A large-scale holographic display system that can be viewed freely

Abstract

The present invention is a freely viewable large-scale holographic display system, which includes a hologram control unit, an optical projection system and a diffraction screen; a computer generates a computational hologram and uploads it to the hologram control unit for modulation. The holographic complex amplitude modulated by the hologram control unit is projected onto the surface of the large-scale diffraction screen through the optical projection system, and each spatial position on the diffraction screen modulates the incident holographic complex amplitude wavefront, and the wavefront at each spatial position is diffracted into discrete diffraction lights of multiple directions, thereby expanding the field of view. At the viewing position behind the diffraction screen, these different orders of emitted light are coherently superimposed at any position, and the human eye is similar to a small optical filtering system, filtering out the diffraction orders whose diffraction angles deviate from the pupil position, receiving different orders of diffraction lights at different spatial positions of the large-scale diffraction screen, and forming coherent images on the retina, thereby realizing a large-scale holographic display with a free range.

Description

Technical Field

[0001] The present invention relates to the technical field of holographic display, and in particular to a freely viewable large-scale holographic display system. Background Art

[0002] With the optimization of modern devices and the development of computer technology, the display field has made great progress, and people have put forward higher requirements for display technology. Among them, holographic display technology is a very important display method and is considered to be one of the most ideal three-dimensional display technologies. It can reconstruct the complex amplitude discrete wavefront of virtual objects and provide complete parallax and depth information for the human eye. It has received more and more attention in recent years.

[0003] However, due to existing process limitations, the pixel size of current liquid crystal spatial light modulators is often larger than 3μm, and the diffraction angle of each pixel modulated light wave is small. When collimated light irradiates the surface of the spatial light modulator for modulation, the human eye can only observe the discrete diffraction light waves of a small part of the pixels in the range far away from the modulation surface, which are presented to the human eye in the form of light spots, and the complete information of the image cannot be observed, such as Figure 1 As shown in (a), the human eye directly observes the hologram control unit (1). To solve this problem, researchers placed a lens behind the spatial light modulator to focus the diffracted light waves into the human eye to complete the holographic display, as shown in Figure 1. Figure 1 As shown in (b), the lens (7) converges the modulated light waves generated by the hologram control unit (1) to complete the imaging display. However, this method has a fixed imaging range and can only be observed at the focal plane of the lens. It is mostly suitable for near-eye display and cannot form a large range of free viewing, which limits the development of holographic display technology. Therefore, how to achieve a large-scale holographic display that can be freely viewed has become a hot topic for researchers.

[0004] The current large-size holographic display systems include: using multiple spatial light modulators to segment the reconstructed image, and finally realizing large-size holographic display by image stitching. However, this system uses multiple spatial light modulators to complete holographic reconstruction, and the structure is relatively complex; using eye tracking technology to complete large-size holographic display, but the free viewing effect of this system is mainly restricted by eye tracking technology. Summary of the invention

[0005] Technical problem: The present invention aims to propose a large-scale holographic display system that can be viewed freely. In this system, an optical projection system is used to project the modulated holographic complex amplitude information onto a large-scale diffraction screen, and the incident light wavefront at each spatial position is discretized according to the structural characteristics of the diffraction screen to generate outgoing light of multiple diffraction orders in multiple directions, so that the human eye can receive diffracted light of different orders at different spatial positions behind the diffraction screen and form coherent images on the retina. A large-scale holographic display with a free range is realized, which makes up for the shortcomings of the traditional holographic display system in imaging size and imaging range due to the limitations of the modulation device.

[0006] Technical solution: The present invention proposes a freely viewable large-scale holographic display system, in which the relay optical path only includes an optical projection system and has a relatively simple structure. The complex amplitude holographic image is modulated by a large-scale diffraction screen, and the discrete diffraction characteristics of the diffraction screen are used to discretize the incident wavefront on the surface into diffraction orders in multiple directions. Within the observation range behind the diffraction screen, the diffracted light of each order is coherently imaged on the retina of the human eye, which is not restricted by the algorithm and can achieve free viewing in a large field of view through the principle of interference diffraction, which is easy to implement.

[0007] The freely viewable large-scale holographic display system of the present invention comprises: a hologram control unit, an optical projection system and a diffraction screen; wherein, a holographic complex amplitude is obtained by modulating a computational hologram generated by a computer and uploaded to the hologram control unit, and then the holographic complex amplitude modulated by the hologram control unit is projected onto the surface of the large-scale diffraction screen through the optical projection system, and each spatial position on the diffraction screen modulates the incident holographic complex amplitude wavefront, and the wavefront at each spatial position is diffracted into discrete diffraction lights of multiple directions and respectively emitted in different directions; at the viewing position behind the diffraction screen, diffraction lights of different orders at different spatial positions on the diffraction screen converge here, and by modulating the complex amplitudes at different positions on the diffraction screen, coherent superposition of diffraction lights of different orders at the viewing position is achieved, and a holographic image is generated on the retina of the human eye.

[0008] The hologram control unit is a holographic image source required by the system, and is a phase-type spatial light modulator, an amplitude-type spatial light modulator or a complex amplitude spatial light modulator.

[0009] The optical projection system comprises a filtering system consisting of a first lens and an aperture, and an image magnifying system consisting of a second lens located behind the filtering system.

[0010] The diffraction screen adopts an imaging component with a grating structure, including a transmission type and a reflection type.

[0011] When the diffraction screen is a transmission light screen, the diffraction unit is a binary grating, a multi-level relief grating or a volume grating of a two-dimensional periodic grating; the diffraction angle of the imaging receiving point is expressed by It is represented by, where m represents the diffraction order, λ represents the wavelength of incident light, d represents the grating period, θ′ represents the incident angle of light wave, n′ represents the refractive index of the space where the incident light is located, and n represents the refractive index of the diffraction screen; using the above formula to examine the spectrum on the same side of the grating normal as the incident light, the sign is positive, that is, m<0, and the spectrum on the opposite side of the grating normal as the incident light takes a negative sign, that is, m>0.

[0012] When the diffraction screen is a reflective light screen, the diffraction unit is a two-dimensional periodic grating, such as a binary grating, a multi-level relief grating, or a volume grating; the diffraction angle of the imaging receiving point is expressed as It is represented by, where m represents the diffraction order, λ represents the wavelength of incident light, d represents the grating period, θ′ represents the incident angle of light wave, n′ represents the refractive index of the space where the incident light is located, and n represents the refractive index of the diffraction screen; using the above formula to examine the spectrum on the opposite side of the grating normal to the incident light, it takes a positive sign, that is, m>0, and the spectrum on the same side of the grating normal to the incident light takes a negative sign, that is, m<0.

[0013] The diffraction screen is an imaging component of a waveguide structure, comprising an in-coupling element, a steering grating and an out-coupling element.

[0014] The diffraction screen is composed of an imaging component of a grating structure and an additional phase.

[0015] The additional phase in the diffraction screen is a lens phase or a tilt phase.

[0016] Each spatial position on the diffraction screen can discretize the wavefront of the incident light wave and generate diffracted light of different orders in multiple directions, thereby expanding the field of view; these diffracted lights of different orders are coherently superimposed and imaged at any viewing position behind the diffraction screen. The human eye is similar to a small optical filtering system, which filters out the diffraction orders whose diffraction angles deviate from the pupil position, and receives diffracted light of different orders at different spatial positions of the large-size diffraction screen, and forms coherent images on the retina.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The present invention proposes a freely viewable large-size holographic display system, which projects the complex amplitude holographic image modulated by the hologram control unit onto a large-size diffraction screen for secondary modulation through an optical projection system, thereby realizing large-size display of the holographic display system.

[0019] 2. The present invention proposes a freely viewable large-scale holographic display system, which utilizes the structural characteristics of the diffraction screen to modulate the incident holographic complex amplitude wavefront at each spatial position on the diffraction screen, and can diffract the wavefront at each spatial position into multiple discrete directional orders. For different spatial positions of the large-scale diffraction screen, the human eye receives diffracted light of different orders and forms coherent images on the retina. The field of view is expanded, and free viewing of the holographic display system is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 (a) is a schematic diagram of SLM diffraction imaging; (b) is a schematic diagram of a holographic display system containing a lens.

[0021] Figure 2 A schematic structural diagram of a freely viewable large-size holographic display system using a transmissive diffraction screen provided by the present invention.

[0022] Figure 3 A schematic structural diagram of a freely viewable large-size holographic display system using a reflective diffraction screen provided by the present invention.

[0023] Figure 4 This is a schematic diagram of the structure of the optical projection system provided by the present invention.

[0024] Figure 5 (a) is a schematic diagram of the free viewing principle of the transmissive rectangular grating diffraction screen provided by the present invention; (b) is a schematic diagram of the free viewing principle of the reflective rectangular grating diffraction screen provided by the present invention

[0025] Figure 6 (a) is a cross-sectional view of grating diffraction screens of different morphologies provided by the present invention; (b) is a schematic diagram of the overall structure of the grating diffraction screen provided by the present invention.

[0026] The figure includes: a hologram control unit 1, an optical projection system 2, a diffraction screen 3, a spatial position 4, diffracted light of different orders 5, a viewing position 6, a first lens 2-1, an aperture 2-2, and a second lens 2-3. DETAILED DESCRIPTION

[0027] The present invention is described in detail below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Based on the embodiments in the present invention, various equivalent transformations of the present invention by ordinary technicians in the field without making creative work all fall within the scope defined in this application.

[0028] The present invention provides a freely viewable large-scale holographic display system, comprising: a hologram control unit 1, an optical projection system 2 and a diffraction screen 3, wherein the optical projection system 2 comprises a first lens 2-1, an aperture 2-2 and a second lens 2-3; a system image source hologram control unit 1 modulates a computer-generated hologram, and the modulated complex amplitude holographic image is projected onto the large-scale diffraction screen 3 through the optical projection system 2, wherein each spatial position 4 on the diffraction screen 3 modulates an incident holographic complex amplitude wavefront, and the wavefront at each spatial position 4 is diffracted into discrete diffraction lights 5 of multiple directions, and respectively emitted in different directions, and at a viewing position 6 behind the diffraction screen, diffraction lights 5 of different orders at different spatial positions 4 on the diffraction screen converge, and by modulating the complex amplitudes at different spatial positions 4 on the diffraction screen, coherent superposition of diffraction lights 5 of different orders at the viewing position 6 is achieved, and a holographic image is generated on the retina of a human eye.

[0029] The hologram control unit 1 is a holographic image source required by the system, and is a phase-type spatial light modulator, an amplitude-type spatial light modulator, or a complex amplitude spatial light modulator.

[0030] Specifically, the hologram control unit uses a phase-type spatial light modulator and uses LCOS-SLM to phase-modulate the phase-type computer-generated hologram.

[0031] The hologram control unit uses an amplitude-type spatial light modulator and a transmissive SLM to perform amplitude modulation on the amplitude-type computer-generated hologram.

[0032] The hologram control unit uses a complex amplitude type spatial light modulator to perform complex amplitude modulation on the computer generated hologram containing complex amplitude information.

[0033] The optical projection system 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 located behind the filtering system.

[0034] The filtering system in the optical projection system filters the frequency domain information. Assuming the input function is U, the filtering function is R, and the output function is FU, then FU = FFT{U}*R. The filtering system is used to filter out the high-frequency components in the image, isolate stray light, and improve image quality.

[0035] The image magnification system in the optical projection system magnifies the diffraction holographic image. Assuming the focal length of the first lens is f1, the focal length of the second lens is f2, and the magnification factor B=f2 / f1. The image magnification system is used to magnify the complex amplitude modulated image and project it onto the surface of a large-size diffraction screen.

[0036] The diffraction screen 3 adopts an imaging component with a grating structure, including a transmission type and a reflection type, which satisfies the grating equation d(nsinθ±n′sinθ′)=mλ, where m represents the diffraction order, λ represents the wavelength of the incident light, d represents the grating period, θ′ represents the incident angle of the light wave, θ represents the diffraction angle, n′ represents the refractive index of the space where the incident light is located, and n represents the refractive index of the diffraction screen. The incident light and the diffracted light are located on the same side of the grating normal and take a positive sign (m<0), and the incident light and the diffracted light are located on the opposite sides of the normal and take a negative sign (m>0). The incident angle and the diffraction angle are defined as the angle between the light and the grating normal. When the direction from the normal to the light is counterclockwise, the angle is positive; when the direction from the normal to the light is clockwise, the angle is negative.

[0037] In order to facilitate understanding during specific implementation, the embodiment uses the above formula to uniformly examine the spectral diffraction angles on the opposite sides of the grating normal line from the incident light, and the case where the positive diffraction order m>0.

[0038] The diffraction screen is a transmission light screen. Considering the positive diffraction order m>0, the incident light and the diffracted light are located on the opposite sides of the grating normal line. The diffraction angle of the imaging receiving point can be It is represented by , where m represents the diffraction order, λ represents the wavelength of the incident light, d represents the grating period, θ′ represents the incident angle of the light wave, n′ represents the refractive index of the space where the incident light is located, and n represents the refractive index of the diffraction screen.

[0039] The diffraction screen is a reflective light screen. Considering the positive diffraction order m>0, the incident light and the diffracted light are located on the opposite sides of the grating normal. The diffraction angle of the imaging receiving point can be It is represented by , where m represents the diffraction order, λ represents the wavelength of the incident light, d represents the grating period, θ′ represents the incident angle of the light wave, n′ represents the refractive index of the space where the incident light is located, and n represents the refractive index of the diffraction screen.

[0040] The diffraction unit of the diffraction screen may be a two-dimensional periodic grating, a binary grating, a multi-level relief grating, a volume grating, etc.

[0041] The diffraction unit of the diffraction screen is a two-dimensional periodic binary rectangular grating. The grating surface is arranged in a groove-type rectangular symmetrical structure and has multiple diffraction orders.

[0042] The diffraction unit of the diffraction screen is a two-dimensional periodic multi-level relief grating arranged in an inclined grating structure, having multiple diffraction orders to increase the diffraction angle.

[0043] The diffraction unit of the diffraction screen is a volume grating. Different from a plane grating, the volume grating is a three-dimensional periodic structure with a certain thickness. The judgment standard is Q≡2πλd0 / nd 2cosθ′>1,d0 / d>10, where λ represents the wavelength of incident light, d0 represents the grating thickness, d represents the grating period, and θ′ represents the plane wave incident angle. When the volume grating medium reaches a certain thickness, the Bragg diffraction effect 2d0 sinθ=mλ will appear.

[0044] The diffraction unit of the diffraction screen is a waveguide structure, including an in-coupling component, a steering grating and an out-coupling component, which folds the optical path, shortens the optical path, and reduces the size of the holographic display system.

[0045] The diffraction unit of the diffraction screen is a waveguide structure, wherein the in-coupling component, the steering grating and the out-coupling component can be a transmission grating or a reflection grating.

[0046] The diffraction unit of the diffraction screen is a waveguide structure, wherein the in-coupling component couples the light wave into the waveguide medium, and total reflection propagation occurs inside the waveguide structure.

[0047] The diffraction unit of the diffraction screen is a waveguide structure, in which the steering grating diffracts part of the incident light wave toward the waveguide out-coupling component, and the remaining part continues to reflect and propagate forward in the medium, repeating the above process, and the light wave diffraction and reflection occur multiple times.

[0048] The diffraction unit of the diffraction screen is a waveguide structure, in which the outcoupling grating is a low diffraction efficiency element, and the light waves that do not meet the total reflection conditions are coupled out from the waveguide medium, while the remaining light waves can be fully totally reflected inside the waveguide medium and then coupled out of the waveguide, completing the pupil expansion.

[0049] The diffraction unit of the diffraction screen is a waveguide structure, and the propagation angle of the light beam in the waveguide satisfies n' is the refractive index of air, and n is the refractive index of the waveguide medium.

[0050] The diffraction screen (3) may be composed of an imaging component of a grating structure and an additional phase.

[0051] The additional phase in the diffraction unit of the diffraction screen may be a lens phase or a tilt phase.

[0052] The additional phase in the diffraction unit of the diffraction screen is the lens phase, and the modulation of the lens phase can be The wave number x, y are the horizontal and vertical coordinates of the lens surface respectively.

[0053] The additional phase in the diffraction unit of the diffraction screen is a tilt phase. When calculating the hologram, the angle α between the tilt surface and the hologram plane along the y direction is considered, and the diffraction image is pre-reduced by cos(α) times along the y direction to supplement the conjugate tilt phase of the diffraction screen.

[0054] Example 1

[0055] Specifically, Figure 2 As shown, in this embodiment 1, the hologram control unit uses a phase-type spatial light modulator to phase modulate the input computer-generated hologram, and the pixel size is 2 cm.

[0056] In the optical projection system, the focal length of the first lens is f1=5 cm, the aperture size is 1 mm*1 mm, and the focal length of the second lens is f2=25 cm. The aperture is placed at the back focal plane f1 of the first lens, and the second lens is placed at a distance f2 from the aperture. f1<f2, and f2=5*f1, and the magnification B=5. The complex amplitude holographic image is filtered and magnified, and then projected onto the surface of the diffraction screen for modulation.

[0057] The diffraction screen adopts an imaging component with a grating structure. In the present embodiment 1, a transmission diffraction screen is used. The size of the diffraction screen is H, and the size of the pupil of the human eye is h.

[0058] The diffraction unit used in this embodiment 1 is a two-dimensional periodic binary rectangular grating. Considering the positive diffraction order m>0, the incident light and the diffracted light are on the opposite sides of the grating normal line, and the diffraction angle of the imaging receiving point can be It is represented by, where m represents the diffraction order, λ represents the wavelength of the incident light, d represents the grating period, θ′ represents the incident angle of the light wave, n′ represents the refractive index of the space where the incident light is located, and n represents the refractive index of the diffraction screen. Using a 532nm green laser as the incident light source, the refractive index of the space where the incident light is located is n′=1, and the refractive index of the diffraction screen is n=1.5. Figure 2 As shown, assuming that the human eye is located at the center of the observation surface L behind the diffraction screen, the maximum diffraction angle of the diffracted light wave is given by Given. Since each spatial position on the diffraction screen discretizes the incident complex amplitude wavefront and generates multiple orders of diffraction light, which are respectively emitted in different directions, at the viewing position behind the diffraction screen, the diffraction lights of different orders at different spatial positions on the diffraction screen converge here. By modulating the complex amplitude at different positions on the diffraction screen, the coherent superposition of the diffraction lights of different orders at the viewing position is achieved, and a holographic image is generated on the retina of the human eye.

[0059] Example 2

[0060] like Figure 3 As shown, in this embodiment 2, the hologram control unit uses a phase-type spatial light modulator to phase modulate the input computer-generated hologram, and the pixel size is 2 cm.

[0061] In the optical projection system, the focal length of the first lens is f1=5cm, the aperture size is 1mm*1mm, and the focal length of the second lens is f2=25cm. The aperture is placed at the back focal plane f1 of the first lens, and the second lens is placed at a distance f2 from the aperture. f1<f2, and f2=5*f1, and the magnification B=5. The complex amplitude holographic image is filtered and magnified, and then projected onto the surface of the diffraction screen for modulation.

[0062] The diffraction screen adopts an imaging component with a grating structure. In the present embodiment 2, a reflective diffraction screen is used. The size of the diffraction screen is H, and the size of the pupil of the human eye is h.

[0063] The diffraction unit used in this embodiment 2 is a two-dimensional periodic binary rectangular grating. Considering the positive diffraction order m>0, the incident light and the diffracted light are on the opposite sides of the grating normal line, and the diffraction angle of the imaging receiving point can be It is represented by, where m represents the diffraction order, λ represents the wavelength of the incident light, d represents the grating period, θ′ represents the incident angle of the light wave, n′ represents the refractive index of the space where the incident light is located, and n represents the refractive index of the diffraction screen. A 532nm green laser is used as the incident light source. Since the incident light and the diffracted light are located on the same side of the grating, n′=n=1. Figure 3 As shown, assuming that the human eye is located at the center of the observation surface L behind the diffraction screen, the maximum diffraction angle of the diffracted light wave is given by Given. Since each spatial position on the diffraction screen discretizes the incident complex amplitude wavefront and generates multiple orders of diffraction light, which are respectively emitted in different directions, at the viewing position behind the diffraction screen, the diffraction lights of different orders at different spatial positions on the diffraction screen converge here. By modulating the complex amplitude at different positions on the diffraction screen, the coherent superposition of the diffraction lights of different orders at the viewing position is achieved, and a holographic image is generated on the retina of the human eye.

[0064] Example 3

[0065] In this embodiment 3, the hologram control unit uses a phase-type spatial light modulator to perform phase modulation on the input computer-generated hologram, and the pixel size is 2 cm.

[0066] In the optical projection system, the focal length of the first lens is f1=5 cm, the aperture size is 1 mm*1 mm, and the focal length of the second lens is f2=50 cm. The aperture is placed at the back focal plane f1 of the first lens, and the second lens is placed at a distance f2 from the aperture. f1<f2, and f2=10*f1, the magnification B=10, the complex amplitude holographic image is filtered and the image is magnified, and then projected onto the surface of the diffraction screen for modulation.

[0067] The diffraction screen adopts an imaging component with a grating structure. In the present embodiment 3, a transmission diffraction screen is used. The size of the diffraction screen is H, and the size of the pupil of the human eye is h.

[0068] The diffraction unit used in this embodiment 3 is a two-dimensional periodic binary rectangular grating. Considering the positive diffraction order m>0, the incident light and the diffracted light are on the opposite sides of the grating normal line, and the diffraction angle of the imaging receiving point can be It is represented by , where m represents the diffraction order, λ represents the wavelength of the incident light, d represents the grating period, θ′ represents the incident angle of the light wave, n′ represents the refractive index of the space where the incident light is located, and n represents the refractive index of the diffraction screen. Using a 532nm green laser as the incident light source, let the incident angle θ′ = 0, the refractive index of the space where the incident light is located n′ = 1, and the refractive index of the diffraction screen n = 1.5. Assuming that the human eye is located at the center of the L observation plane behind the diffraction screen, the maximum diffraction angle of the diffracted light wave is given by Given. Since each spatial position on the diffraction screen discretizes the incident complex amplitude wavefront and generates multiple orders of diffraction light, which are respectively emitted in different directions, at the viewing position behind the diffraction screen, the diffraction lights of different orders at different spatial positions on the diffraction screen converge here. By modulating the complex amplitude at different positions on the diffraction screen, the coherent superposition of the diffraction lights of different orders at the viewing position is achieved, and a holographic image is generated on the retina of the human eye.

[0069] Example 4

[0070] In this embodiment 4, the hologram control unit uses a phase-type spatial light modulator to perform phase modulation on the input computer-generated hologram, and the pixel size is 2 cm.

[0071] In the optical projection system, the focal length of the first lens is f1=5 cm, the aperture size is 1 mm*1 mm, and the focal length of the second lens is f2=50 cm. The aperture is placed at the back focal plane f1 of the first lens, and the second lens is placed at a distance f2 from the aperture. f1<f2, and f2=10*f1, the magnification B=10, the complex amplitude holographic image is filtered and the image is magnified, and then projected onto the surface of the diffraction screen for modulation.

[0072] The diffraction screen adopts an imaging component with a grating structure. In the present embodiment 4, a reflective diffraction screen is used. The size of the diffraction screen is H, and the size of the pupil of the human eye is h.

[0073] The diffraction unit used in this embodiment 4 is a two-dimensional periodic binary rectangular grating. Considering the positive diffraction order m>0, the incident light and the diffracted light are on the opposite sides of the grating normal line, and the diffraction angle of the imaging receiving point can be It is represented by , where m represents the diffraction order, λ represents the wavelength of the incident light, d represents the grating period, θ′ represents the incident angle of the light wave, n′ represents the refractive index of the space where the incident light is located, and n represents the refractive index of the diffraction screen. A 532nm green laser is used as the incident light source. Since the incident light and the diffracted light are located on the same side of the grating, n′=n=1. Assuming that the human eye is located at the center of the observation surface L behind the diffraction screen, the maximum diffraction angle of the diffracted light wave is given by Given. Since each spatial position on the diffraction screen discretizes the incident complex amplitude wavefront and generates multiple orders of diffraction light, which are respectively emitted in different directions, at the viewing position behind the diffraction screen, the diffraction lights of different orders at different spatial positions on the diffraction screen converge here. By modulating the complex amplitude at different positions on the diffraction screen, the coherent superposition of the diffraction lights of different orders at the viewing position is achieved, and a holographic image is generated on the retina of the human eye.

[0074] Example 5

[0075] In this embodiment 5, the hologram control unit uses a phase-type spatial light modulator to perform phase modulation on the input computer-generated hologram, and the pixel size is 2 cm.

[0076] In the optical projection system, the focal length of the first lens is f1=5 cm, the aperture size is 1 mm*1 mm, and the focal length of the second lens is f2=25 cm. The aperture is placed at the back focal plane f1 of the first lens, and the second lens is placed at a distance f2 from the aperture. f1<f2, and f2=5*f1, and the magnification B=5. The complex amplitude holographic image is filtered and magnified, and then projected onto the surface of the diffraction screen for modulation.

[0077] The diffraction screen adopts an imaging component with a grating structure. In this embodiment 5, a transmission diffraction screen is used. The size of the diffraction screen is H, and the size of the pupil of the human eye is h.

[0078] The diffraction unit used in this embodiment 5 is a two-dimensional periodic multi-level relief grating. Considering the positive diffraction order m>0, the incident light and the diffracted light are on the opposite sides of the grating normal line, and the diffraction angle of the imaging receiving point can be It is represented by, where m represents the diffraction order, λ represents the wavelength of the incident light, d represents the grating period, θ′ represents the incident angle of the light wave, n′ represents the refractive index of the space where the incident light is located, and n represents the refractive index of the diffraction screen. A 532nm green laser is used as the incident light source, the refractive index of the space where the incident light is located n′=1, and the refractive index of the diffraction screen is n=1.5. Assuming that the human eye is located at the center of the observation surface L behind the diffraction screen, the maximum diffraction angle of the diffracted light wave is given by Given. Since each spatial position on the diffraction screen discretizes the incident complex amplitude wavefront and generates multiple orders of diffraction light, which are respectively emitted in different directions, at the viewing position behind the diffraction screen, the diffraction lights of different orders at different spatial positions on the diffraction screen converge here. By modulating the complex amplitude at different positions on the diffraction screen, the coherent superposition of the diffraction lights of different orders at the viewing position is achieved, and a holographic image is generated on the retina of the human eye.

[0079] Example 6

[0080] In this embodiment 6, the hologram control unit uses a phase-type spatial light modulator to perform phase modulation on the input computer-generated hologram, and the pixel size is 2 cm.

[0081] In the optical projection system, the focal length of the first lens is f1=5 cm, the aperture size is 1 mm*1 mm, and the focal length of the second lens is f2=25 cm. The aperture is placed at the back focal plane f1 of the first lens, and the second lens is placed at a distance f2 from the aperture. f1<f2, and f2=5*f1, and the magnification B=5. The complex amplitude holographic image is filtered and magnified, and then projected onto the surface of the diffraction screen for modulation.

[0082] The diffraction screen adopts an imaging component with a grating structure. In this embodiment 6, a transmission diffraction screen is used. The size of the diffraction screen is H, and the size of the pupil of the human eye is h.

[0083] The diffraction unit used in this embodiment 6 is a volume grating. Different from a plane grating, a volume grating is a three-dimensional periodic structure with a certain thickness. The judgment standard is Q≡2πλd0 / nd 2 cosθ′>1,d0 / d>10, where λ represents the wavelength of the incident light, d0 represents the grating thickness, d represents the grating period, and θ′ represents the plane wave incident angle. Considering the positive diffraction order m>0, the incident light and the diffracted light are on opposite sides of the grating normal, the diffraction angle of the imaging receiving point can be It is represented by , where m represents the diffraction order, n' represents the refractive index of the space where the incident light is located, and n represents the refractive index of the diffraction screen. Using a 532nm green laser as the incident light source, the refractive index of the space where the incident light is located n' = 1, and the refractive index of the diffraction screen is n = 1.5. Assuming that the human eye is located at the center of the observation surface L behind the diffraction screen, the maximum diffraction angle of the diffracted light wave is given by Given. Since each spatial position on the diffraction screen discretizes the incident complex amplitude wavefront and generates multiple orders of diffraction light, which are respectively emitted in different directions, at the viewing position behind the diffraction screen, the diffraction lights of different orders at different spatial positions on the diffraction screen converge here. By modulating the complex amplitude at different positions on the diffraction screen, the coherent superposition of the diffraction lights of different orders at the viewing position is achieved, and a holographic image is generated on the retina of the human eye.

[0084] Example 7

[0085] In this embodiment 7, the hologram control unit uses a phase-type spatial light modulator to perform phase modulation on the input computer-generated hologram, and the pixel size is 2 cm.

[0086] In the optical projection system, the focal length of the first lens is f1=5 cm, the aperture size is 1 mm*1 mm, and the focal length of the second lens is f2=25 cm. The aperture is placed at the back focal plane f1 of the first lens, and the second lens is placed at a distance f2 from the aperture. f1<f2, and f2=5*f1, and the magnification B=5. The complex amplitude holographic image is filtered and magnified, and then projected onto the surface of the diffraction screen for modulation.

[0087] The diffraction screen adopts an imaging component with a grating structure. In this embodiment 7, a transmission diffraction screen is used. The size of the diffraction screen is H, and the size of the pupil of the human eye is h.

[0088] The diffraction unit used in this embodiment 7 is a waveguide structure light screen, which includes an in-coupling component, a steering grating and an out-coupling component. The in-coupling component couples the light wave into the waveguide medium, and total reflection propagation occurs inside the waveguide structure. The steering grating diffracts part of the incident light wave toward the waveguide out-coupling component, and the remaining part continues to reflect and propagate forward in the medium, repeating the above process, and the light wave diffraction and reflection occur multiple times. The out-coupling grating is a low diffraction efficiency element, and the light waves that do not meet the total reflection conditions are coupled out of the waveguide medium, while the remaining light waves can be fully reflected inside the waveguide medium and then coupled out of the waveguide to complete the pupil expansion. The propagation angle of the light beam in the waveguide satisfies n' is the refractive index of air, and n is the refractive index of the waveguide medium. Considering the positive diffraction order m>0, the incident light and the diffracted light are on the opposite sides of the grating normal, and the diffraction angle of the imaging receiving point can be It is represented by, where m represents the diffraction order, λ represents the wavelength of the incident light, d represents the grating period, θ′ represents the incident angle of the light wave, n′ represents the refractive index of the space where the incident light is located, and n represents the refractive index of the diffraction screen. A 532nm green laser is used as the incident light source, the refractive index of the space where the incident light is located n′=1, and the refractive index of the diffraction screen is n=1.5. Assuming that the human eye is located at the center of the observation surface L behind the diffraction screen, the maximum diffraction angle of the diffracted light wave is given by Given. Since each spatial position on the diffraction screen discretizes the incident complex amplitude wavefront and generates multiple orders of diffraction light, which are respectively emitted in different directions, at the viewing position behind the diffraction screen, the diffraction lights of different orders at different spatial positions on the diffraction screen converge here. By modulating the complex amplitude at different positions on the diffraction screen, the coherent superposition of the diffraction lights of different orders at the viewing position is achieved, and a holographic image is generated on the retina of the human eye.

[0089] Example 8

[0090] In this embodiment 8, the hologram control unit uses a phase-type spatial light modulator to perform phase modulation on the input computer-generated hologram, and the pixel size is 2 cm.

[0091] In the optical projection system, the focal length of the first lens is f1=5 cm, the aperture size is 1 mm*1 mm, and the focal length of the second lens is f2=25 cm. The aperture is placed at the back focal plane f1 of the first lens, and the second lens is placed at a distance f2 from the aperture. f1<f2, and f2=5*f1, and the magnification B=5. The complex amplitude holographic image is filtered and magnified, and then projected onto the surface of the diffraction screen for modulation.

[0092] The diffraction screen adopts an imaging component with a grating structure. In the present embodiment 8, a transmission diffraction screen is used. The size of the diffraction screen is H, and the size of the pupil of the human eye is h.

[0093] The diffraction unit used in this embodiment 8 is composed of a two-dimensional periodic binary rectangular grating and a lens phase. The modulation of the lens phase can be The wave number x, y are the horizontal and vertical coordinates of the lens surface respectively. Considering the positive diffraction order m>0, the incident light and the diffracted light are on the opposite sides of the grating normal, and the diffraction angle of the imaging receiving point can be It is represented by, where m represents the diffraction order, λ represents the wavelength of the incident light, d represents the grating period, θ′ represents the incident angle of the light wave, n′ represents the refractive index of the space where the incident light is located, and n represents the refractive index of the diffraction screen. A 532nm green laser is used as the incident light source, the refractive index of the space where the incident light is located n′=1, and the refractive index of the diffraction screen is n=1.5. Assuming that the human eye is located at the center of the observation surface L behind the diffraction screen, the maximum diffraction angle of the diffracted light wave is given by Given. Since each spatial position on the diffraction screen discretizes the incident complex amplitude wavefront and generates multiple orders of diffraction light, which are respectively emitted in different directions, at the viewing position behind the diffraction screen, the diffraction lights of different orders at different spatial positions on the diffraction screen converge here. By modulating the complex amplitude at different positions on the diffraction screen, the coherent superposition of the diffraction lights of different orders at the viewing position is achieved, and a holographic image is generated on the retina of the human eye.

Claims

1. A large-scale holographic display system that can be viewed freely, characterized in that The system comprises: a hologram control unit (1), an optical projection system (2) and a diffraction screen (3); wherein a computer generates a computational hologram and uploads it to the hologram control unit (1) to modulate a holographic complex amplitude, and then the holographic complex amplitude modulated by the hologram control unit (1) is projected onto the surface of a large-sized diffraction screen (3) through the optical projection system (2); each spatial position (4) on the diffraction screen (3) modulates the incident holographic complex amplitude wavefront, and the wavefront at each spatial position (4) is diffracted into discrete diffraction lights (5) of multiple directions and respectively projected in different directions; at a viewing position (6) behind the diffraction screen (3), diffraction lights (5) of different orders at different spatial positions (4) on the diffraction screen (3) converge there, and by modulating the complex amplitudes at different spatial positions (4) on the diffraction screen (3), coherent superposition of diffraction lights (5) of different orders at the viewing position (6) is achieved, thereby generating a holographic image on the retina of a human eye.

2. A freely viewable large-scale holographic display system according to claim 1, characterized in that: The hologram control unit (1) is a holographic image source required by the system, and is a phase-type spatial light modulator, an amplitude-type spatial light modulator or a complex amplitude spatial light modulator.

3. The freely viewable large-scale holographic display system according to claim 1, characterized in that: The optical projection system (2) comprises 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) located behind the filtering system.

4. The freely viewable large-scale holographic display system according to claim 1, characterized in that: The diffraction screen (3) adopts an imaging component with a grating structure, including a transmission type and a reflection type.

5. The freely viewable large-scale holographic display system according to claim 4, characterized in that: When the diffraction screen (3) is a transmission light screen, the diffraction unit is a binary grating, a multi-level relief grating or a volume grating of a two-dimensional periodic grating; the diffraction angle of the imaging receiving point is expressed as It is represented by, where m represents the diffraction order, λ represents the wavelength of incident light, d represents the grating period, θ′ represents the incident angle of light wave, n′ represents the refractive index of the space where the incident light is located, and n represents the refractive index of the diffraction screen; using the above formula to examine the spectrum on the same side of the grating normal as the incident light, the sign is positive, that is, m<0, and the spectrum on the opposite side of the grating normal as the incident light takes a negative sign, that is, m>0.

6. The freely viewable large-scale holographic display system according to claim 4, characterized in that: When the diffraction screen (3) is a reflective light screen, the diffraction unit is a two-dimensional periodic grating, such as a binary grating, a multi-level relief grating, or a volume grating; the diffraction angle of the imaging receiving point is expressed as It is represented by, where m represents the diffraction order, λ represents the wavelength of incident light, d represents the grating period, θ′ represents the incident angle of light wave, n′ represents the refractive index of the space where the incident light is located, and n represents the refractive index of the diffraction screen; using the above formula to examine the spectrum on the opposite side of the grating normal to the incident light, it takes a positive sign, that is, m>0, and the spectrum on the same side of the grating normal to the incident light takes a negative sign, that is, m<0.

7. A freely viewable large-scale holographic display system according to claim 1, characterized in that The diffraction screen (3) is an imaging component of a waveguide structure, comprising an in-coupling element, a steering grating and an out-coupling element.

8. The large-scale holographic display system capable of being viewed freely according to claim 1, characterized in that The diffraction screen (3) is composed of an imaging component of a grating structure and an additional phase.

9. A freely viewable large-scale holographic display system according to claim 8, characterized in that The additional phase in the diffraction screen (3) is a lens phase or a tilt phase.

10. The freely viewable large-scale holographic display system according to claim 1, characterized in that: Each spatial position (4) on the diffraction screen (3) can discretize the wavefront of the incident light wave and generate diffracted light (5) of different orders in multiple directions, thereby expanding the field of view; these diffracted lights (5) of different orders are coherently superimposed and imaged at any viewing position (6) behind the diffraction screen (3); the human eye is similar to a small optical filtering system, filtering out the diffraction orders whose diffraction angles deviate from the pupil position, and receiving diffracted lights (5) of different orders at different spatial positions (4) of the large-sized diffraction screen, and forming coherent images on the retina.

Images