Projection lens and projection system

Abstract

The present application discloses a projection lens and a projection system. The projection lens comprises: a diaphragm, and a front lens group and a rear lens group respectively located on two sides of the diaphragm. At least one diffractive lens may be provided in the front lens group and / or the rear lens group, and the diffractive lens comprises a lens substrate and a coating located on a surface of the lens substrate. The surface of the lens substrate is provided with a diffraction structure, and the coating covers the diffraction structure. A stacked structure is used for the diffractive lens to achieve high diffraction efficiency across the visible light band. The diffractive lens can correct chromatic aberration of the projection lens, avoiding the problem of pixel offset, and enabling the projection system to obtain high-quality projection images without light loss or glare.

Description

Projection lens and projection system

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411180481.9, filed on August 26, 2024, entitled “A Projection Lens and Projection System”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of projection technology, and in particular to a projection lens and projection system. Background Technology

[0004] With the increasing popularity of laser display products, they have begun to enter countless households as a large-screen alternative to televisions. As user demands rise, the requirements for the throw ratio and image quality of projection lenses are becoming increasingly stringent.

[0005] To improve image quality, projection lenses typically consist of a large number of lenses. However, tolerances are unavoidable during the manufacturing and installation of projection lenses, causing the projection device to deviate from the theoretical image quality. If the projection device is paired with a laser light source, the different refractive indices of the lenses for different wavelengths of light will result in varying focal points for light of different wavelengths after passing through the same lens, leading to chromatic aberration. Summary of the Invention

[0006] This application provides a projection lens, including:

[0007] Aperture;

[0008] The front group of lenses and the rear group of lenses are located on both sides of the aperture stop, respectively; both the front group of lenses and the rear group of lenses include multiple lenses;

[0009] At least one lens in the front group of lenses and / or the rear group of lenses is a diffractive lens; the diffractive lens is used to correct the chromatic aberration of the projection lens;

[0010] The diffractive lens includes: a lens substrate and a coating on the surface of the lens substrate; a diffractive structure is provided on one side surface of the lens substrate, and the coating covers the diffractive structure.

[0011] This application also provides a projection system, including:

[0012] Laser source, used to emit three-color lasers;

[0013] An illumination system is located on the light-emitting side of the laser source; the illumination system includes a homogenizing element and a display element, the homogenizing element being located on the light-emitting side of the laser source and used to homogenize the incident laser; the display element being located on the light-emitting side of the homogenizing element and used to modulate the incident laser before emission.

[0014] A projection lens is located on the light-emitting side of the display element; the projection lens is the aforementioned projection lens;

[0015] A total internal reflection prism is located between the display element and the projection lens; the total internal reflection prism is used to reflect the laser emitted from the homogenizing element back to the display element and transmit the laser modulated by the display element. Attached Figure Description

[0016] Figure 1 is a schematic diagram of the projection system provided in an embodiment of this application;

[0017] Figure 2 is an architecture diagram of the projection device provided in an embodiment of this application;

[0018] Figure 3 is a schematic diagram of the structure of a projection lens provided in an embodiment of this application;

[0019] Figure 4 is a schematic diagram of the structure of the diffraction lens provided in an embodiment of this application;

[0020] Figure 5 is a schematic diagram of the planar structure of the lens substrate provided in an embodiment of this application;

[0021] Figure 6 is a schematic diagram of the color difference correction principle provided in the embodiment of this application;

[0022] Figure 7 is a partially enlarged schematic diagram of the diffraction structure 301a in Figure 4;

[0023] Figure 8 is a schematic diagram of the manufacturing process of the lens substrate provided in the embodiment of this application;

[0024] Figure 9 is a schematic diagram of one of the molds provided in the embodiments of this application;

[0025] Figure 10 is a second structural schematic diagram of the mold provided in the embodiment of this application;

[0026] Figure 11 is one of the spherical aberration curves provided in the embodiments of this application;

[0027] Figure 12 is one of the lateral color difference curves provided in the embodiments of this application;

[0028] Figure 13 is one of the schematic diagrams of astigmatism curves provided in the embodiments of this application;

[0029] Figure 14 is one of the schematic diagrams of distortion curves provided in the embodiments of this application;

[0030] Figure 15 is a second schematic diagram of the structure of the projection lens provided in an embodiment of this application;

[0031] Figure 16 is a second spherical aberration curve provided in an embodiment of this application;

[0032] Figure 17 is a second lateral color difference curve provided in an embodiment of this application;

[0033] Figure 18 is a second schematic diagram of astigmatism curves provided in an embodiment of this application;

[0034] Figure 19 is a second schematic diagram of the distortion curve provided in the embodiment of this application. Detailed Implementation

[0035] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the application will be further described below in conjunction with the accompanying drawings and embodiments. However, the exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to make the application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the figures denote the same or similar structures, and therefore repeated descriptions of them will be omitted. Terms describing position and direction described in this application are illustrative based on the accompanying drawings, but changes can be made as needed, and all such changes are included within the scope of protection of this application. The accompanying drawings of this application are for illustrating relative positional relationships only and do not represent actual scale.

[0036] Projection technology, as an advanced display technology, has been widely used in many fields, including home theaters, business presentations, education, and scientific research. Its working principle involves using light emitted from a light source to form a display image, which is then imaged through an optical system and projected onto a screen for magnified display.

[0037] Figure 1 is a schematic diagram of the projection system provided in an embodiment of this application.

[0038] As shown in Figure 1, the projection system may include a projection device 1 and a projection screen 2. The projection screen 2 is located on the light-emitting side of the projection device 1. The audience faces the projection screen 2. The projection device 1 emits projection light, which is incident on the projection screen 2 and reflected back to the audience's location, thus allowing the audience to view the projected image.

[0039] Projection devices come in various types, including but not limited to portable projectors, home theater projectors, and professional projectors. These products vary in brightness, resolution, and projection size depending on the usage scenario and requirements. Among them, long-throw projectors have a wide range of applications; long-throw projectors primarily refer to projectors that use long-throw lenses.

[0040] The projection ratio (or throw ratio) is a key parameter in projection systems, used to describe the relationship between projection distance and the size of the projected image. The projection ratio is the ratio of the distance between the projection lens and the projection screen (projection distance) to the width (or diagonal length) of the projected image. Based on the projection ratio, projection lenses are generally classified as telephoto lenses, short-throw lenses, and ultra-short-throw lenses. Telephoto lenses have a large projection ratio, typically greater than 1.5 or higher. Short-throw lenses have a projection ratio between 0.6 and 1.5. Ultra-short-throw lenses have a projection ratio less than 0.6, sometimes even less than 0.4.

[0041] In addition to a projection lens, the projection device also includes a projection light source and an illumination system. Figure 2 is an architectural diagram of the projection device provided in an embodiment of this application.

[0042] As shown in Figure 2, the projection device includes a projection light source 10, an illumination system 20, and a projection lens 30. The illumination system 20 is located on the light-emitting side of the projection light source 10, and the projection lens 30 is located on the light-emitting side of the illumination system 20.

[0043] In this embodiment, the projection light source 10 can be a laser light source. The laser light source is used to emit laser light. The laser has better monochromaticity and a higher color gamut, which can present better color performance.

[0044] Laser light sources can be monochromatic lasers, lasers capable of emitting multiple colors of laser light, or multiple lasers emitting different colors of laser light. When using a monochromatic laser, the laser light source also needs to be equipped with a color conversion device and a color wheel. The color conversion device is used for color conversion, and the color wheel is used to filter out monochromatic light according to a set time sequence. A monochromatic laser, in conjunction with a color conversion device and a color wheel, can achieve the emission of different primary colors of light in a time sequence. When using a laser capable of emitting multiple colors of laser light, it is necessary to control the laser to emit different colors of laser light as primary colors in a time sequence.

[0045] In this embodiment, the projection light source 10 can be a three-color laser light source, which is a laser capable of emitting three primary color lasers, such as an MCL laser; or, it can include a red laser, a green laser, and a blue laser that emit three primary color lasers respectively. Using a three-color laser light source is beneficial for improving the color gamut of the projected image, resulting in better color performance and accurate reproduction of the input image.

[0046] The laser source may also include a beam combining component for combining three-color lasers. The beam combining component may include a reflector and a dichroic mirror. The number and position of the reflector and dichroic mirror are set according to the arrangement rules of the laser chips in the laser to achieve beam combining of three-color lasers.

[0047] The illumination system 20 is located on the light-emitting side of the projection light source 10. The illumination system 20 may include a display element 201, a light-diffusing element 202, and a light-shaping component 203. On the one hand, the illumination system 20 shapes and homogenizes the emitted light beam from the projection light source 10. On the other hand, it enables the emitted light from the projection light source 10 to be incident on the display element 201 at a suitable angle, thereby allowing the display element 201 to effectively modulate the incident light to generate an image.

[0048] The light homogenizing element 202 is located on the light emission path of the projection light source 10 and can homogenize the emitted light from the projection light source 10. The light homogenizing element 202 can be a light guide or a compound eye lens, and there is no limitation on it.

[0049] The shaping component 203 can be located on the light-emitting side of the light-diffusing element 202. The shaping component 203 can further shape the light emitted from the light-diffusing element 202 to adapt to the size of the display element 201. The shaping component 203 may include one or more lenses, which is not limited here.

[0050] Display element 201 is used to modulate the homogenized and shaped light beam. Display element 201 can be a transmissive light modulator or a reflective light modulator. This embodiment of the application uses a reflective light modulator as an example. The reflective light modulator can be a digital micromirror device (DMD) or a liquid crystal on silicon (LCoS).

[0051] In some embodiments, the projection device may employ a Digital Light Processing (DLP) system, and the display element 201 may be a DMD. The surface of the DMD includes a plurality of micromirrors, each of which can be individually driven to deflect. By controlling the deflection angle of the DMD, the brightness of the reflected light from each micromirror is controlled, thereby generating a display image.

[0052] In some embodiments, the display element 201 may be an LCoS device, which consists of two substrates, upper and lower, with liquid crystal injected in the middle. The lower substrate is a silicon-based complementary metal-oxide-semiconductor (CMOS) substrate. A driving panel is fabricated using semiconductor processes, and then a metal film is deposited as a reflector. The incident light is modulated and reflected using the electrically controlled birefringence properties of the liquid crystal.

[0053] This application embodiment uses a DMD as an example to illustrate the use of a display element 201. As shown in FIG2, the illumination system 20 may also include a total internal reflection prism 204. The total internal reflection prism 204 is used to separate the illumination light path and the imaging light path. The light emitted from the shaping component 203 first enters the total internal reflection prism 204 and is reflected by the total internal reflection prism 204 towards the display element 201. The display element 201 then modulates the incident light and reflects the modulated light back to the total internal reflection prism 204. The total internal reflection prism 204 transmits the modulated light to the projection lens 30.

[0054] Figure 3 is one of the structural schematic diagrams of the projection lens provided in the embodiments of this application.

[0055] As shown in Figure 3, an image shifting component P can be placed between the projection lens 30 and the total internal reflection prism 204. The image shifting component P can be a flat glass plate, which changes the position of the light entering the projection lens through high-frequency vibration, thereby expanding the pixels of the displayed image and improving the resolution of the projected image. When the display element 201 uses a DMD, its surface also has a protective glass G to protect the DMD from damage. The impact of the surfaces through which the light passes on the imaging must be considered during optical design.

[0056] A projection lens 30 typically includes multiple lenses. To improve image quality, these lenses can include spherical and aspherical lenses. However, due to unavoidable tolerances during lens manufacturing and installation, as well as inherent aberrations within the lenses themselves, the projection lens cannot achieve the theoretical image quality. Furthermore, when a projection device is paired with a laser light source, the different refractive indices of the lenses in the projection lens for different wavelengths of laser light cause the focusing positions of light rays of different wavelengths to differ after passing through the same lens. This results in a shift between sub-pixels of different colors, affecting the display effect.

[0057] To address the aforementioned issues, as shown in Figure 3, the projection lens provided in this embodiment includes a coaxially arranged aperture stop s, a front group of lenses 31, and a rear group of lenses 32, which are located on opposite sides of the aperture stop s. In the optical design of the projection lens, the imaging position is used as the object plane, and the light-emitting surface of the display element is used as the image plane. Utilizing the principle of reversible light paths, image display conforming to the designed size and image quality can be achieved during projection. In this embodiment, the front group of lenses 31 and the rear group of lenses 32 are defined by the order in which light enters the lenses during optical design.

[0058] The front group of lenses 31 and the rear group of lenses 32 each include multiple lenses, and at least one lens in the front group of lenses 31 and / or the rear group of lenses 32 is a diffraction lens 301.

[0059] Figure 4 is a schematic diagram of the structure of the diffraction lens provided in the embodiment of this application.

[0060] As shown in Figure 4, the diffraction lens 301 includes: a lens substrate 3011 and a coating 3012 located on the surface of the lens substrate; a diffraction structure 301a is provided on one side surface of the lens substrate 3011, and the coating 3012 covers the diffraction structure 301a.

[0061] In this embodiment, a diffraction lens 301 is provided in the projection lens 30. The diffraction structure 301a of the diffraction lens 301 has a serrated annular groove structure, which can efficiently diffract light of a specific wavelength of a certain order. A thin coating 3012 is provided on the surface of the lens substrate 3011 with the diffraction structure 301a. By matching the refractive indices of the lens substrate 3011 and the coating 3012, the diffraction lens 301 can have high diffraction efficiency in the visible light band. By precisely designing the diffraction structure of the diffraction lens as part of the projection lens, the phase difference of light of different wavelengths can be compensated, thereby correcting the chromatic aberration of the projection lens. This allows light of different colors belonging to the same pixel to be focused on the same point on the projection screen, avoiding the problem of offset between pixels of different colors.

[0062] In this embodiment, the lens substrate 3011 and the coating 3012 are made of different materials. The lens substrate 3011 can be made of glass, and the coating 3012 can be made of resin.

[0063] Since the projection system provided in this application uses a laser light source, and lasers have high energy, considering issues such as light resistance, heat resistance, and optical performance stability caused by environmental changes, the lens substrate 3011 is made of optical glass material with good light resistance, heat resistance, and optical performance that does not change with environmental factors such as temperature and humidity. Furthermore, a diffraction structure is formed on the surface of the lens substrate 3011. At the same time, the thickness of the coating 3012 is minimized to avoid the problem of decreased optical performance of the resin material under strong light irradiation.

[0064] In practical implementation, the coating 3012 can be made of ultraviolet-cured resin (UV resin). If the coating 3012 is too thin, it may not completely cover the diffraction structure on the surface of the lens substrate 3011, resulting in partial exposure of the diffraction structure and deterioration of the optical performance of the diffraction lens 301. On the other hand, due to the precision issues of the UV resin fixture, it is difficult to control the thickness of the UV resin to below 0.1 mm, while a thickness exceeding 0.2 mm can easily lead to bubble formation. In addition, the transmittance of the diffraction lens 301 will decrease as the thickness of the coating 3012 increases. Considering the above influencing factors, in this embodiment, the thickness of the coating 3012 can be set below 0.2 mm, specifically within the range of 0.1 mm to 0.2 mm.

[0065] Figure 5 is a schematic diagram of the planar structure of the lens substrate provided in an embodiment of this application.

[0066] As shown in Figures 3 to 5, for ease of explanation, the optical axis direction of the projection lens is referred to as the third direction z, and the two mutually perpendicular directions in the plane perpendicular to the optical axis are referred to as the first direction x and the second direction y. Therefore, the thickness of the coating 3012 in the diffraction lens mentioned above refers to the thickness along the direction parallel to the optical axis of the diffraction lens 301, that is, along the third direction z.

[0067] As shown in Figures 4 and 5, the diffraction structure 301a of the diffraction lens 301 consists of concentrically expanding annular grooves, with the center of the annular grooves coinciding with the optical axis of the diffraction lens 301. When light rays are incident on different positions of the annular grooves, phase differences will occur, which are related to the refractive index and the depth of the annular grooves.

[0068] When designing annular grooves, their depth must satisfy: (Nd1-Nd2)d=mλ;

[0069] Where Nd1 represents the refractive index of the lens substrate 3011, Nd2 represents the refractive index of the coating 3012, d represents the depth of the annular groove along the direction parallel to the optical axis (along the third direction z), λ represents the wavelength of the incident light, and m represents the diffraction order.

[0070] If the diffraction lens is designed to order 1, the phase difference produced by the annular groove is 2π. If the depth of the annular groove is d, the refractive index of the lens substrate 3011 is Nd1, and the refractive index of the coating 3012 is Nd2, then the optical path difference ΔL = (Nd1 - Nd2)d. If the wavelength of the transmitted light is λ, then the phase difference Δφ is:

[0071] When the phase difference generated by the diffraction structure 301a on the incident light is 2π, the optical path difference generated by the incident light is ΔL=λ. Therefore, the depth of the annular groove can be calculated based on the wavelength of the incident light and the difference in refractive index between the lens substrate and the coating in the diffraction lens: d=λ / (Nd1-Nd2).

[0072] In this embodiment, the wavelengths corresponding to the three laser colors are 647nm for red laser, 525nm for green laser, and 455nm for blue laser. Using the wavelength of green laser, which is most sensitive to the human eye, as the design wavelength (λ = 525nm in the above formula), if the refractive index Nd1 of the lens substrate 3011 of the diffractive lens is 1.6429 and the refractive index Nd2 of the coating 3012 is 1.6081, then the depth d of the annular groove is 15μm. If the refractive index Nd1 of the lens substrate 3011 of the diffractive lens is 1.6984 and the refractive index Nd2 of the coating 3012 is 1.6081, then the depth d of the annular groove is 5.8μm.

[0073] The diffraction lens 301 is used to correct chromatic aberration in the projection lens. To ensure high diffraction efficiency for incident red, green, and blue lasers, the refractive index and Abbe number ranges of the lens substrate 3011 and coating 3012 need to be limited. Specifically, the refractive index and Abbe number of the diffraction lens satisfy the following conditions:

[0074] Wherein, dn represents the difference between the refractive index of the lens substrate 3011 and the refractive index of the coating 3012, and dv represents the difference between the Abbe number of the lens substrate 3011 and the Abbe number of the coating 3012.

[0075] By limiting the ratio of the refractive index difference between the lens substrate 3011 and the coating 3012 to the Abbe number difference between the lens substrate 3011 and the coating 3012, it is possible to effectively ensure that the materials of the lens substrate 3011 and the coating 3012 have a good matching effect, while ensuring that the diffraction lens has a high diffraction efficiency.

[0076] Furthermore, the refractive index and Abbe number of the lens substrate 3011 satisfy: 1.55≤Nd1≤1.65; 55≤Vd1≤68;

[0077] The refractive index and Abbe number of coating 3012 satisfy: 1.55≤Nd2≤1.61; Vd2≤38;

[0078] Where Nd1 represents the refractive index of the lens substrate, Vd1 represents the Abbe number of the lens substrate, Nd2 represents the refractive index of the coating, and Vd2 represents the Abbe number of the coating.

[0079] The diffraction structure on the surface of the lens substrate 3011 is designed according to the dominant wavelength. Therefore, the lens substrate 3011 has high diffraction efficiency for the dominant wavelength, but the diffraction efficiency decreases for other wavelengths. The projection system uses a three-color laser light source. To ensure that the diffraction lens has high diffraction efficiency for all three wavelengths, a coating 3012 with matching refractive index and Abbe number is applied to the surface of the diffraction structure of the lens substrate 3011. This achieves good diffraction efficiency across the entire visible light spectrum, resulting in a diffraction efficiency of:

[0080] Among them, E R E represents the diffraction efficiency of red laser light. G E represents the diffraction efficiency of green laser. B This indicates the diffraction efficiency of blue laser light.

[0081] As can be seen from the above formula, the average diffraction efficiency of a diffraction lens can reach more than 85%, which can ensure that the overall optical efficiency of the optical system is high, while reducing stray light generated by secondary diffraction and avoiding problems such as glare.

[0082] For example, if the refractive index Nd1 = 1.63858 and the Abbe number Vd1 = 55.18 of the lens substrate 3011 in a diffractive lens, and the refractive index Nd2 = 1.603 and the Abbe number Vd2 = 29 of the coating 3012, then the diffraction efficiency of the diffraction lens can reach 99.8% for red laser (λ = 647 nm), 99.8% for green laser (λ = 525 nm), and 98.7% for blue laser (λ = 455 nm).

[0083] If the refractive index Nd1 = 1.59201 and the Abbe number Vd1 = 67.2 of the lens substrate 3011 in the diffraction lens, and the refractive index Nd2 = 1.56 and the Abbe number Vd2 = 38 of the coating 3012, then the diffraction efficiency of the diffraction lens can reach 98.6% for red laser (λ = 647 nm), 99.8% for green laser (λ = 525 nm), and 99.9% for blue laser (λ = 455 nm).

[0084] If the refractive index Nd1 = 1.5831 and Abbe number Vd1 = 59.46 of the lens substrate 3011 in the diffraction lens, and the refractive index Nd2 = 1.55 and Abbe number Vd2 = 38 of the coating 3012, then the diffraction efficiency of the diffraction lens can reach 99.4% for red laser (λ = 647 nm), 99.6% for green laser (λ = 525 nm), and 99.9% for blue laser (λ = 455 nm).

[0085] Typically, optical systems employ lens combinations to reduce chromatic aberration. Lenses with positive refractive power require low-dispersion materials, while lenses with negative refractive power require high-dispersion materials. Furthermore, the lens shape must be carefully designed, taking into account the overall imaging performance, to correct chromatic aberration in the optical system. Therefore, to ensure the imaging performance of the optical system, an increased number of lenses is required, and it may be necessary to use more expensive materials such as ultra-low dispersion glass. However, the embodiments of this application utilize diffractive lenses to achieve the same or better results.

[0086] Specifically, Figure 6 is a schematic diagram of the color difference correction principle provided in the embodiment of this application. In Figure 6, w represents white light, and r, g, and b represent red light, green light, and blue light, respectively. The wavelengths of red light, green light, and blue light decrease sequentially.

[0087] As shown in Figure 6(1), refractive lenses made of optical glass usually have positive dispersion characteristics. The shorter the wavelength, the greater the change in refractive index characteristics. Therefore, when white light w, which is a mixture of red light r, green light g, and blue light b, is incident on the refractive lens, the degree of deflection of blue light b, green light g, and red light r by the refractive lens decreases in sequence.

[0088] As shown in Figure 6(2), a diffractive lens has negative dispersion characteristics and strong anomalous dispersion characteristics. Therefore, when light of the same wavelength is incident on a diffractive lens, the chromatic aberration directions are opposite on the refractive and diffractive surfaces. Similarly, when white light w, which is a mixture of red light r, green light g, and blue light b, is incident on a diffractive lens, the degree of deflection of blue light b, green light g, and red light r by the diffractive lens increases sequentially.

[0089] Furthermore, the refractive index characteristics of a refractive lens can change due to variations in the glass material, but the refractive index characteristics of a diffractive lens do not change due to variations in the glass material.

[0090] Therefore, as shown in Figure 6(3), a good achromatic effect can be achieved by combining a refracting lens and a diffractive lens. In addition to using the negative dispersion and strong anomalous dispersion characteristics of diffractive lenses to correct chromatic aberration, the effect of an aspherical lens can also be produced by changing the concentrically arranged periodic diffraction structure, thereby significantly improving optical performance. The size of the concentric ring diffraction structure is very small, which means that the space occupancy rate is very low, thus making it easy to achieve lightweight and miniaturized optical systems.

[0091] Figure 7 is a partially enlarged schematic diagram of the diffraction structure 301a in Figure 4.

[0092] As shown in Figure 7, in this embodiment of the application, the included angle at the bottom of the annular groove satisfies: 40° < θ < 90°;

[0093] Where θ represents the bottom angle of the annular groove, which is the angle between the surface of the annular groove along the depth direction and the tangent direction of the surface of the diffractive lens. dL represents the spacing width between adjacent annular grooves in the plane perpendicular to the optical axis of the diffractive lens, and d represents the depth of the annular groove in the direction parallel to the optical axis of the diffractive lens.

[0094] By limiting the included angle at the bottom of the annular groove within the aforementioned range, the sagitta of the diffractive lens at the surface of the diffractive structure is prevented from becoming excessive, while also ensuring the manufacturability of the diffractive lens. Sagitta (Sag) refers to the vertical distance from the vertex of the lens to the supporting surface; the sagitta of a lens reflects, to some extent, the curvature of the lens surface. In the embodiments of this application, the sagitta of the diffractive lens is not excessive, thereby avoiding the diffractive lens bearing a large optical power.

[0095] In this embodiment, as shown in FIG8, the diffraction structure on the surface of the lens substrate 3011 can be formed by transfer using a mold M. The lens substrate 3011 is made of optical glass, and the mold M can be made of materials with good rigidity and durability, such as superhard alloys and SiC.

[0096] As shown in Figures 8 and 9, the microstructure on the surface of mold M is complementary to the diffraction structure on the surface of lens substrate 3011. The microstructure on the surface of mold M can be machined using a cutting tool or a diamond grinding stone. Due to issues such as machining intensity and machining vibration blurring, the tip angle of the tool used to machine mold M needs to be above 50°. Therefore, the bottom included angle of the groove in mold M machined using this tool can be 50° to 90°.

[0097] On the other hand, due to the difference in thermal expansion coefficients between the mold M and the optical glass, shrinkage stress generated during the cooling process of lens substrate molding may cause the lens substrate to crack or the diffraction structure to break. To avoid this problem, a glass material with a suitable thermal expansion coefficient needs to be selected to manufacture the lens substrate 3011. The following table shows the materials and related data that can be used for the lens substrate 3011 and the mold M:

[0098] The transformation point refers to the glass transition temperature; the yield point, also known as the yield temperature, is the temperature at which a material begins to undergo permanent deformation when subjected to external force; and the softening point is the temperature at which a substance begins to soften significantly during heating.

[0099] Since the microstructure of the mold for the transfer lens substrate is processed using a cutting tool or a grinding stone, when the tip of the cutting tool or grinding stone wears down, the mold will form a circular shape at the bottom of the microstructure. In this case, the diffraction structure made with such a mold will produce unwanted light at its rounded corners, resulting in a loss of light efficiency.

[0100] Therefore, as shown in Figure 10, the mold can be divided and processed into annular units m1, and the annular units m1 can be assembled to form mold M. In this way, the grooves of the mold are formed by the contact of the surfaces of different annular units m1, and will not become rounded corners.

[0101] Diffractive lenses formed using laminated resin materials typically require two molds for injection molding and high-precision dispensing technology to avoid misalignment, making the process relatively complex. Furthermore, if the entire diffractive lens is made of resin, it suffers from poor lightfastness; changes in temperature and humidity can alter the diffraction structure and degrade optical performance, while also affecting the lifespan of the resin material. The diffractive lens provided in this application consists of a lens substrate and a coating. After the lens substrate is fabricated, only one mold is needed to laminate the resin coating, making the process relatively simple. The lens substrate, made of optical glass, has good lightfastness, and the diffraction structure on the surface of the lens substrate does not change or degrade in optical performance due to temperature and humidity variations, making it highly suitable for laser projection systems.

[0102] When placing a diffractive lens in a projection lens, the lens should be positioned such that the incident angle of light passing through its surface is small. This prevents glare and other problems caused by light incident on the side of the diffractive structure along its depth direction. In optical design, the diffractive lens can be positioned where the maximum incident angle of light is less than 10°, and preferably less than 5°.

[0103] At the same time, the maximum incident angle of the light rays incident on the diffraction lens also satisfies:

[0104] Among them, AOI MAX θ represents the maximum incident angle of the light rays incident on the diffraction lens, and θ represents the bottom angle of the annular groove.

[0105] This avoids the problem of reduced diffraction efficiency and stray light caused by an excessively large incident angle of the incident light from the diffraction lens. It also prevents the bending angle of the diffraction lens from being too large, which would cause manufacturing difficulties.

[0106] Taking the above factors into consideration, the diffraction lens can be placed in the rear group of lenses 32 or the front group of lenses 31 of the projection lens.

[0107] Specifically, as shown in Figure 3, the front lens group 31 of the projection lens includes a first lens l1, a second lens l2, a third lens l3, and a fourth lens l4 arranged sequentially along the optical axis towards the aperture s; wherein the refractive power of the first lens l1 is negative, the refractive power of the second lens l2 is negative, the refractive power of the third lens l3 is positive, and the refractive power of the fourth lens l4 is positive.

[0108] The rear lens group 32 includes a fifth lens l5, a sixth lens l6, a seventh lens l7, an eighth lens l8, a ninth lens l9, and a tenth lens l10 arranged sequentially along the optical axis away from the aperture s; wherein the refractive power of the fifth lens l5 is positive, the refractive power of the sixth lens l6 is negative, the refractive power of the seventh lens l7 is negative, the refractive power of the eighth lens l8 is positive, the refractive power of the ninth lens l9 is positive, and the refractive power of the tenth lens l10 is positive.

[0109] The projection lens satisfies: L / Bf < 1.75;

[0110] Where L represents the length of the projection lens, and Bf represents the distance from the surface of the tenth lens of the projection lens facing the display element to the display surface of the display element. By incorporating a diffractive lens into the projection lens, chromatic aberration can be corrected. Furthermore, the diffractive lens has a smaller thickness, avoiding the need for complex lens combinations and reducing the overall length of the projection lens.

[0111] This projection lens can be a telephoto lens, with a wide range of applications. Furthermore, the projection lens can employ a telecentric optical system; when the diffractive lens is positioned close to the image or object side, the light rays incident on the diffractive lens are relatively parallel.

[0112] In some embodiments, as shown in FIG3, the ninth lens 19 can be configured as a diffraction lens 301. The diffraction structure of the diffraction lens is located on the surface of the ninth lens 19 facing the tenth lens 110. The focal length of the diffraction lens satisfies: 1.5 < f G9 / f2 < 4.5;

[0113] Where f2 represents the focal length of the rear lens group, f G9 This indicates the focal length of the diffractive lens. This balances the optical power provided by the diffractive lens in the rear lens group.

[0114] In some embodiments, the optical surfaces of the first lens l1, the second lens l2, and the diffraction lens 301 can all be aspherical, specifically even-order aspherical, and their surface shapes satisfy the following formula:

[0115] Where Z represents the surface profile of the optical surface, y represents the height perpendicular to the optical axis, R represents the paraxial radius of curvature, k represents the conic coefficient, and A 2iThis represents the aspheric coefficient.

[0116] The fifth lens l5 and the sixth lens l6 can form a cemented lens, and the seventh lens l7 and the eighth lens l8 can form a cemented lens.

[0117] The phase distribution of the diffraction structure in a diffraction lens satisfies the following equation:

[0118] Here, the diffraction order of the diffracted light is 1. The phase of the diffraction structure is at a radial height (h) relative to the plane perpendicular to the optical axis, and the designed wavelength is λ. n It is the phase coefficient of order n.

[0119] The optical design parameters (radius of curvature, refractive index, Abbe number, thickness or spacing) of each optical surface from the object side to the image side in the projection lens are shown in the table below:

[0120] The optical surfaces marked with "*" in the table above are aspherical surfaces. The optical design parameters for aspherical surfaces are shown in the table below:

[0121] Using the wavelength of green laser as the design wavelength λ = 525 nm, the phase coefficients satisfied by the diffraction structure can be found in the table below:

[0122] The aforementioned projection lens has a focal length of 8.94mm, an F.NO. of 2.0, and a half field of view of 31.8°.

[0123] This application embodiment also simulates the imaging quality of the above-mentioned projection lens.

[0124] Figure 11 is a spherical aberration curve provided in an embodiment of this application.

[0125] Figure 11 shows the aberration curves for red laser r, green laser g, and blue laser b at wavelengths of 647 nm, 525 nm, and 455 nm, respectively. The horizontal axis represents the aberration magnitude in mm, and the vertical axis represents the normalized pupil coordinates. As shown in Figure 11, with a pupil radius of 2.337 mm, the aberrations produced by different colors of lasers in the projection lens are relatively small.

[0126] Figure 12 is a lateral color difference curve provided in an embodiment of this application.

[0127] Figure 12 shows the lateral chromatic aberration of red laser r, green laser g, and blue laser b at wavelengths of 647nm, 525nm, and 455nm when imaging within a maximum field of view of 5.6000mm. The horizontal axis represents the magnitude of the lateral chromatic aberration in μm (also known as magnified chromatic aberration); the vertical axis represents the actual image height in mm. As can be seen from Figure 12, the chromatic aberration produced by red laser r and blue laser b relative to green laser g is less than 1.0μm. This demonstrates that using a diffractive lens in the projection lens can effectively correct the chromatic aberration produced by the projection lens.

[0128] Figure 13 is a schematic diagram of the astigmatism curve provided in an embodiment of this application.

[0129] Figure 13 shows the astigmatism curves in the meridional and sagittal directions of the images formed by red laser r, green laser g, and blue laser b with wavelengths of 647 nm, 525 nm, and 455 nm, respectively. The horizontal axis represents the magnitude of astigmatism in mm, and the vertical axis represents the field of view. In Figure 13, the solid line represents the astigmatism of the three colors of laser light in the meridional direction, and the dashed line represents the astigmatism in the sagittal direction. As can be seen from Figure 13, the astigmatism of the three colors of laser light in both the meridional and sagittal directions is less than 0.03 mm, indicating that the astigmatism of the projection lens is within a reasonable range.

[0130] Figure 14 is a schematic diagram of the distortion curve provided in the embodiment of this application.

[0131] Figure 14 shows the distortion curves for imaging with red laser r, green laser g, and blue laser b at wavelengths of 647 nm, 525 nm, and 455 nm, where the horizontal axis represents the percentage of distortion and the vertical axis represents the field of view. As can be seen from Figure 14, the distortion produced by the projection lens is below 0.8%, which is within a reasonable range.

[0132] In some embodiments, as shown in FIG15, the first lens l1 can be configured as a diffraction lens 301, and the diffraction structure of the diffraction lens is located on the surface of the first lens l1 opposite to the second lens l2.

[0133] Among them, the optical surfaces of the diffractive lens and the second lens l2, as well as the image-side surface of the ninth lens and the object-side surface of the tenth lens, can all be aspherical surfaces, specifically even-order aspherical surfaces, whose surface shapes satisfy the following formula:

[0134] Where Z represents the surface profile of the optical surface, y represents the height perpendicular to the optical axis, R represents the paraxial radius of curvature, k represents the conic coefficient, and A 2i This represents the aspheric coefficient.

[0135] The fifth lens l5 and the sixth lens l6 can form a cemented lens, and the seventh lens l7 and the eighth lens l8 can form a cemented lens.

[0136] The phase distribution of the diffraction structure in a diffraction lens satisfies the following equation:

[0137] Here, the diffraction order of the diffracted light is 1. The phase of the diffraction structure is at a radial height (h) relative to the plane perpendicular to the optical axis, and the designed wavelength is λ. n It is the phase coefficient of order n.

[0138] The optical design parameters (radius of curvature, refractive index, Abbe number, thickness or spacing) of each optical surface from the object side to the image side in the projection lens are shown in the table below:

[0139] The optical surfaces marked with "*" in the table above are aspherical surfaces. The optical design parameters for aspherical surfaces are shown in the table below:

[0140] Using the wavelength of green laser as the design wavelength λ = 525 nm, the phase coefficients satisfied by the diffraction structure can be found in the table below:

[0141] The aforementioned projection lens has a focal length of 8.99mm, an F.NO of 2.20, and a half field of view of 31.69°.

[0142] This application embodiment also simulates the imaging quality of the above-mentioned projection lens.

[0143] Figure 16 is a spherical aberration curve provided in an embodiment of this application.

[0144] Figure 16 shows the aberration curves for red laser r, green laser g, and blue laser b at wavelengths of 647 nm, 525 nm, and 455 nm, where the horizontal axis represents the aberration magnitude in mm, and the vertical axis represents the normalized pupil coordinates. As shown in Figure 16, with a pupil radius of 2.1418 mm, the aberrations produced by different colors of lasers in the projection lens are relatively small.

[0145] Figure 17 is a lateral color difference curve provided in an embodiment of this application.

[0146] Figure 17 shows the lateral chromatic aberration of red laser r, green laser g, and blue laser b at wavelengths of 647nm, 525nm, and 455nm when imaging within a maximum field of view of 5.6000mm. The horizontal axis represents the magnitude of the lateral chromatic aberration in μm (also known as magnified chromatic aberration); the vertical axis represents the actual image height in mm. As can be seen from Figure 17, the chromatic aberration produced by red laser r relative to green laser g is less than 2.0μm, and the chromatic aberration produced by blue laser b relative to green laser g is less than 1.5μm. This demonstrates that using a diffractive lens in the projection lens can effectively correct the chromatic aberration produced by the projection lens.

[0147] Figure 18 is a schematic diagram of the astigmatism curve provided in an embodiment of this application.

[0148] Figure 18 shows the astigmatism curves in the meridional and sagittal directions of the images formed by red laser r, green laser g, and blue laser b with wavelengths of 647 nm, 525 nm, and 455 nm, respectively. The horizontal axis represents the magnitude of astigmatism in mm, and the vertical axis represents the field of view. In Figure 18, the solid line represents the astigmatism of the three-color lasers in the meridional direction, and the dashed line represents the astigmatism in the sagittal direction. As can be seen from Figure 18, the astigmatism of the three-color lasers in both the meridional and sagittal directions is less than 0.06 mm, indicating that the astigmatism of the projection lens is within a reasonable range.

[0149] Figure 19 is a schematic diagram of the distortion curve provided in the embodiment of this application.

[0150] Figure 19 shows the distortion curves for imaging with red laser r, green laser g, and blue laser b at wavelengths of 647 nm, 525 nm, and 455 nm, where the horizontal axis represents the percentage of distortion and the vertical axis represents the field of view. As can be seen from Figure 19, the distortion produced by the projection lens is below 0.4%, which is within a reasonable range.

[0151] The above embodiments are for illustrative purposes only. In practical applications, diffractive lenses can be placed in telephoto lenses, short-throw lenses, and ultra-short-throw lenses. The number of lenses, the number and placement of aspherical lenses, and the number and placement of diffractive lenses in the projection lens all need to be designed according to actual requirements and are not limited here.

[0152] The projection lens and projection system provided in this application include: an aperture stop, a front group of lenses and a rear group of lenses located on either side of the aperture stop. At least one diffractive lens can be disposed in the front group of lenses and / or the rear group of lenses. The diffractive lens includes a lens substrate and a coating on the surface of the lens substrate. A diffraction structure is disposed on the surface of the lens substrate, and the coating covers the diffraction structure. The diffractive lens, employing a layered structure, exhibits high diffraction efficiency across the visible light band. The diffractive lens can correct chromatic aberration in the projection lens, avoiding pixel shift problems and enabling the projection system to obtain a high-quality projection image without light loss or glare.

[0153] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0154] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A projection lens, comprising: Aperture; The front group of mirrors and the rear group of mirrors are located on both sides of the aperture stop, respectively; Both the front group of lenses and the rear group of lenses include multiple lenses; At least one lens in the front group of lenses and / or the rear group of lenses is a diffractive lens; the diffractive lens is used to correct the chromatic aberration of the projection lens; The diffractive lens includes: a lens substrate and a coating on the surface of the lens substrate; a diffractive structure is provided on one side surface of the lens substrate, and the coating covers the diffractive structure.

2. The projection lens as described in claim 1, wherein, The lens substrate and the coating are made of different materials; The lens substrate is made of glass, and the coating is made of resin.

3. The projection lens as described in claim 2, wherein, The thickness of the coating along the direction parallel to the optical axis of the diffraction lens is less than 0.2 mm.

4. The projection lens as described in claim 2, wherein, The refractive index and Abbe number of the diffractive lens satisfy: Wherein, dn represents the difference between the refractive index of the lens substrate and the refractive index of the coating, and dv represents the difference between the Abbe number of the lens substrate and the Abbe number of the coating.

5. The projection lens as described in claim 4, wherein, The refractive index and Abbe number of the lens substrate satisfy: 1.55≤Nd1≤1.65; 55≤Vd1≤68; The refractive index and Abbe number of the coating satisfy: 1.55≤Nd2≤1.61; Vd2≤38; Wherein, Nd1 represents the refractive index of the lens substrate, Vd1 represents the Abbe number of the lens substrate, Nd2 represents the refractive index of the coating, and Vd2 represents the Abbe number of the coating.

6. The projection lens as described in any one of claims 1 to 5, wherein, The diffraction structure of the diffraction lens consists of concentrically expanding annular grooves; the center of the annular grooves coincides with the optical axis of the diffraction lens.

7. The projection lens as described in claim 6, wherein, The depth of the annular groove along the direction parallel to the optical axis of the diffraction lens satisfies: (Nd1-Nd2)d=mλ; Wherein, Nd1 represents the refractive index of the lens substrate, Nd2 represents the refractive index of the coating, d represents the depth of the annular groove along the direction parallel to the optical axis of the diffractive lens, λ represents the wavelength of the incident light, and m represents the diffraction order.

8. The projection lens as described in claim 6, wherein, The included angle at the bottom of the annular groove satisfies: 40° < θ < 90°; Wherein, θ represents the bottom included angle of the annular groove, dL represents the spacing width between adjacent annular grooves in a plane perpendicular to the optical axis of the diffraction lens, and d represents the depth of the annular groove in a direction parallel to the optical axis of the diffraction lens.

9. The projection lens as described in claim 6, wherein, The maximum incident angle of the light rays incident on the diffraction lens and the bottom angle of the annular groove satisfy the following: Among them, AOI MAX θ represents the maximum incident angle of the light rays incident on the diffraction lens, and θ represents the bottom angle of the annular groove.

10. The projection lens as claimed in claim 9, wherein, The front lens group includes a first lens, a second lens, a third lens, and a fourth lens arranged sequentially along the optical axis towards the aperture; the first lens has a negative refractive power, the second lens has a negative refractive power, the third lens has a positive refractive power, and the fourth lens has a positive refractive power. The rear lens group includes a fifth lens, a sixth lens, a seventh lens, an eighth lens, a ninth lens, and a tenth lens arranged sequentially along the optical axis, gradually moving away from the aperture; the fifth lens has a positive refractive power, the sixth lens has a negative refractive power, the seventh lens has a negative refractive power, the eighth lens has a positive refractive power, the ninth lens has a positive refractive power, and the tenth lens has a positive refractive power.

11. The projection lens as claimed in claim 10, wherein, The ninth lens is a diffractive lens, and the diffraction structure is located on the surface of the ninth lens facing the tenth lens.

12. The projection lens as claimed in claim 10, wherein, The first lens is a diffractive lens, and the diffractive structure is located on the surface of the first lens opposite to the second lens.

13. The projection lens as described in any one of claims 10 to 12, wherein, The projection lens satisfies: L / Bf < 1.75; Where L represents the length of the projection lens, and Bf represents the distance between the surface of the lens closest to the display element and the display surface of the display element.

14. The projection lens as claimed in claim 11, wherein, The focal length of the diffractive lens satisfies: 1.5 < fG9 / f2 < 4.5; Where f2 represents the focal length of the rear lens group, and fG9 represents the focal length of the diffractive lens.

15. The projection lens as described in any one of claims 1 to 5, wherein, The diffraction efficiency of the diffraction lens satisfies: Among them, E R E represents the diffraction efficiency of red light. G E represents the diffraction efficiency of green light. B This indicates the diffraction efficiency of blue light.

16. A projection system, comprising: Laser source, used to emit three-color lasers; An illumination system is located on the light-emitting side of the laser source; The lighting system includes a light homogenizing element and a display element. The light homogenizing element is located on the light-emitting side of the laser source and is used to homogenize the incident laser. The display element is located on the light-emitting side of the light homogenizing element and is used to modulate the incident laser before emission. A projection lens is located on the light-emitting side of the display element; the projection lens is the projection lens according to any one of claims 1 to 15; A total internal reflection prism is located between the display element and the projection lens; the total internal reflection prism is used to reflect the laser emitted from the homogenizing element back to the display element and transmit the laser modulated by the display element.

17. The projection system of claim 16, wherein, The projection lens is a telephoto lens and uses a telecentric optical system.

Images