CN109917535B - Refrigeration type compact non-blocking free-form surface optical system - Google Patents
Refrigeration type compact non-blocking free-form surface optical system Download PDFInfo
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Abstract
The invention discloses a refrigeration type compact non-blocking free-form surface optical system, which comprises the following components in sequence: the first reflector, the second reflector and the third reflector. The three reflectors are free-form surfaces, adopt XY polynomial or Zernike polynomial, and have inclination relative to a coaxial system or exist eccentricity and inclination at the same time. The three reflectors are arranged in a circle, and light rays are intersected for many times in space, so that the structure is compact. The incident light is not blocked by the three reflectors and can reach the final image surface by 100 percent. An intermediate image plane is present in the optical path, between the second mirror and the third mirror, close to the second mirror. The system stop is located near the first mirror. The invention reduces the volume of the traditional off-axis three-mirror system, realizes the secondary imaging technology in a compact space, ensures that the exit pupil is positioned behind the third reflector and outside the overlapped light path, can be matched with the cold stop of a refrigeration detector, realizes the cold stop efficiency of 100 percent, and improves the target action distance.
Description
Technical Field
The invention relates to the technical field of optical system design, mainly relates to an off-axis reflective optical system, and particularly relates to a compact non-blocking free-form surface optical system for a refrigeration detector.
Background
The large-aperture (not less than 100mm) optical transmission material is expensive in manufacturing cost, and the characteristics of the uniformity of the refractive index, the transmittance and the like are difficult to guarantee. The reflective optical system has no chromatic aberration, has a wide imaging spectrum range, and can realize the heat difference elimination by matching with a structural material. Therefore, the large-aperture optical system generally adopts a reflective structure. However, the coaxial reflection type system has a central barrier, which affects the received energy and imaging quality of the system, and the off-axis reflection system can avoid the problems, but the traditional off-axis three-mirror optical system has not compact spatial arrangement and can not meet the increasingly strict airborne space requirement.
At present, an infrared off-axis reflective optical system with a compact structure mostly adopts a non-refrigeration detector. For example, the article "research on uncooled off-axis three-mirror optical system" published by wanbo, wherein the off-axis three-mirror optical system is designed to be compact in form and used for uncooled infrared detection imaging. However, optical systems for refrigerated-type infrared detectors typically require cold stop matching, making the optical system complex. JiangZhi Wen of Changchun university designs an off-axis reflection optical system meeting cold stop matching in a refrigeration type off-axis reflection optical system research, but the off-axis reflection optical system has larger volume and can not meet the requirement of compact structure. US8616712 discloses an asymmetric optical system and a design method thereof, which is compact and without obscuration, but does not meet the cold stop matching requirements of a refrigeration detector.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a refrigeration type compact non-blocking free-form surface optical system, which solves the problem of cold stop matching of a refrigeration type off-axis reflection optical system and realizes the compact design of the refrigeration type optical system by utilizing a free-form surface and a secondary imaging technology.
The technical scheme of the invention is as follows:
the refrigerating type compact non-blocking free-form surface optical system is characterized in that: the device comprises a diaphragm, a first reflector, a second reflector and a third reflector; the three reflectors are XY polynomial or Zernike polynomial free-form surfaces, wherein the focal powers of the first surface and the third surface reflector are positive, and the focal power of the second surface is negative; the diaphragm is positioned near the first surface reflector; after the incident light is reflected by the three-surface reflector, the incident light is overlapped three times in the optical system; the exit pupil is positioned outside the connecting line of the upper edges of the first reflector and the second reflector, so that the diaphragm coupling of the refrigeration detector is facilitated.
In a further preferred aspect, the refrigeration-type compact barrier-free-form surface optical system is characterized in that: an intermediate image plane is present in the optical path, the intermediate image plane being located between the first mirror and the second mirror, or between the second mirror and the third mirror.
In a further preferred aspect, the refrigeration-type compact barrier-free-form surface optical system is characterized in that: the optical path parameters satisfy the following formula:
ze＝(b2-b1)/(k1-k2) (1)
ye＝k1*ze+b1 (2)
ye-k3*ze-b3>0 (3)
in the formula: b1、b2The intercept, k, of the light rays reaching the image plane through the center of the entrance pupil and the third reflector respectively in the field of view 0 and the marginal field of view1、k2The slopes of these two rays; the intersection of these two rays is the exit pupil center (y) of the optical systeme ze)；k3、b3The slope and intercept of the ray passing between the first mirror and the second mirror are marginal rays passing through the upper edge of the entrance pupil.
Advantageous effects
The invention has the advantages that the compact arrangement of the reflecting system is realized by utilizing the free curved surface, compared with the traditional off-axis three-mirror, the compact arrangement has the advantage of small volume, and meanwhile, the exit pupil is positioned in front of the final image surface, so that the invention is suitable for matching with the cold stop of a refrigeration detector and realizes the cold stop efficiency of 100 percent. The invention can be applied to infrared refrigeration detection systems and other photoelectric systems needing cold stop matching, and improves the target action distance.
Drawings
Fig. 1 is a schematic structural composition diagram of a refrigeration-type compact non-obscuration free-form surface imaging system of the present invention.
FIG. 2 is a schematic diagram of the coordinate system and spatial ray markers of the present invention.
Fig. 3 is a view of field settings for an embodiment of the present invention.
Figure 4 is a schematic diagram of exit pupil position constraints according to an embodiment of the present invention.
FIG. 5 is a graph of an optical transfer function according to an embodiment of the present invention.
FIG. 6 is a graph of RMS wavefront error for an embodiment of the invention.
Detailed Description
The invention aims to solve the problem of cold stop matching of a refrigeration type off-axis reflection optical system, and the compact design of the refrigeration type optical system is realized by utilizing a free-form surface and a secondary imaging technology.
In order to achieve the above object, the present invention provides a refrigerating compact non-blocking free-form surface optical system and a design method thereof. The free-form surface off-axis three-mirror technology is utilized to enable the principal ray to be overlapped for three times in the area formed by the three reflectors, and the non-blocking and compact design of the refrigeration type off-axis reflection optical system is achieved.
The compact no-block free-form surface optical system of refrigeration type, include: the device comprises a diaphragm, a first reflecting mirror, a second reflecting mirror and a third reflecting mirror. The three-surface reflecting mirror is an XY polynomial or a Zernike polynomial free-form surface, wherein the focal power of the first surface and the focal power of the third surface reflecting mirror are positive, and the focal power of the second surface reflecting mirror is negative. The diaphragm is located adjacent to the first mirror. The incident light is reflected by the three-surface mirror and then is overlapped three times in the system. The exit pupil is positioned outside the connecting line of the upper edges of the first reflector and the second reflector, so that the diaphragm coupling of the refrigeration detector is facilitated.
In order to ensure the cold stop matching of the refrigeration detector, the three-surface reflector of the optical system adopts positive-negative-positive focal power distribution. Meanwhile, in order to reduce the size of each reflector, an aperture diaphragm is arranged near the first reflector, and the exit pupil of the system is positioned outside the connecting line of the upper edges of the first reflector and the second reflector.
The trend of the light is controlled through self-defining constraint, so that each reflector is not blocked by light. To ensure that the system exit pupil is located before the final image plane, after folding the optical path, the following conditions must be satisfied:
1. an intermediate image plane is present in the optical path, the intermediate image plane being located between the first mirror and the second mirror, or between the second mirror and the third mirror.
2. The following formula is satisfied:
ze＝(b2-b1)/(k1-k2) (1)
ye＝k1*ze+b1 (2)
ye-k3*ze-b3>0 (3)
in the formula: b1、b2The intercept, k, of the light rays reaching the image plane through the center of the entrance pupil and the third reflector respectively in the field of view 0 and the marginal field of view1、k2The slopes of these two rays. The intersection of these two rays is the exit pupil center (y) of the optical systeme ze)。k3、b3The slope and intercept of the ray passing between the first mirror and the second mirror are marginal rays passing through the upper edge of the entrance pupil.
And in design, the system exit pupil is ensured to be outside the off-axis three-mirror optical system through constraint control, the distance from the center of the exit pupil to the image plane is controlled, and the rear intercept required by the refrigeration detector is met.
The invention is described in further detail below with reference to the drawings and preferred embodiments.
Fig. 1 is a schematic structural diagram of a refrigeration-type compact barrier-free-form surface optical imaging system according to an embodiment of the present invention. The technical scheme of the invention is as follows: the off-axis three-mirror form is adopted, the requirement of an optical system on large-size transmission materials is reduced, the volume of the system is reduced by adopting a three-surface free-form surface, the imaging quality of the system is improved, and the focal power and the optical path structure are reasonably set to meet the cold stop matching of a refrigeration detector.
The invention relates to a refrigeration type compact non-blocking free-form surface optical system, which comprises: a first mirror S1, a second mirror S2, a third mirror S3, and an image plane Si. The three reflectors are free-form surfaces, adopt Zernike polynomials, and have inclination relative to a coaxial system or both eccentricity and inclination. The three reflectors are arranged in a circle, light rays are overlapped in space for multiple times, and an intermediate image surface is arranged in the light path and is positioned between S2 and S3 and close to S2. The system stop is located near S1, and the exit pupil is located after S3 and outside the folded light path, matching the cold stop of the refrigeration detector.
The working wave band of the optical system is 8-12 μm, the diameter of an entrance pupil is 137.5, the focal length is 550mm, the F number is 4, the field of view is 2 degrees multiplied by 1.6 degrees, and a long-wave refrigeration type detector is adopted.
The coordinate system and ray definition of the optical system is shown in fig. 2. A ray passing through the center of the entrance pupil at a point on the object plane is defined as r1, a ray passing through the upper end of the entrance pupil in the Y-axis direction is defined as r2, a ray passing through the lower end of the entrance pupil in the Y-axis direction is defined as r3, a ray passing through the positive edge of the entrance pupil in the X-axis direction is defined as r4, and a ray passing through the negative edge of the entrance pupil in the X-axis direction is defined as r 5.
The field of view setting of the optical system is shown in fig. 3. The optical system is symmetrical about a YZ plane, only half of the X-direction view field is arranged, and 5 view fields f1 (00), f2 (00.8), f3(0-0.8), f4 (1.00.8) and f5(1.0-0.8) are arranged in total.
In order to ensure the cold stop matching of the refrigeration detector, the three-surface reflector of the optical system adopts positive-negative-positive focal power distribution. Meanwhile, in order to reduce the size of each mirror, an aperture stop is arranged near S1, and the system exit pupil is positioned outside the upper edge connecting line of S1 and S2. The intermediate image plane is located between S2 and S3.
As shown in fig. 4, the coordinate system and the constraint relationship of the optical system according to the embodiment of the present invention. The global coordinate system YOZ, the Z-axis, coincides with the incident ray r1f1, with the origin of coordinates outside the three-mirror. A 0-degree view field ray r1f1 (thin solid line) at the center of the aperture and a 0.8-degree view field ray r1f2 (dotted line) at the center of the aperture are reflected sequentially by S1, S2 and S3 and then intersect at the exit pupil (y)e ze) And finally to Si, respectively.
y＝k1*z+b1R1f1 light ray passing through S3 to Si,y＝k2*z+b2R1f2 passing through the distance from S3 to Si, the intersection of the two rays is the center of the exit pupil of the system and has the coordinates of
ze＝(b2-b1)/(k1-k2) (1)
ye＝k1*ze+b1 (2)
y＝k3*z+b3R2f2 is reflected to S2 through S1, and the distance from the center of the exit pupil to the Y-axis direction of the light ray is
yd＝ye-k3*ze-b3 (3)
Constraint yd>And 0, enabling the exit pupil of the system to be outside the off-axis three-mirror optical system, controlling the distance from the center of the exit pupil to the image plane Si, and constraining the back intercept meeting the requirement of the refrigeration detector.
In the embodiment, the three-surface reflecting mirror adopts a standard Zernike polynomial free-form surface, and the first 13 items are utilized for optimization, so that the processing difficulty is reduced. The basic parameters of each mirror and image plane are shown in Table 1, wherein dyAnd α is the amount of tilt about the X axis for the Y axis offset. The Zernike surface type coefficients for each mirror are shown in table 2, where Zi, i-1 … 13 represent the i-th standard Zernike polynomial coefficients.
TABLE 1
TABLE 2
Fig. 5 is the MTF of the optical transfer function of this embodiment, which can be seen to be close to the diffraction limit. Figure 6 is a plot of RMS wavefront error for an embodiment of the present invention with an average wavefront error of about λ/40, λ being 10 μm. The requirements of the long-wave refrigeration detector on the imaging quality are met.
According to the technical scheme, the off-axis three-mirror form is adopted, the requirement of the system on large-size optical transmission materials is reduced, the size of the system is reduced by using the free-form surface, the imaging quality of the system is improved, the focal power is reasonably distributed, and the optical path structure meets the cold stop matching of a refrigeration detector by adopting a secondary imaging technology.
Claims (2)
1. The utility model provides a compact nothing of refrigeration type obscuration free-form surface optical system which characterized in that: the device comprises a diaphragm, a first reflector, a second reflector and a third reflector; the three reflectors are XY polynomial or Zernike polynomial free-form surfaces, wherein the focal powers of the first surface and the third surface reflector are positive, and the focal power of the second surface is negative; the diaphragm is positioned near the first surface reflector; after the incident light is reflected by the three-surface reflector, the incident light is overlapped three times in the optical system; the exit pupil is positioned outside the connecting line of the upper edges of the first reflector and the second reflector, so that the diaphragm coupling of the refrigeration detector is facilitated;
the optical path parameters satisfy the following formula:
ze＝(b2-b1)/(k1-k2) (1)
ye＝k1*ze+b1 (2)
ye-k3*ze-b3>0 (3)
in the formula: b1、b2The intercept, k, of the light rays reaching the image plane through the center of the entrance pupil and the third reflector respectively in the field of view 0 and the marginal field of view1、k2The slopes of these two rays; the intersection of these two rays is the exit pupil center (y) of the optical systeme ze)；k3、b3The slope and intercept of the ray passing between the first mirror and the second mirror are marginal rays passing through the upper edge of the entrance pupil.
2. The compact, obscuration-free form surface optical system of claim 1 wherein: an intermediate image plane is present in the optical path, the intermediate image plane being located between the first mirror and the second mirror, or between the second mirror and the third mirror.
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| CN110927943A (en) * | 2019-12-26 | 2020-03-27 | 中国科学院长春光学精密机械与物理研究所 | Off-axis three-reflection diffuse reflection plate lighting system |
| CN111238449A (en) * | 2020-01-16 | 2020-06-05 | 中国科学院西安光学精密机械研究所 | Total reflection type underwater camera suitable for deep sea environment |
| CN112083562B (en) * | 2020-08-14 | 2022-09-23 | 清华大学 | Off-axis two-mirror imaging system with real exit pupil |
| CN112180576B (en) * | 2020-09-02 | 2021-09-14 | 中国科学院西安光学精密机械研究所 | Refrigeration type free-form surface off-axis three-mirror optical system |
| CN114879351A (en) * | 2021-02-05 | 2022-08-09 | 清华大学 | Asymmetrical free-form surface optical system |
| CN114675415B (en) * | 2022-02-28 | 2023-02-10 | 南京航空航天大学 | Off-axis two-mirror optical system and design method thereof |
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| US8616712B2 (en) * | 2011-03-24 | 2013-12-31 | University Of Rochester | Nonsymmetric optical system and design method for nonsymmetric optical system |
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| TW201348689A (en) * | 2012-05-23 | 2013-12-01 | Altek Corp | Vision detection device and vision detection method thereof |
| CN108227165A (en) * | 2018-01-18 | 2018-06-29 | 北京理工大学 | Off-axis three anti-imaging spectrometer of free form surface |
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