A large viewing angle holographic 3D display method

Abstract

The present invention proposes a large-viewing-angle holographic 3D display method, which includes three steps: first, for a 3D object, it is regarded as a series of object points, each object point corresponds to a diffraction image point, first, the hologram of the single image point is calculated based on the maximum diffraction angle of the spatial light modulator, and the effective viewing area of ​​the reconstructed image is analyzed based on the overall size of the object, and then a large-scale hologram of the 3D object is calculated; second, to load the large-scale hologram, the spatial light modulators are seamlessly spliced ​​together to form a large-scale spatial light modulator array, and collimated coherent light is used as the reconstructed light for illumination; third, a liquid crystal grating with a special structure is produced, and the liquid crystal grating is used to perform secondary diffraction modulation on the reconstructed image of the holographic 3D display, thereby generating multiple continuous secondary diffraction images, achieving a continuous expansion of the viewing angle.

Description

1. Technical Field

[0001] The present invention relates to holographic display technology, and more particularly, to a large-viewing-angle holographic 3D display method. 2. Background Technology

[0002] Traditional holographic 3D display technology using optical materials such as photorefractive polymers is difficult to achieve dynamic refresh, while holographic 3D display technology based on spatial light modulators can easily achieve dynamic refresh. However, due to the pixel pitch and size limitations of the spatial light modulator, the viewing angle of the holographic reconstruction image is very small. For example, to display a 3D image with a size of 200mm×200mm×200mm and a field of view of 30°, the number of pixels of the spatial light modulator used should be at least 10 12 This is difficult to achieve at this stage. At present, the viewing angle of the holographic reconstruction image based on a single spatial light modulator is usually less than 9°. Although many researchers have proposed time multiplexing or space multiplexing methods based on spatial light modulators to expand the viewing angle of holographic reproduction, the time multiplexing method has high requirements on the refresh rate of the spatial light modulator, and the holographic display system used by the space multiplexing method has a complex structure. In addition, metasurface structures with subwavelength modulation capabilities are also used in holographic display systems to expand the viewing angle. Some researchers have proposed using holographic optical elements in display systems to achieve wide-viewing angle display. However, there are still difficulties and challenges in the processing of metasurface structures and holographic optical elements. At present, existing holographic 3D display technology still finds it difficult to achieve a wide-viewing angle holographic 3D display effect. 3. Summary of the Invention

[0003] The present invention proposes a large viewing angle holographic 3D display method. Figure 1 As shown, the method includes three steps: the first step is to regard a 3D object as a series of object points, each of which corresponds to a diffraction image point, and first calculate the maximum diffraction angle of the spatial light modulator. Calculate the hologram of a single image point, analyze the effective viewing area of ​​the reconstructed image based on the overall size of the object, and then calculate the large-scale hologram of the 3D object; secondly, in order to load the large-scale hologram, seamlessly splice the spatial light modulators together to form a large-scale spatial light modulator array, and use collimated coherent light as the reconstructed light for illumination; thirdly, make a liquid crystal grating with a special structure, and use the liquid crystal grating to perform secondary diffraction modulation on the reconstructed image of the holographic 3D display, thereby generating N continuous secondary diffraction images, realizing the continuous expansion of the viewing angle. The viewing angle of the expanded holographic display is

[0004] In step 1, as shown in the attached Figure 2As shown, the coordinate origin is set at the center of the spatial light modulator, the size of the recorded 3D object is S, the distance between the 3D object and the spatial light modulator is L, the size of the spatial light modulator is H, and S≦H. During the reconstruction of the hologram, the coordinates of the leftmost image point A1 and the rightmost image point A2 in the x-axis direction of the reproduced image are recorded as x1 and x2 respectively, then x2-x1=S. In traditional holographic 3D display methods, due to the size limitation of the spatial light modulator, the maximum diffraction angle of the image point A1 is usually smaller than the maximum diffraction angle of the spatial light modulator. , that is, at the viewing position, the viewing area corresponding to the image point A1 is EF', so the viewing angle of the 3D object reproduction image is less than .

[0005] In order to increase the viewing angle, the present invention uses the maximum diffraction angle of the spatial light modulator As the maximum diffraction angle of each image point, according to the Fresnel diffraction theory and the geometric relationship of the reconstructed image, it is obtained:

[0006]

[0007]

[0008] Where λ is the wavelength and p is the pixel size of the spatial light modulator. At this time, the viewing area corresponding to the image point A1 is expanded to EF, and the viewing area corresponding to the image point A2 is BC. At this time, the holographic interference pattern size H1 of the image point A1 and the hologram size H of the entire 3D object are calculated. D for:

[0009] H1=H+S (3)

[0010] H D =H+2S (4)

[0011] From formula (4), it can be seen that when When the maximum diffraction angle of the image point is used, the size of the hologram of the 3D object to be recorded is larger than the size of the spatial light modulator. At this time, the viewing angle of the reconstructed image is .

[0012] Based on the analysis of formula (4), the hologram of each object point on the 3D object is calculated separately, and the holograms of all object points are superimposed to generate a large-scale hologram of the 3D object.

[0013] In step two, the size of the spatial light modulator (SLM) is expanded to accommodate the large-scale hologram of the 3D object. Based on the resolution of the 3D object being recorded, SLMs of the same model are seamlessly spliced ​​together to form a large-scale SLM array. The size of the large-scale SLM array is guaranteed to be no smaller than the resolution of the large-scale hologram. The large-scale SLM array is treated as a single, large-scale SLM loaded with the 3D object, and collimated coherent light is used as the reconstruction light to illuminate the large-scale SLM array.

[0014] In step 3, the liquid crystal grating is used to diffract and modulate the primary reconstructed image of the holographic 3D display. The structural design of the liquid crystal grating is shown in the attached figure. Figure 3 As shown, it includes an upper glass substrate, a liquid crystal layer, a powered strip electrode, a grounded strip electrode, and a lower glass substrate. The width of the powered strip electrode is w1, the width of the grounded strip electrode is w2, the gap between the powered and grounded strip electrodes is l, and the thickness of the liquid crystal layer is h. When a voltage is applied to the powered strip electrode, an encircling electric field is formed between the powered and grounded strip electrodes. This encircling electric field induces the liquid crystal molecules to deflect, thereby forming a centrally symmetric gradient refractive index distribution, causing light incident on the liquid crystal layer to diffract. The diffraction order N of the liquid crystal grating is expressed as follows:

[0015]

[0016] Where d is the pitch of the liquid crystal grating, θ is the incident angle of the diffracted light to the liquid crystal grating, 60°≦θ≦90°. When no voltage is applied to the liquid crystal grating, the viewing angle of the holographic reproduction image seen by the viewer is When voltage is applied to the liquid crystal grating, the primary reconstructed image generates N secondary diffraction images. When the size and diffraction distance of the reconstructed image are determined, the viewing angle of the secondary diffraction image modulated by the liquid crystal grating is controlled to be continuous. At this time, the viewing angle is IV. Description of the Figures

[0017] Attachment Figure 1 Schematic diagram of a large-viewing-angle holographic 3D display method of the present invention.

[0018] Attachment Figure 2 Schematic diagram of the diffraction principle of a 3D object of the present invention.

[0019] Attachment Figure 3 Schematic diagram of the structure of the liquid crystal grating of the present invention.

[0020] The diagram numbers in the above drawings are:

[0021] (1) 3D object, (2) spatial light modulator, (3) reproduced image, (4) viewing position, (5) upper glass substrate, (6) liquid crystal layer, (7) powered strip electrodes, (8) grounded strip electrodes, (9) lower glass substrate.

[0022] It should be understood that the above drawings are merely schematic and not drawn to scale. V. Specific Implementation Methods

[0023] The following detailed description of an embodiment of a wide-viewing-angle holographic 3D display method proposed by the present invention further illustrates the present invention. It is important to note that the following embodiments are intended only to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by persons skilled in the art based on the above disclosure are still within the scope of protection of the present invention.

[0024] The system embodiment of the present invention is as follows: In the experiment, the spatial light modulator is a pure phase-type spatial light modulator, with a pixel pitch of 3.74 μm, a refresh rate of 60 Hz, a resolution of 3840 × 2160, and a phase modulation capability of 2π. According to formula (1), the maximum diffraction angle of the spatial light modulator is calculated to be ~4.078°. The wavelength of the collimated coherent light is 532 nm. Two spatial light modulators of the same model are used to form a large-scale spatial light modulator array with a resolution of 7680 × 2160. In the liquid crystal grating, the width w1 of the powered strip electrode is 10 μm, the width w2 of the grounded strip electrode is 10 μm, the gap l between the powered strip electrode and the grounded strip electrode is 10 μm, and the thickness h of the liquid crystal layer is 10 μm. When the voltage applied to the powered strip electrode is 7.2 V, the pitch of the liquid crystal grating is 20 μm. At this time, the incident angle and voltage of the diffracted light on the liquid crystal grating are adjusted to achieve a uniform diffraction order of 9. Using a "cylinder" with a certain depth information as the recorded 3D object, its resolution is 1920×2160, and the reproduction distance is 25cm. The calculated resolution of the large-scale hologram is 7680×2160. Collimated coherent light is used to illuminate the large-scale spatial light modulator array. In the initial state, no voltage is applied to the liquid crystal grating, and the viewing angle of the holographic 3D display is ~8.156°. When a voltage is applied to the liquid crystal grating, the diffraction image undergoes secondary diffraction after passing through the liquid crystal grating, thus achieving a large-viewing angle holographic 3D display effect, at which time the viewing angle is ~73.404°.

Claims

1. A large viewing angle holographic 3D display method, characterized in that: The method comprises the following steps: First, for a 3D object, consider it as a series of object points, each object point corresponds to a diffraction image point, first according to the maximum diffraction angle of the spatial light modulator Calculate the hologram of a single image point, analyze the effective viewing area of ​​the reconstructed image based on the overall size of the object, and then calculate the large-scale hologram of the 3D object; secondly, in order to load the large-scale hologram, seamlessly splice the spatial light modulators together to form a large-scale spatial light modulator array, and use collimated coherent light as the reconstructed light for illumination; thirdly, make a liquid crystal grating with a special structure, and use the liquid crystal grating to perform secondary diffraction modulation on the reconstructed image of the holographic 3D display, thereby generating N continuous secondary diffraction images, realizing the continuous expansion of the viewing angle. The viewing angle of the expanded holographic display is In step 1, the coordinate origin is set at the center of the spatial light modulator, the size of the recorded 3D object is S, the distance between the 3D object and the spatial light modulator is L, the size of the spatial light modulator is H, S ≦ H, in the process of hologram reconstruction, in order to increase the viewing angle, the maximum diffraction angle of the spatial light modulator is used. As the maximum diffraction angle of each image point, the following formula is obtained: Where λ is the wavelength and p is the pixel size of the spatial light modulator. At this time, the holographic interference pattern size H1 of the leftmost image point and the hologram size H of the entire 3D object are calculated. D for: H1=H+S H D =H+2S when When the maximum diffraction angle of the image point is used, the size of the hologram of the 3D object to be recorded is larger than the size of the spatial light modulator. At this time, the viewing angle of the reconstructed image is Then the hologram of each object point on the 3D object is calculated separately, and the holograms of all object points are superimposed to generate a large-size hologram of the 3D object.

2. The method for large viewing angle holographic 3D display according to claim 1, wherein: In step 2, in order to load a large-scale hologram of a 3D object, the size of the spatial light modulator is expanded. According to the resolution of the 3D object to be recorded, spatial light modulators of the same model are seamlessly spliced ​​together to form a large-scale spatial light modulator array. The size of the large-scale spatial light modulator array is ensured to be no less than the resolution of the large-scale hologram. The large-scale spatial light modulator array is regarded as a whole to load the large-scale hologram of the 3D object, and collimated coherent light is used as the reproduction light to illuminate the large-scale spatial light modulator array.

3. The method for large viewing angle holographic 3D display according to claim 1, wherein: In step three, a liquid crystal grating is used to diffract and modulate the primary reconstructed image of the holographic 3D display. The structure of the liquid crystal grating includes an upper glass substrate, a liquid crystal layer, a powered strip electrode, a grounded strip electrode, and a lower glass substrate. When a voltage is applied to the powered strip electrode, a surrounding electric field is formed between the powered strip electrode and the grounded strip electrode. The surrounding electric field induces the liquid crystal molecules to deflect, thereby forming a centrally symmetric gradient refractive index distribution, causing light incident on the liquid crystal layer to diffract. The diffraction order N of the liquid crystal grating is expressed by the following formula: Where d is the pitch of the liquid crystal grating, θ is the incident angle of the diffracted light to the adjustable liquid crystal grating, 60°≦θ≦90°, when the liquid crystal grating is not voltage-applied, the viewing angle of the holographic reproduction image seen by the viewer is When voltage is applied to the liquid crystal grating, the primary reconstructed image generates N secondary diffraction images. When the size and diffraction distance of the reconstructed image are determined, the viewing angle of the secondary diffraction image modulated by the liquid crystal grating is controlled to be continuous. At this time, the viewing angle is

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