Large-size wide-viewing-angle holographic near-to-eye 3D display system based on liquid crystal holographic lens

Abstract

The invention provides a large-size wide-view-angle holographic near-to-eye 3D display system based on a liquid crystal holographic lens. The system comprises a laser, a beam expander, a semi-transparent and semi-reflecting mirror, a spatial light modulator, a signal controller, a polaroid, a filter, a polarization converter and the liquid crystal holographic lens. The laser is used for generating coherent light. After being collimated and expanded by the beam expander, the light beam enters the spatial light modulator loaded with the hologram through the semi-transparent and semi-reflecting mirror. The reconstructed light beam diffracted and modulated by the spatial light modulator enters the polaroid, and the polarization state of the reconstructed light beam is modulated into linearly polarized light by the polaroid. The filter is used for filtering stray light, and the polarization converter is used for converting the linear polarization state of the reconstructed light beam into a left-handed circular polarization state and a right-handed circular polarization state. The signal controller is used for loading a hologram and controlling the polarization converter, and the light beam is reflected by the liquid crystal holographic lens to generate a holographic reconstructed image. The near-to-eye 3D display system can realize large-size wide-viewing-angle holographic reconstruction.

Description

I. Technical Field

[0001] This invention relates to holographic display technology, and more specifically, to a large-size, wide-viewing-angle holographic near-eye 3D display system based on a liquid crystal holographic lens. II. Background Technology

[0002] Holographic display technology can reconstruct the complete wavefront information of an object, and it has great development potential in the field of 3D display, especially in near-eye 3D display. However, limited by the pixel pitch and resolution of spatial light modulators, holographic near-eye 3D displays face bottlenecks such as small size and narrow viewing angle. Furthermore, existing holographic near-eye 3D display systems struggle to simultaneously achieve large size and wide viewing angle, hindering the further development of this technology. In 2018, researchers proposed a moving exit pupil optical system based on a fixed exit pupil system, expanding the viewing angle of holographic near-eye 3D displays. In 2019, researchers proposed a holographic near-eye display based on holographic waveguides, which, through input and output coupler splicing, not only expanded the display size but also improved the compactness and high transmittance of the optical path. In 2021, researchers proposed a Michelson holographic near-eye 3D display method based on spatial multiplexing, achieving large-size holographic near-eye 3D displays by seamlessly splicing the reconstructed images from two spatial light modulators. However, existing methods for increasing the size or widening the viewing angle of holographic near-eye 3D displays typically increase system complexity, making it difficult to meet the requirements of lightweight and integrated near-eye displays. Furthermore, achieving both large-size and wide-viewing-angle holographic near-eye 3D display effects simultaneously remains a challenge. Therefore, how to achieve lightweight and integrated large-size, wide-viewing-angle holographic near-eye 3D displays remains an urgent problem to be solved. III. Summary of the Invention

[0003] This invention proposes a large-size, wide-viewing-angle holographic near-eye 3D display system based on a liquid crystal holographic lens. (See attached image) Figure 1 As shown, the system includes a laser, a beam expander, a semi-transparent mirror, a spatial light modulator, a signal controller, a polarizer, a filter, a polarization converter, and a liquid crystal holographic lens. The laser generates coherent light. After collimation and expansion by the beam expander, the beam passes through the semi-transparent mirror and is incident on the spatial light modulator loaded with a hologram. The reconstructed beam, diffracted and modulated by the spatial light modulator, is incident on the polarizer, where its polarization state is modulated into linear polarization. The filter removes stray light, and the polarization converter converts the linear polarization state of the reconstructed beam into left-handed and right-handed circular polarization states. The signal controller loads the hologram and controls the polarization converter. The beam is reflected by the liquid crystal holographic lens to generate a holographic reconstructed image. The holographic reconstructed image is captured by a camera to simulate human eye observation.

[0004] The working principle of the liquid crystal holographic lens is as follows: Figure 2As shown in the attached figure, the liquid crystal holographic lens is fabricated based on a polarization volume hologram. Figure 2 As shown in (a), the bottom light alignment layer determines the period of the local diffraction grating structure, while the top chiral liquid crystal layer exhibits a tilted spiral structure, forming a reflective diffraction grating structure with a Bragg surface tilt angle α. The working principle of the liquid crystal holographic lens is shown in the attached figure. Figure 2 As shown in (b), the liquid crystal holographic lens is polarization sensitive. When collimated left-handed circularly polarized light is incident obliquely on the liquid crystal holographic lens, lens L1 responds, and the beam is reflected and converged to focal point a. When collimated right-handed circularly polarized light is incident obliquely on the liquid crystal holographic lens, lens L2 responds, and the beam is reflected and converged to focal point b. When collimated linearly polarized light is incident obliquely on the liquid crystal holographic lens, both lenses L1 and L2 respond, and the beam is simultaneously reflected and converged to focal points a and b. The horizontal distance between the two focal points is d, and the vertical distance from lens L1 is f.

[0005] The system proposed in this invention achieves large-size, wide-viewing-angle near-eye holographic 3D display through the following method: First, as shown in the attached... Figure 3 As shown in (a), the complete image is resampled to match the resolution of the spatial light modulator, which is set to m×n, and the image resolution to 2m×n. Then, a bisection algorithm is used to divide the processed image into two sub-images, left and right. Each sub-image is processed by a hologram generation algorithm to generate corresponding sub-holograms A and B, both with a resolution of m×n. When left-handed and right-handed circularly polarized light pass through the liquid crystal holographic lens, there is an optical path difference between the two reconstructed beams. To stitch the two reconstructed images together on a plane of the same depth, depth compensation is added during the hologram calculation. The reconstruction distance of sub-hologram A is d1, and the imaging distance is d1'. The reconstruction distance of sub-hologram B is d2, and the imaging distance is d2'. The thickness of the liquid crystal holographic lens is D. According to the Gaussian imaging formula, the image distance between the two sub-reconstructed images is:

[0006]

[0007] To match the viewing distance between the two viewpoints, d2' = d1' + D. Therefore, the reconstruction distance d2 of sub-hologram B is:

[0008] To achieve seamless stitching of the two sub-reconstructed images, displacement compensation is added during hologram generation. Let the size of the sub-reconstructed images be x×y. Let the horizontal offset ratio be the ratio of the distance the image is offset to the right to the horizontal length of the image; if the image is offset to the left, the horizontal offset ratio is negative. Based on the principles of geometric optics, the horizontal offset ratio between sub-reconstructed images A and B is expressed as K. A and K B :

[0009]

[0010] At time T0, the signal controller loads sub-hologram B onto the spatial light modulator, and simultaneously sets the polarization converter to state I, modulating the linearly polarized light into left-handed circularly polarized light. Due to the polarization dependence of the liquid crystal holographic lens, the beam is focused to focal point a, generating sub-reconstructed image B behind the liquid crystal holographic lens. At time T1, sub-hologram A is loaded onto the spatial light modulator, and simultaneously sets the polarization converter to state II, modulating the linearly polarized light into right-handed circularly polarized light. The beam is focused to focal point b, generating sub-reconstructed image A behind the liquid crystal holographic lens. When the switching time is fast enough, based on the persistence of vision effect of the human eye, the reconstructed images of sub-holograms A and B are viewed simultaneously, thus realizing large-size holographic 3D display.

[0011] As attached Figure 3 As shown in (b), the polarization converter is turned off, allowing linearly polarized light to be modulated by the liquid crystal holographic lens. Layers L1 and L2 of the liquid crystal holographic lens reflect and focus left-handed and right-handed circularly polarized light to focal points a and b, respectively. When viewed, the viewer simultaneously sees a virtual reconstructed image and the real surrounding environment through the liquid crystal holographic lens. When viewed from the right side, the reconstructed image of the left-handed circularly polarized light is observed; when viewed from the left side, the reconstructed image of the right-handed circularly polarized light is observed, thus increasing the viewing angle. IV. Description of the attached drawings

[0012] Appendix Figure 1 This is a schematic diagram of the structure of a large-size, wide-viewing-angle holographic 3D near-eye display system based on a liquid crystal holographic lens according to the present invention.

[0013] Appendix Figure 2 This is a schematic diagram illustrating the working principle of the liquid crystal holographic lens of the present invention. (Attached) Figure 2 (a) is a schematic diagram of the liquid crystal holographic lens; (See attached diagram) Figure 2 (b) is a schematic diagram of the working principle of a liquid crystal holographic lens.

[0014] Appendix Figure 3 This is a schematic diagram illustrating the principle of the large-size, wide-viewing-angle near-eye holographic 3D display of the present invention. (Attached) Figure 3 (a) is a schematic diagram illustrating the principle of large-size holographic near-eye 3D display; (attached) Figure 3 (b) is a schematic diagram of the principle of wide-view holographic near-eye 3D display.

[0015] Appendix Figure 4 This is a reconstruction effect diagram of the present invention. (Attached) Figure 4 (a) is a large-size holographic 3D reconstructed image; attached Figure 4 (b) is a wide-view holographic 3D right-side reconstructed image; attached Figure 4 (c) is a wide-view holographic 3D left-side reconstructed image.

[0016] The figure labels in the above figures are as follows:

[0017] (1) Laser, (2) Beam expander, (3) Semi-transparent mirror, (4) Spatial light modulator, (5) Polarizer, (6) Filter, (7) Camera, (8) Signal controller, (9) Polarization converter, (10) Liquid crystal holographic lens.

[0018] It should be understood that the above figures are only schematic and are not drawn to scale. V. Detailed Implementation Methods

[0019] The following detailed description of an embodiment of a large-size, wide-viewing-angle near-eye holographic 3D display system based on a liquid crystal holographic lens, as proposed in this invention, further illustrates the invention. It is important to note that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of protection of this invention. Any non-essential improvements and adjustments made to this invention by those skilled in the art based on the above description are still within the scope of protection of this invention.

[0020] The system embodiment of this invention is as follows: In the experimental system, the wavelength of the green light source is 532nm, the spatial light modulator is a reflective pure phase spatial light modulator, the pixel pitch of the spatial light modulator is 3.74μm, the resolution is 3840×2160, the refresh rate is 180Hz, and the phase modulation capability is 2π. Using an image with a resolution of 7680×2160 as the recorded object, it is divided into two sub-objects. Two sub-holograms with a resolution of 3840×2160 are generated based on the stochastic gradient descent algorithm, and the reconstruction distance is set to 16cm for both. The two sub-holograms are sequentially loaded onto the spatial light modulator. When the reconstructed light illuminates the spatial light modulator, the diffracted light field of the reconstructed target image can be obtained. The diffracted light is incident on a liquid crystal holographic lens, and the lens reflects the light beam. Because the hologram switching time is very fast, the camera can receive both sub-reconstructed images and obtain a complete large-size scene reconstruction image, as shown in the attached figure. Figure 4 As shown in (a). Next, using a "tulip" as the recorded object with a resolution of 1000×2000, a hologram with a resolution of 3840×2160 was generated based on the stochastic gradient descent algorithm, with a reconstruction distance of 16.9 cm. With the polarization converter turned off, the diffracted light modulated by the spatial light modulator was modulated into linearly polarized light by a polarizer and incident on the liquid crystal holographic lens. The liquid crystal holographic lens reflected and converged the light beam to two focal points. The camera received the corresponding reconstructed images in the right and left viewing areas in front of the liquid crystal holographic lens, thus achieving a wide-view holographic display, as shown in the attached figure. Figure 4 As shown in (b)-(c).

Claims

1. A large-size wide-view holographic near-eye 3D display system based on liquid crystal holographic lens, characterized in that, The system comprises a laser, a beam expander, a half-transmission half-reflection mirror, a spatial light modulator, a signal controller, a polarizer, a filter, a polarization converter and a liquid crystal holographic lens; wherein the laser is used to generate coherent light; the collimated and expanded light beam passes through the half-transmission half-reflection mirror and is incident on the spatial light modulator loaded with a hologram; the reconstructed light beam diffracted and modulated by the spatial light modulator is incident on the polarizer, and the polarization state thereof is modulated by the polarizer into linearly polarized light; the filter is used to filter out stray light, and the polarization converter is used to convert the linear polarization state of the reconstructed light beam into left-handed circular polarization and right-handed circular polarization; the signal controller is used to load the hologram and control the polarization converter; the light beam is reflected by the liquid crystal holographic lens to generate a holographic reconstructed image, and a camera simulates a human eye to obtain a large-size wide-view reconstructed image. 2.The large-size wide-view holographic near-eye 3D display system based on liquid crystal holographic lens according to claim 1, wherein, The liquid crystal holographic lens is made based on a polarization volume hologram, a bottom light orientation layer determines a period of a local diffraction grating structure, and a top chiral liquid crystal layer presents an inclined spiral structure to form a reflective diffraction grating structure with a Bragg surface inclination angle α; the liquid crystal holographic lens has polarization sensitivity; when left-handed circularly polarized light is obliquely incident on the liquid crystal holographic lens, the upper layer lens responds, and the light beam is reflected and converged to a right focal point; when right-handed circularly polarized light is obliquely incident on the liquid crystal holographic lens, the lower layer lens responds, and the light beam is reflected and converged to a left focal point; when linearly polarized light is obliquely incident on the liquid crystal holographic lens, the upper and lower layer lenses both respond, and the light beam is simultaneously reflected and converged to the right and left focal points, and the two focal points are located in the same horizontal plane relative to the liquid crystal holographic lens.

3. The large-size wide-view holographic near-eye 3D display system based on the liquid crystal holographic lens according to claim 1, wherein the system realizes large-size wide-view holographic near-eye 3D display by the following method: first, complete image resampling is performed to match the resolution of the spatial light modulator, the spatial light modulator resolution is m x n, and the image resolution is 2m x n; then, the processed image is divided into left and right two sub-images by using a bisection algorithm, and each sub-image is calculated to generate a corresponding sub-hologram A and B by using a hologram generation algorithm, and the resolution of the sub-hologram is m x n; when left-handed circularly polarized light and right-handed circularly polarized light pass through the liquid crystal holographic lens, there is an optical path difference between the two reconstructed light beams; in order to splice the two reconstructed images on the same depth plane, depth compensation calculation is added in the hologram calculation process; the horizontal distance between the two focal points of the liquid crystal holographic lens is d, the vertical distance between the focal point and the upper layer lens is f, the reconstruction distance of the sub-hologram A is d1, the imaging distance is d1', the reconstruction distance of the sub-hologram B is d2, the imaging distance is d2', and the thickness of the liquid crystal holographic lens is D; according to the Gaussian imaging formula, the image distance of the two sub-reconstructed images is: In order to match the viewing distance between the two viewpoints, d2' = d1' + D, so the reconstruction distance d2 of the sub-hologram B is: In order to realize seamless splicing of two sub-reconstruction images, displacement compensation is added in the hologram generation process; the size of the sub-reconstruction image is x×y, and the horizontal displacement ratio is the ratio of the distance of the image offset to the right to the horizontal length of the image, if the image is offset to the left, the horizontal displacement ratio is negative; based on the principle of geometric optics, the horizontal displacement ratio of the sub-reconstruction images A and B is represented as K A and K B : At T0 moment, the signal controller loads the sub-hologram B on the spatial light modulator, and the polarization converter is set to I state, modulating linearly polarized light into left circularly polarized light, due to the polarization dependence of the liquid crystal holographic lens, the light beam is converged to the right focal point, generating a sub-reconstruction image B behind the liquid crystal holographic lens; at T1 moment, the sub-hologram A is loaded onto the spatial light modulator, and the polarization converter is set to II state, modulating linearly polarized light into right circularly polarized light, the light beam is converged to the left focal point, generating a sub-reconstruction image A behind the liquid crystal holographic lens; according to the visual persistence effect of human eyes, the reconstruction images of sub-holograms A and B are simultaneously observed, realizing large-size holographic near-eye 3D display; The polarization converter is turned off, and linearly polarized light is modulated by the liquid crystal holographic lens, and the upper and lower layers of the liquid crystal holographic lens reflect and focus left and right circularly polarized light on the right and left focal points respectively; when the viewer watches, the virtual reconstruction image and the real surrounding environment are simultaneously observed through the liquid crystal holographic lens, when observing from the right observation area, the reconstruction image of left circularly polarized light is observed, when observing from the left observation area, the reconstruction image of right circularly polarized light is observed, realizing wide-view holographic near-eye 3D display.

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