Computer hologram generation method and holographic display device using same

Abstract

The invention discloses a computer hologram generation method for reducing second harmonic images and a holographic display device applying the method. The computer hologram generation method provided by the invention comprises the following steps of: generating complex amplitude image data from original image data; performing diffraction integration on the complex amplitude image data to generate complex amplitude hologram data; adding the virtual second harmonic component to a phase component of the complex amplitude hologram data to generate corrected complex amplitude hologram data; and generating pure phase hologram data using the phase component of the corrected complex amplitude hologram data.

Description

Technical Field

[0001] The present invention relates to a computer generated hologram (CGH) generation method for reducing second harmonic images and a holographic display device using the method. More specifically, it relates to a computer generated hologram generation method for reducing second harmonic images generated when displaying a hologram by utilizing a liquid crystal spatial light modulator and a holographic display device using the method.

[0002] The Korean national research and development projects that support this invention are as follows:

[0003] *Selcos Ltd.

[0004] The research was conducted with funding from the Ministry of Trade, Industry and Energy of South Korea and the Korea Institute of Evaluation and Industrial Technology (KEIT) in fiscal 2024.

[0005] (20026309, Development of 8K-UHD-level LCOS microdisplay panel and system technology for the ultra-realistic metaverse)

[0006] *May Co., Ltd.

[0007] The research was conducted with funding from the Ministry of Science and Technology and the Korea Institute of Infocomm Planning and Evaluation in fiscal 2024.

[0008] (2021-0-00750-001, Development of 4-diopter focus control HOE technology for AR / MR) Background Art

[0009] Holography is an optical technology that generates and reproduces three-dimensional images. It records and reproduces light waves using holography to provide realistic and three-dimensional images.

[0010] In recent years, digital holography has attracted more and more attention. It converts holographic patterns obtained by optoelectronic devices or holographic patterns generated by computers through mathematical models into digital data through optical information processing. Images generated by digital holography are called digital holograms, which are displayed electronically through spatial light modulators (SLMs). Among digital holograms, holograms created by numerically simulating light diffraction and interference phenomena are called computer generated holograms (CGHs).

[0011] Computer holograms include complex amplitude holograms that independently control the light amplitude and phase, pure amplitude holograms that only control the light amplitude, and pure phase holograms that only control the light phase. Although complex amplitude holograms are the best method, they are technically difficult to achieve, and pure amplitude holograms have poor optical efficiency. Therefore, pure phase holograms, which have good optical efficiency and are easy to achieve, are widely used.

[0012] In order to display pure phase holograms, a liquid crystal spatial light modulator such as a liquid crystal on silicon spatial light modulator (LCoS (Liquid Crystal on Silicon) SLM) is used. Figure 1 As shown in FIG. 1 , when a pure phase hologram is displayed, in addition to the well-known DC term and conjugate image, a second harmonic image is also displayed due to the nonlinearity of the liquid crystal response, thereby reducing the quality of the restored image. The second harmonic image may increase or decrease due to the structure of the liquid crystal unit or the pixel size. In order to find the optimal conditions for reducing the second harmonic image, a lot of time and effort is required. Summary of the invention

[0013] Therefore, the object of the present invention is to provide a computer hologram generation method for reducing second harmonic images and a holographic display device using the method, that is, the characteristics and image quality of the hologram can be improved by reducing the second harmonic image generated when displaying a pure phase hologram through a spatial light modulator using liquid crystal.

[0014] The computer hologram generation method of the holographic display device of the present invention for achieving the purpose of the present invention is characterized in that it includes: step (a), generating complex amplitude image data from original image data; step (b), performing diffraction integral on the complex amplitude image data to generate complex amplitude hologram data; step (c), adding a virtual second harmonic component to the phase component of the complex amplitude hologram data to generate corrected complex amplitude hologram data; and step (d), generating pure phase hologram data using the phase component of the corrected complex amplitude hologram data.

[0015] Furthermore, the computer hologram generation method of the present invention is characterized in that it also includes the following step of determining a correction constant of the virtual second harmonic component to offset the second harmonic component generated by the nonlinearity of the silicon-based liquid crystal spatial light modulator when the pure phase hologram data is displayed through the silicon-based liquid crystal spatial light modulator.

[0016] Among them, the computer hologram generation method of the present invention is characterized in that the contrast ratio (CR, Contrast Ratio) obtained by dividing the brightness of the restored image restored by the pure phase hologram data through the silicon-based liquid crystal spatial light modulator by the brightness of the second harmonic image corresponding to the second harmonic component generated by the nonlinearity of the silicon-based liquid crystal spatial light modulator reaches more than 200.

[0017] The computer generated hologram generation method of the present invention is characterized in that the two-dimensional distribution of the amplitude and phase of the correction constant of the virtual second harmonic component is determined so that the contrast reaches 200 or more.

[0018] The computer hologram generation method of the present invention is characterized in that the step (b) includes: step (b-1), after replacing the amplitude component of the complex amplitude hologram data with a constant, inversely transforming the diffraction integral to generate restored image data; step (b-2), replacing the amplitude component of the restored image data with the amplitude component of the complex amplitude image data; step (b-3), performing diffraction integration on the restored image data to generate the complex amplitude hologram data; and repeating steps (b-1) to (b-3) to generate the complex amplitude hologram data retaining only the phase component.

[0019] Furthermore, the computer hologram generation method of the present invention is characterized in that the step (a) includes the following steps: when the original image data is three-dimensional image data corresponding to a three-dimensional object, the complex amplitude image data is divided into multiple layers (layers) representing depth information of the three-dimensional object; in the step (b), the multiple layers constituting the complex amplitude image data are respectively subjected to diffraction integration to generate the complex amplitude hologram data composed of multiple hologram planes corresponding to the multiple layers.

[0020] The computer generated hologram generation method of the present invention is characterized in that, in the step (b), any one of an algorithm for reducing speckle noise and a deep learning technique is applied to generate the complex amplitude hologram data.

[0021] On the other hand, the holographic display device of the present invention includes: a storage unit for storing data and programs required for the operation of the holographic display device; a processor unit for executing the operation program stored in the storage unit to generate pure phase hologram data in which the second harmonic image is canceled; a spatial light modulator for restoring the pure phase hologram data generated by the processor unit into an image using a silicon-based liquid crystal spatial light modulator; and a light source unit for generating coherent laser and outputting it to the spatial light modulator.

[0022] The holographic display device of the present invention is characterized in that the processor unit generates the pure phase hologram data using the phase component of the corrected complex amplitude hologram data generated by adding a virtual second harmonic component to the phase component of the complex amplitude hologram data.

[0023] The holographic display device of the present invention is characterized in that the correction constant of the virtual second harmonic component is stored in the storage unit, the correction constant of the virtual second harmonic component is determined in a manner to offset the second harmonic component generated by the nonlinearity of the silicon-based liquid crystal spatial light modulator when the pure phase hologram data is displayed through the silicon-based liquid crystal spatial light modulator, and the processor unit uses the correction constant to calculate the virtual second harmonic component.

[0024] The holographic display device of the present invention is characterized in that the spatial light modulator restores the pure phase hologram data into an image according to the control of the processor unit, so that the contrast obtained by dividing the brightness of the restored image restored by the pure phase hologram data through the silicon-based liquid crystal spatial light modulator by the brightness of the second harmonic image corresponding to the second harmonic component generated by the nonlinearity of the silicon-based liquid crystal spatial light modulator reaches more than 200.

[0025] The correction constant is stored in the storage section, the correction constant being changed according to characteristics of each model of the LCOS spatial light modulator used as the spatial light modulator.

[0026] Through the computer hologram generation method for reducing second harmonic images and the holographic display device using the method of the present invention, the correction constant can be determined according to the characteristics of the silicon-based liquid crystal spatial light modulator to reduce the second harmonic image, thereby improving the image quality of the restored image. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A diagram showing a second harmonic image generated when displaying a conventional digital hologram.

[0028] Figure 2 FIG. 4 is a schematic diagram showing a method for generating a computer generated hologram according to an embodiment of the present invention.

[0029] Figure 3 and Figure 4 A diagram for explaining another method of generating complex amplitude hologram data in a computer generated hologram generating method according to an embodiment of the present invention.

[0030] Figure 5 The figure is used to illustrate the input-output relationship when a computer generated hologram generated according to an embodiment of the present invention is restored through a liquid crystal on silicon spatial light modulator.

[0031] Figure 6A block diagram showing the brief structure of a holographic display device to which a computer generated hologram method according to an embodiment of the present invention is applied.

[0032] Figure 7 FIG. 4 is a flow chart for illustrating a method for generating a computer generated hologram according to an embodiment of the present invention.

[0033] Figures 8 to 10 This is a graph showing the contrast experimental results of a liquid crystal on silicon spatial light modulator used in a computer hologram generation method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0034] Hereinafter, a computer hologram generation method for reducing second harmonic images and a holographic display device using the method (hereinafter referred to as a computer hologram generation method and a holographic display device) according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0035] Figure 2 2 is a schematic diagram showing a method for generating a computer generated hologram according to an embodiment of the present invention. Figure 3 and Figure 4 A diagram for explaining another method of generating complex amplitude hologram data in a computer generated hologram generating method according to an embodiment of the present invention.

[0036] Reference Figure 2 , the natural color original image data corresponding to the three-dimensional object (I R，G，B (ξ, η)) are separated into red, green and blue (RGB) monochrome image data, and the two-dimensional information and light intensity information of the natural color original image are obtained. Then, a random phase (φ) is added to the square root of the brightness of the red, green and blue monochrome images. r (ξ, η)), generating complex amplitude image data on the object plane

[0037] If laser light is directed at a three-dimensional object, the laser light interacts with the object and diffracts, producing an amplitude and phase distribution. This process is mathematically modeled to generate a computer hologram.

[0038] If the computer hologram generation process is described in detail, Figure 2 As shown in FIG. 1 , the complex amplitude image data on the object plane propagates a distance d along the z axis to generate complex amplitude hologram data on the hologram plane, and there is a Fresnel diffraction integral relationship between the object plane and the hologram plane. The complex amplitude hologram data corresponding to the distribution of the electric field at z can be calculated by the Fresnel diffraction integral shown in Mathematical Formula 1 and expressed by the Fourier transform formula.

[0039] Mathematical formula 1

[0040]

[0041] By using Mathematical Formula 1, if the field distribution on the object plane of z = 0 is known, the field distribution on the hologram plane of z ≠ 0 can be known. In Mathematical Formula 1, u(ξ, η, 0) represents the complex amplitude image data on the object plane of z = 0, λ represents the wavelength of light (Wavelength), k represents the wave number (Wave number), and FT[] represents Fourier transform.

[0042] The calculation formula for generating pure phase hologram data using the complex amplitude image data (u(ξ, η, 0)) on the object plane is shown in Mathematical Formula 2.

[0043] Mathematical formula 2

[0044]

[0045] The reason why only the phase component is used in the complex amplitude hologram data is that the silicon-based liquid crystal spatial light modulator only performs phase modulation. As mentioned above, if the phase component is extracted from the complex amplitude image data through a single diffraction integral, the amplitude information will disappear, thereby generating a large amount of speckle noise in the restored image. Among the technologies for reducing speckle noise, the basic method is the Gerchberg-Saxton algorithm. Figure 3 As shown, the corresponding method goes back and forth between the object plane and the hologram plane, applies constraints on each plane, and ultimately makes the amplitude of the complex amplitude hologram data a constant.

[0046] That is, the complex amplitude hologram data (U R，G，B (x,y)exp[iφ R，G，B (x, y)]) R，G，B (x, y)) is replaced by a constant A (or "1 (one)") and then the inverse transformation is performed, and then the process of diffraction integration is repeated to make the amplitude component a constant A (or "1"), thereby generating a complex amplitude hologram data (U(x, y) = |U(x, y)|exp[iφ(x, y)]) that only retains the phase component (e iφ(x，y) )'s complex amplitude hologram data (i.e., pure phase hologram data (POH)).

[0047] Specifically, a random phase (φ r (ξ, η)) to obtain the complex amplitude image data on the object plane Performing diffraction integration on the complex amplitude image data to obtain complex amplitude hologram data on the hologram plane The amplitude component Replace (apply uniform spectrum condition) with constant A to obtain improved complex amplitude hologram data Inversely transform the improved complex amplitude hologram data into restored image data The restored image data The amplitude component of (image condition) is replaced by the original complex amplitude image data The amplitude component To obtain improved restored image data Then, the improved restored image data is diffraction integrated again to generate complex amplitude hologram data Then, the amplitude component Replace (apply uniform spectrum condition) with constant A. Repeat this process to remove speckle noise and generate a system with only phase component (e i φ(x，y) ) complex amplitude hologram data. The virtual second harmonic component (αe 2iφ(x，y) ) is added to the phase component (e) of the complex amplitude hologram data iφ(x，y) ), generate the corrected complex amplitude hologram data (Ae iθ(x，y) ), and use the phase component of the corrected complex amplitude hologram data to generate pure phase hologram data (P(x, y) = θ(x, y) [0, 2π]).

[0048] Figure 4 A diagram for illustrating a layer-based computer hologram generation method according to an embodiment of the present invention.

[0049] like Figure 4 As shown, when the original image data is three-dimensional image data corresponding to a three-dimensional object, the complex amplitude image data is divided into multiple layers representing the depth information of the three-dimensional object. Diffraction integration is performed on each layer, and multiple complex amplitude hologram data corresponding to all multiple layers are added together to generate complex amplitude hologram data.

[0050] Then, the virtual second harmonic component is added to the phase component of the complex amplitude hologram to generate corrected complex amplitude hologram data, and pure phase hologram data is generated using the phase component of the corrected complex amplitude hologram data.

[0051] Apart from Figure 3 and Figure 4 In addition to the above method, an algorithm for reducing speckle noise generated in complex amplitude hologram data may be applied, or deep learning technology may be applied to generate complex amplitude hologram data.

[0052] Figure 5 The figure is used to illustrate the input-output relationship when a computer generated hologram generated according to an embodiment of the present invention is restored through a liquid crystal on silicon spatial light modulator.

[0053] A liquid crystal on silicon (LCOS) spatial light modulator is a super-small microdisplay that utilizes the light modulation characteristics of liquid crystals and uses a silicon wafer as a backplane. The LCOS spatial light modulator co-integrates pixels and drive circuits through complementary metal oxide semiconductor integrated circuit (CMOS IC) technology, thereby achieving high resolution. As Figure 5 shown, the light input to the LCOS spatial light modulator is affected by factors such as fringe fields in addition to simple diffraction phenomena, thereby exhibiting non-linearity and having output characteristics. The input-output characteristics of the LCOS spatial light modulator can be represented by including higher harmonic components as shown in Mathematical Formula 3.

[0054] Mathematical Formula 3

[0055]

[0056] When n = 1, the diffracted light of e iφ(x，y) shows a restored image. When n = -1, the diffracted light of e iφ(x，y) shows a conjugate image. When n = 0, a DC term is shown. When n = 2, the diffracted light of e 2iφ(x，y) shows a second harmonic image. Among them, in order to cancel the second harmonic image, a corrected phase component (e 2iφ(x，y) ) generated by adding a virtual second harmonic component (αe iφ(x，y) ) to the phase component (e iφ(x，y) +αe 2iφ(x，y) = Ae iθ(x，y) ) is used. The input-output characteristics of the LCOS spatial light modulator with the corrected phase component (e iφ(x，y) +αe 2i φ(x，y) ) can be as shown in Mathematical Formula 4.

[0057] Mathematical Formula 4

[0058]

[0059] The correction constant α is determined in such a way that the coefficient (αC 1 + C 2 ) of the second harmonic component calculated in Mathematical Formula 4 approaches "0 (Zero)", thereby canceling the second harmonic component in the output of the LCOS spatial light modulator. Among them, the correction constant α is a complex number and can be determined by adjusting the amplitude and phase.

[0060] Figures 8 to 10This is a graph showing the contrast experimental results of a liquid crystal on silicon spatial light modulator used in a computer hologram generation method according to an embodiment of the present invention.

[0061] exist Figures 8 to 10 In the experiment, the contrast ratio according to the correction constant α was obtained when the pixel size of the LCOS spatial light modulator panel was the same and the size of the cell gap (Cell Gap) as the upper and lower spacing in the pixel was different from the size of the filled liquid crystal. The size of the cell gap is related to the crosstalk phenomenon between pixels. The smaller the size of the cell gap, the less crosstalk phenomenon. Among them, the contrast ratio is the value of the brightness of the restored image divided by the brightness of the second harmonic image, and the image brightness (IB) is the brightness value of the restored image measured using a photodiode.

[0062] exist Figure 8 In the LCOS spatial light modulator panel with a relatively large cell gap of 2.4 μm and filled with multi-layer cell (MLC) liquid crystal, when the correction constant α is changed to "amplitude 0.35, phase -25 degrees", it can be seen that the contrast is improved from 65 when the correction constant α is "0" to 499. In this case, the image brightness (IB), which is the brightness value of the restored image, is almost unchanged, and only the second harmonic component is reduced, thereby improving the contrast.

[0063] exist Fig. 9 and Fig.10 In , when the correction constant α is changed to "amplitude 0.45, phase -90 degrees", the contrast is improved. That is, the image brightness (IB), which is the brightness value of the restored image, is almost unchanged, and only the second harmonic component is reduced, thereby improving the contrast. Fig. 9 In the experiment, when the cell gap of the LCOS SLM panel is 1.5 μm, the contrast ratio is improved from 55 to 224 according to the change of the correction constant α. Fig.10 In the experiment, when the cell gap of the LCOS spatial light modulator panel is 1.4 μm, the contrast ratio is improved from 72 to 278 according to the change of the correction constant α. Fig. 9 and Fig.10 The LCOS spatial light modulators of the 2016 OLED TVs are all filled with the same electro-optic (ELC) liquid crystal, as the panels differ only in cell gap by 0.1 μm, and their correction constant α is the same.

[0064] Figure 8 The multilayer cell liquid crystal used in the experiment and Fig. 9 , Fig.10 The experiments using electro-optical liquid crystals imply different kinds of liquid crystals.

[0065] According to the results of the above experiments, the correction constant α varies according to the characteristics of each model of the LCOS spatial light modulator, and the type of liquid crystal, cell gap and pixel size of each model are different. For the same model, such as Fig. 9 and Fig.10 As shown, even if the cell gaps have slight differences, if the types of liquid crystals are the same, the same correction constant α can be used.

[0066] When pure phase hologram data generated by correcting the phase component according to the computer generated hologram generation method of the present invention as described above is restored through a silicon-based liquid crystal spatial light modulator, the second harmonic component is offset, so that the contrast is improved to more than 200.

[0067] For a single LCOS SLM panel, the correction constant α has a two-dimensional distribution, and the two-dimensional distribution of the amplitude and phase of the correction constant α is determined by measurement, so that the contrast of the entire panel reaches more than 200. The correction constant α can take different values ​​for each pixel of the LCOS SLM, or it can take the same value regardless of the position of the pixel.

[0068] Generally, computer holograms mostly use the Fresnel diffraction integral, but it can also be evaluated in a variety of ways, such as angular spectrum method, Fourier transform method or point cloud method, etc. And in order to reduce speckle noise, a variety of methods (such as Fienup algorithm, Fidoc algorithm, etc.) have been developed to improve the convergence speed by modifying the Gerchberg-Saxton algorithm. In recent years, the technology of generating computer holograms using deep learning technology has also been reported.

[0069] The present invention has nothing to do with a specific computer hologram generation method or algorithm. Instead, it adds a virtual second harmonic component to the "actual output phase component" on a silicon-based liquid crystal spatial light modulator to generate corrected complex amplitude hologram data, and uses the phase component of the corrected complex amplitude hologram data to generate pure phase hologram data. This is because the second harmonic component is not generated due to the incompleteness of a specific computer hologram generation method or algorithm, but is generated due to the nonlinearity of the response characteristics of the silicon-based liquid crystal (LCoS) panel caused by the influence of the fringe field, etc., which produces the second harmonic component shown in Mathematical Formula 3. In other words, this is a problem of the silicon-based liquid crystal panel itself. Therefore, if a correction constant suitable for the silicon-based liquid crystal panel model can be found, regardless of the computer hologram generation method or algorithm, the second harmonic component can be offset, thereby improving the image quality of the restored image.

[0070] Figure 6The present invention is a block diagram showing a simplified structure of a holographic display device to which a computer generated hologram generation method according to an embodiment of the present invention is applied.

[0071] Reference Figure 6 The holographic display device 100 of the present invention includes a storage unit 110 , a processor unit 130 , a light source unit 150 and a spatial light modulator 170 .

[0072] The storage unit 110 is used to store data and programs required for the operation of the holographic display device 100. In the present invention, in order to generate a computer hologram, the operation program driven by the processor unit 130 and a plurality of data required for the operation processing are stored in the storage unit 110. In addition, the correction constant α determined according to the characteristics of the spatial light modulator 170 described later is stored in the storage unit 110.

[0073] Such storage unit 110 includes random access memory (RAM) such as dynamic random access memory (DRAM), static random access memory (SRAM), etc.; read-only memory (ROM) such as programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), etc.; hard disk drive (HDD), solid state drive (SSD) or flash memory.

[0074] The processor unit 130 executes the program stored in the storage unit 110 to control the operation of the holographic display device 100. In the present invention, the processor unit 130 executes a calculation program for generating a computer generated hologram to cancel the second harmonic image in the image restored by the spatial light modulator 170.

[0075] In more detail, the processor unit 130 generates corrected complex amplitude hologram data by adding the virtual second harmonic component to the phase component of the complex amplitude hologram data generated using Mathematical Formula 1, and generates pure phase hologram data using the phase component of the corrected complex amplitude hologram data. In this case, the processor unit 130 calculates the virtual second harmonic component using the correction constant α stored in the storage unit 110.

[0076] The light source unit 150 generates coherent laser light and outputs it to the spatial light modulator 170 , and a light emitting diode (LED), a laser diode (LD), an organic light emitting diode (OLED), etc. can be used as the light source.

[0077] The spatial light modulator 170 utilizes the properties of liquid crystals and is driven in pixel units to spatially modulate light. In the present invention, a silicon-based liquid crystal spatial light modulator is used as the spatial light modulator 170 to restore the pure phase hologram data into an image. In this case, the correction constant α is different according to the characteristics of each model of the silicon-based liquid crystal spatial light modulator used as the spatial light modulator 170, and is measured through a separate process and stored in the storage unit 110, and the processor unit 130 reads the corresponding value and applies it to data processing.

[0078] Among them, the contrast ratio obtained by dividing the brightness of the restored image restored by the pure phase hologram data through the silicon-based liquid crystal spatial light modulator by the brightness of the second harmonic image corresponding to the second harmonic component generated by the nonlinearity of the silicon-based liquid crystal spatial light modulator reaches more than 200, thereby improving the image quality of the restored image. That is, the characteristics of the second harmonic image generated by the nonlinearity of the silicon-based liquid crystal spatial light modulator are as shown in mathematical formula 3, and before the application of the present invention, the restoration at the position of z / 2 causes the image quality of the restored image to deteriorate. However, with the application of the present invention, the second harmonic image will disappear while the second harmonic component is offset, thereby improving the image quality of the restored image.

[0079] Figure 7 FIG. 4 is a flow chart for illustrating a method for generating a computer generated hologram according to an embodiment of the present invention.

[0080] according to Figure 7 , the processor unit 130 generates complex amplitude image data from the original image data of the object (step S200). That is, after separating the natural color original image data into red, green, and blue monochrome image data, random phases are added to the square roots of the brightness of the red, green, and blue monochrome images to generate complex amplitude image data on the object plane. When the natural color original image data is three-dimensional image data corresponding to a three-dimensional object, the complex amplitude image data is divided into a plurality of layers representing the depth information of the three-dimensional object.

[0081] Then, the processor unit 130 performs a diffraction integral on the complex amplitude image data to generate complex amplitude hologram data (step S220). That is, the processor unit 130 generates complex amplitude hologram data having an amplitude component and a phase component on a hologram plane having a Fresnel diffraction integral relationship with the object plane using Mathematical Formula 1. When the complex amplitude image data is composed of a plurality of layers, the plurality of layers constituting the complex amplitude image data are respectively subjected to a diffraction integral to generate complex amplitude hologram data composed of a plurality of hologram planes corresponding to the plurality of layers.

[0082] Furthermore, in step S220, in order to generate complex amplitude hologram data without speckle noise, the complex amplitude hologram data is inversely transformed into restored image data, and the process of performing diffraction integration on the restored image data is repeated. Figure 3 As shown, after the amplitude component of the complex amplitude hologram data is replaced by the constant A, the diffraction integral is inversely transformed to generate the restored image data. Then, the amplitude component of the restored image data is replaced by the amplitude component of the complex amplitude image data, and the process of performing the diffraction integral on the restored image data is repeated to generate the complex amplitude hologram data with only the phase component retained.

[0083] The processor unit 130 adds a virtual second harmonic component to the phase component of the complex amplitude hologram data to generate corrected complex amplitude hologram data (step S240). In this case, the correction constant α of the virtual second harmonic component is determined according to the characteristics of each model of the LCOS spatial light modulator used as the spatial light modulator 170, and is stored in the storage unit 110. That is, the correction constant α of the virtual second harmonic component is determined in such a manner as to cancel the second harmonic component generated due to the nonlinearity of the LCOS spatial light modulator when the pure phase hologram data is displayed by the LCOS spatial light modulator.

[0084] The processor unit 130 generates pure phase hologram data using the phase component of the corrected complex amplitude hologram data (step S260). In the pure phase hologram data thus generated, the contrast obtained by dividing the brightness of the restored image restored by the silicon-based liquid crystal spatial light modulator by the brightness of the second harmonic image corresponding to the second harmonic component generated by the nonlinearity of the silicon-based liquid crystal spatial light modulator reaches 200 or more. That is, since the amplitude and phase of the correction constant α of the virtual second harmonic component are determined in such a way that the contrast reaches 200 or more, the second harmonic component is offset and the second harmonic image disappears. For the entire panel, the two-dimensional distribution of the amplitude and phase of the correction constant α is determined in such a way that the contrast reaches 200 or more, so the second harmonic image disappears from the entire panel.

[0085] By reducing the second harmonic image generated when displaying a pure phase hologram through the process described above, the quality of the restored image can be improved. That is, the characteristics of the second harmonic image generated by the nonlinearity of the silicon-based liquid crystal spatial light modulator are as shown in Mathematical Formula 3, and before the application of the present invention, the restoration at the position of z / 2 causes the image quality of the restored image to deteriorate. However, with the application of the present invention, the second harmonic image disappears while the second harmonic component is offset, thereby improving the quality of the restored image.

Claims

1. A computer hologram generation method for a holographic display device, characterized in that: include: Step (a), after separating the natural color original image data into red, green and blue monochrome image data respectively, adding a random phase to the square root of the brightness of the red, green and blue monochrome images to generate complex amplitude image data; Step (b), performing diffraction integration on the complex amplitude image data to generate complex amplitude hologram data; Step (c), adding a virtual second harmonic component to the phase component of the complex amplitude hologram data to generate corrected complex amplitude hologram data, wherein the virtual second harmonic component is used to offset the second harmonic component generated by the nonlinearity of the liquid crystal on silicon spatial light modulator; as well as Step (d), generating pure phase hologram data using the phase component of the corrected complex amplitude hologram data.

2. The method for generating a computer generated hologram according to claim 1, characterized in that: The step (c) further includes the step of determining a correction constant of the virtual second harmonic component to cancel the second harmonic component when the pure phase hologram data is displayed through the LCOS spatial light modulator.

3. The method for generating a computer generated hologram according to claim 1, characterized in that: The contrast ratio obtained by dividing the brightness of the restored image restored by the pure phase hologram data through the Si-based liquid crystal spatial light modulator by the brightness of the second harmonic image corresponding to the second harmonic component generated by the nonlinearity of the Si-based liquid crystal spatial light modulator reaches more than 200.

4. The method for generating a computer generated hologram according to claim 3, characterized in that: The two-dimensional distribution of the amplitude and phase of the correction constant of the virtual second harmonic component is determined so that the contrast becomes 200 or more.

5. The method for generating a computer generated hologram according to claim 1, characterized in that: The step (b) comprises: Step (b-1), after replacing the amplitude component of the complex amplitude hologram data with a constant, inversely transforming the diffraction integral to generate restored image data; Step (b-2), replacing the amplitude component of the restored image data with the amplitude component of the complex amplitude image data; Step (b-3), performing diffraction integration on the restored image data to generate the complex amplitude hologram data; and Repeat steps (b-1) to (b-3) to generate the complex amplitude hologram data retaining only the phase component.

6. The method for generating a computer generated hologram according to claim 1, characterized in that: The step (a) comprises the following steps: when the original image data is three-dimensional image data corresponding to a three-dimensional object, dividing the complex amplitude image data into a plurality of layers representing depth information of the three-dimensional object, In the step (b), diffraction integration is performed on each of the plurality of layers constituting the complex amplitude image data to generate the complex amplitude hologram data consisting of a plurality of hologram planes corresponding to the plurality of layers.

7. The method for generating a computer generated hologram according to claim 1, characterized in that: In the step (b), any one of an algorithm for reducing speckle noise and a deep learning technique is applied to generate the complex amplitude hologram data.

8. A holographic display device, characterized in that: include: A storage unit, used to store data and programs required for the operation of the holographic display device; A processor unit that executes a calculation program stored in the storage unit to generate pure phase hologram data in which the second harmonic image is cancelled; a spatial light modulator, which uses a liquid crystal on silicon spatial light modulator to restore the pure phase hologram data generated by the processor unit into an image; and a light source section that generates coherent laser light and outputs it to the spatial light modulator, The processor unit separates the natural color original image data into red, green and blue monochrome image data respectively, adds a random phase to the square root of the brightness of the red, green and blue monochrome images to generate complex amplitude image data, performs diffraction integration on the complex amplitude image data to generate complex amplitude hologram data, then adds a virtual second harmonic component for offsetting the second harmonic component generated by the nonlinearity of the silicon-based liquid crystal spatial light modulator to the phase component of the complex amplitude hologram data to generate corrected complex amplitude hologram data, and uses the phase component of the corrected complex amplitude hologram data to generate the pure phase hologram data.

9. The holographic display device according to claim 8, characterized in that: storing in the storage unit a correction constant of the virtual second harmonic component, wherein the correction constant of the virtual second harmonic component is determined in such a manner as to cancel out a second harmonic component generated due to the nonlinearity of the LCOS spatial light modulator when the pure phase hologram data is displayed by the LCOS spatial light modulator, The processor unit calculates the virtual second harmonic component using the correction constant.

10. The holographic display device according to claim 9, characterized in that: The spatial light modulator restores the pure phase hologram data into an image according to the control of the processor unit, so that the contrast ratio obtained by dividing the brightness of the restored image restored by the pure phase hologram data through the silicon-based liquid crystal spatial light modulator by the brightness of the second harmonic image corresponding to the second harmonic component generated by the nonlinearity of the silicon-based liquid crystal spatial light modulator reaches more than 200.

11. The holographic display device according to claim 9, characterized in that: The correction constant is stored in the storage section, the correction constant being changed according to characteristics of each model of the LCOS spatial light modulator used as the spatial light modulator.

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