Multi-achromatic beam expander

Abstract

The utility model belongs to the technical field of optical elements, and particularly relates to a multi-achromatic beam expander. Comprising a first lens with double-concave negative focal power, a second lens with concave-convex negative focal power, a third lens with double-convex positive focal power and a fourth lens with double-convex positive focal power which are sequentially arranged from a light inlet side to a light outlet side, all the lenses are glass spherical lenses, and the first lens is a front achromatic beam expanding lens group; the second lens, the third lens and the fourth lens form a rear achromatic beam expanding lens group, and the main optical axis of the front achromatic beam expanding lens group and the main optical axis of the rear achromatic beam expanding lens group are coaxial. According to the utility model, the light beam can be expanded for multiple times when sequentially passing through the front achromatic beam expanding lens group and the rear achromatic beam expanding lens group, so that the imaging quality is improved.

Description

Technical Field

[0001] The utility model belongs to the technical field of optical elements, and in particular relates to a multiple achromatic beam expander. Background Art

[0002] In laser technology, it is often necessary to adjust the beam. Existing beam expanders have two main uses: one is to expand the diameter of the laser beam; the other is to reduce the divergence angle of the laser beam. Compared with the unexpanded beam, the expanded beam can be focused smaller.

[0003] With the continuous development of laser communication technology, the demand for achromatic beam expanders in practical applications is increasing. However, most of the existing beam expanders have a single structure, a small beam expansion factor, and low imaging quality. Utility Model Content

[0004] The utility model provides a multiple achromatic beam expander. By arranging a front achromatic beam expander lens group and a rear achromatic beam expander lens group, a light beam can be expanded multiple times when passing through the front achromatic beam expander lens group and the rear achromatic beam expander lens group in sequence, thereby improving imaging quality.

[0005] The utility model adopts the following technical solutions:

[0006] The utility model provides a multiple achromatic beam expander having the following technical features: a first lens with biconcave negative focal power, a second lens with concave-convex negative focal power, a third lens with biconvex positive focal power, and a fourth lens with biconvex positive focal power, which are sequentially arranged from the light input side to the light output side; each lens is a glass spherical lens; the first lens is a front achromatic beam expander lens group, the second lens, the third lens and the fourth lens are a rear achromatic beam expander lens group, and the main optical axis of the front achromatic beam expander lens group and the main optical axis of the rear achromatic beam expander lens group are coaxial.

[0007] Furthermore, the multiple achromatic beam expander provided by the utility model may also have such a technical feature: the focal lengths of the front achromatic beam expander lens group and the rear achromatic beam expander lens group satisfy the following relationship:

[0008] -35mm <f1<-15mm;

[0009] 115mm <f2<135mm;

[0010] -7 <f2 / f1<-4;

[0011] Wherein, f1 is the focal length of the front achromatic beam expander lens group; f2 is the focal length of the rear achromatic beam expander lens group.

[0012] Furthermore, the multiple achromatic beam expander provided by the utility model may also have the following technical features: the refractive index Nd of the first lens and the second lens is ≥1.8, the refractive index Nd of the third lens and the fourth lens is ≤1.65; the Abbe number Vd of the first lens and the second lens is ≤30, the Abbe number Vd of the third lens and the fourth lens is ≥60.

[0013] Furthermore, the multiple achromatic beam expander provided by the utility model may also have the following technical features: the object side mirror surface curvature radius R 41 and image side mirror R 42 Satisfy: |R 42 |<R 41 ≤800mm.

[0014] Furthermore, the multiple achromatic beam expander provided by the utility model may also have the following technical features: the distance between the second lens and the third lens is L2, wherein 0.1 mm≤L2≤0.3 mm.

[0015] Furthermore, the multiple achromatic beam expander provided by the utility model may also have the following technical features: the overall length of the rear achromatic beam expander lens group is 20mm-40mm, and the overall length of the entire multiple achromatic beam expander is 80mm-120mm.

[0016] Furthermore, the multiple achromatic beam expander provided by the utility model may also have the following technical features: the focal lengths of the first lens and the second lens are negative values, and the focal lengths of the third lens and the fourth lens are positive values.

[0017] Furthermore, the multiple achromatic beam expander provided by the utility model may also have the following technical features: the focal length of the first lens is -26.96mm±5%, the focal length of the second lens is -80.25mm±5%, the focal length of the third lens is 115mm±5%, and the focal length of the fourth lens is: 100mm±5%.

[0018] Furthermore, the multiple achromatic beam expander provided by the utility model may also have the following technical features: the refractive index of the first lens is 1.95±5%, the refractive index of the second lens is 1.85±5%, the refractive index of the third lens is 1.62±5%, and the refractive index of the fourth lens is: 1.55±5%.

[0019] Furthermore, the multiple achromatic beam expander provided by the utility model may also have the following technical features: the object side mirror radius of curvature of the first lens is -42.25mm±5%, and the image side mirror radius of curvature is 59.39mm±5%; the object side mirror radius of curvature of the second lens is -90.52mm±5%, and the image side mirror radius of curvature is 230.11mm±5%; the object side mirror radius of curvature of the third lens is 235.26mm±5%, and the image side mirror radius of curvature is -68.72mm±5%; the object side mirror radius of curvature of the fourth lens is 761.03mm±5%, and the image side mirror radius of curvature is -72.35mm±5%.

[0020] Function and effect of utility model

[0021] According to the utility model, during use, the light beam can be initially expanded by the front achromatic beam expansion lens group, and then expanded again by the rear achromatic beam expansion lens group, and the beam expansion ratio is improved by multiple beam expansions; and combined with the number of front achromatic beam expansion lens groups and rear achromatic beam expansion lens groups, it is convenient to reduce tolerance sensitivity, improve imaging effects and assembly yield.

[0022] Furthermore, the utility model achieves the purpose of eliminating chromatic aberration by combining low refractive index and high Abbe number materials with high refractive index and low Abbe number materials, so that both designed wavelengths can achieve ideal beam expansion multiples, thereby achieving the beam expansion effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the structure of an embodiment of the utility model;

[0024] Figure 2 A schematic diagram of the optical path of an embodiment of the utility model;

[0025] Figure 3 This is a schematic diagram of the deviation of the divergence angle of the light beam at each field of view point after beam expansion of lasers with wavelengths of 1540nm and 1564nm in the preferred embodiment of the utility model;

[0026] Figure 4 This is the axial chromatic aberration diagram of the present invention.

[0027] Reference numerals: 1 - front achromatic beam expander lens group; 11 - first lens; 2 - rear achromatic beam expander lens group; 21 - second lens; 22 - third lens; 23 - fourth lens. DETAILED DESCRIPTION

[0028] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the multiple achromatic beam expander of the present invention is specifically described below in conjunction with the embodiments and drawings.

[0029] It should be noted that the structures, proportions, sizes, etc. depicted in the drawings of this specification are only used to match the contents disclosed in the specification so that people familiar with this technology can understand and read them. They are not used to limit the conditions under which the present utility model can be implemented, so they have no substantive technical significance. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed by the present utility model without affecting the effects and purposes that can be achieved by the present utility model.

[0030] In addition, the descriptions of "first", "second", etc. in this application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0031] <Example 1>

[0032] This embodiment proposes a multi-achromatic beam expander, such as Figure 1 As shown, it includes a front achromatic beam expander lens group 1 and a rear achromatic beam expander lens group 2 which are arranged in sequence from the light-incoming side to the light-exiting side, wherein Figure 1 In the figure, the blue line represents the direction of the light path. The light beam enters from the left side of the front achromatic beam expander lens group 1 and finally exits from the rear achromatic beam expander lens group 2. Figure 1 The left side is the light-entry side, and the right side is the light-exiting side. At the same time, the light-entry side can also be called the object plane, and the light-exiting side can also be called the image plane. The light beam enters from the light-entry side of the front achromatic beam expansion lens group 1, and is emitted from the light-exiting side after the initial beam expansion of the front achromatic beam expansion lens group 1. Then, it enters from the light-entry side of the rear achromatic beam expansion lens group 2, and is emitted from the light-exiting side after the secondary beam expansion of the rear achromatic beam expansion lens group 2. Finally, the image is formed. After the original light beam is expanded twice, the beam expansion ratio is greatly increased.

[0033] like Figure 2As shown, the front achromatic beam expander lens group 1 has a first lens 11, and the rear achromatic beam expander lens group 2 has a second lens 21, a third lens 22, and a fourth lens 23 coaxially arranged with the principal optical axis of the first lens 11, wherein the first lens 11 is a biconcave lens, the second lens 21 is a concave-convex lens arranged on the light exit side of the first lens 11, the third lens 22 is a biconvex lens arranged on the light exit side of the second lens 21, and the fourth lens 23 is a biconvex lens arranged on the light exit side of the third lens 22. The second lens 21, the third lens 22, and the fourth lens 23 are sequentially arranged on the light exit side of the first lens 11, and the light beam passes through the first lens 11, the second lens 21, the third lens 22, and the fourth lens 23 in sequence to form an image. The method of setting the number of lenses of the front achromatic beam expander lens group to one and the number of lenses of the rear achromatic beam expander lens group to three facilitates reducing the tolerance sensitivity and improving the assembly yield.

[0034] Since the first lens 11 is a double concave lens, the focal length of the first lens is a negative value; the second lens 21 is a concave-convex lens, and its focal length is a negative value; the third lens 22 and the fourth lens 23 are both double convex lenses, so the focal lengths of both are positive values. Specifically, the focal length of the first lens is -26.96mm±5%, the focal length of the second lens is -80.25mm±5%, the focal length of the third lens is 115mm±5%, and the focal length of the fourth lens is: 100mm±5%. At the same time, in order to achieve a better beam expansion effect, the focal lengths of the front achromatic beam expansion lens group 1 and the rear achromatic beam expansion lens group 2 should also satisfy the following relationship:

[0035] -35mm <f1<-15mm;

[0036] 115mm <f2<135mm;

[0037] -7 <f2 / f1<-4;

[0038] Wherein, f1 is the focal length of the front achromatic beam expander lens group 1 (ie, the focal length of the first lens 11 ); f2 is the focal length of the rear achromatic beam expander lens group 2 .

[0039] In addition, it should be noted that for low-refractive-index and high-Abbe-number materials, such materials have low refractive index but high Abbe number, which means that their refractive index changes for light of different wavelengths are small, so the dispersion is small, and the use of such materials can reduce chromatic aberration; while for high-refractive-index and low-Abbe-number materials, such materials have high refractive index but low Abbe number, which means that their refractive index changes for light of different wavelengths are large, so the dispersion is large, and if such materials are used alone, the chromatic aberration problem will be amplified. Therefore, in this embodiment, by reasonably setting the materials of the four lenses, the combination of low-refractive-index and high-Abbe-number materials and high-refractive-index and low-Abbe-number materials can achieve the purpose of better eliminating chromatic aberration, so that the designed infrared dual wavelengths can achieve the ideal beam expansion multiple, thereby achieving the effect of infrared dual wavelength synchronous beam expansion.

[0040] Specifically, the four lens materials meet the following conditions: the refractive index Nd of the first lens 11 and the second lens 21 is ≥1.8, the refractive index Nd of the third lens 22 and the fourth lens 23 is ≤1.65; the Abbe number Vd of the first lens 11 and the second lens 21 is ≤30, and the Abbe number Vd of the third lens 22 and the fourth lens 23 is ≥60. Wherein, Nd is the refractive index of the lens under d light, and Vd is the Abbe number of the lens under d light. Specifically, the refractive index of the first lens 11 is 1.95±5%, the refractive index of the second lens 21 is 1.85±5%, the refractive index of the third lens 22 is 1.62±5%, and the refractive index of the fourth lens 23 is: 1.55±5%.

[0041] At the same time, the overall length of the rear achromatic beam expander lens group l 后 Set to 20mm-40mm, the overall length of the entire multiple achromatic beam expander is l 总 The spacing between the first lens 11 and the second lens 21 is L1, the spacing between the second lens 21 and the third lens 22 is L2, and the spacing between the third lens 22 and the fourth lens 23 is L3. In order to reduce chromatic aberration and further improve image quality, the air spacing between the second lens 21 and the third lens 22 should be greater than 0.1 mm and less than 0.3 mm, that is, 0.1 mm ≤ L2 ≤ 0.3 mm.

[0042] In order to reduce spherical aberration and improve image quality, the object side mirror surface curvature radius R41 and the image side mirror surface R42 of the fourth lens 23 should satisfy: |R42|<R41≤800mm. Specifically, the object side mirror surface curvature radius of the first lens 11 is -42.25mm±5%, and the image side mirror surface curvature radius is 59.39mm±5%; the object side mirror surface curvature radius of the second lens 21 is -90.52mm±5%, and the image side mirror surface curvature radius is 230.11mm±5%; the object side mirror surface curvature radius of the third lens 22 is 235.26mm±5%, and the image side mirror surface curvature radius is -68.72mm±5%; the object side mirror surface curvature radius of the fourth lens 23 is: 761.03mm±5%, and the image side mirror surface curvature radius is -72.35mm±5%.

[0043] Specifically, the preferred implementation parameter values ​​of the above lens are shown in Table 1 below:

[0044] Table 1 Table of relevant parameters of each lens

[0045] lens Focal length / mm Refractive Index Object side mirror curvature radius / mm Image side mirror curvature radius / mm L1 <![CDATA[f1=-26.96]]> <![CDATA[n1=1.92]]> <![CDATA[R 11 =-42.25]]> <![CDATA[R 12 =59.39]]> L2 <![CDATA[f2=-80.25]]> <![CDATA[n2=1.85]]> <![CDATA[R 21 =-90.52]]> <![CDATA[R 22 =230.11]]> L3 <![CDATA[f3=115]]> <![CDATA[n3=1.62]]> <![CDATA[R 31 =235.26]]> <![CDATA[R 32 =-68.72]]> L4 <![CDATA[f4=100]]> <![CDATA[n4=1.55]]> <![CDATA[R 41 =761.03]]> <![CDATA[R 42 =-72.35]]>

[0046] Among them, L1 represents the first lens, L2 represents the second lens, L3 represents the third lens, and L4 represents the fourth lens. In the above Table 1, f1 to f4 correspond to the focal lengths of the first lens to the fourth lens, n1 to n4 correspond to the refractive indexes of the first lens to the fourth lens, R 11 , R 21 , R 31 , R 41 Corresponding to the object side mirror curvature radius of the first lens to the fourth lens, R 12 , R 22 , R 32 , R 42 These correspond to the curvature radius of the image-side mirror surface of the first to fourth lenses, respectively. “-” indicates that the direction is negative, i.e., the direction bending toward the object surface.

[0047] Among the above-mentioned preferred implementation parameters, it is also necessary to meet the following conditions: entrance pupil diameter D0 = 10 mm, exit pupil diameter D1 = 50 mm, beam expansion ratio of the beam expander is 5 times, total optical length TTL = 100 mm, wavelength is 1540 nm and 1564 nm, field of view angle is ±3 mrad, and focal lengths of the front achromatic beam expander group and the rear achromatic beam expander group are -25 mm and 125 mm respectively.

[0048] like Figure 3As shown in the figure, a schematic diagram of the deviation of the divergence angle of the light beam at each field of view point after the laser beam expansion of wavelengths 1540nm and 1564nm is provided. Among them, the left side is a comprehensive schematic diagram of the two-wavelength light spot at the 0mrad field of view point, and the right side is a comprehensive schematic diagram of the two-wavelength light spot at the 3mrad field of view. The RMS (Root Mean Square) deviation of both is within the Airy disk (an ideal monochromatic light emitted by an infinitely small point light source, after passing through the lens, will form a corrugated image of a certain size on the imaging surface, rather than an infinitely small image point, which is the Airy disk), less than 0.06mrad.

[0049] like Figure 4 As shown, the axial chromatic aberration diagram of the above preferred embodiment is provided, and the axial chromatic aberration is within the range of ±0.014 diopters. Therefore, the above lens can achieve the correction of chromatic aberration while ensuring that the dual-wavelength beam expansion ratio is fixed.

[0050] <Example 2>

[0051] On the basis of the above-mentioned embodiment, the focal length range of the front achromatic beam expanding lens group 1 is set to be smaller than the focal length range of the rear achromatic beam expanding lens group 2. Firstly, this enables more precise focusing and better optical effects; secondly, the narrower focal length range of the front achromatic beam expanding lens group 1 helps to control chromatic aberration and improve imaging quality; thirdly, the narrower focal length range of the front achromatic beam expanding lens group 1 can ensure the compatibility of multiple lenses in the rear achromatic beam expanding lens group, thereby achieving the beam expansion and achromatic effect of the entire system; finally, the narrower focal length range can make the lens easier to produce and more cost-effective.

[0052] In addition, the center thickness of the first lens is recorded as d1, the center thickness of the second lens is recorded as d2, the center thickness of the third lens is recorded as d3, and the center thickness of the fourth lens is recorded as d4. The spacing between the first lens 11 and the second lens 21 is L1, the spacing between the second lens 21 and the third lens 22 is L2, and the spacing between the third lens 22 and the fourth lens 23 is L3. Then, the overall length of the rear achromatic beam expander lens group is l 后 =L2+L3+d2+d3+d4, the overall length of the multi-achromatic beam expander is l 总 =d1+L1+l 后 .

[0053] If you set it to l 后 The range is set to 20mm-40mm, l 总The range is set to 80mm-120mm, and 0.1mm≤L2≤0.3mm, that is: 20mm≤L2+L3+d2+d3+d4≤40mm, 80mm≤d1+L1+L2+L3+d2+d3+d4≤120mm. Since 0.1mm≤L2≤0.3mm, substituting it into the above formula, it can be concluded that: 19.7mm≤L3+d2+d3+d4≤39.9mm and 19.9mm≤L3+d2+d3+d4≤39.7mm. Combining the two inequalities, 19.9mm≤L3+d2+d3+d4≤39.9mm is obtained. Finally, the value range of L3+d2+d3+d4 is substituted into l 总 We can get: 80mm≤d1+L1+L2+19.9mm≤120mm and 80mm≤d1+L1+L2+39.9mm≤120mm, that is: 60.1mm≤d1+L1+L2≤100.1mm, combined with 0.1mm≤L2≤0.3mm, we can finally get: 60mm≤d1+L1≤99.8mm.

[0054] The above embodiment increases the beam expansion ratio of the beam by arranging the front achromatic beam expansion lens group and the rear achromatic beam expansion lens to expand the beam multiple times, and reduces the tolerance sensitivity by combining the number of the front achromatic beam expansion lens group and the rear achromatic beam expansion lens group, thereby improving the imaging effect and assembly yield. In addition, by reasonably arranging the materials of the four lenses, the purpose of eliminating chromatic aberration is achieved by combining low-refractive index and high-Abbe number materials with high-refractive index and low-Abbe number materials, so that the two designed wavelengths can both achieve the ideal beam expansion ratio, thereby achieving the effect of infrared dual-wavelength synchronous beam expansion.

[0055] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A multiple achromatic beam expander, characterized in that: It comprises a first lens with biconcave negative focal power, a second lens with concave-convex negative focal power, a third lens with biconvex positive focal power, and a fourth lens with biconvex positive focal power, which are arranged in sequence from the light-inlet side to the light-outlet side, and each lens is a glass spherical lens; the first lens is a front achromatic beam expander lens group, the second lens, the third lens and the fourth lens are a rear achromatic beam expander lens group, and the main optical axis of the front achromatic beam expander lens group and the main optical axis of the rear achromatic beam expander lens group are coaxial.

2. The multiple achromatic beam expander according to claim 1, characterized in that: The focal lengths of the front achromatic beam expander lens group and the rear achromatic beam expander lens group satisfy the following relationship: -35mm <f1<-15mm; 115mm <f2<135mm; -7 <f2 / f1<-4; Among them, f1 is the focal length of the front achromatic beam expander lens group; f2 is the focal length of the rear achromatic beam expander lens group.

3. The multiple achromatic beam expander according to claim 1, characterized in that: The refractive index N of the first lens and the second lens d ≥1.8, the refractive index N of the third lens and the fourth lens d ≤1.65; Abbe number V of the first lens and the second lens d ≤30, the Abbe number V of the third lens and the fourth lens d ≥60.

4. The multiple achromatic beam expander according to claim 1, characterized in that: The object side mirror surface curvature radius R of the fourth lens 41 and image side mirror R 42 Satisfy: |R 42 |<R 41 ≤800mm.

5. The multiple achromatic beam expander according to claim 1, characterized in that: The air interval between the second lens and the third lens is L2, wherein 0.1 mm≤L2≤0.3 mm.

6. The multiple achromatic beam expander according to claim 5, characterized in that: The overall length of the rear achromatic beam expander lens group is 20mm-40mm, and the overall length of the entire multiple achromatic beam expander is 80mm-120mm.

7. The multiple achromatic beam expander according to claim 2, characterized in that: The focal length of the first lens is -26.96 mm ± 5%, the focal length of the second lens is -80.25 mm ± 5%, the focal length of the third lens is 115 mm ± 5%, and the focal length of the fourth lens is 100 mm ± 5%.

8. The multi-achromatic beam expander according to claim 3, characterized in that: The refractive index of the first lens is 1.95±5%, the refractive index of the second lens is 1.85±5%, the refractive index of the third lens is 1.62±5%, and the refractive index of the fourth lens is 1.55±5%.

9. The multi-achromatic beam expander according to claim 4, characterized in that: The object side mirror surface radius of the first lens is -42.25mm±5%, and the image side mirror surface radius of curvature is 59.39mm±5%; the object side mirror surface radius of curvature of the second lens is -90.52mm±5%, and the image side mirror surface radius of curvature is 230.11mm±5%; the object side mirror surface radius of curvature of the third lens is 235.26mm±5%, and the image side mirror surface radius of curvature is -68.72mm±5%; the object side mirror surface radius of curvature of the fourth lens is: 761.03mm±5%, and the image side mirror surface radius of curvature is -72.35mm±5%.

Images