A 2P small distortion recognition lens

Abstract

This invention relates to a 2P low-distortion recognition lens, comprising a first lens, an aperture stop, a second lens, and a filter arranged sequentially from the object side along the optical axis to the image side; the first lens is a negative lens with a concave surface near the optical axis on the object side and a convex surface near the optical axis on the image side; the second lens is a positive lens, specifically a biconvex lens; and the filter is a plane lens. In this invention, the first lens employs a paraxial concave-convex meniscus negative lens structure, and its object side can introduce higher-order aspherical terms in the off-axis region to produce reverse distortion; the second lens is a biconvex positive lens, providing primary convergence capability and collaboratively correcting field curvature and coma; the combination of these two elements effectively reduces full-field distortion using only two plastic lenses, meeting the requirements of applications with high image geometric accuracy, such as face recognition, liveness detection, and QR code recognition.

Description

Technical Field

[0001] This invention relates to the field of optical equipment technology, and specifically to a 2P small distortion recognition lens. Background Technology

[0002] With the widespread adoption of smartphones, tablets, smart locks, and other fingerprint-enabled electronic products, the market demand for low-distortion, miniaturized fingerprint recognition lenses is growing. Improving the speed and accuracy of fingerprint recognition and reducing false recognition rates allows users to unlock their phones and electronic devices more quickly, conveniently, and securely.

[0003] One of the main invention objectives of the 2P low-distortion recognition lens is to achieve low distortion. By employing two aspherical plastic lenses and appropriately setting the focal length of the two lenses, peripheral field-of-view distortion and aberrations are corrected, significantly reducing the lens's distortion parameters (typically 5% distortion), thereby achieving high-quality imaging and significantly improving fingerprint recognition accuracy. While maintaining image quality, the overall optical length is effectively shortened, achieving miniaturization. The mainstream 2P low-distortion recognition lenses on the market can be divided into four categories: standard, IR confocal, quasi-telecentric, and filter-integrated. All are characterized by low cost, low distortion, and moderate FOV, and are widely used in consumer-grade biometrics and machine vision front-ends.

[0004] The existing technology suffers from the following problems: To simplify the structure, most 2P lenses employ a fully positive focal power distribution or a poorly symmetrical surface combination, resulting in significant pincushion distortion of the entire system; ordinary 2P lenses typically place the aperture stop close to the first lens element or omit the independent aperture stop, causing an excessively large principal ray angle (CRA) at the edge of the field of view. As a result, while the central area imaging is acceptable, the edge sharpness of the image drops sharply; conventional 2P lenses do not perform coordinated optimization for the visible and near-infrared bands, leading to a significant shift in the focal position under daytime (~550nm) and nighttime infrared illumination (such as 850nm / 940nm). This typically manifests as "sharp during the day and blurry at night," making it difficult to meet the needs of applications requiring stable operation around the clock, such as liveness detection, and severely restricting the practicality of the product and the user experience.

[0005] The aforementioned three major problems—high distortion, blurred edges, and day / night incompatibility—have become the main obstacles to the widespread application of low-cost 2P recognition lenses in the field of high-reliability biometrics. Therefore, there is an urgent need for a novel 2P low-distortion recognition lens solution that, without increasing the number of lenses or manufacturing costs, effectively and synergistically suppresses distortion, improves edge imaging quality, and enhances day / night confocal performance through reasonable optical power allocation, surface design, and aperture layout. Summary of the Invention

[0006] Based on the above description, the present invention provides a 2P small distortion recognition lens, aiming to propose a novel 2P small distortion recognition lens.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: This invention provides a 2P small distortion recognition lens, comprising a first lens, an aperture stop, a second lens, and a filter arranged sequentially from the object side along the optical axis to the image side; the first lens is a negative lens with a concave surface near the optical axis on the object side and a convex surface near the optical axis on the image side; the second lens is a positive lens, specifically a biconvex lens; and the filter is a planar lens.

[0008] Furthermore, there is at least one inflection point on the off-axis position of the object-side surface of the first lens.

[0009] Furthermore, the off-axis position of the object-side surface of the first lens is 0.8D~0.89D, and the tangent angle is 45°-63°.

[0010] Furthermore, the first lens element has a focal length of f1, and the lens focal length is f, satisfying the following conditions: 2.333>|f1 / f|>2.721.

[0011] Furthermore, the second lens element has a focal length of f2, and the lens focal length is f, satisfying the following conditions: 1.393 < |f2 / f| < 1.460.

[0012] Furthermore, 4. The thickness of the first lens core is T(L1), and the focal length of the first lens is f1, satisfying the following conditions: 0.242>|T(L1) / f1|>0.403.

[0013] Compared with the prior art, the technical solution of this application has the following beneficial technical effects: (1) In the technical solution of the present invention, the first lens adopts a paraxial concave-convex meniscus negative lens structure, and its object side can introduce higher-order aspherical terms in the off-axis region to generate reverse distortion; the second lens adopts a biconvex positive lens, which provides the main convergence capability and works together to correct field curvature and coma; the two together can effectively reduce the distortion of the entire field of view under the condition of using only two plastic lenses, and meet the application scenarios with high requirements for image geometric accuracy such as face recognition, liveness detection, and QR code recognition; (2) The front-mounted negative lens, combined with the centrally positioned aperture stop, helps to control the incident angle of the chief ray at the edge of the field of view, so that the chief ray angle (CRA) is well matched with the microlens array of the image sensor (especially back-illuminated BSI or global shutter CMOS), reducing edge illumination attenuation and color shift, and improving recognition stability. Attached Figure Description

[0014] Figure 1This is a schematic diagram of the structure of the 2P small distortion recognition lens provided in Embodiment 1 of the present invention; Figure 2 The MTF performance diagram of the 2P small distortion recognition lens provided in Embodiment 1 of the present invention; Figure 3 The MTF defocus curve of the 2P small distortion recognition lens provided in Embodiment 1 of the present invention; Figure 4 The field curvature distortion diagram of the 2P small distortion recognition lens provided in Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the structure of the 2P small distortion recognition lens provided in Embodiment 2 of the present invention; Figure 6 The MTF performance diagram of the 2P small distortion recognition lens provided in Embodiment 2 of the present invention; Figure 7 The MTF defocus curve of the 2P small distortion recognition lens provided in Embodiment 2 of the present invention; Figure 8 The field curvature distortion diagram of the 2P small distortion recognition lens provided in Embodiment 2 of the present invention; Figure 9 This is a schematic diagram of the structure of the 2P small distortion recognition lens provided in Embodiment 3 of the present invention; Figure 10 The MTF performance diagram of the 2P small distortion recognition lens provided in Embodiment 3 of the present invention; Figure 11 The MTF defocus curve of the 2P small distortion recognition lens provided in Embodiment 3 of the present invention; Figure 12 The field curvature distortion diagram of the 2P small distortion recognition lens provided in Embodiment 3 of the present invention; Figure 13 This is a schematic diagram of the structure of the 2P small distortion recognition lens provided in Embodiment 4 of the present invention; Figure 14 The MTF performance diagram of the 2P small distortion recognition lens provided in Embodiment 4 of the present invention; Figure 15 The MTF defocus curve of the 2P small distortion recognition lens provided in Embodiment 4 of the present invention; Figure 16 The field curvature distortion diagram of the 2P small distortion recognition lens provided in Embodiment 4 of the present invention; Figure 17 This is a schematic diagram of the structure of the 2P small distortion recognition lens provided in Embodiment 5 of the present invention; Figure 18 The MTF performance diagram of the 2P small distortion recognition lens provided in Embodiment 5 of the present invention; Figure 19 The MTF defocus curve of the 2P small distortion recognition lens provided in Embodiment 5 of the present invention; Figure 20 The field curvature distortion diagram of the 2P small distortion recognition lens provided in Embodiment 5 of the present invention; Figure 21 This is a schematic diagram of the structure of the 2P small distortion recognition lens provided in Embodiment 6 of the present invention; Figure 22 The MTF performance diagram of the 2P small distortion recognition lens provided in Embodiment 6 of the present invention; Figure 23 The MTF defocus curve of the 2P small distortion recognition lens provided in Embodiment 6 of the present invention; Figure 24 The field curvature distortion diagram of the 2P small distortion recognition lens provided in Embodiment 6 of the present invention; Figure 25 This is a schematic diagram of the structure of the 2P small distortion recognition lens provided in Embodiment 7 of the present invention; Figure 26 The MTF performance diagram of the 2P small distortion recognition lens provided in Embodiment 7 of the present invention; Figure 27 The MTF defocus curve of the 2P small distortion recognition lens provided in Embodiment 7 of the present invention; Figure 28 This is a field curvature distortion diagram of the 2P small distortion recognition lens provided in Embodiment 7 of the present invention.

[0015] The attached diagram lists the components represented by each number as follows: STO, aperture stop; L1, first lens; L2, second lens; IR, filter. Detailed Implementation

[0016] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0018] The existing technology suffers from the following problems: To simplify the structure, most 2P lenses employ a fully positive focal power distribution or a poorly symmetrical surface combination, resulting in significant pincushion distortion of the entire system; ordinary 2P lenses typically place the aperture stop close to the first lens element or omit the independent aperture stop, causing an excessively large principal ray angle (CRA) at the edge of the field of view. As a result, while the central area imaging is acceptable, the edge sharpness of the image drops sharply; conventional 2P lenses do not perform coordinated optimization for the visible and near-infrared bands, leading to a significant shift in the focal position under daytime (~550nm) and nighttime infrared illumination (such as 850nm / 940nm). This typically manifests as "sharp during the day and blurry at night," making it difficult to meet the needs of applications requiring stable operation around the clock, such as liveness detection, and severely restricting the practicality of the product and the user experience.

[0019] In view of this, the present invention provides a 2P small distortion recognition lens, comprising a first lens, an aperture stop, a second lens, and a filter arranged sequentially from the object side along the optical axis to the image side; the first lens is a negative lens with a concave surface near the optical axis on the object side and a convex surface near the optical axis on the image side; the second lens is a positive lens, specifically a biconvex lens; and the filter is a planar lens.

[0020] Furthermore, there is at least one inflection point on the off-axis position of the object-side surface of the first lens.

[0021] Furthermore, the off-axis position of the object-side surface of the first lens is 0.8D~0.89D, and the tangent angle is 45°-63°.

[0022] It should be noted that D here is the effective light transmission diameter, and the off-axis position of the object-side surface of the first lens is 0.8D~0.89D, which means that the off-axis position is within the range of 0.8D~0.89D.

[0023] Furthermore, the first lens element has a focal length of f1, and the lens focal length is f, satisfying the following conditions: 2.333>|f1 / f|>2.721.

[0024] Furthermore, the second lens element has a focal length of f2, and the lens focal length is f, satisfying the following conditions: 1.393 < |f2 / f| < 1.460.

[0025] Furthermore, 4. The thickness of the first lens core is T(L1), and the focal length of the first lens is f1, satisfying the following conditions: 0.242>|T(L1) / f1|>0.403.

[0026] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0027] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0028] Feature parameter description: T(L1) core thickness is the core thickness of the first lens (distance from the center point of L1S1 surface to the center point of L1S2 surface on the central optical axis). f is the lens focal length (focal length is a measure of the convergence or divergence of light in an optical system; it refers to the distance from the optical center of the lens to the focal point where parallel light converges when incident). f1 is the focal length of the first lens element; f2 is the focal length of the second lens element; DFOV is the field of view angle corresponding to the diagonal size of the chip (in optical instruments, the angle between the two edges of the maximum range through which the image of the target object can pass through the lens is called the field of view angle, with the lens of the optical instrument as the vertex). TTL is the total optical length of the lens optical system (the distance from the center point of the L1S1 plane to the center point of the image plane on the central optical axis). Optical DIS refers to optical distortion (optical distortion refers to the optically theoretical height of an ideal image). (θ) The ratio of the difference between the actual image height and the actual image height.

[0029] It should be noted that the full name of the modulation transfer function (MTF) is Modulation Transfer Function. MTF comprehensively reflects the contrast and resolution characteristics of a lens. It is measured by instruments, which can completely eliminate the influence of objective factors such as film and subjective factors of human interpretation.

[0030] MTF (Mean Transmission Factor) is one of the best tools for quantifying the overall imaging performance of a system in terms of resolution and contrast. A higher MTF value indicates a higher system resolution and the ability to convey finer details. MTF is a method of combining resolution and contrast into a single specification or rule. An MTF curve displays both resolution and contrast information simultaneously, allowing it to evaluate lenses according to the needs of a specific application and to compare the performance of multiple lenses.

[0031] The formula for aspherical surfaces is as follows:

[0032] Where Z represents the point on the aspherical surface at a distance h from the optical axis, and its relative distance to the tangent plane of the vertex on the optical axis, i.e., the sag; c represents the vertex curvature, which is the reciprocal of the radius of curvature R at the vertex (c=1 / R); h represents the distance between the point on the aspherical surface and the optical axis; k represents the conic coefficient; and Ai represents the i-th order aspherical coefficient. Substituting the aspherical coefficients of each surface into the aspherical formula in the embodiment yields the surface curve (structure), as illustrated in the embodiment's structural diagram.

[0033] Example 1 This embodiment provides a 2P small distortion recognition lens, the structural schematic diagram of which is shown below. Figure 1 As shown in Table 1, the lens data of the 2P small distortion recognition lens in Example 1 are shown in Table 1.

[0034] Table 1. Lens data of the 2P small distortion recognition lens provided in Example 1

[0035] The aspherical coefficients of the 2P small distortion recognition lens in Example 1 are shown in Table 2.

[0036] Table 2 Aspherical coefficients of the 2P small distortion recognition lens in Example 1

[0037] The characteristic parameter values ​​of the 2P small distortion recognition lens in Example 1 are shown in Table 3.

[0038] Table 3. Feature parameters of the 2P small distortion recognition lens in Example 1

[0039] Example 2 This embodiment provides a 2P small distortion recognition lens, the structural schematic diagram of which is shown below. Figure 5 As shown in Table 4, the lens data of the 2P small distortion recognition lens in Example 2 are shown in Table 4.

[0040] Table 4. Lens data of the 2P small distortion recognition lens provided in Example 2

[0041] The aspherical coefficients of the 2P small distortion recognition lens in Example 2 are shown in Table 5.

[0042] Table 5 Aspherical coefficients of the 2P small distortion recognition lens in Example 2

[0043] The characteristic parameter values ​​of the 2P small distortion recognition lens in Example 2 are shown in Table 6.

[0044] Table 6. Feature parameters of the 2P small distortion recognition lens in Example 2

[0045] Example 3 This embodiment provides a 2P small distortion recognition lens, the structural schematic diagram of which is shown below. Figure 9 As shown in Table 7, the lens data of the 2P small distortion recognition lens in Example 3 are shown in Table 7.

[0046] Table 7. Lens data of the 2P small distortion recognition lens provided in Example 3

[0047] The aspherical coefficients of the 2P small distortion recognition lens in Example 3 are shown in Table 8.

[0048] Table 8 Aspherical coefficients of the 2P small distortion recognition lens in Example 3

[0049] The characteristic parameter values ​​of Example 3 are shown in Table 9.

[0050] Table 9. Feature parameters of the 2P small distortion recognition lens in Example 3

[0051] Example 4 This embodiment provides a 2P small distortion recognition lens, the structural schematic diagram of which is shown below. Figure 13 As shown in Table 10, the lens data of the 2P small distortion recognition lens in Example 4 are shown in Table 10.

[0052] Table 10 Lens data of the 2P small distortion recognition lens provided in Example 4

[0053] The aspherical coefficients of the 2P small distortion recognition lens in Example 4 are shown in Table 11.

[0054] Table 11 Aspherical coefficients of the 2P small distortion recognition lens in Example 4

[0055] The characteristic parameter values ​​of Example 4 are shown in Table 12.

[0056] Table 12 Feature parameters of the 2P small distortion recognition lens in Example 4

[0057] Example 5 This embodiment provides a 2P small distortion recognition lens, the structural schematic diagram of which is shown below. Figure 17As shown in Table 13, the lens data of the 2P small distortion recognition lens in Example 5 are shown in Table 13.

[0058] Table 13 Lens data of the 2P small distortion recognition lens provided in Example 5

[0059] The aspherical coefficients of the 2P small distortion recognition lens in Example 5 are shown in Table 14.

[0060] Table 14 Aspherical coefficients of the 2P small distortion recognition lens in Example 5

[0061] The characteristic parameter values ​​of Example 5 are shown in Table 15.

[0062] Table 15 Feature parameters of the 2P small distortion recognition lens in Example 5

[0063] Example 6 This embodiment provides a 2P small distortion recognition lens, the structural schematic diagram of which is shown below. Figure 21 As shown in Table 16, the lens data of the 2P small distortion recognition lens in Example 6 are as follows.

[0064] Table 16 Lens data of the 2P small distortion recognition lens provided in Example 6

[0065] The aspherical coefficients of the 2P small distortion recognition lens in Example 6 are shown in Table 17.

[0066] Table 17 Aspherical coefficients of the 2P small distortion recognition lens in Example 6

[0067] The characteristic parameter values ​​of Example 6 are shown in Table 18.

[0068] Table 18 Feature parameters of the 2P small distortion recognition lens in Example 6

[0069] Comparative Example 1 This comparative example provides a 2P small distortion recognition lens, the structural schematic of which is shown below. Figure 25 As shown in Table 19, the lens data of the 2P small distortion recognition lens in Comparative Example 1 are shown in Table 19.

[0070] Table 19 shows the lens data of the 2P small distortion recognition lens provided in Comparative Example 1.

[0071] The aspherical coefficients of the 2P small distortion recognition lens in Comparative Example 1 are shown in Table 20.

[0072] Table 20 Aspherical coefficients of the 2P small distortion recognition lens in Comparative Example 1

[0073] The characteristic parameter values ​​of Comparative Example 1 are shown in Table 21.

[0074] Table 21 Feature parameters of the 2P small distortion recognition lens in Comparative Example 1

[0075] Figure 2 , Figure 6 Figure 10 , Figure 14 , Figure 18 , Figure 22 , Figure 26 The figures show the MTF performance of the 2P small distortion recognition lenses in Examples 1 to 6 and Comparative Example 1, respectively. The X and Y axes represent the following: the horizontal axis represents different spatial frequencies (0-66 lp / mm); the vertical axis represents the lens performance percentage from 0 to 100. A higher MTF curve indicates a higher lens MTF score and better performance. A higher density MTF curve score indicates a stronger ability of the lens to observe small objects.

[0076] The meanings of solid and dashed lines: Solid lines represent the MTF curve generated parallel to the diameter direction, called the sagittal curve; dashed lines represent the MTF curve generated perpendicular to the diameter direction, called the meridional curve. The closer the solid and dashed lines are, the closer the MTF performance of the lens is in the meridional and sagittal directions, and the better the lens performance.

[0077] Different solid / dashed line groups represent different field of view heights. A field of view height of 0 indicates the center of the lens. The larger the field of view height, the farther away from the center. The MTF performance of each line is closer, indicating good consistency between the center and the edge of the lens.

[0078] Figure 3 , Figure 7 Figure 11 , Figure 15 , Figure 19 , Figure 23 , Figure 27 The MTF defocus curves of the 2P small distortion recognition lens in Examples 1 to 6 and Comparative Example 1 are shown respectively. It can be seen that the more concentrated the curve is and the higher the peak value is, the better the corresponding lens imaging effect is.

[0079] Figure 4 , Figure 8 Figure 12 , Figure 16 , Figure 20 , Figure 24 , Figure 28 These are schematic diagrams showing the distortion and field curvature of light rays at any pupil of the 2P small distortion recognition lens in Examples 1 to 6 and Comparative Example 1, respectively. The diagrams show the distortion and field curvature of light rays at any pupil in any field of view defined by Wave. The field curvature diagram on the left shows the curve of the distance from the image plane to the paraxial image plane as a function of the field of view coordinates. The distortion diagram on the right shows the difference between the real image height and the ideal image height in each field of view. The closer to the center, the better the imaging effect.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0081] In summary, the technical solution of this application has the following beneficial technical effects: (1) In the technical solution of the present invention, the first lens adopts a paraxial concave-convex meniscus negative lens structure, and its object side can introduce higher-order aspherical terms in the off-axis region to generate reverse distortion; the second lens adopts a biconvex positive lens, which provides the main convergence capability and works together to correct field curvature and coma; the two together can effectively reduce the distortion of the entire field of view under the condition of using only two plastic lenses, and meet the application scenarios with high requirements for image geometric accuracy such as face recognition, liveness detection, and QR code recognition; (2) The front-mounted negative lens, combined with the centrally positioned aperture stop, helps to control the incident angle of the chief ray at the edge of the field of view, so that the chief ray angle (CRA) is well matched with the microlens array of the image sensor (especially back-illuminated BSI or global shutter CMOS), reducing edge illumination attenuation and color shift, and improving recognition stability.

Claims

1. A 2P small distortion recognition lens, characterized in that, It includes a first lens, an aperture stop, a second lens, and a filter arranged sequentially from the object side along the optical axis to the image side; The first lens is a negative lens with a concave surface near the optical axis on the object side and a convex surface near the optical axis on the image side; The second lens is a positive lens, specifically a biconvex lens; The filter is a plane lens.

2. The 2P small distortion recognition lens according to claim 1, characterized in that, There is at least one inflection point on the off-axis position of the object-side surface of the first lens.

3. The 2P small distortion recognition lens according to claim 1, characterized in that, The object-side surface of the first lens is located 0.8D to 0.89D off-axis, and the tangent angle is 45° to 63°.

4. The 2P small distortion recognition lens according to claim 1, characterized in that, The first lens element has a focal length of f1, and the lens focal length is f, satisfying the following conditions: 2.333>|f1 / f|>2.

721.

5. The 2P small distortion recognition lens according to claim 1, characterized in that, The second lens element has a focal length of f2, and the lens focal length is f, satisfying the following condition: 1.393 < |f2 / f| < 1.

460.

6. The 2P small distortion recognition lens according to claim 1, characterized in that, 4. The thickness of the first lens core is T(L1), and the focal length of the first lens is f1, satisfying the following conditions: 0.242>|T(L1) / f1|>0.403.

Images