Pancake lens and near-eye display device

Abstract

This utility model relates to a pancake lens and a near-eye display device, comprising a first lens, a polarization reflection modulation element, a second lens, a semi-transparent and semi-reflective coating, and a display assembly arranged sequentially along the optical axis from the first side to the second side; the first lens has a first surface near the first side and a second surface near the second side, the first surface being an extended odd-order aspherical and the second surface being a plane; the second lens has a third surface near the first side and a fourth surface near the second side, the third surface being a plane or an extended odd-order aspherical and the fourth surface being an extended odd-order aspherical; the polarization reflection modulation element is disposed on the second surface, and the semi-transparent and semi-reflective coating is disposed on the fourth surface; the polarization reflection modulation element replaces the QWP-RP composite film, and the overall lens structure is optimized by utilizing the reflection phase modulation capability of the polarization reflection modulation element, resulting in excellent imaging performance of the lens itself, and the assembly is much easier than the traditional refractive-diffraction hybrid design, and its comprehensive parameter indicators are no less than those of existing lenses.

Description

Technical Field

[0001] This utility model relates to the field of near-eye optical imaging technology, and in particular to a pancake lens and a near-eye display device. Background Technology

[0002] With the development of near-eye optical imaging technology, the pancake lens solution, with its advantages of being thin and light, has gradually replaced aspherical lenses and Fresnel lenses as the mainstream solution. The optical principle of a traditional pancake lens is that a QWP-RP composite film (Quarter Wave Plate + Reflective Polarizer), composed of a quarter-wave plate and a polarizing reflective film, reflects light of one polarization state and transmits light of another orthogonal polarization state. When the imaging light passes through the semi-reflective film, it reaches the QWP-RP composite film. The QWP-RP composite film reflects the light of the first polarization state and transmits light of the second polarization state, which is orthogonal to the first polarization state. The light of the first polarization state is reflected back to the semi-reflective film by the QWP-RP composite film, and after being reflected again by the semi-reflective film, its polarization state becomes the first polarization state, which can then be transmitted by the QWP-RP composite film. By combining the semi-reflective film and the QWP-RP composite film, optical path folding can be achieved, compressing the overall length of the lens and facilitating the thinning of VR lenses.

[0003] Existing pancake lenses generally employ a 2- or 3-element lens design, focusing primarily on pure geometric optics. Due to the limited number of lenses, many aberrations cannot be effectively eliminated, especially on-axis chromatic aberration caused by material dispersion, thus creating a bottleneck in image quality optimization. The use of Micro OLEDs instead of LCD screens in modern VR devices is a major trend. OLED screens are smaller but have higher pixel density, placing higher demands on the spatial resolution of pancake lenses, making the design of lenses based on pure geometric optics increasingly challenging. Traditional pancake lenses typically use a combination of high and low Abbe number materials to eliminate on-axis chromatic aberration. However, the design principles of pancake lenses themselves—thinness and lightness, control of material stress birefringence, and considerations of cost and weight—make it difficult to design a standard-compliant pancake lens using this method.

[0004] Some pancake lens designs integrate a planar diffraction lens, utilizing the property that chromatic aberration from diffraction and refraction can cancel each other out to optimize the pancake lens and enhance its resolving power. However, adding a diffraction lens to an existing pancake lens increases the complexity of lens assembly.

[0005] Furthermore, current pancake lens designs based on traditional geometric optics are increasingly inclined to use curved surfaces for the entire lens to increase the system's modulation capability. This requires the QWP-RP composite film to be attached to the curved surface, and the curved film attachment process remains a major challenge, resulting in low production yield. Utility Model Content

[0006] Therefore, it is necessary to provide a pancake lens and near-eye display device to address the problem that existing pancake lenses with pure geometric optics cannot eliminate chromatic aberration due to the insufficient number of lenses, resulting in poor image quality.

[0007] On one hand, this application provides a pancake lens, including a first lens, a polarization reflection modulation element, a second lens, a semi-transparent and semi-reflective coating, and a display assembly arranged sequentially along the optical axis from a first side to a second side; the first lens has a first surface near the first side and a second surface near the second side, the first surface being curved and the second surface being planar; the second lens has a third surface near the first side and a fourth surface near the second side, the third surface being planar or curved and the fourth surface being curved; the polarization reflection modulation element is disposed on the second surface, and the semi-transparent and semi-reflective coating is disposed on the fourth surface; the polarization reflection modulation element includes a CLC polarization reflection modulation device or a chiral metasurface.

[0008] In one embodiment, the surfaces in both the first and second lenses are extended odd-order aspherical surfaces.

[0009] In one embodiment, the phase modulation model of the polarization reflection modulation element is a binary surface model.

[0010] In one embodiment, the CLC polarization reflection modulation device is one or more combinations of CLC liquid crystal cell, CLC thin film and CLC-PB composite film.

[0011] In one embodiment, the first surface is provided with an anti-reflective film.

[0012] In one embodiment, the third surface is planar, and the polarization reflection modulation element is bonded to the second surface and the third surface.

[0013] In one embodiment, the third surface is curved and has an anti-reflective coating.

[0014] In one embodiment, the polarization reflection modulation element has an anti-reflection coating on the surface near the second lens.

[0015] In one embodiment, the entrance pupil diameter of the Pancake lens ranges from 4 mm to 5 mm.

[0016] In one embodiment, the exit pupil distance of the Pancake lens ranges from 24mm to 27mm.

[0017] In one embodiment, the Pancake lens has a field of view ranging from 90° to 110°.

[0018] In one embodiment, when the display component is the OLED display screen, the diameter of the OLED display screen ranges from 30mm to 38mm, the total length of the Pancake lens ranges from 16mm to 20mm, and the equivalent focal length of the Pancake lens ranges from 18mm to 21mm.

[0019] In one embodiment, the display component is an LCD display screen with a diameter ranging from 50mm to 66mm, the total length of the pancake lens ranging from 23mm to 31mm, and the equivalent focal length of the pancake lens ranging from 25mm to 30mm.

[0020] In one embodiment, the Pancake lens has an F-number range of 4mm to 6mm.

[0021] In one embodiment, the image light emitted by the display component is RGB light.

[0022] On the other hand, this application provides a near-eye display device, comprising: a device body; and a Pancake lens as described above, the Pancake lens being mounted on the device body.

[0023] In summary, the Pancake lens of this application utilizes a polarization reflection modulation element instead of a QWP-RP composite film, and optimizes the overall lens structure by leveraging the reflection phase modulation capability of the polarization reflection modulation element. This results in excellent imaging performance and is much easier to assemble than the traditional refractive-diffraction hybrid design. Its overall performance parameters are comparable to existing lenses. Furthermore, since the polarization reflection modulation element itself possesses phase modulation capability, a CLC plane can be used to replace the curved surface in the existing Pancake design, achieving flat-to-flat replacement, increasing the production yield of the Pancake lens, and reducing costs. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the Pancake lens according to Embodiment 1 of this application;

[0025] Figure 2a The red MTF image of the Pancake lens for Reference Example 1 of this application;

[0026] Figure 2b The green MTF plot of the Pancake lens for Reference Example 1 of this application;

[0027] Figure 2c Blue MTF plot of the Pancake lens for Reference Example 1 of this application;

[0028] Figure 3a The red MTF image of the Pancake lens in Embodiment 1 of this application;

[0029] Figure 3b The green MTF image of the Pancake lens in Embodiment 1 of this application;

[0030] Figure 3c Blue MTF image of the Pancake lens of Embodiment 1 of this application;

[0031] Figure 4 This is a schematic diagram of the Pancake lens in Embodiment 2 of this application;

[0032] Figure 5a The red MTF image of the Pancake lens in Embodiment 2 of this application;

[0033] Figure 5b The green MTF image of the Pancake lens in Embodiment 2 of this application;

[0034] Figure 5c The blue MTF image of the Pancake lens in Embodiment 2 of this application;

[0035] Figure 6 This is a schematic diagram of the Pancake lens according to Embodiment 3 of this application;

[0036] Figure 7a The red MTF image of the Pancake lens in Embodiment 3 of this application;

[0037] Figure 7b The green MTF image of the Pancake lens in Embodiment 3 of this application;

[0038] Figure 7c The blue MTF diagram of the Pancake lens in Embodiment 3 of this application;

[0039] Figure 8 This is a schematic diagram of the Pancake lens in Embodiment 4 of this application;

[0040] Figure 9a The red MTF image of the Pancake lens in Embodiment 4 of this application;

[0041] Figure 9b The green MTF image of the Pancake lens in Embodiment 4 of this application;

[0042] Figure 9c Blue MTF image of the Pancake lens in Embodiment 4 of this application;

[0043] Figure 10 This is a schematic diagram of the Pancake lens in Embodiment 5 of this application;

[0044] Figure 11a The red MTF image of the Pancake lens in Embodiment 5 of this application;

[0045] Figure 11b The green MTF image of the Pancake lens in Embodiment 5 of this application;

[0046] Figure 11c Blue MTF image of the Pancake lens of Embodiment 5 of this application;

[0047] Figure 12 This is a schematic diagram of the Pancake lens in Embodiment Six of this application;

[0048] Figure 13a The red MTF plot of the Pancake lens for Reference Example 2 of this application;

[0049] Figure 13b The green MTF plot of the Pancake lens for Reference Example 2 of this application;

[0050] Figure 13c Blue MTF plot of the Pancake lens for Reference Example 2 of this application;

[0051] Figure 14a The red MTF image of the Pancake lens in Embodiment Six of this application;

[0052] Figure 14b The green MTF image of the Pancake lens in Embodiment Six of this application;

[0053] Figure 14c The blue MTF diagram of the Pancake lens in Embodiment Six of this application.

[0054] Reference numerals: 10, first lens; 11, first surface; 12, second surface; 20, polarization reflection modulation element; 30, second lens; 31, third surface; 32, fourth surface; 40, display component. Detailed Implementation

[0055] To make the above-mentioned objects, features, and advantages of this utility model more apparent and understandable, the specific embodiments of this utility model will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a full understanding of this utility model. However, this utility model can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this utility model. Therefore, this utility model is not limited to the specific embodiments disclosed below.

[0056] In the description of this utility model, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this utility model and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model.

[0057] 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 indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this utility model, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0058] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0059] In this utility model, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0060] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0061] Specifically, this application provides a Pancake lens, which may include a first lens 10, a polarization reflection modulation element 20, a second lens 30, a semi-transparent and semi-reflective film, and a display component 40 arranged sequentially along the optical axis from the first side to the second side; the first lens 10 has a first surface 11 near the first side and a second surface 12 near the second side, the first surface 11 being curved and the second surface 12 being planar; the second lens 30 has a third surface 31 near the first side and a fourth surface 32 near the second side, the third surface 31 being planar or curved and the fourth surface 32 being curved; the polarization reflection modulation element 20 is disposed on the second surface 12, and the semi-transparent and semi-reflective film is disposed on the fourth surface 32; the polarization reflection modulation element 20 includes a CLC polarization reflection modulation device (cholesterol phase liquid crystal polarization reflection modulation device) or a chiral metasurface.

[0062] It is understandable that the polarization reflection modulation element 20 can reflect circularly polarized light within a certain wavelength band and project corresponding orthogonally circularly polarized light, consistent with the optical characteristics of the QWP-RP composite film. Furthermore, the polarization reflection modulation element 20 not only performs the task of polarization reflection but also adds geometric phase while reflecting circularly polarized light, completing phase modulation of the reflected light. The Pancake lens of this application utilizes the polarization reflection modulation element 20 instead of the QWP-RP composite film and optimizes the overall lens structure using the reflection phase modulation capability of the polarization reflection modulation element 20. This results in excellent imaging performance, and the assembly is much easier than the traditional refractive-diffractive hybrid design. Its overall parameter performance is comparable to existing lenses. Moreover, since the polarization reflection modulation element 20 itself possesses phase modulation capability, a CLC plane can be used to replace the curved surface in the existing Pancake design, achieving flat-to-flat replacement, increasing the production yield of the Pancake lens, and reducing costs.

[0063] The surfaces of the first lens element 10 and the second lens element 30 are both extended odd-order aspherical surfaces, ensuring the design flexibility of the pancake lens. The expression for an extended odd-order aspherical surface is as follows:

[0064] ;

[0065] Where z = z(r) is the corresponding sag at lens height r, c is the curvature, r is the lens height variable, k is the conic coefficient, and N is the number of terms in the maximal polynomial. For each term, These are normalized lens aperture coordinates.

[0066] More specifically, in some embodiments, the phase modulation model of the polarization reflection modulation element 20 is a two-dimensional surface model. The phase distribution expression of the two-dimensional surface model is:

[0067]

[0068] Where M is the diffraction order utilized by the polarization reflection modulation element 20, and N is the maximum number of polynomial terms. The coefficients of each term in the phase distribution expression are: These are normalized lens aperture coordinates.

[0069] It is worth noting that during optimization, the normalization coefficient is usually taken as 1, therefore Same as r.

[0070] Preferably, considering the diffraction characteristics of CLC, all diffractions are of the first order, so M is set to 1.

[0071] Optionally, in some embodiments, the CLC polarization reflection modulation device of this application is one or more combinations of CLC liquid crystal cell (cholesterol liquid crystal cell), CLC thin film (cholesterol liquid crystal thin film), and CLC-PB composite film (cholesterol liquid crystal polarization reflection composite film). The CLC liquid crystal cell may include two glass substrates and a layer of CLC liquid crystal sandwiched between the glass substrates, or it may include two glass substrates, a cured multilayer CLC liquid crystal thin film sandwiched between the glass substrates, and a layer of CLC liquid crystal sandwiched between the glass substrates. The CLC thin film may include a glass substrate and one or more CLC liquid crystal thin films cured on the glass substrate, or it may include a soft substrate and one or more CLC liquid crystal thin films cured on the soft substrate. The glass substrate may be made of quartz glass and may or may not have a transparent electrode attached. The thickness of the glass substrate ranges from 0.5 mm to 0.7 mm. The soft substrate may include, but is not limited to, common optical thin film substrate materials such as PET. The CLC-PB composite film or chiral metasurface can achieve dual-channel modulation, thereby further enhancing the modulation capability of the pancake lens while reducing the overall length of the lens.

[0072] Optionally, in some embodiments, the first surface 11 of the first lens 10 is provided with an anti-reflection coating, which can improve the light transmittance of the first lens 10, reduce stray light and ghosting, and improve the imaging quality of the pancake lens.

[0073] Optionally, in some embodiments, the third surface 31 is planar, and the polarization reflection modulation element 20 is bonded to the second surface 12 and the third surface 31. In other words, the first lens 10, the polarization reflection modulation element 20, and the second lens 30 are bonded together, which can reduce the air-to-lens interface and thus reduce the use of anti-reflective coatings.

[0074] It is worth noting that when the polarization reflection modulation element 20 is not bonded to the third surface 31, the surface of the polarization reflection modulation element 20 near the second lens 30 is provided with an anti-reflection film to enhance the transmission effect of the polarization reflection modulation element 20, reduce stray light and ghosting, and improve the imaging quality of the pancake lens.

[0075] Optionally, in some embodiments, the third surface 31 is curved and has an anti-reflection coating. Thus, by providing an anti-reflection coating on the third surface 31 of the second lens 30, the light transmittance of the second lens 30 can be improved, stray light and ghosting can be reduced, and the image quality of the pancake lens can be improved.

[0076] Furthermore, in some embodiments, the Pancake lens of this application adopts a reverse design, with the virtual image plane of the Pancake lens as the object plane, the eyebox of the Pancake lens as the entrance pupil, and the light-emitting surface of the display component 40 as the image plane of the refractive-diffraction hybrid Pancake lens. This makes evaluating image quality more intuitive, allowing the final imaging performance of the Pancake lens to be directly measured using the parameters of the display component 40, especially the pixel density.

[0077] Optionally, considering that the human eye generally only focuses on a field of view of ±5° when viewing an object, and the eyeball rotates when looking at other locations, the Pancake lens in some embodiments of this application is designed according to the characteristics of eyeball rotation to ensure that the position and angle of the entrance pupil of the Pancake lens are optimal within a range of ±5° from the entrance pupil position, thus guaranteeing the clearest field of view. In this way, the entrance pupil size is designed to be essentially the same as the size of the human eye pupil, not too large, which is beneficial for optimizing the performance of the optical system and ensures that the simulation results are consistent with the actual viewing effect of the human eye.

[0078] Optionally, in some embodiments, since the pupil size of the human eye is generally in the range of 4mm to 5mm, the entrance pupil diameter of the Pancake lens of this application is in the range of 4mm to 5mm.

[0079] Optionally, in some embodiments, the equivalent exit pupil distance of the Pancake lens is the sum of the distance from the entrance pupil of the Pancake lens to the first surface 11 of the first lens 10 and the rotation radius of the human eyeball. That is, the range of the equivalent exit pupil distance is increased by 12mm compared with the actual exit pupil distance. Therefore, the range of the exit pupil distance of the Pancake lens of this application is 24mm to 27mm.

[0080] Simultaneously, when designing the Pancake lens, it's necessary to consider that when viewing the edges of an image, the human eye often turns its head rather than continuing to rotate its eyeballs. In this case, the interaction system on the VR device can determine the angle of the user's head rotation, thereby adjusting the image position on the display screen so that the edge of the original image can be observed when the head rotates. In the design of this application's Pancake lens, the field of view angle that needs to be examined and optimized is at most 35° under the equivalent exit pupil distance, to further reduce the optimization difficulty of the Pancake lens. To ensure immersion, a field of view angle of over 90° needs to be maintained when the eyeballs are not rotating, meaning the edges can be seen. Therefore, the image height of this application's Pancake lens needs to be controlled according to the field of view ratio.

[0081] Optionally, in some embodiments, the eyebox size of the Pancake lens of this application ranges from 4mm to 5mm, and the field of view of the Pancake lens of this application ranges from 90° to 110°.

[0082] Optionally, in some embodiments, the display component 40 can be an OLED display or an LCD display. When the display component 40 is an OLED display, the diameter of the OLED display ranges from 30mm to 38mm, the total length of the pancake lens ranges from 16mm to 20mm, and the equivalent focal length of the pancake lens ranges from 18mm to 21mm. When the display component 40 is an LCD display, the diameter of the LCD display ranges from 50mm to 66mm, the total length of the pancake lens ranges from 23mm to 31mm, and the equivalent focal length of the pancake lens ranges from 25mm to 30mm.

[0083] Optionally, in some embodiments, the image light emitted by the display component 40 is RGB light, wherein the wavelength range of red light is 630nm to 650nm, the wavelength range of green light is 530nm to 550nm, and the wavelength range of blue light is 450nm to 470nm.

[0084] Optionally, in some embodiments, the F-number of the Pancake lens of this application ranges from 4 to 6.

[0085] For example, the present application will be further described below with reference to specific embodiments.

[0086] Example 1

[0087] like Figure 1 As shown, the Pancake lens of this embodiment may include a first lens 10, a polarization reflection modulation element 20, a second lens 30, a semi-transparent and semi-reflective film, and a display assembly 40 arranged sequentially along the optical axis from the first side to the second side; the first lens 10 has a first surface 11 near the first side and a second surface 12 near the second side, the first surface 11 is convex and is an extended odd-order aspherical surface, the second surface 12 is planar, the second lens 30 has a third surface 31 near the first side and a fourth surface 32 near the second side, the third surface 31 is planar, and the fourth surface 32 is convex and is an extended odd-order aspherical surface.

[0088] In this embodiment, the display component 40 is an LCD screen with a diameter of 50mm to 65mm. The exit pupil distance of the pancake lens is 15mm, the field of view is 90°, and the eye box size is 5mm, designed to accommodate eye movement. The total length of the pancake lens is 29mm. The polarization reflection modulation element 20 is a CLC liquid crystal cell bonded to the second surface 12 and the third surface 31. The thickness of the CLC liquid crystal layer is 10μm to 60μm, the adhesive thickness is 50μm, and a semi-transparent, semi-reflective film is disposed on the fourth surface 32. In addition, the first surface 11 is coated with an anti-reflective film.

[0089] The specific parameters of the Pancake lens in this embodiment are shown in Table 1 below. The units for radius of curvature, thickness and half-aperture are all mm. The coefficients of the CLC phase plane are shown in Table 2 below. The aspherical coefficients used are shown in Table 3 below. All odd-order terms are 0 and therefore are not shown.

[0090] Table 1: Main parameters of the lens in Example 1

[0091]

[0092] Table 2: CLC phase surface coefficients of Example 1

[0093]

[0094] Table 3: Coefficients of each aspherical surface in Example 1

[0095]

[0096] Refer to Example 1

[0097] In the Pancake lens example of Reference Example 1, the Pancake lens of Reference Example 1 has the same frame and design parameters as that of Embodiment 1. The difference is that the polarization reflection modulation element 20 of the Pancake lens of Reference Example 1 functions the same as the QWP-RP composite film, without phase modulation. However, the polarization reflection modulation element of the Pancake lens of Embodiment 1 has reflection phase modulation function.

[0098] Figure 2a For reference, the red light MTF diagram of the Pancake lens in Example 1 has a wavelength of 0.642 μm. Figure 2b For reference, the green MTF diagram of the Pancake lens in Example 1 has a green light wavelength of 0.542 μm; Figure 2c For reference, the blue light MTF diagram of the Pancake lens in Example 1 has a blue light wavelength of 0.465μm; Figure 3a The image shows the red MTF of the Pancake lens in Example 1, with a red light wavelength of 0.642 μm. Figure 3b The image shows the green MTF of the Pancake lens in Example 1, with a green light wavelength of 0.542 μm. Figure 3cThe image shows the blue light MTF (Medium-to-Frequency Formulation) of the Pancake lens in Example 1, with a blue light wavelength of 0.465 μm. The horizontal axis of the MTF plot represents the field of view, and the vertical axis represents the MTF value. The reference frequencies are 5 lp / mm and 12 lp / mm. As can be seen from the figure, under the same architecture, the Pancake lens in Example 1 has a significant advantage over the Pancake lens in Reference Example 1 in both lens length and optical performance. Therefore, by introducing the polarization reflection modulation element 20, the Pancake lens achieves a significant improvement in imaging performance without changing its underlying architecture.

[0099] Example 2

[0100] like Figure 4 As shown, the Pancake lens of this embodiment may include a first lens 10, a polarization reflection modulation element 20, a second lens 30, a semi-transparent and semi-reflective film, and a display component 40 arranged sequentially along the optical axis from the first side to the second side; the first lens 10 has a first surface 11 near the first side and a second surface 12 near the second side, the first surface 11 is convex and is an extended odd-order aspherical surface, and the second surface 12 is planar; the second lens 30 has a third surface 31 near the first side and a fourth surface 32 near the second side, the third surface 31 is convex and is an extended odd-order aspherical surface, and the fourth surface 32 is convex and is an extended odd-order aspherical surface.

[0101] In this embodiment, the display component 40 is an LCD screen with a diameter of 50mm to 65mm. The exit pupil distance of the pancake lens is 15mm, the field of view is 90°, and the eye box size is 5mm, designed to accommodate eye movement. The total length of the pancake lens is 25mm. The polarization reflection modulation element 20 is a CLC liquid crystal cell bonded to the second surface 12. The thickness of the CLC liquid crystal layer is 10μm to 60μm, the adhesive thickness is 50μm, and a semi-transparent, semi-reflective film is disposed on the fourth surface 32. In addition, the first surface 11 and the third surface 31 are coated with anti-reflective films, and the unbonded surfaces of the CLC liquid crystal cell are coated with anti-reflective films or optical compound eye anti-reflective films.

[0102] The specific parameters of the Pancake lens in this embodiment are shown in Table 4 below. The units for radius of curvature, thickness and half-aperture are all mm. The coefficients of the CLC phase plane are shown in Table 5 below. The aspherical coefficients used are shown in Table 6 below. All odd-order terms are 0 and therefore are not shown.

[0103] Table 4: Main parameters of the lens in Example 2

[0104]

[0105] Table 5: CLC phase surface coefficients of Example 2

[0106]

[0107] Table 6: Coefficients of each aspherical surface in Example 2

[0108]

[0109] Figure 5a The image shows the red MTF of the Pancake lens in Example 2, with a red light wavelength of 0.642 μm. Figure 5b The image shows the green MTF of the Pancake lens in Example 2, with a green light wavelength of 0.542 μm. Figure 5c The image shows the blue light MTF of the Pancake lens in Example 2, with a blue light wavelength of 0.465 μm. The horizontal axis of the MTF chart represents the field of view, and the vertical axis represents the MTF value. The reference frequencies are 5 lp / mm and 12 lp / mm. The image shows that the Pancake lens in Example 2 also exhibits excellent imaging performance. However, due to the size limitation of the LCD screen restricting the system's magnification, the overall length of the lens is nearing its limit and difficult to compress.

[0110] Example 3

[0111] like Figure 6 As shown, the Pancake lens of this embodiment may include a first lens 10, a polarization reflection modulation element 20, a second lens 30, a semi-transparent and semi-reflective film, and a display component 40 arranged sequentially along the optical axis from the first side to the second side; the first lens 10 has a first surface 11 near the first side and a second surface 12 near the second side, the first surface 11 is convex and is an extended odd-order aspherical surface, and the second surface 12 is planar; the second lens 30 has a third surface 31 near the first side and a fourth surface 32 near the second side, the third surface 31 is convex and is an extended odd-order aspherical surface, and the fourth surface 32 is convex and is an extended odd-order aspherical surface.

[0112] In this embodiment, the display component 40 is an OLED display screen with a diameter of 30mm to 38mm. The exit pupil distance of the Pancake lens is 12mm, the field of view is 90°, and the eye box size is 4mm, designed to accommodate eye movement. The total length of the Pancake lens is 19.77mm. The polarization reflection modulation element 20 is a CLC liquid crystal cell bonded to the second surface 12. The thickness of the CLC liquid crystal layer is 10μm to 60μm, the adhesive thickness is 50μm, and a semi-reflective coating is disposed on the fourth surface 32. In addition, the first surface 11 and the third surface 31 are coated with anti-reflective films, and the unbonded surfaces of the CLC liquid crystal cell are coated with anti-reflective films or optical compound eye anti-reflective films.

[0113] The specific parameters of the Pancake lens in this embodiment are shown in Table 7 below. The units for radius of curvature, thickness and half-aperture are all mm. The coefficients of the CLC phase plane are shown in Table 8 below. The aspherical coefficients used are shown in Table 9 below. All odd-order terms are 0 and therefore are not shown.

[0114] Table 7: Main parameters of the lens in Example 3

[0115]

[0116] Table 8: CLC phase surface coefficients of Example 3

[0117]

[0118] Table 9: Coefficients of each aspherical surface in Example 3

[0119]

[0120] Figure 7a The image shows the red MTF of the Pancake lens in Example 3, with a red light wavelength of 0.642 μm. Figure 7b The image shows the green MTF of the Pancake lens in Example 3, with a green light wavelength of 0.542 μm. Figure 7c The image shows the blue light MTF of the Pancake lens in Example 3, with a blue light wavelength of 0.465 μm. The horizontal axis of the MTF image represents the field of view, and the vertical axis represents the MTF value. The reference frequencies are 5 lp / mm, 20 lp / mm, and 40 lp / mm.

[0121] Example 4

[0122] like Figure 8 As shown, the Pancake lens of this embodiment may include a first lens 10, a polarization reflection modulation element 20, a second lens 30, a semi-transparent and semi-reflective film, and a display component 40 arranged sequentially along the optical axis from the first side to the second side; the first lens 10 has a first surface 11 near the first side and a second surface 12 near the second side, the first surface 11 is convex and is an extended odd-order aspherical surface, and the second surface 12 is planar; the second lens 30 has a third surface 31 near the first side and a fourth surface 32 near the second side, the third surface 31 is convex and is an extended odd-order aspherical surface, and the fourth surface 32 is convex and is an extended odd-order aspherical surface.

[0123] In this embodiment, the display component 40 is an OLED display screen with a diameter of 30mm to 38mm. The exit pupil distance of the pancake lens is 12mm, the field of view is 90°, and the eye box size is 4mm, designed to accommodate eye movement. The total length of the pancake lens is 19.2mm. The polarization reflection modulation element 20 is a CLC liquid crystal cell bonded to the second surface 12. The thickness of the CLC liquid crystal layer is 10μm to 60μm, the adhesive thickness is 50μm, and a semi-reflective coating is disposed on the fourth surface 32. In addition, the first surface 11 and the third surface 31 are coated with anti-reflective films, and the unbonded surfaces of the CLC liquid crystal cell are coated with anti-reflective films or optical compound eye anti-reflective films.

[0124] The specific parameters of the Pancake lens in this embodiment are shown in Table 10 below. The units for radius of curvature, thickness and half-aperture are all mm. The coefficients of the CLC phase plane are shown in Table 11 below. The aspherical coefficients used are shown in Table 12 below. All odd-order terms are 0 and therefore are not shown.

[0125] Table 10: Key Lens Parameters of Example 4

[0126]

[0127] Table 11: CLC phase surface coefficients of Example 4

[0128]

[0129] Table 12: Coefficients of each aspherical surface in Example 4

[0130]

[0131] It is worth noting that, compared to Example 3, Example 4 has a smaller back focal distance but better image quality. The combination of Examples 3 and 4 demonstrates that the pancake lens designed based on the polarization reflection modulation element 20 offers greater design flexibility, allowing for optimization and trade-offs based on the required parameter range.

[0132] Figure 9a The image shows the red MTF of the Pancake lens in Example 4, with a red light wavelength of 0.642 μm. Figure 9b The image shows the green MTF of the Pancake lens in Example 4, with a green light wavelength of 0.542 μm. Figure 9c The image shows the blue light MTF of the Pancake lens in Example 4, with a blue light wavelength of 0.465 μm. The horizontal axis of the MTF image represents the field of view, and the vertical axis represents the MTF value. The reference frequencies are 5 lp / mm, 20 lp / mm, and 40 lp / mm.

[0133] Example 5

[0134] like Figure 10 As shown, the Pancake lens of this embodiment may include a first lens 10, a polarization reflection modulation element 20, a second lens 30, a semi-transparent and semi-reflective film, and a display component 40 arranged sequentially along the optical axis from the first side to the second side; the first lens 10 has a first surface 11 near the first side and a second surface 12 near the second side, the first surface 11 is concave and is an extended odd-order aspherical surface, the second surface 12 is planar, the second lens 30 has a third surface 31 near the first side and a fourth surface 32 near the second side, the third surface 31 is convex and is an extended odd-order aspherical surface, and the fourth surface 32 is convex and is an extended odd-order aspherical surface.

[0135] In this embodiment, the display component 40 is an OLED display screen with a diameter of 30mm to 38mm. The exit pupil distance of the Pancake lens is 12mm, the field of view is 100°, and the eye box size is 4mm, designed to accommodate eye movement. The total length of the Pancake lens is 16.03mm. The polarization reflection modulation element 20 is a CLC-PB composite film attached to the second surface 12, with the CLC surface facing the display component 40 and the PB surface facing the human eye. The thickness of the CLC liquid crystal layer is 10μm to 60μm, and the adhesive thickness is 50μm. The polarization reflection modulation element 20 can also be replaced by a chiral metasurface placed on the second surface 12. A semi-transparent and semi-reflective film is disposed on the fourth surface 32. In addition, the first surface 11 and the third surface 31 are coated with anti-reflective films, and the surface of the CLC-PB composite film is coated with an anti-reflective film or an optical compound eye anti-reflective film.

[0136] The specific parameters of the Pancake lens in this embodiment are shown in Table 13 below. The units of radius of curvature, thickness and half aperture are all mm. The coefficients of the CLC phase plane and the phase plane of the PB lens are shown in Table 14 below. The aspherical coefficients used are shown in Table 15 below. All odd-order terms are 0 and therefore not shown.

[0137] Table 13: Key Lens Parameters of Example 5

[0138]

[0139] Table 14: CLC phase surface coefficients of Example 5

[0140]

[0141] Table 15: Coefficients of each aspherical surface in Example 5

[0142]

[0143] It is worth noting that in Example 5, the use of CLC-PB composite film or chiral metasurface enables dual-channel modulation, further enhancing the modulation capability of the Pancake lens while reducing the overall length of the lens.

[0144] Figure 11a The image shows the red MTF of the Pancake lens in Example 5, with a red light wavelength of 0.642 μm. Figure 11b The image shows the green MTF of the Pancake lens in Example 5, with a green light wavelength of 0.542 μm. Figure 11c The image shows the blue light MTF of the Pancake lens in Example 5, with a blue light wavelength of 0.465 μm. The horizontal axis of the MTF image represents the field of view, and the vertical axis represents the MTF value. The reference frequencies are 5 lp / mm, 20 lp / mm, and 40 lp / mm.

[0145] As can be seen from the MTF diagrams of Examples 3 to 5, the Pancake lens exhibits excellent MTF performance. Even with the reference frequency being expanded to 40 lp / mm, the Pancake lens still delivers good optimization results, and the overall lens length is comparable to existing OLED display-based lens products.

[0146] Example 6

[0147] like Figure 12 As shown, the Pancake lens of this embodiment may include a first lens 10, a polarization reflection modulation element 20, a second lens 30, a semi-transparent and semi-reflective film, and a display component 40 arranged sequentially along the optical axis from the first side to the second side; the first lens 10 has a first surface 11 near the first side and a second surface 12 near the second side, the first surface 11 is convex and is an extended odd-order aspherical surface, and the second surface 12 is planar; the second lens 30 has a third surface 31 near the first side and a fourth surface 32 near the second side, the third surface 31 is convex and is an extended odd-order aspherical surface, and the fourth surface 32 is convex and is an extended odd-order aspherical surface.

[0148] In this embodiment, the display component 40 is an OLED display screen with a diameter of 30mm to 38mm. The exit pupil distance of the pancake lens is 12mm, the field of view is 110°, and the eye box size is 4mm, designed to accommodate eye movement. The total length of the pancake lens is 16.2mm. The polarization reflection modulation element 20 is a CLC liquid crystal film attached to the second surface 12, replacing the existing curved-surface-plus-curved-surface-bonded QWP-RP composite film design. The thickness of the CLC liquid crystal layer is 10μm to 60μm, and the adhesive thickness is 50μm. A semi-transparent and semi-reflective film is disposed on the fourth surface 32. In addition, the first surface 11 and the third surface 31 are coated with anti-reflective films.

[0149] The specific parameters of the Pancake lens in this embodiment are shown in Table 16 below. The units of radius of curvature, thickness and half-aperture are all mm. The coefficients of the CLC phase plane and the phase plane of the PB lens are shown in Table 17 below. The aspherical coefficients used are shown in Table 18 below. All odd-order terms are 0 and therefore not shown.

[0150] Table 16: Key Lens Parameters of Example Six

[0151]

[0152] Table 17: CLC phase surface coefficients of Example 6

[0153]

[0154] Table 18: Coefficients of each aspherical surface in Example 6

[0155]

[0156] See Example 2

[0157] In this second reference example, the Pancake lens uses a QWP-RP composite film and has no phase modulation function. The diameter of the OLED display is 30mm to 38mm, the exit pupil distance is 12mm, the field of view is 110°, and the total length of the lens is 15.87mm.

[0158] Figure 13a For reference, the red light MTF diagram of the Pancake lens in Example 2 has a wavelength of 0.642 μm. Figure 13b For reference, the green MTF diagram of the Pancake lens in Example 2 has a green light wavelength of 0.542 μm; Figure 13c For reference, the blue light MTF diagram of the Pancake lens in Example 2 has a blue light wavelength of 0.465μm; Figure 14a The image shows the red MTF of the Pancake lens in Example 6, with a red light wavelength of 0.642 μm. Figure 14b The image shows the green MTF of the Pancake lens in Example 6, with a green light wavelength of 0.542 μm. Figure 14c The image shows the blue light MTF of the Pancake lens in Example 6, with a blue light wavelength of 0.465 μm. The horizontal axis of the MTF chart represents the field of view, and the vertical axis represents the MTF value. The reference frequencies are 5 lp / mm and 12 lp / mm. The image shows that even after replacing the QWP-RP composite film with a polarization reflection modulation element 20 and using a flat mount instead of a curved mount, the imaging performance and overall length of the Pancake lens in Example 6 are still comparable to those in Reference Example 2, demonstrating the feasibility and advancement of Example 6.

[0159] On the other hand, this application provides a near-eye display device, which includes a device body and a pancake lens as described above, the pancake lens being mounted on the device body. This near-eye display device, based on the pancake lens, features miniaturization and thinness, and exhibits excellent imaging performance.

[0160] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0161] The above embodiments only illustrate several implementation methods of this utility model, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the utility model patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this utility model, and these all fall within the protection scope of this utility model. Therefore, the protection scope of this utility model patent should be determined by the appended claims.

Claims

1. A Pancake lens characterized in that, The device includes a first lens, a polarization reflection modulation element, a second lens, a semi-transparent and semi-reflective coating, and a display assembly arranged sequentially along the optical axis from a first side to a second side. The first lens has a first surface near the first side and a second surface near the second side. The first surface is curved, and the second surface is planar. The second lens has a third surface near the first side and a fourth surface near the second side. The third surface is either planar or curved, and the fourth surface is curved. The polarization reflection modulation element is disposed on the second surface, and the semi-transparent and semi-reflective coating is disposed on the fourth surface. The polarization reflection modulation element includes a CLC polarization reflection modulation device or a chiral metasurface.

2. The Pancake Lens according to claim 1, characterized in that, The curved surfaces in both the first and second lenses are extended odd-order aspherical surfaces.

3. The Pancake Lens according to claim 1, characterized in that, The phase modulation model of the polarization reflection modulation element is a binary surface model.

4. The Pancake Lens according to claim 1, characterized in that, The CLC polarization reflection modulation device is one or more combinations of CLC liquid crystal cell, CLC thin film and CLC-PB composite film.

5. The Pancake Lens according to claim 1, characterized in that, The first surface is provided with an anti-reflective film.

6. The Pancake Lens according to claim 1, characterized in that, The third surface is planar, and the polarization reflection modulation element is bonded to the second surface and the third surface.

7. The Pancake Lens according to claim 1, characterized in that, The third surface is curved and has an anti-reflective film.

8. The Pancake Lens according to claim 7, characterized in that, The polarization reflection modulation element has an anti-reflection coating on its surface near the second lens.

9. The Pancake Lens according to any one of claims 1 to 8, characterized in that, The entrance pupil diameter of the Pancake lens ranges from 4mm to 5mm.

10. The Pancake Lens according to any one of claims 1 to 8, characterized in that, The exit pupil distance of the Pancake lens ranges from 24mm to 27mm.

11. The Pancake Lens according to any one of claims 1 to 8, characterized in that, The Pancake lens has a field of view ranging from 90° to 110°.

12. The Pancake Lens according to any one of claims 1 to 8, characterized in that, The display component is an OLED display screen with a diameter ranging from 30mm to 38mm, the total length of the Pancake lens ranges from 16mm to 20mm, and the equivalent focal length of the Pancake lens ranges from 18mm to 21mm.

13. The Pancake Lens according to any one of claims 1 to 8, characterized in that, The display component is an LCD screen with a diameter ranging from 50mm to 66mm, the total length of the Pancake lens ranges from 23mm to 31mm, and the equivalent focal length of the Pancake lens ranges from 25mm to 30mm.

14. The Pancake Lens according to any one of claims 1 to 8, characterized in that, The Pancake lens has an F-number range of 4 to 6.

15. A near-eye display device, characterized in that, include: Equipment body; and The Pancake lens as described in any one of claims 1 to 14, wherein the Pancake lens is mounted on the main body of the device.

Images