Optical systems and display devices

Abstract

An optical system and display device, wherein the optical system is a lens assembly including at least two lenses, the at least two lenses comprising a lens assembly including a first surface, a second surface, a third surface and a fourth surface arranged sequentially along the optical axis of the lens assembly, a semi-transparent reflective film installed on one side of the fourth surface away from the third surface, a polarizing reflective layer installed on one side of the third surface away from the fourth surface, a phase delay film located on one side of the fourth surface away from the semi-transparent reflective film, and an adhesive layer including an adhesive layer lens, wherein at least one of the first and second surfaces is a Fresnel surface, and the adhesive layer is bonded between the second surface and the third surface. The adhesive layer bonded between the second surface and the third surface includes an adhesive layer lens, and the adhesive layer lens and the Fresnel surface can refract light rays to correct chromatic aberration, and the light rays do not pass through the Fresnel surface during the reversal process, reducing stray light.

Description

[Technical Field]

[0001] This application claims priority to Chinese Patent Application No. 202311865201.3, filed on 29 December 2023, and all the contents disclosed in the said Chinese Patent Application are incorporated herein by reference as part of this application.

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

[0003] With the rapid development of virtual reality (VR) technology, head-mounted displays (HMDs) have become popular among the many display devices due to their immersive experience, portability, and the fact that they do not require the user to hold them. As one of the key assemblies of virtual reality devices, the performance of the head-mounted display is a crucial factor that affects the imaging quality and cost of the virtual reality device. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] At least one embodiment of the present disclosure provides an optical system and a display device. [Means for solving the problem]

[0005] At least one embodiment of the present disclosure provides an optical system comprising a lens assembly including at least two lenses, the at least two lenses comprising a first, second, third, and fourth surface arranged sequentially along the optical axis of the lens assembly; a semi-transparent reflective film positioned on one side of the fourth surface away from the third surface; a polarizing reflective layer positioned on one side of the third surface away from the fourth surface; a phase delay film positioned on one side of the fourth surface away from the semi-transparent reflective film; and an adhesive layer including an adhesive layer lens, wherein at least one of the first and second surfaces is a Fresnel surface, and the adhesive layer is bonded between the second and third surfaces.

[0006] For example, according to at least one embodiment of the present disclosure, the distance between the two intersection points where the first surface and the second surface intersect with the optical axis is the first distance, and the ratio of the center thickness of the adhesive layer lens to the first distance is 1 / 6 to 2.

[0007] For example, according to at least one embodiment of the present disclosure, the center thickness of the adhesive layer lens is 0.5 millimeters to 3 millimeters.

[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, the first lens includes a first surface and a second surface, the second lens includes a third surface and a fourth surface, and one of the refractive powers of the first lens and the adhesive layer lens is positive and the other is negative.

[0009] For example, according to at least one embodiment of the present disclosure, the ratio of the refractive power of the first lens to the dispersion coefficient of the first lens is a first ratio, the ratio of the refractive power of the adhesive layer lens to the dispersion coefficient of the adhesive layer lens is a second ratio, and the sum of the first ratio and the second ratio is less than 0.

[0010] For example, according to at least one embodiment of the present disclosure, the refractive index of the first lens is smaller than the refractive index of the adhesive layer lens, the refractive index of the second lens is smaller than the refractive index of the adhesive layer lens, and the refractive index of the first lens is less than or equal to the refractive index of the second lens.

[0011] For example, according to at least one embodiment of the present disclosure, the dispersion coefficient of the first lens is greater than the dispersion coefficient of the adhesive layer lens, the dispersion coefficient of the second lens is greater than the dispersion coefficient of the adhesive layer lens, and the dispersion coefficient of the first lens is greater than or equal to the dispersion coefficient of the second lens.

[0012] For example, according to at least one embodiment of the present disclosure, the refractive index of the first lens is greater than the refractive index of the adhesive layer lens, and the refractive index of the first lens is greater than the refractive index of the second lens.

[0013] For example, according to at least one embodiment of the present disclosure, the dispersion coefficient of the first lens is smaller than the dispersion coefficient of the adhesive layer lens, and the dispersion coefficient of the first lens is smaller than the dispersion coefficient of the second lens.

[0014] For example, according to at least one embodiment of the present disclosure, the ratio of the center thickness to the edge thickness of the first lens is a third ratio, and the ratio of the center thickness to the edge thickness of the second lens is a fourth ratio, and at least one of the third ratio and the fourth ratio is greater than 1 and less than 3.

[0015] 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.

[0016] For example, according to at least one embodiment of the present disclosure, the second surface is convex, and the central thickness of the adhesive layer lens is smaller than the edge thickness.

[0017] For example, according to at least one embodiment of the present disclosure, the second surface is convex, and the absolute value of the radius of curvature of the second surface is smaller than the absolute value of the radius of curvature of the third surface.

[0018] For example, according to at least one embodiment of the present disclosure, the second surface is a convex surface, and the ratio of the radius of curvature of the second surface to the effective focal length of the optical system is -0.5 to -2.

[0019] For example, according to at least one embodiment of the present disclosure, the second surface is a concave surface, and the central thickness of the adhesive layer lens is greater than the edge thickness.

[0020] For example, according to at least one embodiment of the present disclosure, the distance between two intersection points where the first surface and the second surface intersect the optical axis is defined as the first distance, the distance between two intersection points where the third surface and the fourth surface intersect the optical axis is defined as the second distance, and the ratio of the second distance to the first distance is 2 to 4.

[0021] For example, according to at least one embodiment of the present disclosure, the ratio of the first distance to the effective focal length of the optical system is 0.1 to 0.3, and the ratio of the second distance to the effective focal length of the optical system is 0.5 to 0.7.

[0022] For example, according to at least one embodiment of the present disclosure, the first surface is a flat surface, or the first surface is a convex surface, the ratio of the radius of curvature of the first surface to the effective focal length of the optical system is -40 to -50, and the conic coefficient of the first surface is -10 to 0.

[0023] For example, according to at least one embodiment of the present disclosure, the third surface is a flat surface, or the third surface is a concave surface, the ratio of the radius of curvature of the third surface to the effective focal length of the optical system is -3 to -4, and the conic coefficient of the third surface is -10 to -1.

[0024] For example, according to at least one embodiment of the present disclosure, the fourth surface is a convex surface, the ratio of the radius of curvature of the fourth surface to the effective focal length of the optical system is -2 to -3, and the conic coefficient of the fourth surface is -10 to -1.

[0025] 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 order 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 on the side opposite to the third surface, the third lens further includes a sixth surface located between the fifth surface and the fourth surface, the surface shapes of the fifth surface and the sixth surface are the same, one of the refractive power of the first lens and the refractive power of the adhesive layer lens is a positive value, and the other is a negative value, and / or at least one of the dispersion coefficients of the first lens and the second lens is different from the dispersion coefficient of the adhesive layer lens.

[0026] At least one embodiment of the present disclosure provides a display device including the optical system described in any of the above embodiments.

[0027] To more clearly explain the technical solutions of the embodiments of the present disclosure, the drawings of the embodiments will be briefly described below. As is clear, the drawings described below relate only to some embodiments of the present disclosure and do not limit the present disclosure.

Brief Description of the Drawings

[0028] [Figure 1] FIG. 1 is an optical system according to an example of at least one embodiment of the present disclosure. [Figure 2A] FIG. 2A is a spot diagram of the optical system shown in FIG. 1. [Figure 2B] FIG. 2B is a diagram showing the curve of the change in the diffusion spot size of the optical system shown in FIG. 1 according to the viewing angle. [Figure 2C] FIG. 2C is a lateral chromatic aberration diagram of the optical system shown in FIG. 1. [Figure 2D] FIG. 2D is a distortion aberration diagram of the optical system shown in FIG. 1. [Figure 3] FIG. 3 is an optical system according to an example of at least one embodiment of the present disclosure. [Figure 4A]Figure 4A is a schematic diagram of ray deflection with a single lens. [Figure 4B] Figure 4B is a schematic diagram of ray deflection in an example of at least one embodiment of the present disclosure. [Figure 5] Figure 5 shows an optical system relating to a different example in at least one embodiment of the present disclosure. [Figure 6] Figure 6 shows an optical system relating to a different example in at least one embodiment of the present disclosure. [Figure 7] Figure 7 shows an optical system relating to a different example in at least one embodiment of the present disclosure. [Figure 8] Figure 8 shows an optical system relating to a different example in at least one embodiment of the present disclosure. [Figure 9] Figure 9 shows an optical system relating to a different example in at least one embodiment of the present disclosure. [Figure 10] Figure 10 shows a display device according to an example of at least one embodiment of the present disclosure. [Modes for carrying out the invention]

[0029] To further clarify the objectives, technical solutions, and advantages of the embodiments of this disclosure, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the drawings of the embodiments of this disclosure. As is obvious, the embodiments described are only a selection of embodiments of this disclosure, not all embodiments. All other embodiments obtained by a person skilled in the art without requiring any creative work based on the embodiments of this disclosure described are all within the scope of this disclosure.

[0030] Unless otherwise defined, technical or scientific terms used in this disclosure should have meanings generally understood by those skilled in the art. The terms “First,” “Second,” and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similar terms such as “includes” or “incorporates” mean that the element or component listed before the term includes, but does not exclude, the element or component and its equivalents listed after the term.

[0031] The terms “perpendicular,” “parallel,” and “same” used in this disclosure all include features such as “perpendicular,” “parallel,” and “same” in their strict sense, as well as situations involving certain errors such as “approximately perpendicular,” “approximately parallel,” and “approximately the same,” all within an acceptable range determined by a person skilled in the art for a given value, taking into account the errors associated with the measurement of a given quantity (i.e., limitations of the measurement system). In the embodiments of this disclosure, “center” can include a position that is precisely at the geometric center and a position that is approximately at the center within a small area around the geometric center. For example, “approximately” can indicate that it is within one or more standard deviations, or within 10% or 5% of the value.

[0032] In near-eye display optical systems, particularly in some head-mounted display optical systems combining sub-inch 4K high-resolution display screens with wide viewing angles, low dispersion is one of the prerequisites for ensuring imaging resolution and improving the immersive experience. In some optical systems, the impact of the optical system's inherent chromatic aberration on optical performance can be reduced by late-stage digital chromatic aberration correction methods. During research, the inventors of the present invention found that eliminating chromatic aberration through optical design methods at an early stage of optical system development can more fundamentally solve the problem of chromatic aberration compared to digital chromatic aberration correction methods.

[0033] At least one embodiment of the present disclosure provides an optical system comprising a lens assembly including at least two lenses, the at least two lenses comprising a lens assembly including a first surface, a second surface, a third surface and a fourth surface arranged in order along the optical axis of the lens assembly; a semi-transparent reflective film located on one side of the fourth surface away from the third surface; a polarizing reflective layer located on one side of the third surface away from the fourth surface; a phase delay film located on one side of the fourth surface away from the semi-transparent reflective film; and an adhesive layer including an adhesive layer lens, wherein at least one of the first and second surfaces is a Fresnel surface, and the adhesive layer is bonded between the second and third surfaces.

[0034] At least one embodiment of the present disclosure provides a display device including the optical system described above.

[0035] An optical system and display device according to at least one embodiment of the present disclosure provides a bonding position for a semi-transparent reflective film, a polarizing reflective layer, and a phase delay film by installing a lens assembly including at least two lenses, which can refract light rays between the semi-transparent reflective film and the polarizing reflective layer. The adhesive layer bonded between the second and third surfaces includes an adhesive layer lens which, in cooperation with the Fresnel surface, can refract light rays and correct chromatic aberration. In addition, light rays are incident on the Fresnel surface after exiting the polarizing reflective layer, and the light rays do not pass through the Fresnel surface during the refraction process, reducing stray light.

[0036] The optical system and display device will be described below with reference to the drawings, with reference to several embodiments.

[0037] Figure 1 shows an optical system according to an example of at least one embodiment of the present disclosure.

[0038] Referring to Figure 1, at least one embodiment of the present disclosure provides an optical system comprising a lens assembly 100, the lens assembly 100 comprising a semi-transparent reflective film 200, a polarizing reflective layer 300, a phase delay film 400, and an adhesive layer. The lens assembly 100 comprises at least two lenses. For example, as shown in Figure 1, the lens assembly 100 may consist of two lenses, lens 110 and lens 120. For example, the adhesive layer is a light-transmitting adhesive layer.

[0039] 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, one side of the first surface 101 away from the fourth surface 104 is the light-emitting side of the optical system. For example, if the optical system is applied to a display device, the display screen may be located on one side of the fourth surface 104 of the optical system away from the first surface 101, and light rays emitted from the display screen enter through the fourth surface 104 and exit through the first surface 101.

[0040] As shown in Figure 1, the semi-transparent reflective film 200 is installed on one side of the fourth surface 104 away from the third surface 103. The polarizing reflective layer 300 is installed on one side of the third surface 103 away from the fourth surface 104. The phase delay film 400 is located on one side of the fourth surface 104 away from the semi-transparent reflective film 200. For example, light rays that have passed through the semi-transparent reflective film 200 and entered the lens assembly 100 are folded back between the semi-transparent reflective film 200 and the polarizing reflective layer 300 and exit from the polarizing reflective layer 300, thereby forming a folded optical path by the polarizing reflective layer 300, the semi-transparent reflective film 200 and the phase delay film 400.

[0041] As shown in Figure 1, the adhesive layer includes an adhesive layer lens 130, which is bonded between the second surface 102 and the third surface 103. For example, the adhesive layer is tacky, thereby allowing it to bond between the second surface 102 and the third surface 103. The adhesive layer further includes an adhesive layer lens 130 located between the second surface 102 and the third surface 103, which is a lens formed using the adhesive layer. By utilizing the difference in material between the adhesive layer lens 130 and the lens, light rays can be refracted when they enter or exit the adhesive layer lens 130, thereby correcting chromatic aberration.

[0042] As shown in Figure 1, at least one of the first surface 101 and the second surface 102 is a Fresnel surface. A Fresnel surface refers to the non-smooth surface of the two opposite surfaces of a Fresnel lens. For example, the first surface 101 and the second surface 102 may be the two opposite surfaces of a single lens, and this lens may be a Fresnel lens. A Fresnel lens, also called a screw lens, has a smooth surface on one side and a pattern of multiple concentric circles (i.e., Fresnel zones) formed on the other side. These patterns can change the degree of refraction of light rays, thereby allowing Fresnel lenses to effectively reduce lens thickness, even at short focal lengths.

[0043] For example, referring to Figure 1, the second surface 102 can be set as a Fresnel surface. For example, a material with low hardness can be selected for the adhesive layer, and by joining the Fresnel surface and the adhesive layer, the adhesive strength between the adhesive layer and the lenses on both sides of the adhesive layer can be improved, while the adhesive layer can buffer external stress and prevent damage to the toothed structure of the Fresnel surface. In addition, by setting the second surface 102 as a Fresnel surface, the amount of material used in the adhesive layer between the second surface 102 and the third surface 103 can be reduced due to the toothed structure of the Fresnel surface, thereby reducing costs. Furthermore, if the first surface 101 is a smooth surface (no Fresnel surface is provided), the film layer can be easily attached. For example, an anti-reflective film can be attached to the first surface 101.

[0044] For example, in another example, the first surface can be set as a Fresnel surface (not shown in the figure). For example, in another example, both the first and second surfaces can be set as Fresnel surfaces (not shown in the figure). This disclosure is not limited thereto.

[0045] The optical system according to this disclosure provides bonding positions for a semi-transparent reflective film, a polarizing reflective layer, and a phase delay film by installing a lens assembly including at least two lenses, allowing light rays to be refractioned between the semi-transparent reflective film and the polarizing reflective layer. The adhesive layer bonded between the second and third surfaces includes an adhesive layer lens, which, in conjunction with the Fresnel surface, can refract light rays and correct chromatic aberration. The Fresnel surface is also advantageous in improving design flexibility, as light rays are incident on the Fresnel surface after exiting the polarizing reflective layer, and the light rays do not pass through the Fresnel surface during the refraction process, reducing stray light.

[0046] In some optical systems, a Fresnel surface can be introduced into the folded path of the light ray, and different optical materials can be used on either side of the Fresnel surface. For example, a Fresnel surface can be introduced between a semi-transparent reflective film and a polarizing reflective layer, thereby utilizing the different refractive indices and dispersion coefficients of the different optical materials, and combining this with the refractive effect of the Fresnel surface to jointly correct chromatic aberration.

[0047] For example, the adhesive layer material can include an optically transparent adhesive. For example, the lens assembly material can include an optically transparent inorganic polymer or glass. This allows for correction of chromatic aberration by using different materials for the adhesive layer lens and the lenses on either side, due to differences in refractive index and dispersion coefficient between the different materials. For example, the adhesive layer material can further include silica gel material, which has good fluidity and is more advantageous in the process.

[0048] For example, referring to Figure 1, the optical system further includes a linear polarizing film 500, which is located on one side of the polarizing reflective layer 300 away from the semi-transparent reflective layer 200. For example, an adhesive layer can be bonded between the linear polarizing film 500 and the second surface 102. For example, the linear polarizing film 500 may be a linear polarizer or polarizer. For example, the optical axis OA of the linear polarizing film 500 coincides with the optical axis OA of the polarizing reflective layer 300, and for example, the linear polarizing film 500 can be used to filter out other stray light, so that only polarization that passes through the linear polarizing film 500 (e.g., s-linear polarization) can enter the human eye. For example, the linear polarizing film may have a three-layer laminated structure, the intermediate layer in the three-layer laminated structure may be polyvinyl alcohol (PVA) with dichroic molecules added, and at least one layer located on both sides of the intermediate layer in the three-layer laminated structure may be triacetylcellulose (TAC). For example, the air-facing side of the linear polarizing film is treated to prevent reflection. For example, a moth-eye film can be bonded to the air-facing side of a linear polarizing film.

[0049] For example, referring to Figure 1, the semi-transparent reflective film 200 is configured to transmit some light rays and reflect other light rays. For example, the semi-transparent reflective film may have a transmittance of 50% and a reflectance of 50%. For example, the semi-transparent reflective film may have a transmittance of 60% and a reflectance of 40%. For example, the semi-transparent reflective film may have a transmittance of 65% and a reflectance of 35%. The optical system according to this disclosure is not limited thereto, and the transmittance and reflectance of the semi-transparent reflective film can be set according to the needs of the product. For example, the semi-transparent reflective film may be deposited on a fourth surface.

[0050] For example, referring to Figure 1, the function of the polarization reflective layer 300 is as follows: There is one optical axis OA direction within the plane of the film layer, and the transmittance of the polarization component of incident light parallel to the optical axis OA direction (e.g., s-linear polarization) is greater than the transmittance of the polarization component perpendicular to the optical axis OA direction (e.g., p-linear polarization), and the reflectance of the polarization component parallel to the optical axis OA direction (e.g., s-linear polarization) is less than the reflectance of the polarization component perpendicular to the optical axis OA direction (e.g., p-linear polarization). For example, the transmittance of polarization parallel to the optical axis direction of the polarization reflective layer is 85% or more, for example 90% or more, for example 95% or more, for example 98% or more, and the reflectance of polarization perpendicular to the optical axis direction of the polarization reflective layer is 85% or more, for example 90% or more, for example 95% or more, for example 98% or more.

[0051] For example, referring to Figure 1, the polarizing reflective layer 300 is configured to reflect linearly polarized light of one characteristic and transmit linearly polarized light of another characteristic, and the polarizing reflective layer 300 may be located on one side of the third surface 103 away from the fourth surface 104, and the phase delay film 400 may be located between the polarizing reflective layer 300 and the semitransparent reflective film 200. For example, the polarizing reflective layer may also be called a polarizing beam splitter film. For example, the polarizing reflective layer may further include an Advanced Polarizer Film (APF). For example, the polarizing reflective layer may further include an IQPS (Image Quality Polarizer Standard) film or an IQPE (Image Quality Polarizer Enhanced) film.

[0052] For example, the polarizing reflective layer is a cholesteric liquid crystal layer (not shown in the figure), and the phase delay film is placed on one side of the cholesteric liquid crystal layer away from the semi-transparent reflective film. For example, the cholesteric liquid crystal can reflect and transmit circularly polarized light. Referring to the principle of folded light paths described above, the cholesteric liquid crystal layer is placed between the phase delay film and the semi-transparent reflective film. A waveplate can be placed on the display surface side of the display screen, located on one side of the second lens away from the first lens. Image light emitted from the display screen is converted to right-handed circularly polarized light after passing through the waveplate. The right-handed circularly polarized light is incident on the semi-transparent reflective film, and the right-handed circularly polarized light is transmitted through the semi-transparent reflective film without changing its polarization state. The right-handed circularly polarized light is reflected back to the semi-transparent reflective film after passing through the cholesteric liquid crystal layer, where the first reflection occurs. The right-handed circularly polarized light is then reflected by the semi-transparent reflective film, where the second reflection occurs. Due to half-wave loss, the reflected light changes from right-handed circular polarization to left-handed circular polarization. This left-handed circular polarization passes through the cholesteric liquid crystal layer and reaches the phase delay film, where it is converted to s-polarization. This s-linear polarization then passes through the linear polarization film and enters the human eye.

[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 may be a quarter-wave plate. For example, the phase delay film 400 may have a characteristic in which there is one direction with the lowest refractive index and one direction with the highest refractive index within the film layer plane, which 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 is delayed by 1 / 4 wavelength compared to the phase after polarization parallel to the fast axis passes through the phase delay film. For example, the angle between the slow axis of the phase delay film and the optical axis of the polarization reflection layer is 45 degrees.

[0054] For example, referring to Figure 1, the material of the phase delay film 400 can include a liquid crystal polymer. The film thickness of a phase delay film made of a liquid crystal polymer is relatively thin, reaching 1 μm to 5 μm. Thinner phase delay films have a higher adaptability to curved surfaces, can be fabricated more easily based on the surface shape of the curved surface, and reduce the possibility of wrinkles occurring when bonding to a curved surface, which can affect the phase delay accuracy and optical performance. In addition, when a phase delay film made of a liquid crystal polymer is bonded to a curved surface, the resulting optical shift is smaller. Liquid crystal polymers are crosslinked systems, with molecules linked by chemical bonds and having a high elastic modulus. When a phase delay film made of this material is stretched after bonding, only elastic deformation occurs, and strong optical anisotropy effects such as molecular spreading and rearrangement do not occur. Therefore, phase delay films made of liquid crystal polymer materials are suitable for bonding to surface shapes with small radii of curvature. This degree of freedom in the radius of curvature makes it easier to meet index requirements such as resolution, distortion aberration, and dispersion, which is advantageous for the optical system to obtain better image quality.

[0055] For example, the optical system may include a first optical element and a second optical element, the first optical element may include a first surface and a second surface, and the second optical element may include a third surface and a fourth surface. The second optical element may further include a semi-transparent reflective film, a polarizing reflective layer and a phase delay film, and the configuration of the semi-transparent reflective film, polarizing reflective layer and phase delay film can be seen from the examples above and will not be described again here. This allows the second optical element to achieve ray refraction.

[0056] For example, the adhesive layer lens may be bonded between the first optical element and the second optical element. As can be understood, the adhesive layer may be bonded between the second surface and a different film layer, based on the different placement positions of the polarizing reflective layer, phase delay film, or other film layer. For example, if the second optical element does not have a linear polarizing film and the phase delay film is placed between the polarizing reflective layer and the third surface, the adhesive layer may be bonded between the polarizing reflective layer and the second surface. For example, if the second optical element does not have a linear polarizing film and the phase delay film is placed on one side of the polarizing reflective layer (for example, the polarizing reflective layer is a cholesteric liquid crystal layer) away from the semi-transparent reflective film, the adhesive layer may be bonded between the phase delay film and the second surface. For example, if the second optical element has a linear polarizing film, the adhesive layer may be bonded between the second surface and the linear polarizing film.

[0057] For example, referring to Figure 1, when the optical system is applied to a display device, the principle of folded light paths is as follows: A waveplate can be installed on the light-emitting side of the display surface of the display screen located on one side of the fourth surface 104 away from the first surface 101. Image light emitted from the display surface passes through the waveplate and is converted to right-handed circular polarization. The right-handed circular polarization is transmitted through the semi-transparent reflective film 200 without changing its polarization state. The light rays enter and are transmitted to the phase delay film 400. The right-handed circular polarization incident on the phase delay film 400 is converted to p-linear polarization. The p-linear polarization is reflected by the polarization reflective layer 300 and returned to the phase delay film 400, where the first reflection occurs. Subsequently, the p-linear polarization is converted to right-handed circular polarization after passing through the phase delay film 400. This right-handed circular polarization is transmitted to the semi-transparent reflective film 200, where it is reflected, and the second reflection occurs. Due to half-wave loss, the reflected light changes from right-handed circular polarization to left-handed circular polarization. The left-handed circularly polarized light passes through and reaches the phase delay film 400, where it changes to s-linearly polarized light. This s-linearly polarized light then passes through the polarization reflection layer 300 and enters an exit pupil, similar to that of a human eye.

[0058] The above-described folded light path changes the polarization state of the light rays propagating between the polarizing reflective layer 300 and the semi-transparent reflective film 200, thereby achieving the folding of the light rays. As a result, the focal length of the optical system is increased by installing the polarizing reflective layer 300, the phase delay film 400, and the semi-transparent reflective film 200. The system is folded back by, for example, two reflections, thereby significantly compressing the space required between the human eye and the optical system, and consequently making the volume of the optical system smaller and thinner.

[0059] Figure 2A is a spot diagram of the optical system shown in Figure 1. Figure 2B is a curve diagram showing how the diffuse spot size of the optical system shown in Figure 1 changes with respect to the field of view.

[0060] Referring to Figure 2A, a spot diagram refers to the phenomenon where many light rays emitted from a single point pass through an optical system, and due to aberrations, the intersection points with the image plane no longer converge at the same point, forming a single diffuse figure distributed over a certain range. This can be used to evaluate the imaging quality of an optical system. In Figure 2A, using the first set of values ​​in the left vertical direction as an example, 0.00 represents the X-direction normalized field of view, 1.00 represents the Y-direction normalized field of view, 0.000 represents the X-direction field of view angle, and 45.00 represents the Y-direction field of view angle. In Figure 2A, using the first set of values ​​in the right vertical direction as an example, RMS represents the root mean square of the radius from the diffusion point of the diffuse spot to the centroid (or center) of the diffuse spot, and 100% represents the diameter of the diffuse spot. Figure 2A is typically used to evaluate the full field resolution of the optical system, i.e., the imaging resolution of the entire field of view covered by the peripheral field of view when the pupil of the human eye is at the entrance pupil position on the optical axis OA and fixating on the lens center (i.e., the zero field of view), also known as the transient mode. In addition to considering the full field resolution under transient mode, fixation point resolution is one of the more important optical metrics for a wearer, for example, wearing a head-mounted display. Fixation point resolution refers to the screen resolution within a certain angular range that can be directly seen (not seen in the peripheral field of view) when the eye rotates up, down, left, and right.

[0061] In fixation mode, the eyeball rotates by a certain angle, the pupil is offset from the center of the optical axis OA, there is a certain offset in the Z and Y directions of the optical axis OA, and the principal ray passing through the center of the pupil and the Z axis form a certain angle. For example, the range of this angle is ±35 degrees, and the setting of this angle range takes into account the observation habits of the human eye, as people tend to spontaneously turn their heads rather than forcibly moving their eyeballs in order to clearly see objects in front of them that are beyond a 35-degree range from the center of the human eye. Referring to Figure 2B, which shows the relationship between fixation resolution and fixation angle, the diffuse spot in the central field of view is much smaller than a single pixel, and the diameter of the diffuse spot when the human eye rotates 20 degrees is less than 5 microns. As can be seen from Figure 2B, the diffuse spot of the optical system of this disclosure is small and the resolution of the optical system is high. As can be seen from the above, the optical system according to at least one embodiment of this disclosure can clearly image.

[0062] Figure 2C is a transverse chromatic aberration diagram of the optical system shown in Figure 1. Referring to Figure 2C, the transverse chromatic aberration diagram shows the height difference of each wavelength relative to the central wavelength at different image heights on the imaging plane. The horizontal axis represents the transverse chromatic aberration value of each wavelength relative to the central wavelength, and the vertical axis represents the normalized field of view. As shown in Figure 2C, R light is red light, G light is green light, and B light is blue light. R and B light are located at the ends of the sensitive region of the human eye, and G light is located near the spectral line to which the human eye is most sensitive. As can be seen from Figure 2C, the absolute values ​​of the transverse chromatic aberration of B light and R light are controlled within 0.05 millimeters, and the absolute values ​​of the transverse chromatic aberration of B light and G light are controlled within 0.025 millimeters. As can be seen from this, the optical system shown in Figure 1, for example, can correct chromatic aberration at the edges of the field of view and the secondary spectrum across the entire image plane very well.

[0063] Figure 2D is a distortion diagram of the optical system shown in Figure 1. Referring to Figure 2D, the distortion diagram reflects the difference in image plane position where a clear image is formed in different fields of view, and as shown in Figure 2D, the absolute value of the maximum distortion is within 35%. As can be seen from this, the optical system according to at least one embodiment of the present disclosure can correct distortion relatively well and meet high-quality imaging requirements. Furthermore, distortion correction can be pre-processed in software.

[0064] Figure 3 shows an optical system according to an example of at least one embodiment of the present disclosure.

[0065] The difference between the optical system shown in Figure 3 and the optical system shown in Figure 1 is that the second surface 102 and adhesive layer lens 130 of the optical system shown in Figure 3 are different from the second surface 102 and adhesive layer lens 130 of the optical system shown in Figure 1. Of course, there may be other differences between the optical system shown in Figure 3 and the optical system shown in Figure 1, for example, the number of lenses may differ, and this disclosure is not limited thereto. For example, the number of lenses in the optical system shown in Figure 3 may be different from or the same as the number of lenses in the optical system shown in Figure 1. The semi-transparent reflective film 200, polarizing reflective layer 300, phase delay film 400, and linear polarizing film 500 of the optical system shown in Figure 3 may have the same characteristics as the semi-transparent reflective film 200, polarizing reflective layer 300, phase delay film 400, and linear polarizing film 500 of the optical system shown in Figure 1, and will not be described again here.

[0066] For example, the adhesive layer lens 130 shown in Figure 1 is a concave lens, and in the optical system shown in Figure 1, the adhesive layer lens 130 can be manufactured using an optically transparent adhesive. For example, the adhesive layer lens 130 shown in Figure 3 is a convex lens. When the adhesive layer lens 130 is a convex lens, the central thickness of the adhesive layer lens 130 is greater than the edge thickness, requiring more material. In the optical system shown in Figure 3, the adhesive layer lens 130 can be manufactured using optical-grade silica gel material, thereby reducing costs and being advantageous for processing. For example, the central thickness of the adhesive layer lens 130 may be the distance between the two intersection points where the two opposite surfaces of the adhesive layer lens 130 intersect with the optical axis OA. For example, the second surface 102 shown in Figure 1 is a convex surface. For example, the second surface 102 shown in Figure 3 is a concave surface.

[0067] Referring to Figures 1 and 3, in some examples, the distance between the two intersection points where the first surface 101 and the second surface 102 intersect with the optical axis OA is defined as the first distance D1, and the ratio of the central thickness d of the adhesive layer lens 130 to the first distance D1 may be 1 / 6 to 2. By setting the ratio of the central thickness d of the adhesive layer lens 130 to the first distance D1, the adhesive layer can be sufficiently filled between the second surface 102 and the third surface 103. For example, if the second surface 102 is a Fresnel surface, the adhesive layer can be sufficiently filled into the tooth-like structure of the Fresnel surface, so that one side of the adhesive layer lens that adheres to the second surface 102 has a surface shape complementary to the second surface 102.

[0068] For example, referring to Figure 1, the ratio of the central thickness d of the adhesive layer lens 130 to the first distance D1 may be 1 / 6 to 1 / 4. For example, referring to Figure 1, the ratio of the central thickness d of the adhesive layer lens 130 to the first distance D1 may be 1 / 4 to 1 / 2. For example, referring to Figure 3, the ratio of the central thickness d of the adhesive layer lens 130 to the first distance D1 may be 1 / 2 to 2.

[0069] In some optical systems, the adhesive layer used to bond two lenses is typically a thin layer, with a thickness of typically several tens of microns. Referring to Figures 1 and 3, in some examples, the central thickness d of the adhesive layer lens 130 may be 0.5 to 3 millimeters. By installing a thicker adhesive layer, the adhesive layer can be sufficiently filled between the second surface 102 and the third surface 103. For example, if the second surface 102 is a Fresnel surface, the adhesive layer can be sufficiently filled into the dentition of the Fresnel surface. For example, referring to Figure 1, the central thickness d of the adhesive layer lens 130 may be 0.5 to 0.8 millimeters. For example, referring to Figure 1, the central thickness d of the adhesive layer lens 130 may be 0.8 to 1 millimeter. For example, referring to Figure 3, the central thickness d of the adhesive layer lens 130 may be 1 to 1.5 millimeters. For example, referring to Figure 3, the central thickness d of the adhesive layer lens 130 may be 1.5 to 2 millimeters. For example, referring to Figure 3, the central thickness d of the adhesive layer lens 130 may be 2 mm to 2.5 mm. For example, referring to Figure 3, the central thickness d of the adhesive layer lens 130 may be 2.5 mm to 3 mm.

[0070] Referring to Figures 1 and 3, in some examples, at least two lenses include a first lens 110 and a second lens 120 arranged along the optical axis OA direction, 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. For example, the lens assembly 100 may consist of the first lens 110 and the second lens 120.

[0071] Referring to Figures 1 and 3, for example, after forming the first lens 110 and the second lens 120 by injection molding, one lens (e.g., the first lens 110) can be placed in the mold's position limiting ring before the adhesive is injected. A stepped portion may be provided in the position limiting ring to limit the position of the lens and limit the amount of adhesive injected, preventing too much or too little adhesive. Taking the second surface 102 of the first lens 110 as an example, when injecting the adhesive, it is necessary to ensure that the colloid sufficiently fills the gaps between the teeth of the tooth-like structure on the Fresnel surface. Subsequently, the other lens (e.g., the second lens 120) can be placed in the stepped portion of the position limiting ring and pressure can be applied, thereby allowing excess colloid to be discharged through the adhesive discharge hole provided in the position limiting ring. The adhesive discharge hole can also be used simultaneously to discharge gas from inside the colloid. After the excess colloid has been discharged, adhesive fixation can be achieved by heating or ultraviolet irradiation.

[0072] Referring to Figures 1 and 3, in some examples, the distance between the two intersection points where the first surface 101 and the second surface 102 intersect with the optical axis OA is defined as the first distance D1, and the distance between the two intersection points where the third surface 103 and the fourth surface 104 intersect with the optical axis OA is defined as the second distance D2. For example, the first distance D1 is the central thickness of the first lens 110, and the second distance D2 is the central thickness of the second lens 120. The ratio of the second distance D2 to the first distance D1 may be between 2 and 4. For example, the ratio of the second distance D2 to the first distance D1 may be between 2.5 and 3.5. For example, the ratio of the second distance D2 to the first distance D1 may be 3.

[0073] Referring to Figures 1 and 3, in some examples, the ratio of the first distance D1 to the effective focal length of the optical system may be 0.1 to 0.3. For example, the ratio of the first distance D1 to the effective focal length of the optical system may be 0.15 to 0.25. For example, the ratio of the first distance D1 to the effective focal length of the optical system may be 1.2. In some examples, the ratio of the second distance D2 to the effective focal length of the optical system may be 0.5 to 0.7. For example, the ratio of the second distance D2 to the effective focal length of the optical system may be 0.55 to 0.65. For example, the ratio of the second distance D2 to the effective focal length of the optical system may be 0.6.

[0074] Referring to Figures 1 and 3, in some examples, one of the refractive powers of the first lens 110 and the adhesive layer lens 130 is positive, and the other is negative. This allows for correction of chromatic aberration by setting the refractive powers of the first lens 110 and the adhesive layer lens 130 to be positive and negative relative to each other.

[0075] Figure 4A is a schematic diagram of ray deflection of a single lens. Figure 4B is a schematic diagram of ray deflection of an example of at least one embodiment of the present disclosure. Hereinafter, chromatic aberration correction will be explained using the example of light rays incident on the optical system being refracted once.

[0076] Figure 4A illustrates the deflection of light rays by a single lens. As shown in Figure 4A, the single lens L is a convex lens, with the side furthest from the target surface S0 being the incoming side. That is, the light rays enter the single lens L from the left side of Figure 4A, are refracted, and exit the single lens L onto the target surface S0. White light (solid line shown in Figure 4A) disperses after entering the single lens L, decomposing into monochromatic light of different wavelengths. In Figure 4A, 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. As can be seen from Figure 4A, the blue light B has a shorter wavelength and the red light R has a longer wavelength, making it difficult for them to converge onto the target surface S0 after passing through the single lens L.

[0077] Figure 4B illustrates how light rays are deflected into the optical system when the refractive powers of lens L1 and lens L2 in the lens assembly are positive and negative relative to each other. As shown in Figure 4B, one side away from the target plane S0 is considered the incoming side, i.e., the light rays enter the lens assembly from the left side of Figure 4B, are refracted, and exit the lens assembly onto the target plane S0. White light (solid line in Figure 4B) disperses after entering the lens assembly and decomposes into monochromatic light of different wavelengths. In Figure 4B, red light R, which has a longer wavelength, is shown as a dashed line, and blue light B, which has a shorter wavelength, is shown as a dotted line. By setting the refractive powers of lens L1 and lens L2 so that one is positive and the other is negative, the deflection angles of red light R and blue light B can be changed, and ultimately, red light R and blue light B can be focused onto the target plane S0.

[0078] For example, referring to Figure 4B, lens L1 is a convex lens with a positive refractive power, and lens L2 is a concave lens with a negative refractive power. After the incident light rays enter lens L1 and disperse, the blue light B, which has a relatively shorter wavelength, is biased towards the optical axis OA more than the red light R. Because lens L2 has a negative refractive power, after the light rays exit lens L2, the red light R and blue light B can be focused onto the target plane S0, thereby achieving the objective of correcting chromatic aberration.

[0079] For example, referring to Figure 1, the first lens 110 may be a convex lens, and the adhesive layer lens 130 may be a concave lens, and the refractive power of the first lens 110 is positive and the refractive power of the adhesive layer lens 130 is negative, thereby correcting chromatic aberration. Furthermore, the adhesive layer lens 130, which is a concave lens, requires less adhesive layer material. For example, the second surface 102 of the first lens 110 is a Fresnel surface, and the adhesive layer bonds the Fresnel surface and the second lens 120 together, thereby reducing the amount of adhesive layer used due to the toothed structure of the Fresnel surface, and thus reducing costs. In addition, by setting the first lens 110 as a convex lens and the adhesive layer lens 130 as a concave lens, the optical system can be made even thinner.

[0080] For example, referring to Figure 3, the first lens 110 may be a concave lens, and the adhesive layer lens 130 may be a convex lens, and the refractive power of the first lens 110 is negative and the refractive power of the adhesive layer lens 130 is positive, thereby correcting chromatic aberration. In addition, the central thickness of the adhesive layer lens 130 of the convex lens is greater, and it is possible to ensure that the adhesive layer is placed between the center of the first lens 110 and the center of the second lens 120.

[0081] In some examples, referring to Figure 1, the ratio of the refractive power of the first lens 110 to the dispersion coefficient of the first lens 110 is defined as the first ratio, and the ratio of the refractive power of the adhesive layer lens 130 to the dispersion coefficient of the adhesive layer lens 130 is defined as the second ratio. The sum of the first ratio and the second ratio is less than 0. This allows for correction of chromatic aberration by utilizing the combination of positive and negative refractive powers of the first lens 110 and the adhesive layer lens, and also allows for the offsetting of at least a portion of the refractive power of the second lens 120 by the surplus refractive power of the first lens 110 and the adhesive layer lens, thereby improving the chromatic aberration correction effect.

[0082] In some examples, referring to Figure 1, the refractive index of the first lens 110 is smaller than that of the adhesive layer lens 130, the refractive index of the second lens 120 is smaller than that of the adhesive layer lens 130, and the refractive index of the first lens 110 is less than or equal to that of the second lens 120. By setting the refractive indices of the first lens 110, the second lens 120, and the adhesive layer lens 130 to different refractive indices, the deflection angles of light rays of different wavelengths (e.g., red light, blue light) can be changed after the dispersion of white light, and the light rays of different wavelengths can be focused after they exit the lens assembly 100, thereby correcting chromatic aberration. Furthermore, the refractive index of the first lens 110 can be set to a value relatively close to that of the second lens 120, and since the deflection of light rays occurs between the first lens 110 and the second lens 120, which have a small difference in refractive index, the reflection loss of light rays is less than 2% of the reflection loss at the lens-air interface, improving optical efficiency.

[0083] A transparent medium exhibits different refractive indices for light of different wavelengths. Since white light consists of various colored light of different wavelengths, a dispersion phenomenon occurs when a transparent medium refracts white light. The dispersion coefficient (also called the Abbe number) is an index used to indicate the dispersion ability of a transparent medium and is used to determine the degree of light dispersion of the transparent medium. Generally, the larger the refractive index of the medium, the more severe the dispersion and the smaller the Abbe number. Conversely, the smaller the refractive index of the medium, the less severe the dispersion and the larger the Abbe number.

[0084] In some examples, referring to Figure 1, the dispersion coefficient of the first lens 110 is greater than that of the adhesive layer lens 130, the dispersion coefficient of the second lens 120 is greater than that of the adhesive layer lens 130, and the dispersion coefficient of the first lens 110 is greater than or equal to that of the second lens 120. By setting the first lens 110, the second lens 120, and the adhesive layer lens 130 to have different dispersion coefficients, the deflection angles of light rays of different wavelengths (e.g., red light, blue light) can be changed after the dispersion of white light, and the light rays of different wavelengths can be focused after they exit the lens assembly 100, thereby correcting chromatic aberration.

[0085] For example, referring to Figure 1, the dispersion coefficient of the first lens 110 can be set to be much larger than that of the adhesive layer lens 130, the dispersion coefficient of the second lens 120 can be set to be much larger than that of the adhesive layer lens 130, and the dispersion coefficient of the first lens 110 can be set to be greater than or equal to that of the second lens 120.

[0086] In some examples, referring to Figure 3, the refractive index of the first lens 110 is greater than that of the adhesive layer lens 130, and the refractive index of the first lens 110 is greater than that of the second lens 120. By setting the first lens 110, the second lens 120, and the adhesive layer lens 130 to different refractive indices, the deflection angles of light rays of different wavelengths (e.g., red light, blue light) can be changed after the dispersion of white light, and the light rays of different wavelengths can be focused after they exit the lens assembly 100, thereby correcting chromatic aberration.

[0087] For example, referring to Figure 3, the refractive index of the first lens 110 can be set to be greater than that of the adhesive layer lens 130, while the refractive index of the second lens 120 can be set to a value relatively close to that of the adhesive layer lens 130, which is advantageous for correcting chromatic aberration.

[0088] In some examples, referring to Figure 3, the dispersion coefficient of the first lens 110 is smaller than that of the adhesive layer lens 130, and the dispersion coefficient of the first lens 110 is smaller than that of the second lens 120. By setting the first lens 110, the second lens 120, and the adhesive layer lens 130 to have different dispersion coefficients, the deflection angles of light rays of different wavelengths (e.g., red light, blue light) can be changed after the dispersion of white light, and the light rays of different wavelengths can be focused after they exit the lens assembly 100, thereby correcting chromatic aberration.

[0089] For example, referring to Figure 3, the dispersion coefficient of the first lens 110 can be set to be much smaller than that of the adhesive layer lens 130, while the dispersion coefficient of the second lens 120 can be set to a value relatively close to that of the adhesive layer lens 130, which is advantageous for correcting chromatic aberration.

[0090] For example, referring to Figure 1 or Figure 3, the dispersion coefficient of the first lens 110 may be 50 to 60. For example, the dispersion coefficient of the first lens may be 54 to 56. For example, the dispersion coefficient of the adhesive layer lens 130 may be 30 to 40. For example, the dispersion coefficient of the adhesive layer lens may be 34 to 36. For example, the dispersion coefficient of the second lens may be 50 to 60. For example, the dispersion coefficient of the second lens may be 55 to 57. For example, the dispersion coefficient of the second lens may be 56.5.

[0091] For example, referring to Figure 1 or Figure 3, the refractive index of the first lens 110 may be 1.4 to 1.5. For example, the refractive index of the first lens may be 1.41 to 1.49. For example, the refractive index of the first lens may be 1.42 to 1.48. For example, the refractive index of the first lens may be 1.45. For example, the refractive index of the second lens 120 may be 1.5 to 1.6. For example, the refractive index of the second lens may be 1.54 to 1.56. For example, the refractive index of the first lens may be 1.49 and the refractive index of the second lens may be 1.54. For example, the refractive index of the adhesive layer lens may be 1.5 to 1.6. For example, the refractive index of the adhesive layer lens may be 1.53 to 1.57.

[0092] For example, referring to Figure 1 or Figure 3, after the light ray exits the second lens 120, the refractive index of the external air may be 1.52 and the dispersion coefficient may be 64.

[0093] In some examples, referring to Figure 1 or Figure 3, the ratio of the center thickness to the edge thickness of the first lens 110 is set to the third ratio, and the ratio of the center thickness to the edge thickness of the second lens 120 is set to the fourth ratio, with at least one of the third and fourth ratios being greater than 1 and less than 3. For example, the ratio of the center thickness to the edge thickness of the first lens may be 1 to 3. For example, the ratio of the center thickness to the edge thickness of the first lens may be 2 to 2.5. For example, the ratio of the center thickness to the edge thickness of the second lens 120 may be 1 to 3. For example, the ratio of the center thickness to the edge thickness of the second lens may be 2 to 2.5. Setting the ratio relationship between the center thickness and edge thickness of each lens as described above is advantageous in ensuring injection molding of each lens.

[0094] In some examples, the first surface may be a plane. For example, referring to Figure 1, the second surface 102 can be set as a convex surface, thereby making the first lens 110 a convex lens and the adhesive layer lens 130 a concave lens, thereby correcting chromatic aberration. For example, referring to Figure 3, the second surface 102 can be set as a concave surface, thereby making the first lens 110 a concave lens and the adhesive layer lens 130 a convex lens, thereby correcting chromatic aberration.

[0095] Figure 5 shows an optical system according to an example of at least one embodiment of the present disclosure.

[0096] The difference between the optical system shown in Figure 5 and the optical system shown in Figure 1 is that the first surface 101 of the optical system shown in Figure 5 is different from the first surface 101 of the optical system shown in Figure 1. Of course, there may be other differences between the optical system shown in Figure 5 and the optical system shown in Figure 1, for example, the number of lenses may differ, and this disclosure is not limited thereto. For example, the number of lenses in the optical system shown in Figure 5 may be different from or the same as the number of lenses in the optical system shown in Figure 1. The semi-transparent reflective film 200, polarizing reflective layer 300, phase delay film 400, and linear polarizing film 500 of the optical system shown in Figure 5 may have the same characteristics as the semi-transparent reflective film 200, polarizing reflective layer 300, phase delay film 400, and linear polarizing film 500 of the optical system shown in Figure 1, and will not be described again here.

[0097] In some examples, as shown in Figure 5, the first surface 101 may be convex. For example, the second surface 102 can be set as convex, thereby making the first lens 110 a convex lens and the adhesive layer lens 130 a concave lens, thereby correcting chromatic aberration.

[0098] For example, the first surface 101 may be an aspherical surface, which can be represented by the following numerical formula, for example.

[0099]

number

[0100] For example, in the above equation, the height of the aspherical surface in the direction perpendicular to the optical axis OA is Y, the distance from the vertex of the aspherical surface to the projection of the point on the aspherical surface at height Y along the optical axis OA is z, that is, z is the coordinate in the direction of the optical axis OA, C is the curvature (reciprocal of the radius of curvature R), k is the conic constant, and α i is the coefficient of each higher-order term, and 2i is the order of aspherical coefficients.

[0101] When actually optimizing the rational settings 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 the optimization parameters that can correct the aberrations of each lens in the lens assembly are obtained through optical simulation calculations. Through the optimization process, preferred values ​​for the radius of curvature, thickness along the optical axis OA, effective aperture, and conicity coefficient of each lens in the lens assembly are obtained.

[0102] Referring to Figure 5, the ratio of the radius of curvature of the first surface 101 to the effective focal length of the optical system may be -40 to -50, and the conicity coefficient of the first surface 101 may be -10 to 0. For example, the ratio of the radius of curvature of the first surface to the effective focal length of the optical system may be -42 to -48. For example, the ratio of the radius of curvature of the first surface to the effective focal length of the optical system may be -44 to -46. For example, the ratio of the radius of curvature of the first surface to the effective focal length of the optical system may be -45. For example, the conicity coefficient of the first surface may be -9 to -0.5. For example, the conicity coefficient of the first surface may be -8 to -2. For example, the conicity coefficient of the first surface may be -6 to -4. For example, the conicity coefficient of the first surface may be -5.

[0103] Of course, in some other examples, the first surface can be set as a concave surface, and by changing the surface shape parameters of the second surface, the first lens can be made a convex or concave lens, and correspondingly the adhesive layer lens can be made a concave or convex lens. The disclosure is not limited to the fact that the refractive power of the first lens and the refractive power of the adhesive layer lens can be set to be positive or negative relative to each other by setting the surface shape parameters of each surface.

[0104] In some examples, with reference to Figures 1, 3, and 5, the second surface 102 is a curved Fresnel surface. For example, the second surface 102 may be a convex Fresnel surface (see Figures 1 and 5) or a concave Fresnel surface (see Figure 3), and the disclosure is not limited thereto.

[0105] In some examples, referring to Figure 1 or Figure 5, the second surface 102 is convex, and the central thickness of the adhesive layer lens 130 is smaller than the edge thickness. When the second surface 102 is set as convex, the adhesive layer lens 130 can be formed as a concave lens by setting the central thickness of the adhesive layer lens 130 to be smaller than the edge thickness, thereby correcting chromatic aberration in combination with the convex first lens 110.

[0106] In some examples, referring to Figure 1 or Figure 5, the second surface 102 is convex, and the absolute value of the radius of curvature of the second surface 102 is smaller than the absolute value of the radius of curvature of the third surface 103. This results in a smaller curvature of the third surface 103 but a larger curvature of the second surface 102, thereby forming a concave lens in which the adhesive layer lens 130, which is sufficiently filled between the second surface 102 and the third surface 103, is thinner in the middle but thicker at the edges.

[0107] The surface shape of a curved Fresnel surface may be approximated by the surface shape of an aspherical surface, for example, by referring to the aspherical surface shape formula described above. In some examples, referring to Figure 1 or Figure 5, the second surface 102 is convex, and the ratio of the radius of curvature of the second surface 102 to the effective focal length of the optical system may be -0.5 to -2. 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 second surface 102 of the Fresnel surface can be approximated by a smooth and toothless spherical or aspherical 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 can be assumed to be infinitesimally small. 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 -1 to -1.4. 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 -1.25.

[0108] In some examples, referring to Figure 3, the second surface 102 is concave, and the central thickness of the adhesive layer lens 130 is greater than the edge thickness. When the second surface 102 is set as concave, the adhesive layer lens 130 can be formed as a convex lens by setting the central thickness of the adhesive layer lens 130 to be greater than the edge thickness, thereby correcting chromatic aberration when combined with the first lens 110 which has concave lens characteristics.

[0109] Figure 6 shows an optical system according to an example of at least one embodiment of the present disclosure.

[0110] The difference between the optical system shown in Figure 6 and the optical system shown in Figure 1 is that the second surface 102, adhesive layer lens 130, and third surface 103 of the optical system shown in Figure 6 are different from the second surface 102, adhesive layer lens 130, and third surface 103 of the optical system shown in Figure 1. Of course, there may be other differences between the optical system shown in Figure 6 and the optical system shown in Figure 1, for example, the number of lenses may differ, and this disclosure is not limited thereto. For example, the number of lenses in the optical system shown in Figure 6 may be different from or the same as the number of lenses in the optical system shown in Figure 1. The semi-transparent reflective film 200, polarizing reflective layer 300, phase delay film 400, and linear polarizing film 500 of the optical system shown in Figure 6 may have the same characteristics as the semi-transparent reflective film 200, polarizing reflective layer 300, phase delay film 400, and linear polarizing film 500 of the optical system shown in Figure 1, and will not be described again here.

[0111] In some examples, referring to Figure 6, the second surface 102 is a planar Fresnel surface. For example, by setting the second surface 102 as a planar Fresnel surface and the third surface 103 as a convex surface, the adhesive layer lens 130 between the second surface 102 and the third surface 103 can be made a concave lens, thereby correcting chromatic aberration. For example, a phase delay film 400 can be attached to one side of the third surface 103 away from the fourth surface 104, and setting the third surface 103 as a convex surface is further advantageous for attaching the phase delay film 400 and reduces the possibility of adhesion wrinkles. For example, the second surface can be set as a convex Fresnel surface and the third surface can be set as a convex surface, thereby making the adhesive layer lens a concave lens, and this disclosure is not limited thereto.

[0112] For example, a curved Fresnel surface with a curved base can be obtained by discretizing a continuous curved surface and then superimposing the discretized spherical or aspherical curvature (see, for example, Figures 1, 3, and 5). For example, a planar Fresnel surface with a planar base can be obtained by discretizing a continuous curved surface (see, for example, Figure 6). This allows the radius of curvature of the Fresnel surface in an optical system to have a large adjustment range, thereby enabling better deflection and focus of dispersed light rays. Furthermore, the adjustable inclination of the Fresnel surface not only enhances the deflection capability of the second surface for light rays, enabling ultra-short focal length capabilities, but also improves the correction effect against chromatic aberration and enhances resolution.

[0113] For example, by comprehensively considering the light deflection conditions in the optical system and the surface shape parameters of each surface in the lens assembly, parameters such as the draft angle, tooth width, and tooth height of the Fresnel surface can be obtained. This allows for the design of the Fresnel surface shape to reduce stray light that may occur on the back surface of the Fresnel surface, thereby improving the visual effect.

[0114] Referring to Figures 1, 3, and 5, in some examples, the third surface 103 may be concave, the ratio of the radius of curvature of the third surface 103 to the effective focal length of the optical system may be -3 to -4, and the conicity coefficient of the third surface 103 may be -10 to -1. For example, the ratio of the radius of curvature of the third surface 103 to the effective focal length of the optical system may be -3.2 to -3.9. For example, the ratio of the radius of curvature of the third surface 103 to the effective focal length of the optical system may be -3.4 to -3.6. For example, the ratio of the radius of curvature of the third surface 103 to the effective focal length of the optical system may be -3.5. For example, the conicity coefficient of the third surface 103 may be -8 to -2. For example, the conicity coefficient of the third surface 103 may be -6 to -4. For example, the conicity coefficient of the third surface 103 may be -5.

[0115] Figure 7 shows an optical system according to an example of at least one embodiment of the present disclosure.

[0116] The difference between the optical system shown in Figure 7 and the optical system shown in Figure 1 is that the adhesive layer lens 130 and third surface 103 of the optical system shown in Figure 7 are different from the adhesive layer lens 130 and third surface 103 of the optical system shown in Figure 1. Of course, there may be other differences between the optical system shown in Figure 7 and the optical system shown in Figure 1, for example, the number of lenses may differ, and this disclosure 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 1. The semi-transparent reflective film 200, polarizing reflective film 300, phase delay film 400, and linear polarizing film 500 of the optical system shown in Figure 7 may have the same characteristics as the semi-transparent reflective film 200, polarizing reflective film 300, phase delay film 400, and linear polarizing film 500 of the optical system shown in Figure 1, and will not be described again here.

[0117] In some examples, as shown in Figure 7, the third surface 103 may be a plane. If the third surface 103 is a plane, the second surface 102 can be set as a convex surface, thereby making the adhesive layer lens 130 between the second surface 102 and the third surface 103 a concave lens. This allows the concave adhesive layer lens 130 to correct chromatic aberration in combination with the convex first lens 110.

[0118] Referring to Figures 1, 3, and 5-7, in some examples, the fourth surface 104 is convex, the ratio of the radius of curvature of the fourth surface 104 to the effective focal length of the optical system may be -2 to -3, and the conicity coefficient of the fourth surface 104 may be -10 to -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 -2.2 to -2.8. 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 -2.4 to -2.6. 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 -2.5. 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 -6 to -3. For example, the conicity coefficient of the fourth surface 104 may be -5.

[0119] Referring to the above example, for instance, the higher-order term coefficients of the first surface 101 are α4 = 6.0E-06, α6 = 6.1E-08, α8 = -5.2E-10, α 10 = 1.3E-12, α 12 = 8.2E-16, α 14 = -7.6E-18. For example, the higher-order term coefficients of the second surface 102 are α4 = -1.9E-05, α6 = 8.0E-08, α8 = 1.7E-10, α 10 = -4.6E-13, α 12 = -3.93E-15. For example, the higher-order term coefficients of the third surface 103 are α4 = 7.5E-06, α6 = 4.8E-08, α8 = -2.9E-10, α 10 = -1.6E-12, α 12 = 2.2E-14, α 14 = -9.8E-17. For example, the higher-order term coefficients of the fourth surface 104 are α4 = -5.5E-06, α6 = 1.8E-09, α8 = 7.7E-11, α 10 = -5.9E-13, α 12 = 2.4E-15, α 14 = -6.4E-18.

[0120] FIG. 8 is an optical system according to an example of at least one embodiment of the present disclosure.

[0121] The difference between the optical system shown in FIG. 8 and the optical system shown in FIG. 1 is that the number of lenses in the optical system shown in FIG. 8 is different from the number of lenses in the optical system shown in FIG. 1. Of course, there may be further differences between the optical system shown in FIG. 8 and the optical system shown in FIG. 1. For example, the surface shape of each surface, the refractive power of the adhesive layer lens 130, etc. are different, and the present disclosure does not limit this. For example, the surface shape parameters of each surface shape of the optical system shown in FIG. 8 may be different from or the same as the surface shape parameters of each surface shape of the optical system shown in FIG. 1. The semi-transmissive reflection film 200, the polarization reflection layer 300, the phase retardation film 400, and the linear polarization film 500 of the optical system shown in FIG. 8 may have the same characteristics as the semi-transmissive reflection film 200, the polarization reflection layer 300, the phase retardation film 400, and the linear polarization film 500 of the optical system shown in FIG. 1, and will not be described repeatedly here.

[0122] In some examples, referring to Figure 8, at least two lenses include a first lens 110, a second lens 120, and a third lens 140 arranged sequentially along the optical axis OA. For example, an adhesive layer lens 130 is located between the first lens 110 and the second lens 120. For example, a lens assembly 100 may consist of a first lens 110, a second lens 120, and a third lens 140. The first lens 110 includes a first surface 101 and a second surface 102, the second lens 120 includes a third surface 103, the third lens 140 includes a fourth surface 104, the second lens 120 further includes a fifth surface 105 opposite to the third surface 103, and the third lens 140 further includes a sixth surface 106 located between the fifth surface 105 and the fourth surface 104. For example, the third surface 103 and the fifth surface 105 are two opposite surfaces of the second lens 120 in the optical axis OA. For example, the fourth surface 104 and the sixth surface 106 are two surfaces opposite each other in the optical axis OA of the third lens 140. The surface shapes of the fifth surface 105 and the sixth surface 106 are identical, thereby bonding the second lens 120 and the third lens 140 together.

[0123] By installing the second lens 120 and the third lens 140, more film layer attachment positions can be provided. For example, the phase delay film 400 can be installed between the fifth surface 105 and the sixth surface 106.

[0124] As shown in Figure 8, one of the refractive powers of the first lens 110 and the adhesive layer lens 130 is positive, and the other is negative. For example, the refractive power of the first lens 110 may be positive, i.e., the first lens 110 is a convex lens, and the refractive power of the adhesive layer lens 130 may be negative, i.e., the adhesive layer lens 130 is a concave lens. This allows chromatic aberration to be corrected jointly by the first lens 110 and the adhesive layer lens 130.

[0125] As shown in Figure 8, the dispersion coefficient of at least one of the first lens 110 and the second lens 120 is different from the dispersion coefficient of the adhesive layer lens 130. For example, the dispersion coefficients of the first lens 110 and the adhesive layer lens 130 may be different. For example, the dispersion coefficients of the second lens 120 and the adhesive layer lens 130 may be different. This allows chromatic aberration to be corrected by different dispersion coefficients. For example, the refractive index of at least one of the first lens 110 and the second lens 120 may be different from the refractive index of the adhesive layer lens 130, thereby correcting chromatic aberration by different refractive indices.

[0126] Figure 9 shows an optical system according to an example of at least one embodiment of the present disclosure.

[0127] The difference between the optical system shown in Figure 9 and the optical system shown in Figure 8 is that the fifth surface 105 and the sixth surface 106 of the optical system shown in Figure 9 are different from the fifth surface 105 and the sixth surface 106 of the optical system shown in Figure 8. Of course, there may be other differences between the optical system shown in Figure 9 and the optical system shown in Figure 8, for example, the surface shape of each surface, the refractive power of the adhesive layer lens 130, etc., and this disclosure is not limited thereto. For example, the surface shape parameters of each surface shape of the optical system shown in Figure 9 may be different from or the same as the surface shape parameters of each surface shape of the optical system shown in Figure 8. The semi-transparent reflective film 200, polarizing reflective layer 300, phase delay film 400, and linear polarizing film 500 of the optical system shown in Figure 9 may have the same characteristics as the semi-transparent reflective film 200, polarizing reflective layer 300, phase delay film 400, and linear polarizing film 500 of the optical system shown in Figure 8, and will not be described again here.

[0128] For example, referring to Figure 8, both the fifth surface 105 and the sixth surface 106 may be flat. For example, referring to Figure 9, both the fifth surface 105 and the sixth surface 106 may be curved. For example, both the fifth surface 105 and the sixth surface 106 may be convex. For example, both the fifth surface 105 and the sixth surface 106 are curved to one side away from the third surface 103, thereby reducing the difference between the center thickness and edge thickness of the second lens 120, and reducing the difference between the center thickness and edge thickness of the third lens 140, thereby reducing the difficulty of processing.

[0129] Figure 10 shows a display device according to an example of at least one embodiment of the present disclosure.

[0130] As shown in Figure 10, at least one embodiment of the present disclosure provides a display device including the optical system of any of the embodiments described above. For example, the display device further includes a display screen 10, which is located on one side of the fourth surface 104 away from the first surface 101. Since the display devices according to embodiments of the present disclosure include at least one of the optical systems described above, they have corresponding beneficial technical effects which will not be repeated here. To make it clear, the display screen 10 shown in Figure 10 can be combined with the optical systems of Figures 1, 3, 5 to 9 to form different display devices. For example, the display surface of the display screen 10 is located on the light-receiving focal plane of the optical system.

[0131] For example, referring to Figures 1 to 10, the ratio of the total optical length (TTL) of the optical system to the effective focal length may be 0.85 to 1. For example, the ratio of the total optical length to the effective focal length of the optical system may be 0.9 to 0.95. The total optical length refers to the distance from the highest point of the first surface 101 of the lens assembly 100 in the optical system to the center of the display screen 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.

[0132] For example, referring to Figures 1 to 10, the field of view of the optical system may be greater than 90°. For example, the field of view is the total 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 achieve a field of view of 100°, the weight of the binocular lenses is less than 20g.

[0133] For example, referring to Figures 1 to 10, the exit pupil distance (EPD) of the optical system may be 12 to 20 millimeters. For example, the exit pupil distance is the distance from the vertex of the last face of the optical system to the intersection of the exit pupil plane and the optical axis. For example, the exit pupil distance may be 14 to 18 millimeters. For example, the exit pupil distance may be 15 millimeters. The optical system according to this disclosure has a large exit pupil distance and can satisfy the needs of myopic users who wear glasses.

[0134] For example, referring to Figures 1 to 10, the ratio of the effective aperture to the effective focal length of the lens assembly 100 may be 2.3 to 2.7. The effective aperture of the above lens assembly refers to the effective light-passage aperture, which is, for example, the maximum aperture through which light rays can pass through the lens assembly, and this aperture is determined by the maximum light flux of the lens assembly. For example, the ratio of the effective aperture to the effective focal length may be 2.4 to 2.6. For example, the ratio of the effective aperture to the effective focal length may be 2.5.

[0135] For example, referring to Figures 1 to 10, the ratio of the distance between the aperture of the optical system (e.g., 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 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 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 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 at the optical axis OA to the effective focal length is 1.1.

[0136] For example, referring to Figures 1 to 10, the effective aperture of the diaphragm is 4 millimeters. For example, the ratio of the distance between the object surface of the optical system and the diaphragm at the optical axis OA to the effective focal length is -80 or less.

[0137] For example, referring to Figures 1 to 10, the ratio of the distance between the display surface and the image plane of the display screen 10 at 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 and the image plane of the display screen 10 at 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 and the image plane of the display screen 10 at the optical axis OA to the effective focal length is 0.08.

[0138] For example, referring to Figures 1 to 10, the ratio of the distance between the fourth surface 104 and the display surface of the display screen 10 at 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 of the display screen 10 at 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 of the display screen 10 at the optical axis OA to the effective focal length is 0.1.

[0139] For example, the display screen 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, or a projector (e.g., an LCOS microprojector).

[0140] For example, the display screen is a liquid crystal display screen, with a pixel size of approximately 20-something microns. For example, the display screen is an organic light-emitting diode display screen, with a pixel size of approximately several microns.

[0141] 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.

[0142] 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., and the embodiments of this disclosure are not limited thereto.

[0143] The following points need to be explained.

[0144] (1) In the drawings of embodiments of the present disclosure, only structures relevant to embodiments of the present disclosure are shown, and other structures may refer to conventional designs.

[0145] (2) Where there is no inconsistency, features in the same embodiment and different embodiment of the present disclosure can be combined with each other.

[0146] The foregoing are merely exemplary embodiments of the present disclosure and are not intended to limit the scope of protection of the present disclosure, which is determined by the appended claims.

Claims

1. An optical system, A lens assembly comprising at least two lenses, wherein the at least two lenses comprise a first surface, a second surface, a third surface, and a fourth surface arranged sequentially along the direction of the optical axis of the lens assembly, A semi-transparent reflective film is installed on one side of the fourth surface that is away from the third surface, A polarization reflective layer is installed on one side of the third surface that is away from the fourth surface, A phase delay film located on one side of the fourth surface, away from the semi-transparent reflective film, The adhesive layer includes an adhesive layer containing an adhesive layer lens, An optical system in which at least one of the first and second surfaces is a Fresnel surface, and the adhesive layer is bonded between the second and third surfaces.

2. The distance between the two intersection points where the first and second surfaces intersect with the optical axis is defined as the first distance. The optical system according to claim 1, wherein the ratio of the central thickness of the adhesive layer lens to the first distance is 1 / 6 to 2.

3. The optical system according to claim 1 or 2, wherein the central thickness of the adhesive layer lens is 0.5 mm to 3 mm.

4. The at least two lenses include a first lens and a second lens arranged along the direction of 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 3, wherein one of the refractive power of the first lens and the refractive power of the adhesive layer lens is a positive value and the other is a negative value.

5. The ratio of the refractive power of the first lens to the dispersion coefficient of the first lens is defined as the first ratio, and the ratio of the refractive power of the adhesive layer lens to the dispersion coefficient of the adhesive layer lens is defined as the second ratio. The optical system according to claim 4, wherein the sum of the first ratio and the second ratio is less than 0.

6. The optical system according to claim 4 or 5, wherein the refractive index of the first lens is smaller than the refractive index of the adhesive layer lens, the refractive index of the second lens is smaller than the refractive index of the adhesive layer lens, and the refractive index of the first lens is less than or equal to the refractive index of the second lens.

7. The optical system according to any one of claims 4 to 6, wherein the dispersion coefficient of the first lens is greater than the dispersion coefficient of the adhesive layer lens, the dispersion coefficient of the second lens is greater than the dispersion coefficient of the adhesive layer lens, and the dispersion coefficient of the first lens is greater than or equal to the dispersion coefficient of the second lens.

8. The optical system according to claim 4, wherein the refractive index of the first lens is greater than the refractive index of the adhesive layer lens, and the refractive index of the first lens is greater than the refractive index of the second lens.

9. The optical system according to claim 4, wherein the dispersion coefficient of the first lens is smaller than the dispersion coefficient of the adhesive layer lens, and the dispersion coefficient of the first lens is smaller than the dispersion coefficient of the second lens.

10. The ratio of the center thickness to the edge thickness of the first lens is set to the third ratio, and the ratio of the center thickness to the edge thickness of the second lens is set to the fourth ratio. The optical system according to any one of claims 4 to 9, wherein at least one of the third ratio and the fourth ratio is greater than 1 and less than 3.

11. The optical system according to any one of claims 1 to 10, wherein the second surface is a planar Fresnel surface or a curved Fresnel surface.

12. The optical system according to claim 11, wherein the second surface is convex, and the central thickness of the adhesive layer lens is smaller than the edge thickness.

13. The optical system according to claim 11, wherein the second surface is convex, and the absolute value of the radius of curvature of the second surface is smaller than the absolute value of the radius of curvature of the third surface.

14. The optical system according to claim 11, wherein the second surface is convex, and the ratio of the radius of curvature of the second surface to the effective focal length of the optical system is -0.5 to -2.

15. The optical system according to claim 11, wherein the second surface is concave, and the central thickness of the adhesive layer lens is greater than the edge thickness.

16. The distance between the two intersection points where the first and second surfaces intersect with the optical axis is defined as the first distance. The distance between the two intersection points where the third and fourth surfaces intersect with the optical axis is defined as the second distance. The optical system according to any one of claims 1 to 15, wherein the ratio of the second distance to the first distance is 2 to 4.

17. The optical system according to claim 16, wherein the ratio of the first distance to the effective focal length of the optical system is 0.1 to 0.3, and the ratio of the second distance to the effective focal length of the optical system is 0.5 to 0.

7.

18. The first surface is a plane, or The optical system according to any one of claims 1 to 17, wherein the first surface is convex, the ratio of the radius of curvature of the first surface to the effective focal length of the optical system is -40 to -50, and the conicity coefficient of the first surface is -10 to 0.

19. The third surface is a plane, or The optical system according to any one of claims 1 to 18, wherein the third surface is concave, the ratio of the radius of curvature of the third surface to the effective focal length of the optical system is -3 to -4, and the conicity coefficient of the third surface is -10 to -1.

20. The optical system according to any one of claims 1 to 19, wherein the fourth surface is convex, the ratio of the radius of curvature of the fourth surface to the effective focal length of the optical system is -2 to -3, and the conicity coefficient of the fourth surface is -10 to -1.

21. The at least two lenses include a first lens, a second lens, and a third lens arranged in order along the direction of the optical axis. 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 further includes a fifth surface opposite to the third surface, and the third lens further includes a sixth surface located between the fifth surface and the fourth surface, wherein the surface shapes of the fifth surface and the sixth surface are identical. The optical system according to any one of claims 1 to 3, wherein one of the refractive power of the first lens and the refractive power of the adhesive layer lens is a positive value and the other is a negative value.

22. The at least two lenses include a first lens, a second lens, and a third lens arranged in order along the direction of the optical axis. 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 further includes a fifth surface opposite to the third surface, and the third lens further includes a sixth surface located between the fifth surface and the fourth surface, wherein the surface shapes of the fifth surface and the sixth surface are identical. The optical system according to any one of claims 1 to 3, wherein the dispersion coefficient of at least one of the first lens and the second lens is different from the dispersion coefficient of the adhesive layer lens.

23. A display device comprising the optical system according to any one of claims 1 to 22.

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