Lens centering method using laser interference technology

Abstract

The invention relates to a lens centering method using a laser interference technology. A coherent light source, a spectroscope, a converging mirror, a reference reflector, a camera, a to-be-measured lens and a rotary table are included. Wherein a light beam emitted by the coherent light source is collimated to form a collimated light beam, and the collimated light beam is split into a reference arm light beam and a measurement arm light beam through the spectroscope; the reference arm light beam is reflected by the spherical reference reflector to form a curved light beam and returns to the spectroscope; the light beam of the measuring arm is converged near the vertex of the to-be-measured lens through the converging lens, and is reflected by the to-be-measured lens to return to the converging lens and the spectroscope. Due to the adoption of the interference technology, the eccentricity or inclination of the to-be-measured lens is obtained by analyzing the interference pattern, the interference pattern can cover the whole camera target surface, all pixels of the camera can participate in analysis and calculation, the utilization rate of the pixels of the camera is improved, meanwhile, the nm-level precision can be achieved through the light interference measurement technology, and the measurement accuracy is improved. And the limit of the traditional submicron measurement precision based on the light spot position of the camera is broken through.

Description

Technical Field

[0001] The present invention relates to the field of optical lens center deviation measurement, and in particular to a lens centering method using laser interference technology. Background Art

[0002] Traditional optical lens eccentricity measuring instruments typically use incoherent light as a light source and utilize autocollimation to obtain a spot image of the mirror's spherical center. The mirror's eccentricity and tilt are determined by determining the spot image's position on the camera surface. A high-precision air-bearing turntable is typically used to provide a relatively fixed reference axis. To improve measurement accuracy, both the motion accuracy of the air-bearing turntable and the pattern of the spot need to be enhanced. Using a cross-shaped spot pattern, rather than a circular spot, can more easily achieve sub-pixel resolution. Alternatively, a tic-tac-toe or three-line spot pattern can be employed to further enhance the camera's capture resolution. Because these traditional lens eccentricity measuring instruments require an autocollimation optical path through the mirror's spherical center, the probe travel and the focal length of the selected converging lens must match the curvature of the measured mirror surface. Consequently, the probe travel is typically long, and converging lenses with multiple focal lengths must be configured and replaced. Furthermore, despite continuous improvements to the spot pattern, the image spot captured by the camera only represents a small portion of the target surface, resulting in low pixel utilization, thus limiting measurement resolution and accuracy. Summary of the Invention

[0003] The object of the present invention is to provide a lens centering method using laser interference technology.

[0004] To solve the above-mentioned technical problems, the present invention utilizes all the pixels on the camera's target surface, thereby increasing the utilization rate of the camera's target surface and improving detection accuracy. Furthermore, to reduce the need for a large probe travel and the need to frequently change the focal length of the converging lens, the present invention avoids focusing the converging lens at the center of the mirror surface, i.e., the confocal position, for measurement. Instead, the converging lens is focused only near the vertex of the lens to be measured for measurement. With conventional autocollimation systems, when the converging lens focuses on the vertex of the lens to be measured, the return light will not carry information about the eccentricity or tilt of the lens to be measured. Therefore, in order to be able to measure the eccentricity and tilt of the lens to be measured through the vertex of the lens, the conventional optical path needs to be improved.

[0005] Furthermore, it includes a coherent light source, a spectroscope, a converging mirror, a reference reflector, a camera, a lens to be tested, and a turntable; wherein:

[0006] The light beam emitted by the coherent light source is collimated to form a collimated light beam, and then split into a reference arm light beam and a measurement arm light beam by a spectroscope;

[0007] The reference arm beam is reflected by the spherical reference reflector to form a curved beam and then returns to the beam splitter;

[0008] The measuring arm light beam is converged to the vicinity of the vertex of the lens to be measured by the converging mirror, and is reflected by the lens to be measured and returned to the converging mirror and the beam splitter;

[0009] The camera receives the reference arm beam and the measurement arm beam combined by the beam splitter and forms interference fringes;

[0010] By analyzing the shape and density changes of the interference fringes, the eccentricity or tilt of the lens to be tested relative to the turntable axis can be determined.

[0011] Furthermore, the lens to be measured is in a defocused state relative to the converging mirror, and the defocused state enables the measuring arm light beam to carry eccentricity or tilt information of the lens to be measured.

[0012] Furthermore, the interference pattern received by the camera gradually changes from annular stripes to straight stripes during the process of adjusting the interval between the converging mirror and the lens to be tested, i.e., focusing, and the eccentricity or tilt of the lens to be tested is determined based on the density change of the straight stripes.

[0013] Furthermore, the reference reflector is a spherical reflector with an adjustable curvature, so as to achieve a balance between improving the measurement resolution accuracy and extending the measurement range.

[0014] Furthermore, the focal length of the converging mirror is selected according to the curvature of the reference reflector and the curvature of the lens to be measured, so as to ensure that the formed interference fringes cover the camera target surface.

[0015] Furthermore, the lens under test is mounted on a turntable, which drives the lens under test to rotate. By analyzing the change in the density of the linear interference fringes captured by the camera as the turntable rotates, the decentration of the lens under test relative to the turntable and the decentration of the light beam's convergence point relative to the turntable after passing through the converging mirror are distinguished. The former is the component of the linear interference fringes whose density changes with the turntable's rotation, while the latter is the component of the linear interference fringes that does not change with the turntable's rotation.

[0016] Furthermore, the method also includes using a phase shifter to perform phase shift processing on the reference reflector, and obtaining phase information of the interference pattern through phase shift interferometry to improve the calculation accuracy of the eccentricity and tilt.

[0017] Furthermore, the lens to be tested may be a plane lens or a spherical lens. When the curvature of the lens changes, the defocus distance is adjusted to ensure that the interference fringes are transformed from circular fringes to linear fringes.

[0018] Furthermore, according to the paraxial object-image relationship formula, the calculation formula for the defocus distance δ when the mirror to be measured is a plane can be derived as follows:

[0019] ;

[0020] in, is the focal length of the converging mirror, is the curvature radius of the spherical reference reflector. The same applies when the surface to be measured is a spherical surface.

[0021] Furthermore, the tilt of the lens to be tested It can be derived from the object-image magnification relationship formula, which is:

[0022] ;

[0023] in, is the change in the density of the linear interference fringes received by the camera, is the wavelength of the coherent light source, is the radius of curvature of the spherical reference reflector, is the focal length of the converging lens. If the lens to be tested is a spherical surface with a curvature radius of r, the decentering D of the lens to be tested can be calculated using the following formula:

[0024]

[0025] Beneficial effects of the present invention:

[0026] This method uses interference technology to determine the decentration or tilt of the lens under test by analyzing the interference pattern. The interference pattern covers the entire camera target surface, allowing all camera pixels to participate in the analysis and calculation, improving camera pixel utilization. Furthermore, optical interferometry can achieve nanometer-level accuracy, surpassing the traditional sub-micrometer measurement accuracy based on the camera's spot position.

[0027] The present invention only requires adjusting the focus of the probe to near the vertex of the lens to be measured, and the defocus amount can be controlled at the order of tens of millimeters, which greatly reduces the demand for probe stroke. At the same time, there is no need to replace the converging mirror, which reduces equipment costs, improves measurement efficiency, and is suitable for measurement needs with space constraints. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described below with reference to the accompanying drawings and examples.

[0029] Figure 1 It is a schematic diagram of the measurement optical path.

[0030] Figure 2 This is a schematic diagram of the probe focusing process. The left picture shows the stripes in the unfocused state, and the right picture shows the stripes in the focused state.

[0031] Figure 3 This is an example of how the fringes received by the camera change as the turntable rotates, depending on the angle of the turntable.

[0032] Figure 4 Schematic diagram of the change in interference fringe density obtained from interference fringe analysis.

[0033] In the picture:

[0034] Coherent light source 1, spectrometer 2, camera 3, reference reflector 4, converging mirror 5, lens to be tested 6, turntable 7. DETAILED DESCRIPTION

[0035] The present invention will now be described in further detail with reference to the accompanying drawings, which are simplified schematic diagrams that illustrate the basic structure of the present invention in a schematic manner.

[0036] like Figure 1 As shown, the present invention provides a lens centering method using laser interference technology, which involves laser measurement technology and includes a coherent light source, a spectroscope, a converging mirror, a reference reflector, a camera, a lens to be measured, and a turntable. The light beam emitted by the coherent light source is collimated to form a collimated beam, which is then split into a reference arm beam and a measuring arm beam by the spectroscope. The reference arm beam is reflected by a spherical reference reflector to form a curved beam, which is then returned to the spectroscope. The measuring arm beam is converged to the vicinity of the vertex of the lens to be measured by the converging mirror, and is reflected by the lens to be measured back to the converging mirror and the spectroscope. The camera receives the reference arm beam and the measuring arm beam combined by the spectroscope to form interference fringes. The eccentricity or tilt of the lens to be measured relative to the rotation axis of the turntable is determined by analyzing the shape and density of the interference fringes.

[0037] The present invention adopts the optical path structure of the improved Michelson interferometer and uses the light interference technology to measure the eccentricity of the lens to be tested. Figure 1 As shown, the probe part in the optical path structure includes a coherent light source 1, a spectroscope 2, a camera 3, a reference reflector 4 and a converging mirror 5, and the rest includes a lens to be measured 6 and a turntable 7.

[0038] The coherent light source 1 is coherent light, and the light source beam needs to be collimated by a collimator to form a collimated beam. The collimated beam is split by a beam splitter 2. One beam is incident on a reference reflector 4 and returns to the beam splitter 2, referred to as the reference arm beam. Another beam is incident on a converging mirror 5, converges near the vertex of the lens under test 6, and after returning from the lens under test 6, is collimated by the converging mirror 5 and returns to the beam splitter 2, referred to as the measurement arm beam. The reference arm beam and the measurement arm beam are simultaneously received by the target surface of the camera 3 and interfere with each other. The lens under test 6 is placed on a turntable 7. When the turntable 7 drives the lens under test 6 to rotate, the eccentricity or tilt of the lens under test 6 relative to the axis of the turntable 7 can be determined by analyzing the interference fringes received by the camera 3.

[0039] The lens to be tested is in a defocused state relative to the converging mirror. The defocused state causes the measuring arm beam to carry information about the eccentricity or tilt of the lens to be tested. The reference reflector is a spherical reflector with an adjustable curvature, which is used to achieve a balance between improving the measurement resolution accuracy and extending the measurement range. The focal length of the converging mirror is selected according to the curvature of the reference reflector and the curvature of the lens to be tested to ensure that the interference fringes formed cover the camera target surface.

[0040] The reference reflector 4 is a spherical reflector. Figure 1 In the figure, a is a collimated plane beam and b is a curved beam. Plane beam a is transformed into curved beam b after being reflected by reference reflector 4. When the beam in the measuring arm passes through converging mirror 5 and converges to the vertex of the mirror surface of the lens to be measured 6, the interference pattern observed by camera 3 is Figure 2 The annular interference pattern in the image is obtained by adjusting the axial relative position of the probe relative to the lens 6 to be measured, i.e., the focusing process. Figure 2 The ring stripes in the Figure 2 The linear interference pattern in the image is shown in Figure 1. At this point, the point where the measuring arm's light beam converges after passing through the converging mirror 5 no longer coincides with the vertex of the lens 6 under test. This is called a defocused state. The axial distance from the point of convergence to the vertex of the lens 6 under test is called the defocus distance. It is this defocused state that allows the measuring arm's light beam to carry information about the decentration or tilt of the lens 6 under test.

[0041] During the focusing process, the interference pattern received by the camera gradually changes from circular fringes to straight fringes. The eccentricity or tilt of the lens to be tested is determined based on the change in the density of the straight fringes. The lens to be tested is mounted on a turntable, which drives the lens to be tested to rotate. By analyzing the changes in the straight interference fringes obtained by the camera with the rotation angle, the eccentricity of the lens to be tested and the eccentricity of the turntable can be distinguished.

[0042] When the lens 6 to be tested is eccentric or tilted relative to the turntable, the density of the linear interference fringes received by the camera 3 will change as the turntable rotates. When the lens 6 to be tested is not eccentric or tilted relative to the turntable, the density of the linear fringes will be constant. During the rotation of the lens 6 to be tested, the component of the linear interference fringes density that changes with angle is used to determine the eccentricity or tilt of the lens 6 to be tested relative to the turntable, and the component of the linear interference fringes density that remains constant with angle is used to determine the eccentricity of the convergence point of the light beam passing through the converging mirror relative to the turntable. Figure 3 This figure illustrates the fringe patterns detected by camera 3 at different rotation angles of turntable 7, when the lens under test 6 is off-center relative to turntable 7, while the convergence point of the light beam passing through the converging mirror is not off-center relative to turntable 7. When the off-center or tilt of the lens under test 6 relative to turntable 7 is adjusted to zero, the linear fringe density will be zero.

[0043] The lens to be tested 6 can be a plane lens or a spherical lens. When the curvature of the lens changes, the defocus distance is adjusted to ensure that the interference fringes are transformed from circular fringes to linear fringes.

[0044] The mirror surface of the lens 6 under test can be either flat or spherical. When the curvature of the mirror surface of the lens 6 changes, the axial distance between the probe and the lens 6 under test, i.e., the defocus distance, will also change. The goal of adjusting the defocus distance is still to reduce the annular fringes detected by the camera 3, converting them into straight fringes.

[0045] The curvature of the reference reflector 4 can be adjusted based on the required resolution and measurement range for measuring eccentricity and tilt. The smaller the curvature of the reference reflector 4, the greater the required defocus distance of the measuring arm beam. The same eccentricity or tilt of the lens under test 6 will produce a higher density of straight interference fringes detected by the camera 3, improving the measurement resolution but also reducing the measurable range.

[0046] The selection of the focal length of the converging mirror 5 is similar to the selection of the curvature of the reference reflector 4. The smaller the focal length, the higher the measurement resolution but the smaller the measurement range.

[0047] Example 1: Figure 1 The medium-coherent light source 1 is a single-mode fiber laser source, collimated into a collimated laser beam by a fiber collimator. The collimated beam is split by a 1:1 splitting ratio beam splitter 2. One beam of collimated light is incident on a concave reference reflector 4 with a curvature of 1000 mm. The collimated beam a is transformed into a converging beam b and returns to beam splitter 2. The other beam is incident on a converging mirror 5 with a focal length of 150 mm. The convergence point of the beam is approximately 32 mm axially from and above the plane lens 6 under test. After returning from the plane lens 6, the converging beam becomes a diverging beam. The virtual focus of the diverging beam is below the plane lens 6 under test and symmetrical with the convergence point relative to the plane lens 6. The diverging beam is transformed into a converging beam by converging mirror 5 and returns to beam splitter 2. The two beams are simultaneously received by the target surface of camera 3 and interfere with each other. At this point, the convergence angles of the two beams should be the same, and the interference fringes detected by camera 3 will be straight. At this point, if ring fringes still exist in the interference fringes, they can be eliminated by fine-tuning the distance between the probe and the lens under test 6. To accurately obtain the interference pattern information, a phase shifter is used to shift the phase of the reference reflector 4. This phase shift method obtains precise phase information of the interference pattern, where the tilt in this phase information is the fringe density. The lens under test 6 is placed on a turntable 7, which rotates the lens under test 6. The tilt of the lens under test 6 relative to the rotation axis of the turntable 7 is determined by analyzing the interference fringes received by the camera 3. Figure 4 Schematic diagram of the change in interference fringe density obtained from interference fringe analysis. Figure 4A polar coordinate system is established by the turntable angle and the interference fringe density. The lines connecting the points formed by the interference fringe density at all collected angles form a circle, and the length of the line connecting the center of the circle to the origin of the coordinate system is the constant component of the interference fringe density. , the radius of the circle is the variation component of the interference fringe density Stripe density With turntable angle The changing relationship is expressed as:

[0048] ;

[0049] All angles collected and the corresponding fringe density , using the above formula for fitting, we can get the constant component of the interference fringe density and the change in the interference fringe density .

[0050] The defocus distance δ can be calculated by the following formula:

[0051] ;

[0052] in, is the focal length of the converging mirror, is the radius of curvature of the spherical reference reflector.

[0053] The tilt of the lens to be tested Calculated by the following formula:

[0054] ;

[0055] in, is the change in the density of the linear interference fringes received by the camera, is the wavelength of the coherent light source, is the radius of curvature of the spherical reference reflector, is the focal length of the converging mirror.

[0056] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A lens centering method using laser interferometry technology, characterized in that: It includes a coherent light source, a beam splitter, a converging mirror, a reference reflector, a camera, a lens to be tested and a turntable; wherein: The light beam emitted by the coherent light source is collimated to form a collimated light beam, and then split into a reference arm light beam and a measurement arm light beam by a spectroscope; The reference arm beam is reflected by the spherical reference reflector to form a curved beam and then returns to the beam splitter; The measuring arm light beam is converged to the vicinity of the vertex of the lens to be measured by the converging mirror, and is reflected by the lens to be measured and returned to the converging mirror and the beam splitter; The camera receives the reference arm beam and the measurement arm beam combined by the beam splitter and forms interference fringes; By analyzing the shape and density of the interference fringes, the eccentricity or tilt of the lens to be tested relative to the turntable axis can be determined.

2. The lens centering method using laser interference technology according to claim 1, characterized in that: The lens to be measured is in a defocused state relative to the converging mirror. The defocused state enables the measuring arm light beam to carry eccentricity or tilt information of the lens to be measured.

3. The lens centering method using laser interference technology according to claim 2, characterized in that: The interference pattern received by the camera gradually changes from annular fringes to straight fringes during the focusing process, and the eccentricity or tilt of the lens to be tested is judged based on the change in density of the straight fringes, where the density of the straight fringes is the number of fringes per unit length.

4. The lens centering method using laser interference technology according to claim 3, characterized in that: The reference reflector is a spherical reflector with an adjustable curvature, and is used to achieve a balance between improving measurement resolution accuracy and extending measurement range.

5. The lens centering method using laser interference technology according to claim 4, characterized in that: The focal length of the converging mirror is selected according to the curvature of the reference reflector and the curvature of the lens to be measured to ensure that the formed interference fringes cover the camera target surface.

6. The lens centering method using laser interference technology according to claim 5, characterized in that: The lens to be tested is mounted on a turntable, which drives the lens to be tested to rotate. By analyzing the change in the density of the linear interference fringes obtained by the camera with the rotation angle, the lens decentration and the turntable decentration are distinguished.

7. The lens centering method using laser interference technology according to claim 6, characterized in that: The method also includes using a phase shifter to perform phase shifting processing on a reference reflector, and obtaining phase information of an interference pattern by a phase shifting interferometry method, so as to improve the calculation accuracy of the eccentricity and tilt.

8. The lens centering method using laser interference technology according to claim 7, characterized in that: The lens to be tested can be a plane lens or a spherical lens. When the curvature of the lens changes, the defocus distance is adjusted to ensure that the interference fringes are transformed from circular fringes to straight fringes.

9. The lens centering method using laser interference technology according to claim 8, characterized in that: When the lens to be tested is a plane, the defocus distance δ can be calculated by the following formula: ； in, is the focal length of the converging mirror, is the radius of curvature of the spherical reference reflector.

10. The lens centering method using laser interference technology according to claim 9, characterized in that: The tilt value when the lens to be tested is a plane Calculated by the following formula: ； in, is the density change of the linear interference fringes received by the camera, is the wavelength of the coherent light source, is the radius of curvature of the spherical reference reflector, is the focal length of the converging mirror.

Images