A large field of view holographic flat panel display device

Abstract

The present application relates to a kind of large field of view holographic flat-panel display device, belong to holographic display technical field, including LD light source, corner cube, flat-panel waveguide device, spatial light modulator SLM and function screen;Flat-panel waveguide device includes incident holographic grating, exit holographic grating and the light waveguide with flat structure;The direction of light wave emitted by LD light source is converted by corner cube, is shot into light waveguide, then diffraction occurs by incident holographic grating, total internal reflection propagation occurs in light waveguide inside;When light wave reaches the exit holographic grating, light wave diffraction occurs again so that total reflection condition is broken, light wave is parallelly emitted from light waveguide, and is modulated to form output light spot by the spatial light modulator SLM, input function screen;Function screen is arranged on the other side opposite SLM and exit holographic grating, and distance and size are adjustable;Function screen expands reconstruction image by adjusting the position of the plane and imaging plane where it is located, realizes large field of view holographic display.

Description

Technical Field

[0001] The present invention belongs to the technical field of holographic display and relates to a large-field-of-view holographic flat-panel display device. Background Art

[0002] Holography is considered the ultimate technology for achieving perfect 3D displays. With the continuous development of spatial light modulators (SLMs), SLM-based holographic display technology has shown tremendous potential for color, dynamic, and high-resolution holographic displays. However, the pixel size of existing SLMs typically ranges from 6μm to 15μm. Assuming a light source wavelength of 650nm and an SLM pixel size of 8μm, the resulting diffraction angle is only 2.3°. Due to the small diffraction angle of the SLM, the size of the holographic reconstructed image is typically small. While increasing the propagation distance can increase the image size, the increase is very small. Smaller image sizes no longer meet the requirements for large-field-of-view holographic displays. Further reducing the pixel size would increase the diffraction angle, thereby expanding the field of view of the holographic reconstruction. However, due to current technical limitations and production processes, it is difficult to achieve a pixel size on the order of a wavelength for SLMs.

[0003] Current methods for achieving large-field-of-view holographic display include: splicing the reconstructed images of multiple SLMs to achieve large-field-of-view holographic display. However, this method will lead to a complex and costly holographic display system structure, and require precise optical path design to achieve seamless splicing; using divergent spherical light to illuminate the SLM to physically increase the diffraction angle of the SLM to achieve large-field-of-view holographic display, but this type of method has certain restrictions on the light source requirements. Both require a divergent spherical light beam with a smaller radius, and the incident light is a spherical wave, which will lead to uneven intensity and phase of the reconstructed image; introducing some optical elements and designing algorithms to expand the holographic reconstructed image. This method is a relatively simple and effective method, but because it involves multi-segment diffraction calculations, the calculation process is relatively complex and requires too much time investment and experienced designers.

[0004] In addition, current holographic display systems typically rely on optical carriers and components such as SLMs, lasers, polarizers, and beam expanders. These optical carriers and components themselves have a certain weight and volume, and the components need to maintain a certain distance when building the optical path. This results in the final optical system's total volume being always large, making it impossible to achieve a compact holographic display system. Currently, small size and light weight are very important competitive advantages, so it is necessary to achieve a small and lightweight system while ensuring display quality and expanding the field of view. Designs based on flat-panel holography can achieve the advantages of being lightweight and practical, and have greater application potential. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a large-field-of-view holographic flat-panel display device, which realizes large-field-of-view holographic display by combining the proposed holographic flat-panel display system with a functional screen and matching the hologram design method of the system structure.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A large-field holographic flat-panel display device includes an LD light source, a corner prism, a flat-panel waveguide device, a spatial light modulator (SLM), and a functional screen.

[0008] The slab waveguide device comprises an incident holographic grating, an exit holographic grating, and an optical waveguide with a slab structure; the incident holographic grating and a spatial light modulator (SLM) are bonded to both ends of a horizontal surface of one side of the optical waveguide, and the exit holographic grating is bonded to the end of the horizontal surface of the other side opposite to the SLM;

[0009] The light waves emitted by the LD light source are redirected by the corner prism and incident on the optical waveguide. They are then diffracted by the incident holographic grating and propagate through total internal reflection inside the optical waveguide. When the light waves reach the exit holographic grating, they are diffracted again, breaking the total internal reflection condition. The light waves are then emitted from the optical waveguide in parallel and modulated by the spatial light modulator (SLM) to form an output light spot, which is then input into the functional screen.

[0010] The functional screen is arranged on the other side of the SLM opposite to the output holographic grating, and the distance and size are adjustable; the functional screen expands the reconstructed image by adjusting the position of its own plane and the imaging plane to achieve a large-field holographic display.

[0011] Furthermore, the spatial light modulator SLM is a transmissive phase-type SLM or a transmissive amplitude-type SLM.

[0012] Furthermore, the functional screen is a microlens array or other micro-optical elements.

[0013] Furthermore, the light-transmitting size L1 of the functional screen is larger than the light-transmitting size L0 of the SLM, wherein L0=NΔp, N is the number of SLM pixels, and Δp is the SLM pixel spacing.

[0014] Furthermore, the functional screen expands and reconstructs the image by adjusting the position of the plane where the functional screen is located and the imaging plane, specifically including:

[0015] An SLM holographic imaging data set containing the functional screen model is constructed using an angular spectrum diffraction algorithm;

[0016] Constructing a convolutional neural network and training the convolutional neural network using the data set;

[0017] Use the trained convolutional neural network to make predictions about images that have never been seen before;

[0018] Finally, the pure phase hologram predicted by the convolutional neural network is displayed as the final hologram.

[0019] Furthermore, the angular spectrum diffraction algorithm includes the following steps:

[0020] Calculate the light field distribution on the plane in front of the functional screen according to the light field distribution of the hologram;

[0021] The light field distribution of the imaging plane is calculated according to the light field distribution of the plane behind the functional screen.

[0022] Furthermore, assuming that the light field distribution of the SLM plane is U0(x0), and the distance between the SLM plane and the functional screen plane is z1, the light field distribution U1(x1) in front of the functional screen is:

[0023] U1(x1)=F -1 {F[U0(x0)]×H jp (f x0 ,z1)}

[0024] Among them, F and F -1 represent Fourier transform and inverse Fourier transform respectively; H jp is the angular spectrum transfer function, satisfying:

[0025] H jp (f x0 ,z1)=exp[jkz1√1-(λf x0 ) 2 ]

[0026] Where λ is the wavelength, k is the wave number, and k = 2π / λ, f x0 is the spatial frequency;

[0027] The light field distribution U2(x2) on the imaging plane is calculated as follows:

[0028]

[0029] Among them, the distance between the functional screen plane and the imaging plane is z2, It represents the phase transformation factor of the functional screen, and its expression is as follows:

[0030]

[0031] Where p is the period of the unit lens, f is the focal length of the unit lens, M is the number of unit lenses, ξ i is the center coordinate of the i-th unit lens, * represents the convolution operation, and rect is the rectangular function;

[0032] The size of the functional screen plane light field is the same as the size of the SLM, when the total transmission distance z=z1+z2 is determined, the number M, focal length f and period p of the unit lens in the fixed functional screen are fixed, so as to control the distance z2 to obtain the imaging plane light field size L of any size, and the visual angle θ of the imaging plane light field is expressed as follows:

[0033] θ=arctan(L / z)

[0034] According to the need, a reasonable z2 is selected, when z2>2f, the reconstructed image can be enlarged, and the holographic display of a large field of view is realized.

[0035] Further, the convolutional neural network is a convolutional residual network ResNet, which predicts the input image as an amplitude image and a phase image and combines them into a complex amplitude hologram, and the loss function used in training is the mean square error (MSE) between the two images;

[0036] When the network training is completed, the network is used to predict images that have never been seen before;

[0037] The network outputs the predicted complex amplitude hologram, encodes it into a pure phase hologram through the double phase method (DPM), and then reconstructs the hologram through the angular spectrum diffraction algorithm of the functional screen to obtain the reconstructed image, and obtains the image size and calculates the visual angle.

[0038] The beneficial effects of the present application are as follows:

[0039] 1、Compared with the traditional holographic display system, the holographic flat waveguide display system can be very thin, it simplifies the whole optical system, does not need a very complex optical path carrier, can be directly spliced, greatly reduces the volume of the holographic display system, provides small size, light weight and low cost for the flat holographic display, and the cost is low.

[0040] 2、Compared with the traditional holographic display and other large field of view holographic display system, only one functional screen needs to be introduced, and the position of the functional screen and the imaging plane is adjusted and controlled, so that the holographic display of a large field of view can be realized.

[0041] 3、In the hologram design method, the SLM holographic imaging data set containing the functional screen model is constructed through the angular spectrum diffraction algorithm, and the convolutional neural network is constructed, and the network is trained and predicted. This avoids the problem that the quality of the holographic image and the calculation speed are difficult to balance in the traditional design algorithm, realizes the design of the pure phase hologram in tens of milliseconds and improves the visual quality, and also reflects the excellent performance of the neural network in quickly solving complex problems.

[0042] Additional advantages, objects, and features of the application will be apparent to those skilled in the art upon examination of the following specification. It is intended that the application not be limited by the disclosed BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to make the objects, technical solutions and advantages of the present application clearer, the preferred embodiments of the present application will be described in detail below with reference to the drawings, in which:

[0044] Figure 1 Figure 1 is a structural diagram of the device of the present application;

[0045] Figure 2 Figure 2 is a schematic diagram of the principle of the holographic slab waveguide display system;

[0046] Figure 3 Figure 3 is a schematic diagram of designing a pure phase hologram using a neural network;

[0047] Figure 4 Figure 4 is a simulation reconstruction result, in which (a)-(b) are reference images, and (c)-(d) are reconstruction results of the hologram designed by the present application. DETAILED DESCRIPTION

[0048] The present application can be implemented or applied in other different specific embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the drawings provided in the following examples only illustrate the basic concept of the present application in a schematic manner, and the following examples and features in the examples can be combined with each other without conflict.

[0049] The drawings are only used for exemplary illustration, and the representation is only a schematic diagram, not a physical diagram, and should not be understood as a limitation of the present application. In order to better illustrate the embodiments of the present application, some components in the drawings can be omitted, enlarged or reduced, and do not represent the actual size of the product. It is understandable for those skilled in the art that some known structures and their descriptions in the drawings can be omitted.

[0050] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0051] The traditional holographic display system only uses one SLM to reconstruct the holographic image. Due to the small diffraction angle of the SLM, the size of the reconstructed image is also very small. At the same time, the traditional holographic display optical path requires a relatively large space, resulting in a large volume and complex structure of the entire system. The large field of view holographic flat panel display system of the present invention is composed of an LD light source, a corner prism, a flat waveguide, a spatial light modulator SLM and a functional screen. Figure 1 As shown. Among them, LD light source, corner prism, flat waveguide, SLM constitute the holographic flat waveguide display system, and its principle is as follows Figure 2 Specifically, the slab waveguide includes an incident holographic grating, an exit holographic grating, and a slab-structured optical waveguide. The incident holographic grating and a transmissive spatial light modulator (SLM) are bonded to the horizontal surface of one side of the slab-structured optical waveguide, with a distance between them. The exit holographic grating is bonded to the horizontal surface of the other side, aligned in parallel with the transmissive spatial light modulator (SLM). Light waves emitted by an LD light source pass through a corner prism and directly enter the slab-structured optical waveguide to reach the incident holographic grating. The light waves are diffracted by the incident holographic grating, undergo total internal reflection within the optical waveguide, and propagate laterally along the optical waveguide plane. When the light waves reach the exit holographic grating, they are diffracted again, breaking the total reflection condition. The light waves are then emitted in parallel from the optical waveguide and modulated by the transmissive spatial light modulator (SLM) to form an output light spot, which is then exported from the slab waveguide.

[0052] The spatial light modulator (SLM) is a transmissive phase-type SLM or a transmissive amplitude-type SLM, which is attached to the optical waveguide surface of the flat-plate structure, on the same side as the incident holographic grating, and forms a large-field-of-view holographic display system with the functional screen. The functional screen can be a microlens array or other micro-optical element, which is placed in parallel with the SLM. The light wave emitted from the flat-plate waveguide and modulated by the SLM is incident on the functional screen. The incident light is an ideal plane wave, and the reconstructed image is expanded by controlling the distance between the SLM and the functional screen. Specifically, a large-field-of-view holographic display is achieved by regulating the position of the functional screen and the position of the imaging plane.

[0053] Example 1:

[0054] According to the angular spectrum diffraction theory, in a traditional holographic display system, the size L of the light field in the imaging plane is the same as the size L0 of the SLM, and is independent of the distance z between the SLM plane and the imaging plane. That is, it satisfies:

[0055] L=L0=NΔp (1)

[0056] Where N is the number of pixels of the SLM, and Δp is the pixel spacing of the SLM;

[0057] In the large field of view holographic display system of the present invention, the microlens array MLA is used as a functional screen as an example. Assuming that the light field distribution on the SLM plane is U0(x0), and the distance between the SLM plane and the microlens array plane is z1, the light field distribution U1(x1) on the front plane of the microlens array is calculated by formula (2):

[0058] U1(x1)=F -1 {F[U0(x0)]×H jp (f x0 , z1)} (2)

[0059] Among them, F and F -1 represent Fourier transform and inverse Fourier transform respectively; H jp is the angular spectrum transfer function, satisfying:

[0060]

[0061] Where λ is the wavelength, k is the wave number, and k = 2π / λ, f x0 is the spatial frequency.

[0062] The light field distribution U2(x2) on the imaging plane is obtained by equation (3):

[0063]

[0064] Among them, the distance between the microlens array plane and the imaging plane is z2, represents the phase shift factor of the microlens array, which is expressed as follows:

[0065]

[0066] Where p is the period of the unit lens, f is the focal length of the unit lens, M is the number of unit lenses, ξ i is the center coordinate of the i-th unit lens, * represents the convolution operation, and rect is the rectangular function.

[0067] The size of the micro-lens array plane light field is the same as the size of the SLM, and is independent of z1. When the total transmission distance z (i.e., the distance between the SLM plane and the observation plane, and z1+z2=z) is determined, the number M, the focal length f, and the period p of the fixed micro-lens array can be controlled to obtain an imaging plane light field size L of any size. The angle of view θ of the imaging plane light field is expressed as follows:

[0068] θ=arctan(L / z) (6)

[0069] where θ is an angle.

[0070] When z2>2f, the reconstructed image can be enlarged to achieve large field of view holographic display; however, when z2≤2f, the size L of the imaging plane light field is ≤L0, and the effect of expanding the field of view is lost, so a reasonable z2 should be selected according to the needs.

[0071] The design and reconstruction process of the pure phase hologram for large field of view holographic display based on the system of the present application combined with a neural network is as shown in Figure 3 In the design process of the hologram, the SLM holographic imaging data set containing the micro-lens array model is constructed by the above-mentioned angular spectrum diffraction algorithm with a micro-lens array, and a convolutional neural network is constructed and trained and predicted. The constructed neural network is a convolutional neural network (CNN), and the CNN model is a convolutional residual network (ResNet) which predicts the input image as an amplitude image and a phase image and combines them into a complex amplitude hologram. The loss function used in training is the mean square error (MSE) between two images.

[0072] When the network training is completed, the neural network is used to predict images that have never been seen. The neural network outputs the predicted complex amplitude hologram and encodes it into a pure phase hologram by the double phase method (DPM), and then the pure phase hologram is reconstructed by the above-mentioned angular spectrum diffraction algorithm with a micro-lens array to obtain a reconstructed image, and the image size and the angle of view are calculated.

[0073] Example 2:

[0074] In actual experiments, the SLM used is a transmissive pure phase type SLM, the pixel size is 8 μm, and the number of pixels of the hologram is 1920x1080. Therefore, the size of the hologram is 15.36 mm x 8.64 mm. The laser wavelength is 650 nm. If the structure is only a single SLM, the propagation distance is 275 mm, and according to formula (1), the size of the imaging plane is only 15.36 mm x 8.64 mm; if only the horizontal angle of view is considered, according to formula (6), the angle of view of the imaging plane is only 3.2°. According to the system of the present application, the hologram is designed and reconstructed by the neural network, and the reconstructed image size is 15.36 mm x 8.64 mm, and the angle of view is 6.4°. Figure 1The system device structure is as described above, the parameters of the SLM are the same as those described above, the functional screen is the same as in Example 1, a microlens array is selected, the distance between the SLM and the microlens array is 25 mm, the period of the unit lenses in the microlens array is 3 mm, the focal length is 22.458 mm, and the number is 14×11; after propagating 250 mm behind the microlens array, the size of the final imaging plane will be larger than the size of the imaging plane of the single SLM structure. When the total transmission distance is the same (both are 275 mm), the viewing angle of the imaging plane will also be larger than the viewing angle of the single SLM structure.

[0075] In the design process of the hologram, the reference original image is Figure 4 In (a)-(b), the number of pixels is 1920×1080. Figure 1 The system device structure and parameter settings are the same as above. The simulation reconstruction results are as follows: Figure 4 As shown in (c)-(d), if only the horizontal direction is considered, the size of the reconstructed image is 36.86 mm and the viewing angle is 7.63°. Obviously, the system proposed in the present invention can effectively expand the holographic reconstructed image and realize a large-field holographic display. At the same time, through testing, it was found that for a 1920×1080 image, the hologram design method proposed in the present invention can achieve rapid design of pure phase holograms within tens of milliseconds and the reconstructed image quality is good, avoiding the difficult trade-off between holographic image quality and calculation speed.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A large-field-of-view holographic flat-panel display device, characterized in that: It includes LD light source, corner prism, flat waveguide device, spatial light modulator SLM and functional screen; The slab waveguide device comprises an incident holographic grating, an exit holographic grating, and an optical waveguide with a slab structure; the incident holographic grating and a spatial light modulator (SLM) are bonded to both ends of a horizontal surface of one side of the optical waveguide, and the exit holographic grating is bonded to the end of the horizontal surface of the other side opposite to the SLM; The light waves emitted by the LD light source are redirected by the corner prism and incident on the optical waveguide. They are then diffracted by the incident holographic grating and propagate through total internal reflection inside the optical waveguide. When the light waves reach the exit holographic grating, they are diffracted again, breaking the total internal reflection condition. The light waves are then emitted from the optical waveguide in parallel and modulated by the spatial light modulator (SLM) to form an output light spot, which is then input into the functional screen. The functional screen is arranged on the other side of the SLM opposite to the output holographic grating, and the distance and size are adjustable; the functional screen expands the reconstructed image by adjusting the position of its own plane and the imaging plane, thereby realizing a large-field holographic display; The functional screen expands and reconstructs the image by adjusting the position of the plane where the functional screen is located and the imaging plane, specifically including: An SLM holographic imaging data set containing the functional screen model is constructed using an angular spectrum diffraction algorithm; Constructing a convolutional neural network and training the convolutional neural network using the data set; Use the trained convolutional neural network to make predictions about images that have never been seen before; Finally, the pure phase hologram predicted by the convolutional neural network is displayed as the final generated hologram; The angular spectrum diffraction algorithm comprises the following steps: Calculate the light field distribution on the plane in front of the functional screen according to the light field distribution of the hologram; Calculate the light field distribution of the imaging plane according to the light field distribution of the plane behind the functional screen; Assume that the light field distribution on the SLM plane is , the distance between the SLM plane and the functional screen plane is , then the light field distribution in front of the functional screen is for: in, F and F -1 represent Fourier transform and inverse Fourier transform respectively; is the angular spectrum transfer function, satisfying: in, λ is the wavelength, k is the wave number, and k =2π / λ , is the spatial frequency; Light field distribution on the imaging plane The calculation is as follows: Among them, the distance between the functional screen plane and the imaging plane is , φ mla It represents the phase transformation factor of the functional screen, and its expression is as follows: φ mla = [ rect ( )· exp (− ·𝑥)] * in, p is the period of the unit lens, f is the focal length of the unit lens, M is the number of unit lenses, It is i The center coordinates of the unit lens, * represents the convolution operation, rect is a rectangular function; The size of the functional screen plane light field is the same as that of the SLM. When the total transmission distance z = z 1+ z 2 When determining, the number M of unit lenses in the fixed function screen and the focal length f and cycle p , thereby controlling the distance z 2 Obtaining any size of imaging plane light field size L , the viewing angle of the imaging plane light field θ The expression is as follows: θ = arctan( L / z ) Choose reasonable one according to your needs z 2. When z 2>2 f When the image is reconstructed, a large field of view holographic display can be achieved.

2. The large-field-of-view holographic flat-panel display device according to claim 1, wherein: The spatial light modulator SLM is a transmissive phase-type SLM or a transmissive amplitude-type SLM.

3. The large-field-of-view holographic flat-panel display device according to claim 1, wherein: The functional screen is a micro-lens array or other micro-optical elements.

4. The large-field-of-view holographic flat-panel display device according to claim 1, wherein: Light transmission size of the functional screen L 1 Larger than the SLM's light clearance L 0, where L 0= N Δ p , N is the number of SLM pixels, Δ p is the SLM pixel spacing.

5. The large-field-of-view holographic flat-panel display device according to claim 1, wherein: The convolutional neural network is a convolutional residual network (ResNet), which predicts the input image into an amplitude image and a phase image and combines them into a complex amplitude hologram. The loss function used in training is the mean square error (MSE) between the two images. Once the network is trained, make predictions on images the network has never seen before. The network output is predicted to obtain a complex amplitude hologram, which is encoded by the dual-phase method DPM to obtain a pure phase hologram. The pure phase hologram is then holographically reconstructed using the angular spectrum diffraction algorithm of the functional screen to obtain a reconstructed image, and the image size and calculated viewing angle are obtained.

Images