Distortionless compact off-axis near-eye display optical system

Abstract

The present application relates to the field of optical imaging technology, and particularly relates to a non-distortion compact off-axis near-eye display optical system, which comprises a display, a first free curved surface element, a second free curved surface element, and a first sub-light path and a second sub-light path formed by the first free curved surface element and the second free curved surface element; one side of the top of the first free curved surface element is provided with a first light-in curve, a light-out curve is arranged below the light-in curve, and a first reflection curve and a second reflection curve are sequentially arranged from top to bottom on the side of the first free curved surface element away from the first light-in curve; one side of the second free curved surface element is provided with a fitting curve matched with the second reflection curve, and a second light-in curve is arranged on the side away from the fitting curve; the display corresponds to the first light-in curve. The present application has the characteristics of compact structure, small volume of optical parts, and high definition.

Description

Technical Field

[0001] This invention relates to the field of optical imaging technology, and more specifically to a distortion-free, compact off-axis near-eye display optical system. Background Technology

[0002] In recent years, with the development of virtual / augmented reality (VR) technology, related head-mounted display devices have emerged in large numbers. Because head-mounted displays are worn on the user's head, they must be lightweight and compact. Augmented reality technology overlays information from the virtual world with information from the real world, which is perceived by the user's eyes. Therefore, head-mounted displays must achieve a wide field of view and high definition, which places high demands on the structure of the optical system. Existing optical modules for VR display systems are mainly divided into coaxial catadioptric, holographic waveguide, and geometrical waveguide types. Coaxial catadioptric display modules offer high image clarity but are relatively bulky, and their field of view is limited by the structure, resulting in low light energy utilization. Holographic waveguide-based optical modules utilize the principle of optical diffraction. This structure allows the entire module to be made very thin and light, but color distortion caused by diffraction and the resulting limitation on the viewing angle are problems. Summary of the Invention

[0003] This invention provides a distortion-free, compact off-axis near-eye display optical system, which features a compact structure, small optical components, and high resolution.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a distortion-free compact off-axis near-eye display optical system, comprising: a display, a first freeform surface element, and a second freeform surface element, wherein the first freeform surface element and the second freeform surface element constitute a first sub-optical path and a second sub-optical path; a first light-incoming surface is provided on one side of the top of the first freeform surface element, and a light-outcoming surface is provided below the light-incoming surface; a first reflective surface and a second reflective surface are provided sequentially from top to bottom on the side of the first freeform surface element away from the first light-incoming surface; a fitting surface adapted to the second reflective surface is provided on one side of the second freeform surface element, and a second light-incoming surface is provided on the side away from the fitting surface; the display corresponds to the first light-incoming surface.

[0005] Preferably, the first sub-optical path is as follows: it enters through the first light-entry surface, and after being reflected three times by the first reflective surface, the light-exiting surface, and the second reflective surface, it is transmitted through the light-exiting surface again.

[0006] Preferably, the second sub-optical path is: entering through the second light-entry curved surface, and exiting sequentially through the bonding curved surface, the second reflective curved surface, and the light-exiting curved surface.

[0007] Preferably, the diagonal size of the display ranges from 0.65 to 0.75 inches, the field of view of the virtual image display optical path is greater than 45 degrees, and the distortion is less than 0.5%; the distance between the first reflective surface and the light-emitting surface is less than 11 mm.

[0008] Preferably, the second reflective surface is provided with a beam-splitting film, and the beam splitting ratio is 1:1.

[0009] The beneficial effects of this invention are as follows: light is emitted from the light-emitting surface of the display, passes through the protective glass plate covering the display, and then exits. The light then enters the first freeform surface element through the first light-incoming surface, is reflected by the first reflective surface, changes its propagation direction, and reaches the light-exiting surface for the first time. When the light first passes through the light-exiting surface, the angle of incidence satisfies the total internal reflection condition from an optically denser medium to an optically less dense medium, and total internal reflection occurs. The light then reaches the second reflective surface, which is coated with a beam-splitting film. The transmitted light continues to propagate forward until it disappears, while the reflected light reaches the light-exiting surface for the second time. At this time, the angle of incidence does not satisfy the total internal reflection condition, and the light can directly pass through the light-exiting surface and reach the system's exit pupil. The human eye can then observe the image displayed on the display after being magnified by the optical system. This system has a compact structure, small optical components, and high clarity. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 This is the overall optical path diagram of the present invention;

[0012] Figure 2 This is a schematic diagram of the virtual display light path and the perspective light path of the present invention;

[0013] Figure 3 This is a schematic diagram of the overall optical path of the present invention;

[0014] Figure 4 This is a schematic diagram of the optical path for virtual image display in this invention;

[0015] Figure 5 This is a schematic diagram of optical path distortion in the virtual image display of the present invention;

[0016] Figure 6 This is a schematic diagram showing the surface numbering of the optical elements in the virtual image display optical path of the present invention;

[0017] Figure 7 This is a schematic diagram of the optical path distortion of the present invention;

[0018] Figure 8 This is an optical path diagram of Embodiment 1 of the present invention. Detailed Implementation

[0019] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] according to Figure 1 , Figure 2 , Figure 3 As shown, a distortion-free, compact off-axis near-eye display optical system includes: a display 13, a first freeform surface element 12, and a second freeform surface element 14, forming a first sub-optical path and a second sub-optical path through the first freeform surface element 12 and the second freeform surface element 14; a first light-incident surface 12d is provided on one side of the top of the first freeform surface element 12, and a light-outcident surface 12a is provided below the light-incident surface 12d; a first reflective surface 12c and a second reflective surface 12b are provided sequentially from top to bottom on the side of the first freeform surface element 12 away from the first light-incident surface 12d; a fitting surface 14a adapted to the second reflective surface 12b is provided on one side of the second freeform surface element 14, and a second light-incident surface 14b on the side away from the fitting surface 14a; the display 13 corresponds to the first light-incident surface 12d.

[0021] In the above configuration, the first sub-optical path and the second sub-optical path share common optical components, namely the first freeform surface element and the second freeform surface element. In the first sub-optical path, the human eye can observe the image displayed on the monitor, magnified by the optical system.

[0022] like Figure 4 As shown, the virtual image display optical path of the present invention includes a display 13, a first freeform surface element 12, and an optical system exit pupil 11;

[0023] The light is emitted from the light-emitting surface 13b of the display 13, passes through the protective glass plate covering the display, and exits from 13a. Then, the light enters the first freeform surface element 12 through the first light-incoming surface 12d, is reflected by the first reflective surface 12c, changes its propagation direction, and reaches the light-exiting surface 12a for the first time. When the light passes through the light-exiting surface 12a for the first time, the angle of incidence of the light satisfies the total internal reflection condition from the optically denser medium to the optically less dense medium, and total internal reflection occurs. Then, it reaches the second reflective surface 12b, which is coated with a beam-splitting film. The transmitted light continues to propagate forward until it disappears. The reflected light reaches the light-exiting surface 12a for the second time. At this time, the angle of incidence of the light does not satisfy the total internal reflection condition. The light can directly pass through the light-exiting surface 12a and reach the system exit pupil 11. The human eye can then observe the image displayed on the display 13, which has been magnified by the optical system.

[0024] In order to achieve the purpose of beam splitting, the second reflective surface 12b needs to be coated with a beam splitting film. The preferred beam splitting ratio is 1:1, that is, when the light reaches the second reflective surface 12b, ideally 50% of the light is reflected, while the remaining light is transmitted.

[0025] The diagonal size of the display 13 used is in the range of 0.65 to 0.75 inches, and the aspect ratio should be greater than or equal to 16:9. Preferably, a Micro OLED display with high brightness and high resolution is used.

[0026] Specifically, when viewed from the exit pupil position of the system, the field of view of the virtual display optical path of the system is greater than 45°;

[0027] When viewed along the optical axis, the distance from the exit pupil 11 to the light-emitting curved surface 12a ranges from 17mm to 20mm.

[0028] In this system, using the local coordinate system of the exit pupil 11 as the reference coordinate system, the eccentricity range of the light-emitting surface 12a of the first freeform surface element 12 along the Y direction is 2mm to 3mm, and the tilt angle range around the X axis is 0° to 7°; the eccentricity range of the second reflective surface 12b along the Y direction is -1mm to 1mm, the eccentricity range along the Z axis is 22mm to 27mm, and the tilt angle range around the X axis is 20° to 30°; the eccentricity range of the first reflective surface 12c along the Y direction is 18mm to 23mm, and the tilt angle range around the Z axis is 22mm to 27mm. The eccentricity range of the first light-gathering surface 12d is 23mm to 27mm along the Y direction, 16mm to 21mm along the Z direction, and -35° to -25° around the X-axis; the eccentricity range of the first light-gathering surface 12d along the Y direction is 23mm to 27mm, the eccentricity range along the Z-axis is 16mm to 19mm, and the eccentricity range around the X-axis is -33° to -23°.

[0029] This system is an off-axis optical system. In order to correct off-axis aberrations caused by optical axis folding, some surfaces in the components need to be described using freeform surfaces.

[0030] To achieve a high-performance near-eye display system, the system's thickness must be constrained, with the thickness of optical components being less than 11 mm; additionally, the system's optical distortion must be constrained, with the distortion of the virtual display optical path being less than 0.5%.

[0031] The system's virtual image displays optical path distortion, such as Figure 5 As shown; the virtual display optical path uses only one optical element. In order to control the color difference of the system, this element needs to be designed with low dispersion material, and the material Abbe number should be at least greater than 55.

[0032] The perspective optical path in this invention is as follows Figure 6 As shown. It includes a first freeform surface element 12, a second freeform surface element 14, and an optical system exit pupil 11;

[0033] In this system, light emitted / reflected by objects in the real scene passes through the second freeform surface element 14, then through the first freeform surface element 12, and finally reaches the exit pupil 11 of the system, where the human eye can observe the real scene; in this system, when light passes through the first freeform surface element 12 and the second freeform surface element 14, it is equivalent to a lens without optical power.

[0034] Since the light-emitting surface 12a is a freeform surface, in order to correct off-axis aberration in the perspective direction, the second light-entering surface 14b of the second freeform surface element 14 is also described as a freeform surface to obtain a good perspective imaging effect; the bonding surface 14a and the second reflecting surface 12b have the same shape, which facilitates bonding the first and second freeform surface elements together; the first freeform surface element 12 and the second freeform surface element 14 have the same optical material to ensure uniform optical power in the perspective direction.

[0035] Virtual images display the distorted mesh of the optical path, such as Figure 7 As shown, the perspective distortion is less than 1.5%, which is not easily detected by the human eye.

[0036] Example 1: The specific implementation of the present invention will be described in detail with reference to the accompanying drawings. The present invention can 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.

[0037] The optical path of Example 1 is as follows Figure 8As shown. Among them, in order to correct the off-axis aberration of the system, the light-emitting surfaces 12a, 12b, 12c, and 14b are all freeform surfaces, and 12d is an aspherical surface.

[0038] The basic optical system parameters of the perspective light path are shown in Table 1, the aspherical coefficients are shown in Table 2, and the freeform surface coefficients are shown in Table 3. Among them, 12a is a multiplexed surface, and the light passes through this surface twice. The virtual display light path and the perspective light path share the light-emitting surface 12a.

[0039] Table 1 Optical system parameters of the virtual image display optical path

[0040]

[0041] Table 2 Aspherical coefficients

[0042]

[0043] Table 3 Freeform Surface Coefficients

[0044]

[0045] Among the surfaces mentioned above, the surfaces that constitute the aspherical surface satisfy the following equation: The surface, which is formed as a freeform surface, satisfies the following equation: c is the reciprocal of the radius of curvature, r is the radial distance from a point on the surface, k is the quadratic surface constant, and Ai is the coefficient of higher-order terms.

[0046] The basic optical system parameters of the perspective light path are shown in Table 4, and the freeform surface coefficients are shown in Table 5.

[0047] Table 4 Optical system parameters for the perspective display light path

[0048]

[0049] Table 5 Freeform surface coefficients of the optical path in perspective display

[0050]

[0051] Among the surfaces mentioned above, the surfaces that constitute the aspherical surface satisfy the following equation: Among the aforementioned surfaces, those constituting freeform surfaces satisfy the following equation: c is the reciprocal of the radius of curvature, r is the radial distance from a point on the surface, k is the quadratic surface constant, and Ai is the coefficient of higher-order terms.

[0052] In this embodiment, the display uses a self-emissive display with a diagonal size of 0.71 inches, the system field of view is 45°, the optical path distortion of the virtual image display is 0.4%, and the total thickness of the optical lenses is 10.6 mm.

[0053] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A distortion-free, compact off-axis near-eye display optical system, characterized in that... The system includes: a display, a first freeform surface element, and a second freeform surface element, which together form a first sub-optical path and a second sub-optical path. A first light-incoming surface is provided on one side of the top of the first freeform surface element, and a light-outcoming surface is provided below the light-incoming surface. A first reflective surface and a second reflective surface are sequentially provided from top to bottom on the side of the first freeform surface element away from the first light-incoming surface. A fitting surface adapted to the second reflective surface is provided on one side of the second freeform surface element, and a second light-incoming surface on the side away from the fitting surface. The display corresponds to the first light-incoming surface. The first sub-optical path is as follows: it enters through the first light-entry surface, and after being reflected three times by the first reflective surface, the light-exiting surface, and the second reflective surface, it is transmitted through the light-exiting surface again. The second sub-optical path is as follows: it enters through the second light-entry curved surface, and then passes through the bonding curved surface, the second reflective curved surface, and the light-exiting curved surface in sequence; The second reflective surface is provided with a beam-splitting film, and the beam splitting ratio is 1:1; The distance between the first reflective surface and the light-emitting surface is less than 11 mm; The display has a diagonal size ranging from 0.65 to 0.75 inches, a virtual image display optical path field of view greater than 45 degrees, and distortion less than 0.5%. Both the first and second freeform surface elements are made of low-dispersion materials with an Abbe number greater than 55. The light-emitting surface, the first reflection surface, the second reflection surface, and the second light-entry surface are all freeform surfaces used to correct off-axis aberrations.

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