Large-view-field holographic panel display device

Abstract

The invention relates to a large-view-field holographic flat panel display device, which belongs to the technical field of holographic display and comprises an LD light source, a corner prism, a flat panel waveguide device, a spatial light modulator SLM and a functional screen. The slab waveguide device comprises an incident holographic grating, an emergent holographic grating and an optical waveguide with a slab structure; light waves emitted by the LD light source are subjected to direction conversion through the corner prism, enter the optical waveguide, are diffracted through the incident holographic grating, and are subjected to total internal reflection propagation in the optical waveguide; when the light wave reaches the emergent holographic grating, the light wave is diffracted again, so that the total reflection condition is broken, and the light wave is emergent from the optical waveguide in parallel and is modulated by the spatial light modulator SLM to form an output light spot to be input into a function screen; the function screen is arranged on the other side, opposite to the emergent holographic grating, of the SLM, and the distance and the size are adjustable; the function screen enlarges the reconstructed image by adjusting the position of the plane where the function screen is located and the position of the imaging plane, and large-view-field holographic display is achieved.

Description

Technical Field

[0001] The 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 to be the ultimate technology for achieving perfect 3D display. Especially with the continuous development of spatial light modulators (SLM), holographic display technology based on SLM has shown great application potential in color, dynamic, high-resolution holographic display and other directions. However, the pixel size of existing SLM is generally between 6μm and 15μm. Assuming that the wavelength of the light source is 650nm and the pixel size of SLM is 8μm, it can be obtained that the diffraction angle of SLM is only 2.3°. Since the diffraction angle of SLM is very small, the size of the holographic reconstructed image is usually small; although increasing the propagation distance can make the image size larger, its increment is also very small. Smaller image size can no longer meet the needs of large field of view holographic display. Further reducing the pixel size can increase the diffraction angle, thereby expanding the field of view of holographic reconstruction, but due to current technical conditions and production processes, it is difficult for the pixel size of SLM to reach the wavelength level.

[0003] At present, the methods for realizing large-field holographic display include: splicing the reconstructed images of multiple SLMs to realize large-field holographic display, but this method will make the holographic display system complex and costly, and require precise optical path design to achieve seamless splicing; using divergent spherical light to illuminate the SLM and physically increase the diffraction angle of the SLM to realize large-field holographic display, but this type of method has certain restrictions on the light source requirements, and requires 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 complicated and requires too much time investment and experienced designers.

[0004] In addition, current holographic display systems usually rely on optical carriers and components such as SLM, lasers, polarizers, and beam expansion systems. These optical carriers and components themselves have a certain weight and volume. When building the optical path, each component needs to maintain a certain distance, which will cause the total volume of the final optical system to always be large, and it is impossible to achieve a compact holographic display system. At present, 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. The design based on flat-panel holography can achieve the advantages of lightness and practicality, and has greater application potential. Summary of the invention

[0005] In view of this, an object of the present invention is to provide a large-field-of-view holographic flat-panel display device, which realizes a 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 comprises an LD light source, a corner prism, a flat-panel waveguide device, a spatial light modulator SLM and a functional screen;

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

[0009] The light waves emitted by the LD light source are converted in direction by the corner prism and incident on the optical waveguide, and then diffracted by the incident holographic grating and propagated by total internal reflection inside the optical waveguide; when the light waves reach the exit holographic grating, the light waves are diffracted again so that the total reflection condition is broken, and the light waves are emitted in parallel from the optical waveguide, and are modulated by the spatial light modulator SLM to form an output light spot, which is input to 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 transmission size L of the functional screen is 1 Larger than the SLM’s light clearance L 0 , where L 0 =NΔp, N is the number of SLM pixels, Δp is the SLM pixel interval.

[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 by 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 generated hologram.

[0019] Further, the angular spectrum diffraction algorithm comprises the following steps:

[0020] Calculate the light field distribution of 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, let the light field distribution on the SLM plane be U 0 (x 0 ), the distance between the SLM plane and the functional screen plane is z 1 , then the light field distribution U in front of the functional screen 1 (x 1 )for:

[0023] U 1 (x 1 )=F -1 {F[U 0 (x 0 )]×H jp (f x0 ,z 1 )}

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

[0025] H jp (f x0 ,z 1 )=exp[jkz 1 √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] Light field distribution U on the imaging plane 2 (x 2 ) 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 plane light field of the functional screen is the same as that of the SLM. When the total transmission distance z = z 1 +z 2 When determining, the number M, focal length f and period p of the unit lenses in the fixed functional screen are used to control the distance z 2 The imaging plane light field size L of any size is obtained, and the viewing angle θ of the imaging plane light field is expressed as follows:

[0033] θ=arctan(L / z)

[0034] Choose a reasonable z according to your needs 2 , when z 2 When >2f, the reconstructed image can be enlarged to achieve a holographic display with a large field of view.

[0035] Furthermore, 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, and the loss function used in training is the mean square error (MSE) between the two images;

[0036] Once the network is trained, make predictions for images that the network has never seen before;

[0037] The network output predicts 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.

[0038] The beneficial effects of the present invention are:

[0039] 1. Compared with the traditional holographic display system, the holographic flat-panel waveguide display system can be made very light and thin. It simplifies the entire optical path system and does not require a very complex optical path carrier. It can be directly spliced, which greatly reduces the volume of the holographic display system and provides technical support for the small volume and lightweight of flat-panel holographic displays at a lower cost.

[0040] 2. Compared with traditional holographic display and other large-field-of-view holographic display systems, it is only necessary to introduce a functional screen and adjust the position of the plane where the functional screen is located and the imaging plane to achieve a large-field-of-view holographic display.

[0041] 3. In the design method of hologram, an SLM holographic imaging data set containing the functional screen model is constructed through the angular spectrum diffraction algorithm, and a convolutional neural network is constructed and trained and predicted. This avoids the problem of difficult trade-off between holographic image quality and calculation speed in traditional design algorithms, realizes the design of pure phase holograms within tens of milliseconds and improves visual quality, and also reflects the excellent performance of neural networks in quickly solving complex problems.

[0042] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

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

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

[0046] Figure 3 Schematic diagram of designing pure phase hologram using neural network;

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

[0048] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0049] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may 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 the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position 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 small. At the same time, the traditional holographic display optical path construction requires a relatively large space, resulting in a large volume and complex structure of the entire system. The large-field 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 a holographic flat waveguide display system, and its principle is as follows Figure 2 As shown. Specifically, the planar waveguide includes an incident holographic grating, an exit holographic grating and a planar structure optical waveguide, and the incident holographic grating and the transmission type spatial light modulator SLM are respectively attached to the horizontal surface of one side of the planar structure optical waveguide, and the two are separated by a distance, and the exit holographic grating is attached to the horizontal surface of the other side, and is aligned with the transmission type spatial light modulator SLM in parallel; the light wave emitted by the LD light source directly enters the planar structure optical waveguide through the corner prism to reach the incident holographic grating, and the light wave is diffracted by the incident holographic grating, and is totally internally reflected inside the optical waveguide and propagates laterally along the optical waveguide plane; when the light wave reaches the exit holographic grating, the light wave is diffracted again, so that the total reflection condition is broken, and the light wave is emitted in parallel from the optical waveguide, and is modulated by the transmission type spatial light modulator SLM to form an output light spot to be exported from the planar 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 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 elements, which are placed in parallel with the SLM. The light wave emitted from the flat 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 enlarged 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] Embodiment 1:

[0054] According to the angular spectrum diffraction theory, in the traditional holographic display system, the size L of the imaging plane light field is equal to the size L of the SLM. 0 The same is independent of the distance z between the SLM plane and the imaging plane. That is, it satisfies:

[0055] L=L 0 =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 micro lens array MLA is used as an example of a functional screen. Assume that the light field distribution of the SLM plane is U 0 (x 0 ), the distance between the SLM plane and the microlens array plane is z 1 , then the light field distribution U in front of the microlens array is 1 (x 1 ) is obtained from formula (2):

[0058] U 1 (x 1 )=F -1 {F[U 0 (x 0 )]×H jp (f x0 , z 1 )} (2)

[0059] Among them, F and F -1 They 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] Light field distribution U on the imaging plane 2 (x 2 ) is obtained from formula (3):

[0063]

[0064] The distance between the microlens array plane and the imaging plane is z 2 , represents the phase shift factor of the microlens array, and its expression is 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 microlens array plane light field is the same as that of the SLM, and the size of the z 1 When the total transmission distance z (i.e. the distance between the SLM plane and the observation plane, and z 1 +z 2 = z) is determined, the distance z can be controlled by fixing the number M, focal length f and period p of the microlens array. 2 Obtain an imaging plane light field size L of any size. The viewing angle θ of the imaging plane light field is expressed as follows:

[0068] θ=arctan(L / z) (6)

[0069] Here, θ is the angle.

[0070] When z 2 When z > 2f, the reconstructed image can be enlarged to achieve a holographic display with a large field of view; however, when z 2 When ≤2f, the size of the imaging plane light field L≤L 0 , the effect of expanding the field of view is lost, so a reasonable z should be selected according to the needs 2 .

[0071] The design and reconstruction process of pure phase holograms based on the system proposed by the present invention combined with neural networks to achieve large-field holographic display is as follows: Figure 3As shown. In the design process of the hologram, the SLM holographic imaging data set containing the microlens array model is constructed by the above-mentioned angular spectrum diffraction algorithm with a microlens 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 the two images.

[0072] When the network training is completed, the neural network is predicted for images that it has never seen before. The neural network outputs the predicted complex amplitude hologram and encodes it through the dual phase method (DPM) to obtain a pure phase hologram, which is then holographically reconstructed through the angular spectrum diffraction algorithm with the microlens array to obtain a reconstructed image, and the image size and calculated viewing angle are obtained.

[0073] Embodiment 2:

[0074] In the actual experiment, the SLM used is a transmissive pure phase SLM with a pixel size of 8 μm and a hologram pixel number of 1920×1080. Therefore, the size of the hologram is 15.36 mm×8.64 mm. The laser wavelength is 650 nm. If the structure is based on a single SLM and the propagation is 275 mm, according to formula (1), the size of the imaging plane is only 15.36 mm×8.64 mm; if only the horizontal viewing angle is considered, according to formula (6), the viewing angle of the imaging plane is only 3.2°. According to the present invention, Figure 1 The system device structure is as follows: the parameters of the SLM are the same as those described above; the functional screen is the same as in Example 1, and 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 4As 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 enlarge the holographic reconstructed image and realize a large-field holographic display. At the same time, it was found through testing that for a 1920×1080 image, the hologram design method proposed in the present invention can realize the rapid design of a pure phase hologram within tens of milliseconds and the quality of the reconstructed image is good, avoiding the problem of 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 solution of the present invention rather than to limit it. 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 solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A large-field 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 planar waveguide device comprises an incident holographic grating, an exit holographic grating and an optical waveguide with a planar structure; the incident holographic grating and the spatial light modulator SLM are respectively attached to two ends of a horizontal surface of one side of the optical waveguide, and the exit holographic grating is attached to an end of the horizontal surface of the other side opposite to the SLM; The light waves emitted by the LD light source are converted in direction by the corner prism and incident on the optical waveguide, and then diffracted by the incident holographic grating and propagated by total internal reflection inside the optical waveguide; when the light waves reach the exit holographic grating, the light waves are diffracted again so that the total reflection condition is broken, and the light waves are emitted in parallel from the optical waveguide, and are modulated by the spatial light modulator SLM to form an output light spot, which is input to 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 to achieve a large-field holographic display.

2. The large-field-of-view holographic flat-panel display device according to claim 1, characterized in that: 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, characterized in that: The functional screen is a microlens array or other micro-optical elements.

4. The large-field-of-view holographic flat-panel display device according to claim 1, characterized in that: The light-through size L1 of the functional screen is larger than the light-through size L0 of the SLM, wherein L0=NΔp, N is the number of SLM pixels, and Δp is the SLM pixel interval.

5. The large-field-of-view holographic flat-panel display device according to claim 1, characterized in that: 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 by 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.

6. The large-field-of-view holographic flat-panel display device according to claim 5, characterized in that: The angular spectrum diffraction algorithm comprises the following steps: Calculate the light field distribution of the plane in front of the functional screen according to the light field distribution of the hologram; The light field distribution of the imaging plane is calculated according to the light field distribution of the plane behind the functional screen.

7. The large-field-of-view holographic flat-panel display device according to claim 6, characterized in that: Assume 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, then the light field distribution U1(x1) in front of the functional screen is: U1(x1)=F -1 {F[U0(x0)]×H jp (in x0 ,z1)} Among them, F and F -1 They represent Fourier transform and inverse Fourier transform respectively; H jp is the angular spectrum transfer function, satisfying: Where λ is the wavelength, k is the wave number, and k = 2π / λ, f x0 is the spatial frequency; The light field distribution U2(x2) on the imaging plane is calculated as follows: 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: 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; The size of the plane light field of the functional screen is the same as that 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 lenses in the functional screen are fixed, so as to control the distance z2 to obtain an imaging plane light field size L of any size. The viewing angle θ of the imaging plane light field is expressed as follows: θ=arctan(L / z) Select a reasonable z2 according to needs. When z2>2f, the reconstructed image can be expanded to achieve a large field of view holographic display.

8. The large-field-of-view holographic flat-panel display device according to claim 5, characterized in that: 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 for images that the network has never seen before; The network output predicts a complex amplitude hologram, which is encoded through the dual-phase method DPM to obtain a pure phase hologram. The pure phase hologram is then holographically reconstructed through the angular spectrum diffraction algorithm of the functional screen to obtain the reconstructed image, and the image size and calculated viewing angle are obtained.

Images