DISPLAY DEVICE

According to one embodiment, a display device includes a display module configured to emit display light which is linearly polarized light, a first structure including a first retardation film facing the display module, a holographic optical element facing the first retardation film, and a second retardation film facing the holographic optical element, a second structure including a reflective polarizer facing the second retardation film, and a transparent substrate facing the reflective polarizer, and a variable mechanism by which an interval between the first structure and the second structure is made variable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2023-012911, filed Jan. 31, 2023, the entire contents of which are incorporated herein by reference.

FIELD

BACKGROUND

In recent years, technology of using a head-mounted display worn on the head of a user and providing, for example, virtual reality (VR) has been drawing attention. The head-mounted display is configured to display an image on a display provided in front of the eyes of the user. By this configuration, the user who wears the head-mounted display can experience a virtual reality space with realism.

DETAILED DESCRIPTION

In general, according to one embodiment, a display device comprises a display module configured to emit display light which is linearly polarized light, a first structure comprising a first retardation film facing the display module, a holographic optical element facing the first retardation film, and a second retardation film facing the holographic optical element, a second structure comprising a reflective polarizer facing the second retardation film, and a transparent substrate facing the reflective polarizer, and a variable mechanism by which an interval between the first structure and the second structure is made variable.

According to another embodiment, a display device comprises a display module configured to emit display light which is linearly polarized light, a first structure comprising a first retardation film facing the display module, a semi-transmissive layer facing the first retardation film, and a second retardation film facing the semi-transmissive layer, a second structure comprising a reflective polarizer facing the second retardation film, a third retardation film facing the reflective polarizer, and a liquid crystal element facing the third retardation film and having a lens effect, and a variable mechanism by which an interval between the first structure and the second structure is made variable.

In the drawings, in order to facilitate understanding, an X-axis, a Y-axis and a Z-axis orthogonal to each other are shown depending on the need. A direction parallel to the X-axis is referred to as a first direction X. A direction parallel to the Y-axis is referred to as a second direction Y. A direction parallel to the Z-axis is referred to as a third direction Z. The plane defined by the X-axis and the Y-axis is referred to as an X-Y plane. When the X-Y plane is viewed, the appearance is defined as a plan view.

Basic Configuration

FIG.1is a perspective view showing an example of the external appearance of a head-mounted display1.

The head-mounted display1comprises, for example, a display device DSPR for the right eye and a display device DSPL for the left eye. In a state where the user wears the head-mounted display1on the head, the display device DSPR is provided to be located in front of the right eye of the user, and the display device DSPL is provided to be located in front of the left eye of the user.

FIG.2is a diagram for explaining the outline of the configuration of the head-mounted display1shown inFIG.1.

The head-mounted display1comprises a housing HS which accommodates the display device DSPR and the display device DSPL, and a variable mechanism SL provided in each of the display device DSPR and the display device DSPL.

The display device DSPR is configured in substantially the same manner as the display device DSPL. Each of the display device DSPR and the display device DSPL comprises a display module DM and an optical system4. The display module DM is configured to emit display light which is linearly polarized light. The optical system4of the display device DSPR is configured to guide the display light from the display module DM to the right eye ER. The optical system4of the display device DSPL is configured to guide the display light from the display module DM to the left eye EL.

For example, the display module DM consists of a liquid crystal panel and an illumination device. However, the display module DM is not limited to this configuration. For example, the display module DM may be a display panel comprising a self-luminous light emitting element such as an organic electroluminescent (EL) element, a micro LED or a mini LED. When the display module DM is a display panel comprising a light emitting element, the illumination device is omitted.

The variable mechanism SL is secured to the housing HS. As described later, the variable mechanism SL is a mechanism by which the interval between the first and second structures4A and4B of the optical system4is made variable.

Now, some configuration examples of the display device DSP of the embodiment are explained.

First Configuration Example

FIG.3is a cross-sectional view showing the first configuration example of the display device DSP.

The display device DSP explained here can be applied to each of the display devices DSPR and DSPL described above.

The display panel2comprises a display area DA configured to emit display light DL which is linearly polarized light. The display area DA is configured to selectively modulate the illumination light emitted from the illumination device3. Part of the illumination light passes through the second polarizer PL2and is converted into display light DL which is linearly polarized light. The surface of the second polarizer PL2is referred to as a display surface DS.

The optical system4comprises a first structure4A and a second structure4B. The first structure4A is spaced apart from the second structure4B in the normal direction of the display surface DS. An aerial layer4C is interposed between the first structure4A and the second structure4B. The display panel2is provided between the illumination device3and the first structure4A. The first structure4A is provided between the display panel2and the second structure4B (or between the display panel2and the aerial layer4C).

The first structure4A comprises a first retardation film R1facing the display module DM, a holographic optical element20facing the first retardation film R1, and a second retardation film R2facing the holographic optical element20. The holographic optical element20is located between the first retardation film R1and the second retardation film R2. For example, the first retardation film R1, the holographic optical element20and the second retardation film R2are attached to each other.

The first retardation film R1and the second retardation film R2are quarter-wave plates and impart a quarter-wave retardation to the light which passes through the retardation films.

The holographic optical element20reflects and diffracts part of incident light and comprises a lens function for condensing light. The holographic optical element20comprises an interference pattern and diffracts incident light to a predetermined direction.

The second structure4B comprises a reflective polarizer PR facing the second retardation film R2, and a transparent substrate TS facing the reflective polarizer PR. For example, the reflective polarizer PR is attached to the transparent substrate TS. The aerial layer4C is interposed between the second retardation film R2and the reflective polarizer PR.

Of the incident light, the reflective polarizer PR transmits first linearly polarized light and reflects second linearly polarized light orthogonal to the first linearly polarized light. For example, the reflective polarizer PR is a multilayer thin film polarizer or a wire-grid polarizer.

The transparent substrate TS is a glass substrate or a resinous substrate.

The variable mechanism SL and a support body SP are secured to the housing HS.

The first structure4A is supported by the support body SP and is secured to the housing HS across an intervening constant gap. The display module DM is provided between the housing HS and the first structure4A. In this configuration, the display module DM and the first structure4A are held without moving in the normal direction of the display surface DS relative to the housing HS.

The second structure4B is supported by the variable mechanism SL. The variable mechanism SL is configured to move the second structure4B in the normal direction of the display surface DS. When the second structure4B moves, the variable mechanism SL slides the second structure4B in the normal direction of the display surface DS without rotating the second structure4B in a plane. By this configuration, the interval between the first structure4A and the second structure4B can be changed.

FIG.4is a diagram for explaining the optical effect of the display device DSP.

First, the display module DM emits display light DL which is the first linearly polarized light LP1from the display surface DS. The display light DL passes through the first retardation film R1and is converted into first circularly polarized light CP1.

Part of the first circularly polarized light CP1which passed through the first retardation film R1passes through the holographic optical element20. The other first circularly polarized light CP1is reflected on the holographic optical element20. The first circularly polarized light CP1which passed through the holographic optical element20passes through the second retardation film R2and is converted into second linearly polarized light LP2.

When the first circularly polarized light CP1is reflected on the holographic optical element20, the first circularly polarized light CP1is converted into second circularly polarized light CP2which rotates in the opposite direction of the first circularly polarized light CP1. The second circularly polarized light CP2reflected on the holographic optical element20passes through the first retardation film R1, is converted into the second linearly polarized light LP2, and is absorbed in the display module DM.

The second linearly polarized light LP2which passed through the second retardation film R2is reflected on the reflective polarizer PR. The second linearly polarized light LP2reflected on the reflective polarizer PR passes through the second retardation film R2and is converted into the first circularly polarized light CP1.

Part of the first circularly polarized light CP1which passed through the second retardation film R2is reflected and diffracted on the holographic optical element20. The other first circularly polarized light CP1passes through the holographic optical element20. When the first circularly polarized light CP1is reflected and diffracted on the holographic optical element20, the light is converted into the second circularly polarized light CP2. The second circularly polarized light CP2reflected on the holographic optical element20passes through the second retardation film R2and is converted into the first linearly polarized light LP1.

The first circularly polarized light CP1which passed through the holographic optical element20passes through the first retardation film R1and is converted into the first linearly polarized light LP1.

The first linearly polarized light LP1which passed through the second retardation film R2passes through the reflective polarizer PR and is condensed to the eye E of the user by the lens effect of the holographic optical element20.

In the display device DSP comprising the above configuration, the optical system4comprises an optical path in which light passes through the portion between the holographic optical element20and the reflective polarizer PR three times. Thus, in the optical system4, the optical distance between the holographic optical element20and the reflective polarizer PR is approximately three times the actual interval between the holographic optical element20and the reflective polarizer PR. By this configuration, when the display surface DS of the display module DM is regarded an object, the user can observe an enlarged virtual image of the object formed in the distance via the optical system4.

Incidentally, a user with poor eyesight cannot clearly see a virtual image in the distance. With respect to such a user, the position of a virtual image needs to be closer to the user. The position of a virtual image can be adjusted by adjusting the interval between the first structure4A and the second structure4B. For example, the position of a virtual image can be moved closer to the user by moving the optical position of the display surface DS corresponding to an object to a side moving away from the focal point of the optical system4.

Thus, according to the embodiment, the present invention can comprise a diopter scale adjustment function which adjusts the visibility of an image in accordance with the eyesight of the user. Further, as shown inFIG.2, the variable mechanism SL is provided for each of the display device DSPR for the right eye and the display device DSPL for the left eye. Thus, the position of the virtual image of each of the display devices DSPR and DSPL can be independently adjusted. By this configuration, the virtual images of the display devices DSPR and DSPL can be clearly displayed in accordance with the eyesight of the right and left eyes, respectively.

Moreover, when the variable mechanism SL moves the second structure4B, the second structure4B does not rotate in a plane. Thus, the transmission axis (or reflective axis) in the reflective polarizer PR does not rotate in a plane. The reduction in display quality caused by axial displacement can be prevented. Further, the reduction in the use efficiency of light can be prevented.

It should be noted that the first linearly polarized light LP1explained with reference toFIG.4maybe replaced by the second linearly polarized light LP2, or the first circularly polarized light CP1may be replaced by the second circularly polarized light CP2.

Here, an example of the adjustment of the position of a virtual image is explained.

FIG.5is a diagram showing the state before and after the move of the second structure4B.

The second structure4B shown here comprises the reflective polarizer PR and the transparent substrate TS.

The left side of the figure shows a state in which the second structure4B is provided at a first position P1(before the move). The right side of the figure shows a state in which the second structure4B is provided at a second position P2(after the move).

In the state where the second structure4B is provided at the first position P1, a first interval G1is defined between the second retardation film R2and the reflective polarizer PR.

In the state where the second structure4B is provided at the second position P2, a second interval G2is defined between the second retardation film R2and the reflective polarizer PR. The second interval G2is less than the first interval G1. This state is realized when the variable mechanism SL moves the second structure4B so as to be closer to the display module DM.

FIG.6is a diagram in which the optical system of the display device shown inFIG.5is developed at the position of the reflective polarizer PR.

The position having a focal distance f from the holographic optical element20to the front side (in other words, the side of the user's eye) is defined as a first focal point FP1. The position having a focal distance f from the holographic optical element20to the rear side is defined as a second focal point FP2.

When the second structure4B is located at the first position P1, the point at which the line passing through an end portion E11of the display surface DS shown by a solid line and the second focal point FP2intersects with the position of the holographic optical element20is defined as point P11, and the point at which the line passing through an end portion20E of the holographic optical element20and the first focal point FP1intersects with a perpendicular line passing through point P11is defined as point P12. At this time, virtual image V1is formed at the position of point P12as shown by a solid line.

When the second structure4B is located at the second position P2, the point at which the line passing through an end portion E21of the display surface DS shown by a broken line and the second focal point FP2intersects with the position of the holographic optical element20is defined as point P21, and the point at which the line passing through the end portion20E of the holographic optical element20and the first focal point FP1intersects with a perpendicular line passing through point P21is defined as point P22. At this time, virtual image V2is formed at the position of point P22as shown by a broken line.

In this manner, when the second structure4B moves to the second position P2, the display surface DS moves away from the second focal point FP2, and the position of virtual image V2moves closer to the side of the user's eye. Thus, an image which can be clearly viewed can be displayed for a nearsighted user.

Second Configuration Example

FIG.7is a cross-sectional view showing the second configuration example of the display device DSP.

The second configuration example shown inFIG.7is different from the first configuration example shown inFIG.3in respect that the first structure4A and the display module DM are supported by the variable mechanism SL, and the second structure4B is supported by the support body SP. These differences are mainly explained below.

The second structure4B is supported by the support body SP secured to the housing HS. Thus, the second structure4B is secured to the housing HS across an intervening constant gap.

The display module DM is provided between the housing HS and the first structure4A. Although the display module DM is secured to the first structure4A, the display module DM is not secured to the housing HS. These display module DM and first structure4A constitute an integral structure BD.

The structure BD (the block of the display module DM and the first structure4A) is supported by the variable mechanism SL secured to the housing HS. The variable mechanism SL is configured to move the structure BD in the normal direction of the display surface DS. When the structure BD moves, the variable mechanism SL slides the structure BD in the normal direction of the display surface DS without rotating the structure BD in a plane. By this configuration, the interval between the first structure4A and the second structure4B (or the interval between the holographic optical element20and the reflective polarizer PR) can be changed.

FIG.8is a diagram showing the state before and after the move of the structure BD.

The structure BD shown here comprises the display module DM, the first retardation film R1, the holographic optical element20and the second retardation film R2.

The left side of the figure shows a state in which the structure BD is provided at a first position P1(before the move). The right side of the figure shows a state in which the structure BD is provided at a second position P2(after the move).

In the state where the structure BD is provided at the first position P1, a first interval G1is defined between the second retardation film R2and the reflective polarizer PR.

In the state where the structure BD is provided at the second position P2, a second interval G2is defined between the second retardation film R2and the reflective polarizer PR. The second interval G2is less than the first interval G1. This state is realized when the variable mechanism SL moves the structure BD so as to be closer to the reflective polarizer PR.

When the optical system4is developed in the second configuration example described above, a diagram similar to that explained with reference toFIG.6is obtained. Specifically, when the structure BD including the first structure4A moves to the second position P2, the display surface DS moves away from the second focal point FP2, and the position of virtual image V2moves closer to the side of the user's eye. Thus, an image which can be clearly viewed can be displayed for a nearsighted user.

Third Configuration Example

FIG.9is a diagram showing the state before and after the move of the first structure4A.

The third configuration example is different from the second configuration example shown inFIG.7in respect that the display module DM is secured to the housing HS, and the variable mechanism SL is configured to move the first structure4A.

The first structure4A shown here comprises the first retardation film R1, the holographic optical element20and the second retardation film R2.

The left side of the figure shows a state in which the first structure4A is provided at a first position P1(before the move). The right side of the figure shows a state in which the first structure4A is provided at a second position P2(after the move).

In the state where the first structure4A is provided at the first position P1, a first interval G1is defined between the second retardation film R2and the reflective polarizer PR.

In the state where the first structure4A is provided at the second position P2, a second interval G2is defined between the second retardation film R2and the reflective polarizer PR. The second interval G2is less than the first interval G1. This state is realized when the variable mechanism SL moves the first structure4A so as to be closer to the reflective polarizer PR.

When the optical system4is developed in the third configuration example described above, a diagram similar to that explained with reference toFIG.6is obtained. Specifically, when the first structure4A moves to the second position P2, the display surface DS moves away from the second focal point FP2, and the position of virtual image V2moves closer to the side of the user's eye. Thus, an image which can be clearly viewed can be displayed for a nearsighted user.

Fourth Configuration Example

FIG.10is a cross-sectional view showing the fourth configuration example of the display device DSP.

The display device DSP explained here can be applied to each of the display devices DSPR and DSPL described above.

The display module DM comprises the display panel2and the illumination device3. As the configuration of the display panel2is the same as the first configuration example, explanation of the configuration is omitted by adding the same reference numbers.

The optical system4comprises the first structure4A and the second structure4B. The first structure4A is spaced apart from the second structure4B in the normal direction of the display surface DS. The aerial layer4C is interposed between the first structure4A and the second structure4B. The display panel2is provided between the illumination device3and the first structure4A. The first structure4A is provided between the display panel2and the second structure4B (or between the display panel2and the aerial layer4C).

The first structure4A comprises the first retardation film R1facing the display module DM, a semi-transmissive layer HM facing the first retardation film R1, and the second retardation film R2facing the semi-transmissive layer HM. The semi-transmissive layer HM is located between the first retardation film R1and the second retardation film R2. For example, the first retardation film R1, the semi-transmissive layer HM and the second retardation film R2are attached to each other.

The first retardation film R1and the second retardation film R2are quarter-wave plates and impart a quarter-wave retardation to the light which passes through the retardation films.

The semi-transmissive layer HM transmits part of incident light and reflects the other light. For example, the semi-transmissive layer HM is a thin film formed of a metal material such as aluminum or silver. The transmittance of the semi-transmissive layer HM is approximately 50%.

The second structure4B comprises the reflective polarizer PR facing the second retardation film R2, a third retardation film R3facing the reflective polarizer PR, and a liquid crystal element10facing the third retardation film. The third retardation film R3is located between the reflective polarizer PR and the liquid crystal element10. For example, the reflective polarizer PR, the third retardation film R3and the liquid crystal element10are attached to each other. The aerial layer4C is interposed between the second retardation film R2and the reflective polarizer PR.

Of the incident light, the reflective polarizer PR transmits the first linearly polarized light and reflects the second linearly polarized light orthogonal to the first linearly polarized light.

The third retardation film R3is a quarter-wave plate and imparts a quarter-wave retardation to the light which passes through the retardation film.

The crystal element10imparts a half-wave retardation to light having a specific wavelength and has a lens effect of condensing the first circularly polarized light. Here, as an example of an element having a lens effect of condensing circularly polarized light, the liquid crystal element10is shown. However, the element is not limited to an element using a liquid crystal as long as the element has a similar lens effect.

The variable mechanism SL and the support body SP are secured to the housing HS.

The first structure4A is supported by the support body SP and is secured to the housing HS across an intervening constant gap. The display module DM is provided between the housing HS and the first structure4A. In this configuration, the display module DM and the first structure4A are held without moving in the normal direction of the display surface DS relative to the housing HS.

The second structure4B is supported by the variable mechanism SL. The variable mechanism SL is configured to move the second structure4B in the normal direction of the display surface DS. When the second structure4B moves, the variable mechanism SL slides the second structure4B in the normal direction of the display surface DS without rotating the second structure4B in a plane. By this configuration, the interval between the first structure4A and the second structure4B can be changed.

FIG.11is a cross-sectional view showing an example of the liquid crystal element10shown inFIG.10.

The liquid crystal element10comprises a substrate11, an alignment film AL11, a liquid crystal layer (first liquid crystal layer) LC1, an alignment film AL12and a substrate12.

Each of the substrates11and12is a transparent substrate which transmits light, and is, for example, a glass substrate or a resinous substrate. The substrate11is attached to, for example, the third retardation film R3shown inFIG.10. However, the substrate11maybe replaced by the third retardation film R3.

The alignment film AL11is provided on the inner surface11A of the substrate11. In the example shown inFIG.11, the alignment film AL11is in contact with the substrate11. However, a thin film may be interposed between the alignment film AL11and the substrate11.

The alignment film AL12is provided on the inner surface12A of the substrate12. In the example shown inFIG.11, the alignment film AL12is in contact with the substrate12. However, a thin film may be interposed between the alignment film AL12and the substrate12. The alignment film AL12faces the alignment film AL11in a third direction Z.

The alignment films AL11and AL12are formed of, for example, polyimide, and are both horizontal alignment films having an alignment restriction force parallel to the X-Y plane.

The liquid crystal layer LC1is provided between the alignment films AL11and AL12, and is in contact with the alignment films AL11and AL12. The liquid crystal layer LC1has thickness d1in the third direction Z. The liquid crystal layer LC1comprises nematic liquid crystals in which the alignment direction parallel to the third direction Z is uniform.

In other words, the liquid crystal layer LC1comprises a plurality of liquid crystal structures LMS1. When this specification focuses on a liquid crystal structure LMS1, the liquid crystal structure LMS1comprises a liquid crystal molecule LM11located at an end of the liquid crystal structure LMS1, and a liquid crystal molecule LM12located at the other end. The liquid crystal molecule LM11is close to the alignment film AL11, and the liquid crystal molecule LM12is close to the alignment film AL12. The alignment direction of the liquid crystal molecule LM11is substantially coincident with the alignment direction of the liquid crystal molecule LM12. The alignment direction of another liquid crystal molecule LM1between the liquid crystal molecule LM11and the liquid crystal molecule LM12is also substantially coincident with the alignment direction of the liquid crystal molecule LM11. Here, the alignment direction of each liquid crystal molecule LM1corresponds to the direction of the long axis of the liquid crystal molecule in the X-Y plane.

In the liquid crystal layer LC1, a plurality of liquid crystal structures LMS1which are adjacent to each other in a first direction X have alignment directions different from each other. Similarly, a plurality of liquid crystal structures LMS1which are adjacent to each other in a second direction Y have alignment directions different from each other. The alignment directions of the liquid crystal molecules LM11arranged along the alignment film AL11and the alignment directions of the liquid crystal molecules LM12arranged along the alignment film AL12successively (or linearly) change.

This liquid crystal layer LC1is cured in a state where the alignment directions of the liquid crystal molecules LM1including the liquid crystal molecules LM11and the liquid crystal molecules LM12are fixed. In other words, an electric field does not control the alignment directions of the liquid crystal molecules LM1. Thus, the liquid crystal element10does not comprise an electrode for alignment control.

When the refractive anisotropy or double refraction property of the liquid crystal layer LC1(the difference between refractive index ne for extraordinary light and refractive index no for ordinary light in the liquid crystal layer LC1) is defined as Δn, the retardation Δn·d1of the liquid crystal layer LC1is set so as to be half a specific wavelength λ.

FIG.12is a plan view showing an example of the alignment pattern in the liquid crystal layer LC1shown inFIG.11.

FIG.12shows an example of a spacial phase in the X-Y plane of the liquid crystal layer LC1. Here, spacial phases are shown as the alignment directions of the liquid crystal molecules LM11close to the alignment film AL11among the liquid crystal molecules LM1included in each liquid crystal structure LMS1.

In each concentric circle shown by a dotted line in the figure, the spacial phase is uniform. In an annular area surrounded by two adjacent concentric circles, the alignment directions of the liquid crystal molecules LM11are uniform. However, between adjacent annular areas, the alignment directions of the liquid crystal molecules LM11are different from each other.

As seen in plan view, the liquid crystal layer LC1comprises a first annular area C1and a second annular area C2. The second annular area C2is located on the external side relative to the first annular area C1. The first annular area C1consists of first liquid crystal molecules LM111aligned in the same direction. The second annular area C2consists of second liquid crystal molecules LM112aligned in the same direction. The alignment direction of the first liquid crystal molecules LM111is different from that of the second liquid crystal molecules LM112.

Similarly, the alignment directions of the liquid crystal molecules LM11arranged in the radial direction from the area of the center of the concentric circles are different from each other and sequentially change. In other words, in the X-Y plane shown in the figure, the spacial phase of the liquid crystal layer LC1differs in the radial direction and sequentially changes.

When the first circularly polarized light enters the liquid crystal element10comprising the above configuration, the first circularly polarized light is condensed toward the center of the concentric circles, and further, the transmitted light of the liquid crystal element10is converted into the second circularly polarized light which rotates in the opposite direction of the first circularly polarized light.

FIG.13is a diagram for explaining the optical effect of the display device DSP.

First, the display module DM emits display light DL which is the first linearly polarized light LP1from the display surface DS. The display light DL passes through the first retardation film R1and is converted into the first circularly polarized light CP1.

Part of the first circularly polarized light CP1which passed through the first retardation film R1passes through the semi-transmissive layer HM. The other first circularly polarized light CP1is reflected on the semi-transmissive layer HM. The first circularly polarized light CP1which passed through the semi-transmissive layer HM passes through the second retardation film R2and is converted into the second linearly polarized light LP2.

When the first circularly polarized light CP1is reflected on the semi-transmissive layer HM, the first circularly polarized light CP1is converted into the second circularly polarized light CP2which rotates in the opposite direction of the first circularly polarized light CP1. The second circularly polarized light CP2reflected on the semi-transmissive layer HM passes through the first retardation film R1, is converted into the second linearly polarized light LP2, and is absorbed in the display module DM.

The second linearly polarized light LP2which passed through the second retardation film R2is reflected on the reflective polarizer PR. The second linearly polarized light LP2reflected on the reflective polarizer PR passes through the second retardation film R2and is converted into the first circularly polarized light CP1.

Part of the first circularly polarized light CP1which passed through the second retardation film R2is reflected on the semi-transmissive layer HM. The other first circularly polarized light CP1passes through the semi-transmissive layer HM. When the first circularly polarized light CP1is reflected on the semi-transmissive layer HM, the first circularly polarized light CP1is converted into the second circularly polarized light CP2. The second circularly polarized light CP2reflected on the semi-transmissive layer HM passes through the second retardation film R2and is converted into the first linearly polarized light LP1.

The first circularly polarized light CP1which passed through the semi-transmissive layer HM passes through the first retardation film R1and is converted into the first linearly polarized light LP1.

The first linearly polarized light LP1which passed through the second retardation film R2passes through the reflective polarizer PR, and further passes through the third retardation film R3, and is converted into the first circularly polarized light CP1. The first circularly polarized light CP1which passed through the third retardation film R3is converted into the second circularly polarized light CP2in the liquid crystal element10and is condensed to the eye E of the user by a lens effect.

In this fourth configuration example, effects similar to those of the first configuration example are obtained.

It should be noted that the first linearly polarized light LP1explained with reference toFIG.13maybe replaced by the second linearly polarized light LP2, or the first circularly polarized light CP1may be replaced by the second circularly polarized light CP2.

Here, an example of the adjustment of the position of a virtual image is explained.

FIG.14is a diagram showing the state before and after the move of the second structure4B.

The second structure4B shown here comprises the reflective polarizer PR, the third retardation film R3and the liquid crystal element10.

The left side of the figure shows a state in which the second structure4B is provided at a first position P1(before the move). The right side of the figure shows a state in which the second structure4B is provided at a second position P2(after the move).

In the state where the second structure4B is provided at the first position P1, a first interval G1is defined between the second retardation film R2and the reflective polarizer PR.

In the state where the second structure4B is provided at the second position P2, a second interval G2is defined between the second retardation film R2and the reflective polarizer PR. The second interval G2is less than the first interval G1. This state is realized when the variable mechanism SL moves the second structure4B so as to be closer to the display module DM.

FIG.15is a diagram in which the optical system of the display device shown inFIG.14is developed at the positions of the reflective polarizer PR and the semi-transmissive layer HM.

The position having a focal distance f from the liquid crystal element10to the front side (in other words, the side of the user's eye) is defined as a first focal point FP1. The position having a focal distance f from the liquid crystal element10to the rear side is defined as a second focal point FP2.

When the second structure4B is located at the first position P1, the point at which the line passing through an end portion E11of the display surface DS shown by a solid line and the second focal point FP2intersects with the position of the liquid crystal element10is defined as point P11, and the point at which the line passing through an end portion10E of the liquid crystal element10and the first focal point FP1intersects with a perpendicular line passing through point P11is defined as point P12. At this time, virtual image V1is formed at the position of point P12as shown by a solid line.

When the second structure4B is located at the second position P2, the point at which the line passing through an end portion E21of the display surface DS shown by a broken line and the second focal point FP2intersects with the position of the liquid crystal element10is defined as point P21, and the point at which the line passing through the end portion10E of the liquid crystal element10and the first focal point FP1intersects with a perpendicular line passing through point P21is defined as point P22. At this time, virtual image V2is formed at the position of point P22as shown by a broken line.

In this manner, when the second structure4B moves to the second position P2, the display surface DS moves away from the second focal point FP2, and the position of virtual image V2moves closer to the side of the user's eye. Thus, an image which can be clearly viewed can be displayed for a nearsighted user.

Fifth Configuration Example

FIG.16is a cross-sectional view showing the fifth configuration example of the display device DSP.

The fifth configuration example shown inFIG.16is different from the fourth configuration example shown inFIG.10in respect that the first structure4A and the display module DM are supported by the variable mechanism SL, and the second structure4B is supported by the support body SP. These differences are mainly explained below.

The second structure4B is supported by the support body SP secured to the housing HS. Thus, the second structure4B is secured to the housing HS across an intervening constant gap.

The display module DM is provided between the housing HS and the first structure4A. Although the display module DM is secured to the first structure4A, the display module DM is not secured to the housing HS. These display module DM and first structure4A constitute the integral structure BD.

The structure BD (the block of the display module DM and the first structure4A) is supported by the variable mechanism SL secured to the housing HS. The variable mechanism SL is configured to move the structure BD in the normal direction of the display surface DS. When the structure BD moves, the variable mechanism SL slides the structure BD in the normal direction of the display surface DS without rotating the structure BD in a plane. By this configuration, the interval between the first structure4A and the second structure4B (or the interval between the semi-transmissive layer HM and the reflective polarizer PR) can be changed.

FIG.17is a diagram showing the state before and after the move of the structure BD.

The structure BD shown here comprises the display module DM, the first retardation film R1, the semi-transmissive layer HM and the second retardation film R2.

The left side of the figure shows a state in which the structure BD is provided at a first position P1(before the move). The right side of the figure shows a state in which the structure BD is provided at a second position P2(after the move).

In the state where the structure BD is provided at the first position P1, a first interval G1is defined between the second retardation film R2and the reflective polarizer PR.

In the state where the structure BD is provided at the second position P2, a second interval G2is defined between the second retardation film R2and the reflective polarizer PR. The second interval G2is less than the first interval G1. This state is realized when the variable mechanism SL moves the structure BD so as to be closer to the reflective polarizer PR.

When the optical system4is developed in the fifth configuration example described above, a diagram similar to that explained with reference toFIG.15is obtained. Specifically, when the structure BD including the first structure4A moves to the second position P2, the display surface DS moves away from the second focal point FP2, and the position of virtual image V2moves closer to the side of the user's eye. Thus, an image which can be clearly viewed can be displayed for a nearsighted user.

Sixth Configuration Example

FIG.18is a diagram showing the state before and after the move of the first structure4A.

The sixth configuration example is different from the fifth configuration example shown inFIG.16in respect that the display module DM is secured to the housing HS, and the variable mechanism SL is configured to move the first structure4A.

The first structure4A shown here comprises the first retardation film R1, the semi-transmissive layer HM and the second retardation film R2.

The left side of the figure shows a state in which the first structure4A is provided at a first position P1(before the move). The right side of the figure shows a state in which the first structure4A is provided at a second position P2(after the move).

In the state where the first structure4A is provided at the first position P1, a first interval G1is defined between the second retardation film R2and the reflective polarizer PR.

In the state where the first structure4A is provided at the second position P2, a second interval G2is defined between the second retardation film R2and the reflective polarizer PR. The second interval G2is less than the first interval G1. This state is realized when the variable mechanism SL moves the first structure4A so as to be closer to the reflective polarizer PR.

When the optical system4is developed in the sixth configuration example described above, a diagram similar to that explained with reference toFIG.15is obtained. Specifically, when the first structure4A moves to the second position P2, the display surface DS moves away from the second focal point FP2, and the position of virtual image V2moves closer to the side of the user's eye. Thus, an image which can be clearly viewed can be displayed for a nearsighted user.

As explained above, the embodiment can provide a display device comprising a diopter scale adjustment function.