Beam-expanding collimation optical system

Abstract

A beam-expanding collimation optical system is composed of a first lens group with positive focal power and a second lens group with negative focal power, wherein the first lens group and the second lens group are sequentially arranged from a light projection side to a light source side. The first lens group is composed of a first positive lens, a second negative lens and a third positive lens, and the second lens group is composed of a fourth negative lens. By reasonably optimizing the focal length, the surface type and the thickness of each lens, the beam expanding and collimating optical system is adaptive to the broadband of 3-5 [mu] m, the imaging quality is high, the collimating characteristic is good, and the diffraction circle energy is high, so that the contrast ratio is improved.

Description

Technical Field

[0001] The invention relates to a laser collimation optical system, in particular to a beam expansion collimation optical system. Background Art

[0002] Infrared target simulators are widely used in the research, development, and testing of missile guidance systems, infrared thermal imagers, drone reconnaissance, and autonomous driving. Their core purpose is to accurately simulate the infrared radiation characteristics of real-world infrared targets and their surroundings in a controlled experimental environment.

[0003] Because the beam size emitted by a laser source is insufficient to cover the target's receiving surface, the spot size must be expanded and the beam collimated. Existing beam expansion and collimation optical systems generally lack the performance needed for direct application in infrared target simulators. This is primarily due to differences in wavelength range (3-5μm), high wavefront distortion, significant energy loss, and substandard beam expansion. For example, the infrared collimating lens disclosed in CN118244458A is applicable to the C-band (1530-1560μm) and exhibits significant distortion. CN117192787A discloses a large-aperture infrared laser collimating and beam expansion system suitable only for a single wavelength of 1550nm, exhibiting significant distortion and energy loss. CN115755338A discloses a wide-band collimating lens suitable for the 300-1000nm wavelength range, also exhibiting significant distortion and energy loss. Therefore, it is necessary to design a beam expansion and collimating optical system tailored to the application environment of infrared target simulators. Summary of the Invention

[0004] In response to the above technical problems, the present invention proposes a beam expansion and collimation optical system, which is suitable for a wide wavelength band of 3~5μm, realizes the collimation and expansion of infrared light sources, and reduces wavefront distortion and energy loss.

[0005] The beam expander and collimator optical system of the present invention comprises a first lens group and a second lens group arranged sequentially from the light projection side to the light source side. The first lens group has positive optical power, while the second lens group has negative optical power. The combination of positive and negative lens groups allows for a balanced optical power distribution within the beam expander and collimator optical system, reducing the complexity of system design.

[0006] The first lens group consists of a first lens, a second lens, and a third lens, and the second lens group consists of a fourth lens. Specifically: The first lens is a positive lens, the light-projecting side of the first lens is convex, and the light source side of the first lens is concave; The second lens is a negative lens, the light-projecting side of the second lens is a concave surface, and the light source side of the second lens is a concave surface; The third lens is a positive lens, the light-projecting side of the third lens is convex, and the light source side of the third lens is concave; The fourth lens is a negative lens, the light-projecting side of the fourth lens is a convex surface, and the light source side of the fourth lens is a concave surface; Through the reasonable distribution of the above-mentioned optical focal length and surface shape, each lens can reasonably share the optical focal length, avoiding the problem of excessive optical focal length of a single lens, suppressing the aberration of the system, and having good collimation characteristics for infrared light in a wide band.

[0007] According to the beam expansion and collimation optical system of this embodiment, the following conditional formula (1) is satisfied: 1.0 <fG1 / EFL<1.2;-85<fG2 / EFL<-60;0.6<EFL / TTL<1(1) Conditional formula (1) makes the system easy to adapt to a wider infrared band by limiting the focal length distribution range of the first lens group and the second lens group; and further limits the ratio of the system focal length to the total length, making the system miniaturized. Furthermore, it is preferred to satisfy 1.0 <fG1 / EFL<1.1;-75<fG2 / EFL<-70;0.8<EFL / TTL<1。

[0008] According to the beam expansion and collimation optical system of this embodiment, it is preferable to satisfy the following conditional formula (2): 0.4 <f1 / EFL<0.8;-0.8<f2 / EFL<-0.2;1.0<f3 / EFL<3.0(2) Conditional formula (2) reasonably distributes the focal length range of each lens, so that the system aberration is kept within a small range, which facilitates aberration correction.

[0009] According to the beam expansion and collimation optical system of this embodiment, it is preferable to satisfy the following conditional formula (3): 0.2 <D6 / TTL<0.4;5.0<D6 / D2<7.0(3) Conditional formula (3) optimizes the range of the spacing so that the beam expansion and collimation optical system not only has good collimation, but also is easy to achieve a large beam expansion ratio. For example, for a light source with a diameter of about 9.5 mm, the diameter after expansion is about 180 mm, and the beam expansion ratio is greater than 19.

[0010] According to the beam expansion and collimation optical system of this embodiment, it is preferable to satisfy the following conditional formula (4): -0.5<(R1-R2) / (R1+R2)<-0.4; 1.0<(R3-R4) / (R3+R4)<1.5; -0.3<(R5-R6) / (R5+R6)<-0.1; 0<(R7-R8) / (R7+R8)<0.5 (4) Conditional equation (4) reduces system aberrations, especially distortion, by optimizing the surface factors of each lens. Further coordination with lens materials can significantly reduce energy loss. For example, the first and fourth lenses use silicon (SILICON), and the second and third lenses use germanium (GERMANIUM). Furthermore, by selecting appropriate materials and optimizing the surface shape, only a few very simple aspheric surfaces are needed to correct chromatic aberration in a wide band (3-5μm). For example, only the third and fourth lenses use even-order aspheric surfaces, and the aspheric surfaces only have fourth-order, sixth-order, and eighth-order terms.

[0011] Beneficial effects

[0012] The beam expansion and collimation optical system of the present invention is compatible with a wide wavelength range, achieving excellent collimation characteristics for wavelengths from 3μm to 5μm, while also possessing a large beam expansion ratio. The system delivers excellent imaging quality across all fields of view, with high spot uniformity, excellent collimation, minimal aberrations and wavefront distortion, and high diffraction inclusion energy, thereby improving contrast. Furthermore, the beam expansion and collimation optical system of the present invention requires only four lenses, constructed solely from a combination of silicon and germanium. This results in simple materials, a minimal number of aspheric surfaces, and a simple surface geometry, resulting in low manufacturing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 FIG. 4 is an optical structure diagram of an exemplary embodiment of a beam expansion and collimation optical system.

[0014] Figure 2 yes Figure 1 The optical structure diagram of the beam expansion and collimation optical system with multiple fields of view, where the half-field angles are 0°, ±0.5°, and ±1° respectively.

[0015] Figure 3 yes Figure 1 Point diagram of the image plane (actually the light source plane) corresponding to the nine fields of view of the beam expanding and collimating optical system, where the half field angles are 0°, ±0.3°, ±0.5°, ±0.7° and ±1° respectively.

[0016] Figure 4 yes Figure 3 Light trace diagram of the image plane (actually the light source plane) corresponding to the nine fields of view of the beam expansion and collimation optical system.

[0017] Figure 5 It is the field curvature and distortion of the image plane (actually the light source plane) of the beam expanding and collimating optical system.

[0018] Figure 6 It is the optical transfer function diagram of the beam expansion and collimation optical system.

[0019] Figure 7 It is a schematic diagram of the diffraction circle energy curve of the beam expansion and collimation optical system.

[0020] Among them, G1 represents the first lens group, G2 represents the second lens group, L1 to L4 represent the first to fourth lenses respectively, and S1 to S9 represent the serial numbers of each surface. DETAILED DESCRIPTION

[0021] The following is combined with Figures 1 to 7 The beam expansion and collimation optical system of the present invention is described in detail.

[0022] See also Figures 1 to 2 The beam expander and collimator optical system of the present invention comprises a first lens group G1 and a second lens group G2, arranged sequentially from the light projection side to the light source side. The first lens group G1 has positive power, while the second lens group G2 has negative power. The combination of positive and negative lens groups allows for a balanced power distribution within the beam expander and collimator optical system, reducing the complexity of system design.

[0023] The first lens group G1 consists of a first lens L1, a second lens L2, and a third lens L3, and the second lens group G2 consists of a fourth lens L4. Specifically: The first lens L1 is a positive lens, the light-projecting side S1 of the first lens is convex, and the light source side S2 of the first lens is concave; The second lens L2 is a negative lens, the light-projecting side S3 of the second lens is concave, and the light source side S4 of the second lens is also concave; The third lens L3 is a positive lens, the light-projecting side S5 of the third lens is convex, and the light-source side S6 of the third lens is concave; The fourth lens L4 is a negative lens, the light-projecting side surface S7 of the fourth lens is convex, and the light-source side surface S8 of the fourth lens is concave; Through the reasonable distribution of the above-mentioned optical focal length and surface shape, each lens can reasonably share the optical focal length, avoiding the problem of excessive optical focal length of a single lens, suppressing the aberration of the system, and having good collimation characteristics for infrared light in a wide band.

[0024] According to the beam expansion and collimation optical system of this embodiment, the following conditional formula (1) is satisfied: 1.0 <fG1 / EFL<1.2;-85<fG2 / EFL<-60;0.6<EFL / TTL<1(1) Conditional formula (1) limits the focal length distribution range of the first lens group G1 and the second lens group G2, making the system easy to adapt to a wider infrared band range; and further limits the ratio of the system focal length to the total length, making the system miniaturized. Furthermore, it is preferred to satisfy 1.0 <fG1 / EFL<1.1;-75<fG2 / EFL<-70;0.8<EFL / TTL<1。

[0025] The beam expanding and collimating optical system according to this embodiment preferably satisfies the following conditional formula (2): 0.4 < f1 / EFL < 0.8; -0.8 < f2 / EFL < -0.2; 1.0 < f3 / EFL < 3.0 (2) By reasonably distributing the focal length ranges of each lens, conditional formula (2) keeps the system aberrations within a small range, facilitating aberration correction.

[0026] The beam expanding and collimating optical system according to this embodiment preferably satisfies the following conditional formula (3): 0.2 < D6 / TTL < 0.4; 5.0 < D6 / D2 < 7.0 (3) By optimizing the range of the spacing, conditional formula (3) enables the beam expanding and collimating optical system to not only have good collimation but also be easy to achieve a large beam expansion ratio. For example, for a light source with a diameter of about 9.5 mm, the expanded diameter is about 180 mm, and the beam expansion ratio is greater than 19.

[0027] The beam expanding and collimating optical system according to this embodiment preferably satisfies the following conditional formula (4): -0.5 < (R1 - R2) / (R1 + R2) < -0.4; 1.0 < (R3 - R4) / (R3 + R4) < 1.5; -0.3 < (R5 - R6) / (R5 + R6) < -0.1; 0 < (R7 - R8) / (R7 + R8) < 0.5 (4) By optimizing the surface shape factors of each lens, conditional formula (4) reduces the system aberrations, especially with a relatively low distortion value. Further in combination with the materials of the lenses, the energy loss can be significantly reduced. For example, the first lens L1 and the fourth lens L4 are made of silicon (SILICON), and the second lens L2 and the third lens L3 are made of germanium (GERMANIUM). Moreover, by selecting appropriate materials in combination with the optimization of the surface shape, only a few very simple aspherical surfaces are required to correct the chromatic aberration in a wide wavelength band (3 - 5 μm). For example, only the third lens L3 and the fourth lens L4 are aspherical surfaces, and the aspherical surfaces only have fourth-order, sixth-order, and eighth-order terms.

[0028] For the beam expanding and collimating optical system of the present invention, preferably 1 < Fno < 1.8, more preferably 1.2 < Fno < 1.7, and even more preferably 1.4 < Fno < 1.6 Table 1 shows a set of specific data of this embodiment.

[0029] [Table 1] (Unit of length: mm)

[0030] Table 2 shows the aspherical parameters of this embodiment.

[0031] [Table 2]

[0032] Table 3 shows the system parameters of this embodiment.

[0033] [Table 3]

[0034] Table 4 shows the values ​​of some conditional expressions of this embodiment.

[0035] [Table 4]

[0036] The meaning of each parameter is as follows: Fno is the image space F number, TTL is the total length of the system, HFOV is the half field of view angle of the system, EFL is the effective focal length of the system, F B is the back focal length of the system, fG1 is the focal length of the first lens group G1, fG2 is the focal length of the second lens group G2, f1~f4 are the focal lengths of each lens, D2 is the distance between the first lens L1 and the second lens L2, D6 is the distance between the first lens group G1 and the second lens group G2, that is, the distance between the third lens L3 and the fourth lens L4, R1 is the curvature radius of the light-projecting side S1 of the first lens, R2 is the curvature radius of the light-source side S2 of the first lens, R3 is the curvature radius of the light-projecting side S3 of the second lens, R4 is the curvature radius of the light-source side S4 of the second lens, R5 is the curvature radius of the light-projecting side S5 of the third lens, R6 is the curvature radius of the light-source side S6 of the third lens, R7 is the curvature radius of the light-projecting side S7 of the fourth lens, and R8 is the curvature radius of the light-source side S8 of the fourth lens.

[0037] Figure 3 yes Figure 1 Point diagram of the image plane (actually the light source plane) corresponding to the nine fields of view of the beam expanding and collimating optical system, where the half field angles are 0°, ±0.3°, ±0.5°, ±0.7° and ±1° respectively. Figure 4 yes Figure 3 Light traces from the image plane (actually the light source plane) corresponding to the nine fields of view of the beam expander and collimator optical system. The maximum RMS radius in the spot diagram is 3.151 μm, smaller than half the pixel size (3.8 μm) of a typical DMD (Digital Micromirror Device) chip. The system also achieves excellent imaging quality and high spot uniformity across all fields of view, demonstrating the high collimation performance of the beam expander and collimator optical system.

[0038] Figure 5 It is the field curvature and distortion of the image plane (actually the light source plane) of the beam expansion and collimation optical system. It can be seen that the wavefront distortion is very small, which is very suitable for infrared detection.

[0039] Figure 6 The figure below is the optical transfer function diagram of the beam expansion collimating optical system. The optical transfer function value of the collimating optical system at the Nyquist frequency is greater than 0.7, indicating that the optical system has strong reduction ability and good imaging quality.

[0040] Figure 7 This is a schematic diagram of the diffraction-enclosed energy curve for the beam expansion and collimation optical system. The diffraction-enclosed energy curve follows the same trend as the diffraction-limited curve, and the energy concentration within the DMD chip's half-pixel size of 3.8μm exceeds 70%, indicating high energy concentration and improved contrast.

[0041] The above embodiment is only one of the preferred examples made for the convenience of description, and those skilled in the art may make modifications and variations thereto without departing from the spirit and scope of the present disclosure as defined by the claims.

Claims

1. A beam expansion and collimating optical system, comprising a first lens group (G1) and a second lens group (G2) arranged sequentially from the light projection side to the light source side; wherein: The first lens group (G1) has a positive optical power, and the second lens group (G2) has a negative optical power; it is characterized in that: the first lens group (G1) consists of a first lens (L1), a second lens (L2) and a third lens (L3), and the second lens group (G2) consists of a fourth lens (L4); wherein, The first lens (L1) is a positive lens, the light-projecting side surface (S1) of the first lens is a convex surface, and the light source side surface (S2) of the first lens is a concave surface; The second lens (L2) is a negative lens, the light-projecting side surface (S3) of the second lens is a concave surface, and the light source side surface (S4) of the second lens is a concave surface; The third lens (L3) is a positive lens, the light-projecting side surface (S5) of the third lens is a convex surface, and the light source side surface (S6) of the third lens is a concave surface; The fourth lens (L4) is a negative lens, the light-projecting side surface (S7) of the fourth lens is a convex surface, and the light source side surface (S8) of the fourth lens is a concave surface; The beam expansion and collimation optical system satisfies the following condition (1): 1.0 <fG1 / EFL<1.2;-85<fG2 / EFL<-60;0.6<EFL / TTL<1(1); Wherein, EFL is the effective focal length of the beam expanding and collimating optical system; fG1 is the focal length of the first lens group (G1), fG2 is the focal length of the second lens group (G2), and TTL is the total length of the beam expanding and collimating optical system.

2. The beam expansion and collimation optical system according to claim 1, characterized in that Satisfy condition (2): 0.4 <f1 / EFL<0.8;-0.8<f2 / EFL<-0.2; 1.0 <f3 / EFL<3.0(2); Wherein, f1 is the focal length of the first lens (L1), f2 is the focal length of the second lens (L2), and f3 is the focal length of the third lens (L3).

3. The beam expansion and collimation optical system according to claim 1, characterized in that Satisfy condition (3): 0.2 <D6 / TTL<0.4;5.0<D6 / D2<7.0(3); Wherein, D2 is the distance between the first lens (L1) and the second lens (L2), and D6 is the distance between the first lens group (G1) and the second lens group (G2).

4. The beam expansion and collimation optical system according to claim 1, characterized in that Satisfy condition (4): -0.5<(R1-R2) / (R1+R2)<-0.4; 1.0<(R3-R4) / (R3+R4)<1.5; -0.3<(R5-R6) / (R5+R6)<-0.1; 0<(R7-R8) / (R7+R8)<0.5(4); Among them, R1 is the curvature radius of the light-projecting side surface (S1) of the first lens, R2 is the curvature radius of the light source side surface (S2) of the first lens, R3 is the curvature radius of the light-projecting side surface (S3) of the second lens, R4 is the curvature radius of the light source side surface (S4) of the second lens, R5 is the curvature radius of the light-projecting side surface (S5) of the third lens, R6 is the curvature radius of the light source side surface (S6) of the third lens, R7 is the curvature radius of the light-projecting side surface (S7) of the fourth lens, and R8 is the curvature radius of the light source side surface (S8) of the fourth lens.

5. The beam expansion and collimation optical system according to claim 1, wherein: The first lens (L1) and the fourth lens (L4) are made of silicon, and the second lens (L2) and the third lens (L3) are made of germanium.

6. The beam expansion and collimation optical system according to claim 1, wherein: The light-projecting side surface (S5) of the third lens and the light-projecting side surface (S7) of the fourth lens are even-order aspherical surfaces.

7. The beam expansion and collimation optical system according to claim 1, wherein: The beam expansion ratio of the collimation optical system is greater than 19, where the beam expansion ratio is the ratio of the effective diameter of the light projection side surface (S1) of the first lens to the effective diameter of the light source surface.

8. The beam expansion and collimation optical system according to claim 1, wherein: 1 < Fno < 1.8 is satisfied, where Fno is the image space F-number of the beam expansion and collimation optical system.

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