Displacement measurement device and method based on co-resonant cavity coupled frequency modulation Fabry-Perot interferometry

Abstract

The present invention discloses a displacement measurement device and method based on co-resonant cavity coupled frequency modulation Fabry-Perot interferometry, comprising: a dual-frequency laser, an optical isolator, an optical collimator, a first polarization beam splitter prism, a first plane reflector, a second polarization beam splitter prism, a quarter wave plate, a second plane reflector, a first resonant plane reflector, a second resonant plane reflector, a corner cube prism, a third polarization beam splitter prism, a first photoelectric signal receiver, a second photoelectric signal receiver, a displacement sensor to be measured, a measuring board, a signal demodulation module, a data processing module, a micro-motion displacement stage, a first electro-optical modulator, and a second electro-optical modulator. By adopting the technical solution of the present invention, by adjusting the frequency of two lasers, the displacement can be measured with a sub-picometer resolution, and can be used as a higher-level displacement measurement standard to measure and detect other measuring instruments.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical measurement, and in particular relates to a displacement measurement device and method based on co-resonant cavity coupling frequency modulation Fabry-Perot interferometry. Background Art

[0002] Laser interferometry length measurement technology is widely used in the fields of geometric measurement, precision instrument testing, etc., but with the continuous breakthroughs in scientific research and the rapid development of cutting-edge manufacturing, nanometer-level precision laser interferometry length measurement technology is difficult to meet the current needs of micro-displacement measurement and displacement measurement device accuracy inspection. Laser interferometry length measurement technology urgently needs to develop measurement technology with higher precision.

[0003] At present, there are many high-precision displacement measurement methods, such as capacitive sensing, grating length measurement and Michelson interferometry. Among them, the capacitive sensing method uses the change in capacitance to reflect the change in displacement, and the ultimate accuracy can reach sub-nanometers or even higher; the grating length measurement method converts the mechanical displacement into the periodic change of the moiré signal, and by multiplying the grating signal, the resolution of its displacement measurement can currently reach tens of picometers; due to the existence of nonlinear errors, the Michelson laser interferometry method is difficult to achieve tens of picometers and sub-nanometer measurement accuracy. The displacement measurement device formed by the above measurement methods has very poor measurement accuracy. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a displacement measurement device and method based on co-resonant cavity coupled frequency modulation Fabry-Perot interferometry, which can complete the measurement of displacement and the inspection of the accuracy of the displacement measurement device with sub-picometer resolution. The interference peak intervals of the equal-periodic interference signals formed when multi-beam interference occurs with lasers of different wavelengths are different. According to the optical vernier effect, when the wavelengths of the two lasers are very close, the interference peak intervals of the two interference lights are extremely small, thereby obtaining sub-picometer resolution; the two frequency-adjustable lasers are respectively subjected to multi-beam interference in two parallel and common optical path Fabry-Perot cavities, and the measured displacement can be demodulated by adjusting the frequencies of the two lasers; the structure of the co-resonant cavity coupled Fabry-Perot cavity can reduce the nonlinear error while reducing the influence of environmental factors on the measurement results, effectively improving the stability of the displacement measurement device.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A displacement measuring device based on co-resonant cavity coupled frequency modulated Fabry-Perot interferometry comprises: a dual-frequency laser, an optical isolator, an optical collimator, a first polarization beam splitter prism, a first plane reflector, a second polarization beam splitter prism, a quarter wave plate, a second plane reflector, a first resonant plane reflector, a second resonant plane reflector, a corner cube prism, a third polarization beam splitter prism, a first photoelectric signal receiver, a second photoelectric signal receiver, a displacement sensor to be measured, a signal demodulation module, a data processing module, a micro-displacement stage, a measuring board, a first electro-optical modulator, and a second electro-optical modulator;

[0007] Among them, the dual-frequency laser emits two orthogonal linear polarized lights, which are divided into main transmitted light and main reflected light at the first polarization beam splitter prism after passing through an optical isolator, an optical collimator, and a first electro-optical modulator; the main transmitted light passes through a quarter wave plate for the first time after passing through the second polarization beam splitter prism, and is then reflected by the second plane reflector to the first Fabry-Perot cavity composed of a first resonant plane reflector and a corner cube prism, and multi-beam interference occurs in the first Fabry-Perot cavity; the first transmitted interference light is reflected by the second plane transmitting mirror and then passes through the quarter wave plate for the second time, and its polarization direction is rotated 90°, and is collected by the first photoelectric signal receiver; the first reflected interference light is reflected by the first resonant plane reflector and returns along the original optical path, and passes through the quarter wave plate for the second time, and its polarization direction is rotated 90°. The direction of the second polarization beam splitter is rotated by 90°, and it is reflected by the beam splitting surface of the second polarization beam splitter prism and directed to the third polarization beam splitter prism; the main reflected light passes through the first optical reflection surface and is directed to the second electro-optical modulator, and then passes through the quarter-wave plate for the first time, and is then reflected by the second plane reflector to the second Fabry-Perot cavity composed of the second resonant plane reflector and the corner cube prism with a hollow middle, and multi-beam interference occurs in the second Fabry-Perot cavity; the second transmitted interference light is reflected by the second plane transmitting mirror, and then passes through the quarter-wave plate for the second time, and its polarization direction is rotated by 90°, and is directed to the third polarization beam splitter prism; the third polarization beam splitter prism combines the first reflected interference light and the second transmitted interference light, and then outputs the coupled interference light, which is collected by the second photoelectric signal receiver.

[0008] Preferably, the first resonant plane reflector and the corner cube prism form a first Fabry-Perot cavity, and the first resonant plane reflector moves together with the micro-motion displacement stage to form a first Fabry-Perot cavity with a variable cavity length; the second resonant plane reflector with a hollow middle portion and the corner cube prism form a second Fabry-Perot cavity with a fixed cavity length; the first resonant plane reflector and the second resonant plane reflector with a hollow middle portion are arranged in parallel, and the corner cube prism is used to fold the optical path to form a common resonant cavity coupled Fabry-Perot cavity with parallel and common optical paths.

[0009] Preferably, the measuring plate is fixed on the micro-motion displacement stage and moves with the micro-motion displacement stage, and the displacement sensor to be measured measures the displacement of the measuring plate, so that the measurement satisfies the Abbe principle.

[0010] The present invention also provides a displacement measurement method based on co-resonant cavity coupled frequency modulation Fabry-Perot interferometry, comprising:

[0011] Step 1: The dual-frequency laser emits two orthogonal linearly polarized lights, and the frequencies of the two lights are f0 and f1 respectively;

[0012] Step 2, the two paths of light are separated into main transmitted light and main reflected light at the first polarization beam splitter prism after passing through an optical isolator, an optical collimator, and a first electro-optical modulator; wherein the main transmitted light passes through a quarter wave plate for the first time after passing through the second polarization beam splitter prism, and then is reflected by the second plane reflector to the first Fabry-Perot cavity composed of a first resonant plane reflector and a corner cube prism and undergoes multi-beam interference, the first transmitted interference light after interference is reflected by the second plane transmitting mirror and then passes through the quarter wave plate for the second time, and its polarization direction is thereby rotated 90° and collected by the first photoelectric signal receiver; the first reflected interference light after interference is reflected by the first resonant plane reflector and then returns along the original optical path, passes through the quarter wave plate for the second time, and its polarization direction is rotated 90° and collected by the first photoelectric signal receiver. The polarization direction of the light is rotated by 90°, and it is reflected by the beam splitting surface of the second polarization beam splitter prism and directed to the third polarization beam splitter prism; the main reflected light is reflected by the first optical reflection surface to the second electro-optic modulator, and then passes through the quarter-wave plate for the first time, and then is reflected by the second plane reflector to the second Fabry-Perot cavity composed of the second resonant plane reflector and the corner cube prism with a hollow middle, and multi-beam interference occurs in the cavity, and the second transmitted interference light after interference is reflected by the second plane reflector, passes through the quarter-wave plate for the second time, and is directed to the third polarization beam splitter prism; the third polarization beam splitter prism combines the first reflected interference light and the second transmitted interference light to obtain coupled interference light, and the second photoelectric signal receiver collects the coupled interference light;

[0013] Step 3, the second electro-optic modulator changes the frequency of the main reflected light to f1+Δf, and in this process, the interference peak position of the coupled interference light moves, so that the measurement start position is far away from the near-zero point position and the peak point position of the interference peak;

[0014] Step 4: The signal demodulation module sets a single-cycle threshold at a position far from the near-zero point and the peak point of the interference peak, and demodulates the interference peak signal of the first transmitted light interference light. When a value with the same amplitude and a slope that is consistent with the single-cycle threshold is detected, it is determined that the first transmitted light has passed a cycle. The maximum point of the coupled interference light in the cycle is taken as the value of the envelope curve. The same operation is performed on each cycle in turn to fit the envelope curve of the coupled interference light.

[0015] Step 5: The first electro-optic modulator changes the frequency of the main reflected light and the main transmitted light, and the signal demodulation module fits the envelope curve of the coupled interference light. When the signal demodulation module collects the zero point of the envelope fitting curve of the coupled interference light, the signal demodulation module demodulates the initial phase according to the number of periodic changes A of the collected coupled interference light.

[0016] Step 6: The first electro-optic modulator adjusts the frequencies of the two lasers to return to f0 and f1+Δf;

[0017] Step 7, the micro-motion stage moves, and the displacement sensor to be measured collects the displacement change of the measuring plate; the signal demodulation module demodulates according to the number M of periodic changes of the collected first transmitted interference light, obtains the number of periodic changes of the interference signal during the movement of the micro-motion stage, and solves for the displacement integer part L0;

[0018] Step 8: The first electro-optic modulator changes the frequencies of the main reflected light and the main transmitted light. The signal demodulation module fits the envelope curve of the coupled interference light. When the zero point of the envelope fitting curve of the coupled interference light is collected, the main reflected light frequency at this time is recorded as f1+Δf+f B The signal demodulation module demodulates the measured phase according to the number of periodic changes B of the collected coupled interference light.

[0019] Step 9: The first electro-optic modulator adjusts the frequencies of the two lasers to return to f0 and f1+Δf;

[0020] Step 10: The signal demodulation module calculates the phase change ΔL before and after the displacement according to the initial phase and the measured phase, and uses the phase change as the displacement fraction.

[0021] Step 11, the signal demodulation module sums the integer part of the displacement and the fractional part of the displacement to obtain the displacement L of the micro-motion displacement stage;

[0022] Step 12: The second electro-optic modulator changes the frequency of the main reflected light so that its frequency returns to f1; the data processing module collects the measurement result of the displacement sensor under test and the demodulation result of the signal demodulation module to complete the inspection of the displacement sensor under test.

[0023] The present invention also provides a displacement measurement device based on co-resonant cavity coupled frequency-modulated Fabry-Perot interferometry, comprising: a dual-frequency laser, an optical isolator, an optical collimator, a first polarization beam splitter prism, a first plane reflector, a second polarization beam splitter prism, a quarter-wave plate, a second plane reflector, a first resonant plane reflector, a second resonant plane reflector, a corner cube prism, a third polarization beam splitter prism, a first photoelectric signal receiver, a second photoelectric signal receiver, a laser interferometer, a signal demodulation module, a data processing module, a micro-displacement stage, a measuring corner cube prism, a first electro-optical modulator, and a second electro-optical modulator;

[0024] Among them, the dual-frequency laser emits two orthogonal linear polarized lights, which are divided into main transmitted light and main reflected light at the first polarization beam splitter prism after passing through an optical isolator, an optical collimator, and a first electro-optical modulator; the main transmitted light passes through a quarter wave plate for the first time after passing through the second polarization beam splitter prism, and is then reflected by the second plane reflector to the first Fabry-Perot cavity composed of a first resonant plane reflector and a corner cube prism, and multi-beam interference occurs in the first Fabry-Perot cavity; the first transmitted interference light is reflected by the second plane transmitting mirror and then passes through the quarter wave plate for the second time, and its polarization direction is rotated 90°, and is collected by the first photoelectric signal receiver; the first reflected interference light is reflected by the first resonant plane reflector and returns along the original optical path, and passes through the quarter wave plate for the second time, and its polarization direction is rotated 90°. The direction of the second polarization beam splitter is rotated by 90°, and it is reflected by the beam splitting surface of the second polarization beam splitter prism and directed to the third polarization beam splitter prism; the main reflected light passes through the first optical reflection surface and is directed to the second electro-optical modulator, and then passes through the quarter-wave plate for the first time, and is then reflected by the second plane reflector to the second Fabry-Perot cavity composed of the second resonant plane reflector and the corner cube prism with a hollow middle, and multi-beam interference occurs in the second Fabry-Perot cavity; the second transmitted interference light is reflected by the second plane transmitting mirror, and then passes through the quarter-wave plate for the second time, and its polarization direction is rotated by 90°, and is directed to the third polarization beam splitter prism; the third polarization beam splitter prism combines the first reflected interference light and the second transmitted interference light, and then outputs the coupled interference light, which is collected by the second photoelectric signal receiver.

[0025] Preferably, the first resonant plane reflector and the corner cube prism form a first Fabry-Perot cavity, and the first resonant plane reflector moves together with the micro-motion displacement stage to form a first Fabry-Perot cavity with a variable cavity length; the second resonant plane reflector with a hollow middle portion and the corner cube prism form a second Fabry-Perot cavity with a fixed cavity length; the first resonant plane reflector and the second resonant plane reflector with a hollow middle portion are arranged in parallel, and the corner cube prism is used to fold the optical path to form a common resonant cavity coupled Fabry-Perot cavity with parallel and common optical paths.

[0026] Preferably, the measuring corner cube prism is fixed on a micro-motion displacement stage and moves with the micro-motion displacement stage. The laser interferometer measures the displacement of the measuring corner cube prism so that the measurement satisfies the Abbe principle.

[0027] The present invention also provides a displacement measurement method based on co-resonant cavity coupled frequency modulation Fabry-Perot interferometry, comprising:

[0028] Step 1: The dual-frequency laser emits two orthogonal linearly polarized lights, and the frequencies of the two lights are f0 and f1 respectively;

[0029] Step 2, the two paths of light are separated into main transmitted light and main reflected light at the first polarization beam splitter prism after passing through the optical isolator, the optical collimator, and the first electro-optical modulator; the main transmitted light passes through the quarter wave plate for the first time after passing through the second polarization beam splitter prism, and then is reflected by the second plane reflector to the first Fabry-Perot cavity composed of the first resonant plane reflector and the corner cube prism, and multi-beam interference occurs; the first transmitted interference light after interference is reflected by the second plane transmitting mirror and passes through the quarter wave plate for the second time, and its polarization direction is thereby rotated 90° and collected by the first photoelectric signal receiver; the first reflected interference light after interference is reflected by the first resonant plane reflector and returns along the original optical path, passes through the quarter wave plate for the second time, and its polarization direction is It rotates 90°, is reflected by the beam splitting surface of the second polarization beam splitter prism, and is emitted to the third polarization beam splitter prism; the main reflected light is reflected by the first optical reflection surface to the second electro-optic modulator, then passes through the quarter-wave plate for the first time, and then is reflected by the second plane reflector to the second Fabry-Perot cavity composed of the second resonant plane reflector and the corner cube prism with a hollow middle, and multi-beam interference occurs in the cavity, and the second transmitted interference light after interference is reflected by the second plane reflector, passes through the quarter-wave plate for the second time, and is emitted to the third polarization beam splitter prism; the third polarization beam splitter prism combines the first reflected interference light and the second transmitted interference light to obtain coupled interference light, and the second photoelectric signal receiver collects the coupled interference light;

[0030] Step 3, the second electro-optic modulator changes the frequency of the main reflected light to f1+Δf, and in this process, the interference peak position of the coupled interference light moves, so that the measurement start position is far away from the near-zero point position and the peak point position of the interference peak;

[0031] Step 4: The signal demodulation module sets a single-cycle threshold at a position far from the near-zero point and the peak point of the interference peak, and demodulates the interference peak signal of the first transmitted light interference light. When a value with the same amplitude and a slope that is consistent with the single-cycle threshold is detected, it is determined that the first transmitted light has passed a cycle. The maximum point of the coupled interference light in the cycle is taken as the value of the envelope curve. The same operation is performed on each cycle in turn to fit the envelope curve of the coupled interference light.

[0032] Step 5: The first electro-optic modulator changes the frequency of the main reflected light and the main transmitted light, and the signal demodulation module fits the envelope curve of the coupled interference light. When the signal demodulation module collects the zero point of the envelope fitting curve of the coupled interference light, the signal demodulation module demodulates the initial phase according to the number of periodic changes A of the collected coupled interference light.

[0033] Step 6: The first electro-optic modulator adjusts the frequencies of the two lasers to return to f0 and f1+Δf;

[0034] Step 7, the micro-motion stage moves continuously, and the laser interferometer collects and measures the position information of the corner cube prism; the signal demodulation module demodulates according to the number M of periodic changes of the collected first transmitted interference light, obtains the number of periodic changes of the interference signal during the movement of the micro-motion stage, and solves the displacement integer part L0;

[0035] Step 8: The first electro-optic modulator changes the frequencies of the main reflected light and the main transmitted light. The signal demodulation module fits the envelope curve of the coupled interference light. When the zero point of the envelope fitting curve of the coupled interference light is collected, the main reflected light frequency at this time is recorded as f1+Δf+Δf B The signal demodulation module demodulates the measured phase according to the number of periodic changes B of the collected coupled interference light.

[0036] Step 9: The first electro-optic modulator adjusts the frequencies of the two lasers to return to f0 and f1+Δf;

[0037] Step 10: The signal demodulation module calculates the phase change ΔL before and after the displacement according to the initial phase and the measured phase, and uses the phase change as the displacement fraction.

[0038] Step 11, the signal demodulation module sums the displacement integer part and the displacement fraction part to obtain the displacement L of the micro-motion displacement stage;

[0039] Step 12: The second electro-optic modulator changes the frequency of the main reflected light to return it to the initial frequency f1; repeat the above steps to collect the measurement results of the laser interferometer under test and the demodulation results of the signal demodulation module; the data processing module analyzes and processes the collected results to complete the measurement of the nonlinearity of the laser interferometer.

[0040] Compared with the prior art solutions, the present invention has the following beneficial effects:

[0041] 1. The present invention adjusts the frequencies of two lasers, demodulates the interference light in the signal demodulation module, completes the measurement of the movement of the micro-displacement platform, and effectively improves the measurement speed.

[0042] 2. The present invention adopts two parallel Fabry-Perot cavities with a common optical path to form a co-resonant cavity coupled frequency-modulated Fabry-Perot cavity structure, which can effectively reduce the influence of the measurement environment on the calibration results and improve the measurement accuracy and stability of the device;

[0043] 3. The present invention fixes a plane reflector between the micro-motion displacement stage and the displacement sensor to be measured to change the propagation direction of the two lasers. The first resonant plane mirror moving with the micro-motion displacement stage maintains a coaxial position with the displacement sensor to be measured, so that the measurement satisfies the Abbe principle.

[0044] 4. The present invention adopts a frequency sweeping movement method to select the interference peak judgment area. By changing the frequencies of the two lasers, the interference periodic signal is moved, so that the peak judgment threshold is away from the near-zero position and the peak position, thereby reducing the measurement error of the device;

[0045] 5. The present invention demodulates and calculates the interference light of the first Fabry-Perot cavity, and uses the processing result as the integer part of the displacement, so as to complete the displacement measurement in a wide range;

[0046] 6. After counting the number of interference peaks of the interference periodic signal during the displacement process, the present invention determines the phase change of the measured displacement according to the interval of one quarter of the wavelength difference as a small period, and uses the phase change as the fractional part of the displacement, which can effectively improve the measurement resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0048] Figure 1 Schematic diagram of a displacement measurement device based on co-resonant cavity coupled frequency modulation Fabry-Perot interferometry provided in Example 1 of the present invention;

[0049] Figure 2 Schematic diagram of a displacement measurement device based on co-resonant cavity coupled frequency modulation Fabry-Perot interferometry provided in Example 3 of the present invention;

[0050] Among them, 1. dual-frequency laser; 2. optical isolator; 3. optical collimator; 4. first polarization beam splitter prism; 5. first plane reflector; 6. second polarization beam splitter prism; 7. quarter wave plate; 8. second plane reflector; 9. first resonant plane reflector; 10. second resonant plane reflector; 11. corner cube prism; 12. third polarization beam splitter prism; 13. first photoelectric signal receiver; 14. second photoelectric signal receiver; 15. displacement sensor to be measured; 16. signal demodulation module; 17. data processing module; 18. micro-motion displacement stage; 19. measuring board; 20. first electro-optic modulator; 21. second electro-optic modulator; 22. measuring corner cube prism; 23. laser interferometer. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0053] Embodiment 1:

[0054] like Figure 2 The embodiment of the present invention provides a displacement measurement device based on co-resonant cavity coupled frequency-modulated Fabry-Perot interferometry, including: a dual-frequency laser 1, an optical isolator 2, an optical collimator 3, a first polarization beam splitter prism 4, a first plane reflector 5, a second polarization beam splitter prism 6, a quarter-wave plate 7, a second plane reflector 8, a first resonant plane reflector 9, a second resonant plane reflector 10, a corner cube prism 11, a third polarization beam splitter prism 12, a first photoelectric signal receiver 13, a second photoelectric signal receiver 14, a displacement sensor to be measured 15, a signal demodulation module 16, a data processing module 17, a micro-displacement stage 18, a measuring board 19, a first electro-optical modulator 20, and a second electro-optical modulator 21.

[0055] The dual-frequency laser 1 emits two orthogonal linear polarized lights, which are divided into main transmitted light and main reflected light at the first polarization beam splitter prism 4 after passing through the optical isolator 2, the optical collimator 3, and the first electro-optical modulator 20. The main transmitted light passes through the quarter wave plate 7 for the first time after passing through the second polarization beam splitter prism 4, and then is reflected by the second plane reflector 8 to the first Fabry-Perot cavity composed of the first resonant plane reflector 9 and the corner cube prism 11, and multi-beam interference occurs in the first Fabry-Perot cavity. The first transmitted interference light is reflected by the second plane transmitting mirror 8, and then passes through the quarter wave plate 7 for the second time, and the polarization direction is rotated by 90°, and is collected by the first photoelectric signal receiver 14. The first reflected interference light is reflected by the first resonant plane reflector 9 and then returns along the original optical path. After passing through the quarter wave plate 7 for the second time, its polarization direction is rotated by 90°, and is reflected by the splitting surface of the second polarization beam splitter prism 6, and is emitted to the third polarization beam splitter prism 12. The main reflected light passes through the first optical reflection surface and is directed to the second electro-optic modulator 21, then passes through the quarter wave plate 7 for the first time, and then is reflected by the second plane reflector 8 to the second Fabry-Perot cavity composed of the second resonant plane reflector 10 and the corner cube prism 11, where multi-beam interference occurs. The second transmitted interference light is reflected by the second plane transmitting mirror 8 and then passes through the quarter wave plate 7 for the second time, and then the polarization direction is rotated by 90°, and then it is directed to the third polarization beam splitter prism 12. The third polarization beam splitter prism 12 combines the first reflected interference light and the second transmitted interference light, and then outputs the coupled interference light, which is collected by the second photoelectric signal receiver. The first resonant plane reflector 9 and the corner cube prism 11 form a first Fabry-Perot cavity, and the first resonant plane reflector 9 moves with the micro-motion displacement stage 18 to form a first Fabry-Perot cavity with a variable cavity length; the second resonant plane reflector 10 and the corner cube prism 11, which are hollowed out in the middle, form a second Fabry-Perot cavity with a fixed cavity length. The first resonant plane reflector 9 is arranged in parallel with the second resonant plane reflector 10 hollowed out in the middle, and the light path is folded by a corner cube prism 11 to form a parallel, common light path common resonant cavity coupled Fabry-Perot cavity. The measuring plate 19 is fixed on the micro-motion displacement stage 18 and moves with the micro-motion displacement stage 18. The displacement sensor 15 measures the displacement of the measuring plate 19 to ensure that the measurement process meets the Abbe principle.

[0056] Embodiment 2:

[0057] The embodiment of the present invention also provides a displacement measurement method based on co-resonant cavity coupled frequency modulation Fabry-Perot interferometry by using the displacement measurement device of embodiment 1, which can test the accuracy of the high-precision displacement sensor, and the specific steps are as follows:

[0058] Step 1: The dual-frequency laser 1 emits two orthogonal linearly polarized lights, and the frequencies of the two lights are f0 and f1 respectively.

[0059] Step 2, the two paths of light are separated into main transmitted light and main reflected light at the first polarization beam splitter prism 4 after passing through the optical isolator 2, the optical collimator 3, and the first electro-optical modulator 20. Among them, the main transmitted light passes through the quarter wave plate 7 for the first time after passing through the second polarization beam splitter prism 6, and then is reflected by the second plane reflector 8 to the first Fabry-Perot cavity composed of the first resonant plane reflector 9 and the corner cube prism 11, and multi-beam interference occurs. The first transmitted interference light after interference is reflected by the second plane transmitting mirror 8 and passes through the quarter wave plate 7 for the second time, and its polarization direction is thereby rotated by 90°, and is collected by the first photoelectric signal receiver 14. The first reflected interference light after interference is reflected by the first resonant plane reflector 9 and returns along the original optical path, passes through the quarter wave plate 7 for the second time, and its polarization direction is rotated by 90°, and is reflected by the splitting surface of the second polarization beam splitter prism 6, and is emitted to the third polarization beam splitter prism 12. The main reflected light is reflected by the first optical reflection surface 5 to the second electro-optic modulator 21, then passes through the quarter wave plate 7 for the first time, and then is reflected by the second plane reflector 8 to the second Fabry-Perot cavity composed of the second resonant plane reflector 10 and the corner cube prism 11 with a hollow middle, and multi-beam interference occurs in the cavity, and the second transmitted interference light after interference is reflected by the second plane reflector 8, passes through the quarter wave plate 7 for the second time, and is emitted to the third polarization beam splitter prism 12. The third polarization beam splitter prism 12 combines the first reflected interference light and the second transmitted interference light to obtain coupled interference light, and the second photoelectric signal receiver 13 collects the coupled interference light.

[0060] Step 3: The second electro-optic modulator 21 changes the frequency of the main reflected light to f1+Δf. In this process, the interference peak position of the coupled interference light moves, so that the measurement start position is far away from the near-zero point position and the peak point position of the interference peak.

[0061] Step 4, the signal demodulation module 16 sets a single-cycle threshold at a position far away from the near-zero point and the peak point of the interference peak, and demodulates the interference peak signal of the first transmitted light interference light. When a value with the same amplitude and a slope consistent with the single-cycle threshold is detected, it is judged that the first transmitted light has passed a cycle, and the maximum point of the coupled interference light in the cycle is taken as the value of the envelope curve. The same operation is performed on each cycle in turn, thereby fitting the envelope curve of the coupled interference light.

[0062] Step 5: The first electro-optic modulator 20 changes the frequency of the main reflected light and the main transmitted light, and the signal demodulation module 16 fits the envelope curve of the coupled interference light. When the signal demodulation module collects the zero point of the envelope fitting curve of the coupled interference light, the signal demodulation module demodulates the initial phase according to the number of periodic changes A of the collected coupled interference light.

[0063]

[0064] Step 6: The first electro-optic modulator 20 adjusts the frequencies of the two lasers to return to f0 and f1+Δf.

[0065] Step 7: The micro-motion stage 18 moves, and the displacement sensor 15 collects the displacement change of the measuring plate 19. The signal demodulation module 16 demodulates the collected periodic change number M of the first transmitted interference light to obtain the periodic change number of the interference signal during the movement of the micro-motion stage 18, and solves the displacement integer part L0:

[0066]

[0067] Step 8: The first electro-optic modulator 20 changes the frequencies of the main reflected light and the main transmitted light. The signal demodulation module 16 fits the envelope curve of the coupled interference light. When the zero point of the envelope fitting curve of the coupled interference light is collected, the main reflected light frequency at this time is recorded as f1+Δf+f B The signal demodulation module 16 demodulates the measured phase according to the number B of periodic changes of the collected coupling interference light.

[0068]

[0069] Step 9: The first electro-optic modulator 20 adjusts the frequencies of the two lasers to return to f0 and f1+Δf.

[0070] Step 10: The signal demodulation module 16 calculates the phase change ΔL before and after the displacement according to the initial phase and the measured phase, and uses the phase change as the displacement fraction.

[0071]

[0072] Step 11: The signal demodulation module 16 sums the integer part of the displacement and the fractional part of the displacement to obtain the displacement L of the micro-motion displacement stage 18:

[0073]

[0074] Step 12: The second electro-optic modulator 21 changes the frequency of the main reflected light to make its frequency return to f1. The data processing module 17 collects the measurement result of the displacement sensor 15 under test and the demodulation result of the signal demodulation module to complete the inspection of the displacement sensor 15 under test.

[0075] Embodiment 3:

[0076] This embodiment also provides a displacement measurement device based on co-resonant cavity coupling frequency modulation Fabry-Perot interferometry. In the displacement measurement device of Embodiment 1, the measurement plate 19 is replaced by a measurement corner cube prism 22, and the displacement sensor 15 to be measured is replaced by a laser interferometer 23. Figure 2As shown, the displacement measurement device based on co-resonant cavity coupled frequency-modulated Fabry-Perot interferometry includes: a dual-frequency laser 1, an optical isolator 2, an optical collimator 3, a first polarization beam splitter prism 4, a first plane reflector 5, a second polarization beam splitter prism 6, a quarter-wave plate 7, a second plane reflector 8, a first resonant plane reflector 9, a second resonant plane reflector 10, a corner cube prism 11, a third polarization beam splitter prism 12, a first photoelectric signal receiver 13, a second photoelectric signal receiver 14, a laser interferometer 23, a signal demodulation module 16, a data processing module 17, a micro-displacement stage 18, a measuring corner cube prism 22, a first electro-optical modulator 20, and a second electro-optical modulator 21.

[0077] The dual-frequency laser 1 emits two orthogonal linear polarized lights, which are divided into main transmitted light and main reflected light at the first polarization beam splitter prism 4 after passing through the optical isolator 2, the optical collimator 3, and the first electro-optical modulator 20. The main transmitted light passes through the quarter wave plate 7 for the first time after passing through the second polarization beam splitter prism 4, and then is reflected by the second plane reflector 8 to the first Fabry-Perot cavity composed of the first resonant plane reflector 9 and the corner cube prism 11, and multi-beam interference occurs in the first Fabry-Perot cavity. The first transmitted interference light is reflected by the second plane transmitting mirror 8, and then passes through the quarter wave plate 7 for the second time, and the polarization direction is rotated by 90°, and is collected by the first photoelectric signal receiver 14. The first reflected interference light is reflected by the first resonant plane reflector 9 and then returns along the original optical path. After passing through the quarter wave plate 7 for the second time, its polarization direction is rotated by 90°, and is reflected by the splitting surface of the second polarization beam splitter prism 6, and is emitted to the third polarization beam splitter prism 12. The main reflected light passes through the first optical reflection surface and is directed to the second electro-optic modulator 21, then passes through the quarter wave plate 7 for the first time, and then is reflected by the second plane reflector 8 to the second Fabry-Perot cavity composed of the second resonant plane reflector 10 and the corner cube prism 11, where multi-beam interference occurs. The second transmitted interference light is reflected by the second plane transmitting mirror 8 and then passes through the quarter wave plate 7 for the second time, and then the polarization direction is rotated by 90°, and then it is directed to the third polarization beam splitter prism 12. The third polarization beam splitter prism 12 combines the first reflected interference light and the second transmitted interference light, and then outputs the coupled interference light, which is collected by the second photoelectric signal receiver. The first resonant plane reflector 9 and the corner cube prism 11 form a first Fabry-Perot cavity, and the first resonant plane reflector 9 moves with the micro-motion displacement stage 18 to form a first Fabry-Perot cavity with a variable cavity length; the second resonant plane reflector 10 and the corner cube prism 11, which are hollowed out in the middle, form a second Fabry-Perot cavity with a fixed cavity length. The first resonant plane reflector 9 is arranged in parallel with the second resonant plane reflector 10 hollowed out in the middle, and the light path is folded by the corner cube prism 11 to form a parallel, common light path common resonant cavity coupled Fabry-Perot cavity. The measuring corner cube prism 22 is fixed on the micro-motion displacement stage 18 and moves with the micro-motion displacement stage 18. The laser interferometer 23 measures the displacement of the measuring corner cube prism 22 to ensure that the measurement meets the Abbe principle.

[0078] Embodiment 4:

[0079] The embodiment of the present invention also provides a displacement measurement method based on co-resonant cavity coupled frequency modulation Fabry-Perot interferometry implemented by the displacement measurement device of embodiment 3, and the specific steps are as follows:

[0080] Step 1: The dual-frequency laser 1 emits two orthogonal linearly polarized lights, and the frequencies of the two lights are f0 and f1 respectively.

[0081] Step 2, the two paths of light are separated into main transmitted light and main reflected light at the first polarization beam splitter prism 4 after passing through the optical isolator 2, the optical collimator 3, and the first electro-optical modulator 20. Among them, the main transmitted light passes through the quarter wave plate 7 for the first time after passing through the second polarization beam splitter prism 6, and then is reflected by the second plane reflector 8 to the first Fabry-Perot cavity composed of the first resonant plane reflector 9 and the corner cube prism 11, and multi-beam interference occurs. The first transmitted interference light after interference is reflected by the second plane transmitting mirror 8 and passes through the quarter wave plate 7 for the second time, and its polarization direction is thereby rotated by 90°, and is collected by the first photoelectric signal receiver 14. The first reflected interference light after interference is reflected by the first resonant plane reflector 9 and returns along the original optical path, passes through the quarter wave plate 7 for the second time, and its polarization direction is rotated by 90°, and is reflected by the splitting surface of the second polarization beam splitter prism 6, and is emitted to the third polarization beam splitter prism 12. The main reflected light is reflected by the first optical reflection surface 5 to the second electro-optic modulator 21, then passes through the quarter wave plate 7 for the first time, and then is reflected by the second plane reflector 8 to the second Fabry-Perot cavity composed of the second resonant plane reflector 10 with a hollow middle and the corner cube prism 11, where multi-beam interference occurs, and the second transmitted interference light after interference is reflected by the second plane reflector 8, passes through the quarter wave plate 7 for the second time, and is emitted to the third polarization beam splitter prism 12. The third polarization beam splitter prism 12 combines the first reflected interference light and the second transmitted interference light to obtain coupled interference light, and the second photoelectric signal receiver 13 collects the coupled interference light.

[0082] Step 3: The second electro-optic modulator 21 changes the frequency of the main reflected light to f1+Δf. In this process, the interference peak position of the coupled interference light moves, so that the measurement start position is far away from the near-zero point position and the peak point position of the interference peak.

[0083] Step 4, the signal demodulation module 16 sets a single-cycle threshold at a position far away from the near-zero point and the peak point of the interference peak, and demodulates the interference peak signal of the first transmitted light interference light. When a value with the same amplitude and a slope consistent with the single-cycle threshold is detected, it is judged that the first transmitted light has passed a cycle, and the maximum point of the coupled interference light in the cycle is taken as the value of the envelope curve. The same operation is performed on each cycle in turn, thereby fitting the envelope curve of the coupled interference light.

[0084] Step 5: The first electro-optic modulator 20 changes the frequency of the main reflected light and the main transmitted light, and the signal demodulation module 16 fits the envelope curve of the coupled interference light. When the signal demodulation module 16 collects the zero point of the envelope fitting curve of the coupled interference light, the signal demodulation module 16 demodulates the initial phase according to the number of periodic changes A of the collected coupled interference light.

[0085]

[0086] Step 6: The first electro-optic modulator 20 adjusts the frequencies of the two lasers to return to f0 and f1+Δf.

[0087] Step 7, the micro-motion stage 18 moves continuously, and the laser interferometer 23 collects and measures the position information of the corner cube prism 22. The signal demodulation module 16 demodulates according to the number M of periodic changes of the collected first transmitted interference light, obtains the number of periodic changes of the interference signal during the movement of the micro-motion stage 18, and solves the displacement integer part L0:

[0088]

[0089] Step 8: The first electro-optic modulator 20 changes the frequencies of the main reflected light and the main transmitted light. The signal demodulation module 16 fits the envelope curve of the coupled interference light. When the zero point of the envelope fitting curve of the coupled interference light is collected, the main reflected light frequency at this time is recorded as f1+Δf+Δf B The signal demodulation module 16 demodulates the measured phase according to the number B of periodic changes of the collected coupling interference light.

[0090]

[0091] Step 9: The first electro-optic modulator 20 adjusts the frequencies of the two lasers to return to f0 and f1+Δf.

[0092] Step 10: The signal demodulation module 16 calculates the phase change ΔL before and after the displacement according to the initial phase and the measured phase, and uses the phase change as the displacement fraction.

[0093]

[0094] Step 11: The signal demodulation module 16 sums the displacement integer part and the displacement fraction part to obtain the displacement L of the micro-motion displacement stage 18:

[0095]

[0096] Where f0 is the initial frequency of the main transmitted light, f1 is the initial frequency of the main reflected light, Δf is the frequency change of the main reflected light, M is the number of changes in the interference peaks of the first transmitted light interference light during the movement of the micro-motion stage. n is the refractive index of air in the two Fabry-Perot cavities, c is the speed of light, f A is the frequency change of the main reflected light before displacement, f B is the frequency change of the main reflected light after displacement.

[0097] Step 12: The second electro-optic modulator 21 changes the frequency of the main reflected light to return it to the initial frequency f1. Repeat the above steps to collect the measurement results of the laser interferometer 23 under test and the demodulation results of the signal demodulation module 16. The data processing module 17 analyzes and processes the collected results to complete the measurement of the nonlinearity of the laser interferometer.

[0098] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A displacement measurement device based on co-resonant cavity coupling frequency modulation Fabry-Perot interferometry, characterized in that: include: Dual-frequency laser, optical isolator, optical collimator, first polarization beam splitter prism, first plane reflector, second polarization beam splitter prism, quarter wave plate, second plane reflector, first resonant plane reflector, second resonant plane reflector, corner cube prism, third polarization beam splitter prism, first photoelectric signal receiver, second photoelectric signal receiver, displacement sensor to be measured, signal demodulation module, data processing module, micro-displacement stage, measuring board, first electro-optic modulator, second electro-optic modulator; Among them, the dual-frequency laser emits two orthogonal linear polarized lights, which are divided into main transmitted light and main reflected light at the first polarization beam splitter prism after passing through an optical isolator, an optical collimator, and a first electro-optical modulator; the main transmitted light passes through a quarter wave plate for the first time after passing through the second polarization beam splitter prism, and is then reflected by the second plane reflector to the first Fabry-Perot cavity composed of a first resonant plane reflector and a corner cube prism, and multi-beam interference occurs in the first Fabry-Perot cavity; the first transmitted interference light is reflected by the second plane transmitting mirror and then passes through the quarter wave plate for the second time, and its polarization direction is rotated 90°, and is collected by the first photoelectric signal receiver; the first reflected interference light is reflected by the first resonant plane reflector and returns along the original optical path, and passes through the quarter wave plate for the second time, and its polarization direction is rotated 90°. The direction of the second polarization beam splitter is rotated by 90°, and it is reflected by the beam splitting surface of the second polarization beam splitter prism and directed to the third polarization beam splitter prism; the main reflected light passes through the first optical reflection surface and is directed to the second electro-optical modulator, and then passes through the quarter-wave plate for the first time, and then is reflected by the second plane reflector to the second Fabry-Perot cavity composed of the second resonant plane reflector and the corner cube prism with a hollow middle, and multi-beam interference occurs in the second Fabry-Perot cavity; the second transmitted interference light is reflected by the second plane transmitting mirror, and then passes through the quarter-wave plate for the second time, and the polarization direction is rotated by 90°, and it is directed to the third polarization beam splitter prism; the third polarization beam splitter prism combines the first reflected interference light and the second transmitted interference light, and then outputs the coupled interference light, which is collected by the second photoelectric signal receiver; The first resonant plane reflector and the corner cube prism form a first Fabry-Perot cavity, and the first resonant plane reflector moves with the micro-motion displacement stage to form a first Fabry-Perot cavity with a variable cavity length; the second resonant plane reflector with a hollow middle and the corner cube prism form a second Fabry-Perot cavity with a fixed cavity length; the first resonant plane reflector and the second resonant plane reflector with a hollow middle are arranged in parallel, and the corner cube prism is used to fold the optical path to form a common resonant cavity coupled Fabry-Perot cavity with parallel and common optical paths; The measuring plate is fixed on the micro-motion displacement stage and moves with the micro-motion displacement stage. The displacement sensor to be measured measures the displacement of the measuring plate so that the measurement satisfies the Abbe principle.

2. A displacement measurement method based on co-resonant cavity coupled frequency modulation Fabry-Perot interferometry is implemented by using the displacement measurement device based on co-resonant cavity coupled frequency modulation Fabry-Perot interferometry according to claim 1, characterized in that: include: Step 1: The dual-frequency laser emits two orthogonal linearly polarized lights, and the frequencies of the two lights are f0 and f1 respectively; Step 2, the two paths of light are separated into main transmitted light and main reflected light at the first polarization beam splitter prism after passing through an optical isolator, an optical collimator, and a first electro-optical modulator; wherein the main transmitted light passes through a quarter wave plate for the first time after passing through the second polarization beam splitter prism, and then is reflected by the second plane reflector to the first Fabry-Perot cavity composed of a first resonant plane reflector and a corner cube prism and undergoes multi-beam interference, the first transmitted interference light after interference is reflected by the second plane transmitting mirror and then passes through the quarter wave plate for the second time, and its polarization direction is thereby rotated 90° and collected by the first photoelectric signal receiver; the first reflected interference light after interference is reflected by the first resonant plane reflector and then returns along the original optical path, passes through the quarter wave plate for the second time, and its polarization direction is rotated 90° and collected by the first photoelectric signal receiver. The polarization direction of the light is rotated by 90°, and it is reflected by the beam splitting surface of the second polarization beam splitter prism and directed to the third polarization beam splitter prism; the main reflected light is reflected by the first optical reflection surface to the second electro-optic modulator, and then passes through the quarter-wave plate for the first time, and then is reflected by the second plane reflector to the second Fabry-Perot cavity composed of the second resonant plane reflector and the corner cube prism with a hollow middle, and multi-beam interference occurs in the cavity, and the second transmitted interference light after interference is reflected by the second plane reflector, passes through the quarter-wave plate for the second time, and is directed to the third polarization beam splitter prism; the third polarization beam splitter prism combines the first reflected interference light and the second transmitted interference light to obtain coupled interference light, and the second photoelectric signal receiver collects the coupled interference light; Step 3, the second electro-optic modulator changes the frequency of the main reflected light to f1+Δf, and in this process, the interference peak position of the coupled interference light moves, so that the measurement start position is far away from the near-zero point position and the peak point position of the interference peak; Step 4: The signal demodulation module sets a single-cycle threshold at a position far from the near-zero point and the peak point of the interference peak, and demodulates the interference peak signal of the first transmitted light interference light. When a value with the same amplitude and a slope that is consistent with the single-cycle threshold is detected, it is determined that the first transmitted light has passed a cycle. The maximum point of the coupled interference light in the cycle is taken as the value of the envelope curve. The same operation is performed on each cycle in turn to fit the envelope curve of the coupled interference light. Step 5: The first electro-optic modulator changes the frequency of the main reflected light and the main transmitted light, and the signal demodulation module fits the envelope curve of the coupled interference light. When the signal demodulation module collects the zero point of the envelope fitting curve of the coupled interference light, the signal demodulation module demodulates the initial phase according to the number of periodic changes A of the collected coupled interference light. Step 6: The first electro-optic modulator adjusts the frequencies of the two lasers to return to f0 and f1+Δf; Step 7, the micro-motion stage moves, and the displacement sensor to be measured collects the displacement change of the measuring plate; the signal demodulation module demodulates according to the number M of periodic changes of the collected first transmitted interference light, obtains the number of periodic changes of the interference signal during the movement of the micro-motion stage, and solves for the displacement integer part L0; Step 8: The first electro-optic modulator changes the frequencies of the main reflected light and the main transmitted light. The signal demodulation module fits the envelope curve of the coupled interference light. When the zero point of the envelope fitting curve of the coupled interference light is collected, the main reflected light frequency at this time is recorded as f1+Δf+f B The signal demodulation module demodulates the measured phase according to the number of periodic changes B of the collected coupled interference light. Step 9: The first electro-optic modulator adjusts the frequencies of the two lasers to return to f0 and f1+Δf; Step 10: The signal demodulation module calculates the phase change ΔL before and after the displacement according to the initial phase and the measured phase, and uses the phase change as the displacement fraction. Step 11: The signal demodulation module sums the integer part of the displacement and the fractional part of the displacement to obtain the displacement L of the micro-motion stage: Step 12: The second electro-optic modulator changes the frequency of the main reflected light to f1; the data processing module collects the measurement result of the displacement sensor under test and the demodulation result of the signal demodulation module to complete the inspection of the displacement sensor under test.

3. A displacement measurement device based on co-resonant cavity coupled frequency modulation Fabry-Perot interferometry, characterized in that: include: Dual-frequency laser, optical isolator, optical collimator, first polarization beam splitter, first plane reflector, second polarization beam splitter, quarter wave plate, second plane reflector, first resonant plane reflector, second resonant plane reflector, corner cube prism, third polarization beam splitter, first photoelectric signal receiver, second photoelectric signal receiver, laser interferometer, signal demodulation module, data processing module, micro-motion stage, measuring corner cube prism, first electro-optic modulator, second electro-optic modulator; Among them, the dual-frequency laser emits two orthogonal linear polarized lights, which are divided into main transmitted light and main reflected light at the first polarization beam splitter prism after passing through an optical isolator, an optical collimator, and a first electro-optical modulator; the main transmitted light passes through a quarter wave plate for the first time after passing through the second polarization beam splitter prism, and is then reflected by the second plane reflector to the first Fabry-Perot cavity composed of a first resonant plane reflector and a corner cube prism, and multi-beam interference occurs in the first Fabry-Perot cavity; the first transmitted interference light is reflected by the second plane transmitting mirror and then passes through the quarter wave plate for the second time, and its polarization direction is rotated 90°, and is collected by the first photoelectric signal receiver; the first reflected interference light is reflected by the first resonant plane reflector and returns along the original optical path, and passes through the quarter wave plate for the second time, and its polarization direction is rotated 90°. The direction of the second polarization beam splitter is rotated by 90°, and it is reflected by the beam splitting surface of the second polarization beam splitter prism and directed to the third polarization beam splitter prism; the main reflected light passes through the first optical reflection surface and is directed to the second electro-optical modulator, and then passes through the quarter-wave plate for the first time, and then is reflected by the second plane reflector to the second Fabry-Perot cavity composed of the second resonant plane reflector and the corner cube prism with a hollow middle, and multi-beam interference occurs in the second Fabry-Perot cavity; the second transmitted interference light is reflected by the second plane transmitting mirror, and then passes through the quarter-wave plate for the second time, and the polarization direction is rotated by 90°, and it is directed to the third polarization beam splitter prism; the third polarization beam splitter prism combines the first reflected interference light and the second transmitted interference light, and then outputs the coupled interference light, which is collected by the second photoelectric signal receiver; The first resonant plane reflector and the corner cube prism form a first Fabry-Perot cavity, and the first resonant plane reflector moves with the micro-motion displacement stage to form a first Fabry-Perot cavity with a variable cavity length; the second resonant plane reflector with a hollow middle and the corner cube prism form a second Fabry-Perot cavity with a fixed cavity length; the first resonant plane reflector and the second resonant plane reflector with a hollow middle are arranged in parallel, and the corner cube prism is used to fold the optical path to form a common resonant cavity coupled Fabry-Perot cavity with parallel and common optical paths; The measuring corner cube prism is fixed on the micro-motion displacement stage and moves with the micro-motion displacement stage. The laser interferometer measures the displacement of the measuring corner cube prism so that the measurement satisfies the Abbe principle.

4. A displacement measurement method based on co-resonant cavity coupled frequency modulation Fabry-Perot interferometry is implemented by using the displacement measurement device based on co-resonant cavity coupled frequency modulation Fabry-Perot interferometry according to claim 3, characterized in that: include: Step 1: The dual-frequency laser emits two orthogonal linearly polarized lights, and the frequencies of the two lights are f0 and f1 respectively; Step 2, the two paths of light are separated into main transmitted light and main reflected light at the first polarization beam splitter prism after passing through the optical isolator, the optical collimator, and the first electro-optical modulator; the main transmitted light passes through the quarter wave plate for the first time after passing through the second polarization beam splitter prism, and then is reflected by the second plane reflector to the first Fabry-Perot cavity composed of the first resonant plane reflector and the corner cube prism, and multi-beam interference occurs; the first transmitted interference light after interference is reflected by the second plane transmitting mirror and passes through the quarter wave plate for the second time, and its polarization direction is thereby rotated 90° and collected by the first photoelectric signal receiver; the first reflected interference light after interference is reflected by the first resonant plane reflector and returns along the original optical path, passes through the quarter wave plate for the second time, and its polarization direction is It rotates 90°, is reflected by the beam splitting surface of the second polarization beam splitter prism, and is emitted to the third polarization beam splitter prism; the main reflected light is reflected by the first optical reflection surface to the second electro-optic modulator, then passes through the quarter-wave plate for the first time, and then is reflected by the second plane reflector to the second Fabry-Perot cavity composed of the second resonant plane reflector and the corner cube prism with a hollow middle, and multi-beam interference occurs in the cavity, and the second transmitted interference light after interference is reflected by the second plane reflector, passes through the quarter-wave plate for the second time, and is emitted to the third polarization beam splitter prism; the third polarization beam splitter prism combines the first reflected interference light and the second transmitted interference light to obtain coupled interference light, and the second photoelectric signal receiver collects the coupled interference light; Step 3, the second electro-optic modulator changes the frequency of the main reflected light to f1+Δf, and in this process, the interference peak position of the coupled interference light moves, so that the measurement start position is far away from the near-zero point position and the peak point position of the interference peak; Step 4: The signal demodulation module sets a single-cycle threshold at a position far from the near-zero point and the peak point of the interference peak, and demodulates the interference peak signal of the first transmitted light interference light. When a value with the same amplitude and a slope that is consistent with the single-cycle threshold is detected, it is determined that the first transmitted light has passed a cycle. The maximum point of the coupled interference light in the cycle is taken as the value of the envelope curve. The same operation is performed on each cycle in turn to fit the envelope curve of the coupled interference light. Step 5: The first electro-optic modulator changes the frequency of the main reflected light and the main transmitted light, and the signal demodulation module fits the envelope curve of the coupled interference light. When the signal demodulation module collects the zero point of the envelope fitting curve of the coupled interference light, the signal demodulation module demodulates the initial phase according to the number of periodic changes A of the collected coupled interference light. Step 6: The first electro-optic modulator adjusts the frequencies of the two lasers to return to f0 and f1+Δf; Step 7, the micro-motion stage moves continuously, and the laser interferometer collects and measures the position information of the corner cube prism; the signal demodulation module demodulates according to the number M of periodic changes of the collected first transmitted interference light, obtains the number of periodic changes of the interference signal during the movement of the micro-motion stage, and solves the displacement integer part L0; Step 8: The first electro-optic modulator changes the frequencies of the main reflected light and the main transmitted light. The signal demodulation module fits the envelope curve of the coupled interference light. When the zero point of the envelope fitting curve of the coupled interference light is collected, the main reflected light frequency at this time is recorded as f1+Δf+Δf B The signal demodulation module demodulates the measured phase according to the number of periodic changes B of the collected coupled interference light. Step 9: The first electro-optic modulator adjusts the frequencies of the two lasers to return to f0 and f1+Δf; Step 10: The signal demodulation module calculates the phase change ΔL before and after the displacement according to the initial phase and the measured phase, and uses the phase change as the displacement fraction. Step 11, the signal demodulation module sums the displacement integer part and the displacement fraction part to obtain the displacement L of the micro-motion displacement stage; Step 12: The second electro-optic modulator changes the frequency of the main reflected light to return it to the initial frequency f1; repeat the above steps to collect the measurement results of the laser interferometer under test and the demodulation results of the signal demodulation module; the data processing module analyzes and processes the collected results to complete the measurement of the nonlinearity of the laser interferometer.

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