Off-axis three-mirror optical system

Abstract

The present invention relates to an off-axis three-mirror optical system. The first reflector is used to reflect light from the object side to form a first reflected light; the second reflector is arranged in the reflected light path of the first reflector and is used to reflect the first reflected light to form a second reflected light; the third reflector is arranged in the reflected light path of the second reflector and is used to reflect the second reflected light to form a third reflected light directed toward the second reflector. The second reflector is also used to reflect the third reflected light to form a fourth reflected light, and the fourth reflected light forms an image on the image plane. Through this special design, the optical path can be folded without increasing the number of components, which helps to reduce the volume of the off-axis three-mirror optical system.

Description

Technical Field

[0001] The present invention relates to the technical field of optical systems, and in particular to an off-axis three-mirror optical system. Background Art

[0002] With the advancement of ultra-precision machining technology, the description of component surfaces in optical systems is no longer limited to spherical and aspheric surfaces, but has gradually evolved to free-form surfaces without rotational symmetry. The application of free-form surfaces allows for greater design freedom in optical design, opening up new possibilities for improving imaging quality and reducing system size.

[0003] High resolution and compact size have always been the goals of aerospace camera design. Once the detector pixel size is determined, the focal length of the optical system determines the ground resolution of the aerial camera. Improving ground resolution requires an optical system with a very long focal length. However, minimizing the camera's size requires minimizing the length of the optical system in all directions. Therefore, there is a certain contradiction between a long focal length and a small size.

[0004] The off-axis three-mirror optical imaging system in the related art has a long focal length, but its optical structure lacks the necessary optical path folding, which makes the optical imaging system relatively large. Summary of the Invention

[0005] Based on this, the embodiment of the present application proposes an off-axis three-mirror optical system, which is beneficial for further reducing the volume of the optical system while ensuring a long focal length, and is beneficial for realizing a compact off-axis three-mirror optical imaging system.

[0006] The present application proposes an off-axis three-mirror optical system. The off-axis three-mirror optical system includes a first reflector, a second reflector, and a third reflector. The first reflector is used to reflect light from the object side to form a first reflected light. The second reflector is arranged on the reflected light path of the first reflector, and is used to reflect the first reflected light to form a second reflected light. The third reflector is arranged on the reflected light path of the second reflector, and is used to reflect the second reflected light to form a third reflected light directed toward the second reflector. The second reflector is also used to reflect the third reflected light to form a fourth reflected light, and the fourth reflected light is imaged at the image plane.

[0007] In this application, a light beam incident on the off-axis three-mirror optical system is reflected twice by the second reflector, thereby achieving four reflections of the light beam through the three reflectors. This unique design achieves folding of the optical path without increasing the number of components, which helps reduce the size of the off-axis three-mirror optical system while maintaining a long focal length, and reduces the difficulty of installation and alignment. Furthermore, with the same number of three reflectors, the light is reflected four times, which is equivalent to adding a reflector. This helps reduce the optical power of each reflector, reduces the radius of curvature of the mirror surface, and reduces the difficulty of optical component processing.

[0008] Furthermore, the off-axis three-mirror optical system further includes an aperture stop, and the aperture stop is arranged on the first reflecting mirror or the third reflecting mirror.

[0009] Alternatively, in some embodiments, the aperture stop of the off-axis three-mirror optical system is arranged between the object side and the first reflector, and is located on the optical path of the light from the object side.

[0010] In some embodiments, the reflective surfaces of the first reflector, the second reflector, and the third reflector are spherical, aspherical, and free-form surfaces.

[0011] In some embodiments, the reflective surfaces of the first reflector, the second reflector, and the third reflector are all free-form surfaces, and a first three-dimensional rectangular coordinate system (x1, y1, z1) is defined in space;

[0012] In space, relative to the first three-dimensional rectangular coordinate system (x1, y1, z1), a second three-dimensional rectangular coordinate system (x2, y2, z2) is defined based on the first reflector;

[0013] In space, relative to the first three-dimensional rectangular coordinate system (x1, y1, z1), a third three-dimensional rectangular coordinate system (x3, y3, z3) is defined based on the second reflector;

[0014] In space, relative to the first three-dimensional rectangular coordinate system (x1, y1, z1), a fourth three-dimensional rectangular coordinate system (x4, y4, z4) is defined based on the third reflector;

[0015] In space, relative to the first three-dimensional rectangular coordinate system (x1, y1, z1), a fifth three-dimensional rectangular coordinate system (x5, y5, z5) is defined based on the image plane;

[0016] The coordinates of the origin of the second three-dimensional rectangular coordinate system (x2, y2, z2) in the first three-dimensional rectangular coordinate system (x1, y1, z1) are (0 mm, -3.606058 mm, 441.699735 mm), and the positive direction of the z2 axis is rotated counterclockwise by 10.156621 degrees relative to the positive direction of the z1 axis of the first three-dimensional rectangular coordinate system (x1, y1, z1);

[0017] The coordinates of the origin of the third three-dimensional rectangular coordinate system (x3, y3, z3) in the first three-dimensional rectangular coordinate system (x1, y1, z1) are (0 mm, -236.197739 mm, 72.477861 mm), and the positive direction of the z3 axis is rotated 7.664499 degrees counterclockwise relative to the positive direction of the z1 axis of the first three-dimensional rectangular coordinate system (x1, y1, z1);

[0018] The coordinates of the origin of the fourth three-dimensional rectangular coordinate system (x4, y4, z4) in the first three-dimensional rectangular coordinate system (x1, y1, z1) are (0 mm, -257.371562 mm, 456.080600 mm), and the positive direction of the z4 axis is rotated counterclockwise by 0.621483 degrees relative to the positive direction of the z1 axis of the first three-dimensional rectangular coordinate system (x1, y1, z1);

[0019] The coordinates of the origin of the fifth three-dimensional rectangular coordinate system (x5, y5, z5) in the first three-dimensional rectangular coordinate system (x1, y1, z1) are (0mm, -127.405735mm, 471.826343mm), and the positive direction of the z5 axis is rotated 18.815418 degrees counterclockwise relative to the positive direction of the z1 axis of the first three-dimensional rectangular coordinate system (x1, y1, z1).

[0020] In some embodiments, the reflecting surface of the first reflector is a fourth-order polynomial free-form surface about x2y2, the reflecting surface of the second reflector is a sixth-order polynomial free-form surface about x3y3, and the reflecting surface of the third reflector is a sixth-order polynomial free-form surface about x4y4.

[0021] In some embodiments, the equation of the 4th degree polynomial of x2y2 is:

[0022]

[0023] Wherein, c is the base curvature of the first reflector, k is the quadratic surface coefficient of the first reflector, c=-4.212955E-04, k=-4.422194E+00, A3=-4.820757E-03, A4=-3.074835E-05, A6=-1.966639E-06, A8=6.349666E-08, A 10=4.290582E-08, A 11 =4.429853E-11, A 13 =8.264656E-11, A 15 =3.376195E-11.

[0024] In some embodiments, the equation of the 6th degree polynomial of x3y3 is:

[0025]

[0026] Wherein, c is the base curvature of the second reflector, k is the quadratic surface coefficient of the second reflector, c=-3.662751E-04, k=-4.032032E+01, A3=1.154211E-01, A4=-9.521947E-05, A6=3.071521E-05, A8=1.054537E-07, A 10 =-1.547028E-08, A 11 =5.999201E-10, A 13 =1.136090E-09, A 15 =2.627475E-10, A 17 =-4.642604E-13, A 1g =-2.663330E-12, A 21 =0.000000E+00, A 22 =-7.562139E-16, A 24 =-1.412069E-15, A 26 =4.622521E-15, A 28 =-4.318231E-16.

[0027] In some embodiments, the equation of the 6th degree polynomial of x4y4 is:

[0028]

[0029] Wherein, c is the base curvature of the third reflector, k is the quadratic surface coefficient of the third reflector, c=3.055129E-04, k=-4.786315E+01, A3=2.174659E-01, A4=-4.667853E-05, A6=7.647619E-05, A8=2.750348E-07, A 10 =9.428285E-08, A 11 =5.071565E-10, A 13 =1.019023E-09, A15 =5.371274E-10, A 17 =-2.049697E-13, A 19 =-1.267790E-12, A 21 =-5.818602E-13, A 22 =6.683527E-16, A 24 =2.869677E-15, A 26 =8.119148E-15, A 28 =-4.726691E-16.

[0030] In some embodiments, the field of view of the off-axis three-mirror optical system is 4°×3°.

[0031] In some embodiments, materials of the first reflector, the second reflector, and the third reflector include gold, silver, silicon carbide, microcrystalline, or aluminum alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic structural diagram of an off-axis three-mirror optical system according to an embodiment of the present application;

[0033] Figure 2 This is an MTF curve diagram of the off-axis three-mirror optical system according to an embodiment of the present application;

[0034] Figure 3 This is an RMS wavefront aberration diagram of the off-axis three-mirror optical system according to an embodiment of the present application. DETAILED DESCRIPTION

[0035] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0036] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0037] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0038] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two components, or interaction between two components, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0039] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0040] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be an intermediate element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only implementation methods.

[0041] Off-axis reflective optical systems have gradually become a hot topic in optical system design research. This is primarily due to their lack of central obstruction, high light energy utilization, and ability to operate over a wide wavelength range. Furthermore, the use of reflection in typical off-axis reflective optical systems effectively folds the optical path, reducing system size.

[0042] High resolution and compact size have always been the goals of aerospace camera design. Once the detector pixel size is determined, the focal length of the optical system determines the ground-level resolution of the aerial camera. As the demand for ground-level resolution increases, the required focal length of the optical system becomes longer and longer. This makes existing off-axis reflective optical systems unable to meet the requirements of small size. Therefore, there is an urgent need to design a compact off-axis three-mirror optical imaging system with a long focal length.

[0043] Based on this, the present application proposes an off-axis three-mirror optical system 1. Figures 1 to 3 As shown, the off-axis three-mirror optical system 1 includes a first reflector 100, a second reflector 200, and a third reflector 300. The first reflector 100 is configured to reflect light from the object side to form a first reflected light A. The second reflector 200 is disposed in the reflected light path of the first reflector 100 and is configured to reflect the first reflected light A to form a second reflected light B. The third reflector 300 is disposed in the reflected light path of the second reflector 200 and is configured to reflect the second reflected light B to form a third reflected light C directed toward the second reflector 200. The second reflector 200 is further configured to reflect the third reflected light C to form a fourth reflected light D, and the fourth reflected light D forms an image at the image plane 400.

[0044] In the present application, the first reflector 100, the second reflector 200, and the third reflector 300 each reflect the optical path four times, thereby further folding the optical path without adding additional reflectors, thereby realizing a compact off-axis three-mirror optical system with a long focal length and small size. Specifically, the optical path of the off-axis three-mirror optical system 1 during operation is as follows: In this system, light emitted from an infinitely distant object point is incident on the first reflector 100 at a certain angle. Reflected by the first reflector 100, it forms a first reflected light A. The first reflected light A passes through the second reflector 200 for the first time and is reflected by the second reflector 200 to form a second reflected light B. The second reflected light B is reflected by the third reflector 300 to form a third reflected light C. The incident angle of the second reflected light B on the third reflector 300 is relatively small, and the exit angle of the third reflected light C after reflection is also relatively small, so that the second reflected light B passes through the second reflector 200 for a second time after being reflected by the third reflector 300. At this time, the third reflected light C is reflected by the second reflector 200 for the second time to form a fourth reflected light D. It is easy to understand that the second reflected light B can also be considered to be reflected by the third reflector 300 to the fourth reflector, except that the fourth reflector has the same surface parameters and position coordinates as the second reflector 200. Ultimately, the fourth reflected light D is imaged at the image plane 400 between the first reflector 100 and the third reflector 300. The image plane 400 refers to the location of the imaging plane. For example, a photosensitive element such as an image sensor can be disposed at the image plane 400.

[0045] In this application, a light beam incident on the off-axis three-mirror optical system 1 is reflected twice by the second reflector 200, thereby achieving four reflections of the light beam through the three reflectors. This unique design achieves folding of the optical path without increasing the number of components, which helps reduce the size of the off-axis three-mirror optical system 1 while maintaining a long focal length. Furthermore, with the same number of three reflectors, the light is reflected four times, which is equivalent to adding another reflector. This helps reduce the optical power of each reflector, reduces the radius of curvature of the mirror surface, and reduces the difficulty of manufacturing the optical components.

[0046] Furthermore, the off-axis three-mirror optical system 1 also includes an aperture stop (not shown). An aperture stop refers to an aperture screen or the frame of various imaging elements (such as lenses and mirrors) in an optical system that can limit the imaging beam. The position of the aperture stop of the off-axis three-mirror optical system 1 can be flexibly set. For example, the aperture stop can be set on the first reflector 100. Alternatively, the aperture stop can be set on the third reflector 300.

[0047] Alternatively, in some embodiments, an aperture stop can be disposed between the object and the first reflector 100, and located in the optical path of light from the object. The aperture stop is disposed in front of the off-axis three-mirror optical system 1, that is, in the optical path before the light enters the first reflector 100. Because the aperture stop is an independent optical component and not connected to the individual reflectors, it can be freely moved and adjusted in space, thereby further increasing the adjustable freedom of the off-axis three-mirror optical system 1, further improving the optical performance of the off-axis three-mirror optical system 1, and thus improving imaging quality.

[0048] In some embodiments, the materials of the first reflector 100, the second reflector 200, and the third reflector 30 include gold, silver, silicon carbide, microcrystalline, or aluminum alloy. Those skilled in the art can flexibly select materials based on processing costs, material processing difficulty, and usage scenarios.

[0049] In some embodiments, the reflecting surface of the first reflector 100 is one of a spherical surface, an aspherical surface, and a free-form surface. The spherical first reflector 100 is simple to process and easy to inspect, which is conducive to reducing production costs. An aspheric surface refers to a spherical quadratic surface base with an even-order term of the polar diameter added, which itself is still a rotationally symmetric surface. The processing method of an aspheric surface is more complicated than that of a spherical surface, but the use of such an aspheric first reflector 100 is conducive to better correction of aberrations, thereby improving imaging quality. A free-form surface is an optical surface that does not have rotational symmetry. Compared with an aspheric surface, a free-form surface has greater degrees of freedom and can better control the direction of light emission according to needs. The use of a free-form first reflector 100 is conducive to better correction of aberrations, thereby improving imaging quality.

[0050] It is easy to understand that the reflective surface shapes of the second reflector 200 and the third reflector 300 can also be flexibly selected. Specifically, in some embodiments, the reflective surface of the second reflector 200 is one of a spherical surface, an aspherical surface, and a free-form surface. In some embodiments, the reflective surface of the third reflector 300 is one of a spherical surface, an aspherical surface, and a free-form surface.

[0051] In a specific embodiment, the reflective surfaces of the first reflector 100, the second reflector 200, and the third reflector 300 are all free-form surfaces. This configuration provides the off-axis three-mirror optical system 1 with a greater degree of freedom, allowing for flexible configuration of the parameters of each reflector to achieve a high level of imaging quality.

[0052] In some embodiments, a first three-dimensional rectangular coordinate system (x1, y1, z1) is defined in the space. The first three-dimensional rectangular coordinate system (x1, y1, z1) is the global coordinate system of the entire space, that is, the absolute coordinate system.

[0053] In space, relative to the first three-dimensional rectangular coordinate system (x1, y1, z1), a second three-dimensional rectangular coordinate system (x2, y2, z2) is defined based on the first reflector 100. That is, the second three-dimensional rectangular coordinate system (x2, y2, z2) is a spatial coordinate system established based on the first reflector 100, and is a local coordinate system.

[0054] In space, relative to the first three-dimensional rectangular coordinate system (x1, y1, z1), a third three-dimensional rectangular coordinate system (x3, y3, z3) is defined based on the second reflector 200. That is, the third three-dimensional rectangular coordinate system (x3, y3, z3) is a spatial coordinate system established based on the second reflector 200, and is a local coordinate system.

[0055] In space, relative to the first three-dimensional rectangular coordinate system (x1, y1, z1), a fourth three-dimensional rectangular coordinate system (x4, y4, z4) is defined based on the third reflector 300. That is, the fourth three-dimensional rectangular coordinate system (x4, y4, z4) is a spatial coordinate system established based on the third reflector 300, and is a local coordinate system.

[0056] In space, relative to the first three-dimensional rectangular coordinate system (x1, y1, z1), a fifth three-dimensional rectangular coordinate system (x5, y5, z5) is defined based on the image plane 400. That is to say, the fifth three-dimensional rectangular coordinate system (x5, y5, z5) is a spatial coordinate system established based on the image plane 400, and is a local coordinate system.

[0057] In this way, a relative relationship exists between the local coordinate system of each reflector, as well as the local coordinate system at the image plane 400, and the global coordinate system. In other words, when describing the coordinates of each reflector, it can be described according to the local coordinate system in which the reflector resides, and then the coordinate value is converted to the coordinate value in the absolute coordinate system using the relative relationship between the coordinate systems. This arrangement helps simplify the expression of the curved surface of each reflector and facilitates the determination of the coefficients of multiple high-order expressions for each reflector.

[0058] The specific relationship between the coordinate system established by each reflector itself and the coordinate system established by the image plane 400 itself and the absolute coordinate system of the entire space is:

[0059] like Figure 1 As shown, the coordinates of the origin of the second three-dimensional rectangular coordinate system (x2, y2, z2) in the first three-dimensional rectangular coordinate system (x1, y1, z1) are (0mm, -3.606058mm, 441.699735mm), and the positive direction of the z2 axis is rotated counterclockwise by 10.156621 degrees relative to the positive direction of the z1 axis of the first three-dimensional rectangular coordinate system (x1, y1, z1).

[0060] The coordinates of the origin of the third three-dimensional rectangular coordinate system (x3, y3, z3) in the first three-dimensional rectangular coordinate system (x1, y1, z1) are (0mm, -236.197739mm, 72.477861mm), and the positive direction of the z3 axis is rotated counterclockwise by 7.664499 degrees relative to the positive direction of the z1 axis of the first three-dimensional rectangular coordinate system (x1, y1, z1) (not shown in the figure).

[0061] The coordinates of the origin of the fourth three-dimensional rectangular coordinate system (x4, y4, z4) in the first three-dimensional rectangular coordinate system (x1, y1, z1) are (0mm, -257.371562mm, 456.080600mm), and the positive direction of the z4 axis is rotated counterclockwise by 0.621483 degrees relative to the positive direction of the z1 axis of the first three-dimensional rectangular coordinate system (x1, y1, z1).

[0062] The coordinates of the origin of the fifth three-dimensional rectangular coordinate system (x5, y5, z5) in the first three-dimensional rectangular coordinate system (x1, y1, z1) are (0mm, -127.405735mm, 471.826343mm), and the positive direction of the z5 axis is rotated 18.815418 degrees counterclockwise relative to the positive direction of the z1 axis of the first three-dimensional rectangular coordinate system (x1, y1, z1).

[0063] Through the relative relationship of this coordinate system, the coordinate values ​​of the first reflector 100, the second reflector 200, the third reflector 300 and the image plane 400 in different coordinate systems can be converted, which is beneficial to simplify the expression of the surface and facilitate the determination of the coefficients of the expression of the surface.

[0064] Furthermore, the reflective surfaces of the three reflectors are all free-form surfaces, and adopt XY polynomial free-form surfaces. Specifically, the formula of the XY polynomial is:

[0065]

[0066]

[0067] Among them, z is the surface sag, c is the base curvature of the surface, k is the quadratic surface coefficient, A j are the coefficients of each term in the polynomial.

[0068] The number of terms in a polynomial can be infinite, but increasing the number of terms in the xy polynomial without limit during the optimization process will place a huge burden on ray tracing, resulting in excessive optimization time and hindering the efficiency of determining the coefficients of the free-form surface. Therefore, in some embodiments, the reflective surface of the first reflector 100 is a free-form surface of a 4th-degree polynomial with respect to x2y2, the reflective surface of the second reflector 200 is a free-form surface of a 6th-degree polynomial with respect to x3y3, and the reflective surface of the third reflector 300 is a free-form surface of a 6th-degree polynomial with respect to x4y4.

[0069] Since the reflectors of the off-axis three-mirror optical system 1 of this embodiment are symmetrical about the yz plane, only the even-order terms of x can be retained. Specifically, the equation of the fourth-order polynomial of x2y2 of the reflective surface of the first reflector 100 is:

[0070]

[0071] In this embodiment, the base curvature c, the quadratic surface coefficient k, and the coefficients A in the x2y2 polynomial of the reflecting surface of the first reflector 100 are j Please refer to Table 1 for the values ​​of . It can be understood that the base curvature c, the quadratic surface coefficient k and the various coefficients A j The values ​​of are not limited to those in Table 1, and those skilled in the art can adjust them according to actual needs.

[0072] Table 1 Coefficients of the x2y2 polynomial of the reflecting surface of the first reflector

[0073] Base curvature c -4.212955E-04 Quadratic surface coefficient k -4.422194E+00 <![CDATA[A3]]> -4.820757E-03 <![CDATA[A4]]> -3.074835E-05 <![CDATA[A6]]> -1.966639E-06 <![CDATA[A8]]> 6.349666E-08 <![CDATA[A 10 ]]> 4.290582E-08 <![CDATA[A 11 ]]> 4.429853E-11 <![CDATA[A 13 ]]> 8.264656E-11 <![CDATA[A 15 ]]> 3.376195E-11

[0074] In some embodiments, the equation of the sixth-order polynomial of x3y3 of the second reflector 200 is:

[0075]

[0076] In this embodiment, the base curvature c, the quadratic surface coefficient k, and the coefficients A in the x3y3 polynomial of the reflection surface of the second reflector 200 are j Please refer to Table 2 for the values ​​of . It can be understood that the base curvature c, the quadratic surface coefficient k and the various coefficients A j The value of is not limited to that described in Table 2, and those skilled in the art can adjust it according to actual needs.

[0077] Table 2 Coefficients of the x3y3 polynomial of the reflecting surface of the second reflector

[0078] Base curvature c -3.662751E-04 Quadratic surface coefficient k -4.032032E+01 <![CDATA[A3]]> 1.154211E-01 <![CDATA[A4]]> -9.521947E-05 <![CDATA[A6]]> 3.071521E-05 <![CDATA[A8]]> 1.054537E-07 <![CDATA[A 10 ]]> -1.547028E-08 <![CDATA[A 11 ]]> 5.999201E-10 <![CDATA[A 13 ]]> 1.136090E-09 <![CDATA[A 15 ]]> 2.627475E-10 <![CDATA[A 17 ]]> -4.642604E-13 <![CDATA[A 19 ]]> -2.663330E-12 <![CDATA[A 21 ]]> 0.000000E+00 <![CDATA[A 22 ]]> -7.562139E-16 <![CDATA[A 24 ]]> -1.412069E-15 <![CDATA[A 26 ]]> 4.622521E-15 <![CDATA[A 28 ]]> -4.318231E-16

[0079] In some embodiments, the equation of the sixth-order polynomial of x4y4 of the third reflector 300 is:

[0080]

[0081] In this embodiment, the base curvature c, the quadratic surface coefficient k, and the coefficients A in the x4y4 polynomial of the reflective surface of the third reflector 300 are j Please refer to Table 3 for the values ​​of . It can be understood that the base curvature c, the quadratic surface coefficient k and the various coefficients A j The value of is not limited to that described in Table 3, and those skilled in the art can adjust it according to actual needs.

[0082] Table 3 Coefficients of the x3y3 polynomial of the reflecting surface of the second reflector

[0083]

[0084]

[0085] Furthermore, the field of view of the above-mentioned off-axis three-mirror optical system 1 using a free-form surface is 4°×3°.

[0086] Furthermore, the off-axis three-mirror optical system 1 has an F number of 15, a focal length of 2 m, and an entrance pupil diameter of 133 mm.

[0087] like Figure 2 , which is the MTF curve of the above-mentioned off-axis three-mirror optical system 1 using a free-form surface. As can be seen from the curve, the designed off-axis three-mirror optical system 1 has a good imaging quality.

[0088] like Figure 3 Figure 2 shows the RMS wavefront aberration diagram of the off-axis three-mirror optical system 1 using a free-form surface. The RMS wavefront aberration diagram shows that the system has an average wavefront aberration of 0.014964λ and a standard deviation of 0.0022383λ, indicating that the designed off-axis three-mirror optical system 1 has good imaging quality.

[0089] Therefore, compared to conventional off-axis three-mirror optical systems, this application utilizes a three-mirror, four-fold refraction structure, achieving optical path folding without increasing the number of system components, thereby reducing the size of the optical system. Furthermore, with the same number of mirrors, the optical power of the optical system can be distributed across more reflective surfaces, further reducing the radius of curvature of the mirror surface and simplifying manufacturing.

[0090] The various technical features of the embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the various technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0091] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. An off-axis three-mirror optical system, characterized in that: include: a first reflector, configured to reflect light from an object side to form a first reflected light; a second reflecting mirror, the second reflecting mirror being arranged on a reflecting light path of the first reflecting mirror and being used to reflect the first reflected light to form a second reflected light; as well as a third reflecting mirror, the third reflecting mirror being arranged on a reflecting light path of the second reflecting mirror, and being configured to reflect the second reflected light to form a third reflected light directed toward the second reflecting mirror, the second reflecting mirror being further configured to reflect the third reflected light to form a fourth reflected light, and the fourth reflected light forming an image at an image plane; Define a first three-dimensional rectangular coordinate system (x1, y1, z1) in space; In space, relative to the first three-dimensional rectangular coordinate system (x1, y1, z1), a second three-dimensional rectangular coordinate system (x2, y2, z2) is defined based on the first reflector; In space, relative to the first three-dimensional rectangular coordinate system (x1, y1, z1), a third three-dimensional rectangular coordinate system (x3, y3, z3) is defined based on the second reflector; In space, relative to the first three-dimensional rectangular coordinate system (x1, y1, z1), a fourth three-dimensional rectangular coordinate system (x4, y4, z4) is defined based on the third reflector; In space, relative to the first three-dimensional rectangular coordinate system (x1, y1, z1), a fifth three-dimensional rectangular coordinate system (x5, y5, z5) is defined based on the image plane; The coordinates of the origin of the second three-dimensional rectangular coordinate system (x2, y2, z2) in the first three-dimensional rectangular coordinate system (x1, y1, z1) are (0 mm, -3.606058 mm, 441.699735 mm), and the positive direction of the z2 axis is rotated counterclockwise by 10.156621 degrees relative to the positive direction of the z1 axis of the first three-dimensional rectangular coordinate system (x1, y1, z1); The coordinates of the origin of the third three-dimensional rectangular coordinate system (x3, y3, z3) in the first three-dimensional rectangular coordinate system (x1, y1, z1) are (0 mm, -236.197739 mm, 72.477861 mm), and the positive direction of the z3 axis is rotated 7.664499 degrees counterclockwise relative to the positive direction of the z1 axis of the first three-dimensional rectangular coordinate system (x1, y1, z1); The coordinates of the origin of the fourth three-dimensional rectangular coordinate system (x4, y4, z4) in the first three-dimensional rectangular coordinate system (x1, y1, z1) are (0 mm, -257.371562 mm, 456.080600 mm), and the positive direction of the z4 axis is rotated counterclockwise by 0.621483 degrees relative to the positive direction of the z1 axis of the first three-dimensional rectangular coordinate system (x1, y1, z1); The coordinates of the origin of the fifth three-dimensional rectangular coordinate system (x5, y5, z5) in the first three-dimensional rectangular coordinate system (x1, y1, z1) are (0mm, -127.405735mm, 471.826343mm), and the positive direction of the z5 axis is rotated 18.815418 degrees counterclockwise relative to the positive direction of the z1 axis of the first three-dimensional rectangular coordinate system (x1, y1, z1).

2. The off-axis three-mirror optical system according to claim 1, wherein: The off-axis three-mirror optical system further includes an aperture stop, which is arranged on the first reflecting mirror or the third reflecting mirror; Alternatively, the aperture stop is disposed between the object side and the first reflector and is located on the optical path of the light from the object side.

3. The off-axis three-mirror optical system according to claim 1, wherein: The reflecting surfaces of the first reflecting mirror, the second reflecting mirror and the third reflecting mirror are one of spherical surfaces, aspherical surfaces and free-form surfaces.

4. The off-axis three-mirror optical system according to claim 1, wherein: The reflecting surface of the first reflecting mirror is a fourth-order polynomial free-form surface about x2y2, the reflecting surface of the second reflecting mirror is a sixth-order polynomial free-form surface about x3y3, and the reflecting surface of the third reflecting mirror is a sixth-order polynomial free-form surface about x4y4.

5. The off-axis three-mirror optical system according to claim 4, wherein: The equation of the 4th degree polynomial of x2y2 is: Wherein, c is the base curvature of the first reflector, k is the quadratic surface coefficient of the first reflector, c=-4.212955E-04, k=-4.422194E+00, A3=-4.820757E-03, A4=-3.074835E-05, A6=-1.966639E-06, A8=6.349666E-08, A 10 =4.290582E-08, A 11 =4.429853E-11, A 13 =8.264656E-11, A 15 =3.376195E-11.

6. The off-axis three-mirror optical system according to claim 5, wherein: The equation of the sixth-degree polynomial of x3y3 is: Wherein, c is the base curvature of the second reflector, k is the quadratic surface coefficient of the second reflector, c=-3.662751E-04, k=-4.032032E+01, A3=1.154211E-01, A4=-9.521947E-05, A6=3.071521E-05, A8=1.054537E-07, A 10 =-1.547028E-08, A 11 =5.999201E-10, A 13 =1.136090E-09, A 15 =2.627475E-10, A 17 =-4.642604E-13, A 19 =-2.663330E-12, A 21 =0.000000E+00, A 22 =-7.562139E-16, A 24 =-1.412069E-15, A 26 =4.622521E-15, A 28 =-4.318231E-16.

7. The off-axis three-mirror optical system according to claim 6, wherein: The equation of the sixth-degree polynomial of x4y4 is: Wherein, c is the base curvature of the third reflector, k is the quadratic surface coefficient of the third reflector, c=3.055129E-04, k=-4.786315E+01, A3=2.174659E-01, A4=-4.667853E-05, A6=7.647619E-05, A8=2.750348E-07, A 10 =9.428285E-08, A 11 =5.071565E-10, A 13 =1.019023E-09, A 15 =5.371274E-10, A 17 =-2.049697E-13, A 19 =-1.267790E-12, A 21 =-5.818602E-13, A 22 =6.683527E-16, A 24 =2.869677E-15, A 26 =8.119148E-15, A 28 =-4.726691E-16.

8. The off-axis three-mirror optical system according to claim 7, wherein: The field angle of the off-axis three-mirror optical system is 4°×3°.

9. The off-axis three-mirror optical system according to claim 1, wherein: Materials of the first reflecting mirror, the second reflecting mirror and the third reflecting mirror include gold, silver, silicon carbide, microcrystals or aluminum alloy.

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