Low-chromatic-aberration refractive-diffractive hybrid optical system

Abstract

The invention discloses a low-chromatic-aberration refractive-diffractive hybrid optical system, and the system comprises a display image source which is used for emitting imaging light; the first imaging prism unit comprises a first prism, a first polarization reflection film and a 1 / 4 wave plate, the first polarization reflection film is located between the first prism and the second imaging prism unit, and the 1 / 4 wave plate is located between the first prism and the first imaging lens unit; the first imaging lens unit is located on the side, away from the human eyes, of the first imaging prism unit and provided with at least one lens, the two mirror faces on the outermost side of the first imaging lens unit are diffraction faces, and the mirror face away from the first imaging prism unit is further provided with a semi-transparent and semi-reflective film; and the focal length f of the low-chromatic-aberration refractive-diffractive hybrid optical system is 6-14 mm. According to the invention, a large FOV can be realized, the thin and light color difference is small, and the excellent image quality is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical display, and particularly relates to a diffractive-refractive hybrid optical system with low chromatic aberration. Background Art

[0002] With the increasingly wide application of Augmented Reality (AR) technology, such as in smart wearable devices, the corresponding technologies are also constantly developing, making AR products more and more valued by people and being a next-generation mobile terminal expected to replace mobile phones. The core component of the augmented reality technology is the optical module, and the FOV, thickness, and display effect of the optical module will directly determine the quality of the smart wearable device. In particular, achieving a large FOV, being thin and light, and still having excellent image quality at the same time has become the key restricting the development of AR technology.

[0003] In current AR solutions, the mass-produced solutions that can present better imaging effects are the Birdbath solution and the folded optical path solution (pancake solution). However, neither of the two solutions can achieve a large FOV, and since the refractive indices of light with different wavelengths in the same material are different, which will lead to different optical paths, there is a chromatic aberration problem, resulting in an inability to provide a good imaging effect and having relatively serious color deviation and light effect problems. In addition, the Birdbath solution often has a thickness of 18 - 20 mm, and its thickness is difficult to meet the daily wearing needs of people. And the thinner folded optical path solution (pancake solution) has requirements for stress in the polarization system of AR (Augmented Reality) / VR (Virtual Reality) / XR (Extended Reality) / MR (Mix Reality), ensuring that the lens stress is below 30 nm, otherwise there will be inconsistent color temperature. Compared with the prior art, through the combination of different materials, positive / negative chromatic aberration calibration is achieved. Due to the stress requirements of the pancake solution, there is currently only one available material, resulting in the need for all component materials to be the same, making it difficult to calibrate chromatic aberration, and its chromatic aberration performance is relatively poor, becoming a bottleneck problem in AR solutions. Summary of the Invention

[0004] The purpose of the present invention is to propose a diffractive-refractive hybrid optical system with low chromatic aberration for the above problems, which can achieve a large FOV, be thin and light, and have small chromatic aberration while achieving excellent image quality.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A diffractive-refractive hybrid optical system with low chromatic aberration proposed by the present invention has a focal length f of 6 mm to 14 mm, and includes:

[0007] An image display source for emitting imaging light rays;

[0008] A first imaging prism unit, including a first prism, a first polarization reflection film, and a quarter-wave plate. The first polarization reflection film is located between the first prism and the second imaging prism unit. The quarter-wave plate is located between the first prism and the first imaging lens unit, or between the first prism and the first polarization reflection film. The first imaging prism unit is configured to reflect the imaging light rays multiple times and then enter the first imaging lens unit, as well as transmit the reflected light rays of the first imaging lens unit;

[0009] A second imaging prism unit, including a second prism, which is configured to transmit the transmitted light rays of the first imaging prism unit to the human eye;

[0010] A first imaging lens unit, located on the side of the first imaging prism unit away from the human eye and having at least one lens. The outermost two mirror surfaces of the first imaging lens unit are both diffractive surfaces, and a semi-transmissive and semi-reflective film is further provided on the mirror surface away from the first imaging prism unit.

[0011] Preferably, the focal length f4 of the first imaging lens unit is 5 mm to 15 mm.

[0012] Preferably, the first imaging lens unit includes a first lens and both mirror surfaces of the first lens are diffractive surfaces, and the following conditions are satisfied:

[0013] 500 < C41; 30 < C42 < 80

[0014] Wherein, C41 is the radius of curvature of the mirror surface of the first lens close to the first imaging prism unit, and C42 is the radius of curvature of the mirror surface of the first lens away from the first imaging prism unit, with the unit of mm.

[0015] Preferably, the low chromatic aberration refractive-diffractive hybrid optical system further includes a second imaging lens unit having at least one lens, and the focal length f5 of the second imaging lens unit is 5 mm to 15 mm.

[0016] Preferably, the second imaging lens unit includes a second lens, and the following conditions are satisfied:

[0017] 10 < C51 < 80; 30 < C52

[0018] Wherein, C51 is the radius of curvature of the mirror surface of the second lens close to the first imaging prism unit, and C52 is the radius of curvature of the mirror surface of the second lens close to the image display source, with the unit of mm.

[0019] Preferably, the low chromatic aberration refractive-diffractive hybrid optical system further satisfies the following conditions:

[0020] 1 < d2 < 5.0; 1 < d3 < 5.0; 0.5 < d4 < 3.5; 0.5 < d5 < 3.5;

[0021] 0.15 < D1 < 2.0; 0.1 < D2 < 3.0; 0 < D3 < 2.0; 0.05 < D4 < 2.0;

[0022] Among them, d2 is the thickness of the first imaging prism unit along the reflection direction of the first imaging lens unit, d3 is the thickness of the second imaging prism unit along the reflection direction of the first imaging lens unit, d4 is the thickness of the first imaging lens unit, d5 is the thickness of the second imaging lens unit, D1 is the air gap between the second imaging lens unit and the display image source, D2 is the air gap between the first imaging prism unit and the second imaging lens unit, D3 is the air gap between the second imaging prism unit and the first imaging prism unit, D4 is the air gap between the first imaging lens unit and the first imaging prism unit, with the unit of mm.

[0023] Preferably, the apochromatic refractive-diffractive hybrid optical system further satisfies the following conditions:

[0024] 1.5 < n2 < 1.9; 30 < Vd2 < 65;

[0025] 1.5 < n3 < 1.9; 30 < Vd3 < 65;

[0026] 1.5 < n4 < 1.8; 20 < Vd4 < 65

[0027] 1.5 < n5 < 1.7; 20 < Vd5 < 65;

[0028] Among them, n2 is the refractive index of the first imaging prism unit, Vd2 is the Abbe number of the first imaging prism unit, n3 is the refractive index of the second imaging prism unit, Vd3 is the Abbe number of the second imaging prism unit, n4 is the refractive index of the first imaging lens unit, Vd4 is the Abbe number of the first imaging lens unit, n5 is the refractive index of the second imaging lens unit, and Vd5 is the Abbe number of the second imaging lens unit.

[0029] Preferably, at least one surface of the first prism is a diffractive surface, and at least one lens surface of the second imaging lens unit is a diffractive surface.

[0030] Preferably, a linear polarizing film is attached to the light-emitting side of the display image source. The linear polarizing film is used to convert the imaging light into 45° linearly polarized light and has a thickness of 10 μm to 300 μm; a polarizer is attached to the surface of the second imaging prism unit close to the human eye, and the thickness of the polarizer is 10 μm to 300 μm.

[0031] Preferably, the included angle between the slow axis of the quarter-wave plate and the reflection axis of the first polarization reflection film is 45° ± 1°, the thickness of the first polarization reflection film is 10 μm to 300 μm, the thickness of the quarter-wave plate is 10 μm to 300 μm, and the thickness of the semi-transmissive and semi-reflective film is 30 μm to 500 μm.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] The present invention adopts a refractive-diffractive hybrid folding optical path scheme, utilizes the principles of light diffraction, refraction, reflection, and polarization, realizes a shorter optical path through folding optical elements (such as the first imaging prism unit and the first imaging lens unit), and corrects chromatic aberration of different wavelengths through a diffractive surface, compensates for the difference in refractive indices of different wavelengths of materials, obtains a large FOV, thin and light optical system, has small chromatic aberration, realizes excellent image quality, and improves the user experience. Description of the Drawings

[0034] Figure 1 It is a schematic structural diagram of the low-chromatic-aberration refractive-diffractive hybrid optical system of the present invention;

[0035] Figure 2 It is a schematic optical path diagram of the low-chromatic-aberration refractive-diffractive hybrid optical system of the present invention;

[0036] Figure 3 It is a schematic diagram of chromatic aberration modulation of the lens, diffractive surface, and the combination of the lens and the diffractive surface of the present invention;

[0037] Figure 4 It is the MTF diagram of Embodiment 1 of the present invention;

[0038] Figure 5 It is the chromatic aberration diagram of Embodiment 1 of the present invention.

[0039] Description of the reference numerals: 1. Display image source; 2. First imaging prism unit; 3. Second imaging prism unit; 4. First imaging lens unit; 5. Second imaging lens unit. Detailed Embodiments

[0040] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0041] It should be noted that when a component is referred to as being "connected" to another component, it can be directly connected to the other component or there can also be an intermediate component. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field of this application. The terms used in the specification of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0042] As Figures 1 - 5 shown, a low chromatic aberration refractive-diffractive hybrid optical system, the focal length f of the low chromatic aberration refractive-diffractive hybrid optical system is 6 mm to 14 mm, and it includes:

[0043] A display image source 1 for emitting imaging light;

[0044] A first imaging prism unit 2, including a first prism, a first polarization reflection film and a quarter-wave plate. The first polarization reflection film is located between the first prism and the second imaging prism unit 3, and the quarter-wave plate is located between the first prism and the first imaging lens unit 4, or between the first prism and the first polarization reflection film. And the first imaging prism unit 2 is used for reflecting the imaging light multiple times and then entering the first imaging lens unit 4, and transmitting the reflected light of the first imaging lens unit 4;

[0045] A second imaging prism unit 3, including a second prism, and the second prism is used for transmitting the transmitted light of the first imaging prism unit 2 to the human eye;

[0046] A first imaging lens unit 4, located on the side of the first imaging prism unit 2 away from the human eye and having at least one lens. The outermost two lens surfaces of the first imaging lens unit 4 are both diffractive surfaces, and a semi-transmissive and semi-reflective film is also provided on the lens surface far from the first imaging prism unit 2.

[0047] Among them, the display image source 1 includes but is not limited to the following devices: such as being one of an OLED display, an LCOS display, a Microled display, a DLP display, an LBS display, preferably an OLED display and is inclined. The first prism and the second prism are preferably triangular prisms.

[0048] The first imaging prism unit 2 includes a first prism and a film system with a light modulation function. The film system includes a first polarization reflection film and a quarter-wave plate. Among them, the first prism can be made of plastic or glass, and the film system can be attached to the first prism or plated on the first prism, and this film system plays a function of light polarization reflection. The second prism of the second imaging prism unit 3 can be made of plastic or glass. Or the film system can also be attached to or plated on the second prism.

[0049] The first imaging lens unit 4 can adopt a refractive-diffractive hybrid lens with aberration correction function and a lens group with an optical path reflection function. Each lens in the lens group can be made of glass or plastic, and a semi-transmissive and semi-reflective film is also provided on the mirror surface far from the first imaging prism unit 2. The semi-transmissive and semi-reflective film can be realized by coating or laminating.

[0050] This application adopts a diffraction surface to correct chromatic aberration. Through the optical architecture of the refractive-diffractive hybrid lens, chromatic aberration is corrected. The key mechanism to achieve this compensation is phase modulation. The microscopic annular structure of the diffraction surface will generate an additional optical path difference related to the wavelength. By controlling the spacing and step height of these rings, the propagation phase of light waves with different wavelengths can be precisely adjusted. As shown in Figure 3 Figure (a) in, which is the working principle diagram of the lens. Natural light NL passes through the lens. Since different wavelengths have different optical paths in the same material, positive chromatic aberration as shown in the figure will be generated between different light rays (such as red light R and blue light B). As shown in Figure 3 Figure (b) in, which is the working principle diagram of the diffraction surface. Through reasonable diffraction surface design, negative chromatic aberration is generated. As shown in Figure 3 Figure (c) in, which is the working principle diagram of the combination of the lens and the diffraction surface. By canceling the positive chromatic aberration of the lens and the negative chromatic aberration of the diffraction surface, chromatic aberration is eliminated, and it can be applied to the chromatic aberration correction of AR systems, VR systems, XR systems, and MR systems, with a wide range of applications.

[0051] In one embodiment, the focal length f4 of the first imaging lens unit 4 is 5 mm to 15 mm.

[0052] In one embodiment, the first imaging lens unit 4 includes a first lens, and both mirror surfaces of the first lens are diffraction surfaces, and the following conditions are satisfied:

[0053] 500 < C41; 30 < C42 < 80

[0054] Wherein, C41 is the radius of curvature of the mirror surface of the first lens close to the first imaging prism unit 2, and C42 is the radius of curvature of the mirror surface of the first lens far from the first imaging prism unit 2, with the unit of mm.

[0055] In one embodiment, the low-chromatic-aberration refractive-diffractive hybrid optical system further includes a second imaging lens unit 5 having at least one lens, and the focal length f5 of the second imaging lens unit 5 is 5 mm to 15 mm.

[0056] Among them, the second imaging lens unit 5 is a lens group with aberration correction function. The lenses in the lens group can be made of plastic or glass, and the surface types include but are not limited to the following types: refractive-diffractive hybrid lens, spherical lens, aspherical lens, free-form lens, Fresnel lens, flat lens, etc., and preferably a refractive-diffractive hybrid lens.

[0057] In one embodiment, the second imaging lens unit 5 includes a second lens and satisfies the following conditions:

[0058] 10 < C51 < 80; 30 < C52

[0059] where C51 is the radius of curvature of the mirror surface of the second lens close to the first imaging prism unit 2, and C52 is the radius of curvature of the mirror surface of the second lens close to the display image source 1, with the unit of mm.

[0060] In one embodiment, the low chromatic aberration refractive-diffractive hybrid optical system further satisfies the following conditions:

[0061] 1 < d2 < 5.0; 1 < d3 < 5.0; 0.5 < d4 < 3.5; 0.5 < d5 < 3.5;

[0062] 0.15 < D1 < 2.0; 0.1 < D2 < 3.0; 0 < D3 < 2.0; 0.05 < D4 < 2.0;

[0063] where d2 is the thickness of the first imaging prism unit 2 along the reflection direction of the first imaging lens unit 4, d3 is the thickness of the second imaging prism unit 3 along the reflection direction of the first imaging lens unit 4, d4 is the thickness of the first imaging lens unit 4, d5 is the thickness of the second imaging lens unit 5, D1 is the air gap between the second imaging lens unit 5 and the display image source 1, D2 is the air gap between the first imaging prism unit 2 and the second imaging lens unit 5, D3 is the air gap between the second imaging prism unit 3 and the first imaging prism unit 2, and D4 is the air gap between the first imaging lens unit 4 and the first imaging prism unit 3, with the unit of mm.

[0064] In one embodiment, the low chromatic aberration refractive-diffractive hybrid optical system further satisfies the following conditions:

[0065] 1.5 < n2 < 1.9; 30 < Vd2 < 65;

[0066] 1.5 < n3 < 1.9; 30 < Vd3 < 65;

[0067] 1.5 < n4 < 1.8; 20 < Vd4 < 65

[0068] 1.5 < n5 < 1.7; 20 < Vd5 < 65;

[0069] Wherein, n2 is the refractive index of the first imaging prism unit 2, Vd2 is the Abbe number of the first imaging prism unit 2, n3 is the refractive index of the second imaging prism unit 3, Vd3 is the Abbe number of the second imaging prism unit 3, n4 is the refractive index of the first imaging lens unit 4, Vd4 is the Abbe number of the first imaging lens unit 4, n5 is the refractive index of the second imaging lens unit 5, and Vd5 is the Abbe number of the second imaging lens unit 5.

[0070] In one embodiment, at least one surface of the first prism is a diffractive surface, and at least one lens surface of the second imaging lens unit 5 is a diffractive surface.

[0071] Wherein, preferably, both surfaces of the second lens are diffractive surfaces, and the surface of the first prism close to the second imaging lens unit 5 is a diffractive surface.

[0072] In one embodiment, a linear polarizing film is attached to the light-emitting side of the display image source 1. The linear polarizing film is used to convert the imaging light into 45° linearly polarized light and has a thickness of 10 μm to 300 μm; a polarizing sheet is attached to the surface of the second imaging prism unit 3 close to the human eye, and the thickness of the polarizing sheet is 10 μm to 300 μm.

[0073] Wherein, if the thickness of the polarizing sheet is too thin, it is impossible to stack and form to ensure the effect. If the thickness is too thick, light is reflected inside, resulting in ghost images. Therefore, 10 μm to 300 μm can not only ensure the effect but also avoid other negative effects and is used to eliminate external stray light.

[0074] Specifically, when there is no second imaging lens unit 5, no rainbow pattern is generated, and at this time, there is a high design compatibility, which is conducive to mass production. The second imaging lens unit 5 with a positive focal length can constrain and converge the imaging light before the imaging light enters the first imaging prism unit 2. Therefore, when the display image source 1 moves relative to the first imaging prism unit 2 for diopter adjustment, the required movement amount is small. By attaching a polarizing sheet to the near-eye surface of the second imaging prism unit, the rainbow pattern can also be reduced. The principle is to use linearly polarized light in the imaging direction to weaken half of the stray light without affecting imaging, such as weakening the parallel or vertical linearly polarized light of the stray light.

[0075] In one embodiment, the included angle between the slow axis of the quarter-wave plate and the reflection axis of the first polarization reflection film is 45° ± 1°, the thickness of the first polarization reflection film is 10 μm to 300 μm, the thickness of the quarter-wave plate is 10 μm to 300 μm, and the thickness of the semi-transmissive and semi-reflective film is 30 μm to 500 μm.

[0076] Among them, to ensure the imaging effect, there is a certain angular relationship between the first polarization reflection film and the quarter-wave plate. The slow axis of the quarter-wave plate needs to be attached at a 45° angle to the reflection axis of the first polarization reflection film, with a tolerance of plus or minus one degree. This can ensure that linearly polarized light becomes standard circularly polarized light. The reflection axis of the first polarization reflection film and the absorption axis of the polarizer need to be parallel, which is beneficial for eliminating double images.

[0077] Working principle:

[0078] As Figure 1 shown, the display image source 1 emits imaging light rays, which are converted into 45° linearly polarized light (the polarization transmission direction is perpendicular to the paper plane and into the paper) through the linear polarization film. The 45° linearly polarized light passes through the second imaging lens unit 5 and undergoes the first reflection on one side of the first prism close to the quarter-wave plate. The 45° linearly polarized light after the first reflection undergoes the second reflection on one side of the first prism close to the first polarization reflection film and forms left-handed circularly polarized light through the quarter-wave plate. The left-handed circularly polarized light undergoes the third reflection on the semi-transmissive and semi-reflective film to form right-handed circularly polarized light. The right-handed circularly polarized light is again converted into -45° linearly polarized light through the action of the quarter-wave plate and then passes through the first polarization reflection film and the second imaging prism unit 3 in sequence to enter the human eye eye for imaging. The first polarization reflection film is used to transmit -45° linearly polarized light and reflect 45° linearly polarized light, and realizes the conversion between linearly polarized light and circularly polarized light. And in combination with the evaporated semi-transmissive and semi-reflective film, the polarization state of circularly polarized light can be converted.

[0079] For easy understanding, the following will be elaborated in detail through specific embodiments.

[0080] Any surface of the low chromatic aberration refractive-diffractive hybrid optical system that is aspherical adopts an even-order aspherical surface type and satisfies the following formula:

[0081]

[0082] where z is the sagittal height, Y is the lens center height, k is the conic coefficient, C is the curvature, equal to 1 / R, R is the radius of curvature, a i represents the i-th aspherical coefficient, and N is a positive integer.

[0083] The diffractive surfaces of the low chromatic aberration refractive-diffractive hybrid optical system all satisfy the following formula:

[0084]

[0085] where Z(p) is the phase of the diffractive surface, M is the diffraction order, the diffraction order is 1, B j is the high-order term phase coefficient, p is the normalized radius, and K is a positive integer. In the following tables of each embodiment, Max trem represents the maximum number of terms, that is, the total number of terms of B j .

[0086] Example 1:

[0087] As Figures 4 - 5 shown, the optical parameters of this example are as shown in Table 1 and Table 2 below.

[0088] Table 1

[0089] Surface number Surface type Radius of curvature (mm) Thickness (spacing) (mm) Name OBJ Standard Infinity -2500 Virtual image distance Stop Standard Infinity 15 Eyerelief (eye relief) S1 Standard Infinity 2.9 First imaging prism unit S2 Standard Infinity 2.7 Second imaging prism unit S3 Diffraction surface 790 2.1 First imaging lens unit S4 Diffraction surface 29.5 -2.1 First imaging lens unit S5 Standard 20 2.5 Second imaging lens unit S6 Standard Infinity 1 Second imaging lens unit IMG Infinity Display image source

[0090] Table 2

[0091]

[0092] According to the above parameters, as Figure 4 shown, this is the MTF graph of this example. The MTF is greater than 0.3 at 17 lp / mm. Since this optical system belongs to a visual optical system, considering the angular resolution of the human eye, this MTF index can ensure that the human eye receives a very clear and sharp image, effectively guaranteeing the wearing experience. The chromatic aberration is less than 25 um, which is hardly noticeable to the human eye, and the imaging quality is good. Moreover, the field of view FOV of this system can reach 60°, and the thickness is less than 12 mm, all of which are superior to the Birdbath solution in the prior art.

[0093] Example 2:

[0094] The optical parameters of this example are as shown in Table 3 and Table 4 below.

[0095] Table 3

[0096] Surface number Surface type Radius of curvature (mm) Thickness (spacing) (mm) Name OBJ Standard Infinity -2500 Virtual image distance Stop Standard Infinity 15 Eyerelief (eye relief) S1 Standard Infinity 3.5 First imaging prism unit S2 Standard Infinity 2.5 Second imaging prism unit S3 Diffraction surface 860 2.1 First imaging lens unit S4 Diffraction surface 60 -2.1 First imaging lens unit S5 Standard 20 2.5 Second imaging lens unit S6 Standard Infinity 1 Second imaging lens unit IMG Infinity Display image source

[0097] Table 4

[0098]

[0099] According to the above parameters, the MTF of this example is greater than 0.3 at 17 lp / mm. Since this optical system belongs to a visual optical system, considering the angular resolution of the human eye, this MTF index can ensure that the human eye receives a very clear and sharp image, effectively guaranteeing the wearing experience. The chromatic aberration is less than 25 um, which is hardly noticeable to the human eye, and the imaging quality is good. Moreover, the field of view FOV of this system can reach 60°, and the thickness is less than 12 mm, all of which are superior to the Birdbath solution in the prior art.

[0100] Example 3:

[0101] The optical parameters of this example are as shown in Table 5 and Table 6 below.

[0102] Table 5

[0103] Surface number Surface type Radius of curvature (mm) Thickness (spacing) (mm) Name OBJ Standard Infinity -2500 Virtual image distance Stop Standard Infinity 15 Eyerelief (eye relief) S1 Standard Infinity 3.2 First imaging prism unit S2 Standard Infinity 2.4 Second imaging prism unit S3 Diffraction surface Infinity 2.2 First imaging lens unit S4 Diffraction surface 61 -2.2 First imaging lens unit S5 Standard 21 2.8 Second imaging lens unit S6 Standard Infinity 1 Second imaging lens unit IMG Infinity Display image source

[0104] Table 6

[0105]

[0106] According to the above parameters, the MTF of this embodiment is greater than 0.3 at 17 lp / mm. Since this optical system belongs to a visual optical system, combined with the angular resolution of the human eye, this MTF index can ensure that the human eye receives a very clear and sharp image, effectively guaranteeing the wearing experience. The chromatic aberration is less than 25 μm, which is hardly perceptible to the human eye, and the imaging quality is good. Moreover, the field of view (FOV) of this system can reach 60°, and the thickness is less than 12 mm, all of which are superior to the Birdbath solution in the prior art.

[0107] Embodiment 4:

[0108] The optical parameters of this embodiment are shown in Tables 7 and 8 below.

[0109] Table 7

[0110] Surface number Surface type Radius of curvature (mm) Thickness (spacing) (mm) Name OBJ Standard Infinity -2500 Virtual image distance Stop Standard Infinity 15 Eyerelief (eye relief) S1 Standard Infinity 3.0 First imaging prism unit S2 Standard Infinity 2.5 Second imaging prism unit S3 Diffraction surface 790 2.1 First imaging lens unit S4 Diffraction surface 59 -2.1 First imaging lens unit S5 Standard 20 2.6 Second imaging lens unit S6 Standard Infinity 1 Second imaging lens unit IMG Infinity Display image source

[0111] Table 8

[0112]

[0113] According to the above parameters, the MTF of this embodiment is greater than 0.3 at 17 lp / mm. Since this optical system belongs to a visual optical system, combined with the angular resolution of the human eye, this MTF index can ensure that the human eye receives a very clear and sharp image, effectively guaranteeing the wearing experience. The chromatic aberration is less than 25 μm, which is hardly perceptible to the human eye, and the imaging quality is good. Moreover, the field of view (FOV) of this system can reach 60°, and the thickness is less than 12 mm, all of which are superior to the Birdbath solution in the prior art.

[0114] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0115] The above-described embodiments only represent the embodiments of the present application that are described more specifically and in detail, but should not be construed as a limitation on the scope of the application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A refractive-diffractive hybrid optical system with low chromatic aberration, characterized in that: The focal length f of the low chromatic aberration refractive-diffractive hybrid optical system is 6 mm to 14 mm, and it includes: A display image source (1) for emitting imaging light rays; A first imaging prism unit (2), including a first prism, a first polarization reflection film, and a quarter-wave plate. The first polarization reflection film is located between the first prism and the second imaging prism unit (3), and the quarter-wave plate is located between the first prism and the first imaging lens unit (4), or between the first prism and the first polarization reflection film. The first imaging prism unit (2) is configured to reflect the imaging light rays multiple times and then enter the first imaging lens unit (4), as well as transmit the reflected light rays of the first imaging lens unit (4); A second imaging prism unit (3), including a second prism, which is configured to transmit the transmitted light rays of the first imaging prism unit (2) to the human eye; A first imaging lens unit (4), located on the side of the first imaging prism unit (2) away from the human eye and having at least one lens. The outermost two surfaces of the first imaging lens unit (4) are both diffractive surfaces, and a semi-transmissive and semi-reflective film is also provided on the surface away from the first imaging prism unit (2).

2. The diffractive-refractive hybrid optical system with low chromatic aberration according to claim 1, characterized in that: The focal length f4 of the first imaging lens unit (4) is 5 mm to 15 mm.

3. The diffractive-refractive hybrid optical system with low chromatic aberration according to claim 2, characterized in that: The first imaging lens unit (4) includes a first lens, and both surfaces of the first lens are diffractive surfaces, and satisfy the following conditions: 500 < C41; 30 < C42 < 80 Wherein, C41 is the radius of curvature of the surface of the first lens close to the first imaging prism unit (2), and C42 is the radius of curvature of the surface of the first lens away from the first imaging prism unit (2), with the unit of mm.

4. The diffractive-refractive hybrid optical system with low chromatic aberration according to claim 1, characterized in that: The low chromatic aberration refractive-diffractive hybrid optical system further includes a second imaging lens unit (5) having at least one lens, and the focal length f5 of the second imaging lens unit (5) is 5 mm to 15 mm.

5. The diffractive-refractive hybrid optical system with low chromatic aberration according to claim 4, characterized in that: The second imaging lens unit (5) includes a second lens, and satisfies the following conditions: 10 < C51 < 80; 30 < C52 Wherein, C51 is the radius of curvature of the surface of the second lens close to the first imaging prism unit (2), and C52 is the radius of curvature of the surface of the second lens close to the display image source (1), with the unit of mm.

6. The diffractive-refractive hybrid optical system with low chromatic aberration according to claim 4, wherein: The low chromatic aberration refractive-diffractive hybrid optical system further satisfies the following conditions: 1 < d2 < 5.0; 1 < d3 < 5.0; 0.5 < d4 < 3.5; 0.5 < d5 < 3.5; 0.15 < D1 < 2.0; 0.1 < D2 < 3.0; 0 < D3 < 2.0; 0.05 < D4 < 2.0; Wherein, d2 is the thickness of the first imaging prism unit (2) along the reflection direction of the first imaging lens unit (4), d3 is the thickness of the second imaging prism unit (3) along the reflection direction of the first imaging lens unit (4), d4 is the thickness of the first imaging lens unit (4), d5 is the thickness of the second imaging lens unit (5), D1 is the air gap between the second imaging lens unit (5) and the display image source (1), D2 is the air gap between the first imaging prism unit (2) and the second imaging lens unit (5), D3 is the air gap between the second imaging prism unit (3) and the first imaging prism unit (2), D4 is the air gap between the first imaging lens unit (4) and the first imaging prism unit (2), with the unit of mm.

7. The diffractive-refractive hybrid optical system with low chromatic aberration according to claim 4, characterized in that: The low chromatic aberration refractive-diffractive hybrid optical system also satisfies the following conditions: 1.5 < n2 < 1.9; 30 < Vd2 < 65; 1.5 < n3 < 1.9; 30 < Vd3 < 65; 1.5 < n4 < 1.8; 20 < Vd4 < 65 1.5 < n5 < 1.7; 20 < Vd5 < 65; Wherein, n2 is the refractive index of the first imaging prism unit (2), Vd2 is the Abbe number of the first imaging prism unit (2), n3 is the refractive index of the second imaging prism unit (3), Vd3 is the Abbe number of the second imaging prism unit (3), n4 is the refractive index of the first imaging lens unit (4), Vd4 is the Abbe number of the first imaging lens unit (4), n5 is the refractive index of the second imaging lens unit (5), and Vd5 is the Abbe number of the second imaging lens unit (5).

8. The diffractive-refractive hybrid optical system with low chromatic aberration according to claim 4, wherein: At least one surface of the first prism is a diffractive surface, and at least one lens surface of the second imaging lens unit (5) is a diffractive surface.

9. The diffractive-refractive hybrid optical system with low chromatic aberration according to claim 4, wherein: A linear polarizing film is attached to the light-emitting side of the display image source (1), and the linear polarizing film is used to convert imaging light into 45° linearly polarized light with a thickness of 10 μm to 300 μm; a polarizer is attached to the surface of the second imaging prism unit (3) close to the human eye, and the thickness of the polarizer is 10 μm to 300 μm.

10. The diffractive-refractive hybrid optical system with low chromatic aberration according to claim 1, characterized in that: The included angle between the slow axis of the quarter-wave plate and the reflection axis of the first polarization reflection film is 45° ± 1°, the thickness of the first polarization reflection film is 10 μm to 300 μm, the thickness of the quarter-wave plate is 10 μm to 300 μm, and the thickness of the semi-transmissive semi-reflective film is 30 μm to 500 μm.

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