CN1858632A - Method and device for accurately determining optical system focus plane by interferometer - Google Patents

Abstract

A method and device for accurately determining the focal plane of an optical system using an interferometer, which is suitable for the assembly and detection of an optical system with a limited focal length. The working principle of the present invention is to reflect the standard light emitted by a laser interferometer back to the interferometer after passing it through the optical system to be measured. In addition, the principle that the interference fringes can be easily obtained at the "cat's eye" position of the interferometer is used to determine the focal plane of the optical system. Since the present invention utilizes the detection light of the laser interferometer, the positioning accuracy of the focal plane of the optical system is significantly improved. The present invention can realize the precise assembly and detection of optical systems such as photographic objective lenses, microscopes, projector objective lenses, slide projector objective lenses, and movie projection objective lenses, and accurately determine their focal planes. The accuracy of assembly and detection can be significantly improved, and it is easy to implement and adjust, which effectively solves the blindness of determining the focal plane of the optical system.

Description

Method and device for accurately determining the focal plane of an optical system by an interferometer

technical field

The invention relates to the measurement of an optical system, in particular to a method and a device for accurately determining the focal plane of an optical system by an interferometer.

technical background

With the development of science and technology and the improvement of computer technology, the requirements for optical systems are getting higher and higher, so the requirements for various optical components are also getting higher and higher, and interference detection has been continuously improved accordingly. Now the measurement accuracy of the interferometer is constantly improving, and it has been more and more widely used in optical adjustment.

In order to improve the precision of the optical system, many patents relate to assembling the optical system, such as CN00130721.5, CN200420012162.9, CN99251361.8. CN00130721.5 uses a spectrometer to install and adjust the optical system. Light of other wavelengths is needed during the installation and adjustment process, and the focal plane of the system cannot be determined; CN200420012162.9 includes too many components, and the experience of the adjustment personnel is more important. The system is difficult to install and adjust; CN99251361.8 involves adjusting the focus plane, but it still needs to rely on high-precision machining and lacks versatility.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the above-mentioned prior art, and provide a method and device for accurately determining the focal plane of an optical system using an interferometer, which is suitable for the assembly and detection of an optical system with a limited focal length, so as to improve the Assembly accuracy and focal length measurement accuracy of the optical system.

In order to achieve the above and related purposes, the working principle of the present invention is to reflect the standard light emitted by the interferometer back to the interferometer after passing through the measured optical system. Moreover, it is easy to obtain interference fringes at the "cat's eye" position of the interferometer to determine the focal plane of the optical system.

Technical solution of the present invention is as follows:

A method for accurately determining the focal plane of an optical system using an interferometer, characterized in that the method includes the following steps:

(1) Fizeau laser interferometer is selected as the detection instrument for determining the focal plane of the optical system, and the standard plane of the interferometer matches the optical system under test;

(2) The detection beam emitted by the laser interferometer is incident on the optical system to be measured, and the center of the outgoing light of the laser interferometer is adjusted to coincide with the center of the optical system to be measured; continue to adjust the optical system to be measured so that The beam spot is the smallest;

(3) add a standard reflector after described optical system to be measured, make light beam return optical system along original optical path, return described laser interferometer again;

(4) Adjust the standard reflector, and fine-tune the optical system to be measured, so that the laser interferometer produces interference fringes, and the defocus of the optical system to be measured by the laser interferometer is minimum;

(5) Insert a plane reflector at any one beam focal point position behind the laser interferometer outgoing light, the reflective surface of the plane reflector coincides with the datum plane of an adjustment mount, adjust the position of the adjustment mount, Make the reflected light of the plane mirror return to the laser interferometer to generate interference fringes and minimize the defocus amount, which is the "cat's eye" position here. If the plane mirror is removed, the The reference plane of the adjustment frame is the focal plane of the optical system to be tested.

A device for accurately determining the focal plane of an optical system using a laser interferometer is characterized in that it includes a laser interferometer, and an adjustment frame with a reference plane and a plane reflector are arranged coaxially on the exit light path of the laser interferometer mirror and a standard mirror matching the optical system to be tested, the plane mirror is placed on the reference plane of the adjustment frame, and the reflection surface of the plane mirror is perpendicular to the optical axis.

The coherent light emitted by the laser interferometer is incident into the optical system under test in a parallel manner, or at a certain divergence angle, or at a certain convergence angle.

The measured optical system is a refractive optical system, or a reflective optical system, or a catadioptric optical system.

The reflective surface of the block standard reflector is a plane or a spherical surface.

Technical effect of the present invention:

By adopting the invention, the positioning accuracy of the focal plane of the optical system to be tested is significantly improved, and the assembly accuracy and detection accuracy of the whole system are improved. This structure for determining the focal plane is easy to implement and easy to adjust, effectively solving the blindness of determining the focal plane of the optical system. It can effectively improve the adjustment accuracy of photographic objective lenses, microscopes, projector objective lenses, slide projector objective lenses, movie projection objective lenses and other optical systems, and accurately determine their focal planes. The invention is not only applicable to the precise positioning of the focal plane of the optical system, but also to precisely determining the focal position of the optical system and measuring the focal length of the optical system, as well as detecting the adjustment of the optical system and its residual aberration.

The interferometer adopted in the invention emits coherent light beams and is incident into the measured optical system, and has the ability to sensitively reflect the aberration of the optical system.

The measured optical system described in the present invention is a refractive optical system, or a reflective optical system, or a catadioptric optical system. This optical system has a finite focal length.

Description of drawings

Fig. 1 is the basic working principle diagram of the method and device for accurately determining the focal plane of the optical system in the present invention, and the plane reflector is at the focal point position

Figures 2(a) and 2(b) are schematic diagrams of the structure and principle of Embodiment 1 of the method and device for accurately determining the focal plane of the optical system according to the present invention

Figure 3(a) and 3(b) are schematic diagrams of the structural principles of Embodiment 2 of the method and device for accurately determining the focal plane of the optical system in the present invention

Figures 4(a), 4(b) and 4(c) are schematic diagrams of the structural principle of Embodiment 3 of the method and device for accurately determining the focal plane of the optical system of the present invention

Fig. 5 is a schematic diagram of the structural principle of Embodiment 4 of the method and device for accurately determining the focal plane of the optical system in the present invention

Fig. 6 is a schematic diagram of the structural principle of Embodiment 5 of the method and device for accurately determining the focal plane of the optical system according to the present invention

Fig. 7 is a schematic diagram of the structural principle of Embodiment 6 of the method and device for accurately determining the focal plane of the optical system in the present invention

Detailed ways

The present invention will be further described below in conjunction with the embodiments and accompanying drawings, but the protection scope of the present invention should not be limited thereby.

Please refer to FIG. 1 first. FIG. 1 illustrates the basic working principle of the method and device for accurately determining the focal plane of the optical system. As can be seen from the figure, the present invention uses an interferometer to accurately determine the method for the focal plane of an optical system, which is characterized in that the method includes the following steps:

(1) Select the Fizeau laser interferometer 1 as the detection instrument for determining the focal plane of the optical system 2, and the standard plane of the interferometer matches the optical system 2 under test;

(2) The detection beam emitted by the laser interferometer 1 is incident on the measured optical system 2, and the center of the outgoing light of the described laser interferometer 1 is adjusted to coincide with the center of the measured optical system 2; continue to adjust the optical system to be measured System 2, to minimize the beam spot;

(3) add a standard reflector 3 behind described optical system 2 to be measured, make light beam return optical system 2 along original optical path, return described laser interferometer 1 again;

(4) Adjust the standard reflector 3, and fine-tune the measured optical system 2, so that interference fringes are produced on the laser interferometer 1, and the defocus of the measured optical system 2 measured by the laser interferometer 1 is amount is minimum;

(5) Insert a plane reflector 4 at any one of the focal point positions of the light beam after the laser interferometer 1 emits light, the reflective surface of the plane reflector 4 coincides with the reference plane 6 of an adjustment frame 5, adjust the Adjust the position of the frame 5 so that the reflected light of the plane reflector 4 returns to the laser interferometer 1 to generate interference fringes and minimize the defocus, which is the "cat's eye" position here. plane mirror 4, the reference plane 6 of the adjustment frame 5 is the focal plane of the optical system 2 to be tested.

A device for accurately determining the focal plane of an optical system using a laser interferometer, characterized in that it includes a laser interferometer 1, and an adjustment frame 5 with a reference plane 6 is provided coaxially with the optical axis on the outgoing light path of the laser interferometer 1 , a plane reflector 4 and a standard reflector 3 matched with the optical system 2 to be measured, the plane reflector 4 is placed on the reference plane 6 of the adjustment frame 5, the plane reflector 4 The reflective surface is perpendicular to the optical axis.

The coherent light emitted by the laser interferometer 1 is incident into the optical system 2 under test in a parallel manner, or at a certain divergence angle, or at a certain convergence angle.

The measured optical system 2 is a refractive optical system, or a reflective optical system, or a catadioptric optical system.

The reflective surface of the block standard mirror 3 is a plane or a spherical surface.

The coherent beam 7 emitted from the laser interferometer 1 is incident into the optical system 2 under test, and the beam is converged on the focusing plane 6 of the optical system 2 . A standard spherical reflector 3 is added behind the outgoing light beam of the optical system, so that the outgoing light beam is reflected back along the original optical path 8, interference fringes are generated in the laser interferometer 1, and the optical path is adjusted to minimize the defocus amount. All the focus positions of the beams behind the output beam of the laser interferometer 1 can be considered as "cat's eyes". Insert a plane reflector 4 with a datum plane 6 adjustment mount 5 at any "cat's eye" position, and make the plane mirror 4 on the datum plane 6 of the adjustment mount 5. Adjust the adjustment frame 5 so that the plane mirror 4 returns the light beam 7 to the interferometer along the optical path 9 to generate interference fringes at the "cat's eye" and minimize the defocus. Taking away the plane reflector 4, the reference plane 6 of the adjustment frame is the focal plane of the optical system to be tested.

2(a) and 2(b) are schematic diagrams of the structural principle of Embodiment 1 of the method and device for accurately determining the focal plane of an optical system according to the present invention. In Fig. 2(a), the coherent light beam 7 emitted from the interferometer 1 is parallel light, which is incident into the optical system 2 under test, and a standard reflector 3 is added after the outgoing light beam 7 of the optical system 2, which is a concave spherical reflection Mirror, so that the outgoing beam 7 is reflected back along the original optical path 8, interference fringes can be obtained in the laser interferometer 1, and the optical path is adjusted to minimize the aberration of the system. In Fig. 2 (b), a plane reflector 4 is inserted at the "cat's eye" position between the measured optical system 2 and the standard concave spherical reflector 3, and the plane reflector 4 is placed on the adjustment frame 5, so that the The reflection plane of the above-mentioned flat mirror 4 coincides with the above-mentioned reference plane 6 . Adjust the adjustment frame 5 so that the plane mirror 4 returns the light beam 7 to the interferometer along the optical path 9 to generate interference fringes and minimize the amount of defocus. Taking away the plane reflector 4, the reference plane 6 of the adjustment frame is the focal plane of the optical system 2 to be tested. This focal plane is also the focal plane of the optical system. By measuring the size of the entrance pupil of the optical system and knowing the relative aperture of the standard spherical wave mirror, the focal length of the system can be obtained.

3(a) and 3(b) are schematic diagrams of the structural principle of Embodiment 2 of the method and device for accurately determining the focal plane of an optical system according to the present invention. In Figure 3(a), the converging point is on the front focal plane of the optical system. The implementation process is similar to Example 1. The only thing is that the coherent light beam 7 emitted from the laser interferometer 1 is converging light, which first converges on the front focusing surface of the optical system 2, and the outgoing light is parallel light, which is reflected back along the original optical path 8 by a standard flat mirror 14. The "cat's eye" position of the front focal plane of the tested optical system 2 is shown in FIG. 3( b ), where the focal plane of the optical system is determined.

4(a), 4(b) and 4(c) are schematic structural diagrams of Embodiment 3 of the method and device for accurately determining the focal plane of an optical system according to the present invention. In Fig. 4(a), there is a converging point before and after the optical system. The implementation process is similar to Example 1 and Example 2. The coherent light beam 7 emitted from the interferometer 1 first converges on the front focus plane of the optical system, and then converges on the back focus plane after being incident on the measured optical system 2 . A standard reflector 3 is added behind the outgoing light beam of the optical system as a concave spherical reflector, so that the outgoing light beam is reflected back along the original optical path 8 . The "cat's eye" position of the rear focal plane of the tested optical system 2 is shown in FIG. 4( b ), where the rear focal plane of the optical system 2 is determined. After the rear focal plane is determined, a plane mirror 10 with a reference plane 12 and an adjustment mount 11 can also be inserted at the "cat's eye" position of the front focal plane of the optical system 2 under test. Adjust the adjustment frame 11 so that the plane mirror 10 returns the light beam 7 to the interferometer along the optical path 13 to generate interference fringes and minimize the amount of defocus. As shown in Fig. 4(c), the front focal plane of the optical system is determined at this position, so that the front and rear conjugate focal planes of the optical system are determined at the same time.

Fig. 5 is a schematic diagram of the structure and principle of Embodiment 4 of the method and device for accurately determining the focal plane of an optical system according to the present invention. In Fig. 5, the standard reflector of the present invention is convex reflector 15, and this just requires when determining its focal plane, first convex reflector 15 is taken away, and then "cat's eye" on the rear focal plane of this tested optical system 2 Insert a flat reflector 4 with a reference plane 6 adjustment mount 5 in the position ", and determine the focal plane of the optical system at this position.

Fig. 6 is a schematic diagram of the structure and principle of Embodiment 5 of the method and device for accurately determining the focal plane of an optical system according to the present invention. In Fig. 6, the optical system under test of the present invention is made up of multiple systems, has multiple focal planes, such as focal plane 6, focal plane 18, focal plane 19, etc. Adjust the plane mirror of the frame, so that the focal plane of the optical system is determined at the corresponding position.

Precisely adjust the optical system and determine the focal length of the optical system:

Figures 2(a) and 2(b) can also be used as schematic diagrams of Embodiment 1 of the present invention for precisely adjusting the optical system and determining the focal length of the optical system. In Fig. 2 (a), the aberration of the measured system is minimized according to the above-mentioned adjustment of the optical path. At this moment, the size of the aberration shows the adjustment status of the measured optical system 2, and also reflects the adjustment method and device of the present invention. Auxiliary function of optical system adjustment. In Fig. 2(b), the focal plane obtained by adjusting the optical path above is the back focal plane of the optical system under test. By measuring the size of the entrance pupil of the optical system, the back focal length of the system can be obtained.

3(a) and 3(b) can also be used as schematic diagrams of Embodiment 2 of the present invention for precisely adjusting the optical system and determining the focal length of the optical system. In Fig. 3(a), the adjustment status of the optical system 2 under test can also be obtained through aberration. In Fig. 3(b), the focal plane obtained by adjusting the optical path above is the front focal plane of the optical system under test. By measuring the exit pupil size of the optical system, the front focal length of the system can be obtained.

Figures 4(a), 4(b) and 4(c) can also be used as schematic diagrams of embodiments of the present invention for precisely adjusting the optical system and determining the conjugate distance of the optical system. Adjust the optical path as shown in FIG. 4(a) to minimize the aberration of the measured system. At this time, the size of the aberration indicates the adjustment status of the optical system 2 under test. According to 4(b) and 4(c), the two conjugate focal planes before and after the optical system are adjusted and determined, and then the conjugate distance can be measured.

FIG. 5 can also be used as a schematic diagram of an embodiment of the present invention for precisely adjusting the optical system and determining the conjugate distance of the optical system. In Figure 5, a standard convex mirror is placed first, and the optical path is adjusted to minimize the aberration of the measured system. At this time, the size of the aberration indicates the adjustment status of the measured optical system 2. Then remove the standard convex reflector, and insert the plane reflector 4 with the reference plane 6 adjustment frame 5 respectively at the "cat's eye" position of the front and rear focus planes of the measured optical system 2, so as to determine the conjugate focus plane of the optical system.

Fig. 6 can also be used as a schematic diagram of the implementation example of the present invention for precisely adjusting the optical system and determining the conjugate distance of the optical system. The principle of the device is similar to that in Figure 1, except that the device is composed of two sets of optical systems 2 and 17, and the corresponding cat's eye positions 6, 18 and 19 in the optical path are respectively placed with reference planes and adjustment frames. The plane mirror can realize the measurement of two groups of conjugate distances, and can realize the test of the adjustment status of the optical systems 2 and 17.

Claims (5)

1. A method for accurately determining the focal plane of an optical system using an interferometer, characterized in that the method comprises the following steps: (1) Select the Fizeau laser interferometer (1) as the detection instrument for determining the focal plane of the optical system (2), and the standard plane of the interferometer matches the measured optical system (2); (2) The detection beam emitted by the laser interferometer (1) is incident on the measured optical system (2), and the center of the outgoing light of the described laser interferometer (1) and the measured optical system (2) are adjusted. The center coincides; continue to adjust the optical system to be tested (2) to minimize the beam spot; (3) Add a standard reflector (3) behind the described optical system to be measured (2), so that the light beam returns to the optical system (2) along the original optical path, and then returns to the laser interferometer (1); (4) Adjust the standard reflector (3), and fine-tune the measured optical system (2), so that interference fringes are produced on the laser interferometer (1), and the laser interferometer (1) measures The defocus amount of the measured optical system (2) is the smallest; (5) Insert a plane reflector (4) at any beam focal point position after the laser interferometer (1) exits the light, and the reflective surface of the plane reflector (4) is aligned with an adjustment frame (5) Surfaces (6) overlap, adjust the position of the adjustment frame (5), so that the reflected light of the plane reflector (4) returns to the laser interferometer (1) to generate interference fringes, and the defocus amount Minimum, here is the "cat's eye" position, take away the plane mirror (4), then the reference plane (6) of the adjustment frame (5) is the focus surface. 2. A device that adopts a laser interferometer to accurately determine the focal plane of an optical system is characterized in that it includes a laser interferometer (1), and a laser interferometer (1) is coaxially provided with a reference The adjustment frame (5) on the surface (6), a plane reflector (4) and a standard reflector (3) matching the optical system to be measured (2), the said plane reflector (4) is placed in the On the reference plane (6) of the adjustment frame (5), the reflection surface of the plane mirror (4) is perpendicular to the optical axis. 3. The device for accurately determining the focal plane of an optical system using a laser interferometer according to claim 2, characterized in that the coherent light emitted by the laser interferometer (1) is in a parallel manner, or at a certain divergence angle, or It is incident into the optical system under test (2) at a certain convergence angle. 4. The device for accurately determining the focal plane of an optical system using an interferometer according to claim 2, characterized in that the measured optical system (2) is a refractive optical system, or a reflective optical system, or a catadioptric optical system optical system. 5. The device for accurately determining the focal plane of an optical system using an interferometer according to claim 2, characterized in that the reflection surface of the block standard mirror (3) is a plane or a spherical surface.

Images