Optical system and display apparatus

Abstract

An optical system and a display apparatus. The optical system comprises a lens assembly, a polarization reflection layer, a transflective film and a phase retardation film. The lens assembly comprises at least two lenses, and the at least two lenses comprise a first surface, a second surface, a third surface and a fourth surface which are successively arranged in the optical axis direction of the lens assembly. The polarization reflection layer is arranged on the side of the first surface away from the fourth surface, the transflective film is arranged on the side of the fourth surface away from the third surface, and the phase retardation film is arranged on the side of the transflective film facing the first surface. The second surface and the third surface are both Fresnel surfaces, and surface profiles of the second surface and the third surface are complementary to each other. The at least two lenses comprise lenses differing from each other in terms of at least one of the dispersion coefficient or the refractive index. The second surface and the third surface are configured to be Fresnel surfaces, and the at least two lenses are configured to differ from each other in terms of at least one of the dispersion coefficient or the refractive index, thus helping to achieve chromatic aberration correction by means of cooperation of the Fresnel surfaces and the at least two lenses.

Description

Optical system and display device

[0001] This application claims priority to Chinese Patent Application No. 202311864589.5 filed on December 29, 2023, and the contents of the above-mentioned Chinese patent application disclosure are hereby incorporated by reference in their entirety as a part of this application. Technical Field

[0002] At least one embodiment of the present disclosure relates to an optical system and a display device. Background Art

[0003] Head-mounted display (HMD) technology is a simulation technology that uses a head-mounted display optical system to project digital images generated by a computer and output by an image source into the user's field of view, thereby reproducing a specific environment. Summary of the Invention

[0004] At least one embodiment of the present disclosure provides an optical system, which includes: a lens assembly including at least two lenses, the at least two lenses including a first surface, a second surface, a third surface and a fourth surface arranged in sequence along the optical axis direction of the lens assembly; a polarizing reflection layer provided on a side of the first surface away from the fourth surface; a transflective film provided on a side of the fourth surface away from the third surface; a phase delay film provided on a side of the transflective film facing the first surface; wherein the first surface is a concave surface and the fourth surface is a convex surface; the second surface and the third surface are both Fresnel surfaces, and the surface shapes of the second surface and the third surface are complementary; the at least two lenses include lenses with at least one of different dispersion coefficients and refractive indices.

[0005] For example, according to at least one embodiment of the present disclosure, a ratio of a radius of curvature of the second surface to an effective focal length of the optical system is -6 to 2.

[0006] For example, according to at least one embodiment of the present disclosure, the tooth width of the second surface is comprised between 0.3 mm and 1 mm.

[0007] For example, according to at least one embodiment of the present disclosure, the second surface is a planar Fresnel surface or a curved Fresnel surface.

[0008] For example, according to at least one embodiment of the present disclosure, the at least two lenses include a first lens and a second lens arranged along the optical axis direction, the first lens includes the first surface and the second surface, and the second lens includes the third surface and the fourth surface; wherein the dispersion coefficient of the first lens is greater than the dispersion coefficient of the second lens.

[0009] For example, according to at least one embodiment of the present disclosure, the Abbe coefficient of the first lens is 25-65, and the Abbe coefficient of the second lens is 30-54.

[0010] For example, according to at least one embodiment of the present disclosure, the at least two lenses include a first lens and a second lens arranged along the optical axis direction, the first lens includes the first surface and the second surface, and the second lens includes the third surface and the fourth surface; wherein the refractive index of the first lens is less than the refractive index of the second lens.

[0011] For example, according to at least one embodiment of the present disclosure, a ratio of the curvature radius of the first surface to the curvature radius of the fourth surface is 1.2 to 1.7.

[0012] For example, according to at least one embodiment of the present disclosure, the ratio of the curvature radius of the first surface to the effective focal length of the optical system is -3.5 to -1.5, and the conic coefficient of the first surface is -10 to -0.5.

[0013] For example, according to at least one embodiment of the present disclosure, the ratio of the radius of curvature of the fourth surface to the effective focal length of the optical system is -2.0 to 2.0, and the conic coefficient of the fourth surface is -10 to -0.1.

[0014] For example, according to at least one embodiment of the present disclosure, 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 ratio of the first distance to the second distance is 2 to 4.

[0015] For example, according to at least one embodiment of the present disclosure, a ratio of the first distance to the effective focal length of the optical system is 0.3 to 0.5, and a ratio of the second distance to the effective focal length of the optical system is 0.1 to 0.3.

[0016] For example, according to at least one embodiment of the present disclosure, the at least two lenses include a first lens and a second lens arranged along the optical axis direction, the first lens includes the first surface and the second surface, and the second lens includes the third surface and the fourth surface; 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 2.

[0017] For example, according to at least one embodiment of the present disclosure, the at least two lenses include a first lens, a second lens and a third lens arranged in sequence along the optical axis direction, the first lens includes the first surface and the second surface, the second lens includes the third surface, and the third lens includes the fourth surface; the second lens also includes a fifth surface opposite to the third surface, and the third lens also includes a sixth surface located between the fifth surface and the fourth surface; wherein, at least two of the first lens, the second lens and the third lens have different chromatic aberration coefficients.

[0018] For example, according to at least one embodiment of the present disclosure, the ratio of the curvature radius of the fifth surface to the curvature radius of the second surface is 0.9-1.1, the fifth surface and the sixth surface are both Fresnel surfaces, and the surface shapes of the fifth surface and the sixth surface are complementary.

[0019] For example, according to at least one embodiment of the present disclosure, the fifth surface is a planar Fresnel surface or a curved Fresnel surface.

[0020] At least one embodiment of the present disclosure provides a display device, comprising a display screen and the optical system described in any one of the above embodiments, wherein the display screen is located on a side of the transflective film away from the polarizing reflective layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present disclosure, rather than limiting the present disclosure.

[0022] FIG1 is a schematic diagram of an optical system provided in an example of at least one embodiment of the present disclosure.

[0023] 2A and 2B are schematic diagrams of light deflection in an example of at least one embodiment of the present disclosure.

[0024] FIG2C is a schematic diagram of light deflection in another example of at least one embodiment of the present disclosure.

[0025] FIG3 is a schematic diagram of an optical path of a display device provided in an example of at least one embodiment of the present disclosure.

[0026] FIG4 is a schematic diagram of an optical system provided in an example of at least one embodiment of the present disclosure.

[0027] FIG5A is a point diagram of the optical system shown in FIG1.

[0028] FIG5B is a graph showing how the diffuse spot size of the optical system shown in FIG1 changes with the field of view angle.

[0029] FIG5C is a distortion diagram of the optical system shown in FIG1 .

[0030] FIG5D is a diagram of vertical chromatic aberration of an optical system.

[0031] FIG. 5E is a diagram of vertical chromatic aberration of the optical system shown in FIG. 1 .

[0032] FIG6 is a schematic diagram of an optical system provided in an example of at least one embodiment of the present disclosure.

[0033] FIG7 is a schematic diagram of an optical system provided in an example of at least one embodiment of the present disclosure. DETAILED DESCRIPTION

[0034] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0035] Unless otherwise defined, technical or scientific terms used in this disclosure should have the ordinary meanings understood by people with ordinary skills in the field to which this disclosure belongs. The words "first", "second" and similar terms used in this disclosure do not indicate any order, quantity or importance, but are simply used to distinguish different components. The words "include" or "comprising" and similar terms mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0036] The features such as "perpendicular", "parallel" and "same" used in this disclosure include the features such as "perpendicular", "parallel" and "same" in the strict sense, as well as the cases where "approximately perpendicular", "approximately parallel" and "approximately the same" include certain errors, taking into account the errors associated with the measurement and the measurement of specific quantities (that is, the limitations of the measurement system), and are expressed as being within the acceptable deviation range for a specific value determined by a person of ordinary skill in the art. The "center" in the embodiments of the present disclosure can include a position strictly at the geometric center and a position approximately at the center of a small area around the geometric center. For example, "approximately" can mean within one or more standard deviations, or within 10% or 5% of the value.

[0037] The imaging principle of the head-mounted display (also known as HMD) optical system is similar to that of a magnifying glass, that is, the object (image source or video source) is located in front of the object focal plane of the optical lens (for example, within one focal length), and the human eye on the other side of the optical lens can see through the optical lens that an upright, magnified virtual image will be formed in the distance on the same side of the object. The head-mounted display optical system includes single-piece or multi-piece thick lenses, Fresnel lenses, reentrant optical systems (also known as pancakes), and liquid crystal lenses and super lenses with variable optical power. While focusing on reducing thickness and weight to provide users with a better wearing experience, the head-mounted display optical system still needs to meet the requirements of imaging optical performance. For example, the head-mounted display optical system needs to consider basic indicators such as clarity, field of view, distortion, and chromatic aberration. Many optical indicators need to meet design requirements in the hardware design stage and precision requirements in the optical processing, manufacturing and assembly stages, and be combined with later software (image) processing technologies (such as foveated rendering technology to improve clarity, asymmetric field of view applications, anti-distortion image processing, and anti-dispersion image processing to improve the field of view experience) to bring a better experience to users of head-mounted display optical systems.

[0038] During their research, the inventors of this application discovered that the aforementioned optical specifications often complement each other, but also conflict with each other. For example, low dispersion or low chromatic aberration, and distortion-free optical systems are beneficial for providing better clarity. However, a wide field of view brings challenges to clarity, distortion, and dispersion.

[0039] Taking some liquid crystal displays as an example, the size of the LCD display (e.g., diagonal length) exceeds 2 inches to 2.3 inches, and the diameter of the optical lens of the head-mounted display optical system is, for example, 30 mm to 50 mm (this diameter varies with the field of view angle). The screen size is sufficiently compatible with the optical lens. For example, the screen and the optical lens are relatively close in size, and the angle of incidence of light from the screen reaching the optical lens surface is very small. After refraction and reflection, the angular deviation of light of different wavelengths is also relatively small. At the same time, the size of a single pixel on the screen is relatively large (e.g., a single pixel size is greater than 20 microns). Therefore, the height difference (vertical chromatic aberration) caused by light of different wavelengths on the image plane has a relatively small impact on image quality.

[0040] In a head-mounted display optical system using a silicon-based organic light-emitting diode (OLED) display, due to process limitations, the screen size is usually 1 inch to 1.4 inches. When matching this screen with a small-aperture optical lens (for example, a diameter of 25 mm), the matching difficulty is relatively small. A small-aperture optical lens corresponds to a smaller field of view angle. In order to adapt to a certain wearing error, the field of view ultimately obtained by the user mostly does not exceed 90°. If the field of view angle is to be increased, the aperture of the optical lens needs to be increased accordingly. When matching a large-aperture optical lens with a small-sized screen, the inventors found that the incident angle of light in the large field of view at the edge of the screen on the optical lens is relatively large, resulting in an increase in vertical chromatic aberration. In addition, since the pixel size of a silicon-based OLED screen is less than 10 microns, the tolerance for vertical chromatic aberration is much stricter than that of an LCD screen. Therefore, in a large-field head-mounted display optical system using an inch-level high-definition display, it is more difficult to correct chromatic aberration.

[0041] At least one embodiment of the present disclosure provides an optical system, comprising a lens assembly, a polarizing reflective layer, a transflective film, and a phase delay film. The lens assembly comprises at least two lenses, and the at least two lenses comprise a first surface, a second surface, a third surface, and a fourth surface arranged in sequence along the optical axis of the lens assembly. The polarizing reflective layer is disposed on a side of the first surface away from the fourth surface. The transflective film is disposed on a side of the fourth surface away from the third surface. The phase delay film is disposed on a side of the transflective film facing the first surface. The first surface is concave, and the fourth surface is convex. The second surface and the third surface are both Fresnel surfaces, and the surface shapes of the second surface and the third surface are complementary. At least two lenses comprise lenses having at least one different dispersion coefficient and refractive index.

[0042] At least one embodiment of the present disclosure provides a display device, including a display screen and the optical system of any of the above embodiments, wherein the display screen is located on a side of the transflective film away from the polarizing reflective layer.

[0043] At least one embodiment of the present disclosure provides an optical system and display device that, through a lens assembly comprising at least two lenses, provides attachment locations for a polarizing reflective layer, a transflective film, and a phase retardation film, thereby enabling light to be reflected through the polarizing reflective layer and the transflective film. Furthermore, the second and third surfaces are configured as Fresnel surfaces, and at least two lenses are configured to have at least one of aberration coefficient and refractive index that differ. This facilitates increased design freedom through the Fresnel surfaces, thereby coordinating with the at least two lenses to correct chromatic aberration, resulting in a larger field of view, higher clarity, and a thinner and lighter optical system.

[0044] The optical system and the display device are described below with reference to the accompanying drawings and through some embodiments.

[0045] FIG1 is a schematic diagram of an optical system provided in accordance with an example of at least one embodiment of the present disclosure. Referring to FIG1 , at least one embodiment of the present disclosure provides an optical system comprising a lens assembly 100, a polarizing reflective layer 200, a transflective film 300, and a phase retarder film 400. The lens assembly 100 includes at least two lenses. For example, as shown in FIG1 , the lens assembly 100 may be composed of two lenses, lens 110 and lens 120.

[0046] As shown in FIG1 , at least two lenses include a first surface 101, a second surface 102, a third surface 103, and a fourth surface 104, arranged sequentially along the optical axis OA of the lens assembly 100. For example, the side of the first surface 101 facing away from the fourth surface 104 serves as the light-emitting side of the optical system. For example, when the optical system is used in a display device, the display screen is located on the side of the fourth surface 104 of the optical system facing away from the first surface 101. Light emitted from the display screen enters through the fourth surface 104 and exits through the first surface 101.

[0047] As shown in Figure 1, the polarizing reflective layer 200 is disposed on the side of the first surface 101 away from the fourth surface 104, the transflective film 300 is disposed on the side of the fourth surface 104 away from the third surface 103, and the phase retarder film 400 is disposed on the side of the transflective film 300 facing the first surface 101. For example, when the optical system is applied to a display device, the display screen is located on the side of the transflective film 300 of the optical system away from the polarizing reflective layer 200. For example, light incident on the lens assembly 100 after being transmitted through the transflective film 300 is configured to be folded between the transflective film 300 and the polarizing reflective layer 200 and emitted from the polarizing reflective layer 200, thereby forming a folded optical path through the polarizing reflective layer 200, the transflective film 300, and the phase retarder film 400.

[0048] As shown in Figure 1, at least two lenses include lenses with different dispersion coefficients and refractive indices. Because the same transparent medium has different refractive indices for light of different wavelengths, and white light is composed of various colors of light at different wavelengths, transparent materials experience dispersion when refracting white light. The dispersion coefficient (also known as the Abbe number) is an index used to represent the dispersion ability of a transparent medium and measures the degree of light dispersion within the medium. Generally speaking, the greater the refractive index of the medium, the greater the dispersion and the smaller the Abbe number; conversely, the smaller the refractive index, the less dispersion and the larger the Abbe number.

[0049] As shown in FIG1 , the first surface 101 is a concave surface, and the fourth surface 104 is a convex surface. For example, the first surface 101 is an aspheric surface. For example, the fourth surface 104 is an aspheric surface. For example, the transflective film 300 is disposed on the side of the convex surface away from the concave surface. For example, the polarizing reflective layer 200 and the phase delay film 400 are both disposed on the side of the concave surface away from the convex surface.

[0050] As shown in Figure 1, both second surface 102 and third surface 103 are Fresnel surfaces. A Fresnel surface refers to the non-smooth surface of the two opposing surfaces of a Fresnel lens. A Fresnel lens, also known as a threaded lens, has one smooth surface and the other surface marked with multiple concentric circular patterns (also known as Fresnel zones). These patterns can alter the degree of refraction of light, effectively reducing the thickness of the Fresnel lens at short focal lengths.

[0051] For example, referring to FIG1 , first surface 101 and second surface 102 are two surfaces of lens 110, and third surface 103 and fourth surface 104 are two surfaces of lens 120. Both lens 110 and lens 120 are Fresnel lenses. For example, lens 110 is a convex lens, and lens 120 is a concave lens.

[0052] As shown in Figure 1 , the second surface 102 and the third surface 103 have complementary shapes. Complementary means that after the second surface 102 and the third surface 103 are bonded (or adhered with optical adhesive), there is essentially no gap between the second surface 102 and the third surface 103. For example, the shape of the second surface 102 and the shape of the third surface 103 are positive and negative of each other. For example, at corresponding locations on the second surface 102 and the third surface 103, the tooth-shaped structures on the two Fresnel surfaces can complement each other.

[0053] At least one embodiment of the present disclosure provides an optical system, which, by providing a lens assembly 100 comprising at least two lenses, provides attachment locations for a polarizing reflective layer 200, a transflective film 300, and a phase retarder film 400, thereby enabling light to be reflected by the polarizing reflective layer 200 and the transflective film 300. The second surface 102 and the third surface 103 are configured as Fresnel surfaces, and the at least two lenses are configured to have at least one of different dispersion coefficients and refractive indices. This facilitates increased design freedom through the Fresnel surfaces, thereby correcting chromatic aberration in conjunction with the at least two lenses, resulting in a larger field of view, higher clarity, and a thinner and lighter optical system.

[0054] 2A and 2B are schematic diagrams of light deflection in an example of at least one embodiment of the present disclosure. Below, chromatic aberration correction is described by taking the example of a light incident on an optical system undergoing one refraction.

[0055] Figure 2A illustrates the deflection of light in the optical system when the lens L1 and the lens L2 in the lens assembly have different refractive indices and dispersion coefficients. As shown in Figure 2A, the side away from the target surface S0 is the light incident side, that is, the light enters the lens assembly from the left side of Figure 2A and is emitted from the lens assembly to the target surface S0 after refraction. After the white light (the solid line shown in Figure 2A) enters the lens assembly, the white light is dispersed and decomposed into monochromatic lights with different wavelengths. Figure 2A shows the red light R with a longer wavelength as a short dash line and the blue light B with a shorter wavelength as a dotted line. By setting the lens L1 and the lens L2 to different refractive indices and different dispersion coefficients, the deflection angles of the red light R and the blue light B change, and ultimately the red light R and the blue light B can converge on the target surface S0.

[0056] For example, referring to Figure 2A , lens L1 is a convex lens, and lens L2 is a concave lens. The Abbe number of lens L1 is greater than that of lens L2, and the refractive index of lens L1 is less than that of lens L2. After incident light enters surface S1 and is dispersed, the relatively shorter wavelength blue light B deflects more toward the optical axis OA than the red light R. After refraction through surfaces S2 and S3, because the Abbe number of lens L1 is greater than that of lens L2, the light from lens L1 to lens L2 is deflected away from the optical axis OA, with the shorter wavelength blue light B being deflected more significantly. Consequently, the red light R and blue light B gradually converge. After exiting surface S4, the light continues to deflect away from the optical axis OA, with the shorter wavelength blue light B being deflected even more significantly. This causes the red light R and blue light B to converge on the target surface S0, thereby correcting chromatic aberration.

[0057] Figure 2B simplifies the two lenses shown in Figure 2A into two opposing optical wedges. The inclination of the contact surface between the two lenses is the slope of that surface. As shown in Figure 2B , after white light enters wedge 1, it disperses and decomposes into monochromatic lights of different wavelengths. Figure 2B illustrates the longer-wavelength red light R with a dashed line and the shorter-wavelength blue light B with a dotted line. After the red light R (dashed line) and the blue light B (dotted line) enter wedge 2, the degree of deflection of both the red light R and the blue light B changes, allowing them to converge after exiting onto the target surface S0.

[0058] Figure 2C is a schematic diagram of light deflection in another example of at least one embodiment of the present disclosure. The difference between Figure 2C and Figure 2B is that the slopes of the surfaces where the two optical wedges contact are different.

[0059] Combining FIG2C with FIG1 , FIG2C simplifies lens 110 and lens 120 shown in FIG1 into two opposing optical wedges. FIG2C illustrates the deflection of light in an optical system when two lenses in a lens assembly have different refractive indices and dispersion coefficients, and the contacting surfaces of the two lenses are mutually positive and negative Fresnel surfaces (not shown in FIG2C , but refer to FIG1 for example). As shown in FIG2C , white light is dispersed after entering wedge 1, breaking down into monochromatic lights of different wavelengths. FIG2C illustrates the longer-wavelength red light R with dashed lines and the shorter-wavelength blue light B with dotted lines. As shown in FIG2C , because the contacting surfaces of the two wedges are Fresnel surfaces, the slope of the discretized Fresnel surfaces is larger than that of a continuous aspheric surface, thereby improving the light deflection capability. This allows the red light R (dashed lines) and blue light B (dotted lines) to converge on the closer target surface S0′, thereby making the optical system more compact. Therefore, referring to FIG1 , by configuring the second surface 102 and the third surface 103 as Fresnel surfaces and configuring at least two lenses to have at least one of a different dispersion coefficient and a different refractive index, chromatic aberration can be jointly corrected, thereby making the optical system have a larger field of view, higher clarity, and thinner weight.

[0060] For example, referring to FIG1 , the polarizing reflective layer 200 functions as follows: an optical axis OA exists within the plane of the film layer, and the transmittance of the polarization component of incident light parallel to the optical axis OA (e.g., s-polarized light) is greater than the transmittance of the polarization component perpendicular to the optical axis OA (e.g., p-polarized light), and the reflectivity of the polarization component parallel to the optical axis OA (e.g., s-polarized light) is less than the reflectivity of the polarization component perpendicular to the optical axis OA (e.g., p-polarized light). For example, the transmittance of polarized light parallel to the optical axis OA of the polarizing reflective layer 200 is not less than 85%, such as not less than 90%, such as not less than 95%, such as not less than 98%; and the reflectivity of polarized light perpendicular to the optical axis OA of the polarizing reflective layer 200 is not less than 85%, such as not less than 90%, such as not less than 95%, such as not less than 98%.

[0061] For example, referring to FIG1 , the polarizing reflective layer 200 is configured to reflect linearly polarized light of one characteristic and transmit linearly polarized light of another characteristic. The polarizing reflective layer 200 is disposed on a side of the first surface 101 away from the fourth surface 104 , and the phase retarder film 400 is disposed between the polarizing reflective layer 200 and the transflective film 300 . For example, the polarizing reflective layer may also be referred to as a polarizing beam splitter film. For example, the polarizing reflective layer may also include a multilayer reflective polarizer (Advanced Polarizer Film, APF). For example, the polarizing reflective layer may also include an IQPS (Image Quality Polarizer Standard) film or an IQPE (Image Quality Polarizer Enhanced) film.

[0062] For example, the polarizing reflective layer is a cholesteric liquid crystal layer (not shown in the figure), and the phase retarder film is disposed on the side of the cholesteric liquid crystal layer away from the transflective film. For example, cholesteric liquid crystals can reflect circularly polarized light and transmit circularly polarized light. Referring to the aforementioned principle of folded optical paths, the cholesteric liquid crystal layer is disposed between the phase retarder film and the transflective film. A wave plate can be disposed on the display surface side of the display screen located on the side of the second lens away from the first lens. The image light emitted from the display screen is converted into right-handed circularly polarized light after passing through the wave plate. The right-handed circularly polarized light is incident on the transflective film. After passing through the transflective film, the polarization state of the right-handed circularly polarized light remains unchanged. After passing through the cholesteric liquid crystal layer, the right-handed circularly polarized light is reflected back to the transflective film, where a first reflection occurs; the right-handed circularly polarized light is reflected at the transflective film, 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. The left-handed circularly polarized light passes through the cholesteric liquid crystal layer and reaches the phase delay film, where it is converted into s-polarized light. The s-linearly polarized light then passes through the linear polarization film and is emitted to the human eye.

[0063] For example, referring to FIG1 , the transflective film 300 is configured to transmit a portion of light and reflect another portion of 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 herein is not limited thereto; the transmittance and reflectance of the transflective film may be configured based on product requirements. For example, the transflective film 300 may be plated on the fourth surface 104.

[0064] For example, referring to FIG1 , the phase retarder film 400 is configured to convert the transmitted light between a circularly polarized state and a linearly polarized state. For example, the phase retarder film 400 can be a quarter-wave plate. For example, the phase retarder film 400 has the following characteristics: within the film plane, there exists a direction with the lowest refractive index and a direction with the highest refractive index, which are respectively the fast axis and the slow axis. After passing through the phase retarder film 400, the phase of polarized light parallel to the slow axis is delayed by 1 / 4 wavelength compared to polarized light parallel to the fast axis after passing through the phase retarder film 400. For example, the angle between the slow axis of the phase retarder film 400 and the optical axis OA of the polarizing reflective layer 200 is 45 degrees.

[0065] For example, referring to Figure 1 , the material of the phase retarder film 400 can include a liquid crystal polymer. Because the phase retarder film 400 made of liquid crystal polymer is a polymer, its film thickness can be relatively thin, ranging from 1μm to 5μm. A thinner phase retarder film 400 is more adaptable to curved surfaces, allowing it to more easily conform to the surface shape, reducing the possibility of wrinkles when attached to the curved surface, which could affect phase retardation accuracy and optical performance. Furthermore, the phase retarder film 400 made of liquid crystal polymer experiences less optical shift when attached to a curved surface. Liquid crystal polymer is a cross-linked system, with molecules linked by chemical bonds, resulting in a high modulus. When the phase retarder film 400 made of liquid crystal polymer is stretched after attachment, it only undergoes elastic deformation, without experiencing strong optical anisotropy effects such as molecular stretching and rearrangement. Therefore, phase retarder films 400 made of liquid crystal polymer are suitable for attachment to surfaces with a small radius of curvature. This flexibility in curvature radius also makes it easier to meet requirements for clarity, distortion, and dispersion, thereby facilitating better image quality in the optical system.

[0066] FIG3 is a schematic diagram of the optical path of a display device provided in an example according to at least one embodiment of the present disclosure. At least one embodiment of the present disclosure provides a display device comprising a display screen 10 and an optical system. The display screen 10 is located on the side of a transflective film 300 away from the polarizing reflective layer 200. For example, referring to FIG3 , the principle of the folded optical path is as follows: a wave plate may be provided on the light-emitting side of the display surface 11 of the display screen 10, located on the side of the fourth surface 104 away from the first surface 101. Image light emitted from the display surface 11 is converted to right-handed circularly polarized light after passing through the wave plate. The polarization state of the right-handed circularly polarized light remains unchanged after passing through the transflective film 300. This light enters the lens assembly 100 and, after passing through the lens assembly 100, reaches the phase retarder film 400. The right-handed circularly polarized light incident on the phase retarder film 400 is converted to p-linearly polarized light. The p-linearly polarized light is reflected back to the phase retarder film 400 by the polarizing reflective layer 200, where the first reflection occurs. The p-linearly polarized light then passes through the phase retarder film 400 and is converted into right-handed circularly polarized light. This right-handed circularly polarized light then passes through the lens assembly 100 and reaches the transflective film 300, where it is reflected, undergoing a second reflection. Due to half-wave loss, the reflected light changes from right-handed circularly polarized light to left-handed circularly polarized light. The left-handed circularly polarized light then passes through the lens assembly 100 and reaches the phase retarder film 400. After passing through the phase retarder film 400, it becomes s-linearly polarized light. This s-linearly polarized light then passes through the polarizing reflective layer 200 and is emitted toward the exit pupil, such as the human eye.

[0067] The folded optical path can change the polarization state of light propagating between the polarizing reflective layer 200 and the transflective film 300, thereby folding the light. This causes the original focal length of the optical system to be folded due to, for example, two additional reflections caused by the provision of the polarizing reflective layer 200, the phase delay film 400, and the transflective film 300. This greatly reduces the space required between the human eye and the optical system, thereby making the optical system smaller and thinner.

[0068] For example, the optical system further includes a linear polarizing film 500, which is disposed on a side of the polarizing reflective layer 200 away from the transflective film 300. For example, the linear polarizing film 500 may be a linear polarizer or a polarizer. For example, the optical axis of the linear polarizing film 500 coincides with the optical axis of the polarizing reflective layer 200. For example, the linear polarizing film 500 may be used to further filter out other stray light, allowing only polarized light (such as s-polarized light) that passes through the linear polarizing film 500 to enter the human eye. For example, the linear polarizing film may have a three-layer laminate structure, wherein the middle layer of the three-layer laminate structure may be polyvinyl alcohol (PVA) to which dichroic molecules are added, and at least one layer on both sides of the middle layer of the three-layer laminate structure may be triacetate (TAC). For example, the surface of the linear polarizing film 500 facing the air is subjected to anti-reflection treatment. For example, the surface of the linear polarizing film 500 facing the air may be bonded to a moth-eye film.

[0069] In some examples, referring to FIG1 , the ratio of the radius of curvature of the second surface 102 to the effective focal length of the optical system may be -6 to 2. For example, the second surface 102 may be a curved Fresnel surface, and the radius of curvature of the second surface 102 refers to the radius of curvature of the curved Fresnel surface. For example, the radius of curvature of the second surface 102 refers to the radius of curvature of a Fresnel surface including a toothed structure. For example, the ratio of the radius of curvature of the second surface 102 to the effective focal length of the optical system may be -5 to 1.5. For example, the ratio of the radius of curvature of the second surface 102 to the effective focal length of the optical system may be -4 to 0. For example, the ratio of the radius of curvature of the second surface 102 to the effective focal length of the optical system may be -3 to -1. For example, the ratio of the radius of curvature of the second surface 102 to the effective focal length of the optical system may be -2.

[0070] For example, referring to FIG1 , the second surface 102 of the Fresnel surface can be approximated as a smooth, toothless spherical or aspherical surface. The spherical or aspherical surface is the base surface of the Fresnel surface, and the curvature of the spherical or aspherical surface is the curvature of the Fresnel surface. For example, the tooth width or tooth height of the second surface 102 and the third surface 103 can be assumed to be infinitesimal. For example, the curvature of the base surface is -0.01 to -0.04. For example, the curvature of the base surface is -0.02 to -0.03. In this way, the toothed structure on the Fresnel surface can be prevented from contacting surfaces (e.g., the first surface 101 or the fourth surface 104) located on both sides of the Fresnel surface (e.g., the second surface 102 and the third surface 103) on the optical axis OA.

[0071] FIG4 is a schematic diagram of an optical system provided in an example of at least one embodiment of the present disclosure. The difference between the optical system shown in FIG4 and the optical system shown in FIG1 is that the second surface 102 in the optical system shown in FIG4 is different from the second surface 102 in the optical system shown in FIG1. ​​Of course, the optical system shown in FIG4 may also have other differences from the optical system shown in FIG1, such as the number of lenses included in the lens assembly, etc., which is not limited by the present disclosure. For example, the number of lenses in the optical system shown in FIG4 may be different from or the same as the number of lenses in the optical system shown in FIG1. ​​The polarizing reflective layer 200, the transflective film 300, and the linear polarizing film 500 in the optical system shown in FIG4 may have the same features as the polarizing reflective layer 200, the transflective film 300, and the linear polarizing film 500 in the optical system shown in FIG1, and will not be repeated here.

[0072] In some examples, the second surface 102 is a planar Fresnel surface or a curved Fresnel surface. For example, as shown in FIG1 , the second surface 102 is a curved Fresnel surface; as shown in FIG4 , the second surface 102 is a planar Fresnel surface. It is understood that the second surface 102 can be convex, concave, or planar. For example, a continuous curved surface can be discretized to obtain a planar Fresnel surface with a planar base surface (for example, see FIG4 ). For example, a continuous curved surface can be discretized and then superimposed with a discretized spherical or aspheric curvature to obtain a curved Fresnel surface with a curved base surface (for example, see FIG1 ). As a result, the radius of curvature of the Fresnel surface in the optical system has a large adjustment space, thereby better deflecting and converging dispersed light. Therefore, by making the slope of the Fresnel surface adjustable, the light deflection capabilities of the second surface 102 and the third surface 103 are enhanced, which can not only achieve ultra-short focus but also improve the correction effect of chromatic aberration and enhance clarity.

[0073] For example, referring to Figure 1 , both second surface 102 and third surface 103 are curved toward the side away from first surface 101, meaning both second surface 102 and third surface 103 are convex. This minimizes the difference between the center and edge thicknesses of first lens element 110, and also minimizes the difference between the center and edge thicknesses of second lens element 120, reducing manufacturing complexity. Furthermore, the curved Fresnel lens allows the second and third surfaces 102, 103 to more easily align with the first and fourth surfaces 101, 104, thereby reducing the thickness of lens assembly 100 along optical axis OA and thus controlling the overall optical length of the optical system.

[0074] In some examples, as shown in FIG1 , the ratio of the radius of curvature of the first surface 101 to the fourth surface 104 may be 1.2 to 1.7. For example, the ratio of the radius of curvature of the first surface 101 to the fourth surface 104 may be 1.3 to 1.6. For example, the ratio of the radius of curvature of the first surface 101 to the fourth surface 104 may be 1.4 to 1.5.

[0075] In some examples, as shown in FIG1 , the ratio of the radius of curvature of the first surface 101 to the effective focal length of the optical system may be -3.5 to -1.5, and the conic coefficient of the first surface 101 may be -10 to -0.5. For example, the ratio of the radius of curvature of the first surface 101 to the effective focal length of the optical system may be -3 to -2. For example, the ratio of the radius of curvature of the first surface 101 to the effective focal length of the optical system may be -2.5. For example, the conic coefficient of the first surface 101 may be -9 to -1. For example, the conic coefficient of the first surface 101 may be -8 to -2. For example, the conic coefficient of the first surface 101 may be -7 to -3. For example, the conic coefficient of the first surface 101 may be -6 to -4. For example, the conic coefficient of the first surface 101 may be -5.

[0076] In some examples, as shown in FIG1 , the ratio of the radius of curvature of the fourth surface 104 to the effective focal length of the optical system is between -2.0 and 2.0, and the conic coefficient of the fourth surface 104 is between -10 and -0.1. For example, the ratio of the radius of curvature of the fourth surface 104 to the effective focal length of the optical system may be between -1.8 and 1.8. For example, the ratio of the radius of curvature of the fourth surface 104 to the effective focal length of the optical system may be between -1.5 and 1.5. For example, the ratio of the radius of curvature of the fourth surface 104 to the effective focal length of the optical system may be between -1 and 1. For example, the conic coefficient of the fourth surface 104 may be between -9 and -1. For example, the conic coefficient of the fourth surface 104 may be between -8 and -2. For example, the conic coefficient of the fourth surface 104 may be between -7 and -3. For example, the conic coefficient of the fourth surface 104 may be between -6 and -4. For example, the conic coefficient of the fourth surface 104 may be -5.

[0077] For example, the surface shape of a curved Fresnel surface can be approximated as an aspherical surface, which can be expressed by the following numerical formula:

[0078] For example, in the above formula, the height of the aspheric surface along the direction perpendicular to the optical axis is Y, the distance from the aspheric vertex to the projection of the aspheric surface at the height Y on the optical axis is z, that is, z is the coordinate along the optical axis; C is the curvature (the inverse of the curvature radius R), k is the conic constant, α i is the coefficient of each higher-order term, and 2i is the order of Aspherical Coefficient.

[0079] When optimizing the proper configuration of lens assembly parameters, the curvature radius, conic coefficient, height, and aspheric coefficient of each lens element in the lens assembly are entered into the aforementioned numerical formulas, and optical simulations are performed to obtain the optimized parameters that can correct the aberrations of each lens element in the lens assembly. The optimization process yields the optimal values ​​for the curvature radius, thickness along the optical axis, effective aperture, and conic coefficient of each lens element in the lens assembly.

[0080] For example, as shown in FIG1 , the conic coefficients of the second surface 102 and the third surface 103 can be 0 to improve the efficiency of optimizing the Fresnel surface. For example, the conic coefficients of the second surface 102 and the third surface 103 can be less than 0. For example, the conic coefficients of the second surface 102 and the third surface 103 can be greater than 0.

[0081] In combination with the above example, for example, the high-order coefficients of the first surface 101 satisfy: α4 = -1.0E-05, α6 = 1.5E-07, α8 = 1.1E-09, α 10 =6.0E-12. For example, the high-order coefficients of the second surface 102 satisfy: α4=-3.0E-05, α6=-3.0E-08, α8=0.0E+00, α 10 =0.0E+00. For example, the high-order coefficients of the third surface 103 are exactly the same as those of the second surface 102. For example, the high-order coefficients of the fourth surface 104 satisfy: α4 = -0.00003, α6 = -3.7E-08, α8 = 6.0E-12, α 10 =-2.0E-14.

[0082] In some examples, as shown in FIG1 , the tooth width of the second surface 102 includes 0.3 mm to 1 mm. For example, the second surface 102 includes a toothed structure, and the toothed structure is composed of a plurality of concentrically arranged tooth rings, and the tooth width is the spacing between two adjacent tooth rings. For example, among the plurality of tooth rings, the spacing between two adjacent tooth rings is equal. For example, the tooth width of the second surface 102 includes 0.4 mm to 0.9 mm. For example, the tooth width of the second surface 102 includes 0.5 mm to 0.8 mm. For example, the tooth width of the second surface 102 includes 0.6 mm to 0.7 mm. By setting the tooth width to 0.3 mm to 1 mm, the tooth profile of the second surface 102 can be appropriately dense, which can not only reduce processing errors and improve optical efficiency, but also facilitate the molding and demolding of the teeth during injection molding.

[0083] For example, when light is reflected in an optical system, each time the light passes through a Fresnel surface, the effect of the teeth on the Fresnel surface on the light must be considered to prevent light leakage or light blockage, thereby reducing stray light and improving image contrast. For example, in one example of an embodiment of the present disclosure, as shown in FIG3 , during the process of incident light reflecting through lens assembly 100, it passes through second surface 102 and third surface 103 three times. The tooth height and draft angle of the Fresnel surface can be calculated through optical simulation based on the deflection angle of the light each time it passes through second surface 102 or third surface 103.

[0084] In some examples, as shown in FIG1 , at least two lenses include a first lens 110 and a second lens 120 arranged along an optical axis OA. The first lens 110 includes a first surface 101 and a second surface 102, and the second lens 120 includes a third surface 103 and a fourth surface 104. The Abbe coefficient of the first lens 110 is greater than the Abbe coefficient of the second lens 120. For example, the first lens 110 is a convex lens and the second lens 120 is a concave lens. By setting the Abbe coefficient of the first lens 110 to be greater than the Abbe coefficient of the second lens 120, the deflection of light of different wavelengths is facilitated, thereby better correcting chromatic aberration.

[0085] In some examples, as shown in FIG1 , the Abbe coefficient of the first lens 110 may be 25 to 65, and the Abbe coefficient of the second lens 120 may be 30 to 54. For example, the Abbe coefficient of the first lens 110 may be 30 to 60. For example, the Abbe coefficient of the first lens 110 may be 35 to 55. For example, the Abbe coefficient of the first lens 110 may be 40 to 50. For example, the Abbe coefficient of the first lens 110 may be 45. For example, the Abbe coefficient of the second lens 120 may be 35 to 50. For example, the Abbe coefficient of the second lens 120 may be 40 to 45. For example, the Abbe coefficient of the first lens 110 may be 55 to 65, and the Abbe coefficient of the second lens 120 may be 30 to 40. For example, the Abbe coefficient of the first lens 110 may be 55 to 57, and the Abbe coefficient of the second lens 120 may be 49 to 51. For example, the Abbe coefficient of the first lens 110 may be 56, and the Abbe coefficient of the second lens 120 may be 50. It will be understood that the present disclosure only exemplifies the dispersion coefficient of the first lens 110 and the dispersion coefficient of the second lens 120. The dispersion coefficient of the first lens 110 and the dispersion coefficient of the second lens 120 may be relatively close or may differ greatly. As long as the dispersion coefficient of the first lens 110 is greater than the dispersion coefficient of the second lens 120, the present disclosure does not limit the combination of numerical values.

[0086] In some examples, as shown in FIG1 , at least two lenses include a first lens 110 and a second lens 120 arranged along the optical axis OA. The first lens 110 includes a first surface 101 and a second surface 102, and the second lens 120 includes a third surface 103 and a fourth surface 104. The refractive index of the first lens 110 is lower than that of the second lens 120. For example, the refractive index and the dispersion coefficient are generally inversely proportional. For example, the lower the refractive index, the larger the dispersion coefficient. For example, the lower the dispersion coefficient, the larger the refractive index. For example, the first lens 110 is a convex lens and the second lens 120 is a concave lens. By setting the refractive index of the first lens 110 to be lower than that of the second lens 120, it is beneficial to refract light of different wavelengths, thereby better correcting chromatic aberration.

[0087] For example, as shown in FIG1 , the refractive index of the first lens 110 may be 1.4 to 1.7. For example, the refractive index of the first lens 110 may be 1.5 to 1.6. For example, the refractive index of the second lens 120 may be 1.4 to 1.7. For example, the refractive index of the second lens 120 may be 1.5 to 1.6. For example, the refractive index of the first lens 110 may be 1.55, and the refractive index of the second lens 120 may be 1.59. It will be understood that the present disclosure only exemplifies the refractive index of the first lens 110 and the refractive index of the second lens 120. The refractive index of the first lens 110 and the refractive index of the second lens 120 may be relatively close or significantly different. As long as the refractive index of the first lens 110 is less than the refractive index of the second lens 120, the present disclosure does not limit the combination of numerical values.

[0088] For example, as shown in Figure 1, the first lens 110 and the second lens 120 can be made of different materials so that the Abbe number of the first lens 110 is different from the Abbe number of the second lens 120, and the refractive index of the first lens 110 is different from the refractive index of the second lens 120. For example, the first lens 110 and the second lens 120 can be separately injection molded and then bonded together using an elastic adhesive. For example, after the first lens 110 is injection molded, a liquid optical material can be poured between the first lens 110 and the mold using a casting process and cured to form the second lens 120. For example, by selecting a liquid optical material, the cured second lens 120 can be made of a hard polymer or an elastic optical silicone. For example, the hard polymer can be a monomer polymer with a refractive index of 1.554 and an Abbe number of 39.3. For example, the elastic optical silicone can be silicone rubber. For example, the optical silicone has a refractive index of 1.41 and an Abbe number of 52. For example, the refractive index of optical silicone is 1.41 and the dispersion coefficient is 50. For example, the second lens 120 can be injection molded first, and then the liquid optical material is poured between the second lens 120 and the mold through a casting process and solidified to form the first lens 110.

[0089] For example, FIG1 schematically illustrates the influence of each film layer on the distance between different surfaces of the lens assembly. If the thickness of each film layer is relatively thin, the thickness of the film layer can be ignored.

[0090] In some examples, as shown in FIG1 , the distance between the two intersection points where the first surface 101 and the second surface 102 intersect the optical axis OA is a first distance D1. For example, the first distance D1 is the center thickness of the first lens 110. As shown in FIG1 , the distance between the two intersection points where the third surface 103 and the fourth surface 104 intersect the optical axis OA is a second distance D2. For example, the second distance D2 is the center thickness of the second lens 120. The ratio of the first distance D1 to the second distance D2 can be 2 to 4 (2:1 to 4:1). For example, the ratio of the first distance D1 to the second distance D2 can be 2.5 to 3.5.

[0091] In some examples, as shown in FIG1 , the ratio of the first distance D1 to the effective focal length of the optical system may be 0.3 to 0.5. For example, the ratio of the first distance D1 to the effective focal length of the optical system may be 0.35 to 0.45. For example, the ratio of the first distance D1 to the effective focal length of the optical system may be 0.4. In some examples, the ratio of the second distance D2 to the effective focal length of the optical system may be 0.1 to 0.3. For example, the ratio of the second distance D2 to the effective focal length of the optical system may be 0.15 to 1.25. For example, the ratio of the second distance D2 to the effective focal length of the optical system may be 0.2.

[0092] In some examples, as shown in FIG1 , at least two lenses include a first lens 110 and a second lens 120 arranged along an optical axis OA, the first lens 110 including a first surface 101 and a second surface 102, and the second lens 120 including a third surface 103 and a fourth surface 104. 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 is greater than 1.5 and less than 2.5. 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 2. For example, the ratio of the center thickness to the edge thickness of the second lens 120 is greater than 1 and less than 1.5. By setting the proportional relationship between the center thickness and the edge thickness of each of the above lenses, it is helpful to ensure the injection molding of each lens.

[0093] In conjunction with the above examples, Figure 5A is a spot diagram of the optical system shown in Figure 1. Figure 5B is a graph showing how the diffuse spot size of the optical system shown in Figure 1 changes with the field of view angle.

[0094] Referring to Figure 5A, a spot diagram refers to the pattern of scattered light rays emitted from a single point. After passing through an optical system, due to aberrations, their intersections with the image plane no longer converge at the same point, but rather form a diffuse pattern distributed over a certain range. This pattern can be used to evaluate the imaging quality of an optical system. In Figure 5A, taking the first set of values ​​on the left vertical axis as an example, 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 47.50 represents the field of view angle in the Y direction. In Figure 5A, taking the first set of values ​​on the right vertical axis as an example, RMS represents the root mean square of the radius from the diffusion point to the centroid (or center) of the diffuse spot, and 100% represents the diameter of the diffuse spot. Figure 5A is typically used to evaluate the full-field clarity of an optical system. This refers to the image clarity across the entire field of view covered by the peripheral vision when the human pupil is at the entrance pupil position on the optical axis and looking at the center of the lens (i.e., zero field of view). This is also known as the transient mode. In addition to considering full-field clarity in transient mode, gaze point clarity is an even more important optical indicator for wearers of head-mounted displays. Gaze point clarity refers to the image clarity within a specific angle range that the eye can directly see (not just peripheral vision) as it moves up, down, left, or right.

[0095] In the gaze point mode, the eyeball rotates a certain angle, the pupil deviates from the center of the optical axis, and there is a certain deviation in the Z and Y directions of the optical axis, and the main light passing through the center of the pupil has a certain angle with the Z axis. For example, the range of the angle is ±35 degrees. The range of the angle is set taking into account the observation habits of the human eye. In order to see the objects in front that are more than 35 degrees beyond the center of the human eye, people will actively turn their heads instead of laboriously turning their eyeballs. Referring to Figure 5B, Figure 5B shows the relationship between the clarity of the gaze point and the gaze angle. The diffuse spot of the central field of view is much smaller than a pixel, and the diameter of the diffuse spot when the human eye rotates to 20 degrees is less than 15 microns. As can be seen from Figure 5B, the diffuse spot of the optical system of the present application is small, and the resolution of the optical system is high. In summary, it can be seen that the optical system provided by at least one embodiment of the present disclosure can form clear images.

[0096] Figure 5C is a distortion diagram for the optical system shown in Figure 1. Referring to Figure 5C , the distortion diagram reflects the differences in image plane position for sharp images at different fields of view. As shown in Figure 5C , the absolute value of the maximum distortion is within 50%. This demonstrates that the optical system provided by at least one embodiment of the present disclosure can effectively correct distortion and meet high-quality imaging requirements. Furthermore, distortion correction can be pre-processed in software.

[0097] Figure 5D is a diagram of vertical axial chromatic aberration of an optical system. Figure 5E is a diagram of vertical axial chromatic aberration of the optical system shown in Figure 1.

[0098] Referring to Figures 5D and 5E , the vertical chromatic aberration diagrams show the vertical chromatic aberration values ​​for each wavelength relative to the central wavelength at different image heights on the imaging plane. The horizontal axis represents the vertical chromatic aberration value for each wavelength relative to the central wavelength, and the vertical axis represents the normalized field of view. As shown in Figures 5D and 5E , F light represents cyan, C light represents red, and D light represents yellow. C and F light are located at opposite ends of the human eye's sensitive region, while D light is located in the middle, near the spectral line to which the human eye is most sensitive. Referring to Figure 5D , which shows the vertical chromatic aberration results for a single-element optical system, the absolute values ​​of the vertical chromatic aberration between F and C light are approximately within 0.1 mm, and the absolute values ​​of the vertical chromatic aberration between F and D light are approximately within 0.06 mm. Figure 5E shows that the absolute values ​​of the vertical chromatic aberration between F and C light are controlled within 0.035 mm, and the absolute values ​​of the vertical chromatic aberration between F and D light are controlled within 0.025 mm. By comparing FIG5E with FIG5D , it can be seen that the optical system provided by the present disclosure as shown in FIG1 can reduce the vertical axis chromatic aberration to 1 / 3 at the maximum field of view and the chromatic aberration to 1 / 6 compared to the single-piece optical system. This means that the optical system shown in FIG1 , for example, can excellently correct the chromatic aberration of the marginal field of view and the secondary spectrum of the entire image plane.

[0099] FIG6 is a schematic diagram of an optical system provided in an example of at least one embodiment of the present disclosure. The difference between the optical system shown in FIG6 and the optical system shown in FIG1 is that the number of lenses in the optical system shown in FIG6 is different from the number of lenses in the optical system shown in FIG1. ​​Of course, the optical system shown in FIG6 may also have other differences from the optical system shown in FIG1, such as the surface shape of at least one lens, etc., and the present disclosure does not limit this. For example, the surface shape parameters of the first surface 101 to the fourth surface 104 in the optical system shown in FIG6 may be different from or the same as the surface shape parameters of the first surface 101 to the fourth surface 104 in the optical system shown in FIG1. ​​The polarizing reflective layer 200, the transflective film 300, and the linear polarizing film 500 in the optical system shown in FIG6 may have the same features as the polarizing reflective layer 200, the transflective film 300, and the linear polarizing film 500 in the optical system shown in FIG1, and no further details will be given here.

[0100] In some examples, as shown in FIG6 , at least two lenses include a first lens 011, a second lens 012, and a third lens 013 arranged sequentially along the optical axis OA. The first lens 011 includes a first surface 101 and a second surface 102, the second lens 012 includes a third surface 103, and the third lens 013 includes a fourth surface 104. The second lens 012 also includes a fifth surface 105 opposite the third surface 103, and the third lens 013 also includes a sixth surface 106 located between the fifth surface 105 and the fourth surface 104. At least two of the first lens 011, the second lens 012, and the third lens 013 have different Abbe coefficients. For example, the first lens 011 and the second lens 012 have different Abbe coefficients, while the second lens 012 and the third lens 013 have the same Abbe coefficient. For example, the first lens 011 and the third lens 013 have different Abbe coefficients, while the first lens 011 and the second lens 012 have the same Abbe coefficient. For example, the second lens 012 and the third lens 013 have different Abbe coefficients, and the first lens 011 and the third lens 013 have the same Abbe coefficient. For example, the first lens 011, the second lens 012, and the third lens 013 each have a different Abbe coefficient.

[0101] For example, when two of the first lens 011, the second lens 012, and the third lens 013 are made of the same optical material, optical properties such as spectral transmittance, refractive index, and Abbe number may be considered, as well as processability such as material fluidity, thermal shrinkage, stress, and cost. For example, optical-grade polymethyl methacrylate (PMMA), polycarbonate (PC), cyclic olefin copolymer (COC), cyclic olefin homopolymer (COP), and polyethylene terephthalate (PET) may be used.

[0102] In some examples, as shown in FIG6 , the ratio of the radius of curvature of the fifth surface 105 to the radius of curvature of the second surface 102 is 0.9 to 1.1. For example, the surface shapes of the fifth surface 105 and the second surface 102 are relatively similar. The fifth surface 105 and the sixth surface 106 are both Fresnel surfaces, and the surface shapes of the fifth surface 105 and the sixth surface 106 are complementary. Complementary means that after the fifth surface 105 and the sixth surface 106 are bonded (or adhered by optical glue), there is basically no gap between the fifth surface 105 and the sixth surface 106. For example, the surface shape of the fifth surface 105 and the surface shape of the sixth surface 106 are positive and negative shapes to each other. For example, at the corresponding positions of the fifth surface 105 and the sixth surface 106, the tooth structures on the two Fresnel surfaces can complement each other.

[0103] FIG7 is a schematic diagram of an optical system provided in an example of at least one embodiment of the present disclosure. The difference between the optical system shown in FIG7 and the optical system shown in FIG6 is that the surface parameters in the optical system shown in FIG7 are different from the surface parameters in the optical system shown in FIG6. Of course, the optical system shown in FIG6 may also have other differences from the optical system shown in FIG1 , such as the number of lenses included in the lens assembly, etc., which is not limited by the present disclosure. For example, the number of lenses in the optical system shown in FIG7 may be different from or the same as the number of lenses in the optical system shown in FIG6. The polarizing reflective layer 200, the transflective film 300, and the linear polarizing film 500 in the optical system shown in FIG7 may have the same features as the polarizing reflective layer 200, the transflective film 300, and the linear polarizing film 500 in the optical system shown in FIG6 , and will not be repeated here.

[0104] In some examples, as shown in Figures 6 and 7, the fifth surface 105 is a planar Fresnel surface or a curved Fresnel surface. For example, as shown in Figure 6, both the fifth surface 105 and the sixth surface 106 are curved Fresnel surfaces. For example, as shown in Figure 7, both the fifth surface 105 and the sixth surface 106 are planar Fresnel surfaces. It is understood that the fifth surface 105 can be convex, concave, or planar. For example, both the second surface 102 and the fifth surface 105 are curved away from the first surface 101, thereby minimizing the difference between the center and edge thicknesses of the second lens element 02 and the third lens element 03, thereby reducing processing difficulty.

[0105] For example, as shown in FIG7 , the second surface 102 of the first lens 01 is a planar Fresnel surface, the third surface 103 and the fifth surface 105 of the second lens 02 are planar Fresnel surfaces, and the sixth surface 106 of the third lens 03 is a planar Fresnel surface. For example, as shown in FIG7 , the second surface 102 and the third surface 103 have complementary surface shapes, and the fifth surface 105 and the sixth surface 106 have complementary surface shapes.

[0106] For example, referring to Figure 7, a continuous curved surface can be discretized to obtain a planar Fresnel surface. For example, referring to Figure 6, a continuous curved surface can be discretized and then superimposed with a discretized spherical curvature to obtain a curved Fresnel surface. This allows for a wide range of adjustment for the radius of curvature of the Fresnel surface in the optical system, enabling better deflection and convergence of dispersed light. Thus, by making the slope of the Fresnel surface adjustable, the light deflection capabilities of the fifth and sixth surfaces 105 and 106 are enhanced, enabling ultra-short focus while also improving chromatic aberration correction and enhancing clarity.

[0107] For example, referring to Figures 1 and 3 , the ratio of the total optical length (TTL) of the optical system to the effective focal length is 0.85 to 1. For example, the ratio of the total optical length of the optical system to the effective focal length is 0.9 to 0.95. 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 sagittal height of the lens assembly 100 on the side where the first surface 101 is located.

[0108] For example, as shown in Figures 1 and 3, the optical system has a field of view greater than 90°. For example, the field of view is the full field of view. For example, the optical system's field of view can be, but is not limited to, 90°, 92°, 94°, 96°, 98°, or 100°. For example, based on an effective aperture capable of achieving a field of view of 100°, the binocular lens weighs approximately 20g.

[0109] For example, as shown in Figures 1 and 3, the exit pupil distance (EPD) of the optical system is 12 mm to 20 mm. For example, the exit pupil distance is the distance from the vertex of the last surface of the optical system to the intersection of the exit pupil plane and the optical axis. For example, the exit pupil distance is 14 mm to 18 mm. For example, the exit pupil distance is 15 mm. The optical system provided by the present disclosure has a large exit pupil distance, which can meet the needs of myopic users wearing glasses.

[0110] With reference to FIG3 , at least one embodiment of the present disclosure provides a display device comprising a display screen 10 and an optical system according to any of the above embodiments. The display screen 10 is located on a side of the fourth surface 104 away from the first surface 101. Since the display device according to an embodiment of the present disclosure includes at least one of the above optical systems, it also has corresponding beneficial technical effects, which will not be described in detail here. It is understood that the display screen 10 shown in FIG3 can be combined with the optical systems shown in FIG1 , FIG4 , FIG6 , and FIG7 to form different display devices.

[0111] For example, as shown in FIG3 , the display surface 11 of the display screen 10 is located at the focal plane on the light incident side of the optical system.

[0112] For example, as shown in FIG3 , the ratio of the effective aperture to the effective focal length of the lens assembly 100 is 2.2 to 2.4. 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. This aperture 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 2.3.

[0113] For example, as shown in FIG3 , the ratio of the distance between the aperture (e.g., the human eye) and the first surface 101 on the optical axis OA in the optical system to the effective focal length is 0.7 to 1.5. For example, the ratio of the distance between the aperture and the first surface 101 on the optical axis OA to the effective focal length is 0.8 to 1.4. For example, the ratio of the distance between the aperture and the first surface 101 on the optical axis OA to the effective focal length is 0.9 to 1.3. For example, the ratio of the distance between the aperture and the first surface 101 on the optical axis OA to the effective focal length is 1 to 1.2. For example, the ratio of the distance between the aperture and the first surface 101 on the optical axis OA to the effective focal length is 1.1.

[0114] For example, as shown in FIG3 , the effective aperture of the aperture is 4 mm. For example, the ratio of the distance between the object plane and the aperture on the optical axis OA in the optical system to the effective focal length is less than -80. For example, the ratio of the effective aperture of the image plane to the effective focal length in the optical system is 1.5.

[0115] For example, as shown in FIG3 , the ratio of the distance between the display surface 11 of the display screen 10 and the image plane on the optical axis OA to the effective focal length is 0.03 to 0.12. For example, the ratio of the distance between the display surface 11 of the display screen 10 and the image plane on the optical axis OA to the effective focal length is 0.06 to 0.09. For example, the ratio of the distance between the display surface 11 of the display screen 10 and the image plane on the optical axis OA to the effective focal length is 0.08.

[0116] For example, as shown in FIG3 , the ratio of the distance between the fourth surface 104 and the display surface 11 of the display screen 10 on the optical axis OA to the effective focal length is 0.05 to 0.3. For example, the ratio of the distance between the fourth surface 104 and the display surface 11 of the display screen 10 on the optical axis OA to the effective focal length is 0.06 to 0.2. The ratio of the distance between the fourth surface 104 and the display surface 11 of the display screen 10 on the optical axis OA to the effective focal length is 0.1.

[0117] For example, as shown in FIG3 , the display screen 10 may be any type of display screen, such as a liquid crystal display screen, an organic light emitting diode display screen, an inorganic light emitting diode display screen, a quantum dot display screen, a projector (such as an LCOS micro projector), and the like.

[0118] For example, as shown in FIG3 , the display screen 10 is a liquid crystal display screen with a pixel size of about twenty micrometers. For example, the display screen is an organic light emitting diode display screen with a pixel size of about several micrometers.

[0119] For example, the display device may be a virtual reality display device. For example, the virtual reality display device may be a display device using an ultra-short-throw folded optical path.

[0120] For example, the display device may be a near-eye display device, and the near-eye display device may be a wearable VR helmet, VR glasses, etc., but the embodiments of the present disclosure are not limited thereto.

[0121] There are a few points to note:

[0122] (1) The drawings of the embodiments of the present disclosure only relate to the structures related to the embodiments of the present disclosure, and other structures may refer to conventional designs.

[0123] (2) Unless there is any conflict, the features of the same embodiment or different embodiments of the present disclosure may be combined with each other.

[0124] The foregoing description is merely an exemplary embodiment of the present disclosure and is not intended to limit the scope of protection of the present disclosure. The scope of protection of the present disclosure is determined by the appended claims.

Claims

1. An optical system, comprising: A lens assembly including at least two lenses, where the at least two lenses include a first surface, a second surface, a third surface, and a fourth surface arranged in sequence along the optical axis direction of the lens assembly; A polarization reflection layer disposed on a side of the first surface away from the fourth surface; A transmissive and reflective film disposed on a side of the fourth surface away from the third surface; A phase retardation film disposed on a side of the transmissive and reflective film facing the first surface; Wherein, the first surface is a concave surface and the fourth surface is a convex surface; both the second surface and the third surface are Fresnel surfaces, and the surface profiles of the second surface and the third surface are complementary; The at least two lenses include lenses with at least one of different dispersion coefficients and refractive indices.

2. The optical system according to claim 1, wherein, The ratio of the radius of curvature of the second surface to the effective focal length of the optical system is -6 to 2.

3. The optical system according to claim 1 or 2, wherein, The tooth width of the second surface includes 0.3 mm to 1 mm.

4. The optical system according to any one of claims 1 to 3, wherein, The second surface is a planar Fresnel surface or a curved Fresnel surface.

5. The optical system according to any one of claims 1-4, wherein, The at least two lenses include a first lens and a second lens arranged along the optical axis direction, the first lens includes the first surface and the second surface, and the second lens includes the third surface and the fourth surface; Wherein, the dispersion coefficient of the first lens is greater than the dispersion coefficient of the second lens.

6. The optical system according to claim 5, wherein, The dispersion coefficient of the first lens is 25 to 65, and the dispersion coefficient of the second lens is 30 to 54.

7. The optical system according to any one of claims 1-4, wherein, The at least two lenses include a first lens and a second lens arranged along the optical axis direction, the first lens includes the first surface and the second surface, and the second lens includes the third surface and the fourth surface; Wherein, the refractive index of the first lens is less than the refractive index of the second lens.

8. The optical system according to any one of claims 1-7, wherein, The ratio of the radius of curvature of the first surface to the radius of curvature of the fourth surface is 1.2 to 1.

7.

9. The optical system according to claim 8, wherein, The ratio of the radius of curvature of the first surface to the effective focal length of the optical system is -3.5 to -1.5, and the conic constant of the first surface is -10 to -0.

5.

10. The optical system according to claim 8 or 9, wherein, The ratio of the radius of curvature of the fourth surface to the effective focal length of the optical system is -2.0 to 2.0, and the conic constant of the fourth surface is -10 to -0.

1.

11. The optical system according to any one of claims 1 to 10, wherein, The distance between two intersection points where the first surface and the second surface intersect with the optical axis is a first distance; The distance between two intersection points where the third surface and the fourth surface intersect with the optical axis is a second distance; The ratio of the first distance to the second distance is 2 to 4.

12. The optical system according to claim 11, wherein, The ratio of the first distance to the effective focal length of the optical system is 0.3 to 0.5, and the ratio of the second distance to the effective focal length of the optical system is 0.1 to 0.

3.

13. The optical system according to any one of claims 1-4, wherein, The at least two lenses include a first lens and a second lens arranged along the optical axis direction, the first lens includes the first surface and the second surface, and the second lens includes the third surface and the fourth surface; The ratio of the central thickness to the edge thickness of the first lens is greater than 1 and less than 3; The ratio of the central thickness to the edge thickness of the second lens is greater than 0.5 and less than 2.

14. The optical system according to any one of claims 1-4, wherein, The at least two lenses include a first lens, a second lens, and a third lens arranged in sequence along the optical axis direction. The first lens includes the first surface and the second surface. The second lens includes the third surface. The third lens includes the fourth surface; The second lens further includes a fifth surface opposite to the third surface. The third lens further includes a sixth surface located between the fifth surface and the fourth surface; Wherein, at least two of the first lens, the second lens, and the third lens have different dispersion coefficients.

15. The optical system according to claim 14, wherein, The ratio of the radius of curvature of the fifth surface to the radius of curvature of the second surface is 0.9 to 1.

1. Both the fifth surface and the sixth surface are Fresnel surfaces, and the surface profiles of the fifth surface and the sixth surface are complementary.

16. The optical system according to claim 15, wherein, The fifth surface is a planar Fresnel surface or a curved Fresnel surface.

17. A display device, comprising a display screen and the optical system according to any one of claims 1-16, wherein, The display screen is located on a side of the transmissive and reflective film away from the polarization reflection layer.

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