CN117420668A - Dual-band monitoring system based on free-form surface off-axis four-reflection - Google Patents
Dual-band monitoring system based on free-form surface off-axis four-reflection Download PDFInfo
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- 230000009977 dual effect Effects 0.000 claims abstract description 7
- 230000003287 optical effect Effects 0.000 claims description 131
- 210000001747 pupil Anatomy 0.000 claims description 3
- 238000003384 imaging method Methods 0.000 description 32
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- 201000009310 astigmatism Diseases 0.000 description 2
- 238000012512 characterization method Methods 0.000 description 2
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B17/00—Systems with reflecting surfaces, with or without refracting elements
- G02B17/02—Catoptric systems, e.g. image erecting and reversing system
- G02B17/06—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror
- G02B17/0647—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror using more than three curved mirrors
- G02B17/0663—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror using more than three curved mirrors off-axis or unobscured systems in which not all of the mirrors share a common axis of rotational symmetry, e.g. at least one of the mirrors is warped, tilted or decentered with respect to the other elements
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B17/00—Systems with reflecting surfaces, with or without refracting elements
- G02B17/02—Catoptric systems, e.g. image erecting and reversing system
- G02B17/06—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror
- G02B17/0668—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror having non-imaging properties
- G02B17/0684—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror having non-imaging properties for light collecting, e.g. for use with a detector
Abstract
The invention relates to a dual-band monitoring system based on free-form surface off-axis four-reflection, which comprises a main reflector 1, a secondary reflector 2, a third reflector 3, a fourth reflector 4 and a diaphragm positioned on the main reflector 1, wherein a higher-performance free-form surface is adopted, and a Zernike polynomial aspheric surface is designed, so that the monitoring under the dual bands of visible light and infrared light can be realized, and the system has the characteristics of wide working band, large aperture, large angle of view and compact structure, and can meet the monitoring requirements under a plurality of scenes.
Description
Technical Field
The invention relates to the field of optical lenses and optical designs, in particular to a dual-band monitoring system based on free-form surface off-axis four-reflection.
Background
In recent years, along with the continuous development of optical technology, the importance of the optical remote sensing field is continuously increased, the optical system of the remote sensing field is continuously developed, higher requirements are provided for the optical performance of the optical system, the remote sensing optical system is gradually developed towards the directions of large caliber, large view field, compact whole structure, wide working band and the like, the reflective optical system has unique advantages in achieving the targets, and the reflective optical system has the characteristics of better imaging quality due to the absence of optical color difference, compact whole system structure due to the folded light path and the like, so that the optical system can be well applied to the optical remote sensing field. At present, in the field of optical remote sensing, there are mainly several types of reflective optical systems such as coaxial reflective optical system and off-axis reflective optical system, and the design of reflective optical system used in monitoring on the market is basically based on coaxial reflective system or off-axis three-mirror system, and coaxial reflective system has the problems of narrow working band, difficult large imaging field of view of the system, and off-axis three-mirror system can realize the functions of wide working band, large caliber, large field of view, etc., but has the problems of difficult correction of astigmatism and field curvature of wide field of view of the system, limited aberration balance capability, low imaging quality, etc. Aiming at the series of problems, the invention designs an off-axis four-inverse dual-band monitoring optical system based on a free-form surface.
The conventional spherical reflecting mirror makes the structural design of the reflecting system complex, makes it difficult to reduce the volume thereof, and makes it difficult to correct aberrations. Compared with the traditional spherical reflection system, the aspheric system can correct some primary aberration; however, the traditional aspheric surface has rotational symmetry (axisymmetry), the curvature radiuses in meridian and sagittal directions are not independent, the aberration of the non-rotational symmetry is difficult to correct, the aberration balancing capability is limited to a certain extent, and the imaging quality requirement in design is difficult to meet. Compared with the traditional rotationally symmetrical spherical surface and aspheric surface system, the free-form surface has great design freedom, the optical surface shape can be formed by randomly combining asymmetric, irregular and complex free-form surfaces, the aberration balance and correction capability are strong, although the mathematical characterization of the free-form surfaces is very complex, the system is enabled to be a future development trend along with the continuous development of processing technology and adjustment technology, the free-form surfaces can simplify the system structure to the greatest extent, realize integration and furthest improve and improve the system performance. The invention adopts a higher-performance free-form surface and a Zernike polynomial aspheric surface, can effectively compensate and correct off-axis aberration of the system, and can greatly improve imaging quality.
The invention designs an off-axis four-reflection dual-band monitoring optical system based on a free-form surface, which can be used for monitoring and monitoring environmental protection, urban safety, forest fire and other aspects. The system well solves the problems of narrow working wave band, small imaging field, low imaging quality, large system volume and the like of the optical system for monitoring in the current market, and provides a better technical support for the monitoring field.
Disclosure of Invention
In order to solve the problems that an optical system for monitoring in the current market uses an on-axis reflection type system or an off-axis tri-trans type system, has a narrow working band, a small imaging view field, a large system volume and an axisymmetric aspheric surface, has wide-view field astigmatism and field curvature aberration, is difficult to correct, has limited aberration balance capacity and is difficult to meet imaging quality requirements. The invention provides an off-axis four-inverse dual-band monitoring optical system based on a free curved surface, which has small aperture, the F number of the system can reach 1.24, the imaging view field is large, the maximum half view angle reaches 4.5 degrees multiplied by 4.5 degrees, the working wave band is wide, the system comprises a visible light wave band (0.486 um-0.656 um) and an infrared light wave band (3.7 um-4.8 um), the system structure is compact, the good imaging quality can be realized, the MTF is not less than 0.3 when 100lp/mm, the root mean square radius size is less than 2.5 mu m, the field curvature is better than 0.014mm, the distortion is better than 0.9%, and the system can be applied to monitoring scenes such as environmental protection, urban safety, forest fire and the like.
In order to achieve the above object, the present invention provides a technical solution comprising:
the optical system adopts an off-axis system type reflecting structure, and comprises a main reflecting mirror, a secondary reflecting mirror, a third reflecting mirror, a fourth reflecting mirror and a diaphragm; the main reflector, the secondary reflector, the third reflector and the fourth reflector are all designed and optimized by adopting a free-form surface Zernike polynomial aspheric surface;
the system working wave band comprises a visible light wave band and an infrared light wave band, light rays of the visible light wave band and light rays of the infrared light wave band sequentially pass through the main reflector, the secondary reflector, the third reflector and the fourth reflector, after the light rays of the visible light wave band and the light rays of the infrared light wave band pass through the optical system, the light rays of the visible light wave band and the light rays of the infrared light wave band are converged on an image surface, the diaphragm is positioned on the main reflector, the size of the radius of the image surface is 10mm multiplied by 10mm, and the maximum half field angle is 4.5 degrees multiplied by 4.5 degrees;
the optical paths of the system are spatially arranged in an S shape, and the optical system satisfies the relation: t1<220.5mm, T2<280.44mm, |T1/T2| <0.79;
wherein T1 is the relative distance between the primary mirror and the third mirror, and T2 is the relative distance between the secondary mirror and the fourth mirror;
the optical system satisfies the relation: 457.64< M/|TAN (HFOV) | <488.83;
wherein M is the maximum effective half aperture of the main mirror, HFOV is half of the maximum field angle of the dual band monitoring optical system, and TAN (HFOV) is the tangent of the HFOV;
the optical system satisfies the relation: f/d is less than or equal to 1.9.
According to one aspect of the invention, the optical system satisfies the relation: 3.42<|TAN(HFOV)/BFL|×10 4 <3.73；
Wherein the HFOV is half of the maximum field angle of the dual band monitoring optical system, and the TAN (HFOV) is the tangent of the HFOV; BFL is the distance between the fourth mirror to the image plane.
According to one aspect of the invention, the system satisfies the relationship: 36.00mm < D <122.75mm;
wherein D is the maximum effective half caliber of all the reflectors in the optical system.
According to one aspect of the invention, the primary mirror, the secondary mirror, the third mirror and the fourth mirror are arranged and placed in a globally inclined eccentric relative position.
Compared with the prior art, the invention has the advantages that:
(1) The optical system disclosed by the invention adopts the dual-band monitoring system formed by the off-axis four-piece reflecting mirror designed by the free curved surface, the system is compact in structure and small in volume, the adjustment difficulty can be reduced, the main reflecting mirror, the secondary reflecting mirror, the third reflecting mirror and the fourth reflecting mirror are all designed and optimized by adopting the Zernike polynomial aspheric surface, the aberration of a wide view field can be corrected, the imaging quality of the whole system is improved, and the MTF (modulation transfer function) of the system can reach more than 0.3 at 100 lp/mm;
(2) The imaging view field of the optical system disclosed by the invention is large, the maximum half view angle reaches 4.5 degrees multiplied by 4.5 degrees, the monitoring range of the system can be effectively enlarged, the working wavelength is wide, the optical system comprises a visible light wave band (0.486 um-0.656 um) and an infrared light wave band (3.7 um-4.8 um), and the optical system can be suitable for monitoring various scenes;
the system parameters achieved by the invention are as follows: the F number of the system can reach 1.24, the aperture is large, the maximum half field angle reaches 4.5 degrees multiplied by 4.5 degrees, the observation range of the monitoring system is effectively improved, the MTF is not less than 0.3 when the MTF is 100lp/mm, the root mean square radius size is less than 2.5 mu m, the field curvature is better than 0.014mm, the distortion is better than 0.9%, and the imaging quality of the system is good. The off-axis four-inverse dual-band monitoring optical system based on the free curved surface disclosed by the invention solves the problems of narrow working band, small imaging field of view, low imaging quality, large system volume and the like of the optical system for monitoring in the current market.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural view of an optical system disclosed in a first embodiment of the present application.
Fig. 2 is a MTF multi-field diffraction transfer function diagram of an optical system disclosed in the first embodiment of the present application.
Fig. 3 is a field diagram of an optical system disclosed in a first embodiment of the present application.
Fig. 4 is a distortion chart of an optical system disclosed in the first embodiment of the present application.
Fig. 5 is a root mean square spot size diagram of an optical system disclosed in the first embodiment of the present application.
Fig. 6 is a schematic structural view of an optical system disclosed in a second embodiment of the present application.
Fig. 7 is a MTF multi-field diffraction transfer function diagram of an optical system disclosed in a second embodiment of the present application.
Fig. 8 is a field curvature diagram of an optical lens disclosed in the second embodiment of the present application.
Fig. 9 is a distortion diagram of an optical lens disclosed in the second embodiment of the present application.
Fig. 10 is a root mean square spot size diagram of an optical lens disclosed in a second embodiment of the present application.
Detailed Description
Compared with the traditional rotationally symmetrical spherical surface and the traditional aspherical surface, the free-form surface has great design freedom, the optical surface type can be formed by random combination of asymmetric, irregular and complex free-form surfaces, and the aberration balance and correction capability are strong.
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In the present invention, the terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal" and the like indicate an azimuth or a positional relationship based on that shown in the drawings. These terms are only used to better describe the present invention and its embodiments and are not intended to limit the scope of the indicated devices, elements or components to the particular orientations or to configure and operate in the particular orientations. Also, some of the terms described above may be used to indicate other meanings in addition to orientation or positional relationships, for example, the term "upper" may also be used to indicate some sort of attachment or connection in some cases. The specific meaning of these terms in the present invention will be understood by those of ordinary skill in the art according to the specific circumstances. Furthermore, the terms "mounted," "configured," "provided," "connected," and "connected" are to be construed broadly. For example, it may be a fixed connection, a removable connection, or a unitary construction; may be a mechanical connection, or an electrical connection; may be directly connected, or indirectly connected through intervening media, or may be in internal communication between two devices, elements, or components. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances. Furthermore, the terms "first," "second," and the like, are used primarily to distinguish between different devices, elements, or components (the particular species and configurations may be the same or different), and are not used to indicate or imply the relative importance and number of devices, elements, or components indicated. Unless otherwise indicated, the meaning of "a plurality" is two or more.
The invention provides an off-axis four-inverse dual-band monitoring optical system based on a free-form surface, which comprises the following components in light path sequence: the light rays of visible light and infrared wave bands are reflected by the main reflector, reflected by the secondary reflector and reflected by the third reflector in sequence, and collected on an image surface after being reflected by the fourth reflector; the system adopts the design of a free-form surface to achieve the purposes of correcting aberration, improving imaging quality of the system and compacting the structure.
The optical system according to the present disclosure will be described in detail below by referring to examples, specific parameters and accompanying drawings.
Example 1
As shown in fig. 1, the off-axis four-inverse dual-band monitoring optical system based on the free curved surface is respectively as follows in the light path sequence: the light beam of the visible light wave band and the infrared light wave band sequentially passes through the structure of the system and finally is collected on the image plane, and the light beam of the visible light wave band and the infrared light wave band in the figure S1 represents the image plane. The embodiment is designed to use a right-hand coordinate system, and in the meridian plane, the Z axis is from left to right in FIG. 1, and the Y axis is perpendicular to the Z axis.
Specifically, taking the system parameters of the embodiment, i.e. the focal length f= 67.14mm, the F number=1.24, and the maximum half field angle hfov=4.5° of the optical system as an example, other parameters of the optical system are given in table 1 below. Wherein the elements from the object side to the image side along the optical axis of the optical system are sequentially arranged in the order of the elements shown in fig. one. In the same mirror, the radius of curvature in table 1 is the radius of curvature of the object side or image side of the corresponding surface number at the optical axis. The first value in the "thickness" parameter column of the mirror is the thickness of the lens on the optical axis, and the second value is the distance from the image side of the mirror to the object side of the latter surface on the optical axis. The direction from the object side surface of the first reflecting mirror to the object side surface of the last reflecting mirror is the positive direction of the optical axis by default, when the value is negative, the mirror surface is arranged on the image side of the vertex of the rear surface, and if the value is positive, the mirror surface is arranged on the object side of the vertex of the rear surface. It is understood that the units of radius of curvature, thickness, and focal length in table 1 are all mm. And the refractive index in table 1 is obtained at a reference wavelength of 0.486um and the focal length is obtained at a reference wavelength of 0.486 um.
The optical system data table of this example is shown in table 1 below.
Table 1 parameters of dual band monitoring optical system
The optical system satisfies the relation: t1<220.5mm, T2<280.44mm, |T1/T2| <0.79; by limiting the relative distances between the main mirror 1 and the third mirror 3, and between the secondary mirror 2 and the fourth mirror 4 in the system, the effect of making the whole optical system more compact is achieved, and portability is increased.
The optical system satisfies the relation: 457.64< M/|TAN (HFOV) | <488.83, and reducing the maximum effective half aperture of the main reflector in the optical system while ensuring that the optical system can realize a large imaging view field of 4.5 degrees, wherein the maximum effective half aperture of the main reflector of the optical system is 38.4715mm, thereby being beneficial to the reduction of the whole volume of the optical system, leading the application scene of the system to be wider and being convenient for installation.
The optical system satisfies the relation: f/d is less than or equal to 1.9; the system has a certain focal length, the entrance pupil diameter of the optical system can be increased while a certain monitoring distance is ensured, the aperture of the optical system is increased, and the system is facilitated to receive more optical information.
The optical system satisfies the relation: 3.42<|TAN(HFOV)/BFL|×10 4 <3.73; the optical system can realize a large imaging view field of 4.5 degrees, and meanwhile, the distance from the fourth reflecting mirror of the last reflecting mirror to the image surface in the optical system is reduced, so that the size of the whole system is reduced, and the adjustment difficulty of the system is reduced.
The optical system satisfies the relation: 36.00mm < D <122.75mm; the maximum effective half aperture of the reflecting mirror of the optical system is 122.702mm, and the maximum effective half aperture of all reflecting mirrors in the dual-band monitoring optical system is limited, so that the effect of reducing the volume of the system and enabling the structure of the system to be more compact is achieved, and the portability of the system in application is improved.
In the first embodiment, the primary mirror 1, the secondary mirror 2, the third mirror 3 and the fourth mirror 4 are each formed by using Zernike polynomial aspheric surfaces, and the surface shape of each Zernike polynomial aspheric mirror can be defined by, but not limited to, the following aspheric equation:
wherein Z is the rise of the free-form surface, c is the curvature of the free-form surface, k is the quadric surface coefficient, A i For Zernike polynomials,expansion term for Zernike polynomials,/->Polar coordinates of free curved points; n is the number of items.
The free curved surface has great design freedom, the optical surface type can be formed by random combination of asymmetric, irregular and complex free curved surfaces, the aberration balance and correction capability are strong, although the mathematical characterization of the free curved surface is very complex, the system is applied to the future development trend along with the continuous development of the processing technology and the adjustment technology, the free curved surface can simplify the system structure, realize integration and improve the system performance. The invention adopts a higher-performance free-form surface and a Zernike polynomial aspheric surface, can effectively compensate and correct off-axis aberration of the system, and can greatly improve imaging quality.
The following table 2 gives data of the higher order coefficients G3, G4, G7, G8, G10, G11, G14, G15, G16, G19, G20 that can be used for the Zernike polynomial aspheric surface in the first embodiment.
TABLE 2 Zernike polynomial aspheric coefficients
The reflecting mirror in the embodiment is optimized by using the Zernike polynomial aspheric surface, and the Zernike polynomial aspheric surface high order term coefficients are eleven coefficients of G3, G4, G7, G8, G10, G11, G14, G15, G16, G19 and G20, so that the freedom degree of the dual-band monitoring optical system in design is increased, the off-axis aberration of the system can be effectively corrected, the imaging quality of the system is improved, the system structure is more compact, the volume of the system is reduced, and the portability of the dual-band monitoring system is improved.
Referring to fig. 2, an MTF diffraction transfer function diagram of the dual-band monitoring system according to the first embodiment is shown, wherein an abscissa along the X-axis direction represents a line pair in mm, and an ordinate along the Y-axis direction represents the MTF diffraction transfer function value, and as can be seen from fig. 2, the MTF transfer function value of each field of view of the dual-band monitoring system is not less than 0.3, which indicates that the imaging quality of the dual-band monitoring system is good and the imaging quality of each field of view is very stable.
Referring to fig. 3, a graph of a field curve of the dual-band monitoring system at a reference wavelength (0.486 um) in the first embodiment is shown, wherein the abscissa along the X-axis direction represents the field curve size in mm, and the ordinate along the Y-axis direction represents the normalized field of view, and as can be seen in fig. 3, the field curve of the dual-band monitoring system is better than 0.013mm at the reference wavelength (0.486 um), which indicates that the field curve of the dual-band monitoring system is better compensated.
Referring to fig. 4, a graph of distortion of the dual-band monitoring system at a defined wavelength of visible light in the first embodiment is shown, wherein the abscissa along the X-axis represents the magnitude of distortion, and the ordinate along the Y-axis represents the normalized field of view, and as can be seen in fig. 4, the distortion of the dual-band monitoring system is better than 0.77% at the reference wavelength (0.486 um), which indicates that the distortion of the dual-band monitoring system is well corrected.
Referring to fig. 5, a root mean square radius size diagram of the dual-band monitoring system in the first embodiment at the reference wavelength (0.486 um), wherein the abscissa along the X-axis represents the relative field of view, and the ordinate along the Y-axis represents the root mean square radius size in mm, and as can be seen from fig. 5, the root mean square radius size of the dual-band monitoring system is better than 2.5um at the reference wavelength (0.486 um), which indicates that the spherical aberration of the dual-band monitoring system is better compensated.
Example 2
As shown in fig. 6, the off-axis four-inverse dual-band monitoring system based on the free curved surface is respectively as follows in the light path sequence: the main reflector 5, the secondary reflector 6, the third reflector 7, the fourth reflector 8 and the diaphragm are positioned on the main reflector 5, S2 in the figure represents an image plane, and light rays in a visible light wave band and an infrared light wave band sequentially pass through the structure of the system and finally are collected on the image plane. The embodiment is designed to use a right-hand coordinate system, and in the meridian plane, the Z axis is from left to right in FIG. 6, and the Y axis is perpendicular to the Z axis.
Specifically, taking the example of the system parameters of the second embodiment, i.e. the focal length f=103 mm, the F number=1.9, and the maximum half field angle hfov=4.5° of the optical system as an example, other parameters of the optical system are given in table 3 below. Wherein the elements from the object side to the image side along the optical axis of the optical system are sequentially arranged in the order of the elements shown in fig. 6. In the same mirror, the radius of curvature in table 3 is the radius of curvature of the object side or image side of the corresponding surface number at the optical axis. The first value in the "thickness" parameter column of the mirror is the thickness of the lens on the optical axis, and the second value is the distance from the image side of the mirror to the object side of the latter surface on the optical axis. The direction from the object side surface of the first reflecting mirror to the object side surface of the last reflecting mirror is the positive direction of the optical axis by default, when the value is negative, the mirror surface is arranged on the image side of the vertex of the rear surface, and if the value is positive, the mirror surface is arranged on the object side of the vertex of the rear surface. It is understood that the units of radius of curvature, thickness, and focal length in table 3 are all mm. And the refractive index in table 3 is obtained at a reference wavelength of 0.486um and the focal length is obtained at a reference wavelength of 0.486 um.
The optical system data table of this example is shown in Table 3 below
Table 3 parameters of dual band monitoring optical system
The optical system satisfies the relation: t1<220.5mm, T2<280.44mm, |T1/T2| <0.79; by limiting the relative distances between the primary mirror 5 and the third mirror 7 and between the secondary mirror 6 and the fourth mirror 8 in the system, the effect of making the whole optical system more compact is achieved, and portability is increased.
The optical system satisfies the relation: 457.64< M/|TAN (HFOV) | <488.83; the maximum effective half aperture of the main reflector in the optical system is reduced while the optical system can realize a large imaging view field of 4.5 degrees, and the maximum effective half aperture of the main reflector of the optical system is 36.0166mm, so that the reduction of the whole volume of the optical system is facilitated, the application scene of the system is wider, and the installation is convenient.
The optical system satisfies the relation: f/d is less than or equal to 1.9; the system has a certain focal length, the entrance pupil diameter of the optical system can be increased while a certain monitoring distance is ensured, the aperture of the optical system is increased, and the system is facilitated to receive more optical information.
The optical system satisfies the relation: 3.42<|TAN(HFOV)/BFL|×10 4 <3.73; the optical system can realize a large imaging view field of 4.5 degrees, and meanwhile, the distance from the fourth reflecting mirror of the last reflecting mirror to the image surface in the optical system is reduced, so that the size of the whole system is reduced, and the adjustment difficulty of the system is reduced.
The optical system satisfies the relation: 36.00mm < D <122.75mm; the maximum effective half aperture of the reflecting mirror of the optical system is 98.5734mm, and the maximum effective half aperture of all reflecting mirrors in the dual-band monitoring optical system is limited, so that the effect of reducing the volume of the system and enabling the structure of the system to be more compact is achieved, and the portability of the system in application is improved.
In the second embodiment, the main mirror 5, the secondary mirror 6, the third mirror 7 and the fourth mirror 8 are each formed by using Zernike polynomial aspheric surfaces, and the surface shape of each Zernike polynomial aspheric mirror can be defined by, but not limited to, the following aspheric equation:
wherein Z is the rise of the free-form surface, c is the curvature of the free-form surface, k is the quadric surface coefficient, ai is the Zernike polynomial expansion term coefficient,expansion term for Zernike polynomials,/->Polar coordinates of free curved points; n is the number of items.
The following table 4 gives data for the higher order coefficients G3, G4, G7, G8, G10, G11, G14, G15 that can be used for the Zernike polynomial aspheric surfaces in the second embodiment.
TABLE 4 Zernike polynomial aspheric coefficients
The reflecting mirror in the embodiment is optimized by using the Zernike polynomial aspheric surface, and the Zernike polynomial aspheric surface high order term coefficients use eight coefficients of G3, G4, G7, G8, G10, G11, G14 and G15, so that the degree of freedom of the dual-band monitoring optical system in design is increased, the off-axis aberration of the system can be effectively corrected, the imaging quality of the system is improved, the system structure is more compact, the volume of the system is reduced, and the portability of the dual-band monitoring system is improved.
Referring to fig. 7, an MTF diffraction transfer function diagram of the dual-band monitoring system according to the first embodiment is shown, wherein the abscissa along the X-axis direction represents line pairs in mm, and the ordinate along the Y-axis direction represents the magnitude of the MTF diffraction transfer function value, and as can be seen from fig. 7, the MTF transfer function value of each field of view of the dual-band monitoring system is not less than 0.4, which indicates that the imaging quality of the dual-band monitoring system is good and the imaging quality of each field of view is very stable.
Referring to fig. 8, a graph of a field curve of the dual-band monitoring system at a reference wavelength (0.486 um) in the first embodiment is shown, wherein the abscissa along the X-axis direction represents the field curve size in mm, and the ordinate along the Y-axis direction represents the normalized field of view, and as can be seen in fig. 8, the field curve of the dual-band monitoring system is better than 0.014mm at the reference wavelength (0.486 um), which indicates that the field curve of the dual-band monitoring system is better compensated.
Referring to fig. 9, a graph of distortion of the dual-band monitoring system at a defined wavelength of visible light in the first embodiment is shown, wherein the abscissa along the X-axis represents the magnitude of distortion, and the ordinate along the Y-axis represents the normalized field of view, and as can be seen in fig. 9, the distortion of the dual-band monitoring system is better than 0.9% at the reference wavelength (0.486 um), which indicates that the distortion of the dual-band monitoring system is well corrected.
Referring to fig. 10, a root mean square radius size diagram of the dual-band monitoring system in the first embodiment at the reference wavelength (0.486 um), wherein the abscissa along the X-axis represents the relative field of view, and the ordinate along the Y-axis represents the root mean square radius size in mm, and as can be seen from fig. 10, the root mean square radius size of the dual-band monitoring system is better than 1.4um at the reference wavelength (0.486 um), which indicates that the spherical aberration of the dual-band monitoring system is better compensated.
The technical effect of the application is to provide a dual-band monitoring optical system based on free-form surface off-axis four-reflection. The system adopts a higher-performance free-form surface, the Zernike polynomial aspheric surface is designed, the system structure is integrated, the off-axis aberration of the system can be effectively compensated and corrected, the system performance is improved and improved to the maximum extent, and the good imaging quality can be realized, and the system parameters achieved by the invention are as follows: the F number of the system can reach 1.24, the aperture is large, the maximum half field angle reaches 4.5 degrees multiplied by 4.5 degrees, the observation range of the monitoring system is effectively improved, the MTF is not less than 0.3 when the MTF is 100lp/mm, the root mean square radius size is less than 2.5 mu m, the field curvature is better than 0.014mm, the distortion is better than 0.9%, and the imaging quality of the system is good. The off-axis four-inverse dual-band monitoring optical system based on the free curved surface disclosed by the invention solves the problems of narrow working band, small imaging field of view, low imaging quality, large system volume and the like of the optical system for monitoring in the current market.
The description of the embodiments of the specification should be taken in conjunction with the accompanying drawings, which are a complete description of the embodiments. Any references to directions and orientations in the above description of the embodiments are for convenience of description only and are not to be construed as limiting the scope of the invention. The description of the preferred embodiments will refer to combinations of features, which may be present alone or in combination, and the present invention is not particularly limited to the preferred embodiments, but the description of the above embodiments is merely for aiding in understanding the optical lens and the design core ideas thereof; meanwhile, as those skilled in the art will vary in the specific embodiments and application scope according to the idea of the present invention, the present disclosure should not be construed as limiting the present invention in summary. The scope of the invention is defined by the claims.
Claims (4)
1. The dual-band monitoring optical system based on free-form surface off-axis four-reflection is characterized in that the optical system adopts an off-axis system type reflecting structure and comprises a main reflecting mirror, a secondary reflecting mirror, a third reflecting mirror, a fourth reflecting mirror and a diaphragm; the main reflector, the secondary reflector, the third reflector and the fourth reflector are all designed and optimized by adopting a free-form surface Zernike polynomial aspheric surface;
the system working wave band comprises a visible light wave band and an infrared light wave band, light rays of the visible light wave band and light rays of the infrared light wave band sequentially pass through the main reflector, the secondary reflector, the third reflector and the fourth reflector and are converged on an image surface, the diaphragm is positioned on the main reflector, the size of the radius of the image surface is 10mm multiplied by 10mm, and the maximum half field angle is 4.5 degrees multiplied by 4.5 degrees;
the optical paths of the system are spatially arranged in an "S" shape, and the optical system satisfies the following relationship:
T1<220.5mm，T2<280.44mm，|T1/T2|<0.79；
wherein T1 is the relative distance between the primary mirror and the third mirror, and T2 is the relative distance between the secondary mirror and the fourth mirror;
the optical system satisfies the following relationship:
457.64<M/|TAN(HFOV)|<488.83；
wherein M is the maximum effective half aperture of the main reflector, HFOV is half of the maximum field angle of the dual band monitoring optical system, and TAN (HFOV) is the tangent of the HFOV;
the optical system satisfies the following relationship:
f/d≤1.9；
wherein f is the effective focal length of the optical system, and d is the entrance pupil diameter of the optical system.
2. The optical system of claim 1, wherein the optical system satisfies the following relationship:
3.42<|TAN(HFOV)/BFL|×10 4 <3.73；
wherein the HFOV is half of the maximum field angle of the dual band monitoring optical system, and the TAN (HFOV) is the tangent of the HFOV; BFL is the distance between the fourth mirror to the image plane.
3. The optical system of claim 1, wherein the optical system satisfies the following relationship:
36.00mm<D<122.75mm；
wherein D is the maximum effective half aperture of all mirrors in the optical system.
4. The optical system of claim 1, wherein the primary mirror, secondary mirror, third mirror, and fourth mirror are arranged in a globally tilted off-center relative position.
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