A method and system for simultaneous measurement of picometer displacement and micro-radian tilt

Abstract

This invention provides a method and system for synchronously measuring picometer-level displacement and micro-radian tilt angle. The system splits the beam to form an f0 transmitted beam and an f0 reflected beam. The f0 transmitted beam is modulated and filtered to obtain a laser beam of f0+Δf. The reflected beam is reflected, modulated, and filtered to form a laser beam of f0-Δf. The f0+Δf laser beam is the first beam, which is split into an f0+Δf transmitted beam and an f0-Δf reflected beam after projection and reflection by a beam splitter. The f0-Δf laser beam is the second beam, which is split into an f0-Δf transmitted beam and an f0-Δf reflected beam after projection and reflection by a beam splitter. The f0-Δf transmitted beam is reflected, forming a first interference beam with the f0+Δf reflected beam at the beam splitter. The f0+Δf transmitted beam is reflected by a mirror that moves with the object being measured, forming a second interference beam with the f0-Δf reflected beam at the beam splitter, serving as the measurement light source. The synchronous measurement of displacement and micro-radian tilt angle is obtained by computer calculation of the two detection signals. The present invention provides a method and system for synchronous measurement of picometer-level displacement and micro-radian tilt angle, which realizes the measurement of displacement and micro-radian and improves the measurement accuracy.

Description

Technical Field

[0001] This invention belongs to the field of optical interferometry precision measurement technology, specifically relating to a method and system for synchronous measurement of picometer-level displacement and micro-radian tilt angle. Background Technology

[0002] Modern cutting-edge technologies such as ultra-precision instrument and equipment processing, ultra-large-scale integrated circuit processing, and nanometer-level measurement technology require strong support and precise calibration from ultra-precision measurement technology.

[0003] Traditional ranging methods mainly include infrared ranging, ultrasonic ranging, and laser ranging, but they suffer from low measurement accuracy and poor directionality. Traditional angle measurement methods mainly include: grating angle sensors and code disks that utilize the moiré fringe phenomenon; and capacitive angle and angular displacement sensors, inductive synchronizers, and magnetic grating sensors that operate on electromagnetic principles. Traditional angle measurement methods have some systematic errors, such as instrument fixation errors and prism constant errors.

[0004] Heterodyne laser interferometry, as an important component of ultra-precision technology, has been widely applied in various ultra-precision measurement and processing fields due to its advantages such as high measurement resolution and accuracy, non-contact measurement, strong anti-interference ability, and good traceability and reproducibility of measurement values.

[0005] Currently, the rapid development of cutting-edge technologies internationally has placed new demands on heterodyne laser interferometry, requiring measurements to improve from the nanometer to the picometer level. Improving measurement accuracy remains a significant challenge for laser heterodyne interferometry.

[0006] Chinese patent application CN115077390A, published on September 20, 2022, discloses a large-range picometer-level displacement measurement system and method based on dual-wavelength vortex light self-conjugate interferometry. It employs a Mach-Zehnder interferometer structure, resulting in a compact system with high stability and measurement accuracy. This invention can obtain interference light intensity distribution images of the sample before and after displacement at different wavelengths. Computer processing is used to calculate the full-stroke rotation angle of the interference images before and after displacement, and then the displacement Z of the sample is calculated, achieving rapid measurement of large-range picometer-level displacement. However, the measurement accuracy of this scheme is affected by the stability of the light source. The stability of the light source directly impacts the measurement results; poor light source stability may reduce measurement accuracy.

[0007] PCT international patent application WO2023284592A1, published on 2023-01-19, proposes a micro-displacement measurement system and method with picometer-level resolution. By processing the optical power and voltage signal through a static lock-in amplification module, a voltage-piezoelectric ceramic nanopositioner output displacement curve is established, enabling simple and direct detection of micro-displacements smaller than nanometers. The micro-nano measurement system using fiber Bragg gratings as sensing elements can achieve picometer-level resolution for micro-displacement detection. It obtains reliable optical power and voltage signals that follow changes in micro-displacement and establishes a voltage-piezoelectric ceramic nanopositioner output displacement curve, thus enabling the identification and detection of micro-displacements smaller than nanometers. However, in this technical solution, if the surface of the object being measured is uneven, it may affect the measurement results, as an uneven surface may lead to a large uneven distribution of the optical power and voltage signal; when the temperature reaches the Curie temperature of the piezoelectric ceramic, the piezoelectric ceramic will lose its piezoelectric properties. In addition, temperature can affect the physical properties of piezoelectric ceramics, such as elastic modulus, density, and coefficient of thermal expansion, thus affecting the measurement results of piezoelectric ceramics; and ambient humidity can affect the physical properties of piezoelectric ceramics, such as dielectric constant and conductivity, thus affecting the measurement results of piezoelectric ceramics.

[0008] Therefore, how to measure picometer-level displacement while providing a measurement method and system that can measure displacement and microradian, eliminate some systematic errors by using a common optical path, has low requirements for light source, and is highly adaptable to the environment is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0009] The first objective of this invention is to provide a method for the simultaneous measurement of picometer-level displacement and micro-radian tilt angle, addressing the problems in the prior art.

[0010] Therefore, the above-mentioned objectives of the present invention are achieved through the following technical solutions:

[0011] A method for simultaneously measuring picometer-level displacement and micro-radian tilt angle, characterized in that:

[0012] S1, the laser outputs an optical signal with a frequency of f0, which is split into a transmitted beam of f0 and a reflected beam of f0; the transmitted beam of f0 is modulated and filtered to obtain a laser with a frequency of f0+Δf, and the reflected beam is reflected, modulated and filtered to form a laser with a frequency of f0-Δf.

[0013] S2, the laser with frequency f0+Δf is the first beam of light. After the polarization state is adjusted, it is split into a transmitted beam f0+Δf and a reflected beam f0-Δf after being projected and reflected by the beam splitter.

[0014] The laser with a frequency of f0-Δf is the second beam. After the polarization state is adjusted, it is split into an f0-Δf transmitted beam and an f0-Δf reflected beam after being projected and reflected by the beam splitter.

[0015] S3, the transmitted beam of f0-Δf is reflected and forms a first interference beam with the reflected beam of f0+Δf at the beam splitter. The first interference beam is detected by the photodetector to generate a first detection signal.

[0016] S4, the f0+Δf transmitted beam is reflected by a mirror that moves with the object being measured, and forms a second interference beam with the f0-Δf reflected beam at the beam splitter, which serves as the measurement source. The second interference beam is then photodetected to generate a second detection signal.

[0017] S5, the first detection signal obtained in step S3 is the phase φ of the reference signal. r (t), the second detection signal obtained in step S4 is the phase φ of the measurement signal. m (t), the measured displacement ΔL is

[0018]

[0019] The measured angle α is

[0020]

[0021] Where b is the radius of rotation.

[0022] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions:

[0023] As a preferred technical solution of the present invention:

[0024] In step S4, the f0+Δf transmitted beam passes through the plane mirror (19) mounted on the moving platform of the object under test, generating a Doppler frequency shift f. d :

[0025] f d =2nV / λ1 Equation (1)

[0026] Where V is the velocity of the object being measured, λ1 is the wavelength of the transmitted beam f0+Δf, and n is the refractive index of the medium in the measurement environment.

[0027] The second objective of this invention is to provide a synchronous measurement system for picometer-level displacement and micro-radian tilt angle, addressing the problems in the prior art.

[0028] Therefore, the above-mentioned objectives of the present invention are achieved through the following technical solutions:

[0029] A measurement system for simultaneously measuring picometer-level displacement and micro-radian tilt angle is characterized in that: a plane mirror is mounted on the moving platform of the object to be measured.

[0030] The laser beam output from the laser is incident on the first acousto-optic modulator, where the frequency is changed. The beam then passes through the first wedge to adjust the direction of light propagation. Stray light is filtered on the first aperture to obtain a laser with a frequency of f0+Δf, which is then emitted as the first beam into the first fiber coupler.

[0031] The f0 reflected beam is incident on the first plane mirror, changes its direction, and then is incident on the second acousto-optic modulator. The frequency is changed in the second acousto-optic modulator, and the propagation direction of the light is adjusted by the second wedge. Stray light is filtered on the second aperture to obtain a laser with a frequency of f0-Δf, which is then emitted as the second beam into the second fiber coupler.

[0032] The first beam of light passes through the third fiber coupler and is incident on the first polarizer. After the polarization state is adjusted by the first polarizer, it is incident on the third beam splitter. After being projected and reflected by the third beam splitter, it is split into a transmitted beam of f0+Δf and a reflected beam of f0-Δf.

[0033] The second beam of light passes through the fourth fiber coupler and is incident on the second polarizer. After the polarization state is adjusted by the second polarizer, it is incident on the fourth beam splitter. After being projected and reflected by the fourth beam splitter, it is split into an f0-Δf transmitted beam and an f0-Δf reflected beam.

[0034] The f0-Δf transmitted beam passes through the second plane mirror and interferes with the f0+Δf reflected beam at the fifth beam splitter, serving as a reference light source. The interfering light is incident on the first four-quadrant detector, generating the first detection signal. The f0+Δf transmitted beam passes through the plane mirror installed on the moving platform of the object under test and interferes with the f0-Δf reflected beam at the sixth beam splitter, serving as a measurement light source. The interfering light is incident on the second four-quadrant detector, generating the second detection signal.

[0035] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions:

[0036] As a preferred embodiment of the present invention: the plane mirror is located on the transmitted light path of the third beam splitter and forms reflected light; the sixth beam splitter is installed on the reflected light path of the plane mirror, and the fourth beam splitter is installed on the emitted light path of the sixth beam splitter; the second plane mirror is located on the transmitted light path of the fourth beam splitter and forms reflected light; and the fifth beam splitter is located on the reflected light path of the second mirror.

[0037] As a preferred embodiment of the present invention, both the reference light formed by interference at the fifth beam splitter and the measurement light formed by interference at the sixth beam splitter are orthogonally linearly polarized lights.

[0038] As a preferred embodiment of the present invention, the optical path of the measurement optical path is equal to that of the reference optical path.

[0039] Compared with existing technologies, this invention has the following advantages: A method and system for synchronously measuring picometer-level displacement and micro-radian tilt angle, through the design of a laser heterodyne interferometry reference optical path and a laser heterodyne interferometry measurement optical path, achieves laser frequency modulation through two acousto-optic modulators in the laser modulation section. In the laser interferometry section, laser heterodyne interferometry and interference signal detection are achieved by four beam splitters, one plane mirror, one plane mirror mounted on the moving platform of the measured object, and two four-quadrant detectors. Furthermore, it utilizes a glue-free process of laser heterodyne interferometry and hydroxide catalytic bonding to simultaneously measure displacement and micro-radian tilt angle, thus improving measurement accuracy. This invention employs a common optical path scheme, eliminating some system errors, has low requirements for the light source, and is highly adaptable to various environments. This method and system for synchronously measuring picometer-level displacement and micro-radian tilt angle is suitable for high-precision measurement of displacement and micro-angles, achieving picometer-level accuracy, and has great application prospects in the field of optical interferometry precision measurement. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the structure of a system for simultaneously measuring picometer-level displacement and microradian tilt angle according to the present invention;

[0041] In the attached diagram, the components are: laser 1; first beam splitter 2; first plane mirror 3; first acousto-optic modulator 4; second acousto-optic modulator 5; first wedge 6; second wedge 7; first aperture 8; second aperture 9; first fiber coupler 10; second fiber coupler 11; laser external interference section including third fiber coupler 12; fourth fiber coupler 13; first polarizer 14; second polarizer 15; third beam splitter 16; fourth beam splitter 17; second plane mirror 18; plane mirror 19 mounted on the moving platform of the object under test; fifth beam splitter 20; sixth beam splitter 21; first quadrant detector 22; second quadrant detector 23. Detailed Implementation

[0042] The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

[0043] The present invention discloses a synchronous measurement system for picometer-level displacement and micro-radian tilt angle, comprising a laser modulation section and a laser heterodyne interferometry section. The laser modulation section includes a laser 1, a first beam splitter 2, a first plane mirror 3, a first acousto-optic modulator 4, a second acousto-optic modulator 5, a first wedge 6, a second wedge 7, a first aperture 8, a second aperture 9, a first fiber coupler 10, and a second fiber coupler 11. The laser heterodyne interferometry section includes a third fiber coupler 12, a fourth fiber coupler 13, a first polarizer 14, a second polarizer 15, a third beam splitter 16, a fourth beam splitter 17, a second plane mirror 18, a plane mirror 19 mounted on the moving platform of the object under test, a fifth beam splitter 20, a sixth beam splitter 21, a first four-quadrant detector 22, and a second four-quadrant detector 23.

[0044] Laser 1 outputs a signal with frequency f0, which is incident on the first beam splitter 2. After transmission and reflection by the first beam splitter 2, an f0 transmitted beam and an f0 reflected beam are formed. The f0 transmitted beam is incident on the first acousto-optic modulator 4, where the frequency is changed. The propagation direction of the light is adjusted by the first wedge plate 6, and stray light is filtered on the first aperture 8 to obtain a laser with frequency f0+Δf. This laser beam is then emitted as the first beam into the first fiber coupler 10.

[0045] The f0 reflected beam is incident on the first plane mirror 3, and after the direction of reflection is changed, it is incident on the second acousto-optic modulator 5. The frequency is changed in the second acousto-optic modulator 5, and the propagation direction of the light is adjusted by the second wedge plate 7. Stray light is filtered on the second aperture 9 to obtain a laser with a frequency of f0-Δf, which is then emitted as the second beam into the second fiber coupler 11.

[0046] The first beam of light passes through the third fiber coupler 12 and is incident on the first polarizer 14. After the polarization state is adjusted by the first polarizer 14, it is incident on the third beam splitter 16. After being projected and reflected by the third beam splitter 16, it is split into a transmitted beam of f0+Δf and a reflected beam of f0-Δf.

[0047] The second beam of light passes through the fourth fiber coupler 13 and is incident on the second polarizer 15. After the polarization state is adjusted by the second polarizer 15, it is incident on the fourth beam splitter 17. After being projected and reflected by the fourth beam splitter 17, it is divided into an f0-Δf transmitted beam and an f0-Δf reflected beam.

[0048] The f0-Δf transmitted beam passes through the second plane mirror 18 and interferes with the f0+Δf reflected beam at the fifth beam splitter 20, serving as a reference light source. The interference light is incident on the first four-quadrant detector 22, generating the first detection signal. The f0+Δf transmitted beam passes through the plane mirror 19 installed on the moving platform of the object under test and interferes with the f0-Δf reflected beam at the sixth beam splitter 21, serving as a measurement light source. The interference light is incident on the second four-quadrant detector 23, generating the second detection signal.

[0049] The measuring device includes a data acquisition module and a computer. The first quadrant detector 22 and the second quadrant detector 23 are both connected to the computer via the data acquisition module. The reference signal output by the first quadrant detector 22 and the measurement signal output by the second quadrant detector 23 are transmitted to the computer for processing via the data acquisition module.

[0050] The plane mirror 19 installed on the moving platform of the object under test is located directly above the third beam splitter 16; the plane mirror 19 installed on the moving platform of the object under test is shifted to the left of the sixth beam splitter 21; the sixth beam splitter 21 is located directly above the fourth beam splitter 17; the second plane mirror 18 is located to the right of the fourth beam splitter 17; and the fifth beam splitter 20 is located directly above the second mirror 18.

[0051] The reference light formed by interference at the fifth beam splitter 20 and the measurement light formed by interference at the sixth beam splitter 21 are both orthogonally linearly polarized lights.

[0052] The optical path lengths of the measuring optical path and the reference optical path are theoretically strictly equal.

[0053] Example 1

[0054] like Figure 1 As shown, the present invention provides a method for simultaneously measuring picometer-level displacement and microradian tilt angle, comprising a laser modulation section and a laser heterodyne interferometry section. The specific implementation process is as follows:

[0055] Laser 1 outputs a signal with frequency f0, which is incident on the first beam splitter 2. After transmission and reflection by the first beam splitter 3, an f0 transmitted beam and an f0 reflected beam are formed. The f0 transmitted beam is incident on the first acousto-optic modulator 4 to change its frequency, and then the propagation direction of the light is adjusted by the first wedge 6. Stray light is filtered on the first aperture 8 to obtain a laser beam with frequency f0+Δf, which is then emitted as the first beam into the first fiber coupler 10. The f0 reflected beam is incident on the first plane mirror 3 to change its direction, and then the second acousto-optic modulator 5 to change its frequency. After the second wedge 6 is used to adjust the direction of light propagation, stray light is filtered out on the first aperture 8 to obtain a laser beam with frequency f0+Δf. This laser beam is then emitted as the first beam into the first fiber coupler 10. The beam splitter 7 adjusts the direction of light propagation, filters stray light on the second aperture 9 to obtain laser light with a frequency of f0-Δf, and outputs as the second beam into the second fiber coupler 11; the first beam passes through the third fiber coupler 12, enters the first polarizer 14, and after adjusting the polarization state, enters the third beam splitter 16, splitting into an f0+Δf transmitted beam and an f0-Δf reflected beam; the second beam passes through the fourth fiber coupler 13, enters the second polarizer 15, and after adjusting the polarization state, enters the fourth beam splitter 17, splitting into an f0-Δf transmitted beam and an f0-Δf reflected beam.

[0056] The f0-Δf transmitted beam passes through the second plane mirror 18 and interferes with the f0+Δf reflected beam at the fifth beam splitter 20, serving as a reference light source. The interference light is incident on the first four-quadrant detector 22, generating the first detection signal. The f0+Δf transmitted beam passes through the plane mirror 19 installed on the moving platform of the object under test and interferes with the f0-Δf reflected beam at the sixth beam splitter 21, serving as a measurement light source. The interference light is incident on the second four-quadrant detector 23, generating the second detection signal.

[0057] In the specific implementation, the laser 1 has a frequency f0 = 150 MHz and a center wavelength λ = 1064 nm.

[0058] Specifically, this is implemented through the following examples:

[0059] Before the measurement begins, the plane mirror 19 is installed on the moving platform of the object under test, and the fiber optic couplers 12 and 13 are adjusted so that the laser spot can be incident on the center of the two quadrant detectors.

[0060] A 150MHz laser beam is output from a laser. The transmitted beam passes through a first beam splitter and is incident on a first acousto-optic modulator. It then passes through a first wedge, where the beam's propagation direction is adjusted. Afterward, it passes through a first aperture to filter stray light, resulting in a 151MHz laser beam. This beam exits as the first light and enters the first fiber coupler. The reflected beam passes through a first planar mirror and then to a second acousto-optic modulator. After the propagation direction is adjusted by a second wedge, stray light is filtered by a second aperture, resulting in a 149MHz laser beam. This beam exits as the second light and enters the second fiber coupler. The two beams then pass through third and fourth fiber couplers, and after their polarization states are adjusted by first and second polarizers, they pass through third and fourth beam splitters, resulting in a 151MHz transmitted and reflected beam and a 149MHz transmitted and reflected beam. The 149MHz transmitted beam passes through the second plane mirror and interferes with the 151MHz reflected beam at the fifth beam splitter, forming a laser heterodyne interferometry reference path before being incident on the first four-quadrant detector. The 151MHz transmitted beam, after passing through a plane mirror mounted on the moving platform of the object under test, undergoes a Doppler frequency shift. This beam then interferes with the 149MHz reflected beam at the sixth beam splitter, forming an interference laser heterodyne interferometry measurement path before being incident on the second four-quadrant detector.

[0061] The transmitted beam f0+Δf passes through the plane mirror (19) mounted on the moving platform of the object under test, producing a Doppler frequency shift f d :

[0062] f d =2nV / λ1 Equation (1)

[0063] Where V is the velocity of the object being measured, λ1 is the wavelength of the transmitted beam f0+Δf, and n is the refractive index of the medium in the measurement environment.

[0064] The first detection signal is the phase φ of the reference signal. r (t), the second detection signal is the phase φ of the measurement signal. m (t), the measured displacement ΔL is

[0065]

[0066] The measured angle α is

[0067]

[0068] Where b is the radius of rotation.

[0069] This invention employs a glue-free technique of hydroxyl catalytic bonding to fix optical components. Compared with traditional mechanical fixing methods, this avoids deformation caused by different expansion coefficients and effectively eliminates systematic errors. Furthermore, it eliminates the influence of systematic errors in the measurement of laser heterodyne interference displacement and microradius, effectively improving measurement accuracy and perfecting the measurement method for laser heterodyne interference displacement and microradius. Moreover, the optical path structure is simple, easy to use, and has significant technical benefits.

[0070] The above specific embodiments are used to explain and illustrate the present invention, and are only preferred embodiments of the present invention, not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for synchronously measuring picometer-level displacement and micro-radian tilt angle, characterized in that: S1, the laser outputs an optical signal with a frequency of f0, which is split into a transmitted beam of f0 and a reflected beam of f0; the transmitted beam of f0 is modulated and filtered to obtain a laser with a frequency of f0+Δf, and the reflected beam is reflected, modulated and filtered to form a laser with a frequency of f0-Δf. S2, the laser with frequency f0+Δf is the first beam of light. After the polarization state is adjusted, it is split into a transmitted beam f0+Δf and a reflected beam f0-Δf after being projected and reflected by the beam splitter. The laser with a frequency of f0-Δf is the second beam. After the polarization state is adjusted, it is split into an f0-Δf transmitted beam and an f0-Δf reflected beam after being projected and reflected by the beam splitter. S3, the transmitted beam of f0-Δf is reflected and forms a first interference beam with the reflected beam of f0+Δf at the beam splitter. The first interference beam is detected by the photodetector to generate a first detection signal. S4, the f0+Δf transmitted beam is reflected by a mirror that moves with the object being measured, and forms a second interference beam with the f0-Δf reflected beam at the beam splitter, which serves as the measurement source. The second interference beam is then photodetected to generate a second detection signal. S5, the first detection signal obtained in step S3 is the phase φ of the reference signal. r (t), the second detection signal obtained in step S4 is the phase φ of the measurement signal. m (t), the measured displacement ΔL is The measured angle α is Where b is the radius of rotation.

2. The method for synchronous measurement of picometer-level displacement and micro-radian tilt angle as described in claim 1, characterized in that: The In step S4, the f0+Δf transmitted beam passes through the plane mirror (19) mounted on the moving platform of the object under test, generating a Doppler frequency shift f. d : f d =2nV / λ1 Equation (1) Where V is the velocity of the object being measured, λ1 is the wavelength of the transmitted beam f0+Δf, and n is the refractive index of the medium in the measurement environment.

3. A measurement system employing the synchronous measurement method for picometer-level displacement and micro-radian tilt angle as described in claim 1 or 2, characterized in that: A plane mirror (19) is mounted on the moving platform of the object to be measured. The beam output from the laser (1) is incident on the first acousto-optic modulator (4), the frequency is changed by the first acousto-optic modulator (4), the propagation direction of the light is adjusted by the first wedge (6), the stray light is filtered on the first aperture (8) to obtain a laser with a frequency of f0+Δf, and the laser beam is emitted as the first beam into the first fiber coupler (10). The f0 reflected beam is incident on the first plane mirror (3), and after changing its direction, it is incident on the second acousto-optic modulator (5). The frequency is changed in the second acousto-optic modulator (5), and the propagation direction of the light is adjusted by the second wedge (7). Stray light is filtered on the second aperture (9) to obtain a laser with a frequency of f0-Δf, which is then emitted as the second beam into the second fiber coupler (11). The first beam of light passes through the third fiber coupler (12) and is incident on the first polarizer (14). After the polarization state is adjusted by the first polarizer (14), it is incident on the third beam splitter (16). After being projected and reflected by the third beam splitter (16), it is divided into a transmitted beam of f0+Δf and a reflected beam of f0-Δf. The second beam of light passes through the fourth fiber coupler (13), is incident on the second polarizer (15), and after the polarization state is adjusted by the second polarizer (15), it is incident on the fourth beam splitter (17). After being projected and reflected by the fourth beam splitter (17), it is divided into an f0-Δf transmitted beam and an f0-Δf reflected beam. The f0-Δf transmitted beam passes through the second plane mirror (18) and interferes with the f0+Δf reflected beam in the fifth beam splitter (20) as a reference light source. The interference light is incident on the first four-quadrant detector (22) to generate the first detection signal. The f0+Δf transmitted beam passes through the plane mirror (19) installed on the moving platform of the object under test, and interferes with the f0-Δf reflected beam in the sixth beam splitter (21) as a measurement light source. The interference light is incident on the second quadrant detector (23) to generate the second detection signal.

4. The measurement system as described in claim 3, characterized in that: It is also equipped with a data acquisition module and a computer. The first quadrant detector (22) and the second quadrant detector (23) are connected to the computer through the data acquisition module. The reference signal output by the first quadrant detector (22) and the measurement signal output by the second quadrant detector (23) are transmitted to the computer for processing through the data acquisition module.

5. The measurement system as described in claim 3, characterized in that: The plane mirror (19) is located on the transmitted light path of the third beam splitter (16) and forms reflected light; the sixth beam splitter (21) is installed on the reflected light path of the plane mirror (19), and the fourth beam splitter (17) is installed on the emitted light path of the sixth beam splitter (21); the second plane mirror (18) is located on the transmitted light path of the fourth beam splitter (17) and forms reflected light; the fifth beam splitter (20) is located on the reflected light path of the second plane mirror (18).

6. The measurement system as described in claim 3, characterized in that: The reference light formed by interference at the fifth beam splitter (20) and the measurement light formed by interference at the sixth beam splitter (21) are both orthogonally linearly polarized lights.

7. The measurement system as described in claim 3, characterized in that: The optical path of the measuring optical path is equal to that of the reference optical path.

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