Distance measuring method based on Fabry-Perot interference

Abstract

The invention discloses a distance measuring method based on Fabry-Perot interference, belongs to the technical field of laser measurement, and solves the problem that the distance measuring method is insufficient in measuring precision, and the method comprises the following steps: a measuring system is connected to a measuring head through an optical fiber, the distance measuring system is provided with emergent light, and collimated measuring light emitted by the measuring head is irradiated to the surface of a measured object; and after being reflected by the surface of the measured object, the light is transmitted back to a measurement system, fringes are calculated by using internal Fabry-Perot interference to obtain an optical path difference, then the linear distance from the measuring head to the measured surface is calculated, and the calculated result data is transmitted to a computer for subsequent data processing. The method is used for surface type measurement and distance measurement feedback, the measurement range is wider, and the precision is higher.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser measurement, and particularly relates to a ranging method based on Fabry-Perot interference. Background Art

[0002] The existing ranging methods mainly use capacitive or inductive rangefinders, which are limited by short measurement distances and are greatly affected by measurement space factors, and can only be used for special usage scenarios. The measurement methods with higher precision mainly use laser rangefinders, typically dual-frequency laser rangefinders, whose measurement accuracy reaches the nm level. However, since the laser main body is used as the measurement main body, which includes a laser light source, a collimation system, a calculation module, and other auxiliary modules, it is larger in volume compared to other rangefinders, not convenient to be installed in a narrow measurement space, and has high environmental requirements. It is difficult to ensure the accuracy of the measurement method in a harsh usage environment. Summary of the Invention

[0003] The object of the present invention is to:

[0004] To solve the problem of low measurement accuracy in the existing ranging methods, a ranging method based on Fabry-Perot interference is provided.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A ranging method based on Fabry-Perot interference includes the following steps:

[0007] The measurement system is connected to the probe through an optical fiber. The ranging system emits light, and the collimated measurement light emitted through the probe irradiates the surface of the object to be measured. After being reflected by the surface of the object to be measured, it is transmitted back to the measurement system. The internal Fabry-Perot interference is used to calculate the fringes to obtain the optical path difference, and then the straight-line distance from the probe to the measured surface is calculated. The calculated result data is transmitted to the computer for subsequent data processing.

[0008] Further, the probe adopts a parallel light shaping probe, and a polarization beam splitter feedback module is arranged on the optical path between the parallel light shaping probe and the object to be measured. The ranging system is provided with multiple light emissions and multiple parallel light shaping probes. The multiple collimated parallel measurement lights emitted through the multiple probes are irradiated onto the surface of the object to be measured after passing through the polarization beam splitter (polarization beam splitter) feedback module for measurement. After the result data calculated by the measurement system is transmitted to the computer, subsequent data processing is carried out in combination with the polarization beam splitter feedback module.

[0009] Further, the method for subsequent data processing in combination with the polarization beam splitter feedback module is:

[0010] The incident light and the reflected light passing through the polarization beam splitter feedback module are received by a charge-coupled device (CCD) camera, and the yaw angles of the two are calculated to obtain the real-time measured yaw angle. The final measured distance of the yaw angle feedback is calculated by a computer to eliminate the Abbe error caused by the non-collinearity of the incident light and the reflected light, and the data processing is completed.

[0011] Further, the probe head adopts a focusing and shaping probe head, and no more than one focusing and shaping probe head is arranged in the measurement optical path.

[0012] Further, the distance calculation method of the measurement system includes the following steps:

[0013] Step A: Using the orthogonal signal sin 2 (KX)+cos 2 (KX)=1;

[0014] The optical path difference of the interference light is △ = cos(KX),

[0015] where K = 4π / λ, X is the displacement value; K is the number of full waves appearing in a length of 4π, and λ is the wavelength;

[0016] Put the signals S = cos(KX) and S Q = sin(KX) in the X and Y components of a coordinate system, then the comprehensive trajectory forms a circle, and the accurate displacement value X is obtained by the differential method at non-extreme points;

[0017] where a = λ / 2, N is an integer, representing the count value within the range of λ / 2 of the displacement;

[0018] Step B: Modulate the above signal in time;

[0019] Then, at this time S = cos[K(X + X0(t))]+S0; where S0 is an arbitrary time constant background signal with an uncertain zero point, and X0(t) represents the modulation of the zero point of X in time;

[0020] Select the special case X0(t)=X0cos(ωt); where ω = 2*n*f, where f is the modulation frequency; n = 0, 1, 2... takes integers; t is the time variable of the wavelength fluctuation;

[0021] Then S = cos[K(X + X0(t))]+S0 can be deduced to S = cos[KX]cos[KX0cos(ωt)] - sin[KX]sin[KX0cos(ωt)]+S0;

[0022] In the case of normal modulation, the amplitude modulation KX0 << 1, so S ≈ cos[KX][1 - (KX0) 2(cos(ωt)) 2 / 2]-KX0cos(ωt)sin[KX]+S0;

[0023] Using the double - angle formula cos(ωt) 2 =(cos(2ωt)+1) / 2, at this time S≈cos[KX][1 - (KX0) 2 (cos(2ωt)+1) / 4]-KX0cos(ωt)sin[KX]+S0;

[0024] Then S can be divided into S DC 、S ω 、S 2ω in three parts; S = S DC +S ω +S 2ω ;

[0025] At this time S DC =cos(KX)(1 - (KX0 / 2) 2 )+S0;

[0026] S ω =-KX0cos(ωt)sin(KX);

[0027] S 2ω =-cos(KX)[KX0 / 2) 2 cos(2ωt)];

[0028] After demodulation:

[0029] S=-KX0sin(KX);

[0030] S Q =-cos(KX)(KX0 / 2) 2 ;

[0031] After orthogonalizing the current S and S Q :

[0032]

[0033] Step C, modulate the full - wave number K;

[0034] At this time K = K0+δKcos(ωt); where K0 is the full - wave number reference at any moment; δK is the modulated change in the full - wave number;

[0035] Similar to step B, the normalized signal S = cos(KX)+S0 becomes S = cos[K0X+δKcos(ωt)X]+S0;

[0036] From this, it is deduced that S DC= cos(K0X)(1 - (δKX / 2) 2 ) + S0;

[0037] S ω = -δKXcos(ωt)sin(K0X);

[0038] S 2ω = -cos(K0X)[δKX / 2) 2 cos(2ωt)];

[0039] After demodulation:

[0040] S = -δKXsin(K0X);

[0041] S Q = -cos(K0X)(δKX / 2) 2 ;

[0042] At this time, S and S Q on the path form an ellipse, and the diameter ratio is δKX / (δKX / 2) 2 = 4 / (δKX); then the radius ratio is 2 / (δKX);

[0043] Step D. Improve the accuracy

[0044] The absolute position X calculated from the orthogonal paths of S and S Q obtained through step C has a finite accuracy relative to the zero point X0. To improve the accuracy, it is necessary to ensure the integrity of the signals S and S Q during demodulation. Then, the displacement signal is placed within the range of λ / 4 for demodulation, and X estim ≈ (2 / δK)max(S Q ) / max(S) is introduced to determine the position of X at this time;

[0045] Demodulate the orthogonal signal in step C near the position of X estim to obtain a higher-precision and accurate X. At this time:

[0046] S ≈ -δKX estim sin(K0X);

[0047] S Q ≈ -cos(K0X)(δKX estim / 2) 2 ;

[0048] Then, after orthogonalizing S and S Q we get:

[0049] where N1 is an integer, representing the count value when the displacement is within the range of λ / 4.

[0050] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows:

[0051] The ranging method based on Fabry-Perot interference of the present invention has the characteristics of high precision (resolution up to pm level and repeatability precision up to nm level) and easy operation. This ranging method mainly utilizes the Fabry-Perot interference of laser in a micro-optical fiber, and then converts it into an electrical signal for ranging calculation in an electronic circuit. The present invention also measures different targets by selecting a collimated beam shaping probe and a focusing beam shaping probe. The collimated beam shaping probe is used to measure the distance of distant objects, and the focusing beam shaping probe with a depth of focus can be used to measure the surface profile of an object. The specific beneficial effects are as follows:

[0052] (1) The beneficial effects brought by the use of the collimated beam shaping probe are as follows:

[0053] Wide measurement range: The beam emitted by the collimated beam shaping probe has a large divergence angle, which means it can cover a wider area. Therefore, in the case of measuring a relatively long distance or a large target, the collimated beam shaping probe can better cover the target to ensure the accuracy and reliability of the measurement.

[0054] Low requirement for the target surface: Since the beam generated by the collimated beam shaping probe is relatively uniform, the requirement for the reflection characteristics of the target surface is relatively low. Even if there is a certain degree of roughness or irregularity on the target surface, relatively accurate measurement results can still be obtained.

[0055] Simplified optical system: The design of the collimated beam shaping probe is relatively simple and does not require a complex optical system to focus the beam. This helps to reduce the manufacturing cost, improve the reliability of the system, and reduce the complexity of maintenance.

[0056] (2) The beneficial effects brought by the use of the focusing beam shaping probe are as follows:

[0057] High-precision measurement: The focusing beam shaping probe can focus the beam on a smaller area, thereby achieving high-precision measurement of the target. It is very beneficial for application scenarios that require precise measurement of the target size or position.

[0058] Suitable for small target measurement: Since the focusing beam shaping probe can generate a smaller light spot, it is particularly suitable for measuring small targets or scenarios that require precise positioning. In this case, the focusing beam shaping probe can provide higher measurement accuracy and resolution.

[0059] Reduced background noise interference: The focusing beam shaping probe can concentrate the beam in a smaller area, reducing the interference of background noise on the measurement results. This is beneficial for improving the stability and reliability of the measurement, especially applicable under complex environmental conditions. Description of the Drawings

[0060] Figure 1 This is a schematic diagram of the measurement principle of the collimated light shaping probe of the present invention;

[0061] Figure 2 This is a schematic diagram of the measurement principle of the focused light shaping probe of the present invention;

[0062] Figure 3 This is the waveform diagram of signals S and S Q of the present invention;

[0063] Figure 4 This is the trajectory diagram of signals S and S Q in the coordinate system of the present invention;

[0064] Figure 5 This is a schematic diagram of the working principle of the polarization beam splitter feedback module of the present invention.

[0065] Figures 1 - 5 The meanings of Chinese and English abbreviations are as follows:

[0066] PBS: Polarization beam splitter (polarization beam splitter) feedback module;

[0067] CCD: Charge-coupled device camera receiver target surface;

[0068] PC: Computer control terminal. Specific embodiments

[0069] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0070] A ranging method based on Fabry-Perot interference includes the following steps:

[0071] The measurement system is connected to the probe through an optical fiber. The ranging system emits light, and the collimated measurement light emitted through the probe irradiates the surface of the object to be measured. After being reflected by the surface of the object to be measured, it is transmitted back to the measurement system. The internal Fabry-Perot interference is used to calculate the fringes, the optical path difference is obtained, and then the straight-line distance from the probe to the surface of the object to be measured is calculated. The calculated result data is transmitted to the computer for subsequent data processing.

[0072] Embodiment 1

[0073] In this embodiment, the probe uses a collimated light shaping probe, and a polarization beam splitter feedback module is arranged on the optical path between the collimated light shaping probe and the object to be measured. The ranging system is set to emit multiple beams of light and multiple collimated light shaping probes. The multiple collimated parallel measurement lights emitted through the multiple probes are irradiated onto the surface of the object to be measured after passing through the polarization beam splitter (polarization beam splitter) feedback module for measurement. After the result data calculated by the measurement system is transmitted to the computer, subsequent data processing is performed in combination with the polarization beam splitter feedback module.

[0074] The measurement system is connected to the collimated light shaping probe through an optical fiber. According to the collimation characteristics of collimated light, the ranging system can be set to emit multiple beams of light, such as Figure 1 As shown, it illustrates the measurement with 3 outgoing light paths. Three collimated parallel measurement lights are emitted through probes 1, 2, and 3. After passing through the polarization beam splitter feedback module, they are irradiated onto the surface of the object to be measured. After being reflected by the surface, they are transmitted back to the measurement system. The internal Fabry-Perot interference is used to calculate the fringes to obtain the optical path difference, thereby calculating the straight-line distance from the probe to the surface to be measured. Finally, the calculated result data is transmitted to the PC computer and combined with the polarization beam splitter feedback module for subsequent data processing.

[0075] Preferably, the method for subsequent data processing in combination with the polarization beam splitter feedback module is as follows:

[0076] The incident light and the reflected light passing through the polarization beam splitter feedback module are received by a charge-coupled device (CCD) camera. Its working principle is as Figure 5 shown. The yaw angles of the two are calculated to obtain the real-time measurement yaw angle. The final measurement distance fed back by the yaw angle is calculated by a computer to complete the data processing.

[0077] The polarization beam splitter feedback module is a feedback module combining a polarization beam splitter prism and a charge-coupled device camera. Among them, the polarization beam splitter is an optical element that divides an incident beam of light into two beams of light with perpendicular propagation directions. However, different from general optical beam splitting elements, there is a special relationship between the two beams of light it splits, that is: they are both linearly polarized lights, and their polarization directions are perpendicular to each other.

[0078] The basic principle of a polarization beam splitter prism is to use a polarizer to select and decompose the polarization state of light. A polarizer is an optical element that can select a specific polarization direction. When a light wave is incident perpendicularly on a polarizer, the polarization component of the light wave that is the same as the direction of the polarizer itself can be selected from the light wave, while the polarization component perpendicular to the direction of the polarizer is filtered out. Therefore, a polarizer can select a light wave with a specific polarization direction. Usually, a lens is used to focus the incident light beam. The lens can adjust the spreading direction of the light beam, making it easier for the focused light to be selected by the polarizer for a specific polarization direction. Next, the incident light beam is split into two light beams by an element called a "beam splitter". The polarization directions of the two light beams are perpendicular to each other, and the intensities of the light beams are equal. The beam splitter usually consists of an equilateral biconvex lens, which splits the incident light beam into two light beams with different polarization directions. After splitting the two light beams, each light beam is reflected by a mirror. The function of the mirror is to change the propagation direction of the light and keep its polarization state unchanged. At this time, the light that has moved multiple times moves along two directions respectively. Finally, the two light beams converge on an element called a coincidence mirror. Since the polarization directions of the two light beams are different, when they converge, the two light beams will be intensity-added in different directions. This addition is optical interference.

[0079] Specifically, the incident light is split by the polarization beam splitter prism of the polarization beam splitter. The incident light forms a reflected light after being reflected by the surface of the object to be measured, and then is reflected by the polarization beam splitter prism of the polarization beam splitter to the charge-coupled device camera. When measuring the light, it is always impossible to ensure absolute perpendicularity between the probe and the surface to be measured. This results in the incident light and the reflected light not being collinear, generating a yaw angle, which in turn affects the finally calculated distance value. The charge-coupled device receives the incident light and the reflected light passing through the polarization beam splitter prism of the polarization beam splitter, calculates the yaw angle between the two, and then reflects the real-time measurement yaw angle. Finally, the computer calculates the yaw angle feedback to the final measurement distance to eliminate the Abbe error caused by the non-collinearity of the incident light and the reflected light.

[0080] Embodiment 2

[0081] In this embodiment, the probe uses a focusing and shaping probe. There is no more than one focusing and shaping probe set in the measurement optical path, and its specific setting is as Figure 2 shown.

[0082] The measurement principle of the focusing and shaping probe is the same as that of the collimated light shaping probe in Embodiment 1 above. The difference is that the focusing and shaping probe has a certain focusing depth and allows a certain angular deviation and redundancy in the detection of the object surface when irradiating the surface of the object to be measured. Therefore, this method does not require an angle compensation by the polarization beam splitter feedback module, and the focusing and shaping probe is commonly used for following measurement. It is recommended that there be at most and only one focusing and shaping probe used for each measurement.

[0083] The distance calculation method of the measurement system of the present invention includes the following steps:

[0084] A. Using the orthogonal signals sin 2 (KX)+cos 2 (KX)=1;

[0085] The optical path difference of the interfering light is △ = cos(KX),

[0086] where K = 4π / λ, X is the displacement value; K is the number of full waves appearing in the length of 4π, and λ is the wavelength;

[0087] It can be considered that S = cos(KX) is a signal that changes with the displacement X: such a signal S repeats at λ / 2: X = n*λ / 2 can measure the displacement X, but at non-extreme points, due to the non-linearity of the cosine arc change, the accuracy at this time is very poor. If there is an orthogonal signal S Q = sin(KX) at the same time, this increases the number of extreme points within one period and improves the measurement accuracy.

[0088] Placing the signals S = cos(KX) and SQ = sin(KX) in the X and Y components of a coordinate system, the combined trajectory forms a circle, and thus an accurate displacement value X can be obtained through the differential method at non-extreme points;

[0089] B. Using the Fabry-Perot interference technique to produce the orthogonal components S and S Q ; their waveform diagrams and trajectories in the coordinate system are as shown in Figure 3 、 Figure 4 shown, Figure 3 in which the solid-line curve represents the waveform of the orthogonal component S, and the dashed-line curve represents the waveform of the orthogonal component S Q ; and the waveform part from A to B marked and significantly thickened, that is, the waveform diagram corresponding to the trajectory from A to B shown in Figure 4 ;

[0090] Step A. Using the orthogonal signals sin 2 (KX)+cos 2 (KX)=1;

[0091] The optical path difference of the interfering light is △ = cos(KX),

[0092] where K = 4π / λ, X is the displacement value; K is the number of full waves appearing in the length of 4π, and λ is the wavelength;

[0093] Placing the signals S = cos(KX) and S Q= sin(KX) is placed in the X and Y components of a coordinate system, and the combined trajectory forms a circle. Thus, an accurate displacement value X is obtained through the method of difference at non-extreme points;

[0094] where a = λ / 2, N is an integer, representing the count value within the range of λ / 2 for displacement;

[0095] Step B: Modulate the above signal in time;

[0096] Then, at this time, S = cos[K(X + X0(t))] + S0; where S0 is an arbitrary time-constant background signal of the uncertain zero point, and X0(t) represents the modulation of the zero point of X in time;

[0097] Select the special case X0(t) = X0cos(ωt); where ω = 2*n*f, where f is the modulation frequency; n = 0, 1, 2... takes integers; t is the time variable of the wavelength fluctuation;

[0098] Then S = cos[K(X + X0(t))] + S0 can be deduced to S = cos[KX]cos[KX0cos(ωt)] - sin[KX]sin[KX0cos(ωt)] + S0;

[0099] In the case of normal modulation, the amplitude modulation KX0 << 1, so S ≈ cos[KX][1 - (KX0) 2 (cos(ωt)) 2 / 2] - KX0cos(ωt)sin[KX] + S0;

[0100] Using the double-angle formula cos(ωt) 2 = (cos(2ωt) + 1) / 2, at this time S ≈ cos[KX][1 - (KX0) 2 (cos(2ωt) + 1) / 4] - KX0cos(ωt)sin[KX] + S0;

[0101] Then S can be divided into S DC 、S ω 、S 2ω three parts; S = S DC + S ω + S 2ω ;

[0102] At this time S DC = cos(KX)(1 - (KX0 / 2) 2 ) + S0;

[0103] S ω = -KX0cos(ωt)sin(KX);

[0104] S 2ω = -cos(KX)[KX0 / 2) 2 cos(2ωt)];

[0105] After demodulation:

[0106] S = -KX0sin(KX);

[0107] S Q = -cos(KX)(KX0 / 2) 2 ;

[0108] After orthogonalizing the current S and S Q :

[0109]

[0110] Step C, modulate the number of full waves K;

[0111] At this time, K = K0 + δKcos(ωt); where K0 is the full wave number reference at any moment; δK is the number of full waves with modulated change;

[0112] Similar to Step B, the normalized signal S = cos(KX) + S0 becomes S = cos[K0X + δKcos(ωt)X] + S0;

[0113] From this, it is deduced that S DC = cos(K0X)(1 - (δKX / 2) 2 ); + S0;

[0114] S ω = -δKXcos(ωt)sin(K0X);

[0115] S 2ω = -cos(K0X)[δKX / 2) 2 cos(2ωt)];

[0116] After demodulation:

[0117] S = -δKXsin(K0X);

[0118] S Q = -cos(K0X)(δKX / 2) 2 ;

[0119] The current S and S Q are an ellipse on the path, and the diameter ratio is δKX / (δKX / 2) 2 = 4 / (δKX); then the radius ratio is 2 / (δKX);

[0120] Step D, improve the accuracy

[0121] S and S obtained through step C Q The absolute position X calculated based on the orthogonalized path has a finite precision relative to the zero point X0. To improve the precision, it is necessary to ensure the integrity of signals S and S during demodulation Q Then, the displacement signal is placed within the range of λ / 4 for demodulation, and X estim ≈(2 / δK)max(S Q ) / max(S) is used to determine the position of X at this time;

[0122] At the position of X estim Demodulating the orthogonal signal of step C near the position to obtain a higher-precision and accurate X. At this time:

[0123] S≈-δKX estim sin(K0X);

[0124] S Q ≈-cos(K0X)(δKX estim / 2) 2 ;

[0125] Then, after orthogonalizing S and S Q the following is obtained:

[0126] where N1 is an integer, representing the count value when the displacement is within the range of λ / 4.

[0127] The present invention uses an optical fiber in-line Fabry-Perot standard component, which forms an interference cavity by splicing a hollow fiber between two single-mode optical fibers. The light beam in the interference cavity of the hollow fiber also propagates in the air. Since the diameter of the hollow fiber in the middle is basically the same as that of the single-mode optical fibers at both ends, there will be no stress concentration under large axial stress, the temperature sensitivity is relatively small, and it is not sensitive to transverse loads. However, because the hollow fiber has a poor ability to confine the propagation of light in the core, the diffraction of the light beam will bring additional losses. Therefore, in most cases, the length of the interference cavity is greatly limited, which is not conducive to multiplexing.

[0128] To solve this problem, a method of using a photonic bandgap photonic crystal fiber to replace the hollow fiber to make a Fabry-Perot cavity can be adopted. In this way, not only can the new structure have all the advantages of the Fabry-Perot cavity based on the hollow fiber, but also it can overcome the above-mentioned disadvantages, confine the propagation of the light beam in the core, and the loss becomes very small.

[0129] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A ranging method based on Fabry-Perot interference, characterized in that, It includes the following steps: The measurement system is connected to the probe through an optical fiber. The ranging system emits light. After collimation by the probe, the measurement light is irradiated onto the surface of the object to be measured. After being reflected by the surface of the object to be measured, it is transmitted back to the measurement system. The internal Fabry-Perot interference is used to calculate the fringes to obtain the optical path difference, and then the straight-line distance from the probe to the surface of the object to be measured is calculated. The calculated result data is transmitted to a computer for subsequent data processing; The distance calculation method of the measurement system includes the following steps: Step A: Using the orthogonal signal sin 2 (KX) + cos 2 (KX) = 1; The optical path difference of the interference light is △ = cos(KX), where K = 4π / λ, X is the displacement value; K is the number of full waves that appear in a length of 4π, and λ is the wavelength; Put the signals S = cos(KX) and S Q = sin(KX) on the X and Y components of a coordinate system. Then the combined trajectory forms a circle, and thus an accurate displacement value X can be obtained by the method of differentiation at non-extreme points; where a = λ / 2, N is an integer, representing the count value within the displacement range of λ / 2; Step B: Modulate the above signal in time; Then, at this time, S = cos[K(X + X0(t))] + S0; where S0 is an arbitrary time constant background signal with an uncertain zero point, and X0(t) represents the modulation of the zero point of X in time; Select the special case X0(t) = X0cos(ωt); where ω = 2*n*f, where f is the modulation frequency; n = 0, 1, 2... takes integers; t is the time variable of the wavelength fluctuation; Then S = cos[K(X + X0(t))] + S0 can be deduced to S = cos[KX]cos[KX0cos(ωt)] - sin[KX]sin[KX0cos(ωt)] + S0; In the case of normal modulation, the amplitude modulation \(KX_0\ll1\), so \(S\approx\cos[KX][1 - (KX_0)\) 2 \((\cos(\omega t))\) 2 / 2]-KX_0\cos(\omega t)\sin[KX]+S_0;\) Using the double - angle formula cos(ωt) 2 =(cos(2ωt)+1) / 2, and at this time S≈cos[KX][1 - (KX0) 2 (cos(2ωt)+1) / 4]-KX0cos(ωt)sin[KX]+S0; Then S can be divided into S DC , S ω , S 2ω into three parts; S = S DC + S ω + S 2ω ; At this time, S DC = cos(KX)(1 - (KX0 / 2) 2 ) + S0; S ω = -KX0 cos(ωt) sin(KX); S 2ω = -cos(KX)[KX0 / 2) 2 cos(2ωt)]; After demodulation: S = -KX0sin(KX); S Q = -cos(KX)(KX0 / 2) 2 ; At this time, S and S Q After being orthogonal: Step C: Modulate the number of full waves K; At this time, K = K0 + δKcos(ωt); where K0 is the reference number of full waves at any moment; δK is the number of full waves of the modulation change; Similar to step B, the normalized signal S = cos(KX) + S0 becomes S = cos[K0X + δKcos(ωt)X] + S0; It follows that S DC = cos(K0X)(1 - (δKX / 2) 2 ) + S0; S ω = -δKX cos(ωt) sin(K0X); S 2ω = -cos(K0X)[δKX / 2) 2 cos(2ωt)]; After demodulation: S = -δKXsin(K0X); S Q = -cos(K0X)(δKX / 2) 2 ; At this time, S and S Q on the path is an ellipse, and the diameter ratio is δKX / (δKX / 2) 2 = 4 / (δKX); then the radius ratio is 2 / (δKX); Step D: Improve the accuracy S and S obtained through step C Q The absolute position X calculated from the orthogonalized path has a finite precision relative to the zero point X0. To improve the precision, it is necessary to ensure the integrity of signals S and S Q during demodulation. Then, the displacement signal is placed within the range of λ / 4 for demodulation, and X estim ≈ (2 / δK) max(S Q ) / max(S) is used to determine the position of X at this time; Demodulate the quadrature signal of step C near the position of X to obtain a higher-precision and accurate X, where: estim ​ S≈-δKX estim sin(K0X); S Q ≈ -cos(K0X)(δKX estim / 2) 2 ; After orthogonalizing S and S Q we obtain: Where N1 is an integer, representing the count value within the displacement range of λ / 4.

2. The ranging method based on Fabry-Perot interference according to claim 1, wherein, The probe adopts a parallel light shaping probe, and a polarization beam splitter feedback module is set on the optical path between the parallel light shaping probe and the object to be measured. The ranging system sets multiple light emissions and multiple parallel light shaping probes. After multiple probes emit multiple collimated parallel measurement lights, they are irradiated onto the surface of the object to be measured through the polarization beam splitter feedback module for measurement. After the result data calculated by the measurement system is transmitted to the computer, subsequent data processing is carried out in combination with the polarization beam splitter feedback module.

3. The ranging method based on Fabry-Perot interference according to claim 2, characterized in that, The method for subsequent data processing in combination with the polarization beam splitter feedback module is: The charge-coupled device camera receives the incident light and the reflected light passing through the polarization beam splitter feedback module, calculates the yaw angle between the two to obtain the real-time measurement yaw angle, and calculates the final measurement distance of the yaw angle feedback through the computer to eliminate the Abbe error caused by the non-collinearity of the incident light and the reflected light, and complete the data processing.

4. A ranging method based on Fabry-Perot interference according to claim 1, characterized in that, The probe adopts a focusing shaping probe, and no more than one focusing shaping probe is set in the measurement optical path.

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