Optical systems and display devices

Abstract

An optical system and display device, wherein the optical system includes a lens assembly, a polarizing reflective layer, a semitransparent film, and a phase delay film. The lens assembly includes at least two lenses, each having a first, second, third, and fourth surface arranged sequentially along the optical axis of the lens assembly. The polarizing reflective layer is provided on the side of the first surface away from the fourth surface, the semitransparent film is provided on the side of the fourth surface away from the third surface, and the phase delay film is provided on the side of the semitransparent film facing the first surface. Both the second and third surfaces are Fresnel surfaces, and the surface shapes of the second and third surfaces are complementary. The at least two lenses include lenses with at least one different dispersion coefficient and refractive index. By setting the second and third surfaces to be Fresnel surfaces and the at least two lenses to have at least one different dispersion coefficient and refractive index, chromatic aberration can be easily corrected through the cooperation of the Fresnel surfaces and the at least two lenses.

Description

Technical Field

[0001] This application claims the priority of Chinese Patent Application No. 202311864589.5 filed on December 29, 2023, and all the disclosure contents of the above Chinese patent application are incorporated herein by reference as part of this application.

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

Background Art

[0003] A head-mounted display (HMD) is a simulation technology that reproduces a specific environment by imaging a digitized image generated by a computer and output from an image source onto the user's field of view using the head-mounted display optical system.

Summary of the Invention

Means for Solving the Problems

[0004] At least one embodiment of the present invention provides an optical system, the optical system includes a lens assembly including at least two lenses including a first surface, a second surface, a third surface, and a fourth surface sequentially arranged along the optical axis direction, a polarization reflection layer provided on a side of the first surface away from the fourth surface, a semi-transmissive film provided on a side of the fourth surface away from the third surface, and a phase retardation film provided on a side of the semi-transmissive film facing the first surface, the first surface is concave, the fourth surface is convex, the second surface and the third surface are both Fresnel surfaces, the surface profiles of the second surface and the third surface are complementary, and the at least two lenses include lenses having at least one of different dispersion coefficients and refractive indices.

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

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

[0007] For example, according to at least one embodiment of the present invention, 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 invention, the at least two lenses include a first lens and a second lens arranged along the optical axis, the first lens includes a first surface and a second surface, the second lens includes a third surface and a fourth surface, and the dispersion coefficient of the first lens is greater than that of the second lens.

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

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

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

[0012] For example, according to at least one embodiment of the present invention, 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 conicity coefficient of the first surface is -10 to -0.5.

[0013] For example, according to at least one embodiment of the present invention, 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 conicity coefficient of the fourth surface is -10 to -0.1.

[0014] For example, according to at least one embodiment of the present invention, the distance between two intersection points where the first surface and the second surface intersect the optical axis is the first distance, the distance between two intersection points where the third surface and the fourth surface intersect the optical axis is the 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 invention, 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.

[0016] For example, according to at least one embodiment of the present invention, the at least two lenses include a first lens and a second lens arranged along the optical axis, the first lens includes a first surface and a second surface, the second lens includes a third surface and a fourth surface, the ratio of the center thickness to the edge thickness of the first lens is greater than 1 and less than 3, and 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 invention, the at least two lenses include a first lens, a second lens, and a third lens arranged sequentially along the optical axis, wherein the first lens includes a first surface and a second surface, the second lens includes a third surface, the third lens includes a fourth surface, the second lens further includes a fifth surface facing the third surface, and the third lens further includes a sixth surface located between the fifth surface and the fourth surface, and at least two of the first lens, the second lens, and the third lens have different dispersion coefficients.

[0018] For example, according to at least one embodiment of the present invention, 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.

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

[0020] At least one embodiment of the present invention provides a display device including a display and an optical system according to any one of the above embodiments, wherein the display is disposed on a side away from the polarization reflection layer of the semi-transmissive film.

[0021] To more clearly explain the technical solution of the embodiments of the present invention, the drawings of the embodiments are briefly introduced below. Needless to say, the drawings described below relate to only some embodiments of the present invention and do not limit the present invention.

Brief Description of the Drawings

[0022] [Figure 1] FIG. 1 is a schematic diagram of an optical system according to at least one embodiment of the present invention. [Figure 2A] FIG. 2A is a schematic diagram of the deflection of light rays according to an example of at least one embodiment of the present invention. [Figure 2B] FIG. 2B is a schematic diagram of the deflection of light rays according to an example of at least one embodiment of the present invention. [Figure 2C] FIG. 2C is a schematic diagram of the deflection of light rays according to another example of at least one embodiment of the present invention. [Figure 3] FIG. 3 is a schematic diagram of the optical path of a display device according to an example of at least one embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram of an optical system according to an example of at least one embodiment of the present invention. [Figure 5A] FIG. 5A is a spot diagram of the optical system shown in FIG. 1. [Figure 5B] FIG. 5B is a graph showing the change in the diffused spot size according to the viewing angle of the optical system shown in FIG. 1. [Figure 5C] FIG. 5C is a distortion aberration diagram of the optical system shown in FIG. 1. [Figure 5D] FIG. 5D is a longitudinal chromatic aberration diagram of the optical system. [Figure 5E] FIG. 5E is a diagram of the vertical chromatic aberration of the optical system shown in FIG. 1. [Figure 6] FIG. 6 is a schematic diagram of an optical system according to an example of at least one embodiment of the present invention. [Figure 7] FIG. 7 is a schematic diagram of an optical system according to an example of at least one embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0023] In order to more clearly explain the object, technical solution, and merits of the present invention, hereinafter, referring to the drawings of the embodiments of the present invention, the technical solution of the embodiments of the present invention will be clearly and completely described. As is clear, the described embodiments are some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention described above, all other embodiments that can be obtained on the premise that those skilled in the art do not need to perform creative labor all belong to the scope of the present invention.

[0024] Unless otherwise defined, technical terms or scientific terms used in the present invention should have the ordinary meaning understood by those skilled in the art. The "first", "second", and similar terms used in the present invention do not indicate order, quantity, or importance, and are only used to distinguish different components. Similar terms such as "comprising" or "including" refer to the fact that the element or thing before the appearance of the term includes the element or thing listed after the appearance of the term and equivalents, and do not mean to exclude other elements or things.

[0025] The features used in this invention, such as “perpendicular,” “parallel,” and “identical,” include features in the strict sense of “perpendicular,” “parallel,” and “identical,” as well as cases including certain errors such as “substantially perpendicular,” “substantially parallel,” and “substantially identical,” and represent a range of acceptable deviations to a particular value determined by a person skilled in the art, taking into account the errors associated with measurement and the measurement of a particular quantity (i.e., limitations of the measurement system). In embodiments of this invention, “center” may include a position precisely located at the geometric center and a position substantially located at the center of a small region around the geometric center. For example, “substantially” may mean within one or more standard deviations, or within 10% or 5% of the value.

[0026] The imaging principle of head-mounted display (HMD) optics is similar to that of a magnifying glass; that is, the object (image source or video source) is located in front of the object-side focal plane of the optical lens (e.g., within 1x focal length), and the human eye on the opposite side of the optical lens can see through it, forming an erect, magnified virtual image at a distance on the same side of the object. Head-mounted display optics include single-element and multi-element thick lenses, Fresnel lenses, refractive optics (also called Pancake lenses), variable-power liquid crystal lenses, and superlenses. In addition to the initial goal of providing a better wearing experience for the user by focusing on thinning and lightening, head-mounted display optics must also meet imaging optical performance requirements. For example, head-mounted display optics must consider basic indicators such as sharpness, field of view, distortion, and chromatic aberration. Many optical indicators must meet design requirements during the hardware design phase, meet precision requirements during the optical processing, manufacturing, and assembly phases, and, combined with later software (image) processing technologies (e.g., gaze point rendering technology for improved sharpness, asymmetric field of view application for improved field of view experience, anti-distortion image processing, anti-dispersion image processing), provide a better experience for users wearing head-mounted display optics.

[0027] According to research by the inventors of this invention, the above optical indicators tend to be complementary and contradictory to each other. For example, optical systems with low dispersion or low chromatic aberration and no distortion are advantageous in providing better sharpness, but they have problems with sharpness, distortion, and dispersion because widening the field of view is difficult.

[0028] Taking some liquid crystal displays as examples, the size of the liquid crystal display (e.g., diagonal length) exceeds 2 to 2.3 inches, the optical lens diameter of the head-mounted display optics is, for example, 30 mm to 50 mm (this diameter size varies depending on the field of view), and the screen size only needs to be suitable for the optical lens. For example, the sizes of the screen and the optical lens are relatively close, the angle of incidence at which light from the screen reaches the surface of the optical lens is very small, the angle deviation after refraction and reflection of light of different wavelengths is also relatively small, and at the same time, the size of a single pixel on the screen is large (e.g., the size of a single pixel exceeds 20 μm), so the height difference (vertical axis chromatic aberration) formed by light of different wavelengths on the image plane has almost no effect on the image quality.

[0029] In head-mounted display optics employing silicon-based organic light-emitting diode (OLED) displays, the screen size is typically 1 to 1.4 inches due to process constraints. Matching this screen with a small-diameter (e.g., 25 mm diameter) optical lens is relatively easy. Small-diameter optical lenses accommodate small viewing angles, and to accommodate certain mounting errors, the user's final field of view is often less than 90°. To increase the viewing angle, the optical lens diameter must be increased accordingly. The inventors have found that when a large-diameter optical lens is fitted to a small screen, the angle of incidence of wide-field light rays to the optical lens increases, resulting in increased vertical-axis chromatic aberration. Furthermore, because the pixel size of silicon-based OLED screens is less than 10 microns, the tolerance for vertical-axis chromatic aberration is far stricter than that of liquid crystal displays. Therefore, correcting chromatic aberration is difficult in large-field head-mounted display optics employing inch-class high-definition displays. Correcting chromatic aberration is particularly difficult in wide-field head-mounted display optics using inch-class high-definition displays.

[0030] At least one embodiment of the present invention provides an optical system comprising a lens assembly, a polarizing reflective layer, a semitransparent film, and a phase delay film. The lens assembly includes at least two lenses, each having a first, second, third, and fourth surface arranged sequentially along the optical axis of the lens assembly. The polarizing reflective layer is provided on the side of the first surface away from the fourth surface. The semitransparent film is provided on the side of the fourth surface away from the third surface. The phase delay film is provided on the side of the semitransparent film facing the first surface. The first surface is concave, and the fourth surface is convex. The second and third surfaces are both Fresnel surfaces, and the surface shapes of the second and third surfaces are complementary. The at least two lenses include lenses with different dispersion coefficients and refractive indices.

[0031] A display device according to at least one embodiment of the present invention comprises a display and an optical system of any of the above embodiments, wherein the display is positioned away from the polarizing reflective layer of the semitransparent film.

[0032] An optical system and display device according to at least one embodiment of the present invention provides a lens assembly with at least two lenses, where the attachment positions of a polarizing reflective layer, a semitransparent film, and a phase delay film are provided, and the reflection of light rays is achieved through the polarizing reflective layer and the semitransparent film. On the other hand, by making the second and third surfaces Fresnel surfaces and setting at least two lenses so that at least one of the dispersion coefficient and refractive index is different, the design freedom due to the Fresnel surface is improved, and by combining it with at least two lenses, chromatic aberration can be corrected, the field of view of the optical system can be enlarged, the sharpness can be increased, and it is advantageous to make it thinner.

[0033] The optical system and display device will be described below with reference to the attached drawings, using several embodiments.

[0034] Figure 1 is a schematic diagram of an optical system according to at least one embodiment of the present invention. Referring to Figure 1, the optical system according to at least one embodiment of the present invention includes a lens assembly 100, a polarizing reflective layer 200, a semitransparent film 300, and a phase delay film 400. The lens assembly 100 includes at least two lenses. For example, as shown in Figure 1, the lens assembly 100 may be composed of two lenses, lens 110 and lens 120.

[0035] As shown in Figure 1, 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 direction of the lens assembly 100. For example, the side of the first surface 101 away from the fourth surface 104 is the light-emitting side of the optical system. For example, when the optical system is applied to a display device, the display is located on the side of the optical system away from the first surface 101 of the fourth surface 104, and light rays emitted from the display enter from the fourth surface 104 and exit from the first surface 101.

[0036] As shown in Figure 1, the polarizing reflective layer 200 is provided on the side of the first surface 101 away from the fourth surface 104, the semitransparent film 300 is provided on the side of the fourth surface 104 away from the third surface 103, and the phase delay film 400 is provided on the side of the semitransparent film 300 facing the first surface 101. For example, when an optical system is applied to a display device, the display is located on the side of the semitransparent film 300 of the optical system away from the polarizing reflective layer 200. For example, light rays that have passed through the semitransparent film 300 and entered the lens assembly 100 are configured to fold back between the semitransparent 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 semitransparent film 300, and the phase delay film 400.

[0037] As shown in Figure 1, at least two lenses include lenses with different dispersion coefficients and refractive indices. Since the same transparent medium has different refractive indices for different wavelengths of light, and white light consists of light of each color at different wavelengths, a dispersion phenomenon occurs when a transparent material refracts white light. The dispersion coefficient (also called the Abbe number) is an index that represents the dispersion ability of a transparent medium and is used to measure the degree of ray dispersion of a transparent medium. Generally, the higher the refractive index of the medium, the more severe the dispersion and the lower the Abbe number. Conversely, the lower the refractive index of the medium, the less severe the dispersion and the higher the Abbe number.

[0038] As shown in Figure 1, the first surface 101 is concave and the fourth surface 104 is convex. For example, the first surface 101 is aspherical. For example, the fourth surface 104 is aspherical. For example, the semitransparent film 300 is provided on the side of the convex surface away from the concave surface. For example, both the polarizing reflective layer 200 and the phase delay film 400 have their concave surfaces provided on the side of the convex surface away from the convex surface.

[0039] As shown in Figure 1, both the second surface 102 and the third surface 103 are Fresnel surfaces. A Fresnel surface is the non-smooth surface of the opposing surfaces of a Fresnel lens. A Fresnel lens, also called a screw lens, has one surface that is the optical surface and the other surface that is divided into a pattern of multiple concentric circles (i.e., Fresnel zones). These patterns can change the degree of bending of light rays, so a Fresnel lens effectively reduces the thickness of the lens at short focal lengths.

[0040] For example, referring to Figure 1, the first surface 101 and the second surface 102 are both surfaces of lens 110, and the third surface 103 and the fourth surface 104 are both surfaces of lens 120, and both lens 110 and lens 120 are Fresnel lenses. For example, lens 110 is a convex lens, and lens 120 is a concave lens.

[0041] As shown in Figure 1, the surface profiles of the second surface 102 and the third surface 103 are complementary. Complementarity means that after joining (or attaching with optical adhesive) the second surface 102 and the third surface 103, there is virtually no gap between them. For example, the surface profiles of the second surface 102 and the third surface 103 have positive and negative shapes relative to each other. For example, at the position of the second surface 102 corresponding to the third surface 103, the tooth-like structures of the two Fresnel surfaces may be complementary to each other.

[0042] An optical system according to at least one embodiment of the present invention provides a lens assembly 100 including at least two lenses, which provides the attachment positions for a polarizing reflective layer 200, a semitransparent film 300, and a phase delay film 400, thereby realizing the folding of light rays through the polarizing reflective layer 200 and the semitransparent film 300. By setting the second surface 102 and the third surface 103 as Fresnel surfaces and setting at least two lenses as lenses with at least one different dispersion coefficient and refractive index, the design freedom due to the Fresnel surface is improved, which is advantageous for correcting chromatic aberration in combination with at least two lenses, and the optical system has a wide field of view, high sharpness, and is thin and lightweight.

[0043] Figures 2A and 2B are schematic diagrams of ray deflection according to an example of at least one embodiment of the present invention. Chromatic aberration correction will be explained below using the example of a ray incident on an optical system undergoing one refraction.

[0044] Figure 2A shows how light rays are deflected in an optical system when lenses L1 and L2 have different refractive indices and dispersion coefficients in a lens assembly. As shown in Figure 2A, the side furthest from the target surface S0 is considered the incident side, i.e., the light ray enters the lens assembly from the left side of Figure 2A, is refracted, and then exits the lens assembly onto the target surface S0. When white light (solid line shown in Figure 2A) enters the lens assembly, the white light is dispersed and decomposed into monochromatic light of different wavelengths. By making lenses L1 and L2 have different refractive indices and different dispersion coefficients, the deflection angles of red light R and blue light B can be changed, and ultimately the red light R and blue light B can be focused on the target surface S0. In Figure 2A, the longer wavelength red light R is shown as a dashed line, and the shorter wavelength blue light B is shown as a dotted line.

[0045] For example, referring to Figure 2A, lens L1 is a convex lens and lens L2 is a concave lens. The dispersion coefficient of lens L1 is greater than that of lens L2, and the refractive index of lens L1 is smaller than that of lens L2. After the incident light ray is incident on surface S1 and dispersed, the relatively short wavelength blue light B is biased towards the optical axis OA more than the red light R. After refraction through surfaces S2 and S3, because the dispersion coefficient of lens L1 is greater than that of lens L2, the light ray, after being incident on lens L1 and lens L2, is deflected away from the optical axis OA. As the degree of deflection of the relatively short wavelength blue light B increases, the red light R gradually approaches the blue light B. Even after the light ray passes through surface S4 and exits, it continues to be deflected away from the optical axis OA, and the degree of deflection of the relatively short wavelength blue light B increases, causing the red light R and blue light B to converge on the target surface S0, achieving the objective of chromatic aberration correction.

[0046] Figure 2B simplifies the two lenses shown in Figure 2A into two opposing optical wedges, where the degree of inclination of the contact surfaces of the two lenses is the inclination of those surfaces. As shown in Figure 2B, white light is dispersed after being incident on optical wedge 1 and decomposed into monochromatic light of different wavelengths. In Figure 2B, the longer wavelength red light R is shown by a dashed line, and the shorter wavelength blue light B is shown by a dotted line. After the red light R (dashed line) and blue light B (dotted line) are incident on optical wedge 2, the degree of deflection of both the red light R and the blue light B changes, and the red light R and blue light B can converge after being emitted to the target surface S0.

[0047] Figure 2C is a schematic diagram of ray deflection according to another example of at least one embodiment of the present invention. Figure 2C differs from Figure 2B in that the inclination of the contact surfaces of the two optical wedges is different.

[0048] By combining Figure 2C and Figure 1, Figure 2C simplifies the lenses 110 and 120 shown in Figure 1 as two opposing optical wedges. Figure 2C schematically illustrates how light rays are deflected in an optical system when, in a lens assembly, the two lenses have different refractive indices and dispersion coefficients, and the two contacting surfaces of the two lenses are positive and negative Fresnel surfaces (not shown in Figure 2C; see, for example, Figure 1). As shown in Figure 2C, white light is dispersed after entering the optical wedge 1 and decomposed into monochromatic light of different wavelengths. In Figure 2C, the long-wavelength red light R is shown by a dashed line, and the short-wavelength blue light B is shown by a dotted line. As shown in Figure 2C, since the contact surface of the two optical wedges is a Fresnel surface, the inclination of the discretizable Fresnel surface is larger than that of a continuous aspherical surface. This improves the deflection capability for light rays, allowing the red light R (dashed line) and blue light B (dotted line) to be focused on a closer target surface S0', and enabling a more compact optical system structure. Therefore, referring to Figure 1, by making the second surface 102 and the third surface 103 Fresnel surfaces and setting at least two lenses so that at least one of their dispersion coefficients and refractive indices is different, chromatic aberration can be corrected together, increasing the field of view of the optical system, improving sharpness, and making it thinner.

[0049] For example, referring to Figure 1, the function of the polarizing reflective layer 200 is as follows: there is one optical axis OA direction within the film layer plane, the transmittance of the polarization component of incident light parallel to the optical axis OA direction (e.g., s-polarization) is greater than the transmittance of the polarization component perpendicular to the optical axis OA direction, such as p-polarization, and the reflectance of the polarization component parallel to the optical axis OA direction, such as s-polarization, is smaller than the reflectance of the polarization component perpendicular to the optical axis OA direction, such as p-polarization. For example, the transmittance of polarized light in the direction parallel to the optical axis OA of the polarizing reflective layer 200 is 85% or more, such as 90% or more, 95% or more, and 98% or more. The reflectance of polarized light in the direction perpendicular to the optical axis OA of the polarizing reflective layer 200 is 85% or more, such as 90% or more, 95% or more, and 98% or more.

[0050] For example, referring to Figure 1, the polarizing reflective layer 200 is configured to reflect linearly polarized light of one characteristic and transmit linearly polarized light of the other characteristic, and the polarizing reflective layer 200 is positioned on the side of the first surface 101 away from the fourth surface 104, and a phase delay film 400 is positioned between the polarizing reflective layer 200 and the semitransparent film 300. For example, the polarizing reflective layer can also be called a polarizing beam split film. For example, the polarizing reflective layer may further include a multilayer reflective polarizing sheet (Advanced Polarizer Film, APF). The polarizing reflective layer may further include an IQPS (Image Quality Polarizer Standard) film or an IQPE (Image Quality Polarizer Enhanced) film.

[0051] For example, the polarization reflection layer is a cholesteric liquid crystal layer (not shown), and a phase delay film is provided on the side of the cholesteric liquid crystal layer away from the semitransparent film. For example, a cholesteric liquid crystal can reflect and transmit circularly polarized light. Referring to the folding optical path principle described above, a cholesteric liquid crystal layer is arranged between the phase delay film and the semitransparent film. A waveplate is provided on the display surface side of the display, located on the side of the second lens away from the first lens, and image light emitted from the display is converted to right-circular polarization after passing through the waveplate. The right-circular polarization is incident on the semitransparent film, and the polarization state of the right-circular polarization after passing through the semitransparent film may remain unchanged. The right-circular polarization passes through the cholesteric liquid crystal layer and is reflected by the semitransparent film, where the first reflection occurs. The right-circular polarization is then reflected by the semitransparent film, where the second reflection occurs. The reflected light changes from right-circular polarization to left-circular polarization due to half-wave loss. This left-circular polarization passes through the cholesteric liquid crystal layer and reaches the phase delay film, where it changes to s-polarization. This s-polarization then passes through the linear polarization film and heads towards the human eye.

[0052] For example, referring to Figure 1, the semi-transparent film 300 is configured to transmit a portion of the light rays and reflect the other portion. For example, the transmittance of the semi-transparent film 300 may be 50% and the reflectance 50%. For example, the transmittance of the semi-transparent film 300 may be 60% and the reflectance 40%. For example, the transmittance of the semi-transparent film 300 may be 65% and the reflectance 35%. The optical system according to the present invention is not limited thereto, and the transmittance and reflectance of the semi-transparent film can be set according to the needs of the product. For example, the semi-transparent film 300 may be provided on the fourth surface 104.

[0053] For example, referring to Figure 1, the phase delay film 400 is configured to enable the conversion of transmitted light between a circularly polarized state and a linearly polarized state. For example, the phase delay film 400 may be a quarter-wave plate. For example, the phase delay film 400 is characterized in that within the film layer plane, there are directions where the lowest refractive index and the highest refractive index are the fast axis and the slow axis, respectively, and the phase after polarization parallel to the slow axis passes through the phase delay film 400 is delayed by 1 / 4 wavelength compared to the phase after polarization parallel to the fast axis passes through the phase delay film 400. The angle between the slow axis of the phase delay film 400 and the optical axis OA of the polarization reflection layer 200 is 45 degrees.

[0054] For example, referring to Figure 1, the material of the phase delay film 400 may include a liquid crystal polymer. Since the phase delay film 400 made of a liquid crystal polymer is a polymer, its film thickness is relatively thin, reaching 1 μm to 5 μm. Thinner phase delay films 400 have a higher adaptability to curved surfaces, can be molded more easily according to the shape of the curved surface, and reduce the possibility of wrinkles occurring during bonding to the curved surface, which can affect the phase delay accuracy and optical performance. In addition, the optical shift that occurs after the liquid crystal polymer phase delay film 400 is attached to the curved surface is reduced. Liquid crystal polymers are crosslinked systems, with molecules bonded chemically, and have a high elastic modulus. When the phase delay film 400 made of this material is stretched after bonding, only elastic deformation occurs, and strong optical anisotropy effects such as molecular stretching and rearrangement do not occur. Therefore, the phase delay film 400 using a liquid crystal polymer material is suitable for bonding surfaces with small radii of curvature. This degree of freedom in the radius of curvature makes it easier to satisfy the requirements for indicators such as sharpness, distortion, and dispersion, which is advantageous for the optical system to obtain better image quality.

[0055] Figure 3 is a schematic diagram of the optical path of a display device according to an example of at least one embodiment of the present invention. At least one embodiment of the present invention provides a display device which includes a display 10 located on the side of the semitransparent film 300 away from the polarizing reflective layer 200 and an optical system. Referring to Figure 3, for example, the folding optical path principle is as follows: a waveplate can be placed on the light-emitting side of the display surface 11 of the display 10, located on the side of the fourth surface 104 away from the first surface 101, and the image light emitted from the display surface 11 is converted to right-circular polarization after passing through the waveplate, and the polarization state of the right-circular polarization remains unchanged after passing through the semitransparent film 300. The light ray is incident on the lens assembly 100, passes through the lens assembly 100 and then reaches the phase-delay film 400, where the right-circular polarization incident on the phase-delay film 400 is converted to p-polarization which is reflected by the phase-delay film 400 in the polarizing reflective layer 200, where the first reflection occurs. Subsequently, the p-polarized light passes through the phase delay film 400 and is converted to right-circular polarization. This right-circular polarization then passes through the lens assembly 100 and reaches the semi-transparent film 300, where it is reflected, resulting in a second reflection. Due to half-wave loss, the reflected light changes from right-circular polarization to left-circular polarization. The left-circular polarization passes through the lens assembly 100 and then reaches the phase delay film 400. After passing through the phase delay film 400, it becomes s-polarized light, which then passes through the polarization reflection layer 200 and is emitted towards the exit pupil, similar to a human eye.

[0056] The above-described folded optical path allows for a change in the polarization state of light rays propagating between the polarizing reflective layer 200 and the semi-transparent film 300. By arranging the polarizing reflective layer 200, the phase delay film 400, and the semi-transparent film 300, the folding of light rays can be achieved to increase the focal length of the optical system. This significantly compresses the space required between the human eye and the optical system, resulting in a smaller and thinner optical system.

[0057] For example, the optical system further includes a linear polarizing film 500 positioned away from the semitransparent film 300 of the polarizing reflective layer 200. For example, the linear polarizing film 500 may be a linear polarizer or a polarizer. For example, since the optical axis of the linear polarizing film 500 coincides with the optical axis of the polarizing reflective layer 200, the linear polarizing film 500 can be used to further filter out other stray light, allowing only polarized light (e.g., s-polarized light) that has passed through the linear polarizing film 500 to enter the human eye. For example, the linear polarizing film may employ a three-layer laminated structure in which the intermediate layer is polyvinyl alcohol (PVA) with dichroic molecules added, and at least one layer on both sides of the intermediate layer is cellulose triacetate (TAC). For example, the linear polarizing film 500 may be treated with an anti-reflective coating on the air-facing side. For example, the air-facing side of the linear polarizing film 500 may be laminated to a moth-eye film.

[0058] In some examples, as shown in Figure 1, the ratio of the radius of curvature of the second surface 102 to the effective focal length of the optical system is -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 means the radius of curvature of the curved Fresnel surface. For example, the radius of curvature of the second surface 102 means the radius of curvature of a Fresnel surface having 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 is -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 is -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 is -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 is -2.

[0059] For example, referring to Figure 1, the second surface 102 of the Fresnel surface is the base surface of the Fresnel surface and can be approximated as a smooth, toothless spherical or aspherical surface. This spherical or aspherical surface is the base surface of the Fresnel surface, and the curvature of this 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 infinitesimally small. 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. This prevents the tooth structure of the Fresnel surface from contacting surfaces on the optical axis OA located on either side of the Fresnel surface (e.g., the first surface 101 or the fourth surface 104).

[0060] Figure 4 is a schematic diagram of an optical system according to an example of at least one embodiment of the present invention. The optical system shown in Figure 4 differs from the optical system shown in Figure 1 in that the second surface 102 in the optical system shown in Figure 4 is different from the second surface 102 in the optical system shown in Figure 1. Of course, there may be other differences between the optical system shown in Figure 4 and the optical system shown in Figure 1, such as the number of lenses included in the lens assembly, but the present invention is not limited thereto. For example, the number of lenses in the optical system shown in Figure 4 may be different from or the same as the number of lenses in the optical system shown in Figure 1. The polarizing reflective layer 200, semi-transparent film 300, and linearly polarizing film 500 in the optical system shown in Figure 4 may have the same characteristics as the polarizing reflective layer 200, semi-transparent film 300, and linearly polarizing film 500 in the optical system shown in Figure 1, and such a description is omitted here.

[0061] In some examples, the second surface 102 is either a planar Fresnel surface or a curved Fresnel surface. For example, as shown in Figure 1, the second surface 102 is a curved Fresnel surface, and as shown in Figure 4, the second surface 102 is a planar Fresnel surface. The second surface 102 may be convex, concave, or planar. For example, a planar Fresnel surface with a planar base can be obtained by discretizing a continuous curved surface (see, for example, Figure 4). For example, after discretizing a continuous curved surface, a curved Fresnel surface with a curved base can be obtained by superimposing the discretized spherical or aspherical curvatures (see, for example, Figure 1). This increases the adjustment space for the radius of curvature of the Fresnel surface in the optical system, allowing for better deflection and focusing of dispersed light rays. By making the inclination of the Fresnel surface adjustable, the deflection capability of the second surface 102 and the third surface 103 for light rays is improved, enabling ultra-short focal length, improving the correction effect of chromatic aberration, and improving sharpness.

[0062] For example, referring to Figure 1, both the second surface 102 and the third surface 103 are curved toward the side away from the first surface 101, that is, both the second surface 102 and the third surface 103 are convex surfaces, which reduces the difference between the center thickness and edge thickness of the first lens 110 and the difference between the center thickness and edge thickness of the second lens 120, thereby reducing the difficulty of processing. In addition, the curved Fresnel allows the surface shapes of the second surface 102 and the third surface 103 to be easily fitted to the first surface 101 and the fourth surface 104, reducing the thickness of the lens assembly 100 in the optical axis direction OA and allowing control of the total optical length of the optical system.

[0063] For example, as shown in Figure 1, the ratio of the radii of curvature between the first surface 101 and the fourth surface 104 may be 1.2 to 1.7. For example, the ratio of the radii of curvature between the first surface 101 and the fourth surface 104 may be 1.3 to 1.6. For example, the ratio of the radii of curvature between the first surface 101 and the fourth surface 104 may be 1.4 to 1.5.

[0064] In some examples, as shown in Figure 1, the ratio of the radius of curvature of the first surface 101 to the effective focal length of the optical system is -3.5 to -1.5, and the conicity coefficient of the first surface 101 is -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 is -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 is -2.5. For example, the conicity coefficient of the first surface 101 may be -9 to -1. For example, the conicity coefficient of the first surface 101 may be -8 to -2. For example, the conicity coefficient of the first surface 101 may be -7 to -3. For example, the conicity coefficient of the first surface 101 may be -6 to -4. For example, the conicity coefficient of the first surface 101 may be -5.

[0065] In some examples, as shown in Figure 1, the ratio of the radius of curvature of the fourth surface 104 to the effective focal length of the optical system is -2.0 to 2.0, and the conicity coefficient of the fourth surface 104 is -10 to -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 is -1.8 to 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 is -1.5 to 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 is -1 to 1. For example, the conicity coefficient of the fourth surface 104 may be -9 to -1. For example, the conicity coefficient of the fourth surface 104 may be -8 to -2. For example, the conicity coefficient of the fourth surface 104 may be -7 to -3. For example, the conicity coefficient of the fourth surface 104 may be -6 to -4. For example, the conicity coefficient of the fourth surface 104 may be -5.

[0066] For example, the surface shape of a curved Fresnel surface can be approximated to the shape of an aspherical surface, as shown by the following formula.

[0067]

number

[0068] For example, in the above equation, let Y be the height of the aspherical surface in the direction perpendicular to the optical axis, and let z be the distance from the vertex of the aspherical surface to the projection of the aspherical surface on the optical axis at height Y, i. that is, z is the coordinate in the direction of the optical axis, C is the curvature (reciprocal of the radius of curvature R), k is the conic constant, αi is the coefficient of each higher-order term, and 2i is the order of the aspherical coefficients.

[0069] In actually optimizing the rational arrangement of each parameter of the lens assembly, values ​​such as the radius of curvature, conicity coefficient, height, and asphericity coefficient of each lens in the lens assembly are substituted into the above numerical formula, and calculations are performed by optical simulation to determine the optimal parameters that can correct the aberrations of each lens in the lens assembly. Through the optimization process, preferred values ​​for the radius of curvature, thickness along the optical axis, effective aperture, and conicity coefficient of each lens in the lens assembly are determined.

[0070] For example, as shown in Figure 1, the optimization efficiency of the Fresnel surface can be improved by setting the conicity coefficients of the second surface 102 and the third surface 103 to 0. For example, the conicity coefficients of the second surface 102 and the third surface 103 may be less than 0. For example, the conicity coefficients of the second surface 102 and the third surface 103 may be greater than 0.

[0071] In addition to the examples above, for example, the higher-order coefficients of the first face 101 satisfy α4=-1.0E-05, α6=1.5E-07, α8=1.1E-09, and α10=6.0E-12. For example, the higher-order coefficients of the second face 102 satisfy α4=-3.0E-05, α6=-3.0E-08, α8=0.0E+00, and α10=0.0E+00. For example, the higher-order coefficients of the third face 103 are exactly the same as those of the second face 102. For example, the higher-order coefficients of the fourth face 104 satisfy α4=-0.00003, α6=-3.7E-08, α8=6.0E-12, and α10=-2.0E-14.

[0072] In some examples, as shown in Figure 1, the tooth width of the second surface 102 is 0.3 mm to 1 mm. For example, the second surface 102 has a toothed structure consisting of multiple concentrically arranged ring gears, and the tooth width is the gap between two adjacent ring gears. For example, among the multiple ring gears, the gap between two adjacent ring gears is always equal. For example, the tooth width of the second surface 102 is 0.4 mm to 0.9 mm. For example, the tooth width of the second surface 102 is 0.5 mm to 0.8 mm. For example, the tooth width of the second surface 102 is 0.6 mm to 0.7 mm. By setting the tooth width to 0.3 mm to 1 mm, the density of the tooth profile of the second surface 102 can be appropriately adjusted, reducing machining errors and improving optical efficiency, as well as facilitating the shaping and drafting of the teeth during injection molding.

[0073] For example, when a light ray folds in an optical system, it is necessary to consider the effect of the teeth on the Fresnel surface on the light ray each time the light ray passes over the Fresnel surface in order to prevent leakage and light blocking, reduce stray light, and improve the contrast of the image. For example, in one embodiment of the present invention, as shown in Figure 3, the incident light ray passes over the second surface 102 and the third surface 103 three times in a row while being folded over in the lens assembly 100, and the tooth height and draft angle of the Fresnel surface may be calculated by optical simulation according to the deflection angle of the light ray each time it passes over the second surface 102 or the third surface 103.

[0074] In some examples, as shown in Figure 1, the lens comprises at least two lenses, a first lens 110 and a second lens 120, arranged along the optical axis OA direction, where 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 dispersion coefficient of the first lens 110 is greater than that of the second lens 120. For example, if the first lens 110 is a convex lens and the second lens 120 is a concave lens, and the dispersion coefficient of the first lens 110 is greater than that of the second lens 120, the deflection of light rays of different wavelengths can be facilitated and chromatic aberration can be better corrected.

[0075] In some examples, as shown in Figure 1, the dispersion coefficient of the first lens 110 may be 25-65 and the dispersion coefficient of the second lens 120 may be 30-54. For example, the dispersion coefficient of the first lens 110 may be 30-60. For example, the dispersion coefficient of the first lens 110 may be 35-55. For example, the dispersion coefficient of the first lens 110 may be 40-50. For example, the dispersion coefficient of the first lens 110 may be 45. For example, the dispersion coefficient of the second lens 120 may be 35-50. For example, the dispersion coefficient of the second lens 120 may be 40-45. For example, the dispersion coefficient of the first lens 110 may be 55-65 and the dispersion coefficient of the second lens may be 30-40. For example, the dispersion coefficient of the first lens 110 may be 55-57 and the dispersion coefficient of the second lens may be 49-51. For example, the dispersion coefficient of the first lens 110 may be 56, and the dispersion coefficient of the second lens 120 may be 50. In this invention, only the dispersion coefficients of the first lens 110 and the second lens 120 are given as examples, and the dispersion coefficients of the first lens 110 and the second lens 120 may be relatively close or different, and the combination of values ​​is not limited as long as the dispersion coefficient of the first lens 110 is greater than the dispersion coefficient of the second lens 120.

[0076] In some examples, as shown in Figure 1, the lenses include at least two lenses, a first lens 110 and a second lens 120 arranged along the optical axis, where 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 greater than that of the second lens 120. For example, there is an approximately inverse relationship between the refractive index and the dispersion coefficient. For example, the smaller the refractive index, the larger the dispersion coefficient relatively. For example, the smaller the dispersion coefficient, the larger the refractive index relatively. For example, if the first lens 110 is a convex lens and the second lens 120 is a concave lens, and the refractive index of the first lens 110 is smaller than that of the second lens 120, the deflection of light rays of different wavelengths can be facilitated and chromatic aberration can be better corrected.

[0077] For example, as shown in Figure 1, 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. To make it clear, the present invention only illustrates the refractive indices of the first lens 110 and the second lens 120, and the refractive indices of the first lens 110 and the second lens 120 may be relatively close or significantly different. The present invention does not limit the combination of values ​​as long as the refractive index of the first lens 110 is smaller than the refractive index of the second lens 120.

[0078] For example, as shown in Figure 1, the first lens 110 and the second lens 120 may be made of different materials such that the dispersion coefficient of the first lens 110 is different from that of the second lens 120, and the refractive index of the first lens 110 is different from that of the second lens 120. For example, the first lens 110 and the second lens 120 may be injection molded and then bonded together with an elastic adhesive. For example, after injection molding the first lens 110, the second lens 120 can be formed by injecting a liquid optical material between the first lens 110 and the mold using a casting process, and then curing and molding it. For example, by selecting a liquid optical material, the material of the cured second lens 120 may be a hard polymer or an elastic optical silicone. For example, the hard polymer may be a monomer polymer with a refractive index of 1.554 and a dispersion coefficient of 39.3. For example, the elastic optical silicone may be silicone rubber. For example, the refractive index of the optical silicone is 1.41 and the dispersion coefficient is 52. For example, the refractive index of the optical silicone is 1.41 and the dispersion coefficient is 50. For example, the first lens 110 may be formed by processing the second lens 120 by injection molding, and then injecting a liquid optical material between the second lens 120 and the mold, and curing it.

[0079] For example, Figure 1 schematically shows the effect of each film layer on the distance between different surfaces of the lens assembly, and if the thickness of each film layer is thin, the thickness of the film layer can be ignored.

[0080] In some examples, as shown in Figure 1, the distance between the two intersection points where the first surface 101 and the second surface 102 intersect the optical axis OA is the first distance D1. For example, the first distance D1 is the center thickness of the first lens 110. As shown in Figure 1, the distance between the two intersection points where the third surface and the fourth surface intersect the optical axis is the second distance, and the second distance D2 is, for example, the center thickness of the second lens 120. The ratio of the first distance to the second distance may be 2 to 4 (2:1 to 4:1). For example, the ratio of the first distance to the 2.5th distance may be 2 to 3.5.

[0081] In some cases, as shown in Figure 1, the ratio of the first distance D1 to the effective focal length of the optical system may be between 0.3 and 0.5. For example, the ratio of the first distance D1 to the effective focal length of the optical system may be between 0.35 and 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 cases, the ratio of the second distance D2 to the effective focal length of the optical system may be between 0.1 and 0.3. For example, the ratio of the second distance D2 to the effective focal length of the optical system may be between 0.15 and 1.25. For example, the ratio of the second distance D2 to the effective focal length of the optical system may be 0.2.

[0082] In some examples, as shown in Figure 1, the lens comprises at least two lenses, a first lens 110 and a second lens 120 arranged along the optical axis OA direction, where the first lens 110 comprises a first surface 101 and a second surface 102, and the second lens comprises 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. Setting the proportional relationship between the center thickness and edge thickness of each lens as described above is advantageous in ensuring injection molding of each lens.

[0083] In addition to the example described above, Figure 5A is a spot diagram of the optical system shown in Figure 1. Figure 5B is a graph showing the change in diffuse spot size with respect to the field of view of the optical system shown in Figure 1.

[0084] Referring to Figure 5A, a spot diagram is a dispersion pattern formed when many light rays emitted from a single point pass through an optical system. Due to aberrations, the points of intersection with the image plane do not converge at the same point, but are instead scattered 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 numbers in the left vertical direction 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 numbers in the right vertical direction as an example, RMS is the root mean square of the radius from the dispersion point of the dispersion spot to the center of the dispersion spot (or the center of the dispersion spot), and 100% represents the diameter of the dispersion spot. Figure 5A is typically used to evaluate the overall field of view clarity of this optical system, that is, the imaging clarity of the entire field of view covered by the peripheral field of view when the human pupil is at the entrance pupil position on the optical axis and the lens center (i.e., zero field of view) is being gazed upon. This is also called the transient mode. In addition to considering full-field clarity in transient modes, for wearers such as those wearing head-mounted displays, the clarity of the fixation point is one of the more important optical indicators. Fixation point clarity refers to the clarity of the screen within a certain angular range that is directly visible (not visible in the peripheral field of view) when the eyes are moved up, down, left, or right.

[0085] In fixation mode, the eyeball moves a certain angle, the pupil shifts from the center of the optical axis, a certain deviation occurs in the Z and Y directions of the optical axis, and the principal ray passing through the center of the pupil has a certain angle with the Z axis. For example, this angle range is ±35 degrees, and this angle range is set considering the observation habits of the human eye. To clearly see an object in front of the human eye that is beyond 35 degrees from the center of the human eye, a person will spontaneously rotate their head rather than move their eyeball. Referring to Figure 5B, Figure 5B shows the relationship between the clarity of the fixation point and the fixation angle, and the spot in the center of the field of view is much smaller than one pixel, and the diameter of the spot when a person moves their eye 20 degrees is less than 15 μm. As can be seen from Figure 5B, the dispersed spot of the optical system of this application is small, and the resolution of the optical system is high. From the above, it can be seen that the optical system according to at least one embodiment of the present invention can produce a clear image.

[0086] Figure 5C is a distortion diagram of the optical system shown in Figure 1. Referring to Figure 5C, the distortion diagram reflects the difference in image plane position that forms a sharp image in different fields of view, and referring to Figure 5C, it shows that the absolute value of the maximum distortion is within 50%. From this, it can be seen that the optical system according to at least one embodiment of the present invention can effectively correct distortion and meet high-quality imaging requirements. Furthermore, distortion correction may be pre-processed in software.

[0087] Figure 5D is a vertical axis chromatic aberration diagram of the optical system. Figure 5E is a vertical axis chromatic aberration diagram of the optical system shown in Figure 1.

[0088] Referring to Figures 5D and 5E, the vertical axis chromatic aberration diagram shows the difference in height of each wavelength relative to the central wavelength at different image heights on the imaging plane, the horizontal axis shows the vertical axis chromatic aberration value of each wavelength relative to the central wavelength, and the vertical axis shows the normalized field of view. As shown in Figures 5D and 5E, F light is blue light, C light is red light, and D light is yellow light. C light and F light are located at the ends of the region where the human eye is highly sensitive, and D light is located in between and close to the spectral line to which the human eye is most sensitive. Referring to Figure 5D, Figure 5D shows the results of vertical axis chromatic aberration for a single-lens optical system. From this figure, it can be seen that the absolute value of the vertical axis chromatic aberration of F light and C light is within approximately 0.1 mm, and the absolute value of the vertical axis chromatic aberration of F light and D light is within approximately 0.06 mm. From Figure 5E, it can be seen that the absolute value of the vertical axis chromatic aberration of F light and C light is controlled to within 0.035 mm, and the absolute value of the vertical axis chromatic aberration of F light and D light is controlled to within 0.025 mm. Comparing Figure 5E and Figure 5D, it can be seen that the optical system shown in Figure 1 according to the present invention can reduce vertical axis chromatic aberration to 1 / 3 and chromatic aberration to 1 / 6 at the maximum field of view compared to a single-lens optical system. This means that the optical system shown in Figure 1 can correct chromatic aberration in the edge field of view and the secondary spectrum of the entire image plane very well.

[0089] Figure 6 is a schematic diagram of an optical system according to an example of at least one embodiment of the present invention. The difference between the optical system shown in Figure 6 and the optical system shown in Figure 1 is that the number of lenses in the optical system shown in Figure 6 is different from the number of lenses in the optical system shown in Figure 1. Of course, the optical system shown in Figure 6 and the optical system shown in Figure 1 may have other differences, such as the surface shape of at least one lens, but the present invention is not limited thereto. For example, the surface shape parameters of the first surface 101 to the fourth surface 104 in the optical system shown in Figure 6 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 Figure 1. The polarizing reflective layer 200, semi-transparent film 300, and linear polarizing film 500 in the optical system shown in Figure 6 may have the same characteristics as the polarizing reflective layer 200, semi-transparent film 300, and linear polarizing film 500 in the optical system shown in Figure 1, and their explanation is omitted here.

[0090] In some examples, as shown in Figure 6, 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 direction, where the first lens 011 includes a first surface 101 and a second surface 102, and the second lens 012 includes a third surface 103 and a fourth surface 104. The second lens 012 further includes a fifth surface 105 opposite the third surface 103, and the third lens 013 further 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 dispersion coefficients. For example, the first lens 011 has a different dispersion coefficient than the second lens 012, and the second lens 012 has the same dispersion coefficient as the third lens 013. For example, the first lens 011 has a different dispersion coefficient than the third lens 013, and the first lens 011 has the same dispersion coefficient as the second lens 012. For example, the second lens 012 has a different dispersion coefficient than the third lens 013, and the first lens 011 has the same dispersion coefficient as the third lens 013. For example, the first lens 011, the second lens 012, and the third lens 013 each have different dispersion coefficients.

[0091] For example, if the first lens 011, the second lens 012, and the third lens 013 are formed from the same type of optical material, optical properties such as spectral transmittance, refractive index, and Abbe number can be considered, and processability such as material fluidity, thermal shrinkage rate, stress, and cost may also be considered. For example, optical-grade materials such as polymethyl methacrylate (PMMA), polycarbonate (PC), cyclic olefin copolymer (COC), cyclic olefin homopolymer (COP), and polyethylene terephthalate (PET) can be used.

[0092] In some cases, as shown in Figure 6, 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 profiles of the fifth surface 105 and the second surface 102 are relatively similar. Both the fifth surface 105 and the sixth surface 106 are Fresnel surfaces, and the surface profiles of the fifth surface 105 and the sixth surface 106 are complementary. Complementarity means that after the fifth surface 105 and the sixth surface 106 are joined (or glued together with optical adhesive), there is virtually no gap between them. For example, the surface profiles of the fifth surface 105 and the sixth surface 106 are complementary shapes. For example, at corresponding positions on the fifth surface 105 and the sixth surface 106, the tooth-like structures on the two Fresnel surfaces may be complementary to each other.

[0093] Figure 7 is a schematic diagram of an optical system according to an example of at least one embodiment of the present invention. The difference between the optical system shown in Figure 7 and the optical system shown in Figure 6 is that the plane shape parameters in the optical system shown in Figure 7 are different from those in the optical system shown in Figure 6. Of course, the optical system shown in Figure 6 and the optical system shown in Figure 1 may have other differences, such as the number of lenses included in the lens assembly, but the present invention is not limited thereto. For example, the number of lenses in the optical system shown in Figure 7 may be different from or the same as the number of lenses in the optical system shown in Figure 6. The polarizing reflective layer 200, semi-transparent film 300, and linear polarizing film 500 in the optical system shown in Figure 7 may have the same characteristics as the polarizing reflective layer 200, semi-transparent film 300, and linear polarizing film 500 in the optical system shown in Figure 6, and their description is omitted here.

[0094] In some examples, as shown in Figures 6 and 7, the fifth surface 105 is either 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. To make it clear, the fifth surface 105 may be convex, concave, or planar. For example, since both the second surface 102 and the fifth surface 105 are curved toward the side away from the first surface 101, the difference between the center thickness and edge thickness of the second lens 02 is small, and the difference between the center thickness and edge thickness of the third lens 03 is small, reducing the difficulty of processing.

[0095] For example, as shown in Figure 7, 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 Figure 7, the surface profiles of the second surface 102 and the third surface 103 are complementary, and the surface profiles of the fifth surface 105 and the sixth surface 106 are complementary.

[0096] For example, referring to Figure 7, a planar Fresnel surface can be obtained by discretizing a continuous curved surface. For example, referring to Figure 6, a curved Fresnel surface can be obtained by discretizing a continuous curved surface and then superimposing it with the discretized spherical curvature. This allows for a larger adjustment range for the radius of curvature of the Fresnel surface in the optical system, enabling better deflection and convergence of dispersed light rays. By adjusting the inclination of the Fresnel surface, the deflection capability of the 5th surface 105 and the 6th surface 106 for light rays is improved, enabling ultra-short focal length, as well as improving the chromatic aberration correction effect and enhancing sharpness.

[0097] 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 to the effective focal length of the optical system is 0.9 to 0.95. The total optical length refers to the distance from the highest point on the first surface 101 of the lens assembly 100 in the optical system to the center of the display 10 along the optical axis OA. The highest point of the first surface 101 includes the edge sag of the lens assembly 100 on the side where the first surface 101 is located.

[0098] For example, as shown in Figures 1 and 3, the field of view of the optical system is greater than 90°. For example, the field of view is the entire 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, when calculated with an effective aperture that can reach a field of view of 100°, the weight of the binocular lenses is approximately 20g.

[0099] 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 final surface of the optical system to the intersection point 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 according to the present invention has a large exit pupil distance and can satisfy the need for myopic users to wear glasses while using it.

[0100] Referring to Figure 3, at least one embodiment of the present invention provides a display device comprising a display 10 and an optical system of any of the above embodiments. The display 10 is located on the side of the fourth surface 104 away from the first surface 101. Since the display device according to the embodiment of the present invention includes at least one of the optical systems described above, it also has corresponding beneficial technical effects, which are omitted from this description. To make it clear, the display 10 shown in Figure 3 can be combined with the optical systems in Figures 1, 4, 6, and 7 to form different display devices.

[0101] For example, as shown in Figure 3, the display surface 11 of the display 10 is located at the focal plane on the light incidence side of the optical system.

[0102] For example, as shown in Figure 3, 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 mentioned above refers to the effective light-passage aperture, such as the maximum aperture through which light rays can pass through the lens assembly 100, determined by the maximum light flux of the lens assembly 100. For example, the ratio of the effective aperture to the effective focal length is 2.3.

[0103] For example, as shown in Figure 3, the ratio of the distance between the aperture (such as the human eye) and the first surface 101 at the optical axis OA 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 at 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 at 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 at 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 at the optical axis OA to the effective focal length is 1.1.

[0104] For example, as shown in Figure 3, the effective aperture of the diaphragm is 4 mm. For example, the ratio of the distance between the object plane and the diaphragm at the optical axis OA to the effective focal length in the optical system is -80 or less. For example, the ratio of the effective aperture of the image plane to the effective focal length in the optical system is 1.5.

[0105] For example, as shown in Figure 3, the ratio of the distance between the display surface 11 and the image plane of the display 10 along 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 and the image plane of the display 10 along 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 and the image plane of the display 10 along the optical axis OA to the effective focal length is 0.08.

[0106] For example, as shown in Figure 3, the ratio of the distance between the fourth surface 104 and the display surface 11 of the display 10 along 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 10 along 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 10 along the optical axis OA to the effective focal length is 0.1.

[0107] For example, as shown in Figure 3, the display 10 may be any type of display, such as a liquid crystal display, an organic light-emitting diode display, an inorganic light-emitting diode display, a quantum dot display, or a projector (e.g., an LCOS microprojector).

[0108] For example, as shown in Figure 3, display 10 is a liquid crystal display, and the pixel size is approximately 20 microns. For example, the display is an organic light-emitting diode display, and the pixel size is only a few microns.

[0109] For example, the display device may be a virtual reality display device. For example, the virtual reality display device may be a display device that uses an ultra-short-throw folded-back optical path.

[0110] For example, this display device may be a myopia display device, and this myopia display device may be a wearable VR helmet, VR glasses, etc., and the embodiments of the present invention are not limited thereto.

[0111] The following points need to be explained.

[0112] (1) In the drawings of embodiments of the present invention, only structures related to embodiments of the present invention are shown, and for other structures, conventional designs can be referred to.

[0113] (2) Features in the same and different embodiments of the present invention can be combined with each other, as long as they do not contradict each other.

[0114] The above description is merely an exemplary embodiment of the present invention and does not limit the scope of protection of the present invention, which is determined by the appended claims.

Claims

1. An optical system, A lens assembly including at least two lenses, each containing a first, second, third, and fourth surface arranged sequentially along the optical axis, A polarization reflective layer provided on the side of the first surface away from the fourth surface, A semi-transparent film provided on the side of the fourth surface away from the third surface, The semitransparent film includes a phase delay film provided on the side of the semitransparent film facing the first surface, The first surface is concave, the fourth surface is convex, the second and third surfaces are both Fresnel surfaces, and the surface shapes of the second and third surfaces are complementary. The optical system includes at least two lenses, each having a different coefficient of dispersion and refractive index.

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

8. The optical system according to any one of claims 1 to 7, wherein the ratio of the radii of curvature of the first surface to 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 conicity coefficient 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 conicity coefficient of the fourth surface is -10 to -0.

1.

11. The distance between the two intersection points where the first surface and the second surface intersect the optical axis is the first distance. The distance between the two intersection points where the third surface and the fourth surface intersect the optical axis is the second distance. The optical system according to any one of claims 1 to 10, wherein 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 at least two lenses include a first lens and a second lens arranged along the optical axis, the first lens includes a first surface and a second surface, and the second lens includes a third surface and a 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 optical system according to any one of claims 1 to 4, wherein the ratio of the center thickness to the edge thickness of the second lens is greater than 0.5 and less than 2.

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

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 shapes 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 and an optical system according to any one of claims 1 to 16, The display is a display device located on the side of the semitransparent film away from the polarizing reflective layer.

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