A heterodyne shearing interferometry dynamic angle measurement method and device thereof

Abstract

This application discloses a method and apparatus for measuring the dynamic angle of heterodyne shearing interference, belonging to the field of optical angle measurement technology. The method includes: providing dual-frequency beams with different frequencies and orthogonal polarization states, propagating along a quasi-common optical path to the object under test; receiving the outgoing beam after deflection by the object under test, maintaining its quasi-common optical path propagation; separating the outgoing beam into two orthogonally polarized sheared beams, forming an interference optical path with transverse shear; performing heterodyne interference on the sheared beams, receiving and outputting a difference-frequency interference electrical signal by a photodetector; and finally, calculating the dynamic deflection angle of the object under test by demodulating the phase change of the difference-frequency signal. This application, through the combination of quasi-common optical path design and shearing interference, achieves a natural decoupling of displacement and rotation at the physical level, exhibiting high precision, high dynamic response, strong anti-interference capability, and good engineering practicality.

Description

Technical Field

[0001] This application relates to the field of optical angle measurement technology, and more specifically to a method and apparatus for measuring the dynamic angle of heterodyne shear interference. Background Technology

[0002] The application of laser technology is leading the development of modern precision measurement. Among them, laser angle measurement technology, due to its high precision, high resolution, and dynamic continuous measurement capabilities, has become the core means of angle measurement. This advantage stems from the comprehensive characteristics of optical measurement methods, including large range, high precision, and high measurement speed, making it a continuous research hotspot in the field of ultra-precision measurement. Angle parameters can be divided into static angles and dynamic angles according to their motion characteristics. Currently, static angle measurement technology is highly mature, and the accuracy of instruments generally reaches the sub-arcsecond level. However, in cutting-edge fields such as airborne remote sensing and laser communication, the measured target is often in a state of high-speed or continuous variable-speed rotation. Traditional static measurement methods, due to their inherent limitations of insufficient sampling frequency and dynamic response lag, can no longer meet the real-time tracking requirements.

[0003] In recent years, high-precision dynamic angle measurement technology has made continuous breakthroughs, with two representative schemes showing different technical paths. In 2024, Laxman Mandal et al. proposed an enhanced Michelson interferometer based on the side-reflecting surface of a right-angle prism (Journal of Optics, 2024, 53(2): 1545-1550.). Its core innovation lies in using the two right-angled surfaces of the prism as reflectors. Through the principle of optical path difference amplification, it theoretically achieves twice the measurement sensitivity compared to the traditional structure. Experiments have verified its superiority in sub-micro-radian measurement, but its structure is relatively sensitive to the motion interference of the measured target. To improve dynamic performance, Xu Xin's team at Tsinghua University proposed a dual-frequency laser differential dynamic angle measurement method (IEEE Transactions on Industrial Electronics, 2022, 70(6): 6405-6413.). This method, based on the principle of frequency modulation feedback interferometry, establishes a direct mapping between laser frequency difference and angular displacement through dual-optical frequency phase decoupling, achieving sub-arcsecond resolution over a large dynamic range (better than ±5°). Experimentally, it achieved a resolution of 0.02 arcseconds and long-term stability of 0.15 arcseconds. However, this scheme relies on complex subsystems such as acousto-optic modulation and frequency locking, significantly increasing the complexity of the optical path structure and assembly, posing engineering challenges in scenarios requiring millisecond-level response, such as airborne remote sensing.

[0004] Therefore, there is an urgent need for a method and device for measuring the dynamic angle of heterodyne interference based on quasi-common optical path, to solve the technical problems of poor measurement stability, difficulty in completely eliminating fundamental errors, and extremely demanding requirements on the operating environment in the existing technology. Summary of the Invention

[0005] The purpose of this application is to provide a method and apparatus for measuring dynamic angles based on quasi-common optical path heterodyne interferometry, which can solve at least one of the aforementioned technical problems. The specific solution is as follows:

[0006] According to a specific embodiment of this application, this application provides a method for measuring the dynamic angle of heterodyne shearing interference, including the following steps:

[0007] The object to be measured is measured using a heterodyne laser beam;

[0008] Acquire the emitted light beam carrying information about the angle change of the object under test;

[0009] While maintaining the quasi-common optical path propagation of the outgoing beam, the outgoing beam is sheared to separate it into sheared beams with relative shearing relationships.

[0010] The optical path difference formed by the shearing interference beam during propagation corresponds to the beam propagation direction; wherein the optical path difference does not change with the displacement of the object under test;

[0011] Heterodyne interference is performed on the sheared beam to obtain a difference frequency interference signal;

[0012] The dynamic angle of the object under test is determined based on the phase change of the difference frequency interference signal.

[0013] Furthermore, the heterodyne laser beam is a dual-frequency beam, which maintains a quasi-common optical path state during propagation until it is separated into the shear beam, so that the shear beam has the same equivalent incident point at the object under test.

[0014] Furthermore, the heterodyne laser beam consists of two beams with different frequencies and orthogonal polarization states.

[0015] Furthermore, the shearing process involves separating the light components of different polarization states in the emitted beam to form a sheared beam with parallel propagation directions.

[0016] Furthermore, by performing beat frequency demodulation on the difference frequency interference signal, the change in phase difference between the sheared beams is obtained.

[0017] Furthermore, the dynamic angle is calculated using a preset functional relationship between the interference phase difference and the beam deflection angle.

[0018] Furthermore, the preset functional relationship is determined by the optical path geometry parameters of the sheared beam.

[0019] Furthermore, the optical path geometry parameters include the angle between the sheared beams and the propagation distance of the sheared beams on the non-quasi-common optical path.

[0020] Furthermore, the expression for the dynamic angle is:

[0021]

[0022] in, The angle of deflection of the emitted light beam caused by the object under test is denoted by λ; the wavelength of the light beam is denoted by n; the refractive index of the medium is denoted by K; and the constant determined by the structure of the measuring device is denoted by K = L, where L represents the total optical path. This represents the total phase difference of the difference frequency interference signal; This indicates the initial phase of the measured light.

[0023] This application also provides a measuring device for the dynamic angle of heterodyne shear interference, comprising:

[0024] Heterodyne light sources are used to output dual-frequency beams with different frequencies and orthogonal polarization states;

[0025] The measurement module is used to guide the dual-frequency beam to the object under test and to receive the beam emitted by the object under test;

[0026] The shearing interference module includes a beam splitter and a first reflected light path and a second reflected light path derived from the beam splitter;

[0027] The beam splitter is used to separate the outgoing beam into a first polarized beam and a second polarized beam, and couple them to the first reflection path and the second reflection path, respectively; the first reflection path and the second reflection path are configured to cause the first polarized beam and the second polarized beam to form shear interference, and the optical path difference between the first polarized beam and the second polarized beam is related to the deflection angle of the outgoing beam;

[0028] The photoelectric detection module is used to receive the heterodyne interference signal formed by the shearing interference and output the difference frequency interference electrical signal.

[0029] Compared with the prior art, the above-described solutions of this application have at least the following beneficial effects:

[0030] 1. This application discloses a method and apparatus for measuring dynamic angles based on quasi-common optical path heterodyne interference. Through the synergistic design of quasi-common optical path and shearing interference, an angle measurement benchmark insensitive to lateral displacement is constructed at the physical level. The two measurement beams have the same equivalent incident point at the object under test, and the optical path difference when they form shearing interference is only related to the beam deflection angle and independent of the beam's lateral position, thus decoupling the displacement and rotational degrees of freedom. The measurement method of this application does not rely on complex real-time error compensation algorithms, avoiding cross-interference from the source and significantly improving measurement stability and reliability under non-ideal environments such as vibration and drift.

[0031] 2. The present application discloses a method and apparatus for measuring dynamic angles based on quasi-common optical path heterodyne interference. By utilizing the shearing interference principle, the angle to be measured is converted into the optical path difference between two sheared beams, thereby obtaining the interference phase difference and acquiring the dynamic angle. This not only ensures high measurement accuracy across the entire range but also greatly simplifies the signal calculation model, requiring only one multiplication operation to obtain the angle value. Thus, while maintaining sub-arcsecond measurement accuracy, a dynamic response speed of 120° / s is achieved, meeting the real-time tracking requirements of high-speed rotating targets.

[0032] 3. This application discloses a method and apparatus for measuring dynamic angles using heterodyne interferometry based on a quasi-common optical path. The apparatus employs a modular design for the heterodyne light source, measurement module, shearing interferometry module, and photoelectric detection module. The core interferometry component is based on a quasi-common optical path layout, resulting in a compact and symmetrical optical path. The stable difference-frequency signal provided by heterodyne interferometry exhibits strong resistance to light source intensity fluctuations and low-frequency noise, while the tolerance of shearing interferometry to the lateral position of the beam reduces the stringent requirements for mechanical assembly and adjustment. The measurement apparatus maintains high precision while also possessing engineering advantages such as ease of assembly and adjustment, good stability, and strong adaptability, making it more suitable for deployment and use in high-speed, high-precision environments. Attached Figure Description

[0033] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings:

[0034] Figure 1 This is a first structural schematic diagram of a measuring device for dynamic angles based on quasi-common optical path heterodyne interference, provided in an embodiment of this application.

[0035] Figure 2 This is a schematic flowchart illustrating a method for measuring dynamic angles based on heterodyne interference in a quasi-common optical path, as provided in an embodiment of this application.

[0036] Figure 3 This is a schematic diagram of the shearing interferometry principle of a method for measuring dynamic angles based on quasi-common optical path heterodyne interference, provided in an embodiment of this application.

[0037] Figure 4 This is a schematic diagram of the beam deviation angle of a method for measuring the dynamic angle of heterodyne interference based on quasi-common optical path provided in an embodiment of this application.

[0038] Figure 5This is a schematic diagram of the photodetector receiving the spot signal under different beam deviation angles, according to a method for measuring the dynamic angle of heterodyne interference based on quasi-common optical path provided in an embodiment of this application.

[0039] Figure 6 This is a schematic diagram of the cutoff phase of the photodetector receiving spot signal under different beam deviation angles, provided as an embodiment of this application, for measuring the dynamic angle of heterodyne interference based on quasi-common optical path.

[0040] Figure 7 This is a schematic diagram of the cutoff phase of the photodetector receiving spot signal under different beam deviation angles, provided as an embodiment of this application, for measuring the dynamic angle of heterodyne interference based on quasi-common optical path.

[0041] Figure 8 This is a second structural schematic diagram of a measuring device for dynamic angles based on quasi-common optical path heterodyne interference, provided in an embodiment of this application.

[0042] Figure 9 This is a third structural schematic diagram of a measuring device for dynamic angles based on heterodyne interference in a quasi-common optical path, provided in an embodiment of this application.

[0043] Explanation of reference numerals in the attached figures:

[0044] 1. Dual-frequency laser; 2. Beam splitter; 3. Test object; 4. Photodetector; 5. Polarizing beam splitter; 6. First quarter-wave plate; 7. First plane mirror; 8. Second quarter-wave plate; 9. Second plane mirror. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0046] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or device. Without further limitation, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the product or device that includes that element.

[0047] The embodiments of this application are described in detail below with reference to the accompanying drawings.

[0048] Example 1

[0049] This application provides a method for measuring the dynamic angle of heterodyne shearing interference. The dynamic angle is measured using a device based on the heterodyne shearing interference dynamic angle measurement. The measuring device in this application embodiment is as follows: Figure 1 As shown, it includes:

[0050] The heterodyne light source is used to output dual-frequency beams with different frequencies and orthogonal polarization states; the measurement module is used to guide the dual-frequency beams to the test object 3 and receive the outgoing beams from the test object 3; the shearing interference module includes a beam splitter and a first reflection path and a second reflection path derived from the beam splitter; the beam splitter is used to separate the outgoing beam into a first polarized beam and a second polarized beam, and couple them to the first reflection path and the second reflection path respectively; the first reflection path and the second reflection path are configured to cause the first polarized beam and the second polarized beam to form shearing interference, and the optical path difference between the first polarized beam and the second polarized beam is related to the deflection angle of the outgoing beam; the photoelectric detection module is used to receive the beam after shearing interference and output a difference frequency interference electrical signal.

[0051] In this embodiment, the heterodyne light source is a dual-frequency laser 1, which outputs two beams with frequencies of... , Linearly polarized light with polarization directions perpendicular to each other, in the embodiments of this application The frequency of the beam in the horizontal polarization direction. The frequency of the beam in the vertical polarization direction.

[0052] In this embodiment, the beam splitter 2 is a beam splitter prism, and the measurement module includes a beam splitter prism and a test object 3. The beam splitter prism is disposed in the outgoing optical path of the heterodyne light source and is used to transmit part of the incident dual-frequency beam to the test object 3, and reflect the beam that returns after being reflected by the test object 3 to form an outgoing beam.

[0053] In this embodiment, the beam-splitting element in the shearing interference module is a polarizing beam-splitting prism 5. The polarizing beam-splitting prism 5 separates the outgoing beam into a first polarized beam, which is the horizontal polarization frequency in this application. The beam of light; and the second polarized beam, which is the vertically polarized beam in this application with a frequency of... The light beam is coupled to the first reflection optical path and the second reflection optical path respectively.

[0054] In this embodiment, the first polarized beam in the first reflected optical path passes sequentially through the first quarter-wave plate 6, is reflected by the first plane mirror 7, and passes through the first quarter-wave plate 6 again, its polarization state changes to be orthogonal to the incident state, i.e., it becomes a vertically polarized beam. After being reflected again by the polarizing beam splitter 5, it is transmitted to the second quarter-wave plate 8, reflected by the second plane mirror 9, and passes through the second quarter-wave plate 8 again, its polarization state changes to be orthogonal to the incident state, i.e., it becomes a horizontally polarized beam. It is then transmitted through the polarizing beam splitter 5 to the photodetector 4. The second polarized beam in the second reflected optical path is reflected by the polarizing beam splitter 5 to the photodetector 4.

[0055] The first and second polarized beams in the first and second reflected optical paths form shear interference on the photodetector 4. The specific spatial arrangement of the first and second reflected optical paths is configured such that when the first and second polarized beams form shear interference, the optical path difference between them is only related to the deflection angle of the outgoing beam.

[0056] In this embodiment, the photodetector module is a photodetector 4, located in the output optical path of the shearing interference module, used to receive the beam after shearing interference. Because the first polarized beam and the second polarized beam have a fixed frequency difference, heterodyne interference occurs between them on the photosensitive surface of the photodetector 4. The photodetector 4 converts the light intensity signal into a difference-frequency interference electrical signal and outputs it. Because the first polarized beam and the second polarized beam have a frequency difference, the detector outputs a signal with a frequency of ||. The difference frequency interference electrical signal of | contains the angle information to be measured in phase, that is, the interference phase difference.

[0057] In the embodiments of this application, the method for measuring the dynamic angle of heterodyne shearing interference is as follows: Figure 2 As shown, it includes the following steps:

[0058] S1. Measure the test object 3 using a heterodyne laser beam.

[0059] Turn on dual-frequency laser 1 to generate , Two beams of light with different frequencies and orthogonal polarization states are referred to as... Light and Light. These two beams of light, emitted from the dual-frequency laser 1, first pass through a beam splitter, and the transmitted beam is incident on the test object 3 (the object under test). From the dual-frequency laser 1 to the test object 3, and then reflected by the test object 3 back to the polarizing beam splitter 5, the entire front-end optical path continues... , Two beams of light with different frequencies and orthogonal polarization states always propagate along the same spatial path. During the propagation process, until they are separated into shear beams, the two beams maintain a quasi-common optical path state, so that the shear beams have the same equivalent incident point on the surface of the test object 3. The quasi-common optical path state can jointly resist environmental interference.

[0060] The technical solution of this application embodiment limits the propagation of the light beam along a quasi-common optical path, ensuring that there is the same equivalent incident point at the object under test 3. This makes the effects of environmental disturbances such as vibration and airflow on the two beams almost identical, and greatly suppresses them in subsequent interference, thereby enhancing the robustness of the measurement method in actual industrial environments.

[0061] S2. Acquire the emitted beam carrying information on the angle change of the object under test.

[0062] After being reflected by the test object 3, the beam carrying information about the deflection angle of the test object 3 returns along its original path to the beam splitter prism and is reflected by it to form the outgoing beam. The outgoing beam remains in a common-path state and is incident on the polarizing beam splitter 5. In this embodiment, the reflection relationship shows that the deflection angle of the propagation direction of the outgoing beam is twice the deflection angle of the test object 3.

[0063] S3. Maintain the quasi-common optical path propagation of the outgoing beam, and perform shearing processing on the outgoing beam to separate it into sheared beams with relative shearing relationships.

[0064] The polarizing beam splitter 5 separates the common outgoing beams according to their polarization states. The polarizing beam splitter 5 separates the outgoing beams into a first polarized beam, which is the horizontally polarized beam described in this application. Light transmission; and the second polarized beam, which is the vertically polarized beam in this application. Light reflection separates the two beams of light into two fixed reflected light paths with different spatial paths, thus forming sheared beams with a relative shearing relationship. The two sheared beams propagate in parallel directions, meaning their propagation directions remain completely parallel and unchanged; only their degree of overlap changes with the angle. Light and The light is coupled to the first reflected light path and the second reflected light path, respectively.

[0065] The technical solution of this application, through the synergistic design of quasi-common optical path and shearing interferometry, constructs a displacement-insensitive measurement benchmark at the physical principle level. The measurement method converts the change in the measured angle into an optical path difference that is only related to the beam propagation direction, and is independent of the beam's lateral position on the photodetector 4. This fundamentally decouples the degrees of freedom of displacement and rotation, significantly improving the anti-interference capability and reliability of dynamic measurements. Shearing interferometry, as a conversion mechanism, separates a beam of light according to its polarization state and introduces a fixed lateral shearing amount, forming two parallel sheared beams with a fixed included angle. When the deflection angle of the object under test 3 changes, this change is directly converted into a change in the optical path difference between the two sheared beams in the interference overlap region, which is then reflected as a change in the interference phase difference. Therefore, the shearing interferometry mechanism maps the angular change of the object under test 3 into a phase change of the interference signal.

[0066] S4. To create an optical path difference corresponding to the beam propagation direction during the propagation of the shearing interference beam; wherein the optical path difference does not change with the lateral position of the beam.

[0067] In this embodiment, the light does not change its propagation direction when passing through the parallel glass plate. Therefore, the polarizing beam splitter 5, the first reflection light path, and the second reflection light path in the shearing interference module are treated as an equivalent air layer of corresponding thickness. At this time, the dynamic angle measurement device can be analyzed as an equivalent model of a reflection imaging system. Figure 3 As shown, let the common point of the two beams incident on the polarizing beam splitter 5 be... After passing through different reflection subsystems, that is, through the corresponding first reflection optical path and second reflection optical path, Light and Light can be considered as coming from two image points respectively. and The emitted light beam. Taking any point B along the propagation direction of the incident light beam, when the beam's deflection angle relative to the X-axis of the model coordinate system is θ, the coordinates of point B can be expressed as ( +cosθ, +sinθ). Thus, vector AB uniquely and quantitatively represents the propagation direction of the incident beam. It is the image point corresponding to point B in the first reflected light path. It is the image point corresponding to point B in the second reflected light path.

[0068] In this embodiment, the coordinates of point A are: Then the image point of point A with respect to the line Y=X Coordinates are The image points formed by the reflection of point A with respect to the lines X = a, Y = X, and Y = b in sequence. Coordinates are ( , -2a-2b), where a and b represent the equivalent optical path lengths in the X and Y directions, respectively. Coordinates are ( +sinθ, +cosθ). Coordinates are ( +sinθ, +cosθ-2a-ab). This is derived based on the shearing interference principle of the reflection imaging system. and It exhibits synchronous motion characteristics in space; regardless of how point A moves, the axial displacement of the object under test (3) causes the beam to move laterally. and The relative distance remains unchanged. and The expressions are (sinθ, cosθ) and (sinθ, cosθ), respectively. It can be seen that from... and Direction vector of emitted light rays and It has the property of being completely synchronized.

[0069] Combining the properties of synchronous motion of image points, we can conclude that: and The optical path difference ΔL between the two emitted beams depends only on the propagation direction θ of the beams, and not on the position of the image point. Irrelevant. The optical path difference is expressed as:

[0070]

[0071] Where a and b represent the equivalent optical path lengths in the X and Y directions, respectively; L represents the total optical path.

[0072] The technical solution of this application embodiment uniquely maps the change in beam direction θ caused by the deflection of the object under test 3 to an optical path difference ΔL, while ensuring that the optical path difference does not change due to the lateral movement of the beam incident point, that is, it does not change due to the axial displacement of the object under test 3, thereby achieving displacement insensitivity at the physical level.

[0073] S5. Perform heterodyne interference on the sheared beam to obtain the difference frequency interference signal.

[0074] In this embodiment of the application, from the equivalent image point and The two emitted beams of light are parallel. When the object under test 3 is not deflected (θ=0), the two beams of light are not only parallel but also coaxial, and they interfere with each other completely collinearly on the detector.

[0075] When the object under test 3 deflects, causing the beam deflection angle θ to be non-zero, from the equivalent image point and The two emitted beams remain parallel but are no longer coaxial, forming transversely sheared interference beams. Since the actual beam has a certain width D, the two beams will still form an overlapping area on the detector surface, thus producing detectable sheared interference fringes. The expression for the dynamic angle measurement range in this embodiment is:

[0076]

[0077] Where, θ max This represents the maximum value of the measured dynamic angle, where D represents the diameter of the incident beam. From the above formula, it can be seen that obtaining a large dynamic angle measurement range is related to the size of the photodetector 4 and its optical design parameters.

[0078] The expression for the complex amplitude of the orthogonally linearly polarized light output from dual-frequency laser 1 is:

[0079]

[0080] in, E This represents the complex amplitude of the orthogonally linearly polarized light output from dual-frequency laser 1; express light amplitude; express light amplitude; The complex amplitude of orthogonally linearly polarized light is represented by t; time is represented by t. express Initial phase of light; express Initial phase of light; i This represents the imaginary unit. Based on the characteristics of the optical path, vertical polarization... The light is always used as a reference light and is horizontally polarized. Light serves as the measuring light that carries angular information.

[0081] After step S4, the measurement light obtains the phase change, or phase difference, caused by the angular deflection. Therefore, the expression for the complex amplitude of the measurement light and the reference light reaching photodetector 4 is:

[0082]

[0083]

[0084]

[0085] in, Indicates the horizontal polarization reaching photodetector 4 Complex amplitude of light; Indicates the vertical polarization reaching photodetector 4 Complex amplitude of light This indicates the phase difference caused by angular deflection.

[0086] The expression for the total light intensity received by photodetector 4 is:

[0087]

[0088] in, This indicates the total light intensity received by photodetector 4; Indicates frequency difference; This represents the initial phase difference.

[0089] Therefore, the total light intensity received by photodetector 4 has an oscillation frequency that is exactly the frequency difference between the two beams, i.e., a difference-frequency interference signal. Ultimately, photodetector 4 outputs a signal with a frequency of | | The beat frequency signal contains a difference frequency interference electrical signal that embeds the phase information to be measured.

[0090] In the quasi-common-path shearing interference structure used in this application embodiment, the deflection of the test object 3 directly causes a change in the direction of the emitted beam. This change is further converted into an optical path difference between the two sheared beams. In the shearing interference optical path, such as Figure 4 As shown, when the beam deflection angle is θ, if the deflection angle is 0, , The phase difference is Because the equiphase surfaces of a laser beam are generally perpendicular to the direction of light propagation, the optical path difference can be calculated by analyzing the change in its spatial length through beam translation. When the light moves along the equiphase surfaces, it does not change the distribution of the equiphase surfaces in space. Therefore... Can be translated to ,at this time and The length difference between them is Lcosθ.

[0091] S6. Determine the dynamic angle of the object under test 3 based on the phase change of the difference frequency interference signal.

[0092] The total phase difference of the difference frequency interference signal includes the initial phase that does not change with the angle and the phase difference caused by the deflection of the object under test 3. ,Right now:

[0093]

[0094] in, This represents the total phase difference of the difference frequency interference signal.

[0095] When the dynamic angle θ of the object under test 3 is 0, .

[0096] Simplifying the above formulas, the expression for the dynamic angle θ of the test object 3 is:

[0097]

[0098] Where θ represents the deflection angle of the emitted beam caused by the test object 3; λ represents the wavelength of the beam; n represents the refractive index of the medium; K represents a constant determined by the structure of the measuring device, and in the embodiments of this application, K is a system constant including equivalent optical path parameters a, b, etc.; nK=L, where L represents the total optical path.

[0099] By continuously sampling and solving the difference frequency signal, a one-dimensional dynamic angle sequence of the test object 3 that changes continuously over time can be output.

[0100] The technical solution of this application embodiment establishes the interference phase difference. The cosine measurement relationship between the laser wavelength λ and the angle θ is established, and the proportionality coefficient of this relationship is determined solely by the defined optical path geometry and measurement structure. This simplifies the computational workload when measuring dynamic angles. The measurement accuracy is directly related to the numerical accuracy of the laser wavelength λ and the structure of the measurement system, ensuring the traceability and long-term stability of the measurement.

[0101] like Figure 5 As shown - Figure 7 As shown, Figure 5 The horizontal axis represents the angular change between the light rays, which is also half of the deflection angle of the object under test 3. The vertical axis represents the phase difference of the two frequencies of light as the angle changes. When the object under test 3 is in a certain fixed axial position, how does the coherent phase difference of the interference signal change with the deflection angle of the object under test 3? Figure 5 The curves in figures a and b correspond to the measurement results of the test object 3 along the Z-axis at Z=0mm and Z=5mm, respectively. The curves corresponding to the two different axial positions almost completely overlap. This proves that the slope, i.e., the sensitivity, of the mapping function from angle to phase in the technical solution of this application does not change with the axial displacement of the test object 3, thus achieving displacement insensitivity at the signal solution level.

[0102] Figure 6 , Figure 7 Corresponding to the measurement results of the object under test 3 along the Z-axis at Z=0mm and Z=5mm respectively, the intercept at X=0 on the XY plane of the detector. , The coherent phase changes with the angle. , The graphs are represented by green and red lines, with the horizontal axis representing the spatial sampling point on the detector and the vertical axis representing the interference phase value extracted at that sampling point. At each Z-axis, six deflections of θ = 0.2°, 0.4°, 0.6°, 0.8°, 1.0°, and 1.2° were applied to the object under test (3). The phase distribution curves for these four different Z-axis values ​​were plotted on the same coordinate system. For the same deflection angle θ, the phase distribution curves under different axial displacements Z highly overlapped; however, when θ changed, the phase distribution curves showed a systematic shift. This strongly demonstrates that the spatial distribution of the interference phase is uniquely determined only by the deflection angle of the beam (i.e., the angle of the object under test 3), and is independent of the incident position of the beam (i.e., the axial displacement of the object under test 3).

[0103] pass Figures 5-7 The results, from both the signal mapping relationship and the physical light field distribution, confirm that the heterodyne shearing interference dynamic angle measurement method and device provided in this embodiment can efficiently and stably encode the angle information of the object under test 3 into the interference phase signal, and fundamentally overcome the measurement interference caused by the axial displacement of the object under test 3, thus realizing high-precision and high-stability dynamic angle measurement.

[0104] This application proposes a method for measuring the dynamic angle of heterodyne shearing interference. The method uses a heterodyne laser beam as the measurement beam to measure the object under test (3). The emitted beam formed by the object under test (3) is sheared to form a sheared beam with a relative shearing relationship. By limiting the optical path difference formed by the sheared beam during propagation to be only related to the beam propagation direction and not changing with the lateral position of the beam, the angular information of the object under test (3) is mapped to the optical path difference between the sheared beams. Furthermore, difference-frequency interference signals are obtained through heterodyne interference.

[0105] The technical solution of this application establishes a deterministic mathematical relationship between the interference phase and the dynamic angle of the object under test by modeling the optical path geometry between the sheared beams. This allows the dynamic angle to be directly calculated from the phase of the difference frequency interference signal, thus forming a dynamic angle measurement method based on heterodyne shearing interference.

[0106] The dynamic angle measurement method based on heterodyne shearing interferometry in this embodiment reduces the influence of the transverse displacement of the test object 3 on the measurement results and improves the stability of dynamic angle measurement by using quasi-common optical path measurement and ensuring that the shearing beam has the same equivalent incident point at the test object 3. Shearing interferometry constructs an optical path difference that is only related to the beam propagation direction, allowing the angle information to be purified and expressed in the interference phase, avoiding optical path interference introduced by changes in the transverse position of the beam. Heterodyne interferometry is used to obtain the difference frequency interference signal, improving the signal-to-noise ratio and resistance to environmental disturbances in the interference phase demodulation, making it suitable for continuous dynamic angle measurement. By establishing a clear mathematical relationship between the interference phase and the dynamic angle, the measurement results have clear physical meaning and predictability, facilitating system design, calibration, and engineering implementation. This method is not dependent on the specific structural form of the test object 3 and is applicable to various measurement objects that undergo rotation or rolling motion, exhibiting good versatility and application scalability.

[0107] Example 2

[0108] This application embodiment also provides a measuring device for the dynamic angle of heterodyne shear interference, such as... Figure 8 As shown, the measuring device is a rotating structure, and the beam splitter 2 is a beam splitting prism. By omitting the quarter-wave plate, the optical path is simplified. This simplified reflection optical path scheme does not rely on the quarter-wave plate, but it can still achieve precise angle measurement. Its working principle is similar to that of Embodiment 1. The beam is separated by the polarizing beam splitter 5, and after passing through different reflection optical paths, shearing interference is formed. Finally, the phase change is detected by the photodetector 4 and the angle is calculated.

[0109] Example 3

[0110] This application embodiment also provides a measuring device for the dynamic angle of heterodyne shear interference, such as... Figure 9 As shown, in this embodiment, the beam splitter 2 is a diffraction grating, which also serves as the object under test 3. The dynamic angle, i.e., the roll angle of the grating, is measured by the diffraction of the grating. By optimizing the incident light path design and adopting a specific incident angle and quasi-common optical path design, it is ensured that the first-order diffracted light can always be effectively captured by the photodetector 4 within the expected motion range of the grating. This physically expands the effective field of view and alignment tolerance of the system, ensuring the continuity and stability of the roll angle measurement signal. Its working principle is similar to that of Embodiment 1. The beam is separated by the polarizing beam splitter 5, and after passing through different reflected light paths, shear interference is generated. Finally, the phase change is detected by the photodetector 4 and the angle is calculated.

[0111] The heterodyne shearing interferometry dynamic angle measurement device in this application features a quasi-common optical path design, which highly integrates the core interferometric optical path and relatively reduces the requirements for mechanical stability. The shearing interferometry module and measurement module can be compactly arranged, significantly reducing the difficulty and cost of system assembly and adjustment, improving the overall structural stability and reliability, and making it more suitable for deployment and application in non-ideal environments such as industrial sites. This solves the technical problems of complex optical paths, difficult assembly and adjustment, and poor environmental adaptability in existing high-precision dynamic interferometers.

[0112] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems or apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

[0113] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for measuring the dynamic angle of heterodyne shear interference, characterized in that, Includes the following steps: The object to be measured is measured using a heterodyne laser beam; Acquire the emitted light beam carrying information about the angle change of the object under test; While maintaining the quasi-common optical path propagation of the outgoing beam, the outgoing beam is sheared to separate it into sheared beams with relative shearing relationships. The optical path difference formed by the sheared beam during its propagation, corresponding to the beam propagation direction, is obtained; wherein the optical path difference does not change with the displacement of the object under test; Heterodyne interference is performed on the sheared beam to obtain a difference frequency interference signal; The dynamic angle of the object under test is determined based on the phase change of the difference frequency interference signal.

2. The measurement method according to claim 1, characterized in that, The heterodyne laser beam is a dual-frequency beam that maintains a quasi-common optical path state during propagation until it is separated into the shear beam, so that the shear beam has the same equivalent incident point at the object under test.

3. The measurement method according to claim 2, characterized in that, The heterodyne laser beam consists of two beams with different frequencies and orthogonal polarization states.

4. The measurement method according to claim 1, characterized in that, The shearing process involves separating the light components of different polarization states in the emitted beam to form a sheared beam with parallel propagation directions.

5. The measurement method according to claim 1, characterized in that, The phase change between the sheared beams is obtained by beat frequency demodulation of the difference frequency interference signal.

6. The measurement method according to claim 5, characterized in that, The dynamic angle is calculated using a preset function relationship between the interference phase difference and the beam deflection angle.

7. The measurement method according to claim 6, characterized in that, The preset functional relationship is determined by the optical path geometry parameters of the sheared beam.

8. The measurement method according to claim 7, characterized in that, The optical path geometry parameters include the angle between the sheared beams and the propagation distance of the sheared beams on the non-quasi-common optical path.

9. The measurement method according to claim 8, characterized in that, The expression for the dynamic angle is: in, The angle of deflection of the emitted light beam caused by the object under test is denoted by λ; the wavelength of the light beam is denoted by n; the refractive index of the medium is denoted by K; and the constant determined by the structure of the measuring device is denoted by K = L, where L represents the total optical path. This represents the total phase difference of the difference frequency interference signal; This indicates the initial phase of the measured light.

10. A measuring device for implementing the measurement method as described in any one of claims 1 to 9, characterized in that, include: Heterodyne light sources are used to output dual-frequency beams with different frequencies and orthogonal polarization states; The measurement module is used to guide the dual-frequency beam to the object under test and to receive the beam emitted by the object under test; The shearing interference module includes a beam splitter and a first reflected light path and a second reflected light path derived from the beam splitter; The beam splitter is used to separate the outgoing beam into a first polarized beam and a second polarized beam, and couple them to the first reflection path and the second reflection path, respectively; the first reflection path and the second reflection path are configured to cause the first polarized beam and the second polarized beam to form shear interference, and the optical path difference between the first polarized beam and the second polarized beam is related to the deflection angle of the outgoing beam; The photoelectric detection module is used to receive the heterodyne interference signal formed by the shearing interference and output the difference frequency interference electrical signal.

Images