Birdbath near-eye display module for eliminating ghost images

Abstract

The application discloses a Birdbath near-eye display module capable of eliminating ghost images and belongs to the technical field of optical imaging. The module comprises an image generating unit, a lens unit, a plane mirror unit and a curved mirror unit in sequence along an optical path. The plane mirror unit comprises a plane mirror and a second polarization converter. The second polarization converter comprises a second polarizer and a first reflective polarizer. A second phase difference plate is arranged in the plane mirror unit and / or the curved mirror unit. The second phase difference plate is a liquid crystal type phase difference plate, and the thickness of the second phase difference plate is less than 10 microns. By adopting the ultra-thin liquid crystal type phase difference plate, the optical path of ghost image light generated by interface reflection is nearly coincident with the optical path of main image light, so that the ghost image is eliminated. Meanwhile, the oblique angle θ of the plane mirror unit satisfies tan(θ) = n2 / n1, and the ghost image reflectivity can be further reduced. The first polarization converter can be cancelled, the structure is simplified, the cost is reduced, and the imaging quality and user experience are improved.

Description

Technical Field

[0001] This invention relates to the field of optical imaging technology, and more specifically to a Birdbath near-eye display module that eliminates ghosting. Background Technology

[0002] Augmented Reality (AR) technology displays real-world scenes while simultaneously providing virtual information to users through images, videos, 3D models, and other technologies. This seamlessly integrates virtual information with the real world, offering users a sensory experience that transcends reality. Among numerous AR optical solutions, the Birdbath solution has garnered significant attention due to its low cost, compact structure, and superior optical performance. In the Birdbath solution, polarization elements such as reflective polarizers, absorptive polarizers, quarter-wave plates, and beam splitters in the optical path manipulate the image output from the display. This image is then superimposed on ambient light and input into the user's eye. However, interface reflections or imperfections in the polarization devices within the imaging optical path can cause varying degrees of ghosting, interfering with the target signal in the image. Therefore, the ability to eliminate these ghosting effects is a decisive factor in whether a Birdbath-based AR glasses solution will be accepted by users.

[0003] Figure 1It is a traditional Birdbath structure. In the traditional Birdbath optical path structure, the first polarization converter 10' at the image signal end polarizes the image signal light. The first polarization converter 10' includes a first polarizer and a first phase retardation plate. Then, it passes through the lens unit 2' and enters the inclined plane mirror unit 3'. The plane mirror unit 3' has a second polarization converter 31' attached to the plane mirror 30'. The second polarization converter 31' includes a second polarizer 311', a third polarizer 312' and a second phase retardation plate 5'. The third polarizer is specially required to be a reflective polarizer. After the signal light passes through the lens unit 2' and enters the plane mirror unit 3' for the first time, it is reflected by the third polarizer and reaches the curved mirror unit 4'. The curved mirror unit 4' is coated with a transmissive or total reflective film and reflects the signal light back into the plane mirror unit 3' and enters the human eye after passing through the plane mirror unit 3'. Alternatively, in a modified scheme, the first polarization converter 10' includes a first polarizer. Signal light sequentially passes through the first polarization converter 10' and lens unit 2' before entering the plane mirror unit 3'. The plane mirror unit 3' has a second polarization converter 31' attached, which includes a second polarizer and a third polarizer. The third polarizer is specifically designed to be a reflective polarizer. After passing through lens unit 2' and initially entering the plane mirror unit 3', the signal light is reflected by the third polarizer and reaches the curved mirror unit 4'. The curved mirror unit 4' is coated with a transmissive / reflective film and has a third polarization converter attached. The third polarization converter 40' includes a first phase retardation plate. The light reaches the curved mirror unit 4', is reflected twice, and then passes through the third polarization converter 40' before finally entering the plane mirror unit 3' a second time and passing through it to enter the human eye. Figure 2 In both of the above schemes, the order of the first polarization converter 10' and the lens unit 2' is not restricted.

[0004] The above ray tracing process refers to the signal light imaging optical path (hereinafter referred to as the main image). Simultaneously, when light encounters interfaces with refractive index differences (such as a medium-air interface, or a medium-one-medium-two interface) during propagation, Fresnel reflection occurs. Especially in the Birdbath optical path, light rays are generally obliquely incident at the interface, further increasing Fresnel reflection. This Fresnel reflection, resulting in an image deviating from the main image imaging optical path, is called a ghost image, affecting the user experience. Figure 1 Traditional Birdbath optical paths typically exhibit two main types of reflected ghost images. In the first ghost image path, the signal light passes through the first polarization converter 10', lens unit 2', and is initially incident on the plane mirror unit 3'. Before being converted and reflected by the third polarizer, it is reflected by the phase retardation plate-air interface of the plane mirror unit 3', and subsequently reflected by the curved mirror unit 4' to form an image. This imaging optical path deviates from the primary image, resulting in a ghost image. (See...) Figure 3The ghost image optical path is as follows: the signal light passes through the first polarization converter 10' and lens unit 2' and is initially incident on the plane mirror unit 3'. Due to the polarization converter deviating from its ideal performance, some light passes directly through the plane mirror unit 3' and is reflected at the air interface of the plane mirror 30' on the human eye side. This reflection then occurs between the plane mirror 30' and the curved mirror 41', resulting in an image. This imaging optical path deviates from the primary image, thus creating the ghost image. (See...) Figure 4 The two types of ghost images mentioned above are caused by interface reflection. In the traditional Birdbath optical path, due to the presence of the first polarization converter 10' at the signal end, the light-locking effect between the first polarization converter 10' and the second polarization converter 31' weakens these two types of ghost images to a certain extent. However, in order to save costs and reduce manufacturing process difficulty, the first polarization converter 10' usually needs to be removed, at which point the two ghost images will be significantly enhanced. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a Birdbath near-eye display module that eliminates ghosting. By employing an ultra-thin liquid crystal phase retardation plate, the ghosting light path generated by interface reflection is nearly coincident with the main image light path, thereby eliminating ghosting. Simultaneously, the tilt angle θ of the plane mirror unit satisfies tan(θ)=n2 / n1, which can further reduce ghosting reflectivity. This invention can eliminate the need for a first polarization converter, simplifying the structure, reducing costs, and improving imaging quality and user experience.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A Birdbath near-eye display module for eliminating ghosting includes, along the optical path, an image generation unit, a lens unit, a plane mirror unit, and a curved mirror unit. The plane mirror unit includes a plane mirror and a second polarization converter. The second polarization converter includes a second polarizer and a first reflective polarizer. A second phase retardation plate is disposed in the plane mirror unit and the curved mirror unit. The second phase retardation plate is a liquid crystal phase retardation plate with a thickness of less than 10 μm.

[0007] Furthermore, the second phase retardation plate is disposed in the plane mirror unit and is attached to the surface of the first reflective polarizer. The slow axis of the second phase retardation plate forms a 45° angle with the transmission axis of the first reflective polarizer, and the transmission axes of the second polarizer and the first reflective polarizer are parallel.

[0008] The module further includes a first polarization converter, which is disposed between the image generation unit and the lens unit. The first polarization converter includes a first polarizer and a first phase retardation plate. The slow axis of the first phase retardation plate forms a 45° angle with the transmission axis of the first polarizer. The slow axes of the first phase retardation plate and the second phase retardation plate are parallel or orthogonal. The transmission axes of the first polarizer and the second polarizer are parallel or orthogonal.

[0009] Furthermore, both the first polarizer and the second polarizer are absorption polarizers.

[0010] Furthermore, the curved mirror unit includes a third polarization converter and a curved mirror. The third polarization converter includes a second phase retardation plate attached to the surface of the curved mirror. The second polarization converter includes a second polarizer and a first reflective polarizer.

[0011] The module further includes a first polarization converter, which is disposed between the image generation unit and the lens unit. The first polarization converter includes a first polarizer, which is an absorption polarizer, and the transmission axes of the first polarizer and the second polarizer are orthogonal.

[0012] Furthermore, both polarizers are absorption polarizers, with the transmission axes of the first reflective polarizer and the second polarizer parallel, and the slow axis of the second phase difference plate forming a 45° angle with the transmission axis of the second polarizer.

[0013] Furthermore, the tilt angle θ of the plane mirror unit satisfies tan(θ) = n2 / n1, where n2 is the air refractive index, n1 is the refractive index of the plane mirror, and the tolerance of the tilt angle θ is ±20°.

[0014] Furthermore, the plane mirror contains an AR functional layer on the side closest to the human eye, and the curved mirror surface is coated with a transflective film.

[0015] Furthermore, the transmission axes of the second polarizer and the first reflective polarizer are parallel to each other and parallel to the optical path cross section of the module.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. Effectively eliminates ghosting and significantly improves image quality: This invention incorporates a liquid crystal phase retardation plate in the plane mirror unit and / or curved mirror unit, with its thickness strictly controlled (below 10μm). This ensures that the ghosting light path generated by reflection at the phase retardation plate-air interface almost coincides with the main image light path, making it visually imperceptible to the user. This effectively eliminates ghosting interference caused by Fresnel reflection at the interface, as seen in the traditional Birdbath scheme. Simultaneously, through a specific design of the oblique angle of the plane mirror unit (satisfying tan(θ) = n2 / n1), the reflectivity of directly transmitted light on the side of the plane mirror closest to the human eye is significantly reduced, even approaching zero, thereby blocking the subsequent propagation of the ghosting light path and further suppressing the ghosting to an invisible state for the user.

[0017] 2. Allows for simplified module structure and reduced manufacturing costs: The technical solution of this invention allows the first polarization converter to be eliminated without causing an increase in ghost image intensity. In traditional Birdbath optical paths, eliminating the first polarization converter leads to a significant increase in ghost image intensity due to the lack of polarization-locking effect; however, thanks to the ultra-thin characteristics and special axial design of the liquid crystal phase retardation plate, this invention can effectively eliminate or suppress ghost images even without the first polarization converter, thereby reducing the overall process and manufacturing costs of the module.

[0018] 3. Optimized polarization device configuration to improve optical path efficiency: This invention rationally configures the transmission axis direction of each polarization device: the transmission axis of the second polarizer is parallel to that of the first reflective polarizer and parallel to the optical path cross-section of the module; the slow axis of the second phase retardation plate forms a 45° angle with the transmission axis of the first reflective polarizer (or the second polarizer). Simultaneously, both the first and second polarizers are absorption-type polarizers, making polarization state conversion in the optical path more precise and efficient, reducing stray light caused by imperfect performance of the polarization devices.

[0019] 4. Enhanced ambient light transmittance and improved user experience: The present invention sets an AR functional layer (anti-reflective film) on the side of the plane mirror close to the human eye, and the surface of the curved mirror is coated with a transflective film, which not only optimizes the transmission efficiency of the imaging light path, but also enhances the transmittance of external ambient light, so that users can observe the real scene more clearly when wearing it, and improve the overall effect of the augmented reality experience.

[0020] 5. Flexible solutions and wide applicability: This invention provides multiple embodiments, which can be set in either a plane mirror unit or a curved mirror unit; the first polarization converter can be selected as a complete solution including the first polarizer and the first phase retardation plate, or it can be simplified to a solution including only the first polarizer; the arrangement order and film application position of each polarization device are not strictly limited, which has high design flexibility and wide applicability. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments 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, wherein: Figure 1 A schematic diagram of the traditional Birdbath optical path structure Figure 1 ; Figure 2 A schematic diagram of the traditional Birdbath optical path structure Figure 2 ; Figure 3A schematic diagram of the traditional Birdbath optical path structure Figure 3 ; Figure 4 A schematic diagram of the traditional Birdbath optical path structure Figure 4 ; Figure 5 This is a schematic diagram of the Birdbath near-eye display module of the present invention. Figure 1 ; Figure 6 This is a schematic diagram of the Birdbath near-eye display module of the present invention. Figure 2 ; Figure 7 For Figure 6 A schematic diagram showing the separation of the ghost optical path G1 and the main image optical path M using PC material in the second phase retardation plate under the same architecture; Figure 8 This is a schematic diagram of the Birdbath near-eye display module of the present invention. Figure 3 ; Figure 9 This is a schematic diagram of the Birdbath near-eye display module of the present invention. Figure 4 ; The following are labeled in the figure: 1, image generation unit; 10, first polarization converter; 2, lens unit; 3, plane mirror unit; 30, plane mirror; 31, second polarization converter; 311, second polarizer; 312, first reflective polarizer; 4, curved mirror unit; 40, third polarization converter; 41, curved mirror; 5, second phase difference plate. Detailed Implementation

[0022] In the description of this invention, it should be noted that the directional terms such as "center", "horizontal (X)", "longitudinal (Y)", "vertical (Z)", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", and "counterclockwise" indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific protection scope of this invention.

[0023] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features. Thus, the use of "first" and "second" to define a feature may explicitly or implicitly include one or more of that feature. In the description of this invention, "several" or "a number" means two or more, unless otherwise explicitly specified.

[0024] Example 1 (for Ghost Image 1): like Figure 5 As shown, the optical path sequentially includes an image generation unit 1, a first polarization converter 10, a lens unit 2, a plane mirror unit 3, and a curved mirror unit 4. The first polarization converter 10 includes a first polarizer and a first phase retardation plate. The plane mirror unit 3 includes a plane mirror 30 and a second polarization converter 31. The second polarization converter 31 includes a second polarizer 311, a first reflective polarizer 312, and a second phase retardation plate 5. The surface of the curved mirror unit 4 is coated with a transmissive or total reflective film.

[0025] Both the first polarizer and the second polarizer 311 are absorption polarizers. The transmission axes of the first polarizer and the second polarizer 311 are parallel or orthogonal. The transmission axes of the first reflective polarizer 312 and the second polarizer 311 are parallel. The slow axis of the first phase retardation plate forms a 45° angle (typical value or other angle) with the transmission axis of the first polarizer. The slow axis of the second phase retardation plate 5 forms a 45° angle with the transmission axis of the first reflective polarizer 312. The slow axes of the first phase retardation plate and the second phase retardation plate 5 are parallel or orthogonal. In particular, the second phase retardation plate 5 uses a liquid crystal phase retardation plate.

[0026] In this architecture, the ghost image optical path G1 is almost identical to the main image optical path M because the thickness of the liquid crystal phase retardation plate is much thinner than that of the ordinary PC phase retardation plate, so it is not perceived by the user. The second phase retardation plate 5 in the figure uses a liquid crystal phase retardation plate with a thickness of less than 10μm, so there is no thickness. It is attached to the surface of the first reflective polarizer 312.

[0027] Furthermore, in the present invention, the first polarization converter 10 can be eliminated. In the traditional Birdbtah optical path, eliminating the first polarization converter 10 will cause the reflectivity of the ghost image optical path G1 to increase significantly due to the lack of polarization-locking effect, resulting in a significant increase in ghost image intensity. However, in the present invention, the ghost image optical path G1 will not be perceived by the user because it overlaps with the main image optical path M, thus reducing the overall process technology and manufacturing cost of the module.

[0028] Example 2 (for Ghost Image 1): like Figure 6 As shown, along the optical path, there are sequentially an image generation unit 1, a first polarization converter 10, a lens unit 2, a plane mirror unit 3, and a curved mirror unit 4. The first polarization converter 10 includes a first polarizer. The plane mirror unit 3 includes a plane mirror 30 and a second polarization converter 31. The second polarization converter 31 includes a second polarizer 311 and a first reflective polarizer 312. The curved mirror unit 4 includes a third polarization converter 40 and a curved mirror 41. The third polarization converter 40 includes a second phase retardation plate 5. The surface of the curved mirror unit 4 is coated with a transmissive or total reflective film.

[0029] Both the first polarizer and the second polarizer 311 are absorption polarizers. The transmission axes of the first polarizer and the second polarizer 311 are orthogonal. The transmission axes of the first reflective polarizer 312 and the second polarizer 311 are parallel. The slow axis of the second phase retardation plate 5 forms a 45° angle (typical value or other angle) with the transmission axis of the second polarizer 311. A specific second phase retardation plate 5 uses a liquid crystal phase retardation plate.

[0030] Under this architecture, the ghost image reflected from the central optical path and the main image almost overlap under the condition of other PC material phase retardation plates. It is necessary to analyze the ghost image of the large-angle optical path. The ghost image optical path G1 still comes from the reflection of the phase retardation plate-air interface. Since the thickness of the liquid crystal phase retardation plate is much thinner than that of the ordinary PC phase retardation plate, the ghost image optical path and the main image optical path are almost overlapped and are not perceived by the user. The second phase retardation plate 5 in the figure uses a liquid crystal phase retardation plate with a thickness of about 10μm or less, so there is no thickness. It is attached to the surface of the curved mirror 41.

[0031] Furthermore, in the present invention, the first polarization converter 10 can be eliminated. In the traditional Birdbtah optical path, eliminating the first polarization converter 10 will cause the reflectivity of the ghost image optical path G1 to increase significantly due to the lack of polarization-locking effect, resulting in a significant increase in ghost image intensity. However, in the present invention, the ghost image optical path G1 will not be perceived by the user because it overlaps with the main image optical path M, thus reducing the overall process technology and manufacturing cost of the module. Figure 7 For the same Figure 6 Under the same architecture, the second phase difference plate 5 uses PC material, which will cause the ghost image optical path G1 to separate from the main image optical path M.

[0032] In the above example, the first polarization converter 10 and the lens unit 2 are not restricted in their order or the position of the film. The other polarization devices only need to meet the requirement that from the human eye side to the environment side, they are an absorptive polarizer, a reflective polarizer, and a liquid crystal phase difference plate. It is also not restricted whether an AR film is added at the medium-air interface.

[0033] In the above embodiments, except for the specific description of adding the AR functional layer, the AR functional layer can be added to other media-air interfaces as appropriate.

[0034] Example 3 (for ghost images one and two): like Figure 8As shown, the optical path sequentially includes an image generation unit 1, a first polarization converter 10, a lens unit 2, a plane mirror unit 3, and a curved mirror unit 4. The first polarization converter 10 includes a first polarizer and a first phase reversal plate. The plane mirror unit 3 includes a plane mirror 30 and a second polarization converter 31. The plane mirror 30 has an AR functional layer (coated or applied) added to the surface near the human eye. The second polarization converter 31 includes a second polarizer 311, a first reflective polarizer 312, and a second phase reversal plate 5. The surface of the curved mirror unit 4 is coated with a transflective film.

[0035] Both the first polarizer and the second polarizer 311 are absorption polarizers. The transmission axes of the first polarizer and the second polarizer 311 are parallel (or or orthogonal). The transmission axes of the first reflective polarizer 312 and the second polarizer 311 are parallel and parallel to the optical path cross section. The slow axis of the first phase retardation plate forms a 45° angle (typical value or other angle) with the transmission axis of the first polarizer. The slow axis of the second phase retardation plate 5 forms a 45° angle with the transmission axis of the first reflective polarizer 312. In this embodiment, the second phase retardation plate 5 still uses a liquid crystal type to eliminate ghost image optical path G1. The slow axes of the first phase retardation plate and the second phase retardation plate 5 are parallel or orthogonal. The design value of the oblique angle θ of the plane mirror unit 3 must satisfy tan(θ) = n2 / n1, where n2 is the air refractive index and n1 is the refractive index of the plane mirror 30. At the same time, the angle θ can have a tolerance of ±20°.

[0036] In this architecture, the first reflection of the ghost image in the part of the plane mirror 30 through the second polarizer 311 and the first reflective polarizer 312 is P light relative to the incident surface due to the transmission axis direction of the second polarizer 311 and the first reflective polarizer 312. According to the oblique angle θ of the plane mirror unit 3, the reflectivity will be greatly reduced or even close to 0 according to optical principles. This blocks the subsequent light path propagation and suppresses the ghost image to a state that is invisible to the user. Based on this principle, the AR function layer on the side of the plane mirror 30 near the human eye can be cancelled as appropriate.

[0037] Furthermore, in the present invention, the first polarization converter 10 can be eliminated. In the traditional Birdbtah optical path, eliminating the first polarization converter 10 will cause the ghost image second optical path G2 to increase significantly during the first direct light transmission due to the lack of polarization locking effect, and the reflectivity and light intensity will also increase significantly, resulting in a significant increase in ghost image intensity. However, in the present invention, the ghost image second optical path G2 can reduce the first reflectivity to near 0 even with a large amount of light leakage due to its special axial design, thereby eliminating the ghost image second optical path G2 and reducing the overall process technology and manufacturing cost of the module.

[0038] Example 4 (for ghost images one and two): like Figure 9As shown, along the optical path, there are sequentially an image generation unit 1, a first polarization converter 10, a lens unit 2, a plane mirror unit 3, and a curved mirror unit 4. The first polarization conversion unit 10 includes a first polarizer, the plane mirror unit 3 includes a plane mirror 30 and a second polarization converter 31, the plane mirror 30 has an AR functional layer on the side near the human eye (the method of film application or coating is not limited), the second polarization converter 31 includes a second polarizer 311 and a first reflective polarizer 312, the curved mirror unit 4 includes a third polarization converter 40 and a curved mirror 41, the third polarization converter 40 includes a second phase retardation plate 5, and the surface of the curved mirror 41 is coated with a transflective film.

[0039] Both the first polarizer and the second polarizer 311 are absorption polarizers. The transmission axes of the first polarizer 1 and the second polarizer 311 are orthogonal. The transmission axes of the first reflective polarizer 312 and the second polarizer 311 are parallel and parallel to the optical path cross-section. The slow axis of the second phase retardation plate 5 forms a 45° angle (typical value or other angles) with the transmission axis of the second polarizer 311. A specific second phase retardation plate 5 uses a liquid crystal phase retardation plate to eliminate ghost images in optical path G1. The design value of the tilt angle θ of the plane mirror unit 3 must satisfy tan(θ) = n2 / n1, where n2 is the air refractive index and n1 is the refractive index of the plane mirror 30. At the same time, the angle θ can have a tolerance of ±20°. In this architecture, the ghost image light path G2 first reflects light at the part of the plane mirror 30 ternary 3 that is directly transmitted through the plane mirror 30. Since the transmission axis direction of the second polarizer 311 and the first reflective polarizer 312 is set to P light relative to the incident surface, and the plane mirror unit 3 is set at the above-mentioned oblique angle θ, the reflectivity will be greatly reduced or even close to 0 according to the optical principle. This blocks the subsequent light path propagation and suppresses the ghost image to a state that is invisible to the user (regardless of the angle or the center light). Based on this principle, the AR function layer on the side of the plane mirror 30 near the human eye can be cancelled as appropriate.

[0040] Furthermore, in the present invention, the first polarization converter 10 can be eliminated. In the traditional Birdbtah optical path, eliminating the first polarization converter 10 will cause the ghost image second optical path G2 to increase significantly during the first direct light transmission due to the lack of polarization locking effect, and the reflectivity and light intensity will also increase significantly, resulting in a significant increase in ghost image intensity. However, in the present invention, the ghost image second optical path G2 can reduce the first reflectivity to near 0 even with a large amount of light leakage due to its special axial design, thereby eliminating the ghost image second optical path G2 and reducing the overall process technology and manufacturing cost of the module.

[0041] In the above embodiments, the first polarization converter 10 and the lens unit 2 are not restricted in their order or the position of the film. The other polarization devices only need to be an absorptive polarizer, a reflective polarizer, and a liquid crystal phase difference plate in sequence from the human eye side to the environment side. It is also not restricted whether an AR film is added at the medium-air interface.

[0042] In the above embodiments, except for the specific description of adding the AR functional layer, the AR functional layer can be added to other media-air interfaces as appropriate.

[0043] advantage: 1. Effectively eliminates ghosting and significantly improves image quality: This invention incorporates a liquid crystal phase retardation plate in the plane mirror unit 3 and / or the curved mirror unit 4, with its thickness strictly controlled (below 10μm). This ensures that the ghosting light path generated by reflection at the phase retardation plate-air interface almost coincides with the main image light path, making it visually imperceptible to the user and effectively eliminating ghosting interference caused by Fresnel reflection at the interface in the traditional Birdbath scheme. Simultaneously, through a specific design of the oblique angle of the plane mirror unit 3 (satisfying tan(θ) = n2 / n1), the reflectivity of directly transmitted light on the side of the plane mirror 30 closest to the human eye is significantly reduced, even approaching 0, thereby blocking the subsequent propagation of the ghosting light path and further suppressing the ghosting to a state invisible to the user.

[0044] 2. Allows for simplified module structure and reduced manufacturing costs: The technical solution of this invention allows the first polarization converter 10 to be eliminated without causing an increase in ghost image intensity. In the traditional Birdbath optical path, eliminating the first polarization converter 10 leads to a significant increase in ghost image intensity due to the lack of polarization-locking effect; however, thanks to the ultra-thin characteristics and special axial design of the liquid crystal phase retardation plate, this invention can effectively eliminate or suppress ghost images even if the first polarization converter 10 is eliminated, thereby reducing the overall process technology and manufacturing cost of the module.

[0045] 3. Optimized polarization device configuration to improve optical path efficiency: This invention rationally configures the transmission axis direction of each polarization device: the transmission axis of the second polarizer 311 is parallel to that of the first reflective polarizer 312 and parallel to the optical path cross-section of the module; the slow axis of the second phase difference plate 5 forms a 45° angle with the transmission axis of the first reflective polarizer 312 (or the second polarizer 311). Simultaneously, both the first and second polarizers 311 are absorption-type polarizers, making polarization state conversion in the optical path more precise and efficient, reducing stray light caused by imperfect performance of the polarization devices.

[0046] 4. Enhanced ambient light transmittance and improved user experience: The present invention sets an AR functional layer (anti-reflective film) on the side of the plane mirror 30 near the human eye, and the surface of the curved mirror 41 is coated with a transflective film, which not only optimizes the transmission efficiency of the imaging light path, but also enhances the transmittance of external ambient light, so that users can observe the real scene more clearly when wearing it, and improve the overall effect of the augmented reality experience.

[0047] 5. Flexible solutions and wide applicability: This invention provides multiple embodiments, in which the second phase retardation plate 5 can be placed in the plane mirror unit 3 or in the curved mirror unit 4; the first polarization converter 10 can be selected as a complete solution including the first polarizer and the first phase retardation plate, or it can be simplified to a solution including only the first polarizer; the arrangement order and film application position of each polarization device are not strictly limited, which has high design flexibility and wide applicability.

[0048] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A Birdbath near-eye display module for eliminating ghosting, characterized in that: The device includes, in sequence along the optical path, an image generation unit, a lens unit, a plane mirror unit, and a curved mirror unit. The plane mirror unit includes a plane mirror and a second polarization converter. The second polarization converter includes a second polarizer and a first reflective polarizer. The plane mirror unit and the curved mirror unit are provided with a second phase retardation plate. The second phase retardation plate is a liquid crystal phase retardation plate with a thickness of less than 10 μm.

2. The Birdbath near-eye display module for eliminating ghosting as described in claim 1, characterized in that: The second phase retardation plate is disposed in the plane mirror unit and is attached to the surface of the first reflective polarizer. The slow axis of the second phase retardation plate forms a 45° angle with the transmission axis of the first reflective polarizer, and the transmission axes of the second polarizer and the first reflective polarizer are parallel.

3. A Birdbath near-eye display module for eliminating ghosting as described in claim 1 or 2, characterized in that: The module also includes a first polarization converter, which is disposed between the image generation unit and the lens unit. The first polarization converter includes a first polarizer and a first phase retardation plate. The slow axis of the first phase retardation plate forms a 45° angle with the transmission axis of the first polarizer. The slow axes of the first phase retardation plate and the second phase retardation plate are parallel or orthogonal. The transmission axes of the first polarizer and the second polarizer are parallel or orthogonal.

4. The Birdbath near-eye display module for eliminating ghosting as described in claim 3, characterized in that: Both the first polarizer and the second polarizer are absorption polarizers.

5. The Birdbath near-eye display module for eliminating ghosting as described in claim 1, characterized in that: The curved mirror unit includes a third polarization converter and a curved mirror. The third polarization converter includes a second phase retardation plate attached to the surface of the curved mirror. The second polarization converter includes a second polarizer and a first reflective polarizer.

6. The Birdbath near-eye display module for eliminating ghosting as described in claim 5, characterized in that: The module also includes a first polarization converter, which is disposed between the image generation unit and the lens unit. The first polarization converter includes a first polarizer, which is an absorption polarizer, and the transmission axes of the first polarizer and the second polarizer are orthogonal.

7. A Birdbath near-eye display module for eliminating ghosting as described in claim 5 or 6, characterized in that: The second polarizer is an absorption polarizer. The transmission axis of the first reflective polarizer is parallel to that of the second polarizer, and the slow axis of the second phase difference plate forms a 45° angle with the transmission axis of the second polarizer.

8. A Birdbath near-eye display module for eliminating ghosting as described in claim 2 or 5, characterized in that: The tilt angle θ of the plane mirror unit satisfies tan(θ) = n2 / n1, where n2 is the air refractive index and n1 is the refractive index of the plane mirror, and the tolerance of the tilt angle θ is ±20°.

9. A Birdbath near-eye display module for eliminating ghosting as described in claim 8, characterized in that: The plane mirror contains an AR functional layer on the side closest to the human eye, and the curved mirror surface is coated with a transflective film.

10. A Birdbath near-eye display module for eliminating ghosting as described in claim 9, characterized in that: The transmission axes of the second polarizer and the first reflective polarizer are parallel to each other and parallel to the optical path cross section of the module.

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