Small volume long focal length infrared confocal optical lens

Abstract

The application discloses a small-size long-focal-length infrared confocal optical lens, which comprises first to fifth lenses L1 to L5 arranged in sequence along the light incidence direction, wherein the first lens L1 is a convex-concave plastic aspheric lens with negative focal power; the second lens L2 is a concave-convex plastic aspheric lens with positive focal power; the third lens L3 is a double-convex glass spherical lens with positive focal power; the fourth lens L4 is a double-convex plastic aspheric lens with positive focal power; the fifth lens L5 is a double-concave plastic aspheric lens with negative focal power, and the focal length of the lens satisfies 5.8mm<=f<=6.2mm. The lens can clearly image under visible light and near-infrared light, and is not out of focus under different temperature changes, which is helpful to improve the edge image quality, obtain high resolution and high imaging quality, and is small in size, low in cost, and suitable for complex environments and long-distance monitoring.

Description

Technical Field

[0001] This invention belongs to the field of optical lens technology, specifically relating to a small-volume, long-focal-length infrared confocal optical lens. Background Technology

[0002] With increasingly fierce market competition, lens miniaturization, multi-functionality, and strong environmental adaptability are the main development trends. In the security field, all-weather operation is a basic requirement for lenses. Currently, most lenses used in security systems have the following shortcomings: 1) Short focal length, making long-distance monitoring difficult; 2) F-numbers greater than 2.0, small aperture, low resolution, and significant temperature sensitivity, making them unsuitable for complex environments; 3) Severe purple fringing, poor edge field of view imaging, and poor day-night confocal performance. Furthermore, to improve performance, a larger number of lenses are often used to enhance image quality, but the complexity of the manufacturing process makes it difficult to guarantee manufacturing precision, thus affecting performance. They are also larger, more expensive, and easily limited by installation space. Therefore, it is essential to develop a lens that can operate normally day and night, is miniaturized, and can adapt to extreme environments. Summary of the Invention

[0003] The purpose of this invention is to address the above-mentioned problems by proposing a small-volume, long-focal-length infrared confocal optical lens that can clearly image under visible and near-infrared light, remains in focus within a temperature range of -30℃ to 70℃, and achieves high resolution by improving edge image quality. It has good image quality, small size, low cost, and is suitable for complex environments and long-distance monitoring.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] This invention proposes a small-volume, long-focal-length infrared confocal optical lens, comprising a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, and a fifth lens L5 arranged sequentially along the incident light direction, wherein:

[0006] The first lens L1 is a convex-concave plastic aspherical lens with negative optical power;

[0007] The second lens L2 is a concave-convex plastic aspherical lens with positive optical power;

[0008] The third lens L3 is a biconvex glass spherical lens with positive optical power;

[0009] The fourth lens, L4, is a biconvex plastic aspherical lens with positive optical power;

[0010] The fifth lens, L5, is a biconcave plastic aspherical lens with negative optical power;

[0011] The focal lengths of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are -11.2±5%, 205±5%, 11±5%, 5±5%, and -6.5±5%, respectively, and their refractive indices are 1.5±5%, 1.5±5%, 1.4±5%, 1.5±5%, and 1.6±5%, respectively. The object-side radius of curvature of the third lens L3 is 42±5%, and the image-side radius of curvature is -5.3±5%. "-" indicates a negative direction. The small-volume long-focal-length infrared confocal optical lens satisfies 5.8mm≤f≤6.2mm, where f is the lens focal length.

[0012] Preferably, the small-volume, long-focal-length infrared confocal optical lens also meets the following conditions:

[0013]

[0014] Where f1 is the focal length of the first lens L1, f2 is the focal length of the second lens L2, f4 is the focal length of the fourth lens L4, and f5 is the focal length of the fifth lens L5.

[0015] Preferably, the first lens L1, the second lens L2, the fourth lens L4, and the fifth lens L5 satisfy the aspherical equation:

[0016]

[0017] Where Z is the sagitta, c is the curvature, h is the radial coordinate, k is the conic conic coefficient, and α4, α6, α8, α... 10 α 12 α 14 α 16 These are higher-order coefficients for aspherical surfaces.

[0018] Preferably, the mirror surfaces of the first lens L1, the second lens L2, the fourth lens L4, and the fifth lens L5, distributed sequentially along the incident direction of light, have corresponding k values ​​of -0.5, -0.9, 28.8, -3.615, -12, -1, -1.5, and -0.3, respectively, and corresponding α4 values ​​of -4.6e-03, -5.8e-03, -2e-03, -3e-03, 9.9e-03, 2.7e-03, 0.018, and 0, respectively. The α6 values ​​corresponding to .015 are -2.8e-4, -3.8e-04, -8.6e-06, 1.2e-04, -1.9e-03, 2.9e-04, -1.9e-3, and -1.0e-03, respectively. The corresponding α8 values ​​are 9.5e-06, -1.6e-04, 5.5e-05, 5.7e-06, 2.9e-4, -1.6e-04, 8.3e-05, and 6.8e-05, respectively. 10The values ​​are 6.1e-07, 4.4e-05, 1.2e-06, 2.3e-07, -3.4e-05, 1.8e-05, 3.9e-06, and -2.4e-06, respectively, corresponding to α. 12 The values ​​are -1.3e-09, 1.8e-07, 2.0e-07, -1.5e-07, 2.5e-06, -9.2e-07, -1e-06, and -5.8e-7, corresponding to α. 14 The values ​​are 1.4e-10, -5.1e-07, 1.4e-07, 3.6e-08, -1e-07, 2.7e-08, 9.5e-08, and 7.6e-08, corresponding to α. 16 The values ​​are -1.8e-10, 1.9e-08, 1.0e-07, -1.5e-09, 1.7e-09, -8.6e-10, -3.5e-09, and -2.3e-09, respectively.

[0019] Preferably, the small-volume, long-focal-length infrared confocal optical lens satisfies the following:

[0020] TTL≤20.5mm

[0021] Where TTL stands for total optical length.

[0022] Preferably, the image side of the fifth lens L5 is provided with a filter IR.

[0023] Preferably, the small-volume long-focal-length infrared confocal optical lens also includes an aperture stop, which is located between the first lens L1 and the second lens L2.

[0024] Preferably, the working wavelength of the small-volume long-focal-length infrared confocal optical lens is visible light or 850±20nm near-infrared light.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The lens can clearly image under visible and near-infrared light. For example, the focal shift is less than 6μm under near-infrared light 850±20nm or visible light environment. Furthermore, the edge image quality is improved by reasonably allocating plastic aspherical lenses to avoid purple fringing. It has high resolution and good imaging quality, meets the clear imaging requirements of 2μm*2μm pixels, and ensures that the imaging resolution reaches 200lp / mm. The F number is 1.6 and the focal length is 5.8mm~6.2mm. It is suitable for long-distance monitoring and mass production.

[0027] (2) It adopts a 1G4P architecture, which is simple in structure and low in cost. By reasonably allocating the optical power, the lens structure is compact, which greatly reduces the sensitivity. It does not defocus in the range of -30℃ to 70℃ and is suitable for complex environments. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the optical structure of the present invention;

[0029] Figure 2 This is the MTF chart of Embodiment 1 of the present invention at a normal temperature of 20°C;

[0030] Figure 3 This is a defocusing curve of Embodiment 1 of the present invention at a low temperature of -30℃.

[0031] Figure 4 This is a defocusing curve of Embodiment 1 of the present invention under a high temperature environment of 70°C;

[0032] Figure 5 This is a defocus curve diagram of Embodiment 1 of the present invention under visible light conditions;

[0033] Figure 6 This is a defocus curve of Embodiment 1 of the present invention under 850nm near-infrared light environment;

[0034] Figure 7 This is the MTF chart of Embodiment 2 of the present invention at a normal temperature of 20°C;

[0035] Figure 8 This is a defocusing curve diagram of Embodiment 2 of the present invention at a low temperature of -30℃.

[0036] Figure 9 This is a defocusing curve diagram of Embodiment 2 of the present invention under a high temperature environment of 70°C;

[0037] Figure 10 This is a defocus curve diagram of Embodiment 2 of the present invention under visible light conditions;

[0038] Figure 11 This is a defocus curve of Embodiment 2 of the present invention under 850nm near-infrared light environment. Detailed Implementation

[0039] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0040] It should be noted that, 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 limit the scope of this application.

[0041] The symbols used in this application specification are defined as follows: r is the radius of curvature in mm, d is the thickness in mm, D is the effective aperture in mm, nd is the refractive index, vd is the Abbe number; R11 is the object-side surface of the first lens L1, R12 is the image-side surface of the first lens L1, R21 is the object-side surface of the second lens L2, R22 is the image-side surface of the second lens L2, R31 is the object-side surface of the third lens L3, R32 is the image-side surface of the third lens L3, R41 is the object-side surface of the fourth lens L4, R42 is the image-side surface of the fourth lens L4, R51 is the object-side surface of the fifth lens L5, R52 is the image-side surface of the fifth lens L5; Stop is the aperture stop; IR is the filter; IMAGE is the image plane, "-" indicates the negative direction.

[0042] like Figure 1 As shown, a small-volume long-focal-length infrared confocal optical lens includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, and a fifth lens L5 arranged sequentially along the incident light direction, wherein:

[0043] The first lens L1 is a convex-concave plastic aspherical lens with negative optical power;

[0044] The second lens L2 is a concave-convex plastic aspherical lens with positive optical power;

[0045] The third lens L3 is a biconvex glass spherical lens with positive optical power;

[0046] The fourth lens, L4, is a biconvex plastic aspherical lens with positive optical power;

[0047] The fifth lens, L5, is a biconcave plastic aspherical lens with negative optical power;

[0048] The focal lengths of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are -11.2±5%, 205±5%, 11±5%, 5±5%, and -6.5±5%, respectively, and their refractive indices are 1.5±5%, 1.5±5%, 1.4±5%, 1.5±5%, and 1.6±5%, respectively. The object-side radius of curvature of the third lens L3 is 42±5%, and the image-side radius of curvature is -5.3±5%. "-" indicates a negative direction. The small-volume long-focal-length infrared confocal optical lens satisfies 5.8mm≤f≤6.2mm, where f is the lens focal length.

[0049] When light is incident, it passes through the object side R11 of the first lens L1 and enters the image side R12, then along the object side R21 of the second lens L2 and enters the image side R22. The second lens L2 balances the spherical aberration generated by the first lens L1. After that, the light passes through the object side R31 of the third lens L3 and enters the image side R32. The third lens L3 is the only glass spherical lens in this lens, which can balance chromatic aberration and perform thermal compensation to control temperature drift. Then, the light passes through the object side R41 of the fourth lens L4 and enters the image side R42. This positive lens can effectively correct the off-axis aberrations generated by the first lens L1, the second lens L2, and the third lens L3. Finally, the light passes through the object side R51 of the fifth lens L5 and enters the image side R52, correcting the distortion of the entire system, improving edge image quality, avoiding purple fringing, and optimizing and balancing aberrations. This results in clearer and better image quality, meeting the clear image requirements of 2μm*2μm pixels and ensuring an image resolution of 200lp / mm. Furthermore, the focal shift of the positive and negative lenses varies with temperature. By rationally allocating the positive and negative optical power, temperature drift compensation is achieved, resulting in a heat-free design. The lens structure is compact, significantly reducing tolerance sensitivity. It remains in focus within a temperature range of -30℃ to 70℃, making the lens's performance more stable. This lens can produce clear images in visible and near-infrared light. For example, the focal shift is less than 6μm in near-infrared light (850±20nm) or visible light environments. It has an f / 1.6 aperture, a focal length of 5.8mm to 6.2mm, and adopts a 1G4P architecture. Its simple structure and low cost make it suitable for complex environments, long-distance monitoring, and mass production.

[0050] In one embodiment, the small-volume long-focal-length infrared confocal optical lens also satisfies the following condition:

[0051]

[0052] Where f1 is the focal length of the first lens L1, f2 is the focal length of the second lens L2, f4 is the focal length of the fourth lens L4, and f5 is the focal length of the fifth lens L5.

[0053] Among them, the sum of the optical power of the first lens L1, the second lens L2, the fourth lens L4, and the fifth lens L5, when meeting the above conditions, helps to ensure that the image is not in focus when the temperature is between -30℃ and +70℃, thus obtaining a more stable imaging effect and ensuring imaging quality.

[0054] In one embodiment, the first lens L1, the second lens L2, the fourth lens L4, and the fifth lens L5 satisfy the aspherical equation:

[0055]

[0056] Where Z is the sag, c is the curvature, h is the radial coordinate, k is the conic conic coefficient, and α4, α6, α8, α...10 α 12 α 14 α 16 These are higher-order coefficients for aspherical surfaces.

[0057] In one embodiment, the small-volume, long-focal-length infrared confocal optical lens satisfies:

[0058] TTL≤20.5mm

[0059] Where TTL stands for total optical length.

[0060] In one embodiment, the image side of the fifth lens L5 is provided with a filter IR.

[0061] Among them, the IR filter is located between the fifth lens L5 and the image plane IMAGE. During the day, it participates in the optical path imaging, filters out near-infrared light to reduce photoelectric noise, and allows near-infrared light to participate in imaging at night to enhance the photosensitivity and improve the image quality, thus achieving day and night confocal focus.

[0062] In one embodiment, the small-volume long-focal-length infrared confocal optical lens further includes an aperture stop, which is located between the first lens L1 and the second lens L2.

[0063] When light is incident, it passes through the object side R11 of the first lens L1 and enters the image side R12, where it is focused. After the light is limited by the stop aperture, it enters the image side R22 along the object side R21 of the second lens L2. This allows for adjustment of the light flux according to actual conditions to meet different needs.

[0064] In one embodiment, the small-volume long-focal-length infrared confocal optical lens operates in the visible light or 850±20nm near-infrared light band.

[0065] Example 1:

[0066] The lens parameters in this embodiment are shown in Table 1:

[0067] Table 1

[0068]

[0069]

[0070] Lens L1, lens L2, lens L4, and lens L5 are aspherical lenses, and the parameters of each aspherical lens satisfy Table 2:

[0071] Table 2

[0072] R11 -0.5 -4.6e-03 -2.8e-4 9.5e-06 6.1e-07 -1.3e-09 1.4e-10 -1.8e-10 R12 -0.9 -5.8e-03 -3.8e-04 -1.6e-04 4.4e-05 1.8e-07 -5.1e-07 1.9e-08 R21 28.8 -2e-03 -8.6e-06 5.5e-05 1.2e-06 2.0e-07 1.4e-07 1.0e-07 R22 -3.615 -3e-03 1.2e-04 5.7e-06 2.3e-07 -1.5e-07 3.6e-08 -1.5e-09 R41 -12 9.9e-03 -1.9e-03 2.9e-4 -3.4e-05 2.5e-06 -1e-07 1.7e-09 R42 -1 2.7e-03 2.9e-04 -1.6e-04 1.8e-05 -9.2e-07 2.7e-08 -8.6e-10 R51 -1.5 0.018 -1.9e-3 8.3e-05 3.9e-06 -1e-06 9.5e-08 -3.5e-09 R52 -0.3 0.015 -1.0e-03 6.8e-05 -2.4e-06 -5.8e-7 7.6e-08 -2.3e-09

[0073] Based on the above data, by Figure 2As shown, this lens meets the requirement of clear imaging of 2µm*2µm pixels at the extreme resolution of 200lp / mm. Figure 2 , 3 As shown in Figure 4, this lens exhibits a 3μm MTF defocus under extreme conditions ranging from 20℃ to -30℃ and 70℃, with minimal impact on image quality. It demonstrates strong temperature adaptability and stable performance under varying temperatures. Figure 5 , Figure 6 As shown, the focus shift is less than 6μm under visible light or 850nm near-infrared light conditions, resulting in excellent image quality. This lens produces clear images in visible light, at night, and in low-light conditions. The lens has a total optical length (TTL) of 20.5mm, a compact structure, a larger aperture, an F-number of 1.6, and a longer focal length of up to 6mm.

[0074] Example 2:

[0075]

[0076]

[0077] Lens L1, lens L2, lens L4, and lens L5 are aspherical lenses, and the parameters of each aspherical lens satisfy Table 2:

[0078] Table 2

[0079] R11 -0.5 -4.6e-03 -2.8e-4 9.5e-06 6e-07 -1.3e-09 1.4e-10 -1.8e-10 R12 -0.9 -5.8e-03 -3.8e-04 -1.6e-04 4.4e-05 1.8e-07 -5.1e-07 1.9e-08 R21 28.8 -2e-03 -8.4e-06 5.5e-05 1.2e-06 2.0e-07 1.4e-07 1.0e-07 R22 -3.615 -3e-03 1.1e-04 5.7e-06 2.3e-07 -1.5e-07 3.6e-08 -1.5e-09 R41 -12 9.9e-03 -1.9e-03 2.9e-4 -3.4e-05 2.5e-06 -1e-07 1.71e-09 R42 -1 2.7e-03 2.9e-04 -1.6e-04 1.8e-05 -9.2e-07 2.7e-08 -8.59e-10 R51 -1.5 0.018 -1.9e-3 8.2e-05 3.9e-06 -1e-06 9.5e-08 -3.48e-09 R52 -0.3 0.015 -1.0e-03 6.9e-05 -2.4e-06 -5.8e-7 7.6e-08 -2e-09

[0080] Based on the above data, by Figure 7 As shown, this lens meets the requirement of clear imaging of 2µm*2µm pixels at the extreme resolution of 200lp / mm. Figure 7 , 8 As shown in Figure 9, this lens exhibits a 3μm MTF defocus under extreme conditions ranging from 20℃ to -30℃ and 70℃, with minimal impact on image quality. It demonstrates strong temperature adaptability and stable performance under varying temperatures. Figure 10 , Figure 11 As shown, the focus shift is less than 6μm under visible light or 850nm near-infrared light conditions, resulting in excellent image quality. This lens produces clear images in visible light, at night, and in low-light conditions. The lens has a total optical length (TTL) of 20.48mm, a compact structure, a larger aperture, an F-number of 1.6, and a longer focal length of up to 6mm.

[0081] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0082] The embodiments described above are merely specific and detailed examples of the embodiments described in this application, and should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A compact, long-focal-length infrared confocal optical lens, characterized in that: The small-volume long-focal-length infrared confocal optical lens includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, and a fifth lens L5 arranged sequentially along the light incident direction, wherein: The first lens L1 is a convex-concave plastic aspherical lens with negative optical power; The second lens L2 is a concave-convex plastic aspherical lens with positive optical power; The third lens L3 is a biconvex glass spherical lens with positive optical power; The fourth lens L4 is a biconvex plastic aspherical lens with positive optical power; The fifth lens L5 is a biconcave plastic aspherical lens with negative optical power; The focal lengths of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are -11.2±5%, 205±5%, 11±5%, 5±5%, and -6.5±5%, respectively, and their refractive indices are 1.5±5%, 1.5±5%, 1.4±5%, 1.5±5%, and 1.6±5%, respectively. The object-side radius of curvature of the third lens L3 is 42±5%, and the image-side radius of curvature is -5.3±5%. "-" indicates a negative direction. The small-volume long-focal-length infrared confocal optical lens satisfies 5.8 mm≤f≤6.2 mm, where f is the lens focal length. The small-volume, long-focal-length infrared confocal optical lens also meets the following conditions: Wherein, f1 is the focal length of the first lens L1, f2 is the focal length of the second lens L2, f4 is the focal length of the fourth lens L4, and f5 is the focal length of the fifth lens L5. The thicknesses of the first lens L1, second lens L2, third lens L3, fourth lens L4, and fifth lens L5 are 1.577 mm, 2.685 mm, 3.154 mm, 2.787 mm, and 1.4 mm, respectively. The air gap between the first lens L1 and the second lens L2 is 2.231 mm, the air gap between the second lens L2 and the third lens L3 is 0.293 mm, the air gap between the third lens L3 and the fourth lens L4 is 0.593 mm, and the air gap between the fourth lens L4 and the fifth lens L5 is 0.31 mm. 6mm; or, the thicknesses of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L are 1.58mm, 2.68mm, 3.1mm, 2.7mm, and 1.44mm respectively, the air gap between the first lens L1 and the second lens L2 is 2.21mm, the air gap between the second lens L2 and the third lens L3 is 0.27mm, the air gap between the third lens L3 and the fourth lens L4 is 0.6mm, and the air gap between the fourth lens L4 and the fifth lens L5 is 0.32mm; The small-volume, long-focal-length infrared confocal optical lens satisfies the following requirements: TTL≤20.5mm Where TTL stands for total optical length.

2. The small-volume, long-focal-length infrared confocal optical lens as described in claim 1, characterized in that: The first lens L1, the second lens L2, the fourth lens L4, and the fifth lens L5 satisfy the aspherical equation: Where Z is the sagitta, c is the curvature, h is the radial coordinate, k is the conic conic coefficient, and α4, α6, α8, α... 10 α 12 α 14 α 16 These are higher-order coefficients for aspherical surfaces.

3. The small-volume, long-focal-length infrared confocal optical lens as described in claim 2, characterized in that: The mirror surfaces on the first lens L1, the second lens L2, the fourth lens L4, and the fifth lens L5, distributed sequentially along the incident direction of light, have k values ​​of -0.5, -0.9, 28.8, -3.615, -12, -1, -1.5, and -0.3, respectively, and α4 values ​​of -4.6e-03, -5.8e-03, -2e-03, -3e-03, 9.9e-03, 2.7e-03, 0.018, and 0, respectively. The corresponding α6 values ​​for 015 are -2.8e-4, -3.8e-04, -8.6e-06, 1.2e-04, -1.9e-03, 2.9e-04, -1.9e-3, and -1.0e-03, respectively. The corresponding α8 values ​​are 9.5e-06, -1.6e-04, 5.5e-05, 5.7e-06, 2.9e-4, -1.6e-04, 8.3e-05, and 6.8e-05, respectively. 10 The values ​​are 6.1e-07, 4.4e-05, 1.2e-06, 2.3e-07, -3.4e-05, 1.8e-05, 3.9e-06, and -2.4e-06, respectively, corresponding to α. 12 The values ​​are -1.3e-09, 1.8e-07, 2.0e-07, -1.5e-07, 2.5e-06, -9.2e-07, -1e-06, and -5.8e-7, corresponding to α. 14 The values ​​are 1.4e-10, -5.1e-07, 1.4e-07, 3.6e-08, -1e-07, 2.7e-08, 9.5e-08, and 7.6e-08, corresponding to α. 16 The values ​​are -1.8e-10, 1.9e-08, 1.0e-07, -1.5e-09, 1.7e-09, -8.6e-10, -3.5e-09, and -2.3e-09, respectively.

4. The small-volume, long-focal-length infrared confocal optical lens as described in claim 1, characterized in that: The fifth lens L5 has an IR filter on its image side.

5. The small-volume, long-focal-length infrared confocal optical lens as described in claim 1, characterized in that: The small-volume long-focal-length infrared confocal optical lens also includes an aperture stop, which is located between the first lens L1 and the second lens L2.

6. The small-volume, long-focal-length infrared confocal optical lens as described in claim 1, characterized in that: The small-volume long-focal-length infrared confocal optical lens operates in the visible light or 850±20nm near-infrared light band.

Images