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

Abstract

The invention provides a folded optical path lens, an optical imaging system and a head-mounted display device. The folded optical path lens comprises: a first lens having a first surface and a second surface arranged oppositely, the first surface being a convex surface; the light splitting film is arranged on the first surface, the difference value between the reflectivity and the transmissivity of the light splitting film is smaller than or equal to 20%, the light splitting film comprises multiple optical coating layers which are arranged in a stacked mode, and the multiple optical coating layers comprise at least one non-metal transparent coating and at least one metal layer. Through the arrangement of the metal layer, the consistency of the transmittance of the folded light path lens to obliquely-incident light component s polarized light and p polarized light can be improved, then the ovality of the folded light path lens is effectively improved, the ovality of the folded light path lens is closer to 1, and then ghosting and stray light of the folded light path lens can be effectively reduced.

Description

Technical Field

[0001] The present invention 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

[0002] In virtual reality (VR) devices, near-eye display devices use lenses to magnify the image on the display screen, giving people an immersive feeling. The current mainstream lens technology has evolved from Fresnel lenses to ultra-short-focus folded optical path (Pancake) lenses, which greatly reduce the required distance between near-eye display devices and human eyes by folding the optical path, making VR devices lighter and thinner.

[0003] In a pancake lens, the key to folding the optical path is the mutual conversion between circularly polarized light and linearly polarized light, and the ellipticity of the circularly polarized light in the folded optical path of the pancake lens is an important physical quantity that determines the optical performance of the pancake. When the ellipticity is 1, it means that the polarized light is circularly polarized light, when the ellipticity is 0, it means that the polarized light is linearly polarized light, and when the ellipticity is between 0 and 1, it is elliptically polarized light. The closer to 1, the closer it is to circularly polarized light. The principle of the pancake lens requires that the ellipticity of the circularly polarized light in the folded optical path is as close to 1 as possible. If the ellipticity is low, a part of the light will not follow the designed folded optical path, and form stray light or ghost images, affecting the imaging experience. Summary of the invention

[0004] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, one object of the present invention is to provide a folded light path lens, which has a high ellipticity and can effectively reduce ghost images and stray light of the folded light path lens.

[0005] In one aspect of the present invention, the present invention provides a folded light path lens. According to an embodiment of the present invention, the folded light path lens includes: a first lens, the first lens has a first surface and a second surface arranged opposite to each other, the first surface is a convex surface; a spectroscopic film, 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 multi-layer stacked optical coating layer, the multi-layer optical coating layer includes at least one layer of non-metallic transparent coating and at least one layer of metal layer. Thus, by setting the metal layer, the consistency of the transmittance of the folded light path lens to the 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.

[0006] According to an embodiment of the present invention, the folded light path lens further comprises: a quarter wave plate, which is arranged on a side of the first lens away from the convex surface; and a reflective polarizing film, which is arranged on a side of the quarter wave plate away from the first lens.

[0007] According to an embodiment of the present invention, when 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%.

[0008] According to an embodiment of the present invention, 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%.

[0009] According to an embodiment of the present invention, when 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%.

[0010] According to an embodiment of the present invention, 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.

[0011] According to an embodiment of the present invention, 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.

[0012] According to an embodiment of the present invention, the outermost optical coating layer of the beam splitting film is the non-metallic transparent coating.

[0013] According to an embodiment of the present invention, the absorption rate of the prismatic film to visible light is less than or equal to 25%.

[0014] According to an embodiment of the present invention, the folded light 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 a side of the second lens away from the first lens.

[0015] According to an embodiment of the present invention, 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.

[0016] In another aspect of the present invention, the present invention provides an optical imaging system. According to an embodiment of the present invention, the optical imaging system includes a display screen and the folded light path lens described above, wherein the folded light path lens is located on the light exiting 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 image 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 can understand 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.

[0017] According to an embodiment of the present invention, the display screen is a micro OLED display screen.

[0018] In another aspect of the present invention, the present invention provides a head-mounted display device. According to an embodiment of the present invention, the head-mounted display device includes the above-mentioned optical imaging system. Thus, the imaging quality of the head-mounted display device is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0020] Figure 1 is a schematic diagram of the structure of a folded light path lens in one embodiment of the present invention;

[0021] Figure 2 It is the light path diagram in the folded light path lens;

[0022] Figure 3 is a schematic structural diagram of a folded optical path lens in another embodiment of the present invention;

[0023] Figure 4 is a schematic structural diagram of a folded optical path lens in another embodiment of the present invention;

[0024] Figure 5 is a schematic structural diagram of a folded optical path lens in Embodiment 1 of the present invention;

[0025] Figure 6is a reflectivity and transmittance curve of light when light with incident angles of 0° and 40° respectively enters the folded light path lens in Example 1 of the present invention;

[0026] Figure 7 It is a schematic structural diagram of the folded optical path lens in Comparative Example 1 of the present invention;

[0027] Figure 8 is the reflectivity and transmittance curve of the light when the light in comparative example 1 of the present invention is incident on the folded light path lens in embodiment 1 at incident angles of 0° and 40° respectively;

[0028] Fig. 9 is a schematic structural diagram of a folded optical path lens in Embodiment 2 of the present invention;

[0029] Fig.10 is a reflectivity and transmittance curve of light when light at incident angles of 0° and 40° respectively enters the folded light path lens in Example 1 in Example 2 of the present invention;

[0030] Fig.11 is a schematic structural diagram of a folded optical path lens in Comparative Example 2 of the present invention;

[0031] Fig.12 is the reflectivity and transmittance curve of the light when the light in comparative example 2 of the present invention is incident on the folded light path lens in embodiment 1 at incident angles of 0° and 40° respectively;

[0032] Fig.13 It is a schematic diagram of the positional relationship between the folded light path lens and the display screen. DETAILED DESCRIPTION

[0033] The scheme of the present invention will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used are not indicated by the manufacturer and are all conventional products that can be obtained commercially.

[0034] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0035] In one aspect of the present invention, the present invention provides a folded optical path lens. According to an embodiment of the present invention, referring to Figure 1The folded light path lens comprises: 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 being arranged on the convex surface, and the spectroscopic film comprising a plurality of optical coating layers stacked in layers, the plurality of optical coating layers comprising at least one layer of non-metallic transparent coating and at least one layer of metal layer. Thus, by setting the metal layer, the consistency of the transmittance of the folded light path lens to the obliquely incident light component s-polarized light and p-polarized light can be improved (that is, the difference in the transmittance of the light component s-polarized light and p-polarized light is made smaller), thereby effectively improving the ellipticity of the folded light path lens, making the ellipticity closer to 1, thereby effectively reducing the ghost image and stray light of the folded light path lens.

[0036] 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 / cosθ, ns = n cosθ, where np and ns are the equivalent refractive indices of p-light and s-light at the interface of the 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 the light is obliquely incident on the dielectric multilayer film. The response of metal materials to light is different from that of the medium. The reflection of the metal is generated by the induced current of the electrons in the metal to the incident optical field. According to the free electron model of metal materials (Drude model), the electrical conductivity of the metal is isotropic, which makes the metal reflectivity of the visible light very small on the angle of incidence. Therefore, in the present application, the setting of the metal layer can reduce the difference in the transmittance of the light components s-polarized light and p-polarized light, improve the consistency of the transmittance of the folded light path lens to the obliquely incident light components s-polarized light and p-polarized light, and then effectively improve the ellipticity of the folded light path lens, making its ellipticity close to 1.

[0037] The second surface of the first lens may be a plane or a concave surface, and those skilled in the art may flexibly select the specific structure of the first lens according to actual needs.

[0038] According to an embodiment of the present invention, referring to Figure 1 The folded optical path lens further includes: a quarter wave plate (i.e., a quarter wavelength phase delay film) 20, which is disposed on the side of the first lens 11 away from the convex surface; and a reflective polarizing film 30, which is disposed on the side of the quarter wave plate 20 away from the first lens 11. In the folded optical path (Pancake) lens, the function of the quarter wave plate is to change the polarization state of light, so that circularly polarized light becomes linearly polarized light, and linearly polarized light becomes circularly polarized light; the function of the reflective polarizing film is to reflect polarized light in another direction (such as p-polarized light) through polarized light in one direction (such as s-polarized light).

[0039] Combined with the structure of a specific folded optical path lens, refer to Figure 2 The specific principle of the folded light path lens is as follows: the display screen surface is equipped with a 1 / 4 wave plate (1 / 4 wavelength phase retardation film) to emit right-handed circularly polarized light 1. After passing through the beam splitter film, the polarization state of light 2 remains unchanged and is still right-handed circularly polarized light. Figure 2 After the 1 / 4 wavelength phase delay film is applied, the right-handed circularly polarized light becomes linearly polarized light polarized in the z-axis direction as shown in the figure 3. In the folded light path (Pancake) lens, the primary determinant of the ellipticity is the 1 / 4 wavelength phase delay film (QWP). The ideal QWP needs to delay the linear polarized light exactly to 1 / 4 of its wavelength when the linear polarized light is incident at a 45° angle to its optical axis, so that circularly polarized light with an ellipticity of 1 can be formed. If the delay is insufficient or greater than 1 / 4 of the wavelength, elliptical polarized light with an ellipticity lower than 1 will be formed. However, the inventors have found that the beam splitter film will also affect the ellipticity of the folded light path lens. If the incident angle of a beam splitter film is 0°, the transmittance of the s-polarized light and the p-polarized light of the incident light of the beam splitter film is 50% each. However, when the incident angle is larger, the difference in the transmittance of the s-polarized light and the p-polarized light of the incident light of the beam splitter film becomes significantly larger, which will seriously affect the ellipticity of the folded light path lens. Based on this, the inventors added at least one metal layer to the spectroscopic film, thereby greatly reducing the difference in transmittance of s-polarized light and p-polarized light of the incident light of the folded light path lens, thereby increasing the ellipticity of the folded light path lens and making its value closer to 1, thereby effectively reducing the ghost images and stray light of the folded light path lens.

[0040] According to some embodiments of the present invention, when light is incident on the folded 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 folded 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 folded light path lens is less than or equal to 20, or further, the difference is less than or equal to 10%. It can be seen that even if the light is incident on the folded 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 folded light path lens can still be made to have a high consistency (the smaller the difference in transmittance between the s-polarized light and the p-polarized light of the incident light of the folded light path lens, the smaller the difference in reflectance, and the higher the consistency), thereby ensuring a better ellipticity of the folded light path lens and effectively reducing ghost images and stray light of the folded light path lens. Furthermore, according to some embodiments of the present invention, when 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%.

[0041] Furthermore, the difference in transmittance of the s-polarized light and the p-polarized light incident on the folded light path lens is less than or equal to 10%, and the difference in reflectance of the s-polarized light and the p-polarized light incident on the folded light path lens is less than or equal to 10%. It can be seen that even if the light is incident on the folded light path lens at a larger incident angle (such as 40°, 42°, 45°, 47°, 50°, etc.), the transmittance and reflectance of the obliquely incident light components s-polarized light and p-polarized light of the folded light path lens can still be highly consistent, ensuring a better ellipticity of the folded light path lens and effectively reducing ghost images and stray light of the folded light path lens.

[0042] According to an embodiment of the present invention, the difference between the reflectivity and transmittance of the dichroic film is less than or equal to 20%, for example, the difference between the reflectivity (R) and transmittance (T) of the dichroic film is 20%, 18%, 15%, 12%, 8%, 6%, 4%, 2%, 0%, etc. In some specific embodiments, the reflectivity and transmittance of the dichroic film are specifically R40% / T60%, R60% / T40%, or R50% / T50. Since the metal layer has a certain light absorption to light, the reflectivity and transmittance of the dichroic film are specifically R48% / T48%, R45% / T45%, R40% / T50%, or R50% / T40%, etc.

[0043] According to an embodiment of the present invention, 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 trioxide, 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 light transmittance of the non-metallic transparent coating of the above material are relatively high. In some embodiments of the present invention, 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 by 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%, and at the same time, the absorption rate of the spectroscopic film to visible light will not be too large. According to some embodiments of the present invention, the absorption rate of the spectroscopic film to visible light is less than or equal to 25%, for example, the absorption rate of the spectroscopic film to visible light is 25%, 23%, 20%, 18%, 15%, 12%, 10%, 9%, 8%, 7%, 6%, 5%, 3%, 1%, etc. In this way, the better transmittance and reflectance of the folded light path lens can be better guaranteed. More preferably, in some embodiments, the absorption rate of the spectroscopic film to visible light is less than or equal to 10%.

[0044] According to an embodiment of the present invention, 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 well help to reduce the difference in transmittance of the s-polarized light and the 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 the ghost and stray light of the folded light path lens.

[0045] According to an embodiment of the present invention, the outermost optical coating layer of the spectroscopic film is a non-metallic transparent coating, that is, the metal layer is located in the middle of the spectroscopic film. Thus, the metal layer can be prevented from being oxidized, and if the metal layer is on the surface, it is difficult to achieve full spectrum spectroscopic consistency, that is, the spectroscopic film can be better designed to make the reflectivity and transmittance as close to the design value (such as 50%) as possible in the entire visible band.

[0046] According to an embodiment of the present invention, the metal layer can be formed by physical vapor deposition, such as thermal evaporation, electron beam evaporation, ion-assisted evaporation, magnetron sputtering, etc., or by chemical vapor deposition, atomic layer deposition, or electrochemical deposition, etc. The non-metallic transparent coating can be formed by physical vapor deposition, such as thermal evaporation, electron beam evaporation, ion-assisted evaporation, magnetron sputtering, etc., or by chemical vapor deposition, atomic layer deposition, or electrochemical deposition, etc.

[0047] According to some embodiments of the present invention, referring to Figure 3 The folded optical 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 arranged close to the second surface, or the second lens being arranged on the first lens 11 and away from the convex surface, a quarter wave plate 20 being arranged between the first lens 11 and the second lens 12, and a reflective polarizing film 30 being arranged on the side of the second lens 12 away from the first lens 11. Furthermore, in some embodiments, Figure 3 On the basis of the above, the folded optical path lens may further include a linear polarization film, a hardening film or an anti-reflection film between the reflective polarization 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 then can be bonded to the first lens 11 by optical adhesive.

[0048] According to other embodiments of the present invention, Figure 4 The folded optical path lens further includes: a third lens 13, which is disposed on the side of the first lens 11 close to 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 close to the third lens 13, and a reflective polarizing film 30 is disposed on the side of the quarter wave plate 20 close to the third lens 13; a fourth lens 14, which is disposed on the side of the beam splitting film 40 away from the first surface of the first lens 11; and an anti-reflection coating 52, which is disposed on the surface of the fourth lens 14 away from the first lens 11. Furthermore, in some embodiments, Figure 4On the basis of the above, the folded optical path lens may further include a linear polarization film, a hardening film or an anti-reflection film on the surface of the third lens 13 away from the first lens 11. In addition, the beam splitting film 40 is arranged on the convex surface of the first lens 11, and then can be bonded to the fourth lens 14 by optical adhesive.

[0049] According to an embodiment of the present invention, 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.

[0050] In another aspect of the present invention, the present invention provides an optical imaging system. According to an embodiment of the present invention, the optical imaging system includes a display screen and the folded light path lens described above, wherein 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 being emitted through the folded light path lens. As a result, the ghost images and stray lights 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 appreciate 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 herein. Among them, the first surface (i.e., the convex surface) of the first lens in the optical imaging system is arranged facing the display screen, and the second surface is arranged facing away from the display screen.

[0051] According to an embodiment of the present invention, the display screen is a micro OLED display screen. As mentioned above, in the present invention, even if the light is incident on the folding light path lens at a larger incident angle (such as 40°, 42°, 45°, 47°, 50°, etc.), the transmittance and reflectivity of the folding light path lens for the obliquely incident light components s-polarized light and p-polarized light can still be highly consistent, thereby ensuring a better ellipticity of the folding light path lens and effectively reducing the ghost and stray light of the folding 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 size of the display screen, the more likely it is that a larger incident angle will appear at the edge of the folding light path lens, such as Fig.13 As shown in the figure, 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, effectively reducing the ghost and stray light of the Pancake lens. That is to say, the Pancake lens of the present invention can be used in conjunction with small-sized and high-resolution micro OLED screens, helping to improve the display quality of virtual reality devices (such as virtual reality VR glasses) to a higher level than the current status.

[0052] Of course, those skilled in the art will appreciate that the display screen in the optical imaging system is also suitable for relatively large LCD display screens, wherein the closer the size of the display screen is to the size of the folded optical path lens, the less likely it is that a large incident angle will occur.

[0053] In another aspect of the present invention, the present invention provides a head-mounted display device. According to an embodiment of the present invention, the head-mounted display device includes the above-mentioned optical imaging system. Therefore, the imaging quality of the head-mounted display device is relatively high.

[0054] According to an embodiment of the present invention, the head-mounted display is virtual reality VR glasses.

[0055] Example

[0056] Example 1

[0057] The structure of the folded light path lens is as follows Figure 3 As shown, the first lens and the second lens are COC lenses respectively. The structure of the beam splitter film and the thickness of each layer of optical coating can be referred to Figure 5 .

[0058] When light rays with incident angles of 0° and 40° are incident on the folded light path lens in Example 1, the reflectivity and transmittance of the light rays passing through the folded light path lens can be referred to as Figure 6 (The horizontal axis is wavelength / nm, and the vertical axis is reflectivity R and transmittance T), where the reflectivity curve of the light incident on the folded light path lens at an incident angle of 0° is curve 1, the transmittance curve of the light incident on the folded light path lens at an incident angle of 0° is curve 2, the transmittance curve of the s-polarized light incident on the folded light path lens at an incident angle of 40° is curve 3, and the transmittance curve of the p-polarized light incident on the folded light path lens at an incident angle of 40° is curve 4. Figure 6 It can be seen that when a light ray with an incident angle of 40° enters the folded light path lens, the difference between the transmittance of the s-polarized light and the transmittance of the p-polarized light of the light ray is small, within 15%.

[0059] Comparative Example 1

[0060] The structure of the folded light path lens is as follows Figure 3 As shown, the first lens and the second lens are COC lenses respectively. The structure of the beam splitter film and the thickness of each layer of optical coating can be referred to Figure 7 .

[0061] When light rays with incident angles of 0° and 40° are incident on the folded light path lens in comparative example 1, the reflectivity and transmittance of the light rays passing through the folded light path lens can be referred to as Figure 8(The horizontal axis is wavelength / nm, and the vertical axis is reflectivity R and transmittance T), where the reflectivity curve of the light incident on the folded light path lens at an incident angle of 0° is curve 1, the transmittance curve of the light incident on the folded light path lens at an incident angle of 0° is curve 2, the transmittance curve of the s-polarized light incident on the folded light path lens at an incident angle of 40° is curve 3, and the transmittance curve of the p-polarized light incident on the folded light path lens at an incident angle of 40° is curve 4. Figure 8 It can be seen that when a light ray with an incident angle of 40° enters the folded light path lens, the difference between the transmittance of the s-polarized light and the transmittance of the p-polarized light of the light ray is relatively large, greater than 20%.

[0062] Example 2

[0063] The structure of the folded light path lens is as follows Figure 4 As shown, 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 Fig. 9 .

[0064] When light rays with incident angles of 0° and 40° are incident on the folded light path lens in Example 2, the reflectivity and transmittance of the light rays passing through the folded light path lens can be referred to as Fig.10 (The horizontal axis is wavelength / nm, and the vertical axis is reflectivity R and transmittance T), where the reflectivity curve of the light incident on the folded light path lens at an incident angle of 0° is curve 1, the transmittance curve of the light incident on the folded light path lens at an incident angle of 0° is curve 2, the transmittance curve of the s-polarized light incident on the folded light path lens at an incident angle of 40° is curve 3, and the transmittance curve of the p-polarized light incident on the folded light path lens at an incident angle of 40° is curve 4. Fig.10 It can be seen that when a light ray with an incident angle of 40° enters the folded light path lens, the difference between the transmittance of the s-polarized light and the transmittance of the p-polarized light of the light ray is small, within 6%.

[0065] Comparative Example 2

[0066] The structure of the folded light path lens is as follows Figure 4 As shown, 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 Fig.11 .

[0067] When light rays with incident angles of 0° and 40° are incident on the folded light path lens in comparative example 2, the reflectivity and transmittance of the light rays passing through the folded light path lens can be referred to as Fig.12(The horizontal axis is wavelength / nm, and the vertical axis is reflectivity R and transmittance T), where the reflectivity curve of the light incident on the folded light path lens at an incident angle of 0° is curve 1, the transmittance curve of the light incident on the folded light path lens at an incident angle of 0° is curve 2, the transmittance curve of the s-polarized light incident on the folded light path lens at an incident angle of 40° is curve 3, and the transmittance curve of the p-polarized light incident on the folded light path lens at an incident angle of 40° is curve 4. Fig.12 It can be seen that when a light ray with an incident angle of 40° enters the folded light path lens, the difference between the transmittance of the s-polarized light and the transmittance of the p-polarized light of the light ray is relatively large, greater than 30%.

[0068] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0069] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. 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 invention. 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 the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0070] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A folded light path lens, characterized in that: include: 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, characterized in that: Also includes: 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, characterized in that: When light is incident on the folded 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 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, characterized in that: 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, characterized in that: When light is incident on the folded light path lens at an angle of 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 light path lens according to claim 1 or 2, characterized in that: 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.

7. The folded light path lens according to claim 6, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: Also includes: 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, characterized in that: Also includes: 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, characterized in that: It comprises 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 at the light emitting side of the display screen, and the 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, characterized in that: The display screen is a micro OLED display screen.

14. A head mounted display device, characterized in that: Comprising the optical imaging system of claim 12 or 13.

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