is indicated by a two-dot chain line Lg. Note that, inFIGS. 6A to 6CandFIGS. 7A and 7B, the first diffraction element50and the second diffraction element70are illustrated in a perspective view, and the first diffraction element50, the second diffraction element70, and an optical unit L60are indicated by arrows.

As illustrated inFIG. 6A, when the first diffraction element50and the second diffraction element70are in the conjugated relationship, divergent light emitted from a point A (a first position) of the first diffraction element50is converged by the optical unit L90(lens) having positive power, and is incident on a point B (a second position corresponding to the first position) of the second diffraction element70. Thus, a color aberration due to diffraction occurring at the point B can be compensated at the point A.

On the other hand, as illustrated inFIGS. 6B and 6C, when the first diffraction element50and the second diffraction element70are not in the conjugated relationship, divergent light beams emitted from the point A of the first diffraction element50are converged by the optical unit L90(lens) having positive power at the center. However, the divergent light beams emitted from the point A cross each other in a position farther or closer with respect to the point B on the second diffraction element70and are incident. Thus, the point A and the point B do not have a one-to-one relationship. Here, since a compensation effect increases when interference fringes are uniform within a region, the compensation effect decreases when the first diffraction element50and the second diffraction element70are not in the conjugated relationship. On the other hand, it is difficult to compensate for the entire projection region of the second diffraction element70by the first diffraction element50. Thus, in a case of the aspects illustrated inFIGS. 6B and 6C, sufficient wavelength compensation cannot be performed, and resolution degradation occurs.

Note that there is an error of about ±0.4 mm from the point B that the light having the specific wavelength reaches in the light having the wavelength of ±10 nm with respect to the specific wavelength, but a decrease in resolution is not noticeable. As a result of considering an allowable range, as illustrated inFIG. 7A, when the light beams having the specific wavelength cross each before the point B on the second diffraction element70where the light beams having the specific wavelength ideally reach, and are incident within a range of ±0.8 mm, a decrease in resolution is not noticeable. Further, as illustrated inFIG. 7B, when the light beams having the specific wavelength cross each other in the rear of the point B on the second diffraction element70where the light beams having the specific wavelength ideally reach, and are incident within a range of ±0.8 mm, a decrease in resolution is not noticeable. Therefore, even when the first diffraction element50and the second diffraction element70are not completely in the conjugated relationship, a decrease in resolution is allowable when the first diffraction element50and the second diffraction element70are substantially in the conjugated relationship, and the light reaches within the range of ±0.8 mm from the ideal point B. In other words, in the present exemplary embodiment, “the first diffraction element50and the second diffraction element70have a conjugated relationship” means that an incident position of the light having the specific wavelength falls within an error range of ±0.8 mm from an ideal incident point.

FIG. 8is a light beam diagram of the optical system10in the present exemplary embodiment.

InFIG. 8, each optical unit disposed along an optical axis is indicated by a thick arrow. Further, a light beam emitted from one pixel of the image light generating device31is indicated by a solid line La, a main light beam emitted from an end portion of the image light generating device31is indicated by a dot-and-dash line Lb, and a position in which the light beam is in a conjugated relationship with the first diffraction element50is indicated by a long dashed line Lc. Here, an “intermediate image” is a place where the light beams (solid lines La) emitted from one pixel converge, and a “pupil” is a place where the main light beams (dot-and-dash line Lb) at each angle of view converge.FIG. 8also illustrates a path of the light emitted from the image light generating device31. Note that, inFIG. 8, all optical units are illustrated in a perspective view in order to simplify the drawing.

As illustrated inFIG. 8, in the optical system10in the present exemplary embodiment, the first optical unit L10having positive power, the second optical unit L20that includes the first diffraction element50and has positive power, the third optical unit L30having positive power, and the fourth optical unit L40that includes the second diffraction element70and has positive power are provided along an optical path of the image light emitted from the image light generating device31.

A focal length of the first optical unit L10is L/2. Focal lengths of the second optical unit L20, the third optical unit L30, and the fourth optical unit L40are all L. Therefore, an optical distance from the second optical unit L20to the third optical unit L30and an optical distance from the third optical unit L30to the fourth optical unit L40are equal.

In the optical system10, a first intermediate image P1of the image light is formed between the first optical unit L10and the third optical unit L30. A pupil R1is formed between the second optical unit L20and the fourth optical unit L40. A second intermediate image P2of the image light is formed between the third optical unit L30and the fourth optical unit L40. The fourth optical unit L40collimates the image light and forms an exit pupil R2. At this time, the third optical unit L30causes the image light emitted from the second optical unit L20to be incident as divergent light on the fourth optical unit L40. The second optical unit L20causes the image light emitted from the first optical unit L10to be incident as convergent light on the third optical unit L30. In the optical system10in the present exemplary embodiment, the pupil R1is formed in the vicinity of the third optical unit L30between the second optical unit L20and the fourth optical unit L40. The vicinity of the third optical unit L30refers to a position, between the second optical unit L20and the third optical unit L30, closer to the third optical unit L30than the second optical unit L20, or a position, between the third optical unit L30and the fourth optical unit L40, closer to the third optical unit L30than the fourth optical unit L40.

The third optical unit L30causes, of the image light from one point of the image light generating device31, light having a peripheral wavelength deviated from the specific wavelength deflected by the first diffraction element50to be incident on a predetermined range of the second diffraction element70. In other words, the first diffraction element50and the second diffraction element70are in a conjugated relationship or a substantially conjugated relationship. Here, an absolute value of magnification of the projection on the second diffraction element70by the third optical unit L30of the first diffraction element50ranges from 0.5 times to 10 times. The absolute value of the magnification may range from 1 time to 5 times.

Therefore, according to the optical system10in the present exemplary embodiment, the first intermediate image P1of the image light is formed between the projection optical system32and the light-guiding optical system60, the pupil R1is formed in the vicinity of the light-guiding optical system60, the second intermediate image P2of the image light is formed between the light-guiding optical system60and the second diffraction element70, and the second diffraction element70collimates the image light and forms the exit pupil R2.

In the optical system10in the present exemplary embodiment, the first intermediate image P1is formed between the first optical unit L10(projection optical system32) and the second optical unit L20(first diffraction element50).

The optical system10in the present exemplary embodiment satisfies four conditions (Condition 1, Condition 2, Condition 3, and Condition 4) described below.

Condition 1: A light beam emitted from one point of the image light generating device31forms an image as one point in the retina E0.

Condition 2: An incident pupil of the optical system and a pupil of an eye are conjugated.

Condition 3: The first diffraction element50and the second diffraction element70are appropriately disposed so as to compensate for a peripheral wavelength.

Condition 4: The first diffraction element50and the second diffraction element70are in a conjugated relationship or a substantially conjugated relationship.

More specifically, as clearly seen from the dot-and-dash line Lb illustrated inFIG. 8, a light beam emitted from one point of the image light generating device31satisfies [Condition 1] that an image is formed as one point in the retina E0. Thus, an observer can visually recognize one pixel. Further, as clearly seen from the solid line La illustrated inFIG. 8, [Condition 2] that the relationship between the incident pupil of the optical system10and the pupil E1of the eye E is conjugated (conjugation of the pupil) is satisfied. Thus, the entire image generated by the image light generating device31can be visually recognized. Further, [Condition 3] that the first diffraction element50and the second diffraction element70are appropriately disposed so as to compensate for a peripheral wavelength is satisfied. Thus, a color aberration generated by the second diffraction element70can be canceled by performing wavelength compensation. Further, as clearly seen from the long dashed line Lc illustrated inFIG. 8, [Condition 4] that the first diffraction element50and the second diffraction element70are in a conjugated relationship or a substantially conjugated relationship is satisfied. Thus, a light beam can be incident on a place having the same interference fringes in the first diffraction element50and the second diffraction element70, and wavelength compensation can be appropriately performed. As described above, degradation of resolution of an image can be suppressed.

Hereinafter, the image light generating device31will be described.

The image light generating device31in the present exemplary embodiment emits image light acquired by synthesizing a plurality of color light beams from a plurality of image display panels configured to emit image light that does not have a polarization characteristic.

FIG. 9is a perspective view of the image light generating device31.

As illustrated inFIG. 9, the image light generating device31includes a first panel212R (first light emitting panel), a second panel212G (second light emitting panel), a third panel212B (third light emitting panel), and a cross dichroic prism213(color synthesis element). Each of the first panel, the second panel, and the third panel is a light emitting panel that does not include a lighting device such as a backlight. Therefore, light that does not have a polarization characteristic is emitted from each of the first panel, the second panel, and the third panel.

The first panel212R includes an image generation region212fin which a plurality of pixels are provided in a matrix, and a non-image generation region. An organic EL element is provided in each of the plurality of pixels. The second panel212G includes an image generation region212fin which a plurality of pixels are provided in a matrix, and a non-image generation region. An organic EL element is provided in each of the plurality of pixels. The third panel212B includes an image generation region212fin which a plurality of pixels are provided in a matrix, and a non-image generation region. A top-emitting organic EL element is provided in each of the plurality of pixels.

In the present exemplary embodiment, the plurality of organic EL elements provided in the image generation region212fof the first panel212R emit first image light in a red wavelength region. Further, the plurality of organic EL elements provided in the image generation region212fof the second panel212G emit second image light in a green wavelength region. Further, the plurality of organic EL elements provided in the image generation region212fof the third panel212B emit third image light in a blue wavelength region.

Hereinafter, a configuration of the first panel212R, the second panel212G, and the third panel212B will be described. The first panel212R, the second panel212G, and the third panel212B differ from each other in material of a light emitting layer and a transport layer formed of an organic EL material, but have the same basic configuration of the panel. Therefore, a configuration of the panel will be described below with reference to the first panel212R.

FIG. 10is a cross-sectional view illustrating a configuration of one organic EL element35of the first panel212R. As illustrated inFIG. 10, in the organic EL element35, a reflective electrode72, an anode73, a light-emitting functional layer74, and a cathode75are provided on one surface of a substrate79in order from the substrate79side. The substrate79is formed of a semiconductor material such as silicon, for example. The reflective electrode72is formed of a light-reflective conductive material containing, for example, aluminum, silver, or the like. More specifically, the reflective electrode72may be formed of a single material such as aluminum, silver, or the like, or may be formed of a layered film of titanium (Ti)/AlCu (aluminum copper alloy), or the like.

The anode73is formed of a conductive material having optical transparency, such as indium tin oxide (ITO), for example. Although not illustrated, the light-emitting functional layer74is formed of a plurality of layers including a light-emitting layer including an organic EL material, a hole injecting layer, an electron injecting layer, and the like. The light-emitting layer is formed of a known organic EL material corresponding to each light emission color of red, green, and blue.

The cathode75functions as a semi-transmissive reflective layer having properties (semi-transmissive reflective properties) that transmit some light and reflect the remaining light. For example, by forming a photoreflective conductive material, such as an alloy containing silver or magnesium, into a sufficiently thin film, the cathode75having the semi-transmissive reflective properties can be achieved. The emitted light from the light-emitting functional layer74has a component of a specific resonance wavelength being selectively amplified during reciprocation between the reflective electrode72and the cathode75, is transmitted through the cathode75, and is emitted to an observation side (opposite to the substrate79). In other words, a plurality of layers from the reflective electrode72to the cathode75constitute an optical resonator80.

The plurality of layers from the reflective electrode72to the cathode75are covered by a sealing film76. The sealing film76is a film for preventing entry of air and moisture, and is constituted of a single layer or a plurality of layers of an inorganic material or an organic material having optical transparency. A color filter77is provided on one surface of the sealing film76. In the third panel212B, the color filter77is constituted of a light-absorbing filter layer that absorbs light in a wavelength range other than the blue wavelength range and transmits light in the blue wavelength range. Similarly, in the first panel212R, a color filter is constituted of a light-absorbing filter layer that absorbs light in a wavelength range other than the red wavelength range and transmits light in the red wavelength range. In the second panel212G, a color filter is constituted of a light-absorbing filter layer that absorbs light in a wavelength range other than the green wavelength range and transmits light in the green wavelength range.

In the present exemplary embodiment, each of the first panel212R, the second panel212G, and the third panel212B includes the optical resonator80, and thus light corresponding to each color is emitted by resonance of light at a resonance wavelength. Furthermore, the color filter77is provided on a light emission side of the optical resonator80, and thus color purity of the light emitted from each of the panels212R,212G, and212B is further enhanced.

A cover glass78for protecting each of the panels212R,212G, and212B is provided on one surface of the color filter77.

As illustrated inFIG. 9, the first panel212R emits the first image light LR in the red wavelength region. Therefore, the image light emitted from the first panel212R is incident on the cross dichroic prism213as the first image light LR in red. The second panel212G emits the second image light LG in the green wavelength region. Therefore, the image light emitted from the second panel212G is incident on the cross dichroic prism213as the second image light LG in green. The third panel212B emits the third image light LB in the blue wavelength region. Therefore, the image light emitted from the third panel212B is incident on the cross dichroic prism213as the third image light LB in blue.

A peak wavelength in the red wavelength region is, for example, greater than or equal to 630 nm and less than or equal to 680 nm. A peak wavelength in the green wavelength region is, for example, greater than equal to 495 nm and less than or equal to 570 nm. A peak wavelength in the blue wavelength region is, for example, greater than or equal to 450 nm and less than or equal to 490 nm. Each of the first image light LR, the second image light LG, and the third image light LB is light that does not have a polarization characteristic. In other words, each of the first image light LR, the second image light LG, and the third image light LB is unpolarized light that does not have a specific vibration direction. Note that unpolarized light, namely, light that does not have a polarization characteristic is light that is not in a completely unpolarized state and includes a polarization component to some extent. For example, the light has a degree of polarization to the extent that does not actively affect an optical member such as a dichroic film, for example, in terms of optical performance, for example, a degree of polarization of less than or equal to 20%.

The cross dichroic prism213is constituted of a transparent member having a quadrangular columnar shape. The cross dichroic prism213includes a first incident surface213a, a third incident surface213cfacing the first incident surface213a, a second incident surface213bcontacting perpendicularly to the first incident surface213aand the third incident surface213c, an emission surface213dfacing the second incident surface213b, a fifth surface213econtacting perpendicularly to the first incident surface213a, the second incident surface213b, the third incident surface213c, and the emission surface213d, and a sixth surface213ffacing the fifth surface213e.

The cross dichroic prism213includes a first dichroic film DM1that does not have a polarization separation characteristic, and a second dichroic film DM2that does not have a polarization separation characteristic. The first dichroic film DM1and the second dichroic film DM2cross each other at an angle of 90°. Hereinafter, an axis in which the first dichroic film DM1and the second dichroic film DM2cross each other is referred to as a cross axis CR.

The “dichroic film that does not have a polarization separation characteristic” in the specification is a film having a substantially similar wavelength separation characteristic regardless of a polarization direction (S-polarized light, P-polarized light) of light incident on the dichroic film. A specific example is indicated below to define the “dichroic film that does not have a polarization separation characteristic”.

FIG. 11is a diagram illustrating one example of a transmittance-wavelength characteristic of a dichroic film that does not have a polarization separation characteristic.

InFIG. 11, the horizontal axis is a wavelength [nm], and the vertical axis is a transmittance [%]. A solid line graph indicated by a reference numeral Ts indicates a transmittance-wavelength characteristic of S-polarized light, and a dashed line graph indicated by a reference numeral Tp indicates a transmittance-wavelength characteristic of P-polarized light.

The “dichroic film that does not have a polarization separation characteristic” refers to a film having, when unpolarized light is incident on the dichroic film, a similar trend in the transmittance Ts of the S-polarized light and the transmittance Tp of the P-polarized light in a wavelength region to be controlled, such as a wavelength region A inFIG. 11: for example, a blue wavelength region of greater than or equal to 450 nm and less than or equal to 490 nm, a wavelength region B: for example, a green wavelength region of greater than or equal to 495 nm and less than or equal to 570 nm, and a wavelength region C: for example, a red wavelength region of greater than or equal to 630 nm and less than or equal to 680 nm. It also refers to the film having a characteristic such that an average difference between the transmittance Ts and the transmittance Tp in each of the wavelength regions is less than or equal to 30% and may be less than or equal to 10%.

Note that a transmittance is used for expression inFIG. 11, but the same is true when a reflectance is used for expression. The “dichroic film that does not have a polarization separation characteristic” refers to a film having, when unpolarized light is incident on the dichroic film, a similar trend in a reflectance of S-polarized light and a reflectance of P-polarized light in a wavelength region to be controlled, and having a characteristic such that an average difference in reflectance in each wavelength region is less than or equal to 30% and may be less than or equal to 10%.

The first dichroic film DM1has a characteristic so as to reflect the first image light LR and transmit the second image light LG and the third image light LB. The second dichroic film DM2has a characteristic so as to reflect the second image light LG and transmit the first image light LR and the third image light LB. In this way, the first image light LR, the second image light LG, and the third image light LB are synthesized, and the image light L0in full color is emitted from the emission surface213d.

The first panel212R is disposed so as to face the first incident surface213a. The second panel212G is disposed so as to face the second incident surface213b. The third panel212B is disposed so as to face the third incident surface213c.

Each of the first panel212R, the second panel212G, and the third panel212B includes the rectangular image generation region212fhaving long sides and short sides. The image generation region212fis a region of the surface facing the cross dichroic prism213of each panel except for a non-image generation region of a peripheral portion and that substantially generates an image. Each of the first panel212R, the second panel212G, and the third panel212B faces the cross dichroic prism213, and is disposed such that a longitudinal direction FR of the image generation region212fis parallel to the cross axis CR of the cross dichroic prism213.

Each of the first panel212R, the second panel212G, and the third panel212B may include an external terminal regions for electrically coupling a drive circuit board (not illustrated) and a panel outside the long sides of the image generation region. In this case, the external terminal region does not contribute to generation of an image, and thus may not need to be disposed so as to face the cross dichroic prism213. Therefore, each of the first panel212R, the second panel212G, and the third panel212B may be bonded together such that the image generation region faces the cross dichroic prism213and the external terminal region protrudes to the outside of the cross dichroic prism213.

A direction in which the external terminal region of each panel protrudes to the outside of the cross dichroic prism213is not particularly limited as long as the direction is not a direction in which adjacent panels do not interfere with each other. For example, the first panel212R may protrude to the left side of the cross dichroic prism213inFIG. 9, the second panel212G may protrude to the upper side of the cross dichroic prism213inFIG. 9, and the third panel212B may protrude to the right side of the cross dichroic prism213inFIG. 9. Alternatively, the first panel212R and the third panel212B may both protrude to the right side of the cross dichroic prism213inFIG. 9, and the second panel212G may protrude to the lower side of the cross dichroic prism213inFIG. 9.

In the present exemplary embodiment, as described above, each of the first panel212R, the second panel212G, and the third panel212B is disposed such that the longitudinal direction FR of the image generation region is parallel to the cross axis CR of the cross dichroic prism213. Thus, a dimension A of one side of the cross dichroic prism213can be made smaller than that when the longitudinal direction FR of the image generation region212fis disposed perpendicular to the cross axis CR of the cross dichroic prism213.

According to the image display device100in the present exemplary embodiment, the first diffraction element50and the second diffraction element70formed of the reflection-type volume holograms85and86are used, and the first diffraction element50and the second diffraction element70are appropriately disposed. Thus, a color aberration can be corrected, and degradation of resolution of an image due to the color aberration can be suppressed.

However, according to consideration of the inventors, a wavelength width of a reflection wavelength region in a reflection-type hologram is extremely narrow, for example, 20 nm. Thus, in a known display device using two reflection-type holograms, a lot of image light emitted from the display is not reflected by the holograms and is transmitted through the holograms. As a result, it was found that there is a problem in that light-guiding efficiency from the display to an eye of an observer decreases to, for example, less than or equal to 10%.

For this problem, in the image display device100in the present exemplary embodiment, the above-described problem is solved by a combination of the following configurations.

In a case of the image display device100according to the present embodiment, the first panel212R, the second panel212G, and the third panel212B are constituted of a light emitting panel in which each pixel includes the organic EL element35. Therefore, light that does not have a polarization characteristic is emitted from each of the first panel212R, the second panel212G, and the third panel212B. Further, the image light emitted from the first panel212R, the second panel212G, and the third panel212B including the organic EL elements has high contrast and is bright.

A general cross dichroic prism has two dichroic films having a polarization characteristic. It is assumed that a display device including this cross dichroic prism is a display device in a comparative example. In the display device in the comparative example, in a case in which image light is unpolarized light, that is, light that does not have a polarization characteristic, only one linear polarized light beam among two linear polarized light beams that are included in the image light and are orthogonal to each other contributes to formation of an image, and the other linear polarized light beam does not contribute to the formation of the image. Thus, in the display device in the comparative example, the light utilization efficiency is low and a bright image is not acquired.

In contrast, in the image display device100in the present exemplary embodiment, the cross dichroic prism213includes the first dichroic film DM1and the second dichroic film DM2that do not have a polarization separation characteristic. In this way, even though the image light L0is light that does not have a polarization characteristic, both linear polarized light beams can contribute to formation of an image. Thus, according to the image display device100in the present exemplary embodiment, the light utilization efficiency is higher and a brighter image is acquired as compared to the display device in the comparative example.

Further, in the image display device100in the present exemplary embodiment, a bright image is acquired, and thus there is no need to unnecessarily increase a current supplied to the first panel212R, the second panel212G, and the third panel212B. Thus, a life of the organic EL element can be maintained, and rapid degradation of the brightness can be suppressed.

Further, in the image display device100in the present exemplary embodiment, the image light L0is guided in air between the first diffraction element50and the second diffraction element70, and a member such as a light-guiding plate is not used. Thus, the weight of a front portion of the image display device100can be reduced, and a load applied to a nose can be reduced. In this way, the image display device100is less likely to slip off, and the comfort of the image display device100can be improved.

Further, in the image light generating device31, as described above, each of the first panel212R, the second panel212G, and the third panel212B is disposed such that the longitudinal direction FR of the image generation region is parallel to the cross axis CR of the cross dichroic prism213. Thus, a dimension A of one side of a surface of the cross dichroic prism213perpendicular to the cross axis CR can be reduced. As a result, size reduction of the image display device100can be achieved.

Note that the technical scope of the present disclosure is not limited to the above-described exemplary embodiment, and various modifications can be made to the above-described exemplary embodiment without departing from the spirit and gist of the present disclosure.

For example, in the exemplary embodiments described above, each of the first panel212R, the second panel212G, and the third panel212B is constituted of an organic EL panel including a pixel having an organic EL element, but may also be constituted of an inorganic light-emitting diode (LED) panel including a pixel having an inorganic LED element.

Further, in the exemplary embodiment described above, an example has been illustrated in which the first diffraction element and the second diffraction element are constituted of a reflection-type volume hologram, but the first diffraction element and the second diffraction element may be constituted of another hologram element, for example, a surface relief hologram, a blazed hologram, and the like. Even when these hologram elements are used, a thin diffraction element having high diffraction efficiency is acquired.

Further, the specific configuration of the image display device exemplified in the exemplary embodiment described above such as the number, arrangement, shape, and the like of each component may be appropriately changed.