Liquid crystal lens device and image display device

A liquid crystal lens device includes a first electrode unit, a counter electrode and a liquid crystal layer. The first electrode unit includes a first and a second electrode. The liquid crystal layer is provided between the first electrode unit and the counter electrode. A threshold voltage Vth of the liquid crystal layer, an absolute value V1 of a potential difference between the first electrode and the counter electrode, a distance P1 between a center of the first electrode and a center of the second electrode, a thickness d1 of the liquid crystal layer, an effective elastic constant keff of the liquid crystal layer, a dielectric anisotropy Δε of the liquid crystal layer, and a dielectric constant ε0 of a vacuum satisfyV1>Vth×(P1/2)/d1,V1<Vth×(P1/d1), and(P1/2)/d1<ε0×(Δε/keff).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2015-054202, filed on Mar. 18, 2015; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a liquid crystal lens device and an image display device.

BACKGROUND

There is a liquid crystal lens device in which the distribution of the refractive index is changed according to an applied voltage by utilizing the birefringence of liquid crystal molecules. There is an image display device in which an image display unit is combined with the liquid crystal lens device. By changing the distribution of the refractive index of the liquid crystal optical element, the image display device switches between a state in which an image displayed by the image display unit is caused to be incident on the eyes of a viewer as displayed by the image display unit and a state in which the image displayed by the image display unit is caused to be incident on the eyes of the viewer as multiple parallax images. Thereby, a two-dimensional image display operation and a three-dimensional image display operation are realized. High display quality is desirable in such an image display device.

DETAILED DESCRIPTION

According to one embodiment, a liquid crystal lens device includes a first electrode unit, a counter electrode and a liquid crystal layer. The first electrode unit includes a first electrode and a second electrode. The first electrode extends in a first direction. The second electrode extends in the first direction. The second electrode is arranged with the first electrode in a second direction. The second direction intersects the first direction. The liquid crystal layer is provided between the first electrode unit and the counter electrode. A threshold voltage Vth of the liquid crystal layer, an absolute value V1of a potential difference between the first electrode and the counter electrode, a distance P1(micrometers) between a center in the second direction of the first electrode and a center in the second direction of the second electrode, a thickness d1(micrometers) of the liquid crystal layer in a third direction intersecting the first direction and the second direction, an effective elastic constant keff(piconewtons) of the liquid crystal layer, a dielectric anisotropy Δε of the liquid crystal layer, and a dielectric constant ε0 of a vacuum satisfy
V1>Vth×(P1/2)/d1,
V1<Vth×(P1/d1), and
(P1/2)/d1<ε0×(Δε/keff).

According to another embodiment, a liquid crystal lens device includes a first electrode unit, a counter electrode and a liquid crystal layer. The first electrode unit includes a first electrode and a second electrode. The first electrode extends in a first direction. The second electrode extends in the first direction. The second electrode is arranged with the first electrode in a second direction. The second direction intersects the first direction. The liquid crystal layer is provided between the first electrode unit and the counter electrode. A threshold voltage Vth of the liquid crystal layer, an absolute value V1of a potential difference between the first electrode and the counter electrode, a focal length f of the liquid crystal layer, a distance P1(micrometers) between a center in the second direction of the first electrode and a center in the second direction of the second electrode, a thickness d1(micrometers) of the liquid crystal layer in a third direction intersecting the first direction and the second direction, an effective elastic constant keff(piconewtons) of the liquid crystal layer, a dielectric anisotropy Δε of the liquid crystal layer, and a dielectric constant ε0 of a vacuum satisfy
V1>Vth×(f/P1),
V1<Vth×(P1/d1), and
(P1/2)/d1<ε0×(Δε/keff).

According to another embodiment, an image display device includes a liquid crystal lens device and an image display unit. The liquid crystal lens device includes a first electrode unit, a counter electrode and a liquid crystal layer. The first electrode unit includes a first electrode and a second electrode. The first electrode extends in a first direction. The second electrode extends in the first direction. The second electrode is arranged with the first electrode in a second direction. The second direction intersects the first direction. The liquid crystal layer is provided between the first electrode unit and the counter electrode. The threshold voltage Vth of the liquid crystal layer, an absolute value V1of a potential difference between the first electrode and the counter electrode, a distance P1(micrometers) between a center in the second direction of the first electrode and a center in the second direction of the second electrode, a thickness d1(micrometers) of the liquid crystal layer in a third direction intersecting the first direction and the second direction, an effective elastic constant keff(piconewtons) of the liquid crystal layer, a dielectric anisotropy Δε of the liquid crystal layer, and a dielectric constant ε0 of a vacuum satisfy
V1>Vth×(P1/2)/d1,
V1<Vth×(P1/d1), and
(P1/2)/d1<ε0×(Δε/keff).

The image display unit includes a display unit. The display unit emits light including image information. The image display unit and the liquid crystal lens device overlap in the third direction.

According to another embodiment, an image display device includes a liquid crystal lens device and an image display unit. The liquid crystal lens device includes a first electrode unit, a counter electrode and a liquid crystal layer. The first electrode unit includes a first electrode and a second electrode. The first electrode extends in a first direction. The second electrode extends in the first direction. The second electrode is arranged with the first electrode in a second direction. The second direction intersects the first direction. The liquid crystal layer is provided between the first electrode unit and the counter electrode. The threshold voltage Vth of the liquid crystal layer, an absolute value V1of a potential difference between the first electrode and the counter electrode, a focal length f of the liquid crystal layer, a distance P1(micrometers) between a center in the second direction of the first electrode and a center in the second direction of the second electrode, a thickness d1(micrometers) of the liquid crystal layer in a third direction intersecting the first direction and the second direction, an effective elastic constant keff(piconewtons) of the liquid crystal layer, a dielectric anisotropy Δε of the liquid crystal layer, and a dielectric constant ε0 of a vacuum satisfy
V1>Vth×(f/P1),
V1<Vth×(P1/d1), and
(P1/2)/d1<ε0×(Δε/keff).

The image display unit includes a display unit. The display unit emits light including image information. The image display unit and the liquid crystal lens device overlap in the third direction.

Various embodiments of the invention will be described hereinafter with reference to the accompanying drawings.

The drawings are schematic or conceptual; and the relationships between the thicknesses and widths of portions, the proportions of sizes between portions, etc., are not necessarily the same as the actual values thereof. The dimensions and/or the proportions may be illustrated differently between the drawings, even in the case where the same portion is illustrated.

In this specification and each drawing, components similar to ones described in reference to an antecedent drawing are marked with the same reference numerals, and a detailed description is omitted as appropriate.

First Embodiment

FIG. 1is a schematic cross-sectional view showing a liquid crystal lens device and an image display device according to a first embodiment.

As shown inFIG. 1, the image display device311according to the embodiment includes the liquid crystal lens device211and an image display unit80. The image display unit80displays an image. The image display unit80may include any display device. For example, a liquid crystal display device, an organic EL display device, a plasma display, etc., may be used.

The liquid crystal lens device211includes a liquid crystal optical element111and a drive unit70. For example, the liquid crystal optical element111is provided on the image display unit80. For example, the liquid crystal optical element111functions as a liquid crystal GRIN lens (gradient index lens). The liquid crystal optical element111has a refractive index distribution31. The refractive index distribution31is changeable. One state of the refractive index distribution31corresponds to a first state in which an image displayed by the image display unit80is caused to be incident as displayed by the image display unit80on the eyes of a viewer. Another state of the refractive index distribution31corresponds to a second state in which the image displayed by the image display unit80is caused to be incident on the eyes of the viewer as multiple parallax images.

By changing the distribution of the refractive index of the liquid crystal optical element111in the image display device311, it is possible to selectively switch between a display of a two-dimensional image (hereinbelow, called a 2D display) and a display of a three-dimensional image (hereinbelow, called a 3D display) by which stereoscopic viewing by the naked eyes can be performed.

The drive unit70is electrically connected to the liquid crystal optical element111. For example, the drive unit70switches between the first state and the second state of the liquid crystal optical element111. The drive unit70switches the liquid crystal optical element111to the first state when performing the 2D display and switches the liquid crystal optical element111to the second state when performing the 3D display.

An image signal is input to the image display unit80from a recording medium, an external input, etc. The image display unit80displays an image corresponding to the image signal that is input. When performing the 2D display, the image display unit80displays an image for the 2D display; and when performing the 3D display, the image display unit80displays an image for the 3D display.

The liquid crystal optical element111includes a first substrate unit10u, a second substrate unit20u, and a liquid crystal layer30. The first substrate unit10uincludes a first substrate10and multiple first electrode units11. The first substrate10has a first major surface10a. The multiple first electrode units11are provided on the first major surface10a. Each of the multiple first electrode units11extends in a first direction. The multiple first electrode units11are arranged in a second direction intersecting the first direction. InFIG. 1, two of the multiple first electrode units11are shown. The number of multiple first electrode units11is arbitrary.

The first direction is taken as a Y-axis direction. A direction parallel to the first major surface10aand perpendicular to the Y-axis direction is taken as an X-axis direction. A direction perpendicular to the X-axis direction and the Y-axis direction is taken as a Z-axis direction. For example, the multiple first electrode units11are arranged in the X-axis direction. In the example, the second direction is the X-axis direction. The second direction is not limited to the X-axis direction and may be any direction intersecting the first direction.

Two most proximal first electrode units11of the multiple first electrode units11are focused upon. One of the two most proximal first electrode units11is taken as a first major electrode (a first electrode)11a. The other of the two most proximal first electrode units11is taken as a second major electrode (a second electrode)11b.

A central axis59is between the two most proximal first electrode units11(the first major electrode11aand the second major electrode11b). When projected onto the X-Y plane (a plane parallel to the first major surface10a), the central axis59is parallel to the Y-axis direction and passes through the midpoint of a line segment connecting a center11acin the X-axis direction of the first major electrode11aand a center11bcin the X-axis direction of the second major electrode11b.

The second substrate unit20uincludes a second substrate20and a counter electrode21. The second substrate20has a second major surface20aopposing the first major surface10a. Each of the multiple first electrode units11is provided between the first substrate10and the second substrate20.

The counter electrode21is provided between the first substrate unit10uand the second substrate20. In other words, the counter electrode21is provided on the second major surface20a. The counter electrode21opposes each of the multiple first electrode units11.

The first substrate10, the first electrode units11, the second substrate20, and the counter electrode21are transmissive to light. Specifically, the first substrate10, the first electrode units11, the second substrate20, and the counter electrode21are transparent.

The first substrate10and the second substrate20include, for example, a transparent material such as glass, a resin, etc. The first substrate10and the second substrate20have plate configurations or sheet configurations. The thicknesses of the first substrate10and the second substrate20are, for example, not less than 50 micrometers (μm) and not more than 2000 μm. However, the thicknesses are arbitrary.

The first electrode units11and the counter electrode21include, for example, an oxide including at least one (one type of) element selected from the group consisting of In, Sn, Zn, and Ti. These electrodes include, for example, ITO. For example, at least one of In2O3or SnO3may be used. The thicknesses of these electrodes are, for example, about 200 nanometers (nm) (e.g., not less than 100 nm and not more than 350 nm). For example, the thickness of each electrode is set to a thickness that can obtain a high transmittance for visible light.

The arrangement pitch of the first electrode units11(the distance between the centers in the X-axis direction of every two most proximal first electrode units11) is, for example, not less than 50 μm and not more than 1000 μm. The arrangement pitch is set to match the desired specifications (the characteristics of the gradient index lens). The length (the width) along the X-axis direction of the first electrode units11is, for example, not less than 5 μm and not more than 300 μm.

The liquid crystal layer30is provided between the first substrate unit10uand the second substrate unit20u. The liquid crystal layer30is provided between the counter electrode21and the first electrode units11. The liquid crystal layer30includes a liquid crystal material. The liquid crystal material includes a nematic liquid crystal (having a nematic phase at the temperature of use of the liquid crystal optical element111). The liquid crystal material has a positive dielectric anisotropy or a negative dielectric anisotropy Δε, a refractive index nofor ordinary rays, a refractive index nefor extraordinary rays, and an effective elastic constant keff. In the case of the positive dielectric anisotropy, the initial alignment of the liquid crystal of the liquid crystal layer30(the alignment when a voltage is not applied to the liquid crystal layer30) is, for example, a horizontal alignment. In the case of the negative dielectric anisotropy, the initial alignment of the liquid crystal of the liquid crystal layer30is a vertical alignment. A threshold voltage Vth (volts (V)) which is the voltage when the liquid crystal starts to align is expressed by Formula 1 using a dielectric constant ε0 (faradays/meter (F/m)) of a vacuum, the dielectric anisotropy Δε of the liquid crystal material, and the effective elastic constant keff(piconewtons (pN)) of the liquid crystal material.

The effective elastic constant keffis expressed by a splay elastic constant k11, a twist elastic constant k22, and a bend elastic constant k33. The effective elastic constant keffis expressed using Formula 2 for any twist angle ωm. For example, these elastic constant are obtained by measuring the threshold voltages of liquid crystal layers having different alignments.
keff=k11+(ωm/π)2×(k33−2k22)  (2)

Formula 2 is as follows in the case where the twist angle ωmis, for example, 90 degrees, i.e., ωm=π/2.
keff=k11−0.5k22+0.25k33

A length (a thickness) d1(micrometers (μm)) of the liquid crystal layer30along the Z-axis direction is determined using Formula 3 based on the arrangement pitch of the first electrode units11, i.e., a lens pitch P1, any lens focal length f, and the relationship of the birefringence (the refractive index noand the refractive index ne). For example, the thickness d1of the liquid crystal layer30is about 25 μm in the case where the refractive index nofor ordinary rays is 1.5, the refractive index nefor extraordinary rays is 1.7, the lens pitch P1is 200 μm, and the focal length f is 1 mm. In other words, the thickness d1in the Z-axis direction of the liquid crystal layer30is the distance along the Z-axis direction between the first substrate unit10uand the second substrate unit20u.
d1=(P1/2)2/2f(ne−no)  (3)

The drive unit70is electrically connected to each of the first electrode units11and the counter electrode21. InFIG. 1, some of the interconnects between the drive unit70and the first electrode units11are not shown for easier viewing of the drawing.

Each of the multiple liquid crystal molecules included in the liquid crystal layer30has the horizontal alignment when a voltage is not applied between the first major electrode11aand the counter electrode21and between the second major electrode11band the counter electrode21. Thereby, a substantially uniform refractive index distribution is obtained in the X-axis direction and the Y-axis direction. Therefore, when the voltage is not applied, the travel direction of the light including the image displayed by a display unit82substantially is not changed. In other words, when the voltage is not applied, the liquid crystal optical element111is in the first state. A voltage such that the refractive index distribution does not occur in the liquid crystal layer30is applied to the first major electrode11a, the second major electrode11b, and the counter electrode21of the liquid crystal optical element111.

When switching the liquid crystal optical element111from the first state to the second state, the drive unit70sets the potentials of the first major electrode11a, the second major electrode11b, and the counter electrode21. The drive unit70sets the absolute value of the potential difference between the first major electrode11aand the counter electrode21and between the second major electrode11band the counter electrode21to V1. In other words, V1is the absolute value of the voltage between the first major electrode11aand the counter electrode21and between the second major electrode11band the counter electrode21. Hereinbelow, the absolute value of the voltage is called the first voltage V1for convenience. The drive unit70applies the first voltage V1between the first major electrode11aand the counter electrode21and between the second major electrode11band the counter electrode21. The same voltage is applied to the first major electrode11aand the second major electrode11b. In the case where the potentials are different between the first major electrode11aand the second major electrode11b, the first voltage V1is taken as the difference between the potential of the counter electrode21and the average potential of the first major electrode11aand the second major electrode11b.

For example, in the case where electrodes other than the first electrode units11are provided, the first voltage V1is the maximum voltage of the electrodes. Thus, when the first voltage V1is applied, the tilt angle of the liquid crystal molecules becomes large in a first portion30aof the liquid crystal layer30where the first electrode unit11and the counter electrode21oppose each other. For example, the liquid crystal molecules approach the vertical alignment in the first portion30a. On the other hand, the liquid crystal molecules remain in the horizontal alignment in a second portion30bof the liquid crystal layer30at the central vicinity of the two mutually-adjacent first electrode units11. The angle (the tilt angle) of the liquid crystal molecules changes in the portion between the first portion30aand the second portion30bto gradually approach the vertical alignment from the second portion30btoward the first portion30a. The angle of the long axis of the liquid crystal molecules changes in the Z-X plane. The angle of the long axis of the liquid crystal molecules changes using the Y-axis direction as the rotation axis.

The liquid crystal molecules have birefringence. The refractive index in the long-axis direction of the liquid crystal molecules for polarized light is higher than the refractive index of the liquid crystal molecules in the short-axis direction. When the angle of the liquid crystal molecules is changed as recited above, the refractive index of the liquid crystal layer30for linearly polarized light traveling in the Z-axis direction and having the polarizing axis oriented in the X-axis direction is high in the second portion30bof the liquid crystal layer30and gradually decreases toward the first portion30a. Thereby, a refractive index distribution that has a convex lens configuration (a semicircular configuration) is formed.

The multiple first electrode units11extend along the Y-axis direction. Therefore, the refractive index distribution of the liquid crystal layer30has a cylindrical lens configuration extending along the Y-axis direction when applying the voltage. The multiple first electrode units11are arranged in the X-axis direction. Therefore, the refractive index distribution of the liquid crystal layer30when applying the voltage has a lenticular lens configuration in which cylindrical lenses extending along the Y-axis direction are multiply arranged in the X-axis direction when the liquid crystal layer30is viewed as an entirety.

For example, the polarity of the first voltage V1may be changed periodically. For example, the potential of the counter electrode21may be fixed; and the potential of the first electrode units11may be changed by alternating current. The polarity of the potential of the counter electrode21may be changed periodically; and the potential of the first electrode units11may be changed with the reverse polarity in conjunction with the change of the polarity of the potential of the counter electrode21. In other words, common inversion driving may be performed. Thereby, the power supply voltage of the drive circuit can be small; and the breakdown voltage specifications of the drive IC are relaxed.

The refractive index distribution having the convex lens configuration formed in the liquid crystal layer30opposes multiple pixels PX of the display unit82arranged in the X-axis direction. In the example, among four pixels PX arranged in the X-axis direction, the two pixels PX positioned at the vicinity of the central axis59are opposed by the portion (the second portion30b) of the refractive index distribution of the liquid crystal layer30where the refractive index is high.

The refractive index distribution of the liquid crystal layer30when applying the voltage causes the light (the image) emitted from the pixels PX to travel toward the eyes of the viewer. Thereby, the image that is formed by the four pixels PX opposing the refractive index distribution becomes a parallax image. In other words, in the example, four parallax images are formed by the four pixels PX arranged in the X-axis direction. The parallax image for the right eye is selectively incident on the right eye of the viewer; and the parallax image for the left eye is selectively incident on the left eye of the viewer. Thereby, the 3D display is possible. In other words, the liquid crystal optical element111is switched to the second state when the voltages are applied to the multiple first electrode units11(the first major electrode11aand the second major electrode11b) and the counter electrode21.

When the liquid crystal optical element111is in the first state, the light that is emitted from the pixels PX travels straight and is incident on the eyes of the viewer. Thereby, the 2D display is possible. In the 2D display, a normal 2D image can be displayed with a resolution that is greater than that of the 3D display by a factor of the number of parallax images (in the example, four times).

Color filters that include the three primary colors RGB may be provided respectively at the multiple pixels PX. Thereby, a color display is possible. Other than the three primary colors RGB, the color filters may further include white (colorless) and other color components.

Thus, the liquid crystal optical element111of the image display device311changes the refractive index distribution of the liquid crystal layer30by whether or not the voltage is applied to the counter electrode21and the multiple first electrode units11. Thereby, the 2D display and the 3D display are switched.

Here, as shown inFIG. 1, the lens pitch P1is the distance (hereinbelow, called the distance P1) between the center11acin the X-axis direction of the first major electrode11aand the center11bcin the X-axis direction of the second major electrode11b.

FIG. 2is a graph of characteristics of the liquid crystal lens device and the image display device according to the first embodiment.

The vertical axis is the first voltage V1(having units of volts (V)); and the horizontal axis is the distance P1(having units of μm).

FIG. 2is the results of a simulation of the first voltage V1when the distance P1is changed for a material A and a material B that have different effective elastic constant keff. In the example, the first voltage V1is plotted for the distance P1when the lens condensing ratio of the liquid crystal lens device211is 80% or more. That is, for voltages outside the graph, the refractive index distribution of the liquid crystal layer30is inappropriate; and the lens condensing performance undesirably degrades easily. By appropriately setting the refractive index distribution of the liquid crystal layer30, the refractive index distribution of the liquid crystal layer30can function as a liquid crystal lens having high lens condensing performance.

For example, by setting the lens condensing ratio to be 80% or more, the scattering of the light and the like are suppressed; crosstalk of the parallax images and the like for the 3D display, etc., are suppressed; and high display quality can be obtained.

FIG. 3AtoFIG. 3Dare schematic views showing refractive index distributions of the liquid crystal layer30.

FIG. 3Ashows a refractive index distribution having an ideal configuration in which the first voltage V1is set appropriately.

FIG. 3BandFIG. 3Cshow refractive index distributions when the first voltage V1is too high.

FIG. 3Dshows the refractive index distribution when the first voltage V1is too low or when the thickness d1is too thin.

InFIG. 3AtoFIG. 3D, the horizontal axis is the position in the lens pitch direction of the liquid crystal layer30; and the vertical axis is the refractive index.

In the liquid crystal optical element111of the embodiment, the threshold voltage Vth (V), the first voltage V1(V), the thickness d1(μm), the distance P1(μm), the effective elastic constant keff(pN), the dielectric anisotropy Δε, and the dielectric constant ε0 (F/m) of a vacuum satisfy the relationships of the following Formula 4 to Formula 6.
V1>Vth×(P1/2)/d1  (4)
V1<Vth×(P1/d1)  (5)
(P1/2)/d1<ε0×(Δε/keff)  (6)

However, the thickness d1is determined using Formula 3.

The inventors discovered as a result of performing simulations that an ideal refractive index distribution such as that shown inFIG. 3Ais obtained when the relationships of Formula 4 to Formula 6 recited above are satisfied.

In the liquid crystal optical element111, the distance P1is set to satisfy the relationship of Formula 4. The drive unit70sets the first voltage V1to satisfy the relationship of Formula 4. In other words, the drive unit70sets the potentials of the counter electrode21and the multiple first electrode units11to satisfy the relationship of Formula 4. In Formula 4, the units of the distance P1are μm; and the units of the first voltage V1are V. The thickness d1is determined to satisfy the relationship of Formula 3.

In the liquid crystal optical element111, the distance P1, the lens focal length f, the threshold voltage Vth, and the first voltage V1may be set to satisfy the relationship of the following Formula 7.
V1>Vth×(f/P1)  (7)

For example, the dielectric anisotropy Δε of the material A is 9.2. The effective elastic constant keffis 14.975 (pN). The distance P1is 260 μm. The focal length f is 970 μm. In such a case, the thickness d1is 40 μm; the threshold voltage Vth is 1.347 V; and the first voltage V1is 6.3 V.

The upper limit of the first voltage V1is determined using Formula (5). In other words, the lower limit of the first voltage V1is determined using Formula (4) or Formula (7); and the upper limit of the first voltage V1is determined using Formula (5).

FIG. 4AtoFIG. 4Care graphs of characteristics of the liquid crystal lens device and the image display device according to the first embodiment.

FIG. 4Ais a three-axis graph of the relationship between a condensing ratio α, a ratio β, and a ratio γ.

FIG. 4Bis a two-axis graph of the relationship between the condensing ratio α and the ratio β.

FIG. 4Cis a two-axis graph of the relationship between the condensing ratio α and the ratio γ.

The ratio β is V1/(Vth×(P1/2)/d1).

The ratio γ is ((P1/2)/d1)/(ε0×(Δε/keff)).

The conditions of Formula 4 mean that V1/(Vth×(P1/2)/d1)>1, i.e., β>1.

The conditions of Formula 5 mean that V1/(Vth×(P1/2)/d1)<2, i.e., β<2.

As shown inFIG. 4B, it can be seen that the condensing ratio α concentrates where the condensing ratio α is 0.8 (80%) or more in the range of 1<β<2.

The conditions of Formula 6 mean that ((P1/2)/d1)/(ε0×(Δε/keff))<1, i.e., γ<1.

As shown inFIG. 4C, it can be seen that the condensing ratio α concentrates where the condensing ratio α is 0.8 (80%) or more in the range of γ<1.

Thus, according to the embodiment, a high condensing ratio can be obtained by satisfying Formula 4 to Formula 6.

The pretilt of the liquid crystal layer30will now be described.

The alignment of the liquid crystal of the liquid crystal layer30may have a pretilt. In the pretilt, for example, a director30d(the axis in the long-axis direction of the liquid crystal molecules) of the liquid crystal is oriented from the first substrate unit10utoward the second substrate unit20ualong the +X direction from the first major electrode11atoward the second major electrode11b.

The pretilt angle is the angle between the X-Y plane and the director30dof the liquid crystal. In the case of the horizontal alignment, the pretilt angle is, for example, greater than 0° and less than 45°. For the vertical alignment, the pretilt angle is, for example, greater than 45° and less than 90°.

For convenience in the specification, the horizontal alignment refers to the case where the pretilt angle is less than 45°; and for convenience, the vertical alignment refers to the case where the pretilt angle exceeds 45°.

For example, the direction of the pretilt can be determined by a crystal rotation method, etc. Also, the direction of the pretilt can be determined by changing the alignment of the liquid crystal by applying a voltage to the liquid crystal layer30and by observing the optical characteristics of the liquid crystal layer30at this time.

In the case where alignment processing of the first substrate unit10uis performed by, for example, rubbing, etc., the direction of the alignment processing is along the +X direction. In the example, the direction of the alignment processing of the first substrate unit10uis, for example, the +X direction. The axis of the director30dmay be parallel or non-parallel to the +X direction when the director30dof the liquid crystal is projected onto the X-Y plane. The direction of the pretilt has a +X direction component when the direction of the pretilt is projected onto the X-axis.

The alignment direction of the liquid crystal layer30at the vicinity of the second substrate unit20uis antiparallel to the alignment direction of the liquid crystal layer30at the vicinity of the first substrate unit10u. In the example, the direction of the alignment processing of the second substrate unit20uis the −X direction. In other words, the initial alignment is not a splay alignment.

The first substrate unit10ufurther includes a first alignment film41. The first alignment film41is provided between the first substrate10and the liquid crystal layer30. The multiple first electrode units11are provided between the first alignment film41and the first substrate10. The second substrate unit20ufurther includes a second alignment film42. The second alignment film42is provided between the second substrate20and the liquid crystal layer30. The counter electrode21is provided between the second alignment film42and the second substrate20. The first alignment film41and the second alignment film42include, for example, polyimide. The initial alignment of the liquid crystal layer30is obtained by, for example, performing rubbing of the first alignment film41and the second alignment film42. The direction of the rubbing of the first alignment film41is antiparallel to the direction of the rubbing of the second alignment film42. The initial alignment may be obtained by performing light irradiation of the first alignment film41and the second alignment film42.

The thicknesses of the first alignment film41and the second alignment film42are, for example, 100 nm (e.g., not less than 30 nm and not more than 300 nm). The distance in the Z-axis direction between the liquid crystal layer30and each of the multiple first electrode units11is, for example, not less than 30 nm and not more than 300 nm.

The case will now be described where the dielectric anisotropy of the liquid crystal included in the liquid crystal layer30is positive and the initial alignment is the horizontal alignment.

By applying voltages between the counter electrode21and the first electrode units11, an electric field acts on the liquid crystal molecules of the liquid crystal layer30; and the liquid crystal alignment changes. A refractive index distribution is formed in the liquid crystal layer30according to this change; and the travel direction of the light that is incident on the liquid crystal optical element111is changed by the refractive index distribution. The change of the travel direction of the light is mainly based on the refraction effect.

The image display unit80includes the display unit82and a light source unit84. The display unit82and the light source unit84are stacked with the liquid crystal optical element111. The display unit82and the light source unit84are stacked with the liquid crystal lens device211(the liquid crystal optical element111) in a third direction intersecting the first direction and the second direction. The third direction is, for example, the Z-axis direction. The third direction is not limited to the Z-axis direction and may be any direction intersecting the first direction and the second direction. In the example, the display unit82is provided between the liquid crystal optical element111and the light source unit84. The light source unit84irradiates light toward the display unit82. The display unit82transmits the light that is incident and emits light including image information. In other words, in the example, the display unit82is a transmission-type display device. The light source unit84is a so-called backlight. The display unit82causes the light including the image information to be incident on the liquid crystal optical element111. For example, the light source unit84may be omitted in the case where the display unit82includes a self-emitting display device such as an organic EL display device or the like.

The image display unit80may further include a display controller86that controls the display unit82. The display unit82produces light that is modulated based on the signal supplied from the display controller86. For example, the display unit82emits light that includes multiple parallax images.

The drive unit70may be connected to the display controller86by a wired or wireless method (an electrical method, an optical method, etc.). The image display device311may further include a controller (not shown) that controls the drive unit70and the display controller86.

The display unit82has a display surface82a. The display unit82emits the light including the image information from the display surface82a. For example, the display surface82ahas a rectangular configuration. The liquid crystal optical element111is provided on the display surface82a. The length in the Y-axis direction of the first electrode units11is slightly longer than the length in the Y-axis direction of the display surface82a. The first electrode units11cross the display surface82ain the Y-axis direction.

The display unit82includes the multiple pixels PX aligned in a two-dimensional matrix configuration. The multiple pixels PX are arranged in the X-axis direction and the Y-axis direction. The display surface82ais formed of the multiple pixels PX.

The region that is between two most proximal first electrode units11opposes multiple pixels PX arranged in the X-axis direction. In the example, the region between the two most proximal first electrode units11opposes four pixels PX arranged in the X-axis direction. In other words, the spacing of the multiple first electrode units11is wider than the spacing in the X-axis direction of the multiple pixels PX. The number of multiple pixels PX arranged in the X-axis direction to oppose the region between the two most proximal first electrode units11is not limited to four and may be two, three, five, or more.

For example, the display unit82emits light including the image displayed on the display surface82a. The light is in a linearly polarized light state traveling substantially in the Z-axis direction. The polarizing axis of the linearly polarized light (the orientation axis in the X-Y plane which is the vibration plane of the electric field) is the X-axis direction. In other words, the polarizing axis of the linearly polarized light is a direction parallel to the director (the long axis) of the liquid crystal molecules. For example, the linearly polarized light is formed by disposing an optical filter (a polarizer) having the X-axis direction as the polarizing axis in the optical path.

According to the embodiment, a refractive index distribution having a good convex lens configuration can be formed in the liquid crystal layer30according to the liquid crystal lens device211and the image display device311according to the embodiment. For example, the decrease of the lens condensing performance can be suppressed. For example, a high-quality 3D display can be provided.

Second Embodiment

FIG. 5is a schematic cross-sectional view showing a liquid crystal lens device and an image display device according to a second embodiment.

As shown inFIG. 5, the image display device312and the liquid crystal lens device212include a liquid crystal optical element112. In the example, the drive unit70and the image display unit80are not shown.

The liquid crystal optical element112includes the first substrate10. Multiple second electrode units12are further provided on the first major surface10aof the first substrate10. The multiple second electrode units12include a first sub electrode12aand a second sub electrode12b. The first sub electrode12ais provided between the first major electrode11aand the central axis59. The second sub electrode12bis provided between the second major electrode11band the central axis59. The first sub electrode12aand the second sub electrode12bare arranged with the central axis59interposed when projected onto a plane (the X-Y plane) parallel to the X-axis direction and the Y-axis direction. The second electrode units12are light-transmissive. The second electrode units12are, for example, transparent. The second electrode units12may include, for example, the material described in reference to the first electrode units11.

The drive unit70sets the absolute value of the potential difference between the first sub electrode12aand the counter electrode21and between the second sub electrode12band the counter electrode21to V2. In the example, there are two second electrode units12. In other words, V2is the absolute value of the voltage between the counter electrode21and each of the multiple second electrode units12. Hereinbelow, the absolute value of the voltage is called the second voltage V2for convenience. The drive unit70applies the second voltage V2between the counter electrode21and each of the multiple second electrode units12. The first voltage V1is set to a value that is higher than the second voltage V2. That is, the relationship of V1>V2is satisfied.

Thus, in the region where the electric field effect of the first electrode units11is weaker, the electric field due to the second electrode units12is caused to act easily; and the refractive index distribution of the convex lens configuration is formed more easily. Thereby, for example, the condensing performance of the refractive index distribution having the convex lens configuration can be improved further. An electrode may be further provided on the central axis59to more easily adjust the refractive index distribution having the convex lens configuration.

The first voltage V1that is applied to the first electrode units11is higher than the second voltage V2that is applied to the second electrode units12. In the liquid crystal layer30, a strong electric field effect occurs at a vicinity positioned the distance d1(a distance equal to the thickness of the liquid crystal layer30) away from the first electrode units11in the X-axis direction. When the action of the electric field is too strong, liquid crystal alignment disorder occurs; the refractive index distribution becomes concave easily (referring toFIG. 3B); and the refractive index distribution undesirably approaches a prism configuration (referring toFIG. 3C). Conversely, when the action of the electric field is too weak, the lens center vicinity of the refractive index distribution undesirably becomes flattened (referring toFIG. 3D). The strength with which the electric field acts is different according to the dielectric anisotropy Δε and the effective elastic constant keffof the liquid crystal material.

The number of second electrodes disposed between the two most proximal first electrode units11is not limited to two and may be three ore more. Electrodes other than the second electrode units12may be further provided between the two most proximal first electrode units11.

According to the liquid crystal lens device212and the image display device312according to the embodiment, by adding the second electrodes, a refractive index distribution having a favorable convex lens configuration can be formed in the liquid crystal layer30. For example, the decrease of the lens condensing performance can be suppressed. For example, a high-quality 3D display can be provided.

Here, the drive unit70may set the absolute value of the potential difference between the first sub electrode12aand the counter electrode21and between the second sub electrode12band the counter electrode21to be V3. In other words, V3is the absolute value of the voltage between the counter electrode21and each of the multiple second electrode units12. Hereinbelow, V3is called the third voltage V3for convenience. The drive unit70applies the third voltage V3between the counter electrode21and each of the multiple second electrode units12. The third voltage V3is set to a value that is higher than the second voltage V2and lower than the first voltage V1. That is, the relationship of V1>V3>V2is satisfied. In such a case, the electric field due to the second electrode units12can be caused to act more strongly. Thereby, for example, a refractive index distribution having a Fresnel lens-like configuration can be formed.

Third Embodiment

FIG. 6is a schematic cross-sectional view showing a liquid crystal lens device and an image display device according to a third embodiment.

As shown inFIG. 6, the image display device313and the liquid crystal lens device213include a liquid crystal optical element113. In the example, the drive unit70and the image display unit80are not shown.

The liquid crystal optical element113includes the first substrate10. In addition to the multiple second electrode units12, multiple third electrode units13are further provided on the first major surface10aof the first substrate10. The multiple third electrode units13include a third sub electrode13aand a fourth sub electrode13b. The third sub electrode13ais provided between the first major electrode11aand the first sub electrode12a. The fourth sub electrode13bis provided between the second major electrode11band the second sub electrode12b. The third sub electrode13aand the fourth sub electrode13bare arranged with the central axis59interposed when projected onto a plane (the X-Y plane) parallel to the X-axis direction and the Y-axis direction. The third electrode units13are light-transmissive. The third electrode units13are, for example, transparent. The third electrode units13may include, for example, the material described in reference to the first electrode units11.

The drive unit70sets the absolute value of the potential difference between the third sub electrode13aand the counter electrode21and between the fourth sub electrode13band the counter electrode21to V3. In other words, V3is the absolute value of the voltage between the counter electrode21and each of the multiple third electrode units13. The absolute value of the voltage is set to the third voltage V3. The drive unit70applies the third voltage V3between the counter electrode21and each of the multiple third electrode units13. The third voltage V3is set to a value that is lower than the first voltage V1and higher than the second voltage V2. That is, the relationship of V2<V3<V1is satisfied.

In the structure in which the two third electrode units13are provided in addition to the two second electrode units12, the refractive index distribution can be formed in a Fresnel lens-like configuration; and it is possible for the thickness d1of the liquid crystal layer30to be thinner.

FIG. 7is a schematic cross-sectional view showing another liquid crystal lens device and another image display device according to the third embodiment.

As shown inFIG. 7, the image display device314and the liquid crystal lens device214include a liquid crystal optical element114. In the example, the drive unit70and the image display unit80are not shown.

The liquid crystal optical element114includes the first substrate10. Two third electrode units13and three or more second electrode units12are further provided on the first major surface10aof the first substrate10. In the example, five second electrode units12are provided between the third sub electrode13aand the fourth sub electrode13b. That is, fifth to seventh sub electrodes12cto12eare provided in addition to the first sub electrode12aand the second sub electrode12b. The second electrode units12may be provided between the first major electrode11aand the third sub electrode13aand between the second major electrode11band the fourth sub electrode13b.

Thus, in the structure in which the two third electrode units13and the three or more second electrode units12are provided, it is easy to reduce the degradation of the curved portions or the Fresnel jump portions of the refractive index distribution; and the condensing performance of the refractive index distribution can be improved further.

According to the liquid crystal lens devices213and214and the image display devices313and314according to the embodiment, by adding the third electrodes, a refractive index distribution having a good Fresnel lens-like configuration can be formed in the liquid crystal layer30. For example, the decrease of the lens condensing performance can be suppressed. For example, a high-quality 3D display can be provided.

In the embodiments recited above, the display unit82includes a transmission-type display device. The display unit82is not limited thereto and may include, for example, a reflection-type display device. In the case where the display unit82includes the reflection-type display device, the light source unit84may be omitted. In the case where the display unit82includes the reflection-type display device, for example, a front-light type light source unit84may be used. For example, the liquid crystal optical element111may be provided on the display surface82aof the display unit82; and the light source unit84may be provided on the liquid crystal optical element111.

According to the embodiments, a liquid crystal lens device and an image display device that provide a high-quality display can be provided.

Hereinabove, embodiments of the invention are described with reference to specific examples. However, the invention is not limited to these specific examples. For example, one skilled in the art may similarly practice the invention by appropriately selecting specific configurations of components such as the first electrode, the second electrode, the counter electrode, the liquid crystal layer, etc., from known art; and such practice is within the scope of the invention to the extent that similar effects can be obtained.

Moreover, all liquid crystal lens devices and image display devices practicable by an appropriate design modification by one skilled in the art based on the liquid crystal lens devices and the image display devices described above as embodiments of the invention also are within the scope of the invention to the extent that the spirit of the invention is included.