Display device

According to one embodiment, a display device includes a first polarizing element, a second polarizing element, and a light-modulating layer located between the first polarizing element and the second polarizing element, each of the first polarizing element and the second polarizing element includes a guest-host liquid crystal layer and a control electrode in an active area including at least one sub-area, the guest-host liquid crystal layer including dye having anisotropy in absorptive power for visible light, the control electrode controlling an alignment direction of the dye in the sub-area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2016-074341, filed Apr. 1, 2016, the entire contents of which are incorporated herein by reference.

FIELD

BACKGROUND

Recently, various optical devices have been proposed. For example, an actively absorptive polarizer to which a guest-host type liquid crystal cell is applicable, a first statically reflective polarizer, an active polarization rotor, and an electronically light-controllable optical device comprising the first statically reflective polarizer have been proposed. In addition, a reflectance variable system or transmittance variable system comprising a variable polarizer to which a gust-host type liquid crystal cell is applicable has also been proposed. The optical device is required to improve the transmittance or transparency on one hand and to implement black display and improve the display quality on the other hand.

DETAILED DESCRIPTION

In general, according to one embodiment, a display device includes: a first polarizing element; a second polarizing element; and a light-modulating layer located between the first polarizing element and the second polarizing element, each of the first polarizing element and the second polarizing element comprising a guest-host liquid crystal layer and a control electrode in an active area including at least one sub-area, the guest-host liquid crystal layer including dye having anisotropy in absorptive power for visible light, the control electrode controlling an alignment direction of the dye in the sub-area.

According to another embodiment, a display device include: a first polarizing element comprising first dye having a first long axis; a second polarizing element comprising second dye having a second long axis; and a display panel located between the first polarizing element and the second polarizing element, the display device having a display mode in which the first long axis and the second long axis intersect each other in a main surface of the display device, and a transmittance mode in which the first long axis and the second long axis are parallel to each other and intersect the main surface.

FIG. 1is a perspective view showing a configuration example of a display device DSP of the embodiments. In the figure, a first direction X, a second direction Y and a third direction Z are orthogonal to each other but may intersect at an angle other than 90 degrees. The third direction Z corresponds to a direction of arrangement of the optical elements constituting the display device DSP.

The display device DSP comprises a first polarizing element1, a second polarizing element2, a display panel3and a driver DR.

Each of the first polarizing element1, the second polarizing element2and the display panel3is formed in, for example, a flat plate shape. An X-Y plane defined by the first direction X and the second direction Y corresponds to a main surface of the display device DSP. The first polarizing element1, the second polarizing element2and the display panel3have main surfaces1A,2A, and3A, respectively, which are parallel to the X-Y plane. In the example illustrated, the third direction Z is parallel to each of the normals of the main surfaces1A,2A, and3A. Each of the first polarizing element1and the second polarizing element2is configured to transmit or absorb the light incident on the own polarizing element. In other words, each of the first polarizing element1and the second polarizing element2is configured to change a transmission state of transmitting the light and an absorption state of absorbing the light.

The display panel3is located between the first polarizing element1and the second polarizing element2. The display panel3is, for example, a liquid crystal display panel comprising a liquid crystal layer as a light-modulating layer but is not limited to this, and may be a display panel comprising a light-modulating layer having a function of varying a phase difference (or retardation) imparted to the light transmitted through the own body or a light-modulating layer having a function of varying in the X-Y plane a plane of vibration of the light transmitted through the own body.

The driver DR drives the first polarizing element1, the second polarizing element2, and the display panel3. In other words, the driver DR controls change of the transmission state of transmitting the light and the absorption state of absorbing the light at each of the first polarizing element1and the second polarizing element2. In addition, the driver DR controls the phase difference for the transmitted light on the display panel3.

FIG. 2is an illustration showing a configuration example of a polarizing element10applicable to a first polarizing element1and a second polarizing element2shown inFIG. 1. The polarizing element10explained below is a configuration example applicable to both the first polarizing element1and the second polarizing element2.FIG. 2(a)is a cross-sectional view showing the polarizing element10controlled in the first mode andFIG. 2(b)is a cross-sectional view showing the polarizing element10controlled in the second mode.

The polarizing element10comprises support substrates11and12, a control electrode (first electrode)13, a control electrode (second electrode)14, alignment films15and16, and a guest-host liquid crystal layer (hereinafter simply called a liquid crystal layer)17. The control electrode13is located between the support substrate11and the alignment film15, and the control electrode14is located between the support substrate12and the alignment film16. The liquid crystal layer17is located between the alignment films15and16or between the control electrodes13and14. The support substrates11and12are substrates which are transparent with respect to visible light such as glass substrates or resin substrates. The control electrodes13and14are formed of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO). The liquid crystal layer17contains a dye (for example, dichroic dye)17G which is anisotropic to the absorptive power (absorptivity) of visible light as guest molecules, and liquid crystal molecules17H of nematic liquid crystal as host molecules. For example, the molecule of dye is shaped in a rod and, for example, azo dye, anthraquinone dye, perylene dye, merocyanine dye and the like are preferable as the dye. The rod-shaped dye has an absorptive power of absorbing a polarization component of vibrating in a long-axis direction of the molecule more strongly than a polarization component of vibrating in a short-axis direction of the molecule. In the liquid crystal layer17, the dye can be aligned in a desired direction in accordance with the alignment of the liquid crystal. A configuration having a positive dielectric anisotropy and a configuration having a negative dielectric anisotropy can be employed as the liquid crystal layer17. Each of the alignment films15and16may be horizontal alignment films having an alignment restriction force of urging the liquid crystal molecules17H to be aligned in a direction parallel to the main surface or vertical alignment films having an alignment restriction force of urging the liquid crystal molecules17H to be aligned in a direction parallel to a normal of the main surface.

A configuration example in which the liquid crystal layer17has a positive dielectric anisotropy and the alignment films15and16are horizontal alignment films will be explained.

FIG. 2(a)illustrates an off state in which a voltage is not applied to the control electrodes13and14opposed to sandwich the liquid crystal layer17. At this time, the liquid crystal molecules17H and the dye17G in the liquid crystal layer17are subjected to initial alignment along the main surface (or the X-Y plane). In the example illustrated, the liquid crystal molecules17H and the dye17G are aligned such that their long axes oriented in a direction parallel to the second direction Y. In this case, the dye17G absorbs a second polarization component parallel to the second direction Y more strongly than a first polarization component parallel to the first direction X, of the light made incident on the liquid crystal layer17in the third direction Z. The initial alignment direction of the liquid crystal molecules17H and the dye17G is determined based on alignment treatment directions of the alignment films15and16. As the alignment treatment of the alignment films15and16, rubbing treatment, optical alignment treatment and the like can be employed. In the example illustrated, the alignment treatment directions of the alignment films15and16are parallel to the second direction Y but may be opposite to each other or the same as each other. A state in which the long axis of the dye17G is aligned along the main surface indicates not only a case where the long axis is completely parallel to the main surface, but also a case where the long axis is slightly angled to the main surface.

FIG. 2(b)illustrates an on state in which a voltage is applied to the control electrodes13and14. At this time, an electric field is formed in a third direction Z, between the control electrodes13and14, in the liquid crystal layer17. The liquid crystal molecules17H and the dye17G in the liquid crystal layer17are aligned such that their long axes are oriented in a direction parallel to the electric field. In other words, the long axes of the respective liquid crystal molecules17H and the dye17G are aligned in a direction intersecting the main surface. For example, the long axis of each of the liquid crystal molecules17H and the dye17G is aligned in a direction parallel to the normal of the main surface, i.e., the third direction Z. In this case, the dye17G hardly absorbs the first polarization component and the second polarization component of the light made incident on the liquid crystal layer17in the third direction Z. Even if the dye17G absorbs part of the light, the absorptive power of the first polarization component is equivalent to the absorptive power of the second polarization component. A state in which the long axis of the dye17G is aligned in a direction intersecting the main surface indicates not only a case where the long axis is completely parallel to the normal of the main surface, but also a case where the long axis is slightly angled to the normal of the main surface.

FIG. 3is an illustration showing another configuration example of the polarizing element10applicable to the first polarizing element1and the second polarizing element2shown inFIG. 1.FIG. 3(a)is a cross-sectional view showing the polarizing element10controlled in the second mode andFIG. 3(b)is a cross-sectional view showing the polarizing element10controlled in the first mode.

The configuration example shown inFIG. 3is different from the configuration example shown inFIG. 2with respect to a feature that the liquid crystal layer17has a negative dielectric anisotropy and the alignment films15and16are vertical alignment films.

FIG. 3(a)illustrates an off state in which a voltage is not applied to the control electrodes13and14. At this time, the liquid crystal molecules17H and the dye17G in the liquid crystal layer17are subjected to initial alignment in the third direction Z parallel to the normal of the main surface. In this case, the dye17G hardly absorbs the first polarization component and the second polarization component of the light made incident on the liquid crystal layer17along the third direction Z.

FIG. 3(b)illustrates an on state in which a voltage is applied to the control electrodes13and14. At this time, an electric field is formed in a third direction Z, between the control electrodes13and14, in the liquid crystal layer17. An inclined electric field angled to the third direction Z is desirably included in the electric field. This inclined electric field can be formed by forming protrusions between the support substrate11and the liquid crystal layer17, between the support substrate12and the liquid crystal layer17and the like or forming slits in the control electrodes13and14. The protrusions and slits are often called inclined electric field forming portions. In addition, an effect similar to that of the inclined electric field can also be obtained by preliminarily forming pre-tilt on the vertical alignment film by rubbing treatment, and restricting the orientation of inclination of the liquid crystal layer17by the longitudinal electric field formed between the control electrodes13and14. The liquid crystal molecules17H and the dye17G in the liquid crystal layer17are aligned such that their long axes are oriented in a direction intersecting the electric field. In other words, the liquid crystal molecules17H and the dye17G are aligned to be oriented in a direction parallel to the X-Y plane. In the example illustrated, the dye17G is aligned such that its long axis is oriented in the direction parallel to the second direction Y, and absorbs the second polarization component more strongly than the first polarization component, of the light made incident on the liquid crystal layer17.

In the present embodiments, a mode of aligning the dye17G in the direction parallel to the main surface as shown inFIG. 2(a)andFIG. 3(b)is defined as a first mode, and a mode of aligning the dye17G in the direction parallel to the normal of the main surface as shown inFIG. 2(b)andFIG. 3(a)is defined as a second mode. In the first mode, however, all the dyes17G do not need to be aligned in the direction completely parallel to the main surface, but the dye17G may be aligned so as to express difference in absorptive power of both the first polarization component and the second polarization component with respect to an average absorptive power of the dye17G contained in the liquid crystal layer17. In the second mode, all the dyes17G do not need to be aligned in the direction completely parallel to the normal of the main surface, but the dye17G may be aligned so as to hardly absorb the first polarization component and the second polarization component or to be considered to have substantially equivalent absorptive power of the first polarization component and the second polarization component with respect to the average absorptive power of the dye17G contained in the liquid crystal layer17. Thus, a pair of control electrodes13and14control the first mode and the second mode in accordance with the voltage applied to the liquid crystal layer17between the control electrodes.

In the second mode, i.e., the state in which the magnitude of absorption is hardly varied irrespective of the polarization component, the transparency is more excellent as the dye17G is aligned in the direction parallel to the normal of the main surface. In other words, aligning the dye17G by the alignment restriction force of the vertical alignment film as shown inFIG. 3(a)is preferable to aligning the dye17G by the electric field as shown inFIG. 2(b), from the viewpoint of enhancing the transparency. This is because the alignment of the dye17G in close vicinity to the alignment film surface cannot easily be changed, the applied voltage is limited practically, and fluctuation of the liquid crystal is hardly influenced by the optical characteristics in the configuration example shown inFIG. 3(a)as compared with the configuration example shown inFIG. 2(b).

Next, a configuration example of the control electrodes13and14applicable to the polarizing element10will be explained.

FIG. 4is a plan view showing a configuration example of control electrodes13and14. The polarizing element10includes an active area AA in which the light can be transmitted, in an X-Y plane. For example, the active area AA is shaped in a rectangle having short sides extending along the first direction and long sides extending along the second direction and the shape is not limited to the example illustrated but may be the other polygon or a circle, an ellipsoid or the like.

In the configuration example shown inFIG. 4(a), each of the control electrodes13and14is composed of a single sheet electrode elongated over the whole of the active area AA without a rip. As explained above, the control electrodes13and14are opposed to sandwich the liquid crystal layer17. The driver DR is electrically connected to each of the control electrodes13and14. In this configuration example, the alignment direction of the dye17G of the liquid crystal layer17is controlled on the whole of the active area AA by controlling the voltage applied to the control electrodes13and14by the driver DR. The polarizing element10can thereby control the first mode (i.e., the mode of mainly transmitting the light) and the second mode (i.e., the mode of mainly absorbing the light) on the whole of the active area AA.

The configuration example shown inFIG. 4(b)is different from the configuration example shown inFIG. 4(a)with respect to a feature that the active area AA of the polarizing element10includes a plurality of strip-shaped sub-areas SA. The control electrode13is composed of a single sheet electrode, similarly to the configuration example shown inFIG. 4(a). The control electrode14is composed of strip electrodes141to147spaced apart from each other. In the example illustrated, the strip electrodes141to147are shaped in a rectangle elongated in the first direction X and arranged in the second direction Y so as to be spaced apart from each other. The control electrode13and the strip electrodes141to147are opposed to each other. The driver DR is electrically connected to the control electrodes13and also electrically connected to each of the strip electrodes141to147. A sub-area SA corresponds to an overlaid portion in which the control electrodes13and one of the strip electrodes141to147are overlaid in the X-Y plane. In the example illustrated, each sub-area SA is a strip-shaped region elongated in the first direction X.

The strip electrodes141to147may be elongated in the second direction Y and arranged in the first direction X so as to be spaced apart from each other. In this configuration example, one of the control electrodes13and14is composed of a sheet electrode and the other is composed of a plurality of strip electrodes, but the control electrode13may be composed of strip electrodes and the control electrode14may be composed of a single sheet electrode.

In this configuration example, the alignment direction of the dye17G is controlled in each of the sub-areas SA by controlling a voltage applied to the strip electrodes141to147independently by the driver DR. The polarizing element10can thereby control the first mode and the second mode in each sub-area SA. It should be noted that the polarizing element10of this configuration example can control the first mode and the second mode on the whole of the active area AA by driving all the strip electrodes141to147together.

The configuration example shown inFIG. 4(c)is different from the configuration example shown inFIG. 4(a)with respect to a feature that the active area AA of the polarizing element10includes a plurality of sub-areas SA arrayed in a matrix. The control electrode13is composed of strip electrodes131to135spaced apart from each other. The control electrode14is composed of strip electrodes141to146spaced apart from each other. The strip electrodes131to135correspond to the first strip electrodes and the strip electrodes141to146correspond to the second strip electrodes. In the example illustrated, the strip electrodes131to135are elongated in the second direction Y and arranged in the first direction X so as to be spaced apart from each other. The strip electrodes141to146may be elongated in the first direction X and arranged in the second direction Y so as to be spaced apart from each other. The strip electrodes131to135and the strip electrodes141to146are opposed to each other. The driver DR is electrically connected to each of the strip electrodes131to135and also connected to each of the strip electrodes141to146. Each of the sub-areas SA corresponds to a square intersection portion in which one of the strip electrodes131to135and one of the strip electrodes141to146intersect in the X-Y plane. In the example illustrated, the sub-areas SA are arrayed in a matrix in the first direction X and the second direction Y.

In this configuration example, the alignment direction of the dye17G is controlled in each of the sub-areas SA by controlling a voltage applied to the strip electrodes131to135and141to146independently by the driver DR. The polarizing element10can thereby control the first mode and the second mode in each sub-area SA. It should be noted that the polarizing element10of this configuration example can control the first mode and the second mode on the whole of the active area AA by driving all the strip electrodes131to135and141to146together.

In the configuration example, the shape of the sub-area SA is not limited to a rectangle, but may be the other polygons, a circle, an ellipsoid or any arbitrary shape. Shapes of the control electrodes13and14which define the shapes of the sub-areas SA can be selected freely.

FIG. 5is a plan view showing another configuration example of the control electrodes13and14. The configuration example shown inFIG. 5is different from the configuration example inFIG. 4with respect to a feature that sub-areas SA1and SA2are locally formed in the active area AA. The sub-area SA does not need to be formed on the whole of the active area AA, unlike the configuration example shown inFIG. 4, and can be optionally provided in a region where optical transmission or absorption needs to be controlled.

In the example illustrated, the active area AA includes the sub-areas SA1and SA2and a non-control area SB. The sub-area SA1is an elliptic region and is formed in a region where a pair of control electrodes131and141are opposed to each other. The sub-area SA2is an elongated region and is formed in a region where a pair of control electrodes132and142are opposed to each other. None of the control electrodes is formed in the non-control area SB. In the example illustrated, a total size of the sub-areas SA1and SA2is smaller than a total size of the non-control area SB in the active area AA. However, the total size of the sub-areas SA1and SA2may be larger than the total size of the non-control area SB.

In this configuration example, the sub-areas SA1and SA2correspond to the control areas where the first mode and the second mode can be controlled. In contrast, the non-control area SB other than the sub-area SA is maintained in the second mode and most of the light is transmitted in the area. In other words, the non-control area SB corresponds to a transmissive region.

The sub-areas SA of the polarizing element10are driven in the passive mode in the configuration example shown inFIG. 4andFIG. 5but may be driven in an active mode. In other words, the polarizing element10may comprise an active element in each sub-area SA and at least one of the control electrodes13and14may be electrically connected with the active element. In this case, the first mode and the second mode can be controlled independently in each sub-area SA.

FIG. 6is a cross-sectional view showing a configuration example of a display panel3shown inFIG. 1. A liquid crystal display device is explained as an example of the display device3.

The display panel3includes a first substrate SUB1, a second substrate SUB2and a light-modulating layer (liquid crystal layer) LC. The first substrate SUB1and the second substrate SUB2are bonded to each other by a sealing member SE. The light-modulating layer LC is held between the first substrate SUB1and the second substrate SUB2. The first substrate SUB1is located on a side opposed to the first polarizing element1. The second substrate SUB2is located on a side opposed to the second polarizing element2. The light-modulating layer LC is located between the first polarizing element1and the second polarizing element2.

FIG. 7is an illustration showing a configuration example of the display panel3shown inFIG. 6.

The display panel3includes a display area DA where an image is displayed. The display area DA is composed of pixels PX arrayed in a matrix. The first substrate SUB1includes scanning lines G (also called gate lines), and signal lines S (also called data lines or source lines) intersecting the scanning lines G. Each scanning line G is drawn outside the display area DA to be connected to a scanning line driver GD. Each signal line S is drawn outside the display area DA to be connected to a signal line driver SD. The scanning line driver GD and the signal line driver SD are connected to a controller CNT. The controller CNT controls the scanning line driver GD and the signal line driver SD, based on data of the image displayed in the display area DA. Since the scanning lines G and the signal lines S are formed of an opaque metal material, the lines are desirably made as narrow as possible from the viewpoint of enhancing the transmittance of the display panel3. In addition, the surface of the scanning lines G and the signal lines S is desirably subjected to antireflection treatment from the viewpoint if reducing an influence of the reflected light on the scanning lines G and the signal lines S to the display images.

Each of the pixels PX comprises a switching element SW (for example, thin-film transistor), a pixel electrode PE, a common electrode CE and the like. The switching element SW is electrically connected to the scanning line G and the signal line S. The switching element SW may be a top-gate type switching element or a bottom-gate type switching element and may employ a single-gate structure or a double-gate structure. In addition, a semiconductor layer of the switching element SW can be formed of amorphous silicon, polycrystalline silicon or oxide semiconductor. The semiconductor layer is desirably formed of the oxide semiconductor from the viewpoint of reducing leakage due to the incident light to the semiconductor layer. Alternatively, the semiconductor layer is desirably formed of the transparent oxide semiconductor from the viewpoint of enhancing the transmittance of the display panel3. The pixel electrode PE is electrically connected to the switching element SW. The common electrode CE is opposed to the pixel electrodes PE. The pixel electrodes PE and the common electrode CE function as drive electrodes which drive the light-modulating layer LC. The pixel electrodes PE and the common electrode CE are formed of a transparent conductive material such as ITO and IZO. The pixel electrodes PE and the common electrode CE desirably do not contain an opaque metal material from the viewpoint of enhancing the transmittance of the display panel3.

Detailed explanations of the configuration of the display panel3are omitted here, but, the common electrode CE is disposed on the second substrate SUB2while the pixel electrodes PE are disposed on the first substrate SUB1in a mode of mainly using a longitudinal electric field along a direction of the normal of the display panel3or in a mode of mainly using an inclined electric field angled to the normal. In addition, in a mode of mainly using a lateral electric field along the main surface3A of the display panel3, both the pixel electrode PE and the common electrode CE are disposed on the first substrate SUB1or the second substrate SUB2.

The mode using the longitudinal electric field is, for example, a twisted nematic (TN) mode, a polymer dispersed liquid crystal (PDLC) mode, an optically compensated bend (OCB) mode, an electrically controlled birefringence (ECB) mode, or a vertical aligned (VA) mode. In addition, the mode using the lateral electric field is, for example, a fringe field switching (FFS) mode, an in-plane switching (IPS) mode or the like. The mode using the longitudinal electric field and the mode using the lateral electric field may be combined.

The display panel3has, for example, a transmissive display function of displaying an image by urging the light traveling from the first substrate SUB1toward the second substrate SUB2or the light traveling from the second substrate SUB2toward the first substrate SUB1to be selectively transmitted in the whole of the display area DA. The display panel3may have a reflective display function of displaying an image by urging the light traveling from the first substrate SUB1toward the second substrate SUB2or the light traveling from the second substrate SUB2toward the first substrate SUB1to be selectively reflected in a part of the display area DA. In addition, at least several pixels PX located in the display area DA may have both the transmissive display function and the reflective display function.

FIG. 8is a cross-sectional view showing a configuration example of the display panel3shown inFIG. 7. A cross-sectional structure of the display panel3using the FFS mode which is one of the display modes using the lateral electric field will be explained in brief. In the example illustrated, the display panel3includes a red pixel PXR which exhibits a red color, a green pixel PXG which exhibits a green color, and a blue pixel PXB which exhibits a blue color, in the display area DA, but may include a pixel which exhibits the other color. For example, the display panel3desirably includes a pixel which exhibits a white color or transparent pixel from the viewpoint of enhancing the transmittance of the display panel3.

The first substrate SUB1includes a first insulating substrate100, a first insulating film110, the common electrode CE, a second insulating film120, pixel electrodes PE1to PE3, a first alignment film AL1and the like. The common electrode CE extends across the red pixel PXR, the green pixel PXG and the blue pixel PXB. Each of a pixel electrode PE1of the red pixel PXR, a pixel electrode PE2of the green pixel PXG, and a pixel electrode PE3of the blue pixel PXB is opposed to the common electrode CE and includes slits SLA. In the example illustrated, the common electrode CE is located between the first insulating film110and the second insulating film120, and the pixel electrodes PE1to PE3are located between the second insulating film120and the first alignment film AL1. The pixel electrodes PE1to PE3may be located between the first insulating film110and the second insulating film120, and the common electrode CE may be located between the second insulating film120and the first alignment film AL1. In this case, the slits SLA are formed on the common electrode CE.

The second substrate SUB2includes a second insulating substrate200, a light-shielding layer BM, color filters CFR, CFG and CFB, an overcoat layer OC, a second alignment film AL2, and the like. The color filters CFR, CFG and CFB are opposed to the pixel electrodes PE1to PE3, respectively, through the light-modulating layer LC. The color filter CFR is a red color filter, the color filter CFG is a green color filter, and the color filter CFB is a blue color filter.

The color filters CFR, CFG and CFB are formed on the second substrate SUB2in the example illustrated, but may be formed on the first substrate SUB1. The light-shielding layer BM is located between adjacent color filters but desirably is not disposed from the viewpoint of enhancing the transmittance of the display panel3. If the color display is unnecessary, the transmittance of the display panel3can be further enhanced by disposing no color filters.

The light-modulating layer LC is sealed between the first alignment film AL1and the second alignment film AL2. The first alignment film AL1and the second alignment film AL2are horizontal alignment films.

In an off state in which an electric field is not formed between a pixel electrode PE and a common electrode CE, the liquid crystal molecules LM contained in the light-modulating layer LC are set in an initial alignment in a direction substantially parallel to the X-Y plane by an alignment restriction force of the first alignment film AL1and the second alignment film AL2. In an on state in which the electric field is formed between the pixel electrodes PE and the common electrode CE, the liquid crystal molecules LM are aligned in a direction different from the initial alignment direction in the X-Y plane. An average alignment direction of the liquid crystal molecules LM is determined in accordance with the magnitude of the electric field or the potential difference between the pixel electrodes PE and the common electrode CE. In the light-modulating layer LC, the retardation Δn·d assigned for the linearly polarized light transmitted through the own layer is, for example, zero in the off state and λ/2 at maximum in the on state. An represents refractive anisotropy of the light-modulating layer LC, d represents a substantial thickness (length in the third direction Z) of the light-modulating layer LC, and X represents the wavelength of the light transmitted through the light-modulating layer LC. In other words, the retardation of the light-modulating layer LC can be adjusted within a range from zero to λ/2 in accordance with the magnitude of the electric field, and the like. For this reason, the linearly polarized light transmitted through the light-modulating layer LC in the off state is transmitted through the display panel3while maintaining its polarized state. In addition, the linearly polarized light transmitted through the light-modulating layer LC in the on state is converted into linearly polarized light in the polarized state in which its axis of polarization is rotated at 90 degrees in the X-Y plane.

FIG. 9is an illustration for explanation of a transmission mode applied to the display device DSP of the embodiments. Two sub-areas SA21and SA22of the sub-areas disposed in the first polarizing element1and the second polarizing element2will be explained here. The sub-areas SA21and SA22are opposed to sandwich the display panel3. For example, the sub-areas SA21and SA22have a positional relationship of being overlaid in the X-Y plane.

Each of the first polarizing element1and the second polarizing element2is controlled in the second mode, and the dye21G included in the first polarizing element1and the dye22G included in the second polarizing element2are aligned parallel to each other. In other words, the dye21G included in the first polarizing element1and the dye22G included in the second polarizing element2are aligned such that their long axes are oriented in the third direction Z.

FIG. 10is an illustration for explanation of the transmittance of the display device DSP in the transmission mode shown inFIG. 9. The transmittance of the light traveling from the first polarizing element1toward the second polarizing element2in the display device DSP will be explained, but the transmittances of the light in opposite directions are substantially equal to each other. In addition, absorption at the dye in each polarizing element in the short axis direction or absorption on the display panel is not considered in the following descriptions on the transmittance.

The pixels PX11and PX12included in the display panel3are located between the sub-area SA21of the first polarizing element1and the sub-area SA22of the second polarizing element2. The retardation Δn·d in the pixel PX11is zero while the retardation Δn·d in the pixel PX12is λ/2. The pixel PX11corresponds to the first pixel and the retardation of the pixel PX11corresponds to the first retardation. The pixel PX12corresponds to the second pixel and the retardation of the pixel PX12corresponds to the second retardation. The long axis L1of the dye21G and the long axis L2of the dye22G are aligned in the third direction Z. In other words, the long axes L1and L2are parallel to each other and intersect the X-Y plane (or the main surface of the display device DSP). The dye21G corresponds to the first dye and the long axis L1of the dye21G corresponds to the first long axis. The dye22G corresponds to the second dye and the long axis L2of the dye22G corresponds to the second long axis.

The light transmitted through the first polarizing element1(for example, the natural light having a random plane of vibration) is hardly absorbed into the dye21G of the sub-area SA21and is made incident on the display panel3. The component having a plane of vibration, which is part of the light made incident on the display panel3, is modulated in the pixels PX11and PX12but most of the light is not absorbed and made incident on the second polarizing element2. The light made incident on the second polarizing element2is hardly absorbed into the dye22G of the sub-area SA22and is transmitted. Since the light made incident on the display device DSP in the transmission mode is thus hardly absorbed into the display device DSP, the transmittance TO of the light transmitted through the display device DSP is equivalent irrespective of the retardations of the pixels PX11and PX12. For example, the transmittance TO is substantially 100%. In the transmission mode, even if a video signal is written to each pixel to display an image on the display panel3, the display image is hardly recognized visually and the transmittance is not lowered.

Thus, according to the present embodiments, the transmittance can be enhanced by controlling the first polarizing element1and the second polarizing element2of the display device DSP in the transmission mode, as compared with a display device comprising an absorption-type static polarizer. In addition, since the transmitted light is hardly absorbed in the display device DSP, the transparency can be enhanced at a portion which needs to be observed through a background via the display device DSP.

FIG. 11is an illustration for explanation of a display mode applied to the display device DSP of the embodiments.

Each of the first polarizing element1and the second polarizing element2is controlled in the first mode, and the dye21G included in the first polarizing element1and the dye22G included in the second polarizing element2are aligned in directions perpendicular to each other in the X-Y plane. In the example illustrated, the dye21G is aligned such that its long axis L1is oriented in the first direction X, and the dye22G is aligned such that its long axis L2is oriented in the second direction Y. In other words, the long axes L1and L2intersect each other on the X-Y plane (or the main surface of the display device DSP).

FIG. 12is an illustration for explanation of transmittance of the display device DSP in the display mode shown inFIG. 11.

First, the transmittance of the light incident on the first polarizing element1will be explained. Since the dye21G is aligned in the first direction X in the first polarizing element1, a component having a plane of vibration parallel to the first direction X, of the light incident on the first polarizing element1, is absorbed into the dye21G and a component having a plane of vibration parallel to the second direction Y is transmitted. For this reason, the transmittance of the light incident on the first polarizing element1is approximately 50%. The light transmitted through the first polarizing element1becomes linearly polarized light having a plane of vibration in the second direction Y and is made incident on the display panel3.

The light made incident on the pixel PX11, of the linearly polarized light made incident on the display panel3, is transmitted through the display panel3while maintaining its polarized state since the retardation Δn·d of the pixel PX11is zero. The light made incident on the pixel PX12, of the linearly polarized light made incident on the display panel3, has the polarization axis rotated, is converted into the linearly polarized light having a plane of vibration in the first direction X, and transmitted through the display panel3since the retardation Δn·d of the pixel PX12is λ/2. The linearly polarized light transmitted through the display panel3is made incident on the second polarizing element2.

Next, the transmittance of the light incident on the second polarizing element2will be explained. Since the dye22G is aligned in the second direction Y in the second polarizing element2, a component having a plane of vibration parallel to the second direction Y, of the light incident on the second polarizing element2, is absorbed into the dye22G and a component having a plane of vibration parallel to the first direction X is transmitted. Since the light transmitted through the pixel PX11is the linearly polarized light having a plane of vibration in the second direction Y, the light is almost absorbed into the dye22G. In contrast, since the light transmitted through the pixel PX12is the linearly polarized light having a plane of vibration in the first direction X, the light is hardly absorbed into the dye22G. For this reason, the transmittance TL of the light transmitted through the pixel PX11is smaller than the transmittance TH of the light transmitted through the pixel PX12in the display device DSP. For example, the transmittance TL becomes substantially zero. In the pixel PX11, black display (Bk) is thereby implemented. In addition, the transmittance TH becomes approximately 50%. In the pixel PX12, white display (W) or the color display is thereby implemented. Therefore, the display image can be visually recognized by writing the video signal to display the image in each pixel PX of the display panel3, in this display mode.

Thus, according to the present embodiments, the black display can be implemented and the contrast ratio can be enhanced by controlling the first polarizing element1and the second polarizing element2of the display device DSP in the display mode, as compared with a display device comprising a transmissive spontaneous light-emitting element. For this reason, the display quality can be enhanced.

Next, examples of the present embodiments will be described. In the following examples, only constituent elements necessary for explanations are illustrated.

FIG. 13is a cross-sectional view showing the display device DSP according to an example of the embodiments. The first polarizing element1comprises support substrates31and32, a control electrode (first electrode)33, a control electrode (second electrode)34, alignment films35and36, and a liquid crystal layer (guest-host liquid crystal layer)37. The second polarizing element2comprises support substrates41and42, a control electrode (first electrode)43, a control electrode (second electrode)44, alignment films45and46, and a liquid crystal layer (guest-host liquid crystal layer)47.

The display panel3comprises the first insulating substrate100, the common electrode CE, the insulating film120, the pixel electrode PE, the first alignment film AL1, the second insulating substrate200, the second alignment film AL2, and the light-modulating layer LC. The first insulating substrate100is opposed to the support substrate32. The second insulating substrate200is opposed to the support substrate41. Air layers or transparent members may be interposed between the first insulating substrate100and the support substrate32and between the second insulating substrate200and the support substrate41or the insulating substrates and the support substrates may be bonded by an adhesive.

As explained above, the display device DSP capable of enhancing the transmittance and the display quality can be provided by the embodiments.

FIG. 14is a cross-sectional view showing the display device DSP according to another example of the embodiments. The example shown inFIG. 14is different from the example shown inFIG. 13with respect to a feature that the number of substrates is reduced. In the example illustrated, the first polarizing element1and the second polarizing element2have the same configuration as that in the example shown inFIG. 13, and illustration of the first insulating substrate and the second insulating substrate of the display panel3is omitted.

The common electrode CE of the display panel3is located on a side opposed to the light-modulating layer LC of a support substrate32and is opposed to the pixel electrode PE through an insulating film120. The second alignment film AL2of the display panel3is located on a side opposed to the light-modulating layer LC of a support substrate41.

As explained above, the display device DSP capable of enhancing the transmittance and the display quality can be provided by the embodiments. In addition, the number of the components can be reduced, the manufacturing costs can be reduced and the display device DSP can be thinned as compared with the example shown inFIG. 13.

An example of application of the display device DSP of the embodiments will be hereinafter explained. For example, the display device DSP can comprise an lux meter (or an external light sensor) and adjust the transmittance in accordance with brightness of the surrounding, brightness of the background of the display device DSP, and the like. The adjustment of the transmittance can be executed uniformly over the entire area of the active area AA (full dimming) or for each of the sub-areas SA in the active area AA (local dimming). In the local dimming, the visibility can be reduced by assigning gradation of the transmittance to the vicinity of boundaries of the sub-areas SA. In addition, in the image display on the display panel3, the transmittance can be adjusted to enhance the visibility of the display image. The display device DSP can dim on a necessary area in the active area AA, enlarge or reduce the dimming area, and freely select the shape of the area in accordance with the image taken by a camera.

In addition, in an application example shown inFIG. 15(a)andFIG. 15(b), the display device DSP comprises phase difference compensating layers4and5. The phase difference compensating layer4is disposed between the first polarizing element1and the display panel3, and the phase difference compensating layer5is disposed between the second polarizing element2and the display panel3. When the display device DSP is observed from an oblique direction angled with respect to the third direction Z, the phase difference compensating layers4and5optically compensate for the phase difference of the light transmitted through the sub-areas of the first polarizing element1and the second polarizing element2and the pixels of the display panel3. Even if the display device DSP is observed from the oblique direction, a viewing angle at which high transmittance can be obtained in the transmittance mode shown inFIG. 15(a)can be extended, and a viewing angle at which an image of preferable display quality can be observed in the display mode shown inFIG. 15(b)can be extended. In the example illustrated, the phase difference compensating layers4and5are disposed on both sides to sandwich the display panel3. For this reason, even if the position for observing the display device DSP is on the first polarizing element1side or the second polarizing element2side with respect to the display panel3, the transmittance and the display quality can be enhanced equally. Only one of the phase difference compensating layers4and5may be disposed in the display device DSP of the present embodiments and, in this case, the same advantages can be obtained similarly to the case of observing the display device DSP from at least one of the sides.

As explained above, the liquid crystal display device capable of enhancing the display device can be provided by the embodiments.

The present invention is not limited to the embodiments described above but the constituent elements of the invention can be modified in various manners without departing from the spirit and scope of the invention. Various aspects of the invention can also be extracted from any appropriate combination of a plurality of constituent elements disclosed in the embodiments. Some constituent elements may be deleted in all of the constituent elements disclosed in the embodiments. The constituent elements described in different embodiments may be combined arbitrarily.