Low-cost large target surface long-wave athermal all-sulfur lens

Abstract

The present application relates to an optical lens, in particular to a low-cost large target surface long-wave athermal full-sulfur lens, aiming to solve the problem that the existing long-wave infrared lens relies on single crystal germanium, resulting in high cost, and the existing three-piece or four-piece structure is difficult to balance high transmittance, large target surface high imaging quality and compact athermal design. The present application comprises a first lens, a second lens, a diaphragm, a third lens and a fourth lens arranged in turn along the direction of propagation of incident light; the four lenses are all meniscus lenses with convex surfaces facing the object side, and the optical power is positive, negative, positive and negative in turn. The low-cost large target surface long-wave athermal full-sulfur lens provided by the present application relies on a four-piece compact optical architecture, combines the mixed design of aspheric surface and binary diffractive surface, effectively corrects the off-axis aberration caused by large target surface imaging, and has the comprehensive advantages of wide temperature range adaptation, high resolution and compact structure.

Description

Technical Field

[0001] This invention relates to an optical lens, specifically to a low-cost, large-area, long-wavelength, thermal-free, all-sulfur lens. Background Technology

[0002] With the continuous evolution of uncooled long-wave infrared detector technology, the pixel size of detectors is constantly shrinking and the array size is continuously expanding. This places higher demands on the resolution, light transmission, and thermal stability of the accompanying optical lenses in imaging systems. At the same time, the commercial aerospace sector's spaceborne Earth observation and rocket-borne telemetry missions have increasingly urgent needs for miniaturization, weight reduction, and wide-temperature adaptability of infrared optical payloads. Meanwhile, civilian applications such as security monitoring, intelligent driving assistance, and industrial thermal imaging are also placing higher standards on the low-light detection capabilities and imaging clarity of infrared lenses.

[0003] However, existing long-wave infrared optical lenses still have many shortcomings in meeting the above comprehensive requirements:

[0004] 1) In terms of material selection, most existing lenses use single-crystal germanium as the lens material, which has a refractive index temperature coefficient as high as 4×10⁻⁶. -4 / ℃, changes in ambient temperature will cause significant thermal drift of the focal plane, requiring the introduction of a mechanical focusing module or an active temperature control module for compensation, which can easily increase the size, weight, and power consumption of the entire imaging system. For example, Chinese patent CN218824938U discloses a four-element high-resolution infrared athermalized lens, whose lenses rely on expensive single-crystal germanium material (as stated in paragraph

[0039] of its specification: at least one of the four lenses is made of chalcogenide glass; the remaining lenses are all made of germanium material). This results in high lens material costs.

[0005] 2) At the structural design level, to achieve high-resolution imaging of large target surfaces and correct off-axis aberrations, mainstream imaging systems typically use five or more lenses, which easily leads to excessive axial dimensions and reduced energy transmittance. Existing three- or four-lens solutions also have many shortcomings. For example, Chinese patent CN103941378A discloses a three-lens refractive-diffraction hybrid optical system based on all-chalcogenide glass. While it utilizes chalcogenide glass for low-cost molding, its three-lens structure limits the size of the matched detector target surface, making it difficult to meet the current needs of large target surfaces and small pixel detectors. Chinese patent CN218824938U discloses an infrared athermalized lens adapted to 4K resolution components. Although its four-lens solution improves resolution, the edge field-of-view image quality still tends to deteriorate when matched with small pixel detectors. Furthermore, its power distribution makes it difficult to simultaneously improve half-image height and image quality while maintaining a compact structure, failing to fully utilize the imaging potential of high-resolution detectors. Summary of the Invention

[0006] The purpose of this invention is to solve the problem that existing long-wave infrared lenses rely heavily on single-crystal germanium materials, resulting in high costs, and the problem that existing three-element or four-element lens structures cannot achieve a good balance between high transmittance, large target area, high imaging quality, and compact calorimetric design. The invention provides a low-cost, large-target area, long-wave calorimetric, calorimetric all-sulfur lens.

[0007] The concept of this invention is to achieve a low-cost, large-target-area long-wave infrared optical lens using only two types of chalcogenide glass and a four-element structure. By rationally allocating the optical power of each lens and introducing aspherical and diffractive surfaces, large-target-area detector adaptation and passive, thermal optical transformation can be achieved simultaneously with only four lenses.

[0008] To achieve the above objectives and complete the above concepts, the technical solution provided by this invention is as follows:

[0009] A low-cost, large-area, long-wavelength, thermal-free, all-chalcogenide lens, its special feature is:

[0010] The system includes a first lens, a second lens, an aperture, a third lens, and a fourth lens arranged sequentially along the direction of incident light propagation. Air gaps are provided between each pair of the first lens, second lens, aperture, third lens, and fourth lens, with each air gap referring to a gap located on the central axis of the lens or aperture. The light incident surface of the first lens, second lens, third lens, and fourth lens is defined as the object-side surface, and the light exit surface is defined as the image-side surface. The first lens is a meniscus lens with positive optical power and a convex surface facing the object-side direction, its object-side surface being an even-order aspherical surface, and its image-side surface being a spherical surface. The second lens is a meniscus lens with negative optical power and a convex surface facing the object-side direction, its object-side surface being a spherical surface, and its image-side surface being an even-order aspherical surface. The third lens is a meniscus lens with positive optical power and a convex surface facing the object-side direction, its object-side surface being a binary diffraction surface, and its image-side surface being a spherical surface. The fourth lens is a meniscus lens with negative optical power and a convex surface facing the object-side direction, its object-side surface being an even-order aspherical surface, and its image-side surface being an even-order aspherical surface.

[0011] Furthermore, the object-side radius of curvature R1o of the first lens satisfies: 38.55mm≤R1o≤40.85mm; the image-side radius of curvature R1i satisfies: 122.15mm≤R1i≤125.19mm; the object-side radius of curvature R2o of the second lens satisfies: 215.25mm≤R2o≤217.35mm; the image-side radius of curvature R2i satisfies: 30.05mm≤R2i≤32.12mm; the object-side radius of curvature R3o of the third lens satisfies: 34.40mm≤R3o≤36.45mm; the image-side radius of curvature R3i satisfies: 94.92mm≤R3i≤96.97mm; the object-side radius of curvature R4o of the fourth lens satisfies: 159.43mm≤R4o≤165.55mm; the image-side radius of curvature R4i satisfies: 32.12mm≤R4i≤44.15mm.

[0012] Furthermore, the first lens, the third lens, and the fourth lens are all made of IRG206; the second lens is made of IRG202.

[0013] Furthermore, the air gap between the first lens and the second lens is 1.50mm~1.77mm; the air gap between the second lens and the aperture is 6.90mm~7.17mm; the air gap between the aperture and the third lens is 12.05mm~12.35mm; and the air gap between the third lens and the fourth lens is 9.05mm~9.55mm.

[0014] Furthermore, the center thickness of the first lens is 6.12mm~6.78mm, the center thickness of the second lens is 6.10mm~6.75mm, the center thickness of the third lens is 8.60mm~9.10mm, and the center thickness of the fourth lens is 7.11mm~7.81mm.

[0015] Furthermore, the aspherical coefficients α4, α6, α8, and α on the side surface of the first lens are... 10 The values ​​are -8.57e-7, -3.83e-9, 4.44e-12, and -8.69e-014, respectively; the aspherical coefficients α4, α6, α8, and α5 on the image-side surface of the second lens are respectively. 10 The values ​​are -1.21e-6, -3.68e-8, 1.75e-10, and -6.58e-13, respectively; the aspherical coefficients α4, α6, α8, and α5 on the object side of the third lens are respectively. 10 The diffraction orders are 6.38e-7, 3.37e-10, -4.30e-12, and 1.36e-15, respectively; the diffraction order M=1; and the diffraction surface coefficients A1 and A2 are -0.1 and -5.53e-5, respectively. The aspherical coefficients α4, α6, α8, and α... of the object side of the fourth lens are...10 The values ​​are 6.39e-7, 3.37e-10, -4.30e-12, and 1.36e-15, respectively; the aspherical coefficients α4, α6, α8, and α5 on the image side of the fourth lens are respectively. 10 The values ​​are 5.07e-6, -2.34e-8, 6.45e-10, and 4.39e-12, respectively.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects:

[0017] 1. The low-cost, large-area, long-wavelength, athermalized, all-chalcogenide lens provided by this invention relies on a compact four-element optical architecture, combined with a hybrid design of aspherical and binary diffraction surfaces, to effectively correct off-axis aberrations caused by large-area imaging. While achieving a 35mm focal length and a large F / 1.0 aperture, the half-image height reaches 9.84mm, significantly better than the current mainstream 4.92mm specification, perfectly matching a large-area detector with a 1280×1024 resolution and a 12μm pixel size. In the 8μm~12μm band at a Nyquist frequency of 42lp / mm, the MTF value across the entire field of view is better than 0.3, combining the advantages of a wide temperature range, high resolution, and compact structure.

[0018] 2. The low-cost, large-area, long-wavelength, athermalized all-chalcogenide lens provided by this invention innovatively adopts all-chalcogenide glass materials (IRG202, IRG206), achieving a passive, athermalized optical design. Within a wide temperature range of -40℃ to +60℃, it maintains image plane stability without mechanical focusing or active temperature control, effectively reducing system size, weight, and power consumption, and significantly improving environmental adaptability and overall reliability.

[0019] 3. The low-cost, large-area, long-wavelength, thermally calcified all-chalcogenide lens provided by this invention uses all-chalcogenide glass to replace traditional germanium materials, with raw material costs only about one-third of those of germanium. Furthermore, thanks to the physical properties of all-chalcogenide glass, each lens can be directly adapted to mature precision molding processes. Compared to traditional single-point diamond turning processes, processing efficiency can be increased by more than ten times, significantly reducing mass production costs and substantially improving product consistency and stability. This invention maintains excellent imaging quality while possessing significant material and manufacturing cost advantages, providing a cost-effective technical path for the large-scale industrial application of high-performance infrared lenses.

[0020] 4. The low-cost, large-area, long-wavelength, athermalized, all-sulfur lens provided by this invention has the combined advantages of large aperture, high resolution, stable athermalized imaging over a wide temperature range, compact and lightweight structure, and mass production capability. It can be widely used in diverse scenarios such as security monitoring, intelligent driving assistance, industrial thermal imaging, and spaceborne / rocket-borne telemetry in the commercial aerospace field, and has broad market application prospects. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of an embodiment of the low-cost, large-area, long-wavelength, thermal, all-chalcogenide lens of the present invention;

[0022] Figure 2 This is an optical transfer function (OTF) graph of a low-cost, large-area, long-wavelength, athermalized, all-sulfur lens embodiment of the present invention at room temperature (20°C). The horizontal axis represents the spatial frequency in periods / mm, and the vertical axis represents the OTF (Optical Transfer Function) modulus, which is dimensionless.

[0023] Figure 3 The image shows a dot plot at room temperature (20°C) for an embodiment of the low-cost, large-area, long-wavelength, thermal, all-sulfur lens of the present invention. (a) is the dot plot at the center of the image plane (image height 0.000 mm), (b) is the dot plot at the image height 4.920 mm, (c) is the dot plot at the image height 6.880 mm, and (d) is the dot plot at the maximum image height 9.840 mm.

[0024] Figure 4 The optical system field curve and distortion curve of the embodiment of the low-cost, large-area, long-wavelength, athermalized, all-sulfur lens of the present invention at room temperature (20°C) are shown. Among them, (a) is the field curve, where the horizontal axis represents the focal offset in mm and the vertical axis represents the field of view in degrees; (b) is the distortion curve, where the horizontal axis represents the distortion rate as a percentage and the vertical axis represents the field of view in degrees.

[0025] Figure 5 This is a geometric ingress energy diagram at room temperature (20°C) for an embodiment of the low-cost, large-area, long-wavelength, thermal, all-sulfur lens of the present invention. The horizontal axis represents the radius from the center of the spot, in μm; the vertical axis represents the ingress energy fraction (i.e., the proportion of energy falling within the circle of that radius to the total energy), which is dimensionless.

[0026] Figure 6 The optical transfer function (OTF) graph of the low-cost, large-area, long-wavelength, athermalized, all-sulfur lens embodiment of the present invention is shown at -40°C. The horizontal axis represents the spatial frequency in periods / mm, and the vertical axis represents the OTF (Optical Transfer Function) modulus, which is dimensionless.

[0027] Figure 7 The image shows a dot plot at -40°C for an embodiment of the low-cost, large-area, long-wavelength, thermal, all-sulfur lens of the present invention. (a) is the dot plot at the center of the image plane (image height 0.000 mm), (b) is the dot plot at the image height 4.920 mm, (c) is the dot plot at the image height 6.880 mm, and (d) is the dot plot at the maximum image height 9.840 mm.

[0028] Figure 8 The optical system field curve and distortion curve of the embodiment of the low-cost, large-area, long-wavelength, athermalized, all-sulfur lens of the present invention at -40℃ are shown; where (a) is the field curve, the horizontal axis represents the focal offset in mm, and the vertical axis represents the field of view in degrees; (b) is the distortion curve, the horizontal axis represents the distortion rate as a percentage, and the vertical axis represents the field of view in degrees.

[0029] Figure 9 This is a geometric ingress energy diagram at -40℃ for an embodiment of the low-cost, large-area, long-wavelength, athermalized, all-sulfur lens of the present invention. The horizontal axis represents the radius from the center of the spot, in μm; the vertical axis represents the ingress energy fraction (i.e., the proportion of energy falling within the circle of that radius to the total energy), which is dimensionless.

[0030] Figure 10 The optical transfer function (OTF) graph of the low-cost, large-area, long-wavelength, athermalized, all-sulfur lens embodiment of the present invention is shown at 60°C. The horizontal axis represents the spatial frequency in periods / mm, and the vertical axis represents the OTF (Optical Transfer Function) modulus, which is dimensionless.

[0031] Figure 11 The image shows a dot plot at 60°C for an embodiment of the low-cost, large-area, long-wavelength, thermal, all-sulfur lens of the present invention. (a) is the dot plot at the center of the image plane (image height 0.000 mm), (b) is the dot plot at the image height 4.920 mm, (c) is the dot plot at the image height 6.880 mm, and (d) is the dot plot at the maximum image height 9.840 mm.

[0032] Figure 12 The optical system field curve and distortion curve of the embodiment of the low-cost, large-area, long-wavelength, athermalized, all-sulfur lens of the present invention at 60°C are shown; where (a) is the field curve, the horizontal axis represents the focal offset in mm, and the vertical axis represents the field of view in degrees; (b) is the distortion curve, the horizontal axis represents the distortion rate as a percentage, and the vertical axis represents the field of view in degrees.

[0033] Figure 13 This is a geometric ingress energy diagram at 60°C for an embodiment of the low-cost, large-area, long-wavelength, thermal, all-sulfur lens of the present invention. The horizontal axis represents the radius from the center of the spot, in μm; the vertical axis represents the ingress energy fraction (i.e., the proportion of energy falling within the circle of that radius to the total energy), which is dimensionless.

[0034] The annotations in the attached figures are explained as follows:

[0035] 1-First lens, 2-Second lens, 3-Third lens, 4-Fourth lens. Detailed Implementation

[0036] To make the objectives, advantages, and features of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0037] like Figure 1 As shown, this embodiment provides a low-cost, large-area, long-wavelength, athermalized, all-sulfur lens, which includes a first lens 1, a second lens 2, an aperture stop, a third lens 3, and a fourth lens 4 arranged sequentially along the incident light propagation direction; each of the first lens 1, the second lens 2, the aperture stop, the third lens 3, and the fourth lens 4 is provided with its own air gap, which refers to the gap located on the central axis of the lens or the aperture stop.

[0038] The light incident surfaces of the first lens 1, the second lens 2, the third lens 3, and the fourth lens 4 are defined as the object-side surfaces, and the light exit surfaces are defined as the image-side surfaces. The parameters of each lens are described in detail below.

[0039] The first lens 1 is a meniscus lens with positive optical power, a convex surface facing the object side, and made of IRG206 material. Its object side is an even-order aspherical surface, and its image side is a spherical surface. The radius of curvature R1o of the object side of the first lens 1 satisfies: 38.55mm≤R1o≤40.85mm; the radius of curvature R1i of the image side satisfies: 122.15mm≤R1i≤125.19mm; and the center thickness of the first lens 1 is 6.75mm.

[0040] The second lens 2 is a meniscus lens with negative optical power, a convex surface facing the object side, and made of IRG202. Its object side is spherical, and its image side is an even-order aspherical surface. The radius of curvature R2o of the object side of the second lens 2 satisfies: 215.25mm≤R2o≤217.35mm; the radius of curvature R2i of the image side satisfies: 30.05mm≤R2i≤32.12mm; and the center thickness of the second lens 2 is 6.4mm.

[0041] The third lens 3 is a meniscus lens with positive optical power, a convex surface facing the object side, and made of IRG206. Its object side is a binary diffraction surface, and its image side is a spherical surface. The radius of curvature R3o of the object side of the third lens 3 satisfies: 34.40mm≤R3o≤36.45mm; the radius of curvature R3i of the image side satisfies: 94.92mm≤R3i≤96.97mm; and the center thickness of the third lens 3 is 9.01mm.

[0042] The fourth lens 4 is a meniscus lens with negative optical power, convex surface facing the object side, and made of IRG206. Its object side surface is an even-order aspherical surface, and its image side surface is an even-order aspherical surface. The radius of curvature R4o of the object side surface of the fourth lens 4 satisfies: 159.43mm≤R4o≤165.55mm; the radius of curvature R4i of the image side surface satisfies: 32.12mm≤R4i≤44.15mm; the center thickness of the fourth lens 4 is 7.40mm.

[0043] The air gaps between the lenses are as follows:

[0044] The air gap between the first lens 1 and the second lens 2 is 1.71 mm; the distance between the second lens 2 and the third lens 3 is 19.50 mm; the air gap between the third lens 3 and the fourth lens 4 is 9.47 mm; and the total optical length of the fixed-focus optical system from the vertex of the object side of the first lens 1 to the image plane is 68.09 mm.

[0045] Table 1 shows the aspherical coefficients of the aspherical surfaces in the four lenses in this embodiment.

[0046] Table 1 Aspheric coefficients of the four lenses in this embodiment

[0047]

[0048] In the table above and throughout the text, "e" represents powers of 10. All aspherical surfaces conform to the following even-order aspherical formula:

[0049]

[0050] Where z is the sag of the aspherical surface at a height r perpendicular to the optical axis (i.e., the axial displacement of this point from the vertex of the aspherical surface); r is the perpendicular radial distance (aperture) from a point on the aspherical surface to the optical axis; c is the paraxial curvature at the vertex of the aspherical surface; k is the conic coefficient; α is the higher-order aspherical coefficient, whose values ​​are taken from the aspherical coefficient table; i is a positive integer representing the order number of the aspherical polynomial, α i For the 2ith order (i.e., r) 2i The even-order aspheric coefficients of the terms; 2i represents the higher powers of the aspheric terms, for example, when i=2, it corresponds to r 4 Term coefficient α 4 (i.e., the coefficients of the fourth-order terms in the table); ∑ is the summation symbol; N1 is the highest order of the aspherical surface involved in the optimization.

[0051] Specifically, the binary diffraction surface in the third lens adopts the binary surface model in the Zemax optical design software, and its phase distribution satisfies the following equation:

[0052]

[0053] in, The diffraction phase is represented by M, the diffraction order is represented by M=1 in this embodiment, ρ is the normalized radial aperture coordinate (i.e., the ratio of the distance from a point on the surface to the optical axis to the maximum aperture radius, dimensionless, ranging from 0 to 1), j is a positive integer representing the order number of the diffraction phase polynomial coefficients, and A is the diffraction phase polynomial coefficient. j ∑ represents the j-th order phase coefficient; ∑ is the summation symbol; N2 is the highest order of the diffraction phase involved in the optimization calculation.

[0054] In this embodiment, the diffraction plane coefficients are A1 = -0.1 and A2 = -5.53e-5, and the designed center wavelength is 10 μm. At this center wavelength, the optical refractive index of the substrate material (i.e., IRG206) is n = 2.7781. Furthermore, this binary diffraction plane contains a total of eight effective diffraction rings.

[0055] By setting up the aforementioned binary diffraction surface, the negative dispersion characteristics of the diffraction element are used to compensate for the positive dispersion of the lens material, effectively correcting the axial chromatic aberration and second-order spectrum of the optical system. At the same time, a portion of the optical power is allocated to the diffraction surface, further simplifying the lens structure and improving the imaging quality.

[0056] Depend on Figure 2 , Figure 6 and Figure 10 It can be seen that under normal temperature (20℃), low temperature (-40℃), and high temperature (60℃) conditions, the system's MTF value at the Nyquist frequency of 42 lp / mm is greater than 0.3 across the entire field of view. Figure 2 The MTF (Modulation Transfer Function) curves for each field of view approach the diffraction limit. This indicates that the present embodiment has good resolution over a wide temperature range and can be well matched with a high-resolution large-target detector with a 12μm pixel size.

[0057] Depend on Figure 3 , Figure 7 and Figure 11 It can be seen that under normal temperature (20℃), low temperature (-40℃), and high temperature (60℃) conditions, the RMS (root mean square) spot radius at each field of view is smaller than the Ally spot radius (approximately 12.86μm), and the maximum edge field of view RMS spot radius does not exceed 7.14μm. Figure 7 (In the middle). This demonstrates that the present embodiment has good aberration correction across the entire field of view and can achieve good matching with a large target detector with a 12μm pixel size.

[0058] Depend on Figure 4 , Figure 8 and Figure 12It can be seen that the maximum field curvature of the system is less than 0.08 mm and the maximum distortion rate is less than 0.7% under normal temperature (20℃), low temperature (-40℃) and high temperature (60℃) conditions. This indicates that the image plane of this embodiment is flat and the distortion is minimal, which can ensure that the large target detector can obtain high-fidelity infrared thermal images.

[0059] Depend on Figure 5 , Figure 9 and Figure 13 It can be seen that under normal temperature (20℃), low temperature (-40℃), and high temperature (60℃) conditions, the geometric ingress energy fraction of the system within a radius of 12μm (corresponding to a 12μm pixel size) all reaches above 0.8. This indicates that the system energy is highly concentrated within a single pixel, with extremely low inter-pixel crosstalk, and can fully utilize the detector's response capability.

[0060] In summary, this embodiment achieves optical passive calorimetry within a wide temperature range of -40℃ to +60℃, maintaining excellent imaging quality at both normal and extreme temperatures without the need for mechanical focusing or active temperature control. It also boasts significant advantages such as a large target area, low-cost manufacturing, and compact and lightweight design.

[0061] This invention utilizes a compact four-piece optical architecture, combining aspherical and binary diffraction surface designs to effectively correct off-axis aberrations caused by large target surface imaging. While achieving a 35mm focal length and a large F / 1.0 aperture, the half-image height reaches 9.84mm, significantly superior to the current mainstream 4.92mm specification, perfectly matching a large target surface detector with a 1280×1024 resolution and 12μm pixel size. In the 8μm~12μm band and at a Nyquist frequency of 42lp / mm, the MTF value across the entire field of view is better than 0.3, combining the advantages of wide temperature range adaptability, high resolution, and compact structure.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. A low-cost, large-area, long-wavelength, thermally unheated, all-chalcogenide lens, characterized in that: It includes a first lens (1), a second lens (2), an aperture, a third lens (3), and a fourth lens (4) arranged sequentially along the direction of incident light propagation; air gaps are provided between each pair of the first lens (1), the second lens (2), the aperture, the third lens (3), and the fourth lens (4), and the air gaps refer to the distances located on the central axis of the lens or the aperture; The light incident surface of the first lens (1), the second lens (2), the third lens (3), and the fourth lens (4) are defined as the object side surface, and the light exit surface is defined as the image side surface. The first lens (1) is a meniscus lens with positive optical power and a convex surface facing the object side direction. Its object side surface is an even-order aspherical surface, and its image side surface is a spherical surface. The second lens (2) is a meniscus lens with negative optical power and a convex surface facing the object side direction. Its object side surface is a spherical surface, and its image side surface is an even-order aspherical surface. The third lens (3) is a meniscus lens with positive optical power and a convex surface facing the object side direction. Its object side surface is a binary diffraction surface, and its image side surface is a spherical surface. The fourth lens (4) is a meniscus lens with negative optical power and a convex surface facing the object side direction. Its object side surface is an even-order aspherical surface, and its image side surface is an even-order aspherical surface.

2. The low-cost, large-area, long-wavelength, thermally calcareous, all-chalcogenide lens according to claim 1, characterized in that: The object-side radius of curvature R1o of the first lens (1) satisfies: 38.55mm≤R1o≤40.85mm; the image-side radius of curvature R1i satisfies: 122.15mm≤R1i≤125.19mm; The object-side radius of curvature R2o of the second lens (2) satisfies: 215.25mm≤R2o≤217.35mm; the image-side radius of curvature R2i satisfies: 30.05mm≤R2i≤32.12mm; The object-side radius of curvature R3o of the third lens (3) satisfies: 34.40mm≤R3o≤36.45mm; the image-side radius of curvature R3i satisfies: 94.92mm≤R3i≤96.97mm; The object-side radius of curvature R4o of the fourth lens (4) satisfies: 159.43mm≤R4o≤165.55mm; the image-side radius of curvature R4i satisfies 32.12mm≤R4i≤44.15mm.

3. The low-cost, large-area, long-wavelength, thermally calorimetric lens according to claim 2, characterized in that: The first lens (1), the third lens (3) and the fourth lens (4) are all made of IRG206; the second lens (2) is made of IRG202.

4. The low-cost, large-area, long-wavelength, thermally calorimetric lens according to claim 3, characterized in that: The air gap between the first lens (1) and the second lens (2) is 1.50mm~1.77mm; The air gap between the second lens (2) and the aperture is 6.90mm~7.17mm; The air gap between the aperture and the third lens (3) is 12.05mm~12.35mm; The air gap between the third lens (3) and the fourth lens (4) is 9.05mm to 9.55mm.

5. The low-cost, large-area, long-wavelength, thermally calorimetric lens according to claim 4, characterized in that: The center thickness of the first lens (1) is 6.12mm~6.78mm, the center thickness of the second lens (2) is 6.10mm~6.75mm, the center thickness of the third lens (3) is 8.60mm~9.10mm, and the center thickness of the fourth lens (4) is 7.11mm~7.81mm.

6. The low-cost, large-area, long-wavelength, thermally calcareous, all-chalcogenide lens according to claim 5, characterized in that: The aspherical coefficients α4, α6, α8, and α on the object side of the first lens (1) 10 The values ​​are -8.57e-7, -3.83e-9, 4.44e-12, and -8.69e-014, respectively. The aspherical coefficients α4, α6, α8, α on the image side of the second lens (2) 10 The values ​​are -1.21e-6, -3.68e-8, 1.75e-10, and -6.58e-13, respectively. The aspherical coefficients α4, α6, α8, and α of the object side of the third lens (3) are... 10 The diffraction orders are 6.38e-7, 3.37e-10, -4.30e-12, and 1.36e-15, respectively, with a diffraction order M=1 and diffraction surface coefficients A1 and A2 being -0.1 and -5.53e-5, respectively. The aspherical coefficients α4, α6, α8, and α of the object side of the fourth lens (4) 10 The values ​​are 6.39e-7, 3.37e-10, -4.30e-12, and 1.36e-15, respectively. The aspherical coefficients α4, α6, α8, and α on the image side of the fourth lens (4) 10 The values ​​are 5.07e-6, -2.34e-8, 6.45e-10, and 4.39e-12, respectively.

Images