CN220305554U - Three-piece type optical system for far infrared band - Google Patents

Abstract

The present disclosure provides a three-plate optical system for the far infrared band. The optical system comprises a first optical element, a second optical element and a third optical element which are sequentially arranged along the object side to the image side of the optical system, wherein the first optical element is provided with a first object side surface and a first image side surface, and the first object side surface and the first image side surface are both protruded towards the direction of the object side of the three-piece optical system; the second optical element is a superlens and is provided with a second object side surface and a second image side surface; the third optical element has a third object side surface and a third image side surface, the third image side surface protruding toward the image side of the three-plate optical system; the first optical element, the second optical element, and the third optical element each have positive optical power; the optical power of the first optical element and the third optical element are both greater than the optical power of the second optical element. The technical scheme utilizes the superlens to correct residual aberration and spherical aberration, and the superlens is combined with the traditional lens to eliminate chromatic aberration, so that the aperture of the lens and the volume of the system are controlled while the large aperture is ensured.

Description

Three-piece type optical system for far infrared band

Technical Field

The present disclosure relates to the technical field of optical systems, and more particularly, to a three-plate optical system with a large aperture suitable for a far infrared band.

Background

Far infrared optical systems often operate in extremely harsh environments, in which case as much energy as possible should be detected into the optical system to increase imaging contrast, thus requiring a large aperture lens.

In the prior art, there is a three-plate type long-wave infrared lens, the image side surface of the near object side lens and the object side surface of the near image side lens are both aspheric lenses, the image side surface of the near object side lens also adopts a diffraction surface, and a meniscus glass lens is arranged between the near object side lens and the near image side lens, so that the system is complex and heavy as a whole, the optical length is long, and the overall cost is high.

Disclosure of Invention

In order to ameliorate the above-described deficiencies of the prior art, embodiments of the present disclosure provide a three-piece optical system for the far infrared band. Comprises a first optical element, a second optical element and a third optical element which are sequentially arranged along the object side to the image side of the three-piece optical system; wherein,

the first optical element is provided with a first object side surface and a first image side surface, and the first object side surface and the first image side surface are both protruded towards the object side of the three-piece optical system;

the second optical element is a superlens and is provided with a second object side surface and a second image side surface;

the third optical element has a third object side surface and a third image side surface, the third object side surface protruding toward the image side of the three-plate optical system;

wherein the first optical element, the second optical element, and the third optical element each have positive optical power; the optical power of the first optical element and the third optical element are both greater than the optical power of the second optical element.

Optionally, the first optical element, the second optical element and the third optical element have an operating band of 8 μm to 12 μm.

Alternatively, the f# of the three-plate optical system satisfies: 0.76< f# <1.

Optionally, the focal length f of the first optical element ₁ And focal length f of third optical element ₃ The method meets the following conditions:

optionally, the first object side surface has an optically effective aperture D ₁ An optically effective aperture D of the first image side ₂ An optically effective aperture D of the third object side surface ₃ An optically effective aperture D of the third image side surface ₄ The method meets the following conditions:

optionally, the first object side surface has an optically effective aperture D ₁ An optically effective aperture D of a third image side surface ₄ The f# satisfies:

wherein Imgh is half the diagonal length of the effective pixel area on the image plane of the three-plate optical system.

Alternatively, the firstOptical effective caliber D of object side surface ₁ An optically effective aperture D of a third image side surface ₄ The optical length TTL of the three-plate optical system satisfies:

optionally, the three-plate optical system further comprises a diaphragm, and the diaphragm is disposed between the first image side surface and the second object side surface or between the second image side surface and the third object side surface.

Optionally, when the diaphragm is disposed between the first image side surface and the second object side surface, a distance between the diaphragm and the second object side surface is greater than or equal to zero;

when the diaphragm is arranged between the second image side surface and the third object side surface, the distance between the diaphragm and the second image side surface is equal to zero.

Optionally, when the diaphragm is disposed between the first image side and the second object side, the second object side is provided with nanostructures;

when the diaphragm is arranged between the second image side surface and the third object side surface, the third object side surface is provided with a nano structure.

Optionally, the three-plate optical system further includes an optical filter disposed between the third image side surface and an image plane of the three-plate optical system.

Optionally, the first optical element and the third optical element are spherical lenses with positive refractive power, and the second optical element has positive refractive power.

Through the technical scheme and the preferable scheme thereof, the optical system provided by the disclosure comprises a super lens and two spherical mirrors, the working wave band is 8-12 mu m, under the working condition of the far infrared optical system, the super lens is used for correcting residual aberration and spherical aberration, and the chromatic aberration is eliminated by combining with the traditional lens, so that the imaging contrast is ensured, and meanwhile, the aperture of the lens and the volume of the system are considered.

Drawings

The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the present disclosure and, together with the description, serve to explain the principles of the disclosure.

Fig. 1 shows a schematic structural diagram of a three-plate optical system provided in example 1 of the present disclosure;

FIG. 2 shows a modulation transfer function diagram of a three-plate optical system provided by example 1 of the present disclosure;

fig. 3 shows a schematic structural diagram of a three-plate optical system provided in example 2 of the present disclosure;

FIG. 4 shows a modulation transfer function diagram of a three-plate optical system provided by example 2 of the present disclosure;

fig. 5 shows a schematic structural diagram of a three-plate optical system provided in example 3 of the present disclosure;

FIG. 6 shows a modulation transfer function diagram of a three-plate optical system provided by example 3 of the present disclosure;

fig. 7 shows a schematic structural diagram of a three-plate optical system provided in example 4 of the present disclosure;

FIG. 8 shows a modulation transfer function diagram of a three-plate optical system provided by example 4 of the present disclosure;

fig. 9 shows a schematic structural diagram of a three-plate optical system provided in example 5 of the present disclosure;

FIG. 10 shows a modulation transfer function diagram of a three-plate optical system provided by example 5 of the present disclosure;

reference numerals in the drawings denote:

1: a first optical element; 2: a second optical element; 3: a third optical element; 4: a diaphragm; 5: a light filter;

11: a first object side surface; 12: a first image side surface;

21: a second object side; 22: a second image side surface;

31: a third object side surface; 32: and a third image side surface.

Detailed Description

The present application will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments are shown. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers refer to like elements throughout. Also, in the drawings, the thickness, ratio, and size of the parts are exaggerated for clarity of illustration.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, unless the context clearly indicates otherwise, "a," "an," "the," and "at least one" are not meant to limit the amount, but are intended to include both the singular and the plural. For example, unless the context clearly indicates otherwise, the meaning of "a component" is the same as "at least one component". The "at least one" should not be construed as limited to the number "one". "or" means "and/or". The term "and/or" includes any and all combinations of one or more of the associated listed items.

Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms as defined in commonly used dictionaries should be interpreted as having the same meaning as the relevant art context and are not interpreted in an idealized or overly formal sense unless expressly so defined herein.

The meaning of "comprising" or "including" indicates a property, quantity, step, operation, component, element, or combination thereof, but does not preclude other properties, quantities, steps, operations, components, elements, or combinations thereof.

Embodiments are described herein with reference to cross-sectional illustrations that are idealized embodiments. Thus, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments described herein should not be construed as limited to the particular shapes of regions as illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, a region shown or described as being flat may typically have rough and/or nonlinear features. Also, the acute angles shown may be rounded. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region and are not intended to limit the scope of the claims.

Hereinafter, exemplary embodiments according to the present application will be described with reference to the accompanying drawings. In the embodiments of the present application, the height of the nanostructure is too small with respect to the overall thickness of the second optical element 2, and thus the second optical element 2 is represented in the form of a rectangle in the drawings.

The presently disclosed embodiments provide a three-plate optical system for the far infrared band, as shown in fig. 1 or 3, which mainly includes a first optical element 1, a second optical element 2, and a third optical element 3 sequentially disposed along an object side (left side in fig. 1) to an image side (right side in fig. 1) of the three-plate optical system.

The object side optical path further upstream of the first optical element 1 in the drawing is not the embodiment of the present disclosure, so the disclosure is omitted for the sake of brevity, and the right side of the third optical element 3 in the drawing shows the optical path modulated by the three-plate optical system provided by the embodiment of the present disclosure, and the incident light reaches the image plane of the three-plate optical system after being modulated by the three-plate optical system.

To achieve the desired technical effect, the three optical devices in the embodiment include two refractive lenses and one optical device having a super surface.

In one exemplary embodiment, two refractive lenses are made of a high refractive index material that provides a greater optical power while correcting the dominant aberrations of paraxial rays. In addition, the optical device with the super surface provides smaller focal power, mainly corrects residual aberration of the full view field and spherical aberration of the edge view field, and further improves the imaging quality of the system.

In the above embodiment, the combination with the refractive lens is advantageous for achromatism due to the nature of the super surface having negative dispersion.

In one embodiment, the optical device having a supersurface is a superlens comprising a substrate and sub-wavelength nanostructures having particular phase distribution characteristics disposed on the surface of the substrate. The specific configuration, phase distribution, etc. of the superlens may be implemented by those skilled in the art based on the prior art and the technical solutions in the embodiments of the present disclosure.

In one embodiment, both refractive lenses and superlenses are coaxially arranged, optionally coaxially with the optical axis of the three-piece optical system provided by the present embodiment.

In an exemplary embodiment, a superlens is disposed between two refractive lenses.

In one embodiment, the optical system according to the foregoing embodiment is applied to a far infrared optical system, so that more light can pass through the optical system and be received by a detector at an image plane of the optical system, and the three-plate optical system provided in this embodiment has a larger aperture, can increase imaging contrast, and is suitable for a severe environment.

In one embodiment, the optical system is confined within the lens.

In one embodiment, the active surfaces of the refractive lenses are spherical.

In one embodiment, the optical length of the overall system is less than 12mm. The operating band of each optical device is 8 to 12 μm.

In order to more clearly describe the technical solution in the embodiments, each optical element is described below in units.

As shown in fig. 1, 3, 5, 7, and 9, the first optical element 1 has a first object side surface 11 and a first image side surface 12, and the first object side surface 11 and the first image side surface 12 each protrude toward the object side of the three-plate optical system.

The second optical element 2 is a superlens, the second optical element 2 having a second object side 21 and a second image side 22. The nanostructures of the superlens may be arranged on the second object-side 21 or the second image-side 22; the nanostructures of the superlens may also be arranged on both the second object-side 21 and the second image-side 22.

The third optical element 3 has a third object side surface 31 and a third image side surface 32, the third image side surface 32 protruding toward the image side of the three-plate optical system; the third object side surface 31 may protrude in the direction of the image side of the three-plate optical system or in the direction of the object side of the three-plate optical system.

In the present embodiment, the first object side surface 11 projects toward the object side, and the third image side surface 32 projects toward the image side with the diaphragm disposed therebetween, forming a "(|)" like structure that is advantageous in eliminating coma and astigmatism.

In a typical embodiment, the first optical element 1 and the third optical element 3 are both crescent shaped with a concave surface facing the second optical element 2.

In one embodiment, the first object side surface 11 and the first image side surface 12 are spherical surfaces having a radius of approximately (a radius difference of not more than 1 mm).

In one embodiment, the first object-side surface 11 and the first image-side surface 12, the third object-side surface 31 and the third image-side surface 32 are spherical surfaces.

In one embodiment, the first optical element 1, the second optical element 2 and the third optical element 3 each have positive optical power, which facilitates the reduction of the system volume while maintaining a large aperture.

In the above-described embodiment, the optical powers of the first optical element 1 and the third optical element 3 are each larger than the optical power of the second optical element 2.

In the above embodiment, the first optical element 1 and the third optical element 3 are used to correct the main aberrations of paraxial rays, and the second optical element 2 is used to correct the residual aberrations of the full field of view and the spherical aberration of the fringe field of view.

According to an embodiment of the present disclosure, the f# of the three-plate optical system provided in the examples satisfies: 0.76< f# <1.

Further, the three-piece optical system provided in the embodiment satisfies the following relation:

the upper limit of 21mm is to prevent the optical power of the third optical element 3 from being too large while ensuring the thirdThe surface form of the optical element 3 is easier to process and manufacture, and the lower limit of 18.5mm is used for ensuring that the system has a sufficiently large aperture, so that the system aperture is relatively large and the focal power of the system is distributed in a reasonable range. F in the formula ₁ F is the focal length of the first optical element 1 ₃ Is the focal length of the third optical element 3.

In a preferred embodiment, the limitation of the effective aperture is set for two refractive lenses, in particular the optically effective aperture D of the first object side 11 ₁ An optically effective aperture D of the first image side 12 ₂ The optical effective aperture D of the third object side surface 31 ₃ And an optically effective aperture D of the third image side surface 32 ₄ The method meets the following conditions:

the limitation is to control the range of the light propagation path, and it can be seen from the light path diagrams in fig. 1, 3 or 5 that the light propagation path is smoother in the system, the sensitivity of the system is reduced, and the yield of the system in production and assembly is improved.

In a preferred embodiment, the first object side surface 11 has an optically effective aperture D ₁ An optically effective aperture D of the third image side surface 32 ₄ The f# satisfies:

wherein Imgh is half the diagonal length of the effective pixel area on the image plane of the three-plate optical system. In the above limitation, the upper limit is to reasonably control the caliber of the system as small as possible and ensure the system to have a larger image surface, and the lower limit is favorable for ensuring the system to have a larger light inlet amount and the relative illumination under the maximum field.

In one embodiment, the first object side surface 11 has an optically effective aperture D ₁ An optically effective aperture D of the third image side surface 32 ₄ Of three-plate optical systemsThe optical length TTL satisfies:

the lower limit of the limitation is to be favorable for the system to effectively avoid the overlength of the length, be used for the lens, make the lens lighter and thinner, and the upper limit is to be favorable for the system to effectively avoid the overlarge caliber of the lens, so that the lens is more miniaturized.

In one embodiment, the base of the second optical element 2 may be curved or planar. And the substrate of the second optical element 2 is transparent to the operating band, that is, the second optical element 2 may have both the ability to modulate the refraction of light and the ability to modulate the phase of light through its upper supersurface/nanostructure.

In one embodiment, the second optical element 2 may be a reflective lens, that is, the second optical element 2 may have both the ability to reflectively modulate light and the ability to phase modulate light through its upper supersurface/nanostructure.

The disclosed embodiments provide expressions for the phase distribution of the adopted hypersurfaces, in particular as follows:

wherein: r is the distance from the center of the superlens to any nanostructure; lambda is the working wavelength of the superlens;any phase associated with the superlens operating wavelength; (x, y) is the mirror coordinates of the superlens, f ₂ Is the focal length of the superlens; a, a _i And b _i Is a real coefficient. In the above equations 9, 10, and 11, the phase distribution can be optimized in both cases where the i value is odd and even, and the degree of freedom in designing the superlens is increased.

In a preferred embodiment, the three-plate optical system further comprises a diaphragm 4, the diaphragm 4 being arranged upstream or downstream of the optical path of the super-surface or coplanar with the super-surface.

In one embodiment, the diaphragm 4 is arranged between the first image side 12 and the second object side 22 or between the second image side 22 and the third object side 31.

In an alternative embodiment, when the diaphragm 4 is arranged between the first image side 12 and the second object side 21, the distance between the diaphragm 4 and the second object side 21 is greater than or equal to zero;

when the diaphragm 4 is arranged between the second image side surface 22 and the third object side surface 31, the distance between the diaphragm 4 and the second image side surface 22 is equal to zero.

When the distance between the diaphragm 4 and the second object side 21 is zero, the diaphragm 4 is coplanar with the second object side 21. When the distance between the diaphragm 4 and the second image side 22 is zero, the diaphragm 4 is coplanar with the second image side 22.

In an alternative embodiment, the diaphragm 4 may be embedded in the transparent substrate of the superlens.

In an alternative embodiment, the second object side 21 is provided with nanostructures when the diaphragm 4 is arranged between the first image side 12 and the second object side 21;

when the diaphragm 4 is arranged between the second image side 22 and the third object side 31, the third object side 31 is provided with nanostructures.

In a preferred embodiment, the first optical element 1 and the third optical element 3 are each spherical lenses with positive refractive power; the second optical element 2 also has positive refractive power based on the phase distribution of the nanostructures on the supersurface.

The optical system in the embodiment of the disclosure has the advantages of small system volume, low cost, large system aperture and the like, wherein the total system length (Total Track Length, abbreviated as TTL) is smaller than 12mm, the maximum field of view is larger than 0.35 at the spatial cutoff frequency of 14 line pairs/millimeter (lp/mm), and the modulation transfer function (Modulation Transfer Function, abbreviated as MTF) is larger than 0.35.

To further describe the features of the optical system provided by the embodiments of the present disclosure, the present disclosure provides various embodiments that satisfy the above conditional expression constraints, as follows:

example 1

As shown in fig. 1, the optical system includes a first optical element 1, a second optical element 2, and a third optical element 3, which are disposed in this order along the object side to the image side of the optical system. Wherein the first optical element 1 and the third optical element 3 are spherical refractive lenses, and the second optical element 2 is a superlens. The optical system further comprises a diaphragm 4, the diaphragm 4 being coplanar with the second image side 22. The second image side 22 is provided with nanostructures. The optical system further comprises a filter 5, and the filter 5 is disposed between the third optical element 3 and the image plane.

The system parameters of the optical system are shown in Table 1-1, and the parameters of the radius, thickness, material, etc. of each lens surface in the optical system are shown in Table 1-2.

TABLE 1-1

TABLE 1-2

Fig. 2 shows a polychromatic diffraction modulation transfer function (Polychromatic Diffraction MTF) curve of the optical system as shown in fig. 1. As shown in FIG. 2, the MTF value of the maximum visual angle of the optical system at the space cut-off frequency of 14lp/mm is larger than 0.4, so that the design requirement is met. In addition, the MTF curve of the optical system under each view angle approaches to the diffraction limit, and excellent resolution is realized.

Example 2

As shown in fig. 3, the optical system includes a first optical element 1, a second optical element 2, and a third optical element 3, which are disposed in this order along the object side to the image side of the optical system. Wherein the first optical element 1 and the third optical element 3 are spherical refractive lenses, and the second optical element 2 is a superlens. The optical system further comprises a diaphragm 4, the diaphragm 4 being coplanar with the second object side 21. The second object side 21 is provided with nanostructures. The optical system further comprises a filter 5, and the filter 5 is disposed between the third optical element 3 and the image plane.

The system parameters of the optical system are shown in Table 2-1, and the parameters of the radius, thickness, material, etc. of each lens surface in the optical system are shown in Table 2-2.

TABLE 2-1

Parameters (parameters)	Data
		Total length of system (TTL)	11.5mm
Visual field (2 omega)	54.2°
		F number	0.9
Equivalent Focal Length (EFL)	7.08mm
		Operating band	Far infrared (8 μm-12 μm)

TABLE 2-2

Fig. 4 shows a polychromatic diffraction modulation transfer function (Polychromatic Diffraction MTF) curve of the optical system as shown in fig. 3. As shown in fig. 4, the MTF value of the maximum viewing angle of the optical system at the spatial cut-off frequency of 14lp/mm is greater than 0.35, so as to meet the design requirement. In addition, the MTF curve of the optical system under each view angle approaches to the diffraction limit, and excellent resolution is realized.

Example 3

As shown in fig. 5, the optical system includes a first optical element 1, a second optical element 2, and a third optical element 3, which are disposed in this order along the object side to the image side of the optical system. Wherein the first optical element 1 and the third optical element 3 are spherical refractive lenses, and the second optical element 2 is a superlens. Also included in this example is a diaphragm 4 arranged between the first image side 12 and the second image side 21, and a filter 5 arranged in the image space of the third optical element. The second object side 21 is provided with nanostructures.

The system parameters of the optical system are shown in Table 3-1, and the parameters of the radius, thickness, material, etc. of each lens surface in the optical system are shown in Table 3-2.

TABLE 3-1

Parameters (parameters)	Data
		Total length of system (TTL)	11.5mm
Visual field (2 omega)	54.3°
		F number	0.85
Equivalent Focal Length (EFL)	6.98mm
		Operating band	Far infrared (8 μm-12 μm)

TABLE 3-2

Fig. 6 shows a polychromatic diffraction modulation transfer function (Polychromatic Diffraction MTF) curve of the optical system as shown in fig. 5. As shown in fig. 6, the MTF value of the maximum viewing angle of the optical system at the spatial cut-off frequency of 14lp/mm is greater than 0.4, so as to meet the design requirement. In addition, the MTF curve of the optical system under each view angle approaches to the diffraction limit, and excellent resolution is realized.

Example 4

As shown in fig. 7, the optical system includes a first optical element 1, a second optical element 2, and a third optical element 3, which are disposed in this order along the object side to the image side of the optical system. Wherein the first optical element 1 and the third optical element 3 are spherical refractive lenses, and the second optical element 2 is a superlens. The diaphragm 4 arranged between the first image side 12 and the second image side 21 and the filter 5 in the image side space of the third optical element 3 are also embodied in this example. The second object side 21 and the second image side 22 are each provided with nanostructures.

The system parameters of the optical system are shown in Table 4-1, and the parameters of the radius, thickness, material, etc. of each lens surface in the optical system are shown in Table 4-2.

TABLE 4-1

TABLE 4-2

Fig. 8 shows a polychromatic diffraction modulation transfer function (Polychromatic Diffraction Modulation Transfer Function, MTF) curve of the optical system as shown in fig. 7. As shown in fig. 8, the maximum viewing angle of the optical system has an MTF value of about 0.5 at a spatial cutoff frequency of 14lp/mm, satisfying the design requirements. In addition, the MTF curve of the optical system under each view angle approaches to the diffraction limit, and excellent resolution is realized.

Example 5

As shown in fig. 9, the optical system includes a first optical element 1, a second optical element 2, and a third optical element 3, which are disposed in this order along the object side to the image side of the optical system. Wherein the first optical element 1 and the third optical element 3 are spherical refractive lenses, and the second optical element 2 is a superlens. The example also shows a diaphragm 4 arranged between the first image side 12 and the second image side 21 and a filter 5 of the image space of the third optical element 3. The second object side 21 and the second image side 22 are each provided with nanostructures.

The system parameters of the optical system are shown in Table 5-1, and the parameters of the radius, thickness, material, etc. of each lens surface in the optical system are shown in Table 5-2.

TABLE 5-1

Parameters (parameters)	Data
		Total length of system (TTL)	11.5mm
Visual field (2 omega)	54.4°
		F number	0.78
Equivalent Focal Length (EFL)	6.98mm
		Work ofWave band	Far infrared (8 μm-12 μm)

TABLE 5-2

Fig. 10 shows a polychromatic diffraction modulation transfer function (Polychromatic Diffraction MTF) curve of the optical system as shown in fig. 9. As shown in fig. 10, the MTF value of the maximum viewing angle of the optical system at the spatial cut-off frequency of 14lp/mm is greater than 0.4, thereby meeting the design requirement. In addition, the MTF curve of the optical system under each view angle approaches to the diffraction limit, and excellent resolution is realized.

As can be seen in fig. 2, 4, 6, 8 and 10, the MTF of the optical system at the spatial cutoff frequency at the maximum viewing angle is greater than 0.4 under different system parameters, and the MTF curves at different viewing angles are all close to the diffraction limit, i.e. the provided optical system has good imaging effect and excellent resolution.

A summary of the conditions for each example is provided below:

TABLE 6

In the above embodiments and examples, the conventional spherical lens is used to provide the main optical power and eliminate the on-axis aberration, the superlens is used to compensate the phase to eliminate the residual aberration and the spherical aberration of the fringe field of view, and the combination of different materials, the negative dispersion of the superlens and the positive dispersion of the conventional lens are combined to form achromatics, so that the better imaging effect can be realized by using two refractive lens groups.

It should be noted that the superlens provided by the embodiment of the application can be processed through a semiconductor process, and has the advantages of light weight, thin thickness, simple structure and process, low cost, high mass production consistency and the like.

The foregoing is merely a specific implementation of the embodiments of the present application, but the protection scope of the embodiments of the present application is not limited thereto, and any person skilled in the art may easily think about changes or substitutions within the technical scope of the embodiments of the present application, and all changes and substitutions are included in the protection scope of the embodiments of the present application. Therefore, the protection scope of the embodiments of the present application shall be subject to the protection scope of the claims.

Claims (10)

1. A three-plate optical system for the far infrared band, characterized by comprising a first optical element (1), a second optical element (2) and a third optical element (3) which are sequentially arranged along the object side to the image side of the three-plate optical system; wherein,

the first optical element (1) has a first object side surface (11) and a first image side surface (12), the first object side surface (11) and the first image side surface (12) each protruding in the direction of the object side of the three-plate optical system;

the second optical element (2) is a superlens, the second optical element (2) having a second object side (21) and a second image side (22);

the third optical element (3) has a third object side surface (31) and a third image side surface (32), the third image side surface (32) protruding toward the image side of the three-plate optical system;

wherein the first optical element (1), the second optical element (2) and the third optical element each have positive optical power; and, the optical power of the first optical element (1) and the third optical element (3) is larger than the optical power of the second optical element (2).

2. The three-piece optical system according to claim 1, wherein an f# of the three-piece optical system satisfies: 0.76< f# <1.

3. Three-plate optical system according to claim 2, characterized in that the focal length f of the first optical element (1) ₁ And a focal length f of the third optical element (3) ₃ The method meets the following conditions:

4. a three-plate optical system according to any one of claims 1-3, characterized in that the first object side surface (11) has an optically effective aperture D ₁ An optically effective aperture D of the first image side surface (12) ₂ An optically effective aperture D of the third object side surface (31) ₃ And an optically effective aperture D of the third image side surface (32) ₄ The method meets the following conditions:

5. three-plate optical system according to claim 2, characterized in that the first object side (11) has an optically effective aperture D ₁ An optically effective aperture D of the third image side surface (32) ₄ The f# satisfies:

wherein Imgh is half the diagonal length of the effective pixel region on the image plane of the three-plate optical system.

6. Three-plate optical system according to claim 1, characterized in that the first object side (11) has an optically effective aperture D ₁ An optically effective aperture D of the third image side surface (32) ₄ The optical length TTL of the three-plate optical system satisfies:

7. the three-plate optical system according to any one of claims 1-3 and 5-6, further comprising a diaphragm (4), the diaphragm (4) being arranged between the first image side (12) and the second object side (21) or between the second image side (22) and a third object side (31).

8. The three-plate optical system according to claim 7, wherein when the diaphragm (4) is disposed between the first image side surface (12) and the second object side surface (21), a distance between the diaphragm (4) and the second object side surface (21) is greater than or equal to zero;

when the diaphragm (4) is arranged between the second image side surface (22) and the third object side surface (31), the distance between the diaphragm (4) and the second image side surface (22) is equal to zero.

9. The three-plate optical system according to claim 7, characterized in that the second object side (21) is provided with nanostructures when the diaphragm (4) is arranged between the first image side (12) and the second object side (21);

when the diaphragm (4) is arranged between the second image side surface (22) and the third object side surface (31), the third object side surface (31) is provided with nanostructures.

10. The three-plate optical system according to any one of claims 1-3, 5-6 and 8-9, further comprising a filter (5), the filter (5) being arranged between the third image side (32) and an image plane of the three-plate optical system.