Display device and head-mounted display apparatus

Abstract

To provide a technique for avoiding deterioration in the quality of a display image due to a diffraction phenomenon in a laminated light field type display device.SOLUTION: A display device 1 is a light field type display device in which a first liquid crystal display panel 10 and a second liquid crystal display panel 20 are laminated by interposing a medium layer 30. The first liquid crystal display panel has a light source 11 that emits light, which is at least partially coherent. A phase shifter film 26 is formed on a pixel opening of at least one of the first liquid crystal display panel and the second liquid crystal display panel, and a phase of the light emitted from pixels adjacent in at least one direction is different from 170° or more and 190° or less in the second liquid crystal display panel.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a display device, and more particularly to a display device using light field technology, and also to a head-mounted display device to which the display device is applied. [Background technology]

[0002] In recent years, light field technology, which controls the light rays emitted from a display device and incident on the observer's eyes, has been attracting attention. Humans can see various objects when light rays reflected from the object enter the eye. Light field technology artificially reproduces these reflected light rays on a display, resulting in a sense of depth similar to what humans see in nature.

[0003] There are several types of display devices using light field technology, and representative ones include a microlens array type and a stacked type. In the microlens array method, an array with lenses with diameters on the order of micrometers is attached to the surface of a display panel. In the microlens array method, the microlens array splits the light emitted from the display panel into bundles of light rays in specific directions and guides them to the viewer's eyes.

[0004] The other stacking method has a structure in which two display panels are stacked with a medium layer sandwiched between them, as described in Patent Document 1. The first display panel located farther from the viewer is equipped with a backlight and has a function of emitting light. The second display panel located closer to the viewer does not have a function of emitting light, and is illuminated by the light emitted from the first display. In the stacked method, a light ray emitted from a pixel on a first display panel passes through a pixel on a second display panel and enters the viewer's eye, and the light ray is controlled by the combination of pixels through which it passes.

[0005] In the microlens array method, one microlens covers multiple pixels, so in principle a reduction in display resolution is unavoidable. On the other hand, the stacking method requires sufficient alignment of the first and second display panels, but has the advantage that it is not so difficult to increase the resolution. Some of the latest liquid crystal display panels have been reported to have a resolution of 1000 pixels per inch (1000 ppi) or more. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2020-521174 Summary of the Invention [Problem to be solved by the invention]

[0007] The inventors have found that, when the pixel size is reduced in the stacking method, the quality of the displayed image deteriorates due to the phenomenon of diffraction of light. The inventors have solved this problem and completed the present invention.

[0008] An object of the present invention is to provide a technique for avoiding deterioration of the quality of a displayed image caused by diffraction phenomena in a stacked light field display device. [Means for solving the problem]

[0009] The first aspect of the present invention is a light field type display device in which a first liquid crystal display panel 10 and a second liquid crystal display panel 20 are stacked with a medium layer 30 sandwiched between them. The first liquid crystal display panel comprises a light source 11 emitting light that is at least partially coherent. A phase shifter film 26 is formed over the pixel openings of at least one of the first and second liquid crystal display panels, and in the second liquid crystal display panel, the phases of light emitted from adjacent pixels in at least one direction differ by 170° or more and 190° or less.

[0010] A second aspect of the present invention is a head mounted display device comprising the display device according to the first aspect and an eyepiece lens arranged closer to the observer than the second liquid crystal display panel. Effect of the Invention

[0011] The present invention contributes to avoiding deterioration of the quality of a displayed image due to the diffraction phenomenon in a light field display device. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic diagram showing a display device according to an embodiment of the present invention; [Diagram 2] 1 is a schematic diagram showing the relationship between the retina of the human eye and light rays. [Diagram 3] 1 is a schematic diagram showing the relationship between the retina and light rays when viewing a light field display device. [Figure 4] FIG. 1 is a schematic diagram showing image blurring caused by the principle of reverse light propagation; [Diagram 5] 1 is a schematic diagram showing the relationship between a pixel aperture and diffraction. [Figure 6] 11 is a schematic diagram showing superposition of diffracted lights when the light phases of the apertures of adjacent pixels are the same. FIG. [Figure 7] 13 is a schematic diagram showing superposition of diffracted light when a phase shifter film is provided in one of the openings of adjacent pixels. FIG. [Figure 8] FIG. 1 is a diagram showing the behavior of light emitted from adjacent pixels in a conventional light field display device. [Figure 9] 1 is a diagram showing the behavior of light emitted from adjacent pixels in a display device according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 is a diagram illustrating a display device 1 according to this embodiment. The display device 1 is a light field type display device, and includes two liquid crystal display panels, a first panel 10 and a second panel 20. The second panel 20 side of the display device 1 faces the front, and an observer views the displayed image from the front side.

[0014] The first panel 10 has a light source 11, a liquid crystal layer 12, and a color filter 13 arranged in this order, and has a structure generally similar to that of a known color liquid crystal display panel. The second panel 20 has a structure obtained by removing the light source 11 from the first panel 10. Furthermore, the first panel 10 and the second panel 20 each have a plurality of pixels that are partitioned by a black matrix 50. The first panel 10 and the second panel 20 have the same pixel aperture size. Since the pixel 40A of the first panel 10 and the pixel 40B of the second panel 20 have the same aperture size, the first panel 10 and the second panel 20 can be manufactured using the same manufacturing process. This has the advantage of reducing the total manufacturing cost of the display device 1.

[0015] A phase shifter film 26 is formed on every other pixel in both the up-down and left-right directions on the surface of the pixel 40B of the second panel 20. As a result, the phase shifter films 26 are arranged in a checkered pattern (similar to the arrangement of black and white on a chessboard) when the second panel 20 is viewed from the front.

[0016] In this embodiment, the first panel 10 and the second panel 20 have a rectangular or square shape of the same dimensions when viewed from the front. The first panel 10 and the second panel 20 are arranged such that their four sides coincide with each other when viewed from the front of the display device 1 as seen from the second panel 20 side.

[0017] The first panel 10 and the second panel 20 are disposed with the medium layer 30 therebetween. That is, the first panel 10 and the second panel 20 are disposed generally parallel to each other and separated by a distance corresponding to the thickness of the medium layer 30. A typical example of the material for the medium layer 30 is an air layer, but layers made of argon (refractive index 1.000281), carbon dioxide (refractive index 1.000449), helium (refractive index 1.000036), hydrogen (refractive index 1.000140), nitrogen (refractive index 1.000297), oxygen (refractive index 1.000276), etc., which have refractive indices almost similar to those of air (refractive index 1.0002926), or layers made of mixtures of these can also be used. Furthermore, a vacuum layer (refractive index 1.0000) can also be used and is included in the medium layer of the present invention.

[0018] Materials that can be used for the phase shifter film 26 include PMMA (polymethyl methacrylate resin) (refractive index at a wavelength of 550 nm: 1.490), silicon dioxide (refractive index at a wavelength of 550 nm: 1.460), resist (refractive index at a wavelength of 550 nm: 1.51 to 1.53), Teflon (registered trademark) resin (refractive index at a wavelength of 550 nm: 1.35 to 1.42), etc.

[0019] In the process of developing a stacked light field display device, the inventors have found that the quality of a displayed image is degraded due to the diffraction of light. Consider the case where an observer sees a light spot 101 in space, as shown in Figure 2. The light spot 101 is focused as an image 102 on the retina in the observer's eyeball 103 by the lens action of the crystalline lens of the observer's eye.

[0020] When an observer views a stacked light field display device, light rays are reproduced by a plurality of display panels, and an image 202 formed on the retina by the light rays reproduced by two display panels is visually recognized as shown in Fig. 3. At this time, the light rays are diffused after passing through the openings 205 and 206 on the second display panel 212, and therefore the image 202 of the light spot 201 is formed on the retina larger than the image 102 shown in Fig. 2. In other words, the observer visually recognizes a blurred image.

[0021] Based on the principle of reverse light propagation, the blur shown in Figure 3 can be considered as the blur of image 301 that occurs when light that is incident on apertures 205, 206 from the opposite direction and diffuses is gathered at the position of light spot 201 shown in Figure 2, as shown in Figure 4. Therefore, the relationship between the size of the aperture and the amount of blur will be considered using Figure 5. When the width of the aperture 405 is D, the size of the blur δ at a position with a rear distance L is expressed as δ = λ·L / D, where λ represents the wavelength of light. For example, when the wavelength is 0.5 μm and the aperture size is 50 μm, the size of the blur δ at a position with a rear distance of 10 mm is 0.5 x 10000 ÷ 50 = 100, or 100 μm. Since the width D of the aperture is usually equal to the size of a pixel on a display panel, it can be theoretically seen that the size of the blur is twice the pixel, which is a size that cannot be ignored.

[0022] Next, the effect of the blur caused by the diffraction phenomenon on the resolution of the pixels will be described. As shown in FIG. 6, when the light emitted from the adjacent pixel apertures 505 and 506 is diffused, some of the light overlaps at the image position. The light intensity distribution at the image position can be obtained by taking the sum of the amplitudes of the overlapping light and squaring it. In the example shown in FIG. 6, the light spreads due to diffraction, resulting in a single peak in the light intensity distribution at the image position, and the light from the two pixels, which originally have different peaks, cannot be separated. This means that when attempting to display an object located farther away from the second display panel, the finer the pixels of the second display panel are, the greater the blur caused by diffraction, and a blurred reproduced image is formed on the observer's retina. In other words, the observer will see a deteriorated reproduced image.

[0023] Next, consider the light emitted from the apertures 605, 606 of adjacent pixels of the second panel 20 in the display device 1. As shown in Fig. 7, the light emitted from the aperture 606 passes through the phase shifter film 26, and therefore becomes light with a phase shift of 180 degrees with respect to the light emitted from the other aperture 605. The light emitted from each pixel is diffused and partially overlaps with each other as in Fig. 9, but since there is a phase shift of 180 degrees between the lights emitted from each pixel, the lights overlap with the signs of their amplitudes reversed. As a result, the amplitudes of the overlapping parts cancel each other out, and a valley appears in the intensity distribution obtained by taking the square of the amplitudes, instead of a single peak, and the light from the two pixels can be separated. As described above, the inventors have succeeded in avoiding the occurrence of blurring due to diffraction by making the phases of light of adjacent pixels different enough to be nearly inverted by the phase shifter film 26. This shows that when attempting to display an object located far away from the second panel 20, blurring due to diffraction can be avoided even if the pixel size of the second panel 20 is reduced, and the viewer can view a reproduced image with less blurring.

[0024] In order to obtain the above-mentioned effect, the light emitted from adjacent pixel apertures needs to interfere with each other, so the light source 11 of the first panel 10 needs to emit coherent light, that is, coherent light. Examples of light sources that emit coherent light include a supercontinuum laser, an RGB synthetic white laser, a semiconductor laser, etc. However, since it is only necessary that the light entering the pupil interferes, the specific configuration of the light source 11 is not limited to these, and light sources of other configurations that emit at least partially coherent light, such as a monochromatic LED light source with a narrow wavelength width or various light sources combined with a bandpass filter, can also be used. The size of a human pupil is about 4.5 mm on average, varying from approximately 2.5 mm to 6.9 mm depending on the brightness, so the coherence length of the at least partially coherent light emitted by light source 11 is preferably 2.5 mm or greater, and more preferably 4.5 mm or greater.

[0025] The operation of the display device 1 according to this embodiment configured as above will be described. Light emitted from the light source 11 of the first panel 10 passes through the liquid crystal layer 12 and the color filter 13, and further the medium layer 30, toward the second panel 20.

[0026] In a stacked light field display device, the display resolution on the display panels can be improved by reducing the aperture size of the pixels 40 in the two display panels. For example, if the aperture size of each pixel 40 is reduced to 1 / 3, the display resolution will theoretically be tripled.

[0027] However, as mentioned above, it has been found that the diffraction of light causes image blurring in the second panel 20 located closer to the viewer, resulting in a deterioration in the quality of the displayed image at a position farther from the second panel. This theoretically occurring image blurring due to diffraction is called the diffraction limit here.

[0028] In a conventional display device 80 shown in Fig. 8, which does not include a phase shifter film 26 and has a configuration generally similar to that of the display device 1 in other respects, the phases of the amplitudes of light emitted from two adjacent pixels 40 match as shown in (b). As a result, the peaks of the light intensity distribution at the image point position on the observer's retina become one as shown in (c) due to the diffraction described in Fig. 6. In other words, the two lights are recognized as one combined light by the observer, and as a result, blur is visually recognized.

[0029] 9, on the other hand, a resolution exceeding the diffraction limit is realized by the phase shifter film 26. The phase shifter film 26 is arranged in a checkerboard pattern when the second panel 20 is viewed from the front, so that one of two adjacent pixels has the phase shifter film 26 and the other does not have the phase shifter film 26 in either of the two orthogonal directions, that is, the up-down direction and the left-right direction.

[0030] The phase of a light ray emitted from the first panel 10 and incident on a pixel 40B1 in the second panel 20 that does not have a phase shifter film 26 does not change even when it passes through the second panel 20. On the other hand, the phase of a light ray emitted from the first panel 10 and incident on a pixel 40B2 in the second panel 20 that has a phase shifter film 26 passes through the second panel 20 with a change in phase. The optical path difference ΔL between a light ray passing through a pixel not having a phase shifter film 26 (hereinafter sometimes referred to as a "first pixel") and a light ray passing through a pixel having a phase shifter film 26 (hereinafter sometimes referred to as a "second pixel") is expressed by the following formula (1). ΔL = (n1 - n0) d … (1)

[0031] In formula (1), n1 and n0 are the refractive indexes of the phase shifter film 26 and the medium layer 30, respectively, and d is the light passing distance. If n0 is the refractive index of air, which is approximately 1, formula (1) becomes formula (2) below. ΔL = (n1-1)d … (2)

[0032] In order to shift the phase of the light passing through the second pixel by 180° (λ / 2) from the light passing through the first pixel, ΔL must be set to λ / 2. Therefore, the suitable value of the film thickness of the phase shifter film 26 is obtained by the following formula (3). d = λ / (2 (n1-1)) … (3)

[0033] In formula (3), λ is the wavelength of the light. Therefore, when the pixel 40 of the second panel 20 has sub-pixels such as R (red), G (green), and B (blue), the central wavelength of the light passing through each sub-pixel is different, so that the optimal thickness of the phase shifter film 26 is slightly different for each sub-pixel. For this reason, it is ideal to form the phase shifter film 26 with an optimized thickness for each sub-pixel. In another embodiment, the phase shifter film 26 may be provided with the same thickness for all sub-pixels, with λ set to 550 nm, which is close to the median of the visible light wavelength range of 350 to 780 nm and to which the human eye has high sensitivity. In either embodiment, the phase of the light passing through the second pixel can be made to differ by approximately 180° from the light passing through the first pixel. The amount of phase shift does not need to be exactly 180°, and as long as the difference is within the range of 170° to 190°, a sufficient cancellation effect due to interference can be obtained.

[0034] As described above, the phase of the amplitude distribution of the light beam that has passed through the first pixel and the light beam that has passed through the second pixel differs by 180° due to the phase shifter film 26, as shown in (b) of Fig. 9. This allows the two beams to be distinguished at the image point on the observer's retina, as shown in (c) of Fig. 9. As a result, the observer can view the display with good image quality without feeling any blur. Since the human retina recognizes the intensity of light as the square of the amplitude, the light intensity distribution at the image point is as shown in (d) of Fig. 9. Therefore, the observer does not recognize the difference in phase between the light ray that passed through the first pixel and the light ray that passed through the second pixel, and there is no difference in the visual appearance between the light ray that passed through the first pixel and the light ray that passed through the second pixel.

[0035] As described above, the display device 1 according to this embodiment contributes to realizing an image resolution exceeding the diffraction limit in a stacked light field display device. Apart from the light source, the second panel 20 differs from the first panel 10 only in that it is provided with a phase shifter film 26, and therefore the second panel 20 can be produced simply by forming the phase shifter film 26 on the manufactured first panel. This has the advantage that a dedicated manufacturing line for the second panel 20 is not required, making it easier to reduce manufacturing costs.

[0036] The display device according to the present invention will be further described using examples and comparative examples. The technical scope of the present invention is not limited solely by the specific contents of the examples.

[0037] Example 1 Two IPS (In-Plane Switching) liquid crystal display panels of the same size and rectangular shape when viewed from the front were prepared. A supercontinuum laser light source and a color filter (RGB) were attached to one display to make it the first panel, and the other was attached only to a color filter to make it the second panel.

[0038] The display resolution of the first panel and the second panel is the same, 377 pixels per inch (377 ppi), the aperture size of each pixel is 63.0 μm, and the width of the black matrix formed between the pixels is 4.3 μm.

[0039] In the second panel, a phase shifter film made of silicon dioxide with a thickness of 598 nm was formed on the surface of every other pixel by covering the surface of the second panel with a metal mask with openings of the same size as the pixel openings formed in a checkerboard pattern, and sputtering silicon material under an oxygen atmosphere.

[0040] The first panel and the second panel were completely overlapped in a front view with a gap of 20 mm between them and fixed in this state to obtain the display device according to Example 1. This display device has an air layer with a thickness of 20 mm as a medium layer. Furthermore, an eyepiece was attached to this display device to fabricate a head mounted display (HMD) device according to Example 1.

[0041] When a predetermined image was displayed on the first panel using the HMD device according to Example 1 and evaluated visually, no blurring of the display was observed and the result was good.

[0042] Example 2 The display resolution of the first and second panels was 1539 pixels per inch (ppi). The aperture size of each pixel was 12.9 μm. The width of the black matrix was 3.6 μm. The light source in the first panel was an RGB synthesized white light laser. The thickness of the phase shifter film was 561 nm.

[0043] The first panel and the second panel were completely overlapped in a front view with a gap of 10 mm between them and fixed in this state to obtain a display device according to Example 2. This display device has an air layer with a thickness of 10 mm as a medium layer. Furthermore, an eyepiece was attached to this display device to fabricate an HMD device according to Example 2.

[0044] When a predetermined image was displayed on the first panel using the HMD device according to Example 2 and a visual evaluation was performed, no blurring of the display was observed and the result was good.

[0045] Comparative Example 1 A display device and an HMD device according to Comparative Example 1 were produced in the same manner as in Example 1, except that a phase shifter film was not formed on the second panel.

[0046] When a predetermined image was displayed on the first panel by using the HMD device according to Comparative Example 1 and evaluated visually, blurred display was observed for the image signal input to the first panel, and the result was not satisfactory.

[0047] Comparative Example 2 A display device and an HMD device according to Comparative Example 2 were produced in the same manner as in Example 2, except that a phase shifter film was not formed on the second panel.

[0048] When a predetermined image was displayed on the first panel by using the HMD device according to Comparative Example 2 and evaluated visually, blurred display was observed for the image signal input to the first panel, and the result was not satisfactory.

[0049] Although each embodiment and example of the present invention has been described above, the specific configurations are not limited to these embodiments, and modifications and combinations of the configurations that do not depart from the gist of the present invention are also included.

[0050] The display device according to the present invention may include three or more display panels. The phase shifter film may be provided on any of the display panels, but the effect can be maximized by providing the phase shifter film on the display panel closest to the viewer. Furthermore, the phase shifter films may be distributed among a number of display panels.

[0051] The phase shifter film according to the present invention is best arranged in the above-mentioned checkerboard pattern, but may be arranged in stripes extending in the vertical or horizontal direction. In this case, only the light emitted from the pixels adjacent in the horizontal or vertical direction will be canceled out by interference, but even with such a configuration, a certain degree of blur suppression effect can be achieved.

[0052] The phase shifter film according to the present invention is not limited to the one formed by the above-mentioned film forming technique such as sputtering, etc. Therefore, the phase shifter film according to the present invention also includes a film formed by attaching a film-like or sheet-like member, etc., as long as it has a similar effect. [Explanation of symbols]

[0053] 1 Display device 10 First Panel (First Liquid Crystal Display Panel) 11 Light source 20 Second panel (second liquid crystal display panel) 26 Phase shifter film 30 Medium Layer

Claims

1. A light field type display device in which a first liquid crystal display panel and a second liquid crystal display panel are stacked with a medium layer therebetween, the first liquid crystal display panel having a light source emitting at least partially coherent light; a phase shifter film is formed over pixel apertures of at least one of the first liquid crystal display panel and the second liquid crystal display panel; In the second liquid crystal display panel, the phases of light emitted from adjacent pixels in at least one direction differ from each other by 170° or more and 190° or less. Display device.

2. the phase shifter film is arranged in a checkerboard pattern when viewed from the front of the display device, In the second liquid crystal display panel, the phases of light emitted from adjacent pixels in two orthogonal directions differ from each other by 170° or more and 190° or less.

2. The display device of claim 1.

3. The phases of the lights emitted from adjacent pixels in the one direction are different by 180°.

3. A display device according to claim 1 or 2.

4. The light source is any one of a supercontinuum laser, an RGB synthetic white light laser, a semiconductor laser, and an LED light source; 2. The display device of claim 1.

5. A display device according to claim 1 or 2; an eyepiece disposed closer to an observer than the second liquid crystal display panel; Equipped with Head mounted display device.

Images