Folding optical path lens group, optical imaging module and head-mounted display equipment

Abstract

The embodiment of the invention discloses a folded optical path lens group, an optical imaging module and head-mounted display equipment. According to the embodiment of the invention, the first lens and the second glass lens are arranged in the folded light path lens group, and the four surfaces of the two lenses from the light inlet surface to the light outlet surface are the first convex surface and the second convex surface of the first lens and the third plane and the fourth convex surface of the second glass lens in sequence, so that a convex lens structure is formed on the first lens; the second glass lens is only provided with one convex surface, the processing technology is simplified through the full convex surface and the plane structure, the processing cost is integrally reduced, meanwhile, it is guaranteed that final imaging has good resolution through the second glass lens, and good imaging visual experience for a user is guaranteed.

Description

Technical Field

[0001] This application relates to the field of display technology, and more particularly to foldable optical path mirror assemblies, optical imaging modules, and head-mounted display devices. Background Technology

[0002] With the continuous development of electronic technologies, display technologies and devices derived from displays are constantly emerging. For example, AR (Augmented Reality) devices and VR (Virtual Reality) devices such as Pancake are display devices derived from displays. These derived display devices are usually head-mounted display devices.

[0003] In head-mounted display devices, an optical imaging module, which is formed by combining optical components such as optical resin lenses, optical glass lenses, optical films, optical coatings, and display units, can magnify the image source presented in the display unit and form a virtual image at a certain distance from the display unit. When the virtual image falls exactly on the retina, the user can visually perceive the imaging effect of the head-mounted display device.

[0004] The inventors' research on existing head-mounted devices revealed that the folded optical path lens assembly, as a key component in head-mounted display devices that enables users to view the image source, usually requires complex surface design of the lenses in the folded optical path lens assembly, resulting in higher processing costs, in order to ensure good resolution in the imaging of the folded optical path lens assembly. Summary of the Invention

[0005] This invention provides a folded optical path mirror assembly, an optical imaging module, and a head-mounted display device to solve the technical problem that the lenses in the folded optical path mirror assembly require complex surface design and high processing costs in order to ensure good resolution in the imaging of the folded optical path mirror assembly.

[0006] In a first aspect, embodiments of this application provide a folded optical path mirror assembly, including a first lens and a second glass lens;

[0007] The first lens is located on the light-inlet side of the folded optical path mirror group, and the second glass lens is located on the light-outlet side of the folded optical path mirror group. The first lens has a first convex surface and a second convex surface on both sides, and the second glass lens has a third plane and a fourth convex surface on both sides. The first convex surface, the second convex surface, the third plane and the fourth convex surface are arranged sequentially along the optical axis.

[0008] A second quarter-wave plate is located at the third plane.

[0009] As described above, a first lens and a second glass lens are set in the folded optical path lens assembly. The four surfaces of the two lenses from the light-inlet surface to the light-outlet surface are, in sequence, the first convex surface and the second convex surface of the first lens, the third plane and the fourth convex surface of the second glass lens. Thus, the first lens forms a convex lens structure, and the second glass lens has only one convex surface. The design of each surface being a convex or planar structure simplifies the manufacturing process and reduces the overall manufacturing cost. At the same time, the second glass lens ensures that the final image has good resolution, ensuring a good imaging visual experience for the user.

[0010] The first convex surface is also provided with a semi-reflective and semi-transparent film, and the third plane is also provided with a reflective polarizer.

[0011] The second quarter-wave plate, the reflective polarizer, and the second glass lens are arranged sequentially along the optical axis.

[0012] The above-mentioned surface structure and combination of the first lens and the second glass lens, with the semi-reflective and semi-transparent film, the second quarter wave plate and the reflective polarizer set at specific positions, can provide an image with better resolution and improve the user's visual experience.

[0013] Among them, the first convex surface, the second convex surface, and the fourth convex surface are all aspherical surfaces.

[0014] The aforementioned aspherical first and second glass lenses offer a wide range of surface options, allowing for more detailed variations based on specific display requirements. This enables precise control over lens thickness, minimizing the overall size, weight, and thickness of the optical imaging module while improving image quality.

[0015] The expression for the aspherical surface type is:

[0016]

[0017] Where z is the sag of the aspherical surface, r is the radius of the aspherical surface, k is the quadratic surface coefficient, c is the curvature, and A4~A 16 For higher-order terms of aspherical surfaces.

[0018] As described above, by designing a specific aspherical surface, the curvature of the two convex surfaces appearing in the first lens and the convex surface appearing in the second glass lens can be effectively controlled, thereby effectively controlling distortion.

[0019] The thickness of the first lens and / or the second glass lens is 1 to 3 mm.

[0020] As mentioned above, with a lens thickness of 1 to 3 mm, good imaging results can be achieved with the smallest and lightest possible optical devices.

[0021] In a second aspect, embodiments of this application also provide an optical imaging module that applies any of the folded optical path mirror groups in the first aspect. The optical imaging module includes a display unit, a first 1 / 4 wave plate, and a folded optical path mirror group arranged coaxially in sequence.

[0022] The display unit, the first quarter wave plate, and the folded optical path mirror group are arranged sequentially along the optical axis;

[0023] The angle between the fast axis direction of the first quarter wave plate and the fast axis direction of the second quarter wave plate is 90°.

[0024] As described above, by using a low-cost and low-weight resin lens with a specific surface condition, a glass lens with good optical properties, and other optical devices selected and arranged according to the surface conditions of the two lenses, it is possible to polarize, refract, and reflect the light emitted from the display unit while ensuring that the weight and cost of the optical imaging module are as small as possible. Ultimately, this results in an image with good resolution entering the user's retina, avoiding ghosting in the image viewed by the user, and providing the user with a good visual experience.

[0025] The optical imaging module also includes an absorptive polarizer, which is disposed between a reflective polarizer and a second glass lens; or

[0026] An absorptive polarizer is positioned between the display unit and the first quarter-wave plate.

[0027] As mentioned above, by setting an absorptive polarizer at the light-emitting position or the image source position, stray light output from the optical imaging module can be effectively reduced, further improving the contrast of the entire display screen.

[0028] The aperture of the optical imaging module is 43mm to 50mm.

[0029] As mentioned above, by mirroring the size of optical components in the range of 43mm to 50mm, the overall size of the optical imaging module can be controlled as much as possible without affecting the user's visual experience.

[0030] Thirdly, embodiments of this application provide a head-mounted display device, which includes any of the optical imaging modules in the second aspect.

[0031] The head-mounted display device made using any of the optical imaging modules described in the second aspect has the same beneficial effects as the optical imaging module. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of the optical imaging module provided in the embodiments of this application.

[0033] Figure 2The field curvature and distortion simulation results of the optical imaging module provided in the embodiments of this application are shown in the graph.

[0034] Figure 3 A schematic diagram of the light propagation process of the optical imaging module provided in the embodiments of this application.

[0035] Among them, 10-display unit; 11-first quarter-wave plate; 20-first lens; 21-semi-reflective and semi-transparent surface; 30-second glass lens; 31-absorbent polarizer; 32-reflective polarizer; 33-second quarter-wave plate; 40-retina. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and not for limiting the invention. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention and not the entire structure.

[0037] It should be noted that, due to space limitations, this application specification does not exhaustively list all possible implementation methods. Those skilled in the art should be able to conceive after reading this application specification that, as long as the technical features do not contradict each other, any combination of technical features can constitute an optional implementation method.

[0038] The embodiments of the present invention will be described in detail below.

[0039] The inventors, through research on existing head-mounted display devices, discovered that the folded optical path lens assembly is a key component in head-mounted displays, enabling users to view the image source. The lenses in the folded optical path lens assembly, whose shape is determined by concave and convex curved surfaces on both sides, have a relatively complex structure and high manufacturing costs. For example, two or more lenses need to be placed in the folded optical path lens assembly, and the surface curvature of each lens must be designed and processed. Moreover, as an electronic device with both visual and wearing comfort, the more lenses and the more complex the structure of the folded optical path lens assembly, the heavier the final assembled head-mounted display device becomes. If the user uses it for a long time, their neck will become quite tired, resulting in a poor overall user experience.

[0040] To address the aforementioned technical issues, this application provides a folded optical path mirror assembly. The folded optical path mirror assembly includes a first lens and a second glass lens. The four surfaces of the two lenses, from the light-inlet surface to the light-outlet surface, are, in sequence, the first convex surface and the second convex surface of the first lens, the third plane surface and the fourth convex surface of the second glass lens. This forms a convex lens structure in the first lens and a single convex surface in the second glass lens. This fully convex and planar structure simplifies the manufacturing process and reduces overall manufacturing costs. Simultaneously, the second glass lens ensures good resolution in the final image, guaranteeing a good visual experience for the user.

[0041] Please refer to Figure 1 This is a schematic diagram of the overall structure when the folded optical path lens provided in the embodiments of this application is applied to an optical imaging module. Figure 1 As shown, the folded optical path mirror assembly includes a first lens 20 and a second glass lens 30. The first lens 20 is located on the light-inlet side of the folded optical path mirror assembly, and the second glass lens 30 is located on the light-outlet side of the folded optical path mirror assembly. The first lens 20 has a first convex surface and a second convex surface on both sides, and the second glass lens has a third plane and a fourth convex surface on both sides. The first convex surface, the second convex surface, the third plane and the fourth convex surface are arranged sequentially along the optical axis. A second 1 / 4 wave plate 33 is provided at the third plane.

[0042] In the folded optical path mirror assembly, a first lens 20 and a second glass lens 30 are arranged. The four surfaces of the two lenses from the light-inlet surface to the light-outlet surface are, in sequence, the first convex surface and the second convex surface of the first lens 20, and the third plane and the fourth convex surface of the second glass lens 30. Thus, the first lens 20 forms a convex lens structure, and the second glass lens 30 has one convex surface and one plane. This all-convex and plane structure simplifies the manufacturing process and reduces overall manufacturing costs. Simultaneously, the second glass lens 30 ensures that the final image has good resolution, guaranteeing a good visual experience for the user. In this embodiment, using... Figure 1 The image shown and the position of the human eye's retina 40 are used as references. From right to left, the direction is along the optical axis. The light-entry surface is on the right side of the folded optical path mirror group, and the light-exit surface is on the left side of the folded optical path mirror group.

[0043] The folded optical path mirror assembly in this embodiment may also have a semi-reflective and semi-transparent film on the first convex surface and a reflective polarizer 32 on the third plane; the second quarter-wave plate 33, the reflective polarizer 32, and the second glass lens 30 are arranged sequentially along the optical axis. By adapting to the surface structure and combination of the first lens 20 and the second glass lens 30, and by setting the semi-reflective and semi-transparent film, the second quarter-wave plate 33, and the reflective polarizer 32 at specific positions, an image with good resolution can be provided, enhancing the user's visual experience.

[0044] In another alternative implementation, the first convex surface, the second convex surface, and the fourth convex surface are all aspherical. The aspherical first lens 20 and the second glass lens 30 have a wide range of surface options, allowing for more detailed variations according to specific display requirements. This enables precise control of the lens thickness, improving image quality while minimizing the overall size, weight, and thickness of the optical imaging module.

[0045] In a specific implementation, the expressions for the aspherical surface types corresponding to the first convex surface, the second convex surface, and the fourth convex surface are as follows:

[0046]

[0047] Where z is the sag of the aspherical surface, r is the radius of the aspherical surface, k is the quadratic surface coefficient, c is the curvature, and A4~A 16 These are the higher-order coefficients of the aspherical surface. By designing the specific aspherical surface shape, the curvature of the two convex surfaces appearing in the first lens and the convex surface appearing in the second glass lens can be effectively controlled, thus effectively controlling distortion.

[0048] When setting the convex surface, the curvature of the first, second, and fourth convex surfaces can be set to decrease sequentially. This is equivalent to setting the two convex surfaces with larger curvatures on the same lens (the first lens). It is only necessary to concentrate the processing of complex convex surfaces on a relatively thick substrate. The glass substrate corresponding to the second glass lens can be made of a relatively thin glass substrate to complete the flat processing and the processing of a convex surface with smaller curvature.

[0049] In a specific implementation detail, the thickness of the first lens 20 and / or the second glass lens 30 is 1 to 3 mm.

[0050] As mentioned above, with a lens thickness of 1 to 3 mm, good imaging results can be achieved with the smallest and lightest possible optical devices.

[0051] In another specific implementation detail, the first lens 20 can be a resin lens or a glass lens. Specifically, for example, the first lens 20 can be a resin lens used in conjunction with the second glass lens 30, or the first lens 20 can be a glass lens used in conjunction with the second glass lens 30. Taking the use of a resin lens with the second glass lens 30 as an example, because resin has a lower density than glass, using a resin lens for the first lens 20 allows for better control of the overall structural weight. Furthermore, resin lenses are easier to process for convex surfaces, resulting in better control of overall processing costs. The second glass lens 30 utilizes the excellent optical properties of glass lenses to ensure good resolution in the imaging based on the folded optical path lens group, while simplifying the lens structure and controlling costs, thus guaranteeing a good visual experience for the user.

[0052] The imaging process of the folded optical path lens in this application is described in detail in the corresponding embodiment when the folded optical path lens is applied to the optical imaging module.

[0053] In embodiments corresponding to the optical imaging module, compared to the folded optical path lens assembly, it at least includes a display unit and a first quarter-wave plate. The first quarter-wave plate is disposed at the light-emitting position of the display unit. The light from the image source displayed by the display unit enters the folded optical path lens from the light-inlet surface through the first quarter-wave plate, and then enters the user's retina for imaging after exiting from the light-emitting surface. Corresponding to the specific implementation in the folded optical path lens assembly, the optical imaging module can have different implementations with corresponding layouts for the display unit and the first quarter-wave plate. In addition, an absorptive polarizer can be added to any implementation (with different corresponding placement methods). Furthermore, the aperture of the optical imaging module can be designed as a whole, for example, within the aperture range of 43mm to 50mm.

[0054] Please refer to Figure 1 This is a schematic diagram of the optical imaging module provided in an embodiment of this application. The following is based on... Figure 1 The overall embodiment design of the folded optical path mirror assembly mentioned above provides a detailed description of the optical imaging module. For example... Figure 1 As shown, the optical imaging module in this embodiment includes a display unit 10, a first quarter-wave plate 11, and a folded optical path lens (corresponding to a first lens 20, a second quarter-wave plate 33, a reflective polarizer 32, and a second glass lens 30) arranged coaxially in sequence; the surface of the first lens 20 facing the first quarter-wave plate 11 is convex (i.e., the first convex surface) and is provided with a semi-reflective and semi-transparent film. Figure 1 (not shown in the image); the surface of the first lens 20 facing the second glass lens 30 is a convex surface (i.e., the second convex surface); the surface of the second glass lens 30 facing the first lens 20 is a plane (i.e., the third plane), and the surface of the second glass lens 30 facing away from the first lens 20 is a convex surface (i.e., the fourth convex surface); the angle between the fast axis direction of the first quarter wave plate 11 and the fast axis direction of the second quarter wave plate 33 is 90°.

[0055] like Figure 1As shown, when the display unit 10 acts as an image source for imaging, the outgoing light (s-polarized light) passes sequentially through the first quarter-wave plate 11, the first lens 20, the second quarter-wave plate 33, and the second glass lens 30. Since the angle between the fast axis direction of the first quarter-wave plate 11 and the fast axis direction of the second quarter-wave plate 33 is 90°, the polarization state of the s-polarized light is not changed and it remains s-polarized light. Then, the s-polarized light is reflected by the reflective polarizer 32 (the reflective polarizer 32 can reflect s-polarized light and transmit p-polarized light), and then passes sequentially through the second quarter-wave plate 33 and the first lens 20. Since the right surface of the first lens 20 is coated with a semi-reflective and semi-transparent film, a portion of the light is reflected by the right surface of the first lens 20, and then passes sequentially through the first lens 20 and the second quarter-wave plate 33. At this time, the s-polarized light is converted into p-polarized light, which can pass through the reflective polarizer 32, and finally enters the retina 40 (the position of the human eye) through the second glass lens 30.

[0056] As described above, by using a low-cost and low-weight resin lens with a specific surface condition, a glass lens with good optical properties, and other optical components selected and arranged according to the surface conditions of the two lenses, it is possible to polarize, refract, and reflect light emitted from the display unit based on the fully convex and planar structures, while ensuring that the weight and cost of the optical imaging module are as small as possible. Ultimately, this results in an image with good resolution entering the user's retina, avoiding ghosting in the image viewed by the user, and providing the user with a good visual experience.

[0057] In one alternative implementation, the optical imaging module further includes an absorptive polarizer disposed between a reflective polarizer and a second glass lens.

[0058] Please refer to further information. Figure 1The emitted light (s-polarized light) from display unit 10 passes sequentially through a first quarter-wave plate 11, a first lens 20, a second glass lens 30, and a second quarter-wave plate 33. Since the angle between the fast axis direction of the first quarter-wave plate 11 and the fast axis direction of the second quarter-wave plate 33 is 90°, the polarization state of the s-polarized light remains unchanged; it is still s-polarized light. Then, the s-polarized light is reflected by a reflective polarizer 32 (the reflective polarizer 32 can reflect s-polarized light and transmit p-polarized light), and then passes sequentially through the second... The 1 / 4 wave plate 33 and the first lens 20 are used. Because the right surface of the first lens 20 is coated with a semi-reflective and semi-transparent film, part of the light is reflected by the right surface of the first lens 20, and then passes through the first lens 20 and the second 1 / 4 wave plate 33 in sequence. At this time, the s-polarized light is converted into p-polarized light, which can pass through the reflective polarizer 32 and the absorptive polarizer 31 (the transmission axis of the absorptive polarizer 31 is the same as the polarization direction of the p-polarized light), and finally enters the retina 40 (the position of the human eye) through the second glass lens 30.

[0059] In the embodiments of this application, the propagation direction and polarization direction of the light are as follows: Figure 3 As shown. The display unit 10 emits s-polarized light, whose polarization direction is perpendicular to the plane of the paper. After passing through the first quarter-wave plate 11, it becomes left-handed circularly polarized light. Then, it passes through the semi-reflective and semi-transparent surface 21 (the right surface of the first lens 20 is defined as a semi-reflective and semi-transparent surface 21, resulting in a 50% energy loss), and then passes through the second quarter-wave plate 33, becoming s-polarized light again (since the angle between the fast axis direction of the first quarter-wave plate 11 and the fast axis direction of the second quarter-wave plate 33 is 90°, the phase difference between the two quarter-wave plates cancels each other out). The reflective polarizer 32 reflects the s-polarized light, which then passes through the second quarter-wave plate 33, becoming right-handed circularly polarized light. It is then reflected again by the semi-reflective and semi-transparent surface 21 (again resulting in a 50% energy loss), and after passing through the second quarter-wave plate 33 again, it becomes p-polarized light. This p-polarized light then passes through the reflective polarizer 32 and the absorptive polarizer (…). Figure 3 (not shown in the image), and finally enters the human eye through the second glass lens 30 to form an image.

[0060] The semi-reflective surface 21 of the first lens 20 is coated with a semi-reflective film. When light emitted from the display unit 10 passes through this surface, 50% of the energy is lost; when the light is reflected by this surface, 50% of the energy is also lost. Therefore, theoretically, the energy utilization rate of this optical imaging module is 25%. In reality, the reflective polarizer 32 does not have 100% reflectivity for S-polarized light, so a small amount of S-polarized light will pass through. The absorptive polarizer 31 can absorb the transmitted S-polarized light, which can reduce stray light in the system and improve the contrast of the entire display screen.

[0061] The simulation results of field curvature and distortion of the optical imaging module at this time are as follows: Figure 2 As shown, the vertical axis of field curvature and distortion is the field of view, with a maximum field of view of 100 degrees. The horizontal axis of field curvature is in millimeters, and the horizontal axis of distortion is in percentage. At this point, a good field of view is clearly achieved, while distortion is effectively controlled.

[0062] As described above, by placing an absorptive polarizer near the light-emitting position, stray light ultimately output from the optical imaging module can be effectively reduced, further improving the contrast of the entire display image. For example, when the image content is black on a white background, it can provide users with a clearer imaging effect, the boundary between black and white is more distinct, and the appearance of ghosting is reduced.

[0063] In another optional implementation, the optical imaging module also includes an absorptive polarizer positioned between the display unit 10 and the first quarter-wave plate 11. This approach is more suitable when the display unit 10 emits natural light (i.e., unpolarized light). In this case, by adding an absorptive polarizer (whose transmission axis is aligned with the polarization direction of s-polarized light, i.e., perpendicular to the paper) between the display unit 10 and the first quarter-wave plate 11, the absorptive polarizer polarizes the unpolarized light emitted by the display unit 10, thus obtaining s-polarized light. By using an absorptive polarizer positioned at the image source, stray light can be processed at the image source, thereby ultimately controlling the stray light output from the optical imaging module and further improving the contrast of the entire display image. For example, when the image content is black on a white background, it can provide the user with a clearer imaging effect, and the boundary between black and white is more distinct.

[0064] In one specific implementation, one or more of the following surfaces—the surface of the first lens facing the second glass lens, the surface of the first lens facing the first quarter-wave plate, and the surface of the second glass lens facing away from the reflective polarizer—are aspherical. The aspherical surface of the first and second glass lenses allows for a wide range of surface variations, enabling more detailed adjustments based on specific display requirements. This allows for precise control of the lens thickness, improving image quality while minimizing the overall size, weight, and thickness of the optical imaging module.

[0065] In a more specific implementation, the expression for an aspherical surface type is:

[0066]

[0067] Where z is the sag of the aspherical surface, r is the radius of the aspherical surface, k is the quadratic surface coefficient, c is the curvature (the reciprocal of the radius of curvature), A4~A 16 For higher-order terms of aspherical surfaces.

[0068] As described above, by designing a specific aspherical surface, the curvature of the concave and convex surfaces appearing in the first lens, as well as the curvature of the convex surface appearing in the second glass lens, can be effectively controlled, thus effectively controlling distortion.

[0069] Regarding the specific hardware selection, the display unit is a FastLCD screen. Using a FastLCD screen ensures the image refresh rate of the image source, improving the imaging effect provided to the user. Regardless of the type of display screen chosen, the display unit can be a 2.56-inch screen. A 2.56-inch screen ensures a consistent field of view for the entire optical imaging module.

[0070] In a specific implementation detail, the thickness of the first lens and / or the second glass lens can be 1 to 3 mm, for example, 1.7 mm or 2 mm. With a lens thickness of 1 to 3 mm, good imaging results can be achieved with the smallest and lightest possible optical device.

[0071] In another specific implementation detail, the aperture of the optical imaging module can be 43mm to 50mm. By using an optical component size of 43mm to 50mm, the overall size of the optical imaging module can be controlled as much as possible without affecting the user's visual experience.

[0072] This application also provides a head-mounted display device, which includes the optical imaging module as described in any of the preceding embodiments. Examples of head-mounted display devices include AR devices and PancakeVR devices. The head-mounted display device in this application has the same technical effects as the optical imaging module embodiments described above.

[0073] In one optional implementation, for a head-mounted display device with two display units 10, adjusting the angle of the display units 10 allows for staggered and differentiated displays for the left and right eyes, thereby increasing the horizontal and vertical viewing angles. For example, when the display unit 10 is directly facing the user's retina 40, the viewing distance is 46mm. Rotating the angle of the display unit 10 by 23° increases the viewing distance to 51.94mm, thus adjusting the viewing angle from the user's perspective. Overall, by rotating between 19° and 25°, the viewing angle can be flexibly adjusted to suit different users.

[0074] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0075] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A folding optical path mirror assembly, characterized in that, Includes a first lens (20) and a second glass lens (30); The first lens (20) is located on the light-inlet side of the folded optical path mirror group, and the second glass lens (30) is located on the light-outlet side of the folded optical path mirror group. The first lens (20) has a first convex surface and a second convex surface on both sides, and the second glass lens has a third plane and a fourth convex surface on both sides. The first convex surface, the second convex surface, the third plane and the fourth convex surface are arranged in sequence along the optical axis. A second quarter wave plate (33) is provided at the third plane.

2. The folded optical path mirror assembly according to claim 1, characterized in that, The first convex surface is also provided with a semi-reflective and semi-transparent film, and the third plane is also provided with a reflective polarizer (32); The second quarter wave plate (33), the reflective polarizer (32), and the second glass lens (30) are arranged sequentially along the optical axis.

3. The folding optical path mirror assembly according to claim 1, characterized in that, The first convex surface, the second convex surface, and the fourth convex surface are all aspherical surfaces.

4. The folded optical path mirror assembly according to claim 3, characterized in that, The expression for the aspherical surface type is: Where z is the sag of the aspherical surface, r is the radius of the aspherical surface, k is the quadratic surface coefficient, c is the curvature, and A4~A 16 For higher-order terms of aspherical surfaces.

5. The folded optical path mirror assembly according to claim 1, characterized in that, The thickness of the first lens (20) and / or the second glass lens (30) is 1 to 3 mm.

6. The folded optical path mirror assembly according to claim 1, characterized in that, The first lens (20) is a resin lens or a glass lens.

7. An optical imaging module using the folded optical path mirror assembly according to any one of claims 1-6, characterized in that, It includes a display unit (10), a first quarter-wave plate (11), and the folded optical path mirror group arranged coaxially in sequence; The display unit (10), the first 1 / 4 wave plate (11), and the folded optical path mirror group are arranged sequentially along the optical axis; The angle between the fast axis direction of the first quarter wave plate (11) and the fast axis direction of the second quarter wave plate (33) is 90°.

8. The optical imaging module according to claim 7, characterized in that, It also includes an absorptive polarizer (31), which is disposed between the reflective polarizer (32) and the second glass lens (30); or The absorptive polarizer (31) is disposed between the display unit (10) and the first quarter-wave plate (11).

9. The optical imaging module according to claim 7, characterized in that, The aperture of the optical imaging module is 43mm to 50mm.

10. A head-mounted display device, characterized in that, The head-mounted display device includes the optical imaging module as described in any one of claims 7-9.

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