Three-degree-of-freedom heterodyne interferometry apparatus and method with angle information recovery

Abstract

A three-degree-of-freedom heterodyne interferometer device with angle information recovery and a method thereof belong to the technical field of laser interferometry. The device comprises a heterodyne light source, a heterodyne interference mirror group, a wavefront control target mirror, an angle information recovery optical path, an optoelectronic conversion unit and an electronic signal processing unit. The heterodyne light source outputs two beams of light with different frequencies, and the beams are divided into measurement light and reference light by the interference mirror group; the wavefront control target mirror is deflected with the measured object to ensure the effectiveness of the light beam interference under a large angle; the angle information recovery optical path converts the change of the optical axis position of the light beam into the difference in the focal plane phase distribution, and then the difference is sampled by a fiber array. The optoelectronic conversion unit completes the conversion of the optoelectronic signal, the rear-end processing unit demodulates the phase, and the displacement, pitch angle and yaw angle of the measured object are calculated. The present application solves the problem that the angle information is difficult to extract under a large angle in the existing scheme, expands the angle measurement range, and the device structure is compact and has high integration, and three-degree-of-freedom synchronous high-precision measurement can be realized.

Description

Technical Field

[0001] This invention belongs to the field of laser interferometry technology, and particularly relates to a three-degree-of-freedom heterodyne interferometry device and method with angular information recovery. Background Technology

[0002] Laser interferometry is one of the fundamental core technologies in precision engineering, with wide applications in precision displacement measurement, attitude detection, and ultra-precision motion platform position measurement. As precision equipment increasingly demands miniaturization, integration, and simultaneous multi-degree-of-freedom measurement capabilities, single-beam three-degree-of-freedom laser interferometry systems capable of simultaneously measuring one displacement degree of freedom and two angular degrees of freedom are gradually becoming an important development direction in this field.

[0003] For single-beam three-degree-of-freedom measurement requirements, existing technologies mainly include single-beam three-degree-of-freedom heterodyne laser interferometry schemes based on array detectors, single-beam three-degree-of-freedom zero-difference laser interferometry schemes based on array detectors, and single-beam three-degree-of-freedom measurement schemes based on differential wavefront sensing principles. All of these schemes achieve displacement and angle measurement and calculation by receiving the spatial distribution information of the interference light field and combining it with corresponding calculation methods. In addition, existing technologies also include schemes that utilize receiving optical fibers for sparse sampling reception of the interference signal. These schemes offer advantages such as compact structure, flexible arrangement, and ease of separation from subsequent photoelectric conversion modules.

[0004] However, existing single-beam three-degree-of-freedom measurement schemes still have shortcomings in terms of angle measurement range. Although array-type integrated receiver schemes and differential wavefront sensing schemes can achieve three-degree-of-freedom measurement and calculation, their angle measurement range is usually still limited. Although sparse sampling receiver schemes can reduce the complexity of the receiver structure and improve system flexibility, they still rely on the receiver side to obtain the phase distribution difference directly corresponding to the angle change. Therefore, their angle measurement range is also limited and cannot directly meet the requirements for stable three-degree-of-freedom measurement under large angle conditions.

[0005] In particular, for technical solutions that employ target-side wavefront modulation of the target mirror to improve interference preservation capabilities at large angles, the effect of the target mirror deflection on the returned measurement light after modulation manifests more as a change in the optical axis position between the returned measurement light and the reference light, which are approximately parallel, rather than a direct change in the wavefront angle that can be used for angle calculation. While this state is beneficial for improving the system's interference preservation capabilities at large angles, it does not directly create a phase distribution difference suitable for three-degree-of-freedom angle calculation at the receiving end. In other words, under this condition, the composite optical field is more likely to characterize displacement changes, but it is difficult to directly characterize angle information. This problem cannot be solved simply by increasing the receiver sensitivity or the number of sampling points; rather, it is because the form of angle information changes after target-side wavefront modulation, requiring the receiving end to re-establish the mapping relationship between the optical axis position change and the focal plane phase distribution difference.

[0006] Therefore, even with a large-angle interference-preserving structure at the target end, if it is still desired to use a focal plane fiber array to measure one displacement degree of freedom and two angular degrees of freedom, a dedicated angle information restoration optical path needs to be added to the receiving side. This path restores the received information, which was originally mainly manifested as changes in the optical axis position, to the phase distribution differences corresponding to the angle changes. The focal plane fiber array then performs sparse sampling and reception of this spatial distribution. If only a large-angle interference-preserving structure at the target end and a focal plane fiber array are used for reception, although signal changes at different locations can be received, it is difficult to stably extract the two angular degrees of freedom information. This makes it difficult to expand the angle measurement range of the single-beam method and achieve stable three-degree-of-freedom measurement.

[0007] Therefore, existing technologies lack a corresponding single-beam three-degree-of-freedom heterodyne interferometry device and method for remapping the angle information corresponding to the target mirror deflection onto the focal plane through an angle information restoration optical path, and for measuring and calculating one displacement degree of freedom and two angle degrees of freedom using a focal plane fiber array. Based on this, it is necessary to propose a focal plane fiber array-based single-beam three-degree-of-freedom ultra-precision heterodyne interferometry device with an angle information restoration optical path. This device should maintain the compact structure and large-angle interference preservation capability of the single-beam design, enabling the focal plane fiber array to stably obtain spatial sampling information for three-degree-of-freedom calculation, thereby improving the angle measurement range of the single-beam method. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a three-degree-of-freedom heterodyne interferometry device and method with angle information restoration. In a single-beam heterodyne interferometry system, by adding an angle information restoration optical path after the large-angle interference holding structure at the target end, the angle information corresponding to the target mirror deflection is remapped into phase differences at different sampling positions on the focal plane. Combined with focal plane fiber array reception and electronic signal processing, synchronous high-precision measurement of one displacement degree of freedom and two angle degrees of freedom is achieved, thereby improving the angle measurement range of the single-beam method. The key technical point of this invention is not simply adding a focal plane receiving channel, but rather converting the information, which mainly manifests as changes in optical axis position after wavefront modulation at the target end, back into a phase distribution difference that can be sampled and solved by the focal plane fiber array through the angle information restoration optical path. The technical solution adopted by this invention is as follows:

[0009] A three-degree-of-freedom heterodyne interferometry device with angular information recovery includes:

[0010] Heterodyne light source, used to emit two input beams with different frequencies;

[0011] Heterodyne interferometer array is used to separate an input beam into a first measurement beam and a first reference beam, and another input beam into a second measurement beam and a second reference beam.

[0012] The wavefront-controlled target mirror is used to be installed on the object under test to reflect the second measurement beam back to the heterodyne interferometer group. When the object under test moves and the pitch or yaw angle changes, the wavefront-controlled target mirror deflects synchronously with the object under test, so that the two-way propagation path of the second measurement beam between the heterodyne interferometer group and the wavefront-controlled target mirror remains parallel.

[0013] The heterodyne interferometer array couples the first measurement beam with the second reference beam to form a reference interference light signal, and outputs the returning second measurement beam and the first reference beam in the same direction to form a measurement interference beam.

[0014] Angle information recovery optical path is set on the propagation path of the measurement interference beam. It is used to convert the change in the center position of the second measurement beam when it returns due to the deflection of the target mirror controlled by the wavefront into a detectable change in the position and phase distribution of the light spot, thus forming a measurement interference light signal.

[0015] The photoelectric conversion unit is used to receive the measurement interference optical signal and the reference interference optical signal, and convert them into corresponding measurement interference electrical signal and reference interference electrical signal;

[0016] The electronic signal processing unit is used to demodulate and process the measurement interference signal and the reference interference signal to obtain the displacement, pitch angle and yaw angle of the wavefront-controlled target mirror along the measurement direction.

[0017] Furthermore, the angle information restoration optical path includes a coaxially arranged angle information restoration lens and a fiber array structure. The fiber array structure has a first fiber channel, a second fiber channel, a third fiber channel, and a fourth fiber channel arranged in a circle. The first and fourth fiber channels are positioned on the upper and lower sides of the axis of the angle information restoration optical path, respectively, while the second and third fiber channels are positioned on the left and right sides of the axis of the angle information restoration optical path, respectively. The output ends of the first, second, third, and fourth fiber channels are respectively connected to the photoelectric conversion unit. The first sampling point at the input end of the first fiber channel, the second sampling point at the input end of the second fiber channel, the third sampling point at the input end of the third fiber channel, and the fourth sampling point at the input end of the fourth fiber channel are all located on the focal plane of the angle information restoration lens.

[0018] Furthermore, the heterodyne light source includes a single-frequency laser, an optical isolator, and a Wollaston prism arranged sequentially. An optical isolator is provided between the emitting end of the single-frequency laser and the incident end of the Wollaston prism. The two refractive ends of the Wollaston prism are respectively oriented towards the input ends of two acousto-optic frequency shifters. The output ends of the two acousto-optic frequency shifters are respectively connected to one end of two first fiber couplers via optical fibers.

[0019] Furthermore, the heterodyne interferometer assembly includes a base and a first fiber collimator, a second fiber collimator, a first polarizing beam splitter, a second polarizing beam splitter, and a second fiber coupler fixed on the base. The reflecting ends of the first and second polarizing beam splitters are arranged opposite each other. A half-wave plate is provided between the first and second polarizing beam splitters. The incident ends of the first and second polarizing beam splitters are arranged in the same direction. The output end of the first fiber collimator faces the incident end of the first polarizing beam splitter, and the output end of the second fiber collimator faces the incident end of the second polarizing beam splitter. The second fiber coupler... The input end of the first polarizing beam splitter faces the reflection end of the second polarizing beam splitter. The transmission end of the first polarizing beam splitter is provided with a first reflecting mirror. A first quarter-wave plate is provided between the first reflecting mirror and the first polarizing beam splitter. The transmission end of the second polarizing beam splitter is provided with a second quarter-wave plate. A wavefront-controlled target mirror is provided on the path of the transmission end of the second polarizing beam splitter. The output end of the second fiber coupler is connected to the electronic signal processing unit through a photoelectric conversion unit. The input ends of the first fiber collimator and the second fiber collimator are respectively connected to the other ends of the two first fiber couplers through optical fibers. The measurement interference beam is emitted from the side of the second polarizing beam splitter away from the reflection end.

[0020] Furthermore, the first polarizing beam splitter has a first polarizer at its incident end, a third quarter-wave plate on the side of the first polarizing beam splitter facing the second fiber coupler, a third polarizer between the third quarter-wave plate and the first polarizing beam splitter, a second polarizer at its incident end, a fourth quarter-wave plate on the side of the second polarizing beam splitter from which the measurement interference beam is emitted, and a fourth polarizer between the fourth quarter-wave plate and the second polarizing beam splitter.

[0021] Furthermore, the wavefront-controlled target mirror includes a lens assembly and a second reflecting mirror, with the lens assembly positioned closer to the second polarizing beam splitter relative to the second reflecting mirror.

[0022] This invention also provides a three-degree-of-freedom heterodyne interferometry method with angle information recovery, which is based on the aforementioned three-degree-of-freedom heterodyne interferometry device with angle information recovery, and includes the following steps:

[0023] Step 1: Based on the displacement measurement range of the object under test along the predetermined axis, the allowable pitch angle range, the allowable yaw angle range, the diameter of the second measurement beam, the large-angle interference holding condition of the wavefront control target mirror, the focal length of the angle information restoration lens, the focal plane position of the angle information restoration lens, and the positions of the first sampling point, the second sampling point, the third sampling point, and the fourth sampling point, determine the installation position relationship between the wavefront control target mirror and the angle information restoration optical path. This ensures that after the returning second measurement beam is restored by the angle information restoration lens, it forms light spots with phase distribution differences at different positions on the focal plane of the angle information restoration lens, which can be used for three-degree-of-freedom calculation.

[0024] Step 2: Install the wavefront control target mirror on the object under test, so that the wavefront control target mirror moves synchronously with the object under test as it moves along the measurement direction, and deflects synchronously with the object under test when the object under test pitches or yaws.

[0025] Step 3: The input beam is collimated and polarized sequentially by the first fiber collimator and the first polarizing beam splitter to form a first measurement beam and a first reference beam. The first reference beam is emitted from the reflecting end of the first polarizing beam splitter, first undergoes polarization state transformation by a half-wave plate, and then is directed to the angle information restoration optical path by the second polarizing beam splitter. The first measurement beam is emitted from the transmitting end of the first polarizing beam splitter, first undergoes polarization state transformation by a first quarter-wave plate, then is reflected back to the first polarizing beam splitter by the first reflecting mirror, and finally is reflected by the cemented surface of the first polarizing beam splitter and directed to the second fiber coupler.

[0026] The other input beam is collimated, polarization-state converted, and polarization-splitting sequentially by the second fiber collimator and the second polarization beam splitter to form a second measurement beam and a second reference beam. The second reference beam is emitted from the reflecting end of the second polarization beam splitter, undergoes polarization state transformation by passing through a half-wave plate, and then passes through the first polarization beam splitter to the second fiber coupler. The second measurement beam is emitted from the transmitting end of the second polarization beam splitter, undergoes polarization state transformation by passing through a second quarter-wave plate, and then passes through the lens assembly to the second reflecting mirror. The second measurement beam is reflected back to the cemented surface of the second polarization beam splitter by the second reflecting mirror and reflected to restore the optical path of angle information.

[0027] When the object under test undergoes pitch or yaw motion, the combined structure formed by the lens assembly and the second reflector regulates the propagation state of the returning second measurement beam, so that the returning second measurement beam can still maintain effective interference with the first reference light.

[0028] Step 4: The returning second measurement beam and the first reference beam at least partially overlap in the output optical path of the heterodyne interferometer group to form a measurement interference beam. The measurement interference beam passes through the angle information restoration lens to form an angle information restoration beam, and is mapped at the focal plane of the angle information restoration lens as a light spot with detectable phase distribution. The phase distribution of the light spot corresponds to the angle change of the wavefront-controlled target mirror. The first sampling point, the second sampling point, the third sampling point and the fourth sampling point respectively perform sparse sampling on the light spot and form four measurement interference light signals sent to the photoelectric conversion unit.

[0029] Step 5: The photoelectric conversion unit converts the four measurement interference optical signals output from the first, second, third, and fourth fiber channels into four corresponding measurement interference electrical signals. The electronic signal processing unit performs heterodyne phase demodulation on the four measurement interference electrical signals and the reference interference electrical signal to obtain the phase change at the first, second, third, and fourth sampling points. Based on each phase change, it performs a three-degree-of-freedom joint calculation to obtain the displacement degree of freedom Z of the measured object along the measurement direction, as well as the pitch angle α and yaw angle β.

[0030] Let the phase change at the first sampling point be S1, the phase change at the second sampling point be S2, the phase change at the third sampling point be S3, and the phase change at the fourth sampling point be S4. Let the displacement of the measured object along the measurement direction be Z, the pitch angle be α, and the yaw angle be β. Then α, β, and Z satisfy the simultaneous equations (1)-(3):

[0031] (1)

[0032] (2)

[0033] (3)

[0034] In the formula, K1 is the proportionality coefficient of displacement along the measurement direction, K2 is the proportionality coefficient of pitch angle and K3 is the proportionality coefficient of yaw angle, and their values ​​are determined by the system structural parameters and calibration results.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] 1. This invention introduces an angle information restoration optical path into a single-beam heterodyne interferometry system. This transforms the second measurement beam information, which initially manifests primarily as a change in the overall optical axis position after being controlled by the wavefront-tuned target mirror, into phase distribution differences at different sampling positions on the focal plane of the angle information restoration lens. This solves the problem of the difficulty in stably extracting two angular degrees of freedom information when using only a fiber array receiver, thus improving the angle measurement range of the single-beam method. This invention first restores the angle information to a sampleable phase distribution characteristic on the focal plane using the angle information restoration optical path, and then performs sparse sampling using a fiber array.

[0037] 2. This invention organically combines a heterodyne interferometer group for single-beam measurement, a wavefront-controlled target mirror, an angle information recovery optical path, and a focal plane fiber array receiving method. This allows the system to achieve simultaneous high-precision measurement of one displacement degree of freedom and two angle degrees of freedom while maintaining its compact structure and ease of integration. Compared to existing single-beam differential wavefront detection schemes or array-based detector overall receiving schemes, this invention combines angle information recovery with focal plane sparse sampling reception, allowing the angle information to be reflected in the phase distribution differences at different sampling positions on the receiving side, thereby facilitating the expansion of the angle measurement range.

[0038] 3. This invention utilizes an optical fiber array structure with the input end located at the focal plane of the angle information restoration lens to perform sparse sampling reception of the interference light field of the angle information restoration beam. Compared with the overall area array detection method, it has the advantages of flexible reception method, easy separation and arrangement with photoelectric conversion module, and suitability for miniaturized system integration. At the same time, the sparse sampling reception method can match the phase distribution characteristics of the focal plane after angle information restoration, thereby helping to improve the engineering implementation capability and application flexibility of the system. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the structure of the device of the present invention;

[0040] Figure 2 This is a schematic diagram of the heterodyne light source;

[0041] Figure 3 This is a schematic diagram of the heterodyne interference mirror assembly;

[0042] Figure 4This is a schematic diagram showing the polarizers and waveplates installed on the second polarizing beam splitter and the first polarizing beam splitter;

[0043] Figure 5 This is a schematic diagram of the wavefront-controlled target mirror;

[0044] Figure 6 This is a schematic diagram of the optical path for reconstructing the optical path by measuring the incident angle information of the interference beam;

[0045] Figure 7 This is a schematic diagram showing the locations of the first, second, third, and fourth sampling points.

[0046] In the diagram, 1. Heterodyne light source, 11. Single-frequency laser, 12. Optical isolator, 13. Wollaston prism, 14. Acousto-optic frequency shifter, 15. First fiber coupler, 2. Heterodyne interferometer group, 21. First fiber collimator, 22. Second fiber collimator, 23. First polarizer, 24. Second polarizer, 25. First polarizing beam splitter, 26. Second polarizing beam splitter, 27. First quarter-wave plate, 28. Second quarter-wave plate, 29. Third polarizer, 210. Fourth polarizer, 211. Third quarter-wave plate, 212. Fourth quarter-wave plate, 213. Second fiber coupler, 214. First reflector, 215. Half-wave plate, 3. Wavefront-controlled target mirror, 31. Lens assembly, 32. Second reflector, 4. Photoelectric conversion unit, 5. Electronic signal processing unit, 6. Angular information restoration optical path, 61. 62. Angle information restoration lens; 63. Fiber optic array structure; 64. First fiber optic channel; 65. Second fiber optic channel; 66. Third fiber optic channel; 67. Fourth fiber optic channel; 68. First sampling point; 69. Second sampling point; 60. Third sampling point; 610. Fourth sampling point; 71. Second measurement beam; 72. Measurement interference beam; 73. Angle information restoration beam. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below with reference to specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0048] The connections mentioned in this invention are divided into fixed connections and detachable connections. Fixed connections, also known as non-detachable connections, include but are not limited to conventional fixed connection methods such as folded connections, riveted connections, adhesive connections, and welded connections. Detachable connections include but are not limited to conventional disassembly methods such as bolted connections, snap-fit ​​connections, pin connections, and hinged connections. When a specific connection method is not explicitly defined, it is assumed that at least one existing connection method can be found to achieve this function, and those skilled in the art can choose according to their needs. For example, a welded connection can be chosen for fixed connections, and a bolted connection can be chosen for detachable connections.

[0049] The present invention will be further described in detail below with reference to the accompanying drawings. The following embodiments are explanations of the present invention, but the present invention is not limited to the following embodiments.

[0050] Example 1: As Figures 1 to 7 As shown, a three-degree-of-freedom heterodyne interferometry device with angular information recovery includes:

[0051] Heterodyne source 1 is used to emit two input beams with different frequencies;

[0052] Heterodyne interferometer group 2 is used to separate one input beam into a first measurement beam and a first reference beam, and to separate another input beam into a second measurement beam 71 and a second reference beam;

[0053] The wavefront-controlled target mirror 3 is used to be installed on the object under test and reflect the second measurement beam 71 back to the heterodyne interferometer group 2. When the object under test moves and the pitch or yaw angle deflects, the wavefront-controlled target mirror 3 deflects synchronously with the object under test, so that the two-way propagation path of the second measurement beam 71 between the heterodyne interferometer group 2 and the wavefront-controlled target mirror 3 remains parallel.

[0054] The heterodyne interferometer group 2 couples the first measurement beam with the second reference beam to form a reference interference light signal, and outputs the returning second measurement beam 71 in the same direction as the first reference beam to form a measurement interference beam 72.

[0055] Angle information recovery optical path 6 is set on the propagation path of the measurement interference beam 72. It is used to convert the change in the center position of the second measurement beam 71 when it returns due to the deflection of the wavefront-controlled target mirror 3 into a detectable change in the position of the light spot and the change in the phase distribution, thus forming a measurement interference light signal.

[0056] The photoelectric conversion unit 4 is used to receive the measurement interference optical signal and the reference interference optical signal, and convert them into corresponding measurement interference electrical signal and reference interference electrical signal;

[0057] The electronic signal processing unit 5 is used to demodulate and process the measurement interference signal and the reference interference signal, thereby obtaining the displacement, pitch angle and yaw angle of the wavefront-controlled target mirror 3 along the measurement direction.

[0058] The wavefront-controlled target mirror 3 is mounted on the object under test and moves together with the object. When the object under test pitches or yaws, the second measurement beam 71 reflected by the wavefront-controlled target mirror 3 is more of a change in the overall optical axis position, making the optical paths of the second measurement beam basically parallel before and after reflection. This reduces angle mismatch and wavefront mismatch, and reduces the decrease in interference contrast. By setting the angle information to restore the optical path 6, the pitch and yaw rotational degree of freedom information formed by the deflection of the wavefront-controlled target mirror 3 can be remapped to the phase difference at different sampling positions. This provides conditions for subsequent three-degree-of-freedom calculations of displacement, pitch, and yaw along the measurement direction and improves the angle measurement range of the system.

[0059] The angle information restoration optical path 6 includes a coaxially arranged angle information restoration lens 61 and an optical fiber array structure 62. The optical fiber array structure 62 has a first optical fiber channel 63, a second optical fiber channel 64, a third optical fiber channel 65, and a fourth optical fiber channel 66 arranged in a circle. The first optical fiber channel 63 and the fourth optical fiber channel 66 are positioned on the upper and lower sides of the axis of the angle information restoration optical path 6, respectively, and the second optical fiber channel 64 and the third optical fiber channel 65 are positioned on the left and right sides of the axis of the angle information restoration optical path 6. The output ends of the first optical fiber channel 63, the second optical fiber channel 64, the third optical fiber channel 65, and the fourth optical fiber channel 66 are respectively connected to the photoelectric conversion unit 4. The first sampling point 67 at the input end of the first optical fiber channel 63, the second sampling point 68 at the input end of the second optical fiber channel 64, the third sampling point 69 at the input end of the third optical fiber channel 65, and the fourth sampling point 610 at the input end of the fourth optical fiber channel 66 are all located on the focal plane of the angle information restoration lens 61.

[0060] After the angle information restored beam 73 is incident on the fiber array structure 62, the first fiber channel 63, the second fiber channel 64, the third fiber channel 65 and the fourth fiber channel 66 respectively receive the light spot information at different spatial positions. The fiber array structure 62 can restore the light field distribution of the focal plane of the lens 61 according to the angle information by using a linear array, a surface array or other matching forms.

[0061] The heterodyne light source 1 includes a single-frequency laser 11, an optical isolator 12, and a Wollaston prism 13 arranged in sequence. An optical isolator 12 is provided between the emitting end of the single-frequency laser 11 and the incident end of the Wollaston prism 13. The two refractive ends of the Wollaston prism 13 are respectively facing the input ends of two acousto-optic frequency shifters 14. The output ends of the two acousto-optic frequency shifters 14 are respectively connected to one end of two first fiber optic couplers 15 through optical fibers.

[0062] The heterodyne interferometer assembly 2 includes a base and a first fiber collimator 21, a second fiber collimator 22, a first polarizing beam splitter 25, a second polarizing beam splitter 26, and a second fiber coupler 213 fixed on the base. The reflecting ends of the first polarizing beam splitter 25 and the second polarizing beam splitter 26 are arranged opposite each other. A half-wave plate 215 is provided between the first polarizing beam splitter 25 and the second polarizing beam splitter 26. The incident ends of the first polarizing beam splitter 25 and the second polarizing beam splitter 26 are arranged in the same direction. The output end of the first fiber collimator 21 faces the incident end of the first polarizing beam splitter 25, and the output end of the second fiber collimator 22 faces the incident end of the second polarizing beam splitter 26. The second fiber coupler 213... The input end faces the reflection end of the second polarizing beam splitter 26. The transmission end of the first polarizing beam splitter 25 is provided with a first reflecting mirror 214. A first quarter-wave plate 27 is provided between the first reflecting mirror 214 and the first polarizing beam splitter 25. The transmission end of the second polarizing beam splitter 26 is provided with a second quarter-wave plate 28. A wavefront-modulated target mirror 3 is provided on the path of the transmission end of the second polarizing beam splitter 26. The output end of the second fiber coupler 213 is connected to the electronic signal processing unit 5 through the photoelectric conversion unit 4. The input ends of the first fiber collimator 21 and the second fiber collimator 22 are respectively connected to the other ends of the two first fiber couplers 15 through optical fibers. The measurement interference beam 72 is emitted from the side of the second polarizing beam splitter 26 away from the reflection end.

[0063] The first polarizing beam splitter 25 has a first polarizer 23 at its incident end, a third quarter-wave plate 211 on the side of the first polarizing beam splitter 25 facing the second fiber coupler 213, a third polarizer 29 between the third quarter-wave plate 211 and the first polarizing beam splitter 25, a second polarizer 24 at its incident end, a fourth quarter-wave plate 212 on the side of the second polarizing beam splitter 26 from which the measurement interference beam 72 is emitted, and a fourth polarizer 210 between the fourth quarter-wave plate 212 and the second polarizing beam splitter 26.

[0064] The wavefront-controlled target mirror 3 includes a lens assembly 31 and a second reflector 32. The lens assembly 31 is closer to the second polarizing beam splitter 26 than the second reflector 32.

[0065] Example 2: Figures 1 to 7 As shown, a three-degree-of-freedom heterodyne interferometry method with angular information restoration is implemented based on the three-degree-of-freedom heterodyne interferometry device with angular information restoration described in Example 1, and includes the following steps:

[0066] Step 1: Based on the displacement measurement range of the object under test along the predetermined axis, the allowable pitch angle range, the allowable yaw angle range, the diameter of the second measurement beam 71, the large-angle interference holding conditions of the wavefront control target mirror 3, the focal length of the angle information restoration lens 61, the focal plane position of the angle information restoration lens 61, and the positions of the first sampling point 67, the second sampling point 68, the third sampling point 69, and the fourth sampling point 610, determine the installation position relationship between the wavefront control target mirror 3 and the angle information restoration optical path 6. This will allow the returning second measurement beam 71 to be restored by the angle information restoration lens 61, forming light spots with phase distribution differences at different positions on the focal plane of the angle information restoration lens 61, which can be used for three-degree-of-freedom calculation.

[0067] Step 2: Install the wavefront control target mirror 3 on the object under test, so that the wavefront control target mirror 3 moves synchronously with the object under test as it moves along the measurement direction, and deflects synchronously with the object under test when the object under test pitches or yaws. When the object under test deflects at a large angle, the wavefront control target mirror 3 can maintain the effective interference state between the returning second measurement beam 71 and the first reference beam.

[0068] Step 3: The input beam is collimated and polarized sequentially by the first fiber collimator 21 and the first polarizing beam splitter 25 to form a first measurement beam and a first reference beam. The first reference beam is emitted from the reflecting end of the first polarizing beam splitter 25, first undergoes polarization state transformation by the half-wave plate 215, and then is emitted into the angle information restoration optical path 6 by the second polarizing beam splitter 26. The first measurement beam is emitted from the transmitting end of the first polarizing beam splitter 25, first undergoes polarization state transformation by the first quarter-wave plate 27, then is emitted into the first reflecting mirror 214 and reflected back into the first polarizing beam splitter 25, and finally is emitted into the second fiber coupler 213 after being reflected by the cemented surface of the first polarizing beam splitter 25.

[0069] The other input beam is collimated, polarization-state converted, and polarization-splitting sequentially by the second fiber collimator 22 and the second polarization beam splitter 26 to form the second measurement beam 71 and the second reference beam. The second reference beam is emitted from the reflecting end of the second polarization beam splitter 26, first undergoes polarization state conversion by the half-wave plate 215, and then is emitted to the second fiber coupler 213 by the first polarization beam splitter 25. The second measurement beam 71 is emitted from the transmitting end of the second polarization beam splitter 26, first undergoes polarization state conversion by the second quarter-wave plate 28, and then is emitted to the second reflecting mirror 32 through the lens assembly 31. The second measurement beam 71 is reflected back to the cemented surface of the second polarization beam splitter 26 by the second reflecting mirror 32 and reflected towards the angle information restoration optical path 6.

[0070] When the object under test undergoes pitch or yaw motion, the combined structure of the lens assembly 31 and the second reflector 32 regulates the propagation state of the returning second measurement beam 71, so that the returning second measurement beam 71 and the first reference light can still maintain effective interference.

[0071] Step 4: The returning second measurement beam 71 and the first reference beam at least partially overlap in the output optical path of the heterodyne interferometer group 2 to form a measurement interference beam 72. The measurement interference beam 72 passes through the angle information restoration lens 61 to form an angle information restoration beam 73, and is mapped at the focal plane of the angle information restoration lens 61 as a light spot with a detectable phase distribution. The phase distribution of the light spot corresponds to the angle change of the wavefront-controlled target mirror 3. The first sampling point 67, the second sampling point 68, the third sampling point 69 and the fourth sampling point 610 respectively perform sparse sampling on the light spot and form a measurement interference light signal sent to the photoelectric conversion unit 4.

[0072] Step 5: The photoelectric conversion unit 4 converts the four measurement interference optical signals output from the first fiber channel 63, the second fiber channel 64, the third fiber channel 65, and the fourth fiber channel 66 into the corresponding four measurement interference electrical signals. The electronic signal processing unit 5 performs heterodyne phase demodulation on the four measurement interference electrical signals and the reference interference electrical signal to obtain the phase change at the first sampling point 67, the second sampling point 68, the third sampling point 69, and the fourth sampling point 610. Based on each phase change, a three-degree-of-freedom joint calculation is performed to obtain the displacement degree of freedom Z of the measured object along the measurement direction, as well as the pitch angle α and the yaw angle β.

[0073] Let the phase change at the first sampling point 67 be S1, the phase change at the second sampling point 68 be S2, the phase change at the third sampling point 69 be S3, and the phase change at the fourth sampling point 610 be S4. Let the displacement of the measured object along the measurement direction be Z, the pitch angle be α, and the yaw angle be β. Then α, β, and Z satisfy the simultaneous equations (1)-(3):

[0074] (1)

[0075] (2)

[0076] (3)

[0077] In the formula, K1 is the proportionality coefficient of displacement along the measurement direction, K2 is the proportionality coefficient of pitch angle and K3 is the proportionality coefficient of yaw angle, and their values ​​are determined by the system structural parameters and calibration results.

[0078] The above embodiments are merely illustrative examples of the present invention and do not limit its scope of protection. Those skilled in the art can make partial changes to them, as long as they do not exceed the spirit and essence of the present invention, they are all within the scope of protection of the present invention.

Claims

1. A three-degree-of-freedom heterodyne interferometry device with angular information recovery, characterized in that, include: Heterodyne source (1) is used to emit two input beams with different frequencies; Heterodyne interferometer group (2) is used to separate one input beam into a first measurement beam and a first reference beam, and to separate another input beam into a second measurement beam (71) and a second reference beam; The wavefront-controlled target mirror (3) is used to be installed on the object under test to reflect the second measurement beam (71) back to the heterodyne interferometer group (2). When the object under test undergoes pitch or yaw angle deflection during movement, the wavefront-controlled target mirror (3) deflects synchronously with the object under test, so that the two-way propagation path of the second measurement beam (71) between the heterodyne interferometer group (2) and the wavefront-controlled target mirror (3) remains parallel. The heterodyne interferometer group (2) couples the first measurement beam with the second reference beam to form a reference interference light signal, and outputs the returning second measurement beam (71) in the same direction as the first reference beam to form a measurement interference beam (72). Angle information restoration optical path (6) is set on the propagation path of the measurement interference beam (72) to convert the change in the center position of the second measurement beam (71) when it returns due to the deflection of the wavefront-controlled target mirror (3) into a detectable change in the position of the spot and the change in the phase distribution, thereby forming a measurement interference optical signal; The photoelectric conversion unit (4) is used to receive the measurement interference optical signal and the reference interference optical signal, and convert them into the corresponding measurement interference electrical signal and the reference interference electrical signal; The electronic signal processing unit (5) is used to demodulate the measurement interference signal and the reference interference signal to obtain the displacement, pitch angle and yaw angle of the wavefront-controlled target mirror (3) along the measurement direction; The angle information restoration optical path (6) includes an angle information restoration lens (61) and a fiber array structure (62) arranged coaxially. The fiber array structure (62) is provided with a first fiber channel (63), a second fiber channel (64), a third fiber channel (65), and a fourth fiber channel (66) arranged in a circle. The first fiber channel (63) and the fourth fiber channel (66) are positioned on the upper and lower sides of the axis of the angle information restoration optical path (6), respectively, and the second fiber channel (64) and the third fiber channel (65) are positioned on the axis of the angle information restoration optical path (6). On the left and right sides, the output ends of the first fiber channel (63), the second fiber channel (64), the third fiber channel (65) and the fourth fiber channel (66) are connected to the photoelectric conversion unit (4) respectively. The first sampling point (67) at the input end of the first fiber channel (63), the second sampling point (68) at the input end of the second fiber channel (64), the third sampling point (69) at the input end of the third fiber channel (65) and the fourth sampling point (610) at the input end of the fourth fiber channel (66) are all set on the focal plane of the angle information restoration lens (61).

2. The three-degree-of-freedom heterodyne interferometry measuring device with angular information restoration according to claim 1, characterized in that: The heterodyne light source (1) includes a single-frequency laser (11), an optical isolator (12) and a Wollaston prism (13) arranged in sequence. An optical isolator (12) is provided between the emitting end of the single-frequency laser (11) and the incident end of the Wollaston prism (13). The two refractive ends of the Wollaston prism (13) are respectively facing the input ends of two acousto-optic frequency shifters (14). The output ends of the two acousto-optic frequency shifters (14) are respectively connected to one end of two first fiber couplers (15) through optical fibers.

3. The three-degree-of-freedom heterodyne interferometry measuring device with angular information restoration according to claim 2, characterized in that: The heterodyne interferometer assembly (2) includes a base and a first fiber collimator (21), a second fiber collimator (22), a first polarizing beam splitter (25), a second polarizing beam splitter (26), and a second fiber coupler (213) fixed on the base. The reflecting ends of the first polarizing beam splitter (25) and the second polarizing beam splitter (26) are arranged opposite to each other. A half-wave plate (215) is provided between the first polarizing beam splitter (25) and the second polarizing beam splitter (26). The incident ends of the first polarizing beam splitter (25) and the second polarizing beam splitter (26) are arranged in the same direction. The output end of the first fiber collimator (21) faces the incident end of the first polarizing beam splitter (25), and the output end of the second fiber collimator (22) faces the incident end of the second polarizing beam splitter (26). The second fiber coupler (213) is fixed on the base. The input end faces the reflection end of the second polarizing beam splitter (26). The transmission end of the first polarizing beam splitter (25) is provided with a first reflecting mirror (214). A first quarter-wave plate (27) is provided between the first reflecting mirror (214) and the first polarizing beam splitter (25). The transmission end of the second polarizing beam splitter (26) is provided with a second quarter-wave plate (28). A wavefront control target mirror (3) is provided on the path of the transmission end of the second polarizing beam splitter (26). The output end of the second fiber coupler (213) is connected to the electronic signal processing unit (5) through the photoelectric conversion unit (4). The input ends of the first fiber collimator (21) and the second fiber collimator (22) are respectively connected to the other ends of the two first fiber couplers (15) through optical fibers. The measurement interference beam (72) is emitted from the side of the second polarizing beam splitter (26) away from the reflection end.

4. A three-degree-of-freedom heterodyne interferometry measuring device with angle information restoration according to claim 3, characterized in that: The first polarizing beam splitter (25) has a first polarizer (23) at its incident end, a third quarter-wave plate (211) on the side of the first polarizing beam splitter (25) facing the second fiber coupler (213), a third polarizer (29) between the third quarter-wave plate (211) and the first polarizing beam splitter (25), a second polarizer (24) at its incident end, a fourth quarter-wave plate (212) on the side of the second polarizing beam splitter (26) from which the measurement interference beam (72) is emitted, and a fourth polarizer (210) between the fourth quarter-wave plate (212) and the second polarizing beam splitter (26).

5. A three-degree-of-freedom heterodyne interferometry measuring device with angular information restoration according to claim 4, characterized in that: The wavefront-controlled target mirror (3) includes a lens assembly (31) and a second reflector (32), with the lens assembly (31) being closer to the second polarizing beam splitter (26) than the second reflector (32).

6. A three-degree-of-freedom heterodyne interferometry method with angular information recovery, implemented based on the three-degree-of-freedom heterodyne interferometry device with angular information recovery as described in claim 5, characterized in that, Includes the following steps: Step 1: Based on the displacement measurement range of the object under test in the predetermined axis, the allowable pitch angle range, the allowable yaw angle range, the diameter of the second measurement beam (71), the large angle interference holding condition of the wavefront control target mirror (3), the focal length of the angle information restoration lens (61), the focal plane position of the angle information restoration lens (61), and the positions of the first sampling point (67), the second sampling point (68), the third sampling point (69), and the fourth sampling point (610), determine the installation position relationship between the wavefront control target mirror (3) and the angle information restoration optical path (6), so that after the returning second measurement beam (71) is restored by the angle information restoration lens (61), a light spot with phase distribution difference is formed at different positions of the focal plane of the angle information restoration lens (61) that can be used for three-degree-of-freedom calculation; Step 2: Install the wavefront control target mirror (3) on the object under test, so that the wavefront control target mirror (3) moves synchronously with the object under test as it moves along the measurement direction, and deflects synchronously with the object under test when the object under test pitches or yaws. Step 3: The input beam is collimated and polarized by the first fiber collimator (21) and the first polarization beam splitter (25) in sequence to form a first measurement beam and a first reference beam. The first reference beam is emitted from the reflecting end of the first polarization beam splitter (25), first passes through a half-wave plate (215) to obtain a polarization state transformation, and then passes through the second polarization beam splitter (26) to be emitted into the angle information restoration optical path (6). The first measurement beam is emitted from the transmitting end of the first polarization beam splitter (25), first passes through a first quarter-wave plate (27) to obtain a polarization state transformation, then passes through the first reflecting mirror (214) and is reflected back to the first polarization beam splitter (25), and finally passes through the cemented surface of the first polarization beam splitter (25) and is emitted into the second fiber coupler (213). The other input beam is collimated, polarization-state converted, and polarization-splitting by the second fiber collimator (22) and the second polarization beam splitter (26) in sequence to form a second measurement beam (71) and a second reference beam. The second reference beam is emitted from the reflecting end of the second polarization beam splitter (26), first undergoes polarization state conversion by a half-wave plate (215), and then is emitted to the second fiber coupler (213) by the first polarization beam splitter (25). The second measurement beam (71) is emitted from the transmitting end of the second polarization beam splitter (26), first undergoes polarization state conversion by a second quarter-wave plate (28), and then is emitted to the second reflector (32) through the lens assembly (31). The second measurement beam (71) is reflected back to the cemented surface of the second polarization beam splitter (26) by the second reflector (32) and reflected to the angle information restoration optical path (6). When the object under test undergoes pitch or yaw motion, the combination structure of the lens assembly (31) and the second reflector (32) regulates the propagation state of the returning second measurement beam (71), so that the returning second measurement beam (71) and the first reference light can still maintain effective interference. Step 4: The returning second measurement beam (71) and the first reference beam at least partially overlap in the output optical path of the heterodyne interferometer group (2) to form a measurement interference beam (72). The measurement interference beam (72) passes through the angle information restoration lens (61) to form an angle information restoration beam (73), and is mapped at the focal plane of the angle information restoration lens (61) as a light spot with detectable phase distribution. The phase distribution of the light spot corresponds to the angle change of the wavefront-controlled target mirror (3). The first sampling point (67), the second sampling point (68), the third sampling point (69) and the fourth sampling point (610) sparsely sample the light spot and form a measurement interference light signal sent to the photoelectric conversion unit (4). Step 5: The photoelectric conversion unit (4) converts the four measurement interference optical signals output from the first fiber channel (63), the second fiber channel (64), the third fiber channel (65) and the fourth fiber channel (66) into the corresponding four measurement interference electrical signals. The electronic signal processing unit (5) performs heterodyne phase demodulation on the four measurement interference electrical signals and the reference interference electrical signal to obtain the phase change at the first sampling point (67), the second sampling point (68), the third sampling point (69) and the fourth sampling point (610). Based on each phase change, the three degrees of freedom are jointly calculated to obtain the displacement degree of freedom Z of the measured object along the measurement direction, as well as the pitch angle α and the yaw angle β. Let the phase change at the first sampling point (67) be S1, the phase change at the second sampling point (68) be S2, the phase change at the third sampling point (69) be S3, and the phase change at the fourth sampling point (610) be S4. Let the displacement of the measured object along the measurement direction be Z, the pitch angle be α, and the yaw angle be β. Then α, β, and Z satisfy the simultaneous equations (1) and (3): ；(1) ；(2) ；(3) In the formula, K1 is the proportionality coefficient of displacement along the measurement direction, K2 is the proportionality coefficient of pitch angle and K3 is the proportionality coefficient of yaw angle, and their values ​​are determined by the system structural parameters and calibration results.

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