Pancake lens, optical imaging system, and head-mounted display device

Abstract

The present disclosure provides a pancake lens, an optical imaging system, and a head-mounted display device. The pancake lens comprises: a first lens, wherein the first lens has a first surface and a second surface which are arranged opposite to each other, and the first surface is a convex surface; a beam splitting film, wherein the beam splitting film is arranged on the first surface, the difference between the reflectivity and transmittance of the beam splitting film is less than or equal to 20%, the beam splitting film comprises multiple optical coating layers which are stacked, and the multiple optical coating layers include at least one non-metal transparent coating layer and at least one metal layer. By means of the provision of the metal layer, the consistency of the transmittance of the pancake lens to obliquely-incident light components s-polarized light and p-polarized light can be improved, and then the ellipticity of the pancake lens is effectively improved to make the ellipticity closer to 1, thereby effectively reducing the ghosting and stray light of the pancake lens.

Description

Folded optical path lens, optical imaging system and head-mounted display device

[0001] This application claims priority to the Chinese invention patent application entitled “Folded optical path lens, optical imaging system and head-mounted display device” and application number 202311133538.5 filed on September 4, 2023. The entire contents of that application are incorporated by reference into this application. Technical Field

[0002] The present disclosure relates to the field of optical technology, and in particular, to a folded optical path lens, an optical imaging system, and a head-mounted display device. Background Art

[0003] In virtual reality (VR) devices, near-eye displays (NEDs) use lenses to magnify the image on the display, creating an immersive experience. Currently, mainstream lens technology has evolved from Fresnel lenses to ultra-short-throw Pancake lenses. By folding the optical path, these lenses significantly reduce the required distance between the NED and the human eye, making VR devices thinner and lighter.

[0004] In a pancake lens, the key to folding the optical path is the conversion between circularly polarized light and linearly polarized light. The ellipticity of the circularly polarized light within the folded optical path of the pancake lens is a crucial physical quantity that determines the optical performance of the pancake. An ellipticity of 1 indicates circular polarization, while a 0 indicates linear polarization. Ellipticities between 0 and 1 indicate elliptically polarized light, with values ​​closer to 1 indicating circular polarization. The principle of a pancake lens requires that the ellipticity of the circularly polarized light within the folded optical path be as close to 1 as possible. If the ellipticity is low, some light will not follow the designed folded optical path, resulting in stray light or ghosting, affecting the imaging experience.

[0005] Summary of the Invention

[0006] The present disclosure aims to solve at least one of the technical problems in the related art to a certain extent. To this end, one purpose of the present disclosure is to provide a folded optical path lens with a high ellipticity, which can effectively reduce ghost images and stray light of the folded optical path lens.

[0007] In one aspect of the present disclosure, the present disclosure provides a folded light path lens. According to an embodiment of the present disclosure, the folded light path lens includes: a first lens, the first lens having a first surface and a second surface arranged opposite to each other, the first surface being a convex surface; a spectroscopic film, the spectroscopic film being arranged on the first surface, the difference between the reflectivity and the transmittance of the spectroscopic film being less than or equal to 20%, and the spectroscopic film including a plurality of optical coating layers stacked together, the plurality of optical coating layers including at least one layer of non-metallic transparent coating and at least one layer of metal layer. Thus, by providing the metal layer, the consistency of the transmittance of the folded light path lens for obliquely incident light components, s-polarized light and p-polarized light, can be improved, thereby effectively improving the ellipticity of the folded light path lens, making its ellipticity closer to 1, thereby effectively reducing the ghost and stray light of the folded light path lens.

[0008] According to an embodiment of the present disclosure, the folded optical path lens further includes: a quarter wave plate, which is arranged on the side of the first lens away from the convex surface; and a reflective polarizing film, which is arranged on the side of the quarter wave plate away from the first lens.

[0009] According to an embodiment of the present disclosure, when light is incident on the folding light path lens at an angle of less than or equal to 40°, the difference in transmittance of the s-polarized light and the p-polarized light of the incident light on the folding light path lens is less than or equal to 20%, and the difference in reflectivity of the s-polarized light and the p-polarized light of the incident light on the folding light path lens is less than or equal to 20%.

[0010] According to an embodiment of the present disclosure, the difference in transmittance between s-polarized light and p-polarized light of the incident light of the folded light path lens is less than or equal to 10%, and the difference in reflectivity between s-polarized light and p-polarized light of the incident light of the folded light path lens is less than or equal to 10%.

[0011] According to an embodiment of the present disclosure, when light is incident on the folding light path lens at an angle of less than or equal to 50°, the difference in transmittance of the s-polarized light and the p-polarized light of the incident light on the folding light path lens is less than or equal to 20%, and the difference in reflectivity of the s-polarized light and the p-polarized light of the incident light on the folding light path lens is less than or equal to 20%.

[0012] According to an embodiment of the present disclosure, the material of the metal layer includes at least one of silver, aluminum, chromium, titanium, platinum, silver-gold alloy, silver-indium alloy and indium-tin alloy; the material of the non-metallic transparent coating includes at least one of titanium dioxide, silicon dioxide, niobium pentoxide, aluminum oxide, tantalum dioxide, hafnium dioxide, magnesium fluoride, zinc sulfide, zinc selenide, zirconium dioxide, lanthanum oxide, praseodymium oxide and cerium oxide.

[0013] According to an embodiment of the present disclosure, the thickness of the metal layer is 1 to 50 nanometers, and the thickness of the non-metallic transparent coating is 1 to 250 nanometers.

[0014] According to an embodiment of the present disclosure, the outermost optical coating layer of the beam splitter film is the non-metallic transparent coating.

[0015] According to an embodiment of the present disclosure, the absorption rate of the prismatic film to visible light is less than or equal to 25%.

[0016] According to an embodiment of the present disclosure, the folded optical path lens also includes: a second lens, the second lens having a third surface and a fourth surface, the third surface being arranged close to the second surface, the 1 / 4 wave plate being arranged between the first lens and the second lens, and the reflective polarizing film being arranged on the side of the second lens away from the first lens.

[0017] According to an embodiment of the present disclosure, the folded optical path lens also includes: a third lens, which is arranged on the side of the first lens close to the second surface, the 1 / 4 wave plate is arranged on the side of the first lens close to the third lens, and the reflective polarizing film is arranged on the side of the 1 / 4 wave plate close to the third lens; a fourth lens, which is arranged on the side of the splitter film away from the first surface of the first lens; and an anti-reflection coating, which is arranged on the surface of the fourth lens away from the first lens.

[0018] In another aspect of the present disclosure, an optical imaging system is provided. According to an embodiment of the present disclosure, the optical imaging system includes a display screen and the aforementioned folded light path lens. The folded light path lens is located on the light-emitting side of the display screen, and light emitted by the display screen is imaged after exiting through the folded light path lens. As a result, the optical imaging system has low ghosting and stray light, thereby helping to improve the imaging quality of the optical imaging system. Those skilled in the art will appreciate that the optical imaging system has all the features and advantages of the folded light path lens described above, and no further elaboration will be given here.

[0019] According to an embodiment of the present disclosure, the display screen is a micro OLED display screen.

[0020] In another aspect of the present disclosure, a head-mounted display device is provided. According to an embodiment of the present disclosure, the head-mounted display device includes the optical imaging system described above. Thus, the imaging quality of the head-mounted display device is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and / or additional aspects and advantages of the present disclosure will become apparent and readily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0022] FIG1 is a schematic structural diagram of a folded optical path lens according to an embodiment of the present disclosure;

[0023] FIG2 is a diagram of light paths in a folded light path lens;

[0024] FIG3 is a schematic structural diagram of a folded optical path lens in another embodiment of the present disclosure;

[0025] FIG4 is a schematic structural diagram of a folded optical path lens in another embodiment of the present disclosure;

[0026] FIG5 is a schematic structural diagram of a folded optical path lens in Example 1 of the present disclosure;

[0027] FIG6 is a curve showing the reflectivity and transmittance of light when light is incident on the folded optical path lens in Example 1 at incident angles of 0° and 40°, respectively;

[0028] FIG7 is a schematic structural diagram of a folded optical path lens in Comparative Example 1 of the present disclosure;

[0029] FIG8 is a curve showing the reflectivity and transmittance of light when light at incident angles of 0° and 40° respectively enters the folded optical path lens in Example 1 in Comparative Example 1 of the present disclosure;

[0030] FIG9 is a schematic structural diagram of a folded optical path lens in Example 2 of the present disclosure;

[0031] FIG10 is a curve showing the reflectivity and transmittance of light when light at incident angles of 0° and 40° respectively enters the folded optical path lens in Example 1 in Example 2 of the present disclosure;

[0032] FIG11 is a schematic structural diagram of a folded optical path lens in Comparative Example 2 of the present disclosure;

[0033] FIG12 is a curve showing the reflectivity and transmittance of light when light at incident angles of 0° and 40° respectively enters the folded optical path lens in Example 1 in Comparative Example 2 of the present disclosure;

[0034] FIG13 is a schematic diagram showing the positional relationship between the folded optical path lens and the display screen. DETAILED DESCRIPTION

[0035] The scheme of the present disclosure will be explained below in conjunction with the examples. Those skilled in the art will understand that the following examples are only used to illustrate the present disclosure and should not be considered to limit the scope of the present disclosure. Where specific techniques or conditions are not specified in the examples, they are carried out according to the techniques or conditions described in the literature in this area or according to the product instructions. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0036] The present disclosure is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present disclosure in any way.

[0037] In one aspect of the present disclosure, the present disclosure provides a folded light path lens. According to an embodiment of the present disclosure, referring to FIG1 , the folded light path lens includes: a first lens 11, the first lens having a first surface and a second surface arranged opposite to each other, the first surface being a convex surface; a spectroscopic film 40, the spectroscopic film 40 being arranged on the first surface of the first lens 11, that is, the spectroscopic film is arranged on the convex surface, and the spectroscopic film includes a multi-layer stacked optical coating layer, the multi-layer optical coating layer including at least one layer of non-metallic transparent coating and at least one layer of metal layer. Thus, by providing the metal layer, the consistency of the transmittance of the folded light path lens for obliquely incident light components s-polarized light and p-polarized light can be improved (that is, the difference in the transmittance of the light components s-polarized light and p-polarized light is made smaller), thereby effectively improving the ellipticity of the folded light path lens, making its ellipticity closer to 1, thereby effectively reducing the ghost and stray light of the folded light path lens.

[0038] According to Brewster's law, the equivalent refractive index of the dielectric material for s-polarized light and p-polarized light is different: np = n / cos θ, ns = ncos θ, where np and ns are the equivalent refractive indices of p-light and s-light at the interface of a medium with a refractive index of n, respectively, and θ is the angle of incidence. The above is the reason why the reflectivity and transmittance of the s- and p-polarized components are inconsistent when light is obliquely incident on a dielectric multilayer film. However, the response of metal materials to light is different from that of dielectrics. The reflection of metals is caused by the induced current of electrons in the metal to the incident optical field. According to the free electron model of metal materials (Drude model), the electrical conductivity of metals is isotropic, which makes the metal's reflectivity of visible light very small in dependence on the angle of incidence. Therefore, in the present application, the provision of a metal layer can reduce the difference in transmittance between the s-polarized light and p-polarized light components, improve the consistency of the transmittance of the folded light path lens for the obliquely incident s-polarized light and p-polarized light components, and thereby effectively improve the ellipticity of the folded light path lens, making its ellipticity close to 1.

[0039] The second surface of the first lens may be a flat surface or a concave surface, and those skilled in the art may flexibly select the specific structure of the first lens according to actual needs.

[0040] According to an embodiment of the present disclosure, referring to FIG1 , the folded optical path lens further includes: a quarter-wave plate (i.e., a quarter-wave phase retardation film) 20, disposed on the side of the first lens 11 away from the convex surface; and a reflective polarizing film 30, disposed on the side of the quarter-wave plate 20 away from the first lens 11. In a folded optical path (Pancake) lens, the quarter-wave plate changes the polarization state of light, converting circularly polarized light into linearly polarized light and vice versa; and the reflective polarizing film reflects polarized light in one direction (e.g., s-polarized light) while reflecting polarized light in another direction (e.g., p-polarized light).

[0041] Referring to Figure 2, the structure of a specific folded optical path lens is as follows: A quarter-wave plate (quarter-wave retarder) is mounted on the display screen surface, emitting right-handed circularly polarized light 1. After passing through the beam splitter, the polarization state of light 2 remains unchanged, remaining right-handed circularly polarized. After passing through the quarter-wave retarder in Figure 2, the right-handed circularly polarized light becomes linearly polarized light 3, polarized along the z-axis, as shown. In a folded optical path (Pancake) lens, the primary determinant of ellipticity is the quarter-wave retarder (QWP). An ideal QWP requires that when linearly polarized light is incident at a 45° angle to its optical axis, it retards the linearly polarized light by exactly one-quarter of its wavelength, resulting in circularly polarized light with an ellipticity of 1. If the retardation is insufficient or exceeds one-quarter of the wavelength, elliptically polarized light with an ellipticity below 1 will result. However, the inventors discovered that the beam splitter film also affects the ellipticity of the folded light path lens. For example, if the incident angle of a beam splitter film is 0°, the transmittance of the s-polarized light and p-polarized light is 50% each. However, at higher angles of incidence, the difference in transmittance between the s-polarized and p-polarized light incident on the beam splitter film becomes significantly larger, which can seriously affect the ellipticity of the folded light path lens. Based on this, the inventors added at least one metal layer to the beam splitter film, thereby significantly reducing the difference in transmittance between the s-polarized and p-polarized light incident on the folded light path lens. This in turn improves the ellipticity of the folded light path lens, bringing its value closer to 1, thereby effectively reducing ghost images and stray light in the folded light path lens.

[0042] According to some embodiments of the present disclosure, when light enters the folding light path lens at an angle of less than or equal to 40°, the difference in transmittance between the s-polarized light and the p-polarized light of the incident light of the folding light path lens is less than or equal to 20%, or further, the difference is less than or equal to 10%, and the difference in reflectance between the s-polarized light and the p-polarized light of the incident light of the folding light path lens is less than or equal to 20, or further, the difference is less than or equal to 10%. Thus, even if light enters the folding light path lens at a larger incident angle, the transmittance and reflectance of the obliquely incident light components s-polarized light and p-polarized light of the folding light path lens can still be made highly consistent (the smaller the difference in transmittance between the s-polarized light and the p-polarized light of the incident light of the folding light path lens, the smaller the difference in reflectance, and the higher the consistency), thereby ensuring a better ellipticity of the folding light path lens and effectively reducing ghosting and stray light of the folding light path lens. Furthermore, according to some embodiments of the present disclosure, when light is incident on the folded light path lens at an angle of less than or equal to 50°, the difference in transmittance of the s-polarized light and the p-polarized light of the incident light on the folded light path lens is less than or equal to 20%, and the difference in reflectivity of the s-polarized light and the p-polarized light of the incident light on the folded light path lens is less than or equal to 20%.

[0043] Furthermore, the difference in transmittance between s-polarized light and p-polarized light incident on the folded optical path lens is less than or equal to 10%, and the difference in reflectance between s-polarized light and p-polarized light incident on the folded optical path lens is less than or equal to 10%. This shows that even if light enters the folded optical path lens at a larger incident angle (such as 40°, 42°, 45°, 47°, 50°, etc.), the transmittance and reflectance of the obliquely incident s-polarized light and p-polarized light components of the folded optical path lens can still be highly consistent, ensuring the folded optical path lens's optimal ellipticity and effectively reducing ghost images and stray light.

[0044] According to an embodiment of the present disclosure, the difference between the reflectivity and transmittance of the bezel is less than or equal to 20%. For example, the difference between the reflectivity (R) and transmittance (T) of the bezel is 20%, 18%, 15%, 12%, 8%, 6%, 4%, 2%, 0%, etc. In some specific embodiments, the reflectivity and transmittance of the bezel are specifically R40% / T60%, R60% / T40%, or R50% / T50%. Because the metal layer has a certain degree of light absorption, the reflectivity and transmittance of the bezel are specifically R48% / T48%, R45% / T45%, R40% / T50%, or R50% / T40%, etc.

[0045] According to an embodiment of the present disclosure, the material of the metal layer includes at least one of silver, aluminum, chromium, titanium, platinum, silver-gold alloy, silver-indium alloy and indium-tin alloy. In this way, the metal layer of the above material can effectively reduce the difference in transmittance of s-polarized light and p-polarized light of the incident light of the folded light path lens, thereby improving the ellipticity of the folded light path lens and making its value closer to 1, thereby effectively reducing the ghost and stray light of the folded light path lens; the material of the non-metallic transparent coating includes at least one of titanium dioxide, silicon dioxide, niobium pentoxide, aluminum oxide, tantalum dioxide, hafnium dioxide, magnesium fluoride, zinc sulfide, zinc selenide, zirconium dioxide, lanthanum oxide, praseodymium oxide, cerium oxide and multi-metal oxides (such as Merck's H4 product (lanthanum titanate)). In this way, the transparency and transmittance of the non-metallic transparent coating of the above material are high. In some embodiments of the present disclosure, the specific number of layers of non-metallic transparent coatings and metal layers, the specific materials of each layer, and the specific thickness of a single layer can be flexibly adjusted using the above-mentioned materials. Optimally, the transmittance and reflectance of the s-polarized light and p-polarized light components of the incident light of the folded light path lens when the incident angle is 0° can be completely consistent, for example, each is 50%, while at the same time, the spectroscopic film does not absorb too much visible light. According to some embodiments of the present disclosure, the spectroscopic film has an absorbance of less than or equal to 25% for visible light, such as 25%, 23%, 20%, 18%, 15%, 12%, 10%, 9%, 8%, 7%, 6%, 5%, 3%, 1%, etc. This can better ensure the optimal transmittance and reflectance of the folded light path lens. More preferably, in some embodiments, the spectroscopic film has an absorbance of less than or equal to 10% for visible light.

[0046] According to the embodiments of the present disclosure, the thickness of the metal layer is 1 to 50 nanometers (for example, the thickness of the metal layer is 1 nanometer, 5 nanometers, 8 nanometers, 10 nanometers, 15 nanometers, 20 nanometers, 25 nanometers, 30 nanometers, 35 nanometers, 40 nanometers, 45 nanometers, and 50 nanometers), and the thickness of the non-metallic transparent coating is 1 to 250 nanometers (for example, the thickness of the non-metallic transparent coating is 1 nanometer, 10 nanometers, 50 nanometers, 80 nanometers, 100 nanometers, 120 nanometers, 150 nanometers, 180 nanometers, 200 nanometers, 230 nanometers, and 250 nanometers). Therefore, the metal layer and the non-metallic transparent coating of the above thickness can effectively help reduce the difference in transmittance between s-polarized light and p-polarized light of the incident light of the folded light path lens, thereby improving the ellipticity of the folded light path lens, making its value closer to 1, thereby effectively reducing ghost images and stray light of the folded light path lens.

[0047] According to the embodiments of the present disclosure, the outermost optical coating layer of the spectroscopic film is a non-metallic transparent coating, meaning the metal layer is located in the center of the spectroscopic film. This prevents oxidation of the metal layer and, if the metal layer were on the surface, would make it difficult to achieve full-spectrum spectroscopic consistency. This allows the spectroscopic film to be designed to keep both reflectivity and transmittance as close to the designed value (e.g., 50%) across the entire visible wavelength range.

[0048] According to embodiments of the present disclosure, the metal layer may be formed by physical vapor deposition, such as thermal evaporation, electron beam evaporation, ion-assisted evaporation, magnetron sputtering, or the like, or by chemical vapor deposition, atomic layer deposition, or electrochemical deposition. Non-metallic transparent coatings may be formed by physical vapor deposition, such as thermal evaporation, electron beam evaporation, ion-assisted evaporation, magnetron sputtering, or the like, or by chemical vapor deposition, atomic layer deposition, or electrochemical deposition.

[0049] According to some embodiments of the present disclosure, referring to FIG3 , the folded light path lens further includes: a second lens 12, the second lens 12 having a third surface and a fourth surface, the third surface of the second lens being disposed close to the second surface, or in other words, the second lens being disposed on the first lens 11 and away from the convex surface, a quarter wave plate 20 being disposed between the first lens 11 and the second lens 12, and a reflective polarizing film 30 being disposed on the side of the second lens 12 away from the first lens 11. Furthermore, in some embodiments, based on FIG3 , the folded light path lens may further include a linear polarizing film, a hardened film, or an anti-reflection film between the reflective polarizing film 30 and the second lens 12. In addition, the quarter wave plate 20 is disposed on the convex surface of the second lens 12 and can be bonded to the first lens 11 by optical adhesive.

[0050] According to other embodiments of the present disclosure, referring to FIG4 , the folded optical path lens further includes: a third lens 13, disposed on the side of the first lens 11 near the second surface (that is, the third lens 13 is disposed on the side of the first lens 11 away from the convex surface); a quarter-wave plate 20 is disposed on the side of the first lens 11 near the third lens 13; and a reflective polarizing film 30 is disposed on the side of the quarter-wave plate 20 near the third lens 13; a fourth lens 14, disposed on the side of the beam splitter film 40 away from the first surface of the first lens 11; and an anti-reflection coating 52, disposed on the surface of the fourth lens 14 away from the first lens 11. Furthermore, in some embodiments, based on FIG4 , the folded optical path lens may further include a linear polarizing film, a hardened film, or an anti-reflection coating on the surface of the third lens 13 away from the first lens 11. Furthermore, the beam splitter film 40 is disposed on the convex surface of the third lens 11 and can be bonded to the fourth lens 14 using optical adhesive.

[0051] According to an embodiment of the present disclosure, the materials of the first lens, the second lens, the third lens, and the fourth lens may be respectively PMMA (polymethyl methacrylate), COC (cyclic olefin copolymer), or glass with low birefringence.

[0052] In another aspect of the present disclosure, the present disclosure provides an optical imaging system. According to an embodiment of the present disclosure, the optical imaging system includes a display screen and the folded light path lens described above, the folded light path lens is located on the light-emitting side of the display screen, and the light emitted by the display screen is imaged after exiting through the folded light path lens. As a result, the ghost and stray light of the optical imaging system are relatively weak, thereby helping to improve the imaging quality of the optical imaging system. Those skilled in the art will understand that the optical imaging system has all the features and advantages of the folded light path lens described above, and will not be elaborated on here. In the optical imaging system, the first surface (i.e., the convex surface) of the first lens is arranged facing the display screen, and the second surface is arranged facing away from the display screen.

[0053] According to an embodiment of the present disclosure, the display screen is a micro OLED display screen. As previously described, in the present disclosure, even if light enters the folded light path lens at a larger incident angle (such as 40°, 42°, 45°, 47°, 50°, etc.), the transmittance and reflectivity of the folded light path lens for the obliquely incident light components, s-polarized light and p-polarized light, can still be highly consistent, ensuring the folded light path lens's optimal ellipticity and effectively reducing ghost images and stray light from the folded light path lens. Therefore, even if a smaller micro OLED display screen is selected for the display screen in the optical imaging system of the present invention (the smaller the display screen size, the more likely a larger incident angle will appear at the edge of the folded light path lens, as shown in FIG13 ), the transmittance and reflectivity of the folded light path lens for the obliquely incident light components, s-polarized light and p-polarized light, can still be made highly consistent, effectively reducing the ghost and stray light of the Pancake lens. In other words, the Pancake lens of the present invention can be used in conjunction with small-sized and high-resolution screens such as micro OLEDs, helping to improve the display quality of virtual reality devices (such as virtual reality VR glasses) to a higher level than the current level.

[0054] Of course, those skilled in the art will appreciate that the display screen in the optical imaging system is also applicable to relatively large LCD displays. The closer the size of the display screen is to the size of the folded optical path lens, the less likely a large incident angle will occur.

[0055] In another aspect of the present disclosure, a head-mounted display device is provided. According to an embodiment of the present disclosure, the head-mounted display device includes the aforementioned optical imaging system. As a result, the imaging quality of the head-mounted display device is relatively high.

[0056] According to an embodiment of the present disclosure, the head-mounted display is virtual reality VR glasses.

[0057] Example

[0058] Example 1

[0059] The structure of the folded optical path lens is shown in FIG3 , wherein the first lens and the second lens are COC lenses respectively, and the structure of the beam splitter film and the thickness of each optical coating layer can be referred to FIG5 .

[0060] When light is incident on the folded optical path lens in Example 1 at incident angles of 0° and 40°, respectively, the reflectivity and transmittance thereof passing through the folded optical path lens can be seen with reference to FIG6 (the horizontal axis is wavelength / nm, and the vertical axis is reflectivity R and transmittance T). The reflectivity curve for light incident on the folded optical path lens at an incident angle of 0° is Curve 1, the transmittance curve for light incident on the folded optical path lens at an incident angle of 0° is Curve 2, the transmittance curve for s-polarized light incident on the folded optical path lens at an incident angle of 40° is Curve 3, and the transmittance curve for p-polarized light incident on the folded optical path lens at an incident angle of 40° is Curve 4. As can be seen from FIG6 , when light is incident on the folded optical path lens at an incident angle of 40°, the difference between the transmittance of s-polarized light and the transmittance of p-polarized light of the light is small, within 15%.

[0061] Comparative Example 1

[0062] The structure of the folded optical path lens is shown in FIG3 , wherein the first lens and the second lens are COC lenses respectively, and the structure of the beam splitter film and the thickness of each optical coating layer can be referred to FIG7 .

[0063] When light rays at incident angles of 0° and 40° are incident on the folded optical path lens in comparative example 1, their reflectivity and transmittance through the folded optical path lens can be seen in FIG8 (the horizontal axis is wavelength / nm, and the vertical axis is reflectivity R and transmittance T). The reflectivity curve for light rays at an incident angle of 0° incident on the folded optical path lens is curve 1, the transmittance curve for light rays at an incident angle of 0° incident on the folded optical path lens is curve 2, the transmittance curve for s-polarized light at an incident angle of 40° incident on the folded optical path lens is curve 3, and the transmittance curve for p-polarized light at an incident angle of 40° incident on the folded optical path lens is curve 4. As can be seen from FIG8 , when light rays at an incident angle of 40° are incident on the folded optical path lens, the difference between the transmittance of s-polarized light and the transmittance of p-polarized light of the light rays is relatively large, exceeding 20%.

[0064] Example 2

[0065] The structure of the folded optical path lens is shown in FIG4 , wherein the first lens, the third lens, and the fourth lens are COC lenses respectively. The structure of the beam splitter film and the thickness of each optical coating layer can be referred to FIG9 .

[0066] When light is incident on the folded optical path lens in Example 2 at incident angles of 0° and 40°, respectively, the reflectivity and transmittance thereof passing through the folded optical path lens can be seen with reference to FIG10 (the horizontal axis is wavelength / nm, and the vertical axis is reflectivity R and transmittance T). The reflectivity curve for light incident on the folded optical path lens at an incident angle of 0° is Curve 1, the transmittance curve for light incident on the folded optical path lens at an incident angle of 0° is Curve 2, the transmittance curve for s-polarized light incident on the folded optical path lens at an incident angle of 40° is Curve 3, and the transmittance curve for p-polarized light incident on the folded optical path lens at an incident angle of 40° is Curve 4. As can be seen from FIG10 , when light incident on the folded optical path lens at an incident angle of 40° has a small difference between the transmittance of s-polarized light and the transmittance of p-polarized light of the light, within 6%.

[0067] Comparative Example 2

[0068] The structure of the folded optical path lens is shown in FIG4 , wherein the first lens, the third lens, and the fourth lens are COC lenses respectively. The structure of the beam splitter film and the thickness of each optical coating layer can be referred to FIG11 .

[0069] When light rays at incident angles of 0° and 40° are incident on the folded optical path lens in Comparative Example 2, their reflectivity and transmittance through the folded optical path lens can be seen in FIG12 (the horizontal axis is wavelength / nm, and the vertical axis is reflectivity R and transmittance T). The reflectivity curve for light rays at an incident angle of 0° incident on the folded optical path lens is Curve 1, the transmittance curve for light rays at an incident angle of 0° incident on the folded optical path lens is Curve 2, the transmittance curve for s-polarized light at an incident angle of 40° incident on the folded optical path lens is Curve 3, and the transmittance curve for p-polarized light at an incident angle of 40° incident on the folded optical path lens is Curve 4. As can be seen from FIG12 , when light rays at an incident angle of 40° are incident on the folded optical path lens, the difference between the transmittance of the s-polarized light and the transmittance of the p-polarized light of the light rays is relatively large, exceeding 30%.

[0070] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0071] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification and features of different embodiments or examples, unless they are mutually inconsistent.

[0072] Although embodiments of the present disclosure have been shown and described above, it is understood that the above embodiments are illustrative and are not to be construed as limitations of the present disclosure. A person skilled in the art may change, modify, replace, and vary the above embodiments within the scope of the present disclosure.

Claims

1. A folded light path lens, comprising: A first lens, wherein the first lens has a first surface and a second surface arranged opposite to each other, and the first surface is a convex surface; A spectroscopic film, wherein the spectroscopic film is arranged on the first surface, the difference between the reflectivity and the transmittance of the spectroscopic film is less than or equal to 20%, and the spectroscopic film includes a plurality of stacked optical coating layers, wherein the plurality of optical coating layers include at least one non-metallic transparent coating layer and at least one metal layer.

2. The folded light path lens according to claim 1, further comprising: A quarter wave plate, the quarter wave plate being arranged on a side of the first lens away from the convex surface; A reflective polarizing film is disposed on a side of the 1 / 4 wave plate away from the first lens.

3. The folded light path lens according to claim 1 or 2, wherein when the light is incident on the folded light path lens at an angle less than or equal to 40°, the difference in transmittance between the s-polarized light and the p-polarized light of the incident light on the folded light path lens is less than or equal to 20%, and the difference in reflectivity between the s-polarized light and the p-polarized light of the incident light on the folded light path lens is less than or equal to 20%.

4. The folded light path lens according to claim 3, wherein the difference in transmittance between the s-polarized light and the p-polarized light of the incident light of the folded light path lens is less than or equal to 10%, and the difference in reflectivity between the s-polarized light and the p-polarized light of the incident light of the folded light path lens is less than or equal to 10%.

5. The folded light path lens according to claim 3, wherein when the light is incident on the folded light path lens at an angle less than or equal to 50°, the difference in transmittance between the s-polarized light and the p-polarized light of the incident light on the folded light path lens is less than or equal to 20%, and the difference in reflectivity between the s-polarized light and the p-polarized light of the incident light on the folded light path lens is less than or equal to 20%.

6. The folded optical path lens according to claim 1 or 2, wherein the material of the metal layer comprises at least one of silver, aluminum, chromium, titanium, platinum, silver-gold alloy, silver-indium alloy and indium-tin alloy; The material of the non-metallic transparent coating includes at least one of titanium dioxide, silicon dioxide, niobium pentoxide, aluminum oxide, tantalum dioxide, hafnium dioxide, magnesium fluoride, zinc sulfide, zinc selenide, zirconium dioxide, lanthanum oxide, praseodymium oxide and cerium oxide. 7 . The folded optical path lens according to claim 6 , wherein the thickness of the metal layer is 1 to 50 nanometers, and the thickness of the non-metallic transparent coating is 1 to 250 nanometers.

8. The folded light path lens according to claim 1 or 2, wherein the outermost optical coating layer of the beam splitting film is the non-metallic transparent coating.

9. The folded light path lens according to claim 1 or 2, wherein the absorption rate of the beam splitting film to visible light is less than or equal to 25%.

10. The folded light path lens according to claim 2, further comprising: The second lens has a third surface and a fourth surface, the third surface is arranged close to the second surface, the 1 / 4 wave plate is arranged between the first lens and the second lens, and the reflective polarizing film is arranged on a side of the second lens away from the first lens.

11. The folded light path lens according to claim 2, further comprising: a third lens, wherein the third lens is arranged on a side of the first lens close to the second surface, the 1 / 4 wave plate is arranged on a side of the first lens close to the third lens, and the reflective polarizing film is arranged on a side of the 1 / 4 wave plate close to the third lens; a fourth lens, wherein the fourth lens is disposed on a side of the beam splitter film away from the first surface of the first lens; An anti-reflection coating is provided on a surface of the fourth lens away from the first lens.

12. An optical imaging system, comprising a display screen and the folded light path lens described in any one of claims 1 to 11, wherein the folded light path lens is located on the light emitting side of the display screen, and light emitted by the display screen is imaged after being emitted through the folded light path lens.

13. The optical imaging system according to claim 12, wherein the display screen is a micro OLED display screen.

14. A head-mounted display device, comprising the optical imaging system according to claim 12 or 13.

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