Single-frame non-time-sequence color holographic display system and method

Abstract

The invention provides a single-frame non-time-sequence color holographic display system and method. The system comprises a red, green and blue three-color laser, a beam expanding and collimating system, a first polarizer, a spatial light modulator, a beam splitter and a band-limited filtering plane which are sequentially arranged along a light path, the spatial light modulator is connected with a computer and is used for loading a single phase type hologram generated through an iterative optimization algorithm; according to the iterative optimization algorithm, a phase hologram is generated based on a Fresnel diffraction model and a stochastic gradient descent method, laser emitted by a red-green-blue three-color laser is irradiated to a spatial light modulator through a beam splitter, modulated by the hologram in the spatial light modulator and then transmitted to a band-limited filtering plane, and a single-frame non-time-sequence color holographic image is reproduced. According to the invention, the wavefront information of the color object can be completely recorded and reproduced only by using one hologram without depending on high-refresh-rate equipment or complex synchronous control, so that the light path structure is effectively simplified, the cost is reduced, and the reproduction quality and stability of the image are improved at the same time.

Description

Technical Field

[0001] This invention relates to the field of optoelectronics technology, and in particular to a single-frame non-time-sequential color holographic display system and method. Background Technology

[0002] Color holographic display technology records the wavefront information of colored objects based on the principle of light interference and reconstructs a colored image using the principle of light diffraction. This technology has greatly enriched the expressive power of holographic displays, leading to wider attention and application in fields such as medicine, education, industry, and entertainment.

[0003] However, traditional color holographic display methods have some limitations in their implementation. For example, time-division multiplexing typically uses red, green, and blue light to illuminate the red, green, and blue holograms sequentially, relying on the persistence of vision to achieve color holographic reconstruction. However, this method places extremely high demands on the refresh rate of the spatial light modulator (SLM) and the synchronization control performance of the synchronization module, which to some extent limits the realization of dynamic display effects, making the system complex and costly. While spatial division multiplexing avoids the impact of the SLM refresh rate on the color display effect, using multiple SLMs and LEDs of different colors as reconstruction light sources not only increases the complexity and cost of the system but also significantly affects the quality of the reconstructed color image due to the wide spectrum and weak coherence of LEDs. Therefore, existing color holographic display methods cannot simultaneously achieve the goals of recording color information in a single hologram, high image quality, and system simplification. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned defects and provide a color holographic display method that can simultaneously achieve the goals of recording color information with a single frame hologram, high image quality, and system simplification. It records and reproduces the wavefront information of a color object using only one hologram, breaks through the limitations of spatiotemporal multiplexing, simplifies the system structure, and improves the quality and stability of the reproduced image.

[0005] To achieve the above objectives, this invention proposes a single-frame non-temporal color holographic display system, comprising:

[0006] Along the optical path are arranged sequentially a red, green and blue laser, a beam expander and collimator system, a first polarizer, a spatial light modulator, a beam splitter and a band-limited filter plane;

[0007] The spatial light modulator is connected to a computer and is used to load a single phase-type hologram generated by an iterative optimization algorithm;

[0008] The iterative optimization algorithm generates a phase hologram based on the Fresnel diffraction model and stochastic gradient descent method, and its execution steps include:

[0009] (1) Generate a random initial phase hologram φ inii (x,y);

[0010] (2) At the red, green and blue wavelengths, the initial phase hologram is propagated to the reconstruction plane by Fresnel diffraction to obtain a color holographic reconstruction image I(x,y);

[0011] (3) Calculate the loss function L between the color holographic reconstruction image I(x,y) and the target color image T(x,y);

[0012] (4) Update the phase using the stochastic gradient descent algorithm:

[0013] (5) Iterate through steps (2)-(4) until convergence, and obtain the optimized hologram.

[0014] Furthermore, the iterative optimization algorithm simultaneously encodes the holographic light wave information under the red, green, and blue wavelengths into a single hologram, realizing the reuse of information of different wavelengths.

[0015] Furthermore, in step (2), the Fresnel diffraction propagation employs a band-limited filtering operation, specifically including: 1) propagating the random initial phase hologram wavefront Fourier transform to the eye-moving frame plane; 2) filtering the wavefront of the eye-moving frame plane using a digital filtering function that is opaque at the center to block the zero-order noise beam; 3) propagating the filtered wavefront in reverse to the reconstruction plane after inverse Fresnel diffraction calculation;

[0016] The Fresnel diffraction propagation adopts a band-limited diffraction model, the expression of which is:

[0017]

[0018] Where z represents the propagation distance, l represents the wavelength of the light wave, k = 2p / l is the wave number, i represents the imaginary unit, (x, y) are the spatial coordinates of the band-limited filter plane, and (ξ, η) are the spatial coordinates of the hologram plane.

[0019] Furthermore, in step (3), the loss function L is:

[0020]

[0021] Where σ is the energy scaling factor, which maintains the energy balance between the target color image T(x,y) and the holographic reconstruction image I(x,y). It is usually obtained by dividing the average intensity of the target color image by the average intensity of the holographic reconstruction image.

[0022] Furthermore, in the single-frame non-temporal color holographic display system, a Fourier lens and a second polarizer are provided between the spatial light modulator and the band-limited filter plane; the band-limited filter plane is located at the back focal plane of the Fourier lens and is provided with a central opaque mask to block zero-order noise beams.

[0023] Furthermore, the mask is an adjustable black pigment pattern aligned with the zero-order light convergence point of the back focal plane of the Fourier lens.

[0024] Furthermore, the output beam of the three-color laser is bundled by optical fiber and then incident on the beam expander and collimator system.

[0025] Furthermore, the observation area of ​​the band-limited filter plane is also equipped with observation devices.

[0026] Furthermore, the spatial light modulator has a resolution of 1920×1080 and a pixel pitch of 8μm; the beam expanding and collimating system includes a plano-convex lens with a focal length of 150mm.

[0027] This invention also proposes a single-frame non-temporal color holographic display method, using the aforementioned single-frame non-temporal color holographic display system, comprising the following steps:

[0028] S1: Using a computer, the phase hologram generated by the iterative optimization algorithm is loaded into the spatial light modulator;

[0029] S2: The three-color lasers emitted by the red, green and blue lasers are irradiated onto the spatial light modulator through the beam expansion and collimation system and the first polarizer, and modulated using the phase hologram;

[0030] S3: The modulated beam is propagated onto the band-limited filter plane to reproduce a single-frame non-temporally sequential color holographic image.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] 1. Compared to traditional holographic display technologies that rely on time-series multiplexing or space-division multiplexing, resulting in high hardware costs and poor optical path stability due to the need for high refresh rate drive modules or multiple modulation devices, this invention innovatively encodes three wavelengths of information synchronously through a single hologram. It requires only a single spatial light modulator and a fixed three-color laser light source, eliminating the need for time-series switching or spatial splicing, as well as high refresh rate equipment or complex synchronization control. The laser beam is directly modulated after a single beam combining, simplifying the optical path structure and completely avoiding the technical difficulties of high-speed synchronization control. This significantly reduces system complexity and manufacturing costs while improving image reproduction quality and stability.

[0033] 2. Compared to traditional methods that suffer from spectral aliasing due to time-division / spatial reconstruction, resulting in severe color shift and speckle noise in the reconstructed image, this invention combines gradient descent optimization algorithm with Fresnel band-limited diffraction model to optimize holograms. Through iterative optimization, it further suppresses speckle noise in hologram diffraction reconstruction. During the iteration process, the Fresnel diffraction fields of the red, green, and blue channels are calculated simultaneously. The amplitude and phase distribution of the three-color light waves are dynamically constrained by the loss function, suppressing crosstalk between wavelengths at its source and achieving multi-wavelength joint optimization.

[0034] 3. This invention uses Fresnel diffraction algorithm and stochastic gradient descent algorithm to generate holograms, and combines them with spatial light modulator to realize the design of a single-frame non-temporal color holographic display system based on Fresnel diffraction. This effectively reduces color crosstalk in the color reproduction process of holograms during calculation and reproduction.

[0035] 4. This invention introduces a tunable band-limited filter mask at the back focal plane of a Fourier lens to precisely block unmodulated zero-order strong light (a noise source that traditional algorithms cannot eliminate), thereby improving the contrast of the reproduced image to the threshold of human eye comfort.

[0036] 5. Compared to temporal multiplexing, which is limited by the refresh rate of the spatial light modulator, making it difficult to achieve smooth dynamic display; and spatial multiplexing, which is only applicable to static scenes due to the difficulty of optical path calibration: after loading a single frame hologram, the present invention continuously and synchronously illuminates it with three-color lasers, so that the reproduced image is flicker-free and color separation-free; combined with real-time calculation, a holographic video stream is realized, providing a technical foundation for mobile holographic display (such as AR glasses and holographic mobile phones). Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of a single-frame non-temporal color holographic display system according to Embodiment 1 of the present invention;

[0038] Figure 2 This is a flowchart of the holographic iterative optimization algorithm based on Fresnel band-limited diffraction in Embodiment 1 of the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be further described below.

[0040] Example 1

[0041] Example 1 proposes a single-frame non-temporal color holographic display system, such as... Figure 1As shown, the system includes: a red-green-blue three-color laser 6, a beam expander and collimator system 7, a first polarizer 5, a spatial light modulator 1, a beam splitter 8, a Fourier lens 2, a second polarizer 10, and a band-limited filter plane 3 arranged sequentially along the optical path. The spatial light modulator 1 has a resolution of 1920×1080 and a pixel pitch of 8μm. It is connected to a computer 9 and used to load a single phase hologram generated by the computer 9 into the spatial light modulator 1. The beam expander and collimator system 7 includes a plano-convex lens with a focal length of 150mm. The red, green, and blue beams output from the three-color laser 6 are coupled and bundled through an optical fiber before being incident on the beam expander and collimator system 7 (i.e., collimated by the plano-convex lens with a focal length of 150mm), then pass through the first polarizer 5, and finally pass through the beam splitter 8 before being incident on the spatial light modulator 1.

[0042] In this embodiment, the location of the spatial light modulator 1 is used as the holographic surface; the band-limited filter plane 3 is the receiving screen, and its location serves as the reproduction plane for observing the color holographic image. Simultaneously, a camera 4 is also provided in the observation area of ​​the band-limited filter plane 3, with the camera 4 facing the band-limited filter plane 3 for viewing the color holographic image.

[0043] In this embodiment, the computer 9 employs an iterative optimization algorithm based on the Fresnel diffraction model and stochastic gradient descent method to generate a phase hologram for displaying a color holographic image, such as... Figure 2 The flowchart shown is for an iterative optimization algorithm for holograms based on band-limited diffraction. The specific steps of the algorithm include:

[0044] (1) Input the target color scene information;

[0045] (2) Generate a random initial phase and combine it with the plane wave to form an initial random complex amplitude, the expression of which is as follows: Where, φ inii (x,y) is a randomly initialized phase hologram;

[0046] (3) The initial random complex amplitude (initial phase hologram wavefront) is Fourier transformed and then propagated to the filtering plane for band-limited filtering. The specific process is as follows: a. The initial random phase hologram wavefront Fourier transform is propagated to the eye-moving frame plane; b. A digital filter function with a center opaque structure is established, and the wavefront of the eye-moving frame plane is filtered by the digital filter function with a center opaque structure. This filtering process blocks and filters the zero-order noise beam located in the center region of the entire wavefront distribution by setting a center opaque area; c. After performing inverse Fresnel diffraction calculation on the filtered wavefront, it is propagated in reverse at red, green and blue wavelengths respectively, so that the filtered complex amplitude is propagated to the reconstruction plane of the holographic image at each wavelength;

[0047] (4) The filtered initial random complex amplitude is propagated to a reconstruction plane at a certain distance through Fresnel diffraction. Images of different wavelengths are reconstructed and combined into a color reconstructed image to obtain a color holographic reconstruction image I(x,y), the expression of which is:

[0048]

[0049] Where z represents the propagation distance, l represents the wavelength of the light wave, k = 2p / l is the wave number, i represents the imaginary unit, (x, y) are the spatial coordinates of the band-limited filter plane, and (ξ, η) are the spatial coordinates of the hologram plane.

[0050] (5) To optimize the hologram, a loss function is applied to both the reconstructed color image and the target color image. The loss function L between the reconstructed color hologram I(x,y) and the target color image T(x,y) is calculated, and the initial random phase is updated by calculating the gradient of the loss function. This optimization process essentially solves the problem of...

[0051] The following optimization problem:

[0052]

[0053] Wherein, σ is the energy scaling factor, which is used to maintain the energy conservation between the target color image T(x,y) and the holographic reconstruction image I(x,y). It is usually obtained by dividing the average intensity of the target color image by the average intensity of the holographic reconstruction image.

[0054] (6) Iteratively update the phase using stochastic gradient descent:

[0055] (7) Iterate through the above steps (3)-(6) a certain number of times until convergence, and obtain the final optimized hologram.

[0056] In this embodiment 1, the iterative optimization algorithm simultaneously encodes the holographic light wave information under the red, green and blue wavelengths into a single hologram, realizing the reuse of information of different wavelengths.

[0057] In this embodiment 1, as Figure 1 As shown, the band-limited filter plane 3 is located on the back focal plane of the Fourier lens 2, and the band-limited filter plane 3 is provided with a central opaque mask to block the zero-order noise beam. The mask is an adjustable black pigment pattern aligned with the zero-order light convergence point of the back focal plane of the Fourier lens 2.

[0058] Example 2

[0059] Based on the single-frame non-temporal color holographic display system of Embodiment 1 above, Embodiment 2 proposes a single-frame non-temporal color holographic display method, which includes the following steps:

[0060] S1: Deploy a single-frame non-temporal color holographic display system as shown in Example 1:

[0061] S2: An iterative optimization algorithm based on Fresnel diffraction model and stochastic gradient descent is used to generate a phase hologram for displaying color holographic images;

[0062] S3: The phase hologram generated by the iterative optimization algorithm is transmitted and loaded into the spatial light modulator 1 via computer 9, and a hologram with a resolution of 1920×1080 is loaded onto the spatial light modulator 1;

[0063] S4: The red, green and blue lasers emitted by the red, green and blue laser 7 are irradiated onto the screen of the spatial light modulator 1 through the beam expansion and collimation system 7 and the first polarizer 5, and the beam is modulated by the phase hologram loaded in the spatial light modulator 1.

[0064] S5: The modulated beam is propagated through the Fourier lens 2 and the second polarizer 10 to the band-limited filter plane 3 (filter window) to reproduce a single frame of non-time-sequential color holographic image. The reproduced color holographic image is directly captured at the window position of the camera 4, which is suitable for displaying and reproducing high-quality color holographic images.

[0065] In this embodiment, the modulated beam is filtered by a mask placed on a band-limited filter plane 3 on the back focal plane of a Fourier lens 2 with a focal length of 150mm. For example... Figure 1 As shown, after passing through the Fourier lens 2, the zero-order light wave converges in the central region of the filter plane 3, forming a high-intensity bright spot. This bright spot, the zero-order light, typically contains a DC component and unmodulated light, thus negatively impacting the hologram's reconstruction quality. To eliminate this zero-order noise, a mask is applied to the filter plane 3. This mask is made by forming black dots of a specific size on a glass substrate using a special black pigment. By adjusting the mask's position, the zero-order noise in the diffracted light wave is effectively blocked. This method significantly improves the color reconstruction quality of the hologram without affecting the viewing angle.

[0066] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the present invention. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions and content disclosed in the present invention without departing from the scope of the present invention shall be deemed to have remained within the scope of protection of the present invention.

Claims

1. A single-frame non-temporal color holographic display system, characterized in that, include: Along the optical path are arranged sequentially a red, green and blue laser, a beam expander and collimator system, a first polarizer, a spatial light modulator, a beam splitter and a band-limited filter plane; The spatial light modulator is connected to a computer and is used to load a single phase-type hologram generated by an iterative optimization algorithm; The iterative optimization algorithm generates a phase hologram based on the Fresnel diffraction model and stochastic gradient descent method, and its execution steps include: (1) Generate a random initial phase hologram φ inii (x,y); (2) At the red, green and blue wavelengths, the initial phase hologram is propagated to the reconstruction plane by Fresnel diffraction to obtain a color holographic reconstruction image I(x,y); (3) Calculate the loss function L between the color holographic reconstruction image I(x,y) and the target color image T(x,y); (4) Update the phase using the stochastic gradient descent algorithm: (5) Iterate through steps (2)-(4) until convergence, and obtain the optimized hologram.

2. The single-frame non-temporal color holographic display system according to claim 1, characterized in that, The iterative optimization algorithm simultaneously encodes the holographic light wave information under the red, green, and blue wavelengths into a single hologram, realizing the reuse of information of different wavelengths.

3. The single-frame non-temporal color holographic display system according to claim 1, characterized in that, In step (2), the Fresnel diffraction propagation adopts a band-limited filtering operation, specifically including: 1) propagating the random initial phase hologram wavefront Fourier transform to the eye-moving frame plane; 2) filtering the wavefront of the eye-moving frame plane through a digital filtering function that is opaque at the center to block the zero-order noise beam; 3) propagating the filtered wavefront in the reverse direction to the reconstruction plane after inverse Fresnel diffraction calculation; The Fresnel diffraction propagation adopts a band-limited diffraction model, the expression of which is: Where z represents the propagation distance, l represents the wavelength of the light wave, k = 2p / l is the wave number, i represents the imaginary unit, (x, y) are the spatial coordinates of the band-limited filter plane, and (ξ, η) are the spatial coordinates of the hologram plane.

4. The single-frame non-temporal color holographic display system according to claim 1, characterized in that, In step (3), the loss function L is: Wherein, σ is the energy scaling factor, which is used to maintain the energy conservation between the target color image T(x,y) and the holographic reconstruction image I(x,y). It is usually obtained by dividing the average intensity of the target color image by the average intensity of the holographic reconstruction image.

5. The single-frame non-temporal color holographic display system according to claim 1, characterized in that, In the single-frame non-temporal color holographic display system, a Fourier lens and a second polarizer are provided between the spatial light modulator and the band-limited filter plane; the band-limited filter plane is located at the back focal plane of the Fourier lens and is provided with a central opaque mask to block zero-order noise beams.

6. The single-frame non-temporal color holographic display system according to claim 5, characterized in that, The mask is an adjustable black pigment pattern aligned with the zero-order light convergence point of the back focal plane of the Fourier lens.

7. The single-frame non-temporal color holographic display system according to claim 1, characterized in that, The output beam of the three-color laser is bundled by optical fiber and then incident on the beam expander and collimator system.

8. The single-frame non-temporal color holographic display system according to claim 1, characterized in that, The observation area of ​​the band-limited filter plane is also equipped with observation devices.

9. The single-frame non-temporal color holographic display system according to claim 1, characterized in that, The spatial light modulator has a resolution of 1920×1080 and a pixel pitch of 8μm; the beam expansion and collimation system includes a plano-convex lens with a focal length of 150mm.

10. A method for single-frame non-temporal color holographic display, using the single-frame non-temporal color holographic display system as described in any one of claims 1-9, characterized in that, Includes the following steps: S1: Using a computer, the phase hologram generated by the iterative optimization algorithm is loaded into the spatial light modulator; S2: The three-color lasers emitted by the red, green and blue lasers are irradiated onto the spatial light modulator through the beam expansion and collimation system and the first polarizer, and modulated using the phase hologram; S3: The modulated beam is propagated onto the band-limited filter plane to reproduce a single-frame non-temporally sequential color holographic image.

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