Optical system and display device

Abstract

The invention discloses an optical system and a display device. The optical system comprises a lens assembly, a polarization reflection layer, a transflective film and a phase delay film. The lens assembly comprises at least two lenses, and the at least two lenses comprise a first surface, a second surface, a third surface and a fourth surface which are sequentially arranged in the optical axis direction of the lens assembly. The polarization reflection layer is arranged on the side, away from the fourth surface, of the first surface, the transflective film is arranged on the side, away from the third surface, of the fourth surface, and the phase delay film is arranged on the side, facing the first surface, of the transflective film. The second surface and the third surface are Fresnel surfaces, and the surface types of the second surface and the third surface are complementary. The at least two lenses comprise lenses with at least one different dispersion coefficient and refractive index. The second surface and the third surface are set as the Fresnel surfaces, and at least one of the dispersion coefficients and the refractive indexes of the at least two lenses is set to be different, so that the Fresnel surfaces are matched with the at least two lenses to correct chromatic aberration.

Description

Technical Field

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

[0002] Head Mounted Display (HMD) is a simulation technology that uses a head-mounted display optical system to image a digital image generated by a computer or output by an image source into the user's field of view, so as to reproduce a specific environment. Summary of the Invention

[0003] At least one embodiment of the present disclosure provides an optical system, which includes: a lens assembly including at least two lenses, the at least two lenses including a first surface, a second surface, a third surface, and a fourth surface arranged in sequence along the optical axis direction of the lens assembly; a polarization reflection layer disposed on a side of the first surface away from the fourth surface; a transmissive-reflective film disposed on a side of the fourth surface away from the third surface; a phase retardation film disposed on a side of the transmissive-reflective film facing the first surface; wherein, the first surface is a concave surface, and the fourth surface is a convex surface; the second surface and the third surface are both Fresnel surfaces, and the surface profiles of the second surface and the third surface are complementary; the at least two lenses include lenses with at least one of different dispersion coefficients and refractive indices.

[0004] For example, according to at least one embodiment of the present disclosure, the ratio of the radius of curvature of the second surface to the effective focal length of the optical system is -6 to 2.

[0005] For example, according to at least one embodiment of the present disclosure, the tooth width of the second surface includes 0.3 mm to 1 mm.

[0006] 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.

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

[0008] For example, according to at least one embodiment of the present disclosure, the dispersion coefficient of the first lens is 25 to 65, and the dispersion coefficient of the second lens is 30 to 54.

[0009] For example, according to at least one embodiment of the present disclosure, the at least two lenses include a first lens and a second lens arranged along the optical axis direction, the first lens includes the first surface and the second surface, and the second lens includes the third surface and the fourth surface; wherein, the refractive index of the first lens is less than the refractive index of the second lens.

[0010] For example, according to at least one embodiment of the present disclosure, the ratio of the radius of curvature of the first surface to the radius of curvature of the fourth surface is 1.2 to 1.7.

[0011] For example, according to at least one embodiment of the present disclosure, the ratio of the radius of curvature of the first surface to the effective focal length of the optical system is -3.5 to -1.5, and the conic constant of the first surface is -10 to -0.5.

[0012] For example, according to at least one embodiment of the present disclosure, the ratio of the radius of curvature of the fourth surface to the effective focal length of the optical system is -2.0 to 2.0, and the conic constant of the fourth surface is -10 to -0.1.

[0013] For example, according to at least one embodiment of the present disclosure, the distance between the two intersection points of the first surface and the second surface intersecting the optical axis is a first distance; the distance between the two intersection points of the third surface and the fourth surface intersecting the optical axis is a second distance; the ratio of the first distance to the second distance is 2 to 4.

[0014] 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 0.3 to 0.5, and the ratio of the second distance to the effective focal length of the optical system is 0.1 to 0.3.

[0015] For example, according to at least one embodiment of the present disclosure, the at least two lenses include a first lens and a second lens arranged along the optical axis direction, the first lens includes the first surface and the second surface, and the second lens includes the third surface and the fourth surface; the ratio of the central thickness to the edge thickness of the first lens is greater than 1 and less than 3; the ratio of the central thickness to the edge thickness of the second lens is greater than 0.5 and less than 2.

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

[0017] For example, according to at least one embodiment of the present disclosure, the ratio of the radius of curvature of the fifth surface to the radius of curvature of the second surface is 0.9 to 1.1. Both the fifth surface and the sixth surface are Fresnel surfaces, and the surface profiles of the fifth surface and the sixth surface are complementary.

[0018] For example, according to at least one embodiment of the present disclosure, the fifth surface is a planar Fresnel surface or a curved Fresnel surface.

[0019] At least one embodiment of the present disclosure provides a display device, including a display screen and the optical system described in any of the above embodiments. Among them, the display screen is located on the side of the transmissive-reflective film away from the polarization reflection layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present disclosure and do not limit the present disclosure.

[0021] Figure 1 It is a schematic diagram of an optical system provided by an example in at least one embodiment of the present disclosure.

[0022] Figure 2A and Figure 2B It is a schematic diagram of the light ray deflection in an example in at least one embodiment of the present disclosure.

[0023] Figure 2C It is a schematic diagram of the light ray deflection in another example in at least one embodiment of the present disclosure.

[0024] Figure 3 It is a schematic diagram of the optical path of a display device provided by an example in at least one embodiment of the present disclosure.

[0025] Figure 4 It is a schematic diagram of an optical system provided by an example in at least one embodiment of the present disclosure.

[0026] Figure 5A For Figure 1Spot diagram of the optical system shown.

[0027] Figure 5B is Figure 1 Graph showing the variation of the blur spot size of the optical system shown with the field angle.

[0028] Figure 5C is Figure 1 Distortion diagram of the optical system shown.

[0029] Figure 5D is the lateral chromatic aberration diagram of an optical system.

[0030] Figure 5E is Figure 1 Lateral chromatic aberration diagram of the optical system shown.

[0031] Figure 6 Schematic diagram of the optical system provided by an example in at least one embodiment of the present disclosure.

[0032] Figure 7 Schematic diagram of the optical system provided by an example in at least one embodiment of the present disclosure. Detailed implementation manners

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present disclosure clearer, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present disclosure. Apparently, the described embodiments are some but not all of the embodiments of the present disclosure. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present disclosure without creative efforts shall fall within the scope of protection of the present disclosure.

[0034] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure shall have the ordinary meanings understood by those of ordinary skill in the art to which the present disclosure pertains. The "first", "second", and similar terms used in the present disclosure do not denote any order, quantity, or importance, but are only used to distinguish different components. The terms such as "including" or "comprising" mean that the elements or items appearing before this term cover the elements or items listed after this term and their equivalents, without excluding other elements or items.

[0035] Features such as "vertical", "parallel", and "identical" used in this disclosure include the strictly defined features of "vertical", "parallel", "identical", etc., as well as cases with certain errors such as "substantially vertical", "substantially parallel", "substantially identical", etc. Considering measurement and errors associated with the measurement of a specific quantity (i.e., limitations of the measurement system), it means within the acceptable deviation range for a specific value determined by a person of ordinary skill in the art. The "center" in the embodiments of this disclosure may include a position strictly located at the geometric center and a position of a substantially center within a small area around the geometric center. For example, "substantially" can mean within one or more standard deviations, or within 10% or 5% of the value.

[0036] The imaging principle of a head-mounted display (also known as a head-mounted device) optical system is similar to that of a magnifying glass. That is, the object (picture source or video source) is located in front of the object-side focal plane of the optical lens (for example, within one focal length), and the human eye on the other side of the optical lens can see that a virtual upright magnified image is formed in the distance on the same side as the object. The head-mounted display optical system includes a single-piece or multi-piece thick lens, a Fresnel lens, a folded optical system (also known as Pancake), and a liquid crystal lens and a meta-lens with variable optical power, etc. With the original intention of focusing on thinning and weight reduction to bring a better wearing experience for users, the head-mounted display optical system still needs to meet the requirements of imaging optical performance. For example, the head-mounted display optical system needs to consider basic indicators such as clarity, field of view, distortion, and chromatic aberration. Many optical indicators need to meet the design requirements in the hardware design stage, meet the accuracy requirements in the optical processing, manufacturing, and assembly stage, and combine with later software (image) processing technologies (such as the fixation point rendering technology for improving clarity, the asymmetric field of view application, anti-distortion image processing, and anti-chromatic aberration image processing for improving the field of view experience), so as to bring a better experience to the users of the head-mounted display optical system.

[0037] In the research, the inventors of this application found that the aforementioned optical indicators are often complementary and also mutually opposed. For example, an optical system with low dispersion or low chromatic aberration and no distortion is conducive to providing better clarity. However, a large field of view brings challenges to clarity, distortion, and dispersion.

[0038] Taking some liquid crystal displays as an example, the size of the liquid crystal display (such as the diagonal length) exceeds 2 inches to 2.3 inches, and the diameter of the optical lens of the head-mounted display optical system is, for example, 30 mm to 50 mm (this diameter size varies with the change of the field of view angle), and the size of the screen is sufficiently adapted to the optical lens. For example, the sizes of the screen and the optical lens are relatively close, the incident angle of the light from the screen reaching the surface of the optical lens is very small, and after the light of different wavelengths passes through refraction and reflection, the deviation of the angle is also relatively small. At the same time, the single-pixel size of the screen is large (for example, the single-pixel size is greater than 20 microns). Therefore, the height difference (axial chromatic aberration) formed by the light of different wavelengths on the image plane has a small impact on the imaging quality.

[0039] In a head-mounted display optical system using a silicon-based organic light-emitting diode (OLED) display screen, due to process limitations, the screen size is usually 1 inch to 1.4 inches. When this screen is matched with an optical lens with a small aperture (such as a diameter of 25 mm), the matching difficulty is relatively small. The small-aperture optical lens corresponds to a small field of view angle. To adapt to a certain wearing error, the field of view finally obtained by the user mostly does not exceed 90°. If the field of view angle is to be increased, the aperture of the optical lens needs to be increased accordingly. When a large-aperture optical lens is adapted to a small-size screen, the inventors found that the incident angle of the light with a large field of view at the edge of the screen on the optical lens is too large, resulting in an increase in the axial chromatic aberration. In addition, since the pixel size of the silicon-based OLED screen is less than 10 microns, the tolerance for axial chromatic aberration is much more stringent than that of the liquid crystal display screen. Therefore, in a large-field-of-view head-mounted display optical system using an inch-level high-definition display, the difficulty of chromatic aberration correction is relatively large.

[0040] At least one embodiment of the present disclosure provides an optical system, which includes a lens assembly, a polarization reflection layer, a transmissive-reflective film, and a phase retardation film. The lens assembly includes at least two lenses, and the at least two lenses include a first surface, a second surface, a third surface, and a fourth surface arranged in sequence along the optical axis direction of the lens assembly. The polarization reflection layer is disposed on a side of the first surface away from the fourth surface. The transmissive-reflective film is disposed on a side of the fourth surface away from the third surface. The phase retardation film is disposed on a side of the transmissive-reflective film facing the first surface. The first surface is a concave surface, and the fourth surface is a convex surface. Both the second surface and the third surface are Fresnel surfaces, and the surface profiles of the second surface and the third surface are complementary. The at least two lenses include lenses with at least one of different dispersion coefficients and refractive indices.

[0041] At least one embodiment of the present disclosure provides a display device, which includes a display screen and the optical system of any one of the above embodiments, and the display screen is located on a side of the transmissive-reflective film away from the polarization reflection layer.

[0042] The optical system and display device provided by at least one embodiment of the present disclosure provide an attachment position for a polarization reflection layer, a transmissive-reflective film, and a phase retardation film by providing a lens assembly including at least two lenses, so as to achieve the refolding of light through the polarization reflection layer and the transmissive-reflective film. At the same time, the second surface and the third surface are set as Fresnel surfaces, and at least two lenses are set to have at least one of different dispersion coefficients and refractive indices, which is beneficial to improving the design freedom through the Fresnel surfaces, thereby correcting chromatic aberration in cooperation with at least two lenses, making the optical system have a larger field of view, higher clarity, and be thinner and lighter.

[0043] The optical system and display device will be described below with reference to the accompanying drawings and through some embodiments.

[0044] Figure 1 The following is a schematic diagram of an optical system provided by an example in at least one embodiment of the present disclosure. Refer to Figure 1 , at least one embodiment of the present disclosure provides an optical system, which includes a lens assembly 100, a polarization reflection layer 200, a transmissive-reflective film 300, and a phase retardation film 400. The lens assembly 100 includes at least two lenses. For example, as Figure 1 shown, the lens assembly 100 may be composed of two lenses, namely, a lens 110 and a lens 120.

[0045] As Figure 1 shown, the at least two lenses include a first surface 101, a second surface 102, a third surface 103, and a fourth surface 104 arranged in sequence along the optical axis OA direction of the lens assembly 100. For example, the side of the first surface 101 away from the fourth surface 104 is the light-emitting side of the optical system. For example, when the optical system is applied to a display device, the display screen is located on the side of the fourth surface 104 of the optical system away from the first surface 101, and the light emitted by the display screen enters from the fourth surface 104 and exits from the first surface 101.

[0046] As Figure 1 shown, the polarization reflection layer 200 is disposed on the side of the first surface 101 away from the fourth surface 104, the transmissive-reflective film 300 is disposed on the side of the fourth surface 104 away from the third surface 103, and the phase retardation film 400 is disposed on the side of the transmissive-reflective film 300 facing the first surface 101. For example, when the optical system is applied to a display device, the display screen is located on the side of the transmissive-reflective film 300 of the optical system away from the polarization reflection layer 200. For example, the light incident on the lens assembly 100 after passing through the transmissive-reflective film 300 is configured to be refolded between the transmissive-reflective film 300 and the polarization reflection layer 200 and exit from the polarization reflection layer 200, thereby forming a folded optical path through the polarization reflection layer 200, the transmissive-reflective film 300, and the phase retardation film 400.

[0047] As Figure 1As shown, at least two lenses include lenses with different dispersion coefficients and / or refractive indices. Since the refractive index of the same transparent medium varies for different wavelengths of light, and white light is composed of various colors of light with different wavelengths, dispersion occurs when white light is refracted by a transparent substance. The dispersion coefficient (also known as the Abbe number) is an index used to represent the dispersion ability of a transparent medium and to measure the degree of light dispersion in the transparent medium. Generally speaking, the greater 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.

[0048] As Figure 1 shown, the first surface 101 is concave, and the fourth surface 104 is convex. For example, the first surface 101 is an aspherical surface. For example, the fourth surface 104 is an aspherical surface. For example, the transmissive-reflective film 300 is disposed on the side of the convex surface away from the concave surface. For example, the polarization reflection layer 200 and the phase retardation film 400 are both disposed on the side of the concave surface away from the convex surface.

[0049] As Figure 1 shown, both the second surface 102 and the third surface 103 are Fresnel surfaces. The Fresnel surface refers to the non-smooth side surface of the two opposite surfaces of a Fresnel lens. The Fresnel lens is also known as a thread lens. One side surface of the Fresnel lens is a smooth surface, and the other side surface of the Fresnel lens is divided into multiple concentric circular patterns (i.e., Fresnel zones). Through these patterns, the degree of bending of light refraction can be changed, enabling the Fresnel lens to effectively reduce the thickness of the lens in the case of a short focal length.

[0050] For example, referring to Figure 1 , the first surface 101 and the second surface 102 are the two surfaces of the lens 110, and the third surface 103 and the fourth surface 104 are the two surfaces of the lens 120. Both the lens 110 and the lens 120 are Fresnel lenses. For example, the lens 110 is a convex lens, and the lens 120 is a concave lens.

[0051] As Figure 1 shown, the surface profiles of the second surface 102 and the third surface 103 are complementary. Complementary means that after the second surface 102 and the third surface 103 are fitted together (or pasted with optical glue), there is basically no gap between the second surface 102 and the third surface 103. For example, the surface profile of the second surface 102 and the surface profile of the third surface 103 are positive and negative shapes of each other. For example, at the corresponding positions of the second surface 102 and the third surface 103, the tooth-shaped structures on the two Fresnel surfaces can complement each other.

[0052] The optical system provided by at least one embodiment of the present disclosure provides an attachment position for the polarization reflection layer 200, the transmissive and reflective film 300, and the phase retardation film 400 by arranging the lens assembly 100 including at least two lenses, so as to realize the refolding of light through the polarization reflection layer 200 and the transmissive and reflective film 300. The second surface 102 and the third surface 103 are set as Fresnel surfaces, and at least two lenses are set to include lenses with at least one of different dispersion coefficients and refractive indices, which is beneficial to improve the design freedom through the Fresnel surfaces, so as to correct chromatic aberration in cooperation with at least two lenses, making the optical system have a larger field of view, higher clarity, and be thinner and lighter.

[0053] Figure 2A and Figure 2B It is a schematic diagram of light deflection in an example of at least one embodiment of the present disclosure. Hereinafter, taking the light incident on the optical system undergoing one refraction as an example, the chromatic aberration correction will be described.

[0054] Figure 2A It shows the situation where light is deflected in the optical system when the lenses L1 and L2 in the lens assembly have different refractive indices and dispersion coefficients. As Figure 2A shown, taking the side far from the target surface S0 as the light incident side, that is, the light enters the lens assembly from the left side of Figure 2A and exits the lens assembly to the target surface S0 after refraction. After white light (such as the solid line shown in Figure 2A ) is incident on the lens assembly, the white light is dispersed and decomposed into monochromatic lights with different wavelengths. Figure 2A The red light R with a longer wavelength is indicated by a dash line, and the blue light B with a shorter wavelength is indicated by a dotted line. By setting the lenses L1 and L2 to have different refractive indices and different dispersion coefficients, the deflection angles of the red light R and the blue light B are changed, and finally the red light R and the blue light B can converge on the target surface S0.

[0055] For example, referring to Figure 2A , the lens L1 is a convex lens, the lens L2 is a concave lens, the dispersion coefficient of the lens L1 is greater than that of the lens L2, and the refractive index of the lens L1 is less than that of the lens L2. After the incident light is dispersed when entering the surface S1, the blue light B with a relatively shorter wavelength is more deflected towards the optical axis OA than the red light R. After being refracted by the surfaces S2 and S3, since the dispersion coefficient of the lens L1 is greater than that of the lens L2, the light deflects away from the optical axis OA after entering the lens L2 from the lens L1, and the blue light B with a relatively shorter wavelength has a greater degree of deflection. Therefore, the red light R and the blue light B gradually approach. After the light exits through the surface S4, the light continues to deflect away from the optical axis OA, and the blue light B with a relatively shorter wavelength has a greater degree of deflection, so that the red light R and the blue light B converge on the target surface S0, thereby achieving the purpose of correcting chromatic aberration.

[0056] Figure 2B The Figure 2A two lenses shown are simplified into two relatively placed optical wedges, and the inclination degree of the contact surface of the two lenses is the slope of this surface. As Figure 2B shown, after white light enters optical wedge 1, dispersion occurs and it is decomposed into monochromatic lights with different wavelengths. Figure 2B The red light R with a longer wavelength is indicated by a dash line, and the blue light B with a shorter wavelength is indicated by a dotted line. After the red light R (dash line) and the blue light B (dotted line) enter optical wedge 2, the deflection degrees of both the red light R and the blue light B change, so that the red light R and the blue light B can converge after exiting onto the target surface S0.

[0057] Figure 2C It is a schematic diagram of the deflection of light rays for another example in at least one embodiment of the present disclosure. Figure 2C Differing from Figure 2B is that the slopes of the surfaces where the two optical wedges are in contact are different.

[0058] Combining Figure 2C and Figure 1 shown, Figure 2C the Figure 1 lenses 110 and 120 shown are simplified into two relatively placed optical wedges. Figure 2C It is shown that in the lens assembly, the two lenses have different refractive indices and dispersion coefficients, and the two surfaces where the two lenses are in contact are mutually positive and negative Fresnel surfaces ( Figure 2C not shown in Figure 1 ), for example, reference can be made to Figure 2C shown, after white light enters optical wedge 1, dispersion occurs and it is decomposed into monochromatic lights with different wavelengths. Figure 2C The red light R with a longer wavelength is indicated by a dash line, and the blue light B with a shorter wavelength is indicated by a dotted line. As Figure 2C shown, since the contact surface of the two optical wedges is a Fresnel surface, compared with a continuous aspherical surface, the slope of the discretizable Fresnel surface is larger, so that the ability to deflect light rays can be improved, enabling the red light R (dash line) and the blue light B (dotted line) to converge on a closer target surface S0', and further making the structure of the optical system more compact. Therefore, referring to Figure 1 , by setting the second surface 102 and the third surface 103 as Fresnel surfaces and setting at least two lenses to have different dispersion coefficients and refractive indices at least one of them, chromatic aberration can be corrected jointly, making the field of view of the optical system larger, the clarity higher and the optical system thinner and lighter.

[0059] For example, referring to Figure 1, the functions of the polarization reflection layer 200 are as follows: There is an optical axis OA direction in the plane of the film layer. The transmittance of the polarization component of the incident light parallel to the optical axis OA direction (such as s-line polarized light) is greater than that of the polarization component perpendicular to the optical axis OA direction (such as p-line polarized light), and the reflectance of the polarization component parallel to the optical axis OA direction (such as s-line polarized light) is less than that of the polarization component perpendicular to the optical axis OA direction (such as p-line polarized light). For example, the transmittance of the polarized light parallel to the optical axis OA direction of the polarization reflection layer 200 is not less than 85%, such as not less than 90%, such as not less than 95%, such as not less than 98%; the reflectance of the polarized light perpendicular to the optical axis OA direction of the polarization reflection layer 200 is not less than 85%, such as not less than 90%, such as not less than 95%, such as not less than 98%.

[0060] For example, referring to Figure 1 , the polarization reflection layer 200 is configured to reflect linearly polarized light of one characteristic and transmit linearly polarized light of another characteristic; the polarization reflection layer 200 is disposed on the side of the first surface 101 away from the fourth surface 104, and the phase retardation film 400 is disposed between the polarization reflection layer 200 and the transmissive-reflective film 300. For example, the polarization reflection layer can also be called a polarization beam splitter film. For example, the polarization reflection layer can also include a multilayer film reflective polarizer (Advanced Polarizer Film, APF). For example, the polarization reflection layer can also include an IQPS (Image Quality Polarizer Standard) film or an IQPE (Image Quality Polarizer Enhanced) film.

[0061] For example, the polarization reflection layer is a cholesteric liquid crystal layer (not shown in the figure), and the phase retardation film is disposed on the side of the cholesteric liquid crystal layer away from the transmissive-reflective film. For example, cholesteric liquid crystals can reflect circularly polarized light and transmit circularly polarized light. Referring to the aforementioned folding optical path principle, the cholesteric liquid crystal layer is disposed between the phase retardation film and the transmissive-reflective film. A wave plate can be disposed on the display surface side of the display screen on the side of the second lens away from the first lens. The image light emitted from the display screen is converted into right-handed circularly polarized light after passing through the wave plate. The right-handed circularly polarized light is incident on the transmissive-reflective film, and the polarization state of the right-handed circularly polarized light remains unchanged after passing through the transmission of the transmissive-reflective film. The right-handed circularly polarized light is reflected back to the transmissive-reflective film after passing through the cholesteric liquid crystal layer, and the first reflection occurs here; the right-handed circularly polarized light is reflected at the transmissive-reflective film, and the second reflection occurs here. Due to the half-wave loss, the reflected light changes from right-handed circularly polarized light to left-handed circularly polarized light. The left-handed circularly polarized light reaches the phase retardation film after passing through the cholesteric liquid crystal layer and is converted into s-polarized light by the phase retardation film, and then the s-line polarized light is transmitted through the linear polarizing film and directed towards the human eye.

[0062] For example, referring to Figure 1, the transmissive-reflective film 300 is configured to transmit part of the light and reflect the other part of the light. For example, the transmittance of the transmissive-reflective film 300 can be 50%, and the reflectance can be 50%. For example, the transmittance of the transmissive-reflective film 300 can be 60%, and the reflectance can be 40%. For example, the transmittance of the transmissive-reflective film 300 can be 65%, and the reflectance can be 35%. The optical system provided by the present disclosure is not limited thereto, and the transmittance and reflectance of the transmissive-reflective film can be set according to product requirements. For example, the transmissive-reflective film 300 can be deposited on the fourth surface 104.

[0063] For example, refer to Figure 1 , the phase retardation film 400 is configured to convert the transmitted light between a circular polarization state and a linear polarization state. For example, the phase retardation film 400 can be a quarter-wave plate. For example, the phase retardation film 400 has the following characteristics: there is a direction with the lowest refractive index and a direction with the highest refractive index in the film plane, which are the fast axis and the slow axis respectively. The phase of the polarized light parallel to the slow axis is delayed by 1 / 4 wavelength after passing through the phase retardation film 400 compared with the polarized light parallel to the fast axis after passing through the phase retardation film 400. For example, the angle between the slow axis of the phase retardation film 400 and the optical axis OA of the polarization reflection layer 200 is 45 degrees.

[0064] For example, refer to Figure 1 , the material of the phase retardation film 400 can include liquid crystal polymer. Since the phase retardation film 400 made of liquid crystal polymer material is a polymer, its film thickness is relatively thinner, which can reach 1μm - 5μm. The thinner phase retardation film 400 has a higher degree of adaptation to the curved surface, can be more easily shaped according to the surface shape of the curved surface, and reduces the possibility of generating wrinkles when fitting with the curved surface, which affects the phase retardation accuracy and optical performance. Moreover, the optical offset of the phase retardation film 400 made of liquid crystal polymer material after being attached to the curved surface is smaller. Liquid crystal polymer is a cross-linked system, and the molecules are connected by chemical bonds, with a higher modulus. When the phase retardation film 400 made of this material is stretched after being attached, only elastic deformation occurs, and strong optical anisotropic effects such as molecular stretching and rearrangement do not occur. Therefore, the phase retardation film 400 made of liquid crystal polymer material is suitable for fitting with the surface shape of a small radius of curvature. Such a degree of freedom of the radius of curvature is also more likely to meet the index requirements such as clarity, distortion, and dispersion, which is beneficial to obtaining better image quality of the optical system.

[0065] Figure 3 is a schematic diagram of the optical path of the display device provided by an example in at least one embodiment of the present disclosure. At least one embodiment of the present disclosure provides a display device, and the display device includes a display screen 10 and an optical system. The display screen 10 is located on the side of the transmissive-reflective film 300 away from the polarization reflection layer 200. For example, refer to Figure 3, the principle of the folded optical path is as follows: A wave plate can be set on the light-emitting side of the display surface 11 of the display screen 10 on the side of the fourth surface 104 away from the first surface 101. The image light emitted from the display surface 11 is converted into right-handed circularly polarized light after passing through the wave plate, and the polarization state remains unchanged after passing through the transmissive-reflective film 300. This light enters the lens assembly 100 and reaches the phase retardation film 400 after passing through the lens assembly 100. The right-handed circularly polarized light incident on the phase retardation film 400 is converted into p-linearly polarized light, and the p-linearly polarized light is reflected back to the phase retardation film 400 by the polarization reflection layer 200, and the first reflection occurs here. Then, the p-linearly polarized light is converted into right-handed circularly polarized light after passing through the phase retardation film 400. This right-handed circularly polarized light passes through the lens assembly 100 and reaches the transmissive-reflective film 300, and is reflected at the transmissive-reflective film 300, and the second reflection occurs here. Due to the half-wave loss, the reflected light changes from right-handed circularly polarized light to left-handed circularly polarized light. The left-handed circularly polarized light passes through the lens assembly 100 and reaches the phase retardation film 400, becomes s-linearly polarized light after passing through the phase retardation film 400, and then the s-linearly polarized light passes through the polarization reflection layer 200 and is directed towards the exit pupil, such as the human eye.

[0066] The above-mentioned folded optical path can change the polarization state of the light propagating between the polarization reflection layer 200 and the transmissive-reflective film 300, realize the folding of the light, so that the focal length of the original optical system increased due to the setting of the above-mentioned polarization reflection layer 200, phase retardation film 400 and transmissive-reflective film 300, such as two reflections, is folded, thereby greatly compressing the space required between the human eye and the optical system, and making the optical system smaller, thinner and lighter.

[0067] For example, the optical system further includes a linear polarization film 500, and the linear polarization film 500 is arranged on the side of the polarization reflection layer 200 away from the transmissive-reflective film 300. For example, the linear polarization film 500 can be a linear polarizer or a polarizer. For example, the optical axis of the linear polarization film 500 coincides with the optical axis of the polarization reflection layer 200. For example, the linear polarization film 500 can be used to further filter other stray light and only allow the polarized light (such as s-linearly polarized light) passing through the linear polarization film 500 to enter the human eye. For example, the linear polarization film can adopt a three-layer stacked structure, the middle layer in the three-layer stacked structure can be polyvinyl alcohol (PVA) added with dichroic molecules, and at least one layer on both sides of the middle layer in the three-layer stacked structure can be triacetyl cellulose (TAC). For example, the surface of the linear polarization film 500 facing the air is subjected to an antireflection treatment. For example, the surface of the linear polarization film 500 facing the air can be attached with a moth-eye film.

[0068] In some examples, refer to Figure 1, the ratio of the radius of curvature of the second surface 102 to the effective focal length of the optical system can be -6 to 2. For example, the second surface 102 can be a curved Fresnel surface, and the radius of curvature of the second surface 102 refers to the radius of curvature of the curved Fresnel surface. For example, the radius of curvature of the second surface 102 refers to the radius of curvature of the Fresnel surface including a toothed structure. For example, the ratio of the radius of curvature of the second surface 102 to the effective focal length of the optical system can be -5 to 1.5. For example, the ratio of the radius of curvature of the second surface 102 to the effective focal length of the optical system can be -4 to 0. For example, the ratio of the radius of curvature of the second surface 102 to the effective focal length of the optical system can be -3 to -1. For example, the ratio of the radius of curvature of the second surface 102 to the effective focal length of the optical system can be -2.

[0069] For example, referring to Figure 1 , the second surface 102 of the Fresnel surface can be approximated as a smooth and toothless spherical or aspherical surface, and this spherical or aspherical surface is the base surface of the Fresnel surface, and the curvature of this spherical or aspherical surface is the curvature of the Fresnel surface. For example, the tooth width or tooth height of the second surface 102 and the third surface 103 can be assumed to be infinitesimal. For example, the curvature of the base surface is -0.01 to -0.04. For example, the curvature of the base surface is -0.02 to -0.03. Thus, it is possible to prevent the toothed structure on the Fresnel surface from contacting the surfaces (such as the first surface 101 or the fourth surface 104) on both sides of the Fresnel surface (such as the second surface 102 and the third surface 103) on the optical axis OA.

[0070] Figure 4 Schematic diagram of the optical system provided by an example in at least one embodiment of the present disclosure. Figure 4 The optical system shown is different from Figure 1 the optical system shown in that Figure 4 the second surface 102 in the optical system shown is different from Figure 1 the second surface 102 in the optical system shown. Of course, Figure 4 the optical system shown and Figure 1 the optical system shown may also have other differences, such as the number of lenses included in the lens assembly, etc., and the present disclosure does not limit this. For example, Figure 4 the number of lenses in the optical system shown can be different from Figure 1 the number of lenses in the optical system shown, or can be the same. Figure 4 The polarization reflection layer 200, the transmissive-reflective film 300, and the linear polarization film 500 in the optical system shown can have the same characteristics as Figure 1 the polarization reflection layer 200, the transmissive-reflective film 300, and the linear polarization film 500 in the optical system shown, and will not be elaborated here.

[0071] In some examples, the second surface 102 is a planar Fresnel surface or a curved Fresnel surface. For example, as Figure 1 shown, the second surface 102 is a curved Fresnel surface; as Figure 4 shown, the second surface 102 is a planar Fresnel surface. It can be understood that the second surface 102 can be a convex surface, a concave surface, or a planar surface. For example, a continuous curved surface can be discretized to obtain a planar Fresnel surface with a planar base (for example, refer to Figure 4 ). For example, after discretizing a continuous curved surface, a discretized spherical curvature or aspherical curvature can be superimposed to obtain a curved Fresnel surface with a curved base (for example, refer to Figure 1 ). Thus, there is a large adjustment space for the radius of curvature of the Fresnel surface in the optical system, so that the dispersed light can be better deflected and converged. Thus, by adjusting the slope of the Fresnel surface, the deflection ability of the second surface 102 and the third surface 103 for light is enhanced, which can not only achieve an ultra-short focal length, but also improve the correction effect of chromatic aberration and enhance the clarity.

[0072] For example, refer to Figure 1 , both the second surface 102 and the third surface 103 are curved away from the first surface 101, that is, both the second surface 102 and the third surface 103 are convex surfaces, so that the difference between the central thickness and the edge thickness of the first lens 110 is small, and the difference between the central thickness and the edge thickness of the second lens 120 is small, reducing the processing difficulty. In addition, the curved Fresnel can also make the surface shapes of the second surface 102 and the third surface 103 more easily match the first surface 101 and the fourth surface 104, thereby reducing the thickness of the lens assembly 100 in the optical axis OA direction, and thus controlling the optical total length of the optical system.

[0073] In some examples, as Figure 1 shown, the ratio of the radius of curvature of the first surface 101 to the fourth surface 104 can be 1.2 to 1.7. For example, the ratio of the radius of curvature of the first surface 101 to the fourth surface 104 can be 1.3 to 1.6. For example, the ratio of the radius of curvature of the first surface 101 to the fourth surface 104 can be 1.4 to 1.5.

[0074] In some examples, as Figure 1As shown, the ratio of the radius of curvature of the first surface 101 to the effective focal length of the optical system can be -3.5 to -1.5, and the conic coefficient of the first surface 101 can be -10 to -0.5. For example, the ratio of the radius of curvature of the first surface 101 to the effective focal length of the optical system can be -3 to -2. For example, the ratio of the radius of curvature of the first surface 101 to the effective focal length of the optical system can be -2.5. For example, the conic coefficient of the first surface 101 can be -9 to -1. For example, the conic coefficient of the first surface 101 can be -8 to -2. For example, the conic coefficient of the first surface 101 can be -7 to -3. For example, the conic coefficient of the first surface 101 can be -6 to -4. For example, the conic coefficient of the first surface 101 can be -5.

[0075] In some examples, such as Figure 1 As shown, the ratio of the radius of curvature of the fourth surface 104 to the effective focal length of the optical system is -2.0 to 2.0, and the conic coefficient of the fourth surface 104 is -10 to -0.1. For example, the ratio of the radius of curvature of the fourth surface 104 to the effective focal length of the optical system can be -1.8 to 1.8. For example, the ratio of the radius of curvature of the fourth surface 104 to the effective focal length of the optical system can be -1.5 to 1.5. For example, the ratio of the radius of curvature of the fourth surface 104 to the effective focal length of the optical system can be -1 to 1. For example, the conic coefficient of the fourth surface 104 can be -9 to -1. For example, the conic coefficient of the fourth surface 104 can be -8 to -2. For example, the conic coefficient of the fourth surface 104 can be -7 to -3. For example, the conic coefficient of the fourth surface 104 can be -6 to -4. For example, the conic coefficient of the fourth surface 104 can be -5.

[0076] For example, the surface profile of the curved Fresnel surface can be approximated as the surface profile of an aspheric surface, such as can be expressed by the following numerical formula:

[0077]

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

[0079] When actually optimizing the reasonable configuration of the parameters of the lens assembly, the values of the curvature radius, conic coefficient, height, aspheric coefficient, etc. of each lens in the lens assembly are put into the above numerical formula, and each optimization parameter capable of correcting the aberration of each lens in the lens assembly is obtained through optical simulation calculation. The preferred values of the curvature radius, thickness along the optical axis, effective aperture, and conic coefficient of each lens in the lens assembly are obtained through the optimization process.

[0080] For example, as Figure 1 shown, the conic coefficients of the second surface 102 and the third surface 103 can be 0 to improve the efficiency of optimizing the Fresnel surface. For example, the conic coefficients of the second surface 102 and the third surface 103 can be less than 0. For example, the conic coefficients of the second surface 102 and the third surface 103 can be greater than 0.

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

[0082] In some examples, as Figure 1 shown, the tooth width of the second surface 102 includes 0.3 mm to 1 mm. For example, the second surface 102 includes a tooth-shaped structure, and the tooth-shaped structure is composed of a plurality of concentric tooth rings, and the tooth width is also the distance between adjacent two tooth rings. For example, among the plurality of tooth rings, the distance between adjacent two tooth rings is equal. For example, the tooth width of the second surface 102 includes 0.4 mm to 0.9 mm. For example, the tooth width of the second surface 102 includes 0.5 mm to 0.8 mm. For example, the tooth width of the second surface 102 includes 0.6 mm to 0.7 mm. By setting the tooth width to 0.3 mm to 1 mm, the tooth density of the second surface 102 can be made appropriate, which can not only reduce the processing error and improve the optical efficiency, but also facilitate the molding and demolding of the tooth part during injection molding.

[0083] For example, when light rays are refracted and reflected in an optical system, each time the light rays pass through the Fresnel surface, the influence of the teeth on the Fresnel surface on the light rays needs to be considered to prevent light leakage or light blocking, thereby reducing stray light and improving the contrast of imaging. For example, in an example of an embodiment of the present disclosure, as Figure 3 shown, during the process of the incident light rays being refracted and reflected in the lens assembly 100, the light rays pass through the second surface 102 and the third surface 103 three times successively. The tooth height and draft angle of the Fresnel surface can be obtained by optical simulation calculation respectively according to the deflection angle of the light rays each time they pass through the second surface 102 or the third surface 103.

[0084] In some examples, as Figure 1 shown, 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 includes a first surface 101 and a second surface 102, and the second lens 120 includes a third surface 103 and a fourth surface 104. The dispersion coefficient of the first lens 110 is greater than that of the second lens 120. For example, the first lens 110 is a convex lens and the second lens 120 is a concave lens. By setting the dispersion coefficient of the first lens 110 to be greater than that of the second lens 120, it is beneficial to the deflection of light rays of different wavelengths, thereby being able to better correct chromatic aberration.

[0085] In some examples, as Figure 1 shown, the dispersion coefficient of the first lens 110 can be 25 - 65, and the dispersion coefficient of the second lens 120 can be 30 - 54. For example, the dispersion coefficient of the first lens 110 can be 30 - 60. For example, the dispersion coefficient of the first lens 110 can be 35 - 55. For example, the dispersion coefficient of the first lens 110 can be 40 - 50. For example, the dispersion coefficient of the first lens 110 can be 45. For example, the dispersion coefficient of the second lens 120 can be 35 - 50. For example, the dispersion coefficient of the second lens 120 can be 40 - 45. For example, the dispersion coefficient of the first lens 110 can be 55 - 65, and the dispersion coefficient of the second lens 120 can be 30 - 40. For example, the dispersion coefficient of the first lens 110 can be 55 - 57, and the dispersion coefficient of the second lens 120 can be 49 - 51. For example, the dispersion coefficient of the first lens 110 can be 56, and the dispersion coefficient of the second lens 120 can be 50. It can be understood that the present disclosure only exemplifies the dispersion coefficients of the first lens 110 and the second lens 120. The dispersion coefficients of the first lens 110 and the second lens 120 can be relatively close or quite different. As long as the dispersion coefficient of the first lens 110 is greater than that of the second lens 120, the present disclosure does not limit the combination of numerical values.

[0086] In some examples, as Figure 1As shown, 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 includes a first surface 101 and a second surface 102, and the second lens 120 includes a third surface 103 and a fourth surface 104. The refractive index of the first lens 110 is less than that of the second lens 120. For example, there is generally an inverse relationship between the refractive index and the dispersion coefficient. For example, the smaller the refractive index, the relatively larger the dispersion coefficient. For example, the smaller the dispersion coefficient, the relatively larger the refractive index. For example, the first lens 110 is a convex lens and the second lens 120 is a concave lens. By setting the refractive index of the first lens 110 to be less than that of the second lens 120, it is beneficial to the deflection of light of different wavelengths, thereby enabling better correction of chromatic aberration.

[0087] For example, as Figure 1 shown, the refractive index of the first lens 110 can be 1.4 to 1.7. For example, the refractive index of the first lens 110 can be 1.5 to 1.6. For example, the refractive index of the second lens 120 can be 1.4 to 1.7. For example, the refractive index of the second lens 120 can be 1.5 to 1.6. For example, the refractive index of the first lens 110 can be 1.55 and the refractive index of the second lens 120 can be 1.59. It can be understood that the present disclosure only exemplifies the refractive indices of the first lens 110 and the second lens 120. The refractive indices of the first lens 110 and the second lens 120 can be relatively close or quite different. As long as the refractive index of the first lens 110 is less than that of the second lens 120, the present disclosure does not limit the combination of values.

[0088] For example, as Figure 1As shown, the first lens 110 and the second lens 120 can be made of different materials, so that the dispersion coefficient of the first lens 110 is different from that of the second lens 120, and the refractive index of the first lens 110 is different from that of the second lens 120. For example, after the first lens 110 and the second lens 120 are injection-molded respectively, the first lens 110 and the second lens 120 can be glued together with an elastic adhesive. For example, after the first lens 110 is injection-molded, a casting process can be used to pour a liquid optical material between the first lens 110 and a mold and cure it to form the second lens 120. For example, by selecting the liquid optical material, the material of the cured second lens 120 can be a hard polymer or an elastic optical silica gel. For example, the hard polymer can be a monomer polymer with a refractive index of 1.554 and a dispersion coefficient of 39.3. For example, the elastic optical silica gel can be silicone rubber. For example, the refractive index of the optical silica gel is 1.41 and the dispersion coefficient is 52. For example, the refractive index of the optical silica gel is 1.41 and the dispersion coefficient is 50. For example, the second lens 120 can be injection-molded first, and then a casting process can be used to pour a liquid optical material between the second lens 120 and a mold and cure it to form the first lens 110.

[0089] For example, Figure 1 Schematically shows the influence of each film layer on the distance between different surfaces of the lens assembly. When the thickness of each film layer is relatively thin, the film layer thickness can be ignored.

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

[0091] In some examples, such as Figure 1As shown, the ratio of the first distance D1 to the effective focal length of the optical system can be 0.3 to 0.5. For example, the ratio of the first distance D1 to the effective focal length of the optical system can be 0.35 to 0.45. For example, the ratio of the first distance D1 to the effective focal length of the optical system can be 0.4. In some examples, the ratio of the second distance D2 to the effective focal length of the optical system can be 0.1 to 0.3. For example, the ratio of the second distance D2 to the effective focal length of the optical system can be 0.15 to 1.25. For example, the ratio of the second distance D2 to the effective focal length of the optical system can be 0.2.

[0092] In some examples, such as Figure 1 As shown, 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 includes a first surface 101 and a second surface 102, and the second lens 120 includes a third surface 103 and a fourth surface 104. In some examples, the ratio of the central thickness to the edge thickness of the first lens 110 is greater than 1 and less than 3. For example, the ratio of the central thickness to the edge thickness of the first lens 110 is greater than 1.5 and less than 2.5. In some examples, the ratio of the central thickness to the edge thickness of the second lens 120 is greater than 0.5 and less than 2. For example, the ratio of the central thickness to the edge thickness of the second lens 120 is greater than 1 and less than 1.5. By setting the ratio relationship between the central thickness and the edge thickness of the above lenses, it is beneficial to ensure the injection molding of each lens.

[0093] Combined with the foregoing examples, Figure 5A is Figure 1 the spot diagram of the optical system shown. Figure 5B is Figure 1 the curve graph of the spot size of the optical system shown changing with the field angle.

[0094] Referring to Figure 5A , the spot diagram refers to a dispersion pattern formed by a large number of rays emitted from a point after passing through an optical system. Due to aberration, the intersection points with the image plane are no longer concentrated at the same point, but are scattered within a certain range, and can be used to evaluate the imaging quality of the optical system. Figure 5A In Figure 5A , taking the first set of values on the left vertical as an example, 0.00 represents the normalized field of view in the X direction, 1.00 represents the normalized field of view in the Y direction, 0.000 represents the field angle in the X direction, and 47.50 represents the field angle in the Y direction. Figure 5AIt is usually used to evaluate the full field of view clarity of the optical system, that is, when the human pupil is at the entrance pupil position on the optical axis and looking at the center of the lens (i.e., zero field of view), the imaging clarity of the full field of view that can be covered by the peripheral vision is also called transient mode. In addition to considering the full field of view clarity in transient mode, for wearers wearing head-mounted displays, for example, gaze point clarity is one of the more important optical indicators. Gaze point clarity refers to the image clarity within a certain angle range that can be directly seen (not seen by peripheral vision) when the eyes move up, down, left, and right.

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

[0096] Figure 5C for Figure 1 Distortion diagram of the optical system shown. Figure 5C , the distortion diagram reflects the difference in image plane position of clear images in different fields of view, see Figure 5C As shown, the absolute value of the maximum distortion is within 50%. It can be seen that the optical system provided by at least one embodiment of the present disclosure can well correct the distortion and meet the requirements of high-quality imaging. In addition, the distortion correction can be pre-processed in the software.

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

[0098] refer to Figure 5D and Figure 5E , the vertical axis chromatic aberration diagram represents the height difference of each wavelength relative to the central wavelength at different image heights on the imaging surface, the horizontal axis represents the vertical axis chromatic aberration value of each wavelength relative to the central wavelength, and the vertical axis represents the normalized field angle. Figure 5D and Figure 5E As shown, F light is cyan light, C light is red light, and D light is yellow light. C light and F light are located at the two ends of the sensitive area of ​​the human eye, while D light is located in the middle, close to the spectrum line that the human eye is most sensitive to.Figure 5D , Figure 5D is the result of the lateral chromatic aberration of a single-chip optical system. As can be seen from the figure, the absolute value of the lateral chromatic aberration between F light and C light is generally within 0.1 mm, and the absolute value of the lateral chromatic aberration between F light and D light is generally within 0.06 mm. From Figure 5E it can be seen that the absolute value of the lateral chromatic aberration between F light and C light is controlled within 0.035 mm, and the absolute value of the lateral chromatic aberration between F light and D light is controlled within 0.025 mm. By comparing Figure 5E with Figure 5D , it can be known that for the optical system provided by the present disclosure as shown in Figure 1 , compared with the single-chip optical system, the lateral chromatic aberration can be reduced to 1 / 3 at the maximum field of view, and the chromatic aberration can be reduced to 1 / 6, indicating that the optical system as shown in, for example, Figure 1 can excellently correct the chromatic aberration of the edge field of view and the secondary spectrum of the entire image plane.

[0099] Figure 6 is a schematic diagram of the optical system provided by an example in at least one embodiment of the present disclosure. Figure 6 The difference between the shown optical system and Figure 1 the shown optical system is that Figure 6 the number of lenses in the shown optical system is different from Figure 1 the number of lenses in the shown optical system. Of course, Figure 6 the shown optical system and Figure 1 the shown optical system may also have other differences, such as the surface shape of at least one lens, etc. The present disclosure does not limit this. For example, Figure 6 the surface shape parameters of the first surface 101 to the fourth surface 104 in the shown optical system may be different from or the same as Figure 1 the surface shape parameters of the first surface 101 to the fourth surface 104 in the shown optical system. Figure 6 The polarization reflection layer 200, the transmissive and reflective film 300, and the linear polarization film 500 in the shown optical system may have the same characteristics as Figure 1 the polarization reflection layer 200, the transmissive and reflective film 300, and the linear polarization film 500 in the shown optical system, and will not be elaborated here.

[0100] In some examples, such as Figure 6As shown, at least two lenses include a first lens 011, a second lens 012, and a third lens 013 arranged in sequence along the optical axis OA direction. The first lens 011 includes a first surface 101 and a second surface 102. The second lens 012 includes a third surface 103. The third lens 013 includes a fourth surface 104. The second lens 012 further includes a fifth surface 105 opposite to the third surface 103. The third lens 013 further includes a sixth surface 106 located between the fifth surface 105 and the fourth surface 104. At least two of the first lens 011, the second lens 012, and the third lens 013 have different dispersion coefficients. For example, the first lens 011 and the second lens 012 have different dispersion coefficients, and the second lens 012 and the third lens 013 have the same dispersion coefficient. For example, the first lens 011 and the third lens 013 have different dispersion coefficients, and the first lens 011 and the second lens 012 have the same dispersion coefficient. For example, the second lens 012 and the third lens 013 have different dispersion coefficients, and the first lens 011 and the third lens 013 have the same dispersion coefficient. For example, the first lens 011, the second lens 012, and the third lens 013 have different dispersion coefficients respectively.

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

[0102] In some examples, as Figure 6 shown, the ratio of the radius of curvature of the fifth surface 105 to the radius of curvature of the second surface 102 is 0.9 to 1.1. For example, the surface profiles of the fifth surface 105 and the second surface 102 are relatively similar. Both the fifth surface 105 and the sixth surface 106 are Fresnel surfaces, and the surface profiles of the fifth surface 105 and the sixth surface 106 are complementary. Complementary means that after the fifth surface 105 and the sixth surface 106 are fitted together (or pasted with optical glue), there is basically no gap between the fifth surface 105 and the sixth surface 106. For example, the surface profile of the fifth surface 105 and the surface profile of the sixth surface 106 are positive and negative shapes of each other. For example, at the corresponding positions of the fifth surface 105 and the sixth surface 106, the tooth-shaped structures on the two Fresnel surfaces can complement each other.

[0103] Figure 7 It is a schematic diagram of an optical system provided by an example in at least one embodiment of the present disclosure. Figure 7 The shown optical system and Figure 6The difference of the optical system shown lies in that Figure 7 the surface type parameters in the optical system shown are different from Figure 6 those in the optical system shown. Of course, Figure 6 the optical system shown and Figure 1 the optical system shown may also have other differences, such as the number of lenses included in the lens assembly, etc., and the present disclosure does not limit this. For example, Figure 7 the number of lenses in the optical system shown may be different from Figure 6 that in the optical system shown, or may be the same. Figure 7 The polarization reflection layer 200, the transmissive and reflective film 300, and the linear polarization film 500 in the optical system shown may have the same characteristics as Figure 6 those in the optical system shown, and will not be elaborated herein.

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

[0105] For example, as Figure 7 shown, the second surface 102 of the first lens 01 is a planar Fresnel surface, the third surface 103 and the fifth surface 105 of the second lens 02 are planar Fresnel surfaces, and the sixth surface 106 of the third lens 03 is a planar Fresnel surface. For example, as Figure 7 shown, the surface types of the second surface 102 and the third surface 103 are complementary, and the surface types of the fifth surface 105 and the sixth surface 106 are complementary.

[0106] For example, referring to Figure 7 , a continuous curved surface can be discretized to obtain a planar Fresnel surface. For example, referring to Figure 6, a continuous surface can be discretized and then a discretized spherical curvature can be superimposed to obtain a Fresnel surface of the surface. Thus, there is a large adjustment space for the radius of curvature of the Fresnel surface in the optical system, so that the dispersed light can be deflected and converged better. Thus, by adjusting the slope of the Fresnel surface, the deflection ability of the fifth surface 105 and the sixth surface 106 for light is enhanced, which can not only achieve an ultra-short focal length, but also improve the correction effect on chromatic aberration and enhance the clarity.

[0107] For example, referring to Figure 1 and Figure 3 , the ratio of the total optical length (TTL) to the effective focal length of the optical system is 0.85 to 1. For example, the ratio of the total optical length to the effective focal length of the optical system is 0.9 to 0.95. The total optical length refers to the distance from the highest point on the first surface 101 of the lens assembly 100 along the optical axis OA to the center of the display screen 10. The highest point on the first surface 101 includes the edge sag of the lens assembly 100 on the side where the first surface 101 is located.

[0108] For example, as Figure 1 and Figure 3 shown, the field of view angle of the optical system is greater than 90°. For example, the field of view angle is the full field of view angle. For example, the field of view angle of the optical system can be but is not limited to 90°, 92°, 94°, 96°, 98°, 100°. For example, when calculating with an effective aperture that can achieve a field of view angle of 100°, the weight of the binocular lens is about 20 g.

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

[0110] Referring to Figure 3 , at least one embodiment of the present disclosure provides a display device, including a display screen 10 and the optical system of any one of the above embodiments. The display screen 10 is located on the side of the fourth surface 104 away from the first surface 101. Since the display device according to the embodiment of the present disclosure includes at least one of the above optical systems, it also has corresponding beneficial technical effects, which will not be elaborated here. It can be understood that Figure 3 the display screen 10 shown, in cooperation with the optical systems such as Figure 1 , Figure 4 , Figure 6 and Figure 7 can form different display devices.

[0111] For example, as Figure 3 shown, the display surface 11 of the display screen 10 is located on the focal plane of the light incident side of the optical system.

[0112] For example, as Figure 3 shown, the ratio of the effective aperture to the effective focal length of the lens assembly 100 is 2.2 to 2.4. The effective aperture of the above lens assembly 100 refers to the effective light passing aperture, such as the maximum aperture through which light can pass through the lens assembly 100, and this aperture is determined by the maximum luminous flux of the lens assembly 100. For example, the ratio of the effective aperture to the effective focal length is 2.3.

[0113] For example, as Figure 3 shown, the ratio of the distance between the diaphragm (such as the human eye) and the first surface 101 on the optical axis OA to the effective focal length is 0.7 to 1.5. For example, the ratio of the distance between the diaphragm and the first surface 101 on the optical axis OA to the effective focal length is 0.8 to 1.4. For example, the ratio of the distance between the diaphragm and the first surface 101 on the optical axis OA to the effective focal length is 0.9 to 1.3. For example, the ratio of the distance between the diaphragm and the first surface 101 on the optical axis OA to the effective focal length is 1 to 1.2. For example, the ratio of the distance between the diaphragm and the first surface 101 on the optical axis OA to the effective focal length is 1.1.

[0114] For example, as Figure 3 shown, the effective aperture of the diaphragm is 4 mm. For example, the ratio of the distance between the object surface and the diaphragm on the optical axis OA in the optical system to the effective focal length is below -80. For example, the ratio of the effective aperture of the image surface to the effective focal length in the optical system is 1.5.

[0115] For example, as Figure 3 shown, the ratio of the distance between the display surface 11 of the display screen 10 and the image surface on the optical axis OA to the effective focal length is 0.03 to 0.12. For example, the ratio of the distance between the display surface 11 of the display screen 10 and the image surface on the optical axis OA to the effective focal length is 0.06 to 0.09. For example, the ratio of the distance between the display surface 11 of the display screen 10 and the image surface on the optical axis OA to the effective focal length is 0.08.

[0116] For example, as Figure 3 shown, the ratio of the distance between the fourth surface 104 and the display surface 11 of the display screen 10 on the optical axis OA to the effective focal length is 0.05 to 0.3. For example, the ratio of the distance between the fourth surface 104 and the display surface 11 of the display screen 10 on the optical axis OA to the effective focal length is 0.06 to 0.2. The ratio of the distance between the fourth surface 104 and the display surface 11 of the display screen 10 on the optical axis OA to the effective focal length is 0.1.

[0117] For example, as Figure 3As shown, the display screen 10 can be any type of display screen, such as a liquid crystal display screen, an organic light-emitting diode display screen, an inorganic light-emitting diode display screen, a quantum dot display screen, a projector (such as an LCOS micro-projector), etc.

[0118] For example, as Figure 3 shown, the display screen 10 is a liquid crystal display screen, and the pixel size is about twenty-something micrometers. For example, the display screen is an organic light-emitting diode display screen, and the pixel size is about a few micrometers.

[0119] For example, the display device can be a virtual reality display device. For example, the virtual reality display device can be a display device using an ultra-short focal length folding optical path.

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

[0121] The following points need to be explained:

[0122] (1) In the accompanying drawings of the embodiments of the present disclosure, only the structures related to the embodiments of the present disclosure are involved, and other structures can refer to the general design.

[0123] (2) Without conflict, the features in the same embodiment and different embodiments of the present disclosure can be combined with each other.

[0124] The above is only an exemplary implementation manner of the present disclosure, rather than being used to limit the protection scope of the present disclosure. The protection scope of the present disclosure is determined by the appended claims.

Claims

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

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

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

4. The optical system according to claim 1, wherein, The second surface is a planar Fresnel surface or a curved Fresnel surface.

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

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

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

8. The optical system according to any one of claims 1-4, wherein, The ratio of the radius of curvature of the first surface to the radius of curvature of the fourth surface is 1.2 to 1.

7.

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

5.

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

1.

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

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

3.

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

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

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

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

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

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

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