GB2539844A

GB2539844A - Dual-optical-path optical centering instrument for eliminating stray light

Info

Publication number: GB2539844A
Application number: GB1617404.7A
Authority: GB
Inventors: Liu Weisen; Xu Min; Wang Junhua
Original assignee: Fudan University
Current assignee: Fudan University
Priority date: 2015-01-19
Filing date: 2016-01-19
Publication date: 2016-12-28
Anticipated expiration: 2036-01-19
Also published as: WO2016116036A1; CN104567752A; GB201617404D0; GB2539844B

Abstract

A dual-optical-path optical centering instrument for eliminating stray light, composed of a photodetector (1), an autocollimator (2), a polarizer (3), a polarization beam splitter (4), polarization analyzers (6, 7, 8), pancratic telescopes (9, 10), a computer platform (16), etc., wherein the polarization beam splitter (4) divides parallel light provided by the autocollimator (2) into reflected S light and transmitted P light; the S light is focused on the center of curvature of an upper surface of a detected lens of a to-be-detected optical part (11) by one pancreatic telescope (10) via the polarization analyzers (6, 7); the P light is reflected by a plane mirror (5) and is focused on the center of curvature of a lower surface of the detected lens by the pancratic telescope (9) via the polarization analyzer (8); and the photodetector (1) captures crisscross images of the reflected light in two optical paths, and the computer platform (16) calculates the center deviation of the detected lens, so as to adjust the lens according to the center deviation of the lens to conduct correction and centering. The instrument has low costs and a high measurement accuracy, and can measure the center deviation of two measurement surfaces of an optical component simultaneously, thereby realizing efficient and quick correction of the center deviation.

Description

OPTICAL CENTERING APPARATUS WITH DUAL OPTICAL PATHS FOR ELIMINATING A STRAY LIGHT

TECHNICAL FIELD

The present invention relates to the field of optical assembly technologies, and particularly to an apparatus for measuring center deviations of coaxial optical components in an optical system and centering calibration.

BACKGROUND

Recently, precise optical systems (such as an object lens of an optical lithographic apparatus, an aerial survey camera lens, and a standard telescope, etc.) have higher requirements on imaging quality of camera lenses. During system assembly, there will be a deviation, namely, a center deviation, between an optical axis of a lens and a reference axis thereof Existence of the center deviation radically destroys a theoretical basis of optical design coaxial theory, resulting in astigmatism of imaging and asymmetry of distortion, and thereby reducing imaging quality. An optical centering apparatus is an indispensable measurement device for measuring a center deviation of a precise optical system. The precision of optical centering is about 100 times higher than that of a mechanical centering method. It plays an important role in optical lens adhesion, assembly and calibration, and detection of an optical system.

Currently, common centering devices generally adopt a single-optical-path reflective measurement method. Such a method requires to sequentially measure both front and rear faces of measurement of a lens, and a measured value of a center deviation of the rear face of measurement is a composite value of center deviations of the two faces of measurement of the lens, requiring a solution to obtain the center deviation of the rear face of measurement. Therefore, accuracy of the rear face measurement is always affected by measurement accuracy of the front face of measurement, resulting in a cumulative effect of errors. A dual-optical-path optical centering apparatus may directly measure center deviations of two faces of measurement of a lens, so as to eliminate an influence of the accuracy of a front face of measurement on the accuracy of a rear face of measurement, thereby solving the problem of error accumulation.

A light beam of an optical path in the dual-optical-path optical centering apparatus is transmitted through a to-be-measured optical component and can form strong stray light in another optical path. The stray light can cause interference to an information light of said another optical path and even overwhelm the information light. A polarization beam splitter is used to generate two linearly polarized light paths having polarization directions perpendicular to each other, and the orthogonal design of the polarization analyzers used in the two optical paths can eliminate the interference of the stray light on the information light. Both measurement optical paths use a rotation axis of a pneumatic bearing turntable as a reference axis, and the center deviations measured by the two optical paths are both displayed in the same photoelectric detector, so that the same reference standard is advantageous to reduce the measurement errors of the center deviations. Only one autocollimator is used to generate two optical paths, and one photoelectric detector is used to simultaneously measure the two optical paths, thereby having low costs and improving centering efficiency.

During the lens assembly of an optical system, a roundness instrument detects a resetting state of a to-be-measured optical component with complicated operations and low resetting efficiency. After centering of a first lens of the optical system, when subsequent lenses are centered and assembled by using the dual-optical-path centering instrument, the rapid detection and resetting of the to-be-measured optical component can be implemented by using a lower optical path, thereby improving the overall centering efficiency.

SUMMARY

An objective of the present invention is to provide an optical centering apparatus which has low manufacturing costs and high measurement precision, and which is capable of simultaneously measuring the center deviations of two measurement surfaces of an optical component, thereby resulting rapid center deviation calibration.

An optical centering apparatus provided by the present invention, the structure of which is shown in FIG. 1, includes a photoelectric detector 1, an autocollimator 2, a polarizer 3, a polarization beam splitter 4, three plane reflecting mirrors 5, 13, 14, three polarization analyzers 6, 7, 8, two short-distance variable focus telescopes 9, 10, a pneumatic bearing turntable 12, a roundness instrument 15, and a computer platform 16; the autocollimator is configured to provide parallel lights carrying a cross-image signal to the polarizer 3 to generate linearly polarized lights, and for the polarization beam splitter 4 to generate an S light and a P light. The polarization directions of the S light and the P light are perpendicular to each other; the S light passes through a first polarization analyzer 6 and a second polarization analyzer 7 and is focused by a second short-distance variable focus telescope 10 on a curvature center of an upper surface of a measured lens of a to-be-measured optical component 1 I fixed on the pneumatic bearing turntable 12; the P light is reflected by a first plane reflecting mirror 5 to pass through a third polarization analyzer 8 and is focused by a first short-distance variable focus telescope 9 on a curvature center of a lower surface of the measured lens; the S light and the P light are reflected by the upper and lower surfaces of the measured lens, and the photoelectric detector I captures the cross-image signal of the reflected light, and the computer platform 16 calculates and analyzes a center deviation of the measured lens and adjusts the lens according to the center deviation of the lens to perform calibration and centering; and the roundness instrument 15 is configured to detect coaxiality between a lens cone of the to-be-measured optical component I I and the pneumatic bearing turntable I 2.

In the present invention, the photoelectric detector 1 may be a CCD, a CMOS, or other photoelectric detectors. The photoelectric detector can simultaneously capture the cross-image signals of the reflected S light and the transmitted P light and simultaneously measure the center deviations of the upper and lower surfaces of the measured lens in the same coordinate system, thereby improving the measurement precisions of the center deviations.

In the present invention, the rotary polarizer 3 may be a polarizer plate, a Nicol prism, or the like. The polarizer can convert natural light into linearly polarized light, and a light intensity ratio between the reflected S light and the transmitted P light may be changed by rotating the polarizer.

In the present invention, the polarization beam splitter 4 can split a beam of linearly polarized light into the reflected S light and the transmitted P light having polarization directions perpendicular to each other. A principle diagram of the polarization beam splitter 4 is shown in FIG. 2. For a light beam A that is vertically incident on an end surface of a polarization beam splitter Ml, after being split by a polarization beam splitter M2, a P light vertically emits from an end surface M3, and an S light vertically emits from an end surface M4, where the P light and the S light are linearly polarized lights having their polarization directions perpendicular to each other.

In the present invention, the polarization analyzer can be a polarization plate. The polarization analyzers of the optical paths of the reflected S light and the transmitted P light are orthogonal, and the polarization transmission directions of the foregoing polarization analyzers are the same as the polarization directions of the S light and the P respectively. The reflected S light that passes through the to-be-measured optical component cannot pass through the polarization analyzer in the optical path of the transmitted P light, and likewise, the reflected P light that passes through the to-be-measured optical component also cannot pass through the polarization analyzers in the optical path of the transmitted S light. Specifically, the polarization transmission direction of the first polarization analyzer 6 is the same as the polarization direction of the S light emitted from the M4 end face of the polarization beam splitter 4, and the second polarization analyzer 7 may change the light intensity of the S light, so that when the directions of the polarization transmission of the second polarization analyzer 7 and the first polarization analyzer 6 are parallel, the light intensity of the S light is the greatest, and when being orthogonal the light intensity of the S light is the smallest; a matching state between the two cross-image signals in the photoelectric detector 1 and the curvature I 0 centers of the two measurement surfaces of a lens are analyzed by using the second rotary polarization analyzer 7. The first polarization analyzer 6 and the third polarization analyzer 8 are orthogonal so that the S light that passes through the to-be-measured component 11 cannot pass through the third polarization analyzer 8. Similarly, the P light that passes through the to-be-measured component I I also cannot pass through the first polarization analyzer 6, thereby eliminating the interference of a stray light in an information light.

In the present invention, the short-distance variable focus telescope may be rotated to change a focal length thereof, so as to focus the reflected S light and the transmitted P light onto a center of curvature of a measured surface of the to-be-measured optical component.

Structures of the two short-distance variable focus telescopes are shown in FIG. 3. In a structure a, positive lenses Li, L2 share an optical axis, and F I and F2 are the focal point locations of Ll, L2 respectively, and H1 is a distance between the lenses Li, L2 along the optical axis. When the focal point locations Fl, F2 overlap each other, and a beam of parallel lights is incident on the short-distance variable focus telescope 3, the emitted light is also parallel light. A point of convergence of emergent light beams may be changed by changing the distance H1, that is, a focal length of the short-distance variable focus telescope may be changed. Likewise, in a structure b, L7 is a negative lens, and a focal length of the short-distance variable focus telescope may also be changed by changing a distance H2. The short-distance variable focus telescope may be rotated to change a focal length thereof, so as to focus the reflected S light and the transmitted P light onto a center of curvature of a measured surface.

In the present invention, the to-be-measured optical component 11 may include a lens cone and a lens. The roundness instrument 15 may detect coaxiality between the lens cone of the to-be-measured optical component 11 and the pneumatic bearing turntable 12 and displays it on the computer platform 16.

In the present invention, the pneumatic bearing turntable 12 may have a transmission aperture and have a leveling and centering stage, and the stage may be configured to fix the to-be-measured optical component 11.

In the present invention, the computer platform may be configured to analyze the cross-image signal of the photoelectric detector, to calculate a center deviation of a measured surface of the to-be-measured optical component, and to process a detection result of the roundness instrument.

In the present invention, both of the reflected S light and the transmitted P light may use a rotation axis of the pneumatic bearing turntable 12 as a reference axis to reduce measurement errors of center deviations.

In the present invention, only one autocollimator 2 is needed to provide light beams of the two optical paths, thereby lowering costs.

In the present invention, only one photoelectric detector 1 is required to simultaneously display information of the S light and the P light, and coordinate conversion is not required during information processing, thereby reducing measurement errors and lowering costs.

In the present invention, a rotation axis of the pneumatic bearing turntable 12 can serve as a common reference axis between the S light and the P light. The common reference axis can reduce transfer errors during data processing, so that interference of the strong stray light can be eliminated.

The stray light elimination dual-optical-path optical centering instrument provided by the I 0 present invention can simultaneously detect center deviations of two measurement surfaces of an optical component, thereby improving detection and centering efficiency.

The stray light elimination dual-optical-path optical centering instrument provided by the present invention can simultaneously detect center deviations of two measurement surfaces of an optical component, thereby solving an error accumulation problem during a single-optical-path centering instrument measuring and improving measurement precision of center deviations.

In the present invention, when an optical component includes multiple lenses, the P light may be used to detect and rapidly reset the to-be-measured optical component I I, which replaces the roundness instrument 15 to detect the resetting state of the to-be-measured optical component I I, thereby reducing operation difficulty and improving detection efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural diagram of a stray light elimination dual-optical-path optical centering instrument; FIG. 2 is a principle diagram of a polarization beam splitter 4; FIG. 3 is a structural diagram of short-distance variable focus telescopes 9, 10; and FIG. 4 is a structural diagram of a to-be-measured optical component II.

Reference numerals in the drawings: 1 refers to a photoelectric detector; 2 refers to an autocollimator; 3 refers to a polarizer; 4 refers to a polarization beam splitter; 5, 13, 14 refer to plane reflecting mirrors; 6, 7, 8 refer to polarization analyzers; 9, 10 refer to short-distance variable focus telescopes; 11 refers to a to-be-measured optical component; 12 refers to a pneumatic bearing turntable; 15 refers to a roundness instrument; 16 refers to a computer platform; Ml, M3, M4 refer to three end surfaces of the polarization beam splitter 4; M2 refers to a polarization beam splitting surface of the polarization beam splitter 4; Li, L2, L3 refer to positive lenses; L4 refers to a negative lens; Fl, F2, F3, F4 refer to focal point locations of LI, L2, L3, L4,respectively; HI refers to a distance between lenses Li and L2 along an optical axis; H2 refers to a distance between lenses L3 and L4 along an optical axis; Kl, 1(2 refer to lenses; E refers to a lens cone; 01, 02 refer to curvature centers of the upper and lower surfaces of the lens K1; 04, 03 refer to curvature centers of the upper and lower surfaces of the lens K2; D1 refers to a connection line between 01, 02; D2 refers to a connection line between 03, 04; and D3 is an axis of rotational symmetry of the lens cone E.

DETAILED DESCRIPTION OF THE INVENTION

To enable persons skilled in the art to better understand the technical solution of the present invention, specific embodiments of the present invention will be described in detail in the following by referring to the accompanying drawings.

FIG. 4 is a structure of a to-be-measured optical component 11 including a lens cone E and lenses Kl, K2, where 01, 02 refer to centers of curvature of the upper and lower surfaces of the lens Kl; 04, 03 refer to curvature centers of the upper and lower surfaces of the lens 1(2; D1 refers to a connection line between Oland 02, namely, an optical axis of the lens Kl; D2 refers to a connection line between 03 and 04, namely an optical axis of the lens K2; and D3 is an axis of rotational symmetry of the lens cone E. The specific steps are as follows: 1) fixing the to-be-measured optical component 11 on a pneumatic bearing turntable 12, rotating the pneumatic bearing turntable 12, and detecting coaxiality between the lens cone of the to-be-measured optical component 11 and the pneumatic bearing turntable 12 by using a roundness instrument 15; 2) fine-tuning a location of the to-be-measured optical component 11 to make the coaxiality between the lens cone of the to-be-measured optical component 11 and the pneumatic bearing turntable 12 gradually converge to an allowed tolerance; 3) adjusting a short-distance variable focus telescope 10 to focus S light onto the curvature center 04 of the upper surface of the lens K2 and adjusting a short-distance variable focus telescope 9 to focus P light onto the curvature center 03 of the lower surface of the lens K2; 4) observing a cross image captured by a photoelectric detector 1 via a computer platform 16, rotating the polarizer 3 to adjust the brightness values of the two cross images to desired brightness value(s), and rotating the polarization analyzer 7 to adjust the brightness value of the cross image formed by the S light and determining a matching relationship between the two cross images and the curvature centers 03, 04; 5) calculating a tilt amount and an offset of the lens K2 via the computer platform 16, and fine-tuning the lens K2 according to the tilt amount and the offset; 6) performing a looping measurement by repeating steps 1) to 5) until the two cross images not moving while rotating a pneumatic bearing; 7) when centering the lens IC1, detecting the coaxiality between the lens cone of the to-be-measured optical component 11 and the pneumatic bearing turntable 12. The coaxiality detection does not use the roundness instrument 15, instead the S light of the centering apparatus can directly detect concentricity of the lens K2, thereby rapidly resetting the to-be-measured optical component I I; 8) adjusting the short-distance variable focus telescope 10 to focus the S light onto the curvature center 04 of the upper surface of the lens K! and adjusting the short-distance variable focus telescope 9 to focus the P light onto the curvature center 03 of the lower surface of the lens K I; 9) observing the cross image captured by a photoelectric detector 1 via the computer platform 16, rotating the polarizer 3 to adjust the brightness value of the two cross images to desired brightness values, and rotating the polarization analyzer 7 to adjust the brightness value of the cross image formed by the S light and determining a matching relationship between the two cross images and the centers of curvature 01, 02; 10) calculating a tilt amount and an offset of the lens K1 by using the computer platform 16 and fine-tuning the lens 1(1 according to the tilt amount and the offset; and 11) performing a looping measurement by repeating steps 7) to 10) until the two cross images not moving while rotating the pneumatic bearing. l0

Claims

CLAIMS1. An optical centering apparatus with dual optical paths for eliminating a stray light, characterized by comprising a photoelectric detector (1), an autocollimator (2), a polarizer (3), a polarization beam splitter (4), three plane reflecting mirrors (5, 13, 14), three polarization analyzers (6, 7, 8), two short-distance variable focus telescopes (9, 10), a pneumatic bearing turntable (12), a roundness instrument (15), and a computer platform (16); wherein the autocollimator is operable to provide parallel lights carrying a cross-image signal to the polarizer (3) to generate linearly polarized light, and for the polarization beam splitter (4) to generate an S light and a P light having polarization directions perpendicular to each other; wherein the S light passes through a first polarization analyzer (6) and a second polarization analyzer (7) and is focused by a second short-distance variable focus telescope (10) onto a curvature center of an upper surface of a measured lens of a to-be-measured optical component (11) fixed on the pneumatic bearing turntable (12); wherein the P light is reflected by a first plane reflecting mirror (5) to pass through a third polarization analyzer (8) and is focused by a first short-distance variable focus telescope (9) onto a curvature center of a lower surface of the measured lens; wherein the S light and the P light are reflected by the upper and lower surfaces of the measured lens, and the photoelectric detector (I) captures a cross-image signal of the reflected lights, and wherein the computer platform (16) calculates and analyzes a center deviation of the measured lens and adjusts the lens according to the center deviation of the lens to perform calibration and centering; and wherein the roundness instrument (15) is configured to detect coaxiality between a lens cone of the to-be-measured optical component (II) and the pneumatic bearing turntable (12).
2. The optical centering apparatus with dual optical paths for eliminating a stray light according to claim 1, characterized in that the photoelectric detector is a CCD, a CMOS, or other photoelectric detectors.
3. The optical centering apparatus with dual optical paths for eliminating a stray light according to claim I, characterized in that the polarizer is a polarizer plate or a Nicol prism; wherein the polarizer converts a natural light into a linearly polarized light, and a light intensity ratio between the reflected S light and the transmitted P light is changed by rotating the polarizer.
4. The optical centering apparatus with dual optical paths for eliminating a stray light according to claim 1, characterized in that the polarization analyzer is a polarization plate; wherein the polarization analyzers of optical paths of the reflected S light and the transmitted P light are orthogonal, and the directions of the transmitted polarization of the foregoing polarization analyzers are the same as the polarization directions of the S light and the P light respectively; wherein the reflected S light that passes through the to-be-measured optical component cannot pass through the polarization analyzer in the optical path of the transmitted P light, and likewise, the reflected P light that passes through the to-be-measured optical component cannot pass through the polarization analyzers in the optical path of transmitted S
5. The optical centering apparatus with dual optical paths for eliminating a stray light according to claim 1, characterized in that the short-distance variable focus telescope is rotated to change a focal length thereof, so as to focus the reflected S light and the transmitted P light onto a center of curvature of a measured surface of the to-be-measured optical component.
6. The optical centering apparatus with dual optical paths for eliminating a stray light according to claim 1, characterized in that the pneumatic bearing turntable has a transmission aperture and has a leveling and centering stage, and the stage is configured to fix the to-be-measured optical component.
7. The optical centering apparatus with dual optical paths for eliminating a stray light according to claim I, characterized in that the computer platform is configured to analyze the cross-image signal of the photoelectric detector, and to calculate a center deviation of a measured surface of the to-be-measured optical component, and to process a detection result of the roundness instrument.
8. The optical centering apparatus with dual optical paths for eliminating a stray light according to claim 1, characterized in that both of the reflected S light and the transmitted P light use a rotation axis of the pneumatic bearing turntable as a reference axis.