Polarization modulation element and stereoscopic image display device

Abstract

To provide a polarization modulation element and a stereoscopic image display device capable of emitting a polarization component having a desired polarization direction with high intensity at low voltage.SOLUTION: A polarization modulation element 10 includes N (N is an integer of 3 or more) twisted nematic liquid crystal cells 110 to 140 having the same twist direction. A sum of the twist angles of the respective twisted nematic liquid crystal cells 110 to 140 is 90°. In at least one adjacent twisted nematic liquid crystal cell 120 and 130, an alignment axis direction 224 of a light-emitting side substrate and an alignment axis direction 232 of a light incident side substrate are orthogonal to each other. In the other adjacent twisted nematic liquid crystal cells 110, 120, 130, and 140, an alignment axis directions 214 and 234 of the light-emitting side substrate and an alignment axis directions 222 and 242 of the light incident side substrate coincide with each other.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present disclosure relates to a polarization modulation element and a stereoscopic image display device. [Background technology]

[0002] Display devices, optical switches, and the like equipped with a polarization modulation element using twisted nematic liquid crystal are known. For example, Patent Document 1 discloses a three-dimensional display device equipped with a display device that alternately displays two two-dimensional images, a polarizing plate that outputs light emitted from the display device as polarized light, a polarization switching device (polarization modulation element) that switches the polarization direction of the light emitted from the polarizing plate, and a polarized bifocal lens. Patent Document 2 discloses a liquid crystal optical switch equipped with a liquid crystal polarization rotator (polarization modulation element) consisting of multiple liquid crystal cells.

[0003] In the multiple liquid crystal cells that make up the liquid crystal polarization rotator of Patent Document 2, the ratio of cell thickness to twist angle is approximately equal, the twist directions are the same, and the liquid crystal director azimuth angles of the liquid crystal layer in contact with the light-emitting substrate and the liquid crystal director azimuth angles of the liquid crystal layer in contact with the light-incident substrate between the liquid crystal cells are approximately equal. As a result, the cell thickness of each liquid crystal cell is thinned, thereby realizing a reduction in the response time of the liquid crystal cell (i.e., the liquid crystal optical switch). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-129983 A [Patent Document 2] JP 2003-75800 A Summary of the Invention [Problem to be solved by the invention]

[0005] In a TN (Twisted Nematic) cell, the liquid crystal molecules near the interface between the liquid crystal layer and the substrate (alignment film) are unlikely to respond to the applied voltage, so birefringence due to the liquid crystal molecules remains near the interface. In a 90° TN cell, in which the liquid crystal director azimuth angle of the liquid crystal layer in contact with the light-incident substrate and the liquid crystal director azimuth angle of the liquid crystal layer in contact with the light-exit substrate are mutually perpendicular, the liquid crystal director azimuth angle near the interface can be set to 0° and 90° with respect to the polarization direction of the incident linearly polarized light. In this case, linearly polarized light that enters a 90° TN cell is not affected by the birefringence remaining near the interface between the light-incident substrate and the light-exit substrate, and is emitted as linearly polarized light while maintaining its polarization state.

[0006] In Patent Document 2, the response time is shortened by dividing a 90° TN cell into multiple TN liquid crystal cells. When a 90° TN cell is divided into multiple TN cells, there are substrates (light incident side substrate and light exit side substrate) whose liquid crystal director azimuth angle near the interface is not 0° or 90° with respect to the polarization direction of linearly polarized light. Therefore, when linearly polarized light is incident while a voltage is applied, the light emitted from the liquid crystal optical switch of Patent Document 2 becomes elliptically polarized light due to residual birefringence, and the intensity of the polarized component having the desired polarization direction decreases. In addition, if a high voltage is applied to the TN cell to make the liquid crystal molecules near the interface respond, power consumption increases and there is also a risk of the TN cell being short-circuited.

[0007] The present disclosure has been made in consideration of the above circumstances, and aims to provide a polarization modulation element and a stereoscopic image display device that can emit a polarized component having a desired polarization direction with high intensity at a low voltage. [Means for solving the problem]

[0008] In order to achieve the above object, a polarization modulation element according to a first aspect comprises: The liquid crystal display device includes N (N is an integer of 3 or more) twisted nematic liquid crystal cells having the same twist direction, Each of the twisted nematic liquid crystal cells has a light-incident side substrate and a light-emitting side substrate that sandwich a liquid crystal therebetween, The sum of the twist angles of the twisted nematic liquid crystal cells is 90°; The twisted nematic liquid crystal cells are stacked in order with the light incident side substrate of one of the twisted nematic liquid crystal cells facing the light exit side substrate of the other of the twisted nematic liquid crystal cells, In at least one of the adjacent twisted nematic liquid crystal cells, an alignment axis direction of the light exit side substrate of one of the twisted nematic liquid crystal cells is perpendicular to an alignment axis direction of the light incident side substrate of the other of the twisted nematic liquid crystal cells; In the adjacent twisted nematic liquid crystal cells, excluding the at least one adjacent twisted nematic liquid crystal cell, the alignment axis direction of the light-exiting substrate of one of the twisted nematic liquid crystal cells is consistent with the alignment axis direction of the light-incident substrate of the other of the twisted nematic liquid crystal cells.

[0009] A stereoscopic image display device according to a second aspect comprises: The above polarization modulation element, a display unit that sequentially displays a first image and a second image and outputs a display light of the first image and a display light of the second image as polarized light having a polarization direction in a predetermined first direction and that is incident on the polarization modulation element; a polarized bifocal lens into which the light emitted from the polarization modulation element is incident and whose focal length with respect to the light emitted from the polarization modulation element varies depending on the polarization direction of the light, the first image and the second image are two-dimensional images obtained by projecting a display object from a viewer's side onto a first display surface and a second display surface that are located at different positions in a depth direction as viewed from the viewer, respectively; the polarization modulation element, when the polarized light is display light for the first image, outputs the polarized light while maintaining the polarization direction of the polarized light in the predetermined first direction, and, when the polarized light is display light for the second image, changes the polarization direction of the polarized light to a second direction perpendicular to the predetermined first direction and outputs the polarized light, thereby switching the polarization direction of the output light between the predetermined first direction and the second direction, The polarized bifocal lens forms the first image and the second image as virtual images on the first display surface and the second display surface, respectively. Effect of the Invention

[0010] According to the present disclosure, in at least one adjacent twisted nematic liquid crystal cell, the alignment axis direction of the light-exiting substrate of one twisted nematic liquid crystal cell is perpendicular to the alignment axis direction of the light-incident substrate of the other twisted nematic liquid crystal cell, thereby canceling out the birefringence remaining near the interface between the liquid crystal layer and the substrate in the twisted nematic liquid crystal cell, and enabling polarized light with high light intensity in the desired polarization direction to be emitted at a low voltage. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing a cross section of a polarization modulation element according to a first embodiment. [Diagram 2] FIG. 1 is a schematic diagram showing a cross section of a TN cell according to embodiment 1. [Diagram 3] FIG. 2 is a schematic diagram showing an orientation axis direction according to the first embodiment. [Figure 4] FIG. 2 is a diagram showing the alignment and alignment axis direction of nematic liquid crystal in a first TN cell in accordance with the first embodiment. [Diagram 5] FIG. 4 is a diagram showing the alignment and alignment axis direction of nematic liquid crystal in a second TN cell in accordance with the first embodiment. [Figure 6] FIG. 11 is a diagram showing the alignment and alignment axis direction of nematic liquid crystal in a third TN cell in accordance with the first embodiment. [Figure 7] FIG. 11 is a diagram showing the alignment and alignment axis direction of nematic liquid crystal in a fourth TN cell in accordance with the first embodiment. [Figure 8] FIG. 3 is a schematic diagram showing the alignment state of nematic liquid crystal of the polarization modulation element in the initial state according to the first embodiment. [Figure 9] FIG. 2 is a schematic diagram showing the alignment state of nematic liquid crystal of the polarization modulation element in the ON state according to the first embodiment. [Figure 10]FIG. 11 is a diagram showing the polarization state of light emitted from a second TN cell in the ON state according to the first embodiment. [Figure 11] FIG. 11 is a diagram showing the polarization state of light emitted from a third TN cell in the ON state according to the first embodiment. [Figure 12] FIG. 4 is a diagram showing the polarization state of emitted light in an ON state according to the first embodiment. [Figure 13] FIG. 4 is a diagram showing the relationship between the voltage applied to each TN cell and the polarization contrast in the first embodiment. [Figure 14] 10 is a schematic diagram showing the alignment state of nematic liquid crystal of a polarization modulation element in the ON state according to Comparative Example 1. FIG. [Figure 15] 11 is a diagram showing the polarization state of emitted light in an ON state according to Comparative Example 1. FIG. [Figure 16] 5 is a schematic diagram showing a cross section of a polarization modulation element according to embodiment 2. FIG. [Figure 17] FIG. 11 is a diagram showing the alignment and alignment axis direction of nematic liquid crystal in a first TN cell according to the second embodiment. [Figure 18] FIG. 11 is a diagram showing the alignment and alignment axis direction of nematic liquid crystal in a second TN cell according to the second embodiment. [Figure 19] FIG. 11 is a diagram showing the alignment and alignment axis direction of nematic liquid crystal in a third TN cell according to the second embodiment. [Figure 20] FIG. 11 is a diagram showing the relationship between the voltage applied to each TN cell and the polarization contrast in the second embodiment. [Figure 21] FIG. 11 is a diagram showing the polarization contrast and the optimum voltage according to the second embodiment. [Figure 22] FIG. 4 is a schematic diagram showing a birefringent plate according to a second embodiment. [Diagram 23] FIG. 4 is a schematic diagram showing a birefringent plate according to a second embodiment. [Figure 24] FIG. 4 is a schematic diagram showing a birefringent plate according to a second embodiment. [Diagram 25] FIG. 11 is a schematic diagram showing an orientation model according to the second embodiment. [Figure 26] FIG. 11 is a diagram showing the relationship between the voltage applied to a TN cell and the birefringence remaining in the TN cell in the ON state according to the second embodiment. [Figure 27] FIG. 11 is a diagram showing the alignment and alignment axis direction of nematic liquid crystal in a second TN cell according to the third embodiment. [Figure 28] FIG. 11 is a diagram showing the alignment and alignment axis direction of nematic liquid crystal in a third TN cell according to the third embodiment. [Figure 29] FIG. 11 is a diagram showing the alignment and alignment axis direction of nematic liquid crystal in a fourth TN cell according to the third embodiment. [Diagram 30] FIG. 11 is a diagram showing the relationship between the voltage applied to each TN cell and the polarization contrast in the third embodiment. [Diagram 31] FIG. 11 is a diagram showing the polarization contrast and the optimum voltage according to the third embodiment. [Diagram 32] FIG. 11 is a diagram showing the orientation axis direction of a TN cell according to embodiment 4. [Diagram 33] FIG. 11 is a diagram showing the relationship between the voltage applied to each TN cell and the polarization contrast in accordance with the fourth embodiment. [Diagram 34] FIG. 11 is a diagram showing the orientation axis direction of a TN cell according to embodiment 5. [Diagram 35] FIG. 11 is a diagram showing the relationship between the voltage applied to each TN cell and the polarization contrast in accordance with the fifth embodiment. [Diagram 36] FIG. 13 is a diagram showing the polarization contrast and the optimum voltage according to the fifth embodiment. [Figure 37] FIG. 13 is a schematic diagram showing a stereoscopic image display device according to a sixth embodiment. [Figure 38] FIG. 13 is a plan view showing a liquid crystal display panel according to embodiment 6. [Figure 39] FIG. 11 is a cross-sectional view showing a polarized bifocal lens according to embodiment 6. [Diagram 40] FIG. 13 is a block diagram showing a control unit according to the sixth embodiment. [Diagram 41] FIG. 13 is a diagram illustrating a hardware configuration of a control unit according to a sixth embodiment. [Diagram 42]FIG. 13 is a diagram showing the orientation axis direction of a TN cell according to Modification 1. [Diagram 43] FIG. 11 is a diagram showing the orientation axis direction of a TN cell according to Modification 2. [Diagram 44] FIG. 13 is a schematic diagram showing the light distribution axis direction of a first TN cell and the polarization direction of incident light according to a modified example. [Diagram 45] FIG. 11 is a diagram showing the polarization contrast in the initial alignment state of the polarization modulation element of embodiment 1 according to a modified example. [Diagram 46] FIG. 13 is a diagram showing the polarization contrast in the initial alignment state of the polarization modulation element of embodiment 3 according to a modified example. [Figure 47] FIG. 13 is a diagram showing the polarization contrast in the initial alignment state of the polarization modulation element of embodiment 5 according to a modified example. [Figure 48] FIG. 13 is a diagram showing the polarization contrast in the initial alignment state of the polarization modulation element of Comparative Example 1 according to the modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a polarization modulation element and a stereoscopic image display device according to an embodiment will be described with reference to the drawings.

[0013] <Embodiment 1> A polarization modulation element 10 according to this embodiment will be described with reference to Figs. 1 to 15. As shown in Fig. 1, the polarization modulation element 10 includes four (N=4) twisted nematic liquid crystal cells 110 to 140 having the same twist direction. The polarization modulation element 10 is formed by sequentially stacking the twisted nematic liquid crystal cells 110 to 140 via an adhesive layer (not shown). In a state where no voltage is applied (initial alignment state), the polarization modulation element 10 rotates the polarization direction of linearly polarized light (incident light) L1 incident on the twisted nematic liquid crystal cell 110 by 90° and outputs the light as output light L2. In a state where a voltage is applied (ON state), the polarization modulation element 10 maintains the polarization direction of the linearly polarized light L1 and attempts to output the light as output light L2.

[0014] In this specification, for ease of understanding, the right direction (right direction on the paper) of the polarization modulation element 10 in Fig. 1 is described as the +X direction, the upward direction (upward on the paper) as the +Z direction, and the direction perpendicular to the +X direction and the +Z direction (into the paper) as the +Y direction. The polarization direction of the linearly polarized light L1 incident on the polarization modulation element 10 is described as the X direction. A twisted nematic liquid crystal cell is also referred to as a TN (Twisted Nematic) cell, and is also referred to as the m-th TN cell (m is an integer of 1 or more) from the side where the linearly polarized light L1 is incident. Furthermore, twisted nematic liquid crystal cells (TN cells) are also collectively referred to as a twisted nematic liquid crystal cell 100 or a TN cell 100.

[0015] First, the TN cell 100 will be described. As shown in Fig. 2, the TN cell 100 includes a light incident side substrate 102, a light emitting side substrate 104, and a nematic liquid crystal 106. As shown in Fig. 1, the TN cells 100 are stacked in order, with the light incident side substrate 102 of one TN cell 100 facing the light emitting side substrate 104 of the other TN cell 100.

[0016] The light-incident side substrate 102 is a substrate located on the side where linearly polarized light L1 is incident, as shown in Fig. 1. The light-incident side substrate 102 faces the light-emitting side substrate 104, as shown in Fig. 2. The light-incident side substrate 102 and the light-emitting side substrate 104 sandwich a nematic liquid crystal 106 between them. The light-incident side substrate 102 is, for example, a glass substrate. The light-incident side substrate 102 has a translucent electrode 102b and an alignment film 102c on a main surface 102a facing the light-emitting side substrate 104.

[0017] The transparent electrode 102b of the light-incident side substrate 102 is formed from ITO (Indium Tin Oxide) over the entire main surface 102a. The alignment film 102c of the light-incident side substrate 102 aligns the nematic liquid crystal 106 in a predetermined direction. The alignment film 102c of the light-incident side substrate 102 is, for example, a polyimide alignment film. The alignment of the nematic liquid crystal 106 will be described later.

[0018] The light-emitting side substrate 104 is a substrate located on the side from which the emitted light L2 is emitted, as shown in Fig. 1. The light-incident side substrate 102 and the light-emitting side substrate 104 are bonded together with a sealant 108, as shown in Fig. 2. The light-emitting side substrate 104 is, for example, a glass substrate. The light-emitting side substrate 104 has a translucent electrode 104b and an alignment film 104c on a main surface 104a facing the light-incident side substrate 102.

[0019] The light-transmitting electrode 104b of the light-emitting substrate 104 is made of ITO and covers the entire main surface 104a. The alignment film 104c of the light-emitting substrate 104 aligns the nematic liquid crystal 106 in a predetermined direction. The alignment film 104c of the light-emitting substrate 104 is, for example, a polyimide alignment film.

[0020] The nematic liquid crystal 106 is sandwiched between the light incident side substrate 102 and the light exit side substrate 104. In this embodiment, the refractive index anisotropy Δn of the nematic liquid crystal 106 is 0.1948 at a wavelength of 380 nm and 0.1403 at a wavelength of 535 nm. The dielectric constant anisotropy Δε of the nematic liquid crystal 106 is 4.8 at 20° C. The cell thickness (thickness of the nematic liquid crystal 106) of the TN cell 100 of this embodiment is 5.47 μm. The refractive index anisotropy Δn and the cell thickness of the nematic liquid crystal 106 are set to values ​​such that, in the initial orientation state, the polarization direction of linearly polarized light L1 having a predetermined wavelength is rotated by 90° and is output from the polarization modulation element 10 as output light L2.

[0021] Here, the orientation of the nematic liquid crystal 106 (i.e., the liquid crystal molecules 106M) will be described. The nematic liquid crystal 106, like the nematic liquid crystal of a general TN cell, is twisted by the alignment film 102c of the light-incident side substrate 102 and the alignment film 104c of the light-emitting side substrate 104 in a state where no voltage is applied (initial alignment state). In this specification, as shown in FIG. 3, the initial alignment direction of the liquid crystal molecules 106M at the interface between the nematic liquid crystal 106 and the alignment film 102c or the alignment film 104c is defined as the alignment axis direction 200 of the light-incident side substrate 102 or the light-emitting side substrate 104. The alignment axis directions of the TN cells 110 to 140 are collectively referred to as the alignment axis direction 200.

[0022] In the initial alignment state of the TN cells 110-140, the nematic liquid crystal 106 is aligned and twisted clockwise when viewed in plan from the +Z side, as shown in Figures 4-7. The twist angles α of the TN cells 110-140 (i.e., the twist angles of the nematic liquid crystal 106) are 22.5°, and the sum of the twist angles α of the TN cells 110-140 is 90°. On the other hand, the alignment axis directions 200 of the TN cells 110-140 are different.

[0023] Specifically, in the first TN cell 110 into which the linearly polarized light L1 is incident, the alignment axis direction 212 of the light-incident side substrate 102 is the +X direction, as shown in Fig. 4. The alignment axis direction 214 of the light-exit side substrate 104 of the TN cell 110 is tilted by 22.5° clockwise with respect to the +X direction.

[0024] 5, in the second TN cell 120, the alignment axis direction 222 of the light-incident side substrate 102 is tilted by 22.5° clockwise with respect to the +X direction and coincides with the alignment axis direction 214 of the light-exit side substrate 104 of the TN cell 110. The alignment axis direction 224 of the light-exit side substrate 104 of the TN cell 120 is tilted by 45° clockwise with respect to the +X direction.

[0025] 6, in the third TN cell 130, the alignment axis direction 232 of the light-incident side substrate 102 is tilted 135° clockwise with respect to the +X direction and is perpendicular to the alignment axis direction 224 of the light-exit side substrate 104 of the TN cell 120. The alignment axis direction 234 of the light-exit side substrate 104 of the TN cell 130 is tilted 157.5° clockwise with respect to the +X direction.

[0026] 7, in the fourth TN cell 140, the alignment axis direction 242 of the light-incident side substrate 102 is tilted 157.5° clockwise with respect to the +X direction and coincides with the alignment axis direction 234 of the light-exit side substrate 104 of the TN cell 130. The alignment axis direction 224 of the light-exit side substrate 104 of the TN cell 140 is rotated 180° clockwise with respect to the +X direction.

[0027] In this embodiment, as described later, in the adjacent second (N / 2th) TN cell 120 and third ((N / 2)+1th) TN cell 130, the alignment axis direction 224 of the light-emitting side substrate 104 of the TN cell 120 and the alignment axis direction 232 of the light-incident side substrate 102 of the TN cell 130 are perpendicular to each other, so that in the ON state, the birefringence of the nematic liquid crystal 106 remaining near the interface is offset. As a result, in the ON state, the polarization modulation element 10 can emit a polarized component having a desired polarization direction with high intensity.

[0028] Next, the operation of the polarization modulation element 10 will be described. FIG. 8 is a schematic diagram showing the alignment state of the nematic liquid crystal 106 in a state where no voltage is applied (initial alignment state). FIG. 9 is a schematic diagram showing the alignment state of the nematic liquid crystal 106 in a state where a predetermined voltage (for example, 20 V) is applied to each of the TN cells 110 to 140 (ON state). FIG. 10 is a diagram showing the polarization state of the output light L12 output from the second TN cell 120 in the ON state, and FIG. 11 is a diagram showing the polarization state of the output light L13 output from the third TN cell 130 in the ON state. Furthermore, FIG. 12 is a diagram showing the polarization state of the output light L2 output from the polarization modulation element 10 in the ON state. Note that the light incident side substrate 102, the light exit side substrate 104, etc. are omitted in FIGS. 8 and 9. 10 to 12 show the locus of the tip of the electric field vector of the emitted light, with the electric field intensity (light intensity) of linearly polarized light L1 having a polarization direction in the X direction that is incident on the polarization modulation element 10 being set to 1. The wavelength of the linearly polarized light L1 is 380 nm.

[0029] In the initial alignment state, the nematic liquid crystals 106 of the TN cells 110-140 are twisted as shown in Fig. 8. The nematic liquid crystals 106 of the TN cells 110-140 are twisted in the same direction, and the sum of the twist angles α is 90°. By setting the refractive index anisotropy Δn and cell thickness of the nematic liquid crystals 106 as described above, when linearly polarized light L1 is incident on the polarization modulation element 10, the polarization modulation element 10 rotates the polarization direction of the linearly polarized light L1 at a predetermined wavelength by 90° and emits output light L2 having a polarization direction in the Y direction.

[0030] In the ON state (a state in which a predetermined voltage is applied between the translucent electrode 102b of the light-incident side substrate 102 and the translucent electrode 104b of the light-emitting side substrate 104), the nematic liquid crystal 106 of each of the TN cells 110-140 is aligned perpendicular to the light-incident side substrate 102 or the light-emitting side substrate 104, except for liquid crystal molecules 106M near the interface between the nematic liquid crystal 106 and the light-incident side substrate 102 or the light-emitting side substrate 104, as shown in Fig. 9. In this case, the outgoing light L12 emitted from the second TN cell 120 becomes elliptically polarized light close to circularly polarized light due to the birefringence of the nematic liquid crystal 106 remaining in the TN cells 110 and 120, as shown in Fig. 10.

[0031] In this embodiment, the alignment axis direction 224 of the light exit side substrate 104 of the TN cell 120 and the alignment axis direction 232 of the light entrance side substrate 102 of the TN cell 130 are perpendicular to each other, so that the birefringence of the nematic liquid crystal 106 remaining in the TN cell 110 and the TN cell 120 is offset by the birefringence of the nematic liquid crystal 106 remaining in the TN cell 130. Therefore, as shown in FIG. 11, the outgoing light L13 emitted from the third TN cell 130 becomes elliptically polarized light close to linearly polarized light having a polarization direction in the X direction. Furthermore, as shown in FIG. 12, the outgoing light L2 is emitted from the polarization modulation element 10 (TN cell 140) as elliptically polarized light close to linearly polarized light having a polarization direction in the X direction.

[0032] Here, the polarization contrast pCR is defined. The polarization contrast pCR indicates the ratio of the transmitted light intensity I2 when the output light L2 is transmitted through an analyzer having a transmission axis parallel to the polarization direction of the desired polarization component to the transmitted light intensity I1 when the output light L2 is transmitted through an analyzer having a transmission axis perpendicular to the polarization direction of the desired polarization component, and is expressed as pCR=I2 / I1. A higher polarization contrast pCR indicates a higher intensity of the polarization component having the desired polarization direction.

[0033] In the ON state, the polarization modulation element 10 attempts to emit the output light L2 while maintaining the polarization direction of the linearly polarized light L1, so that the polarization direction of the desired polarization component in the ON state is the X direction. In this embodiment, as shown in FIG. 12, elliptically polarized light close to linearly polarized light having a polarization direction in the X direction is emitted from the polarization modulation element 10 as the output light L2, so that the polarization contrast pCR of the polarization modulation element 10 in the ON state is high. For example, as shown in FIG. 13, the polarization contrast pCR of the polarization modulation element 10 is 40 when 20 V is applied to each of the TN cells 110-140. In order to make the polarization contrast pCR 20, it is necessary to apply 17 V to each of the TN cells 110-140.

[0034] On the other hand, in the polarization modulation element 50A (Comparative Example 1, FIG. 14) in which the alignment axis direction 232 of the TN cell 130 coincides with the alignment axis direction 224 of the TN cell 120, when the linearly polarized light L1 is incident on the polarization modulation element 50A in the ON state (20V), the output light L2A shown in FIG. 15 is output. The output light L2A is closer to circular polarization than the output light L2 of the polarization modulation element 10 and is tilted toward the Y direction side than the output light L2 of the polarization modulation element 10. As a result, the polarization modulation element 50A of Comparative Example 1 has a low polarization contrast pCR (polarization contrast pCR=0.5), and it is not possible to obtain a sufficient amount of polarized components having the desired polarization direction. In addition, as shown in FIG. 13, the polarization modulation element 50A of Comparative Example 1 requires a very high voltage to obtain a polarization contrast pCR comparable to that of the polarization modulation element 10.

[0035] In the polarization modulation element 50A of Comparative Example 1, the alignment axis direction 232 of the third TN cell 130 is tilted 45° clockwise with respect to the +X direction and coincides with the alignment axis direction 224 of the TN cell 120, as shown in Fig. 14. In the polarization modulation element 50A of Comparative Example 1, the alignment axis direction 242 of the fourth TN cell 140 coincides with the alignment axis direction 234 of the third TN cell 130, and the alignment axis direction 244 of the fourth TN cell 140 is the -Y direction. The other configurations of the polarization modulation element 50A of Comparative Example 1 are similar to those of the polarization modulation element 10.

[0036] As described above, in the polarization modulation element 10, in the adjacent second TN cell 120 and third TN cell 130, the alignment axis direction 224 of the light-emission side substrate 104 of the TN cell 120 and the alignment axis direction 232 of the light-incident side substrate 102 of the TN cell 130 are perpendicular to each other, so that the polarization modulation element 10 can emit polarized components having the desired polarization direction with high intensity at a low voltage.

[0037] <Embodiment 2> In the first embodiment, the polarization modulation element 10 includes four TN cells 100. The polarization modulation element 10 may include N (N is an integer equal to or greater than 3) TN cells 100. In this embodiment, a polarization modulation element 10 including three TN cells 100 will be described.

[0038] The polarization modulation element 10 of this embodiment includes three TN cells 110 to 130 having the same twist direction, as shown in Fig. 16. The TN cells 110 to 130 are stacked in sequence. The configuration of the TN cells 110 to 130 of this embodiment is the same as that of the TN cell 100 of the first embodiment, except for the cell thickness (5.42 µm) and the orientation axis direction 200.

[0039] In the initial alignment state, as shown in Figures 17 to 19, the nematic liquid crystals 106 of the TN cells 110 to 130 of this embodiment are aligned with a clockwise twist when viewed in plan from the +Z side. The twist angles α of the TN cells 110 to 130 (the twist angles of the nematic liquid crystals 106) are 30°, and the sum of the twist angles α of the TN cells 110 to 130 is 90°. The alignment axis directions 200 of the TN cells 110 to 130 of this embodiment are different, similar to the TN cell 100 of embodiment 1.

[0040] The alignment axis direction 212 of the light-incident side substrate 102 of the first TN cell 110 is the +X direction, as shown in Fig. 17. The alignment axis direction 214 of the light-exit side substrate 104 of the TN cell 110 is tilted 30° clockwise with respect to the +X direction.

[0041] 18, the alignment axis direction 222 of the light-incident side substrate 102 of the second TN cell 120 is tilted 120° clockwise with respect to the +X direction and is perpendicular to the alignment axis direction 214 of the light-exit side substrate 104 of the TN cell 110. The alignment axis direction 224 of the light-exit side substrate 104 of the TN cell 120 is tilted 150° clockwise with respect to the +X direction.

[0042] 19, the alignment axis direction 222 of the light-incident side substrate 102 of the third TN cell 130 is tilted 150° clockwise with respect to the +X direction and coincides with the alignment axis direction 224 of the light-exit side substrate 104 of the TN cell 120. The alignment axis direction 234 of the light-exit side substrate 104 of the TN cell 130 is rotated 180° clockwise with respect to the +X direction.

[0043] FIG. 20 shows the relationship between the voltage applied to each of the TN cells 110-130 in the ON state, and the polarization contrast pCR of the polarization modulation element 10 of this embodiment and the polarization contrast pCR of the polarization modulation element of Comparative Example 2. The polarization modulation element of Comparative Example 2 includes three TN cells 110-130, similar to the polarization modulation element 10 of this embodiment. In the polarization modulation element of Comparative Example 2, the alignment axis direction 222 of the TN cell 120 coincides with the alignment axis direction 214 of the TN cell 110. Specifically, the alignment axis direction 222 of the second TN cell coincides with the alignment axis direction 214 of the TN cell 110, tilted 30° clockwise with respect to the +X direction. In addition, in the polarization modulation element of Comparative Example 2, the alignment axis direction 232 of the third TN cell 130 coincides with the alignment axis direction 224 of the TN cell 120, and the alignment axis direction 234 of the third TN cell 130 is the -Y direction. The other configurations of the polarization modulation element of Comparative Example 2 are similar to those of the polarization modulation element 10 of this embodiment.

[0044] In the polarization modulation element 10 of this embodiment, a high polarization contrast pCR can be obtained at a low voltage, as shown in Fig. 20. That is, the polarization modulation element 10 of this embodiment can emit a polarized component having a desired polarization direction with high intensity at a low voltage. For example, in order to set the polarization contrast pCR to 20, it is sufficient to apply 31 V to each of the TN cells 110 to 130.

[0045] Furthermore, in the polarization modulation element 10 of this embodiment, a high polarization contrast pCR can be obtained at a lower voltage by optimizing the voltages applied to the TN cells 110 to 130. For example, as shown in Fig. 21, in order to set the polarization contrast pCR to 20, 14.4 V should be applied to the TN cells 110 and 120, and 6.1 V should be applied to the TN cell 130. A method for determining the optimal voltage will be described below.

[0046] First, each of the TN cells 110 to 130 is modeled as two birefringent plates. Specifically, the TN cell 110 to which a voltage is applied is a birefringent plate 110A having an optical axis 310A in the alignment axis direction 212 of the light-incident side substrate 102, and a birefringent plate 110B having an optical axis 310B in the alignment axis direction 214 of the light-exit side substrate 104, as shown in Fig. 22. The TN cell 120 to which a voltage is applied is a birefringent plate 120A having an optical axis 320A in the alignment axis direction 222 of the light-incident side substrate 102, and a birefringent plate 120B having an optical axis 320B in the alignment axis direction 224 of the light-exit side substrate 104, as shown in Fig. 23. Furthermore, the TN cell 130 to which a voltage is applied becomes a birefringent plate 130A having an optical axis 330A in the alignment axis direction 232 of the light-incident side substrate 102, and a birefringent plate 130B having an optical axis 330B in the alignment axis direction 234 of the light-exiting side substrate 104, as shown in Figure 24.

[0047] Here, a voltage V1 is applied to the TN cell 110, a voltage V2 is applied to the TN cell 120 and the TN cell 130, the thickness of the birefringent plates 110A and 110B is d1, the thickness of the birefringent plates 120A to 130B is d2, and the refractive index anisotropy of the birefringent plates 110A to 130B is Δn. When viewed in a plan view from the +Z side, the crossing angle between the optical axis 310A of the birefringent plate 110A and the optical axis 310B of the birefringent plate 110B, the crossing angle between the optical axis 320A of the birefringent plate 120A and the optical axis 320B of the birefringent plate 120B, and the crossing angle between the optical axis 330A of the birefringent plate 130A and the optical axis 330B of the birefringent plate 130B are φ (φ=30°). Furthermore, the crossing angle between the optical axis 310B of the birefringent plate 110B and the optical axis 320A of the birefringent plate 120A is θ (θ=90°). The optical axis 320B of the birefringent plate 120B and the optical axis 330A of the birefringent plate 130A are coincident. The crossing angle φ corresponds to the twist angle α (α=30°) of the TN cell 100. The crossing angle θ corresponds to an angle difference of 90° between the alignment axis direction 222 of the light-incident side substrate 102 of the TN cell 120 and the alignment axis direction 214 of the light-exit side substrate 104 of the TN cell 110.

[0048] The Jones matrix of a birefringent plate is expressed by the following formula (1), and when viewed in a plane from the +Z side, the Jones matrix of a birefringent plate whose optical axis is inclined at an angle φ with respect to incident light L1 having a polarization direction in the X direction is expressed by the following formula (2), so the Jones matrices of each of the birefringent plates 110A to 130B are expressed by the following formulas (3) to (8).

[0049]

number

number

[0050]

number

number

number

number

number

number

[0051] Moreover, the Jones matrix of the entire birefringent plates 110A to 130B (that is, equivalent to the entire polarization modulation element 10) is expressed by the following formula (9), where Γ1 and Γ2 are expressed by the following formulas (10) and (11), where λ is the wavelength of the incident light L1.

[0052]

number

number

number

[0053] Next, the polarization contrast pCR is expressed using the Jones matrix. If the Jones matrix of the entire birefringent plates 110A to 130B is expressed by the following formula (12), when the output light L2 is transmitted through an analyzer having a transmission axis perpendicular to the polarization direction (X direction) of the desired polarization component, the transmitted light is expressed by the following formula (13), and the transmitted light intensity I1 is expressed by the following formula (14). Here, the symbol * denotes complex conjugate.

[0054]

number

number

number

[0055] Furthermore, when the output light L2 is transmitted through an analyzer having a transmission axis parallel to the polarization direction (X direction) of the desired polarization component, the transmitted light is expressed by the following equation (15), and the transmitted light intensity I2 is expressed by the following equation (16).

[0056]

number

number

[0057] From the above formulas (9) to (11), (14), and (16), the polarization contrast pCR is expressed by the following formulas (17) and (18).

[0058]

number

number

[0059] On the other hand, the relationship between the voltage V applied to the TN cell 100 and the birefringence Δnd remaining in the TN cell 100 in the ON state can be calculated as follows.

[0060] First, as shown in Fig. 25, an orientation model is set in which the angle δ of the liquid crystal director with respect to the principal surface of the substrate increases as the thickness h from the principal surface of the substrate increases. The ordinary refractive index of the liquid crystal is no, the extraordinary refractive index is ne, the refractive index in the orientation axis direction of the liquid crystal at the position (x, y, z) is neff(x, y, z), the number of divisions into which the thickness h is divided into a plurality of regions in the thickness direction is M, the refractive index anisotropy (phase difference) of the i-th divided region is Δni, the refractive index anisotropy (phase difference) at the position (x, y, z) is Δn(x, y, z), and the cell thickness of the TN cell 100 is d. The birefringence Δnd is expressed by the following formulas (19) to (21).

[0061]

number

number

number

[0062] The relationship between the applied voltage V and the angle δ of the liquid crystal director with respect to the main surface of the substrate is obtained, for example, by a liquid crystal simulator (LCD master manufactured by Shintech Co., Ltd.) From the obtained relationship between the applied voltage V and the angle δ of the liquid crystal director with respect to the main surface of the substrate and the above equations (19) to (21), for example, the relationship between the voltage V applied to the TN cell 100 and the birefringence Δnd remaining in the TN cell 100 in the ON state, as shown in FIG.

[0063] By determining a combination that satisfies the set polarization contrast pCR and minimizes the sum of the voltage V1 applied to the TN cell 110 and the voltage V2 applied to the TN cell 120 and the TN cell 130 from the relationship between the applied voltage V and the birefringence Δnd remaining in the TN cell 100 in the ON state and from the above equations (17) and (18), the optimal voltages to be applied to the TN cells 110 to 130 can be obtained.

[0064] As described above, in the polarization modulation element 10 of the present embodiment, the alignment axis direction 214 of the light-emitting side substrate 104 of the TN cell 110 and the alignment axis direction 222 of the light-incident side substrate 102 of the TN cell 120 are perpendicular to each other in the first TN cell 110 and the second TN cell 120, which are adjacent to each other, so that the polarization modulation element 10 of the present embodiment can emit a polarization component having a desired polarization direction with high intensity at a low voltage. Furthermore, by optimizing the voltages V1 and V2 applied to the TN cells 110 to 130, a high polarization contrast pCR can be obtained at a lower voltage. That is, by optimizing the voltages V1 and V2 applied to the TN cells 110 to 130, the polarization modulation element 10 of the present embodiment can emit a polarization component having a desired polarization direction with high intensity at a lower voltage.

[0065] <Embodiment 3> In the first embodiment, in one adjacent TN cell 100 (the second TN cell 120 and the third TN cell 130), the alignment axis direction 200 of the light-emitting side substrate 104 and the alignment axis direction 200 of the light-incident side substrate 102 are orthogonal. In the polarization modulation element 10, it is sufficient that in at least one adjacent TN cell 100, the alignment axis direction 200 of the light-emitting side substrate 104 and the alignment axis direction 200 of the light-incident side substrate 102 are orthogonal.

[0066] The polarization modulation element 10 of this embodiment includes stacked TN cells 110-140, similar to the polarization modulation element 10 of embodiment 1. In the polarization modulation element 10 of this embodiment, in two adjacent TN cells 100 (the first TN cell 110 and the second TN cell 120, and the third TN cell 130 and the fourth TN cell 140), the alignment axis direction 200 of the light exit side substrate 104 and the alignment axis direction 200 of the light incident side substrate 102 are perpendicular to each other. The configuration of the TN cells 110-140 of this embodiment is similar to that of the TN cells 110-140 of embodiment 1, except for the alignment axis direction 200.

[0067] In the TN cell 110 of this embodiment, the alignment axis direction 212 of the light-incident side substrate 102 is the +X direction, as in the TN cell 110 of embodiment 1. Also, the alignment axis direction 214 of the light-exiting side substrate 104 is tilted by 22.5° clockwise with respect to the +X direction.

[0068] 27, in the TN cell 120 of this embodiment, the alignment axis direction 222 of the light-incident side substrate 102 is tilted by 112.5° clockwise with respect to the +X direction and is perpendicular to the alignment axis direction 214 of the light-exiting side substrate 104 of the TN cell 110. The alignment axis direction 224 of the light-exiting side substrate 104 is tilted by 135° clockwise with respect to the +X direction.

[0069] 28, in the TN cell 130 of this embodiment, the alignment axis direction 232 of the light-incident side substrate 102 is tilted 135° clockwise with respect to the +X direction and coincides with the alignment axis direction 224 of the light-exit side substrate 104 of the TN cell 120. The alignment axis direction 234 of the light-exit side substrate 104 is tilted 157.5° clockwise with respect to the +X direction.

[0070] 29, in the TN cell 140 of this embodiment, the alignment axis direction 242 of the light-incident side substrate 102 is rotated 247.5° clockwise with respect to the +X direction and is perpendicular to the alignment axis direction 234 of the light-exit side substrate 104 of the TN cell 130. The alignment axis direction 244 of the light-exit side substrate 104 is rotated 270° clockwise with respect to the +X direction.

[0071] Fig. 30 shows the relationship between the voltage applied to each of the TN cells 110-140 in the ON state and the polarization contrast pCR of the polarization modulation element 10 of this embodiment and the polarization contrast pCR of the polarization modulation element of Comparative Example 1. As shown in Fig. 30, the polarization modulation element 10 of the embodiment can obtain a high polarization contrast pCR at a low voltage. That is, the polarization modulation element 10 of the embodiment can emit a polarized component having a desired polarization direction with high intensity at a low voltage. For example, in order to set the polarization contrast pCR to 20, 36 V should be applied to each of the TN cells 110-140.

[0072] Furthermore, in the polarization modulation element 10 of this embodiment, similarly to the polarization modulation element 10 of embodiment 2, a high polarization contrast pCR can be obtained at a lower voltage by optimizing the voltages applied to the TN cells 110 to 140. For example, as shown in FIG. 31, in order to set the polarization contrast pCR to 20, 5.4 V should be applied to the TN cell 110, 11.8 V should be applied to the TN cells 120 and 130, and 5.9 V should be applied to the TN cell 140. Furthermore, when the voltages applied to the TN cells 110 to 140 are optimized, a high polarization contrast pCR can be obtained at a lower voltage than the polarization modulation element 10 of embodiment 1. The optimal voltage of this embodiment is determined by the same method as the optimal voltage of embodiment 2.

[0073] As described above, in the polarization modulation element 10 of this embodiment, the orientation axis direction 200 of the light-emitting side substrate 104 and the orientation axis direction 200 of the light-incident side substrate 102 are perpendicular to each other in two adjacent TN cells 100, and a polarized component having a desired polarization direction can be output with high intensity at a low voltage. Furthermore, by optimizing the voltage applied to the TN cells 100, the polarization modulation element 10 of this embodiment can output a polarized component having a desired polarization direction with high intensity at an even lower voltage.

[0074] <Embodiment 4> In the first and third embodiments, the polarization modulation element 10 includes four TN cells 100. The polarization modulation element 10 may include six TN cells 100 (N=6).

[0075] The polarization modulation element 10 of this embodiment includes six TN cells 100 with the same twist direction. The TN cells 100 of this embodiment are stacked in sequence, with the light-incident side substrate 102 of one TN cell 100 facing the light-exit side substrate 104 of the other TN cell 100. The configuration of the TN cell 100 of this embodiment is the same as that of the TN cell 100 of embodiment 1, except for the cell thickness (3.65 μm) and the orientation axis direction 200.

[0076] In the initial alignment state, the nematic liquid crystal 106 of the TN cell 100 of this embodiment is aligned in a clockwise twisted manner when viewed in plan from the +Z side. The twist angle α of the TN cell 100 (the twist angle of the nematic liquid crystal 106) is 15°, and the sum of the twist angles α of the TN cells 100 is 90°.

[0077] Fig. 32 shows the alignment axis direction 200 of the TN cell 100 of this embodiment. As shown in Fig. 32, in this embodiment, in the third (N / 2th) TN cell 100 and the fourth ((N / 2)+1th) TN cell 100, the alignment axis direction 200 of the light-emitting side substrate 104 and the alignment axis direction 200 of the light-incident side substrate 102 are perpendicular to each other. In the other adjacent TN cells 100, the alignment axis direction 200 of the light-emitting side substrate 104 and the alignment axis direction 200 of the light-incident side substrate 102 are the same.

[0078] Fig. 33 shows the relationship between the voltage applied to each of the TN cells 100 and the polarization contrast pCR of the polarization modulation element 10 of this embodiment and the polarization contrast pCR of the polarization modulation element of Comparative Example 3. As shown in Fig. 33, the polarization modulation element 10 of the embodiment can obtain a high polarization contrast pCR at a low voltage. For example, in order to make the polarization contrast pCR 20, it is sufficient to apply 18 V to each of the TN cells 100.

[0079] The polarization modulation element of Comparative Example 3 includes six TN cells 100 with the same twist direction (twist angle α: 15°) like the polarization modulation element 10 of this embodiment. In the polarization modulation element of Comparative Example 3, the alignment axis direction 200 of the light exit side substrate 104 and the alignment axis direction 200 of the light incident side substrate 102 are the same in any adjacent TN cells 100. The other configurations of the polarization modulation element of Comparative Example 3 are the same as those of the polarization modulation element 10 of this embodiment.

[0080] As described above, in this embodiment, a high polarization contrast pCR can be obtained at a low voltage. Therefore, the polarization modulation element 10 of this embodiment can emit a polarized component having a desired polarization direction with high intensity at a low voltage.

[0081] <Embodiment 5> In the fourth embodiment, in one TN cell 100 (the third TN cell 100 and the fourth TN cell 100), the alignment axis direction 200 of the light-emitting side substrate 104 and the alignment axis direction 200 of the light-incident side substrate 102 are orthogonal. In a polarization modulation element 10 including six (N=6) TN cells 100, the alignment axis direction 200 of the light-emitting side substrate 104 and the alignment axis direction 200 of the light-incident side substrate 102 may also be orthogonal in two adjacent TN cells 100.

[0082] The configuration of the TN cell 100 of this embodiment is similar to that of the TN cell 100 of embodiment 4, except for the cell thickness (4.0 μm) and the alignment axis direction 200. As shown in Fig. 34, in this embodiment, the alignment axis direction 200 of the light-emitting side substrate 104 and the alignment axis direction 200 of the light-incident side substrate 102 are orthogonal in the first TN cell 100 and the second TN cell 100, and in the fourth TN cell 100 and the fifth TN cell 100. In the other adjacent TN cells 100, the alignment axis direction 200 of the light-emitting side substrate 104 and the alignment axis direction 200 of the light-incident side substrate 102 are the same.

[0083] Fig. 35 shows the relationship between the voltage applied to each of the TN cells 100 and the polarization contrast pCR of the polarization modulation element 10 of this embodiment and the polarization contrast pCR of the polarization modulation element of Comparative Example 4. As shown in Fig. 35, the polarization modulation element 10 of the embodiment can obtain a high polarization contrast pCR at a low voltage. For example, in order to make the polarization contrast pCR 20, it is sufficient to apply 13 V to each of the TN cells 100. The polarization modulation element of Comparative Example 4 is similar to the polarization modulation element of Comparative Example 3, except for the cell thickness (4.0 μm) of the TN cell 100.

[0084] Furthermore, in the polarization modulation element 10 of this embodiment, similarly to the polarization modulation elements 10 of the second and third embodiments, a high polarization contrast pCR can be obtained at a lower voltage by optimizing the voltage applied to the TN cell 100. For example, as shown in FIG. 36, in order to set the polarization contrast pCR to 20, 5.4 V is applied to the first TN cell 100, 17.3 V is applied to the second to fourth TN cells 100, and 11.3 V is applied to the fifth and sixth TN cells 100. In this case, the average value of the voltage applied to one TN cell 100 is 13.3 V. Therefore, when the voltage applied to the TN cell 100 is optimized, a high polarization contrast pCR can be obtained at a lower voltage than the polarization modulation element 10 of the fourth embodiment. The optimal voltage of this embodiment is obtained by the same method as the optimal voltage of the second embodiment.

[0085] As described above, in this embodiment, a high polarization contrast pCR can be obtained at a low voltage. Therefore, the polarization modulation element 10 of this embodiment can emit a polarized component having a desired polarization direction with high intensity at a low voltage.

[0086] <Embodiment 6> In this embodiment, a stereoscopic image display device 510 using the polarization modulation element 10 of any one of the first to fifth embodiments will be described. The polarization modulation element 10 is used in the stereoscopic image display device 510 that displays stereoscopic images by, for example, a DFD (Depth Fused 3D) method. In the stereoscopic image display device 510, the polarization modulation element 10 functions as a polarization switching element.

[0087] The stereoscopic image display device 510 is used as a head-mounted display in combination with, for example, an eyepiece lens. Note that, in this embodiment, a stereoscopic image display device 510 using a monochrome liquid crystal panel will be described as an example.

[0088] As shown in FIG. 37, the stereoscopic image display device 510 includes a display unit 520, a polarization modulation element 10, a polarized bifocal lens 560, and a control unit 580. The display unit 520 sequentially displays a first image and a second image in a time-division manner. The display unit 520 also emits display light L51 representing the first image and the second image as polarized light whose polarization direction is a predetermined first direction. The polarization modulation element 10 switches the polarization direction of the display light L51 emitted from the display unit 520 between a predetermined first direction and a predetermined second direction. The polarized bifocal lens 560 forms the first image and the second image as virtual images on the first display surface 512 and the second display surface 514, respectively. The control unit 580 supplies the display unit 520 with a first image signal representing the first image and a second image signal representing the second image. The control unit 580 also controls switching of the polarization direction of the polarization modulation element 10.

[0089] In this embodiment, the predetermined first direction is the X direction, and the predetermined second direction is the Y direction. Moreover, the display light L51 corresponds to the linearly polarized light L1 incident on the polarization modulation element 10 in embodiments 1 to 5. Furthermore, the first image signal representing the first image and the second image signal representing the second image are also collectively referred to as image signals.

[0090] The display unit 520 of the stereoscopic image display device 510 includes a liquid crystal display panel 522 and a light source section 532. The liquid crystal display panel 522 modulates light emitted from the light source section 532 based on a first image signal representing a first image and a second image signal representing a second image supplied from the control section 580, and sequentially displays the first image and the second image in a time-division manner. The liquid crystal display panel 522 emits display light L51 representing an image (for example, the first image and the second image) as polarized light whose polarization direction is a predetermined first direction. The display light L51 emitted from the liquid crystal display panel 522 is incident on the polarization modulation element 10.

[0091] The first and second images are two-dimensional images of a display object projected from the observer side onto first and second display surfaces 512 and 514, which are located at different positions in the depth direction (-Z direction) as seen from the observer. The first and second display surfaces 512 and 514 will be described later.

[0092] The liquid crystal display panel 522 is, for example, a transmissive TN liquid crystal panel that is active-matrix driven by TFTs (Thin Film Transistors). As shown in FIG. 38, the liquid crystal display panel 522 has pixels P arranged in a matrix, a gate driver 523G, and a data driver 523D. The gate driver 523G sequentially selects the pixels P row by row and performs line-sequential scanning in the -Y direction. The data driver 523D supplies a voltage corresponding to an image signal to each of the selected pixels P, and writes the image signal into each of the pixels P. Note that FIG. 38 shows only a portion of the pixels P arranged in a matrix. The liquid crystal display panel 522 also includes a polarizing plate, liquid crystal, etc. (not shown).

[0093] The light source unit 532 is a light source that irradiates light onto the liquid crystal display panel 522. As shown in Fig. 37, the light source unit 532 is disposed on the rear side (-Z side) of the liquid crystal display panel 522. The light source unit 532 is, for example, a direct type backlight. The light source unit 532 includes a white LED (Light emitting diode) element, a reflective sheet, a diffusion sheet, and the like (none of which are shown).

[0094] The polarization modulation element 10 of the stereoscopic image display device 510 switches the polarization direction of the display light L51 emitted from the display unit 520 between a predetermined first direction (X direction) and a predetermined second direction (Y direction) based on a switching signal supplied from the control unit 580 and synchronized with the image signal. Specifically, when a first image is displayed on the liquid crystal display panel 522 of the display unit 520, the polarization modulation element 10 maintains the polarization direction of the incident display light L51 in the X direction and emits it. On the other hand, when a second image is displayed on the liquid crystal display panel 522 of the display unit 520, the polarization modulation element 10 switches the polarization direction of the incident display light L51 to the Y direction and emits it.

[0095] When an OFF level switching signal is supplied to the polarization modulation element 10, it rotates the polarization direction of the display light L51 by 90° and emits display light L52 whose polarization direction is in the Y direction (initial orientation state). On the other hand, when an ON level switching signal is supplied to the polarization modulation element 10, it maintains the polarization direction of the display light L51 in the X direction and emits the display light L52 (ON state). The display light L52 corresponds to the emitted light L2 emitted from the polarization modulation element 10 in the first to fifth embodiments.

[0096] The display light L52 emitted from the polarization modulation element 10 is incident on the polarized bifocal lens 560. The switching signal will be described later.

[0097] The polarized bifocal lens 560 of the stereoscopic image display device 510 is a lens whose focal length with respect to the display light L52 emitted from the polarization modulation element 10 varies depending on the polarization direction (X direction and Y direction) of the display light L52. The polarized bifocal lens 560 forms the first image and the second image on the first display surface 512 and the second display surface 514, respectively, as virtual images as seen by the observer. The first display surface 512 and the second display surface 514 are virtual display surfaces located at different positions in the depth direction (-Z direction) as seen by the observer. In this embodiment, as shown in FIG. 37, the first display surface 512 and the second display surface 514 are located farther away from the observer than the display unit 520. Also, the second display surface 514 is located closer to the observer (+Z side) than the first display surface 512.

[0098] The observer sees a virtual image of the first image on the first display surface 512 and a virtual image of the second image on the second display surface 514, which are displayed sequentially in a time-division manner, and recognizes that the display object is located between the first display surface 512 and the second display surface 514. The position of the display object recognized by the observer can be changed by adjusting the ratio of brightness (e.g., luminance) between the first image and the second image. For example, when the ratio of brightness between the first image and the second image is 1:1, the observer recognizes that the display object is located midway between the first display surface 512 and the second display surface 514.

[0099] The polarized bifocal lens 560 is, for example, a liquid crystal lens. The polarized bifocal lens (liquid crystal lens) 560 includes a first light-transmissive substrate 561, a second light-transmissive substrate 562, and a liquid crystal 564, as shown in FIG.

[0100] The first light-transmitting substrate 561 and the second light-transmitting substrate 562 are, for example, glass substrates. The first light-transmitting substrate 561 has a resin Fresnel lens 566 on a main surface 561a facing the second light-transmitting substrate 562. The first light-transmitting substrate 561 and the second light-transmitting substrate 562 are bonded together with a sealant 567, and sandwich a liquid crystal 564. The liquid crystal 564 is, for example, a nematic liquid crystal having a positive refractive index anisotropy (Δn=ne-no>0, ne: extraordinary refractive index, no: ordinary refractive index). The liquid crystal 564 is aligned in the X direction by an alignment film (not shown).

[0101] When display light L52 of a first image having a polarization direction in the X direction is incident on the polarized bifocal lens 560, the liquid crystal (nematic liquid crystal) 564 having positive refractive index anisotropy is oriented in the X direction, so that the focal length of the polarized bifocal lens 560 with respect to the display light L52 is short, and the first image is formed on the first display surface 512. On the other hand, when display light L52 of a second image having a polarization direction in the Y direction is incident on the polarized bifocal lens 560, the focal length of the polarized bifocal lens 560 with respect to the display light L52 is long, and the second image is formed on the second display surface 514.

[0102] A control unit 580 of the stereoscopic image display device 510 controls the liquid crystal display panel 522 of the display unit 520 and the polarization modulation element 10 based on an input signal input from an external device (not shown). The control unit 580 has a display drive unit 582 and a polarization modulation element drive unit 584, as shown in FIG.

[0103] The display driver 582 of the control unit 580 generates a first image signal for displaying a first image and a second image signal for displaying a second image from the input signal. The display driver 582 also supplies the image signal to the liquid crystal display panel 522. Furthermore, the display driver 582 supplies a synchronization signal to the polarization modulation element driver 584, which is synchronized with the start of supply of the image signal.

[0104] The polarization modulation element driving section 584 of the control section 580 generates a switching signal based on the synchronization signal supplied from the display driving section 582. In addition, the polarization modulation element driving section 584 supplies the generated switching signal to the polarization modulation element 10. In this embodiment, when the first image is displayed on the liquid crystal display panel 522, the polarization modulation element driving section 584 sets the switching signal to ON level and supplies it to the polarization modulation element 10.

[0105] FIG. 41 shows a hardware configuration of the control unit 580. The control unit 580 includes a CPU (Central Processing Unit) 592, a ROM (Read Only Memory) 594, a RAM (Random Access Memory) 596, and an input / output interface 598. The CPU 592, the ROM 594, the RAM 596, and the input / output interface 598 are connected by a bus 599. The CPU 592 executes various processes. The ROM 594 stores programs and data. The RAM 596 stores data. The input / output interface 598 inputs and outputs signals between the CPU 592, the liquid crystal display panel 522, the polarization modulation element 10, and an external device. The functions of the control unit 580 are realized by the CPU 592 executing a program stored in the ROM 594.

[0106] As described in the first to fifth embodiments, the polarization modulation element 10 can emit a polarized component having a desired polarization direction (X direction) with high intensity at a low voltage. Therefore, in the stereoscopic image display device 510 including the polarization modulation element 10, the phenomenon in which a stereoscopic image is not displayed correctly due to mixing of a virtual image of the first image and a virtual image of the second image on the second display surface 514 can be suppressed at a low voltage.

[0107] <Modification> Although the embodiments have been described above, the present disclosure can be modified in various ways without departing from the gist of the present disclosure.

[0108] For example, the transparent electrodes 102b and 104b are not limited to ITO and may be formed of other materials.

[0109] In the embodiment, the twist angles α of the TN cells 100 forming the polarization modulating element 10 are equal. The twist angles α of the TN cells 100 forming the polarization modulating element 10 may be different from each other.

[0110] The polarization modulation element 10 may include N (N is an integer of 3 or more) TN cells 100, and in at least one adjacent TN cell 100, the alignment axis direction 200 of the light-emission side substrate 104 of one TN cell 100 and the alignment axis direction 200 of the light-incident side substrate 102 of the other TN cell 100 may be perpendicular to each other. For example, as in the following Modification 1 and Modification 2, the polarization modulation element 10 may include eight (N=8) TN cells 100.

[0111] (Variation 1) The polarization modulation element 10 of this modification includes eight (N=8) TN cells 100 with the same twist direction. The TN cells 100 are stacked in order with the light-incident side substrate 102 of one TN cell 100 facing the light-exiting side substrate 104 of the other TN cell 100. The configuration of the TN cell 100 of this modification is the same as that of the TN cell 100 of the first embodiment, except for the cell thickness (2.74 μm) and the alignment axis direction 200. In the initial alignment state, the nematic liquid crystal 106 of the TN cell 100 of this modification is aligned in a clockwise twisted manner when viewed in plan from the +Z side. The twist angle α of the TN cell 100 is 11.25°, and the sum of the twist angles α of the TN cells 100 is 90°. FIG. 42 shows the alignment axis direction 200 of the TN cell 100 of this modification. As shown in FIG. 42, in this modification, in the fourth (N / 2th) TN cell 100 and the fifth ((N / 2)+1th) TN cell 100, the alignment axis direction 200 of the light-emitting side substrate 104 and the alignment axis direction 200 of the light-incident side substrate 102 are perpendicular to each other. In the other adjacent TN cells 100, the alignment axis direction 200 of the light-emitting side substrate 104 and the alignment axis direction 200 of the light-incident side substrate 102 are coincident. In this modification, as in the first to fifth embodiments, a high polarization contrast pCR can be obtained at a low voltage, and a polarized component having a desired polarization direction can be emitted with high intensity. Furthermore, since the number of TN cells 100 is large, the cell thickness of the TN cells 100 can be thinned. By thinning the cell thickness of the TN cells 100, the response time of the TN cells 100 can be shortened.

[0112] (Variation 2) In the polarization modulation element 10 having eight (N=8) TN cells 100, the alignment axis direction 200 of the light-emitting side substrate 104 and the alignment axis direction 200 of the light-incident side substrate 102 may be perpendicular to each other in two adjacent TN cells 100. The configuration of the TN cell 100 of this modification is the same as that of the TN cell 100 of modification 1, except for the cell thickness (2.74 μm) and the alignment axis direction 200. As shown in FIG. 43, in this modification, the alignment axis direction 200 of the light-emitting side substrate 104 and the alignment axis direction 200 of the light-incident side substrate 102 are perpendicular to each other in the second TN cell 100 and the third TN cell 100, and the sixth TN cell 100 and the seventh TN cell 100. In the other adjacent TN cells 100, the alignment axis direction 200 of the light-emitting side substrate 104 and the alignment axis direction 200 of the light-incident side substrate 102 are the same. In this modification, as in the first to fifth embodiments, a high polarization contrast pCR can be obtained at a low voltage, and a polarized component having a desired polarization direction can be emitted with high intensity. Furthermore, since there are a large number of TN cells 100, the cell thickness of the TN cells 100 can be made thin. By making the cell thickness of the TN cells 100 thin, the response time of the TN cells 100 can be made shorter.

[0113] In the case where the polarization modulation element 10 includes an even number of TN cells 100, and the alignment axis direction 200 of the light exit side substrate 104 and the alignment axis direction 200 of the light incident side substrate 102 are orthogonal in the N / 2th TN cell 100 and the (N / 2)+1th TN cell 100 (Embodiment 1, Embodiment 4, Modification 1), the polarization contrast pCR in the initial alignment state hardly changes even if the polarization direction 250 of the incident linearly polarized light L1 is deviated from the alignment axis direction 200 of the light incident side substrate 102 of the first TN cell 100. Therefore, the above-mentioned polarization modulation element 10 can emit a polarized component having a desired polarization direction with high intensity at a low voltage, even if the polarization direction 250 of the linearly polarized light L1 is deviated from the alignment axis direction 200 of the light incident side substrate 102 of the first TN cell 100.

[0114] For example, as shown in Fig. 44, when the angle between the alignment axis direction 200 of the first TN cell 100 and the polarization direction 250 of the linearly polarized light L1 is set to angle β, the polarization contrast pCR in the initial alignment state of the polarization modulation element 10 of the first embodiment hardly changes with the angle β as shown in Fig. 45. Moreover, the polarization contrast pCR in the initial alignment state of the polarization modulation element 10 of the third embodiment hardly changes with the angle β as shown in Fig. 46. Furthermore, the polarization contrast pCR in the initial alignment state of the polarization modulation element 10 of the fifth embodiment hardly changes with the angle β as shown in Fig. 47. On the other hand, the polarization contrast pCR in the initial alignment state of the polarization modulation element 50A of the first comparative example changes greatly depending on the angle β as shown in Fig. 48.

[0115] Although the preferred embodiments have been described above, the present disclosure is not limited to such specific embodiments, and the present disclosure includes the invention described in the claims and their equivalents. [Explanation of symbols]

[0116] 10,50A Polarization modulation element, 80 Control unit, 100,110,120,130,140 TN cell (twisted nematic liquid crystal cell), 102 Light incident side substrate, 102a Main surface, 102b Light-transmitting electrode, 102c Alignment film, 104 Light exit side substrate, 104a Main surface, 104b Light-transmitting electrode, 104c Alignment film, 104 Light exit side substrate, 106 Nematic liquid crystal, 106M Liquid crystal molecule, 108 Sealing material, 110A,110B,120A,120B,130A,130B Birefringent plate, 200,212,214,222,224,232,234,242,244 Alignment axis direction, 250 Polarization direction, 310A, 310B, 320A, 320B, 330A, 330B optical axis, 510 stereoscopic image display device, 512 first display surface, 514 second display surface, 520 display unit, 522 liquid crystal display panel, 523D data driver, 523G gate driver, 532 light source unit, 560 polarized bifocal lens, 561 first light-transmitting substrate, 561a main surface, 562 second light-transmitting substrate, 564 liquid crystal, 566 Fresnel lens, 567 seal material, 580 control unit, 582 display drive unit, 584 polarization modulation element drive unit, 592 CPU, 594 ROM, 596 RAM, 598 input / output interface, 599 bus, d, d1, d2, h thickness, pCR polarization contrast, Δn birefringence anisotropy (phase difference), no Ordinary refractive index, ne extraordinary refractive index, Δε dielectric anisotropy, Δnd birefringence, α torsion angle, β, δ angle, λ wavelength, θ, φ crossing angle, I1, I2 transmitted light intensity, L1 linearly polarized light (incident light), L12, L13, L2, L2A output light, L51, L52 display light, N,m number, M Number of divisions, P pixels, V, V1, V2 voltage

Claims

1. The liquid crystal display device includes N (N is an integer of 3 or more) twisted nematic liquid crystal cells having the same twist direction, Each of the twisted nematic liquid crystal cells has a light-incident side substrate and a light-emitting side substrate that sandwich a liquid crystal therebetween, the sum of the twist angles of the twisted nematic liquid crystal cells is 90°; The twisted nematic liquid crystal cells are stacked in order with the light incident side substrate of one of the twisted nematic liquid crystal cells facing the light exit side substrate of the other twisted nematic liquid crystal cell, In at least one of the adjacent twisted nematic liquid crystal cells, an alignment axis direction of the light exit side substrate of one of the twisted nematic liquid crystal cells is perpendicular to an alignment axis direction of the light incident side substrate of the other of the twisted nematic liquid crystal cells; In the at least one adjacent twisted nematic liquid crystal cell, except for the adjacent twisted nematic liquid crystal cell, an alignment axis direction of the light exit side substrate of one of the twisted nematic liquid crystal cells is consistent with an alignment axis direction of the light incident side substrate of the other twisted nematic liquid crystal cell. Polarization modulation element.

2. N is an even number, In the (N / 2)th twisted nematic liquid crystal cell and the (N / 2)+1th twisted nematic liquid crystal cell, an alignment axis direction of the light exit side substrate of one of the twisted nematic liquid crystal cells is perpendicular to an alignment axis direction of the light incident side substrate of the other twisted nematic liquid crystal cell. The polarization modulating element according to claim 1 .

3. In two adjacent twisted nematic liquid crystal cells, an alignment axis direction of the light exit side substrate of one of the twisted nematic liquid crystal cells is perpendicular to an alignment axis direction of the light incident side substrate of the other twisted nematic liquid crystal cell. The polarization modulating element according to claim 1 .

4. N is 4, In the first twisted nematic liquid crystal cell, the second twisted nematic liquid crystal cell, the third twisted nematic liquid crystal cell, and the fourth twisted nematic liquid crystal cell, an alignment axis direction of the light exit side substrate of one of the twisted nematic liquid crystal cells is perpendicular to an alignment axis direction of the light incident side substrate of the other twisted nematic liquid crystal cell. The polarization modulation element according to claim 3 .

5. N is 6; In the first twisted nematic liquid crystal cell, the second twisted nematic liquid crystal cell, the fourth twisted nematic liquid crystal cell, and the fifth twisted nematic liquid crystal cell, an alignment axis direction of the light exit side substrate of one of the twisted nematic liquid crystal cells is perpendicular to an alignment axis direction of the light incident side substrate of the other twisted nematic liquid crystal cell. The polarization modulation element according to claim 3 .

6. N is 8, In the second twisted nematic liquid crystal cell, the third twisted nematic liquid crystal cell, the sixth twisted nematic liquid crystal cell, and the seventh twisted nematic liquid crystal cell, an alignment axis direction of the light exit side substrate of one of the twisted nematic liquid crystal cells is perpendicular to an alignment axis direction of the light incident side substrate of the other twisted nematic liquid crystal cell. The polarization modulation element according to claim 3 .

7. the twist angles of each of the twisted nematic liquid crystal cells are equal; The polarization modulating element according to claim 1 .

8. The polarization modulation element according to any one of claims 1 to 7, a display unit that sequentially displays a first image and a second image and outputs a display light of the first image and a display light of the second image as polarized light incident on the polarization modulation element, the polarized light having a predetermined first direction; a polarized bifocal lens into which the light emitted from the polarization modulation element is incident and whose focal length with respect to the light emitted from the polarization modulation element varies depending on the polarization direction of the light, the first image and the second image are two-dimensional images obtained by projecting a display object from a side of an observer onto a first display surface and a second display surface that are located at different positions in a depth direction as viewed from the observer, respectively; the polarization modulation element, when the polarized light is display light for the first image, outputs the polarized light while maintaining the polarization direction of the polarized light in the predetermined first direction, and, when the polarized light is display light for the second image, changes the polarization direction of the polarized light to a second direction perpendicular to the predetermined first direction and outputs the polarized light, thereby switching the polarization direction of the output light between the predetermined first direction and the second direction, The polarized bifocal lens forms the first image and the second image as virtual images on the first display surface and the second display surface, respectively. Stereoscopic image display device.

Images