Spatial light modulator and holographic three-dimensional display device

Abstract

To enable independent driving of pixels with a minute pixel pitch.SOLUTION: The spatial light modulator includes a first substrate, a second substrate provided to face the first substrate, and a liquid crystal layer provided between the first substrate and the second substrate, the first substrate including: driving electrodes arranged on both sides of pixels arranged in a first direction of pixels arranged in a matrix on a surface of the substrate; and grounding electrodes arranged between rows of the driving electrodes arranged in the first direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a spatial light modulation element and the like. [Background technology]

[0002] 3D (three-dimensional) displays can express depth, giving viewers a highly realistic feeling. Development of services such as 3D movies and 3D television is being considered, and they are expected to be the next generation of displays. Among these, electronic holographic displays are attracting attention as a next-generation three-dimensional display system because they can perfectly reproduce the wavefront of object light, achieving natural three-dimensional vision that matches human sensibilities.

[0003] In electronic holography, as shown in FIG. 13, for example, an electronic device called a spatial light modulator (SLM) is used to reproduce the wavefront of object light, and an electronic holography image is reproduced using the diffraction of light by the SLM. Known modulation methods include an amplitude method that reproduces a two-dimensional amplitude distribution of light, and a phase method that reproduces a phase distribution of light. Compared to the amplitude method, the phase method has a higher light utilization efficiency and can suppress higher-order diffracted light that interferes with the observation of the reproduced image, making it a useful method for practical application. For example, Patent Document 1 discloses technology related to a spatial light modulator called an LCOS-SLM (Liquid Crystal on Silicon) that uses liquid crystal.

[0004] However, in order to make electronic holography practical, the range over which the image can be observed (viewing angle) is narrow, and high-resolution operation of the spatial light modulator is essential to widen the viewing angle. An example of a graph showing the relationship between pixel pitch (μm) and viewing angle (deg) is shown in Figure 14. The viewing angle is determined by the diffraction angle of the SLM, which in turn is determined by the pixel pitch, which is the size of the pixels that make up the SLM on a two-dimensional plane. For practical use, a viewing angle of 30° or more is required, which requires a pixel pitch of 1 μm or less. However, when the pixel pitch is set to 1 μm or less, there is a problem that it is difficult to drive pixels (individual pixels) independently due to electric field leakage between adjacent pixels when an electric field is applied. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7379262 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above-mentioned problems, and one of its objects is to enable independent driving of pixels at a minute pixel pitch. [Means for solving the problem]

[0007] According to a first aspect of the present invention, a spatial light modulation element has a first substrate, a second substrate arranged opposite the first substrate, and a liquid crystal layer arranged between the first substrate and the second substrate, and the first substrate has, on its surface, drive electrodes arranged on both sides of pixels arranged in a first direction in pixels arranged in a matrix, and ground electrodes arranged between columns of drive electrodes arranged in the first direction. According to a second aspect of the present invention, a holographic stereoscopic display device includes the spatial light modulation element described above, and drives a liquid crystal layer with a horizontal electric field between drive electrodes arranged on both sides of pixels arranged in a first direction. [Effects of the Invention]

[0008] According to the present invention, it is possible to independently drive pixels at a small pixel pitch. In addition, the drive electrodes arranged on both sides of the pixels arranged in the first direction and the ground electrodes arranged between the rows of the drive electrodes arranged in the first direction can effectively suppress electric field leakage. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 10 is a diagram showing an example of a simulation result of the liquid crystal alignment direction. [Figure 2] FIG. 1 is an explanatory diagram of a continuous potential difference in-plane switching driving method. [Figure 3] FIG. 2 is a schematic plan view of a first substrate of the spatial light modulation element. [Figure 4] FIG. 10 is a diagram showing an example of a simulation configuration and results of a continuous potential difference in-plane switching driving method. [Figure 5] FIG. 10 is a diagram showing an example of a simulation configuration and results of a simple in-plane switching driving method. [Figure 6] FIG. 10 is a diagram showing an example of an experimental result when a continuous potential difference in-plane switching driving method is applied. [Figure 7] FIG. 10 is a diagram showing an example of an experimental result when a conventional vertical electric field driving method is applied. [Figure 8] FIG. 10 is a diagram showing an example of a simulation result regarding independent driving of pixels. [Figure 9] FIG. 10 is a diagram showing an example of a first simulation configuration regarding the effect of suppressing electric field leakage by a ground electrode. [Figure 10] FIG. 10 is a diagram showing an example of a simulation result of a phase modulation distribution. [Figure 11] FIG. 10 is a diagram showing an example of a second simulation configuration regarding the suppression effect of electric field leakage by a ground electrode. [Figure 12] FIG. 10 is a diagram showing an example of a simulation result of a phase modulation distribution. [Figure 13] FIG. 1 is an explanatory diagram of a spatial light modulation element. [Figure 14] 10 is an example of a graph showing the relationship between pixel pitch and viewing angle. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. The components described in this embodiment are merely examples and are not intended to limit the scope of the present invention.

[0011] 1 Introduction The LCOS-SLM mentioned above is a reflective optical device with a structure in which liquid crystal is sandwiched between a glass substrate with a transparent common electrode and a drive electrode that also functions as a reflector on a backplane with a voltage drive circuit formed on a silicon substrate. A thin polymer film called an alignment film is applied to the interface between the liquid crystal and the substrate, and the alignment constraint force applied to the liquid crystal molecules from the alignment film determines the long axis direction of the molecules in one direction within the plane, while also constraining the long axis to be parallel to the substrate. Therefore, when no electric field is applied, the liquid crystal is aligned parallel to the substrate.

[0012] When linearly polarized light vibrating parallel to the long axis of the liquid crystal molecules is incident, the refractive index acting on the incident light is high. On the other hand, when an electric field is applied perpendicular to the substrate, the liquid crystal molecules rotate so that their long axes approach parallel to the direction of the electric field lines due to their dielectric anisotropy, and the refractive index experienced by the incident linearly polarized light is low. As a result, a difference in phase occurs between the light reflected from the ON-state pixel and the light reflected from the OFF-state pixel, making it possible to modulate the phase two-dimensionally by applying an electric field to each pixel.

[0013] The holographic stereoscopic display device of this embodiment has an LCOS-SLM (liquid crystal on silicon-spatial light modulator) as a spatial light modulator. However, the spatial light modulation element is not limited to a phase modulation function, and may be provided with a function to modulate the amplitude of incident light by the phase difference of orthogonal polarized light controlled by voltage using the refractive index anisotropy of the liquid crystal (in this case, the spatial light modulation element is required to have a π phase modulation capability for amplitude modulation, and an optical system such as a polarizing plate is required). In other words, the spatial light modulation element of the present invention may include a spatial light phase modulation element and a spatial light amplitude modulation element.

[0014] To solve the problem of electric field leakage mentioned above, a dielectric shield wall structure technology has been proposed. In this technology, dielectric walls are placed at the boundaries of pixels with a grid-like pixel pitch of 1 μm to divide the two-dimensionally arranged pixels. The walls suppress the electric field, reduce leakage, and enable independent driving of each pixel.

[0015] However, this method requires the placement of dielectric walls at pixel boundaries in a microstructure with a pixel pitch of 1 μm, which complicates the manufacturing process and increases manufacturing costs. Therefore, to achieve high resolution over a wider field of view, other methods and structures with simplified manufacturing processes are needed.

[0016] Figure 1 shows an example of the simulation results for the liquid crystal alignment direction. In this figure, the horizontal axis is the axis horizontal to the substrate (x-axis), and the vertical axis is the axis vertical to the substrate (z-axis). For this calculation, a liquid crystal alignment simulator (LCD-Master, Shintech Co., Ltd.) based on the elastic continuum theory of liquid crystals was used. Figure 1(a) is a diagram showing a conventional electric field application method (hereinafter referred to as the "vertical electric field driving method (vertical electric field drive)"), and shows the equipotential line distribution and liquid crystal orientation distribution when pixels in the ON state (5V) and pixels in the OFF state (0V) are arranged alternately, with the solid lines in the figure showing the equipotential lines in increments of "0.5V". The common electrode 13 is represented by "0V" and the drive electrode 11 by "5V". In the vertical electric field driving method, an electric field is applied perpendicular to the substrate. However, with this method, the electric field spreads radially over a small area, resulting in significant leakage of the electric field to adjacent pixels. The spread (magnitude of spread) of the electric field leakage is shown schematically by the dashed line, and it can be seen that the electric field is leaking from an ON-state pixel to an OFF-state pixel.

[0017] In contrast, FIG. 1(b) shows an example of a simulation result when an in-plane switching driving method (hereinafter referred to as "simple in-plane switching driving method") used in, for example, a direct-view liquid crystal display (IPS-LCD) is applied. In this example, as shown in the region of the pixel in the ON state on the left side of the drawing, the drive electrode 11 is placed at the center of the pixel, and an electric field is applied toward the common electrode 13 placed at the pixel boundary. In this case, even if a voltage of the same magnitude as that of the vertical electric field drive system is applied, the spread of the electric field is smaller than that of the vertical electric field drive system. Therefore, by using the simple horizontal electric field drive system, electric field leakage is more easily suppressed than in the vertical electric field drive system, even if a voltage of the same magnitude as that of the vertical electric field drive system is applied. In fact, the spread of the electric field leakage shown by the dashed line in FIG. 1(b) is smaller than the spread of the electric field leakage shown by the dashed line in FIG. 1(a).

[0018] Therefore, in this embodiment, instead of sandwiching the liquid crystal layer between two electrodes and driving the liquid crystal molecules with a vertical electric field as in the conventional method, the liquid crystal molecules are driven with a horizontal electric field generated by an in-plane electrode pattern provided on one of the substrates, thereby significantly reducing electric field leakage. The in-plane electric field driving method has the advantage of not requiring a dielectric wall.

[0019] 2 Continuous potential difference in-plane driving method When the above-mentioned simple in-plane driving method is applied, the initial alignment of the liquid crystal molecules is aligned perpendicular to the substrate (substrate perpendicular alignment). This is because the in-plane rotation (rotating the liquid crystal molecules in-plane) used in LCOS IPS also changes the polarization state, making it impossible to obtain high light utilization efficiency. Note that the alignment may be approximately perpendicular rather than strictly perpendicular.

[0020] However, in the simple in-plane switching driving method, the driving electrode 11 is placed at the center of the pixel, and an electric field is applied toward the common electrode 13 placed at the pixel boundary. This causes a problem that the liquid crystal orientation on the driving electrode 11 does not change, making it difficult to obtain modulation in the center of the pixel. In addition, because it is composed of three electrodes, limitations on the fine formation of the electrodes make it difficult to achieve high resolution.

[0021] Therefore, in this embodiment, a transverse electric field driving method based on a continuous potential difference by a transverse electrode (hereinafter, this method will be referred to as a "continuous potential difference transverse electric field driving method" (continuous potential difference transverse electric field driving)) is proposed. In the continuous potential difference in-plane switching drive method, drive electrodes 11 are placed on the boundaries of pixels (on both sides of the pixels) instead of using a common electrode 13 as in the simple in-plane switching drive method. Then, for example, by continuously applying a voltage, an electric field is applied using the potential difference between each drive electrode 11. In other words, a voltage difference is applied between the pixel electrode in the x-axis direction in the plane and the adjacent pixel. As a result, the continuous potential difference in-plane switching drive can double the resolution compared to the simple in-plane switching drive with the same electrode spacing. Even when the continuous potential difference in-plane switching driving method is applied, the initial alignment of the liquid crystal molecules may be perpendicular to the substrate.

[0022] FIG. 2 is an explanatory diagram of the continuous potential difference in-plane switching driving method. FIG. 2(b) shows a block diagram illustrating the concept of the continuous potential difference in-plane switching driving method proposed in this embodiment, and for comparison, FIG. 2(a) shows a block diagram illustrating the concept of the simple in-plane switching driving method. As shown in FIG. 2(b), drive electrodes 11 are arranged on both sides of each pixel (each pixel) arranged on the first substrate, and a voltage is continuously applied to each drive electrode 11, thereby applying an electric field by utilizing the potential difference between the drive electrodes 11. Specifically, for multiple drive electrodes 11 arranged in the horizontal direction (x-axis direction) on the xy plane, a potential difference is created between the first drive electrode 11 and the second drive electrode 11, thereby generating ON pixels and OFF pixels. The first drive electrode 11 may be a single electrode or multiple consecutive electrodes. The second drive electrode 11 may also be a single electrode or multiple consecutive electrodes. This method requires fewer electrodes than the simple in-plane switching method, has a simple pixel structure, and is an effective structure for achieving high resolution.

[0023] In this case, with regard to the configuration of the pixels and electrodes of the spatial light modulation element of this embodiment, the spatial light modulation element may have a first substrate, a second substrate provided opposite the first substrate, and a liquid crystal layer provided between the first and second substrates, and the first substrate may have, on its surface, drive electrodes arranged on both sides of pixels arranged in a first direction in a two-dimensional matrix (the same applies below). The first direction may be the horizontal direction of the substrate. However, it may not be strictly horizontal, but may be approximately horizontal.

[0024] Furthermore, based on this configuration, a holographic stereoscopic display device may be configured as a holographic stereoscopic display device using a spatial light modulation element and reference light, and this holographic stereoscopic display device may be equipped with the above-mentioned spatial light modulation element, and may drive the liquid crystal layer (liquid crystal molecules) with a horizontal electric field between drive electrodes arranged on both sides of pixels arranged in the first direction.

[0025] Furthermore, as an example of a method for driving the liquid crystal layer with a horizontal electric field between drive electrodes arranged on both sides of pixels arranged in the first direction, the liquid crystal layer may be driven by a potential difference between drive electrodes arranged on both sides of pixels arranged in the first direction.

[0026] Furthermore, in an initial alignment state in which the liquid crystal molecules of the liquid crystal layer are aligned in the direction perpendicular to the substrate, the alignment of the liquid crystal molecules may be changed by the horizontal electric field. That is, after vertical alignment control (vertical alignment process) is performed to align the liquid crystal molecules in the direction perpendicular to the substrate as the initial alignment, the alignment of the liquid crystal molecules may be changed by the horizontal electric field.

[0027] 3 Ground electrode When the driving electrodes 11 are arranged on the first substrate as shown in FIG. 2(b), electric field leakage may occur in the y-axis direction in the xy plane. Therefore, in this embodiment, in addition to the above configuration, a ground electrode 15 may be provided between the electrode rows (between the electrode rows).

[0028] 3 is a schematic plan view of the first substrate in this case. The horizontal axis is the x-axis (axis in the horizontal direction of the substrate, unit: μm), and the vertical axis is the y-axis (axis perpendicular to the x-axis in the plane, unit: μm), which is perpendicular to the x-axis and z-axis. The spacing between the drive electrodes 11 in the x-axis direction is 1 μm, and the spacing between the ground electrodes 15 in the y-axis direction is also 1 μm.

[0029] As described above, pixels are arranged in a matrix on the surface of the first substrate, and drive electrodes 11 are provided on both sides of the pixels arranged in the x-axis direction (horizontal direction of the substrate, first direction). Furthermore, ground electrodes 15 are provided between the electrode rows of pixels arranged in the x-axis direction (between the electrode rows aligned in the x-axis direction). In other words, ground electrodes 15 are provided between the drive electrodes 11 in the y-axis direction. These ground electrodes 15 suppress electric field leakage in the y-axis direction.

[0030] In this case, with regard to the configuration of the pixels and electrodes of the spatial light modulation element of this embodiment, the spatial light modulation element may have a first substrate, a second substrate arranged opposite the first substrate, and a liquid crystal layer arranged between the first substrate and the second substrate, and the first substrate may have, on its surface, drive electrodes arranged on both sides of the pixels arranged in a first direction in the pixels arranged in a matrix, and ground electrodes arranged between the columns of drive electrodes arranged in the first direction.

[0031] 4. Verification of the continuous potential difference in-plane switching driving method In a liquid crystal spatial light modulator that uses phase modulation, the required phase modulation amount is 2π. However, when using a reflective type, the incident light travels back and forth through the liquid crystal layer, so it is sufficient to obtain a phase modulation of π in one direction. Furthermore, because the horizontal electric field has little spread, it is difficult to achieve perfect horizontal alignment within the plane. Therefore, a liquid crystal material with large refractive index anisotropy and dielectric constant anisotropy is used. After considering this imperfect liquid crystal alignment, it was determined that the liquid crystal layer thickness required for sufficient phase modulation was 2 μm.

[0032] The thickness of the liquid crystal layer was set to 2 μm, and simulations were carried out for both the simple in-plane switching driving method and the continuous potential difference in-plane switching driving method, and a comparative analysis was carried out using the phase modulation distribution and the potential alignment distribution. The simulation conditions were as follows: Liquid crystal material: birefringence "0.5", dielectric anisotropy "19.5" Initial alignment of liquid crystal molecules: vertical alignment Anchoring Strength: 10 -6 [J / m 2 ] Pixel pitch: 1μm

[0033] FIG. 4 shows an example of a simulation configuration and results of a continuous potential difference in-plane switching driving method. To confirm the independent driving of each pixel, pixels driven so that the phase modulation is "0" (OFF pixels, marked "OFF" in the drawings) and pixels driven so that the phase modulation is "π" (ON pixels, marked "OFF" in the drawings) are arranged alternately. To achieve this state, the drive electrodes 11 that make up the OFF pixels must be at the same potential, and the drive electrodes 11 that make up the ON pixels must be at a different potential. As an example, we set the width of the drive electrodes 11 to "0.2 μm" and the width between the electrodes to "0.8 μm," and tested whether the required amount of phase modulation could be obtained in each pixel and whether each pixel could be driven independently when driven in these states. In this calculation, a liquid crystal alignment simulator (LCD-Master, Shintech Co., Ltd.) based on the elastic continuum theory of liquid crystals was used.

[0034] Figure 4(a) shows a structure in which ON and OFF pixels are alternately driven, with the horizontal axis representing the x-axis (units: μm) and the vertical axis representing the z-axis (units: μm). Figure 4(b) shows the phase modulation amount for each pixel, with the horizontal axis representing the x-axis (units: μm) and the vertical axis representing the phase modulation amount (units: rad). The graph also shows the results when the potential difference of the ON pixel (corresponding to the potential nVpp in Figure 4(a)) is set to "0 Vpp," "9.8 Vpp," and "10.8 Vpp" (where Vpp is the difference between the maximum and minimum AC voltages), with each phase modulation amount indicated by a different line thickness. The ideal value of the phase modulation amount is indicated by a dashed line, and the allowable error of the phase modulation amount is indicated by a rectangular area. For comparison, an example of the simulation configuration and results for the simple in-plane switching driving method is shown in Figure 5. The diagram should be interpreted in the same way as Figure 4. Note that Figure 5 shows the results when the potential difference of the ON pixel (corresponding to the potential mVpp in Figure 5(a)) is set to "0 Vpp," "10.8 Vpp," and "20 Vpp."

[0035] The results in Figure 4 show that with the continuous potential difference in-plane switching driving method of this embodiment, the amount of phase modulation falls within the tolerance and a sufficient amount of phase modulation is ensured. In other words, by using the continuous potential difference in-plane switching driving method with a pixel pitch of 1 μm, a sufficient amount of phase modulation, "π," is ensured and independent pixel driving is possible.

[0036] In the simple in-plane switching driving method, the center of the pixel is not modulated, which may be disadvantageous in terms of further narrowing the pixel pitch. In this respect, the continuous potential difference in-plane switching driving method is advantageous.

[0037] In addition, to observe the above simulation results, an experiment was conducted in which a liquid crystal cell was fabricated and observed under a polarizing microscope. Furthermore, an experiment was conducted in which the brightness value distribution was calculated from the polarizing microscope image to determine the modulation degree (λ=500 nm) during driving. Here, the results of the experiment are shown for both the conventional vertical electric field driving method and the continuous potential difference horizontal electric field driving method of this embodiment.

[0038] FIG. 6 shows an example of experimental results when the continuous potential difference in-plane switching driving method of this embodiment is applied. FIG. 6(a) shows the structure of the fabricated liquid crystal cell, FIG. 6(b) shows a cross-sectional view taken along line X-ray X in FIG. 6(a), and FIG. 6(c) shows the observed results of light modulation. A glass substrate with an ITO (Indium Tin Oxide) electrode pattern formed on it was used as the lower substrate, and a plain glass substrate was used as the upper substrate. The fabricated liquid crystal cell was observed under crossed Nicols using a polarizing microscope. ON pixel areas displayed bright, and OFF pixel areas displayed dark.

[0039] The maximum modulation was calculated according to the following formula (1). Maximum modulation depth = (P max -P min ) / (P max +P min ) ···(1) However, "P max "," "P min " are the maximum and minimum luminance values ​​in the modulation area, respectively.

[0040] The observation results in Figure 6(c) show that the ON pixel area is bright and the OFF pixel area is dark. The maximum modulation depth calculated according to equation (1) was 0.90.

[0041] Figure 7 shows an example of experimental results when the conventional vertical electric field driving method is applied. Figure 7(a) shows the structure of the fabricated liquid crystal cell, Figure 7(b) shows a cross section of Figure 7(a) taken along line YY, and Figure 7(c) shows the observed results of light modulation. The diagrams can be viewed in the same way as Figure 6. In this case, the maximum modulation degree calculated according to equation (1) was "0.59."

[0042] The continuous potential difference lateral electric field driving method of this embodiment achieved a maximum modulation index (0.90) that was larger than the maximum modulation index of 0.59 achieved by the conventional longitudinal electric field driving method, demonstrating the superiority of the continuous potential difference lateral electric field driving method of this embodiment.

[0043] From these results, it was observed that the pixels could be independently driven at a pixel pitch of 1 μm in the continuous potential difference in-plane switching driving method of this embodiment.

[0044] Furthermore, in order to confirm the effectiveness of the continuous potential difference in-plane switching driving method of this embodiment, a simulation analysis was performed with the pixel pitch set to a value smaller than "1 μm." The simulation conditions were as follows. Liquid crystal material: birefringence "0.5", dielectric anisotropy "19.5" Initial alignment of liquid crystal molecules: vertical alignment Anchoring Strength: 10 -6 [J / m 2 ] Pixel pitch: 0.8μm

[0045] Figure 8 shows an example of the simulation results in this case. The diagram can be viewed in the same way as Figure 4. Here, the results are shown when the potential difference of the ON pixel (corresponding to kVpp in Figure 8(a)) is set to "0 Vpp," "12.1 Vpp," and "13.8 Vpp." These results show that by using the continuous potential difference lateral electric field driving method at a pixel pitch of less than 1 μm, it is possible to ensure a sufficient phase modulation amount of π and drive pixels independently.

[0046] From the above results, it was confirmed that the continuous potential difference in-plane switching driving method of this embodiment is useful for holographic stereoscopic display devices that require a pixel structure with a pixel pitch of "1 μm or less."

[0047] 5. Verification of the effect of the ground electrode in suppressing electric field leakage (electric field shielding effect) In the continuous potential difference lateral electric field driving method of this embodiment, electric field leakage can affect the driving of pixels in adjacent columns, making it difficult to independently drive all pixels arranged in a two-dimensional plane. Therefore, a structure that suppresses electric field leakage between columns is required. Therefore, as described above, a ground electrode 15 can be placed between columns. To confirm the effectiveness of this, the ground electrode 15 was used to suppress electric field leakage between columns, and simulations were carried out to verify whether all pixels on a two-dimensional plane were independently driven.

[0048] 9A and 9B are diagrams showing an example of the configuration of a first simulation regarding the suppression effect of electric field leakage by a ground electrode. Fig. 9A shows the configuration of a liquid crystal element, and Fig. 9B shows a schematic plan view of the first substrate of the liquid crystal element corresponding to Fig. 3. As shown in this figure, the horizontal electrodes in the rows between "y=1" and "y=2" are driven to alternate between "ON" and "OFF" pixels. The horizontal electrodes in the columns between "y=0" and "y=1" and between "y=2" and "y=3" are not driven and are all OFF pixels. As an example, we applied 10.8 Vpp, which ensures a sufficient amount of phase modulation. We then analyzed the phase modulation distribution at three cross sections: observation cross section A at y=0.5, observation cross section B at y=2.5, and observation cross section C within the element plane at z=0.5.

[0049] Figure 10 shows an example of the simulation results of the phase modulation distribution in this case. Here, the results for observation cross section A are shown in Figure 10(a), and the results for observation cross section C within the element plane are shown in Figures 10(b) and (c). Note that observation cross section B is not shown because the same results were obtained as for observation cross section A. Figure 10(a) shows a graph with the x-axis (unit: μm) as the horizontal axis and the phase modulation amount (unit: rad) as the vertical axis for the cases with and without the ground electrode 15, Figure 10(b) shows the distribution of the phase modulation amount in the xy plane for the case with the ground electrode 15, and Figure 10(c) shows the distribution of the phase modulation amount in the xy plane for the case without the ground electrode 15. These results confirm that when driven at a pixel pitch of 1 μm, the phase modulation amount of the surrounding OFF pixels is suppressed to almost 0, and that the ground electrode 15 shields electric field leakage, making it possible to independently drive the two-dimensionally arranged pixels.

[0050] FIG. 11 is a diagram showing an example of the configuration of a second simulation regarding the effect of suppressing electric field leakage by the ground electrode. FIG. 11(a) shows the configuration of a liquid crystal element, and FIG. 11(b) shows a schematic plan view of the first substrate of the liquid crystal element corresponding to FIG. The diagram can be viewed in the same way as in Figure 9, but here the pixel pitch is set to the aforementioned "0.8 μm," which is smaller than "1 μm," and as an example, "13.8 Vpp" is applied, which ensures a sufficient amount of phase modulation. Then, the phase modulation distribution was analyzed for three cross sections: observation cross section A at "y=0.4", observation cross section B at "y=2", and observation surface within the element plane at "z=0.5".

[0051] Figure 12 shows an example of the simulation results of the phase modulation distribution in this case. Here, the results for observation cross section A are shown in Figure 12(a), and the results for observation cross section C within the element plane are shown in Figures 12(b) and (c). The diagrams are read in the same way as in Figure 10, and observation cross section B is omitted from the illustration because the same results were obtained for observation cross section A. These results confirm that even when driven at a pixel pitch of 0.8 μm, which is smaller than the pixel pitch of 1 μm, the phase modulation amount of the surrounding OFF pixels is suppressed to almost 0, and that the ground electrode 15 shields electric field leakage, making it possible to independently drive two-dimensionally arranged pixels.

[0052] 6. Effects of the embodiment The spatial light modulation element of this embodiment has a first substrate, a second substrate arranged opposite the first substrate, and a liquid crystal layer arranged between the first substrate and the second substrate, and the first substrate has, on its surface, drive electrodes arranged on both sides of pixels arranged in a first direction in pixels arranged in a matrix, and ground electrodes arranged between the columns of drive electrodes arranged in the first direction.

[0053] Furthermore, a holographic stereoscopic display device (a holographic stereoscopic display device using a spatial light modulation element and a reference light) may be configured that includes this spatial light modulation element and drives a liquid crystal layer with a horizontal electric field between driving electrodes arranged on both sides of pixels arranged in the first direction.

[0054] This configuration enables independent driving of pixels at a fine pixel pitch. In addition, the drive electrodes arranged on both sides of the pixels arranged in the first direction and the ground electrodes arranged between the rows of drive electrodes arranged in the first direction effectively suppress electric field leakage.

[0055] As an example of a method for driving the liquid crystal layer with a horizontal electric field between drive electrodes arranged on both sides of pixels arranged in the first direction, the liquid crystal layer may be driven by a potential difference between drive electrodes arranged on both sides of pixels arranged in the first direction.

[0056] The simple in-plane switching drive method, in which a drive electrode is placed at the center of a pixel and an electric field is applied toward a common electrode placed at the pixel boundary, has the problem that no change in the liquid crystal orientation on the drive electrode is obtained, and therefore no modulation is obtained in the center of the pixel. However, this problem can be solved by driving the liquid crystal layer with a horizontal electric field between drive electrodes arranged on both sides of the pixels arranged in the first direction (for example, by driving the liquid crystal layer with a potential difference between drive electrodes arranged on both sides of the pixels arranged in the first direction), as in this embodiment.In addition, the number of electrodes can be reduced compared to the simple horizontal electric field driving method, making it possible to achieve a narrower pixel pitch (even higher resolution).

[0057] In addition, in an initial alignment state in which the liquid crystal molecules of the liquid crystal layer are aligned in the direction perpendicular to the substrate, the alignment of the liquid crystal molecules may be changed by a horizontal electric field. This allows the orientation of the liquid crystal molecules to be changed to the horizontal direction (tilting the liquid crystal molecules horizontally) by a horizontal electric field, thereby achieving high light utilization efficiency.

[0058] Furthermore, the holographic stereoscopic display device of this embodiment may have a pixel pitch of 1 μm or less in the first direction, and a viewing angle of 30° or more. This makes it possible to provide a practical holographic stereoscopic display device. [Explanation of symbols]

[0059] 11 Drive electrode 13 Common electrode 15 Ground electrode

Claims

1. a first substrate, a second substrate provided opposite to the first substrate, and a liquid crystal layer provided between the first substrate and the second substrate; The first substrate has, on a surface thereof, drive electrodes arranged on both sides of pixels arranged in a first direction in pixels arranged in a matrix, and ground electrodes arranged between columns of the drive electrodes arranged in the first direction. Spatial light modulator.

2. The spatial light modulation element according to claim 1 is provided, the liquid crystal layer is driven by a horizontal electric field between the drive electrodes arranged on both sides of the pixels arranged in the first direction; Holographic stereoscopic display device.

3. the liquid crystal layer is driven by a potential difference between the drive electrodes arranged on both sides of the pixels arranged in the first direction; 3. The holographic stereoscopic display device according to claim 2.

4. The liquid crystal molecules of the liquid crystal layer are initially aligned in a direction perpendicular to the substrate, and the alignment of the liquid crystal molecules is changed by the horizontal electric field.

4. The holographic stereoscopic display device according to claim 2 or 3.

5. a pixel pitch of the pixels in the first direction is 1 μm or less; 3. The holographic stereoscopic display device according to claim 2.

6. The viewing angle of the holographic stereoscopic display device is 30° or more.

3. The holographic stereoscopic display device according to claim 2.

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