Display optical system and projection device

Abstract

The application discloses a display optical system and a projection device. The display optical system comprises, in sequence along the light propagation direction, a color combining element, a third lens, a second lens and a first lens. The first lens and the third lens are positive lenses, and the second lens is a negative lens. The ratio of the focal length of each lens to the total focal length of the system is constrained in a suitable range, so that the refractive power of each lens is reasonably distributed. The combination of the positive lens, the negative lens and the positive lens and the arrangement order can effectively correct aberration while shortening the total length of the optical system, thereby significantly reducing the volume of the optical system on the basis of ensuring good imaging performance, and realizing the miniaturization of the projection device.

Description

Technical Field

[0001] This invention relates to the field of optical imaging technology, and more specifically to a display optical system and projection device. Background Technology

[0002] Near-eye display technology is rapidly developing towards higher performance and smaller size. Micro LED (micron-sized light-emitting diode), as an emerging display technology, has shown great application potential, especially in augmented reality (AR) applications where size, brightness, and reliability are critical, due to its advantages such as self-illumination, high brightness, fast response speed, long lifespan, and good stability.

[0003] Because single-chip full-color Micro LEDs have low light output brightness, they cannot meet the core requirement of high brightness for near-eye displays. Therefore, multiple independent high-brightness monochrome Micro LED chips are typically used, combined with an efficient optical color combining system to achieve high-brightness full-color Micro LED projection. However, existing optical systems are bulky and have low integration, making them unsuitable for scenarios such as AR that require miniaturized optical systems. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a display optical system and projection device that reduces the size of the optical system while ensuring imaging effect.

[0005] In a first aspect, one embodiment of the present invention provides a display optical system, including a color combining element, a third lens, a second lens, and a first lens arranged sequentially along the light propagation direction, wherein the first lens and the third lens have positive optical power, and the second lens has negative optical power; The focal lengths of the first lens 1, the second lens 2, and the third lens 3, together with the total focal length of the display optical system, satisfy the following: 0.65 < f1 / f < 0.95; -1.1 < f2 / f < -0.9; 1.1 < f3 / f < 1.3; Where f1 is the focal length of the first lens 1, f2 is the focal length of the second lens 2, and f3 is the focal length of the third lens 3. The focal lengths of the first lens 1, the second lens 2, and the third lens 3, together with the total focal length of the display optical system, satisfy the following: 0.65 < f1 / f < 0.95; -1.1 < f2 / f < -0.9; 1.1 < f3 / f < 1.3; Wherein, f1 is the focal length of the first lens 1, f2 is the focal length of the second lens 2, f3 is the focal length of the third lens 3, and f is the total focal length of the display optical system.

[0006] Optionally, the focal length f1 of the first lens satisfies: 3mm < f1 < 7mm; The focal length f2 of the second lens satisfies: -7mm < f2 < -2mm; The focal length f3 of the third lens satisfies: 5mm < f3 < 9mm.

[0007] Optionally, the refractive index Nd1 of the first lens satisfies: 1.56 < Nd1 < 1.72; The refractive index Nd2 of the second lens satisfies: 1.56 < Nd2 < 1.72; The refractive index Nd3 of the third lens satisfies: 1.49 < Nd3 < 1.62; The refractive index Nd4 of the color-combining element satisfies: 1.47 < Nd4 < 1.62.

[0008] Optionally, the Abbe number Vd1 of the first lens 1 satisfies: 57 < Vd1 < 70; The Abbe number Vd2 of the second lens 2 satisfies: 15 < Vd2 < 28; The Abbe number Vd3 of the third lens 3 satisfies: 50 < Vd3 < 62; The Abbe number Vd4 of the color-combining element 4 satisfies: 55 < Vd4 < 69.

[0009] Optionally, the thickness d1 of the first lens satisfies: d1 < 1 mm; The thickness d2 of the second lens satisfies: d2 < 0.7 mm; The thickness d3 of the third lens satisfies: d3 < 0.9 mm.

[0010] Optionally, the light-incident surface of the first lens has a convex structure; The incident surface of the second lens is a convex structure, and the exit surface of the second lens is a concave structure. The incident surface of the third lens is concave, and the exit surface of the third lens is convex.

[0011] Optionally, any surface of the first lens, the second lens, and the third lens is an even-order aspherical surface, wherein the even-order aspherical surface satisfies:

[0012] Where Z is the sag, Y is the center height of the lens, k is the conic coefficient, C is the radius of curvature, and a i Let represent the aspherical coefficient of the i-th iteration.

[0013] Optionally, the distance between the first lens and the second lens is 0.85 mm, the distance between the second lens and the third lens is 0.1 mm, and the distance between the third lens and the color combining element is 0.5 mm.

[0014] Optionally, the total length of the display optical system is less than 7.79 mm, the lens diameter of the display optical system is less than 4 mm, and the total focal length f of the display optical system satisfies: 4.7 mm < f < 6.6 mm.

[0015] Optionally, the first lens is a glass lens, the second and third lenses are plastic lenses, and the color-combining element is a glass prism.

[0016] Optionally, the display optical system further includes an aperture stop and three display image sources. The aperture stop is disposed on the light-emitting side of the first lens, and the three display image sources are respectively disposed corresponding to the three incident surfaces of the color combining element.

[0017] Optionally, the diameter D of the aperture stop satisfies: 2.1mm < D < 4.2mm.

[0018] Secondly, in one embodiment of the present invention, a projection device is provided, comprising: Equipment body; The display optical system as described above is installed within the main body of the device.

[0019] One embodiment of the present invention provides a display optical system and a projection device. The display optical system includes a color combining element, a third lens, a second lens, and a first lens arranged sequentially along the direction of light propagation. The first and third lenses have positive optical power, and the second lens has negative optical power. By constraining the ratio of the focal length of each of the first, second, and third lenses to the total focal length of the system within a suitable range, the optical power of each lens is rationally distributed. This combination of positive and negative lenses and their arrangement order can effectively correct aberrations while shortening the overall length of the optical system, thereby significantly reducing the size of the optical system and achieving miniaturization of the projection device while ensuring good imaging performance. Attached Figure Description

[0020] The above and other objects, features and advantages of the invention will become clearer from the following description of an embodiment of the invention with reference to the accompanying drawings, in which: Figure 1 This is a structural diagram of the display optical system provided in an embodiment of the present invention; Figure 2 This is an optical path diagram of a display optical system provided in an embodiment of the present invention; Figure 3This is the optical path diagram of red light entering the color combining element provided in the embodiment of the present invention; Figure 4 This is the optical path diagram of blue light entering the color combining element provided in the embodiment of the present invention; Figure 5 This is the optical path diagram of green light entering the color combining element provided in the embodiment of the present invention; Figure 6 This is an MTF curve diagram of the display optical system provided in the embodiments of the present invention; Figure 7 This is a defocus curve diagram of the display optical system provided in an embodiment of the present invention; Figure 8 This is a relative illumination diagram of the display optical system provided in an embodiment of the present invention.

[0021] Explanation of reference numerals in the attached figures: 1-First lens; 2-Second lens; 3-Third lens; 4-Color combining element; 5-Aperture stop; 6-Display image source; L1-First beam; L2-Second beam; L3-Third beam; L4-Fourth beam; L5-Fifth beam; L6-Sixth beam. Detailed Implementation

[0022] The present application is described below based on embodiments, but it is not limited to these embodiments. In the detailed description of the present application below, certain specific details are described in detail. Those skilled in the art can fully understand the present application without these details. To avoid obscuring the substance of the present application, well-known methods, processes, flows, elements, and circuits are not described in detail.

[0023] Furthermore, those skilled in the art should understand that the accompanying drawings provided herein are for illustrative purposes only and are not necessarily drawn to scale.

[0024] Unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0025] For ease of explanation, spatially related terms such as “inside,” “outside,” “below,” “below,” “lower,” “above,” “upper,” etc., are used herein to describe the relationship between one element or feature illustrated in the figure and another. It will be understood that spatially related terms may be intended to encompass different orientations of the device in use or operation besides those depicted in the figure. For example, if the device in the figure is flipped, an element described as “below” or “below” another element or feature would then be positioned “above” that other element or feature. Thus, the exemplified term “below” can encompass both above and below orientations. The device may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatially related descriptive terms used herein should be interpreted accordingly.

[0026] Unless the context explicitly requires it, words such as "including" or "contains" throughout the application should be interpreted as including rather than exclusive or exhaustive; that is, meaning "including but not limited to".

[0027] In the description of this application, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0028] In the accompanying drawings, the thickness, size, and shape of the lenses have been slightly exaggerated for ease of illustration. Specifically, the shapes of the aspherical surfaces shown in the drawings are illustrated by way of example. That is, the shapes of the aspherical surfaces are not limited to those shown in the drawings. The drawings are for illustrative purposes only and are not drawn strictly to scale.

[0029] An aspherical lens is a lens whose surface has at least one aspherical element, and whose radius of curvature changes continuously along its central axis. The complex geometry of aspherical lenses allows light rays to converge more precisely to a single point, regardless of whether they are incident from the center or the edge, significantly reducing spherical aberration, coma, and higher-order aberrations. Furthermore, aspherical lenses often have a thinner profile and lighter weight, improving overall resolution and contrast.

[0030] Focal length refers to the distance from the optical center of a lens to the point where light rays converge to a point of sharpness. The smaller the focal length, the greater the refraction of light. The size of the focal length affects the sharpness of the final image and aberration correction. Because different colors have different refractive indices when passing through a lens, fringe may appear at the edges of the final image. To reduce aberrations, a combination of positive and negative power lenses is used in lens systems. The positive power lens converges light rays, while the negative power lens diverges them.

[0031] Furthermore, when a single lens forms an image, field curvature caused by the curvature of the focal plane results in a sharp center but blurred edges. By combining a positive-power lens with a negative-power lens, the curved focal plane can be flattened, ensuring sharpness at the image edges. The combination of positive and negative-power lenses also allows for maintaining a relatively long focal length for a specific lens within the optical system while keeping the overall focal length short, reducing image aberrations and enabling miniaturization of the optical system.

[0032] To ensure high-brightness, full-color projection, three independent monochrome Micro LED chips are used as the display image source 6, combined with a color combining system for imaging. That is, each independent monochrome Micro LED chip emits monochromatic light, which is then separated and combined by the color combining system to ultimately form colored light that is emitted outwards, meeting the application requirements. It should be understood that the above selection of the display image source 6 is merely an example and not a limitation. Depending on the actual situation, the display image source 6 can also be OLED (Organic Light Emitting Diode), LCD (Liquid Crystal Display), LCOS (Liquid Crystal on Silicon), etc.

[0033] Because the light source is small and has a large divergence angle when modeling according to the actual optical path, a large number of light rays need to be tracked to cover the eye movement range. Therefore, according to the principle of optical path reversibility, when performing optical system simulation optimization, the reverse modeling method is usually adopted. Light rays are emitted from the area where the human eye pupil is located to cover the field of view. By verifying whether the light rays of different fields of view can be well focused on the surface where the display image source 6 is located, the reverse verification is performed to see whether all the field of view light rays emitted by the display image source 6 can overlap at the human eye pupil. Figure 1 The diagram shows the optical path after using the reverse modeling method. In actual use, the three display image sources 6 emit monochromatic light. The surfaces of the lenses and color combining elements 4 are marked according to the propagation sequence of the simulated light rays, resulting in eight surfaces marked S1-S8. Among them, S1-S2 are the surfaces of the first lens 1, S3-S4 are the surfaces of the second lens 2, S5-S6 are the surfaces of the third lens 3, and S7-S8 are the surfaces of the color combining elements 4.

[0034] Reference Figure 1 , Figure 2 In one embodiment of the present invention, the display optical system includes a color combining element 4 and a third lens 3, a second lens 2, and a first lens 1 arranged sequentially along the direction of light propagation. The first lens 1 and the third lens 3 are of positive optical power, and the second lens 2 is of negative optical power. That is, viewed from the direction of light propagation, the three lenses of the display optical system in this embodiment are arranged in an alternating pattern of positive optical power lens, negative optical power lens, and positive optical power lens. Figure 1 , Figure 2Combining positive and negative power lenses can cancel out some aberrations, significantly improving image clarity and quality. While ensuring imaging performance, it also enables the miniaturization of the display optical system and reduces its size.

[0035] In some embodiments, such as Figure 2 As shown, the display optical system also includes an aperture stop 5 and three display image sources 6. The aperture stop 5 is located on the light-emitting side of the first lens 1 to control the amount of light entering and improve image quality. The three display image sources 6 correspond to three independent monochrome Micro LED chips, providing red, green, and blue light beams to synthesize a color image. The three display image sources 6 are respectively positioned corresponding to the three incident surfaces of the color combining element 4. The light emitted by the three display image sources 6 first passes through the color combining element 4 to achieve color combining, and then passes sequentially through the third lens 3, the second lens 2, and the first lens 1 before exiting through the aperture stop 5, propagating to the human eye, and forming an image. Among them, the first lens 1 is a glass lens, and the second lens 2 and the third lens 3 are plastic lenses.

[0036] Preferably, the first lens 1 is made of low-melting-point glass, which can reduce costs and improve yield. The color combining element 4 uses a color combining prism, so that the light emitted from the color combining prism is colored light that has achieved monochromatic superposition. The color combining prism is made of glass. The diameter D of the aperture stop 5 is limited to: 2.1mm < D < 4.2mm. When the diameter D is close to 2.1mm, the diameter of the aperture stop 5 is small, less light is collected, and the image clarity is high; when the diameter D is close to 4.2mm, the diameter of the aperture stop 5 is large, more light is collected, and the image brightness is high.

[0037] To achieve better coordination, the focal lengths of the three lenses are limited. The ratio of the focal length of a single lens to the total focal length is used to measure the contribution of a single lens to the refractive power of the entire display optical system. When the ratio is greater than 1, the lens is usually used for aberration correction and fine-tuning of the optical path to ensure the sharpness and edge quality of the final image.

[0038] In some embodiments, the focal lengths of the first lens 1, the second lens 2, and the third lens 3 satisfy the following condition with respect to the total focal length of the display optical system: 0.65 < f1 / f < 0.95; -1.1 < f2 / f < -0.9; 1.1 < f3 / f < 1.3; Where f1 is the focal length of the first lens 1, f2 is the focal length of the second lens 2, f3 is the focal length of the third lens 3, and f is the total focal length of the display optical system.

[0039] Based on this, the focal length range of each lens is defined. In some embodiments, the focal length of the first lens 1 satisfies: 3mm < f1 < 7mm, the focal length f2 of the second lens 2 satisfies: -7mm < f2 < -2mm, and the focal length f3 of the third lens 3 satisfies: 5mm < f3 < 9mm. Based on this, the total focal length f of the final display optical system satisfies: 4.7mm < f < 6.6mm. Specifically, for each individual lens, its actual focal length satisfies:

[0040] Among them, f i R1 is the actual focal length of the lens, R2 is the refractive index of the lens, R1 is the radius of curvature of the front surface of the lens, R2 is the radius of curvature of the rear surface of the lens, and d is the thickness of the lens.

[0041] The Abbe number reflects the degree of chromatic dispersion of a lens, that is, the degree to which different colors of light are separated due to differences in refractive index when white light passes through the lens. Refractive index is the ratio of the speed of light in a vacuum to its speed in a medium; the higher the refractive index of a medium, the greater the degree of light deflection within it. In other words, the Abbe number is inversely proportional to the refractive index of the lens and inversely proportional to the degree of dispersion. A smaller Abbe number indicates a larger refractive index, more pronounced dispersion, and poorer image quality. Significant chromatic dispersion affects image quality and can easily cause eye strain; therefore, effective dispersion correction is necessary.

[0042] Specifically, in some embodiments, the refractive index Nd1 of the first lens 1 satisfies: 1.56 < Nd1 < 1.72, and the Abbe number Vd1 satisfies: 57 < Vd1 < 70; the refractive index Nd2 of the second lens 2 satisfies: 1.56 < Nd2 < 1.72, and the Abbe number Vd2 satisfies: 15 < Vd2 < 28; the refractive index Nd3 of the third lens 3 satisfies: 1.49 < Nd3 < 1.62, and the Abbe number Vd3 satisfies: 50 < Vd3 < 62; the refractive index Nd4 of the color combining element 4 satisfies: 1.47 < Nd4 < 1.62, and the Abbe number Vd4 satisfies: 55 < Vd4 < 69.

[0043] In this embodiment, preferably, the first lens 1 has a refractive index Nd1 of 1.62 and an Abbe number Vd1 of 64; the second lens 2 has a refractive index Nd2 of 1.64 and an Abbe number Vd2 of 22.4; the third lens 3 has a refractive index Nd3 of 1.53 and an Abbe number Vd3 of 64.2; and the chromatic aberration element 4 has a refractive index Nd4 of 1.52 and an Abbe number Vd4 of 64.2. This embodiment, by arranging lenses with different refractive indices and Abbe numbers, can effectively reduce chromatic aberration and improve imaging performance.

[0044] In some embodiments, the thickness d1 of the first lens 1 satisfies: d1 < 1 mm, the thickness d2 of the second lens 2 satisfies: d2 < 0.7 mm, and the thickness d3 of the third lens 3 satisfies: d3 < 0.9 mm. To minimize volume and optical length, the thickness of each lens is reduced as much as possible while ensuring manufacturing feasibility. In this embodiment, preferably, the thickness d1 of the first lens 1 is 0.915 mm, the thickness d2 of the second lens 2 is 0.7 mm, and the thickness d3 of the third lens 3 is 1.53 mm. Correspondingly, the thickness of the color combining element 4 is also reduced as much as possible; in this embodiment, the thickness d4 of the color combining element 4 is 1.52 mm. By reducing the thickness of each lens, this embodiment reduces both axial and transverse chromatic aberration, increases the light transmittance of the lens, and thus improves the overall light transmittance of the display optical system; furthermore, the volume and weight of the display optical system are reduced, achieving lightweighting and miniaturization.

[0045] In some embodiments, the total length of the display optical system is less than 7.79 mm, the total focal length f satisfies: 4.7 mm < f < 6.6 mm, the lens diameter is less than 4 mm, and the optical drainage volume is less than 0.2 cc. The lens diameter is the effective diameter through which light passes in the optical system, determining the eye-tracking range of the AR device and affecting the completeness of the image display. A larger lens diameter collects more light and produces a brighter image, but also introduces more aberrations. The optical drainage volume refers to the volume of liquid displaced when the lens or optical element is completely immersed in liquid, accurately representing the actual material volume of the element. This embodiment uses a combination of positive and negative power lenses to adjust edge images, reduce aberrations, ensure imaging quality, and reduce the overall length and volume of the display optical system.

[0046] Table 1 below shows the basic parameters of each lens and color-combining prism in the optical system.

[0047] Table 1

[0048] S1-S8 are markings on the surfaces of the lens and the color combining element 4 according to the propagation sequence of simulated light. S1-S2 are the surfaces of the first lens 1, S3-S4 are the surfaces of the second lens 2, S5-S6 are the surfaces of the third lens 3, and S7-S8 are the surfaces of the color combining element 4.

[0049] In some embodiments, the light-incident surface of the first lens 1 is convex; the light-incident surface of the second lens 2 is convex and the light-outcident surface is concave; and the light-incident surface of the third lens 3 is concave and the light-outcident surface is convex. Furthermore, those skilled in the art can choose between a concave or concave light-outcident surface for the first lens 1 based on actual needs. This embodiment, by setting different combinations and arrangements of concave and convex surfaces of the lenses, enables the display optical system to better correct aberrations, improve image sharpness, reduce unnecessary refraction and reflection, improve edge brightness, and enhance imaging effects. Simultaneously, specific combinations of concave and convex surfaces can better converge light rays, effectively compressing optical length and optical volume. Any surface of the first lens 1, the second lens 2, and the third lens 3 is an even-order aspherical surface. Even-order aspherical lenses can provide thinner thickness and lighter weight, optimize image brightness and sharpness, and effectively achieve miniaturization of the display optical system while ensuring imaging effects. The even-order aspherical surface satisfies the following:

[0050] Where Z is the sag, Y is the center height of the lens, k is the conic coefficient, C is the radius of curvature, and a i This represents the aspherical coefficient of the i-th order. Sag refers to the vertical height of a point on the lens surface relative to the reference plane. In this formula, when Y is the lens center height, it refers to the height of the lens center point from the reference plane.

[0051] Table 2 below shows the conic coefficient k and the i-th aspherical coefficients a4, a6, and a8 of each lens in the optical system.

[0052] Table 2

[0053] In this table, S1-S6 are markings on the surfaces of the lens and the color combining element 4 according to the propagation sequence of simulated light; S1-S2 are the surfaces of the first lens 1; S3-S4 are the surfaces of the second lens 2; and S5-S6 are the surfaces of the third lens 3. As can be seen from Table 2, by adjusting the even-order aspherical surface parameters of the first lens 1, the second lens 2, and the third lens 3, the display optical system can achieve better imaging brightness and sharpness while maintaining miniaturization.

[0054] To further reduce the optical volume of the display optical system, the spacing between lenses is limited. In some embodiments, the spacing d1 between the first lens 1 and the second lens 2 satisfies: 0.1mm ≤ d1 ≤ 1mm; the spacing d2 between the second lens 2 and the third lens 3 satisfies: 0.1mm ≤ d2 ≤ 0.8mm; and the spacing d3 between the third lens 3 and the color combining element 4 satisfies: 0.3mm ≤ d3 ≤ 0.8mm. Preferably, in this embodiment, the spacing between the first lens 1 and the second lens 2 is 0.85mm, the spacing between the second lens 2 and the third lens 3 is 0.1mm, and the spacing between the third lens 3 and the color combining element 4 is 0.5mm. This embodiment controls the aberrations of each optical element by minimizing the spacing between optical elements, optimizes imaging quality, and further reduces the size and weight of the display optical system, thereby achieving lightweighting and miniaturization.

[0055] In some embodiments, refer to Figures 1-5 The color-combining prism is composed of four small prisms bonded together. The cross-sections of the four small prisms form isosceles right triangles. Each small prism, in conjunction with the emission spectrum characteristics of the display image source 6, is coated with a filter cutoff film with different requirements, ensuring that the light emitted from the color-combining prism is precisely mixed colored light. Specifically, in this embodiment, the boundary formed by the bonded four small prisms, i.e., the two diagonals of the color-combining prism, are described as surfaces A and B. Surfaces A and B correspond to the diagonals formed by different combinations of small prisms.

[0056] Three monochromatic lights are incident from the three faces of the color combining prism, as shown in the reference. Figures 1-5 A Cartesian coordinate system is established with the plane perpendicular to the height of the small prism as the reference. Red light enters along the positive x-axis, green light along the positive y-axis, and blue light along the negative x-axis. At this time, the angle between the two diagonals of the color-combining prism and the coordinate axes is 45°. Surface A is the surface corresponding to the diagonal extending along the first and third quadrants of the xOy plane, and this surface is coated with a filter that reflects blue light and transmits red and green light. Surface B is the surface corresponding to the diagonal extending along the second and fourth quadrants of the xOy plane, and this surface is coated with a filter that reflects red light and transmits blue and green light.

[0057] Specifically, refer to Figure 3When a red light beam enters the color combining element 4 from the positive x-axis direction, the red light is transmitted through surface A and reflected through surface B. Taking the first beam L1 and the second beam L2 as examples: The first beam L1 first contacts surface A, forming an incident angle of 45° with surface A. Since red light is transmitted through surface A, the first beam L1 passes through surface A and reaches surface B. Since red light is reflected through surface B, the first beam L1 exits at a 45° exit angle and propagates along the positive y-axis direction, exiting the color combining element 4. The second beam L2 first contacts surface B, forming an incident angle of 45° with surface B. Since red light is reflected through surface B, the second beam L2 exits at a 45° exit angle and propagates along the positive y-axis direction, reaching surface A. Since red light is transmitted through surface A, the second beam L2 passes through surface A and exits the color combining element 4.

[0058] like Figure 4 As shown, when a blue light beam enters the color combining element 4 from the negative x-axis direction, the blue light is transmitted through surface B and reflected through surface A. Taking the third beam L3 and the fourth beam L4 as examples: The third beam L3 first contacts surface B, forming an incident angle of 45° with surface B. Since blue light is transmitted through surface B, the third beam L3 passes through surface B and reaches surface A. Since blue light is reflected through surface A, the third beam L3 exits at a 45° exit angle and propagates along the positive y-axis out of the color combining element 4. The fourth beam L4 first contacts surface A, forming an incident angle of 45° with surface A. Since blue light is reflected through surface A, the fourth beam L4 exits at a 45° exit angle and propagates along the positive y-axis to surface B. Since blue light is transmitted through surface B, the fourth beam L4 passes through surface B and exits the color combining element 4.

[0059] like Figure 5 As shown, a green light beam enters the color combining element 4 from the positive y-axis direction. Taking the fifth beam L5 and the sixth beam L6 as examples, since both surface A and surface B transmit green light, the fifth beam L5 and the sixth beam L6 pass through surface A and surface B and propagate out of the color combining element 4 along the positive y-axis direction.

[0060] In other words, when three independent monochrome Micro LED chips are used as the display image source 6, and red, blue and green light are simultaneously incident from three directions, the color combining element 4, located on the side of the positive y-axis, can couple the emitted red, blue and green light in the same direction into a beam of mixed full-color light. Then, through the aberration correction of the lens, it provides a high-sharpness, clear full-color projection while ensuring the imaging brightness.

[0061] Table 3 below shows the optical parameters of surfaces A and B of the color combining element. The transmittance of surfaces A and B varies for different wavelengths of light depending on the incident angle. 430-480nm corresponds to the wavelength of blue light, 600-650nm to the wavelength of red light, 505-570nm to the wavelength of green light, and 430-650nm to the visible light wavelength range. The 50% transmittance point is used to define the cutoff wavelength corresponding to that surface. The offset of the 50% transmittance point represents the range within which the cutoff wavelength may drift; the smaller the offset of the 50% transmittance point, the higher the accuracy of the color combining element 4. Reflectivity represents the ability of an object's surface to reflect light; the lower the reflectivity, the fewer reflections, ghosting, and other aberrations in the image.

[0062] Table 3

[0063] Figure 6 This is a modulation transfer function (MTF) graph according to an embodiment of the present invention, used to describe the ability of an optical system to reproduce contrast and resolution at different spatial frequencies. Figure 6 As shown, the horizontal axis represents spatial frequency, and the vertical axis represents the MTF value. In the MTF curve, the closer the MTF value is to 1, the stronger the optical system's rendering capability; the higher the MTF curve and the slower its decline, the better the optical system's resolution and imaging sharpness. As the spatial frequency increases, the MTF value decreases gradually, reflecting that the optical system can form good edge image quality. Figure 6 In the MTF curve of this embodiment shown, the MTF values ​​are almost all greater than 0.75 at a spatial frequency of 100 and almost all greater than 0.68 at a spatial frequency of 125, indicating good contrast and reproduction capabilities.

[0064] Figure 7 This is a defocus curve diagram according to an embodiment of the present invention, used to characterize the change in MTF when the image plane deviates from the design value. The horizontal axis represents the defocus amount, in μm or mm; the vertical axis represents the MTF value. In the defocus curve diagram, the center of the horizontal axis is the optimal focus. The higher the MTF value at the optimal focus, the more convergent the curves of each field of view, and the better and clearer the imaging effect. Figure 7 In the defocus curve diagram of this embodiment shown, the MTF value corresponding to the center of the horizontal axis, which is the optimal focus point, is close to 0.9, indicating that the optical system has a strong reproduction capability and a clear imaging effect; moreover, the defocus curves of each color are coaxial, reflecting good convergence and good imaging quality.

[0065] Figure 8This is a relative illuminance diagram according to an embodiment of the present invention, which refers to the ratio of illuminance at different coordinate points on the image plane to the illuminance at the center point, and is used to evaluate the uniformity of light in the optical system at different positions. The closer the relative illuminance is to 1, the brighter and more uniform the image; the lower the relative illuminance value, the more obvious the corners of the image will be, resulting in vignetting. Figure 8 In the relative illuminance curve of this embodiment shown, all Y fields of view at 1.26mm are still in a state of relative illuminance above 0.9, which shows that the light uniformity of the optical display system of this embodiment is good.

[0066] Based on this, this application provides a projection device, which includes a device body and a display optical system as described above, with the display optical system installed within the device body. In this embodiment, the projection device is a miniature projection device such as AR glasses. Depending on actual needs, the projection device can also be other miniaturized near-eye display devices. By employing a miniaturized display optical system with clear imaging effects, the device body can be further reduced in size and weight, improving the user experience and providing a clearer and brighter imaging effect to meet user needs.

[0067] This application provides a display optical system and a projection device. The display optical system includes a color combining element, a third lens, a second lens, and a first lens arranged sequentially along the light propagation direction. The first and third lenses have positive optical power, while the second lens has negative optical power. By constraining the ratio of the focal length of each of the first, second, and third lenses to the total focal length of the system within a suitable range, the optical power of each lens is rationally distributed. This combination of positive and negative lenses, and their arrangement, can effectively correct aberrations while shortening the overall length of the optical system. Therefore, while ensuring good imaging performance, the size of the optical system is significantly reduced, achieving miniaturization of the projection device.

[0068] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A display optical system, characterized in that, The display optical system includes a color combining element, a third lens, a second lens, and a first lens arranged sequentially along the direction of light propagation. The first lens and the third lens have positive optical power, and the second lens has negative optical power. The focal lengths of the first lens, the second lens, and the third lens, together with the total focal length of the display optical system, satisfy the following: 0.65 < f1 / f < 0.95; -1.1 < f2 / f < -0.9; 1.1 < f3 / f < 1.3; Where f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, and f is the total focal length of the display optical system.

2. The display optical system according to claim 1, characterized in that, The focal length f1 of the first lens satisfies: 3mm < f1 < 7mm; The focal length f2 of the second lens satisfies: -7mm < f2 < -2mm; The focal length f3 of the third lens satisfies: 5mm < f3 < 9mm.

3. The display optical system according to claim 1, characterized in that, The refractive index Nd1 of the first lens satisfies: 1.56 < Nd1 < 1.72; The refractive index Nd2 of the second lens satisfies: 1.56 < Nd2 < 1.72; The refractive index Nd3 of the third lens satisfies: 1.49 < Nd3 < 1.62; The refractive index Nd4 of the color-combining element satisfies: 1.47 < Nd4 < 1.

62.

4. The display optical system according to claim 1, characterized in that, The Abbe number Vd1 of the first lens satisfies: 57 < Vd1 < 70; The Abbe number Vd2 of the second lens satisfies: 15 < Vd2 < 28; The Abbe number Vd3 of the third lens satisfies: 50 < Vd3 < 62; The Abbe number Vd4 of the color-combining element satisfies: 55 < Vd4 < 69.

5. The display optical system according to claim 1, characterized in that, The thickness d1 of the first lens satisfies: d1 < 1 mm; The thickness d2 of the second lens satisfies: d2 < 0.7 mm; The thickness d3 of the third lens satisfies: d3 < 0.9 mm.

6. The display optical system according to claim 1, characterized in that, The light-incident surface of the first lens has a convex structure; The incident surface of the second lens is a convex structure, and the exit surface of the second lens is a concave structure. The incident surface of the third lens is concave, and the exit surface of the third lens is convex.

7. The display optical system according to claim 1, characterized in that, Each surface of the first lens, the second lens, and the third lens is an even-order aspherical surface, and the even-order aspherical surface satisfies: Where Z is the sag, Y is the center height of the lens, k is the conic coefficient, C is the radius of curvature, and a i Let represent the aspherical coefficient of the i-th iteration.

8. The display optical system according to claim 1, characterized in that, The distance d1 between the first lens and the second lens satisfies: 0.1mm≤d1≤1mm, the distance d2 between the second lens and the third lens satisfies: 0.1mm≤d2≤0.8mm, and the distance d3 between the third lens and the color combining element satisfies: 0.3mm≤d3≤0.8mm.

9. The display optical system according to claim 1, characterized in that, The total length of the display optical system is less than 7.79 mm, the lens diameter of the display optical system is less than 4 mm, and the total focal length f of the display optical system satisfies: 4.7 mm < f < 6.6 mm.

10. The display optical system according to claim 1, characterized in that, The first lens is a glass lens, the second and third lenses are plastic lenses, and the color combining element is a glass prism.

11. The display optical system according to any one of claims 1-10, characterized in that, The display optical system further includes an aperture stop and three display image sources. The aperture stop is disposed on the light-emitting side of the first lens, and the three display image sources are respectively disposed corresponding to the three incident surfaces of the color combining element.

12. The display optical system according to claim 11, characterized in that, The diameter D of the aperture stop satisfies: 2.1mm < D < 4.2mm.

13. A projection device, characterized in that, The projection device includes: Equipment body; The display optical system as described in any one of claims 1-12, wherein the display optical system is installed within the device body.

Images