Far infrared optical system and far infrared optical lens

Abstract

The utility model discloses a far infrared optical system and a far infrared optical lens. The far infrared optical system sequentially comprises a first aspheric lens, a super lens and a second aspheric lens from an object side to an image side along an optical axis, the focal power of the first aspheric lens is positive, and the object side surface and the image side surface of the first aspheric lens both protrude towards the object side; the focal power of the super lens is positive; the focal power of the second aspheric lens is positive. The far infrared optical system meets the condition that fa1 + fa2 is smaller than fm, fa1 is the focal length of the first aspheric lens, fa2 is the focal length of the second aspheric lens, and fm is the focal length of the super lens. The far-infrared optical system provided by the utility model is good in imaging quality, the number of lenses included in the far-infrared optical system is small, the size of the far-infrared optical system is small, and the production cost is low. In addition, the far-infrared optical system comprises the super lens, and the cost of a single super lens is low during batch production, so that the production cost of the far-infrared optical system can be further reduced.

Description

Technical Field

[0001] This application relates to the field of optical systems, and particularly to a far-infrared optical system and a far-infrared optical lens. Background Art

[0002] Far-infrared optical systems use far-infrared light for imaging, and far-infrared optical systems have been widely used in fields such as security and vehicle-mounted applications.

[0003] Improving the imaging quality has always been one of the development trends of far-infrared optical systems. Since the more lenses there are, the more complex optical designs can usually be achieved, and thus better imaging quality may be obtained. Therefore, increasing the number of lenses has become a common method to improve the imaging quality of far-infrared optical systems. However, increasing the number of lenses to improve the imaging quality will lead to an increase in the volume and production cost of the far-infrared optical system. Summary of the Utility Model

[0004] In view of the above technical problems, embodiments of this application provide a far-infrared optical system and a far-infrared optical lens, aiming to provide a far-infrared optical system and a far-infrared optical lens with better imaging quality, smaller volume, and lower production cost.

[0005] According to one aspect of the embodiments of this application, a far-infrared optical system is disclosed. The far-infrared optical system sequentially includes, along the optical axis from the object side to the image side: a first aspheric lens, a metasurface lens, and a second aspheric lens; the optical power of the first aspheric lens is positive, the object side surface of the first aspheric lens bulges towards the object side, and the image side surface of the first aspheric lens bulges towards the object side; the optical power of the metasurface lens is positive, the metasurface lens includes a substrate and a micro-nano structure, and the micro-nano structure is disposed on the object side surface and / or the image side surface of the substrate; the optical power of the second aspheric lens is positive;

[0006] The far-infrared optical system satisfies: f a1 +f a2 <f m wherein, the f a1 is the focal length of the first aspheric lens, the f a2 is the focal length of the second aspheric lens, and the f m is the focal length of the metasurface lens.

[0007] In some embodiments, the far-infrared optical system satisfies: wherein, the f is the effective focal length of the far-infrared optical system.

[0008] In some embodiments, the far-infrared optical system satisfies: Wherein, Sag1 is the distance between the first point and the second point on the optical axis. The first point is the intersection of the object side surface of the first aspherical lens and the optical axis, and the second point is the point on the image side surface of the first aspherical lens corresponding to the maximum optical diameter. If the second point is located on the object side of the first point, Sag1 is negative; if the second point is located on the image side of the first point, Sag1 is positive. R1 is the curvature radius of the object side surface of the first aspherical lens.

[0009] In some embodiments, the far-infrared optical system satisfies: Wherein, C 16 is the distance between the object side surface of the first aspherical lens and the image side surface of the second aspherical lens on the optical axis. BFL is the distance between the image side surface of the second aspherical lens and the image plane of the far-infrared optical system on the optical axis. FOV is the maximum field of view angle of the far-infrared optical system.

[0010] In some embodiments, the far-infrared optical system satisfies: Wherein, R1 is the curvature radius of the object side surface of the first aspherical lens, R2 is the curvature radius of the image side surface of the first aspherical lens, and FOV is the maximum field of view angle of the far-infrared optical system.

[0011] In some embodiments, the far-infrared optical system satisfies: CT1 is the central thickness of the first aspherical lens, and CT3 is the central thickness of the second aspherical lens.

[0012] In some embodiments, the far-infrared optical system satisfies: Wherein, f is the effective focal length of the far-infrared optical system, n is the refractive index of the first aspherical lens, FNO is the f-number of the far-infrared optical system, and R1 is the curvature radius of the object side surface of the first aspherical lens.

[0013] In some embodiments, the far-infrared optical system satisfies: Wherein, f is the effective focal length of the far-infrared optical system, and EPD is the entrance pupil diameter of the far-infrared optical system.

[0014] In some embodiments, the far-infrared optical system further includes a diaphragm, and the diaphragm is disposed on the object side of the first aspherical lens; or, the diaphragm is disposed between any two adjacent lenses.

[0015] In a second aspect of the embodiments of the present application, a far-infrared optical lens is provided. The far-infrared optical lens includes an imaging detector and the far-infrared optical system as described in any one of the above. The imaging detector is disposed on the image plane of the far-infrared optical system.

[0016] The far-infrared optical system provided by the present application sequentially includes, along the optical axis from the object side to the image side: a first aspherical lens, a metasurface lens, and a second aspherical lens. The optical power of the first aspherical lens is positive. The object side surface of the first aspherical lens bulges towards the object side, and the image side surface of the first aspherical lens bulges towards the object side. The optical power of the metasurface lens is positive. The metasurface lens includes a substrate and a micro-nano structure, and the micro-nano structure is disposed on the object side surface and / or the image side surface of the substrate. The optical power of the second aspherical lens is positive. The far-infrared optical system satisfies: f a1 +f a2 <f m , where f a1 is the focal length of the first aspherical lens, f a2 is the focal length of the second aspherical lens, and f m is the focal length of the metasurface lens. The far-infrared optical system provided by the present application has better imaging quality. Moreover, the far-infrared optical system contains fewer lenses, has a smaller volume, and lower production costs. The far-infrared optical system includes a metasurface lens, and the cost of a single metasurface lens is lower during mass production. Therefore, the production cost of the far-infrared optical system can be further reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] By referring to the accompanying drawings and describing its exemplary embodiments in detail, the above and other objects, features, and advantages of the present application will become more apparent.

[0018] Figure 1 FIG. shows a schematic diagram of the architecture layout of the far-infrared optical system in an embodiment of the present application.

[0019] Figure 2 FIG. shows the MTF field-of-view curve graph of the far-infrared optical system in an embodiment of the present application.

[0020] Figure 3 FIG. shows a schematic diagram of the architecture layout of the far-infrared optical system in an embodiment of the present application.

[0021] Figure 4 FIG. shows the MTF field-of-view curve graph of the far-infrared optical system in an embodiment of the present application.

[0022] Figure 5 FIG. shows a schematic diagram of the architecture layout of the far-infrared optical system in an embodiment of the present application.

[0023] Figure 6 FIG. shows the MTF field-of-view curve graph of the far-infrared optical system in an embodiment of the present application.

[0024] Figure 7 Shows the schematic diagram of the architecture layout of the far-infrared optical system in an embodiment of the present application.

[0025] Figure 8 Shows the MTF field-of-view curve graph of the far-infrared optical system in an embodiment of the present application.

[0026] Figure 9 Shows the schematic diagram of the architecture layout of the far-infrared optical system in an embodiment of the present application.

[0027] Figure 10 Shows the MTF field-of-view curve graph of the far-infrared optical system in an embodiment of the present application.

[0028] Reference numerals

[0029] 100, far-infrared optical system;

[0030] 10, first aspherical lens;

[0031] 20, metasurface lens; 210, substrate; 220, micro-nano structure;

[0032] 30, second aspherical lens;

[0033] 40, aperture stop;

[0034] 50, protective glass;

[0035] A, object plane; B, image plane; S, optical axis. Detailed implementation manners

[0036] Now, the example embodiments will be described more comprehensively with reference to the accompanying drawings. However, the example embodiments can be implemented in various forms and should not be construed as limited to the examples set forth herein; rather, these example embodiments are provided so that the description of the present application will be more comprehensive and complete, and the concept of the example embodiments will be fully conveyed to those skilled in the art. The accompanying drawings are only schematic diagrams of the present application and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and thus their repeated description will be omitted.

[0037] In addition, the described features, structures, or characteristics can be combined in any suitable manner in one or more example embodiments. In the following description, many specific details are provided to give a thorough understanding of the example embodiments of the present application. However, those skilled in the art will realize that the technical solutions of the present application can be practiced without one or more of the specific details, or other modules, components, etc. can be adopted. In other cases, well-known structures, methods, implementations, or operations are not shown or described in detail to avoid obscuring the various aspects of the present application.

[0038] Please refer to Figure 1 , Figure 1 which shows a schematic diagram of the architecture layout of the far-infrared optical system 100 in an embodiment of the present application. Among them, the optical axis S is the center line of the light beam. In Figure 1 , the object is located on the left side of the leftmost lens, that is, the object side is located on the left side of the leftmost lens, and the object plane A is located on the object side. The image formed by the far-infrared optical system 100 is located on the right side of the rightmost lens, that is, the image side is located on the right side of the rightmost lens, and the image plane B is located on the image side. Therefore, the direction from the object plane A to the image plane B along the optical axis S is the same as the direction from the object side to the image side along the optical axis S.

[0039] For the far-infrared optical system 100, the side close to the object side of each optical element is the object side of the corresponding optical element, and the side close to the image side of the far-infrared optical system 100 is the image side of the corresponding optical element. For example, the side close to the object side of the aperture 40 is the object side of the aperture 40. The surface of each optical element of the far-infrared optical system 100 close to the object side is the object side surface of the corresponding optical element, and the surface of each optical element of the far-infrared optical system 100 close to the image side is the image side surface of the corresponding optical element. For example, the surface of the aperture 40 close to the image side is the image side surface of the aperture 40.

[0040] The far-infrared optical system 100 includes a first aspherical lens 10, a meta-lens 20, and a second aspherical lens 30. The first aspherical lens 10, the meta-lens 20, and the second aspherical lens 30 are arranged in sequence along the direction from the object side to the image side of the optical axis S.

[0041] The optical power of the first aspherical lens 10 is positive. The object side surface of the first aspherical lens 10 bulges towards the object side, and the image side surface of the first aspherical lens 10 bulges towards the object side.

[0042] The optical power of the meta-lens 20 is positive. The meta-lens 20 includes a substrate 210 and a micro-nano structure 220. The micro-nano structure 220 is provided on the object side surface and / or the image side surface of the substrate 210. According to the adopted phase modulation method, the parameters of the micro-nano structure 220 can be configured adaptively using the corresponding phase modulation formula, so that the meta-lens 20 has the expected optical performance.

[0043] The optical power of the second aspherical lens 30 is positive.

[0044] The far-infrared optical system 100 satisfies Condition 1: f a1 +f a2 <f m , where f a1 is the focal length of the first aspherical lens 10, f a2 is the focal length of the second aspherical lens 30, and f mis the focal length of the metalens 20. From Equation (1), it can be known that the focal length of the metalens 20 is greater than the sum of the focal lengths of the first aspherical lens 10 and the second aspherical lens 30. That is, the metalens 20 mainly corrects the aberration of the entire field of view and the spherical aberration of the marginal field of view in the far-infrared optical system 100, so as to improve the imaging quality of the far-infrared optical system 100. Moreover, since the metalens 20 has negative dispersion, it has a good dispersion cancellation effect when combined with the first aspherical lens 10 and the second aspherical lens 30.

[0045] The far-infrared optical system 100 provided by this application has better imaging quality. Moreover, the far-infrared optical system 100 includes fewer lenses, has a smaller volume and lower production cost. The far-infrared optical system 100 includes a metalens 20. When mass-produced, the cost of a single metalens 20 is relatively low. Therefore, the production cost of the far-infrared optical system 100 can be further reduced.

[0046] Please refer to Figure 1 、 Figure 3 、 Figure 5 In some embodiments, the object side surface of the second aspherical lens 30 bulges towards the object side, and the image side surface of the second aspherical lens 30 bulges towards the object side.

[0047] Please refer to Figure 7 and Figure 9 In some embodiments, the object side surface of the second aspherical lens 30 bulges towards the object side, and the edge of the object side surface of the second aspherical lens 30 has an inflection point; the image side surface of the second aspherical lens 30 bulges towards the object side, and the edge of the image side surface of the second aspherical lens 30 has an inflection point.

[0048] Please refer to Figure 3 、 Figure 5 、 Figure 7 In some embodiments, the micro-nano structure 220 is disposed on the surface of the substrate 210 close to the object side.

[0049] Please refer to Figure 1 In some embodiments, the micro-nano structure 220 is disposed on the surface of the substrate 210 close to the image side.

[0050] Please refer to Figure 9 In some embodiments, the micro-nano structure 220 is disposed on both the surface of the substrate 210 close to the object side and the surface of the substrate 210 close to the image side, so that the metalens 1 has a high degree of design freedom.

[0051] In some embodiments, the micro-nano structure 220 is a positive micro-nano structure.

[0052] In some embodiments, the micro-nano structure 220 is a negative micro-nano structure.

[0053] In some embodiments, the micro-nano structure 220 is provided with a layer to make the processing technology of the superlens 1 compatible with the existing semiconductor processing technology, which is convenient for the processing and manufacturing of the superlens 1.

[0054] In some embodiments, the micro-nano structure 220 has two or more layers.

[0055] For the superlens 1, the side of the substrate 210 where the micro-nano structure 220 is disposed, the positive and negative of the micro-nano structure 220, and the number of layers of the micro-nano structure 220 can be freely combined as long as the superlens 1 has the expected optical performance.

[0056] In some embodiments, the far-infrared optical system 100 satisfies Conditional Equation Two: where f a1 is the focal length of the first aspherical lens 10, f a2 is the focal length of the second aspherical lens 30, f m is the focal length of the superlens 20, and f is the effective focal length of the far-infrared optical system 100. f, f a1 and f a2 and f m have the same dimension, which is a length unit, such as millimeters.

[0057] Conditional Equation Two reflects the focal length relationship of each lens in the far-infrared optical system 100. Through the constraint of Conditional Equation One, the optical power of the far-infrared optical system 100 can be reasonably distributed, which is beneficial to correcting the aberration in the far-infrared optical system 100 and reducing the optical sensitivity of the far-infrared optical system 100.

[0058] In some embodiments, the far-infrared optical system 100 satisfies Conditional Equation Three: where R1 is the radius of curvature of the object side surface of the first aspherical lens 10, Sag1 is the distance between the first point and the second point on the optical axis S, that is, Sag1 is the projection length of the line connecting the first point and the second point on the optical axis S. The first point is the intersection point of the object side surface of the first aspherical lens 10 and the optical axis S, and the second point is the point corresponding to the maximum optical diameter on the image side surface of the first aspherical lens 10. In this application, the maximum effective diameter of the object side surface of the lens refers to the diameter of the maximum light-transmitting area of the object side surface of the lens, and the maximum effective diameter of the image side surface of the lens refers to the diameter of the maximum light-transmitting area of the image side surface of the lens, and the same applies hereinafter. The value of Sag1 has positive and negative values, and the positive and negative value-taking rules of Sag1 are as follows: if the second point is located on the object side of the first point, Sag1 is negative, and if the second point is located on the image side of the first point, Sag1 is positive. Sag1 and R1 have the same dimension, which is a length unit, such as millimeters.

[0059] The upper limit of Conditional Equation 3 can prevent the shape of the first aspherical lens from being too curved. If the shape of the lens is too curved, it may lead to poor processability of the lens. That is, the upper limit of Conditional Equation 3 can ensure that the first aspherical lens has good processability, which is beneficial to the fabrication and molding of the first aspherical lens 10. The lower limit of Conditional Equation 3 is used to ensure that the first aspherical lens 10 has an appropriate thickness, can ensure that the first aspherical lens 10 has a certain strength, and at the same time can reduce the space occupied by the first aspherical lens 10, enabling the lens arrangement of the far-infrared optical system 100 to be relatively compact.

[0060] In some embodiments, the far-infrared optical system 100 satisfies Conditional Equation 4: where C 16 is the distance between the object side surface of the first aspherical lens 10 and the image side surface of the second aspherical lens 30 on the optical axis S. FOV (Field of View, abbreviated as FOV) is the maximum field of view angle of the far-infrared optical system 100. The unit of FOV is an angular unit, such as degrees. BFL is the distance between the image side surface of the second aspherical lens 30 and the image plane B of the far-infrared optical system 100 on the optical axis S. C 16 and BFL have the same dimension, both being length units, such as millimeters.

[0061] The upper limit of Conditional Equation 4 can ensure that the far-infrared optical system 100 leaves enough space for the structural members located between the far-infrared optical system 100 and the image detector on the premise of having a small volume, thus facilitating the design of the structural members. The lower limit of Conditional Equation 4 can ensure that the far-infrared optical system 100 still has good imaging quality on the premise of having a small volume.

[0062] In some embodiments, the far-infrared optical system 100 satisfies Conditional Equation 5: where R1 is the curvature radius of the object side surface of the first aspherical lens 10, R2 is the curvature radius of the image side surface of the first aspherical lens 10, and FOV is the maximum field of view angle of the far-infrared optical system 100. R1 and R2 have the same dimension, both being length units, such as millimeters.

[0063] The upper limit of Conditional Equation 5 can prevent the first aspherical lens 10 from introducing excessive spherical aberration and astigmatism. The lower limit of Conditional Equation 5 can ensure that the far-infrared optical system 100 has a small volume and weight.

[0064] In some embodiments, the far-infrared optical system 100 satisfies Conditional Equation 6: CT1 is the central thickness of the first aspherical lens 10, that is, CT1 is the thickness of the first aspherical lens 10 on the optical axis S. CT3 is the central thickness of the second aspherical lens 30, that is, CT3 is the thickness of the second aspherical lens 30 on the optical axis S. CT1 and CT3 have the same dimension, both being length units, such as millimeters.

[0065] Conditional formula six can avoid excessive spherical aberration and astigmatism introduced by the first aspherical lens 10 or the third aspherical lens. If excessive spherical aberration and astigmatism are introduced by the first aspherical lens 10 or the third aspherical lens, it may lead to problems where spherical aberration and astigmatism are difficult to correct. That is, when the far-infrared optical system 100 satisfies conditional formula six, it is beneficial to correct the aberration of the far-infrared optical system 100, and thus the imaging quality of the far-infrared optical system 100 can be improved.

[0066] In some embodiments, the far-infrared optical system 100 satisfies conditional formula seven: Wherein, f is the effective focal length of the far-infrared optical system 100, n is the refractive index of the first aspherical lens 10, and R1 is the radius of curvature of the object side surface of the first aspherical lens 10. FNO is the f-number of the far-infrared optical system 100, that is, FNO is the F-number of the far-infrared optical system 100. f and R1 have the same dimension, both being length units, such as millimeters.

[0067] Conditional formula seven indicates that the far-infrared optical system 100 has good adaptability to the target imaging detector, and thus excellent imaging quality can be guaranteed. The target imaging detector includes but is not limited to an imaging detector with 256×192 pixels and a pixel size of 12 microns. For example, imaging detectors close to the above specifications all belong to the above target imaging detector.

[0068] In some embodiments, the far-infrared optical system 100 satisfies conditional formula eight: Wherein, f is the effective focal length of the far-infrared optical system 100, and EPD (Entrance Pupil Diameter, abbreviated as EPD) is the entrance pupil diameter of the far-infrared optical system 100. f and EPD have the same dimension, both being length units, such as millimeters.

[0069] Conditional formula eight reflects the range of the F-number of the far-infrared optical system 100. From conditional formula eight, it can be seen that the F-number of the far-infrared optical system 100 is smaller, and the light input amount of the far-infrared optical system 100 is larger, and thus excellent imaging quality can be guaranteed.

[0070] The far-infrared optical system 100 further includes a diaphragm 40, and the diaphragm 40 is used to control the light input amount of the far-infrared optical system 100 to ensure that the far-infrared optical system 100 can work effectively and generate high-quality images.

[0071] In some embodiments, the aperture 40 is disposed on the object side of the first aspherical lens 10. Specifically, the position where the aperture 40 is disposed can be any of the following cases:

[0072] (1) The aperture 40 is disposed on the object side of the first aspherical lens 10, and the aperture 40 is spaced apart from the first aspherical lens 10;

[0073] (2) The aperture 40 is disposed on the object side of the first aspherical lens 10, and the aperture 40 is disposed on the object side surface of the first aspherical lens 10, that is, the aperture 40 is disposed in contact with the object side surface of the first aspherical lens 10.

[0074] In some embodiments, the aperture 40 is disposed between any two adjacent lenses. Specifically, the position where the aperture 40 is disposed can be any of the following cases:

[0075] (1) The aperture 40 is disposed between the first aspherical lens 10 and the metalens 20, and the aperture 40 is disposed on the image side surface of the first aspherical lens 10;

[0076] (2) The aperture 40 is disposed between the first aspherical lens 10 and the metalens 20, and the aperture 40 is spaced apart from both the first aspherical lens 10 and the metalens 20;

[0077] (3) The aperture 40 is disposed between the first aspherical lens 10 and the metalens 20, and the aperture 40 is disposed on the object side surface of the metalens 20;

[0078] (4) The aperture 40 is disposed between the metalens 20 and the second aspherical lens 30, and the aperture 40 is disposed on the image side surface of the metalens 20;

[0079] (5) The aperture 40 is disposed between the metalens 20 and the second aspherical lens 30, and the aperture 40 is spaced apart from both the metalens 20 and the second aspherical lens 30;

[0080] (6) The aperture 40 is disposed between the metalens 20 and the second aspherical lens 30, and the aperture 40 is disposed on the object side surface of the second aspherical lens 30.

[0081] Please refer to Figure 1 、 Figure 3 、 Figure 5 、 Figure 7 、 Figure 9 , in some embodiments, the far-infrared optical system 100 further includes a protective glass 50. The protective glass 50 is located between the second aspherical lens 30 and the image plane B, and is disposed close to the image plane B. The protective glass 50 is used to protect the imaging detector matched with the far-infrared optical system 100 to reduce the probability of damage to the imaging detector.

[0082] The far-infrared optical system 100 provided by this application has the following benefits:

[0083] (1) The total optical length TTL (Total Track Length) is less than 32 mm;

[0084] (2) At room temperature, the MTF (Modulation Transfer Function) is greater than 0.32 at the cut-off frequency of 42 lp / mm in the full field of view.

[0085] This application exemplarily provides five far-infrared optical systems 100 that meet the usage requirements in five embodiments. Next, the far-infrared optical systems 100 provided by each embodiment of this application will be introduced in detail.

[0086] Embodiment 1

[0087] Figure 1 FIG. shows a schematic diagram of the architecture layout of the far-infrared optical system 100 provided by Embodiment 1. Figure 1 The mid- and far-infrared optical system 100 sequentially includes, along the optical axis S from the object plane A to the image plane B: a diaphragm 40, a first aspherical lens 10, a metalens 20, a second aspherical lens 30, and a protective glass 50. Among them, the micro-nano structure 220 is disposed on the image side surface of the substrate 210. Some parameters of the far-infrared optical system 100 provided by Embodiment 1 are shown in Table 1-1.

[0088] Table 1-1. Some parameters of the far-infrared optical system 100 provided by Embodiment 1

[0089] Parameter Data Total Track Length (TTL) 31.493 mm Maximum Field Angle (2ω) 8.78° F - number 1.0 Effective Focal Length 24.905 mm Operating Wavelength Band 8 μm - 12 μm

[0090] As can be seen from Table 1-1, the total optical length of the far-infrared optical system 100 is relatively short, only 31.493 mm. Therefore, the volume of the far-infrared optical system 100 provided by Embodiment 1 is relatively small. The F number of the far-infrared optical system 100 is 1.0, which can greatly improve the light input of the far-infrared optical system 100 and collect as much energy as possible entering the far-infrared optical system 100 when the imaging detector has a low response to light energy, thereby ensuring excellent imaging quality.

[0091] Along the direction of the optical axis S from the object plane A to the image plane B, starting from the first aspherical lens 10, each surface in the far-infrared optical system 100 is numbered, and after summarizing the parameters of each surface, the following Table 1-2 is obtained.

[0092] Table 1-2. Parameters of each surface in the far-infrared optical system 100 provided by Embodiment 1

[0093]

[0094]

[0095] For each of the surfaces in Table 1-2, surface 1 is the aperture stop 40, surface 2 is the object side surface of the first aspheric lens, and surface 3 is the image side surface of the first aspheric lens 10. Surface 4 is the object side surface of the superlens 20, and surface 5 is the image side surface of the superlens 20. Surface 6 is the object side surface of the second aspheric lens, and surface 7 is the image side surface of the second aspheric lens 30. Surface 8 is the object side surface of the protective glass 50, and surface 9 is the image side surface of the protective glass 50. Surface 10 is the image plane B. Since the micro-nano structure 220 is provided on surface 10, surface 10 is denoted as the structured surface.

[0096] As can be seen from Table 1-2, the radius of curvature of surface 1 is infinite. Therefore, surface 1 is a plane. The distance between surface 1 and surface 2 is -5.839 mm. The negative sign in "-5.839 mm" here means that the vertex of surface 2 protrudes towards the object side from surface 1, and the material between surface 1 and surface 2 is air. Surface 2 is an even aspheric surface, the radius of curvature of surface 2 is 15.644 mm, the distance between surface 2 and surface 3 is 3.546 mm, and the material between surface 2 and surface 3 is chalcogenide glass. Surface 3 is an even aspheric surface, the radius of curvature of surface 3 is 17.662 mm, the distance between surface 3 and surface 4 is 15.781 mm, and the material between surface 3 and surface 4 is air. Surface 4 is a spherical surface, and the radius of curvature of surface 4 is infinite, that is, surface 4 is a plane. The distance between surface 4 and surface 5 is 0.300 mm, and the material between surface 4 and surface 5 is silicon. The radius of curvature of surface 5 is infinite, that is, surface 5 is a plane. The distance between surface 5 and surface 6 is 1.589 mm, and the material between surface 5 and surface 6 is air. Surface 6 is an even aspheric surface, the radius of curvature of surface 6 is 12.923 mm, the distance between surface 6 and surface 7 is 1.830 mm, and the material between surface 6 and surface 7 is chalcogenide glass. Surface 7 is an even aspheric surface, the radius of curvature of surface 7 is 14.394 mm, the distance between surface 7 and surface 8 is 7.847 mm, and the material between surface 7 and surface 8 is air. Surface 8 is a spherical surface, the radius of curvature of surface 8 is infinite, that is, surface 8 is a plane. The distance between surface 8 and surface 9 is 0.500 mm, and the material between surface 8 and surface 9 is silicon. Surface 9 is a spherical surface, the radius of curvature of surface 9 is infinite, that is, surface 9 is a plane. The distance between surface 9 and surface 10 is 0.100 mm, and the material between surface 9 and surface 10 is air.

[0097] Surfaces 2, 3, 6, and 7 are even aspheric surfaces, and their surface profiles satisfy the following relationship:

[0098]

[0099] Among them, Z(r) is the distance sagitta from the vertex of the aspheric surface at the position with height r along the optical axis S direction of the aspheric surface; c is the surface curvature of the aspheric surface, c = 1 / R, and R is the radius of curvature of the aspheric surface; k is the conic coefficient; A, B, C, D... are the aspheric coefficients. After summarizing the values of k, A, B, C, D... for surfaces 2, 3, 6, and 7, the following Table 1-3 is obtained.

[0100] Table 1-3. Coefficients of each order of even aspheric surfaces in the far-infrared optical system 100 provided in Example 1

[0101] Surface Number k A B C D E 2 -1.449 3.04E-05 1.99E-07 2.57E-10 -1.13E-11 9.16E-14 3 0.094 -2.85E-05 5.60E-07 -5.09E-09 3.25E-11 -1.88E-13 6 -24.040 1.01E-03 -7.08E-05 2.97E-06 -9.76E-08 1.95E-09 7 1.012 -4.45E-04 -9.58E-06 3.67E-07 -2.13E-08 4.53E-10

[0102] Please refer to Table 1-3. For surface 2, k is -1.449, A is 3.04E-05, B is 1.99E-07, C is 2.57E-10, D is -1.13E-11, and E is 9.16E-14. The coefficients of each order of even aspheric surfaces of surfaces 3, 6, and 7 can all be queried from Table 1-3, and will not be elaborated one by one here.

[0103] Please refer to Figure 2 , Figure 2 shows the MTF field curve diagram of the far-infrared optical system 100 provided in Example 1. Figure 2 The horizontal axis in Figure 2 is the image height, and its unit is millimeter, that is, Figure 2 the horizontal axis of Figure 2 measures the field of view with the image height; Figure 2 The vertical axis in

[0104] Example 2

[0105] Figure 3 shows the schematic diagram of the architecture layout of the far-infrared optical system 100 provided in Example 2. Figure 3 In

[0106] Table 2-1. Partial parameters of the far-infrared optical system 100 provided in Example 2

[0107]

[0108]

[0109] As can be seen from Table 2-1, the total optical length of the far-infrared optical system 100 is relatively short, only 31.885 mm. Therefore, the volume of the far-infrared optical system 100 provided in Example 2 is relatively small. The F number of the far-infrared optical system 100 is 1.0, which can greatly improve the light input of the far-infrared optical system 100 and collect as much energy as possible entering the far-infrared optical system 100 under the condition that the imaging detector has a low response to light energy, thereby ensuring excellent imaging quality.

[0110] Along the optical axis S from the object surface A to the image surface B direction, starting from the first aspherical lens 10, each surface in the far-infrared optical system 100 is numbered, and after summarizing the parameters of each surface, the following Table 2-2 is obtained.

[0111] Table 2-2. Parameters of each surface in the far-infrared optical system 100 provided in Example 2

[0112] Surface Number Surface Type Radius of Curvature (mm) Thickness (mm) Material 1 Even - Aspheric Surface 16.121 3.203 Chalcogenide Glass 2 Even - Aspheric Surface 18.599 10.075 - 3 Metasurface Infinity 0.300 Silicon 4 Spherical Surface Infinity 0.500 - 5 Aperture Stop Infinity 7.261 - 6 Even - Aspheric Surface 12.126 1.817 Chalcogenide Glass 7 Even - Aspheric Surface 13.322 8.129 - 8 Spherical Surface Infinity 0.500 Silicon 9 Spherical Surface Infinity 0.100 - 10 Image Plane Infinity - -

[0113] For the analysis of each surface in Table 2-2, reference can be made to Example 1, and this example will not be elaborated here.

[0114] Surfaces 1, 2, 6, and 7 are even aspherical surfaces, and their surface profiles satisfy the following relational expressions:

[0115]

[0116] Among them, Z(r) is the distance sag from the vertex of the aspherical surface along the optical axis S at the position with a height of r; c is the curvature of the aspherical surface, c = 1 / R, and R is the radius of curvature of the aspherical surface; k is the conic coefficient; A, B, C, D... are aspherical coefficients. After summarizing the values of k, A, B, C, D... for surfaces 1, 2, 6, and 7, the following Table 2-3 is obtained.

[0117] Table 2-3. Coefficients of each order of even aspherical surfaces in the far-infrared optical system 100 provided in Example 2

[0118] Surface Number k A B C D E 1 -1.423 3.00E-05 1.86E-07 2.71E-11 -1.33E-11 8.43E-14 2 -0.013 -1.70E-05 4.95E-07 -5.44E-09 2.63E-11 -1.80E-13 6 -17.233 1.08E-03 -6.35E-05 2.75E-06 -9.88E-08 2.00E-09 7 -0.172 -1.37E-04 -1.23E-05 2.01E-07 -1.51E-08 4.64E-10

[0119] The coefficients of each order of even aspherical surfaces of k, A, B, C, D... for surfaces 1, 2, 6, and 7 can all be queried from Table 2-3, and will not be elaborated one by one here.

[0120] Please refer to Figure 4 , Figure 4 which shows the MTF field curve graph of the far-infrared optical system 100 provided in Embodiment 2. Figure 4 In Figure 4 , the horizontal axis is the image height, and its unit is millimeter, that is Figure 4 the horizontal axis in Figure 4 measures the field of view with the image height; Figure 4 The vertical axis in

[0121] Embodiment 3

[0122] Figure 5 shows a schematic diagram of the architecture layout of the far-infrared optical system 100 provided in Embodiment 3. Figure 5 In the far-infrared optical system 100 along the optical axis S from the object surface A to the image surface B, it successively includes: a diaphragm 40, a first aspherical lens 10, a superlens 20, a second aspherical lens 30, and a protective glass 50. Among them, the micro-nano structure 220 is arranged on the object side surface of the substrate 210. Some parameters of the far-infrared optical system 100 provided in Embodiment 3 are shown in Table 3-1.

[0123] Table 3-1. Some parameters of the far-infrared optical system 100 provided in Embodiment 3

[0124] Parameter Data Total Track Length (TTL) 32.089 mm Maximum Field Angle (2ω) 8.75° F - number 0.95 Effective Focal Length 25.004 mm Operating Wavelength Band 8 μm - 12 μm

[0125] As can be seen from Table 3-1, the overall optical length of the far-infrared optical system 100 is relatively short, only 32.089 millimeters. Therefore, the volume of the far-infrared optical system 100 provided in Embodiment 3 is relatively small. The F number of the far-infrared optical system 100 is 0.95, which can greatly improve the light input amount of the far-infrared optical system 100, and can collect as much energy entering the far-infrared optical system 100 as possible when the imaging detector has a low response to light energy, thereby ensuring excellent imaging quality.

[0126] Along the direction of the optical axis S from the object surface A to the image surface B, starting from the first aspherical lens 10, each surface in the far-infrared optical system 100 is numbered, and after summarizing the parameters of each surface, the following Table 3-2 is obtained.

[0127] Table 3-2. Parameters of Each Surface in the Far-Infrared Optical System 100 Provided in Embodiment 3

[0128] Surface Number Surface Type Radius of Curvature (mm) Thickness (mm) Material 1 Aperture Stop Infinity -6.862 - 2 Even - Aspheric Surface 15.741 3.101 Chalcogenide Glass 3 Even - Aspheric Surface 17.873 12.855 - 4 Structural Surface Infinity 0.300 Silicon 5 Spherical Surface Infinity 4.949 - 6 Even - Aspheric Surface 11.166 1.833 Chalcogenide Glass 7 Even - Aspheric Surface 11.984 8.451 - 8 Spherical Surface Infinity 0.500 Silicon 9 Spherical Surface Infinity 0.100 - 10 Image Plane Infinity - -

[0129] For the analysis of each surface in Table 3-2, reference can be made to Embodiment 1, and details will not be repeated in this embodiment.

[0130] Surfaces 2, 3, 6, and 7 are even aspherical surfaces, and their surface profiles satisfy the following relationship:

[0131]

[0132] Where Z(r) is the distance sagitta from the vertex of the aspherical surface along the optical axis S direction at a height of r; c is the curvature of the aspherical surface, c = 1 / R, and R is the radius of curvature of the aspherical surface; k is the conic coefficient; A, B, C, D... are the aspherical coefficients. After summarizing the values of k, A, B, C, D... for Surfaces 2, 3, 6, and 7, the following Table 3-3 is obtained.

[0133] Table 3-3. Coefficients of Each Order of Even Aspherical Surfaces in the Far-Infrared Optical System 100 Provided in Embodiment 3

[0134] Surface Number k A B C D E 2 -1.261 2.64E-05 1.74E-07 6.51E-10 -1.30E-11 8.59E-14 3 0.057 -2.36E-05 5.41E-07 -5.22E-09 3.36E-11 -1.40E-13 6 -17.021 1.32E-03 -6.97E-05 2.98E-06 -9.45E-08 1.69E-09 7 -0.118 -1.42E-04 -3.75E-06 9.15E-08 -1.42E-08 4.17E-10

[0135] The coefficients of each order of even aspherical surfaces of k, A, B, C, D... for Surfaces 2, 3, 6, and 7 can all be queried from Table 3-3, and will not be elaborated one by one here.

[0136] Please refer to Figure 6 , Figure 6 which shows the MTF field curve graph of the far-infrared optical system 100 provided in Embodiment 3. Figure 6 The horizontal axis in Figure 6 is the image height, and its unit is millimeter, that is, Figure 6 the horizontal axis in Figure 6 measures the field of view with the image height; The vertical axis in Figure 6 is the MTF value. Figure 6 lists the sagittal curve S1 and meridional curve T1 of the MTF varying with the field of view at a spatial frequency of 10 lp / mm, the sagittal curve S2 and meridional curve T2 of the MTF varying with the field of view at a spatial frequency of 21 lp / mm, and the sagittal curve S3 and meridional curve T3 of the MTF varying with the field of view at a spatial frequency of 42 lp / mm. As can be seen from Figure 6 , within the field of view of 1.0 (image height of 1.92 millimeters), the MTF is greater than 0.45, and the imaging quality of the far-infrared optical system 100 is excellent.

[0137] Embodiment 4

[0138] Figure 7Shows a schematic diagram of the architecture layout of the far-infrared optical system 100 provided in Embodiment 4. Figure 7 The mid- and far-infrared optical system 100 successively includes, along the optical axis S from the object surface A to the image surface B: a diaphragm 40, a first aspherical lens 10, a metasurface lens 20, a second aspherical lens 30, and a protective glass 50. Among them, the micro-nano structure 220 is disposed on the object side surface of the substrate 210. Some parameters of the far-infrared optical system 100 provided in Embodiment 4 are shown in Table 4-1.

[0139] Table 4-1. Some parameters of the far-infrared optical system 100 provided in Embodiment 4

[0140] Parameter Data Total Track Length (TTL) 32.003 mm Maximum Field Angle (2ω) 8.75° F - number 0.95 Effective Focal Length 25.004 mm Operating Wavelength Band 8 μm - 12 μm

[0141] As can be seen from Table 4-1, the overall optical length of the far-infrared optical system 100 is relatively short, only 32.002 mm. Therefore, the volume of the far-infrared optical system 100 provided in Embodiment 4 is relatively small. The F-number of the far-infrared optical system 100 is 0.95, which can greatly improve the light input amount of the far-infrared optical system 100, and can collect as much energy as possible entering the far-infrared optical system 100 when the imaging detector has a low response to light energy, thereby ensuring excellent imaging quality.

[0142] Along the direction of the optical axis S from the object surface A to the image surface B, starting from the first aspherical lens 10, each surface in the far-infrared optical system 100 is numbered, and after summarizing the parameters of each surface, the following Table 4-2 is obtained.

[0143] Table 4-2. Parameters of each surface in the far-infrared optical system 100 provided in Embodiment 4

[0144] Surface Number Surface Type Radius of Curvature (mm) Thickness (mm) Material 1 Aperture Stop Infinity -6.270 - 2 Even - Aspheric Surface 16.299 5.055 Chalcogenide Glass 3 Even - Aspheric Surface 16.933 8.508 - 4 Structural Surface Infinity 0.300 Silicon 5 Spherical Surface Infinity 7.404 - 6 Even - Aspheric Surface 11.825 1.611 Chalcogenide Glass 7 Even - Aspheric Surface 13.621 8.525 - 8 Spherical Surface Infinity 0.500 Silicon 9 Spherical Surface Infinity 0.100 - 10 Image Plane Infinity - -

[0145] For the analysis of each surface in Table 4-2, reference can be made to Embodiment 1, and this embodiment will not be elaborated here.

[0146] Surfaces 2, 3, 6, and 7 are even aspherical surfaces, and their surface profiles satisfy the following relational expressions:

[0147]

[0148] Among them, Z(r) is the distance sagitta from the vertex of the aspherical surface along the optical axis S at the position with a height of r; c is the surface curvature of the aspherical surface, c = 1 / R, and R is the radius of curvature of the aspherical surface; k is the conic coefficient; A, B, C, D... are aspherical coefficients. After summarizing the values of k, A, B, C, D... for surfaces 2, 3, 6, and 7, the following Table 4-3 is obtained.

[0149] Table 4-3. Coefficients of even-order aspheres in the far-infrared optical system 100 provided in Example 4

[0150] Surface Number k A B C D E 2 -1.261 2.64E-05 1.74E-07 6.51E-10 -1.30E-11 8.59E-14 3 0.057 -2.36E-05 5.41E-07 -5.22E-09 3.36E-11 -1.40E-13 6 -17.021 1.32E-03 -6.97E-05 2.98E-06 -9.45E-08 1.69E-09 7 -0.118 -1.42E-04 -3.75E-06 9.15E-08 -1.42E-08 4.17E-10

[0151] The coefficients of even-order aspheres of k, A, B, C, D... for surfaces 2, 3, 6, and 7 can all be obtained by querying Table 4-3, and will not be elaborated here one by one.

[0152] Please refer to Figure 8 , Figure 8 which shows the MTF field curve graph of the far-infrared optical system 100 provided in Example 4. Figure 8 The horizontal axis in Figure 8 is the image height, and its unit is millimeter, that is, Figure 8 the horizontal axis in Figure 8 measures the field of view with the image height; Figure 8 The vertical axis in

[0153] Example 5

[0154] Figure 9 shows a schematic diagram of the architecture layout of the far-infrared optical system 100 provided in Example 5. Figure 9 In

[0155] the far-infrared optical system 100 along the optical axis S from the object surface A to the image surface B successively includes: a first aspherical lens 10, a diaphragm 40, a superlens 20, a second aspherical lens 30, and a protective glass 50. Among them, the micro-nano structure 220 is disposed on the object side and the image side of the substrate 210. Some parameters of the far-infrared optical system 100 provided in Example 5 are shown in Table 5-1.

[0156] Parameter Data Total Track Length (TTL) 32.003 mm Maximum Field Angle (2ω) 8.75° F - number 0.95 Effective Focal Length 25.004 mm Operating Wavelength Band 8 μm - 12 μm

[0157] As can be seen from Table 5-1, the total optical length of the far-infrared optical system 100 is relatively short, only 32.003 mm. Therefore, the volume of the far-infrared optical system 100 provided in Embodiment 5 is relatively small. The F number of the far-infrared optical system 100 is 0.95, which can greatly increase the amount of light entering the far-infrared optical system 100, and collect as much energy entering the far-infrared optical system 100 as possible when the imaging detector has a low response to light energy, thereby ensuring excellent imaging quality.

[0158] Along the optical axis S from the object surface A to the image surface B direction, starting from the first aspherical lens 10, each surface in the far-infrared optical system 100 is numbered, and after summarizing the parameters of each surface, the following Table 5-2 is obtained.

[0159] Table 5-2. Parameters of each surface in the far-infrared optical system 100 provided in Embodiment 5

[0160]

[0161]

[0162] For the analysis of each surface in Table 5-2, reference can be made to Embodiment 1, and details will not be repeated in this embodiment.

[0163] Surfaces 1, 2, 6, and 7 are even aspherical surfaces, and their surface profiles satisfy the following relationship:

[0164]

[0165] where Z(r) is the distance sagitta from the vertex of the aspherical surface at the position with height r along the optical axis S direction; c is the surface curvature of the aspherical surface, c = 1 / R, and R is the radius of curvature of the aspherical surface; k is the conic coefficient; A, B, C, D... are the aspherical coefficients. After summarizing the values of k, A, B, C, D... for surfaces 1, 2, 6, and 7, the following Table 5-3 is obtained.

[0166] Table 5-3. Coefficients of each order of even aspherical surfaces in the far-infrared optical system 100 provided in Embodiment 5

[0167] Surface Number K A B C D E 1 -0.926 1.69E-05 7.30E-08 6.01E-10 -1.33E-11 6.88E-14 2 0.096 -2.58E-05 4.58E-07 -7.22E-09 2.74E-11 -1.16E-13 6 -46.582 1.07E-03 -6.92E-05 3.18E-06 -9.49E-08 1.50E-09 7 1.261 -2.17E-04 1.79E-06 1.82E-07 -2.35E-08 5.56E-10

[0168] The coefficients of each order of even aspherical surfaces of k, A, B, C, D... for surfaces 1, 2, 6, and 7 can all be queried from Table 5-3, and will not be elaborated one by one here.

[0169] Please refer to Figure 10 , Figure 10 which shows the MTF field curve graph of the far-infrared optical system 100 provided in Embodiment 5, Figure 10The horizontal axis in [it] is the image height, and its unit is millimeter, that is Figure 10 The horizontal axis of Figure 10 measures the field of view with the image height; Figure 10 The vertical axis in [it] is the MTF value. Figure 10 In [it], the sagittal curve S1 and meridional curve T1 of the MTF varying with the field of view at a spatial frequency of 10 lp / mm, the sagittal curve S2 and meridional curve T2 of the MTF varying with the field of view at a spatial frequency of 21 lp / mm, and the sagittal curve S3 and meridional curve T3 of the MTF varying with the field of view at a spatial frequency of 42 lp / mm are listed. From Figure 10 it can be seen that within the field of view of 1.0 (image height of 1.92 millimeters), the MTF is greater than 0.47, and the imaging quality of the far-infrared optical system 100 is excellent.

[0170] After summarizing the various parameters of the far-infrared optical system 100 provided in the above 5 embodiments, Table 6 as shown below is obtained. The display of Table 6 is mainly used to illustrate that the various conditions satisfied by the far-infrared optical system 100 provided in this application are all experimentally verified and supported.

[0171] Table 6. Various parameters of the far-infrared optical system 100 provided in each embodiment

[0172]

[0173] This application also provides a far-infrared optical lens (not shown in the figure). The far-infrared optical lens includes an imaging detector (not shown in the figure) and the above-mentioned far-infrared optical system 100. The architecture of the far-infrared optical system 100 can be referred to above and will not be elaborated here. The imaging detector is disposed on the image plane B of the far-infrared optical system 100. The imaging detector includes, but is not limited to, CMOS (Complementary Metal Oxide Semiconductor, abbreviated as CMOS, complementary metal oxide semiconductor) and CCD (Charge Coupled Device, abbreviated as CCD, charge coupled device).

[0174] Those skilled in the art will readily think of other implementation schemes of this application after considering the specification and practicing the utility model disclosed here. This application aims to cover any variations, uses, or adaptive changes of this application. These variations, uses, or adaptive changes follow the general principles of this application and include the common general knowledge or conventional technical means in the technical field not disclosed in this application. The specification and embodiments are only regarded as exemplary, and the true scope and spirit of this application are pointed out by the appended claims.

Claims

1. A far-infrared optical system, characterized in that, The far-infrared optical system sequentially includes, from the object side to the image side along the optical axis: a first aspherical lens, a metasurface lens, and a second aspherical lens; the first aspherical lens has a positive optical power, the object side surface of the first aspherical lens bulges toward the object side, and the image side surface of the first aspherical lens bulges toward the object side; the metasurface lens has a positive optical power, the metasurface lens includes a substrate and a micro-nano structure, and the micro-nano structure is disposed on the object side surface and / or the image side surface of the substrate; the second aspherical lens has a positive optical power. The far-infrared optical system satisfies: f a1 + f a2 < f m , where the f a1 is the focal length of the first aspherical lens, the f a2 is the focal length of the second aspherical lens, and the f m is the focal length of the metalens.

2. The far-infrared optical system according to claim 1, wherein The far-infrared optical system satisfies: where f is the effective focal length of the far-infrared optical system.

3. The far-infrared optical system according to claim 1, characterized in that, The far-infrared optical system satisfies: Wherein, Sag1 is the distance between the first point and the second point on the optical axis. The first point is the intersection of the object side surface of the first aspherical lens and the optical axis, and the second point is the point corresponding to the maximum optical diameter on the image side surface of the first aspherical lens; if the second point is on the object side of the first point, Sag1 is negative, and if the second point is on the image side of the first point, Sag1 is positive; R1 is the curvature radius of the object side surface of the first aspherical lens.

4. The far-infrared optical system according to claim 1, wherein The far-infrared optical system satisfies the following: wherein, the C 16 is the distance on the optical axis between the object side surface of the first aspherical lens and the image side surface of the second aspherical lens, the BFL is the distance on the optical axis between the image side surface of the second aspherical lens and the image plane of the far-infrared optical system, and the FOV is the maximum field of view angle of the far-infrared optical system.

5. The far-infrared optical system according to claim 1, wherein The far-infrared optical system satisfies: wherein, R1 is the curvature radius of the object side surface of the first aspherical lens, R2 is the curvature radius of the image side surface of the first aspherical lens, and FOV is the maximum field of view angle of the far-infrared optical system.

6. The far-infrared optical system according to claim 1, characterized in that, The far-infrared optical system satisfies the following: CT1 is the central thickness of the first aspherical lens, and CT3 is the central thickness of the second aspherical lens.

7. The far-infrared optical system according to claim 1, characterized in that, The far-infrared optical system satisfies the following: where f is the effective focal length of the far-infrared optical system, n is the refractive index of the first aspherical lens, FNO is the f-number of the far-infrared optical system, and R1 is the radius of curvature of the object side surface of the first aspherical lens.

8. The far-infrared optical system according to claim 1, characterized in that The far-infrared optical system satisfies the following: Wherein, f is the effective focal length of the far-infrared optical system, and EPD is the entrance pupil diameter of the far-infrared optical system.

9. The far-infrared optical system according to any one of claims 1-8, characterized in that, The far-infrared optical system further includes a diaphragm, and the diaphragm is disposed on the object side of the first aspherical lens; alternatively, the diaphragm is disposed between any two adjacent lenses.

10. A far-infrared optical lens, characterized in that, The far-infrared optical lens includes: an imaging detector and the far-infrared optical system according to any one of claims 1-9; the imaging detector is disposed on the image plane of the far-infrared optical system.

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