Projection lens

Abstract

The utility model provides a projection lens. The projection lens sequentially comprises, from a first side to a second side, a first lens whose first side surface is a curved surface and whose second side surface is a diffraction surface; a second lens; the first side surface of the third lens is a curved surface, and the second side surface of the third lens is a diffraction surface; a fourth lens; wherein the second lens and the fourth lens are both refraction lenses, and the focal length f3 of the third lens and the total focal length f of the projection lens meet the condition that f3 / f is larger than or equal to 2 and smaller than or equal to 0. According to the utility model, the problem that miniaturization and high imaging quality of a projection lens in the prior art are difficult to consider at the same time is solved.

Description

Technical Field

[0001] The utility model relates to the technical field of optical imaging equipment, in particular to a projection lens. Background Art

[0002] With the rapid development of augmented reality (AR) smart wearable devices, consumers can enjoy the convenience brought by AR devices in travel, entertainment, productivity, etc. As a wearable device, miniaturization and wearability are more in line with consumers' usage needs and development trends. Among them, the core component of AR devices is the projection lens. For example, in AR glasses, the projection lens acts as an engine to project image information into the human eye. In this context, wafer-level optical elements (WLO) are particularly suitable for AR micro-projection devices due to their miniaturization and integration advantages.

[0003] However, if the wafer-level projection lens meets the requirements of high-quality projection and miniaturization of structure, the lens surface shape in the lens must be relatively complex. The characteristic of the wafer-level optical component manufacturing process is that the refractive surface is pressed on the glass substrate through optical glue, and more surface shapes are added to meet the high-quality requirements of projection. In order to ensure the imaging quality of the projection lens, multiple surface shapes need to be used, but the increase in surface shapes undoubtedly increases the total length of the system, which is not conducive to miniaturization.

[0004] That is to say, the projection lens in the prior art has the problem that it is difficult to achieve both miniaturization and high imaging quality at the same time. Utility Model Content

[0005] The main purpose of the utility model is to provide a projection lens to solve the problem that it is difficult to simultaneously achieve both miniaturization and high imaging quality in the projection lens in the prior art.

[0006] In order to achieve the above-mentioned purpose, the utility model provides a projection lens, which includes, from the first side to the second side, in sequence: a first lens, wherein the first side surface of the first lens is a curved surface, and the second side surface of the first lens is a diffraction surface; a second lens; a third lens, wherein the first side surface of the third lens is a curved surface, and the second side surface of the third lens is a diffraction surface; and a fourth lens; wherein the second lens and the fourth lens are both refractive lenses, and the focal length f3 of the third lens satisfies the following relationship with the total focal length f of the projection lens: -2≤f3 / f≤0.

[0007] Furthermore, the diffraction surface is a metasurface.

[0008] Furthermore, the first side surface of the first lens is a convex surface, and the first side surface of the third lens is a concave surface.

[0009] Further, the first lens comprises, from the first side to the second side, an embossed glue layer, a glass layer and a diffraction layer, a surface of the embossed glue layer away from the glass layer is a first side surface of the first lens, and a surface of the diffraction layer away from the glass layer is a second side surface of the first lens; and / or the third lens comprises, from the first side to the second side, an embossed glue layer, a glass layer and a diffraction layer, a surface of the embossed glue layer away from the glass layer is a first side surface of the third lens, and a surface of the diffraction layer away from the glass layer is a second side surface of the third lens.

[0010] Further, the first side surface of the second lens is a concave surface or a convex surface, and the second side surface is a plane; and / or the first side surface of the fourth lens is a concave surface, and the second side surface is a convex surface.

[0011] Furthermore, the focal length f1 of the first lens and the total focal length f of the projection lens satisfy: 0≤f1 / f≤1.

[0012] Further, the focal length f2 of the second lens and the total focal length f of the projection lens satisfy: -4≤f2 / f≤0; and / or the focal length f4 of the fourth lens and the total focal length f of the projection lens satisfy: -7≤f4 / f≤0.

[0013] Furthermore, the projection lens system further comprises an aperture, which is located on a first side of the first lens 60, and a size of the aperture matches an entrance pupil size of the optical waveguide structure.

[0014] Furthermore, the field of view FOV of the projection lens is greater than 28° and less than 32°.

[0015] Furthermore, the first side surface of the first lens, the first side surface of the second lens, the first side surface of the third lens, the first side surface of the fourth lens and the second side surface of the fourth lens are all aspherical surfaces.

[0016] By applying the technical solution of the utility model, the projection lens includes a first lens, a second lens, a third lens and a fourth lens in sequence from the first side to the second side; the first side surface of the first lens is a curved surface, and the second side surface of the first lens is a diffractive surface; the first side surface of the third lens is a curved surface, and the second side surface of the third lens is a diffractive surface; wherein the second lens and the fourth lens are both refractive lenses, and the focal length f3 of the third lens satisfies the following relationship with the total focal length f of the projection lens: -2≤f3 / f≤0.

[0017] By setting the second lens and the fourth lens to be refractive lenses, the second lens and the fourth lens can realize the refraction of light. By setting the two side surfaces of the first lens to be curved surfaces and diffraction surfaces respectively, and the two side surfaces of the third lens to be curved surfaces and diffraction surfaces respectively, the first lens and the third lens can integrate the effects of refracted light and diffracted light, improve the functionality of the first lens and the third lens, and help to increase the imaging quality. In addition, by integrating the curved surface and the refractive surface on one lens, it is beneficial to save space and ensure the miniaturization of the projection lens. By constraining the relationship between the focal length f3 of the third lens and the total focal length f of the projection lens, it is beneficial to reasonably allocate the focal length of the third lens and ensure the reliability of the use of the third lens. The image light output by the display chip of the present application can be propagated through each lens, and the aberration of the projected image can be corrected, and finally the display chip can project a high-quality image in the optical system of a small-sized projection lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings:

[0019] Figure 1 A schematic diagram showing the structure of a projection lens of an optional embodiment of the utility model is shown;

[0020] Figure 2 Shows Figure 1 Another structural schematic diagram of the projection lens in FIG.

[0021] Figure 3 Shows Figure 1 MTF curve diagram of the projection lens in;

[0022] Figure 4 Shows Figure 1 Field curvature diagram of the projection lens in ;

[0023] Figure 5 Shows Figure 1 Distortion diagram of the projection lens in ;

[0024] Figure 6 Shows Figure 1 A phase distribution diagram of a diffraction surface of a first lens of a projection lens;

[0025] Figure 7 Shows Figure 1 Phase distribution diagram of the diffraction surface of the third lens of the projection lens.

[0026] The above drawings include the following reference numerals:

[0027] 60. First lens; 2. First side surface of the first lens; 3. Bonding surface of the first lens; 4. Second side surface of the first lens; 20. Second lens; 5. First side surface of the second lens; 6. Bonding surface of the second lens; 7. Second side surface of the second lens; 30. Third lens; 8. First side surface of the third lens; 9. Bonding surface of the third lens; 10. Second side surface of the third lens; 40. Fourth lens; 11. First side surface of the fourth lens; 12. First bonding surface of the fourth lens; 13. Second bonding surface of the fourth lens; 14. Second side surface of the fourth lens; 50. Flat glass; 15. First side surface of the flat glass; 16. Second side surface of the flat glass. DETAILED DESCRIPTION

[0028] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present utility model will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0029] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as commonly understood by ordinary technicians in the technical field to which this application belongs.

[0030] In the present invention, unless otherwise specified, the directional words used, such as "up, down, top, bottom", usually refer to the directions shown in the drawings, or to the components themselves in the vertical, perpendicular or gravity directions; similarly, for ease of understanding and description, "inside and outside" refer to the inside and outside relative to the outline of each component itself, but the above-mentioned directional words are not used to limit the present invention.

[0031] In order to solve the problem that it is difficult to simultaneously achieve both miniaturization and high imaging quality in the projection lens in the prior art, the utility model provides a projection lens.

[0032] like Figures 1 to 7 As shown, the projection lens includes a first lens 60, a second lens 20, a third lens 30 and a fourth lens 40 from the first side to the second side in sequence; the first side surface 2 of the first lens is a curved surface, and the second side surface 4 of the first lens is a diffractive surface; the first side surface 8 of the third lens is a curved surface, and the second side surface 10 of the third lens is a diffractive surface; wherein the second lens 20 and the fourth lens 40 are both refractive lenses, and the focal length f3 of the third lens 30 satisfies the following relationship with the total focal length f of the projection lens: -2≤f3 / f≤0.

[0033] By setting the second lens 20 and the fourth lens 40 to be refractive lenses, the second lens 20 and the fourth lens 40 can realize the refraction of light. By setting the two side surfaces of the first lens 60 to be curved surfaces and diffraction surfaces respectively, and the two side surfaces of the third lens 30 to be curved surfaces and diffraction surfaces respectively, the first lens 60 and the third lens 30 can integrate the functions of refracting light and diffracting light, improve the functionality of the first lens 60 and the third lens 30, and help to increase the imaging quality. In addition, by integrating the curved surface and the refractive surface on one lens, it is beneficial to save space and ensure the miniaturization of the projection lens. By constraining the relationship between the focal length f3 of the third lens 30 and the total focal length f of the projection lens, it is beneficial to the reasonable distribution of the focal length of the third lens 30 and ensure the reliability of the use of the third lens 30. The image light output by the display chip of the present application can be propagated through each lens, and the aberration of the projected image can be corrected, and finally the display chip can project a high-quality image in the optical system of a small-sized projection lens.

[0034] It should be noted that the first side mentioned above is Figure 1 and Figure 2 The left side of the projection lens is shown, and the second side is Figure 1 and Figure 2 On the right side of the projection lens shown, the first side is the exit pupil side, and the second side is the image source side. A display chip is arranged on the image source side of the projection lens, and the image light of the display chip is imaged on the exit pupil side after passing through each lens in sequence.

[0035] Specifically, the diffraction surface is a metasurface. A metasurface is a surface formed by arranging a plurality of nanorod structures in an array, and the shape of the nanorods includes one of a cylindrical column and a polygonal column.

[0036] Depend on Figure 1 and Figure 2As shown, the first lens 60 includes a printed glue layer, a glass layer and a diffraction layer from the first side to the second side. The surface of the printed glue layer away from the glass layer is the first side surface 2 of the first lens, and the surface of the diffraction layer away from the glass layer is the second side surface 4 of the first lens. The first side surface 2 of the first lens is a convex surface, and the first side surface 2 of the first lens can be printed into one of a spherical surface, an aspherical surface and a free-form surface. The glass layer is a flat glass 50. The first lens 60 is an emission divergent element of the image light of the display chip. The first side surface 2 of the first lens is set as a convex surface to achieve large-angle light emission. When the first side surface 2 of the first lens is a convex surface and an aspherical surface, it can better correct aberrations and improve the quality of the projected image. The middle part of the first lens 60 is an optical flat glass, which can be used as a substrate for the printed glue layer and the diffraction layer, and has a certain protective, dust-proof and waterproof effect on the printed glue layer and the diffraction layer. The second side surface 4 of the first lens is configured as a diffraction surface, specifically a super surface, which is conducive to ensuring ultra-thinness and having the optical deflection function of a high-vector optical glue-embossed refractive surface, thereby shortening the size of the overall structure, avoiding the risk of breakage of the thin glass layer, and greatly improving the imaging quality.

[0037] Specifically, the first side surface 5 of the second lens is a concave surface, and the second side surface 7 of the second lens is a plane. Specifically, the second lens 20 includes a printed glue layer and a glass layer from the first side to the second side, and the surface of the printed glue layer away from the glass layer is the first side surface 5 of the second lens, and the surface of the glass layer away from the printed glue layer is the second side surface 7 of the second lens. Optionally, the first side surface 5 of the second lens is a convex surface, and the specific surface shape can be set according to actual conditions. Of course, the first side surface 5 of the second lens can be one of an aspherical surface, a spherical surface and a free-form surface. The first side surface 5 of the second lens is a concave surface, which allows the outgoing light of the image of the display chip to smoothly exit to the first lens 60 on the exit pupil side. When the surface is an aspherical surface, the imaging quality can be more effectively improved and the sensitivity of the tolerance can be reduced.

[0038] like Figure 1 and Figure 2As shown, the third lens 30 includes a printed glue layer, a glass layer and a diffraction layer from the first side to the second side. The surface of the printed glue layer away from the glass layer is the first side surface 8 of the third lens, and the surface of the diffraction layer away from the glass layer is the second side surface 10 of the third lens. The first side surface 8 of the third lens is a concave surface. Of course, the first side surface 8 of the third lens can be designed as one of an aspherical surface, a spherical surface and a free-form surface. The third lens 30 further gently scatters the light converged from the display chip to the exit pupil side. When the first side surface 8 of the third lens is a concave surface and an aspherical surface, it can more effectively correct the aberration and improve the quality. The diffraction surface can be made into a super surface, which has the advantage of extremely small thickness, and has the optical deflection function of a large vector height optical glue printed refractive surface, thereby shortening the size of the overall structure, avoiding the risk of thin substrate breakage, and greatly improving the imaging quality.

[0039] Specifically, the first side surface 11 of the fourth lens is a concave surface, and the second side surface 14 of the fourth lens is a convex surface. The fourth lens 40 includes a first embossed glue layer, a flat glass 50 layer and a second embossed glue layer from the first side to the second side. The fourth lens 40 is a double-sided embossed lens, and the two side surfaces of the fourth lens 40 can be embossed into one of a spherical surface, an aspherical surface and a free-form surface. The fourth lens 40 converges the light projected from the display chip. The second side surface 14 of the fourth lens is a convex surface that can effectively receive and converge the projected image from the display chip, and the first side surface is a concave surface that can project the light from the display chip to the exit pupil position. Since the flat glass layer of the fourth lens 40 is thicker, double-sided embossing is used to prevent the flat glass layer from being broken or damaged.

[0040] like Figure 1 and Figure 2 As shown, the projection lens further includes a flat glass 50, which is located on the second side of the fourth lens 40 and can be a color filter. The flat glass 50 is used to cut off the spectrum of the image projected by the display chip outside the working band.

[0041] Optionally, the glass layer can be made by mechanical processing. When the material is glass, the surface of the optical element can be processed by cutting the lens through a machine tool or other tool. Depending on the usage scenario, the glass layer in the lens can also be replaced by optical plastic. Plastic injection molding is a method of making plastic products. The molten plastic is injected into the plastic product mold under pressure, and the desired plastic parts are obtained by cooling and molding. The materials used for optical products are usually PC or PMMA.

[0042] Specifically, the focal length f1 of the first lens 60 satisfies the following relationship with the total focal length f of the projection lens: 0≤f1 / f≤1. The focal length f2 of the second lens 20 satisfies the following relationship with the total focal length f of the projection lens: -4≤f2 / f≤0; the focal length f4 of the fourth lens 40 satisfies the following relationship with the total focal length f of the projection lens: -7≤f4 / f≤0. By reasonably constraining the focal lengths of the lenses, it is beneficial to reasonably allocate the focal lengths of the lenses, to smoothly transition the light, and to ensure the imaging quality.

[0043] Specifically, the projection lens also includes an aperture, which is located on the first side of the first lens 60. The size of the aperture matches the entrance pupil size of the optical waveguide structure. The imaging light of the projection lens is emitted to the aperture and then enters the optical waveguide structure. By setting the aperture size to be equal to or matching the entrance pupil size of the optical waveguide structure, it is beneficial to ensure the stability of light transmission. The exit pupil diameter of the projection lens is greater than or equal to 3 mm and less than or equal to 5 mm; the total focal length f of the projection lens is greater than or equal to 4.6 mm and less than or equal to 6.6 mm. The maximum field of view FOV of the projection lens is greater than 28° and less than 32°. By reasonably constraining the exit pupil diameter, total focal length and maximum field of view of the projection lens, it is beneficial to ensure that the exit pupil size and field of view match the human eye and ensure the reliability of the projection lens.

[0044] Preferably, the first side surface 2 of the first lens, the first side surface 5 of the second lens, the first side surface 8 of the third lens, the first side surface 11 of the fourth lens, and the second side surface 14 of the fourth lens are all aspherical surfaces. By properly setting the aspherical surfaces, it is beneficial to correct field curvature, compress distortion, achieve high resolution, and ensure imaging quality.

[0045] In summary, the projection lens of the present application can realize the projection function through the combination of different surface shapes and structural design, can be used in the WLO field, and can realize functions such as waterproof, dustproof, and impact-resistant; by setting the first lens 60 and the third lens 30 as refractive lenses, the lens structure size can be greatly reduced, giving more design space for external matching devices; at the same time, the double-sided imprinting process of the thin substrate can be avoided, the risk of cracking of the thin substrate can be reduced, and the production yield of the product can be improved. The diffraction surface is compounded into the WLO lens, which effectively corrects the aberration, chromatic aberration, etc. of the imaging quality, and greatly improves the imaging quality.

[0046] The projection lens of the present application is described below in conjunction with specific embodiments.

[0047] like Figure 1 and Figure 2 , which is a schematic diagram of the structure of a projection lens of an optional embodiment of the present application. The projection lens includes, from the first side to the second side, a first lens 60, a second lens 20, a third lens 30, a fourth lens 40 and a flat glass 50.

[0048] like Figure 1 As shown, the first side surface 2 of the first lens is a convex surface, the second side surface 4 of the first lens is a diffractive surface, and a first lens bonding surface 3 is provided between the two side surfaces of the first lens 60. The first side surface 5 of the second lens is a concave surface, the second side surface 7 of the second lens is a plane, and a second lens bonding surface 6 is provided between the two side surfaces of the second lens 20. The first side surface 8 of the third lens is a concave surface, the second side surface 10 of the third lens is a diffractive surface, and a third lens bonding surface 9 is provided between the two side surfaces of the third lens 30. The first side surface 11 of the fourth lens is a concave surface, the second side surface 14 of the fourth lens is a convex surface, and two bonding surfaces are provided between the two side surfaces of the fourth lens 40, which are the first bonding surface 12 of the fourth lens and the second bonding surface 13 of the fourth lens. Among them, the first side surface 2 of the first lens, the first side surface 5 of the second lens, the first side surface 8 of the third lens, and the two side surfaces of the fourth lens 40 are all optical refractive curved surfaces and are aspherical surfaces. The second side surface 7 of the second lens and the flat glass 50 have a flat glass first side surface 15 and a flat glass second side surface 16, and the two side surfaces of the flat glass 50 are both optical plane transmission surfaces.

[0049] In this embodiment, the exit pupil diameter D of the projection lens is 4 mm, the maximum field angle of the projection lens is 30°, the working band is visible light, the diagonal length of the display chip is 1.7 mm, and the total focal length f of the projection lens is 5.6 mm. f1 / f=0.6, f2 / f=-3.5, f3 / f=-1.02, f4 / f=-6.54.

[0050] Table 1 shows the basic structural parameters of the projection lens of this embodiment, wherein the units of the radius of curvature and thickness / distance are all millimeters (mm).

[0051] Surface number Radius of curvature thickness Refractive Index Abbe number lens 0OBJ Infinity Infinity 1STOP Infinity -0.299 Aperture 2 2.68 0.898 1.72 31.2 First lens 60 3 Infinity 0.300 1.497 81.613 4 Infinity 0.196 5 -10.39 0.618 1.52 54 Second lens 20 6 Infinity 0.211 1.497 81.613 7 Infinity 0.470 8 -3.82 0.105 1.607 27.48 The third lens 30 9 Infinity 0.236 1.497 81.613 10 Infinity 0.716 11 135.57 0.257 1.607 27.48 The fourth lens 40 12 Infinity 0.605 1.497 81.613 13 Infinity 0.772 1.72 31.2 14 22.96 0.314 15 Infinity 0.307 1.52 64.17 Plate glass 50 16 Infinity 0.193 17IMG unlimited 0

[0052] Table 1

[0053] In this embodiment, the surface shape expression of the above-mentioned aspheric surface is as follows:

[0054]

[0055] In the above formula: Z is the height of the distance vector from the vertex of the aspheric surface when the aspheric surface is at a height of r along the optical axis. r represents the Y-axis coordinate value of each point on the lens surface; c is the reciprocal of the radius of curvature r of the lens surface; k is the cone coefficient, A2m is the coefficient of the additional polynomial, i.e., the high-order term of the aspheric surface, m = 2, 3, 4···, and M is the highest number of terms in the additional polynomial.

[0056] Table 2 below lists the high-order coefficients A4, A6, A8, A10, A12, A14, A16, A18, and A20 that can be used for each aspherical surface in this embodiment.

[0057]

[0058] Table 2

[0059] In this embodiment, the phase distribution of the diffraction surface satisfies the following formula:

[0060]

[0061] Where N is the number of polynomial coefficients in the series, Ai is the coefficient of the ith polynomial expansion, and M is the diffraction order.

[0062] Table 3 below shows the diffraction surface coefficients that can be used for each diffraction surface in this embodiment.

[0063] Surface number Diffraction order A2 A4 A6 A8 A10 4 1 -2.00E+02 2.68E+01 -6.99E+00 5.22E-01 -8.11E-02 10 1 6.43E+01 -2.25E+02 3.02E+02 -5.53E+01 -1.39E+01

[0064] Table 3

[0065] Figure 3 shows an MTF curve diagram of the projection lens of this embodiment; Figure 4 A field curvature diagram of the projection lens of this embodiment is shown; Figure 5 shows a distortion diagram of the projection lens of this embodiment; Figure 6 shows a phase distribution diagram of the diffraction surface of the first lens 60 of the projection lens of this embodiment; Figure 7 FIG. 4 shows a phase distribution diagram of the diffraction surface of the third lens 30 of the projection lens of this embodiment. Figures 3 to 7 It can be seen that the projection lens of this embodiment can achieve good imaging quality.

[0066] Obviously, the embodiments described above are only some embodiments of the utility model, not all embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the utility model.

[0067] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0068] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein.

[0069] The above description is only the preferred embodiment of the utility model, and is not intended to limit the utility model. For those skilled in the art, the utility model can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the utility model shall be included in the protection scope of the utility model.

Claims

1. A projection lens, characterized in that: From the first side to the second side, it includes: A first lens (60), wherein a first side surface (2) of the first lens is a curved surface, and a second side surface (4) of the first lens is a diffraction surface; a second lens (20); A third lens (30), wherein the first side surface (8) of the third lens is a curved surface, and the second side surface (10) of the third lens is a diffraction surface; a fourth lens (40); The second lens (20) and the fourth lens (40) are both refractive lenses, and the focal length f3 of the third lens (30) satisfies the following relationship with the total focal length f of the projection lens: -2≤f3 / f≤0.

2. The projection lens according to claim 1, characterized in that: The diffraction surface is a metasurface.

3. The projection lens according to claim 1, characterized in that: The first side surface (2) of the first lens is a convex surface, and the first side surface (8) of the third lens is a concave surface.

4. The projection lens according to claim 1, characterized in that: The first lens (60) comprises, from the first side to the second side, an embossed glue layer, a glass layer and a diffraction layer, a surface of the embossed glue layer away from the glass layer being a first side surface (2) of the first lens, and a surface of the diffraction layer away from the glass layer being a second side surface (4) of the first lens; and / or The third lens (30) comprises, from the first side to the second side, a printed glue layer, a glass layer and a diffraction layer, a surface of the printed glue layer away from the glass layer being a first side surface (8) of the third lens, and a surface of the diffraction layer away from the glass layer being a second side surface (10) of the third lens.

5. The projection lens according to claim 1, wherein: The first side surface (5) of the second lens is a concave surface or a convex surface, and the second side surface is a plane surface; and / or the first side surface (11) of the fourth lens is a concave surface, and the second side surface is a convex surface.

6. The projection lens according to any one of claims 1 to 5, characterized in that: The focal length f1 of the first lens (60) and the total focal length f of the projection lens satisfy the following relationship: 0≤f1 / f≤1.

7. The projection lens according to any one of claims 1 to 5, characterized in that: The focal length f2 of the second lens (20) and the total focal length f of the projection lens satisfy: -4≤f2 / f≤0; and / or the focal length f4 of the fourth lens (40) and the total focal length f of the projection lens satisfy: -7≤f4 / f≤0.

8. The projection lens according to any one of claims 1 to 5, characterized in that: The projection lens also includes an aperture, which is located on a first side of the first lens (60), and the size of the aperture matches the entrance pupil size of the optical waveguide structure.

9. The projection lens according to any one of claims 1 to 5, characterized in that: The field of view FOV of the projection lens is greater than 28° and less than 32°.

10. The projection lens according to claim 1, wherein: The first side surface (2) of the first lens, the first side surface (5) of the second lens, the first side surface (8) of the third lens, the first side surface (11) of the fourth lens, and the second side surface (14) of the fourth lens are all aspherical surfaces.

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