A heterodyne phase interference two-path measurement device and method

Abstract

The application discloses a kind of double-path measurement device and method of heterodyne phase interference, solve the problem that existing laser interferometer is influenced by environmental vibration, device noise etc. during operation and leads to the problem of decline of measurement accuracy.The application makes the measurement light path form two-way synchronous light path, respectively with different frequency light carries displacement measurement information, realizes the measurement purpose of four times optical subdivision by phase coupling, reduces the influence of real-time measurement error in measurement system on measurement result.The application compared with existing displacement measurement device, in the original level, add a measurement light path, the path difference and angle difference of mirror and interferometer assembly are compensated by mutual contrast, four times optical subdivision is realized under two-way movement, compared with other four times optical structure, not only principle is simple, only single detection is needed to obtain measurement light signal, but also assembly is simple, reflection light and measurement light are separated and adjusted, point-to-point alignment can be directly carried out, and accurate displacement measurement is realized.

Description

Technical Field

[0001] This invention relates to laser interferometric measurement devices and methods, specifically to a dual-channel measurement device and method for heterodyne phase interferometry. Background Technology

[0002] Michelson laser interferometry is one of the main methods for micro-displacement measurement using laser interferometers. It utilizes the mutual interference of reference and measurement signals to achieve high-precision displacement measurement by detecting changes in the phase shift of the interference signal. The resulting micro-displacement sensor can be applied to positioning and precision machining of high-end CNC machine tools, as well as to precision control and accurate focusing of the workpiece stage and mask stage of lithography machines. The resulting laser mirror assembly can be applied to multi-dimensional equipment measurement and spatial calibration detection.

[0003] Several researchers both domestically and internationally have also studied phase-coupled measurement methods. In 2012, scholars such as Weichert at the German Federal Institute of Physics and Technology developed a heterodyne phase interferometer that uses a planar plate and spatially separated input beams to achieve dual-path interferometry. By using the same-path characteristic to compensate for the path and angle differences between the mirror and the interferometer components, and employing an XRI interferometer to characterize nonlinearity, a nonlinearity error better than ±10 pm@288 nm was obtained, with a phase period change of 133 nm and an amplitude change of 4.8 pm. Subsequently, in 2018, a full-fiber coupling... The combined heterodyne interferometer is equipped with three different wedge-shaped prisms to separate multiple error sources, achieving a linearity interferometer uncertainty contribution better than 2.6nm within a 220mm range. In 2016, a research team from Tsinghua University proposed a spatial separation interferometer to realize a sub-nm dual-frequency green light interferometer across scales. It uses dual AOMs to modulate the phase noise by a 2MHz phase difference in the modulation signals and an all-fiber incident method. By changing the polarization state of the incident light, it ensures that the two beams are transmitted with the same horizontal polarization to achieve four times optical subdivision. Using a high-precision phase counter, it achieves a measurement uncertainty of 0.3nm within 100mm.

[0004] However, existing laser interferometers are often affected by environmental vibration, device noise, and component installation during operation, which leads to a decrease in measurement accuracy. Therefore, adopting a dual-channel phase-coupled heterodyne displacement measurement method is an effective solution. Summary of the Invention

[0005] The purpose of this invention is to provide a dual-channel measurement device and method for heterodyne phase interferometry, in order to solve the technical problem that the measurement accuracy of existing laser interferometers is often reduced due to environmental vibration, device noise, component installation and other factors during operation.

[0006] The inventive concept of this invention:

[0007] This invention enables the measurement optical path to form two synchronous optical paths, each carrying displacement measurement information with light of different frequencies. Through phase coupling, it achieves the measurement objective of four times optical subdivision, reducing the impact of real-time measurement errors in the measurement system on the measurement results.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A dual-channel measurement device for heterodyne phase interferometry, characterized in that it includes a rectangular polarizing beam splitter with its first side facing the third side and its second side facing the fourth side.

[0010] The first side has a first beam splitter and a first right-angle prism along the side length of the polarizing beam splitter; a second quarter-wave plate is also provided in the optical path between the first right-angle prism and the polarizing beam splitter; a dual-frequency laser for emitting two orthogonally linearly polarized laser beams with different frequencies is provided on the side of the first beam splitter away from the polarizing beam splitter; the first beam splitter is used to split the incident light into two parallel beams that are incident on the polarizing beam splitter; the polarizing beam splitter is used to split the two parallel beams into two beams with different frequencies respectively;

[0011] The second side is provided with a second beam splitter, and the side of the second beam splitter away from the polarizing beam splitter is provided with a first fiber coupler and a second fiber coupler; the second beam splitter is used to reflect light twice or transmit it once, and finally let the light enter the first fiber coupler or the second fiber coupler.

[0012] The third side is provided with a first quarter-wave plate; the side of the first quarter-wave plate away from the polarizing beam splitter is used to set the mirror to be tested;

[0013] The fourth side is provided with a second right-angle prism, the bottom edge of which is set close to the polarizing beam splitter prism;

[0014] The first fiber coupler and the second fiber coupler are respectively used to receive two beams of light with different frequencies emitted from the second beam splitter and form interference respectively, thereby obtaining the displacement measurement signal of the mirror under test.

[0015] Furthermore, it also includes a reference mirror;

[0016] The reference mirror is positioned on the side of the first quarter-wave plate away from the polarizing beam splitter, and the side of the reference mirror away from the first quarter-wave plate is used to set the mirror under test. The dimension of the reference mirror along the side length of the polarizing beam splitter is smaller than the dimension of the first quarter-wave plate along the side length of the polarizing beam splitter, so that the incident light transmitted through the polarizing beam splitter and the light rays near the second side can directly reach the mirror under test after passing through the first quarter-wave plate, and the light rays reflected by the first right-angle prism and the light rays near the fourth side can directly reach the mirror under test after passing through the first quarter-wave plate.

[0017] Furthermore, the fast and slow axes of the first and second quarter-wave plates are aligned at 45°.

[0018] Furthermore, the polarization beam splitter has a polarization ratio of 1:1000, an optical axis parallelism of 10″, and a horizontal plane parallelism of 0.01 mm.

[0019] A dual-channel measurement method for heterodyne phase interferometry, employing the aforementioned dual-channel measurement device for heterodyne phase interferometry, is characterized by comprising the following steps:

[0020] Step 1: Turn on the dual-frequency laser. The dual-frequency laser emits two orthogonally linearly polarized laser beams with a frequency difference of 1MHz to 2MHz to measure the Doppler frequency shift signal of the mirror under test. The first fiber coupler and the second fiber coupler respectively acquire a displacement measurement signal.

[0021] Step 2: Normalize and fit the displacement measurement signals acquired by the first fiber coupler and the second fiber coupler respectively to obtain a displacement measurement error. Compare the two measurement errors and perform subtraction to obtain the real-time linear displacement measurement error.

[0022] Step 3: Correct the laser wavelength output by the dual-frequency laser using the real-time linear displacement measurement error as a correction file. The dual-frequency laser re-emits the corrected laser, and the first fiber coupler and the second fiber coupler respectively obtain a new displacement measurement signal.

[0023] Step 4: Subtract the two new displacement measurement signals to obtain the linear displacement measurement information of the mirror under test.

[0024] Furthermore, step 1 specifically includes:

[0025] Turn on the dual-frequency laser, which emits two orthogonally linearly polarized laser beams with a frequency difference of 1MHz to 2MHz to the first beam splitter for energy splitting;

[0026] The transmitted light from the first beam splitter is incident on the polarization beam splitter for frequency splitting. The transmitted light with frequency f1 is transmitted through the first quarter-wave plate, incident perpendicularly to the mirror under test, reflected, and returns along the same path. It is then transmitted through the first quarter-wave plate again, its polarization state changed, and reflected again by the polarization beam splitter. It undergoes two reflections by the second right-angle prism, and again by the polarization beam splitter. The light is then transmitted through the first quarter-wave plate, incident perpendicularly to the mirror under test, reflected, and returns along the same path. It is then transmitted through the first quarter-wave plate again, its polarization state changed, and transmitted again by the polarization beam splitter. Finally, it is transmitted through the second quarter-wave plate and reflected twice by the first right-angle prism, its polarization state changed again, and it is then split by the polarization beam splitter. The light is reflected twice by the second beam-splitting prism and then incident on the second fiber coupler. The second fiber coupler obtains a Doppler frequency shift signal f1-2Δf with frequency f1. The reflected light with frequency f2 is transmitted through the second beam-splitting prism and incident on the second fiber coupler, which obtains a frequency shift signal f2 with frequency f2. The Doppler frequency shift signal f1-2Δf and the frequency shift signal f2 obtained by the second fiber coupler interfere with each other, and the second fiber coupler obtains a corresponding displacement measurement signal. Δf is the Doppler frequency shift signal carried by the laser beam representing the movement of the mirror under test.

[0027] The reflected light from the first beam splitter is reflected by the first beam splitter and then incident on the polarizing beam splitter for frequency splitting. The transmitted light with frequency f1 is transmitted through the first quarter-wave plate, incident perpendicularly to the mirror under test, reflected, and returns along the same path. It is then transmitted through the first quarter-wave plate again, its polarization state changed, and reflected again by the polarizing beam splitter. It is then reflected twice by the second right-angle prism, reflected again by the polarizing beam splitter, transmitted through the first quarter-wave plate, incident perpendicularly to the mirror under test, reflected, and returns along the same path. It is then transmitted through the first quarter-wave plate again, its polarization state changed, and transmitted again by the polarizing beam splitter. Finally, it is transmitted through the second quarter-wave plate and the first right-angle prism... The light is reflected twice by a mirror, changing its polarization state. It is then reflected by a polarizing beam splitter and reflected twice by a second beam splitter before entering the first fiber coupler. The first fiber coupler obtains a Doppler frequency shift signal f1-2Δf with frequency f1. The reflected light with frequency f2 is transmitted through the second beam splitter and enters the first fiber coupler, which obtains a frequency shift signal f2 with frequency f2. The Doppler frequency shift signal f1-2Δf and the frequency shift signal f2 obtained by the first fiber coupler interfere with each other, and the first fiber coupler obtains a corresponding displacement measurement signal.

[0028] Furthermore, step 1 specifically includes:

[0029] Turn on the dual-frequency laser, which emits two orthogonally linearly polarized laser beams with a frequency difference of 1MHz to 2MHz. The first beam splitter then splits the energy.

[0030] The transmitted light from the first beam splitter is incident on the polarization beam splitter for frequency splitting. The transmitted light with frequency f1 is transmitted through the first quarter-wave plate, incident perpendicularly to the mirror under test, reflected, and returns along the same path. It is then transmitted through the first quarter-wave plate again, its polarization state changed, reflected by the polarization beam splitter, and reflected twice by the second beam splitter before being incident on the first fiber coupler. The first fiber coupler obtains a Doppler frequency shift signal f1-Δf with frequency f1. The reflected light with frequency f2 is reflected twice by the second right-angle prism and then by the polarization beam splitter, transmitted through the second quarter-wave plate, and then reflected twice by the first right-angle prism. The signal is reflected twice, transmitted through the second quarter-wave plate, changing its polarization state, transmitted through the polarization beam splitter, transmitted through the first quarter-wave plate, incident perpendicularly to the reference mirror, reflected, returned along the same path, transmitted through the first quarter-wave plate, changing its polarization state, reflected through the polarization beam splitter, transmitted through the second beam splitter, and incident on the first fiber coupler. The first fiber coupler obtains a frequency shift signal f2 with a frequency of f2. The Doppler frequency shift signal f1-Δf with a frequency of f1 and the frequency shift signal f2 with a frequency of f2 obtained by the first fiber coupler interfere with each other, and the first fiber coupler obtains the corresponding displacement measurement signal.

[0031] The reflected light from the first beam splitter is incident on the polarizing beam splitter for frequency splitting. The transmitted light with frequency f1 is transmitted through the first quarter-wave plate, incident perpendicularly to the reference mirror, reflected, and returns along the same path. It is then transmitted through the first quarter-wave plate again, its polarization state changed, and reflected by the polarizing beam splitter. The second beam splitter reflects it twice, and it is incident on the second fiber coupler, where the second fiber coupler obtains a frequency-shifted signal f1. The reflected light with frequency f2 is reflected twice by the second right-angle prism and the polarizing beam splitter, transmitted through the second quarter-wave plate, and reflected twice by the first right-angle prism, before being incident on the second fiber coupler. A quarter-wave plate transmits light, changing its polarization state. The light then passes through a polarizing beam splitter, and through the first quarter-wave plate, it is perpendicularly incident on the mirror under test and reflected back along the same path. It is then transmitted through the first quarter-wave plate, changing its polarization state again, and through the second beam splitter. The light then passes through the second fiber coupler, which obtains a Doppler frequency shift signal f2-Δf with frequency f2. The frequency shift signal f1 obtained by the second fiber coupler interferes with the Doppler frequency shift signal f2-Δf with frequency f2, and the second fiber coupler obtains the corresponding displacement measurement signal.

[0032] The beneficial effects of this invention are:

[0033] Compared to existing displacement measurement devices, this invention adds an additional measurement optical path at the original level. The two paths are compared to compensate for path and angular differences in the reflector and interferometer components, achieving four times optical subdivision in two round trips. Compared to other four-fold optical structures, this invention is not only simple in principle, requiring only a single detection to obtain the measurement optical signal, but also easy to assemble and adjust. The reflected and measurement beams are adjusted separately, allowing for direct point-to-point alignment and precise displacement measurement. Therefore, the heterodyne phase interferometry dual-path measurement device proposed in this invention reduces environmental errors and component assembly errors while also providing a comparison for the measurement system. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of a dual-channel measurement device for heterodyne phase interferometry according to a first embodiment of the present invention;

[0035] Figure 2 This is a flowchart of an embodiment of a dual-path measurement method for heterodyne phase interferometry according to the present invention;

[0036] Figure 3 This is a schematic diagram of the structure of a dual-channel measurement device for heterodyne phase interferometry according to a second embodiment of the present invention.

[0037] Icon labels:

[0038] 1-Dual-frequency laser, 201-First beam splitter, 202-Second beam splitter, 3-Polarizing beam splitter, 401-First quarter-wave plate, 402-Second quarter-wave plate, 501-First right-angle prism, 502-Second right-angle prism, 6-Reference mirror, 7-Mirror under test, 801-First fiber coupler, 802-Second fiber coupler. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0040] Example 1:

[0041] Embodiment 1 of the present invention provides a dual-channel measurement device for heterodyne phase interferometry, such as... Figure 1 As shown, it includes a rectangular polarizing beam splitter 3, with its first side facing the third side and its second side facing the fourth side;

[0042] A first beam splitter 201 and a first right-angle prism 501 are provided on the first side of the polarizing beam splitter 3 along the side length direction of the polarizing beam splitter 3; a second quarter-wave plate 402 is also provided in the optical path between the first right-angle prism 501 and the polarizing beam splitter 3; a dual-frequency laser 1 for emitting incident light is provided on the side of the first beam splitter 201 away from the polarizing beam splitter 3; the first beam splitter 201 is used to split the incident light into two parallel beams that are incident on the polarizing beam splitter 3; the fast axis and slow axis of the second quarter-wave plate 402 are aligned at 45°.

[0043] A second beam splitter 202 is provided on the second side of the polarizing beam splitter 3. A first fiber optic coupler 801 and a second fiber optic coupler 802 are provided on the side of the second beam splitter 202 away from the polarizing beam splitter 3. The second beam splitter 202 is used to reflect light twice or transmit it once, and finally let the light enter the first fiber optic coupler 801 or the second fiber optic coupler 802.

[0044] A first quarter-wave plate 401 and a reference mirror 6 are sequentially arranged on the third side of the polarizing beam splitter 3 along the direction away from the polarizing beam splitter 3; the fast axis and slow axis of the first quarter-wave plate 401 are aligned at 45°. The side of the reference mirror 6 away from the first quarter-wave plate 401 is used to set the mirror under test 7; the dimension of the reference mirror 6 along the side length of the polarizing beam splitter 3 is smaller than the dimension of the first quarter-wave plate 401 along the side length of the polarizing beam splitter 3, so that the incident light transmitted through the polarizing beam splitter 3 and the light near the second side can directly reach the mirror under test 7 after passing through the first quarter-wave plate 401, and the light reflected by the first right-angle prism 501 and the light near the fourth side can directly reach the mirror under test 7 after passing through the first quarter-wave plate 401.

[0045] A second right-angle prism 502 is provided on the fourth side of the polarizing beam splitter 3, with its bottom edge positioned close to the polarizing beam splitter 3.

[0046] The following section uses the displacement of the test mirror 7 away from the reference mirror 6 as an example, and defines the direction in which the test mirror 7 moves away from the reference mirror 6 as the positive direction. The measurement method of the aforementioned dual-channel measuring device will be explained in detail below. Figure 2 As shown, the method includes the following steps:

[0047] Step 1: Turn on the dual-frequency laser 1. The dual-frequency laser 1 emits two orthogonally linearly polarized lasers with a frequency difference of 1MHz to 2MHz. The first beam splitter prism 201 performs energy splitting.

[0048] The transmitted light from the first beam splitter 201 is incident on the polarization beam splitter 3 for frequency splitting. The transmitted light with frequency f1 is transmitted through the first quarter-wave plate 401, incident perpendicularly to the test mirror 7, reflected, and returns along the same path. It is then transmitted through the first quarter-wave plate 401 again, its polarization state changed, and reflected by the polarization beam splitter 3. After two reflections by the second beam splitter 202, it is incident on the first fiber coupler 801. The first fiber coupler 801 obtains a Doppler frequency shift signal f1-Δf with frequency f1, where Δf is the Doppler frequency shift signal carried by the laser beam representing the movement of the test mirror 7. The reflected light with frequency f2 is reflected twice by the second right-angle prism 502 and by the polarization beam splitter 3, transmitted through the second quarter-wave plate 402, and then... The signal is reflected twice by the first right-angle prism 501, transmitted through the second quarter-wave plate 402, changing its polarization state. It is then transmitted through the polarizing beam splitter 3, transmitted through the first quarter-wave plate 401, and incident perpendicularly to the reference mirror 6 for reflection. It returns along the same path, is transmitted through the first quarter-wave plate 401, changes its polarization state, is reflected by the polarizing beam splitter 3, transmitted through the second beam splitter 202, and incident on the first fiber coupler 801. The first fiber coupler 801 obtains a frequency shift signal f2 with a frequency of f2. The Doppler frequency shift signal f1-Δf with a frequency of f1 obtained by the first fiber coupler 801 and the frequency shift signal f2 with a frequency of f2 interfere with each other, and the first fiber coupler 801 obtains a positive displacement measurement signal f1-f2-Δf.

[0049] The reflected light from the first beam splitter 201 is incident on the polarizing beam splitter 3 for frequency splitting. The transmitted light with frequency f1 is transmitted through the first quarter-wave plate 401, incident perpendicularly to the reference mirror 6, reflected, and returns along the same path. It is then transmitted through the first quarter-wave plate 401 again, its polarization state changed, and reflected by the polarizing beam splitter 3. After two reflections by the second beam splitter 202, it is incident on the second fiber coupler 802, where the second fiber coupler 802 obtains a frequency-shifted signal f1 with frequency f1. The reflected light with frequency f2 is reflected twice by the second right-angle prism 502 and the polarizing beam splitter 3, transmitted through the second quarter-wave plate 402, and reflected twice by the first right-angle prism 501. It is then incident on the second fiber coupler 6. The signal is transmitted through a 1 / 4-wave plate 402, changing its polarization state. It is then transmitted through a polarizing beam splitter 3, through a first quarter-wave plate 401, and perpendicularly incident on the test mirror 6. The signal is reflected back along the same path, transmitted through the first quarter-wave plate 401, changing its polarization state, and reflected by the polarizing beam splitter 3. It is then transmitted through a second beam splitter 202 and incident on a second fiber coupler 802. The second fiber coupler 802 obtains a Doppler frequency shift signal f2-Δf with frequency f2. The frequency shift signal f1 obtained by the second fiber coupler 802 with frequency f1 interferes with the Doppler frequency shift signal f2-Δf with frequency f2, resulting in a reverse displacement measurement signal: f1-f2+Δf.

[0050] Step 2: Normalize the forward displacement measurement signal acquired by the first fiber coupler 801 and the reverse displacement measurement signal acquired by the second fiber coupler 802, and perform data fitting to obtain the forward displacement measurement error (+Δf displacement error) and the reverse displacement measurement error (-Δf displacement error). Compare the two measurement errors and perform subtraction: f1-f2+Δf-(f1-f2-Δf) to obtain the real-time linear displacement measurement error with a 2Δf frequency shift.

[0051] Step 3: Using the real-time linear displacement measurement error obtained in Step 2 as a correction file, the laser wavelength output by the dual-frequency laser 1 is corrected. The dual-frequency laser 1 re-emits the corrected laser, and the first fiber coupler 801 and the second fiber coupler 802 respectively acquire a new displacement measurement signal. In this step, the correction is mainly performed by the host computer, thereby controlling the dual-frequency laser 1 to output the corrected laser beam.

[0052] Step 4: Subtract the two new displacement measurement signals to obtain the linear displacement measurement information of the mirror under test 7, and complete the displacement measurement of the mirror under test 7.

[0053] Example 2:

[0054] like Figure 3 As shown, this embodiment is basically the same as Embodiment 1, except that the dual-channel measurement device for heterodyne phase interferometry provided in Embodiment 2 does not include the reference mirror 6. The measurement steps are as follows:

[0055] Step 1: Turn on the dual-frequency laser 1. The dual-frequency laser 1 emits two orthogonally linearly polarized lasers with a frequency difference of 1MHz to 2MHz. The first beam splitter prism 201 performs energy splitting.

[0056] The transmitted light from the first beam splitter 201 is incident on the polarizing beam splitter 3 for frequency splitting. The transmitted light with frequency f1 is transmitted through the first quarter-wave plate 401, incident perpendicularly to the test mirror 7, reflected, and returns along the same path. It is then transmitted through the first quarter-wave plate 401 again, its polarization state changed, and reflected twice by the second right-angle prism 502. The light is then reflected again by the polarizing beam splitter 3, transmitted through the first quarter-wave plate 401, incident perpendicularly to the test mirror 7, reflected, and returns along the same path. It is then transmitted through the first quarter-wave plate 401 again, its polarization state changed, and transmitted again by the polarizing beam splitter 3. Finally, it is transmitted through the second quarter-wave plate 402 and reflected twice by the first right-angle prism 501. The reflected light changes its polarization state and is reflected twice by the second beam splitter 202 before entering the second fiber coupler 802. The second fiber coupler 802 obtains a Doppler frequency shift signal f1-2Δf with frequency f1. The reflected light with frequency f2 is transmitted through the second beam splitter 202 and enters the second fiber coupler 802, whereby the second fiber coupler 802 obtains a Doppler frequency shift signal f2 with frequency f2. The Doppler frequency shift signal f1-2Δf obtained by the second fiber coupler 802 with frequency f1 interferes with the frequency shift signal f2, and the second fiber coupler 802 obtains the corresponding displacement measurement signal f1-f2-2Δf.

[0057] The reflected light from the first beam splitter 201 is reflected by the first beam splitter 201 and incident on the polarizing beam splitter 3 for frequency splitting. The transmitted light with frequency f1 is transmitted through the first quarter-wave plate 401, incident perpendicularly to the test mirror 7, reflected, and returns along the same path. It is then transmitted through the first quarter-wave plate 401 again, its polarization state changed, and reflected again by the polarizing beam splitter 3. It is then reflected twice by the second right-angle prism 502, reflected again by the polarizing beam splitter 3, transmitted through the first quarter-wave plate 401, incident perpendicularly to the test mirror 7, reflected, and returned along the same path. It is then transmitted through the first quarter-wave plate 401 again, its polarization state changed, and transmitted again by the polarizing beam splitter 3. Finally, it is transmitted through the second quarter-wave plate 402 and the first right-angle prism 502. The polarization state is changed by two reflections. The light is reflected by the polarization beam splitter 3 and then reflected twice by the second beam splitter 202 before entering the first fiber coupler 801. The first fiber coupler 801 obtains a Doppler frequency shift signal f1-2Δf with frequency f1. The reflected light with frequency f2 is transmitted through the second beam splitter 202 and enters the first fiber coupler 801. The first fiber coupler 801 obtains a frequency shift signal f2 with frequency f2. The Doppler frequency shift signal f1-2Δf and the frequency shift signal f2 obtained by the first fiber coupler 801 interfere with each other, and the first fiber coupler 801 obtains a corresponding displacement measurement signal f1-f2-2Δf.

[0058] The signals acquired by the first fiber coupler 801 and the second fiber coupler 802 are completely identical, forming a control group.

[0059] Step 2: Normalize and fit the displacement measurement signals acquired by the first fiber coupler 801 and the second fiber coupler 802 respectively to obtain a displacement measurement error. Compare the two measurement errors and perform subtraction to obtain the linear displacement measurement error.

[0060] Step 3: Using the real-time linear displacement measurement error obtained in Step 2 as a correction file, the laser wavelength output by the dual-frequency laser 1 is corrected. The dual-frequency laser 1 re-emits the corrected laser, and then the first fiber coupler 801 and the second fiber coupler 802 respectively acquire a new displacement measurement signal.

[0061] Step 4: Subtract the two new displacement measurement signals to obtain the linear displacement measurement information of the mirror under test 7, and complete the displacement measurement of the mirror under test 7.

[0062] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A dual-channel measurement device for heterodyne phase interferometry, characterized in that: Including a rectangular polarizing beam splitter (3), with its first side facing the third side and its second side facing the fourth side; The first side is provided with a first beam splitter (201) and a first right-angle prism (501) along the side length of the polarizing beam splitter (3); a second quarter-wave plate (402) is also provided in the optical path between the first right-angle prism (501) and the polarizing beam splitter (3); a dual-frequency laser (1) for emitting incident light as two beams of orthogonally linearly polarized lasers with different frequencies is provided on the side of the first beam splitter (201) away from the polarizing beam splitter (3); the first beam splitter (201) is used to split the incident light into two parallel beams that are incident on the polarizing beam splitter (3); the polarizing beam splitter (3) is used to split the two parallel beams into two beams of light with different frequencies respectively; The second side is provided with a second beam splitter (202), and the side of the second beam splitter (202) away from the polarization beam splitter (3) is provided with a first fiber coupler (801) and a second fiber coupler (802); the second beam splitter (202) is used to reflect light twice or transmit it once, and finally let the light enter the first fiber coupler (801) or the second fiber coupler (802); The third side is provided with a first quarter-wave plate (401); the side of the first quarter-wave plate (401) away from the polarizing beam splitter (3) is used to set the mirror to be tested (7); The fourth side is provided with a second right-angle prism (502), the bottom edge of which is set close to the polarizing beam splitter (3); The first fiber coupler (801) and the second fiber coupler (802) are respectively used to receive two beams of light with different frequencies emitted from the second beam splitter (202) and form interference respectively, thereby obtaining the displacement measurement signal of the mirror under test (7).

2. The dual-channel measurement device for heterodyne phase interferometry according to claim 1, characterized in that: It also includes a reference mirror (6); The reference mirror (6) is positioned on the side of the first quarter-wave plate (401) away from the polarizing beam splitter (3). The side of the reference mirror (6) away from the first quarter-wave plate (401) is used to set the test mirror (7). The dimension of the reference mirror (6) along the side length of the polarizing beam splitter (3) is smaller than the dimension of the first quarter-wave plate (401) along the side length of the polarizing beam splitter (3). This allows the incident light that is transmitted through the polarizing beam splitter (3) and is close to the second side to directly reach the test mirror (7) after passing through the first quarter-wave plate (401), and allows the light that is reflected by the first right-angle prism (501) and is close to the fourth side to directly reach the test mirror (7) after passing through the first quarter-wave plate (401).

3. The dual-channel measurement device for heterodyne phase interferometry according to claim 1 or 2, characterized in that: The fast and slow axes of the first quarter-wave plate (401) and the second quarter-wave plate (402) are aligned at 45°.

4. The dual-channel measurement device for heterodyne phase interferometry according to claim 3, characterized in that: The polarization splitter prism (3) has a polarization splitting ratio of 1:1000, an optical axis parallelism of 10″, and a horizontal plane parallelism of 0.01mm.

5. A dual-channel measurement method for heterodyne phase interferometry, employing the dual-channel measurement device for heterodyne phase interferometry as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Turn on the dual-frequency laser (1). The dual-frequency laser (1) emits two orthogonally polarized lasers with a frequency difference of 1MHz to 2MHz to measure the Doppler frequency shift signal of the mirror under test (7). The first fiber coupler (801) and the second fiber coupler (802) respectively acquire a displacement measurement signal. Step 2: Normalize and fit the displacement measurement signals acquired by the first fiber coupler (801) and the second fiber coupler (802) respectively to obtain a displacement measurement error. Compare the two measurement errors and perform subtraction to obtain the real-time linear displacement measurement error. Step 3: Correct the laser wavelength output by the dual-frequency laser (1) using the real-time linear displacement measurement error as the correction file. The dual-frequency laser (1) re-emits the corrected laser, and the first fiber coupler (801) and the second fiber coupler (802) respectively obtain a new displacement measurement signal. Step 4: Subtract the two new displacement measurement signals to obtain the linear displacement measurement information of the mirror (7) under test.

6. The dual-channel measurement method for heterodyne phase interferometry according to claim 5, characterized in that, Step 1 is as follows: Turn on the dual-frequency laser (1), and the dual-frequency laser (1) emits two orthogonally linearly polarized lasers with a frequency difference of 1MHz to 2MHz to the first beam splitter (201) for energy splitting; The transmitted light from the first beam splitter (201) is incident on the polarizing beam splitter (3) for frequency splitting. The transmitted light with frequency f1 is transmitted through the first quarter-wave plate (401), incident perpendicularly to the test mirror (7), reflected, and returns along the same path. It is transmitted through the first quarter-wave plate (401) to change its polarization state, reflected by the polarizing beam splitter (3), reflected twice by the second right-angle prism (502), reflected by the polarizing beam splitter (3), transmitted through the first quarter-wave plate (401), incident perpendicularly to the test mirror (7), reflected, and returns along the same path. It is transmitted through the first quarter-wave plate (401) to change its polarization state, transmitted through the polarizing beam splitter (3), transmitted through the second quarter-wave plate (402), and reflected twice by the first right-angle prism (501), changing its polarization state. The light is reflected by the polarizing beam splitter (3), reflected twice by the second beam splitter (202), and incident on the second fiber coupler (802). The second fiber coupler (802) obtains a Doppler frequency shift signal f1-2Δf with frequency f1. The reflected light with frequency f2 is transmitted through the second beam splitter (202) and incident on the second fiber coupler (802). The second fiber coupler (802) obtains a frequency shift signal f2 with frequency f2. The Doppler frequency shift signal f1-2Δf with frequency f1 and the frequency shift signal f2 with frequency f2 obtained by the second fiber coupler (802) interfere with each other, and the second fiber coupler (802) obtains the corresponding displacement measurement signal. Δf is the Doppler frequency shift signal of the mirror under test (7) carried by the laser beam. The reflected light from the first beam splitter (201) is reflected by the first beam splitter (201) and incident on the polarizing beam splitter (3) for frequency splitting. The transmitted light with frequency f1 is transmitted through the first quarter-wave plate (401), incident perpendicularly to the test mirror (7), reflected, and returns along the same path. It is transmitted through the first quarter-wave plate (401) to change its polarization state, reflected by the polarizing beam splitter (3), reflected twice by the second right-angle prism (502), reflected by the polarizing beam splitter (3), transmitted through the first quarter-wave plate (401), incident perpendicularly to the test mirror (7), reflected, and returns along the same path. It is transmitted through the first quarter-wave plate (401) to change its polarization state, transmitted by the polarizing beam splitter (3), and transmitted through the second quarter-wave plate (402). The first right-angle prism (501) reflects twice, changing the polarization state. It is then reflected by the polarization beam splitter (3) and reflected twice by the second beam splitter (202) before entering the first fiber coupler (801). The first fiber coupler (801) obtains a Doppler frequency shift signal f1-2Δf with frequency f1. The reflected light with frequency f2 is transmitted through the second beam splitter (202) and enters the first fiber coupler (801). The first fiber coupler (801) obtains a frequency shift signal f2 with frequency f2. The Doppler frequency shift signal f1-2Δf with frequency f1 and the frequency shift signal f2 with frequency f2 obtained by the first fiber coupler (801) interfere with each other, and the first fiber coupler (801) obtains the corresponding displacement measurement signal.

7. The dual-channel measurement method for heterodyne phase interferometry according to claim 5, characterized in that, Step 1 is as follows: Turn on the dual-frequency laser (1), and the dual-frequency laser (1) emits two orthogonally linearly polarized lasers with a frequency difference of 1MHz to 2MHz. The first beam splitter (201) performs energy splitting. The transmitted light from the first beam splitter (201) is incident on the polarization beam splitter (3) for frequency splitting. The transmitted light with frequency f1 is transmitted through the first quarter-wave plate (401), incident perpendicularly on the mirror under test (7), reflected, and returns along the same path. It is transmitted through the first quarter-wave plate (401) to change its polarization state, reflected by the polarization beam splitter (3), and reflected twice by the second beam splitter (202) before being incident on the first fiber coupler (801). The first fiber coupler (801) obtains a Doppler frequency shift signal f1-Δf with frequency f1. The reflected light with frequency f2 is reflected twice by the second right-angle prism (502) and reflected by the polarization beam splitter (3), transmitted through the second quarter-wave plate (402), and then through the first right-angle prism (502). 01) After two reflections, the signal is transmitted through the second quarter-wave plate (402), changing the polarization state. It is then transmitted through the polarization beam splitter (3), and through the first quarter-wave plate (401). It is incident perpendicularly to the reference mirror (6) and reflected back along the same path. It is then transmitted through the first quarter-wave plate (401), changing the polarization state. It is then reflected through the polarization beam splitter (3), and through the second beam splitter (202). It is incident on the first fiber coupler (801). The first fiber coupler (801) obtains a frequency shift signal f2 with a frequency of f2. The Doppler frequency shift signal f1-Δf with a frequency of f1 obtained by the first fiber coupler (801) and the frequency shift signal f2 with a frequency of f2 interfere with each other. The first fiber coupler (801) obtains the corresponding displacement measurement signal. The reflected light from the first beam splitter (201) is incident on the polarization beam splitter (3) for frequency splitting. The transmitted light with frequency f1 is transmitted through the first quarter-wave plate (401), incident perpendicularly to the reference mirror (6) for reflection, returns along the same path, is transmitted through the first quarter-wave plate (401) to change its polarization state, is reflected by the polarization beam splitter (3), and is reflected twice by the second beam splitter (202) before being incident on the second fiber coupler (802). The second fiber coupler (802) obtains a frequency shift signal f1 with frequency f1. The reflected light with frequency f2 is reflected twice by the second right-angle prism (502) and reflected by the polarization beam splitter (3), transmitted through the second quarter-wave plate (402), and reflected twice by the first right-angle prism (501). The signal is transmitted through the second quarter-wave plate (402), changing its polarization state. It is then transmitted through the polarization beam splitter (3), through the first quarter-wave plate (401), and perpendicularly incident on the mirror under test (7). It is reflected back along the same path, transmitted through the first quarter-wave plate (401), changing its polarization state. It is then reflected through the polarization beam splitter (3), through the second beam splitter (202), and incident on the second fiber coupler (802). The second fiber coupler (802) obtains a Doppler frequency shift signal f2-Δf with a frequency of f2. The frequency shift signal f1 obtained by the second fiber coupler (802) with a frequency of f1 interferes with the Doppler frequency shift signal f2-Δf with a frequency of f2, and the second fiber coupler (802) obtains the corresponding displacement measurement signal.

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