CN107621691B - Off-axis total reflection type projection objective optical system - Google Patents

Abstract

The invention discloses an off-axis total reflection type projection objective optical system. The optical system adopts the field of view off-axis, the secondary mirror is arranged on the optical axis of the system, the aperture diaphragm is arranged on the secondary mirror, and the primary mirror and the third mirror are opposite to the system. The optical axes are opposite to each other and off-axis. The light converges after being reflected by the primary mirror, diverges and exits after being reflected by the secondary mirror, and is then reflected and focused by the third mirror to reach the image surface. At the same time, adding a folded mirror in the optical path can further shorten the length of the barrel and make the object images located on both sides of the objective lens. The light from the object plane at a finite distance is imaged on the image plane according to a certain magnification through the projection objective lens. The invention has the advantages of good imaging quality, short tube length, symmetrical structure, etc. It can correct the residual aberration caused by the limited distance of the object by bending the radius of the curved surface and adjusting the aspheric coefficient. At the same time, the problem of image quality degradation caused by excessive chromatic aberration in the wide spectrum of the traditional transmissive projection objective lens is solved.

Description

An off-axis total reflection projection objective optical system

technical field

The invention relates to the technical field of applied optics, in particular to an off-axis total reflection type projection objective optical system.

Background technique

The projection objective refers to an optical imaging objective with a finite object distance. The projection objective can image an object or image with a finite distance on the detector according to a certain magnification. , the resolution is the same.

The traditional projection objective lens usually adopts a transmissive optical system. The transmissive optical system is limited by the optical material, and it is difficult to correct the chromatic aberration when the system band is wide, and the uniformity of the lens material with an excessively large aperture is difficult to guarantee. These factors will affect the final object. image quality. Compared with the transmissive optical system, the total reflection optical system is not affected by chromatic aberration, the image quality is good, and the aperture can be made larger. Among them, the two-reflection system has a simple structure but few degrees of freedom, and cannot completely correct aberrations such as astigmatism and coma in a large field of view. The structure of the three-reflection system consists of three aspherical mirrors, which has more degrees of freedom in optimization and has good imaging quality when the field of view is large, so it is widely used.

As the wavelength of light in the projection optical system becomes wider and wider, it is required to correct chromatic aberration in a larger wavelength range; at the same time, the multi-spectral optical system (such as imaging spectrometer, etc.) also requires the projection objective lens to have the characteristics of wide spectrum and light weight ; In addition, considering factors such as reducing cost and improving integration, it is also required that the same projection objective lens can be applied to various wavelength bands such as ultraviolet, visible, and infrared. However, in the prior art, there is no projection objective optical system that can well meet the above requirements.

SUMMARY OF THE INVENTION

Therefore, it is necessary to provide an off-axis total reflection type projection objective optical system to solve the problems of narrow spectral band, long barrel length and heavy weight of the transmission type projection objective optical system.

In order to achieve the above purpose, the inventor provides an off-axis total reflection type projection objective optical system, the optical system includes a primary mirror (1), a secondary mirror (2), a third mirror (3), and a folding mirror (4) , an aperture stop (5) and an image plane (8); the aperture stop (5) is arranged on the secondary mirror (2), and the secondary mirror (2) is arranged on the system optical axis (6); the primary mirror (1) ) and the three mirrors (3) are respectively opposite to the optical axis (6) of the system and off-axis;

The light from the object surface (7) at finite distance is reflected by the folding mirror (4) to the primary mirror (1), then reflected by the primary mirror (1) and then enters the secondary mirror (2), and then is reflected by the secondary mirror (2) The reflection enters the three mirrors (3), and is finally reflected and focused by the three mirrors (3) to the image plane (8).

Further, the primary mirror (1) and the third mirror (3) are both concave aspherical mirrors with positive refractive power, and the secondary mirror (2) is a convex spherical mirror with negative refractive power.

Further, the centers of curvature of the primary mirror (1), the secondary mirror (2), and the third mirror (3) are all located on the optical axis (6) of the system.

Further, the interval from the primary mirror (1) to the secondary mirror (2) is equal to the interval from the secondary mirror (2) to the third mirror (3), and the interval from the primary mirror (1) to the secondary mirror (2) is : the distance from the center of the primary mirror (1) to the center of the secondary mirror (2) along the optical axis; the interval from the secondary mirror (2) to the third mirror (3) is: the center of the secondary mirror (2) to the third mirror (3) The distance from the center along the optical axis.

The invention has the following characteristics: the optical system adopts the field of view off-axis, the secondary mirror is arranged on the optical axis of the system, the main mirror and the three mirrors are respectively opposite to the optical axis of the system and off-axis, so as to avoid the influence of the occlusion of the optical system on the imaging quality. The light from the object surface at a finite distance is imaged on the image surface according to a certain magnification through the projection objective lens. The diaphragm of the optical system is placed on the secondary mirror, and the diaphragm of the system is not off-axis, so that the system structure has a certain symmetry, which is conducive to the balance and correction of aberrations. The light converges after being reflected by the primary mirror, diverges and exits after being reflected by the secondary mirror, and is reflected and focused by the third mirror to reach the image surface. At the same time, adding a folded mirror in the optical path can further shorten the length of the tube and make the object images located on both sides of the objective lens.

The off-axis total reflection projection objective lens of the present invention is not affected by chromatic aberration, has good imaging quality, short barrel length, and symmetrical structure. The coefficient corrects the residual aberration caused by the limited distance of the object, which can not only be applied to various wavelength bands such as ultraviolet, visible, infrared, etc., but also solves the problem of image quality degradation and tube length caused by excessive chromatic aberration caused by traditional transmissive projection objectives in the broad spectrum. too long question.

Description of drawings

1 is a schematic diagram of an optical system of an off-axis total reflection type projection objective lens according to an embodiment of the present invention;

Reference number:

1. Primary mirror;

2. Secondary mirror;

3. Three mirrors;

4. Folding mirror;

5. Aperture diaphragm;

6. System optical axis;

7. Finite object surface;

8, like face.

Detailed ways

In order to describe in detail the technical content, structural features, achieved objectives and effects of the technical solution, the following detailed description is given in conjunction with specific embodiments and accompanying drawings.

Please refer to FIG. 1 , which is a schematic diagram of an optical system of an off-axis total reflection type projection objective lens according to an embodiment of the present invention. The object plane of the optical system is at a finite distance position, and is imaged at the image plane position according to a certain magnification through the projection objective lens. The optical system includes a primary mirror (1), a secondary mirror (2), a third mirror (3), a folding mirror (4), Aperture diaphragm (5) and image plane (8).

The aperture stop (5) is arranged on the secondary mirror (2), and the secondary mirror (2) is arranged on the system optical axis (6). The aperture diaphragm (5) is not off-axis, so that the system structure has a certain symmetry, which is beneficial to processing and production, and is also beneficial to the balance and correction of aberrations.

The primary mirror (1) and the three mirrors (3) are respectively opposite to and off-axis relative to the optical axis (6) of the system, so as to avoid the influence of the occlusion of the optical system on the imaging quality. Preferably, in this embodiment, the primary mirror (1) and the third mirror (3) are both concave aspherical mirrors with positive refractive power, and the secondary mirror (2) is a convex spherical mirror with negative refractive power , the centers of curvature of the primary mirror (1), the secondary mirror (2), and the third mirror (3) are all located on the optical axis (6) of the system. The primary mirror (1) and the third mirror (3) use aspherical mirrors to correct residual aberrations. When the aperture of the secondary mirror (2) is smaller than a preset threshold (ie, the aperture is small), the secondary mirror (2) can use a convex spherical mirror to facilitate cut costs. The optical system as a whole follows a "positive, negative, positive" symmetrical structure, that is, the secondary mirror (2) is arranged on the optical axis (6) of the system, and the primary mirror (1) and the third mirror (3) are respectively arranged on both sides of the optical axis, The refractive power of the secondary mirror (2) is negative, and the refractive power of the primary mirror (1) and the third mirror (3) is positive. In other embodiments, when the aperture of the secondary mirror (2) is larger than a preset threshold (ie, the aperture is larger), the secondary mirror (2) may also select an aspherical mirror with a negative refractive power for better correction residual aberrations.

The folding mirror (4) is arranged on the optical path of the light emitted by the object surface (7) at the finite distance, and the light emitted from the object surface (7) at the finite distance is reflected by the folding mirror (4) to the main mirror (1), and then reaches the main mirror (1). After being reflected by the primary mirror (1), it enters the secondary mirror (2), then is reflected by the secondary mirror (2) and enters the third mirror (3), and finally is reflected and focused by the third mirror (3) to the image plane (8). Adding a folded mirror to the optical path can further shorten the length of the tube and make the object images located on both sides of the objective lens.

The aspheric surface can be described by formula (1):

Among them, r ² =x ² +y ² ; c is the curvature of the aspheric vertex; k is the quadratic surface coefficient;

When k=0, formula (1) represents a spherical surface;

When k=-1, formula (1) represents a paraboloid;

When -1<k<0, formula (1) represents an ellipsoid;

When k<-1, formula (1) represents a hyperboloid;

When k>0, formula (1) represents an oblate sphere.

In order to facilitate the adjustment and structural support of the optical system, in this embodiment, the interval from the primary mirror (1) to the secondary mirror (2) is equal to the interval from the secondary mirror (2) to the third mirror (3). The interval from the primary mirror (1) to the secondary mirror (2) is: the distance from the center of the primary mirror (1) to the center of the secondary mirror (2) along the optical axis; the secondary mirror (2) to the third mirror (3) The interval is: the distance from the center of the secondary mirror (2) to the center of the third mirror (3) along the direction of the optical axis.

In order to prevent the optical path from being blocked, in this embodiment, the object-side field of view is tilted downward of the optical axis, so that the incident light can avoid being blocked by the secondary mirror after being tilted, and enter the primary mirror after being reflected by the folding mirror. The specific operation is as follows: You can tilt the field of view of the object side first, and keep the secondary mirror fixed on the optical axis of the system. By translating the primary mirror and the third mirror in the direction perpendicular to the optical axis, the primary mirror and the third mirror can receive the tilt respectively. Incident imaging beam.

When configuring the primary mirror, secondary mirror, and third mirror, the residual aberration caused by the finite object distance can be corrected by adjusting the curvature radius and surface coefficient of each lens, thereby solving the problem caused by the excessive chromatic aberration of the traditional transmission projection objective lens in the broad spectrum. Problems with degraded image quality and too long barrel length. Specifically, a preset error can be set. When the calculated residual aberration of each lens is lower than the preset error, the parameters of each lens of the optical system at this time are recorded, and these parameters are used for adjustment.

Taking an optical system with an object height of 27mm, an image height of 8.7mm, a relative aperture of 1/3, a focal length of 40mm, and a field of view tilt angle of 12° as an example, the surface parameters and intervals of the optical system are shown in Table 1:

Table 1

The "spacing" in Table 1 refers to the horizontal spacing between each reflector (or between the reflector and the image surface, between the reflector and the image surface) along the direction of the optical path. For example, 18.19mm in row 3 indicates that the horizontal interval between the primary mirror and the secondary mirror is 18.19 mm; for another example, “36.23” in Table 1 indicates that the horizontal interval between the three mirrors and the image plane is 36.23 mm.

The off-axis total reflection projection objective lens of the present invention is not affected by chromatic aberration, has good imaging quality, short barrel length, and symmetrical structure. The coefficient corrects the residual aberration caused by the limited distance of the object, which can not only be applied to various wavelength bands such as ultraviolet, visible, and infrared, but also solves the problem of image quality degradation and tube length caused by excessive chromatic aberration caused by traditional transmissive projection objectives in the broad spectrum. too long question.

It should be noted that, although the above embodiments have been described herein, it does not limit the scope of the patent protection of the present invention. Therefore, based on the innovative concept of the present invention, changes and modifications to the embodiments described herein, or equivalent structures or equivalent process transformations made by using the contents of the description and drawings of the present invention, directly or indirectly apply the above technical solutions In other related technical fields, all are included within the scope of patent protection of the present invention.

Claims (1)

1. An off-axis total reflection type projection objective optical system, characterized in that: the optical system comprises a primary mirror (1), a secondary mirror (2), a third mirror (3), a folding mirror (4), an aperture light A stop (5) and an image plane (8); the aperture stop (5) is arranged on the secondary mirror (2), and the secondary mirror (2) is arranged on the system optical axis (6); the primary mirror (1) and the third mirror The mirrors (3) are respectively opposite to and off-axis with respect to the optical axis (6) of the system; The field of view on the object side is inclined downward to the optical axis, and the light from the object surface (7) at finite distance is reflected by the folding mirror (4) to the primary mirror (1), and then reflected by the primary mirror (1) and then enters the secondary mirror (2), and then reflected by the secondary mirror (2) into the third mirror (3), and finally reflected and focused by the third mirror (3) to the image plane (8); The primary mirror (1) and the third mirror (3) are both concave aspherical mirrors with positive refractive power, and the secondary mirror (2) is a convex spherical mirror with negative refractive power, The centers of curvature of the primary mirror (1), the secondary mirror (2), and the third mirror (3) are all located on the optical axis (6) of the system, By setting the preset error, adjust the curvature radius and surface coefficient of the primary mirror (1), the secondary mirror (2), and the third mirror (3) to correct the residual aberration caused by the finite object distance; The interval from the primary mirror (1) to the secondary mirror (2) is equal to the interval from the secondary mirror (2) to the third mirror (3), and the interval from the primary mirror (1) to the secondary mirror (2) is: The distance from the center of (1) to the center of the secondary mirror (2) along the optical axis; the interval from the secondary mirror (2) to the third mirror (3) is: the center of the secondary mirror (2) to the third mirror (3) The distance of the center along the optical axis; The object height of the optical system is 27mm, the image height is 8.7mm, the relative aperture is 1/3, the focal length is 40mm, the field of view inclination angle is 12°, the curvature radius of the main mirror (1) is 64.72mm, and the main mirror (1) has a curvature radius of 64.72mm. The quadric surface coefficient of the mirror (1) is -2.278, the curvature radius of the secondary mirror (2) is 23.11 mm, the quadric surface coefficient of the secondary mirror (2) is 0, and the curvature radius of the third mirror (3) is 35.33 mm, the quadratic surface coefficient of the third mirror (3) is 0.103, the horizontal interval between the primary mirror (1) and the secondary mirror (2) is 18.19 mm, the secondary mirror (2) and the third mirror (2) are The horizontal interval of the mirrors (3) is 18.19mm, and the horizontal interval between the three mirrors (3) and the image plane is 36.23mm.

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