Holographic 3D Display System Based on Virtual Array Splicing of Spatial Light Modulator

Abstract

A holographic 3D display system based on virtual array splicing of a spatial light modulator includes a laser configured to generate a coherent light beam, first, second and third beam splitters, first and second reflectors, a shutter array, a spatial filter array, a solid lens, first and second light beam deflection elements and a spatial light modulator. The first and second beam splitters and the first reflector are configured to split the light beam generated by the laser into three parallel light beams to irradiate the shutter array. The shutter array is configured to control the three parallel light beams to sequentially pass therethrough according to a set time sequence. The three parallel light beams passing through the shutter array are expanded and collimated by the spatial filter array and the solid lens to form three parallel light beams with the same size and uniform intensity.

Description

CROSS-REFERENCE TO RELATED APPLICATION

The present disclosure claims the priority to the Chinese patent application with the filing No. CN202110812111.2, filed on Jul. 19, 2021 with the Chinese Patent Office, and entitled “Holographic 3D Display System Based on Virtual Array Splicing of Spatial Light Modulator”, the contents of which are incorporated herein by reference in entirety.

TECHNICAL FIELD

The present disclosure relates to holographic display technology, and more particularly, to a holographic 3D display system based on virtual array splicing of a spatial light modulator.

BACKGROUND ART

The holographic display technology capable of reconstructing all wavefront information of the 3D object is considered as one of the most ideal 3D display methods, but due to limitation of the pixel size of the current spatial light modulator, the viewing visual area and the display size of the holographic reconstructed image based on a single spatial light modulator are quite small at present, which can hardly meet the viewing requirements. In order to solve this problem, researchers propose many solutions. For example, the space division multiplexing technology of using a plurality of spatial light modulators for curved surface splicing is used to obtain a large-visual-area holographic reconstructed image. Although this technology effectively enlarges the visual area of the holographic reconstructed image, the curved surface splicing of the plurality of spatial light modulators greatly increases the complexity and the cost of the system. In order to reduce the system complexity of splicing of a plurality of spatial light modulators, researchers expand the visual area of the holographic reconstructed image by continuously loading a plurality of sub-holograms for a single spatial light modulator and combining the time division multiplexing technology of structure light illumination. Although this solution reduces the cost, it has special requirements on the light source.

On the other hand, as the visual area and the size of the holographic reconstructed image have a mutual restriction relationship, it is quite difficult to expand both the visual area and the size of the holographic reconstructed image. In the aspect of expanding the size of the holographic reconstructed image, SeeReal Technologies in Germany manufactured a holographic 3D display system having a large-size display window of 300 mm×200 mm using the holographic optical elements. A research team from Warsaw University of Technology of Poland proposed a hologram algorithm capable of laterally enlarging, translating, and rotating the holographic reconstructed image, and finally produced a large-size color holographic reconstructed image of 50 mm×50 mm×100 mm. In addition, with the rapid development of metasurface technology in recent years, there are more and more solutions for expanding the size of the holographic reconstructed image by using the metasurface material, but the processing flows of materials specifically involved in the solutions are generally relatively complicated, and the material cost is relatively high, then the aspect of practicability of large-size holographic display needs to be further researched.

SUMMARY

The present disclosure provides a holographic 3D display system based on virtual array splicing of a spatial light modulator. As shown in FIG. 1, the system includes a laser, a beam splitter 1, a beam splitter 2, a reflector 1, a shutter array, a spatial filter array, a solid lens, a light beam deflection element 1, a spatial light modulator, a beam splitter 3, a light beam deflection element 2, and a reflector 2, wherein the laser is configured to generate a coherent light beam. The beam splitter 1, the beam splitter 2, and the reflector 1 are configured to split the light beam generated by the laser into three parallel light beams to irradiate the shutter array. The shutter array is configured to control the three parallel light beams to sequentially pass therethrough according to a set time sequence. The three parallel light beams passing through the shutter array are expanded and collimated by the spatial filter array and the solid lens to form three parallel light beams with the same size and uniform intensity, i.e. a light beam {circle around (1)}, a light beam {circle around (2)}, and a light beam {circle around (3)}. The light beam deflection element 1 is located in an outgoing direction of the three parallel light beams, and is configured to deflect respectively the light beam {circle around (1)}, the light beam {circle around (2)}, and the light beam {circle around (3)} along three specific directions δ, 0, and −δ. The light beam deflection element 1 and the light beam deflection element 2 are of the same model number. At a moment T₁, the shutter array is controlled to enable the light beam {circle around (1)} to pass through the beam splitter 3 to irradiate the spatial light modulator, the diffraction light beam passes through the beam splitter 3, the light beam deflection element 2, and the reflector 2, and a viewer sees the diffraction image of the spatial light modulator at the moment T₁; at a moment T₂, the shutter array is controlled to enable the light beam {circle around (2)} to irradiate the spatial light modulator, the diffraction light beam passes through the beam splitter 3, the light beam deflection element 2, and the reflector 2, and the viewer sees the diffraction image of the spatial light modulator at the moment T₂; at a moment T₃, the shutter array is controlled to enable the light beam {circle around (3)} to irradiate the spatial light modulator, the diffraction light beam passes through the beam splitter 3, the light beam deflection element 2, and the reflector 2, and the viewer sees the diffraction image of the spatial light modulator at the moment T₃. The diffraction image of the spatial light modulator at the three moments is controlled to be spliced seamlessly in space, and when a switching speed is sufficiently fast, the viewer sees the three diffraction images after the virtual array splicing of the spatial light modulator according to the effect of persistence of vision of human eyes.

The structures of the light beam deflection element 1 and the light beam deflection element 2 are as shown in FIG. 2. The light beam deflection element 1 and the light beam deflection element 2 each is formed by gluing two refracting prisms with a refractive index of n and a wedge angle of α and a piece of flat glass with a refractive index of n. The angle between the outgoing light beam and the optical axis is called as deflection angle. Taking the light beam {circle around (1)} as an example, it can be seen through calculation according to the geometrical optical principle that the refractive index n, the incidence angle φ, the wedge angle α, and the deflection angle δ satisfy the following formula:

n×sin φ=sin(α+δ)  (1)

It can be seen from formula (1) that under the premise of unchanged refractive index n and wedge angle α, the deflection angle δ only changes with the change of the incidence angle φ. By designing the wedge angle α, the refractive index n, and the incidence angle φ, the light beam {circle around (1)}, the light beam {circle around (2)}, and the light beam {circle around (3)} pass through the light beam deflection element 1 and the beam splitter 3, and then irradiate on a same area of the spatial light modulator. The light beam {circle around (1)}, the light beam {circle around (2)}, and the light beam {circle around (3)} continue to propagate after being modulated by the spatial light modulator and passing through the beam splitter 3, and irradiate on the light beam deflection element 2. As the light beam deflection element 2 has completely the same optical properties as the light beam deflection element 1, the three diffraction light beams form three parallel light beams again after passing through the light beam deflection element 2.

When the switching speed of the shutter array is sufficiently fast, splicing effect of three parallel light beams is equivalent to spatially forming virtual array splicing of the spatial light modulator with a horizontal size of 3 M×p and a vertical size of N×p, where M is the horizontal resolution (lateral resolution) of the spatial light modulator, Nis the vertical resolution (axial resolution) of the spatial light modulator, and P is the pixel pitch of the spatial light modulator. Hence, the light beam deflection element 1, the spatial light modulator, the beam splitter 3, and the light beam deflection element 2 are equivalent to a virtual array of the spatial light modulator with the horizontal size of 3 M×p and the vertical size of N×p.

The system provided in the present disclosure realizes large-visual-area holographic 3D display by the following method: as shown in FIG. 3, for a 3D object, a large-size hologram with the resolution of 3 M×N using the hologram algorithms such as angular spectrum algorithm, the large-size hologram is averagely divided into three sub-holograms with the resolution of M×N along the direction of the horizontal resolution of the large-size hologram, the three sub-holograms being recorded as the sub-hologram 1, the sub-hologram 2, and the sub-hologram 3. At the moment T₁, the shutter array is controlled to make the light beam {circle around (1)} pass therethrough, and meanwhile the sub-hologram 1 is loaded on the spatial light modulator; at the moment T₂, the shutter array is controlled to make the light beam {circle around (2)} pass therethrough, and meanwhile the sub-hologram 2 is loaded on the spatial light modulator; at the moment T₃, the shutter array is controlled to make the light beam {circle around (3)} pass therethrough, and meanwhile the sub-hologram 3 is loaded on the spatial light modulator; and when the switching is sufficiently fast, due to the effect of persistence of vision of human eyes, the viewer sees a large-visual-area reconstructed 3D object at the viewing distance R.

As shown in FIG. 4, in the holographic reconstruction process, when the virtual array of the spatial light modulator with a horizontal size of 3 M×p is irradiated by the parallel light, the maximum diffraction angle θ satisfies the following formula:

$\begin{array}{cc}\theta ={\sin }^{-1}\left(\frac{\lambda }{p}\right)& \left(2\right)\end{array}$

In the above, λ represents wavelength. According to holographic diffraction principle calculation, it can be known that the dimension D of the object satisfies the following formula:

D≤θ×Z−3M×p  (3)

In the above, Z is the diffraction distance of the holographic reconstructed image. The holographic reconstructed image at the viewing distance R is analyzed based on a maximum size of the object, the visual area V′ in which the complete holographic reconstructed image is visible is called as the effective visual area. By calculating diffraction positions of a highest point and a lowest point of the object, it is obtained:

$\begin{array}{cc}{V}^{\prime }=3M\times p\left(\frac{2R}{Z}-1\right)-\frac{\lambda }{p}\times R& \left(4\right)\end{array}$

In the conventional holographic display system, the single spatial light modulator is usually used for reconstruction, and when the viewing distance is R′, the size of the effective viewing area is represented with V″:

$\begin{array}{cc}{V}^{″}=M\times p\left(\frac{2R^{\prime }}{Z}-1\right)-\frac{\lambda }{p}\times R^{\prime }& \left(5\right)\end{array}$

Therefore, compared with the conventional holographic display system, when the diffraction distance and the viewing distance of the holographic reconstructed image are the same, the system realizes the expansion of the effective viewing area by more than 3 times.

The system provided in the present disclosure realizes large-size holographic 3D display by the following method: as shown in FIG. 5, for an object with the resolution of A×B, first, it is averagely divided along the horizontal resolution direction to obtain three sub-pictures of A/3×B, the three sub-pictures are respectively subjected to calculation using the hologram algorithms such as angular spectrum algorithm, to obtain three sub-holograms each with the resolution of M×N, the blazed grating is accordingly loaded for the three sub-holograms, a digital lens having a focal length of f is generated, the phase map of the digital lens is superimposed with the three sub-holograms respectively, to obtain the hologram 1, the hologram 2, and the hologram 3.

At the moment T₁, the shutter array is controlled to make the light beam {circle around (1)} pass therethrough, and meanwhile the hologram 1 is loaded on the spatial light modulator; at the moment T₂, the shutter array is controlled to make the light beam {circle around (2)} pass therethrough, and meanwhile the hologram 2 is loaded on the spatial light modulator; at the moment T₃, the shutter array is controlled to make the light beam {circle around (3)} pass therethrough, and meanwhile the hologram 3 is loaded on the spatial light modulator; and the above processes are cycled repeatedly, and imaging positions of various holographic reconstructed images are changed by changing the blazed grating of the holograms loaded on the spatial light modulator. When the switching is sufficiently fast (i.e. the switching time is sufficiently short), due to the effect of persistence of vision of human eyes, holographic reconstructed images of the three sub-pictures are seamlessly spliced in space, and the viewer sees a large-size holographic reconstructed image.

At the moment T₁, the size d of the holographic reconstructed image using a single spatial light modulator is:

$\begin{array}{cc}d=\frac{f\lambda }{p}& \left(6\right)\end{array}$

When the switching is sufficiently fast, the size of holographic reconstructed image obtained by splicing of the hologram 1, the hologram 2, and the hologram 3 is 3d. Compared with the conventional holographic display system based on a single spatial light modulator, the system of the present disclosure realizes the expansion of the size of the holographic reconstructed image by 3 times.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is the structural schematic view of a holographic 3D display system based on virtual array splicing of a spatial light modulator.

FIG. 2 is the structural schematic view of a light beam deflection element of the present disclosure.

FIG. 3 shows a method for generating sub-holograms of large-visual-area holographic 3D display of the present disclosure.

FIG. 4 is the principle diagram of large-visual-area holographic 3D display of the present disclosure.

FIG. 5 shows a method for generating holograms of large-size holographic 3D display of the present disclosure.

Reference signs in various drawings above are as follows:

• • (1) laser, (2) beam splitter 1, (3) beam splitter 2, (4) reflector 1, (5) shutter array, (6) spatial filter array, (7) solid lens, (8) light beam deflection element 1, (9) spatial light modulator, (10) beam splitter 3, (11) light beam deflection element 2, (12) reflector 2, (13) 3D object, (14) 3 M×N spatial light modulator, (15) holographic reconstructed image.

It should be understood that the above drawings are merely illustrative, but not drawn to scale.

DETAILED DESCRIPTION OF EMBODIMENTS

An embodiment of a holographic 3D display system based on virtual array splicing of a spatial light modulator provided in the present disclosure is illustrated in detail below to further describe the present disclosure. It is necessary to indicate herein that the following embodiments are merely used to further illustrate the present disclosure, but cannot be construed as limitation to the scope of protection of the present disclosure, and non-essential improvements and adjustments made by a person skilled in the art to the present disclosure according to the contents above still fall within the scope of protection of the present disclosure.

Relevant device parameters and structure parameters actually adopted by a system are as follows: the laser with wavelength of 532 nm; the solid lens with focal length of 300 mm; the beam splitter 1 and the beam splitter 2 with the size of 12.7 mm×12.7 mm×12.7 mm, and the beam splitter 3 with the size of 25.4 mm×25.4 mm×25.4 mm; the shutter array consists of three shutters of completely the same model number, and the light-emitting aperture of each shutter is 5 mm; and the spatial light modulator with pixel count of 1920×1080, size of 12.29 mm×6.91 mm, pixel pitch of 6.4 μm, and refresh speed of 60 Hz. The refractive prism with the refractive index of n=1.516, the wedge angle of α=4°, and the generated light beam deflection angle is 8=2°; the distance from the light beam deflection element 1 to the spatial light modulator is 400 mm; and the diffraction distance of the holographic reconstructed image is 200 mm.

In order to realize large-visual-area holographic 3D display, a “teapot” with the resolution of 320×240 is adopted as the recorded 3D object. A hologram with the resolution of 5760×1080 is generated through calculation using the angular spectrum algorithm, and the hologram is averagely divided into three sub-holograms with the resolution of 1920×1080 which are then loaded on the spatial light modulator in sequence. At a moment T₁, the first sub-hologram is loaded, and the shutters are controlled to make a light beam {circle around (1)} pass therethrough; at a moment T₂, the second sub-hologram is loaded, and meanwhile the shutters are controlled to make a light beam {circle around (2)} pass therethrough; at a moment T₃, the third sub-hologram is loaded, and meanwhile the shutters are controlled to make a light beam {circle around (3)} pass therethrough. Due to the effect of persistence of vision of human eyes, a large-visual-area holographic reconstructed image of the “teapot” can be seen. Through calculation, when the viewing distance is 950 mm, the effective visual area has the size of ˜234.4 mm. When the virtual array splicing of the spatial light modulator is not used, the effective visual area has the size of ˜25.5 mm. The effective visual area is expanded by 9.2 times through the virtual splicing.

In order to realize the large-size holographic 3D display, a “train” with the resolution of 2160×1080 is adopted as the recorded 3D object. It is divided to give three sub-pictures with the resolution of 720×1080, and the focal length of the digital lens is set to 500 mm. Three holograms each with the resolution of 1920×1080 are obtained through calculation using the angular spectrum algorithm. At a moment T₁, the first hologram is loaded, and the shutters are controlled to make a light beam {circle around (1)} pass therethrough; at a moment T₂, the second hologram is loaded, and meanwhile the shutters are controlled to make a light beam {circle around (2)} pass therethrough; at a moment T₃, the third hologram is loaded, and meanwhile the shutters are controlled to make a light beam {circle around (3)} pass therethrough; and the above processes are cycled repeatedly. Due to the effect of persistence of vision of human eyes, the holographic reconstructed image of the “train” has the size of 124.7 mm, which is expanded by 3 times compared with the size of the “train” holographic reconstructed image when the virtual splicing is not used.

Claims

1. A holographic 3D display system based on virtual array splicing of a spatial light modulator, wherein the system consists of a laser, a first beam splitter, a second beam splitter, a first reflector, a shutter array, a spatial filter array, a solid lens, a first light beam deflection element, a spatial light modulator, a third beam splitter, a second light beam deflection element, and a second reflector, wherein the laser is configured to generate a coherent light beam; the first beam splitter, the second beam splitter, and the first reflector are configured to split the light beam generated by the laser into three parallel light beams to irradiate the shutter array; the shutter array is configured to control the three parallel light beams to sequentially pass therethrough according to a set time sequence; the three parallel light beams passing through the shutter array are expanded and collimated by the spatial filter array and the solid lens to form three parallel light beams with the same size and uniform intensity, i.e. a first light beam, a second light beam, and a third light beam; the first light beam deflection element is located in an outgoing direction of the three parallel light beams, and is configured to deflect respectively the first light beam, the second light beam, and the third light beam along three specific directions, and the first light beam deflection element and the second light beam deflection element are of the same model number,wherein at a moment T1, the shutter array is controlled to enable the first light beam to pass through the third beam splitter to irradiate the spatial light modulator, a diffraction light beam passes through the third beam splitter, the second light beam deflection element, and the second reflector, and a viewer sees the diffracted light of the spatial light modulator at the moment T1; at a moment T2, the shutter array is controlled to enable the second light beam to irradiate the spatial light modulator, diffracted light passes through the third beam splitter, the second light beam deflection element, and the second reflector, and a viewer sees a diffraction image of the spatial light modulator at the moment T2; at a moment T3, the shutter array is controlled to enable the third light beam to irradiate the spatial light modulator, the diffraction light beam passes through the third beam splitter, the second light beam deflection element, and the second reflector, and the viewer sees the diffraction image of the spatial light modulator at the moment T3; andthe diffraction image of the spatial light modulator at the three moments is controlled to be spliced seamlessly in space, wherein when a switching speed is sufficiently fast, the viewer sees the three diffraction image after the virtual array splicing of the spatial light modulator according to an effect of persistence of vision of human eyes.

2. The holographic 3D display system based on virtual array splicing of a spatial light modulator according to claim 1, wherein the first light beam deflection element and the second light beam deflection element each is formed by gluing two refracting prisms with a refractive index of n and a wedge angle of α and a piece of flat glass with a refractive index of n, wherein the refractive index n, an incidence angle φ, the wedge angle α, and a deflection angle δ satisfy a following formula: n×sin φ=sin(α+δ)wherein under a premise of unchanged refractive index n and wedge angle α, the deflection angle δ changes only with change of the incidence angle φ; by designing the wedge angle α, the refractive index n, and the incidence angle φ, the first light beam, the second light beam, and the third light beam are made to pass through the first light beam deflection element and the third beam splitter, and then irradiate on a same area of the spatial light modulator; the first light beam, the second light beam, and the third light beam continue to propagate after being modulated by the spatial light modulator and passing through the third beam splitter, and irradiate on the second light beam deflection element;the three diffraction light beams form the three parallel light beam again after passing through the second light beam deflection element, wherein when a switching speed of the shutter array is sufficiently fast, splicing effect of the three parallel light beams is equivalent to spatially forming virtual array splicing of the spatial light modulator with a horizontal size of 3 M×p and a vertical size of N×p, where M is a horizontal resolution of the spatial light modulator, N is a vertical resolution of the spatial light modulator, and P is a pixel pitch of the spatial light modulator; and the first light beam deflection element, the spatial light modulator, the third beam splitter, and the second light beam deflection element are equivalent to a virtual array of the spatial light modulator with the horizontal size of 3 M×p and the vertical size of N×p.

3. The holographic 3D display system based on virtual array splicing of a spatial light modulator according to claim 2, wherein the system realizes large-visual-area holographic 3D display by a following method comprising: computing a large-size hologram of a 3D object with a resolution of 3 M×N, averagely dividing the large-size hologram along a direction of the horizontal resolution of the large-size hologram into three sub-holograms with a resolution of M×N which are recorded as a first sub-hologram, a second sub-hologram, and a third sub-hologram;controlling the shutter array at the moment to make the first light beam pass therethrough, and meanwhile loading the first sub-hologram on the spatial light modulator; controlling the shutter array at the moment to make the second light beam pass therethrough, and meanwhile loading the second sub-hologram on the spatial light modulator; and controlling the shutter array at the moment T3 to make the third light beam pass therethrough, and meanwhile loading the third sub-hologram on the spatial light modulator, wherein when the switching is sufficiently fast, due to the effect of persistence of vision of human eyes, the viewer sees a large-visual-area reconstructed 3D object is seen at a viewing distance R,wherein in the holographic reconstruction process, when the virtual array of the spatial light modulator with the horizontal size of 3 M×p is irradiated by parallel light, a maximum diffraction angle θ satisfies a following formula:

4. The holographic 3D display system based on virtual array splicing of a spatial light modulator according to claim 2, wherein the system realizes large-size holographic 3D display by a following method comprising: first averagely dividing an object with a resolution of A×B along a horizontal resolution direction into three sub-pictures of A/3×B, performing calculating on the three sub-pictures respectively to obtain three sub-holograms each with a resolution of M×N, generating a digital lens with a focal length of f, superimposing a phase map of the digital lens with each of the three sub-holograms to obtain a first hologram, a second hologram, and a third hologram; controlling the shutter array at the moment T1 to make the first light beam pass therethrough, and meanwhile loading the first hologram on the spatial light modulator; controlling the shutter array at the moment to make the second light beam pass therethrough, and meanwhile loading the second hologram on the spatial light modulator; controlling the shutter array at the moment T3 to make the third light beam pass therethrough, and meanwhile loading the third hologram on the spatial light modulator, wherein the method is performed repeatedly, and when the switching is sufficiently fast, due to the effect of persistence of vision of human eyes, holographic reconstructed images of the three sub-pictures are seamlessly spliced in space, and the viewer sees a large-size holographic reconstructed image; at the moment T1, a size d of the holographic reconstructed image using a single spatial light modulator is: