A beam expander for laser scanning projection

Abstract

This invention discloses a beam expander lens for laser scanning projection, relating to the field of laser projection display technology. It includes a first lens group, a second lens group, a third lens group, and a fourth lens group, arranged sequentially along the optical axis. These four lens groups together form the complete lens. The first, second, third, and fourth lens groups are arranged in a positive-negative-negative-negative optical power configuration. Through innovative optical architecture and optical power allocation, a large-angle beam expander function is achieved within a space of less than 35mm in total length, greatly saving internal space. By utilizing the chromatic aberration correction capability of the first lens group and the aberration correction capabilities of the second, third, and fourth lens groups, high-contrast imaging is achieved across the entire field of view and wavelength range, with concentrated dot matrix energy, meeting the requirements of high-resolution projection.

Description

Technical Field

[0001] This invention relates to the field of laser projection display technology, and more specifically to a beam expander lens for laser scanning projection. Background Technology

[0002] Laser beam scanning (LBS) projection technology relies on a laser light source and a high-speed scanning galvanometer (such as a MEMS galvanometer) to project images. It has significant advantages such as small size, excellent light efficiency, high contrast and no need for focusing. In a laser projection system, the mechanical deflection angle of the scanning galvanometer directly determines the field of view that the whole machine can achieve. In order to expand the projection field of view, a beam expanding optical system is usually required behind the scanning galvanometer to convert the small-angle scanning of the galvanometer into a large field of view projection output.

[0003] Existing beam expanders mostly employ Galilean or Keplerian telescope structures to achieve angular magnification. However, in practical engineering applications, traditional beam expanders generally suffer from problems such as lengthy structures and large sizes, making them difficult to integrate into miniaturized projection devices. Furthermore, laser projection systems have high requirements for image quality, distortion control, and beam uniformity, and conventional beam expanders struggle to simultaneously meet the comprehensive performance indicators of large-angle beam expansion, low distortion, and high resolution within a compact structure. Summary of the Invention

[0004] The purpose of this invention is to provide a beam expander lens for laser scanning projection, which solves the technical problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention specifically provides the following technical solution:

[0006] A beam expander lens for laser scanning projection includes a first lens group, a second lens group, a third lens group, and a fourth lens group, wherein the first lens group, the second lens group, the third lens group, and the fourth lens group are arranged sequentially along the optical axis, and the first lens group, the second lens group, the third lens group, and the fourth lens group together form the complete lens.

[0007] The first lens group is a cemented doublet spherical lens with positive optical power, while the second, third, and fourth lens groups are all plastic aspherical lenses with negative optical power.

[0008] As a preferred embodiment of the present invention, the effective focal length of the first lens group is denoted as F1, the effective focal length of the entire lens is denoted as F, and the ratio of F1 to F satisfies: 0.05 < |F1 / F| < 0.10.

[0009] As a preferred embodiment of the present invention, the effective focal length of the second lens group is denoted as F2, and the ratio of F2 to F satisfies: 0.10 < |F2 / F| < 0.15.

[0010] As a preferred embodiment of the present invention, the effective focal length of the third lens group is denoted as F3, and the ratio of F3 to F satisfies: 0.04 < |F3 / F| < 0.06.

[0011] As a preferred embodiment of the present invention, the effective focal length of the fourth lens group is denoted as F4, and the ratio of F4 to F satisfies: 0.12 < |F4 / F| < 0.16.

[0012] As a preferred embodiment of the present invention, the first lens group is formed by bonding a crown glass lens and a flint glass lens together.

[0013] In a preferred embodiment of the present invention, the second, third, and fourth lens groups are all lenses made of K26R.

[0014] As a preferred embodiment of the present invention, the total optical length of the entire lens is less than 35mm.

[0015] As a preferred embodiment of the present invention, the entrance pupil diameter of the entire lens is 2mm.

[0016] In a preferred embodiment of the present invention, the aspherical surface shapes of the second, third, and fourth mirror groups are defined by aspherical equations that include conic coefficients and higher-order terms, as follows:

[0017] ;

[0018] Where Z is the sag along the optical axis, c is the curvature of the surface vertex (1 / R), r is the radial coordinate, and k is the conic coefficient. , , , , , , , It is the aspherical coefficient.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. In this invention, the first lens group, the second lens group, the third lens group and the fourth lens group are arranged in a positive-negative-negative-negative optical power configuration. Through innovative optical architecture and optical power allocation, a large-angle beam expansion function is achieved within a space of less than 35mm in total length, which greatly saves the internal space of the equipment.

[0021] 2. This invention achieves high-contrast imaging across the entire field of view and wavelength range by utilizing the chromatic aberration correction capabilities of the first lens group and the aberration correction capabilities of the second, third, and fourth lens groups. The dot plot energy is concentrated, meeting the requirements for high-resolution projection. Attached Figure Description

[0022] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0023] Figure 1 A simplified optical path structure diagram of a beam expander lens for laser scanning projection is provided as an embodiment of the present invention;

[0024] Figure 2 A geometric modulation transfer function (MTF) curve provided for an embodiment of the present invention;

[0025] Figure 3 This is a standard dot array diagram under different fields of view provided in the embodiments of the present invention;

[0026] Figure 4 This is a schematic diagram of the distorted mesh of the scanning trajectory on the projection plane, provided as an embodiment of the present invention.

[0027] The labels in the diagram represent the following:

[0028] 1. First lens group; 2. Second lens group; 3. Third lens group; 4. Fourth lens group. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] like Figures 1 to 4 As shown, the present invention provides a beam expander lens for laser scanning projection, including a first lens group 1, a second lens group 2, a third lens group 3 and a fourth lens group 4, wherein the first lens group 1, the second lens group 2, the third lens group 3 and the fourth lens group 4 are arranged sequentially along the optical axis, and the first lens group 1, the second lens group 2, the third lens group 3 and the fourth lens group 4 together form the entire lens.

[0031] Among them, the first lens group 1 is a cemented doublet spherical lens with positive optical power, and the second lens group 2, the third lens group 3 and the fourth lens group 4 are all plastic aspherical lenses with negative optical power.

[0032] The entire lens, namely the beam expander lens used in this application for laser scanning projection, consists of a first lens group 1, a second lens group 2, a third lens group 3, and a fourth lens group 4 arranged sequentially along the optical axis from the object side (the side closer to the scanning galvanometer in the projection device) to the image side (the side closer to the projection surface), which strictly limits its total optical length. The first lens group 1 of the cemented doublet spherical lens mainly serves to converge the beam and correct the system chromatic aberration and primary spherical aberration.

[0033] The second lens group 2, the third lens group 3, and the fourth lens group 4 are all manufactured using precision injection molding. The surfaces of the second lens group 2, the third lens group 3, and the fourth lens group 4 are all designed as even-order aspherical surfaces, forming the core part of this application. Through specific optical power allocation and surface design, they work together to diffuse the beam transmitted from the first lens group 1 at a large angle, thereby obtaining a larger field of view. Furthermore, the second lens group 2, the third lens group 3, and the fourth lens group 4 are three aspherical lenses. Utilizing the high degree of freedom of aspherical surfaces, they can more accurately correct the large number of aberrations that are inevitably introduced by large-angle beam expansion. They efficiently correct various aberrations such as field curvature, astigmatism, and distortion caused by large-angle beam expansion, and have excellent aberration correction capabilities.

[0034] By combining the chromatic aberration correction capability of the first lens group 1 with the aberration correction capabilities of the second lens group 2, the third lens group 3 and the fourth lens group 4, the entire lens achieves high-contrast imaging across the entire field of view and wavelength range, with concentrated dot plot energy, which can meet the requirements of high-resolution projection.

[0035] The effective focal length of the first lens group 1 is denoted as F1, and the effective focal length of the entire lens is denoted as F. The ratio of F1 to F satisfies: 0.05 < |F1 / F| < 0.10.

[0036] The effective focal length of the second lens group 2 is denoted as F2. The ratio of F2 to F satisfies: 0.10 < |F2 / F| < 0.15.

[0037] The effective focal length of the third lens group 3 is denoted as F3. The ratio of F3 to F satisfies: 0.04 < |F3 / F| < 0.06.

[0038] The effective focal length of the fourth lens group 4 is denoted as F4. The ratio of F4 to F satisfies: 0.12 < |F4 / F| < 0.16.

[0039] The ratio of the optical power of the first lens group 1, the second lens group 2, the third lens group 3, and the fourth lens group 4 to the effective focal length F of the entire lens is ensured by the specific constraints mentioned above, thus maintaining the lens's beam-expansion capability and image quality balance.

[0040] In this embodiment, the effective focal lengths of the first lens group 1, the second lens group 2, the third lens group 3, and the fourth lens group 4 are shown in the table below:

[0041] lens Effective focal length (mm) First lens group 1 25.00 Second Shot Group 2 -49.54 Third Frame Group 3 -20.37 Fourth Shot Group 4 -61.19

[0042] The first lens group 1 is made of crown glass lens and flint glass lens bonded together.

[0043] The first lens group 1 is composed of a low-dispersion crown glass lens and a high-dispersion flint glass lens bonded together. Its main function is to converge the diverging beam projected by the projection device and to effectively correct the axial chromatic aberration of the entire projection device by utilizing the difference in chromatic aberration characteristics between the crown glass lens and the flint glass lens, so as to provide a beam with preliminary collimation and small chromatic aberration for the subsequent second lens group 2, third lens group 3 and fourth lens group.

[0044] Lenses in the second lens group 2, the third lens group 3, and the fourth lens group 4 are all made of K26R. This material has a moderate refractive index and Abbe number, good machinability, and is suitable for injection molding high-precision aspherical surfaces.

[0045] The overall optical length of the lens is less than 35mm, achieving an ultra-compact design.

[0046] The entrance pupil diameter of the entire lens is 2mm. This is well matched with the effective light exit diameter of common MEMS scanning mirrors, which helps to improve the light energy coupling efficiency.

[0047] The aspherical surface shapes of the second mirror group 2, the third mirror group 3, and the fourth mirror group 4 are defined by aspherical equations that include conic coefficients and higher-order terms, as follows:

[0048] ;

[0049] Where Z is the sag along the optical axis, c is the curvature of the surface vertex (1 / R), r is the radial coordinate, and k is the conic coefficient. , , , , , , , It is the aspherical coefficient.

[0050] The face shape parameters, lens thickness, lens spacing, and materials of the first lens group 1, the second lens group 2, the third lens group 3, and the fourth lens group 4 are shown in Table 1 below:

[0051] Table 1 Lens Parameters

[0052] Face number face shape radius of curvature / mm Thickness / mm Material 1 spherical 61.60 3.19 H-ZF52 2 spherical 223.90 3.02 H-FK61 3 spherical 19.18 6.03 4 even aspherical surface 110.48 2.60 ZEONEX_K22R&K26R_2016 5 even aspherical surface 36.44 8.52 6 even aspherical surface 9.97 2.98 ZEONEX_K22R&K26R_2016 7 even aspherical surface 216.33 4.90 8 even aspherical surface 30.12 2.55 ZEONEX_K22R&K26R_2016 9 even aspherical surface 268.50 1000

[0053] The coefficients of the even-order aspherical surfaces of the second mirror group 2, the third mirror group 3, and the fourth mirror group 4 are shown in Table 2 below:

[0054] Table 2 Even-order aspherical coefficients

[0055] Face number 4th order 6th order 8th order 10th level 12th order 4 -7.10E-05 8.68E-08 2.25E-09 -1.14E-11 -2.48E-13 5 2.39E-05 -1.11E-07 -6.68E-10 1.32E-12 1.55E-14 6 1.39E-05 2.98E-08 -1.95E-09 -7.08E-12 8.15E-14 7 4.08E-06 1.45E-09 -3.98E-12 -9.00E-15 -2.43E-17 8 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 9 -4.18E-07 -4.43E-09 -1.45E-12 3.22E-16 1.48E-18

[0056] In Table 1, the spherical surfaces numbered 1, 2, and 3 are the three surfaces of the first mirror group 1; the even-order aspherical surfaces numbered 4 and 5 are the two surfaces of the second mirror group 2; the even-order aspherical surfaces numbered 6 and 7 are the two surfaces of the third mirror group 3; and the even-order aspherical surfaces numbered 8 and 9 are the two surfaces of the fourth mirror group. The surface numbers in Table 2 correspond to the surface numbers in Table 1, and the orders in Table 2 correspond to the powers of r mentioned in the above aspherical surface equations.

[0057] Figure 2 The figure shows the geometric modulation transfer function (MTF) curves of this application, illustrating the MTF curves of the lens at three operating wavelengths: 447nm, 523nm, and 638nm, from 0 field of view to maximum field of view. It can be observed that at the point corresponding to 0.12 line pairs per millimeter, the MTF values ​​remain above 0.3 for all fields of view and at all wavelengths, and the curves are smooth and decrease slowly. This indicates that the entire lens of this application possesses excellent imaging resolution and contrast reproduction capabilities across the entire field of view, ensuring clear details and sharp outlines in the projected image.

[0058] Figure 3 The diagrams present standard dot plots of the lens in this application under different fields of view. Each sub-plot shows the distribution of imaging points for different wavelengths of light. It is clearly visible that even at the maximum field of view, the imaging points for red, green, and blue light remain highly convergent, with the spot diameter controlled within 4mm. This directly demonstrates that the lens of this invention achieves excellent correction for both chromatic aberration (separation of different colored light) and monochromatic aberration (diffusion of the same colored light), thereby ensuring a small projected spot size and high energy concentration, providing crucial support for the realization of high-brightness, high-definition laser projection.

[0059] Figure 4 The geometric fidelity of the projected image is visually presented through the scanning trajectory of the projection surface. Figure 4 The left side of the image shows the point where the light falls on the actual projection surface after passing through the lens of this application. Figure 4 The image on the right shows the point where the light rays fall on the actual projection surface after passing through the lens of this application. In the narrower direction of the image, the range of the laser scanning projection is expanded from 500mm to 1000mm by the lens. Due to the inherent characteristics of the galvanometer scanning structure, the projection trajectory has a certain inherent distortion, which can be eliminated through pre-correction before projection, fully meeting the high requirements for graphic geometric accuracy in scenarios such as industrial inspection and AR display.

[0060] The above embodiments are merely exemplary embodiments of this application and are not intended to limit this application. The scope of protection of this application is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to this application within its substance and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of this application.

Claims

1. A beam expander lens for laser scanning projection, characterized in that, It includes a first lens group (1), a second lens group (2), a third lens group (3) and a fourth lens group (4), and the first lens group (1), the second lens group (2), the third lens group (3) and the fourth lens group (4) are arranged in sequence along the optical axis, and the first lens group (1), the second lens group (2), the third lens group (3) and the fourth lens group (4) together form the whole lens; Among them, the first lens group (1) is a cemented doublet spherical lens with positive optical power, and the second lens group (2), the third lens group (3) and the fourth lens group (4) are all plastic aspherical lenses with negative optical power.

2. The beam expander lens for laser scanning projection according to claim 1, characterized in that, The effective focal length of the first lens group (1) is denoted as F1, and the effective focal length of the entire lens is denoted as F. The ratio of F1 to F satisfies: 0.05 < |F1 / F| < 0.

10.

3. A beam expander lens for laser scanning projection according to claim 2, characterized in that, The effective focal length of the second lens group (2) is denoted as F2, and the ratio of F2 to F satisfies: 0.10 < |F2 / F| < 0.

15.

4. A beam expander lens for laser scanning projection according to claim 2, characterized in that, The effective focal length of the third lens group (3) is denoted as F3, and the ratio of F3 to F satisfies: 0.04 < |F3 / F| < 0.

06.

5. A beam expander lens for laser scanning projection according to claim 2, characterized in that, The effective focal length of the fourth lens group (4) is denoted as F4, and the ratio of F4 to F satisfies: 0.12 < |F4 / F| < 0.

16.

6. A beam expander lens for laser scanning projection according to claim 1, characterized in that, The first lens group (1) is made of crown glass lens and flint glass lens bonded together.

7. A beam expander lens for laser scanning projection according to claim 1, characterized in that, The second lens group (2), the third lens group (3) and the fourth lens group (4) are all lenses made of K26R.

8. A beam expander lens for laser scanning projection according to claim 1, characterized in that, The total optical length of the lens is less than 35mm.

9. A beam expander lens for laser scanning projection according to claim 1, characterized in that, The entrance pupil diameter of the entire lens is 2mm.

10. A beam expander lens for laser scanning projection according to claim 1, characterized in that, The aspherical surface shapes of the second mirror group (2), the third mirror group (3), and the fourth mirror group (4) are defined by aspherical equations containing conic coefficients and higher-order terms, as follows: ； Where Z is the sag along the optical axis, c is the curvature of the surface vertex (1 / R), r is the radial coordinate, and k is the conic coefficient. , , , , , , , It is the aspherical coefficient.

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