A visual optical imaging device and a near-eye display system with a curved optical combiner for full-color display

Abstract

The present invention relates to a visual optical imaging device and a near-eye display system with a curved optical combiner that can achieve full-color display. This system is composed of two mirror-symmetrical visual optical imaging devices. Each visual optical imaging device includes one image microdisplay, one free-form optical lens, one diffractive optical element, one free-form optical prism, one free-body holographic optical element, and a curved optical combiner. The image optical signal emitted by the image microdisplay passes through the optical system and finally enters the human eye through diffraction by the free-body holographic optical element. The free-body holographic optical element can achieve large-angle unconventional refraction and reflection, and has the characteristics of being thin, light, and having extremely high aberration correction ability. The diffractive optical element has unique dispersion characteristics, and cooperates with the free-form surface to effectively correct the chromatic aberration and monochromatic aberration introduced into the system by the free-body holographic optical element, finally realizing an ultra-thin, light, and full-color binocular near-eye display. In addition, the curved optical combiner is more in line with human body engineering.

Description

Technical Field

[0001] The present invention relates to the technical field of visual display, and in particular to a visual optical imaging device and a near-eye display system with a curved optical combiner that can achieve full-color display. Background Art

[0002] Augmented Reality (hereinafter referred to as AR) can superimpose virtual information on the real world, thereby improving people's interaction experience with the real world and the digital world, and has great market application value in fields such as games, education, military, industry, and commerce.

[0003] The key to AR devices lies in the immersive experience of users. Miniaturization, light weight, full color, large field of view, large eyebox, and high performance are the current development trends of AR devices. Existing near-eye display devices adopt various solutions, such as the free-form surface waveguide solution of Epson, the array waveguide solution of Lumus, the coaxial side-view prism solution of Google Glass, the holographic grating solution of Hololens, and the diffractive waveguide solution of OPPO Air Glass, etc.

[0004] Volume Holographic Optical elements (VHOE) are used in lightweight AR devices and are optical elements made according to the principle of holography. Usually made on photosensitive thin film materials, using the combination of plane waves and spherical waves to generate interference, a hologram is obtained on the photosensitive material. When irradiated by light, the light undergoes an unconventional large-angle deflection due to the diffraction effect. It is a diffraction element that follows the Bragg angle condition. The free volume holographic optical element breaks the traditional exposure method of plane waves and spherical waves and uses a controlled free-form surface wavefront for exposure, greatly improving the aberration control ability of the holographic optical element.

[0005] Diffractive Optical elements (DOE) are based on lithography technology and can concentrate diffracted light on a set diffraction order, thereby realizing functions such as imaging, dispersion, and arbitrarily setting the wavefront. They have the advantages of high precision, light weight, compactness, large design freedom, and unique dispersion characteristics.

[0006] As a holographic optical element, the volume holographic optical element breaks the traditional law of reflection and can achieve large-angle unconventional reflection, thus significantly reducing the volume and weight of the entire system and making miniaturization and light weight possible. The free-form surface is very flexible in regulating the wavefront, while the diffractive optical element has unique dispersion characteristics and can compensate for the dispersion of the volume holographic optical element, thereby effectively correcting the chromatic aberration of the system. In addition, the volume holographic optical element also has the characteristic of being bendable, so that a curved optical combiner can be realized. Therefore, it is very meaningful to combine the free-form surface, diffractive optical element and volume holographic optical element to design a near-eye display system with a curved optical combiner that can achieve full-color display.

[0007] This patent is a further invention based on CN202110663579.X and CN202210294637.0. The earlier two patents respectively obtained a system with light weight and high imaging quality by using volume holographic optical elements and free volume holographic optical elements in a near-eye display system, demonstrating the excellent performance of volume holographic optical elements and free volume holographic optical elements in AR near-eye displays. However, although the near-eye display systems described in these two patents are full-color displays, they only consider the chromatic aberration and aberration control of red, green, and blue colors separately. This results in a certain offset of the red, green, and blue images for the human eye in actual full-color displays. In this patent, a new chromatic aberration control method is proposed by combining volume holographic optical elements, diffractive optical elements, and free-form surface optical elements, which can control chromatic aberration and monochromatic aberration including the chromatic aberration of red, green, and blue colors. The near-eye display system described in the patent is designed based on this method. In addition, in the near-eye display systems described in the earlier two patents, the optical combiner attached to the volume holographic optical element is flat glass, while this patent further explores the bendable characteristics of the volume holographic optical element and designs a curved optical combiner, which is more in line with human body engineering and improves the wearing comfort of the described AR near-eye display system. Summary of the Invention

[0008] The present invention aims to provide a visual optical imaging device and a near-eye display system with a curved optical combiner that can achieve full-color display. The near-eye display system is composed of two mirror-symmetrical visual optical imaging devices combined together, and realizes thin and light optical transmissive binocular near-eye display by synergistically correcting the chromatic aberration and monochromatic aberration of the system through free volume holographic optical elements, diffractive optical elements, and free-form surface optical elements, and can be applied to the application scenarios of RGB color AR and VR.

[0009] The present invention first provides a visual optical imaging device with a curved optical combiner capable of full-color display, which includes an image microdisplay, a free-form optical lens, a diffractive optical element, a free-form optical prism, and a curved optical combiner with a volume holographic optical element attached thereto; the image signal light emitted by the image microdisplay is refracted by the free-form optical lens, then diffracted by the diffractive optical element, and then refracted and reflected by the free-form optical prism and incident on the curved optical combiner, and finally diffracted by the volume holographic optical element attached to the curved optical combiner and enters the human eye. On the other hand, ambient light enters the human eye after passing through the curved optical combiner and the volume holographic optical element by transmission.

[0010] The free-form optical lens, the diffractive optical element, the free-form optical prism, and the volume holographic optical element are designed by the following steps:

[0011] Step 1: Use the exposure coefficient and phase function polynomial of the volume holographic optical element to construct the volume holographic surface, generate the volume holographic optical element, establish the correspondence between the exposure coefficient and phase function polynomial of the volume holographic optical element and the optical wavefront, and obtain the chromatic aberration and the magnitude of monochromatic aberration generated by the volume holographic surface.

[0012] Step 2: Based on the chromatic aberration and the magnitude of monochromatic aberration generated by the volume holographic surface, according to the compensation principle of generating opposite chromatic aberration and monochromatic aberration, use the phase function polynomial of the diffractive optical element to construct the diffractive surface and generate the diffractive optical element.

[0013] Step 3: Use the free-form surface polynomial to construct the free-form surface, generate the free-form optical lens and the free-form optical prism, establish the correspondence between the parameters of each term of the free-form surface polynomial and the actual surface, and thus perform ray tracing to obtain the chromatic aberration and the magnitude of monochromatic aberration generated by each surface.

[0014] Step 4: Considering that the total aberration of the system is the sum of the aberrations of each surface, obtain the relationship between the total aberration of the system and the parameters of each surface, and through optimization and solution, obtain the parameter combination that minimizes the chromatic aberration and monochromatic aberration of the system.

[0015] Step 5: Use the parameter combination obtained in Step 4 as the processing parameters for the free-form optical lens, the diffractive optical element, the free-form optical prism, and the volume holographic optical element for processing.

[0016] As a preferred solution of the present invention, the diffractive optical element includes a plane and a diffractive surface. Light first refracts on the plane and enters the diffractive optical element, and then diffracts on the diffractive surface and leaves the diffractive optical element; the diffractive surface has a series of diffractive units, and each diffractive unit can regulate the wavefront phase distribution, and the parameters of each term of the phase distribution function are matched based on the principle of correcting the system aberration and compensating the chromatic aberration introduced by the volume holographic optical element at the same time.

[0017] As a preferred embodiment of the present invention, the curved optical combiner includes a front surface and a rear surface, both of which have a set radius of curvature; a volume holographic optical element is attached to the front surface close to the human eye. The volume holographic optical element is composed of a free volume holographic optical film. The light incident on the volume holographic optical element through the freeform optical prism satisfies the Bragg incidence relationship of the volume holographic optical element, and thus is diffracted into the human eye; the ambient light is incident through the curved optical combiner and does not satisfy the Bragg incidence relationship of the volume holographic optical element, and thus is transmitted into the human eye. The volume holographic optical element is a structure in which red, green, and blue are composite-exposed in the same layer of film, or a structure in which red, green, and blue are separately exposed in three layers of film and then stacked, or a structure in which two of the red, green, and blue colors are composite-exposed in the same layer of film, and the other color is separately exposed in another layer of film, and then the two layers of film are stacked.

[0018] The present invention also provides a near-eye display system with a curved optical combiner that can achieve full-color display, which includes two of the visual optical imaging devices, and the two visual optical imaging devices are mirror-symmetrical left and right.

[0019] The present invention also provides a method for controlling chromatic aberration of the near-eye display system, which includes four steps:

[0020] Step 1: Select an initial structure for the near-eye display system, including a diffractive optical element, a volume holographic optical element or a free volume holographic optical element, and a freeform optical element.

[0021] Step 2: Use the exposure coefficient and phase function polynomial of the volume holographic optical element to construct the volume holographic surface, use the phase function polynomial of the diffractive optical element to construct the diffractive surface, and use the freeform surface polynomial to construct the freeform surface. Considering that the total chromatic aberration of the system is the sum of the chromatic aberrations of each surface, establish the corresponding relationship between the total chromatic aberration of the system and the parameters of each surface. Here, the chromatic aberration refers to the monochromatic chromatic aberration corresponding to red, green, and blue.

[0022] Step 3: The simulation system performs ray tracing to generate images formed by red, green, and blue respectively. Due to the chromatic aberration between red, green, and blue, there is a relative position offset between the three images. Establish the corresponding relationship between the relative position offset of the three images and the parameters of each surface.

[0023] Step 4: Integrate the corresponding relationships between the red, green, and blue monochromatic chromatic aberrations of the system and the relative position offsets of the red, green, and blue images and the parameters of each surface. After optimization and solution, obtain a parameter combination that satisfies the condition that the relative position offset of the red, green, and blue images is less than the human eye's limit resolution and at the same time minimizes the red, green, and blue monochromatic chromatic aberrations of the system; use the obtained parameter combination to process the near-eye display system to achieve chromatic aberration control.

[0024] Advantages of the present invention: According to the near-eye display system of the present invention, by adopting a free-form optical element, a diffractive optical element, and a free-volume holographic optical element, while greatly improving the degree of freedom for aberration correction of the system, the volume and weight of the system are significantly reduced, achieving high performance and miniaturization of the near-eye display system; according to the chromatic aberration control method adopted by the near-eye display system of the present invention, by adopting a free-form optical element, a diffractive optical element, and a free-volume holographic optical element, the monochromatic chromatic aberration and RGB trichromatic chromatic aberration of the imaging system are corrected, achieving full-color display of the near-eye display system; according to the near-eye display system of the present invention, by utilizing the bendable characteristic of the free-volume holographic optical element, a curved optical combiner is realized, which is more in line with ergonomics. Description of the Drawings

[0025] Figure 1 is the optical path diagram of the visual optical imaging device provided by the embodiment of the present invention;

[0026] Figure 2A 、 Figure 2B and Figure 2C are respectively the MTF curve graphs of the R, G, and B colors of the system in the embodiment of the present invention;

[0027] Figure 3 is the superposition graph of the R, G, and B color aberrations of the system in the embodiment of the present invention;

[0028] Figure 1 In, 11 is the image microdisplay, 12 is the free-form optical lens, 121 is the first transmission surface of the free-form optical lens, 122 is the second transmission surface of the free-form optical lens, 13 is the diffractive optical element, 131 is the plane of the diffractive optical element, 132 is the diffractive surface of the diffractive optical element, 14 is the free-form optical prism, 141 is the first optical transmission surface of the free-form optical prism, 142 is the second optical reflection surface of the free-form optical prism, 143 is the third optical transmission surface of the free-form optical prism, 15 is the volume holographic optical element, 16 is the curved optical combiner, 161 is the front surface of the curved optical combiner, and 162 is the rear surface of the curved optical combiner. Detailed Embodiments

[0029] Hereinafter, the specific embodiments of the present invention will be specifically described according to the drawings. The present invention can be implemented in many different forms and should not be construed as limited to the following embodiments. Instead, this embodiment is provided to make the present disclosure full and complete, and to fully convey the concept of the present invention to those skilled in the art.

[0030] Embodiment

[0031] The binocular near-eye display system according to an embodiment of the present invention includes two sets of visual optical imaging devices with curved optical combiners for full-color display relative to the left and right human eyes. Hereinafter, the visual optical imaging device on the left side relative to the human eye will be used as the specific object of description to illustrate the specific implementation of the present invention. Those skilled in the art can understand that the visual optical imaging device on the right side has the same structure as the left side, but is a left-right mirror image.

[0032] As Figure 1 described, the left visual optical system provided by the embodiment of the present invention includes an image microdisplay 11, a free-form optical lens 12, a diffractive optical element 13, a free-form optical prism 14, and a curved optical combiner 16 with a free volume holographic optical element 15 attached thereto. The image signal light emitted by the image microdisplay 11 is refracted by the free-form optical lens 12, and then diffracted by the diffractive optical element 13 and enters the free-form optical prism 14. Inside the free-form optical prism 14, the light first passes through the first optical transmission surface 141 for refraction, then is reflected by the second optical reflection surface 142, undergoes total internal reflection on the first optical transmission surface 141, and finally is refracted by the third optical transmission surface 143 and exits the prism, and is incident on the curved optical combiner 16. Since the incident light satisfies the Bragg incident relationship of the free volume holographic optical element 15 attached to the curved optical combiner, it is finally diffracted by the free volume holographic optical element 15 and enters the human eye. On the other hand, ambient light enters the free volume holographic optical element 15 through the curved optical combiner 16. Since it does not satisfy the Bragg incident relationship of the free volume holographic optical element 15, the light passes through the free volume holographic optical element 15 and then enters the human eye, realizing optical transmission type near-eye display.

[0033] Among them, the thickness, the radius of each surface, and the coefficients of each free-form surface of the free-form optical lens 12 and the free-form optical prism 14, the coefficients of the phase distribution function of the diffractive surface 132 of the diffractive optical element 13, the exposure parameters and the coefficients of the phase distribution function of the free volume holographic optical element 15 are matched according to the principle of minimizing the control system chromatic aberration and monochromatic aberration. The overall optical path of the visual optical imaging device controlled by the free-form optical lens 12, the diffractive optical element 13, the free-form optical prism 14, and the free volume holographic optical element 15 is designed according to the principle of minimizing the system volume and bending around the head.

[0034] Specifically, the free-form optical lens 12, the diffractive optical element 13, the free-form optical prism 14, and the volume holographic optical element 15 in this embodiment are designed by the following steps:

[0035] Step 1: Use the exposure coefficient and phase function polynomial of the volume holographic optical element to construct the volume holographic surface, generate the volume holographic optical element 15, establish the correspondence between the exposure coefficient and phase function polynomial of the volume holographic optical element and the optical wavefront, and obtain the chromatic aberration and the magnitude of monochromatic aberration generated by the volume holographic surface;

[0036] Step 2: Based on the chromatic aberration and the magnitude of monochromatic aberration generated by the volume holographic surface, according to the compensation principle of generating opposite chromatic aberration and monochromatic aberration, use the phase function polynomial of the diffractive optical element to construct the diffractive surface and generate the diffractive optical element 13;

[0037] Step 3: Use the free-form surface polynomial to construct the free-form surface, generate the free-form optical lens 12 and the free-form optical prism 14, establish the correspondence between the parameters of the free-form surface polynomial and the actual surface, and thus perform ray tracing to obtain the chromatic aberration and the magnitude of monochromatic aberration generated by each surface;

[0038] Step 4: Considering that the total aberration of the system is the sum of the aberrations of each surface, obtain the relationship between the total aberration of the system and the parameters of each surface, and through optimization and solution, obtain the parameter combination that minimizes the chromatic aberration and monochromatic aberration of the system;

[0039] Step 5: Use the parameter combination obtained in Step 4 as the processing parameters for the free-form optical lens 12, the diffractive optical element 13, the free-form optical prism 14, and the volume holographic optical element 15 for processing.

[0040] In a specific embodiment of the present invention, as Figure 1 shown, the first transmission surface 121 and the second transmission surface 122 of the free-form optical lens 12, the first optical transmission surface 141, the second optical reflection surface 142, and the third optical transmission surface 143 of the free-form optical prism 14 are all free-form surfaces. The free volume holographic optical element 15 is attached to the front surface 161 of the curved optical combiner 16. The front surface 161 and the rear surface 162 of the curved optical combiner 16 are both curved surfaces. The fact that 161 and 162 are curved surfaces utilizes the bendable characteristics of the free volume holographic optical element and is more in line with the human body process.

[0041] In an embodiment of the present invention, as a preferred solution of this embodiment, the material of the free-form optical lens 12 is OKP4HT_OSAKA, and the materials of the diffractive optical element 13 and the free-form optical prism 14 are PMMA.

[0042] According to the visual optical imaging device of the present invention, the free-form volume holographic optical element not only breaks the traditional law of refraction and reflection, enabling large-angle unconventional refraction and reflection, but also breaks the preparation method of exposing with traditional spherical waves and plane waves by using a well-regulated free-form wavefront, greatly improving the aberration correction ability of the holographic optical element, significantly reducing the volume and weight of the entire system, and at the same time, the light in the transmission direction can still normally transmit into the human eye, thus realizing an ultra-thin and light-weight binocular near-eye display.

[0043] Aiming at the problem of introducing system chromatic aberration by the volume holographic optical element, the unique dispersion characteristics of the diffractive optical element are used to compensate the dispersion of the volume holographic optical element, and the chromatic aberration and monochromatic aberration of the system are successfully corrected in cooperation with the free-form optical element. At the same time, the diffractive optical element has a larger angular bandwidth and spectral width than the volume holographic optical element, making the system structure more flexible and the diffraction efficiency higher. Considering the high wavelength selectivity of the volume holographic optical element, the present system is set with a spectral width of 6 nm for each of the RGB three colors. In order to make the system applicable to the RGB three-color light, the free-form volume holographic optical element is exposed with different object lights and reference lights for the RGB three-color lights respectively, and the parameters of other optical elements are kept unchanged during the design. In order to solve the problem of non-overlapping of the RGB three-color images that may occur when the system performs RGB full-color display, the control system controls the relative position offset of the RGB three-color images formed on the human eye, and controls the relative position offset within the limit resolution of the human eye, so that the system can perform RGB full-color display with higher quality.

[0044] The two visual optical imaging devices are arranged symmetrically left and right mirror images, that is, a near-eye display system is formed. Based on the above-mentioned idea of solving the system chromatic aberration problem, the present invention further provides a method for controlling the chromatic aberration of the near-eye display system:

[0045] Step 1: Select an initial structure for the near-eye display system, including a diffractive optical element, a free-form volume holographic optical element, and a free-form optical element.

[0046] Step 2: Use the exposure coefficient and phase function polynomial of the volume holographic optical element to construct the volume holographic surface, use the phase function polynomial of the diffractive optical element to construct the diffractive surface, and use the free-form surface polynomial to construct the free-form surface. Considering that the total chromatic aberration of the system is the sum of the chromatic aberrations of each surface, establish the corresponding relationship between the total chromatic aberration of the system and the parameters of each surface. Here, the chromatic aberration refers to the monochromatic chromatic aberration corresponding to the three colors of red, green, and blue.

[0047] Step 3: The simulation system performs ray tracing to generate the images formed by the red, green, and blue three colors respectively. Due to the chromatic aberration between the red, green, and blue three colors, there is a relative position offset between the three images. Establish the corresponding relationship between the relative position offset of the three images and the parameters of each surface.

[0048] Step 4: Based on the correspondence between the single-color chromatic aberration of the red, green, and blue channels of the system, the relative position offsets of the red, green, and blue channel images, and the parameters of each surface, through optimization and solution, obtain a parameter combination that can make the relative position offsets of the red, green, and blue channel images less than the human eye's limit of resolution and at the same time minimize the single-color chromatic aberration of the red, green, and blue channels of the system; use the obtained parameter combination to process the near-eye display system to achieve chromatic aberration control.

[0049] The optical surface parameters according to the embodiments of the present invention can be represented by Table 1 below. Here, a reverse design method is used, that is, starting from the eye position, the actual light propagation is traced backward. Table 2A shows the XY polynomial free-form surface coefficients of the first transmission surface 121 and the second transmission surface 122 of the free-form optical lens 12. Table 2B shows the XY polynomial free-form surface coefficients of the first optical transmission surface 141, the second optical reflection surface 142, and the third optical transmission surface 143 of the free-form optical prism 14. Table 3 shows the phase functions of the diffractive optical element 13 made for RGB three-color light. Table 4 shows the position parameters of the object light and the reference light when making the free-form holographic optical element 15 for RGB three-color light. Table 5 shows the phase perturbation added when making the free-form holographic optical element 15 for RGB three-color light:

[0050] Table 1

[0051]

[0052] Table 2A

[0053]

[0054]

[0055] Table 2B

[0056]

[0057]

[0058] The XY polynomial free-form surface equation describing the free-form surface is:

[0059]

[0060] where R is the radius of curvature of each surface, x, y, and z are the coordinates of points on the surface, K is the quadratic coefficient of the surface, p is the highest-order coefficient, C (m,n) is the coefficient corresponding to the polynomial term x m y n of, m is the exponent of x, and n is the exponent of y.

[0061] Table 3

[0062]

[0063]

[0064] The equation describing the mathematical model of the diffractive optical element is as follows:

[0065]

[0066] where is the phase distribution characterized by a polynomial on the diffractive surface, is the central wavelength at which the diffractive optical element operates, p is the highest-order coefficient, C (m,n) is the coefficient corresponding to the polynomial term x m y n of, m is the exponent of x, n is the exponent of y; d is the annular depth of the diffractive surface, q is the diffraction order, n0 is the refractive index of the substrate material at the central wavelength, and n i is the refractive index of the incident medium.

[0067] Table 4

[0068]

[0069] Table 5

[0070]

[0071]

[0072] The equation describing the mathematical model of the free-form hologram is as follows:

[0073]

[0074] where q is the diffraction order, is the phase distribution on the free-form hologram surface, is the phase distribution of the reference light on the free-form hologram, is the phase distribution of the object light on the free-form hologram, is the phase perturbation characterized by a polynomial, λ0 is the light wavelength during recording, p is the highest-order coefficient, C (m,n) is the coefficient corresponding to the polynomial term x m y n of, m is the exponent of x, n is the exponent of y.

[0075] The free-form holographic optical element 15 is arranged facing the human eye, and its exit pupil diameter is 10 mm, with a relatively large exit pupil, which enhances the user's immersion; moreover, the effective exit pupil distance of the binocular near-eye display system in the present invention can reach 30 mm.

[0076] The field of view of the embodiment of the present invention is equivalent to the field of view generated by an object plane with a size of 397 mm × 705 mm at a distance of 2 m; the field of view size, exit pupil diameter, and exit pupil distance of the system can be represented by Table 6.

[0077] Table 6

[0078]

[0079] Considering the high wavelength selectivity of the volume holographic optical element, the imaging system of the present invention is provided with a spectral width of 6 nm for each of the RGB three colors, and the central wavelengths of RGB are 639 nm, 532 nm, and 473 nm respectively, corresponding to the central wavelengths of the diffractive optical element and the volume holographic optical element; the wavelength setting of the system can be represented by Table 7.

[0080] Table 7

[0081]

[0082] The MTF curve graphs of the imaging system of the present invention for the RGB three colors are shown in Appendix Figure 2A 、 Figure 2B and Figure 2C ; it reaches more than 20% of 80 line pairs on the image plane, and the separation between the meridian and the sagittal is small.

[0083] The distortion graphs of the imaging system of the present invention for the RGB three colors are shown in Appendix Figure 3 ; the grid part composed of straight lines is the ideal position on the image plane, and the position of the cross point with a star is the schematic diagram of the distortion graph of the simulated actual system; due to the large field of view, there is a pincushion distortion with a value less than 8%, but it meets the basic imaging quality requirements; the distortion positions of the RGB three colors basically overlap, and the relative position offset is within the limit resolution of the human eye.

[0084] The image display 11 serving as the image source element in the present invention can be adapted to high-PPI micro display elements such as OLED micro displays and MicroLED micro displays.

[0085] Furthermore, the front and rear surfaces of the free-form optical lens and the three surfaces of the free-form optical prism are all XY polynomial free-form surfaces. However, the optical structure of the present invention is not limited to this. Those skilled in the art can understand that other structural forms can also meet the needs of the present invention. For example, using other surface types, or using more free-form optical lenses to achieve higher image quality.

[0086] The above are only the embodiments of the present invention, and do not impose any formal restrictions on the structure of the present invention. Any simple modifications, equivalent changes, and decorations made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solutions of the present invention.

Claims

1. A visual optical imaging device with a curved optical combiner for full-color display, characterized in that, It includes an image microdisplay (11), a free-form optical lens (12), a diffractive optical element (13), a free-form optical prism (14), and a curved optical combiner (16) with a free-form holographic optical element (15) attached thereto; the image signal light emitted by the image microdisplay (11) is refracted by the free-form optical lens (12), then diffracted by the diffractive optical element (13), and then refracted and reflected by the free-form optical prism (14) and incident on the curved optical combiner (16), and finally diffracted by the free-form holographic optical element (15) attached to the curved optical combiner and enters the human eye. On the other hand, ambient light enters the human eye after passing through the curved optical combiner (16) and the free-form holographic optical element (15) by transmission; The free-form optical lens (12), diffractive optical element (13), free-form optical prism (14), and free-form holographic optical element (15) are designed by the following steps: Step 1: Use the exposure coefficient and phase function polynomial of the free-form holographic optical element to construct a volume holographic surface, generate the free-form holographic optical element (15), establish the correspondence between the exposure coefficient and phase function polynomial of the free-form holographic optical element and the optical wavefront, and obtain the chromatic aberration and the magnitude of monochromatic aberration generated by the volume holographic surface; Step 2: Based on the chromatic aberration and the magnitude of monochromatic aberration generated by the volume holographic surface, according to the compensation principle of generating opposite chromatic aberration and monochromatic aberration, use the phase function polynomial of the diffractive optical element to construct a diffractive surface and generate the diffractive optical element (13); Step 3: Use the free-form surface polynomial to construct a free-form surface, generate the free-form optical lens (12) and the free-form optical prism (14), establish the correspondence between the parameters of the free-form surface polynomial and the actual surface, and thus perform ray tracing to obtain the chromatic aberration and the magnitude of monochromatic aberration generated by each surface; Step 4: Considering that the total aberration of the system is the sum of the aberrations of each surface, obtain the relationship between the total aberration of the system and the parameters of each surface, and through optimization and solution, obtain the parameter combination that minimizes the chromatic aberration and monochromatic aberration of the system; Step 5: Use the parameter combination obtained in Step 4 as the processing parameters of the free-form optical lens (12), diffractive optical element (13), free-form optical prism (14), and free-form holographic optical element (15) for processing.

2. The visual optical imaging device according to claim 1, wherein The image microdisplay (11) is a self-luminous microdisplay.

3. The visual optical imaging device according to claim 1, wherein The free-form optical lens (12) includes a first transmission surface (121) and a second transmission surface (122), and at least one of these two surfaces is a free-form surface, and the other is an aspherical surface or a free-form surface.

4. The visual optical imaging device according to claim 1, wherein The diffractive optical element (13) includes a plane (131) and a diffractive surface (132). Light first refracts into the diffractive optical element (13) on the plane (131), and then diffracts out of the diffractive optical element (13) on the diffractive surface (132). The diffractive surface (132) has a series of diffractive units, and each diffractive unit regulates the wavefront phase distribution. The parameters of the phase distribution function are matched based on the principle of correcting system aberrations and compensating for the chromatic aberration introduced by the free-form holographic optical element (15) at the same time.

5. The visual optical imaging device according to claim 1, wherein The free-form optical prism (14) includes a first optical transmission surface (141), a second optical reflection surface (142), and a third optical transmission surface (143). At least one of these three surfaces is a free-form surface, and the other two surfaces are aspherical or free-form surfaces. The light incident on the free-form optical prism (14) first refracts through the first optical transmission surface (141), then reflects through the second optical reflection surface (142), then undergoes total internal reflection on the first optical transmission surface (141), and finally refracts out of the prism through the third optical transmission surface (143).

6. The visual optical imaging device according to claim 1, characterized in that, The curved optical combiner (16) includes a front surface (161) and a rear surface (162), and both the front and rear surfaces have set curvature radii. The free-form holographic optical element (15) is attached to the front surface (161) close to the human eye. The free-form holographic optical element (15) is composed of a free-form holographic optical film. The light incident on the free-form holographic optical element (15) through the free-form optical prism (14) satisfies the Bragg incident relationship of the free-form holographic optical element (15), and thus is diffracted into the human eye. The ambient light incident through the curved optical combiner (16) does not satisfy the Bragg incident relationship of the free-form holographic optical element (15), and thus is transmitted into the human eye.

7. The visual optical imaging device according to claim 6, wherein The free-form holographic optical element (15) is a structure in which red, green, and blue are composite-exposed in the same layer of film, or a structure in which red, green, and blue are separately exposed in three layers of film and then stacked, or a structure in which two of red, green, and blue are composite-exposed in the same layer of film, and the other color is separately exposed in another layer of film, and then the two layers of film are stacked.

8. A near-eye display system with a curved optical combiner for full-color display, characterized in that, It includes two visual optical imaging devices according to any one of claims 1-7, and the two visual optical imaging devices are left-right mirror-symmetric.

9. A method for controlling chromatic aberration of the near-eye display system according to claim 8, characterized in that, It includes four steps: Step 1: Select an initial structure for the near-eye display system, including a diffractive optical element, a free-form holographic optical element, and a free-form optical element. Step 2: Use the exposure coefficient and phase function polynomial of the free-form holographic optical element to construct the volume holographic surface, use the phase function polynomial of the diffractive optical element to construct the diffractive surface, and use the free-form surface type polynomial to construct the free-form surface. Considering that the total chromatic aberration of the system is the sum of the chromatic aberrations of each surface, establish the corresponding relationship between the total chromatic aberration of the system and the parameters of each surface. Here, the chromatic aberration refers to the monochromatic chromatic aberration corresponding to red, green, and blue. Step 3: The simulation system performs ray tracing to generate images formed by red, green, and blue light respectively. Due to the chromatic aberration between red, green, and blue, there is a relative position offset among the three images. Establish the corresponding relationship between the relative position offsets of the three images and the parameters of each surface. Step 4: Synthesize the chromatic aberration of red, green, and blue monochromatic colors in the system and the corresponding relationship between the relative position offsets of red, green, and blue color images and the parameters of each surface. Through optimization and solution, obtain a parameter combination that satisfies making the relative position offsets of red, green, and blue color images less than the human eye's limit of resolution while minimizing the chromatic aberration of red, green, and blue monochromatic colors in the system. Use the obtained parameter combination to process the near-eye display system to achieve chromatic aberration control.

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