CN108362222B - A Novel Point Diffraction Interferometry System Based on Multidirectional Tilt Carrier Frequency - Google Patents

Abstract

The invention provides a non-zero novel point diffraction interferometry system based on multidirectional tilted carrier frequencies, which comprises a linear polarization laser source, an optical fiber coupler module, an optical fiber array, a piece to be measured and an interference image acquisition system, wherein the polarization laser source, the optical fiber coupler module and the optical fiber array are sequentially arranged on a first optical axis, the piece to be measured is positioned on a second optical axis, an included angle between the second optical axis and the first optical axis is one fourth of the divergence angle of each optical fiber emergent beam, and the best-fit spherical curvature center of the piece to be measured is coincided with the center of the end face of the optical fiber array. The invention uses the optical fiber array to form a point diffraction array, generates wave surface of multidirectional inclined carrier frequency to compensate the surface gradient of the measured piece, and solves the problems that the interference fringe density is too high and the solution cannot be realized when the complex surface-shaped element is measured by an interference method.

Description

A Novel Point Diffraction Interferometry System Based on Multidirectional Tilt Carrier Frequency

technical field

The invention relates to the technical field of surface shape measurement systems for complex surface-shaped optical elements, in particular to a new non-zero position diffraction interferometric measurement system based on multi-directional inclined carrier frequencies.

Background technique

In recent years, with the increasingly high performance requirements of optical systems in various fields, complex surface optical components have been widely used. Compared with traditional optical elements, complex surface optical elements have more degrees of freedom, can more easily correct aberrations in the optical system, and greatly simplify the system structure. However, the surface shape of complex surface optical components is free and complex, and the gradient changes greatly, which brings many difficulties to the high-precision measurement of the surface shape, which limits the large-diameter complex surface components in aerospace, defense, astronomy, lithography. The bottleneck of further application in other fields.

The detection methods of complex surfaces are mainly divided into contact and non-contact. The contact detection method is a method that can be maturely applied by the optical component processing unit, mainly including the three-coordinate measuring machine method, the profiler method and the swing arm profiler method. The contact measurement method adopts a point-by-point scanning method, and the single-point measurement accuracy can reach the nanometer level, but the measurement efficiency is low, and the full-field topography of the tested object cannot be obtained at one time, and the surface of the optical element will be damaged during the measurement process. Non-contact detection methods include microlens array method, structured light three-dimensional measurement method and interference method. Among them, the interferometry is currently recognized as the most accurate and effective method for measuring the surface shape of optical components. However, when the traditional interferometric measurement system measures complex surface components, the interference fringes are often too dense, and the surface shape of the optical components cannot be solved by the fringe information.

The team of Prof. Osten from the University of Stuttgart in Germany invented a multi-tilt wavefront interferometry method based on an array of point light sources. When using the system to measure complex surface shapes, the maximum surface gradient of 10° can be compensated, and the measurement accuracy is better than λ/30. In this method, the standard spherical wave is generated by the standard compensation spherical lens group. Since the system is a non-zero interference system and most of the optical paths are located off-axis, the standard compensation spherical lens group will introduce a large number of wave aberrations, resulting in excessive system errors, limiting the The measurement accuracy of this method; and limited by the processing level, the cost of making a large-diameter standard compensation spherical lens group is very high, which limits the measurement aperture of the entire system, and it is difficult to measure the large-diameter surface shape.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a new non-zero point diffraction interferometric measurement system based on multi-directional tilt carrier frequency, which solves the problem that the prior art cannot realize the high-precision measurement and generalized measurement of large-diameter complex surface optical elements .

The technical solution for realizing the present invention is: a new non-zero point diffraction interferometric measurement system based on multi-directional tilt carrier frequency, comprising a linearly polarized laser light source, an optical fiber coupler module, an optical fiber array, a test piece and an interference image acquisition system , the polarized laser light source, the optical fiber coupler module, and the optical fiber array are arranged in sequence with the first optical axis, the DUT is located on the second optical axis, and the angle between the second optical axis and the first optical axis is the outgoing beam of each optical fiber A quarter of the divergence angle, the best fitting spherical curvature center of the DUT coincides with the center of the end face of the fiber array;

The linearly polarized laser emitted by the fiber laser is introduced into the fiber coupler module by the fiber. The fiber coupler module divides a laser beam into several laser beams, and several laser beams are introduced into the fiber array to generate several standard spherical waves, some of which are used as reference light. Entering the interferogram acquisition system, another part of the standard spherical wave is incident on the DUT as the test light, and the test light is reflected by the DUT and the fiber array into the interferogram acquisition system in turn. The reference light and the test light form a shift in the interferogram acquisition system. Interferogram.

Preferably, the interferogram acquisition system includes a collimating objective lens, a long tube diaphragm, a spatial polarization phase shifting module, an imaging lens and a CCD camera, the collimating objective lens, the long tube diaphragm, a spatial polarization phase shifting module, and an imaging lens It is set on the same third optical axis as the CCD camera. The reference light and the test light are passed through the collimating lens to form several beams of parallel light. Several beams of parallel light are filtered by the long tube aperture and then passed through the spatial polarization phase shift module, and the spatial polarization phase shifts. The module divides each beam into four diffracted beams with phase difference, and forms four spatial phase-shifted interferograms with phase differences of π/2 on the target surface of the CCD camera through the imaging lens.

Preferably, the spatial polarization phase-shifting module includes a phase grating, a converging lens, and a micro-polarizer array. The parallel light after filtering out the stray light through the long tube diaphragm 6 is split by the phase grating to obtain diffracted light, which passes through the converging lens, respectively. Different areas of the micropolarizer array.

Preferably, the second optical axis where the measured object is located and the third optical axis where the interferogram acquisition system is located are symmetrically distributed on both sides of the first optical axis.

Preferably, several laser beams of the optical fiber coupler module are introduced into the optical fiber array through optical fibers.

Compared with the prior art, the present invention has the following significant advantages: (1) the present invention utilizes the thin optical fiber section as a point diffraction device to generate nearly ideal point diffraction spherical waves, so that a standard compensation spherical lens group does not need to be added to the optical path, avoiding The standard compensation spherical lens group introduces a large number of wave aberrations, and at the same time breaks through the limitation of the standard compensation spherical lens group on the measurement aperture of the interference system. (2) The present invention uses an optical fiber array to form a point diffraction array, generates a multi-directional tilted carrier frequency wavefront to compensate the surface gradient of the measured component, and solves the problem that the interference fringe density is too large and cannot be solved when measuring complex surface components by interferometry.

The present invention will be described in further detail below with reference to the accompanying drawings.

Description of drawings

FIG. 1 is a schematic diagram of a new non-zero point diffraction interferometry system based on multidirectional tilt of the present invention.

Detailed ways

A new type of non-zero point diffraction interferometric measurement system based on multidirectional tilt carrier frequency, comprising a linearly polarized laser light source 1, an optical fiber coupler module 2, an optical fiber array 3, a device to be measured 4 and an interference image acquisition system, the polarized laser light source 1. The light source 1, the optical fiber coupler module 2, and the optical fiber array 3 are arranged in sequence with the first optical axis, the DUT 4 is located on the second optical axis, and the angle between the second optical axis and the first optical axis is the divergence of the outgoing beam of each optical fiber. 1/4 of the angle, the best fitting spherical curvature center of the DUT 4 coincides with the center of the end face of the fiber array 3;

The linearly polarized laser emitted by the fiber laser 1 is introduced into the fiber coupler module 2 by the fiber. The fiber coupler module 2 divides a laser beam into several laser beams, and several laser beams are introduced into the fiber array 3 to generate several standard spherical waves, some of which are standard spherical waves. The wave enters the interferogram acquisition system as the reference light, and another part of the standard spherical wave is incident on the DUT 4 as the test light. The test light is reflected by the DUT 4 and the fiber array 3 in turn and enters the interferogram acquisition system. A phase-shifted interferogram is formed in the interferogram acquisition system.

In a further embodiment, the interferogram acquisition system includes a collimating objective lens 5, a long tube aperture 6, a spatial polarization phase shifting module, an imaging lens 10 and a CCD camera 11. The collimating objective lens 5, the long tube aperture 6 , the spatial polarization phase-shifting module, the imaging lens 10 and the CCD camera 11 are arranged in a common third optical axis, the reference light and the test light form several parallel lights through the collimating lens 5, and several parallel lights pass through the long tube diaphragm 6 to filter out impurities After scattering, it passes through the spatial polarization phase-shifting module, which divides each beam into four diffracted beams with phase difference, and forms four space images with phase differences of π/2 on the target surface of the CCD camera 11 through the imaging lens 10. Phase-shifted interferogram.

In a further embodiment, the spatial polarization phase-shifting module includes a phase grating 7, a condensing lens 8, and a micro-polarizer array 9, and the parallel light after filtering the stray light through the long tube diaphragm 6 is split by the phase grating 7 to obtain diffracted light. , respectively pass through different areas of the micro-polarizer array 9 after passing through the condensing lens 8 .

In a further embodiment, the second optical axis where the component under test 4 is located and the third optical axis where the interferogram acquisition system is located are symmetrically distributed on both sides of the first optical axis.

In a further embodiment, several laser beams of the optical fiber coupler module 2 are introduced into the optical fiber array 3 through optical fibers.

In the present invention, the test light emitted from each optical fiber in the optical fiber array 3 can cover the entire surface shape of the DUT 4 . The system is a non-zero interference system, and the test light does not need to return to the center of the end face of the fiber array 3 after being reflected by the DUT 4, as long as the fringe density of the interference pattern does not exceed the resolution of the CCD11.

In order to eliminate the influence of stray light in the present invention, only the reference light emitted by the optical fiber on the axis and the test light reflected by the DUT 4 to the center of the end face of the fiber array 3 can pass through the long tube aperture 6, and the rest of the stray light will be blocked by the long tube light The inner wall of appendix 6 is absorbed.

In the present invention, in order to avoid mutual interference of interference patterns generated by adjacent point light sources, each optical fiber in the optical fiber array 3 can be connected and disconnected by the corresponding optical switch in the optical fiber coupler module 2 .

Finally, by controlling the on-off of the corresponding optical paths of different point light sources, sub-interferograms corresponding to different local surfaces of the DUT are obtained, and the sub-interferograms are spliced and fused to obtain an interferogram corresponding to the entire surface of the DUT. Obtain the surface shape data of the DUT by calculating the interferogram after splicing

A more detailed description is given below in conjunction with the embodiments.

Example 1

As shown in Figure 1, a new non-zero point diffraction interferometry system based on multi-directional tilt, the optical path is an improved reflective point diffraction interference optical path system, including a linearly polarized laser light source 1, a fiber coupling module 2, and a fiber array 3 , DUT 4, collimating objective lens 5, long tube diaphragm 6, phase grating 7, condensing lens 8, micro-polarizer array 9, imaging lens 10 and CCD camera 11; among which fiber array 3 is a gradient compensation module, phase grating 7. The condensing lens 8 and the micro-polarizer array 9 constitute a spatial polarization phase-shifting module; the linearly polarized laser light source 1, the optical fiber coupling module 2, and the optical fiber array 3 are arranged in sequence with a common optical axis, and this optical axis is the first optical axis; 4. The optical axis is the second optical axis, and the included angle between the second optical axis and the first optical axis is a quarter of the divergence angle of the outgoing beam of each fiber; collimating objective lens 5, long tube diaphragm 6, phase grating 7 , a condensing lens 8, a micro-polarizer array 9, an imaging lens 10 and a CCD camera 11 are arranged on the same optical axis in order to form an interference pattern acquisition system, a collimating objective lens 5, a long tube diaphragm 6, a phase grating 7, a converging lens 8, a micro The optical axis where the polarizer array 9, the imaging lens 10 and the CCD camera 11 are located is the third optical axis, and the second optical axis where the DUT 4 is located and the third optical axis where the interferogram acquisition system is located are symmetrical on both sides of the first optical axis Distribution; the linearly polarized laser emitted by the fiber laser 1 is introduced into the fiber coupling module 2 by the fiber, and the fiber coupling module 2 divides a beam of laser light into several beams of laser light, and then the several beams of laser light are introduced into the fiber array 3 by the fiber, and are diffracted by the fiber array 3. Several standard spherical waves, a part of which enters the interferogram acquisition system as reference light, and the other part is incident on the DUT 4 as the test light, and the test light is reflected by the DUT 4 and the fiber array 3 into the interferogram acquisition system , the reference light and the test light firstly pass through the collimating lens 5 to form several parallel beams in the interferogram acquisition system, and then pass through the long tube aperture 6 to filter out the stray light, the beams are split by the phase grating 7 to obtain four diffracted beams. The condensing lens 8 passes through different regions of the micro-polarizer array 9 respectively, and then passes through the imaging objective lens 10 to form a phase-shifting interference pattern on the CCD 11 .

Claims (5)

1. The non-zero novel point diffraction interferometry system based on the multidirectional tilted carrier frequency is characterized by comprising an optical fiber laser (1), an optical fiber coupler module (2), an optical fiber array (3), a piece to be measured (4) and an interference image acquisition system, wherein the optical fiber laser (1), the optical fiber coupler module (2) and the optical fiber array (3) are sequentially arranged on a first optical axis, the piece to be measured (4) is positioned on a second optical axis, the included angle between the second optical axis and the first optical axis is one fourth of the divergence angle of each optical fiber emergent beam, and the best-fit spherical curvature center of the piece to be measured (4) is coincided with the end face center of the optical fiber array (3);

the linear polarization laser emitted by the optical fiber laser (1) is guided into the optical fiber coupler module (2) by an optical fiber, one laser beam is divided into a plurality of laser beams by the optical fiber coupler module (2), the laser beams are guided into the optical fiber array (3) to generate a plurality of standard spherical waves, one part of the standard spherical waves enter the interference pattern acquisition system as reference light, the other part of the standard spherical waves enter a tested piece (4) as test light, the test light is reflected into the interference pattern acquisition system sequentially through the tested piece (4) and the optical fiber array (3), and the reference light and the test light form a phase-shifting interference pattern in the interference pattern acquisition system.

2. The non-null novel point-diffraction interferometry system based on multi-directional tilted carrier frequency according to claim 1, it is characterized in that the interference pattern acquisition system comprises a collimating objective (5), a long-tube diaphragm (6), a space polarization phase-shifting module, an imaging lens (10) and a CCD camera (11), the collimating objective lens (5), the long-tube diaphragm (6), the spatial polarization phase-shifting module, the imaging lens (10) and the CCD camera (11) are arranged on a common third optical axis, the reference light and the test light form a plurality of beams of parallel light through the collimating lens (5), the plurality of beams of parallel light pass through the spatial polarization phase-shifting module after being filtered and scattered by the long-tube diaphragm (6), the spatial polarization phase-shifting module divides each beam of light into four beams of diffracted light with phase difference, and four spatial phase-shifting interferograms with phase differences of pi/2 are formed on a target surface of the CCD camera (11) through the imaging lens (10).

3. The nonzero-digit novel point diffraction interferometry system based on multidirectional tilted carrier frequencies according to claim 2, wherein the spatial polarization phase shifting module comprises a phase grating (7), a converging lens (8) and a micro-polarizer array (9), wherein stray parallel light filtered by the long-tube diaphragm 6 is split by the phase grating (7) to obtain diffracted light, and the diffracted light passes through different areas of the micro-polarizer array (9) respectively after passing through the converging lens (8).

4. The nonzero-digit novel point diffraction interferometry system based on multidirectional tilted carrier frequencies according to claim 1, wherein a second optical axis in which the measured piece (4) is located and a third optical axis in which the interferogram acquisition system is located are symmetrically distributed on two sides of the first optical axis.

5. The nonzero-digit novel point-diffraction interferometry system based on multi-directional tilted carrier frequencies according to claim 1, wherein a plurality of laser beams of the fiber coupler module (2) are guided into the fiber array (3) through optical fibers.

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