Optical phase modulation system, and display device

Abstract

An optical phase modulation system of the present disclosure comprises: an illumination light projection unit that is configured to enable polarization control in which the directions of the polarization of light projected as illumination light are set to a first polarization direction and a second polarization direction different from the first polarization direction, and that is configured to enable the light in the first polarization direction and the light in the second polarization direction to be projected at mutually different timings and in mutually different directions; a phase modulation unit having a first area configured to enable phase modulation of the light in the first polarization direction from the illumination light projection unit, and a second area configured to enable phase modulation of the light in the second polarization direction from the illumination light projection unit; and a synchronization controller that synchronizes the timing at which the light in the first polarization direction and the light in the second polarization direction are projected from the illumination light projection unit and the timing of the phase modulation of the first and second areas of the phase modulation unit.

Description

Optical phase modulation system and display device

[0001] The present disclosure relates to an optical phase modulation system and a display device.

[0002] Generally, in a liquid crystal optical phase modulation element, the thickness of the liquid crystal layer is doubled to ensure twice the phase modulation amount (0 to 2π) compared to a liquid crystal brightness modulation element. A fundamental characteristic of liquid crystal is that the response speed is proportional to the square of the thickness of the liquid crystal layer. Therefore, the response speed of an optical phase modulation element is four times slower than that of a brightness modulation element. In response to this, a technology has been proposed in which two optical phase modulation elements with a phase modulation amount of 0 to π and the same thickness as the brightness modulation element are arranged in the optical path, achieving a normal phase modulation amount (0 to 2π) while achieving the same response speed as a normal brightness modulation element (see Patent Document 1).

[0003] JP 2014-66869 A

[0004] When two optical phase modulation elements are placed in the same optical path, the distance between the two optical phase modulation elements becomes long, and since the light incident on the second optical phase modulation element is already not planar in phase, it becomes very difficult to control the phase front, resulting in a deterioration in image quality.

[0005] It is desirable to provide an optical phase modulation system and a display device that can improve the response speed of phase modulation while suppressing degradation in image quality.

[0006] An optical phase modulation system according to one embodiment of the present disclosure includes an illumination light emitting unit configured to be able to polarize and control the polarization direction of light emitted as illumination light between a first polarization direction and a second polarization direction different from the first polarization direction, and configured to be able to emit light of the first polarization direction and light of the second polarization direction at different times and in different directions; a phase modulation unit having a first region configured to be able to perform phase modulation on the light of the first polarization direction from the illumination light emitting unit and a second region configured to be able to perform phase modulation on the light of the second polarization direction from the illumination light emitting unit; and a synchronization control unit that synchronizes the timing at which the light of the first polarization direction and the light of the second polarization direction are emitted from the illumination light emitting unit with the timing of the phase modulation in the first region and the second region of the phase modulation unit.

[0007] A display device according to one embodiment of the present disclosure includes an illumination light emitting section configured to be capable of polarization control of the polarization direction of light emitted as illumination light between a first polarization direction and a second polarization direction different from the first polarization direction, and configured to be capable of emitting light of the first polarization direction and light of the second polarization direction at different times and in different directions; a phase modulation section having a first region configured to be capable of performing phase modulation on the light of the first polarization direction from the illumination light emitting section and a second region configured to be capable of performing phase modulation on the light of the second polarization direction from the illumination light emitting section; and a synchronization control section that synchronizes the timing at which the light of the first polarization direction and the light of the second polarization direction are emitted from the illumination light emitting section with the timing of the phase modulation in the first region and the second region of the phase modulation section.

[0008] In an optical phase modulation system or a display device according to an embodiment of the present disclosure, light having a first polarization direction and light having a second polarization direction are emitted from an illumination light emitting unit at different timings, and the light having the first polarization direction and the light having the second polarization direction are phase-modulated in a first region and a second region of a phase modulation unit, respectively, by synchronizing the timing of emitting the light having each polarization direction with the timing of the phase modulation in each region.

[0009] 1. A perspective view showing an overview of a display device using a luminance modulation method. 2. A cross-sectional view showing an overview of a display device using a luminance modulation method. 3. A perspective view showing an overview of a display device using a phase modulation method. 4. A cross-sectional view showing an overview of a display device using a phase modulation method. 5. A cross-sectional view showing a comparison between a configuration of a liquid crystal type luminance modulation element and a configuration of a liquid crystal type optical phase modulation element. 6. A cross-sectional view showing an example of a configuration of an optical phase modulation system according to a comparative example. 7. An explanatory diagram showing a problem of the optical phase modulation system shown in FIG. 6. 8. A configuration diagram showing an overview of an optical phase modulation system according to a first embodiment of the present disclosure. 9. A plan view showing an example of a configuration of a phase modulation section in the optical phase modulation system according to the first embodiment. 10. A plan view showing an example of a configuration of a phase modulation section and an illumination light output section in the optical phase modulation system according to the first embodiment. 11. An explanatory diagram showing an example of a driving state of a phase modulation section in the optical phase modulation system according to the first embodiment. 12. An explanatory diagram showing an example of a rising response speed of a liquid crystal type luminance modulation element and a liquid crystal type optical phase modulation element. 13. An explanatory diagram showing an example of a falling response speed of a liquid crystal type luminance modulation element and a liquid crystal type optical phase modulation element. 14. An explanatory diagram showing a first example of a driving state of an optical phase modulation element according to a comparative example. 1 is an explanatory diagram showing a second example of a driving state of an optical phase modulation element according to a comparative example. FIG. 2 is an explanatory diagram showing an example of a driving state of a phase modulation unit in the optical phase modulation system according to the first embodiment. FIG. 3 is a cross-sectional view schematically showing an example of a configuration of an optical phase modulation system according to Modification 1. FIG. 4 is a cross-sectional view schematically showing an example of a configuration of an optical phase modulation system according to Modification 2. FIG. 5 is a cross-sectional view schematically showing an example of a configuration of an optical phase modulation system according to Modification 3. FIG. 6 is a cross-sectional view schematically showing a first example of a configuration of a polarization spectroscopic element. FIG. 7 is a perspective view schematically showing a second example of a configuration of a polarization spectroscopic element. FIG. 8 is a cross-sectional view schematically showing an example of a configuration of an optical phase modulation system according to Modification 4. FIG. 9 is a cross-sectional view schematically showing an example of a configuration of an optical phase modulation system according to Modification 5. FIG. 10 is a cross-sectional view schematically showing an example of a configuration of an optical phase modulation system according to Modification 7. FIG. 11 is a cross-sectional view schematically showing an example of a configuration of an optical phase modulation system according to Modification 8. FIG. 12 is a cross-sectional view schematically showing an example of a configuration of an optical phase modulation system according to Modification 9. FIG. 13 is a cross-sectional view schematically showing an example of a configuration of an optical phase modulation system according to Modification 10.

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The description will be made in the following order: 0. Comparative Example and Background (FIGS. 1 to 7) 1. First Embodiment 1.1 Configuration and Operation (FIGS. 8 to 16) 1.2 Modifications (FIGS. 17 to 28) 1.3 Effects 2. Other Embodiments

[0011] <0. Comparative Examples and Background> (Display Device Using Brightness Modulation Method and Display Device Using Phase Modulation Method) Figures 1 and 2 show an overview of a display device using brightness modulation method. As shown in Figures 1 and 2, a typical projection display device (projector) has a configuration in which uniform illumination light emitted from a light source 500 is irradiated onto a light intensity modulation element 501 to perform light intensity modulation to generate an image, and the generated image is projected onto a screen 50 through a projection lens.

[0012] Typically, an LCD (Liquid Crystal Display) or a DMD (Digital Micro-mirror Device) is used as the light intensity modulation element 501. Liquid crystal projectors using liquid crystal panels, in particular, have excellent color reproducibility and can achieve high image quality. In liquid crystal projectors, the liquid crystal panel is used as an optical shutter. FIGS. 1 and 2 show an example in which a transmissive liquid crystal panel is used as the light intensity modulation element 501. The liquid crystal panel is configured by sandwiching a liquid crystal layer 513 containing a plurality of liquid crystal molecules 514 between a pair of substrates 502 and 503. When the light intensity modulation element 501 is a transmissive liquid crystal panel, a polarizer 521 is arranged in the direction of light incidence and an analyzer 522 is arranged in the direction of light emission. The polarizer 521 emits polarized light that is polarized in a predetermined polarization direction from the incident light L11. In a brightness modulation display device, one pixel of the light intensity modulation element 501 corresponds to one pixel of the final displayed image. When the light intensity modulation element 501 is a liquid crystal panel, when a dark image area is to be displayed, the illumination light must be blocked by the liquid crystal panel, and there is light that is not used for display, which significantly reduces the light utilization efficiency.

[0013] In contrast to this, there is a technology for phase modulation type display devices that uses an SLM (Spatial Light Modulator) as a diffraction element to generate illumination light, thereby distributing part of the light irradiated onto low-brightness pixel areas to high-brightness areas.

[0014] 3 and 4 show an overview of a phase modulation display device. FIGS. 3 and 4 show an example in which a reflective diffraction element is used as the optical phase modulation element 1. In a phase modulation display device, for example, uniform illumination light emitted from a light source 500 is irradiated onto the optical phase modulation element 1 to perform phase modulation, thereby generating a reconstructed image and projecting it onto a screen 50. Phase modulation display devices are highly efficient because they use light diffraction. In a phase modulation display device, one pixel of the optical phase modulation element 1 does not necessarily correspond to one pixel of the final image to be displayed; instead, multiple pixels in the optical phase modulation element 1 can correspond to one pixel of the final image to be displayed. Because multiple pixels in the optical phase modulation element 1 can be used to form one pixel of the final image, this is also characterized by stable pixel display even if a pixel defect occurs in the optical phase modulation element 1. Color display is also possible, and a technology has been disclosed in which illumination light of the three primary colors, R (red), G (green), and B (blue), is generated using different optical phase modulation elements 1 for each color.

[0015] A liquid crystal type optical phase modulation element can also be used as the optical phase modulation element 1. The desired reconstructed image can be obtained by calculating a phase distribution pattern (phase hologram) corresponding to the desired reconstructed image and displaying it on the liquid crystal type optical phase modulation element.

[0016] (Liquid crystal type luminance modulation element and liquid crystal type optical phase modulation element) Figure 5 shows a comparison between the configuration of a liquid crystal type luminance modulation element (Figure 5(A)) and the configuration of a liquid crystal type optical phase modulation element (Figure 5(B)).

[0017] 5 shows an example of a reflective type configuration. Both the brightness modulation element and the optical phase modulation element are configured such that liquid crystal molecules 613 are sealed between two opposing substrates 601 and 602. A pixel electrode (transparent electrode) 611 is provided on the liquid crystal layer side of the substrate 601, and a pixel electrode (reflective electrode) 612 is provided on the liquid crystal layer side of the substrate 601.

[0018] Generally, in a liquid crystal optical phase modulation element, the thickness (cell gap) d of the liquid crystal layer is doubled to ensure twice the phase modulation amount (0 to 2π) compared to a liquid crystal brightness modulation element. A fundamental characteristic of liquid crystal is that the response speed is proportional to the square of the liquid crystal layer thickness. Therefore, the response speed of an optical phase modulation element is four times slower than that of a brightness modulation element. For this reason, phase modulation display devices typically use an optical phase modulation element, even though this may result in a degradation of image quality, or take measures such as turning off the lights. However, in these cases, the frame rate, image quality, and brightness decrease.

[0019] In a liquid crystal type brightness modulation element, it is sufficient to ensure a retardation Δnd=π for any wavelength λ, whereas in a phase modulation type liquid crystal element, it is necessary to ensure a retardation Δnd=2π for the wavelength λ. It is generally known that the rising response speed of a nematic liquid crystal is expressed by the following formula (1), and the falling response speed is expressed by the following formula (2). In formulas (1) and (2), γ １ is the rotational viscosity, ε ０ is the dielectric constant of a vacuum, Δε is the dielectric anisotropy, d is the cell gap, V is the applied voltage, and V ｔｈ is the rotational viscosity.

[0020]

[0021]

[0022] If the thickness of the liquid crystal layer is doubled to ensure a retardation of 2π according to equations (1) and (2), both the rise and fall response speeds will be doubled. ２This limits the possibility of applying liquid crystal optical phase modulation elements to, for example, field sequential holographic displays that require high-speed response, and distance measurement technologies such as LiDAR (Light Detection and Ranging).

[0023] In response to the above-mentioned issue of response speed, Patent Document 1 (JP 2014-66869 A) proposes a technology in which two optical phase modulation elements with a phase modulation amount of 0 to π and a thickness equivalent to that of a brightness modulation element are arranged in the optical path, thereby realizing a normal phase modulation amount (0 to 2π) while making the response speed equivalent to that of a normal brightness modulation element.

[0024] As a comparative example, Fig. 6 shows an outline of an optical phase modulation system based on the technology described in Patent Document 1. This optical phase modulation system includes, as reflective liquid crystal optical phase modulation elements, a first optical phase modulation element 121 with a phase modulation amount of 0 to π and a second optical phase modulation element 122 with a phase modulation amount of 0 to π. A polarizing beam splitter 130, a first quarter-wave plate 141, and a second quarter-wave plate 142 are disposed between the first optical phase modulation element 121 and the second optical phase modulation element 122. In this optical phase modulation system, first, incident light Lin to the polarizing beam splitter 130 passes through the first quarter-wave plate 141 and is phase-modulated by the first optical phase modulation element 121. The light phase-modulated by the first quarter-wave plate 141 passes through the first quarter-wave plate 141, the polarizing beam splitter 130, and the second quarter-wave plate 142, and is phase-modulated by the second optical phase modulation element 122. The light phase-modulated by the second optical phase modulation element 122 passes through the second quarter-wave plate 142 and the polarizing beam splitter 130 and is output as output light Lout.

[0025] Figure 7 shows the problems with the optical phase modulation system shown in Figure 6. In the optical phase modulation system shown in Figure 6, two optical phase modulation elements 121 and 122 are used on the same optical path, so a distance Da is required to place the optical element 120 between the optical phase modulation elements 121 and 122. Therefore, even if the wavefront Wa of the incident light Lin is planar, the wavefront Wb at the stage of incidence on the second optical phase modulation element 122 is no longer planar, making it extremely difficult to control the phase front. Calculation of the phase pattern to be displayed on each optical phase modulation element also becomes difficult.

[0026] 1. First Embodiment [1.1 Configuration and Operation] (Outline of Optical Phase Modulation System) FIG. 8 shows an outline of an optical phase modulation system according to a first embodiment of the present disclosure.

[0027] The optical phase modulation system according to the first embodiment includes a phase modulation unit 20 , an illumination light emitting unit 21 , and a synchronization control unit 22 .

[0028] Fig. 9 shows a schematic configuration example of the phase modulation section 20. Fig. 10 shows a schematic configuration example of the phase modulation section 20 and the illumination light output section 21.

[0029] The phase modulation unit 20 has a first region 31 configured to be capable of performing phase modulation on light of a first polarization direction (e.g., P polarization) from the illumination light emitting unit 21, and a second region 32 configured to be capable of performing phase modulation on light of a second polarization direction (e.g., S polarization) from the illumination light emitting unit 21.

[0030] FIG. 9 shows an example in which the phase modulation section 20 is configured using a single liquid crystal optical phase modulation element 30 having a first region 31 and a second region 32. Note that, for example, positions A and A' in the phase modulation section 20 in FIG. 8 correspond to positions A and A' in the optical phase modulation element 30 in FIG. 9 . For example, the optical phase modulation element 30 has an effective pixel region and a peripheral region 33. The optical phase modulation element 30 has a structure in which the effective pixel region is divided into a first region 31 and a second region 32. In the optical phase modulation element 30, the alignment direction of the liquid crystal molecules 41 is different between the first region 31 and the second region 32. In the configuration example in FIG. 9 , the effective pixel region is divided into left and right halves, and the divided region on the left side is the first region 31, and the alignment direction of the liquid crystal molecules 41 is parallel to the long side of the optical phase modulation element 30. On the other hand, the divided region on the right side is the second region 32, and the orientation direction of the liquid crystal molecules 41 is perpendicular to the long side of the optical phase modulation element 30. This makes it possible to perform phase modulation on P-polarized light in the first region 31, and to perform phase modulation on S-polarized light in the second region 32. Note that the method and shape of dividing the effective pixel region are not limited to the configuration example in Figure 9, and other division methods and shapes may be used.

[0031] Furthermore, the phase modulation unit 20 may be configured with a first optical phase modulation element 30A and a second optical phase modulation element 30B, as in the configuration example shown in FIG. 10 . In this case, the alignment direction of the entire effective pixel region of the first optical phase modulation element 30A may be the same as that of the first region 31 of the optical phase modulation element 30 described above. Furthermore, the alignment direction of the entire effective pixel region of the second optical phase modulation element 30B may be the same as that of the second region 32 of the optical phase modulation element 30 described above. As a result, the first optical phase modulation element 30A (the first region 31) may be capable of performing phase modulation on P-polarized light. Furthermore, the second optical phase modulation element 30B (the second region 32) may be capable of performing phase modulation on S-polarized light.

[0032] The illumination light emitting unit 21 is configured to be able to control the polarization direction of light emitted as illumination light between a first polarization direction (e.g., P-polarized light) and a second polarization direction (e.g., S-polarized light) different from the first polarization direction. The illumination light emitting unit 21 is also configured to be able to emit light in the first polarization direction and light in the second polarization direction at different times and in different directions.

[0033] The illumination light emitting unit 21 has, for example, a polarization rotation element that controls the polarization direction of light to a first polarization direction and a second polarization direction, and an optical path branching element that branches the optical path of light in the first polarization direction and the optical path of light in the second polarization direction.

[0034] The synchronization control unit 22 synchronizes the timing at which light in the first polarization direction and light in the second polarization direction are emitted from the illumination light emitting unit 21 with the timing of phase modulation in the first region 31 and the second region 32 of the phase modulation unit 20. The synchronization control unit 22 synchronizes the timing at which light in the first polarization direction is emitted from the illumination light emitting unit 21 with the timing at which phase modulation of light in the first polarization direction is performed in the first region 31. The synchronization control unit 22 also synchronizes the timing at which light in the second polarization direction is emitted from the illumination light emitting unit 21 with the timing at which phase modulation of light in the second polarization direction is performed in the second region 32.

[0035] 10 , the illumination light output unit 21 includes a light source 60, a polarization rotation element 61, a polarization beam splitter (PBS) 62, and a mirror 63. The polarization rotation element 61 is an element that can electrically rotate the polarization direction of light, and is, for example, a liquid crystal element (e.g., a ferroelectric liquid crystal element). The polarization beam splitter 62 is an optical path branching element that branches the optical path of light having a first polarization direction from the optical path of light having a second polarization direction. The light source 60 is, for example, a laser light source that emits linearly polarized light.

[0036] In the configuration example shown in FIG. 10 , linearly polarized light from a light source 60 enters a polarization rotation element 61 as incident light Lin. The polarization rotation element 61 controls the polarization direction of the incident light Lin to P-polarized light and S-polarized light, and then outputs the light. The P-polarized light enters a first region 31 (first optical phase modulation element 30A) of the phase modulation unit 20 via a polarizing beam splitter 62 and a mirror 63, and undergoes phase modulation in the first region 31. The S-polarized light enters a second region 32 (second optical phase modulation element 30B) of the phase modulation unit 20 via a polarizing beam splitter 62, and undergoes phase modulation in the second region 32. The phase-modulated P-polarized light and S-polarized light are emitted in the same direction, forming a reconstructed image according to the phase modulation pattern.

[0037] The synchronization control unit 22 synchronizes the timing of polarization control by the polarization rotation element 61 with the timing of phase modulation in the first region 31 and the second region 32 of the phase modulation unit 20. The illumination light emitted from the polarization rotation element 61 illuminates either the first region 31 or the second region 32 of the phase modulation unit 20 depending on its polarization direction. The synchronization control unit 22 controls the polarization rotation element 61 to rotate the polarization direction of the illumination light in accordance with the response completion times of the liquid crystal in each of the first region 31 and the second region 32. As a result, phase modulation patterns are displayed alternately in each of the first region 31 and the second region 32.

[0038] Fig. 11 shows an example of the driving state (liquid crystal response state) of the phase modulation unit 20 in the optical phase modulation system shown in Fig. 10. In Fig. 11, the horizontal axis represents time and the vertical axis represents retardation. Fig. 11 shows an example in which 1.0 and 0 are alternately displayed as retardation values ​​in each of the first region 31 (first optical phase modulation element 30A) and the second region 32 (second optical phase modulation element 30B).

[0039] As described above, in the optical phase modulation system according to the first embodiment, by alternately using the first region 31 and the second region 32 of the phase modulation unit 20, the phase modulation unit 20 as a whole can drive liquid crystal at twice the speed of conventional systems. At this time, noise light generated from pixel regions in the refresh state, either the first region 31 or the second region 32, ideally becomes zero-order light because the direction of linear polarization is switched to a direction that does not generate an in-plane phase distribution. This noise light can be easily removed by installing a spatial filter for cutting zero-order light downstream of the phase modulation unit 20. Furthermore, even in applications where a static reconstructed image is continuously output, the linear polarization direction rotates by 90° within each frame, reducing image quality degradation due to speckle.

[0040] (Liquid crystal response speed of phase modulation unit 20) Fig. 12 shows an example of the rising response speed of a liquid crystal brightness modulation element and a liquid crystal optical phase modulation element. Fig. 13 shows an example of the falling response speed of a liquid crystal brightness modulation element and a liquid crystal optical phase modulation element.

[0041] Let us summarize the current state of the response speed that this technology attempts to solve. As mentioned above, a liquid crystal optical phase modulator must ensure twice the retardation compared to a liquid crystal brightness modulator. This creates the problem of a slower response speed. Figures 12 and 13 show an example of the response speed when the thickness of the liquid crystal layer in a liquid crystal optical phase modulator is changed to twice the thickness of the liquid crystal layer in a liquid crystal brightness modulator. According to the theoretical formulas (1) and (2) above, increasing the liquid crystal layer thickness slows down the response speed in both the rise and fall phases. When outputting a desired reconstructed image using a liquid crystal optical phase modulator, it is conceivable that a significant deviation from the ideal phase distribution in the transient state is a factor, and this deviation in the phase distribution leads to a decrease in diffraction efficiency and degradation of image quality.

[0042] FIG. 14 shows a first example of the driving state of the optical phase modulation element according to the comparative example.

[0043] Consider the liquid crystal response when attempting 100 Hz drive using a conventional liquid crystal optical phase modulator. Figure 14 shows the behavior of the liquid crystal response for 8 frames. For 100 Hz drive, 1 frame = 10 ms. Here, we consider a case where the desired retardation values ​​of 1.0 and 0 are alternately displayed every 10 ms. Here, we consider a VA (Vertical Alignment) mode, in which the rotation angle of the nematic liquid crystal is controlled by a vertical electric field mode. First, a voltage of a certain magnitude is applied at t = 0 ms, and at t ≈ 7 ms, the retardation reaches 90% of the target value. Then, at t = 10 ms, the system switches to the next frame, Frame 2, and no more voltage is applied. Therefore, the liquid crystal transitions to the tilt angle of the liquid crystal that achieves the next phase distribution due to the anchoring energy of the alignment film. In this case, the retardation value from 0 ms when the voltage application started to approximately 7 ms when the desired retardation value was achieved was significantly different from the target value, and it was clear that the target phase distribution was not achieved, which resulted in a decrease in diffraction efficiency and degradation of the image quality of the reconstructed image.

[0044] Next, consider the falling response in Frame 2. It can be seen from FIG. 14 that the voltage application ceases at t = 20 ms, and the retardation settles to roughly the target value at t ≈ 18 ms. At this time, as with Frame 1, the transient response has a significant effect for approximately 8 ms after the applied voltage changes, causing degradation of image quality. Similarly, thereafter, the transient response has a significant effect each time a frame is switched, resulting in a decrease in diffraction efficiency and degradation of image quality, which is an issue.

[0045] FIG. 15 shows a second example of the driving state of the optical phase modulation element according to the comparative example.

[0046] To address the above-described issues described with reference to Figure 14, applying the same voltage to the liquid crystal layer every two frames extends the time during which the target retardation value can be stably obtained, thereby minimizing the impact of the liquid crystal's transient response on the reproduced image. Furthermore, by turning off the light source during the transient response region, it is possible to further reduce the impact of image quality degradation on the reproduced image. However, this method presents issues such as reduced light utilization efficiency and limited applicability to applications requiring high-speed operation, such as LiDAR and field-sequential holographic displays.

[0047] FIG. 16 shows an example of the driving state of the phase modulation unit 20 in the optical phase modulation system according to the first embodiment.

[0048] In the optical phase modulation system according to the first embodiment, the above-mentioned problem can be solved by alternately using the first region 31 and the second region 32 of the phase modulation unit 20. As shown in the example of Figure 16, for example, by adopting the concept of sub-frames, which divides each 20 ms frame into a time period in which the first region 31 is used and a time period in which the second region 32 is used, it is possible to prevent a decrease in diffraction efficiency and degradation of the quality of the reproduced image due to the influence of transient response. Note that Figure 16 shows an example in which the first region 31 alternates between displaying retardation values ​​of 1.0 and 0, and the second region 32 alternates between displaying retardation values ​​of 0.9 and 0.1. For example, in Frame 1, by using the second region 32 between t = 0 and 10 ms and the first region 31 between t = 10 and 20 ms, each region has sufficiently passed the transient response during the effective time for actually displaying the reconstructed image, achieving a stable retardation value. By incorporating the concept of sub-frame driving in subsequent frames, it is possible to reduce the effects of the transient response and prevent degradation of the quality of the reconstructed image. Furthermore, as a secondary effect, since half of the light intensity of the final reconstructed image is composed of linearly polarized light that is orthogonal to each other, it is also possible to reduce the effects of speckle degradation on the reconstructed image.

[0049] [1.2 Modifications] (Modification 1) FIG. 17 shows a schematic configuration example of an optical phase modulation system according to Modification 1.

[0050] In the optical phase modulation system according to the first modification, the illumination light output unit 21 further includes a mirror 71 in addition to the configuration example shown in Fig. 10. Furthermore, in addition to the configuration example shown in Fig. 10, a polarizing beam splitter (PBS) 72 is disposed on the output side of the light from the phase modulation unit 20.

[0051] In the optical phase modulation system according to the first modification, linearly polarized light from a light source 60 is incident on a polarization rotation element 61 as incident light Lin. The polarization rotation element 61 controls the polarization direction of the incident light Lin to P-polarized light and S-polarized light, and then outputs the light. The P-polarized light enters a first region 31 (first optical phase modulation element 30A) of the phase modulation unit 20 via a polarizing beam splitter 62 and a mirror 63, and undergoes phase modulation in the first region 31. The S-polarized light enters a second region 32 (second optical phase modulation element 30B) of the phase modulation unit 20 via a polarizing beam splitter 62 and a mirror 71, and undergoes phase modulation in the second region 32. The phase-modulated P-polarized light and S-polarized light are output in the same direction via a polarizing beam splitter 72, and form a reconstructed image according to the phase modulation pattern.

[0052] The optical phase modulation system according to this modified example 1 has a configuration that makes it easier to lay out the optical system subsequent to the phase modulation unit 20 compared to the configuration example shown in FIG.

[0053] Other configurations and operations are the same as those in the configuration example shown in FIG.

[0054] (Modification 2) FIG. 18 shows a schematic configuration example of an optical phase modulation system according to Modification 2. In FIG.

[0055] The optical phase modulation system according to the second modification differs from the configuration example shown in FIG. 10 in that the phase modulation section 20 is configured by one optical phase modulation element 30 shown in FIG.

[0056] Other configurations and operations are the same as those in the configuration example shown in FIG.

[0057] (Modification 3) FIG. 19 shows a schematic configuration example of an optical phase modulation system according to Modification 3. In FIG.

[0058] The optical phase modulation system according to the third modification uses a polarization spectroscopic element 64 instead of the polarizing beam splitter 62 as an optical path branching element that branches the optical path of light having a first polarization direction and the optical path of light having a second polarization direction, in contrast to the configuration example shown in FIG.

[0059] Fig. 20 schematically shows a first configuration example of the polarization spectroscopic element 64. Fig. 21 schematically shows a second configuration example of the polarization spectroscopic element 64. The polarization spectroscopic element 64 may be, for example, a metasurface polarization spectroscopic element 81 as shown in Fig. 20. Alternatively, the polarization spectroscopic element 64 may be, for example, a polarizing prism 82 as shown in Fig. 21.

[0060] In the optical phase modulation system according to the third modification, linearly polarized light from a light source 60 is incident on a polarization rotation element 61 as incident light Lin. The polarization rotation element 61 controls the polarization direction of the incident light Lin to P-polarized light and S-polarized light, and then outputs the light. The P-polarized light enters a first region 31 (first optical phase modulation element 30A) of the phase modulation unit 20 via a polarization spectroscopic element 64, and undergoes phase modulation in the first region 31. The S-polarized light enters a second region 32 (second optical phase modulation element 30B) of the phase modulation unit 20 via the polarization spectroscopic element 64, and undergoes phase modulation in the second region 32. The phase-modulated P-polarized light and S-polarized light are emitted in the same direction, forming a reconstructed image according to the phase modulation pattern.

[0061] Other configurations and operations are the same as those in the configuration example shown in FIG.

[0062] (Modification 4) FIG. 22 shows a schematic configuration example of an optical phase modulation system according to Modification 4. In FIG.

[0063] The optical phase modulation system according to the second modification differs from the third modification shown in FIG. 19 in that the phase modulation section 20 is configured by one optical phase modulation element 30 shown in FIG.

[0064] The other configurations and operations are the same as those of the third modification shown in FIG.

[0065] (Modification 5) FIG. 23 shows a schematic configuration example of an optical phase modulation system according to Modification 5. In FIG.

[0066] The optical phase modulation system according to the fifth modification differs from the configuration example shown in FIG. 10 in that the first optical phase modulation element 30A and the second optical phase modulation element 30B are configured as reflective optical phase modulation elements.

[0067] Other configurations and operations are the same as those in the configuration example shown in FIG.

[0068] (Modification 6) FIG. 24 shows a schematic configuration example of an optical phase modulation system according to Modification 6. In FIG.

[0069] The optical phase modulation system according to the sixth modification differs from the third modification shown in FIG. 19 in that the first optical phase modulation element 30A and the second optical phase modulation element 30B are configured as reflective optical phase modulation elements.

[0070] The other configurations and operations are the same as those of the third modification shown in FIG.

[0071] (Seventh Modification) FIG. 25 shows a schematic configuration example of an optical phase modulation system according to a seventh modification.

[0072] In the optical phase modulation system according to the seventh modification, the illumination light emitting unit 21 has a light source 90, a rotary quarter-wave plate 91, a polarizing beam splitter (PBS) 62, and a mirror 65. The optical phase modulation system according to the seventh modification also has a phase modulation unit 20 configured with one optical phase modulation element 30 shown in Fig. 9. Note that the phase modulation unit 20 can also be configured with a first optical phase modulation element 30A and a second optical phase modulation element 30B, similar to the configuration example shown in Fig. 10.

[0073] The light source 90 is a circularly polarized light source that emits circularly polarized light. The rotatable quarter-wave plate 91 is a polarization rotation element that can mechanically rotate the polarization direction of light, and is a rotatable quarter-wave plate equipped with a mechanical rotation mechanism. The polarizing beam splitter 62 is an optical path branching element that branches the optical path of light having a first polarization direction (P-polarized light) and the optical path of light having a second polarization direction (S-polarized light).

[0074] In the optical phase modulation system according to the seventh modification, circularly polarized light from a light source 90 is incident on a rotary quarter-wave plate 91 as incident light Lin. The rotary quarter-wave plate 91 controls the polarization direction of the incident light Lin to P-polarized light and S-polarized light, and then outputs the light. The P-polarized light enters the first region 31 of the phase modulation unit 20 via the polarizing beam splitter 62 and undergoes phase modulation in the first region 31. The S-polarized light enters the second region 32 of the phase modulation unit 20 via the polarizing beam splitter 62 and the mirror 65 and undergoes phase modulation in the second region 32. The phase-modulated P-polarized light and S-polarized light are emitted in the same direction, forming a reconstructed image according to the phase modulation pattern.

[0075] The synchronization control unit 22 synchronizes the timing of polarization control by the rotary quarter-wave plate 91 with the timing of phase modulation in the first region 31 and the second region 32 of the phase modulation unit 20. The illumination light emitted from the rotary quarter-wave plate 91 illuminates either the first region 31 or the second region 32 of the phase modulation unit 20 depending on its polarization direction. The synchronization control unit 22 controls the rotary quarter-wave plate 91 to rotate the polarization direction of the illumination light in accordance with the response completion times of the liquid crystal in each of the first region 31 and the second region 32. As a result, phase modulation patterns are displayed alternately in each of the first region 31 and the second region 32.

[0076] The optical phase modulation system according to the seventh modification has a configuration that can improve the light utilization efficiency.

[0077] (Modification 8) FIG. 26 shows an outline of an example of the configuration of an optical phase modulation system according to Modification 8. In FIG.

[0078] In the optical phase modulation system according to the eighth modification, the illumination light emitting unit 21 has a light source 60, a galvanometer mirror 92, a mirror 93, and a half-wave plate 94. The optical phase modulation system according to the eighth modification also has a phase modulation unit 20 configured with one optical phase modulation element 30 shown in Fig. 9. Note that the phase modulation unit 20 can also be configured with a first optical phase modulation element 30A and a second optical phase modulation element 30B, similar to the configuration example shown in Fig. 10.

[0079] The light source 60 is, for example, a laser light source that emits P-polarized light as linearly polarized light. The galvanometer mirror 92 is an optical path switching element that switches the optical path of the illumination light between a first optical path and a second optical path different from the first optical path. The half-wave plate 94 is a polarization conversion element that is disposed on the second optical path and converts the polarization direction of the light from the first polarization direction (P-polarized) to the second polarization direction (S-polarized).

[0080] In the optical phase modulation system according to the eighth modification, linearly polarized (P-polarized) light from the light source 60 is incident on a galvanometer mirror 92 as incident light Lin. The galvanometer mirror 92 switches the optical path depending on whether the illumination light is incident on the first region 31 or the second region 32 of the phase modulation unit 20. When the galvanometer mirror 92 switches to the first optical path, the P-polarized light is incident on the first region 31 of the phase modulation unit 20 as illumination light and is phase-modulated in the first region 31. When the galvanometer mirror 92 switches to the second optical path, the P-polarized light is incident on a half-wave plate 94 via a mirror 93 and converted to S-polarized light. The S-polarized light is incident on the second region 32 of the phase modulation unit 20 and is phase-modulated in the second region 32. The phase-modulated P-polarized light and S-polarized light are emitted in the same direction to form a reconstructed image according to the phase modulation pattern.

[0081] The synchronization control unit 22 synchronizes the timing of switching the optical path by the galvanometer mirror 92 with the timing of phase modulation in the first region 31 and the second region 32 of the phase modulation unit 20. As a result, phase modulation patterns are displayed alternately in the first region 31 and the second region 32.

[0082] The optical phase modulation system according to the eighth modification has a configuration that can improve the light utilization efficiency and can perform polarization control using only general optical elements.

[0083] (Modification 9) FIG. 27 shows a schematic configuration example of an optical phase modulation system according to Modification 9. In FIG.

[0084] The optical phase modulation system according to the ninth modification differs from the seventh modification shown in FIG. 25 in that a nematic liquid crystal element 95 is used as the polarization rotation element instead of the rotatable quarter-wave plate 91 .

[0085] In the optical phase modulation system according to the ninth modification, circularly polarized light from a light source 90 is incident as incident light Lin on a nematic liquid crystal element 95. The nematic liquid crystal element 95 controls the polarization direction of the incident light Lin to P-polarized light and S-polarized light, and then outputs the light. The synchronization control unit 22 synchronizes the timing of the polarization control by the nematic liquid crystal element 95 with the timing of the phase modulation in the first region 31 and the second region 32 of the phase modulation unit 20.

[0086] The other configurations and operations are the same as those of the seventh modification shown in FIG.

[0087] (Modification 10) FIG. 28 shows a schematic configuration example of an optical phase modulation system according to Modification 10. In FIG.

[0088] The optical phase modulation system according to the tenth modification uses a ferroelectric liquid crystal element 96 as a polarization rotation element instead of the rotatable quarter-wave plate 91 of the seventh modification shown in Fig. 25. Also, instead of the light source 90 that emits circularly polarized light, a light source 60 that emits P-polarized light as linearly polarized light is used.

[0089] In the optical phase modulation system according to the tenth modification, P-polarized light from the light source 60 is incident as incident light Lin on the ferroelectric liquid crystal element 96. The ferroelectric liquid crystal element 96 controls the polarization direction of the incident light Lin to P-polarized light and S-polarized light, and then outputs the light. The synchronization control unit 22 synchronizes the timing of the polarization control by the ferroelectric liquid crystal element 96 with the timing of the phase modulation in the first region 31 and the second region 32 of the phase modulation unit 20.

[0090] The other configurations and operations are the same as those of the seventh modification shown in FIG.

[0091] [1.3 Effects] As described above, according to the optical phase modulation system according to the first embodiment, light in a first polarization direction and light in a second polarization direction are emitted from the illumination light emission unit 21 at different timings, and the light in the first polarization direction and the light in the second polarization direction are phase-modulated in the first region 31 and the second region 32 of the phase modulation unit 20, respectively. In this case, the timing at which the light in each polarization direction is emitted is synchronized with the timing of the phase modulation in each region. This makes it possible to improve the response speed of the phase modulation while suppressing degradation in image quality.

[0092] According to the optical phase modulation system of the first embodiment, the delay in response speed that occurs when an optical phase modulation element with a phase modulation amount of 0 to 2π is used can be improved by alternately using the two regions of the phase modulation unit 20. In this case, the frame rate can be increased without any deterioration in image quality or brightness (efficiency). Furthermore, because the light incident on the two regions of the phase modulation unit 20 maintains the wavefront (plane) of the illumination light, it is possible to easily calculate a phase pattern for displaying an arbitrary distribution.

[0093] The effects described in this specification are merely examples and are not limiting, and other effects may also be achieved. The same applies to the effects of other embodiments described below.

[0094] 2. Other Embodiments The technology according to the present disclosure is not limited to the above-described embodiments, and various modifications are possible.

[0095] For example, the present technology may be configured as follows. According to the present technology configured as follows, light in a first polarization direction and light in a second polarization direction are emitted from an illumination light emitting unit at different timings, and the light in the first polarization direction and the light in the second polarization direction are phase-modulated in a first region and a second region of a phase modulation unit, respectively. In this case, the timing of emitting the light in each polarization direction and the timing of the phase modulation in each region are synchronized. This makes it possible to improve the response speed of the phase modulation while suppressing degradation in image quality.

[0096] (1) An optical phase modulation system comprising: an illumination light emitting unit configured to be able to polarize and control the polarization direction of light emitted as illumination light between a first polarization direction and a second polarization direction different from the first polarization direction, and configured to be able to emit light of the first polarization direction and light of the second polarization direction at different times and in different directions; a phase modulation unit having a first region configured to be able to perform phase modulation on the light of the first polarization direction from the illumination light emitting unit, and a second region configured to be able to perform phase modulation on the light of the second polarization direction from the illumination light emitting unit; and a synchronization control unit that synchronizes the timing at which the light of the first polarization direction and the light of the second polarization direction are emitted from the illumination light emitting unit with the timing of the phase modulation in the first region and the second region of the phase modulation unit. (2) The optical phase modulation system according to (1) above, wherein the synchronization control unit synchronizes the timing at which light in the first polarization direction is emitted from the illumination light emitting unit with the timing at which phase modulation of the light in the first polarization direction is performed in the first region, and synchronizes the timing at which light in the second polarization direction is emitted from the illumination light emitting unit with the timing at which phase modulation of the light in the second polarization direction is performed in the second region. (3) The optical phase modulation system according to (1) or (2) above, wherein the phase modulation unit includes a first optical phase modulation element having the first region, and a second optical phase modulation element having the second region. (4) The optical phase modulation system according to (1) or (2) above, wherein the phase modulation unit includes a single optical phase modulation element having the first region and the second region. (5) The optical phase modulation system according to any one of (1) to (4), wherein the illumination light output unit has: a polarization rotation element that controls the polarization direction of light to the first polarization direction and the second polarization direction; and an optical path branching element that branches an optical path of light in the first polarization direction and an optical path of light in the second polarization direction; and the synchronization control unit synchronizes the timing of the polarization control by the polarization rotation element with the timing of phase modulation in the first region and the second region of the phase modulation unit.(6) The optical phase modulation system according to (5) above, wherein the polarization rotation element is an element capable of electrically rotating the polarization direction of light. (7) The optical phase modulation system according to (6) above, wherein the polarization rotation element is a liquid crystal element. (8) The optical phase modulation system according to (5) above, wherein the polarization rotation element is an element capable of mechanically rotating the polarization direction of light. (9) The optical phase modulation system according to (8) above, wherein the polarization rotation element is a rotatable wave plate equipped with a mechanical rotation mechanism. (10) The optical phase modulation system according to any one of (5) to (9) above, wherein the optical path branching element is a polarizing beam splitter. (11) The optical phase modulation system according to any one of (5) to (9) above, wherein the optical path branching element is a polarizing spectroscopic element. (12) The optical phase modulation system according to any one of (1) to (4), wherein the illumination light emitting unit has: an optical path switching element that switches an optical path of the illumination light between a first optical path and a second optical path different from the first optical path; and a polarization conversion element that is arranged on the second optical path and converts the polarization direction of the light from the first polarization direction to the second polarization direction, and the synchronization control unit synchronizes the timing of switching the optical path by the optical path switching element with the timing of phase modulation in the first region and the second region of the phase modulation unit. (13) The optical phase modulation system according to any one of (1) to (12), wherein the illumination light emitting unit has a light source that emits linearly polarized light. (14) The optical phase modulation system according to any one of (1) to (12), wherein the illumination light emitting unit has a light source that emits circularly polarized light.(15) A display device comprising: an illumination light emitting unit configured to be able to polarize and control the polarization direction of light emitted as illumination light between a first polarization direction and a second polarization direction different from the first polarization direction, and configured to be able to emit light of the first polarization direction and light of the second polarization direction at different times and in different directions; a phase modulation unit having a first region configured to be able to perform phase modulation on the light of the first polarization direction from the illumination light emitting unit, and a second region configured to be able to perform phase modulation on the light of the second polarization direction from the illumination light emitting unit; and a synchronization control unit that synchronizes the timing of polarization control in the illumination light emitting unit with the timing of phase modulation in the first region and the second region of the phase modulation unit.

[0097] This application claims priority based on Japanese Patent Application No. 2021-194909, filed on November 30, 2021, in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0098] Those skilled in the art will recognize that various modifications, combinations, subcombinations, and variations may occur depending on design requirements and other factors, and are intended to be within the scope of the appended claims and their equivalents.

Claims

1. An optical phase modulation system comprising: an illumination light emitting unit configured to be capable of polarization control of the polarization direction of light emitted as illumination light between a first polarization direction and a second polarization direction different from the first polarization direction, and configured to be capable of emitting light of the first polarization direction and light of the second polarization direction at different times and in different directions; a phase modulation unit having a first region configured to be capable of performing phase modulation on the light of the first polarization direction from the illumination light emitting unit, and a second region configured to be capable of performing phase modulation on the light of the second polarization direction from the illumination light emitting unit; and a synchronization control unit that synchronizes the timing at which the light of the first polarization direction and the light of the second polarization direction are emitted from the illumination light emitting unit with the timing of the phase modulation in the first region and the second region of the phase modulation unit.

2. The optical phase modulation system described in claim 1, wherein the synchronization control unit synchronizes the timing at which light in the first polarization direction is emitted from the illumination light emitting unit with the timing at which phase modulation of the light in the first polarization direction is performed in the first region, and synchronizes the timing at which light in the second polarization direction is emitted from the illumination light emitting unit with the timing at which phase modulation of the light in the second polarization direction is performed in the second region.

3. An optical phase modulation system as described in claim 1, wherein the phase modulation section includes a first optical phase modulation element having the first region, and a second optical phase modulation element having the second region.

4. The optical phase modulation system according to claim 1, wherein the phase modulation section includes one optical phase modulation element having the first region and the second region.

5. The optical phase modulation system of claim 1, wherein the illumination light emission unit has a polarization rotation element that controls the polarization direction of light to the first polarization direction and the second polarization direction, and an optical path branching element that branches an optical path of light in the first polarization direction and an optical path of light in the second polarization direction, and the synchronization control unit synchronizes the timing of the polarization control by the polarization rotation element with the timing of phase modulation in the first region and the second region of the phase modulation unit.

6. The optical phase modulation system according to claim 5, wherein the polarization rotation element is an element capable of electrically rotating the polarization direction of light.

7. The optical phase modulation system according to claim 6, wherein the polarization rotation element is a liquid crystal element.

8. The optical phase modulation system according to claim 5, wherein the polarization rotation element is an element capable of mechanically rotating the polarization direction of light.

9. The optical phase modulation system according to claim 8, wherein the polarization rotation element is a rotatable wave plate equipped with a mechanical rotation mechanism.

10. The optical phase modulation system according to claim 5, wherein the optical path branching element is a polarizing beam splitter.

11. The optical phase modulation system according to claim 5, wherein the optical path branching element is a polarizing spectroscopic element.

12. The optical phase modulation system of claim 1, wherein the illumination light emitting unit has an optical path switching element that switches the optical path of the illumination light between a first optical path and a second optical path different from the first optical path, and a polarization conversion element that is disposed on the second optical path and converts the polarization direction of the light from the first polarization direction to the second polarization direction, and the synchronization control unit synchronizes the timing of the switching of the optical path by the optical path switching element with the timing of phase modulation in the first region and the second region of the phase modulation unit.

13. The optical phase modulation system according to claim 1, wherein the illumination light emitting section has a light source that emits linearly polarized light.

14. The optical phase modulation system according to claim 1, wherein the illumination light emitting section has a light source that emits circularly polarized light.

15. A display device comprising: an illumination light emitting section configured to be capable of polarization control of the polarization direction of light emitted as illumination light between a first polarization direction and a second polarization direction different from the first polarization direction, and configured to be capable of emitting light of the first polarization direction and light of the second polarization direction at different times and in different directions; a phase modulation section having a first region configured to be capable of performing phase modulation on the light of the first polarization direction from the illumination light emitting section, and a second region configured to be capable of performing phase modulation on the light of the second polarization direction from the illumination light emitting section; and a synchronization control section that synchronizes the timing of the polarization control in the illumination light emitting section with the timing of the phase modulation in the first region and the second region of the phase modulation section.

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