A holographic display system with large eyebox

Abstract

The application provides a holographic display system with a large eyebox, which comprises a spatial light modulator, a projection optical module, a beam splitter and a pupil expansion module; a computer-generated computer hologram is uploaded to the spatial light modulator for modulation processing, then the modulated holographic wavefront is filtered by using the projection optical module, the single-order holographic wavefront is passed through the beam splitter, the incident narrow-view holographic wavefront is modulated by the beam splitter, and the continuous wide-view holographic wavefront of multiple orders is expanded, and the large-size continuous holographic image can be observed in the large eyebox behind the pupil expansion module.

Description

Technical Field

[0001] This invention belongs to the field of holographic display technology, specifically relating to a holographic display system with a large eye-tracking range. Background Technology

[0002] With the optimization of modern devices and the development of computer technology, the display field has made great strides, and people have put forward higher requirements for display technology. Among them, holographic display technology, because it directly modulates the wavefront information of light, can provide all the depth cues of a three-dimensional scene, and there is no convergence-modulation conflict, it is considered the most ideal true three-dimensional reconstruction technology. Therefore, holographic retinal display technology has received more and more attention in recent years.

[0003] Holographic retinal display technology, also known as retinal projection display (RPD), refers to projecting a holographically modulated light beam onto the retina through the pupil. By creating a focal point on the observer's pupil, a wide-range, uniform three-dimensional image is generated on the retina. However, due to current technological limitations, the pixel size of current liquid crystal spatial light modulators is often larger than 3μm, resulting in a small diffraction angle for the modulated light wave per pixel. When collimated light is irradiated and modulated on the surface of the spatial light modulator, the beam can be considered as divergent light with a very small divergence angle. After convergence at the focal plane through the eyepiece, the eye movement range (or eyebox) and the field of view (FOV) are mutually constrained; their product equals the spatial bandwidth product of the spatial light modulator. While maintaining the FOV, the human eye can only view the image within a very small area, limiting the development of holographic display technology. Therefore, how to achieve a holographic display with a wide viewing range has become a hot topic of research.

[0004] Augmented Reality (AR) display technology overlays computer-generated virtual images onto real-world scenes, and is hailed as a revolutionary display technology of the 21st century. Holographic waveguides, as the most promising AR display solution, possess advantages such as thinness, expandable exit pupil, and high ambient light transmittance. However, the light source used in commercially available waveguides can be considered a Lambert light source, with a large divergence angle, significantly different from the small diffraction angle light reconstructed by spatial light modulators. Therefore, traditional waveguides are not suitable for holographic light sources. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems that, while ensuring the field of view, the human eye can only view images within a very small range and that traditional waveguides are not suitable for holographic reconstruction beams, and to provide a holographic display system with a large eye movement range.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a holographic display system with a large eye-tracking range, comprising:

[0007] Spatial light modulators are used to modulate incident coherent light into a narrow-view holographic wavefront;

[0008] The projection optics module is used to filter the narrow-view holographic wavefront, eliminate the zeroth and higher diffraction orders, and then amplify the filtered narrow-view holographic wavefront.

[0009] A beam splitter is used to expand the magnified narrow-view holographic wavefront into a multi-level continuous wide-view holographic wavefront.

[0010] And a pupil expansion module, used to further expand the multi-level continuous wide-view holographic wavefront into a large-range, large-size, continuously viewable holographic image.

[0011] Furthermore, the pupil expansion module includes an optical lens group and an optical waveguide assembly. The optical lens group converts the multi-level continuous wide-view holographic wavefront into multiple equally spaced focused beams, and its focusing plane is located at the rear focal plane of the optical lens group. The focused beams are incident on the coupling region of the optical waveguide assembly and undergo total internal reflection to the coupling region of the optical waveguide assembly. The focused beams replicate and couple out a large-range, large-size, continuously viewable holographic image in the coupling region. The area of ​​the coupling region is larger than the area of ​​the coupling region.

[0012] Furthermore, the projection optical module includes a first lens, an aperture stop, and a second lens;

[0013] The holographic wavefront is filtered sequentially by a first lens and an aperture, and the filtered narrow-angle holographic wavefront is magnified by a second lens.

[0014] Furthermore, the effective aperture area of ​​the beam splitter is greater than the reconstructed beam area of ​​the beam splitter.

[0015] Furthermore, in the multi-level continuous wide-view holographic wavefronts, the angle between the outermost wide-view holographic wavefronts is θ, and the angle between each adjacent wide-view holographic wavefront in the multi-level continuous wide-view holographic wavefronts is θ. f And θ=(N-1)θ f , where N is the number of beams split by the beam splitter in the emission direction.

[0016] Furthermore, the point spacing between the focused beams at the back focal plane of the optical lens group is d = f·tanθ. f Where f is the equivalent focal length of the optical lens group, and θ f It is the angle between each adjacent wide-angle holographic wavefront in a multi-level continuous wide-angle holographic wavefront.

[0017] Furthermore, the distance between the reconstructed image after passing through the projection optical module and the principal plane of the optical lens group is u, and the distance between the virtual image formed after passing through the optical lens group and the principal plane of the optical lens group is v. u and v satisfy the following relationship:

[0018]

[0019] Where f is the equivalent focal length of the optical lens group, and satisfies 0 <u<f。

[0020] Furthermore, it also includes a head-up display device (5) for reflecting a holographic image that is expanded to a large eye-tracking range, large size, and can be viewed continuously onto the viewing position.

[0021] Beneficial effects: The beam splitter expands the beam diffraction angle, transforming the holographic reconstructed beam into a Lambertian-like light source; and the image source with depth information is coupled into the waveguide through the pupil expansion module. The waveguide breaks the limitation of the spatial bandwidth product and merges with the real environment, thereby obtaining a large eye movement range, a large size, and a continuously viewable holographic image, realizing the functions of expanding the eye box and augmenting reality. Attached Figure Description

[0022] Figure 1 Schematic diagrams of the structure of holographic retina display under different field of view;

[0023] Figure 2 This is a schematic diagram of the structure of the present invention excluding the head-up display device;

[0024] Figure 3 This is a schematic diagram of the projection optical module of the present invention;

[0025] Figure 4 The following are schematic diagrams of three beam splitter structures in the embodiments of the present invention: a schematic diagram of a binary phase beam splitter (a), a schematic diagram of a multi-step phase beam splitter (b), and a schematic diagram of a continuous phase beam splitter (c).

[0026] Figure 5 The following are schematic diagrams of the optical lens group structure and the topography of the beam splitter on the back focal plane of the optical lens group in the embodiments of the present invention: (a) schematic diagram of the optical lens group structure, (b) schematic diagram of the topography of the one-dimensional beam splitter on the back focal plane of the optical lens group, and (c) schematic diagram of the topography of the two-dimensional beam splitter on the back focal plane of the optical lens group.

[0027] Figure 6 These are schematic diagrams of three structures of the optical waveguide component in the embodiments of the present invention, namely, the first example diagram (a), the second example diagram (b), and the third example diagram (c) of the optical waveguide component;

[0028] Figure 7 The following are schematic diagrams of two structures of the present invention in the embodiments, namely, schematic diagram of the first structure of the present invention (a) and schematic diagram of the second structure of the present invention (b).

[0029] In the diagram: 1. Spatial light modulator, 2. Projection optical module, 2-1. First lens, 2-2. Aperture, 2-3. Second lens, 3. Beam splitter, 4. Pupil expansion module, 4-1. Optical lens group, 4-2. Optical waveguide assembly, 5. Head-up display device, 5-1. Plane mirror, 5-2. Windshield, 6. Ingress coupling component, 7. Optical waveguide sheet, 8. Exgress coupling component. Detailed Implementation

[0030] The invention will now be further explained with reference to the accompanying drawings.

[0031] like Figure 1 As shown, because the pixel size of existing spatial light modulators is much larger than the wavelength, the diffraction angle and spatial bandwidth product are relatively small, resulting in significant limitations for holographic retinal displays. They cannot simultaneously guarantee a sufficient field of view and eye box. When the diffraction angle α of spatial light modulator 1 is small, the field of view... The constraints between the holographic display and the eye box. Furthermore, the relatively small diffraction angle prevents the direct use of optical waveguide devices in holographic displays.

[0032] like Figure 2 As shown, in order to solve the above-mentioned problems, the present invention provides a holographic display system with a large eye-tracking range, comprising:

[0033] Spatial light modulator 1 is used to modulate incident coherent light into a holographic wavefront.

[0034] Projection optics module 2 is used to filter the holographic wavefront, eliminate the zeroth and higher diffraction orders, and then magnify the filtered holographic wavefront into a narrow-view holographic wavefront.

[0035] Beam splitter 3 is used to expand a narrow-view holographic wavefront into a multi-level continuous wide-view holographic wavefront.

[0036] And pupil expansion module 4, used to further expand the multi-level continuous wide-view holographic wavefront into a large-range, large-size, continuously viewable holographic image.

[0037] The spatial light modulator 1 provides the required holographic reconstruction beam for the system. The spatial light modulator 1 can be a phase-type spatial light modulator, an amplitude-type spatial light modulator, or a complex amplitude spatial light modulator.

[0038] Specifically, spatial light modulator 1 is a phase-type spatial light modulator, which uses LCOS-SLM to perform phase modulation on the phase-type computational hologram.

[0039] Spatial light modulator 1 is an amplitude-type spatial light modulator that uses a transmissive SLM to modulate the amplitude of the amplitude-type computational hologram.

[0040] Spatial light modulator 1 is a complex amplitude spatial light modulator that performs complex amplitude modulation on a computational hologram containing complex amplitude information.

[0041] like Figure 3 As shown, the projection optical module 2 includes a filtering system composed of a first lens 2-1 and an aperture 2-2, and an image magnification system composed of a second lens 2-3. The holographic wavefront is filtered by the first lens 2-1 and the aperture 2-2 in sequence, and the filtered holographic wavefront is magnified into a narrow-angle holographic wavefront by the second lens 2-3.

[0042] The filtering system in projection optics module 2 filters frequency domain information. Let the input function be U, the filtering function be R, and the output function be FU, then FU = FFT{U}*R. The filtering system is used to filter out high-frequency components in the image, isolate stray light, and improve image quality.

[0043] The image magnification system of projection optics module 2 magnifies the diffractive holographic image. Let the focal length of the first lens be f1, the focal length of the second lens be f2, and the magnification factor B = f2 / f1. The image magnification system is used to project the amplified wavefront containing holographic image information onto the surface of the beam splitter.

[0044] Beam splitter 3 can be a binary phase-type diffractive optical element, a multi-step phase-type diffractive optical element, or a continuous phase-type diffractive optical element.

[0045] like Figure 4 As shown in (a), beam splitter 3 is a binary phase diffraction optical element.

[0046] like Figure 4 As shown in (b), beam splitter 3 is a multi-step phase diffraction optical element.

[0047] like Figure 4 As shown in (c), beam splitter 3 is a continuous phase diffraction optical element.

[0048] like Figure 1 The three types of beam splitters 3 shown can split the incident beam in one dimension or two dimensions. In this invention, among the multi-order continuous wide-angle holographic wavefronts obtained by the beam splitter 3, the angle between the outermost wide-angle holographic wavefronts is θ, and the angle θ between each adjacent wide-angle holographic wavefront in the multi-order continuous wide-angle holographic wavefronts is... f And θ=(N-1)θ f , where N is the number of beams split by the beam splitter (3) in the emission direction.

[0049] In this embodiment, the pupil dilation module 4 includes an optical lens group and an optical waveguide device 4-2.

[0050] The optical lens group 4-1 can be a single convex lens, a lens group with a fixed equivalent focal length, or a lens group with an adjustable equivalent focal length. For the convenience of understanding, in this embodiment, a single convex lens is used as the optical lens group 4-1. The equivalent focal length of the optical lens group 4-1 is the focal length f of the convex lens, the equivalent principal plane of the optical lens group 4-1 is the principal plane of the convex lens; the equivalent focal plane of the optical lens group 4-1 is the focal plane of the convex lens.

[0051] The relationship between the optical lens group 4-1 and the holographic reconstruction image is determined by the lens imaging formula:

[0052]

[0053] Where u is the distance between the plane where the holographic reconstruction image is located and the principal plane of the optical lens group 4-1, and the position of the virtual image plane formed after passing through the optical lens group 4-1 and the focal plane of the optical lens group 4-1 is v, satisfying 0 < u < f. At this time, v < -f < 0, and the negative sign indicates that the virtual image and the holographic reconstruction image are on the same side with respect to the optical lens group 4-1.

[0054] As Figure 5 shown in (a) of, the optical lens group 4-1 converges the multi-order diffracted light beams expanded by the beam splitter 3 to the focal plane of the optical lens group. The point spacing between the focused light beams at the rear focal plane of the optical lens group 4-1 has the following relationship:

[0055] d = f·tanθ f

[0056] Where d is the point spacing between the focused light beams, and θ f is the included angle between adjacent orders in the diffraction order. Figure 5 (b) of shows the beam morphology of the one-dimensional beam splitter at the focal plane of the optical lens group; Figure 5 (c) of shows the beam morphology of the two-dimensional beam splitter at the focal plane of the optical lens group.

[0057] Furthermore, it is necessary to elaborate on the distance D between the beam splitter 3 and the optical lens group. This distance is not limited in this invention. It should be noted that if the beam splitter 3 uses the standard Fourier transform in the process of designing the phase, the default distance D should be f. The change of this distance D introduces an additional phase to the holographic wavefront. The modulation of this phase can be represented by where the wave number x, y are the abscissa and ordinate of the holographic wavefront respectively. This additional phase does not affect the beam morphology of the beam splitter at the focal plane of the optical lens group. When D ≠ f, t ≠ 0. At this time, the additional phase will modulate the phase of the holographic wavefront and affect the quality of the finally observed image.

[0058] like Figure 6 As shown in (a), the optical waveguide device 4-2 includes an optical waveguide sheet 7 (i.e., waveguide medium), an input coupling component 6 located in the coupling region, and an output coupling component 8 located in the output region. Optionally, the optical waveguide device 4-2 also includes a steering grating (not shown). Specifically, the multi-level subwide-view diffracted wavefront, after being expanded by the beam splitter, is converged and focused by an optical mirror assembly. At this time, the coupling region of the optical waveguide device is aligned with the focal plane, and the focused light enters the input coupling component 6 in the coupling region. The input coupling component 6 couples the light that meets the total internal reflection (TIR) ​​condition of the optical waveguide into the optical waveguide sheet. When the aforementioned light propagates within the optical waveguide sheet to the steering grating, it undergoes multiple diffractions and reflections in the lateral direction (i.e., lateral pupil expansion) before reaching the input coupling component 6 located in the output region. The input coupling component 6 completes longitudinal pupil expansion while simultaneously diffracting and coupling the light out of the waveguide, resulting in a two-dimensionally expanded beam. At this time, a large-range, large-size, continuously viewable holographic display can be realized behind the output region of the optical waveguide.

[0059] The input coupling component 6 and the output coupling component 8 are generally made of reflective gratings. Examples are given below:

[0060] For example, such as Figure 6 As shown in (b), the input coupling component 6 and the output coupling component 8 are located on both sides of the optical waveguide, and the incident light and the output light are in the same direction.

[0061] For example, such as Figure 6 As shown in (c), the input coupling component 6 and the output coupling component 8 are located on the same side of the optical waveguide, and the incident light and the output light are in opposite directions.

[0062] Furthermore, the aforementioned input coupling component 6, steering grating, and output coupling component 8 can be any one of a PB liquid crystal grating, a surface-relief grating (SRG), or a volume holographic grating (VHG) (also known as a holographic polymer volume grating).

[0063] It should be noted that the aforementioned Figure 6 of (a), Figure 6 (b) Figure 6 The examples of optical waveguide devices listed in (c) are all planar optical waveguides. However, in practical applications, the optical waveguide device in this application can also be a curved optical waveguide. In this embodiment and subsequent embodiments, only a planar optical waveguide device is used as an example for description.

[0064] Optionally, a head-up display device 5 is added after the optical waveguide device 4-2, including at least a windshield 5-2. The holographic display system and head-up display device, consisting of a spatial light modulator 1, a projection optical module 2, a beam splitter 3, and a pupil expansion module 4, are installed on vehicles, airplanes, and other means of transportation. In addition, they can also be applied in central control rooms, architectural landscapes, advertising, and other scenarios, without limitation here.

[0065] In the first structure of the present invention, as Figure 7 As shown in (a), the head-up display device 5 contains only one windshield 5-2. The input and output light rays of the optical waveguide device 4-2 in the holographic system are on opposite sides, and the output light rays of the coupled portion of the optical waveguide device 4-2 are reflected to the new observation position via the windshield.

[0066] In the second structure of the present invention, as Figure 7 As shown in (b), the head-up display device 5 includes a plane mirror 5-1 and a windshield 6-2. The input and output light rays of the optical waveguide device 4-2 in the holographic system are on the same side. The output light rays from the coupling portion of the optical waveguide device 4-2 illuminate the plane mirror 5-1, are reflected by the plane mirror onto the windshield 5-2, and are then reflected by the windshield 5-2 to the new observation position. Optionally, the plane mirror in this example can be replaced with a freeform mirror.

[0067] It should be understood that the windshield glass in the aforementioned example is only one example of a light reflecting device. In addition to glass, the light reflecting device can also be transparent ceramic, resin or other optical materials, which are not limited here.

[0068] The implementation process of this invention is as follows:

[0069] The computer-generated computational hologram is uploaded to the spatial light modulator 1 for modulation processing. Then, the projection optics module 2 is used to filter the modulated holographic wavefront. The single-order holographic wavefront is passed through the beam splitter 3, which modulates the incident narrow-angle holographic wavefront and expands it into a multi-order continuous wide-angle holographic wavefront. It is then further expanded by the pupil expansion module 4, so that the human eye can see a large-size, continuous holographic image in a larger range of the exit pupil area of ​​the pupil expansion module 4.

[0070] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A holographic display system with a large eye-tracking range, characterized in that, include: Spatial light modulator (1) is used to modulate incident coherent light into a narrow-view holographic wavefront; The projection optics module (2) is used to filter the narrow-angle holographic wavefront, eliminate the zeroth and higher diffraction orders, and then amplify the filtered narrow-angle holographic wavefront. Beam splitter (3) is used to expand the magnified narrow-view holographic wavefront into a multi-level continuous wide-view holographic wavefront. And a pupil expansion module (4) is used to further expand the multi-level continuous wide-view holographic wavefront into a large-range, large-size, continuously viewable holographic image; the pupil expansion module (4) includes an optical lens group (4-1) and an optical waveguide assembly (4-2). The optical lens group (4-1) replaces the multi-level continuous wide-view holographic wavefront with multiple equally spaced focused beams, and its focusing plane is located at the back focal plane of the optical lens group (4-1). The focused beam is incident on the coupling area of ​​the optical waveguide assembly (4-2) and undergoes total internal reflection to the coupling area of ​​the optical waveguide assembly (4-2). The focused beam replicates and couples out a large-range, large-size, continuously viewable holographic image in the coupling area. The area of ​​the coupling area is larger than the area of ​​the coupling area. In the multi-level continuous wide-angle holographic wavefronts, the angle between the outermost wide-angle holographic wavefronts is... The included angle between each adjacent wide-angle holographic wavefront in the multi-level continuous wide-angle holographic wavefront ,and , where N is the number of beams split by the beam splitter (3) in the emission direction; The point spacing between the focused beams at the back focal plane of the optical lens group (4-1) is ,in The equivalent focal length of the optical lens group (4-1) is... It is the angle between each adjacent wide-angle holographic wavefront in a multi-level continuous wide-angle holographic wavefront.

2. The holographic display system with a large eye-tracking range according to claim 1, characterized in that, The projection optical module (2) includes a first lens (2-1), an aperture (2-2), and a second lens (2-3). The holographic wavefront is filtered sequentially by the first lens (2-1) and the aperture (2-2), and the filtered narrow-angle holographic wavefront is magnified by the second lens (2-3).

3. The holographic display system with a large eye-tracking range according to claim 1, characterized in that, The effective aperture area of ​​the beam splitter (3) is greater than the reconstructed beam area of ​​the beam splitter (3).

4. The holographic display system with a large eye-tracking range according to claim 2, characterized in that, The distance between the reconstructed image location after passing through the projection optical module (2) and the location of the principal plane of the optical lens group (4-1) is... The distance between the location of the virtual image formed after passing through the optical lens group (4-1) and the location of the principal plane of the optical lens group (4-1) is... , and The following relationship must be satisfied: in It is the equivalent focal length of the optical lens group, and satisfies .

5. The holographic display system with a large eye-tracking range according to claim 1, characterized in that, It also includes a head-up display (5) for reflecting a large-size, continuously viewable holographic image, which is extended to a large eye-tracking range, onto the viewing position.

Images