Optical system and display device

Abstract

An optical system and a display device. The optical system comprises a lens assembly, a polarized reflection layer, a transmissive-reflection film and a phase delay film, at least three lenses in the lens assembly comprise first to sixth surfaces arranged in sequence along the optical axis direction, the fourth surface and the fifth surface have the same surface parameters; the polarized reflection layer is arranged on the side of the third surface away from the fourth surface; the transmissive-reflection film is arranged on the side of the fourth surface away from the third surface; the phase delay film is arranged on the side of the transmissive-reflection film facing the second surface; the distance between the two intersection points of the first surface and the second surface with the optical axis is a first distance, the distance between the two intersection points of the third surface and the fourth surface with the optical axis is a second distance, and the distance between the two intersection points of the fifth surface and the sixth surface with the optical axis is a third distance; the ratio of the absolute value of the radius of curvature of the fourth surface to the absolute value of the radius of curvature of the third surface is 0.8-1, the second distance is greater than the first distance, and the second distance is greater than the third distance.

Description

Technical Field

[0001] At least one embodiment of this disclosure relates to an optical system and a display device. Background Technology

[0002] With the increasing popularity of Virtual Reality (VR) devices, consumers are demanding higher standards for their thinness, image quality, and wearing experience. The Pancake optical path structure, with its thinness, excellent image quality, and increasingly mature mass production process, is gradually becoming the development and evolution direction of consumer-grade VR optics. Summary of the Invention

[0003] At least one embodiment of this disclosure provides an optical system, including: a lens assembly comprising at least three lenses, the at least three lenses including a first surface, a second surface, a third surface, a fourth surface, a fifth surface, and a sixth surface arranged sequentially along the optical axis of the lens assembly, the fourth surface and the fifth surface having the same surface profile parameters; a polarizing reflective layer disposed on the side of the third surface away from the fourth surface; a transmissive reflective film disposed on the side of the fourth surface away from the third surface; and a phase retardation film disposed on the side of the transmissive reflective film facing the second surface; wherein the second surface is convex, and the third surface... The fourth surface is concave, the fifth surface is concave, and the sixth surface is convex; the distance between the two intersection points of the first surface and the second surface with the optical axis is the first distance, the distance between the two intersection points of the third surface and the fourth surface with the optical axis is the second distance, and the distance between the two intersection points of the fifth surface and the sixth surface with the optical axis is the third distance; the ratio of the absolute value of the radius of curvature of the fourth surface to the absolute value of the radius of curvature of the third surface is 0.8~1, the second distance is greater than the first distance, and the second distance is greater than the third distance.

[0004] For example, according to an embodiment of this disclosure, the ratio of the absolute value of the radius of curvature of the third surface to the effective focal length of the optical system is 2 to 10, and the conicity of the third surface is -50 to 0; the ratio of the absolute value of the radius of curvature of the fourth surface to the effective focal length of the optical system is 1.5 to 2.5, and the conicity of the fourth surface is -10 to -2.

[0005] For example, according to embodiments of this disclosure, the ratio of the first distance to the effective focal length is 0.1 to 0.3; the ratio of the second distance to the effective focal length is 0.4 to 0.7; and the ratio of the third distance to the effective focal length is 0.1 to 0.2.

[0006] For example, according to an embodiment of this disclosure, there is an air gap between the second surface and the third surface.

[0007] For example, according to an embodiment of this disclosure, the absolute value of the size of the air gap on the optical axis is 0.5 mm to 1 mm.

[0008] For example, according to an embodiment of this disclosure, the ratio of the absolute value of the radius of curvature of the second surface to the effective focal length is 2 to 10, and the conicity of the second surface is -50 to 0.

[0009] For example, according to embodiments of this disclosure, at least one of the second surface, the third surface, and the fourth surface is an aspherical or freeform surface.

[0010] For example, according to an embodiment of the present disclosure, the optical system further includes a linear polarizing film; the linear polarizing film is disposed on the side of the polarizing reflective layer away from the transmissive film.

[0011] For example, according to an embodiment of this disclosure, the linearly polarizing film is disposed on one of the first surface, the second surface, and the third surface.

[0012] For example, according to an embodiment of this disclosure, the third surface and the fourth surface are two surfaces of the same lens.

[0013] For example, according to an embodiment of this disclosure, the lens assembly includes a first lens, a second lens, a third lens, and a fourth lens arranged along the optical axis. The first lens includes a first surface and a second surface, the second lens includes the third surface, the third lens includes the fourth surface, the second lens further includes a seventh surface opposite to the third surface, the third lens further includes an eighth surface located between the fourth surface and the seventh surface, and the fourth lens includes a fifth surface and a sixth surface. The seventh surface and the eighth surface are both planar, or the seventh surface and the eighth surface have the same surface profile parameters. The absolute value of the radius of curvature of the third surface and the absolute value of the radius of curvature of the fourth surface are both less than the absolute value of the radius of curvature of the seventh surface in at least one direction. The phase retardation film is located between the seventh surface and the eighth surface.

[0014] For example, according to an embodiment of this disclosure, the distance between the two intersection points of the seventh surface and the third surface with the optical axis is a fourth distance, and the distance between the two intersection points of the eighth surface and the fifth surface with the optical axis is a fifth distance; the fourth distance is less than the fifth distance.

[0015] For example, according to embodiments of this disclosure, the ratio of the first distance to the fourth distance is 1 to 2; the ratio of the third distance to the fourth distance is 0.75 to 1.5; and the ratio of the fifth distance to the fourth distance is 1.75 to 3.

[0016] For example, according to an embodiment of this disclosure, the fourth distance is less than the first distance, and the fourth distance is less than the third distance.

[0017] For example, according to embodiments of this disclosure, the ratio of the fourth distance to the effective focal length is 0.1 to 0.2; and the ratio of the fifth distance to the effective focal length is 0.3 to 0.5.

[0018] For example, according to embodiments of this disclosure, the ratio of the center thickness to the edge thickness of the first lens is greater than 1 and less than 3; the ratio of the center thickness to the edge thickness of the second lens is greater than 0.5 and less than 1; the ratio of the center thickness to the edge thickness of the third lens is greater than 1 and less than 3; and the ratio of the center thickness to the edge thickness of the fourth lens is greater than 0.5 and less than 1.

[0019] For example, according to an embodiment of this disclosure, the absolute value of the radius of curvature of the seventh surface is 100 mm to 200 mm.

[0020] For example, according to embodiments of this disclosure, the second lens, the third lens, and the fourth lens are made of the same material, and the material of the first lens is different from the material of the second lens.

[0021] For example, according to an embodiment of this disclosure, the first surface is a plane; or the first surface is a curved surface, and the ratio of the absolute value of the radius of curvature of the first surface to the effective focal length is greater than 20.

[0022] For example, according to embodiments of this disclosure, the polarizing reflective layer is configured to reflect linearly polarized light of one characteristic and transmit linearly polarized light of another characteristic; the polarizing reflective layer is disposed on the side of the third surface away from the fourth surface, and the phase retardation film is disposed between the polarizing reflective layer and the transmissive reflective film; or the polarizing reflective layer is a cholesteric liquid crystal layer; the cholesteric liquid crystal layer is disposed on the side of the third surface away from the fourth surface, and the phase retardation film is disposed on the side of the cholesteric liquid crystal layer away from the transmissive reflective film.

[0023] At least one embodiment of this disclosure provides a display device including a display screen and an optical system as described in any of the above embodiments, wherein the display screen is located on the side of the sixth surface away from the first surface. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only relate to some embodiments of this disclosure and are not intended to limit this disclosure.

[0025] Figure 1 This is a cross-sectional view of an optical system provided according to an example of an embodiment of the present disclosure.

[0026] Figure 2 This is a cross-sectional view of an optical system provided according to another example of an embodiment of the present disclosure.

[0027] Figure 3 This is a cross-sectional view of an optical system provided according to yet another example of an embodiment of the present disclosure.

[0028] Figures 4 to 7 Cross-sectional views of optical systems provided according to different examples of embodiments of this disclosure.

[0029] Figure 8A for Figure 4 The diagram shows a dot matrix representation of the optical system.

[0030] Figure 8B for Figure 4 The graph shows the variation of the blur spot size of the optical system with the field of view angle.

[0031] Figure 8C for Figure 4 The distortion diagram of the optical system shown.

[0032] Figure 8D for Figure 4 The transverse chromatic aberration diagram of the optical system shown.

[0033] Figure 9 This is a partial cross-sectional view of a display device provided according to an example of an embodiment of the present disclosure. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. Based on the described embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0035] Unless otherwise defined, the technical or scientific terms used in this disclosure shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms “first,” “second,” and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as “comprising” or “including” mean that an element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0036] The features such as "perpendicular," "parallel," and "identical" used in the embodiments of this disclosure include features in the strict sense of "perpendicular," "parallel," and "identical," as well as cases where "approximately perpendicular," "approximately parallel," and "approximately identical" include certain errors. Taking into account measurement and errors associated with the measurement of a specific quantity (i.e., limitations of the measurement system), they represent the acceptable deviation range for a specific value as determined by a person skilled in the art. The term "center" in the embodiments of this disclosure can include a position strictly located at the geometric center as well as a position approximately at the center within a small area surrounding the geometric center. For example, "approximately" can mean within one or more standard deviations, or within 10% or 5% of the value.

[0037] In some VR-enabled head-mounted display devices, such as VR glasses, the user's visual and auditory senses are blocked, creating a feeling of being in a virtual environment. The display principle involves the left and right eye screens displaying images for each eye separately; the human eye receives this differentiated information and generates a sense of depth in the brain. To improve comfort during wear, it is often necessary to simultaneously consider requirements for optical parameters such as image clarity, field of view, distortion, and chromatic aberration.

[0038] At least one embodiment of this disclosure provides an optical system including a lens assembly, a polarizing reflective layer, a transmissive coating, and a phase retardation coating. The lens assembly includes at least three lenses, each comprising a first surface, a second surface, a third surface, a fourth surface, a fifth surface, and a sixth surface arranged sequentially along the optical axis of the lens assembly. The fourth surface and the fifth surface have the same surface profile parameters. A polarizing reflective layer is disposed on the side of the third surface away from the fourth surface. A transmissive reflective film is disposed on the side of the fourth surface away from the third surface. A phase retardation film is disposed on the side of the transmissive reflective film facing the second surface. The second surface is convex, the third surface is concave, the fourth surface is convex, the fifth surface is concave, and the sixth surface is convex. The distance between two points where the first and second surfaces intersect the optical axis is a first distance; the distance between two points where the third and fourth surfaces intersect the optical axis is a second distance; and the distance between two points where the fifth and sixth surfaces intersect the optical axis is a third distance. The ratio of the absolute value of the radius of curvature of the fourth surface to the absolute value of the radius of curvature of the third surface is 0.8 to 1. The second distance is greater than the first distance, and the second distance is greater than the third distance.

[0039] At least one embodiment of this disclosure provides a display device including a display screen and an optical system as described in any of the above embodiments, wherein the display screen is located on the side of the sixth surface away from the first surface.

[0040] The optical system and display device provided in at least one embodiment of this disclosure, by providing a lens assembly with at least three lenses, offers more attachment positions for the polarizing reflective layer, the transmission-reflective coating, and the phase retardation coating. This allows for light reflection using the polarizing reflective layer and the transmission-reflective coating, while also increasing the freedom of design in terms of the surface parameters of the optical system. Furthermore, by setting the relationship between the radii of curvature of the third and fourth surfaces, and the relationship between the distances between the surfaces, the sharpness of the optical system can be improved.

[0041] The optical system and display device are described below with reference to the accompanying drawings and through some embodiments.

[0042] Figure 1 This is a cross-sectional view of an optical system provided according to an example of an embodiment of the present disclosure.

[0043] refer to Figure 1 At least one embodiment of this disclosure provides an optical system including a lens assembly 100. The lens assembly 100 includes at least three lenses. For example, such as Figure 1 As shown, the lens assembly 100 can be composed of three lenses: lens 110, lens 125, and lens 140.

[0044] like Figure 1 As shown, at least three lenses include a first surface 101, a second surface 102, a third surface 103, a fourth surface 104, a fifth surface 105, and a sixth surface 106 arranged sequentially along the optical axis OA of the lens assembly 100. The fourth surface 104 and the fifth surface 105 have the same surface profile parameters. For example, the fourth surface 104 and the fifth surface 105 having the same surface profile parameters means that, without considering the coating layer between them, the fourth surface 104 and the fifth surface 105 can be substantially completely bonded together.

[0045] like Figure 1 As shown, the polarizing reflective layer 200 is disposed on the side of the third surface 103 away from the fourth surface 104, the transmissive reflective film 300 is disposed on the side of the fourth surface 104 away from the third surface 103, and the phase retardation film 400 is disposed on the side of the transmissive reflective film 300 facing the second surface 102. For example, light rays that are transmitted through the transmissive reflective film 300 and incident on the lens assembly 100 are configured to be reflected back between the transmissive reflective film 300 and the polarizing reflective layer 200 and exit from the polarizing reflective layer 200, thereby forming a folded optical path through the polarizing reflective layer 200, the transmissive reflective film 300, and the phase retardation film 400.

[0046] like Figure 1 As shown, the second surface 102 is convex, the third surface 103 is concave, the fourth surface 104 is convex, the fifth surface 105 is concave, and the sixth surface 106 is convex. For example, the side of the first surface 101 away from the sixth surface 106 is the light-emitting side of the optical system. For example, when the optical system is applied to a display device, the display screen is located on the side of the sixth surface 106 of the optical system away from the first surface 101, and the light emitted from the display screen enters from the sixth surface 106 and exits from the first surface 101. While achieving light reflection by means of the polarizing reflective layer 200 and the transmissive coating 300, the multiple lenses in the lens assembly 100 help to increase the degree of freedom in the design of the surface parameters of the optical system.

[0047] like Figure 1 As shown, the distance between the two intersection points of the first surface 101 and the second surface 102 with the optical axis OA is the first distance D1; the distance between the two intersection points of the third surface 103 and the fourth surface 104 with the optical axis OA is the second distance D2; and the distance between the two intersection points of the fifth surface 105 and the sixth surface 106 with the optical axis OA is the third distance D3. For example, without considering the film thickness, the distance between the two intersection points of the third surface 103 and the fourth surface 104 with the optical axis OA is the distance between the polarizing reflective layer 200 and the transmissive film 300.

[0048] like Figure 1As shown, the ratio of the absolute value of the radius of curvature of the fourth surface 104 to the absolute value of the radius of curvature of the third surface 103 is 0.8 to 1. For example, the ratio of the absolute value of the radius of curvature of the fourth surface 104 to the absolute value of the radius of curvature of the third surface 103 can be, but is not limited to, 0.8, 0.85, 0.9, 0.95, or 1. Figure 1 As shown, the second distance D2 is greater than the first distance D1, and the second distance D2 is greater than the third distance D3. It can be understood that among the first distance D1, the second distance D2, and the third distance D3, the distance between the two intersection points of the third surface 103 and the fourth surface 104 with the optical axis OA is the largest. By setting the distance between the polarizing reflective layer 200 and the transmissive film 300, and by setting the relationship between the radii of curvature of the surfaces containing the two films, the optical power of the entire optical system can be evenly distributed, enabling the optical system to achieve high resolution and better clarity.

[0049] For example, refer to Figure 1 The polarization reflective layer 200 functions as follows: Within the plane of the film layer, there exists a transmission axis OA. The transmittance of the polarization component of incident light parallel to this transmission axis OA (such as s-polarized light) is greater than the transmittance of the polarization component perpendicular to this transmission axis OA (such as p-polarized light), and the reflectance of the polarization component parallel to this transmission axis OA (such as s-polarized light) is less than the reflectance of the polarization component perpendicular to this transmission axis OA (such as p-polarized light). For example, the transmittance of polarized light parallel to the transmission axis OA of the polarization reflective layer 200 is not less than 85%, and is not less than 90%, not less than 95%, and not less than 98%; the reflectance of polarized light perpendicular to the transmission axis OA of the polarization reflective layer 200 is not less than 85%, and is not less than 90%, not less than 95%, and not less than 98%.

[0050] For example, refer to Figure 1 The transflective film 300 is configured to transmit part of the light and reflect another part of the light. For example, the transflective film 300 may have a transmittance of 50% and a reflectance of 50%. For example, the transflective film 300 may have a transmittance of 60% and a reflectance of 40%. For example, the transflective film 300 may have a transmittance of 65% and a reflectance of 35%. The optical system provided in this disclosure is not limited thereto, and the transmittance and reflectance of the transflective film 300 may be set according to product requirements. For example, the transflective film 300 may be deposited on the fourth surface 104.

[0051] For example, refer to Figure 1The phase retardation film 400 is configured to enable the transmitted light to switch between circular and linear polarization states. For example, the phase retardation film 400 can be a quarter-wave plate. For example, the phase retardation film 400 has the following characteristics: there is a direction with the lowest refractive index and a direction with the highest refractive index within the film plane, namely the fast axis and the slow axis, respectively. Polarized light parallel to the slow axis is delayed by 1 / 4 wavelength after passing through the phase retardation film 400 compared to polarized light parallel to the fast axis. For example, the angle between the slow axis of the phase retardation film 400 and the transmission axis OA of the polarizing reflective layer 200 is 45 degrees.

[0052] For example, refer to Figure 1 The phase retardation film 400 can be made of liquid crystal polymers. Since the phase retardation film 400 made of liquid crystal polymers is a polymer, its thickness is relatively thin, reaching 1μm to 5μm. A thinner phase retardation film 400 is more adaptable to curved surfaces, making it easier to shape according to the surface profile and reducing the possibility of wrinkles occurring during bonding with curved surfaces, which could affect phase retardation accuracy and optical performance. Furthermore, the optical shift caused by the phase retardation film 400 made of liquid crystal polymers after being bonded to curved surfaces is smaller. Liquid crystal polymers are cross-linked systems, with molecules linked by chemical bonds and a high modulus. When the phase retardation film 400 made of this material is stretched after bonding, only elastic deformation occurs, without strong optical anisotropy effects such as molecular stretching or rearrangement. Therefore, the phase retardation film 400 made of liquid crystal polymers is suitable for bonding to surfaces with small radii of curvature. This degree of freedom in curvature radius also makes it easier to meet the requirements for sharpness, distortion, and dispersion, which is beneficial for achieving better image quality in the optical system.

[0053] For example, refer to Figure 1The principle of the folded optical path is as follows: A waveplate can be set on the light-emitting side of the display surface of the screen located on the side of the sixth surface 106 away from the first surface 101. The image light emitted from the display surface 11 is converted into right-hand circularly polarized light after passing through the waveplate. The polarization state of the right-hand circularly polarized light remains unchanged after being transmitted through the transmission-reflection film 300. This light enters the lens assembly 100 and reaches the phase retardation film 400 after being transmitted through the lens assembly 100. The right-hand circularly polarized light incident on the phase retardation film 400 is converted into p-linearly polarized light. The p-linearly polarized light is reflected back to the phase retardation film 400 by the polarization reflection layer 200, where the first reflection occurs. Then, the p-linearly polarized light is converted into right-hand circularly polarized light after passing through the phase retardation film 400. This right-hand circularly polarized light is transmitted through the lens assembly 100 and reaches the transmission-reflection film 300, where it is reflected, where the second reflection occurs. Due to half-wave loss, the reflected light changes from right-hand circularly polarized light to left-hand circularly polarized light. Left-handed circularly polarized light is transmitted through the lens assembly 100 and reaches the phase retardation film 400. After passing through the phase retardation film 400, it becomes s-polarized light. Then, the s-polarized light is transmitted through the polarization reflection layer 200 and is directed toward the exit pupil, like the human eye.

[0054] The aforementioned folded optical path can change the polarization state of light propagating between the polarization reflection layer 200 and the transmission reflection film 300, thereby achieving light folding. This folds the focal length of the optical system, which would otherwise be increased by, for example, two reflections due to the presence of the polarization reflection layer 200, the phase retardation film 400, and the transmission reflection film 300, thus greatly compressing the space required between the human eye and the optical system, making the optical system smaller and thinner.

[0055] refer to Figure 1 In some examples, the first surface 101 is planar. A planar first surface 101 provides a relatively smooth surface for the adhesion of the film layer. For example, an anti-reflection film can be disposed on the side of the first surface 101 away from the second surface 102. Similarly, an anti-reflection film can also be disposed on the side of the second surface 102 away from the first surface 101. For example, an anti-reflection film can also be disposed on the side of the sixth surface 106 away from the first surface 101. For example, the anti-reflection film helps to reduce stray light caused by reflection.

[0056] Figure 2 This is a cross-sectional view of an optical system provided according to another example of an embodiment of the present disclosure. Figure 2 The optical system shown is Figure 1 The difference in the optical system shown is that, Figure 2 The first surface in the optical system shown is Figure 1 The first surface profiles in the illustrated optical systems are different. For example, Figure 2 The first surface in the optical system shown is curved. Of course, Figure 2 The optical system shown is Figure 1The optical system shown may also have other differences, such as the number of lenses in the lens assembly, the positional relationship between the coating layers, etc., which are not limited in this disclosure.

[0057] It should be noted that, Figure 2 The lens assembly in the optical system shown can be coupled with Figure 1 The lens components in the optical system shown can be different or the same. Figure 2 The polarization reflective layer 200, the transmission-reflection coating 300, and the phase retardation coating 400 in the optical system shown can be coupled with... Figure 1 The polarizing reflective layer 200, the transmission-reflection coating 300, and the phase retardation coating 400 in the illustrated optical system have the same characteristics and will not be described again here. Referring to some examples described later, Figure 2 The linear polarization film 500 in the middle can also be used with Figure 1 The linear polarizing film 500 in the optical system shown has the same characteristics.

[0058] refer to Figure 2 In some examples, the first surface 101 is curved, and the ratio of the absolute value of the radius of curvature of the first surface 101 to the effective focal length is greater than or equal to 10. The effective focal length refers to the distance from the rear principal image plane to the paraxial image plane. The effective focal length, for example, is the effective focal length of each lens surface of the lens assembly 100 after coating. For example, the first surface 101 can be as follows: Figure 2 The concave surface shown can also be a convex surface. For example, the ratio of the radius of curvature of the first surface 101 to the effective focal length is -20, -21, -22, -23, -24, -25. Alternatively, the ratio can be 10, 15, 20, 25, 30. It is understandable that the radius of curvature of the first surface 101 varies considerably. For example, when the first surface 101 and the second surface 102 are two opposing surfaces of a lens, it is sufficient to ensure that the lens as a whole is a positive power lens.

[0059] refer to Figure 1 In some examples, the ratio of the absolute value of the radius of curvature of the second surface 102 to the effective focal length is 2 to 10. For example, the ratio of the radius of curvature of the second surface 102 to the effective focal length is -10 to -2. For example, the ratio of the radius of curvature of the second surface 102 to the effective focal length can be, but is not limited to, -10, -9, -8, -7, -6, -5, -4, -3, -2. For example, the conicity of the third surface 103 can be, but is not limited to, -50, -45, -40, -35, -30, -25, -20, -15, -10, -5, -1, 0.

[0060] refer to Figure 1In some examples, the ratio of the absolute value of the radius of curvature of the third surface 103 to the effective focal length of the optical system is 2 to 10, and the conicity of the third surface 103 is -50 to 0. For example, the ratio of the radius of curvature of the third surface 103 to the effective focal length is -10 to -2. For example, the ratio of the radius of curvature of the third surface 103 to the effective focal length can be, but is not limited to, -10, -9, -8, -7, -6, -5, -4, -3, and -2. For example, the conicity of the third surface 103 can be, but is not limited to, -50, -45, -40, -35, -30, -25, -20, -15, -10, -5, -1, and 0. For example, the radius of curvature of the third surface 103 is relatively close to the radius of curvature of the second surface 102.

[0061] refer to Figure 1 In some examples, the ratio of the absolute value of the radius of curvature of the fourth surface 104 to the effective focal length of the optical system is 1.5 to 2.5, and the conicity of the fourth surface 104 is -10 to -2. For example, the ratio of the radius of curvature of the fourth surface 104 to the effective focal length of the optical system is -1.5 to -2.5. For example, the ratio of the radius of curvature of the fourth surface 104 to the effective focal length of the optical system can be, but is not limited to, -1.5, -1.75, -2, -2.25, and -2.5. For example, the conicity of the fourth surface 104 can be, but is not limited to, -10, -9, -8, -7, -6, -5, -4, -3, and -2.

[0062] For example, Figure 1 The effect of each coating layer on the distance between different surfaces of the lens assembly 100 is illustrated schematically. When the thickness of each coating layer is thin, the coating layer thickness can be ignored.

[0063] refer to Figure 1 In some examples, the ratio of the first distance D1 to the effective focal length is 0.1 to 0.3. For example, the ratio of the first distance D1 to the effective focal length can be, but is not limited to, 0.1, 0.15, 0.2, 0.25, or 0.3. For example, the first surface 101 and the second surface 102 are two opposite surfaces of a lens 110, and the first distance D1 is the center thickness of the lens 110.

[0064] refer to Figure 1 In some examples, the ratio of the second distance D2 to the effective focal length is 0.4 to 0.7. For example, the ratio of the second distance D2 to the effective focal length can be, but is not limited to, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, and 0.7. (See reference) Figure 1 In some examples, the third surface 103 and the fourth surface 104 are two surfaces of the same lens. For example, the third surface 103 and the fourth surface 104 are as follows: Figure 1The second distance D2 between the two opposing surfaces of the integral lens 125 shown is the center thickness of the lens 125. For example, the aforementioned integral lens can be a single lens. For example, the third surface 103 and the fourth surface 104 are respectively located on... Figure 2 On the two lenses shown (e.g., lens 120 and lens 130).

[0065] refer to Figure 1 In some examples, the ratio of the third distance D3 to the effective focal length is 0.1 to 0.2. For example, the ratio of the third distance D3 to the effective focal length can be, but is not limited to, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, or 0.2. For example, the fifth surface 105 and the sixth surface 106 are as follows: Figure 1 The third distance D3 between the two opposing surfaces of a lens 140 shown is the center thickness of the lens 140.

[0066] refer to Figure 1 In some examples, at least one of the second surface 102, the third surface 103, and the fourth surface 104 is an aspheric surface or a freeform surface. For example, the second surface 102, the third surface 103, and the fourth surface 104 are all aspheric surfaces or freeform surfaces. An aspheric surface can be an even-order aspheric surface (EVENASPH), where the radius of curvature of the aspheric surface is the radius of curvature of the base sphere of its surface. The aforementioned "base sphere" refers to an aspheric surface formed by further deformation based on a sphere; the sphere that forms the basis of this aspheric surface is called the base sphere of the aspheric surface. A freeform surface is, for example, a complex, unconventional continuous surface without a rotational symmetry axis.

[0067] For example, the surface shape of an aspherical surface can be represented by the following numerical formula:

[0068]

[0069] For example, in the above formula, the height of the aspherical surface along the direction perpendicular to the optical axis is Y, and the distance from the vertex of the aspherical surface to the projection of the point at height Y on the aspherical surface onto the optical axis is z. That is, z is the coordinate along the optical axis; C is the curvature (the reciprocal of the radius of curvature R), k is the conic constant, and α... i These are the coefficients of the higher-order terms, and 2i represents the higher-order terms of the aspherical surface (the order of the aspherical coefficient).

[0070] In the actual optimization of the configuration of various parameters of the lens assembly, the values ​​of the radius of curvature, conic coefficient, height, and aspheric coefficient of each lens in the lens assembly are put into the above numerical formula. Optical simulation calculations are then used to obtain the optimized parameters that can correct the aberrations of each lens in the lens assembly. The optimization process yields the preferred values ​​of the radius of curvature, thickness along the optical axis, effective aperture, and conic coefficient of each lens in the lens assembly.

[0071] Combining the previous examples, for instance, the higher-order coefficients of the second surface 102 satisfy: α4 = -1.0E-05, α6 = 3.0E-08, α8 = 2.7E-11, α 10 =-2.0E-13. For example, the higher-order coefficients of the third surface 103 satisfy: α4=8.0E-06, α6=-1.7E-08, α8=6.0E-11, α 10 =-6.0E-14. For example, the higher-order coefficients of the fourth surface 104 satisfy: α4=-4.0E-07, α6=-4.0E-10, α8=-1.5E-12, α 10 =2.0E-14. For example, the higher-order coefficients of the fifth surface 105 are exactly the same as those of the fourth surface 104. For example, the higher-order coefficients of the sixth surface 106 satisfy: α4=-6.0E-05, α6=-6.0E-07, α8=2.0E-08, α 10 =-3.0E-10.

[0072] refer to Figure 1 In some examples, an air gap g exists between the second surface 102 and the third surface 103. The third surface 103 and the air gap g can deflect light, and the air gap g and the second surface 102 can also deflect light, thus achieving a larger field of view on a smaller screen size. Furthermore, the air gap g allows for different surface shapes of the second surface 102 and the third surface 103, increasing the design freedom of the optical system and facilitating aberration correction, especially chromatic aberration correction, thereby enabling the optical system to achieve high resolution. In addition, as... Figure 1 As shown, providing an air gap g only between the second surface 102 and the third surface 103 can also minimize ghosting. In some other embodiments, an air gap g may also be provided between other adjacent surfaces, and this disclosure is not limited to this. For example, with an air gap g between the second surface 102 and the third surface 103, that is, the lens 110 where the second surface 102 is located and the lens 125 where the third surface 103 is located are completely separated, the two lenses (e.g., lens 110 and lens 125) can be fixed by the edge lens barrel during assembly, thereby ensuring that the lenses in the lens assembly 100 are coaxial.

[0073] Figure 3This is a cross-sectional view of an optical system provided according to yet another example of an embodiment of the present disclosure. Figure 3 The optical system shown is Figure 1 The difference in the optical system shown is that, Figure 3 In the optical system shown, there is no air gap between the first and second lenses. Of course, Figure 3 The optical system shown is Figure 1 The optical system shown may also have other differences, such as the number of lenses in the lens assembly, the surface shape of each lens, the positional relationship between the coating layers, etc., which are not limited in this disclosure.

[0074] It should be noted that, Figure 3 The lens assembly in the optical system shown can be coupled with Figure 1 The lens components in the optical system shown can be different or the same. Figure 3 The polarization reflective layer 200, the transmission-reflection coating 300, and the phase retardation coating 400 in the optical system shown can be coupled with... Figure 1 The polarizing reflective layer 200, the transmission-reflection coating 300, and the phase retardation coating 400 in the illustrated optical system have the same characteristics and will not be described again here. Referring to some examples described later, Figure 3 The linear polarization film 500 in the middle can also be used with Figure 1 The linear polarizing film 500 in the optical system shown has the same characteristics.

[0075] For example, refer to Figure 3 The second surface 102 and the third surface 103 can also have the same surface parameters, and the second surface 102 and the third surface 103 are bonded together, thereby alleviating the ghosting problem and improving the compactness of the optical system.

[0076] refer to Figure 1 In some examples, the absolute value of the dimension l of the air gap g on the optical axis OA is 0.5 mm to 1 mm. For example, the absolute value of the dimension l of the air gap g on the optical axis OA can be, but is not limited to, 0.5 mm, 0.55 mm, 0.6 mm, 0.65 mm, 0.7 mm, 0.75 mm, 0.8 mm, 0.85 mm, 0.9 mm, 0.95 mm, and 1 mm. For example, by setting the dimension of the air gap g, it is possible to ensure that the two surfaces after coating do not come into contact, and it is also beneficial to the assembly and adjustment of the optical system. In addition, the dimension l of the air gap g on the optical axis OA can also minimize the overall length of the optical system, making the optical system more compact. It is understood that the shape of the air gap g is mainly determined by the surface profile of the second surface 102 and the third surface 103 on opposite sides along the optical axis OA, and this disclosure does not limit this.

[0077] refer to Figure 1In some examples, the optical system also includes a linear polarizing film 500, disposed on the side of the polarizing reflective layer 200 away from the transmissive reflective film 300. For example, the linear polarizing film 500 can be a linear polarizer or a polarizer. For example, the transmission axis OA of the linear polarizing film 500 coincides with the transmission axis OA of the polarizing reflective layer 200. The linear polarizing film 500 can be used to further filter other stray light, allowing only polarized light (such as s-polarized light) passing through the linear polarizing film 500 to enter the human eye. For example, the linear polarizing film 500 can have a three-layer stacked structure, where the middle layer can be polyvinyl alcohol (PVA) with added dichroic molecules, and at least one layer located on either side of the middle layer can be triacetate cellulose (TAC). For example, the air-facing surface of the linear polarizing film 500 is treated with an anti-reflective coating. For example, the air-facing surface of the linear polarizing film 500 can be fitted with a moth eye membrane.

[0078] Figures 4 to 7 Cross-sectional views of optical systems provided according to different examples of embodiments of this disclosure. Figure 4 The optical system shown is Figure 1 The difference in the optical system shown is that, Figure 4 The positional relationship between the film layers in the optical system shown Figure 1 The positional relationships between the film layers in the illustrated optical system differ. For example, Figure 4 The location of the linearly polarized film in the middle is related to Figure 1 Different. Furthermore... Figure 5 The optical system shown and Figure 6 The optical system shown illustrates the relationship with... Figure 4 The optical system shown has different locations where the linear polarizing film is located. Figure 7 The optical system shown is Figure 6 The difference in the optical system shown is that, Figure 7 The surface profiles of the seventh and eighth surfaces in the optical system shown are similar to... Figure 6 Different. For example, Figure 7 The seventh and eighth surfaces are planes. Figure 6 The seventh and eighth surfaces are curved surfaces.

[0079] certainly, Figures 4 to 7 The optical system shown is Figure 1 The optical system shown may also have other differences, such as the number of lenses in the lens assembly, the surface shape of each lens, the positional relationship between the coating layers, etc., which are not limited in this disclosure.

[0080] It should be noted that, Figures 4 to 7 The lens assembly in the optical system shown can be coupled with Figure 1 The lens components in the optical system shown can be different or the same. Figures 4 to 7The polarization reflective layer 200, transmission-reflection film 300, phase retardation film 400, and linear polarization film 500 in the optical system shown can be combined with... Figure 1 The polarization reflection layer 200, the transmission reflection film 300, the phase retardation film 400, and the linear polarization film 500 in the optical system shown have the same characteristics, which will not be described again here.

[0081] refer to Figures 2 to 4 In some examples, the linear polarizing film 500 is disposed on the first surface 101. In conjunction with the foregoing examples, since the first surface 101 is a plane or a micro-curved surface with a large radius of curvature, it can provide a relatively flat attachment surface for the linear polarizing film 500, reducing the risk of wrinkles appearing on the linear polarizing film 500 after attachment.

[0082] refer to Figure 5 In some examples, the linear polarizing film 500 is disposed on the second surface 102. It can be understood that the first surface 101 and the second surface 102 are, for example, two surfaces of a lens 110. The first surface 101 or the second surface 102 can provide a separate attachment location for the linear polarizing film 500, meaning that when attaching the linear polarizing film 500, there is no need to consider potential interactions with other layers (e.g., the polarizing reflective layer 200 or the phase retardation film 400). Furthermore, the process of attaching the linear polarizing film 500 is easier to implement and less prone to wrinkling.

[0083] refer to Figure 1 and Figure 6 In some examples, the linear polarizing film 500 is disposed on the third surface 103. In this way, the linear polarizing film 500 can fully cover the other film layers, thereby making the linear polarizing film 500 more effective at filtering stray light.

[0084] refer to Figures 4 to 6In some examples, the lens assembly 100 includes a first lens 110, a second lens 120, a third lens 130, and a fourth lens 140 arranged along the optical axis OA. The first lens 110 includes a first surface 101 and a second surface 102. The second lens 120 includes a third surface 103. The third lens 130 includes a fourth surface 104. The second lens 120 also includes a seventh surface 107 opposite to the third surface 103. The third lens 130 also includes an eighth surface 108 located between the fourth surface 104 and the seventh surface 107. The fourth lens 140 includes a fifth surface 105 and a sixth surface 106. It is understood that the third surface 103 and the seventh surface 107 are two opposite surfaces of the second lens 120, and the fourth surface 104 and the eighth surface 108 are two opposite surfaces of the third lens 130. For example, before entering the lens assembly 100, the image light emitted from the display surface 11 is refracted once at the air-medium interface, exits the polarization reflection layer 200, passes through the air gap g between the first lens 110 and the second lens 120, and then exits from the first lens 110 and is refracted again at the medium-air interface. This helps to deflect the light and achieve a larger field of view on a smaller screen size.

[0085] In some examples, the phase retardation film 400 is located between the seventh surface 107 and the eighth surface 108. In this way, the seventh surface 107 and the eighth surface 108 can provide an additional attachment surface for the phase retardation film 400.

[0086] refer to Figure 6 In some examples, the seventh surface 107 and the eighth surface 108 have the same surface parameters, and the absolute values ​​of the radii of curvature of the third surface 103 and the fourth surface 104 are both smaller than the absolute value of the radii of curvature of the seventh surface 107 in at least one direction. By fabricating the seventh surface 107 and the eighth surface 108 as curved surfaces, the center thickness and edge thickness of the second lens 120 and the third lens 130 can be easily adjusted, reducing the processing difficulty. For example, both the seventh surface 107 and the eighth surface 108 are curved away from the first surface 101, making the difference between the center thickness and the edge thickness of the second lens 120 smaller, and making the difference between the center thickness and the edge thickness of the third lens 130 smaller. For example, without considering the film layer disposed between the seventh surface 107 and the eighth surface 108, the seventh surface 107 can be substantially completely bonded to the eighth surface 108.

[0087] refer to Figure 6In some examples, the absolute value of the radius of curvature of the seventh surface 107 is 100 mm to 200 mm. For example, the absolute value of the radius of curvature of the eighth surface 108 is also 100 mm to 200 mm. The radii of curvature of the seventh surface 107 and the eighth surface 108 are set relatively large, meaning that the seventh surface 107 and the eighth surface 108 are constructed as micro-curved surfaces approaching a plane. For example, the seventh surface 107 and the eighth surface 108 are spheres.

[0088] For example, when the seventh surface 107 and the eighth surface 108 are curved surfaces, the example of attaching the phase retardation film 400 to the seventh surface 107 will be used for illustration. During the process of attaching the phase retardation film 400 to the lens assembly 100, the planar phase retardation film 400 needs to be appropriately stretched before being fully attached to the curved seventh surface 107. If the radius of curvature of the seventh surface 107 of the lens assembly 100 is small, for example, its absolute value is less than 100 micrometers and its conicity is greater than or equal to zero, wrinkles may occur when the phase retardation film 400 is stretched and attached to the seventh surface 107. Both the excessive stretching of the phase retardation film 400 and the wrinkles generated during attachment may affect the accuracy of the phase retardation of the phase retardation film 400, thereby affecting the optical performance. In the optical system provided in this disclosure, by setting a larger absolute value of the radius of curvature of the seventh surface 107 or the eighth surface 108 used for bonding the phase retardation film 400, the influence of the surface shape of the seventh surface 107 or the eighth surface 108 on the performance of the phase retardation film 400 can be reduced.

[0089] For example, the seventh surface 107 can be a surface with rotational symmetry. A surface with rotational symmetry is a surface formed by rotating a curve around a straight line, where the plane curve is the generatrix of the surface of revolution, and the straight line is the axis of rotation of the surface of revolution. A surface with rotational symmetry has the same radius of curvature and conic coefficient in different directions.

[0090] For example, the seventh surface 107 can be a surface with axisymmetric properties. A surface with axisymmetric properties is one that is symmetrical along an axis of symmetry; for example, the surface has different radii of curvature or conic coefficients in different directions. For example, a surface with axisymmetric properties can be a cylindrical surface, which is a surface formed by moving a straight line parallel to a fixed curve. When the surface is a cylindrical surface, it is a surface in one direction and a plane in another.

[0091] By setting the shape of the seventh surface 107 to the above-mentioned shape, a better bonding surface can be provided for the phase retardation film 400, which helps to prevent the phase retardation film 400 from having a significant impact on its shape during the stretching and bonding process.

[0092] refer to Figure 7In some examples, both the seventh surface 107 and the eighth surface 108 are planar. The phase retardation film 400 includes a birefringent material. Attaching the phase retardation film 400 to the planar seventh surface 107 or eighth surface 108 can improve the flatness of the film material, overcome the process challenges caused by curved attachment, and avoid the softening and stretching processes of the film material affecting its birefringent properties such as the optical axis OA angle and phase retardation. It is easier to maintain a fixed phase retardation, which is beneficial for improving the overall optical performance of the optical system, such as sharpness, stray light, and field of view, to ensure imaging quality.

[0093] refer to Figure 7 In some examples, the distance between the two intersection points of the seventh surface 107 and the third surface 103 with the optical axis OA is the fourth distance d1, and the distance between the two intersection points of the eighth surface 108 and the fourth surface 104 with the optical axis OA is the fifth distance d2. The fourth distance d1 is less than the fifth distance d2. For example, the fourth distance d1 is the center thickness of the second lens 120. For example, the second lens 120 can be a negative lens. For example, the second lens 120 can be a plano-concave lens. For example, the fifth distance d2 is the center thickness of the third lens 130. For example, the third lens 130 can be a positive lens. For example, the third lens 130 can be a plano-convex lens. For example, when the thickness of each film layer is thin, the film layer thickness can be ignored. In this case, the sum of the center thickness of the second lens 120 and the center thickness of the third lens 130 can be the aforementioned second distance D2. For example, the sum of the fourth distance d1 and the fifth distance d2 is the second distance D2.

[0094] refer to Figures 1 to 7 In some examples, the ratio of the first distance D1 to the fourth distance d1 is 1 to 2. For example, the ratios of the first distance D1 to the fourth distance d1 are 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2. In some examples, the ratio of the third distance D3 to the fourth distance d1 is 0.75 to 1.5. For example, the ratios of the third distance D3 to the fourth distance d1 are 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.2, 1.3, 1.4, and 1.5. In some examples, the ratio of the fifth distance d2 to the fourth distance d1 is 1.75 to 3. For example, the ratios of the fifth distance d2 to the fourth distance d1 are 1.75, 2, 2.25, 2.5, 2.75, and 3. For example, the ratio of the first distance D1, the fourth distance d1, the fifth distance d2, and the third distance D3 is (2~4):2:(3.5~6):(1.5~3). For example, the ratio of the first distance D1, the fourth distance d1, the fifth distance d2, and the third distance D3 is 3:2:5:2.

[0095] refer to Figures 1 to 7In some examples, the fourth distance d1 is less than the first distance D1, and the fourth distance d1 is less than the third distance D3. For example, the center thickness of the second lens 120 is less than the center thickness of the first lens 110, and the center thickness of the second lens 120 is less than the center thickness of the fourth lens 140. For example, among the lenses of the lens assembly 100, the center thickness of the second lens 120 is the smallest.

[0096] refer to Figures 1 to 7 In some examples, the ratio of the fourth distance d1 to the effective focal length is 0.1 to 0.2. For example, the ratio of the center thickness of the second lens 120 to the effective focal length is 0.1 to 0.2. For example, the ratio of the fourth distance d1 to the effective focal length may be, but is not limited to, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, or 0.2.

[0097] refer to Figures 1 to 7 In some examples, the ratio of the fifth distance d2 to the effective focal length is 0.3 to 0.5. For example, the ratio of the center thickness of the third lens 130 to the effective focal length is 0.3 to 0.5. For example, the ratio of the fourth distance d1 to the effective focal length can be, but is not limited to, 0.3, 0.32, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, 0.46, 0.48, or 0.5.

[0098] refer to Figures 1 to 7 For example, considering the surface shape and the overall thickness of the optical system, the thickness of the fourth lens 140 is often better the thinner it is. For example, the ratio of the center thickness of the first lens 110 to the center thickness of the fourth lens 140 is greater than 1, that is, the ratio of the first distance D1 to the third distance D3 is greater than 1, such as 3:2.

[0099] refer to Figures 1 to 7 In some examples, the ratio of the center thickness to the edge thickness of the first lens 110 is greater than 1 and less than 3. For example, the ratio of the center thickness to the edge thickness of the first lens 110 may be, but is not limited to, 1, 1.5, 2, 2.5, or 3.

[0100] refer to Figures 1 to 7 In some examples, the ratio of the center thickness to the edge thickness of the second lens 120 is greater than 0.5 and less than 1. For example, the ratio of the center thickness to the edge thickness of the second lens 120 may be, but is not limited to, 0.5, 0.6, 0.7, 0.8, 0.9, or 1.

[0101] refer to Figures 1 to 7In some examples, the ratio of the center thickness to the edge thickness of the third lens 130 is greater than 1 and less than 3. For example, the ratio of the center thickness to the edge thickness of the third lens 130 may be, but is not limited to, 1, 1.5, 2, 2.5, or 3.

[0102] refer to Figures 1 to 7 In some examples, the ratio of the center thickness to the edge thickness of the fourth lens 140 is greater than 0.5 and less than 1. For example, the ratio of the center thickness to the edge thickness of the fourth lens 140 may be, but is not limited to, 0.5, 0.6, 0.7, 0.8, 0.9, or 1.

[0103] Thus, by setting the ratio of the center thickness to the edge thickness of each lens, it is beneficial to ensure the injection molding of each lens.

[0104] refer to Figures 1 to 7 In some examples, the second lens 120, the third lens 130, and the fourth lens 140 are made of the same material, while the first lens 110 is made of a different material than the second lens 120. For example, the refractive index of each lens can be 1.45 to 1.8, and the Abbe number can range from 25 to 60. For example, the use of the same material for the second lens 120, the third lens 130, and the fourth lens 140, while the material of the first lens 110 is different from that of the second lens 120, is beneficial for correcting chromatic aberration. It should be noted that when the material of the first lens 110 is different from that of the other three lenses, the parameters of each surface type can be adaptively adjusted, and this disclosure does not limit this. For example, the refractive index of the first lens 110 is 1.59, and the refractive indices of the second lens 120, the third lens 130, and the fourth lens 140 are 1.54. By using an optical material different from the other lenses for the first lens 110, combined with the air gap g between the first lens 110 and the second lens 120, it is beneficial to improve the axial and transverse chromatic aberration of the optical system. For example, when the material of the first lens 110 differs from that of the other lenses, a combination of high-dispersion and low-dispersion materials can be used. For instance, if the overall optical power of the second lens 120 and the third lens 130 is greater than that of the first lens 110, the first lens 110 can be made of a material with a low Abbe number, such as an Abbe number not greater than 31. For example, the Abbe number of the first lens 110 is 30.7. Meanwhile, the second lens 120, the third lens 130, and the fourth lens 140 can be made of materials with high Abbe numbers, such as an Abbe number greater than 50. For example, the Abbe numbers of the second lens 120, the third lens 130, and the fourth lens 140 can be 50, 52, 55, 57, and 60, respectively.

[0105] refer to Figures 1 to 7For example, the first lens 110, the second lens 120, the third lens 130, and the fourth lens 140 can also use the same optical material to facilitate the fabrication of the optical system. For example, when the materials of all lenses in the lens assembly 100 are the same, a low-dispersion material with a high refractive index can be used, such as a refractive index greater than 1.5 or an Abbe number greater than 50. For example, the second lens 120 and the third lens 130 can also use the same or different optical materials. For example, the third lens 130 and the fourth lens 140 can also use the same or different optical materials. For example, the second lens 120 and the fourth lens 140 can also use the same or different optical materials.

[0106] refer to Figures 1 to 7 For example, when the first lens 110, the second lens 120, the third lens 130, and the fourth lens 140 are made of the same optical material, optical properties such as spectral transmittance, refractive index, and Abbe number can be considered, as well as processability such as material flowability, thermal shrinkage rate, stress, and cost. For example, optical-grade polymethyl methacrylate (PMMA), polycarbonate (PC), cyclic olefin copolymer (COC), cyclic olefin homopolymer (COP), and polyethylene terephthalate (PET) can be used.

[0107] Based on the examples above, Figure 8A for Figure 4 The diagram shows a point array of the optical system. Figure 8B for Figure 4 The graph shows the variation of the blur spot size of the optical system with the field of view angle.

[0108] refer to Figure 8A A dot plot refers to a pattern formed by the dispersion of light rays emitted from a single point into an image plane. Due to aberrations, the intersection points of these rays with the image plane are no longer concentrated at a single point, but rather form a diffuse pattern scattered over a certain range. This pattern can be used to evaluate the imaging quality of an optical system. Figure 8A In the example, taking the first set of values ​​on the left vertical axis, 0.00 represents the normalized field of view in the X direction, 1.00 represents the normalized field of view in the Y direction, 0.000 represents the field of view angle in the X direction, and 45.00 represents the field of view angle in the Y direction. Figure 8A In the example of the first set of values ​​on the right vertical axis, RMS represents the root mean square of the radius from the diffusion point of the diffusion spot to the centroid of the diffusion spot (or the center of the diffusion spot), and 100% represents the diameter of the diffusion spot. Figure 8AThe field-of-view sharpness of an optical system is typically used to evaluate its overall sharpness. This refers to the image sharpness covering the entire field of view when the pupil is at the entrance pupil position on the optical axis OA and the eye is focused on the center of the lens (i.e., zero field of view). It is also known as transient mode. Besides considering overall field-of-view sharpness in transient mode, fixational sharpness is an even more important optical indicator for users of head-mounted displays, for example. Fixational sharpness refers to the image sharpness within a specific angular range that the eye can directly see (not through peripheral vision) when moving up, down, left, and right.

[0109] In fixational mode, when the eye rotates a certain angle, the pupil deviates from the center of the optical axis OA. This deviation occurs in both the Z and Y directions along OA, and the principal ray passing through the center of the pupil forms a certain angle with the Z-axis. For example, this angle ranges from ±35 degrees. This range is set to take into account human visual habits; to clearly see objects beyond a 35-degree range from the center of the eye, a person will actively turn their head rather than laboriously rotating their eyeballs. (Reference) Figure 8B , Figure 8B This illustrates the relationship between fixation point sharpness and fixation angle. The blur spot in the central field of view is much smaller than one pixel, and the blur spot diameter is less than 20 micrometers when the human eye rotates 25 degrees. Figure 8B It is evident that the optical system of this application has a small spot size and high resolution. In summary, the optical system provided in at least one embodiment of this disclosure is capable of clear imaging.

[0110] Figure 8C for Figure 4 The distortion diagram of the optical system shown. (Reference) Figure 8C The distortion diagram reflects the difference in the position of the image plane that produces a sharp image in different fields of view. See [link / reference]. Figure 8C As shown, the maximum absolute value of distortion is within 50%. Therefore, it can be seen that the optical system provided in at least one embodiment of this disclosure can effectively correct distortion and meet the requirements of high-quality imaging. Furthermore, distortion correction can be pre-processed in software.

[0111] Figure 8D for Figure 4 Transverse chromatic aberration diagram of the optical system shown. (Reference) Figure 8D The transverse chromatic aberration diagram represents the height difference of each wavelength relative to the center wavelength at different image heights on the imaging plane. The horizontal axis represents the transverse chromatic aberration value of each wavelength relative to the center wavelength, and the vertical axis represents the normalized field of view. For example... Figure 8DAs shown, F light is cyan, C light is red, and D light is yellow. C and F light are located at opposite ends of the human eye's sensitive area, while D light is located in the middle, close to the spectral line to which the human eye is most sensitive. The figure shows that the absolute value of the trans-axial chromatic aberration between F and C light is controlled within 0.1 mm, and the absolute value of the trans-axial chromatic aberration between F and D light is also controlled within 0.1 mm. This indicates that the optical system can excellently correct chromatic aberration at the edge of the field of view and the second-order spectrum of the entire image plane.

[0112] refer to Figures 1 to 7 In some examples, the polarization reflective layer 200 is configured to reflect linearly polarized light of one characteristic and transmit linearly polarized light of another characteristic. The polarization reflective layer 200 is disposed on the side of the third surface 103 away from the fourth surface 104, and the phase retardation film 400 is disposed between the polarization reflective layer 200 and the transmission-reflection film 300. For example, the polarization reflective layer 200 can also be called a polarization beam splitter. For example, the polarization reflective layer can include a dual brightness enhancement film (DBEF). For example, the polarization reflective layer can also include a multilayer reflective polarizer film (APF). For example, the polarization reflective layer can also include an IQPS (Image Quality Polarizer Standard) film or an IQPE (Image Quality Polarizer Enhanced) film. For example, the polarization reflective layer 200, the phase retardation film 400, and the transmission-reflection film 300, which are capable of reflecting linearly polarized light of one characteristic and transmitting linearly polarized light of another characteristic, form a folded optical path.

[0113] Figure 9 This is a partial cross-sectional view of a display device provided according to an example of an embodiment of the present disclosure. Figure 9 The optical system shown is Figure 1 The difference in the optical system shown is that, Figure 9 The phase retardation film in the optical system shown Figure 1 The phase retardation films in the illustrated optical systems are different, and the positional relationships between the film layers are also different. Of course, Figure 3 The optical system shown is Figure 1 The optical system shown may also have other differences, such as the number of lenses in the lens assembly, the surface shape of each lens, etc., which are not limited in this disclosure.

[0114] It should be noted that, Figure 9 The lens assembly in the optical system shown can be coupled with Figure 1 The lens components in the optical system shown can be different or the same. Figure 9 The polarizing reflective layer 200, the transmissive reflective film 300, and the linear polarizing film 500 in the optical system shown can be coupled with... Figure 1The polarizing reflective layer 200, the transmissive reflective film 300, and the linear polarizing film 500 in the optical system shown have the same characteristics, which will not be described in detail here.

[0115] refer to Figure 9 In some examples, the polarization reflective layer is a cholesteric liquid crystal layer 201; the cholesteric liquid crystal layer 201 is disposed on the side of the third surface 103 away from the fourth surface 104, and the phase retardation film 400 is disposed on the side of the cholesteric liquid crystal layer 201 away from the transmissive film 300. For example, cholesteric liquid crystal can reflect and transmit circularly polarized light. Referring to the aforementioned principle of folded optical path, the cholesteric liquid crystal layer 201 is disposed between the phase retardation film 400 and the transmissive film 300. A waveplate can be disposed on the display surface 11 side of the display screen 10 located on the side of the fourth lens 140 away from the first lens 110. The image light emitted from the display screen 10 is converted into right-hand circularly polarized light after passing through the waveplate. The right-hand circularly polarized light is incident on the transmissive film 300, and its polarization state remains unchanged after transmission through the transmissive film 300. The right-handed circularly polarized light is reflected back to the transflective film 300 after passing through the cholesteric liquid crystal layer 201, where the first reflection occurs. The right-handed circularly polarized light is then reflected again at the transflective film 300, where a second reflection occurs. Due to half-wave loss, the reflected light changes from right-handed circularly polarized light to left-handed circularly polarized light. This left-handed circularly polarized light is transmitted through the cholesteric liquid crystal layer 201 and reaches the phase retardation film 400, where it is converted into s-polarized light. This s-polarized light is then transmitted through the linear polarization film 500 and reaches the human eye.

[0116] refer to Figures 1 to 9 For example, the ratio of the effective aperture to the effective focal length of the lens assembly 100 is 2.2 to 2.7. The effective aperture of the lens assembly 100 refers to the effective light-transmitting aperture, i.e., the maximum aperture through which light can pass, which is determined by the maximum luminous flux of the lens assembly 100. For example, the ratio of the effective aperture to the effective focal length is 1 to 1.3.

[0117] refer to Figures 1 to 9 For example, the ratio of the total optical length (TTL) to the effective focal length of the optical system is 0.9 to 1.1. The total optical length refers to the distance along the optical axis OA from the highest point on the first surface 101 of the lens assembly 100 in the optical system to the center of the display screen 10. The highest point on the first surface 101 includes the edge sag of the lens assembly 100 on the side of the first surface 101. The ratio of the total optical length to the effective focal length can be, but is not limited to, 0.9, 0.95, 1, 1.05, or 1.1.

[0118] refer to Figures 1 to 9For example, the field of view of optical system 100 is greater than 90°. For example, the field of view is the full field of view. For example, the field of view of the optical system may be, but is not limited to, 90°, 92°, 94°, 96°, 98°, or 100°. For example, calculated based on an effective aperture that achieves a field of view of 100°, the weight of the binocular lens is approximately 35g.

[0119] refer to Figures 1 to 9 For example, in an optical system, the ratio of the distance between the aperture (such as the human eye) and the first surface 101 on the optical axis OA to the effective focal length is 1. For example, the effective aperture of the aperture is 4 mm. For example, in an optical system, the ratio of the distance between the object plane and the aperture on the optical axis OA to the effective focal length is less than 100. For example, in an optical system, the ratio of the distance between the image plane and the sixth surface 106 on the optical axis OA to the effective focal length is 0.2. For example, the ratio of the effective aperture of the image plane to the effective focal length is 0.75 to 2. For example, the ratio of the effective aperture of the image plane to the effective focal length can be, but is not limited to, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.2, 1.4, 1.6, 1.8, or 2.

[0120] refer to Figure 9 At least one embodiment of this disclosure provides a display device including a display screen 10 and an optical system of any of the above embodiments, wherein the display screen 10 is located on the side of the sixth surface 106 away from the first surface 101. Since the display device according to the embodiments of this disclosure includes at least one of the above-described optical systems, it also has corresponding beneficial technical effects, which will not be elaborated further here. It is understood that... Figure 9 The display screen 10 shown herein, in conjunction with the aforementioned Figures 1 to 7 The optical system in the middle can form different display devices.

[0121] For example, the display surface 11 of the display screen 10 is located on the focal plane of the light-incident side of the optical system.

[0122] For example, the display screen 10 can be any type of display screen 10, such as liquid crystal display screen 10, organic light-emitting diode display screen 10, inorganic light-emitting diode display screen 10, quantum dot display screen 10, projector (e.g., LCOS micro projector), etc.

[0123] For example, display screen 10 is a liquid crystal display screen 10 with a pixel size of approximately twenty micrometers. Alternatively, display screen 10 is an organic light-emitting diode display screen 10 with a pixel size of approximately a few micrometers.

[0124] For example, the display device can be a virtual reality display device. For example, a virtual reality display device can be a display device employing an ultra-short-throw folded optical path.

[0125] For example, the display device can be a near-eye display device, such as a wearable VR helmet or VR glasses, but the embodiments disclosed herein are not limited thereto.

[0126] The following points need to be explained:

[0127] (1) The accompanying drawings of the embodiments of this disclosure only involve the structures involved in the embodiments of this disclosure, and other structures can be referred to the general design.

[0128] (2) Where there is no conflict, features of the same embodiment and different embodiments of this disclosure may be combined with each other.

[0129] The above description is merely an exemplary embodiment of this disclosure and is not intended to limit the scope of protection of this disclosure, which is determined by the appended claims.

Claims

1. An optical system, comprising: A lens assembly comprises four lenses, including a first lens, a second lens, a third lens, and a fourth lens; the four lenses include a first surface, a second surface, a third surface, a seventh surface, an eighth surface, a fourth surface, a fifth surface, and a sixth surface arranged sequentially along the optical axis of the lens assembly; the first lens includes the first surface and the second surface, the second lens includes the third surface and the seventh surface, the third lens includes the fourth surface and the eighth surface, and the fourth lens includes the fifth surface and the sixth surface; the first lens is a positive lens, the second lens is a negative lens, the third lens is a positive lens, and the fourth lens is a negative lens; A polarizing reflective layer is disposed between the second surface and the third surface; A transflective membrane is disposed between the fourth surface and the fifth surface; A phase retardation film is located between the seventh surface and the eighth surface; Wherein, the second surface is convex, the third surface is concave, the fourth surface is convex, the fifth surface is concave, and the sixth surface is convex; the fourth surface and the fifth surface have the same surface shape parameters, and the seventh surface and the eighth surface have the same surface shape parameters; The distance between the two intersection points of the first surface and the second surface with the optical axis is the first distance; the distance between the two intersection points of the third surface and the fourth surface with the optical axis is the second distance; and the distance between the two intersection points of the fifth surface and the sixth surface with the optical axis is the third distance. The ratio of the absolute value of the radius of curvature of the fourth surface to the absolute value of the radius of curvature of the third surface is 0.8 to 1, the second distance is greater than the first distance, and the second distance is greater than the third distance.

2. The optical system as claimed in claim 1, wherein, The ratio of the absolute value of the radius of curvature of the third surface to the effective focal length of the optical system is 2 to 10, and the conicity of the third surface is -50 to 0; the ratio of the absolute value of the radius of curvature of the fourth surface to the effective focal length of the optical system is 1.5 to 2.5, and the conicity of the fourth surface is -10 to -2.

3. The optical system as claimed in claim 1, wherein, The ratio of the first distance to the effective focal length of the optical system is 0.1 to 0.3; The ratio of the second distance to the effective focal length is 0.4 to 0.7; The ratio of the third distance to the effective focal length is 0.1 to 0.

2.

4. The optical system as claimed in claim 1, wherein, There is an air gap between the second surface and the third surface.

5. The optical system as claimed in claim 4, wherein, The absolute value of the air gap on the optical axis is 0.5 mm to 1 mm.

6. The optical system of claim 1, wherein, The ratio of the absolute value of the radius of curvature of the second surface to the effective focal length of the optical system is 2 to 10, and the conicity of the second surface is -50 to 0.

7. The optical system of claim 1, wherein, At least one of the second surface, the third surface, and the fourth surface is an aspherical surface or a freeform surface.

8. The optical system according to any one of claims 1-7, wherein, The optical system also includes a linear polarizing film; The linear polarizing film is disposed on the side of the polarizing reflective layer away from the transmissive reflective film.

9. The optical system of claim 8, wherein, The linear polarizing film is disposed on one of the first surface, the second surface, and the third surface.

10. The optical system of claim 1, wherein, Both the seventh and eighth surfaces are planes, or the absolute values ​​of the radii of curvature of the third and fourth surfaces are both less than the absolute value of the radii of curvature of the seventh surface in at least one direction.

11. The optical system of claim 10, wherein, The distance between the two intersection points of the seventh surface and the third surface with the optical axis is the fourth distance, and the distance between the two intersection points of the eighth surface and the fourth surface with the optical axis is the fifth distance; The fourth distance is less than the fifth distance.

12. The optical system of claim 11, wherein, The ratio of the first distance to the fourth distance is 1 to 2; The ratio of the third distance to the fourth distance is 0.75 to 1.5; The ratio of the fifth distance to the fourth distance is 1.75 to 3.

13. The optical system of claim 11, wherein, The fourth distance is less than the first distance, and the fourth distance is less than the third distance.

14. The optical system of claim 11, wherein, The ratio of the fourth distance to the effective focal length of the optical system is 0.1 to 0.2; The ratio of the fifth distance to the effective focal length of the optical system is 0.3 to 0.

5.

15. The optical system of claim 10, wherein, The ratio of the center thickness to the edge thickness of the first lens is greater than 1 and less than 3; The ratio of the center thickness to the edge thickness of the second lens is greater than 0.5 and less than 1; The ratio of the center thickness to the edge thickness of the third lens is greater than 1 and less than 3; The ratio of the center thickness to the edge thickness of the fourth lens is greater than 0.5 and less than 1.

16. The optical system of claim 10, wherein, The absolute value of the radius of curvature of the seventh surface is 100 mm to 200 mm.

17. The optical system of claim 10, wherein, The second lens, the third lens, and the fourth lens are made of the same material, and the material of the first lens is different from that of the second lens.

18. The optical system according to any one of claims 1-7, wherein, The first surface is a plane; or The first surface is curved, and the ratio of the absolute value of the radius of curvature of the first surface to the effective focal length of the optical system is greater than or equal to 20.

19. The optical system according to any one of claims 1-7, wherein, The polarization reflective layer is configured to reflect linearly polarized light with one characteristic and transmit linearly polarized light with another characteristic.

20. The optical system of claim 1, wherein, The higher-order coefficients of the fifth surface are the same as those of the fourth surface.

21. A display device comprising a display screen and an optical system according to any one of claims 1-20, wherein, The display screen is located on the side of the sixth surface away from the first surface.

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