High-resolution displacement measuring device and method

Abstract

The present invention provides a high-resolution displacement measurement device and method. During the movement of a wedge-shaped glass sheet, the frequency change of a laser dual longitudinal mode is measured by a high-frequency photodetector; the dual longitudinal modes are subjected to spectral processing by a beam splitter prism, and the light intensity of a beam one and a beam two is measured by a photodetector 1 and a photodetector 2, respectively. Based on the positive and negative values ​​of the light intensity change and the frequency change value, the displacement of a moving target connected to the wedge-shaped glass sheet is calculated. The device and method associate the frequency difference of the laser oscillation longitudinal mode with the displacement of the target, and can make full use of the high precision and high resolution of frequency measurement, so that the displacement measurement can achieve a high resolution of sub-nanometer, which is conducive to application in the field of micro-displacement measurement.

Description

Technical Field

[0001] The present invention relates to the field of optical measurement technology, and in particular to a high-resolution displacement measurement device and a measurement method. Background Art

[0002] Nanoscale displacement measurement is a major research area in precision measurement, with important applications in ultraprecision and ultramicromachining. Common methods for nanoscale displacement measurement include microscopy, electrical methods, and optical methods. Microscopy, including scanning tunneling microscopy, atomic force microscopy, and scanning electron microscopy, can achieve a resolution of 1 nm or less for displacement or microscopic fluctuations, enabling three-dimensional topography imaging. However, these methods suffer from limited measurement range and low linearity. Electrical methods generally measure target displacement using electrical quantities such as capacitance, inductance, and eddy currents. While their principles and structures are simple and facilitate electronic subdivision, they can achieve nanometer-level displacement resolution. However, they also suffer from significant nonlinear errors that require compensation or correction using optical measurement techniques. Optical methods for microdisplacement measurement employ optical interferometry, gratings, and Fabry-Perot etalons, offering high measurement accuracy and subnanometer resolution. Interferometry, in particular, offers both a large measurement range and excellent linearity, making it suitable for calibrating the aforementioned microscopy and electrical measurement methods. The downside is that optical measurements typically have an optical resolution of half or quarter wavelength. Achieving nanometer-scale displacement measurement requires complex electronic segmentation and direction-determination circuits, and it's difficult to trace the optical wavelength (i.e., frequency) within a single optical stripe. Therefore, it's necessary to develop new displacement measurement technologies that can simultaneously achieve nanometer-scale resolution and measurement accuracy, while also being able to trace back to the laser wavelength or frequency without the need for electronic segmentation. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the optical system displacement measurement method in the prior art and to provide a high-resolution displacement measurement device and measurement method.

[0004] In order to achieve the above object, the present invention first provides a high-resolution displacement measuring device, which adopts the following technical solution:

[0005] High-resolution displacement measurement device, including:

[0006] Laser gain tube: a fixed reflector is provided at the first end and an antireflection window is provided at the second end;

[0007] Independent reflector: arranged at the second end side of the gain tube, outside the anti-reflection window, and combined with the laser gain tube and the fixed reflector to emit dual-longitudinal mode oscillation laser;

[0008] Wedge-shaped glass: placed between the independent reflector and the anti-reflection window, one of its two surfaces on the optical path is perpendicular to the laser axis, and the other surface is inclined to the laser axis;

[0009] Beam splitter: set outside the fixed reflector;

[0010] Polarizer: set on the side of the reflected light path of the beam splitter;

[0011] High-frequency photodetector: set at the light output end of the polarizer, used to receive the beat frequency signal of the two longitudinal modes;

[0012] Frequency meter: receives the electrical signal output by the high-frequency photodetector to measure the frequency difference between the two longitudinal modes;

[0013] Beam splitter: It is placed on the side of the transmission light path of the beam splitter and is used to split the two longitudinal modes into beam one and beam two according to orthogonal polarization states;

[0014] Photoelectric detector: including a first photoelectric detector and a second photoelectric detector, which are respectively arranged on the propagation path of the first light beam and the propagation path of the second light beam to detect the light intensity of the two longitudinal modes;

[0015] Subtractor: The output signal of the first photodetector and the output signal of the second photodetector are respectively input to the subtractor to determine the positive and negative values ​​of the difference in the intensity of the two longitudinal modes;

[0016] Target: Installed with the wedge-shaped glass piece, it can drive the wedge-shaped glass piece to move synchronously;

[0017] Data processing unit: receives the positive and negative values ​​of the light intensity difference calculated by the subtractor, as well as the frequency difference of the two longitudinal modes measured by the frequency meter, and calculates the displacement of the wedge-shaped glass piece by combining the frequency difference and the positive and negative values ​​of the light intensity difference.

[0018] In some embodiments of the present invention, the light transmission direction of the polarizer forms an angle of 45° with the orthogonal polarization direction of the oscillating laser.

[0019] In some embodiments of the present invention, both surfaces of the wedge-shaped glass sheet located in the optical path are coated with anti-reflection coatings.

[0020] In some embodiments of the present invention, the wedge-shaped glass piece is connected to a displacement measuring rod via a fixing frame, and the fixing frame is movably mounted on a guide rail and can move along the guide rail; the displacement measuring rod contacts the target object to be measured, so that during the movement of the target object, the wedge-shaped glass piece is synchronously driven by the displacement measuring rod to move along the laser axis.

[0021] In some embodiments of the present invention, the following steps are included:

[0022] A dual longitudinal mode laser is used as the light source;

[0023] Move the wedge-shaped glass plate, measure the frequency difference between the two longitudinal modes of the laser output, and record the minimum value of the frequency difference between the two longitudinal modes Δ min and the maximum value Δ max , recorded as extreme points;

[0024] Measuring the laser output dual longitudinal mode intensity I / / and I ⊥ The positive and negative values ​​of the light intensity difference:

[0025] s=sign(I ⊥ -I / / );

[0026] During the measurement process, the object being measured and the wedge-shaped glass piece connected to it move synchronously;

[0027] The frequency difference between the two longitudinal modes of laser light at the beginning of the displacement is Δv0, and the frequency difference between the two longitudinal modes of laser light at the end of the displacement is Δv;

[0028] The first time the frequency difference between the two longitudinal modes reaches the extreme point during the displacement process is Δv1, and the last time the frequency difference between the two longitudinal modes passes the extreme point before the end of the displacement is Δv2. The total number of times the frequency difference between the two longitudinal modes passes the extreme point during the displacement process is m, and the light intensity I of the two longitudinal modes is recorded in real time. / / and I ⊥ ;

[0029] Based on the positive and negative frequency difference and intensity difference of the dual longitudinal mode oscillation laser, the fractional part Δl of the single displacement of the measured target is calculated:

[0030]

[0031] Where λ is the laser wavelength;

[0032] If the frequency difference between the two longitudinal modes does not reach the extreme value during the displacement process, then Δv1 = Δv2 = 0, and the displacement of the target object is ΔL = Δl;

[0033] If the frequency difference between the two longitudinal modes reaches an extreme value during the displacement process, the displacement direction is determined according to the sign of Δl, and the displacement of the target object including the integer part is calculated as:

[0034]

[0035] Here, m is an integer.

[0036] In some embodiments of the present invention, the method for obtaining m includes: recording the change of the frequency difference Δv between the two longitudinal modes of laser light during the displacement adjustment process, and whenever the frequency difference Δv between the two longitudinal modes of laser light changes from a maximum value to a minimum value or from a minimum value to a maximum value, the displacement goes through a quarter wavelength period, and the accumulated integer m increases by 1.

[0037] Compared with the prior art, the advantages and positive effects of the present invention are:

[0038] 1. By correlating the frequency difference of the laser oscillation longitudinal mode with the displacement of the target object, the high precision and high resolution of frequency measurement can be fully utilized, so that the displacement measurement can reach sub-nanometer high resolution, which is conducive to application in the field of micro-displacement measurement.

[0039] 2. The target displacement changes by half a wavelength, which corresponds to a frequency difference of one cycle between the two longitudinal modes of the laser. This makes the displacement measurement unnecessary for other reference standards and can be traced back to the natural standard of the laser wavelength.

[0040] 3. This measurement method can perform micro-displacement measurement and direction determination without the need for complex subdivision and direction determination circuits. The measurement device structure is simpler and has high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the coupling principle between the reflected light from the wedge-shaped glass plate in the resonant cavity and the oscillating laser;

[0042] Figure 2 Schematic diagram of the polarization state and frequency difference between the two oscillating longitudinal modes of the laser;

[0043] Figure 3 Schematic diagram of the laser longitudinal mode intensity and frequency difference tuning caused by the displacement of the glass plate in the cavity;

[0044] Figure 4 Schematic diagram of the high-resolution displacement measurement device of the present invention.

[0045] In the above figures:

[0046] 1-Laser gain tube;

[0047] 2-Fixed reflector;

[0048] 3-antireflection window;

[0049] 4-Independent reflector;

[0050] 5- glass piece;

[0051] 601-fixed frame, 602-displacement measuring rod;

[0052] 7-Spectroscope;

[0053] 8-polarizer;

[0054] 9-High frequency photodetector;

[0055] 10-Frequency meter;

[0056] 11-beam splitter prism;

[0057] 1201 - first photodetector, 1202 - second photodetector;

[0058] 13-Subtractor;

[0059] 14-Data processing unit;

[0060] 15-Target object. DETAILED DESCRIPTION

[0061] The present invention is described in detail below by way of exemplary embodiments, but it should be understood that elements, structures, and features of one embodiment may be beneficially combined in other embodiments without further description.

[0062] In the description of the present invention, it should be noted that the terms "upper", "lower", "front", "back", etc., indicating directions or positional relationships, are based on the positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the present invention.

[0063] It should be noted that when an element is referred to as being "disposed on," "connected to," or "fixed to" another element, it may be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or indirectly connected to the other element. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance.

[0064] The present invention provides a high-resolution displacement measurement principle and a measuring device, which can achieve a displacement measurement accuracy of 0.1 nm based on the optical measurement principle.

[0065] First, the principle of the inventive concept is explained.

[0066] refer to Figure 1 The semi-external cavity laser consists of a fixed reflector 2 and an independent reflector 4 forming a laser resonator. Oscillation is achieved through the gain of a laser gain tube 1 between the fixed reflector 2 and the antireflection window 3. The reflection coefficients of the fixed reflector 2 and the independent reflector 4 are assumed to be r1 and r2, respectively, and the transmission coefficients of the two surfaces of the antireflection window 3 are t3 and t4, respectively. A wedge-shaped glass plate 5 is placed in the open portion of the resonator, adjusted so that one surface is perpendicular to the laser axis, resulting in reflection and transmission coefficients of r6 and t6, respectively. The other surface is tilted relative to the laser axis, resulting in a transmission coefficient of r5.

[0067] The surfaces of the wedge-shaped glass piece 5 refer to its two surfaces located in the optical path: one vertical surface and one inclined surface. The vertical surface is perpendicular to the direction of light propagation, while the inclined surface is angled relative to the direction of light propagation. The orientation of the inclined surface is not limited; it can be oriented toward either the fixed reflector 2 or the independent reflector 4, achieving the effects described in the present invention. The following explanation of the principles and embodiments of the present invention uses the example of a wedge-shaped glass piece 5 with its inclined surface oriented toward the fixed reflector 2.

[0068] refer to Figure 2 , the semi-external cavity laser operates in dual longitudinal modes. When the two longitudinal modes are in the left-right symmetrical position of the light output band relative to the center frequency, their respective light intensities are equal. At the same time, due to mode competition, the polarization states of the two longitudinal modes are orthogonal to each other (i.e., perpendicular), respectively expressed as ⊥ polarization state and / / polarization state. Let the longitudinal mode number of ⊥ polarization light be q, and the longitudinal mode number of / / polarization light be q+1, and the frequency difference between them is Δv=v q+1 -v q . If the influence of the wedge-shaped glass piece 5 placed in the resonant cavity is not taken into account, the light intensity and frequency of the two oscillating longitudinal modes are determined only by the gain medium and the resonant cavity parameters. When the laser is in a stable working state, the frequency difference between the two output frequencies remains unchanged. When the wedge-shaped glass piece 5 is placed in the resonant cavity, the reflected light on its surface is coupled with the oscillating laser, and the laser resonance conditions are satisfied together, which will cause the light intensity and frequency of the two longitudinal modes to change. What is particularly important is that for a standing wave laser, the light field distribution in the cavity changes periodically along the axial direction, and its period is half a wavelength. When the wedge-shaped glass piece 5 changes its position in the resonant cavity along the laser axis (i.e., it is displaced), the effect on the light intensity and frequency of the two longitudinal modes also changes periodically, resulting in a tuning effect with a certain amplitude of change.

[0069] refer to, Figure 1 , assume that the complex amplitudes of the electric field vectors of the initial light waves emitted from the fixed reflector 2 in the resonant cavity are E0 and ⊥ , E0 / / , propagates to the right and is reflected by the independent reflector 4, and the light beam formed is in the positive direction. The light wave propagates to the right, is reflected by the independent reflector 4, and propagates to the left to form the main electric field vector E1 ⊥， / / ; At the same time E0 ⊥， / / After being weakly reflected by the surface of the wedge-shaped glass piece 5, the electric field vector propagating to the right is E2 ⊥， / / ;E1 ⊥， / / After being weakly reflected by the surface of the wedge-shaped glass piece 5, it propagates to the right and is reflected by the independent reflector 4. It then passes through the wedge-shaped glass piece 5 to form an electric field vector E3 that propagates to the left. ⊥， / / There are also multiple reflections between the wedge-shaped glass plate 5 and the fixed reflector 2 and the independent reflector 4 to form high-order reflected light beams. Due to the anti-reflection coating on the surface of the wedge-shaped glass plate, the intensity of the high-order reflected light formed by multiple reflections is weakened by more than two orders of magnitude compared with the above-mentioned beams, and its influence on the longitudinal mode of the oscillating laser can be ignored. After the above-mentioned beams return to the initial point after a round trip in the resonant cavity, the electric field vector satisfies:

[0070]

[0071] Among them, gL a is the single-pass gain provided by the laser gain tube, L is the resonant cavity length, l is the distance between the surface of the wedge-shaped glass plate 5 perpendicular to the laser and the independent reflector 4, d is the thickness of the wedge-shaped glass plate 5 passing through the laser position, and n is the refractive index of the wedge-shaped glass plate 5. According to the self-consistency condition satisfied by the light field in the cavity, that is, the electric field vector E remains unchanged after the light wave travels back and forth in the resonant cavity, we can obtain:

[0072]

[0073] The oscillation mode in the laser resonant cavity satisfies the above equation. Simplifying it, we can obtain that the intensity and frequency of each of the two longitudinal modes satisfy the relationship:

[0074]

[0075] Where k1 = 2πv q / c,k2=2πv q+1 / c, is the wave number corresponding to the two longitudinal modes, c is the speed of light in vacuum. Solving the above formula, we can get the light intensity I of the two orthogonal polarization longitudinal modes ⊥ and I / / , and the frequency v q and v q+1 .

[0076] Since the laser operates in the visible light band, its frequency cannot be measured directly. What can be measured is the frequency difference between the two longitudinal modes, i.e. the longitudinal mode spacing. Without considering the tuning effect of the wedge-shaped glass piece 5 on the longitudinal mode, let the output light intensity and the longitudinal mode spacing be I0 and Δ0. Then, when the wedge-shaped glass piece 5 in the resonant cavity is displaced along the laser axis, i.e., the adjacent Figure 1 The distance l from the middle glass sheet to the independent reflector 4 changes, and the relative light intensity harmonic curve I of the two longitudinal modes is calculated according to equations (2) and (3): ⊥， / / / I0 and relative frequency difference tuning curve Δ / Δ0 are shown in the attached Figure 3 shown.

[0077] It can be seen that under the determined laser resonant cavity parameters and the coating parameters of the wedge-shaped glass plate 5, as l changes, the light intensity and frequency difference of the two oscillating longitudinal modes of the laser are modulated respectively, and the tuning curve changes one cycle per half wavelength; the frequency difference of the two oscillating longitudinal modes changes sinusoidally between the maximum and minimum values, and its modulation amplitude and maximum value Δ max and minimum value Δ min The difference is about Δv max =15MHz; the extreme point of the frequency difference tuning curve corresponds to the position where the light intensities of the two longitudinal modes are equal, that is, the equal intensity point of the light intensity tuning curve.

[0078] According to the above calculations, when the wedge-shaped glass piece 5 placed in the resonant cavity is translated along the laser axis, the frequency difference between the two longitudinal modes of the laser light changes accordingly. Furthermore, for every quarter-wavelength displacement of the glass piece (for the He-Ne laser used, the operating wavelength is λ = 632.8 nm), the frequency difference between the two longitudinal modes of the laser light changes from minimum to maximum, or vice versa. Since frequency can be precisely measured, if the measurement resolution of the laser frequency difference is dv = 10 kHz, the corresponding displacement resolution of the wedge-shaped glass piece 5 is approximately:

[0079]

[0080] This allows for sub-nanometer resolution measurement of the displacement of the wedge-shaped glass plate 5 in the cavity. Since the frequency difference between the two longitudinal modes varies periodically, in order to determine the direction of the displacement of the glass plate, a tuning cycle can be divided into two intervals, A and B, based on the intensity of the two polarized lights, as shown in the attached figure. Figure 3 As shown. Among them, the A interval corresponds to the light intensity I of the two polarized lights. ⊥ ≥I / / , interval B corresponds to I / / ≥I ⊥ The displacement direction symbol can be determined by I ⊥ -I / / As a result, we set the A interval as the positive zone and the B interval as the negative zone. When the wedge-shaped glass piece moves along the laser axis, if the laser frequency difference increases, and I ⊥ -I / / If the sign is positive, it means that the displacement direction of the glass sheet is the direction of increasing l (set as positive), that is, area A is along the positive direction of the horizontal coordinate; if the laser frequency difference becomes smaller, and I ⊥ -I / / If the sign is negative, it also means that the displacement direction of the glass sheet is in the direction of increasing l, that is, area B is along the positive direction of the horizontal coordinate. On the contrary, it means that the displacement direction of the glass sheet is in the direction of decreasing l (set as the reverse direction), that is, area A and area B are along the negative direction of the horizontal coordinate. In summary, the sign of the light intensity difference between the two longitudinal modes can be used as the basis for determining the displacement direction, that is, combined with sign(I ⊥ -I / / ) and the change in frequency difference, the displacement measurement of the glass sheet in the cavity can be achieved with a resolution of 0.1nm and the translation direction can be discerned.

[0081] refer to Figure 3 , when the displacement of the wedge glass piece spans area A and area B, that is, in addition to the fractional part of a quarter wavelength, there is also an integer part that passes through the frequency difference extreme point, it can be judged by the following method: Assume that at the beginning of the displacement measurement, the frequency difference value of the two longitudinal mode lasers is Δv0. Therefore, when the frequency difference reaches the extreme point for the first time, the frequency difference extreme value at this time is recorded as Δv1 (Δv1 = Δ max or Δ min ), can be based on the attached Figure 3 The decimal part of the displacement corresponding to the starting segment is calculated as:

[0082]

[0083] Where λ is the laser wavelength; the sign of Δl1 determines the positive or negative direction of the displacement of the wedge glass. After the frequency difference of the two longitudinal modes passes the extreme point, each subsequent change from the maximum value to the minimum value or from the minimum value to the maximum value represents that the displacement has passed the adjacent Figure 3 Half of the mid-frequency difference tuning curve is a quarter wavelength cycle. Assuming that the frequency difference value increases by 1 every time it reaches the extreme point, the number of displacement cycles passed is: (-1). When the displacement ends, the frequency difference between the two longitudinal mode lasers is Δv, and the frequency difference of the last time it passed the extreme point was Δv2 (Δv2 = Δ max or Δ min ), then the decimal part of the displacement from the extreme point to the stop position is:

[0084]

[0085] According to the recorded frequency difference and intensity difference of the two longitudinal modes (I ⊥ -I / / ) can be used to calculate the decimal part of the displacement of the measured target, Δl:

[0086]

[0087] So far, the measurement of the total displacement of the wedge-shaped glass can be divided into two cases:

[0088] (1) When the displacement is very small and the frequency difference between the two longitudinal modes does not reach the extreme point, Δv1 and Δv2 cannot take values ​​and can be set to 0. According to equations (5) and (6), the total displacement is:

[0089]

[0090] (2) When the displacement is large, the two longitudinal modes reach the extreme point many times, the total number of times is m, and the corresponding integer part of the displacement is The total displacement consists of a fractional part Δl1+Δl2 and an integer part. The sign of the integer part can be determined by the direction of the fractional part. The total displacement of the corresponding wedge-shaped glass piece is:

[0091]

[0092] Wherein, Δl is calculated according to formula (7). Based on the above high-resolution displacement measurement principle, the following high-resolution displacement measurement device is provided.

[0093] A first embodiment of the present invention provides a high-resolution displacement measuring device.

[0094] In order to achieve the above object, the present invention first provides a high-resolution displacement measuring device, which adopts the following technical solution:

[0095] High-resolution displacement measurement device, structural reference Figure 4 , the specific composition structure is as follows.

[0096] Laser gain tube 1: A fixed reflector 2 is provided at the first end thereof, and an antireflection window 3 is provided at the second end thereof.

[0097] Independent reflector 4: arranged at the second end side of the laser gain tube 1 and located outside the anti-reflection window 3, it combines with the laser gain tube 1 and the fixed reflector 2 to emit dual-longitudinal mode oscillation laser.

[0098] The wedge-shaped glass piece 5 is disposed between the independent reflector 4 and the anti-reflection window 3. Of the two surfaces located in the optical path, one surface is perpendicular to the laser axis, and the other surface is inclined to the laser axis. In some embodiments of the present invention, both surfaces of the wedge-shaped glass piece 5 located in the optical path are coated with an anti-reflection film.

[0099] The above main structure and Figure 1 The disclosed structures are the same, and the transmission principles of the optical paths are also the same. In order to measure displacement, it is necessary to solve the problems of longitudinal mode frequency difference and the detection of positive and negative directions of light intensity.

[0100] In order to achieve displacement measurement, the measuring device further includes the following structure.

[0101] Beam splitter 7: It is arranged outside the fixed reflector 2 and located on the outgoing light path of the fixed reflector 2 to split the laser into reflected light and transmitted light.

[0102] Polarizer 8: It is arranged on the side of the reflected light path of the beam splitter 7; the light transmission direction of the polarizer 8 forms an angle of 45° with the direction of the bisector of the angles of the orthogonal polarization directions of the two oscillation modes, that is, the light transmission direction of the polarizer 8 forms an angle of 45° with the polarization direction of the oscillating laser.

[0103] High-frequency photodetector 9: Located at the light output end of polarizer 8, it receives the beat signal of the two longitudinal modes. After passing through polarizer 8, the two longitudinal modes form a light beat, the frequency of which is detected by high-speed, high-frequency photodetector 9. Because the beat signal formed by the two longitudinal modes is a high-frequency signal, typically reaching several hundred MHz, a high-frequency photodetector 9 is used here.

[0104] Frequency meter 10: receives the electrical signal output by the high-frequency photoelectric detector 9 to measure the frequency difference between the two longitudinal modes; the electrical signal of the two longitudinal mode frequencies of the high-frequency photoelectric detector 9 is input into the frequency meter 10, and the frequency meter 10 automatically calculates the frequency difference value.

[0105] Beam splitter prism 7: arranged on one side of the transmission light path of the beam splitter 7, used to split the two longitudinal modes into beam one and beam two according to orthogonal polarization states.

[0106] Photoelectric detector: includes a first photoelectric detector 1201 and a second photoelectric detector 1202, which are respectively arranged on the propagation path of light beam one and light beam two; the two photoelectric detectors measure the light intensity of light beam one and light beam two.

[0107] Subtractor 13: The output light from first photodetector 1201 and the output signal from second photodetector 1202 are input to the subtractor to determine the positive or negative value of the intensity difference between the two longitudinal modes. Specifically, subtractor 13 employs a voltage comparator, which converts the intensity values ​​of the two polarization states recorded by first photodetector 1201 and second photodetector 1202 into voltage values ​​and then calculates and compares the positive and negative values.

[0108] Target 15: installed together with the wedge-shaped glass piece 5, can drive the wedge-shaped glass piece 5 to move synchronously.

[0109] Data processing unit 14 receives the positive and negative values ​​of the light intensity difference calculated by subtractor 13, as well as the frequency difference between the two longitudinal modes measured by frequency counter 10. It combines the frequency difference and the positive and negative values ​​of the light intensity difference to calculate the displacement of glass piece 5. Because target object 15 and wedge-shaped glass piece 5 move synchronously, the measured displacement of wedge-shaped glass piece 5 is the displacement of the target object.

[0110] Based on the frequency value measured by the high-frequency photodetector 9 and the light intensity values ​​measured by the first photodetector 1201 and the second photodetector 1202, the following can be plotted: Figure 3 The corresponding curve of the displacement of the wedge-shaped glass piece 5 and the change of light intensity is shown.

[0111] get Figure 3 The curve shown in the figure shows that the upper curve is the frequency difference fluctuation curve, and the lower curve corresponds to the frequency curve of the two longitudinal modes. Figure 3 The curve shown in Figure 2 obtains and stores the following data:

[0112] Δvmax : The maximum value of the fluctuation curve of the frequency difference between the two longitudinal modes, that is, the difference between the maximum value and the minimum value of the fluctuation curve, corresponding to the difference between the peak value and the trough value of the upper frequency difference fluctuation curve;

[0113] Δ min : The minimum value of the fluctuation curve of the frequency difference between the two longitudinal modes corresponds to the minimum frequency value of the upper frequency difference fluctuation curve, that is, the trough value.

[0114] In practical applications, the above measuring device can be adapted and arranged in an optical system to perform synchronous measurement of the displacement of the target object 15 .

[0115] To synchronize the motion of the target 15 and the wedge-shaped glass piece 5, in some embodiments of the present invention, the wedge-shaped glass piece 5 is connected to a displacement measuring rod 602 via a fixture 601. A guide rail is provided below the fixture 601, along which the fixture 601 is movably mounted and movable. The displacement measuring rod 602 contacts the target object, so that the target's motion synchronously drives the wedge-shaped glass piece 5 to move along the laser axis. The motion of the wedge-shaped glass piece 5 reflects the motion of the target 15.

[0116] A second embodiment of the present invention provides a high-resolution displacement measurement method.

[0117] The following steps are involved:

[0118] S1: Use dual longitudinal mode oscillator laser as light source;

[0119] S2: Move the wedge-shaped glass plate, measure the frequency difference between the two longitudinal modes of the laser output, and record the minimum value of the frequency difference between the two longitudinal modes Δ min and the maximum value Δ max , recorded as extreme points;

[0120] Measuring the laser output dual longitudinal mode intensity I / / and I ⊥ The positive and negative values ​​of the light intensity difference:

[0121] s=sign(I ⊥ -I / / );

[0122] During the measurement process, the object being measured and the wedge-shaped glass piece connected to it move synchronously;

[0123] The frequency difference between the two longitudinal modes of laser light at the beginning of the displacement is Δv0, and the frequency difference between the two longitudinal modes of laser light at the end of the displacement is Δv;

[0124] The first time the frequency difference between the two longitudinal modes reaches the extreme point during the displacement process is Δv1, and the last time the frequency difference between the two longitudinal modes passes the extreme point before the end of the displacement is Δv2. The total number of times the two longitudinal modes pass the extreme point during the displacement process is M, and the light intensity I of the two longitudinal modes is recorded in real time. / / and I ⊥ ;

[0125] Based on the positive and negative frequency difference and intensity difference of the dual longitudinal mode oscillation laser, the fractional part Δl of the single displacement of the measured target is calculated:

[0126]

[0127] Where λ is the laser wavelength;

[0128] If the frequency difference between the two longitudinal modes does not reach the extreme value during the displacement process, then Δv1=Δv2=0, and the total displacement is ΔL=Δl;

[0129] If the frequency difference between the two longitudinal modes reaches an extreme value during the displacement process, the displacement direction is determined according to the sign of Δl, and the total displacement including the integer part is calculated as:

[0130]

[0131] Where: m is an integer, Δ min is the minimum value of the frequency difference between the two longitudinal modes of the laser, Δv max is the maximum value of the frequency difference between the two longitudinal modes of the laser, and λ is the laser wavelength.

[0132] The method to obtain m is:

[0133] The method for obtaining m includes: recording the change of the frequency difference Δv between the two longitudinal modes of laser light during the displacement adjustment process, such as Figure 3 As shown, whenever the frequency difference Δv between the two longitudinal modes changes from a maximum value to a minimum value or from a minimum value to a maximum value, the displacement goes through a quarter wavelength cycle, and the accumulated integer m increases by 1.

[0134] Considering displacement direction, in practical applications, the target's movement from the start to the stop is considered a single displacement measurement. If the target continues to move, the above-described displacement measurement results are accumulated. If the target moves back and forth multiple times within a range, the multiple starts and stops during these round trips are considered a combination of multiple single displacement measurements, rather than a single measurement with accumulated m values. Each time the target stops, a single displacement measurement is completed and a result is given. When movement resumes, the next single measurement is continued, and the displacement is accumulated.

[0135] The displacement measurement method of the wedge-shaped glass sheet 5 provided by the present invention, during the displacement measurement process, if the displacement change is within the range of a quarter wavelength, the decimal part of the displacement is calculated by measuring Δv; if the change exceeds .... / / =I ⊥ The position point is recorded cumulatively and the integer value of the displacement is recorded.

[0136] Since the target object 15 and the wedge-shaped glass piece 5 can move synchronously, the displacement of the wedge-shaped glass piece 5 obtained by measurement and calculation is reflected as the displacement of the target object 15 .

[0137] The above description is merely a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any person skilled in the art may utilize the technical contents disclosed above to change or modify them into equivalent embodiments with equivalent changes for application in other fields. However, any simple modification, equivalent change, and modification of the above embodiments made in accordance with the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A high-resolution displacement measurement method, characterized in that: The measuring method is implemented based on a high-resolution displacement measuring device, which comprises: Laser gain tube: a fixed reflector is provided at the first end and an anti-reflection window is provided at the second end; Independent reflector: arranged at the second end side of the gain tube, located outside the anti-reflection window, and combined with the laser gain tube and the fixed reflector to emit dual longitudinal mode oscillation laser; Wedge-shaped glass sheet: arranged between the independent reflector and the anti-reflection window sheet, one of the two surfaces located on the optical path is perpendicular to the laser axis, and the other surface is inclined to the laser axis; Beam splitter: set outside the fixed reflector; Polarizer: set on the reflected light path side of the beam splitter; High-frequency photodetector: set at the light output end of the polarizer, used to receive the beat frequency signals of the two longitudinal modes; Frequency meter: It receives the electrical signal output by the high-frequency photodetector to measure the frequency difference between the two longitudinal modes; Beam splitter: It is set on one side of the transmission light path of the beam splitter and is used to split the two longitudinal modes into beam one and beam two according to orthogonal polarization states; Photoelectric detector: including a first photoelectric detector and a second photoelectric detector, which are respectively arranged on the propagation optical path of the light beam one and the propagation optical path of the light beam two to detect the light intensity of the two longitudinal modes; The measuring method comprises the following steps: A dual longitudinal mode laser is used as the light source; Move the wedge-shaped glass plate, measure the frequency difference between the two longitudinal modes of the laser output, and record the minimum value of the frequency difference between the two longitudinal modes Δ min and the maximum value Δ max , recorded as extreme points; Measuring the laser output dual longitudinal mode intensity I / / and I ⊥ The positive and negative values ​​of the light intensity difference: s=sign(I ⊥ -I / / ); During the measurement process, the target object and the wedge-shaped glass piece connected to it move synchronously; The frequency difference between the two longitudinal modes of the laser is Δv0 at the beginning of the displacement, and the frequency difference between the two longitudinal modes of the laser is Δv after the displacement ends. The first time the two longitudinal mode laser frequency difference reaches the extreme point during the displacement process is Δv1, and the last time the two longitudinal mode laser frequency difference passes the extreme point before the end of the displacement is Δv2. The total number of times the two longitudinal mode laser frequency difference passes the extreme point during the displacement process is m, and the light intensity I of the two longitudinal mode lasers is recorded in real time. / / and I ⊥ ; Based on the frequency difference and intensity difference of the dual longitudinal mode oscillation laser, the fractional part Δl of the single displacement of the measured target is calculated: Where λ is the laser wavelength; If the frequency difference between the two longitudinal modes does not reach the extreme value during the displacement process, then Δv1=Δv2=0, and the displacement of the target object is ΔL=Δl; If the frequency difference between the two longitudinal modes reaches the extreme value during the displacement process, the displacement direction is determined according to the positive and negative signs of Δl, and the displacement of the target object including the integer part is calculated as: Here, m is an integer.

2. The high-resolution displacement measurement method according to claim 1, characterized in that: The measuring device also includes: Subtractor: The output signal of the first photodetector and the output signal of the second photodetector are respectively input to the subtractor to determine the positive and negative values ​​of the intensity difference between the two longitudinal modes; Target: Installed with the wedge-shaped glass piece, it can drive the wedge-shaped glass piece to move synchronously; Data processing unit: receiving the positive and negative values ​​of the light intensity difference calculated by the subtractor, and the frequency difference of the two longitudinal modes measured by the frequency meter, and calculating the displacement of the wedge-shaped glass piece by combining the frequency difference and the positive and negative values ​​of the light intensity difference.

3. The high-resolution displacement measurement method according to claim 1, characterized in that: The light transmission direction of the polarizer forms an angle of 45° with the orthogonal polarization direction of the oscillating laser.

4. The high-resolution displacement measurement method according to claim 1, characterized in that: The two surfaces of the wedge-shaped glass sheet located in the light path are both coated with anti-reflection films.

5. The high-resolution displacement measurement method according to claim 1, characterized in that: The wedge-shaped glass piece is connected to the displacement measuring rod through a fixing frame, and the fixing frame is movably mounted on the guide rail and can move along the guide rail; the displacement measuring rod contacts the target object to be measured, so that during the movement of the target object, the wedge-shaped glass piece is synchronously driven to move along the laser axis through the displacement measuring rod.

6. The high-resolution displacement measurement method according to claim 1, characterized in that: The method for obtaining m includes: recording the change of the frequency difference Δv between the two longitudinal modes of the laser during the displacement adjustment process, and whenever the frequency difference Δv between the two longitudinal modes of the laser changes from a maximum value to a minimum value or from a minimum value to a maximum value, the displacement goes through a quarter wavelength period, and the accumulated integer m increases by 1.

Images