CN117310943A

CN117310943A - Projection system and AR projection device

Info

Publication number: CN117310943A
Application number: CN202311518802.7A
Authority: CN
Inventors: 谢检来; 明玉生; 汪杰; 陈远
Original assignee: Ningbo Sunny Olai Technology Co ltd
Current assignee: Ningbo Sunny Olai Technology Co ltd
Priority date: 2023-11-13
Filing date: 2023-11-13
Publication date: 2023-12-29

Abstract

The invention provides a projection system and an AR projection device. The projection system comprises a diaphragm, a first lens, a second lens, a third lens, a fourth lens, a fifth lens and an imaging module, the projection system is provided with a first optical axis and a second optical axis which are perpendicular to each other, the fourth lens is a polarization beam-splitting prism, and the first optical axis and the second optical axis are intersected in the polarization beam-splitting prism; the first lens has positive optical power; the second lens has optical power; the third lens has optical power, and the object side surface of the third lens is glued with the image side surface of the second lens; the fifth lens has positive focal power; the total optical length TTL from the object side surface to the image surface of the second lens along the second optical axis, the system focal length f of the projection system, the effective maximum field angle FOV of the projection system and the aperture value FNO of the projection system satisfy: 1.60< ttl/(f x FNO x tan (FOV)) <1.75. The invention solves the problem that the miniaturization and high-definition projection of the projection system in the prior art are difficult to be simultaneously compatible.

Description

Projection system and AR projection device

Technical Field

The invention relates to the technical field of optical display equipment, in particular to a projection system and an AR projection device.

Background

With rapid development and application of portable consumer electronic display products, augmented reality (Augmented Reality, abbreviated as AR) equipment has very wide application prospects in the fields of industrial manufacturing and maintenance, education display, outdoor exercises, locomotive navigation and the like.

The projection system is a core device for fusing virtual visual effect and real visual effect of the AR projection device. With the iterative development of AR technology and the demand of consumers for high performance and light weight of portable devices, projection systems are moving toward miniaturization, high definition display and low cost. However, in a general projection system, a large number of lenses are often required for high-definition projection, which makes it difficult to reduce the size in each aspect, and if more aspheric lenses are used for high-definition projection, the manufacturing cost is rapidly increased, and the individual assembly of each lens brings more instability factors to the process and tolerance aspects.

That is, the projection system in the prior art has the problem that miniaturization and high definition projection are difficult to be compatible.

Disclosure of Invention

The invention mainly aims to provide a projection system and an AR projection device, so as to solve the problem that the miniaturization and high-definition projection of the projection system in the prior art are difficult to be simultaneously combined.

In order to achieve the above object, according to one aspect of the present invention, there is provided a projection system including a diaphragm, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and an imaging module, the projection system having a first optical axis and a second optical axis perpendicular to each other, the diaphragm, the first lens, and the fourth lens being sequentially disposed along the first optical axis, the second lens, the third lens, the fourth lens, the fifth lens, and the imaging module being sequentially disposed along the second optical axis, the fourth lens being a polarization beam splitter prism, the first optical axis and the second optical axis intersecting in the polarization beam splitter prism; the first lens has positive focal power, and the object side surface of the first lens is a convex surface; the second lens has optical power, and the object side surface of the second lens is a convex surface; the third lens has optical power, and the object side surface of the third lens is glued with the image side surface of the second lens; the fifth lens has positive focal power; the total optical length TTL from the object side surface to the image surface of the second lens along the second optical axis, the system focal length f of the projection system, the effective maximum field angle FOV of the projection system and the aperture value FNO of the projection system satisfy: 1.60< ttl/(f x FNO x tan (FOV)) <1.75.

Further, the focal length f1 of the first lens and the length T14 of the first lens along the first optical axis to the side surface of the fourth lens away from the diaphragm satisfy: 3.00< f1/T14<6.10.

Further, the focal length f1 of the first lens and the system focal length f of the projection system satisfy: 3.10< f1/f <6.60.

Further, the focal length f1 of the first lens and the center thickness T4 of the fourth lens satisfy: 3.50< f1/T4<7.70.

Further, the length T14 between the first lens element along the first optical axis and the surface of the fourth lens element away from the aperture stop and the total optical length TTL between the object side surface and the image side surface of the second lens element along the second optical axis satisfy: 0.50< T14/TTL <0.70.

Further, the focal length f5 of the fifth lens and the system focal length f of the projection system satisfy: 1.40< f5/f <2.10.

Further, the aperture SD21 of the object side surface of the second lens and the center thickness T4 of the fourth lens satisfy: 1.050< SD21/T4<1.064.

Further, the on-axis distance SP14 between the first lens and the fourth lens, the on-axis distance SP23 between the second lens and the fourth lens, the on-axis distance SP34 between the third lens and the fourth lens, the on-axis distance SP45 between the fourth lens and the fifth lens, and the total optical length TTL from the object side surface to the image plane of the second lens along the second optical axis satisfy: 0.05< (SP14+SP23+SP34+SP45)/TTL <0.12.

Further, the combined focal length f23 of the second lens and the third lens and the focal length f5 of the fifth lens satisfy: 1.00< f23/f5<1.60.

Further, the focal length f2 of the second lens and the focal length f3 of the third lens satisfy: -1.20< f2/f3< -0.90.

Further, the projection system further comprises an optical waveguide structure arranged at the aperture.

Further, the optical waveguide structure has a coupling opening, and the size of the coupling opening is equal to that of the diaphragm.

Further, the optical waveguide structure is one of an array optical waveguide, a geometric optical waveguide and a diffraction optical waveguide.

According to another aspect of the present invention, there is provided an AR projection apparatus including the projection system described above.

By applying the technical scheme of the invention, the projection system comprises a diaphragm, a first lens, a second lens, a third lens, a fourth lens, a fifth lens and an imaging module, the projection system is provided with a first optical axis and a second optical axis which are mutually perpendicular, the diaphragm, the first lens and the fourth lens are sequentially arranged along the first optical axis, the second lens, the third lens, the fourth lens, the fifth lens and the imaging module are sequentially arranged along the second optical axis, the fourth lens is a polarization beam splitter prism, and the first optical axis and the second optical axis are intersected in the polarization beam splitter prism; the first lens has positive focal power, and the object side surface of the first lens is a convex surface; the second lens has optical power, and the object side surface of the second lens is a convex surface; the third lens has optical power, and the object side surface of the third lens is glued with the image side surface of the second lens; the fifth lens has positive focal power; the total optical length TTL from the object side surface to the image surface of the second lens along the second optical axis, the system focal length f of the projection system, the effective maximum field angle FOV of the projection system and the aperture value FNO of the projection system satisfy: 1.60< ttl/(f x FNO x tan (FOV)) <1.75.

The projection system of the application satisfies the conditional expression between the effective maximum field angle FOV of the projection system and the aperture value FNO of the projection system by reasonably arranging the position relation of each lens, restricting the focal power and the surface shape of each lens and restricting the optical total length TTL of the second optical axis from the object side surface to the image surface of the second lens: 1.60< TTL/(f.times.FNO.tan (FOV)) <1.75, which is beneficial to making the main parameter of the projection system compatible with the length dimension of the system under the condition of the target value, making the optical performance and the overall dimension in a state of being balanced, ensuring miniaturization and high definition display, simultaneously being beneficial to having good optical element processing dimension and lower process assembly difficulty under the state of maintaining the projection system in high performance, and greatly improving the mass productivity.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention. In the drawings:

FIG. 1 is a schematic diagram of a projection system according to a first embodiment of the present invention;

FIG. 2 shows an optical path diagram of the projection system of FIG. 1;

FIGS. 3-6 illustrate, respectively, a spherical aberration curve, a field curvature curve, a distortion curve, and a chromatic aberration curve of the projection system of FIG. 1;

FIG. 7 is a schematic diagram of a projection system according to a second embodiment of the present invention;

FIGS. 8-11 illustrate, respectively, a spherical aberration curve, a field curvature curve, a distortion curve, and a chromatic aberration curve of the projection system of FIG. 7;

FIG. 12 is a schematic diagram showing the structure of a projection system according to a third embodiment of the present invention;

fig. 13 to 16 show a spherical aberration curve, a field curvature curve, a distortion curve, and a chromatic aberration curve, respectively, of the projection system of fig. 12;

FIG. 17 is a schematic diagram showing the structure of a projection system according to a fourth embodiment of the present invention;

fig. 18 to 21 show a spherical aberration curve, a field curvature curve, a distortion curve, and a chromatic aberration curve, respectively, of the projection system in fig. 17.

Wherein the above figures include the following reference numerals:

l0 and a diaphragm; l1, a first lens; L1S1, an object side surface of the first lens; L1S2, the image side of the first lens; l2, a second lens; L2S1, object side of the second lens; L2S2, the image side of the second lens; l3, a third lens; L3S1, object side of the third lens; L3S2, the image side of the third lens; l4, a fourth lens; L4S1, object side of the fourth lens; L4S2, the image side of the fourth lens; l5, a fifth lens; L5S1, object side of the fifth lens; L5S2, the image side of the fifth lens; l6, protecting glass.

Detailed Description

It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other. The invention will be described in detail below with reference to the drawings in connection with embodiments.

It is noted that all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs unless otherwise indicated.

In the present invention, unless otherwise indicated, terms of orientation such as "upper, lower, top, bottom" are used generally with respect to the orientation shown in the drawings or with respect to the component itself in the vertical, upright or gravitational direction; also, for ease of understanding and description, "inner and outer" refers to inner and outer relative to the profile of each component itself, but the above-mentioned orientation terms are not intended to limit the present invention.

It should be noted that in the present specification, the expressions of first, second, third, etc. are only used to distinguish one feature from another feature, and do not represent any limitation on the feature. Accordingly, a first lens discussed below may also be referred to as a second lens or a third lens without departing from the teachings of the present application.

In the drawings, the thickness, size, and shape of the lenses have been slightly exaggerated for convenience of explanation. Specifically, the spherical or aspherical shape shown in the drawings is shown by way of example. That is, the shape of the spherical or aspherical surface is not limited to the shape of the spherical or aspherical surface shown in the drawings. The figures are merely examples and are not drawn to scale.

Herein, the paraxial region refers to a region near the optical axis. If the lens surface is convex and the convex position is not defined, then the lens surface is convex at least in the paraxial region; if the lens surface is concave and the concave position is not defined, it means that the lens surface is concave at least in the paraxial region. The surface of each lens near the object side becomes the object side of the lens, and the surface of each lens near the image side is called the image side of the lens. The determination of the surface shape in the paraxial region can be performed by a determination method by a person skilled in the art by positive or negative determination of the concave-convex with R value (R means the radius of curvature of the paraxial region, and generally means the R value on a lens database (lens data) in optical software). In the object side surface, when the R value is positive, the object side surface is judged to be convex, and when the R value is negative, the object side surface is judged to be concave; in the image side, the concave surface is determined when the R value is positive, and the convex surface is determined when the R value is negative.

In order to solve the problem that the miniaturization and high-definition projection of a projection system in the prior art are difficult to be compatible at the same time, the invention provides a projection system and an AR projection device.

As shown in fig. 1 to 21, in an alternative embodiment of the present application, the projection system includes a diaphragm, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and an imaging module, the projection system has a first optical axis and a second optical axis perpendicular to each other, the diaphragm, the first lens, and the fourth lens are sequentially disposed along the first optical axis, the second lens, the third lens, the fourth lens, the fifth lens, and the imaging module are sequentially disposed along the second optical axis, the fourth lens is a polarization beam splitter prism, and the first optical axis and the second optical axis intersect in the polarization beam splitter prism; the first lens has positive focal power, and the object side surface of the first lens is a convex surface; the second lens has optical power, and the object side surface of the second lens is a convex surface; the third lens has optical power, and the object side surface of the third lens is glued with the image side surface of the second lens; the fifth lens has positive focal power; the total optical length TTL from the object side surface to the image surface of the second lens along the second optical axis, the system focal length f of the projection system, the effective maximum field angle FOV of the projection system and the aperture value FNO of the projection system satisfy: 1.60< ttl/(f x FNO x tan (FOV)) <1.75.

In addition, the first optical axis is perpendicular to the diaphragm, and the second optical axis is perpendicular to the imaging module. The imaging module at least comprises a piece of protective glass, and the protective glass is used for protecting an image surface. The first lens receives polarized light reflected by the fourth lens and converges the polarized light to be coupled out through the diaphragm, the converging effect of the first lens is favorable for the fourth lens to have a smaller size, the image side surface of the first lens can be designed to be a plane and glued with the surface of the fourth lens, which faces the first lens, after gluing, assembly tolerance can be further reduced so as to reduce assembly difficulty, improve assembly yield and enhance structural reliability. The object side surface of the second lens is attached or prepared by an optical reflection device, which is an important design for realizing an optical multiplexing function, reflects light rays from an image source and converges the light rays to the first lens through a polarization reflection surface of the fourth lens, so that repeated propagation of the light rays in the second lens, the third lens and the fourth lens is realized; the image side surface of the second lens is glued with the object side surface of the third lens, and the image side surface and the object side surface of the third lens are both curved surfaces, so that the curvatures are the same, assembly tolerance can be reduced after the gluing, and structural reliability is improved; the fourth lens is internally provided with a polarization splitting layer with an included angle of 45 degrees with the first optical axis and the second optical axis, different linear polarized light is respectively transmitted and reflected, the surface of the fourth lens facing the third lens is glued with a transmission type quarter wave plate for changing the polarization of the transmitted light, and the image side surface of the fourth lens is provided with a linear polarizing plate so that the light incident into the fourth lens is reflected at the polarization splitting layer, so that the contrast ratio of a projection image is improved; the image side surface of the third lens can also be designed to be a plane, and the image side surface of the third lens is connected with the fourth lens in a gluing way, so that assembly tolerance can be reduced and structural reliability can be improved after the image side surface of the third lens is glued with the fourth lens; the fifth lens has positive optical power, is favorable for converging illumination light while correcting imaging aberration, and can also be designed to be planar on the image side surface. The first lens and the third lens are respectively provided with a plane which can be designed to be glued with the fourth lens, the reduction of the number of the curved surfaces of the optical lenses is beneficial to reducing the processing cost, and each time of gluing of the optical lenses can reduce the number of the tolerances and the assembly tolerance, thereby greatly improving the mass productivity of the lenses.

The projection system provided by the invention can reduce the material processing cost, reduce the process flow and assembly tolerance so as to improve mass production, and has the advantages of high definition and miniaturization of the projection image.

Preferably, the total optical length TTL from the object side surface to the image plane of the second lens along the second optical axis, the system focal length f of the projection system, the effective maximum field angle FOV of the projection system and the aperture value FNO of the projection system satisfy: 1.62< ttl/(f x FNO x tan (FOV)) <1.72.

In the present embodiment, the focal length f1 of the first lens and the length T14 of the first lens along the first optical axis to the side surface of the fourth lens away from the stop satisfy: 3.00< f1/T14<6.10. The satisfaction of the conditional expression is beneficial to limiting the length of the projection system on the first optical axis, namely controlling the length dimension of the projection system in the coupling-out direction of the diaphragm to be in a smaller range, and is also beneficial to the miniaturization of the whole projection system.

Optionally, the effective maximum field angle FOV of the projection system satisfies: 29 ° < FOV <31 °. The arrangement can limit the projection view angle to a range which gives consideration to the viewing effect of human eyes and the coupling angle capability of various optical waveguide structures, and is favorable for realizing the high-definition projection with small distortion.

In the present embodiment, the focal length f1 of the first lens and the system focal length f of the projection system satisfy: 3.10< f1/f <6.60. The focal length of the first lens is positive and within a certain range, so that the conditions of overlarge size and overlarge overall size of other lenses caused by overlarge focal length of the first lens can be avoided, and the increase of tolerance sensitivity caused by overlarge focal length of the first lens is avoided.

In the present embodiment, the focal length f1 of the first lens and the center thickness T4 of the fourth lens satisfy: 3.50< f1/T4<7.70. The ratio of the focal length of the first lens to the thickness of the fourth lens is in a reasonable range, so that light coupled out from the first lens can be smoothly transmitted in the fourth lens, and aberration generated in the fourth lens can be reduced while the size is kept at a reasonable size.

In the present embodiment, the length T14 between the first lens element along the first optical axis and the surface of the fourth lens element away from the aperture stop and the total optical length TTL between the object side surface and the image side surface of the second lens element along the second optical axis satisfy: 0.50< T14/TTL <0.70. Satisfying the relation is favorable for limiting the dimension of the projection system in the diaphragm direction to be in a smaller range, is favorable for miniaturization of the projection system, and simultaneously, the problem of structural interference of the projection system when the projection system is matched for use due to overlong dimension of the projection system on the second optical axis is avoided.

In the present embodiment, the focal length f5 of the fifth lens and the system focal length f of the projection system satisfy: 1.40< f5/f <2.10. This arrangement is advantageous for the fifth lens balancing part of the system aberrations and the CRA at the modulating image plane is at a smaller level, while positive power is also advantageous for the convergence of the illumination light.

In the present embodiment, the aperture SD21 of the object side surface of the second lens and the center thickness T4 of the fourth lens satisfy: 1.050< SD21/T4<1.064. This arrangement is advantageous in restricting the sizes of the second lens and the fourth lens, and increasing the processing feasibility of the second lens and the fourth lens while ensuring miniaturization.

In the present embodiment, the on-axis distance SP14 between the first lens and the fourth lens, the on-axis distance SP23 between the second lens and the fourth lens, the on-axis distance SP34 between the third lens and the fourth lens, and the on-axis distance SP45 between the fourth lens and the fifth lens satisfy the following conditions: 0.05< (SP14+SP23+SP34+SP45)/TTL <0.12. The arrangement is favorable for fully utilizing the structural space for arranging the imaging lenses, so that the distribution of the lenses in space is more compact, and the miniaturization is favorable.

In the present embodiment, the combined focal length f23 of the second lens and the third lens and the focal length f5 of the fifth lens satisfy: 1.00< f23/f5<1.60. The optical power of each lens in the projection system can be reasonably distributed by meeting the relation, and the aberration balance and tolerance balance in the system are facilitated.

In the present embodiment, the focal length f2 of the second lens and the focal length f3 of the third lens satisfy: -1.20< f2/f3< -0.90. The arrangement is favorable for correcting the chromatic aberration of the system better and greatly improving the imaging quality of the system.

In this embodiment, the projection system further includes an optical waveguide structure provided at the aperture. The optical waveguide structure is provided with a coupling opening, and the size of the coupling opening is equal to that of the diaphragm.

In this embodiment, the optical waveguide structure is one of an array optical waveguide, a geometric optical waveguide, and a diffraction optical waveguide. The array optical waveguide is a structure composed of a plurality of optical waveguides which are arranged in parallel, the geometric optical waveguide is a structure which realizes light refraction and reflection conduction by different refractive index distribution, and the diffraction optical waveguide is a structure which realizes image light beam expansion, coupling-in and coupling-out by using a diffraction grating.

The invention also provides an AR projection device, which comprises the projection system. The arrangement enables the whole size of the AR projection device to be compressed, is beneficial to being applied to miniaturization or head-mounted equipment, and achieves miniaturization while guaranteeing the quality of projection pictures.

For example, the AR projection apparatus of the present application may be a head-mounted virtual display device or an in-vehicle head-up display device.

Specifically, the lens in the projection system of the present invention may be a spherical glass lens or an aspherical glass lens, or may be a spherical injection lens or an aspherical injection lens, which may be specifically set according to actual requirements.

In the present application, at least one of the mirrors of each lens is an aspherical mirror. The aspherical lens is characterized in that: the curvature varies continuously from the center of the lens to the periphery of the lens. Unlike a spherical lens having a constant curvature from the center of the lens to the periphery of the lens, an aspherical lens has a better radius of curvature characteristic, and has advantages of improving distortion aberration and improving astigmatic aberration. By adopting the aspherical lens, aberration occurring at the time of imaging can be eliminated as much as possible, thereby improving imaging quality.

In view of the fact that the aspheric surface is a structure obtained by rotating a curved surface in a meridian plane around an optical axis for one circle, the structure has rotational symmetry, and in an ideal optical system, aberration of the meridian plane and the sagittal plane can be well corrected; meanwhile, due to the unique lens model, enough space can be provided for subsequent relevant adjustment, so that relevant structures and assembly processes are more flexible and excessive imaging quality is not reduced.

Examples of specific facets, parameters, which may be suitable for use in the projection system of the above-described embodiments are further described below with reference to the accompanying drawings.

It should be noted that any one of the following examples one to four is applicable to all the embodiments of the present application.

Example 1

As shown in fig. 1 to 6, a projection system of the first embodiment is described. Fig. 1 shows a schematic configuration of a projection system according to a first embodiment. Fig. 2 shows an optical path diagram of the projection system of fig. 1.

As shown in fig. 1, the projection system includes: stop L0, first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5, and cover glass L6. The diaphragm L0, the first lens L1 and the fourth lens L4 are sequentially arranged along a first optical axis, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the protective glass L6 are sequentially arranged along a second optical axis, the fourth lens L4 is a polarization beam splitter prism, and the first optical axis and the second optical axis are intersected at the fourth lens L4. In the direction of the first optical axis, the diaphragm side is the object side, and the side away from the diaphragm is the image side. On the second optical axis, a side of the second lens L2 away from the third lens L3 is an object side, and a side of the cover glass L6 away from the fifth lens L5 is an image side.

The first lens element L1 has positive refractive power, wherein an object-side surface L1S1 of the first lens element is convex, and an image-side surface L1S2 of the first lens element is planar. The second lens element L2 has positive refractive power, wherein an object-side surface L2S1 of the second lens element is convex, and an image-side surface L2S2 of the second lens element is convex. The third lens element L3 has negative refractive power, wherein an object-side surface L3S1 of the third lens element is concave, and an image-side surface L3S2 of the third lens element is planar. The object side face L4S1 of the fourth lens element is a plane, and the image side face L4S2 of the fourth lens element is a plane. The fifth lens element L5 has positive refractive power, wherein an object-side surface L5S1 of the fifth lens element is convex, and an image-side surface L5S2 of the fifth lens element is planar.

Wherein, the image side face L1S2 of the first lens is glued with a side surface of the fourth lens L4 towards the side surface. The second lens L2 is cemented with the third lens L3, and the third lens LE is cemented with the fourth lens LE.

In this embodiment, the total effective focal length f of the projection system is 6.434mm, the total optical length TTL of the projection system from the object side surface to the image plane of the second lens along the second optical axis is 9.686mm, the maximum field angle FOV of use of the projection system is 30 °, and the aperture value FNO of the projection system is 1.608.

Table 1 shows a basic structural parameter table of the projection system of the first embodiment, in which the unit of curvature radius, thickness/distance is millimeter (mm).

TABLE 1

Fig. 3 shows a spherical aberration curve of the projection system of the first embodiment. Fig. 4 shows a field curvature of a projection system of the first embodiment. Fig. 5 shows a distortion curve of the projection system of the first embodiment. Fig. 6 shows a color difference curve of the projection system of the first embodiment.

As can be seen from fig. 3 to 6, the projection system according to the first embodiment can achieve good imaging quality.

Example two

As shown in fig. 7 to 11, the projection system of the second embodiment is described. Fig. 7 shows a schematic configuration of a projection system according to the second embodiment.

As shown in fig. 7, the projection system includes: stop L0, first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5, and cover glass L6. The diaphragm L0, the first lens L1 and the fourth lens L4 are sequentially arranged along a first optical axis, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the protective glass L6 are sequentially arranged along a second optical axis, the fourth lens L4 is a polarization beam splitter prism, and the first optical axis and the second optical axis are intersected at the fourth lens L4. In the direction of the first optical axis, the diaphragm side is the object side, and the side away from the diaphragm is the image side. On the second optical axis, a side of the second lens L2 away from the third lens L3 is an object side, and a side of the cover glass L6 away from the fifth lens L5 is an image side.

The first lens element L1 has positive refractive power, wherein an object-side surface L1S1 of the first lens element is convex, and an image-side surface L1S2 of the first lens element is planar. The second lens element L2 has negative refractive power, wherein an object-side surface L2S1 of the second lens element is convex, and an image-side surface L2S2 of the second lens element is concave. The third lens element L3 has positive refractive power, wherein an object-side surface L3S1 of the third lens element is convex, and an image-side surface L3S2 of the third lens element is planar. The object side face L4S1 of the fourth lens element is a plane, and the image side face L4S2 of the fourth lens element is a plane. The fifth lens element L5 has positive refractive power, wherein an object-side surface L5S1 of the fifth lens element is a plane, and an image-side surface L5S2 of the fifth lens element is a convex surface.

Wherein, the image side face L1S2 of the first lens is glued with a side surface of the fourth lens L4 towards the side surface. The second lens L2 is cemented with the third lens L3, and the third lens LE is cemented with the fourth lens LE. The object side face L5S1 of the fifth lens is cemented with the fourth lens L4.

In this embodiment, the total effective focal length f of the projection system is 6.132mm, the total optical length TTL of the projection system from the object side surface to the image plane of the second lens along the second optical axis is 9.315mm, the maximum field angle FOV of use of the projection system is 30 °, and the aperture value FNO of the projection system is 1.53.

Table 2 shows a basic structural parameter table of the projection system of the second embodiment, in which the unit of radius of curvature, thickness/distance is millimeter (mm).

TABLE 2

In the second embodiment, the surface shape of each aspherical lens can be defined by, but not limited to, the following aspherical formula:

wherein x is the distance vector height from the vertex of the aspheric surface when the aspheric surface is at the position with the height h along the optical axis direction; c is the paraxial curvature of the aspheric surface, c=1/R (i.e., paraxial curvature c is the inverse of radius of curvature R in table 1 above); k is a conic coefficient; ai is the correction coefficient of the aspherical i-th order. The higher order coefficients A4, A6, A8, A10, A12, A14, A16, A18, A20 for the aspherical mirror surfaces useful in example two are given in Table 3 below.

TABLE 3 Table 3

Fig. 8 shows a spherical aberration curve of the projection system of the second embodiment. Fig. 9 shows a field curvature of the projection system of the second embodiment. Fig. 10 shows a distortion curve of the projection system of the second embodiment. Fig. 11 shows a color difference curve of the projection system of the second embodiment.

As can be seen from fig. 8 to 11, the projection system according to the second embodiment can achieve good imaging quality.

Example III

As shown in fig. 12 to 16, a projection system of the third embodiment is described. Fig. 12 shows a schematic configuration of a projection system of the third embodiment.

As shown in fig. 12, the projection system includes: stop L0, first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5, and cover glass L6. The diaphragm L0, the first lens L1 and the fourth lens L4 are sequentially arranged along a first optical axis, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the protective glass L6 are sequentially arranged along a second optical axis, the fourth lens L4 is a polarization beam splitter prism, and the first optical axis and the second optical axis are intersected at the fourth lens L4. In the direction of the first optical axis, the diaphragm side is the object side, and the side away from the diaphragm is the image side. On the second optical axis, a side of the second lens L2 away from the third lens L3 is an object side, and a side of the cover glass L6 away from the fifth lens L5 is an image side.

The first lens element L1 has positive refractive power, wherein an object-side surface L1S1 of the first lens element is convex, and an image-side surface L1S2 of the first lens element is planar. The second lens element L2 has negative refractive power, wherein an object-side surface L2S1 of the second lens element is convex, and an image-side surface L2S2 of the second lens element is concave. The third lens element L3 has positive refractive power, wherein an object-side surface L3S1 of the third lens element is convex, and an image-side surface L3S2 of the third lens element is convex. The object side face L4S1 of the fourth lens element is a plane, and the image side face L4S2 of the fourth lens element is a plane. The fifth lens element L5 has positive refractive power, wherein an object-side surface L5S1 of the fifth lens element is convex, and an image-side surface L5S2 of the fifth lens element is planar.

Wherein, the image side face L1S2 of the first lens is glued with a side surface of the fourth lens L4 towards the side surface.

In this embodiment, the total effective focal length f of the projection system is 6.395mm, the total optical length TTL of the projection system from the object side surface to the image plane of the second lens along the second optical axis is 9.82mm, the maximum field angle FOV of use of the projection system is 30 °, and the aperture value FNO of the projection system is 1.59.

Table 4 shows a basic structural parameter table of the projection system of the third embodiment, in which the unit of radius of curvature, thickness/distance is millimeter (mm).

TABLE 4 Table 4

Table 5 shows the higher order coefficients that can be used for each aspherical mirror in embodiment two, where each aspherical surface profile can be defined by equation (1) given in embodiment two above.

	Fifth lens
		Aspherical coefficient/surface number	L5S1
R	8.57213618963009
		K	-35.929707623052
A4	0.0199222667708863
		A6	-0.030928347736135
A8	0.0337186435914787
		A10	-0.0222713058809637
A12	0.00913777041956876
		A14	-0.00234947058465942
A16	0.000368318123710091
		A18	-3.21877409978883e-005
A20	1.20223428895953e-006

TABLE 5

Fig. 13 shows a spherical aberration curve of the projection system of the third embodiment. Fig. 14 shows a field curvature of the projection system of the third embodiment. Fig. 15 shows a distortion curve of the projection system of the third embodiment. Fig. 16 shows a color difference curve of the projection system of the third embodiment.

As can be seen from fig. 13 to 16, the projection system according to the third embodiment can achieve good imaging quality.

Example IV

As shown in fig. 17 to 21, the projection system of the fourth embodiment is described. Fig. 17 shows a schematic configuration of a projection system of the fourth embodiment.

As shown in fig. 17, the projection system includes: stop L0, first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5, and cover glass L6. The diaphragm L0, the first lens L1 and the fourth lens L4 are sequentially arranged along a first optical axis, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the protective glass L6 are sequentially arranged along a second optical axis, the fourth lens L4 is a polarization beam splitter prism, and the first optical axis and the second optical axis are intersected at the fourth lens L4. In the direction of the first optical axis, the diaphragm side is the object side, and the side away from the diaphragm is the image side. On the second optical axis, a side of the second lens L2 away from the third lens L3 is an object side, and a side of the cover glass L6 away from the fifth lens L5 is an image side.

The first lens element L1 has positive refractive power, wherein an object-side surface L1S1 of the first lens element is convex, and an image-side surface L1S2 of the first lens element is planar. The second lens element L2 has negative refractive power, wherein an object-side surface L2S1 of the second lens element is convex, and an image-side surface L2S2 of the second lens element is concave. The third lens element L3 has positive refractive power, wherein an object-side surface L3S1 of the third lens element is convex, and an image-side surface L3S2 of the third lens element is convex. The object side face L4S1 of the fourth lens element is a plane, and the image side face L4S2 of the fourth lens element is a plane. The fifth lens element L5 has positive refractive power, wherein an object-side surface L5S1 of the fifth lens element is convex, and an image-side surface L5S2 of the fifth lens element is convex.

In this embodiment, the total effective focal length f of the projection system is 6.340mm, the total optical length TTL of the projection system from the object side surface to the image plane of the second lens along the second optical axis is 9.73mm, the maximum field angle FOV of the projection system is 30 °, and the aperture value FNO of the projection system is 1.58.

Table 6 shows a basic structural parameter table of the projection system of the fourth embodiment, in which the unit of radius of curvature, thickness/distance is millimeter (mm).

TABLE 6

Table 7 shows the higher order coefficients that can be used for each aspherical mirror in embodiment two, where each aspherical surface profile can be defined by equation (1) given in embodiment two above.

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TABLE 7

Fig. 18 shows a spherical aberration curve of the projection system of the fourth embodiment. Fig. 19 shows a field curvature of the projection system of the fourth embodiment. Fig. 20 shows a distortion curve of the projection system of the fourth embodiment. Fig. 21 shows a color difference curve of the projection system of the fourth embodiment.

As can be seen from fig. 18 to 21, the projection system according to the fourth embodiment can achieve good imaging quality.

In summary, examples one to four satisfy the relationships shown in table 8, respectively.

Condition/example	1	2	3	4
					TTL/(fFNOtan(FOV))	1.62	1.72	1.67	1.68
f1/T14	3.60	3.16	6.96	4.12
					f1/f	3.37	3.12	6.54	3.48
f1/T4	3.99	3.60	7.67	4.58
					T14/TTL	0.62	0.65	0.61	0.55
f5/f	1.84	1.41	1.66	2.06
					(SP14+SP23+SP34+SP45)/TTL	0.11	0.11	0.11	0.06
f23/f5	1.03	1.54	1.25	1.01
					F2/F3	-0.97	-1.07	-1.03	-1.16
SD21/T4	1.050	1.064	1.062	1.062

TABLE 8

Table 9 shows the effective focal lengths f of the projection systems of the first to fourth embodiments, the effective focal lengths f1 to f5 of the respective lenses, and the like (units: mm).

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TABLE 9

It will be apparent that the embodiments described above are merely some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.

It should be noted that the terms "first," "second," and the like in the description and claims of the present application and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that embodiments of the present application described herein may be implemented in sequences other than those illustrated or described herein.

The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The projection system is characterized by comprising a diaphragm, a first lens, a second lens, a third lens, a fourth lens, a fifth lens and an imaging module, wherein the projection system is provided with a first optical axis and a second optical axis which are perpendicular to each other, the diaphragm, the first lens and the fourth lens are sequentially arranged along the first optical axis, the second lens, the third lens, the fourth lens, the fifth lens and the imaging module are sequentially arranged along the second optical axis, the fourth lens is a polarization splitting prism, and the first optical axis and the second optical axis are intersected in the polarization splitting prism;

the first lens has positive focal power, and the object side surface of the first lens is a convex surface; the second lens has optical power, and the object side surface of the second lens is a convex surface; the third lens has optical power, and an object side surface of the third lens is glued with an image side surface of the second lens; the fifth lens has positive optical power;

the total optical length TTL from the object side surface to the image surface of the second lens along the second optical axis, the system focal length f of the projection system, the effective maximum field angle FOV of the projection system, and the aperture value FNO of the projection system satisfy: 1.60< ttl/(f x FNO x tan (FOV)) <1.75.

2. The projection system of claim 1, wherein a focal length f1 of the first lens and a length T14 of the first lens along the first optical axis to a side surface of the fourth lens away from the aperture satisfy: 3.00< f1/T14<6.10.

3. The projection system of claim 1, wherein a focal length f1 of the first lens and a system focal length f of the projection system satisfy: 3.10< f1/f <6.60.

4. The projection system of claim 1, wherein a focal length f1 of the first lens and a center thickness T4 of the fourth lens satisfy: 3.50< f1/T4<7.70.

5. The projection system of claim 1, wherein a length T14 from the first lens along the first optical axis to a side surface of the fourth lens away from the aperture stop and an optical total length TTL from an object side surface to an image side surface of the second lens along the second optical axis satisfy: 0.50< T14/TTL <0.70.

6. The projection system of claim 1, wherein a focal length f5 of the fifth lens and a system focal length f of the projection system satisfy: 1.40< f5/f <2.10.

7. The projection system of any of claims 1 to 6, wherein the aperture SD21 of the object side surface of the second lens and the center thickness T4 of the fourth lens satisfy: 1.050< SD21/T4<1.064.

8. The projection system of any of claims 1 to 6, wherein an on-axis distance SP14 between the first lens and the fourth lens, an on-axis distance SP23 between the second lens and the fourth lens, an on-axis distance SP34 between the third lens and the fourth lens, an on-axis distance SP45 between the fourth lens and the fifth lens, and an optical total length TTL along the second optical axis from an object side surface to an image surface of the second lens satisfy: 0.05< (SP14+SP23+SP34+SP45)/TTL <0.12.

9. The projection system of any of claims 1 to 6, wherein a combined focal length f23 of the second lens and the third lens and a focal length f5 of the fifth lens satisfy: 1.00< f23/f5<1.60.

10. An AR projection device, characterized in that it comprises the projection system of any of claims 1 to 9.