Holographic optical element, manufacturing method and near-eye display system

Abstract

The application discloses a holographic optical element, a manufacturing method and a near-eye display system, wherein the holographic optical element comprises a light-transmitting substrate and a holographic grating, the holographic grating is prepared by a holographic photosensitive film layer arranged on the surface of the light-transmitting substrate, the holographic grating has Bragg gratings corresponding to three imaging wavelengths in the same area, the holographic grating is exposed by coherent light of three exposure wavelengths in sequence, the holographic grating is a free wave surface control holographic element prepared by a free light wave surface, and the included angle between incident light and diffracted light of the holographic grating ranges from 5 degrees to 45 degrees. The holographic optical element is a color volume holographic grating, is prepared by multiplexed exposure of holographic optical elements of red, green and blue channels on the same layer of holographic photosensitive film, can realize diffraction of light of three wavelengths, can be used as an optical combiner in augmented reality application, realizes color display, and can correct off-axis aberration in an off-axis optical system.

Description

Technical Field

[0001] This invention relates to a holographic optical element, a method for manufacturing a holographic optical element, and a near-eye display system containing a holographic optical element. Background Technology

[0002] As a current hot topic in the field of information display technology, the development of Augmented Reality (AR) near-eye display technology embodies people's beautiful vision for the future of information interaction and has broad application prospects in various civilian scenarios (such as AR glasses and industrial helmets). Although AR technology is developing rapidly, compared with AR content, computing, and networks, the development of the most basic AR display devices is still relatively lagging behind. The size, weight, and display quality of display modules still cannot meet people's needs.

[0003] Holographic optical elements, as a type of imaging optical component, can be applied to imaging system design and can, to some extent, replace traditional imaging optical components such as lenses and mirrors, offering significant advantages in many aspects. The unique wavelength and angle selectivity of holographic elements, as optical combiners, can achieve excellent optical perspective observation effects; their thin and light characteristics can greatly reduce the overall system size and weight; holographic optical elements can be repeatedly fabricated using the same exposure experimental equipment, facilitating low-cost, mass production.

[0004] However, traditional off-axis reflective imaging systems based on holographic optical elements use holographic elements fabricated only from spherical or plane waves, resulting in limited aberration correction capabilities and an inability to effectively correct off-axis asymmetric aberrations. Furthermore, the system design has limited freedom, leading to poor imaging quality and low diffraction efficiency, which fails to meet practical application requirements. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a holographic optical element, a manufacturing method and a near-eye display system.

[0006] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0007] A color holographic optical element, comprising:

[0008] Transparent substrate

[0009] A holographic grating is fabricated from a holographic photosensitive film layer disposed on the surface of a light-transmitting substrate. The holographic grating has Bragg gratings in the same area, each corresponding to one of the three imaging wavelengths. The holographic grating is formed by sequentially exposing the holographic photosensitive film layer with coherent light of three exposure wavelengths. The holographic grating is a free-wavefront modulated holographic element, fabricated from a free-wavefront. The angle between the incident light and the diffracted light of the holographic grating ranges from 5 degrees to 45 degrees, and the angle ranges of the three color channels are the same.

[0010] Preferably, the three imaging wavelengths correspond to the wavelengths of red, green, and blue light, respectively; the three exposure wavelengths correspond to the wavelengths of red, green, and blue light, respectively; and the imaging wavelength is different from the exposure wavelength for each color channel.

[0011] Preferably, the imaging wavelength is selected as the peak emission wavelength of each color channel of the image display.

[0012] Preferably, the phase function φ(x,y) of the holographic grating is described by one of the following: XY polynomial, Zernike polynomial, and NURBS polynomial.

[0013] Preferably, the phase function φ(x,y) of the holographic grating is described by the following XY polynomial:

[0014]

[0015] Where, λ c A is the exposure wavelength of the holographic optical element. m,n For the polynomial term x m y n The coefficients are m, which is the order of x, n, which is the order of y, and (x,y) are the local coordinates of the substrate plane of the holographic optical element.

[0016] A method for manufacturing a color holographic optical element includes the following steps:

[0017] Provide a light-transmitting substrate,

[0018] A holographic photosensitive film layer is attached to a certain surface of the light-transmitting substrate;

[0019] The holographic photosensitive film is exposed sequentially using three different wavelengths of coherent laser light to form a holographic grating. The exposure beam used during exposure is a free wavefront, and the reference light wave and the signal light wave form a coherent beam that satisfies the phase function φ(x,y).

[0020] Preferably, the phase function φ(x,y) is described by one of the XY polynomial, Zernike polynomial, and NURBS polynomial.

[0021] Preferably, the phase function φ(x,y) of the holographic grating is described by the following XY polynomial:

[0022]

[0023] Where, λ c A is the exposure wavelength of the holographic optical element. m,n For the polynomial term x m y n The coefficients are m, which is the order of x, n, which is the order of y, and (x,y) are the local coordinates of the substrate plane of the holographic optical element.

[0024] A near-eye display system, comprising:

[0025] The holographic optical element, wherein the holographic grating diffracts image light of three imaging wavelengths to the exit pupil position through diffraction;

[0026] An image display is disposed between the exit pupil and the color holographic optical element, and is located in a position that avoids the field of vision of the human eye, for projecting image light onto the holographic grating;

[0027] Ambient light passes through the substrate of the color holographic optical element and is directed towards the exit pupil.

[0028] Preferably, the image display is an LCD display or an OLED display.

[0029] The holographic optical element provided by this invention is a color volume holographic grating, fabricated by exposing holographic optical elements of red, green, and blue channels on the same holographic photosensitive film. It can diffract light of three wavelengths, serving as an optical combiner in augmented reality applications to achieve color display and correct off-axis aberrations in off-axis optical systems. A near-eye display system incorporating this monolithic color holographic optical element uses the holographic optical element as the sole imaging element and optical combiner, with an LCD or OLED as the image source. Light emitted from the image source is diffracted by the holographic optical element and incident on the human eye, allowing the eye to observe a magnified color virtual image at a certain distance, thus achieving the superposition of virtual and real information. This near-eye display system more closely resembles the shape of ordinary eyeglasses, while maintaining system compactness and reducing assembly difficulty. The holographic optical element is perpendicular to the human eye's line of sight, without off-axis tilt. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the optical path of the near-eye display system provided by the present invention;

[0031] Figure 2 This is a schematic diagram of the optical parameters of the color holographic optical element provided by the present invention;

[0032] Figure 3 This is the optical path schematic diagram of the initially constructed system;

[0033] Figure 4 It is the distorted mesh image of the initial system;

[0034] Figure 5 It is the MTF curve of the initial system;

[0035] Figure 6 This is the optical path diagram of the optimized optical system;

[0036] Figure 7 This is the MTF curve of the red channel of the optimized optical system;

[0037] Figure 8 This is the MTF curve of the green channel of the optimized optical system;

[0038] Figure 9 This is the MTF curve of the blue channel of the optimized optical system;

[0039] Figure 10 It is a distorted grid image of the red channel of the optimized optical system;

[0040] Figure 11 It is a distorted grid image of the green channel of the optimized optical system;

[0041] Figure 12 It is a distorted mesh image of the blue channel of the optimized optical system;

[0042] Figure 13 This is a schematic diagram of the exposure beam of a color holographic optical element. Detailed Implementation

[0043] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] like Figure 1As shown, the thin and light color holographic AR near-eye display system provided by this invention includes a miniature image display 1 and a color holographic optical element 2 (hereinafter referred to as the holographic optical element). The miniature image display 1 uses an LCD or OLED display and is used to provide a color image source, such as providing red, green, and blue light to achieve color display. Achieving color display based on the three primary colors of red, green, and blue through a light intensity modulator is fundamental knowledge in the display field and will not be elaborated upon here. The miniature display image source 1 is positioned between the exit pupil and the holographic optical element 2, and is located away from the human eye's field of vision. It is used to project image light onto the holographic optical element 2. The holographic optical element 2 serves as the sole imaging element and optical combiner (the optical combiner is used to combine the imaging light emitted by the image display with the ambient light into the same beam path). The colored imaging light 4 emitted by the image display 1 is diffracted by the holographic grating 202 in the holographic optical element 2, and the colored imaging light is emitted in a predetermined direction to achieve a reflection-like effect. Then, the colored imaging light is incident on the human eye 3 located at the exit pupil in the form of parallel light. The human eye 3 can observe the magnified colored virtual image located at a certain distance. At the same time, the ambient light 5 can pass through the holographic optical element 2 without deflection and be directed to the exit pupil and enter the human eye 3, realizing the superposition of virtual and real information.

[0045] like Figure 2 As shown, the holographic optical element 2 is a color volume holographic grating, fabricated by exposing holographic optical elements of red, green, and blue channels on the same holographic photosensitive film. It can achieve wavelength selectivity and angle selectivity for red, blue, and green light. The angle between the incident light and the diffracted light of the holographic grating ranges from 5 degrees to 45 degrees, and the angle ranges are the same for the three color channels. Specifically, when the three imaging rays 4 emitted by the image display 1 are incident on the holographic optical element 2, the three imaging rays 4 satisfy the Bragg condition of the holographic optical element 2. Therefore, the imaging rays 4 are diffracted by the holographic optical element 2 in the form of parallel light and enter the human eye 3. However, the ambient light 5 does not satisfy the Bragg condition of the holographic optical element 2, so the ambient light 5 can pass through the holographic optical element 2 without deflection and enter the human eye 3.

[0046] The holographic optical element 2 includes a light-transmitting substrate 201 and a holographic grating 202. The light-transmitting substrate 201 can be made of glass or resin material. The holographic grating 202 is formed by exposing a holographic photosensitive film material disposed on the surface of the light-transmitting substrate 201. The holographic grating 202 has Bragg gratings in the same area that correspond to three different imaging wavelengths. The Bragg gratings are formed by exposing coherent light of three different exposure wavelengths in sequence. For each color channel, the exposure wavelength and the imaging wavelength of the light can be different. The exposure beam used for exposure includes both a signal light wave and a reference light wave. At least one of the signal light wave and the reference light wave is a free wavefront. The reference light wave and the signal light wave satisfy the phase function φ(x,y).

[0047] like Figure 1 The near-eye display system shown is an off-axis display system that corrects off-axis aberrations solely through holographic optical elements. Exposure of the holographic grating using rotationally symmetric spherical or plane waves cannot achieve off-axis aberration correction. Therefore, the near-eye display system provided in this application employs a free-wavefront modulated holographic element, using a free-wavefront to expose the holographic film layer, thus fabricating the holographic grating. The phase function of the coherent light used during exposure, corresponding to each color channel of the holographic grating, can be described by any of the following forms: XY polynomial, Zernike polynomial, or NURBS polynomial, preferably XY polynomial.

[0048] Holographic optical elements are fabricated using exposure on specific free-wavefronts, where the free-wavefront is neither a spherical nor a plane wave. Compared to holographic optical elements fabricated using traditional plane or spherical waves, this significantly improves the aberration correction capability of holographic optical elements while substantially reducing the size and weight of the optical system. This allows near-eye display devices to more closely resemble the shape of ordinary eyeglasses, while maintaining system compactness and reducing assembly difficulty. The holographic optical elements are perpendicular to the human eye's visual axis, without off-axis tilt.

[0049] The design and manufacturing process of holographic optical elements will be introduced below in conjunction with this near-eye display system.

[0050] As imaging elements, holographic optical elements are characterized by complex phase functions to correct aberrations introduced by off-axis system structures, enabling effective correction of off-axis asymmetric aberrations. Utilizing the wavelength multiplexing property of holographic optical elements, red, green, and blue channels can be multiplexed simultaneously on the same holographic film. Each color channel's holographic optical element only modulates the imaging light of the corresponding color emitted by the display, thus achieving color display.

[0051] As an optical assembler, the unique angle / wavelength selectivity of holographic optical elements ensures excellent optical transmittance and eliminates perspective distortion. Furthermore, coating holographic optical elements onto a flat resin or glass substrate significantly reduces the size and weight of the optical system.

[0052] In the aforementioned near-eye display system, holographic optical elements are used as the sole imaging optical combiner. To reduce the size and weight of the imaging optical combiner, the wavelength multiplexing property of holography is utilized to simultaneously expose holographic optical elements of the red, green, and blue channels on a single holographic photosensitive film. Each color channel's holographic optical element only modulates the imaging light of the corresponding color channel emitted by the image display to achieve color display.

[0053] Since the peak wavelength of each color channel emitted by the image display differs from the exposure wavelength of the corresponding holographic optical element, the influence of this wavelength difference should be considered during the design process. To ensure the imaging quality of the optical system in practical applications, the peak emission wavelength of each color channel of the image display should be selected as the imaging wavelength of the full-color near-eye display optical system; the imaging wavelength of each color channel and the exposure wavelength of the corresponding holographic optical element are shown in Table 1.

[0054] Table 1. Imaging wavelengths and exposure wavelengths for the red, green, and blue channels.

[0055] Red Channel Green Channel Blue Channel Imaging wavelength 608nm 547nm 448nm Exposure wavelength 639nm 532nm 457nm

[0056] Traditional methods of characterizing holographic optical elements by the position coordinates of the exposure beam have limited degrees of freedom, as they only represent the three-dimensional position coordinates of the exposure beam. This approach cannot effectively correct off-axis asymmetric aberrations in the optical system and can only achieve good imaging quality for beams with small field of view and small aperture. It cannot be applied to optical systems with large field of view and large aperture. Furthermore, the exposure beam of holographic optical elements is only a simple spherical wave or plane wave.

[0057] The holographic optical element in this application is characterized by a phase function φ(x,y) defined in the plane of its substrate, possessing a high degree of freedom in characterization. It can effectively correct off-axis asymmetric aberrations in the optical system and achieve good imaging quality for beams with large field of view and large aperture (field of view greater than 5 degrees, beam aperture greater than 5 mm). The exposure beam of the holographic element is a specific free-wavefront, rather than a simple spherical wave or plane wave.

[0058] The phase function φ(x,y) characterizing a holographic optical element can usually be described by forms such as XY polynomials, Zernike polynomials, and NURBS.

[0059] This application uses the XY polynomial to describe the phase function φ(x,y):

[0060]

[0061] Where, λ c A is the exposure wavelength of the holographic optical element. m,n For the polynomial term x m y n The coefficients are m, which is the order of x, n, which is the order of y, and (x,y) are the local coordinates of the substrate plane of the holographic optical element.

[0062] The design of this color holographic near-eye display optical system consists of two steps. First, an initial system is constructed to meet the object-image imaging relationship required by the system parameters. Then, the initial system is optimized to meet certain imaging quality requirements.

[0063] For the initial system construction, the position coordinates of the image display and the holographic optical element are predefined to ensure symmetry about the meridional plane and that the image display does not obstruct the viewer's line of sight. The position coordinates of the holographic optical element and the image display relative to the global reference coordinate system located at the exit pupil center are shown in Table 2.

[0064] Table 2 Parameters of the image display and holographic optical elements in the initial system

[0065] X Y Z α Holographic optical elements 0mm 0mm 60mm 0° Image display 0mm 30mm 25mm -20°

[0066] Based on the predefined system structure, the paraxial focal length of the initial system can be calculated using optical design software by tracing the paraxial rays from the central field of view. Then, based on the calculated paraxial focal length, by sampling imaging rays at different pupil coordinates at different field points, and using the paraxial imaging formula of an ideal optical system and the ray tracing equation of the holographic optical element, the phase function coefficients of the holographic optical element can be directly calculated to ensure that it satisfies the object-image imaging relationship required by the system parameters. Since the modulation function of the holographic optical element on the imaging wavefront depends on both the imaging wavelength and the exposure wavelength, the holographic phase functions of the red, green, and blue channels need to be calculated separately to achieve color holographic display.

[0067] The initial system constructed is as follows Figure 3As shown, 11 is an image display, 12 is a holographic optical element, 13 is the exit pupil position (human eye position), and 14 is the imaging light emitted by the image display. The miniature image display 11 uses an LCD or OLED display to provide a color image source, specifically providing light of different imaging wavelengths. The miniature image source 11 is positioned between the exit pupil position 13 and the holographic optical element 12, avoiding the viewer's field of vision, and is used to project image light onto the holographic optical element 12. The holographic optical element 12 serves as the sole imaging element and optical combiner. It includes a color volume holographic grating. The color imaging light 14 emitted by the image display 11 is diffracted by the holographic grating, directing the color imaging light in a predetermined direction, achieving a reflection-like effect. The color imaging light enters the viewer's eye at the exit pupil position 13 in the form of parallel light. The viewer can observe a magnified color virtual image at a certain distance. Simultaneously, ambient light 15 passes through the holographic optical element 12 without deflection, reaching the exit pupil position 13 and entering the viewer's eye, achieving the superposition of virtual and real information. The coefficients of the holographic phase functions of the red, green, and blue channels in this initial system are shown in Table 3.

[0068] Table 3. Exposure wavelengths and phase function coefficients for the three color channels in the initial system.

[0069]

[0070]

[0071] The distorted mesh of the initial system is as follows Figure 4 As shown, the MTF curve of the initial system is as follows: Figure 5 As shown. In the initial system, the distortion mesh and MTF curves of the three color channels are all equal. Figure 4 and Figure 5 Only the green channel is displayed. From Figure 4 It can be seen that the actual mesh in the distorted mesh diagram of the initial system coincides with the ideal mesh, meaning that the initial system satisfies the object-image imaging relationship required by the system parameters. However, from... Figure 5 The MTF curves shown indicate that the MTF values ​​in some fields of view are close to zero, indicating poor imaging quality in this initial system, which fails to meet the requirements for human visual observation. The next step is to optimize this initial system to meet the imaging quality requirements of the human eye. This involves setting the position coordinates of the holographic optical element and the image display, as well as the phase function coefficients of the holographic optical element, as variables. System constraints should control the distortion mesh and prevent the image display from obstructing the viewer's line of sight. Furthermore, to avoid significant chromatic aberration, the imaging rays from different color channels at the same field of view should intersect at the same point on the image display.

[0072] Optimized optical system such as Figure 6As shown in the figure, 21 is the image display, 22 is the holographic optical element, 23 is the exit pupil position, and 24 is the imaging ray emitted by the image display. The position coordinates of the image display 21 and the holographic optical element 22 in the optimized optical system, relative to the global reference coordinate system located at the center of the exit pupil, are shown in Table 4.

[0073] Table 4 Optical parameters of the optimized near-eye display system

[0074] X Y Z α Holographic optical elements 0mm 0mm 60mm 0° Image display 0mm 30mm 20mm -14.48°

[0075] In the optimized optical system, a 2.1-inch image source is used, and the image display 21 can be either an LCD or an OLED display. Combined with a 50mm × 40mm holographic optical element 22, a near-eye display optical system is formed, achieving a field of view of 40° × 30°, an exit pupil diameter of 6mm, and an exit pupil distance of 60mm. The holographic phase function coefficients of the red, green, and blue channels in the optimized optical system are shown in Table 5.

[0076] Table 5 shows the exposure wavelengths and phase function coefficients for the three color channels in the optimized system.

[0077]

[0078]

[0079] In the optimized system, the MTF curve of the red channel is as follows: Figure 7 As shown, the MTF curve of the green channel is as follows: Figure 8 As shown, the MTF curve of the blue channel is as follows: Figure 9 As shown. For each color channel, the MTF value for all fields of view is greater than 0.1 at 10 line pairs / mm, which meets the actual observation requirements of the human eye.

[0080] In the optimized system, the distorted mesh of the red channel is as follows: Figure 10 As shown, the distorted mesh of the green channel is as follows: Figure 11 As shown, the distorted mesh of the blue channel is as follows: Figure 12 As shown in the distortion grid diagram, the dashed grid represents the ideal image plane position of the optical system, and the solid grid represents the actual image plane position of the optical system. For each color channel, there is a certain amount of barrel distortion, with the maximum distortion value being less than 12%, which basically meets the requirements of human eye observation. Distortion pre-correction methods can also be used to reduce the image distortion observed by the human eye.

[0081] The optimized color holographic near-eye display optical system improves the imaging quality of each color channel compared to the initial system. The difference between the meridional and sagittal parts in the MTF curve is small, which meets the imaging quality requirements of the human eye. Due to the large field of view of this near-eye display optical system, there will be some barrel distortion, but it basically meets the imaging quality requirements.

[0082] This invention also provides a method for manufacturing the holographic optical element, comprising the following steps: providing a light-transmitting substrate, attaching a holographic photosensitive film layer to a certain surface of the light-transmitting substrate; sequentially exposing the holographic photosensitive film layer with three different wavelengths of coherent laser light to form a holographic grating multiplexed with red, green, and blue channels, wherein the exposure beam used during exposure (including a reference light wave and a signal light wave, see...) Figure 13 ) is the free wavefront, and the reference wave and the signal wave form a coherent beam that satisfies the phase function φ(x,y).

[0083] This application uses the XY polynomial to describe the phase function φ(x,y):

[0084]

[0085] Where, λ c A is the exposure wavelength of the holographic optical element. m,n For the polynomial term x m y n The coefficients are m, which is the order of x, n, which is the order of y, and (x,y) are the local coordinates of the substrate plane of the holographic optical element.

[0086] The aforementioned holographic optical elements are fabricated from specific free-light wavefronts, which can effectively correct off-axis asymmetric aberrations in the system and achieve good imaging quality for beams with large field of view and large aperture.

[0087] In this application, holographic optical elements are coated on a flat resin or glass substrate. Compared to geometric optical solutions using curved substrates, holographic optical elements can significantly reduce system size and weight while maintaining the same imaging quality, ensuring system compactness and aesthetics. Holographic optical elements are easy to fabricate and mass-produce, and compared to surface-embossed grating elements, they can greatly reduce the fabrication cost of optical systems.

[0088] The foregoing has provided a detailed description of the holographic optical element, manufacturing method, and near-eye display system provided by this invention. Any obvious modifications made by those skilled in the art without departing from the essence of this invention will constitute an infringement of the patent rights of this invention and will incur corresponding legal liability.

Claims

1. A method for manufacturing a color holographic optical element, wherein the color holographic optical element is used in a near-eye display system, characterized in that... The manufacturing method includes the following steps: Provide a light-transmitting substrate, A holographic photosensitive film layer is attached to a certain surface of the light-transmitting substrate; The same area of ​​the holographic photosensitive film is exposed sequentially using three different wavelengths of coherent laser light to form a holographic grating. The exposure beam used during exposure is a free-wavefront beam, and the reference and signal beams form a coherent beam that satisfies the phase function of the holographic grating. ; The phase function of the holographic grating Described by the following XY polynomial: Where, λ c A is the exposure wavelength of the holographic optical element. m,n For the polynomial term x m y n The coefficients, m is the order of x, n is the order of y, and (x, y) are the local coordinates of the substrate plane of the holographic optical element; The phase function of the holographic grating Obtained through the following steps: Construct an initial system consisting only of an image display and a color holographic optical element, and make the initial system meet the object-image imaging relationship required by the system parameters. The color holographic optical element is perpendicular to the visual axis and serves as the only imaging element and optical combiner. The micro-display image source is set between the exit pupil position and the holographic optical element, and is located in a position that avoids the field of vision of the human eye. The initial system is then optimized to meet the imaging quality requirements of the human eye. The position coordinates of the holographic optical element and the image display, as well as the phase function coefficients of the holographic optical element, are set as variables. The system constraints should control the distortion grid and prevent the image display from obstructing the human eye's view. At the same time, to avoid large color differences, the imaging rays of different color channels under the same field of view should be controlled to intersect at the same point on the image display.

2. The method for manufacturing a color holographic optical element as described in claim 1, characterized in that: The construction of an initial system consisting only of an image display and color holographic optical elements, and ensuring that the initial system satisfies the object-image imaging relationship required by the system parameters, includes the following steps: First, the position coordinates of the image display and the holographic optical element are predefined to make them symmetrical about the meridional plane, and the image display does not obstruct the viewer's line of sight. Based on this predefined system structure, the paraxial focal length of the initial system can be calculated by tracing the paraxial rays of the central field of view using optical design software. Based on the calculated paraxial focal length of the system, by sampling imaging rays from different field points and pupil coordinates, and using the paraxial imaging formula of the ideal optical system and the ray tracing equation of the holographic optical element, the phase function coefficient of the holographic optical element is directly calculated to ensure that it meets the object-image imaging relationship required by the system parameters.

3. A near-eye display system, characterized in that... include: A color holographic optical element obtained by the manufacturing method of claim 1 or 2 includes a light-transmitting substrate and a holographic grating. The holographic grating is fabricated from a holographic photosensitive film layer disposed on the surface of the light-transmitting substrate. The holographic grating has Bragg gratings in the same region, each corresponding to one of the three imaging wavelengths. The holographic grating is formed by sequentially exposing the holographic photosensitive film layer with coherent light of three exposure wavelengths. For each color channel, the imaging wavelength is different from the exposure wavelength. The holographic grating is a free-wavefront modulated holographic element, fabricated from a free-wavefront. The angle between the incident light and the diffracted light of the holographic grating ranges from 5 degrees to 45 degrees, and the angle ranges are the same for the three color channels. The phase function of the holographic grating... Described by the following XY polynomial: Where, λ c A is the exposure wavelength of the holographic optical element. m,n For the polynomial term x m y n The coefficients, m is the order of x, n is the order of y, and (x, y) are the local coordinates of the substrate plane of the holographic optical element; An image display is disposed between the exit pupil and the color holographic optical element, and is located in a position that avoids the field of vision of the human eye, for projecting image light onto the holographic grating; The color holographic optical element is perpendicular to the visual axis and is used as the sole imaging element and optical combiner. The holographic grating therein diffracts the image light of three imaging wavelengths to the exit pupil position by reflection. Ambient light passes through the light-transmitting substrate of the color holographic optical element and is directed toward the exit pupil position.

4. The near-eye display system as described in claim 3, characterized in that: The three imaging wavelengths correspond to the wavelengths of red, green, and blue light, respectively. The three exposure wavelengths correspond to the wavelengths of red, green, and blue light, respectively.

5. The near-eye display system as described in claim 4, characterized in that: The imaging wavelength is selected as the peak emission wavelength of each color channel of the image display.

6. The near-eye display system as described in claim 3, characterized in that: The image display is an LCD display or an OLED display.

7. The near-eye display system as described in claim 3, characterized in that: The field of view reaches 40°×30°, the exit pupil diameter is 6mm, and the exit pupil distance is 60mm.

Images