A projection lens and projection system

Abstract

This invention discloses a projection lens and projection system, including an aperture stop, a front group of lenses and a rear group of lenses located on either side of the aperture stop. A diffractive lens is disposed in the rear group of lenses. The diffractive lens includes a lens substrate, one side surface of which has a first diffraction structure, a first coating covering the first diffraction structure, and a second diffraction structure on the side surface of the first coating facing away from the lens substrate, with a second coating covering the second diffraction structure. By introducing a diffractive lens into the projection lens, and the diffractive lens having a double-layer diffraction surface, the system can maintain a high diffraction efficiency through the mutual matching of refractive indices, while simultaneously utilizing the negative chromatic aberration characteristics of the diffraction surface to complement the positive chromatic aberration of the lens's refractive surface. This significantly reduces chromatic aberration in the optical system and overcomes the problem of red and blue fringing in projected text. The introduction of the diffractive lens also provides more optimization freedom for the entire optical system, thereby achieving a small size and high performance for the projection lens.

Description

Technical Field

[0001] This invention relates to the field of projection technology, and more particularly to a projection lens and projection system. Background Technology

[0002] In recent years, laser projection products have developed rapidly, and their application demand modes have become more and more diversified. As a smart projection product, small size and good image quality have become an important development trend.

[0003] As three-color laser technology matures, laser projection equipment will be equipped with three-color laser light sources. Three-color laser light sources have the advantages of high color gamut and high brightness. However, as the spectral range increases, achieving small color difference while ensuring image quality becomes increasingly important.

[0004] Introducing a three-color laser light source into a projection device will make the color difference problem more obvious, resulting in red and blue edges when projecting text. Summary of the Invention

[0005] This invention provides a projection lens, comprising:

[0006] Aperture;

[0007] The front group of lenses includes multiple lenses; and

[0008] The rear lens group includes multiple lenses;

[0009] The front group of lenses and the rear group of lenses are located on opposite sides of the aperture stop; the rear group of lenses includes a diffraction lens, which comprises:

[0010] A lens substrate, wherein one side surface of the lens substrate has a first diffraction structure;

[0011] A first coating is located on a first diffraction structure of the lens substrate; the surface of the first coating facing away from the lens substrate has a second diffraction structure; and

[0012] The second coating is located on the second diffraction structure of the first coating.

[0013] In some embodiments of the present invention, 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; wherein the first lens and the second lens are aspherical lenses, and the third lens and the fourth lens are spherical lenses;

[0014] The first lens has a positive refractive power on its image side and a negative refractive power on its object side; the second lens has a positive refractive power on its image side and a negative refractive power on its object side; the third lens has a negative refractive power on its image side and a positive refractive power on its object side; and the fourth lens has a positive refractive power on its image side and a negative refractive power on its object side.

[0015] 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 away from the aperture; wherein the ninth lens is an aspherical lens, and the fifth lens, the sixth lens, the seventh lens, the eighth lens, and the tenth lens are spherical lenses;

[0016] The fifth lens and the sixth lens constitute a first cemented lens, and the seventh lens and the eighth lens constitute a second cemented lens; the ninth lens is a diffraction lens;

[0017] The refractive power of the image side of the fifth lens is negative, the refractive power of the object side of the fifth lens and the image side of the sixth lens are positive, the refractive power of the object side of the sixth lens is negative, the refractive power of the image side of the seventh lens is positive, the refractive power of the object side of the seventh lens and the image side of the eighth lens are negative, the refractive power of the object side of the eighth lens is positive, the refractive power of the image side of the ninth lens is positive, the refractive power of the object side of the ninth lens is positive, the refractive power of the image side of the tenth lens is negative, and the refractive power of the object side of the tenth lens is positive.

[0018] In some embodiments of the present invention, the first coating and the second coating are located on the side of the lens substrate of the ninth lens facing the tenth lens;

[0019] Both the first and second diffraction structures are concentrically arranged annular grooves that expand sequentially.

[0020] In some embodiments of the present invention, the depth of the annular groove of the first diffraction structure is less than 0.02 mm, and the depth of the annular groove of the second diffraction structure is less than 0.02 mm.

[0021] The bottom included angle of the annular groove of the first diffraction structure is less than 70°, and the bottom included angle of the annular groove of the second diffraction structure is less than 70°.

[0022] In some embodiments of the present invention, the maximum incident angle of the light rays incident on the diffraction lens satisfies:

[0023] 0 ≤ AOR1 ≤ 2.5°;

[0024] Wherein, AOR1 represents the maximum value of the incident angle of the principal ray incident on the diffraction lens.

[0025] In some embodiments of the present invention, the radii of curvature of the first cemented lens and the second cemented lens satisfy the following:

[0026] -2.0 < R7_8 / R5_6 < -1.5;

[0027] Wherein, R7_8 represents the radius of curvature of the cemented surface of the seventh lens and the eighth lens, and R5_6 represents the radius of curvature of the cemented surface of the fifth lens and the sixth lens.

[0028] In some embodiments of the present invention, the ninth lens and the tenth lens satisfy the following:

[0029] 8 < (f9 + f10) / (h9 + h10) < 10;

[0030] Wherein, f9 represents the focal length of the ninth lens, f10 represents the focal length of the tenth lens, h9 represents the center thickness of the ninth lens along the optical axis, and h10 represents the center thickness of the tenth lens along the optical axis.

[0031] In some embodiments of the present invention, the first lens and the second lens satisfy the following:

[0032] (abv1+abv2)>110;

[0033] Where abv1 represents the Abbe number of the first lens and abv2 represents the Abbe number of the second lens.

[0034] In some embodiments of the present invention, the image height of the projection lens is greater than 7.5 mm;

[0035] The tenth lens satisfies:

[0036] R_L10 > 10mm;

[0037] Wherein, R_L10 represents the aperture of the tenth lens;

[0038] The telecentricity of the projection lens is less than 0.8°.

[0039] This invention also provides a projection system, comprising:

[0040] Laser source used to emit three-color lasers;

[0041] An illumination system is located on the light-emitting side of the laser source; the illumination system includes a display element, which is used to modulate the incident laser to form an image beam;

[0042] A projection lens, located on the light-emitting side of the display element, is used to image the image beam; the projection lens is any of the projection lenses described above.

[0043] 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 laser source back to the display element and transmit the image beam modulated by the display element to the projection lens.

[0044] The projection lens and projection system provided in this invention include: an aperture stop, a front group of lenses and a rear group of lenses located on both sides of the aperture stop. Both the front and rear group of lenses include multiple lenses, and a diffractive lens is provided in the rear group of lenses. The diffractive lens includes a lens substrate, one side surface of which has a first diffraction structure, a first coating covering the first diffraction structure, and a second diffraction structure on the side surface of the first coating facing away from the lens substrate, with a second coating covering the second diffraction structure. By introducing a diffractive lens into the projection lens, and the diffractive lens having a double-layer diffraction surface, the system can maintain a high diffraction efficiency through the mutual matching of refractive indices, while simultaneously utilizing the negative chromatic aberration characteristics of the diffraction surface to complement the positive chromatic aberration of the lens's refractive surface. This significantly reduces chromatic aberration in the optical system and overcomes the problem of red and blue fringes in projected text. The introduction of the diffractive lens also provides more optimization freedom for the entire optical system, thereby achieving a small size and high performance for the projection lens. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a schematic diagram of the projection system provided in an embodiment of the present invention;

[0047] Figure 2 An architectural diagram of a projection device provided in an embodiment of the present invention;

[0048] Figure 3 This is a schematic diagram of the projection lens provided in an embodiment of the present invention;

[0049] Figure 4 This is a schematic diagram of the structure of a diffraction lens provided in an embodiment of the present invention;

[0050] Figure 5 A schematic diagram of the planar structure of a diffraction lens provided in an embodiment of the present invention;

[0051] Figure 6This is a partially enlarged schematic diagram of a diffraction lens provided in an embodiment of the present invention;

[0052] Figure 7 This is a light path tracing diagram of a projection lens provided in an embodiment of the present invention;

[0053] Figure 8 A modulation transfer function curve provided for an embodiment of the present invention;

[0054] Figure 9 The defocus curve provided for embodiments of the present invention;

[0055] Figure 10 A lateral color difference diagram provided for an embodiment of the present invention;

[0056] Figure 11 The relative illuminance curve provided for the embodiments of the present invention;

[0057] Figure 12 This is one of the aberration curve diagrams provided in the embodiments of the present invention;

[0058] Figure 13 This is the second aberration curve provided in an embodiment of the present invention;

[0059] Figure 14 This is the third aberration curve provided in the embodiments of the present invention;

[0060] Figure 15 A longitudinal spherical aberration curve is provided for an embodiment of the present invention;

[0061] Figure 16 Astigmatism curves provided for embodiments of the present invention;

[0062] Figure 17 The distortion curve is provided for an embodiment of the present invention. Detailed Implementation

[0063] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the present invention 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 present invention 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 as described in this invention 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 invention. The accompanying drawings of this invention are for illustrating relative positional relationships only and do not represent actual proportions.

[0064] Projection display technology is a technique that uses optical systems and projection space to magnify and display images. The projection system ultimately displays the image using an optical imaging system. With the continuous development of projection technology, laser projection systems, with their unique advantages, have been widely used in large-screen displays, laser TVs, digital cinemas, and portable projection displays. Laser projection displays can display more realistic and vibrant dynamic images on ultra-large screens, achieving a visually stunning effect that other display technologies cannot achieve.

[0065] In practical applications, projection systems can be divided into front projection systems and rear projection systems. In a front projection system, the audience and the projection device are located on the same side of the projection screen. The projection device emits projection light onto the screen, which then reflects the light back to the audience, allowing them to see the projected image. In a rear projection system, the audience and the projection device are located on opposite sides of the projection screen. The projection device emits projection light onto the screen, which then passes through the screen and projects the light back to the audience, allowing them to see the projected image.

[0066] Figure 1 A schematic diagram of a front-projection system is shown.

[0067] like Figure 1 As shown, 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.

[0068] Figure 2 This is an architectural diagram of a projection device provided in an embodiment of the present invention.

[0069] like Figure 2 As shown, 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.

[0070] In this embodiment of the invention, 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.

[0071] Laser source materials 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 source, a color wheel is also required for color conversion. The monochromatic laser, in conjunction with the color wheel, can emit different primary colors of light sequentially. 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 sequentially as primary colors.

[0072] In this embodiment of the invention, 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.

[0073] 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.

[0074] 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.

[0075] The homogenizing element 202 is located on the light emission path of the projection light source 10 and can homogenize the light emitted from the projection light source 10. The homogenizing element 202 can be a light guide or a compound eye lens, and there is no limitation on it.

[0076] 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.

[0077] 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 invention 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).

[0078] 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.

[0079] 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.

[0080] This embodiment of the invention will be illustrated using a 0.47-inch DMD as an example of a display element 201. Figure 2 As shown, the lighting system 20 may also include a total internal reflection prism 204. The total internal reflection prism 204 is used to separate the lighting 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 towards the total internal reflection prism 204. The total internal reflection prism 204 transmits the incident light to the projection lens 30.

[0081] 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. Long-throw projectors have a wide range of applications; they primarily refer to projectors using long-throw lenses. The projection ratio (or throw ratio) is a key parameter in a projection system, describing the relationship between projection distance and projected image size. 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 long-throw lenses, short-throw lenses, and ultra-short-throw lenses. Long-throw 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.

[0082] Figure 3 This is a schematic diagram of the projection lens provided in an embodiment of the present invention.

[0083] like Figure 3 As shown, 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 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.

[0084] Projection lens 30 typically includes multiple lenses. To improve image quality, these lenses can include spherical lenses and aspherical lenses. Due to unavoidable tolerances during lens manufacturing and installation, the projection lens cannot achieve the theoretical image quality. Furthermore, when the projection device is paired with a three-color laser light source, the different refractive indices of the lenses in the projection lens for different wavelengths of laser light will cause the focusing positions of different wavelengths of light to differ after passing through the same lens. This results in offsets between sub-pixels of different colors, leading to red and blue edges when projecting text.

[0085] To solve the above problems, such as Figure 3 As shown, the projection lens provided in this embodiment of the invention includes: a coaxially arranged aperture stop s, a front group of lenses 31, and a rear group of lenses 32, which are located on both sides of the aperture stop s. Both the front group of lenses 31 and the rear group of lenses 32 include multiple lenses, and the rear group of lenses includes a diffraction lens 321.

[0086] Figure 4 This is a schematic diagram of the structure of a diffraction lens provided in an embodiment of the present invention.

[0087] like Figure 4 As shown, the diffractive lens 321 includes: a lens substrate 321a, a first coating 321b, and a second coating 321c. One side surface of the lens substrate 321a has a first diffraction structure s1; the first coating 321b covers the first diffraction structure s1 of the lens substrate 321a, and the surface of the first coating 321b facing away from the lens substrate 321a has a second diffraction structure s2; the second coating 321c covers the second diffraction structure s2 of the first coating 321b. The first diffraction structure s1 and the second diffraction structure s2 constitute a double-layer diffraction surface, which can improve the diffraction efficiency of the three-color laser across the entire wavelength range.

[0088] This invention introduces a diffractive lens into the projection lens, and the diffractive lens has a double diffraction surface. By matching the refractive indices, it can ensure that the system has a high diffraction efficiency while utilizing the negative chromatic aberration characteristics of the diffraction surface to complement the positive chromatic aberration of the lens's refractive surface. This greatly reduces the chromatic aberration of the optical system and overcomes the problem of red and blue fringes in projected text. The introduction of the diffractive lens also provides more degrees of freedom for the entire optical system, thereby achieving a small size and high performance for the projection lens.

[0089] Figure 5 A schematic diagram of the planar structure of a diffraction lens provided in an embodiment of the present invention; Figure 6 This is a partially enlarged schematic diagram of a diffraction lens provided in an embodiment of the present invention.

[0090] like Figure 5 and Figure 6 As shown, the first diffraction structure s1 on the lens substrate surface and the second diffraction structure s2 on the first coating surface are both concentrically expanding annular grooves. The depth of the annular groove formed by the first diffraction structure s1 is d1, and the depth of the annular groove formed by the second diffraction structure s2 is d2. The diffraction lens 321 introduces a double-layer diffraction surface. Through the combination of three materials and the matching design of the heights of the two diffraction structures (the depths d1 and d2 of the annular grooves), diffraction efficiency can be improved. When used with a three-color laser in the 455nm–650nm wavelength range, a diffraction efficiency >99% can be achieved, thus ensuring imaging quality and minimizing the introduction of stray light. Even under large incident angles and microstructure processing errors, the diffraction efficiency remains at a high level.

[0091] When designing a diffractive lens, the refractive index combination must satisfy the following:

[0092]

[0093] Where η represents the diffraction efficiency, d represents the height of the diffraction structure (depth of the annular groove), Δn represents the difference in refractive index between the two closely spaced materials, m represents the diffraction order, and λ represents the design wavelength.

[0094] Based on the above formula, the refractive index of the lens substrate 321a of the diffractive lens designed in this embodiment of the invention is higher than that of the materials of the first coating 321b and the second coating 321c. When the difference between the two refractive indices is substituted into the above formula and the diffraction efficiency is greater than 99% at different wavelengths, it is considered that the refractive index combination is better. At the same time, the diffraction efficiency at different wavelengths can be improved by adjusting the height d of the diffraction structure.

[0095] In this embodiment of the invention, the lens substrate 321a of the diffractive lens can be made of glass, and the first coating 321b and the second coating 321c can be made of resin material. Through reasonable design, the depth of the annular groove formed by the first diffraction structure s1 is less than 0.02 mm, and the depth of the annular groove formed by the second diffraction structure s2 is less than 0.02 mm. By controlling the height of the diffraction structures, i.e., ensuring the depth of the annular grooves meets the aforementioned range, the two diffraction surfaces of the diffractive lens can be more easily processed, thereby improving the manufacturability of the diffractive lens. Simultaneously, a diffraction efficiency greater than 99% can be achieved in the 455 nm to 650 nm wavelength range.

[0096] Furthermore, such as Figure 6 As shown, the bottom included angle θ1 of the annular groove formed by the first diffraction structure s1 is less than 70°, and the bottom included angle θ2 of the annular groove formed by the second diffraction structure s2 is less than 70°.

[0097] Setting the bottom angle of the annular groove formed by the first diffraction structure s1 and the second diffraction structure to less than 70° can reduce the amount of light incident on the side of the diffraction structure, thereby avoiding problems such as glare.

[0098] The maximum incident angle of the light rays incident on the diffraction lens satisfies:

[0099] 0 ≤ AOR1 ≤ 2.5°;

[0100] Where AOR1 represents the maximum value of the incident angle of the principal ray incident on the diffraction lens.

[0101] Since diffraction efficiency is related to the incident angle, the diffraction efficiency of the optical system can be effectively guaranteed by controlling the incident angle of light at the diffraction surface of the incident diffraction lens to be as small as possible, thereby reducing secondary diffraction, avoiding glare problems, and making the imaging effect of the optical system better.

[0102] In some embodiments, such as Figure 3As shown, the front lens group 31 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; 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.

[0103] Among them, the first lens l1, the second lens l2 and the ninth lens l9 are aspherical lenses, and the third lens l3, the fourth lens l4, the fifth lens l5, the sixth lens l6, the seventh lens l7, the eighth lens l8 and the tenth lens l10 are spherical lenses.

[0104] The fifth lens l5 and the sixth lens l6 constitute the first cemented lens, and the seventh lens l7 and the eighth lens l8 constitute the second cemented lens.

[0105] The ninth lens l9 is a diffractive lens, and the first coating 321b and the second coating 321c are located on the side of the lens substrate 321a of the ninth lens l9 facing the tenth lens l10.

[0106] The image beam emitted from the display element 201 enters the lens from the tenth lens side and finally exits from the first lens side before entering the imaging medium such as the projection screen. Therefore, the side of each lens facing the display element 201 is the object side, and the side of each lens facing the imaging medium is the image side.

[0107] The image-side refractive power of the first lens l1 is positive, and the object-side refractive power of the first lens l1 is negative. The image-side refractive power of the second lens l2 is positive, and the object-side refractive power of the second lens l2 is negative. The image-side refractive power of the third lens l3 is negative, and the object-side refractive power of the third lens l3 is positive. The image-side refractive power of the fourth lens l4 is positive, and the object-side refractive power of the fourth lens l4 is negative.

[0108] The object-side surface of the fifth lens l5 is cemented with the image-side surface of the sixth lens l6, and the object-side surface of the seventh lens l7 is cemented with the image-side surface of the eighth lens l8. The refractive power and surface shape of the cemented surfaces are the same. The refractive power of the image-side surface of the fifth lens l5 is negative, the refractive power of the object-side surface of the fifth lens l5 and the image-side surface of the sixth lens l6 is positive, the refractive power of the object-side surface of the sixth lens l6 is negative, the refractive power of the image-side surface of the seventh lens l7 is positive, the refractive power of the object-side surface of the seventh lens l7 and the image-side surface of the eighth lens l8 is negative, the refractive power of the object-side surface of the eighth lens l8 is positive, the refractive power of the image-side surface of the ninth lens l9 is positive, the refractive power of the object-side surface of the ninth lens l9 is positive, and the refractive power of the image-side surface of the tenth lens l10 is negative and the refractive power of the object-side surface of the tenth lens l10 is positive.

[0109] The first lens l1, the second lens l2, and the ninth lens l9 are all aspherical lenses. The first lens l1 is made of plastic, while the second and ninth lenses l2 and l9 are made of glass. Since the first lens l1 has the largest aperture in the optical system, using plastic as the material for the aspherical lens effectively reduces the difficulty of lens manufacturing, thus lowering processing costs. Furthermore, the lightweight nature of plastic lenses effectively reduces the overall weight of the lens. The ninth lens l9 is closest to the display element 201. When the projection system uses a three-color laser light source, the image beam emitted from the display element 201 is a laser beam with high energy. Therefore, using glass for the aspherical lens closest to the display element 201 avoids deformation under high-energy laser irradiation. Additionally, the refractive index of the glass material is more compatible with the refractive indices of its first and second coatings, which is beneficial for achieving higher diffraction efficiency.

[0110] The first lens l1 and the second lens l2 satisfy:

[0111] (abv1+abv2)>110;

[0112] Where abv1 represents the Abbe number of the first lens l1 and abv2 represents the Abbe number of the second lens l2.

[0113] The first lens l1 and the second lens l2 are meniscus aspherical lenses. Both lenses are made of low dispersion material, which can reduce the generation of chromatic aberration, thereby reducing the pressure of chromatic aberration correction by the diffraction lens.

[0114] The fifth lens l5 and the sixth lens l6 form the first cemented lens, and the seventh lens l7 and the eighth lens l8 form the second cemented lens. The two cemented lenses can help correct the chromatic aberration of the optical system. When used in conjunction with a diffractive lens, they can reduce the pressure on the diffractive lens to correct chromatic aberration and reduce the design difficulty of the diffractive lens.

[0115] The radii of curvature of the first cemented lens and the second cemented lens satisfy the following:

[0116] -2.0 < R7_8 / R5_6 < -1.5;

[0117] R7_8 represents the radius of curvature of the cemented surface of the seventh lens l7 and the eighth lens l8, and R5_6 represents the radius of curvature of the cemented surface of the fifth lens l5 and the sixth lens l6.

[0118] By controlling the ratio of the curvature radii of the two cemented lenses to be negative, so that one cemented surface bends toward the aperture stop s and the other cemented surface faces away from the aperture stop s, it is beneficial to correct coma and astigmatism in the optical system.

[0119] The ninth lens l9 and the tenth lens l10 satisfy:

[0120] 8 < (f9 + f10) / (h9 + h10) < 10;

[0121] Where f9 represents the focal length of the ninth lens l9, f10 represents the focal length of the tenth lens l10, h9 represents the center thickness of the ninth lens l9 along the optical axis, and h10 represents the center thickness of the tenth lens l10 along the optical axis.

[0122] The refractive index of the ninth lens l9 is less than that of the tenth lens l10. By combining the low-refractive and high-refractive indexes of the two lenses with an aspherical surface, spherical aberration and telecenty can be corrected.

[0123] The projection lens provided in this embodiment of the invention is an optical system architecture designed to be used with a 0.47-inch DMD. The image height of the projection lens is greater than 7.5mm, and can reach 8mm. The aperture R_L10 of the tenth lens is greater than 10mm.

[0124] The projection lens provided in this embodiment of the invention is a telephoto lens, employing a telecentric optical system with a telecentricity of less than 0.8°. When the diffraction lens 321 is positioned close to the object side, the incident light rays are relatively parallel, which helps to reduce the design difficulty of the diffraction surface.

[0125] like Figure 3 As shown, the gaps between the projection lens, the image shifting component P, the total internal reflection prism 204, and the display element 201 are adjustable, thereby enabling zoom imaging at different projection distances. The projection lens has a back focus distance Fb ≥ 24 mm, providing a longer back focus and making it easier to match various lighting systems.

[0126] In some embodiments of the present invention, the optical design parameters (surface shape, radius of curvature, spacing, and refractive index) of each optical surface of the projection lens from the image side to the object side are shown in the table below:

[0127]

[0128]

[0129] The optical design parameters for aspherical surfaces are shown in the table below:

[0130]

[0131]

[0132] The phase coefficients satisfied by the diffraction structure can be found in the table below:

[0133] Diffraction plane 1 Diffraction surface 2 Second-order coefficients -0.000135 -0.000230 4th order coefficients -6.16E-08 2.6248E-06 6th order coefficients 4.16E-10 -1.5475E-07 8th order coefficients 1.00E-11 -

[0134] Wherein, diffraction plane 1 refers to the surface where the first diffraction structure is located, and diffraction plane 2 refers to the surface where the second diffraction structure is located. The phase distributions of both the first and second diffraction structures satisfy:

[0135]

[0136] Here, 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.

[0137] Based on the above parameters, the projection lens is a telephoto lens with a throw ratio of 1.2, a focal length of 12.48mm, and a length of only 53mm, significantly reducing the size of the optical engine in commercial projection products and achieving overall miniaturization. The lens offset is 100%-105%, and the resolution reaches MTF≥60% at 93lp / mm, with a projectable size of 100 inches. The projection lens employs a hybrid refractive-diffraction optical system, achieving a chromatic aberration of only 0.2 pixels.

[0138] This invention also evaluates the image quality of the projection lens based on the above parameter optimization results, and the optical path tracing of the projection lens is as follows: Figure 7 As shown.

[0139] Figure 8 The modulation transfer function curve of the projection lens provided in the embodiment of the present invention.

[0140] Figure 8 The diagram shows the modulation transfer function (MTF) curves of three primary colors with center wavelengths of 647nm, 525nm, and 455nm in different fields of view. The horizontal axis represents spatial frequency, expressed as cycles per millimeter of image space (cycles / mm), and the vertical axis represents the MTF value. MTF characterizes the resolving power of a resolving lens. Figure 8 As can be seen, the MTF values ​​of the three primary colors are all above 0.6 and the curves are relatively flat, indicating that the imaging difference between the edge and center of the projection lens is small and the imaging quality is good.

[0141] Figure 9 The defocus curve of the projection lens provided in the embodiment of the present invention.

[0142] Figure 9The defocusing curves of the three primary colors with center wavelengths of 647nm, 525nm, and 455nm in different fields of view are shown at a spatial frequency of 93.0 cycles / mm. The horizontal axis represents the defocusing position in mm, and the vertical axis represents the MTF value (Modulation). Figure 9 It can be seen that the MTF values ​​of the three primary colors at the optical axis are all above 0.6, and the image plane offset is within a reasonable range.

[0143] Figure 10 This is a lateral chromatic aberration diagram of a projection lens provided in an embodiment of the present invention.

[0144] Figure 10 The diagram shows the lateral chromatic aberration of red light (r), green light (g), and blue light (b) with center wavelengths of 647nm, 525nm, and 455nm at different imaging sizes within a field of view of 0–0.9. The horizontal axis represents the lateral chromatic aberration in μm, and the vertical axis represents the actual image size in mm. The maximum lateral chromatic aberration of the projection lens is 0.49 μm. Therefore, the refractive-diffraction hybrid projection lens provided in this embodiment can effectively correct the chromatic aberration generated by the projection lens.

[0145] Figure 11 This is a schematic diagram of the relative illumination curve provided in an embodiment of the present invention.

[0146] like Figure 11 As shown, the horizontal axis of the relative illuminance curve represents the image height of the principal ray, in mm, and the vertical axis represents the relative illuminance at the peripheral positions when the central light intensity is 100%, in %. Figure 11 It can be seen that the relative illumination of the projection lens is over 70%, which has a large normal value.

[0147] Figures 12-14 The aberration curve of the projection lens provided in the embodiment of the present invention.

[0148] Figures 12-14 The diagram shows the aberration curves along the meridional and sagittal directions for the three primary colors with center wavelengths of 647nm, 525nm, and 455nm in 12 normalized fields of view. The smaller the fluctuation of the curve and the closer it is to a horizontal line, the smaller the aberration. Figures 12-14 It can be seen that the projection lens has small aberrations and good image quality.

[0149] Figure 15 This is an axial chromatic aberration diagram of a projection lens provided in an embodiment of the present invention.

[0150] Figure 15The longitudinal spherical aberration of red light (r), green light (g), and blue light (b) at 647 nm, 525 nm, and 485 nm is shown, where the horizontal axis represents the magnitude of the longitudinal spherical aberration in mm, and the vertical axis represents the relative aperture. Figure 15 It can be seen that the spherical aberration of the three primary colors is small, resulting in good image quality.

[0151] Figure 16 This is a schematic diagram of the field curvature curve of the projection lens provided in an embodiment of the present invention.

[0152] Figure 16 The diagram shows the field curvature curves of the projection lens in the meridional (T) and sagittal (S) directions under different fields of view. The horizontal axis represents the field curvature magnitude in mm, and the vertical axis represents the image height (field of view). Figure 16 It can be seen that the field curvature of the projection lens is controlled within 0.02mm.

[0153] Figure 17 This is a schematic diagram of the distortion curve of a projection lens provided in an embodiment of the present invention.

[0154] Figure 17 The distortion curves of the projection lens under different fields of view are shown, where the horizontal axis represents the percentage of image distortion and the vertical axis represents the image height (field of view). Figure 17 It can be seen that the distortion of the projection lens is controlled within 0.5%.

[0155] Based on the same inventive concept, embodiments of the present invention also provide a projection system, such as... Figure 1 As shown, the projection system may include a projection device 1 and a projection screen 2. The projection device may include any of the projection lenses mentioned above. The projection lens can be applied to a three-color laser projection system, achieving a color difference of less than 0.2 pixels while ensuring a total lens length of only 53mm. The projected image still exhibits minimal distortion even at large sizes.

[0156] Although preferred embodiments of the invention 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 both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0157] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A projection lens, characterized in that, include: Aperture; A front group of lenses, the front group of lenses comprising multiple lenses; and The rear lens group includes multiple lenses; The front group of lenses and the rear group of lenses are located on opposite sides of the aperture stop; the rear group of lenses includes a diffraction lens, which comprises: A lens substrate, wherein one side surface of the lens substrate has a first diffraction structure; A first coating is located on a first diffraction structure of the lens substrate; the surface of the first coating facing away from the lens substrate has a second diffraction structure; and The second coating is located on the second diffraction structure of the first coating.

2. The projection lens as described in claim 1, characterized in that, 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; wherein the first lens and the second lens are aspherical lenses, and the third lens and the fourth lens are spherical lenses; The first lens has a positive refractive power on its image side and a negative refractive power on its object side; the second lens has a positive refractive power on its image side and a negative refractive power on its object side; the third lens has a negative refractive power on its image side and a positive refractive power on its object side; and the fourth lens has a positive refractive power on its image side and a negative refractive power on its object side. 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 away from the aperture; wherein the ninth lens is an aspherical lens, and the fifth lens, the sixth lens, the seventh lens, the eighth lens, and the tenth lens are spherical lenses; The fifth lens and the sixth lens constitute a first cemented lens, and the seventh lens and the eighth lens constitute a second cemented lens; the ninth lens is a diffraction lens; The refractive power of the image side of the fifth lens is negative, the refractive power of the object side of the fifth lens and the image side of the sixth lens are positive, the refractive power of the object side of the sixth lens is negative, the refractive power of the image side of the seventh lens is positive, the refractive power of the object side of the seventh lens and the image side of the eighth lens are negative, the refractive power of the object side of the eighth lens is positive, the refractive power of the image side of the ninth lens is positive, the refractive power of the object side of the ninth lens is positive, the refractive power of the image side of the tenth lens is negative, and the refractive power of the object side of the tenth lens is positive.

3. The projection lens as described in claim 2, characterized in that, The first coating and the second coating are located on the side of the lens substrate of the ninth lens facing the tenth lens; Both the first and second diffraction structures are concentrically arranged annular grooves that expand sequentially.

4. The projection lens as described in claim 3, characterized in that, The depth of the annular groove in the first diffraction structure is less than 0.02 mm, and the depth of the annular groove in the second diffraction structure is less than 0.02 mm. The bottom included angle of the annular groove of the first diffraction structure is less than 70°, and the bottom included angle of the annular groove of the second diffraction structure is less than 70°.

5. The projection lens as described in claim 4, characterized in that, The maximum incident angle of the light rays incident on the diffractive lens satisfies: 0 ≤ AOR1 ≤ 2.5°; Wherein, AOR1 represents the maximum value of the incident angle of the principal ray incident on the diffraction lens.

6. The projection lens as described in claim 2, characterized in that, The radii of curvature of the first cemented lens and the second cemented lens satisfy: -2.0 < R7_8 / R5_6 < -1.5; Wherein, R7_8 represents the radius of curvature of the cemented surface of the seventh lens and the eighth lens, and R5_6 represents the radius of curvature of the cemented surface of the fifth lens and the sixth lens.

7. The projection lens as described in claim 2, characterized in that, The ninth lens and the tenth lens satisfy the following: 8 < (f9 + f10) / (h9 + h10) < 10; Wherein, f9 represents the focal length of the ninth lens, f10 represents the focal length of the tenth lens, h9 represents the center thickness of the ninth lens along the optical axis, and h10 represents the center thickness of the tenth lens along the optical axis.

8. The projection lens as described in claim 2, characterized in that, The first lens and the second lens satisfy the following: (abv1+abv2)>110; Where abv1 represents the Abbe number of the first lens and abv2 represents the Abbe number of the second lens.

9. The projection lens as described in any one of claims 2 to 8, characterized in that, The image height of the projection lens is greater than 7.5mm; The tenth lens satisfies: R_L10 > 10mm; Wherein, R_L10 represents the aperture of the tenth lens; The telecentricity of the projection lens is less than 0.8°.

10. A projection system, characterized in that, include: Laser source, used to emit three-color lasers; An illumination system is located on the light-emitting side of the laser source; the illumination system includes a display element, which is used to modulate the incident laser to form an image beam; A projection lens, located on the light-emitting side of the display element, is used to image the image beam; the projection lens is the projection lens according to any one of claims 1 to 9; 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 laser source back to the display element and transmit the image beam modulated by the display element to the projection lens.

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