A single-channel light and small augmented reality near-eye display system

Abstract

The present application relates to a kind of light small enhanced reality near-eye display systems, and the system is combined by two mirror symmetry visual optical imaging devices, each visual optical imaging device includes 1 piece of free curved surface element, 2 pieces of glass flat plate, 1 piece of optical filter, 2 pieces of free body holographic element and 1 image micro display.The signal light emitted by image micro display is filtered into specific wavelength range by optical filter, then passes through subsequent optical system and finally enters human eye imaging.Meanwhile, external light can also be transmitted into human eye, to realize ultra-thin light double near-eye display.The design of the free curved surface element multi-surface common body greatly reduces the volume and weight of optical path, and reduces the influence of stray light and positioning difficulty, improves the overall performance of the system.

Description

Technical Field

[0001] This invention relates to the field of near-eye display technology, and more particularly to a single-channel, lightweight, and compact augmented reality near-eye display system. Background Technology

[0002] Augmented Reality (AR) is a technology that overlays virtual information onto real-world information, enriching various sensory experiences such as vision, hearing, smell, and even touch. It has enormous market application value in multimedia entertainment, as well as in military, industrial, and medical fields.

[0003] Volume holographic optical elements (VHOEs) are used in lightweight AR devices. They are optical elements made based on the principles of holography. Typically fabricated on a photosensitive thin film material, they utilize the interference between a reference light wave and an object light wave to form a corresponding refractive index distribution on the photosensitive material. When illuminated again, the light undergoes unconventional large-angle deflection due to diffraction. It is a diffraction element.

[0004] The key to AR devices lies in the immersive user experience. Miniaturization, lightweight design, large field of view, large eye-box, and high performance are the current development trends of AR devices. Existing near-eye display devices employ various solutions, such as Epson's freeform waveguide solution, Lumus' array waveguide solution, Google Glass's coaxial side-view prism solution, HoloLens' holographic grating solution, and OPPO Air Glass's diffractive waveguide solution. Our research group has also proposed some solutions before, but these inevitably use multiple optical components. Therefore, the positioning between these components is crucial. If the positioning error of any one component is too large, the imaging effect of the entire system will be greatly reduced. The previous optical path had many folds, which aggravated the influence of stray light, resulting in ghosting and affecting the user experience. In terms of size, the excessive number of optical path folds in the horizontal direction prevented the size from being reduced, affecting the aesthetics and comfort of wearing them. Summary of the Invention

[0005] The present invention aims to provide a single-channel, lightweight, and compact augmented reality near-eye display system. The near-eye display system is composed of two mirror-symmetrical visual optical systems. It achieves a thin and light optical transmissive binocular near-eye display by correcting chromatic aberration and monochromatic aberration through two free-body holographic optical elements, which can be applied to AR and VR application scenarios.

[0006] The present invention first provides a single-channel lightweight augmented reality near-eye display system, which is composed of two mirror-symmetric visual optical imaging devices. Each visual optical imaging device includes an image microdisplay, a filter, a freeform surface element, a first free-body holographic optical element, a first glass plate, a second free-body holographic optical element, and a second glass plate; wherein the first free-body holographic optical element and the second free-body holographic optical element are respectively attached to the surfaces of the first glass plate and the second glass plate;

[0007] The freeform surface element is a prism, which includes at least a first surface, a second surface, and a third surface, and the first surface, the second surface, and the third surface are all xy polynomial freeform surfaces;

[0008] The image signal light generated by the image microdisplay, after passing through a filter, is incident on the first surface of a freeform surface element, and then, after passing through the second surface, is incident on a first free-body holographic optical element. The image signal light satisfies the Bragg diffraction condition of the first free-body holographic optical element, resulting in diffraction on its surface. The diffracted light then passes through the second surface again, exits from the third surface, and is incident on a second free-body holographic optical element. There, the image signal light satisfies the Bragg diffraction condition of the second free-body holographic optical element, resulting in diffraction on its surface, before entering the human eye. Simultaneously, ambient light, not satisfying the Bragg condition of the second free-body holographic optical element, is directly transmitted into the human eye for image formation.

[0009] The freeform surface element is designed using the following process:

[0010] 1) Define the three requirements for freeform surface element design:

[0011] a) Calculate the coordinates of the light rays landing on the three surfaces of the freeform element using the laws of refraction and diffraction; based on the principle that the light rays landing on the first and third surfaces do not overlap, adjust the coordinates of the landing points by adjusting the surface shape and relative position of each surface; the relationship between the landing point coordinates and the surface shape is as follows: the direction of the incident light rays on the three surfaces can be calculated from the landing point coordinates, and then the normal direction of each surface can be calculated according to the law of refraction to obtain the surface shape of each surface.

[0012] b) Using imaging and distortion formulas, control the point and size of light rays falling on the virtual image surface formed at the eye's viewing distance to minimize distortion while maintaining image quality. Specifically, adjust the surface shape and relative position of each surface of the freeform element so that the size of the point where light rays from each field of view converge at the virtual image surface is smaller than the resolution of the human eye. Use the difference between the point of light falling on the virtual image surface of each field of view and the ideal position as the condition for distortion control, and adjust the surface shape and relative position of each surface of the freeform element to minimize distortion.

[0013] c) Adjust the surface shape and relative position of each surface of the freeform element so that the light rays incident on each field of view of the free volume holographic element satisfy its Bragg condition, thereby maximizing and homogenizing the efficiency of the free volume holographic element in the full field of view.

[0014] 2) Set the surface shape coefficients and relative positions of each surface of the freeform surface element as optimization variables, and take the three requirements in step 1) as three optimization terms. Assign each optimization term its own weight, and sum the three optimization terms to form the optimization problem.

[0015] 3) Use the least squares method to obtain the optimal solution of the optimization problem, and design the freeform surface element based on the surface coefficients and relative positions of each surface of the freeform surface element in the optimal solution.

[0016] As a preferred embodiment of the present invention, the freeform surface element is a freeform surface prism with three coexisting surfaces.

[0017] As a preferred embodiment of the present invention, the first free-body holographic optical element is attached to the front surface of the first glass plate; the image signal light generated by the image microdisplay is incident on the first free-body holographic optical element after passing through a filter, thereby satisfying the Bragg condition of the first free-body holographic optical element.

[0018] As a preferred embodiment of the present invention, the second free-body holographic optical element is attached to the front surface of the second glass plate; the light transmitted from the third surface of the free-form surface element to the second free-body holographic optical element satisfies the Bragg condition of the second free-body holographic optical element; ambient light is incident on the second holographic optical element through the second glass plate and does not satisfy the Bragg condition of the second holographic optical element.

[0019] As a preferred embodiment of the present invention, the image microdisplay can be an OLED microdisplay, an LCOS microdisplay, or a MicroLED microdisplay.

[0020] As a preferred embodiment of the present invention, the filter and the image microdisplay have a predetermined air gap for separable installation.

[0021] As a preferred embodiment of the present invention, the front and rear surfaces of the first glass plate are both planar, and the front and rear surfaces of the second glass plate are both planar.

[0022] The present invention also provides a near-eye display method for the above-mentioned near-eye display system, which includes the following steps:

[0023] In the left-side single-channel lightweight augmented reality near-eye display system, the image signal light generated by its image microdisplay is filtered and then incident on the first surface of the freeform surface element. After passing through the second surface, it is incident on the first free-body holographic optical element. Due to the Bragg diffraction condition of the first free-body holographic optical element, diffraction occurs on the surface of the first free-body holographic optical element. The reflected light passes through the second surface of the freeform surface element again, exits from the third surface, and is incident on the second free-body holographic optical element. Due to the Bragg diffraction condition of the second free-body holographic optical element, diffraction occurs on the surface of the second free-body holographic optical element, and the reflected light enters the left eye. Ambient light, because it does not meet the Bragg condition of the second free-body holographic optical element, is directly transmitted into the human eye for imaging.

[0024] Because the right-side near-eye display system has the same structure and operation as the left-side near-eye display system, optical transmission binocular near-eye display can be achieved through the mirror symmetry of the left and right sides.

[0025] The beneficial effects of the present invention include: the visual optical imaging device according to the present invention, by employing freeform surface optical elements and free volume holographic optical elements, greatly improves the degree of freedom of aberration correction of the system while significantly reducing the size and weight of the system, achieving high performance and miniaturization of the near-eye display system. More importantly, the three-sided prism design of the freeform surface optical elements greatly reduces the number of optical elements in the optical path, making positioning much easier and improving system stability. At the same time, it reduces the number of optical path folds, reduces the impact of stray light on the system, and improves the system's usability.

[0026] The three surfaces of the freeform surface element in this invention must not only meet the Bragg conditions of two free-body holographic optical elements, satisfying specific optical path orientations while maximizing efficiency across the entire field of view, but also correct for the significant distortion and off-axis aberrations caused by large-angle deflection of light due to diffraction, while maintaining a simple and compact overall structure. After light is emitted from the image microdisplay, it undergoes refraction and diffraction to eventually reach a corresponding optical path. However, this is only one of many feasible optical paths, and there may be situations where the average efficiency across the entire field of view is not high and the efficiency uniformity is poor. Therefore, this design also needs to satisfy the Bragg conditions of the free-body holographic element to achieve the highest diffraction efficiency. Since the field of view of this design is relatively large, it is impossible to adjust the efficiency of each field of view to the maximum. There must be mutual constraints, requiring continuous trade-offs to reach a balance point. Meanwhile, using a three-sided freeform surface element to simultaneously satisfy the requirements of two freeform holographic elements is limited by the fact that it only has three surfaces and the law of refraction, which restricts the angle and range of light rays incident on these three surfaces, further constraining the entire optical path. These conditions are mutually restrictive, yet their intersection must be continuously found. Therefore, this invention creatively proposes a design method for a freeform surface element suitable for the near-eye display system of this invention. Attached Figure Description

[0027] Figure 1 This is an optical path diagram of a visual optical imaging device provided in an embodiment of the present invention;

[0028] Figure 2 This is an MTF curve diagram of an embodiment of the present invention;

[0029] Figure 3 This is a distortion curve diagram of an embodiment of the present invention;

[0030] In the figure, 11 is an image microdisplay, 12 is a filter, 13 is a freeform surface element, 131 is the first surface of the freeform surface element, 132 is the second surface of the freeform surface element, 133 is the third surface of the freeform surface element, 14 is a first free-body holographic element, 15 is a first glass plate, 151 is the front surface of the first glass plate, 152 is the rear surface of the first glass plate, 16 is a second free-body holographic element, 17 is a second glass plate, 171 is the front surface of the second glass plate, and 172 is the rear surface of the second glass plate. Detailed Implementation

[0031] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The present invention may be implemented in many different forms and should not be construed as limited to the embodiments described below. Rather, these embodiments are provided so that the disclosure is sufficient and complete and fully conveys the concept of the present invention to those skilled in the art.

[0032] The binocular near-eye display system according to an embodiment of the present invention includes two sets of freeform surface-free volume holographic visual optical imaging devices relative to the human eye. In the following description, the specific implementation of the present invention will be described with the visual optical imaging device on the left relative to the human eye as the specific object. Those skilled in the art will understand that the visual optical imaging device on the right has the same structure as the left, only mirror image.

[0033] like Figure 1 As shown, the left-side visual optical system provided in this embodiment of the invention includes an image microdisplay 11, a filter 12, a freeform surface element 13, a first free-body holographic element 14, a first glass plate 15, a second free-body holographic element 16, and a second glass plate 17. The image signal light generated by the image microdisplay 11 passes through the filter 12 and the first surface 131 and the second surface 132 of the freeform surface element 13 before being incident on the first free-body holographic optical element 14. Due to the Bragg condition of the first free-body holographic optical element 14 being satisfied, the light diffracts on the surface of the first free-body holographic optical element, reflecting the light to the second surface 132 of the freeform surface element 13, and then through the third surface 133 to be transmitted onto the second free-body holographic optical element 16. Due to the Bragg condition of the second free-body holographic optical element 16 being satisfied, the light diffracts on its surface, and the diffracted light enters the user's eye and forms an image. On the other hand, ambient light is incident on the second free-body holographic optical element 16 through the second glass plate 17. Since the Bragg condition of the second free-body holographic optical element 16 is not satisfied, the light does not diffract and passes directly through the second free-body holographic optical element 16 before entering the human eye, thus realizing optical transmission-type near-eye display.

[0034] Specifically, such as Figure 1 As shown, the three surfaces 131, 132 and 133 of the freeform surface element 13 are all freeform surfaces. The first free-body holographic optical element 14 is attached to the front surface 151 of the first glass plate 15. The front surface 151 and the rear surface 152 of the first glass plate 15 are both planar. The second free-body holographic optical element 16 is attached to the front surface 171 of the second glass plate 17. The front surface 171 and the rear surface 172 of the second glass plate 17 are both planar.

[0035] In this embodiment of the invention, the freeform surface element 13 is designed using the following method:

[0036] 1) Define the three requirements for freeform surface element design:

[0037] a) Calculate the coordinates of the light rays landing on the three surfaces of the freeform element using the laws of refraction and diffraction; based on the principle that the light rays landing on the first and third surfaces do not overlap, adjust the coordinates of the landing points by adjusting the surface shape and relative position of each surface; the relationship between the landing point coordinates and the surface shape is as follows: the direction of the incident light rays on the three surfaces can be calculated from the landing point coordinates, and then the normal direction of each surface can be calculated according to the law of refraction to obtain the surface shape of each surface.

[0038] b) Using imaging and distortion formulas, control the point and size of light rays falling on the virtual image surface formed at the eye's viewing distance to minimize distortion while maintaining image quality. Specifically, adjust the surface shape and relative position of each surface of the freeform element so that the size of the point where light rays from each field of view converge at the virtual image surface is smaller than the resolution of the human eye. Use the difference between the point of light falling on the virtual image surface of each field of view and the ideal position as the condition for distortion control, and adjust the surface shape and relative position of each surface of the freeform element to minimize distortion.

[0039] c) Adjust the surface shape and relative position of each surface of the freeform element so that the light rays incident on each field of view of the free volume holographic element satisfy its Bragg condition, thereby maximizing and homogenizing the efficiency of the free volume holographic element in the full field of view.

[0040] 2) Set the surface coefficients of each surface of the freeform surface element and the relative positions of each surface as optimization variables. Take the three requirements in step 1) as three optimization terms, assign each optimization term its own weight, and sum the three optimization terms to form the optimization problem. In this invention, each optimization term is a function of the optimization variables. The value of the optimization term represents the score of the term when the optimization variables are selected as the corresponding surface coefficients and the relative positions of each surface. The goal of solving the optimization problem is to find the optimal solution that minimizes the total score.

[0041] 3) Use the least squares method to obtain the optimal solution of the optimization problem, and design the freeform surface element based on the surface coefficients and relative positions of each surface of the freeform surface element in the optimal solution.

[0042] In this embodiment of the invention, the freeform surface element 13 is a preferred embodiment, and its material is OKP4HT, while the material of the filter 12 is HK9_NHG.

[0043] According to the visual optical imaging device of the present invention, the free-form holographic optical element not only breaks the traditional law of refraction and reflection, enabling unconventional refraction and reflection at large angles, but also, by employing a well-controlled free-form wavefront for exposure, breaks away from the traditional methods of exposure using spherical waves and plane waves. This significantly improves the aberration correction capability of the volume holographic optical element, substantially reduces the size and weight of the entire system, and allows for the correction of chromatic aberration by combining two free-form holographic optical elements to achieve imaging within a certain spectral width, realizing high performance and miniaturization of the near-eye display system. More importantly, the three-sided prism design of the free-form optical element greatly reduces the number of optical elements in the optical path, significantly reducing positioning difficulty and improving system stability; it also reduces the number of optical path reflections, lowers the impact of stray light on the system, and improves the system's usability. Simultaneously, light in the transmission direction can still pass normally into the human eye, thereby achieving an ultra-thin and lightweight binocular near-eye display.

[0044] The optical surface parameters according to embodiments of the present invention can be represented by Table 1 below, designed with the human eye pupil as the aperture. Table 2 shows the first surface 131, the second surface 132, and the second surface 133 in the freeform surface element. Table 3 shows the relevant parameters of the first free-body holographic optical element 13 and the second free-body holographic optical element 16:

[0045] Table 1

[0046]

[0047] Table 2

[0048]

[0049] The XY polynomial equation describing a freeform surface is:

[0050]

[0051] Where R is the radius of curvature of each surface, x, y, z are the coordinates of points on the surface, K is the quadratic coefficient of the surface, p is the highest-order coefficient, and C... (m,n) For the corresponding polynomial term x m y n The coefficients, m is the exponent of x, and n is the exponent of y.

[0052] Table 3

[0053]

[0054] The equations describing the mathematical model of a free-body holography are:

[0055]

[0056]

[0057] Where d is the diffraction order, and φ HOE It is the phase distribution on the free-body holographic surface, φ R It is the phase distribution of the reference light on the free-body hologram, φ o It is the phase distribution of the object light on a free-body hologram, φ p The phase perturbation is characterized by a polynomial, where λ is the wavelength of light during recording, p is the highest-order coefficient, and C... (m,n) For the corresponding polynomial term x m y n The coefficients, where m is the exponent of x and n is the exponent of y. Where φ p This is something that ordinary volume holographic optical elements do not possess. It is precisely because of this that our free volume holographic optical elements can correct more aberrations, making the entire system lighter.

[0058] Table 4 shows the diffraction efficiencies of each field of view calculated according to coupled-wave theory under full-field (15 fields of view) conditions. The average efficiency of the full-field is 30.2%, and the uniformity (RMS) is 6.3%.

[0059] Table 4

[0060]

[0061] The second holographic optical element 16 is positioned directly facing the human eye, with an exit pupil of 5mm*5mm rectangle. The relatively large exit pupil enhances the user's immersive experience. Furthermore, the effective exit pupil distance of the binocular near-eye display system in this invention can reach 30mm. The field of view of this invention reaches a diagonal of 20°, with a working center wavelength of 532nm and a spectral width of 8nm.

[0062] The MTF curve of the imaging system of this invention is attached. Figure 2 The image plane has a line pair ratio of over 20% and a meridional-sagittal separation of less than 60 lines.

[0063] The distortion diagram of the imaging system of the present invention is shown in the appendix. Figure 3 The uniform grid formed by darker lines represents the ideal position on the image plane, while the non-uniform grid formed by lighter curves represents the distortion pattern of the simulated actual system. Due to the large field of view, there is some trapezoidal distortion, but the basic imaging quality requirements are met.

[0064] The image microdisplay 11, which serves as the image source element in this invention, can be adapted to high PPI microdisplay elements such as OLED microdisplays, LCOS microdisplays, and MicroLED microdisplays.

[0065] Furthermore, all three surfaces of the freeform surface element are XY polynomial freeform surfaces. However, the optical structure of the present invention is not limited to this. Those skilled in the art will understand that other structural forms can also meet the needs of the present invention, for example, using other surface shapes or using more optical lenses to achieve higher image quality.

[0066] When using this invention, in the left-side single-channel lightweight augmented reality near-eye display system, the image signal light generated by its image microdisplay is filtered and then incident on the first surface of the freeform surface element. After passing through the second surface, it is incident on the first free-body holographic optical element. Due to the Bragg diffraction condition of the first free-body holographic optical element being satisfied, diffraction occurs on the surface of the first free-body holographic optical element. The reflected light passes through the second surface of the freeform surface element again, exits from the third surface, and is incident on the second free-body holographic optical element. Due to the Bragg diffraction condition of the second free-body holographic optical element being satisfied, diffraction occurs on the surface of the second free-body holographic optical element, and is reflected into the left eye. Ambient light, because it does not satisfy the Bragg condition of the second free-body holographic optical element, is directly transmitted into the human eye for imaging. The right-side near-eye display system has the same structure and working method as the left-side near-eye display system. Therefore, optical transmission binocular near-eye display can be realized through the mirror symmetry of the left and right sides.

[0067] The above description is merely an embodiment of the present invention and does not constitute any limitation on the structure of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A single-channel, lightweight, near-eye augmented reality display system, characterized in that... The system is composed of two mirror-symmetric visual optical imaging devices. Each visual optical imaging device includes an image microdisplay (11), a filter (12), a freeform surface element (13), a first free-body holographic optical element (14), a first glass plate (15), a second free-body holographic optical element (16), and a second glass plate (17); wherein the first free-body holographic optical element and the second free-body holographic optical element are respectively attached to the surfaces of the first glass plate and the second glass plate; The freeform surface element (13) is a prism, which includes at least a first surface, a second surface and a third surface, and the first surface, the second surface and the third surface are all xy polynomial freeform surfaces; The image signal light generated by the image microdisplay is filtered and then incident on the first surface of the freeform surface element. After passing through the second surface of the freeform surface element, it is incident on the first free-body holographic optical element. The image signal light satisfies the Bragg diffraction condition of the first free-body holographic optical element and diffracts on the surface of the first free-body holographic optical element. The diffracted light passes through the second surface of the freeform surface element again, exits from the third surface of the freeform surface element, and is incident on the second free-body holographic optical element. The image signal light satisfies the Bragg diffraction condition of the second free-body holographic optical element and diffracts on the surface of the second free-body holographic optical element before entering the human eye. At the same time, ambient light, which does not satisfy the Bragg condition of the second free-body holographic optical element, is directly transmitted into the human eye for imaging.

2. The near-eye display system according to claim 1, characterized in that, The freeform surface element (13) is designed using the following design process: 1) Define the three requirements for freeform surface element design: a) Calculate the coordinates of the light rays landing on the three surfaces of the freeform element using the laws of refraction and diffraction; based on the principle that the light rays landing on the first and third surfaces do not overlap, adjust the coordinates of the landing points by adjusting the surface shape and relative position of each surface; the relationship between the landing point coordinates and the surface shape is as follows: the direction of the incident light rays on the three surfaces can be calculated from the landing point coordinates, and then the normal direction of each surface can be calculated according to the law of refraction to obtain the surface shape of each surface. b) Using imaging and distortion formulas, control the point and size of light rays falling on the virtual image surface formed at the eye's viewing distance to minimize distortion while maintaining image quality. Specifically, adjust the surface shape and relative position of each surface of the freeform element so that the size of the point where light rays from each field of view converge at the virtual image surface is smaller than the resolution of the human eye. Use the difference between the point of light falling on the virtual image surface of each field of view and the ideal position as the condition for distortion control, and adjust the surface shape and relative position of each surface of the freeform element to minimize distortion. c) Adjust the surface shape and relative position of each surface of the freeform element so that the light rays incident on each field of view of the free volume holographic element satisfy its Bragg condition, thereby maximizing and homogenizing the efficiency of the free volume holographic element in the full field of view. 2) Set the surface shape coefficients and relative positions of each surface of the freeform surface element as optimization variables, and take the three requirements in step 1) as three optimization terms. Assign each optimization term its own weight, and sum the three optimization terms to form the optimization problem. 3) Use the least squares method to obtain the optimal solution of the optimization problem, and design the freeform surface element based on the surface coefficients and relative positions of each surface of the freeform surface element in the optimal solution.

3. The near-eye display system as described in claim 1, characterized in that, Image microdisplays include OLED microdisplays, LCOS microdisplays, and MicroLED microdisplays.

4. The near-eye display system as described in claim 1, characterized in that, An air gap with a predetermined interval is provided between the filter and the image microdisplay for separate mounting.

5. The near-eye display system as described in claim 1, characterized in that, The front surface (151) and rear surface (152) of the first glass plate (15) are both flat, and the front surface (171) and rear surface (172) of the second glass plate (17) are both flat.

6. A near-eye display method based on the near-eye display system of claim 1, characterized in that, Includes the following steps: In the left-side single-channel lightweight augmented reality near-eye display system, the image signal light generated by its image microdisplay is filtered and then incident on the first surface of the freeform surface element. After passing through the second surface, it is incident on the first free-body holographic optical element. Due to the Bragg diffraction condition of the first free-body holographic optical element, diffraction occurs on the surface of the first free-body holographic optical element. The reflected light passes through the second surface of the freeform surface element again, exits from the third surface, and is incident on the second free-body holographic optical element. Due to the Bragg diffraction condition of the second free-body holographic optical element, diffraction occurs on the surface of the second free-body holographic optical element, and the reflected light enters the left eye. Ambient light, because it does not meet the Bragg condition of the second free-body holographic optical element, is directly transmitted into the human eye for imaging. Because the right-side near-eye display system has the same structure and operation as the left-side near-eye display system, optical transmission binocular near-eye display can be achieved through the mirror symmetry of the left and right sides.

Images