Wideband achromatic objective and application thereof

Abstract

The application relates to a broadband achromatic objective and application, and belongs to the technical field of optical achromatism. The objective is a three-cemented lens group, comprising a first lens, a second lens and a third lens, wherein the first lens and the third lens are positive power lenses, and the second lens is a negative power lens; the Abbe number of the second lens L2 is less than or equal to 23.000, and the refractive index of the first lens and the refractive index of the third lens are each independently less than or equal to 2.000. Through the structure design and material parameter collaborative optimization of the three-cemented lens group, the broadband dispersion compensation is realized, the achromatism in the 500-1000nm waveband is realized without a complex multi-piece separation structure, and the advantages of high-precision achromatism and structure simplification are considered.

Description

Technical Field

[0001] This invention relates to the field of optical achromatic technology, and more particularly to a broadband achromatic objective lens and its application. Background Technology

[0002] In the field of optical imaging, chromatic aberration is one of the key aberrations affecting image quality. Especially in wide-band imaging applications (such as visible light to near infrared), traditional monolithic lenses or ordinary cemented doublet achromatic lenses are difficult to achieve good chromatic aberration correction. The residual secondary spectrum can lead to problems such as image blurring and color edges.

[0003] Currently, existing wideband achromatic objectives typically employ complex and precise multi-element split lens structures, combined with various special optical glasses, to achieve extremely high achromatic accuracy. They achieve wideband chromatic aberration correction through the synergistic compensation of multiple lens groups. Although they can achieve apochromatic performance over a wide band, the multi-element split lens optical system has a complex structure, usually containing multiple separate lens groups or cemented lens groups. The large number of lenses (generally 6 to 11) makes processing, coating, and assembly difficult and costly, making it difficult to meet the application requirements of low-cost, mass production.

[0004] Cemented triplet lens groups, as an optical structure with simple structure, convenient processing and assembly, and low cost, are widely used in conventional narrow-band achromatic applications. However, due to their simplified structure, it is difficult to achieve effective chromatic aberration correction over a wide band. Therefore, traditional cemented triplet lens groups using conventional optical glass cannot achieve effective chromatic aberration correction over a wide band without the introduction of special dispersive materials. Consequently, cemented triplet structures are rarely used directly in the design of wide-band high-precision achromatic objectives when using only conventional glass. Instead, special materials such as ultra-low dispersion glass are selected. Due to the limited design freedom, cemented triplet lens groups are difficult to achieve the maximum chromatic aberration control level of high-precision objectives when applied to broadband achromatic applications. For example, it is difficult to control the maximum chromatic aberration value below 10 micrometers or even below 5 micrometers.

[0005] In summary, existing high-precision wide-band achromatic objectives are complex in structure and expensive; while traditional cemented lens groups are difficult to achieve high-precision wide-band achromatic aberration, failing to meet the wide-band imaging requirements of such scenarios. Therefore, there is an urgent need for a high-precision objective that is simple in structure, low in cost, easy to manufacture and adjust, and capable of achieving wide-band achromatic aberration, to overcome the shortcomings of existing technologies. Summary of the Invention

[0006] In view of the above analysis, the present invention aims to provide a broadband achromatic objective and its application to solve at least one of the following technical problems: (1) Existing high-precision broadband achromatic objectives have complex structures, high costs, and are difficult to assemble and adjust; (2) Traditional triple-cemented lens groups have broadband achromatic performance that is difficult to reach the level of high-precision objectives.

[0007] The first aspect of the present invention provides a broadband achromatic objective lens, the objective lens being a cemented lens group, comprising: a first lens L1, a second lens L2, and a third lens L3 arranged sequentially along the optical axis from the object side to the image side, wherein the first lens L1 and the third lens L3 are each independently positive power lenses, and the second lens L2 is a negative power lens; the Abbe number vd2 of the second lens L2 is ≤23.000, and the refractive index nd1 of the first lens L1 and the refractive index nd3 of the third lens L3 are each independently ≤2.000.

[0008] Furthermore, the refractive index nd1 of the first lens L1 satisfies: 1.660≤nd1≤2.000, and the Abbe number vd1 satisfies: 24.232≤vd1≤54.045; the refractive index nd3 of the third lens L3 satisfies: 1.660≤nd3≤2.000, and the Abbe number vd3 satisfies: 24.232≤vd3≤54.045; the refractive index nd2 of the second lens L2 satisfies: 1.718≤nd2≤2.057, and the Abbe number vd2 satisfies: 15.725≤vd2≤23.000.

[0009] Furthermore, the refractive index nd1 of the first lens L1 satisfies: 1.747≤nd1≤1.954, and the Abbe number vd1 satisfies: 32.309≤vd1≤50.950; the refractive index nd3 of the third lens L3 satisfies: 1.747≤nd3≤1.954, and the Abbe number vd3 satisfies: 32.309≤vd3≤50.950; the refractive index nd2 of the second lens L2 satisfies: 1.808≤nd2≤1.959, and the Abbe number vd2 satisfies: 17.472≤vd2≤22.698.

[0010] Furthermore, the Abbe number vd2 of the second lens L2 is less than the Abbe number vd1 of the first lens L1, and less than the Abbe number vd3 of the third lens L3.

[0011] Furthermore, the refractive indices nd1 of the first lens L1, nd2 of the second lens L2, and nd3 of the third lens L3 satisfy the following condition: the difference between the maximum and minimum refractive indices Δnd < 0.210.

[0012] Furthermore, the first lens L1 and the third lens L3 are each independently a biconvex lens, and the second lens L2 is a biconcave lens.

[0013] Furthermore, the first lens L1 and the third lens L3 are made of the same optical glass material.

[0014] Furthermore, the objective lens operates in the wavelength range of 500-1000 nm.

[0015] Furthermore, the maximum chromatic difference value is ≤7μm, the maximum focal length difference is ≤18μm, the relative focal length difference rate is ≤0.46%, and the maximum wavefront aberration is ≤0.13λ.

[0016] The second aspect of the present invention provides an application of the objective lens described in the first aspect in the fabrication of fiber collimators or optical systems for fiber collimation, fluorescence detection, or spectral analysis.

[0017] This invention can achieve at least one of the following beneficial effects: 1. This invention adopts a simplified three-layer cemented lens integrated structure, abandoning the complex multi-element separate design of traditional wide-band achromatic objectives. At the same time, it precisely optimizes the optical power distribution, refractive index, and Abbe number of the three lenses. Without the need for complex compensation structures, it achieves wide-band (500-1000nm) achromatic correction and stably controls the maximum chromatic difference value to ≤7μm, maximum focal length difference ≤18μm, relative focal length difference rate ≤0.46%, and maximum wavefront aberration ≤0.13λ. This solves the problem that traditional conventional three-layer cemented lens groups cannot adapt to high-precision wide-band achromatic correction, and avoids the structural redundancy of high-precision objectives. It significantly reduces the lens processing difficulty, assembly and adjustment costs, and mass production threshold, and solves the problems of high cost and poor adaptability of wide-band microscopic observation equipment in non-high-precision scenarios.

[0018] 2. In this invention, by precisely controlling the refractive index and Abbe number ratio of the first, third, and second lenses, and synergistically adapting to the minimalist three-cemented structure system, a "positive-negative-positive" optical power arrangement is formed. The second lens undertakes the main chromatic aberration correction function, using its high dispersion characteristics to accurately offset the dispersion deviation of light of different wavelengths in a wide band. At the same time, by leveraging the integrated advantages of the three-cemented structure, the structural stability and environmental robustness of the objective lens are improved. In the 500-1000nm wide band, the maximum chromatic aberration value is ≤7μm, the maximum focal length difference is ≤18μm, the relative focal length difference rate is ≤0.46%, and the maximum wavefront aberration is ≤0.13λ, realizing the low-cost and large-scale application of wide-band achromatic correction.

[0019] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0020] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0021] Figure 1 This is a schematic diagram of the structure of the broadband achromatic objective lens of the present invention.

[0022] Figure 2 This is a ray tracing diagram of the objective lens in Example 1.

[0023] Figure 3 This is a light aberration diagram of the objective lens in Example 1.

[0024] Figure 4 This is a chromatic aberration diagram of the objective lens in Example 1.

[0025] Figure 5 This is a ray tracing diagram of the objective lens in Example 2.

[0026] Figure 6 This is a light aberration diagram of the objective lens in Example 2.

[0027] Figure 7 This is a chromatic aberration diagram of the objective lens in Example 2.

[0028] Figure Labels 1: First lens L1; 2: Second lens L2; ​​3: Third lens L3. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, exemplary embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. For clarity and brevity, not all features of actual embodiments are described in the specification.

[0030] Existing broadband apochromatic objectives suffer from high performance accompanied by high complexity and high cost, while simple structures cannot meet the requirements for broadband achromatic correction. Therefore, the first aspect of this invention provides a broadband apochromatic objective, which is a triple-cemented lens group, comprising: a first lens L1, a second lens L2, and a third lens L3 arranged sequentially along the optical axis from the object side to the image side, wherein the first lens L1 and the third lens L3 are each independently positive power lenses, and the second lens L2 is a negative power lens; The Abbe number vd2 of the second lens L2 is ≤23.000, and the refractive index nd1 of the first lens L1 and the refractive index nd3 of the third lens L3 are each ≤2.000 independently.

[0031] In this invention, the Abbe number of the second lens L2 is less than 23.000, forming dispersion complementarity with the positive power lenses (L1 and L3), thus canceling chromatic aberration over a wide wavelength range. No additional compensation lens is needed, simplifying the structure while ensuring achromatic aberration performance. Furthermore, the second lens L2, paired with the first lens L1 and the third lens L3, with parameters satisfying the aforementioned range, enables the second lens L2 to possess a large dispersion capability, effectively complementing the dispersion with the two positive lenses. This allows for simultaneous correction of first-order chromatic aberration and second-order spectral density within a wide wavelength range of 500nm-1000nm, achieving apochromatic aberration performance.

[0032] It should be noted that the refractive index and Abbe number meeting the above-mentioned ranges enable the objective lens to achieve a maximum chromatic aberration value ≤7μm, a maximum focal length difference ≤18μm, a relative focal length difference rate ≤0.46%, and a maximum wavefront aberration ≤0.13λ. If the refractive index of the first lens L1 or the third lens L3 is greater than 2.000, its dispersion matching with the second lens L2 will be unbalanced, making it difficult to simultaneously suppress the secondary spectrum in a wide wavelength range of 500nm-1000nm, resulting in a decrease in achromatic aberration effect and a significant increase in the maximum chromatic aberration value; if the Abbe number of the first lens L1 or the third lens L3 is higher than 54.045, the material cost will increase sharply, and the system's optical power distribution will be difficult.

[0033] According to a preferred embodiment of the present invention, the physical aperture D of the objective lens can be 2.5 mm, and the relationship between the focal length f, the F number f#, and the working distance WD satisfies: 1.2≤f / D≤2.5, 2.3≤f#≤6, 0.125≤WD / f≤0.5.

[0034] Furthermore, the refractive index nd1 of the first lens L1 satisfies: 1.660 ≤ nd1 ≤ 2.000, and the Abbe number vd1 satisfies: 24.232 ≤ vd1 ≤ 54.045; the refractive index nd3 of the third lens L3 satisfies: 1.660 ≤ nd3 ≤ 2.000, and the Abbe number vd3 satisfies: 24.232 ≤ vd3 ≤ 54.045; the refractive index nd2 of the second lens L2 satisfies: 1.718 ≤ nd2 ≤ 2.057, and the Abbe number vd2 satisfies: 15.725 ≤ vd2 ≤ 23.000. If the Abbe number of the second lens L2 is higher than 23.000, its dispersion complementarity with the positive lens is weakened, and the first-order chromatic aberration remains significantly. If its Abbe number is lower than 15.725, the material is scarce and the processability is poor, while also introducing excessively large higher-order aberrations. Similarly, refractive indices exceeding the above ranges will also affect aberration balance and process feasibility.

[0035] Preferably, the refractive index nd1 of the first lens L1 satisfies: 1.747≤nd1≤1.954, and the Abbe number vd1 satisfies: 32.309≤vd1≤50.950; the refractive index nd3 of the third lens L3 satisfies: 1.747≤nd3≤1.954, and the Abbe number vd3 satisfies: 32.309≤vd3≤50.950; the refractive index nd2 of the second lens L2 satisfies: 1.808≤nd2≤1.959, and the Abbe number vd2 satisfies: 17.472≤vd2≤22.698.

[0036] For example, the refractive index nd1 of the first lens L1 can be 1.747, 1.833, 1.883, 1.901, or 1.954; the Abbe number vd1 of the first lens L1 can be 32.309, 37.051, 40.847, or 50.950.

[0037] For example, the refractive index nd2 of the second lens L2 can be 1.808, 1.923, 1.946, or 1.959; the Abbe number vd2 of the second lens L2 can be 17.472, 17.942, 18.896, or 22.698.

[0038] For example, the refractive index nd3 of the third lens L3 can be 1.747, 1.833, 1.883, 1.884, 1.901, or 1.954; and the Abbe number vd3 of the third lens L3 can be 32.309, 37.051, 37.199, 40.847, or 50.950.

[0039] According to some embodiments of the present invention, the Abbe number vd2 of the second lens L2 is less than the Abbe number vd1 of the first lens L1 and less than the Abbe number vd3 of the third lens L3.

[0040] In this invention, vd2 being less than vd1 and vd3 ensures that the second lens L2 has a stronger dispersion capability than the two positive lenses. Under the positive-negative-positive power distribution, the low Abbe number second lens L2 can form effective dispersion complementarity with the high Abbe number positive lens, thereby simultaneously correcting first-order chromatic aberration and second-order spectral distortion in a wide wavelength range of 500nm-1000nm.

[0041] Furthermore, the high refractive index of the second lens L2 helps to provide sufficient negative optical power while maintaining a small radius of curvature, thereby reducing the light deflection angle on the lens surface and reducing the generation of higher-order aberrations (such as spherical aberration).

[0042] In this invention, through the dual relative constraints of the Abbe number and refractive index, the invention can achieve wide-band achromatic performance that can only be achieved by traditional complex multi-group lenses in a minimal structure with only three cemented lenses, while avoiding the difficulties in the cementing process caused by excessive material differences.

[0043] According to some embodiments of the present invention, the refractive index nd1 of the first lens L1, the refractive index nd2 of the second lens L2, and the refractive index nd3 of the third lens L3 satisfy the following: the difference between the maximum and minimum refractive index Δnd < 0.2100.

[0044] In this invention, Δnd < 0.210 can control the refractive index difference between different lens materials in a cemented lens group. If the refractive index difference is too large (Δnd ≥ 0.210), it will cause severe light deflection at the cemented interface, significantly increasing higher-order spherical aberration and higher-order chromatic aberration, and making the radius of curvature of the lens surface too small, increasing the difficulty and sensitivity of processing and cementing assembly. By controlling Δnd within 0.210, the refractive index distribution of each lens can be made more balanced, the light deflection is smoother, thereby suppressing the generation of higher-order aberrations, reducing the extreme requirements on the radius of curvature, and improving the manufacturing feasibility and achromatic stability of the objective lens. For example, Δnd can be 0.040, 0.053, 0.055, 0.071, 0.073, 0.076, 0.090, 0.096, 0.136, 0.140, 0.154, 0.201, or 0.210, with Δnd ≤ 0.154 being preferred.

[0045] According to some preferred embodiments of the present invention, when the focal length f is 3.5 mm and the F-number f# is 5, the total optical power of the objective lens is defined as follows: ,in This refers to the optical power of each lens in the three-colloidal lens group, where i is 1-3, and the optical power of the first lens L1 is... 1. Optical power of the second lens L2 2 and the optical power of the third lens L3 The relationship with the total optical power satisfies: | 2 / | > | 1 / |; | 2 / | > | 3 / |.

[0046] In the present invention, the optical power 1 of the first lens L1, the optical power 2 of the second lens L2, and the optical power 3 of the third lens L3 and the total optical power satisfy the above relational expression, ensuring that the second lens L2 provides sufficient dispersion compensation ability, enabling the system to effectively correct secondary spectrum within a wide wavelength range of 500nm - 1000nm and achieving apochromatism. At the same time, the reasonable distribution of negative optical power helps to balance spherical aberration, ensure the achromatic effect, and improve the imaging quality.

[0047] According to some preferred embodiments of the present invention, when the focal length f is 3.5mm and the F - number f# is 5, the ratio of the optical power of the first lens L1 to the total optical power is 1.285 to 1.547, the absolute value of the ratio of the optical power of the second lens L2 to the total optical power is 1.432 to 2.149, and the ratio of the optical power of the third lens L3 to the total optical power is 1.005 to 1.673.

[0048] In the present invention, if the proportion of the optical power of L1 and L3 is relatively large, it will introduce relatively large spherical aberration and higher - order spherical aberration, and obvious primary chromatic aberration will also occur, which is difficult for L2 to fully compensate. Due to the decrease in the radius of curvature, the edge of the lens becomes thinner, and the manufacturing and processing will be more difficult.

[0049] It should be noted that an increase in the proportion of the optical power of L2 will lead to a decrease in the total optical power. In order to ensure the focal length, it is necessary to increase the optical power of L1 or L3 lens, thus falling into a vicious cycle. If the proportion of the optical power of L1 and L3 lenses is relatively small, in order to maintain the focal length, the lens thickness will increase, resulting in an increase in the total length of the lens group and making the lens bulky. However, if the proportion of the optical power of L2 is relatively small, it will not be able to offset the chromatic aberration generated by the positive lens group, and the purpose of apochromatism cannot be achieved.

[0050] According to some specific embodiments of the present invention, the first lens L1 and the third lens L3 are each independently a biconvex lens, and the second lens L2 is a biconcave lens.

[0051] In this invention, the use of biconvex and biconcave lens shapes facilitates a smooth curvature transition at the cemented interface, reducing the difficulty of the cementing process. It also allows for the allocation of optical power and correction of aberrations by adjusting the curvature radii of each surface. Specifically, the biconvex positive lens provides sufficient positive optical power and good symmetry, reducing spherical and coma aberrations; the biconcave negative lens, on the other hand, helps generate stable negative optical power and matches the surface curvature of the two biconvex lenses, ensuring uniform light refraction between the cemented surfaces and maintaining high achromatic performance over a wide wavelength range.

[0052] According to some particularly preferred embodiments of the present invention, when the focal length f is 3.5 mm and the F number f# is 5, the first lens L1 and the third lens L3 are made of the same optical glass material.

[0053] In this invention, when the focal length f is 3.5mm and the F-number f# is 5, the first lens L1 and the third lens L3 are made of the same optical glass material. In the above positive-negative-positive triplet structure, the fact that the positive lenses on both sides are made of the same material can make the objective lens optically symmetrical and simplify the chromatic aberration correction variables. Wide-band chromatic aberration matching can be achieved by only optimizing the negative lens material and optical power.

[0054] Furthermore, the fabrication process according to the above structure not only simplifies the bonding process and enhances robustness to processing tolerances, but also does not sacrifice wide-band achromatic performance.

[0055] According to some particularly preferred embodiments of the present invention, when the focal length f is 3.5 mm and the F-number f# is 5, the first lens and the third lens are made of the same optical glass material H-ZLaF68C, and the second lens is selected from the optical glass material H-ZF72A. At the same time, the relationship between the parameters of each lens is matched: the refractive index nd1 of the first lens L1 is 1.833 and the Abbe number vd1 is 40.847; the refractive index nd2 of the second lens L2 is 1.923 and the Abbe number vd2 is 18.896; the refractive index nd3 of the third lens L3 is 1.883 and the Abbe number vd3 is 40.847. The maximum chromatic aberration value of the manufactured objective lens can be as low as 4.643 μm, the relative focal length difference rate can be as low as 0.017%, and the maximum wavefront aberration can be as low as 0.021347λ, which significantly improves the achromatic aberration accuracy.

[0056] In this invention, the selection method for the optical glass materials of each lens in the objective lens can be carried out according to the following method: Step 1: Initial Screening: Select candidate material combinations for the first lens L1, the second lens L2, and the third lens L3 from the optical glass database, where L1 and L3 are positive power lenses, L2 is a negative power lens, and the following initial screening conditions must be met: The Abbe number vd of the positive lens material is greater than 40, and the relative dispersion deviates from the normal glass line by a value ΔP < -0.0012; The Abbe number of the negative lens material is vd < 30, and the relative dispersion deviates from the normal glass line by ΔP > 0.002; Step 2: Among the material combinations obtained in Step 1, further select combinations that meet the refractive index difference condition. The condition is: the difference between the maximum and minimum values ​​of the refractive indices nd1, nd2, and nd3 of L1, L2, and L3 is less than 0.210. Step 3: For each material combination selected in Step 2, under the system constraints of a working wavelength of 500-1000nm, physical aperture D=2.5mm, focal length f satisfying 1.2≤f / D≤1.6, F number f# satisfying 2.3≤f#≤5.71, and working distance WD and focal length f satisfying 0.125≤WD / f≤0.5, the thin lens approximation and nonlinear programming method are used to solve for the optimal optical power allocation that minimizes the focal length difference and restricts axial chromatic aberration, with 750nm as the main wavelength. The maximum focal length difference Δf and the maximum chromatic aberration value Δl under this allocation are then calculated. Step 4: Select a material combination that satisfies Δf≤8.8μm and Δl≤5.7μm and has a reasonable optical power distribution as the initial structure for optimization.

[0057] The refractive index of each wavelength can be calculated using the Sellmeier formula, and the calculated wavelengths include 500nm, 600nm, 700nm, 750nm, 800nm, 900nm, and 1000nm.

[0058] Preferably, the second lens L2 selected according to the above method can be selected from optical glass materials H-ZF62, H-ZF62GT, H-ZF71, H-ZF71GT, H-ZF72A, H-ZF72AGT, H-ZF73, H-ZF73GT, H-ZF88, and H-ZF88GT.

[0059] Furthermore, the first lens L1 and the third lens L3 selected according to the above method are each independently selected from optical glass materials H-LaK3, H-LaF4, H-LaF4GT, H-LaFL5, H-LaF6LA, H-LaF7, H-LaF10LA, H-LaF50B, H-LaF52, H-LaF54, H-LaF55, H-ZLaF1, H-ZLaF2A, and H-ZL. aF3, H-ZLaF4LB, H-ZLaF50E, H-ZLaF50D, H-ZLaF51, H-ZLaF52A, H-ZLaF52, H-ZLaF53B, H-ZL aF53BGT, H-ZLaF55D, H-ZLaF55C, H-ZLaF56B, H-ZLaF66, H-ZLaF66GT, H-ZLaF68C, H-ZLaF68 N, H-ZLaF68B, H-ZLaF69, H-ZLaF69A, H-ZLaF73, H-ZLaF78B, H-ZLaF89L, D-LaF50, D-LaF50- 25. D-LaF050, D-LaF050-25, D-ZLaF50, D-ZLaF50-25, D-ZLaF52LA, D-ZLaF52LA-25, D-ZLaF 61. D-ZLaF61-25, D-ZLaF67, D-ZLaF67-25, D-ZLaF81, D-ZLaF81-25, D-ZLaF85A, D-ZLaF85A -25, D-ZLaF85LN, D-ZLaF85LN-25, D-ZLaF85L, D-ZLaF85L-25, D-ZLaF85LS, D-ZLaF85LS-25.

[0060] Specifically, the objective lens operates in the wavelength range of 500-1000 nm.

[0061] In this invention, with Figure 2 Taking Table 1-13 as an example, in the objective lens, the radius of curvature of each lens and the thickness of each lens satisfy the following: the radius of curvature of the front surface of the first lens L1 (corresponding to serial number s1) is 3.200mm-6.117mm; the radius of curvature of the cemented surface of the first lens L1 and the second lens L2 (corresponding to serial number s2) is -3.6247mm to -3.180mm; the radius of curvature of the cemented surface of the second lens L2 and the third lens L3 (corresponding to serial number s3) is 3.178mm-6.302mm; and the radius of curvature of the rear surface of the third lens L3 (corresponding to serial number s4) is -3.365mm to -3.097mm.

[0062] The thickness of the first lens L1 is 2.599 mm to 3.753 mm; the thickness of the second lens L2 is 0.499 mm to 1.949 mm; and the thickness of the third lens L3 is 2.599 mm to 3.857 mm.

[0063] It should be noted that in the objective lens, the thickness between the rear surface of the third lens L3 and the image plane is 0.497 mm to 1.500 mm.

[0064] Under the synergistic constraints of the aforementioned radius of curvature and thickness, the triple-cemented lens group can simultaneously correct chromatic aberration and spherical aberration within a wide wavelength range of 500-1000nm without the need for additional separate lenses, achieving higher precision achromatic correction (maximum chromatic aberration value ≤7μm, maximum focal length difference ≤18μm, relative focal length difference rate ≤0.46%, maximum wavefront aberration). ≤ 0.13λ), while maintaining a simple structure that is easy to process and glue for assembly.

[0065] The second aspect of the present invention provides an application of the objective lens described in the first aspect in the fabrication of fiber collimators or optical systems for fiber collimation, fluorescence detection, or spectral analysis.

[0066] In the following embodiments, the working wavelength range is set to 500-1000 nm in the Zemax optical design software. The axial color difference analysis function is used to calculate the maximum difference of all wavelengths as the maximum color difference value, with the unit being micrometers (μm).

[0067] In Zemax, the effective focal length at wavelengths of 500nm, 600nm, 700nm, 750nm, 800nm, 900nm, and 1000nm is calculated respectively. The difference between the maximum and minimum values ​​is taken as the maximum focal length difference, with the unit being micrometers (μm).

[0068] Maximum wavefront aberration: In Zemax, the peak-to-valley value (PV value) of the wavefront error is calculated using wavefront map or point spread function (PSF) analysis, in units of wavelength λ (λ is the maximum PV value among 500nm, 600nm, 700nm, 750nm, 800nm, 900nm, and 1000nm).

[0069] The relative ratio of the maximum focal length difference (Δf) to the focal length (f) (Δf / f×100%) is used to represent the chromatic aberration reduction effect. The smaller the relative focal length difference and the smaller the maximum focal length difference, the better the chromatic aberration reduction effect.

[0070] Example 1 This embodiment provides a method for selecting and combining lenses in a three-component composite lens: Step 1: Initial Screening: Select candidate optical glass material combinations for the first lens L1, the second lens L2, and the third lens L3 from the Chengdu Guangming Optical Glass Database, and set the initial screening conditions: First lens L1 and third lens L3: Abbe number vd>40, and the relative dispersion deviates from the normal glass line by a value ΔP<-0.0012; Second lens L2: Abbe number vd < 30, and relative dispersion deviates from the normal glass line by a value ΔP > 0.002.

[0071] After screening, 99 combinations were obtained for the first lens L1 and the third lens L3 (including optical glass material H-ZLaF68C, with vd=40.85 and ΔP calculated value of -0.0013), and 18 combinations were obtained for the second lens L2 (including optical glass material H-ZF72A, with vd=18.90 and ΔP calculated value of +0.0056). The total number of combinations is 99 × 18 × 99 = 176,418.

[0072] Step Two: Refractive Index Difference Screening: In the above combinations, the difference between the maximum and minimum refractive indices of the three lenses is further restricted to be less than 0.210. The refractive index nd of optical glass material H-ZLaF68C is 1.883, and that of optical glass material H-ZF72A is 1.923, with a difference Δnd = 0.04, satisfying the condition of being less than 0.210. After this screening, the number of combinations is reduced to approximately 27,000.

[0073] Step 3: Optimization of optical power allocation and performance calculation: Set the focal length f=3.5mm, the working wavelength band 500-1000nm, and use the Sellmeier formula to calculate the refractive index of each wavelength and the dispersion D(λ). Using a nonlinear programming optimization method, with Δf ≤ 8.8 μm and Δl ≤ 5.7 μm set, the optimal optical power allocation was solved, resulting in 32 combinations. Optical glass materials H-ZLaF68C, H-ZF71, and D-LaF50 were selected as the initial structure and optimized in Zemax. The results showed: maximum focal length difference Δf = 5.965 μm, maximum chromatic aberration Δl = 4.643 μm, and relative focal length difference rate Δf / f × 100% = 0.17%. The parameter values ​​for L1, L2, and L3 are shown in Table 1.

[0074] like Figures 2-4 As shown, this embodiment employs a specific three-colloid lens selected according to the above method, with a designed focal length f of 3.5mm and an F-number f# of 5. Specific optical parameters are shown in Table 1. Specifically, the first lens L1 and the third lens L3 use the same optical glass material, H-ZLaF68C, while the second lens L2 uses H-ZF72A optical glass.

[0075] In Table 1, the serial numbers s1, s2, s3, and s4 correspond to the front surface of the first lens L1, the cemented surface between the first lens L1 and the second lens L2, the cemented surface between the second lens L2 and the third lens L3, and the rear surface of the third lens L3, respectively. The thickness of the first lens L1 is 3.2846 mm, the thickness of the second lens L2 is 0.5000 mm, the thickness of the third lens L3 is 2.6000 mm, and the thickness between the rear surface of the third lens L3 and the image plane is 0.5000 mm.

[0076] Table 1

[0077] The ratio of the optical power of the first lens L1 to the total optical power (0.2857) is 1.373, the absolute value of the ratio of the optical power of the second lens L2 to the total optical power is 1.967, and the ratio of the optical power of the third lens L3 to the total optical power is 1.564.

[0078] Example 2 The method is the same as in Example 1, except that, Figure 5-7 As shown in Table 2, the parameters of the three-colloid mirror system in this embodiment are shown in Table 2.

[0079] Table 2

[0080] The ratio of the optical power of the first lens L1 to the total optical power (0.2857) is 1.4, the absolute value of the ratio of the optical power of the second lens L2 to the total optical power is 1.9, and the ratio of the optical power of the third lens L3 to the total optical power is 1.5.

[0081] Example 3 Following the method of Example 1, the difference lies in the selection of different lens optical glass materials. The optical glass materials for L1, L2, and L3 are H-ZLAF68C, H-ZF73, and D-ZLAF67, respectively, and they are fabricated into three-component composite lenses with a designed focal length f of 3.5 mm and an F-number f# of 5. Specific optical parameters are shown in Table 3.

[0082] Table 3

[0083] Example 4 Following the method of Example 1, the difference lies in the selection of different lens optical glass materials. The optical glass materials for L1, L2, and L3 are H-ZLAF89L, H-ZF88GT, and H-ZLAF68C, respectively, and they are fabricated into three-component composite lenses with a designed focal length f of 3.5mm and an F-number f# of 5. Specific optical parameters are shown in Table 4.

[0084] Table 4

[0085] Example 5 Following the method of Example 1, the difference lies in the selection of different lens optical glass materials. The optical glass materials for L1, L2, and L3 are H-ZLAF78B, H-ZF88GT, and H-ZLAF89L, respectively, and they are fabricated into three-component composite lenses with a designed focal length f of 3.5 mm and an F-number f# of 5. Specific optical parameters are shown in Table 5.

[0086] Table 5

[0087] Example 6 Following the method of Example 1, except that the designed focal length f is 3.5mm and the F-number f# is 5, different lens optical glass materials were selected. The optical glass materials for L1, L2 and L3 are H-LAK3, H-ZF71 and H-ZLAF68C, respectively, and they were fabricated into three-component composite lenses. Specific optical parameters are shown in Table 6.

[0088] Table 6

[0089] Example 7 Following the method of Example 1, the difference is that different lens optical glass materials were selected. The optical glass materials for L1, L2, and L3 are H-ZLAF76A, H-ZF72A, and H-ZLAF68C, respectively, and they were fabricated into three-component composite lenses with a designed focal length f of 3.8 mm and an F-number f# of 5.42. Specific optical parameters are shown in Table 7.

[0090] Table 7

[0091] Example 8 Following the method of Example 1, the difference is that different lens optical glass materials were selected. The optical glass materials for L1, L2, and L3 are H-ZLAF76A, H-ZF88, and H-ZLAF68C, respectively, and they were fabricated into three-component composite lenses with a designed focal length f of 4mm and an F-number f# of 2.6. Specific optical parameters are shown in Table 8.

[0092] Table 8

[0093] Example 9 Following the method of Example 1, the difference is that different lens optical glass materials were selected. The optical glass materials for L1, L2, and L3 are H-ZLAF68C, H-ZF72AGT, and H-ZLAF68C, respectively, and they were fabricated into three-component composite lenses with a designed focal length f of 3.8 mm and an F-number f# of 5.42. Specific optical parameters are shown in Table 9.

[0094] Table 9

[0095] Example 10 Following the method of Example 1, the difference is that different lens optical glass materials were selected. The optical glass materials for L1, L2, and L3 are ZF7LTT, H-ZF73GT, and H-ZLAF68C, respectively, and they were fabricated into three-component composite lenses with a designed focal length f of 4mm and an F-number f# of 3. Specific optical parameters are shown in Table 10.

[0096] Table 10

[0097] Example 11 Following the method of Example 1, the designed focal length f is 3.5mm and the F-number f# is 5. Specific optical parameters are shown in Table 1. The first lens L1 and the third lens L3 use the same optical glass material, H-ZLaF68C, while the second lens L2 uses H-ZF72A optical glass material, consistent with Example 1, except for the relationship between the refractive index and the Abbe number. Specific parameters are shown in Table 11.

[0098] Table 11

[0099] Comparative Example 1 Following the method of Example 1, the difference is that the designed focal length f is 3.5mm and the F-number f# is 2.3. Different lens optical glass materials L1, L2, and L3 were selected as D-ZLAF67-25, H-ZF73, and H-ZF52, respectively. Specific parameters are shown in Table 12.

[0100] Table 12

[0101] Comparative Example 2 Following the method of Example 1, the difference is that the designed focal length f is 3.2mm and the F-number f# is 3.2. Different lens optical glass materials L1, L2, and L3 were selected as H-LAK53A, H-ZF13, and H-ZLAF68C, respectively. Specific parameters are shown in Table 13.

[0102] Table 13

[0103] Comparative Example 3 Following the method of Example 1, the difference lies in the selection of different lens optical glass materials. The optical glass materials for L1, L2, and L3 are H-ZLAF4LA, H-ZF73, and H-ZLAF96, respectively, and they are fabricated into three-component composite lenses with a designed focal length f of 3mm and an F-number f# of 2.3. Specific optical parameters are shown in Table 14.

[0104] Table 14

[0105] Comparative Example 4 Following the method of Example 1, the difference is that different lens optical glass materials were selected. The optical glass materials for L1, L2, and L3 are H-ZLAF91, H-ZF88GT, and H-ZLAF89LA, respectively, and they were fabricated into three-component composite lenses with a designed focal length f of 3mm and an F-number f# of 4.28. Specific optical parameters are shown in Table 15.

[0106] Table 15

[0107] Comparative Example 5 Following the method of Example 1, the difference is that different lens optical glass materials were selected. The optical glass materials for L1, L2, and L3 are H-ZLAF76A, H-ZF73GT, and H-ZLAF96, respectively, and they were fabricated into three-component composite lenses with a designed focal length f of 3.5 mm and an F-number f# of 2.3. Specific optical parameters are shown in Table 16.

[0108] Table 16

[0109] Comparative Example 6 Following the method of Example 1, the designed focal length f is 3.5mm and the F-number f# is 5. Specific optical parameters are shown in Table 1. The first lens L1 and the third lens L3 use the same optical glass material, H-ZLaF68C, while the second lens L2 uses H-ZF72A optical glass material, consistent with Example 1, except for the relationship between the refractive index and the Abbe number. Specific parameters are shown in Table 17.

[0110] Table 17

[0111] Achromatic tests were conducted on the objectives of the above embodiments and comparative examples. The results of relative focal length difference rate, maximum chromatic aberration value, and maximum wavefront aberration are shown in Table 18 below.

[0112] Table 18

[0113] The results above show that in Examples 1 and 2, the first lens L1 and the third lens L3 use the same optical glass material H-ZLaF68C, while the second lens L2 uses optical glass material H-ZF72A. The refractive index and Abbe number meet the preferred range, giving the second lens L2 a moderately high dispersion capability, which complements lenses L1 and L3. This effectively compensates for first-order chromatic aberration in the 500-1000nm wide wavelength range without introducing excessively large higher-order spherical aberrations and second-order spectral distortions due to excessive dispersion. Simultaneously, the refractive index matching is good (L2's refractive index is higher than that of L1 and L3), which facilitates a smooth transition of light at the cemented interface and reduces higher-order aberrations. Therefore, the maximum chromatic aberration value is <4.868μm, the relative focal length difference rate is <0.02%, and the wavefront aberration is ≤0.022197λ, resulting in the best overall performance. Furthermore, it can adapt to lenses with different surface curvature radii and thickness intervals.

[0114] In Examples 3-11, the Abbe number, refractive index, and other parameters of each lens do not meet the preferred range, resulting in a slight imbalance in dispersion matching or an increase in higher aberrations, leading to slightly poorer performance. However, they still meet the basic requirements of cemented triplet lenses in the broadband achromatic field (maximum chromatic difference value ≤7μm, relative focal length difference rate ≤0.46%, maximum wave aberration ≤0.13λ).

[0115] The broadband achromatic objective proposed in this invention achieves engineerable achromatic performance within a wide design range of f=3-4mm, f#=2.3-5.42, and WD / f=0.125-0.5. This allows it to be flexibly adapted to various applications with different magnifications, working distances, and light transmission requirements, such as in the fabrication of fiber collimators or optical systems for fiber collimation, fluorescence detection, or spectral analysis, thus possessing significant industrial application value.

[0116] In Comparative Examples 1-6, since the Abbe number, refractive index, and other parameters of each lens are not within the protection range, the relative focal length difference rate or the maximum chromatic aberration value increases, and the chromatic aberration reduction effect is inferior to that of Examples 1-11.

Claims

1. A broadband achromatic objective lens, characterized in that, The objective lens is a triple-colloidal lens group, comprising: a first lens L1, a second lens L2, and a third lens L3 arranged sequentially from the object side to the image side along the optical axis, wherein the first lens L1 and the third lens L3 are each independently positive power lenses, and the second lens L2 is a negative power lens. The Abbe number vd2 of the second lens L2 is ≤23.000, and the refractive index nd1 of the first lens L1 and the refractive index nd3 of the third lens L3 are each ≤2.000 independently.

2. The objective lens according to claim 1, characterized in that, The refractive index nd1 of the first lens L1 satisfies: 1.660≤nd1≤2.000, and the Abbe number vd1 satisfies: 24.232≤vd1≤54.045; the refractive index nd3 of the third lens L3 satisfies: 1.660≤nd3≤2.000, and the Abbe number vd3 satisfies: 24.232≤vd3≤54.045; the refractive index nd2 of the second lens L2 satisfies: 1.718≤nd2≤2.057, and the Abbe number vd2 satisfies: 15.725≤vd2≤23.

000.

3. The objective lens according to claim 1, characterized in that, The refractive index nd1 of the first lens L1 satisfies: 1.747≤nd1≤1.954, and the Abbe number vd1 satisfies: 32.309≤vd1≤50.950; the refractive index nd3 of the third lens L3 satisfies: 1.747≤nd3≤1.954, and the Abbe number vd3 satisfies: 32.309≤vd3≤50.950; the refractive index nd2 of the second lens L2 satisfies: 1.808≤nd2≤1.959, and the Abbe number vd2 satisfies: 17.472≤vd2≤22.

698.

4. The objective lens according to claim 2, characterized in that, The Abbe number vd2 of the second lens L2 is less than the Abbe number vd1 of the first lens L1, and less than the Abbe number vd3 of the third lens L3.

5. The objective lens according to claim 4, characterized in that, The refractive indices nd1 of the first lens L1, nd2 of the second lens L2, and nd3 of the third lens L3 satisfy the following condition: the difference between the maximum and minimum refractive indices Δnd < 0.

210.

6. The objective lens according to claim 1, characterized in that, The first lens L1 and the third lens L3 are each independently a biconvex lens, and the second lens L2 is a biconcave lens.

7. The objective lens according to claim 1, characterized in that, The first lens L1 and the third lens L3 are made of the same optical glass material.

8. The objective lens according to claim 1, characterized in that, The objective lens operates in the wavelength range of 500-1000nm.

9. The objective lens according to claim 1, characterized in that, The objective lens has a maximum chromatic aberration value ≤7μm, a maximum focal length difference ≤18μm, a relative focal length difference rate ≤0.46%, and a maximum wavefront aberration ≤0.13λ.

10. The use of the objective lens according to any one of claims 1-9 in the fabrication of fiber collimators or optical systems for fiber collimation, fluorescence detection or spectral analysis.

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