Holographic 3D display system based on multiple sets of SLM-ML-PDLCs

Abstract

The present invention discloses a holographic 3D display system based on multiple groups of SLM-ML-PDLCs, combining a spatial light modulator SLM with ML-PDLCs into a SLM-ML-PDLCs group, first calculating the holograms of different layers of the object to be displayed, and then reproducing them through the SLM, placing ML-PDLCs at the position of the reproduced image, and the reproduced images of different layers correspond one to one with the ML-PDLCs film layers. ML-PDLCs are used as the SLM projection two-dimensional image receiving screen. At the beginning, all the film layers of ML-PDLCs are in an energized transparent state. When reproducing a certain layer of the image, the corresponding film layer is in an off-power scattering state, and the reproduced image is displayed on this film layer. The output images of multiple groups of SLM-ML-PDLCs can be fused through a beam splitter prism to form a three-dimensional image with more than 19 layers. After the output images of each group of SLM-ML-PDLCs are fused, the three-dimensional images do not overlap. By controlling the SLM projection frame rate and the ML‑PDLCs film layer power-on timing, different two-dimensional images can be projected onto different ML‑PDLCs film layers for display, and a complete three-dimensional image with continuous depth will be seen.

Description

Technical Field

[0001] The present invention belongs to the technical field of holographic three-dimensional display, and in particular relates to a holographic 3D display system based on multiple groups of SLM-ML-PDLCs. Background Art

[0002] Holographic three-dimensional display can reproduce the light wavefront carrying three-dimensional object information as it is. It is a display technology based on wavefront reconstruction. Therefore, this technology is considered to be the most ideal true three-dimensional display technology currently.

[0003] The original hologram was an optical hologram, which is an object that is illuminated by a laser as a light source. After being transmitted or reflected (scattered) by the object, an object light wave is formed. When the object light wave W meets another light wave called reference light C, interference fringes are formed. The interference fringes are recorded using photosensitive materials to obtain a hologram. The information of the object light wave is encoded into the hologram. When the hologram is illuminated by a laser, due to diffraction, the outgoing light wave will contain the original object light wave, so that the image of the object can be reproduced.

[0004] Computer generated holography does not require the actual existence of the object. It only needs to input the mathematical description of the object light wave into the computer, and obtain a digital hologram after computer encoding. Then it can be output through a plotter or a dedicated computer generated hologram microfilm system to become a hologram that can be optically reproduced, or it can be output to a spatial light modulator for direct display. Computer generated holograms can not only fully record the amplitude and phase of actual light waves, but also synthesize the wavefront of objects that do not exist in the world. Therefore, they have unique advantages and great flexibility. Computer generated holograms are digital and can be processed into actual transparent sheets through printing and other processes. They are different from optical holograms. Figure 1 In the same way, the object light wave can be reproduced by laser illumination. It can also be directly transmitted to an optoelectronic display device for display. A spatial light modulator is a device that modulates the spatial distribution of light waves. Under the control of an electrical drive signal, it changes the amplitude or intensity, phase, polarization state, etc. of the light distribution in space. The computer-generated hologram is input into the spatial light modulator, and when illuminated by a laser, the image can be reproduced. The spatial light modulator has a high refresh rate, so it can perform dynamic holographic display, which is not possible with optical holograms.

[0005] At present, holographic 3D display has made some encouraging progress. The most recent influential result is that the German SeeReal technology company pointed out in 2017 that [1] , using very low-resolution SLM (pixel spacing of 135 μm, vertical 35 μm), holographic optical elements and window tracking technology to realize a holographic display with a field of view of 300 mm * 200 mm, but only for one person to observe; its principle is based on the concept of tomographic hologram [2]和[3], assuming that the 3D object O is composed of multiple layers of cross sections, each of which is a two-dimensional image, like a CT image. The Fresnel hologram of each layer of the two-dimensional image is calculated one by one. Figure 1 It is the principle optical path of tomographic hologram recording, which decomposes the target (object to be displayed 1) layer by layer into a two-dimensional image (Lay 0 ,Lay 1 …Lay n ), for each layer of images, record (calculate) its hologram, and the distance Z between different layers of images and the hologram plane Q is different according to their relative positions n Also different. Let the distance between adjacent layers be ΔZ l , then the nth layer slice Lay n The distance Q from the hologram plane is:

[0006] Z n =Z 0 +nΔZ l (0-1)

[0007] Each layer of hologram is input into the spatial light modulator SLM in a certain time sequence, and the SLM is illuminated by a beam expansion laser. As each layer of hologram is input, the SLM reconstructs the reconstructed image of each layer of hologram in the corresponding position in space, forming a longitudinal scan of the image plane. If the SLM frame rate is fast enough so that the total scanning time of all sections is less than the visual residual time of the human eye (about 0.1-0.4 seconds), a complete three-dimensional reconstructed image will be formed. However, due to the relatively low spatial resolution of the current SLM, the divergence angle of the reproduced image point is very small, so that the two eyes cannot see the same image point at the same time. Figure 2 In the figure, the cone angle of the conical light beam emitted from point A of the holographic reconstruction image is ω (field of view angle FOV), which is much smaller than the minimum angle Ω required for binocular stereoscopic vision. Although the holographic reconstruction image is three-dimensional, the human eye cannot use the convergence of the visual axis to obtain the feeling of a three-dimensional image.

[0008] Therefore, expanding the field of view of the holographic reconstructed image is one of the most critical technologies that need to be overcome in holographic display.

[0009] [1] R. Y.GRITSAI,E.ZSCHAU,R.MISSBACH,H.SAHM,M.STOCK, ANDH.STOLLE, Large real-time holographic 3D displays:enabling components and results, Applied Optics, 56(13), 2017.

[0010] [2]Trester S.Computer-simulated Fresnel holography[J].EuropeanJournal of Physics, 21(4), 2000,

[0011] [3] Cao Xuemei, Sang Xinzhu, Computer generated hologram of complex 3D scenes based on 2D color images and depth maps, Chinese Journal of Lasers, 41(6), 2014. Summary of the invention

[0012] In order to solve the current technical problem that the human eye cannot distinguish the three-dimensional reconstructed image reproduced by SLM, the present invention combines the spatial light modulator SLM with ML-PDLCs. First, the holograms of different layers of the object to be displayed are calculated, and then reproduced through SLM. ML-PDLCs are placed at the position of the reproduced image, and the reconstructed images of different layers correspond to the ML-PDLCs film layers one by one. ML-PDLCs are used as the receiving screen for SLM projection of two-dimensional images. At the beginning, all the film layers of ML-PDLCs are in a powered transparent state. When reproducing a certain layer of image, the corresponding film layer is in a powered off scattering state, and the reproduced image is displayed on this film layer. All tomographic holograms are combined. Figure 1 The corresponding ML-PDLCs film layer is powered on and off in sequence, and the reconstructed image will be displayed on the corresponding film layer in sequence. Assuming that the object is decomposed into N layers, it takes ΔT for the SLM to display N layers of holograms. Using ML-PDLCs as the SLM projection two-dimensional image receiving screen, by controlling the SLM projection frame rate and the ML-PDLCs film layer power-on sequence, different two-dimensional images can be projected onto different film layers of ML-PDLCs for display, forming a longitudinal scan of the two-dimensional image. If ΔT is less than the visual residual time of the human eye, a complete three-dimensional image with continuous depth will be seen. However, based on the transmittance of the PDLC film, the number of PDLC films set in ML-PDLCs does not exceed 10 layers, but the thickness of the current 3D object from its rear end plane to the front end plane may exceed the thickness of 10 layers of the reconstructed image. When the PDLC film is set to 10 layers, it cannot meet the needs of reproducing thicker 3D objects.

[0013] The technical solution of the present invention is: a holographic 3D display system based on multiple groups of SLM-ML-PDLCs, images output by H groups of SLM-ML-PDLCs are fused into the same area through a beam splitter prism to holographically display a 3D object, and each group of SLM-ML-PDLCs includes: a group of spatial light modulators, a group of diffusion laminates and an aperture;

[0014] The spatial light modulator receives a Fresnel hologram of n-layer two-dimensional images created and encoded by a computer, modulates the illumination light emitted by the light source module, and reconstructs the reconstructed images of each layer of the hologram in the reconstructed light field in sequence according to the loading sequence, and the H groups of n-layer two-dimensional images correspond to the H×n layers of equidistant and parallel cross sections of the three-dimensional image of the 3D object decomposed layer by layer from its rear end plane to the front end plane; the position of the reconstructed n-layer reconstructed image corresponds to the position of the two-dimensional image of the reconstructed image in the three-dimensional image, and the size of the reconstructed image is consistent with that of the three-dimensional image of the 3D object;

[0015] The diffusion laminate is composed of M layers of parallel polymer scattering liquid crystal films, n≤M≤19, and the positions of the n layers of reconstructed images from the rear end plane to the front end plane in the reconstructed light field are sequentially overlapped with the positions of the n layers of polymer scattering liquid crystal films in the diffusion laminate. The n layers of polymer scattering liquid crystal films are controlled by a computer. When the reconstructed image of the nth layer of the hologram is reconstructed, the polymer scattering liquid crystal films that overlap with the position of the reconstructed image of this layer are in a scattering state, scattering the reconstructed image into a three-dimensional image, while the remaining polymer scattering liquid crystal films are in a transparent state, allowing the reconstructed image to pass through without interference.

[0016] An aperture is disposed at the output window end face of the diffusion laminate and is used to block the zero-order term and conjugate image of the diffracted light;

[0017] The response time of the polymer scattering liquid crystal film is T, the frame rate of the spatial light modulator is at least 1 / T Hz, and the pixel interval d of the spatial light modulator is slm Satisfies the following formula: d slm ≤λZ o / 2L o , L o is the plane size of the reconstructed image, λ is the wavelength of the illumination light, and Z o To reproduce the distance between the image and the spatial light modulator, the plane size of the diffuse laminate is not less than L o , the response time refers to the total time for the polymer scattering liquid crystal film to change from the scattering state when the power is off to the transparent state after the power is on, and then to the scattering state after the power is off;

[0018] The distances between the polymer scattering liquid crystal film in the diffuse laminate and the spatial light modulator in different SLM-ML-PDLCs groups differ by a thickness of Λ, where Λ is equal to one Hth of the thickness of the polymer scattering liquid crystal film, so that after the three-dimensional images scattered by the H groups of ML-PDLCs are fused by the beam splitter prism, the three-dimensional images do not overlap, but differ by a thickness of Λ.

[0019] Preferably, H≤5.

[0020] Furthermore, the response time refers to the total time for the polymer scattering liquid crystal film to change from a scattering state with a transmittance of no more than 20% when powered off to a transparent state after powered on, and then to a scattering state with a transmittance of no more than 20% when powered off.

[0021] Furthermore, it takes 10 ms for the polymer scattering liquid crystal film to change from a scattering state with a transmittance of no more than 20% when powered off to a transparent state after powered on, and it takes 100 ms for the polymer scattering liquid crystal film to change from a scattering state with a transmittance of no more than 20% after powered on to a scattering state with a transmittance of no more than 20%.

[0022] Furthermore, it takes 10 ms for the polymer scattering liquid crystal film to change from a scattering state with a transmittance of no more than 20% when powered off to a transparent state after powered on, and it takes 60 ms for the polymer scattering liquid crystal film to change from a scattering state with a transmittance of no more than 20% after powered on to a scattering state with a transmittance of no more than 20%.

[0023] Furthermore, the frame rate of the spatial light modulator is at least 25n / H Hz, and the response time of the polymer scattering liquid crystal film is no more than H / 25n seconds.

[0024] Furthermore, each set of SLM-ML-PDLCs further includes: a lens L 1 , each set of SLM-ML-PDLCs inner aperture and lens L 1 The n-layer reconstructed images are sequentially arranged between the spatial light modulator and the diffusion laminate along the normal line G of the reconstructed image, the n-layer reconstructed images are located on the inner periphery of the frame of the aperture, and the n-layer reconstructed images are closest to the lens L. 1 The 0th layer reproduces the image distance lens L 1 Over a focal length, the diffuser laminate is closest to the lens L 1 The nth layer of polymer scattering liquid crystal film lens L 1 The imaging optical path is L 1 Over a focal length, lens L 1 The n-layer reproduced image is magnified and imaged into the diffusion laminate, the n-layer magnified real image is sequentially overlapped with the positions of the n-layer polymer scattering liquid crystal films in the diffusion laminate, and the plane size of the real image is not larger than the plane size of the diffusion laminate, and the center distance Δl' of adjacent polymer scattering liquid crystal films in the diffusion laminate is n’ Equal, Δl' n’ =Δl' 1 , and Δl 1 is the distance between the 0th and 1st layers of the reconstructed image. When creating the hologram, the computer transforms the spatial coordinates of the original object in the holograms of different layers to compensate for the distance between the original object and the hologram after the lens L. 1 The deformation caused by imaging makes the lens L 1 The reconstructed image is successively enlarged in proportion to the corresponding polymer scattering liquid crystal films arranged at equal intervals in the diffusion laminate.

[0025] Furthermore, when calculating the hologram, the coordinates x of the actual object point are converted to on Perform the transformation as follows: And the coordinate x of the n'th layer of the two-dimensional image of the actual object along the normal G direction on Perform the transformation as follows: Where Z Ha The nth layer reconstructed image and lens L 1 The distance from the input side focus, ΔZ Hn’ is the distance between the nth layer reconstruction image and the n'th layer reconstruction image, f 1 For lens L 1 focal length.

[0026] Furthermore, the lens L 2 , arranged along the normal line C of the fused three-dimensional image on the output window side of the beam splitter prism, and lens L 2 The H×n layers of three-dimensional image are magnified and the interval between adjacent image layers after magnification is less than the resolution limit of the human eye along the normal line C. The lens L 2 The distance from the nth three-dimensional imaging layer in the diffusion laminate is more than a focal length.

[0027] Furthermore, the layer interval of the reconstructed image from the n'th layer to the n'+1th layer is Δl n’ , The nth three-dimensional image layer and the lens L 2 The distance of the focus is z ia , z e is the observation distance, that is, the distance between the human eye and the lens L 2 put BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram for recording tomographic holograms;

[0029] Figure 2 is the field of view of the holographic reconstructed image;

[0030] Figure 3 To expand the viewing angle of holographic reproduction images by using PDLC;

[0031] Figure 4 For direct projection of holographic image point diffusion;

[0032] Figure 5 This is the schematic diagram of ML-PDLCs astigmatism;

[0033] Figure 6 It is a polymer liquid crystal structure diagram;

[0034] Figure 7 Reconstructing the optical path diagram for the hologram;

[0035] Figure 8 This is the “on-off” time response curve of the PDLC film;

[0036] Fig. 9 It is a spatiotemporally integrated SLMs-ML-PDLC computer-generated holographic 3D dynamic display system;

[0037] Fig.10 It is a schematic diagram of the expansion of the viewing angle of the PDLC film to the image point;

[0038] Fig.11 This is the optical path diagram of holographic three-dimensional display imaging based on the laminated PDLCs film;

[0039] Fig.12 This is the relationship diagram between the structures and positions of three groups of ML-PDLCs in the 3SLMs-ML-PDLCs system;

[0040] Fig.13 This is the timing relationship diagram of three groups of ML-PDLCs in the 3SLMs-ML-PDLCs system. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] Comparative Example 1

[0043] Figure 3An embodiment of the present invention comprises: a light source module, a spatial light modulator SLM, a diffusion laminate ML-PDLCs, an aperture AP, and a computer. The computer decomposes the three-dimensional image of the 3D object layer by layer from the rear plane to the front plane into a two-dimensional image set composed of n layers of equidistant parallel sections, and calculates the Fresnel hologram of each layer of the two-dimensional image one by one. The spatial light modulator sequentially loads the Fresnel hologram through a computer according to a loading sequence, modulates the illumination light emitted by the light source module, and sequentially emits n layers of hologram reconstruction images in the G direction according to the loading sequence, so that the n layers of reconstruction images are sequentially reconstructed in the reconstruction light field, and the positions of the n layers of reconstruction images correspond to the positions of the two-dimensional images of the reconstruction images in the three-dimensional image, and the reconstruction images are consistent in size with the three-dimensional image of the 3D object, wherein the n layers of reconstruction images are perpendicular to the G direction, and M layers of polymer scattering liquid crystal films are sequentially arranged along the G direction to form a diffusion laminate, n≤M≤19, and the spacing between adjacent layers in the M layers of polymer scattering liquid crystal films is equal to the spacing between adjacent decomposition layers in the three-dimensional image of the 3D object, and the M layers of polymer scattering liquid crystal films are placed so that the positions of the n layers of reconstruction images from the rear end plane to the front end plane in the reconstructed reconstruction light field correspond sequentially to the n layers in the diffusion laminate. The positions of the n layers of polymer scattering liquid crystal films overlap one by one. These n layers of polymer scattering liquid crystal films are controlled by a computer, so that when the spatial light modulator emits a reconstruction image of the nth layer of the hologram, the polymer scattering liquid crystal films that overlap with the position of the reconstruction image of this layer are in a scattering state, and the remaining polymer scattering liquid crystal films are in a transparent state. When in the scattering state, the reconstruction image is scattered into a three-dimensional image, and when in the transparent state, the reconstruction image is allowed to pass through without interference. The front end face of the diffusion laminate is away from the spatial light modulator and is placed on the inner periphery of the frame of the aperture.

[0044] When in use, different layers of holograms are input into the SLM in sequence, illuminated by laser, and a "laminated polymer scattering liquid crystal film (PDLCs)" is placed in the holographic reconstruction image area. The position of each layer of the reconstruction image corresponds to the position of the scattering film PDLC. When the nth layer of the hologram is reproduced at a certain moment, its reconstruction image is located on the nth layer of the ML-PDLCs (diffusion laminate). At this time, the film is in a power-off state, the reconstruction image is scattered, and the eyes can see the reconstruction image on this plane. When the SLM completes the reconstruction of all layers of the hologram, the reconstruction images of all layers complete a scan along the scanning direction shown in the figure. Figure 4 The AP in the middle is an aperture used to block the zero-order term and conjugate image of the diffracted light.

[0045] like Figure 5 Schematic diagram, multi-layer PDLC is superimposed in the holographic image area to form ML-PDLCs. There are 5 PDLCs in the figure, respectively using PDLC 1 ,PDLC 2 ,PDLC 3 ,PDLC 4 ,PDLC5 Indicates. PDLC 1 ,PDLC 2 、PDLC 3 , and PDLC 5 In the powered state, PDLC 4 No power is applied. Suppose a thin parallel beam A is incident on the ML-PDLCs. 1 ,PDLC 2 ,PDLC 3 When powered on, it is in a transparent state and light will pass straight through. 4 In the scattered state, when light is incident on PDLC 4 When it reaches point B, scattering will occur, forming a cone-shaped beam with B as the vertex. The scattered light continues to pass directly through the PDLC. 5 , the human eye can see a spot of light at point B.

[0046] "Multi-layer polymer liquid crystal scattering film screen" is hereinafter referred to as ML-PDLCs (multi-layer polymerdispersed liquid crystal films) and is composed of multi-layer polymer liquid crystal (PDLC) scattering films (such as Figure 6 ). The characteristic of PDLC film is that it is in transparent and scattering states when powered on and off, respectively. The principle is that liquid crystal is dispersed in a solid organic polymer matrix in the form of micron-sized droplets. Since the optical axis of the droplets composed of liquid crystal molecules is in free orientation, its refractive index does not match the refractive index of the matrix. When light passes through the matrix, it is strongly scattered by the droplets and presents an opaque milky white state or a translucent state. Applying voltage can adjust the optical axis orientation of the liquid crystal droplets. When the refractive indexes of the two match, they are transparent. When the electric field is removed, the droplets return to their initial scattering state. This embodiment uses this characteristic to scatter image points of different cross sections, thereby expanding the viewing angle. Obviously, the performance of the PDLC film directly affects the success or failure of this embodiment. Table 1 shows the performance parameters of the PDLC film currently seen on the market. It can be seen from the following application analysis that the current time response of this PDLC film is far from meeting the requirements. Because energy attenuation will occur after light enters ML-PDLCs, there are two main reasons for the loss of light: surface reflection and internal absorption. The outermost layer of the PDLC film is PET material. Assuming its refractive index is about n, when it is reflected from one side, r = [(n-1) / (n+1) 2] energy is reflected. Assume that the transmittance of a single PDLC film in the open state is T, and the absorptivity is α (the concept of absorption coefficient is not used here because the inside of the PDLC film is not uniform). Assume that the energy of the incident light is 1. For a single PDLC film, the energy loss of the reflected light during incident light is r, the energy of the light incident into the film is 1-r, the energy loss of the light absorbed in the interface is (1-r)α, the energy of the light reaching the exit interface is 1-(1-r)α, and the reflection loss during exit is [1-(1-r)α]r. The total energy loss is:

[0047] ε=r+(1-r)α+[1-(1-r)α]r=2r+(1-r) 2 α=1-T (1-1)

[0048] From this the absorbance can be calculated as:

[0049] Table 1 Typical technical parameters of common PDLC films

[0050] Optical transmittance power ups Approximately 80% (+ / - 3%) Haze power ups <7.5％ Power outage >90％ Viewing Angle power ups About 150° Electrical Power adapter power ups 65VAC Response time Power on-off 100 ms Power off-Power on 10 ms Power consumption power ups About 5W / square meter thickness About 0.4 mm

[0051] Assuming that there are N layers of ML-PDLCs and that the bonding between each PDLC is tight (or that there is no emission from the air interface on the PET surface between the layers in the stack), the reflection and absorption losses of each layer and the total transmittance are:

[0052] First layer reflection loss: σ ri =r

[0053] The first layer absorption loss: σ 1 =(1-r)α

[0054] Second layer absorption loss: σ 2 =[1-r-(1-r)α]α=(1-r)(1-α)α

[0055] The third layer absorption loss: σ 3 =[1-r-(1-r)α-(1-r)(1-α)α]α=(1-r)(1-α) 2 α

[0056] The fourth layer absorption loss: σ 4 =[1-r-(1-r)α-(1-r)(1-α)α-(1-r)(1-α) 2 α]α=(1-r)(1-α) 3 α

[0057] The Nth layer absorption loss σ N =(1-r)(1-α) N-1 α

[0058] N layers absorb a total of:

[0059] The last layer of reflection loss:

[0060] Total energy loss: σ = σ ri +σ α +σ re

[0061] Transmitted Energy:

[0062] Transmittance:

[0063] (1-3)

[0064] At present, the maximum transmittance of PDLC products can reach T=82% when it is turned on. The refractive index of PET is about 1.6. If ML-PDLCs has 30 layers, the above formula can be used to calculate τ≈6.8%. It can be seen that the energy loss is very large and the output light will be very weak. If ML-PDLCs has 10 layers, τ≈38% can be obtained. Therefore, in this embodiment, ML-PDLCs are preferably set to 10 layers. If ML-PDLCs has 19 layers, τ≈17.6% can be obtained. The output light is relatively weak. If a high-power laser is used as the reproduction light source, the brightness of the reproduced image can be increased to a certain extent. Therefore, in this embodiment, ML-PDLCs can be optionally set to 19 layers.

[0065] In addition, according to the principle of layered 3D display based on stacked liquid crystal control films, in order to obtain continuous dynamic 3D images, there are high requirements for the refresh rate of the spatial light modulator SLM. Assuming that there are N layers of objects to be displayed, all N layers must be scanned once to display "one frame" of the object. According to the requirements of the human eye's time resolution, at least 25 to 30 frames per second are required to obtain continuous dynamic display, which requires the refresh rate of the spatial light modulator to be at least 25 to 30NHz. The frame rate of the 3D display is determined by the frame rate of the spatial light modulator FPSslm=FPS 3d ×N Hz, if N=10, the spatial light modulator frame rate requirement is 250-300 Hz. If N=19, the spatial light modulator frame rate requirement is 475-570 Hz.

[0066] The PDLC response time can determine the 3D display frame rate Since currently The final frame rate of the 3D display is determined by the response of the PDLC.

[0067] Although this design can meet the frame rate requirements with existing SLM, the current ordinary PDLC film has a very slow time response. According to Table 1, the film takes 10ms to respond from the scattering state to the transparent state, and 100ms to respond from the transparent state to the scattering state, which is not enough. In fact, studies have shown that the entire response time of PDLC film from off-on to on-off can reach milliseconds or even microseconds. [4] .

[0068] As far as the current situation is concerned, for the selected ordinary PDLC film, it can satisfy the effect of using the visual aftereffect to make people feel a complete 3D static image composed of 10 layers of three-dimensional images. For the selection of the spatial light modulator SLM, if only the imaging resolution is considered, the more pixels the better. If the size of the reproduced image is also considered, the smaller the pixel the better. For dynamic display, the higher the frame rate the better. In this embodiment, when N=10, the frame rate is required to be at least 250Hz. In this embodiment, when N=19, the frame rate is required to be at least 475Hz.

[0069] When selecting SLM, the pixel spacing d of SLM slm The following requirements are set. Let the number of pixels in the horizontal direction of SLM be N. slm , the number of pixels in the vertical direction is M slm , then its maximum spatial frequency is Display size is horizontal L hx =d slm N slm , longitudinal L hy =d slm M slm See also Figure 7 , let the reconstructed image I 1 The horizontal width is L o , the wavelength of the reconstructed image light is λ, and the distance between the reconstructed image and the SLM is z o , assuming that lensless Fourier transform holography is used, in order to ensure the separation of the holographic reconstruction image and the zero-order light, the spatial frequency of the interference fringes of the hologram must satisfy:

[0070]

[0071] In order to be able to reproduce through SLM, it is required that f h ≤f slm ,Right now

[0072] Reproducible image sizes:

[0073] According to the Rayleigh criterion, the resolvable pixel size of the holographic reconstruction image is:

[0074] According to the magnification factor M of the reconstructed image output by the SLM and the size of the image finally presented to the observer, the reconstructed image I 1 The horizontal width is L o For color display using SLM, the wavelengths of the three primary laser colors reproduced are λ R =0.65×10 -3 mm,λ G =0.53×10 -3 mm,λ B =0.46×10 -3 mm, if L 0 =21.5mm According to formula (1-6), the relationship between SLM pixel spacing, image distance and reproduced image size is:

[0075]

[0076] In order to ensure that the reconstructed images of the three primary colors are of sufficient size, the smallest image, i.e. 1.069×10 -5 z 0 mm is used as the basis for calculation. o =350mm. That is, the maximum SLM pixel spacing corresponding to the reconstructed image of sufficient size is d slm =3.74×10 -3 mm.

[0077] Example 1

[0078] Considering that the PDLC film in Comparative Example 1 is set to 10 layers, but the thickness of the current 3D object from its rear end plane to the front end plane may exceed the thickness of the 10-layer reproduced image, the PDLC film cannot meet the demand for reproducing thicker 3D objects when it is set to 10 layers, and if the reproduced image has 30 layers, according to the layered three-dimensional display principle based on the stacked liquid crystal control film, in order to obtain a continuous dynamic three-dimensional image, the refresh rate of the spatial light modulator SLM needs to reach 900Hz.

[0079] At present, there is a negative relationship between the number of pixels and the frame rate of commercial spatial light modulators, that is, the larger the number of pixels, the smaller the frame rate. Considering the number of pixels and the size of the pixel, and combining the performance of the PDLC film and the spatial light modulator, if they are simply used directly for holographic dynamic display, it is difficult to achieve the expected purpose because the maximum frame rate selected in this embodiment is lower than 900Hz. Therefore, this embodiment designs a spatiotemporal integrated SLMs-ML-PDLCs computational holographic 3D dynamic display system, making full use of existing optoelectronic technology and computer control technology to maximize the performance of existing devices and materials.

[0080] The basic principle of the system is to integrate the three groups of SLM-ML-PDLCs in comparative example 1 in space, and use the reflection and refraction of the beam splitter prism to superimpose the three-dimensional images scattered by the three groups of SLM-ML-PDLCs into one area to form a 30-layer three-dimensional image, such as Fig. 9 Each group of SLM-ML-PDLCs includes: the spatial light modulator, the diffusion laminate, and the aperture in Example 1. The number of layers of each group of ML-PDLCs is N f It is 1 / 3 of the total number of layers 30. When placing ML-PDLCs, the position of ML-PDLCs is precisely adjusted so that the distance between ML-PDLCs and SLM in different SLM-ML-PDLCs groups differs by 1 / 3 of the thickness of the PDLC film. The three-dimensional images scattered by the upper and lower groups of SLM-ML-PDLCs are reflected by the dichroic prism and superimposed on the three-dimensional image scattered by the middle SLM-ML-PDLCs in a mirror image, but they do not overlap, but differ by 1 / 3 of the thickness of the PDLC film, and finally form an equivalent 3ML-PDLCs. If the thickness of the -PDLC film is Λ 0 If ML-PDLCs 1 With lens L 1-1 The distance is z 1 , then ML-PDLCs 2 With lens L 1-2 The distance is z 1 +Λ 0 / 3,ML-PDLCs 3 With lens L 1-3 The distance is z 1 +2Λ 0 / 3, such as Figure 12-13 As shown in the figure, the final effect of three ML-PDLCs is equivalent to that of a layer with N=3N. f , the membrane spacing is Stacked ML-PDLCs 123 In order to make three SLM-ML-PDLCs equivalent to one stacked ML-PDLCs in terms of timing 123 , under computer control, the scanning time of each group of adjacent layers can be increased by 3 times, and the scanning time can be delayed by 1 / 3 in turn. 123 For each layer, the scanning time is T 123 , then the scanning time of the three SLM-ML-PDLCs is T 0 =3T 123 , relative to SLM-ML-PDLCs 1 , SLM-ML-PDLCs 2 Delay T 123 , SLM-ML-PDLCs 3 Delay 2T123 . (It is not necessary to stagger the loading of the three SLM-ML-PDLCs. The simultaneous imaging of the three SLM-ML-PDLCs does not affect the fusion of the images in the beam splitter prism.) The calculated layered holograms are sent to the three spatial modulators in time-sharing order. Assume that the total number of layers of 3ML-PDLCs is 30. Because each group of ML-PDLCs has only 1 / 3 of the total number of layers, for each SLM, refreshing "one frame" of 3D image only requires scanning 10 layers. If it is displayed dynamically, the frame rate is required to be 10×30Hz=300Hz. Assume that the first layer of hologram is displayed by SLM1, the second layer of hologram is displayed by SLM2, and the third layer of hologram is displayed by SLM3; the fourth layer of hologram is displayed by SLM1, the fifth layer of hologram is displayed by SLM2, and the sixth layer of hologram is displayed by SLM3..., and this cycle repeats. Assuming that the SLM frame rate is set to 300Hz, the time required to scan each layer is Seconds = 3.33ms, so as long as the three SLMs are displayed, the difference between them is The frame rate can reach 900Hz in seconds. Suppose the time when SLM1 displays the first hologram is t, and the time when SLM2 displays the second hologram is seconds, and the moment when SLM3 displays the third layer of hologram is Second.......

[0081] Although this design can meet the frame rate requirements with existing SLM, the current ordinary PDLC film has a very slow time response. According to Table 1, the film takes 10ms to respond from the scattering state to the transparent state, and 100ms to respond from the transparent state to the scattering state, which is not enough. In fact, studies have shown that the entire response time of PDLC film from off-on to on-off can reach milliseconds or even microseconds. [4] .

[0082] As far as the current situation is concerned, the selected ordinary PDLC film can satisfy the use of visual aftereffect, allowing people to feel the effect of a complete 3D static image composed of 30 layers of three-dimensional images.

[0083] During the operation of the PDLC of this embodiment, the ML-PDLCs are mainly in the open state, that is, if no reproduced image appears, all layers of the ML-PDLCs are in a transparent state. When a certain layer of image reproduced by the hologram in the SLM is imaged on a certain layer of the PDLC film, this layer of film is in the closed state, thereby scattering the image, and when the next layer of image appears, the film corresponding to it is in the closed state, and at the same time, the film corresponding to the previous layer of image is in the open state... According to the characteristics of the existing PDLC film, the opening and closing of the front and rear layers of the image requires 110 milliseconds. In order to adapt to the response speed of the PDLC film, the time for the SLM to display each layer of the hologram is also determined to be 110 milliseconds. If each group of ML-PDLCs still consists of 10 layers of PDLC film, the time required to complete a refresh is 1.1 seconds. For three groups of ML-PDLCs, it means that 30 layers of images appear in the field of view in sequence within 1.1 seconds. Using the visual residual effect, the human eye can feel a complete 3D static image composed of 30 layers of images.

[0084] Preferably, the response speed can be improved by reducing the off-state time. The on-off response time of 100ms refers to the time required for the PDLC film to change from transparent to fully scattered state. If this time is reduced a little, the scattering of the PDLC film will become smaller. Figure 8 This is a time response curve of the "on-off" of the PDLC film. It can be seen that as the off-state time becomes longer, the transmittance gradually decreases, accompanied by a gradual increase in scattering. From 1400 milliseconds to 1520 milliseconds, the time is 120 milliseconds. The PDLC film reaches the maximum scattering. At 1460 milliseconds, the transmittance is already 20%, and most of the energy has been scattered. If the scattering angle of the image point can meet the viewing requirements of the human eye at this time, 1460 milliseconds can be used as the cutoff point of the off state. In this way, the "on-off" response time is only 60 milliseconds.

[0085] If the spatial light modulator in Example 1 is selected as the spatial light modulator RSLM-4K70-P with a maximum frame rate of only 480 Hz, the number of pixels is large and the pixel is smaller than 3.74 μm, which meets the requirement of static display of clear 30-layer three-dimensional images.

[0086] Comparative Example 2

[0087] Considering the mutual constraints between CGH and SLM and ML-PDLCs parameters, the lens imaging method used in the solution of Example 1 can increase the freedom of parameter selection, that is, the holographic image reproduced by SLM passes through a lens L 1 Imaging onto ML-PDLCs, e.g. Fig.10 It is another embodiment of the present invention.

[0088] Holographic image reproduced by SLM I 0Located near the aperture AP, and then through the lens L 1 The real image is magnified and ML-PDLCs are placed at the real image to expand the layered divergence angle of the reconstructed image. The n-layer reconstructed image near the aperture AP is closest to the lens L. 1 The 0th layer reproduces the image distance lens L 1 Over a focal length, the diffuser laminate is closest to the lens L 1 The nth layer of polymer scattering liquid crystal film lens L 1 The imaging optical path is L 1 Over a focal length, lens L 1 The n-layer reproduced image is magnified and imaged into the diffusion laminate, and the n-layer magnified real image is sequentially overlapped with the positions of the n-layer polymer scattering liquid crystal films in the diffusion laminate.

[0089] It can be seen from the figure that the images of different layers are 1 The lateral and longitudinal magnifications will be different depending on the position of the object, which will cause distortion of the overall three-dimensional image and must be corrected.

[0090] For holograms, the more pixels there are, the greater the amount of information that can be reproduced. In practical applications, the amount of information in a three-dimensional reproduced image is mainly reflected in the image size, field of view, and color. When the amount of information is constant, these three can be traded off as needed.

[0091] like Fig.10 The computer generated hologram is input to the spatial light modulator SLM, the reconstructed light C illuminates the SLM, and the reconstructed image I of the nth layer hologram is Hn Near the aperture AP plane, the front end of the entire reconstructed image layer is a H , the back end is b H , let z Ha and z Hb They are respectively a H Point and b H Point and lens L 1 Input side focus F 1 The distance, let z Ha -z Hb =D H , D H To reproduce the vertical depth of the image (depth of field). 1 to I Hn Imaging, the image is located at lens L 1 Output side focus F 1 'Outside, there is an enlarged real image I Pn The front and rear ends of all real image layers after imaging are a P With b P , let a P 、b PWith focus F 1 The distances of ′ are z Pa 、z Pb , then the depth of field of the real image is D P =z Pa -z Pb .

[0092] Suppose the reconstructed image I of the n'th layer hologram is Hn 'The plane and the front end a H The distance is Δz Hn’ , then with the focus F 1 The distance is: z Hn’ =z Ha +Δz Hn’ (2-1)

[0093] Further set I Hn’ Real image I Pn’ The plane is the same as a P The distance between the planes is Δz Pn’ , then with the focus F 1 ′The distance is: z Pn’ =z Pa -Δz Pn’ (2-2)

[0094] The lateral magnification of the n'th layer image is:

[0095] 1≤n'≤n, n' is the distance from all the reconstructed image layers closest to the lens L 1 The front end of a H To the back end b H The number of layers between 1 It is lens L 1 Center to output side focus F 1 ′ distance.

[0096] According to Newton's formula of ideal imaging system, we can get: Hn’ z Pn’ =f 1 2 (2-4)

[0097] Right now

[0098] Let I Hn’ With adjacent reconstructed image I Hn’+1 The layer interval is Δl n’ , then for I Hn’+1 , by L 1 After imaging:

[0099]

[0100] Where Δl′n ' is the distance between adjacent real image layers after lens imaging. Subtracting (2-6) from (2-5) yields:

[0101] From this we can get the longitudinal magnification:

[0102]

[0103] ΔZ Hn′ = 0,

[0104] From the above analysis, it can be seen that after the reconstructed image is imaged by the lens, the lateral magnification and longitudinal magnification of the image increase with the depth Δz of the object. Hn’ The real image IP will be distorted. In particular, the intervals between adjacent real image layers (Formula 2-7) are no longer equal. If the film layers in ML-PDLCs are arranged at equal intervals, the image layer and the film layer cannot correspond to each other, which makes it difficult for the distances between the polymer scattering liquid crystal film in the diffuse laminate and the spatial light modulator in the three groups of SLM-ML-PDLCs to differ by a thickness of Λ.

[0105] Example 2

[0106] Since the PDLC films in ML-PDLCs are arranged at equal intervals, it is relatively easy to make them. In this case, in order to achieve a one-to-one correspondence between the image layer and the film layer, it is hoped that the L 1 The image is enlarged in proportion to the original object. To achieve this purpose, when one of the three groups of SLM-ML-PDLCs is arranged in the arrangement of comparative example 1, the spatial coordinates of the original object in the holograms at different levels can be transformed when calculating the hologram to compensate for the distortion caused by the lens L. 1 The deformations generated by imaging are then sequentially input into the SLM, illuminated by laser, and projected onto the corresponding PDLC films arranged with equal spacing in the ML-PDLCs.

[0107] The spatial lateral coordinate transformation of the original object:

[0108] Assume that the distance between the front face of the original object and the hologram recording plane is Z ao , the distance between the nth layer in the object and the front face of the object is Δz on , the distance between this surface and the hologram recording plane is:

[0109] Z on =Z ao -Δz on (2-9)

[0110] Assume that the n'th level I on The coordinates of a point on theo , according to formula (2-3), the coordinates of its image are:

[0111]

[0112] When Δz Hn = 0, that is, a on the front face of the original object 0 The coordinates of a point are x o , by L 1 After the lens forms an image, 1 The coordinates of the conjugate point on the front plane ap are x Pn0 , With Δz Hn’ Increase, the coordinates on different levels are x on The image coordinate x Pn Gradually become smaller. In order to make When calculating the hologram, the coordinate x of the actual object point is converted to on Perform the transformation as follows:

[0113] The spatial longitudinal coordinate transformation of the original object:

[0114] For the longitudinal spacing, according to formula (2-7), when Δz Hn’ = 0, In order to make the image formed by L1 enlarged in proportion to the original object, the interval Δl between the corresponding reconstructed image layer (i.e., aH layer, where n'=0) and the adjacent layer (n'=1) is set 1 is a fixed value, which is the layer spacing between the 0th and 1st layers of the 3D object.

[0115] In order to ensure that the interval between different adjacent image layers is always According to formula (2-7), let:

[0116]

[0117] If the spacing between adjacent PDLC films in ML-PDLCs is determined to be can be written as:

[0118]

[0119]

[0120] make:

[0121] The above formula can be simplified to

[0122]

[0123] Solving the above equations, we finally get the intervals between the various layers when calculating the hologram:

[0124]

[0125] The positive and negative signs of the above equation are determined according to the actual parameters. For example, let Δl 1 =0.3mm, z Ha =30mm, the object depth of field is For n = 2, z Ha2 =z Ha +Δl 1 =30.3mm

[0126] When Δl is negative 2 =0.3124mm, take the timing Δl 2 =2939.1mm, obviously, the negative sign is in line with the actual situation:

[0127]

[0128] or

[0129] The calculation of the above formula is relatively complicated, and can be calculated using computer recursion method, namely:

[0130]

[0131] Substitute ΔZ into equation (2-13) Hn′ After that, it can be transformed into When calculating the hologram, the coordinate x of the nth layer of the actual object is on According to the above formula, the deformation caused by the imaging of lens L1 is compensated, so that when the PDLC films in ML-PDLCs are arranged at equal intervals, the tomographic hologram reconstructed image displayed by SLM passes through L 1 The image is magnified in proportion to the original object, so that the image layer and the film layer correspond to each other, and the center distance between adjacent polymer scattering liquid crystal films in the diffusion laminate is Δl' 1 are equal, and Δl 1 is the distance between the reconstructed images of layers 0 and 1.

[0132] Example 3

[0133] In order to obtain a 3D display with a larger field of view, the three-dimensional image formed by the ML-PDLCs of Example 2 needs to be further enlarged. Fig.11 The optical path illustrates the imaging process of a group of SLM-ML-PDLCs. The image is taken using lens L2 The three-dimensional image layer scattered by ML-PDLCs is imaged. 2 The diffuser laminate faces away from the lens L 1 One side is arranged along the normal line C of the real image, and the lens L 2 The n-layer three-dimensional image layer scattered by the diffuse laminate is magnified and imaged, and the interval between adjacent image layers after magnification is less than the resolution limit of the human eye along the normal line C direction. The lens L 2 The distance between the nth three-dimensional image layer in the diffusion laminate and the adjacent three-dimensional image layers in the ML-PDLCs is determined by formula (2-12). Assume that the nth image layer and the focal point F 2 The distance is z in , by L 2 After imaging, the longitudinal magnification is:

[0134]

[0135] The intervals of the corresponding magnified image layers are:

[0136]

[0137] The above formula shows that, when other parameters remain unchanged, the closer the three-dimensional image layer is to the focus F2 (i.e., z in The smaller the in The larger the F 2 The nearest 3D image layer is the front end of the object. p , assuming that the frontmost 3D image layer and the focal point F 2 The distance is z ia , then the maximum spacing of the magnified image layer is:

[0138]

[0139] When using tomography to display three-dimensional images, when the interval between adjacent magnified image layers is less than the vertical resolution limit of the human eye, the vertical change can be considered continuous. [5] yes:

[0140] ε is the resolution angle of the human eye, and the limit value is ε = 2.9 × 10 -4 rad, in practical applications, ε=4×10 - 4 rad,L e ≈65mm is the pupil distance, z e is the observation distance, that is, the distance between the human eye and the image. The above formula can be written as:

[0141] Δz e =6.7×10 -6 ze 2 (3-5)

[0142] In order to ensure that the image layer is continuous when the human eye observes the magnified image, it is required to satisfy Δl′ imax <Δz e ,Right now

[0143]

[0144] Formula (3-5) is the basis for parameter selection when designing the overall display system.

[0145] For example: Let z Ha =30mm,f 1 =50mm,z ia =10mm, f 2 =70mm, z e =1500mm, the layer spacing of the object reconstruction image when calculating the hologram is obtained as:

[0146]

[0147] Corresponding to the spacing between adjacent 3D imaging layers in ML-PDLCs

[0148]

[0149] Referring to formula (2-12), the lateral magnification of the final image is:

[0150] When designing, parameters should be selected based on the actual situation of the device.

[0151] As a preferred embodiment of the present invention: a holographic 3D display system based on multiple sets of SLM-ML-PDLCs, comprising: a computer, multiple sets of SLM-ML-PDLCs, a beam splitter prism, a lens L 2 In each group of SLM-ML-PDLCs, the spatial light modulator and the diffusion laminate are arranged in the manner of Example 2, the PDLC films in the diffusion laminate are arranged at equal intervals, and the lens L 2 The output window of the beam splitter is arranged along the normal line C of the fused three-dimensional image, and the arrangement is similar to that of Example 4. When calculating the hologram, the computer transforms the spatial coordinates of the original object in the holograms of different layers according to the method of Example 2 to compensate for the distortion caused by the lens L. 1 The deformation caused by imaging. Among them, the layer interval of the reconstructed image from layer n' to layer n'+1 is Δl n ', The nth three-dimensional image layer and the lens L 2 The distance of the focus is z ia , ze is the observation distance, that is, the distance between the human eye and the lens L 2 The distance of the magnified image, f 2 For lens L 2 The distance between adjacent 3D image layers in ML-PDLCs is Δl 1 =Δl n’ .

[0152] [4] Zheng Jihong, Zhong Yangwan, et al., Study on electrically controlled polymer dispersed liquid crystal holographic lens and its characteristics, Chinese Journal of Physics, 59(3), 2010

[0153] [5] Wang Hui. Wavefront Reconstruction of Three-Dimensional Display, Beijing, Science Press, 2016: 11.

Claims

1. A holographic 3D display system based on multiple sets of SLM-ML-PDLCs, characterized in that: The images output by H groups of SLM-ML-PDLCs are fused into the same area through a beam splitter prism to holographically display a 3D object, and each group of SLM-ML-PDLCs includes: a set of spatial light modulators, a set of diffusion laminates, and an aperture; The spatial light modulator receives a Fresnel hologram of n-layer two-dimensional images created and encoded by a computer, modulates the illumination light emitted by the light source module, and sequentially reconstructs the reconstructed images of each layer of the hologram in the reconstructed light field according to the loading sequence, and the H groups of n-layer two-dimensional images correspond to the H×n layers of equidistant and parallel cross sections of the three-dimensional image of the 3D object decomposed layer by layer from the rear end plane to the front end plane; the position of the reconstructed n-layer reconstructed image corresponds to the position of the two-dimensional image of the reconstructed image in the three-dimensional image, and the size of the reconstructed image is consistent with that of the three-dimensional image of the 3D object; The diffusion laminate is composed of M layers of parallel polymer scattering liquid crystal films, n≤M≤19, and the positions of the n layers of reconstructed images from the rear end plane to the front end plane in the reconstructed light field are sequentially overlapped with the positions of the n layers of polymer scattering liquid crystal films in the diffusion laminate. The n layers of polymer scattering liquid crystal films are controlled by a computer. When the reconstructed image of the nth layer of the hologram is reconstructed, the polymer scattering liquid crystal films that overlap with the position of the reconstructed image of this layer are in a scattering state, scattering the reconstructed image into a three-dimensional image, while the remaining polymer scattering liquid crystal films are in a transparent state, allowing the reconstructed image to pass through without interference. An aperture is disposed at the output window end face of the diffusion laminate and is used to block the zero-order term and conjugate image of the diffracted light; The response time of the polymer scattering liquid crystal film is T, the frame rate of the spatial light modulator is at least 1 / T Hz, and the pixel interval d of the spatial light modulator is slm Satisfies the following formula: d slm ≤λZ o / 2L o , L o is the plane size of the reconstructed image, λ is the wavelength of the illumination light, and Z o To reproduce the distance between the image and the spatial light modulator, the planar dimension of the diffuse laminate is not less than L o , the response time refers to the total time for the polymer scattering liquid crystal film to change from the scattering state when the power is off to the transparent state after the power is on, and then to the scattering state after the power is off; The distances between the polymer scattering liquid crystal film in the diffuse laminate and the spatial light modulator in different SLM-ML-PDLCs groups differ by a thickness of Λ, where Λ is equal to the thickness of the polymer scattering liquid crystal film of 1 / H, so that after the three-dimensional images scattered by the H groups of ML-PDLCs are fused by the beam splitter prism, the three-dimensional images do not overlap, but differ by a thickness of Λ.

2. The holographic 3D display system based on multiple sets of SLM-ML-PDLCs according to claim 1, characterized in that: The response time refers to the total time for the polymer scattering liquid crystal film to change from a scattering state with a transmittance of no more than 20% when powered off to a transparent state after powered on, and then to a scattering state with a transmittance of no more than 20% when powered off.

3. The holographic 3D display system based on multiple sets of SLM-ML-PDLCs according to claim 2, characterized in that: The polymer scattering liquid crystal film takes 10ms to change from a scattering state with a transmittance of no more than 20% when powered off to a transparent state after powered on, and it takes 100ms to change from a scattering state with a transmittance of no more than 20% when powered on to a scattering state with a transmittance of no more than 20%.

4. The holographic 3D display system based on multiple sets of SLM-ML-PDLCs according to claim 2, characterized in that: The polymer scattering liquid crystal film takes 10 ms to change from a scattering state with a transmittance of no more than 20% when powered off to a transparent state after powered on, and takes 60 ms to change from a scattering state with a transmittance of no more than 20% after powered on.

5. The holographic 3D display system based on multiple sets of SLM-ML-PDLCs according to claim 2, characterized in that: The frame rate of the spatial light modulator is at least 25n / H Hz, and the response time of the polymer scattering liquid crystal film is no more than H / 25n seconds.

6. The holographic 3D display system based on multiple sets of SLM-ML-PDLCs according to any one of claims 1 to 5, characterized in that: Each group of SLM-ML-PDLCs also includes: a lens L1. The aperture and lens L1 in each group of SLM-ML-PDLCs are sequentially arranged between the spatial light modulator and the diffusion laminate along the normal G of the reconstructed image. The n layers of reconstructed image are located on the inner periphery of the frame of the aperture, and the 0th layer of the reconstructed image closest to the lens L1 among the n layers of reconstructed image is more than one focal length away from the lens L1. The imaging optical path of the nth layer of polymer scattering liquid crystal film lens L1 closest to the lens L1 in the diffusion laminate is more than one focal length away from the lens L1. The lens L1 magnifies the n layers of reconstructed image and images it into the diffusion laminate. The n layers of magnified real images sequentially coincide with the positions of the n layers of polymer scattering liquid crystal films in the diffusion laminate, and the plane size of the real image is not greater than the plane size of the diffusion laminate. The center distance Δl' of adjacent polymer scattering liquid crystal films in the diffusion laminate is n’ Equal, Δl' n’ =Δl'1, and Δl1 is the distance between the 0th and 1st layer reconstructed images. When creating the hologram, the computer transforms the spatial coordinates of the original object in the holograms of different layers to compensate for the deformation caused by imaging through lens L1, so that lens L1 can proportionally magnify the reconstructed image in sequence onto the corresponding polymer scattering liquid crystal films arranged at equal intervals in the diffuse laminate.

7. The holographic 3D display system based on multiple sets of SLM-ML-PDLCs according to claim 6, characterized in that: When calculating the hologram, the coordinates x of the actual object point are converted to on Perform the transformation as follows: And the coordinate x of the n'th layer of the two-dimensional image of the actual object along the normal G direction on Perform the transformation as follows: Where Z Ha is the distance between the nth layer's reconstructed image and the input-side focus of lens L1, ΔZ Hn’ is the distance between the nth layer reconstruction image and the n'th layer reconstruction image, and f1 is the focal length of lens L1.

8. The holographic 3D display system based on multiple sets of SLM-ML-PDLCs according to claim 7, characterized in that: It also includes a lens L2, which is arranged on one side of the output window of the dichroic prism along the normal C of the fused three-dimensional image. The lens L2 magnifies H×n three-dimensional image layers to form an image, and the interval between adjacent image layers after magnification is less than the resolution limit of the human eye along the normal C direction. The lens L2 is more than a focal length away from the nth three-dimensional image layer in the diffusion laminate.

9. The holographic 3D display system based on multiple sets of SLM-ML-PDLCs according to claim 8, characterized in that: The layer interval between the n'th to n'+1th layers of the reconstructed image is Δl n’ , The distance between the nth 3D image layer and the focus of lens L2 is z ia , z e is the observation distance, that is, the distance between the human eye and the image magnified by lens L2, and f2 is the focal length of lens L2.

Images