Micro displacement measurement method and system based on laser self-mixing interferometer

Abstract

The invention provides an infinitesimal displacement measurement method and system based on a laser self-mixing interferometer, and relates to the technical field of displacement measurement, and the method comprises the steps: obtaining a to-be-measured object; the method comprises the following steps: modulating a self-mixing interferometer through a sinusoidal phase of a helium-neon laser, and extracting an interference signal containing displacement information of an object to be measured; extracting an in-phase component and an orthogonal component from the interference signal through a phase generation carrier technology to form an orthogonal signal pair; correcting a Lissajous figure generated by the orthogonal signal pair by using an ellipse fitting algorithm to obtain a corrected orthogonal signal pair; phase demodulation is carried out on the corrected orthogonal signal pair, and phase information of the object to be measured is extracted; and determining the displacement of the to-be-measured object based on the phase information. According to the method, the ellipse fitting algorithm is used for correcting the Lissajous figure generated by the orthogonal signal pair, non-ideal factors are effectively compensated in the process, the phase demodulation precision is guaranteed, and the displacement measurement accuracy is remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of displacement measurement, in particular to a micro-displacement measurement method and system based on a laser self-mixing interferometer. BACKGROUND

[0002] Displacement measurement is a fundamental technology in the field of precision measurement, playing a bridge role in the measurement of other physical quantities such as force, pressure, temperature, etc. With the progress of science and technology, traditional displacement measurement methods are gradually facing challenges in terms of measurement accuracy, speed, and cost. Laser-based non-contact micro-displacement measurement technology has been widely used in industrial production, aerospace, civil engineering, biomedicine, etc. due to its advantages of high precision, non-contact, and long-distance measurement. Among these technologies, the laser self-mixing interferometer (SMI) has gradually become an important tool in the field of displacement measurement due to its low cost, small size, and no need for complex optical structures.

[0003] Currently, the laser self-mixing interferometer (SMI) based on optical feedback effect is widely used for micro-displacement measurement. This technology encodes the displacement information of an object by reflecting or scattering the light emitted by a laser on the surface of the object. When the feedback light returns to the laser cavity, it interferes with the light field inside the cavity, causing changes in the output power and frequency of the laser. By accurately demodulating these changes, the micro-displacement information of the object can be extracted.

[0004] However, existing technologies usually ignore the non-ideal factors caused by phase modulation depth and carrier phase delay, which significantly reduce the demodulation accuracy and affect the accuracy and stability of the measurement results. SUMMARY

[0005] In view of the above shortcomings of the prior art, the purpose of the embodiments of the present application is to provide a micro-displacement measurement method based on a laser self-mixing interferometer, which can solve the technical problem that existing technologies usually ignore the non-ideal factors caused by phase modulation depth and carrier phase delay, which significantly reduce the demodulation accuracy and affect the accuracy and stability of the measurement results.

[0006] The first aspect of the embodiments of the present application proposes a micro-displacement measurement method based on a laser self-mixing interferometer, comprising:

[0007] S1: obtaining an object to be measured;

[0008] S2: extracting an interference signal containing displacement information of the object to be measured through a sinusoidal phase modulation self-mixing interferometer of a helium-neon laser;

[0009] S3: extracting in-phase and quadrature components from the interference signal through a phase generation carrier technique to form a quadrature signal pair;

[0010] S4: correcting a Lissajous figure generated by the quadrature signal pair by using an ellipse fitting algorithm to obtain a corrected quadrature signal pair;

[0011] S5: performing phase demodulation on the corrected quadrature signal pair to extract phase information of the object to be measured;

[0012] S6: determining displacement of the object to be measured based on the phase information.

[0013] A second aspect of the embodiment of the present application provides a micro-displacement measurement system based on a laser self-mixing interferometer, comprising a processor and a memory.

[0014] The memory stores programs or instructions executable on the processor, and the programs or instructions are executed by the processor to implement the steps of the micro-displacement measurement method based on the laser self-mixing interferometer according to the first aspect.

[0015] A third aspect of the embodiment of the present application provides a readable storage medium, and the readable storage medium stores programs or instructions, and the programs or instructions are executed by a processor to implement the steps of the micro-displacement measurement method based on the laser self-mixing interferometer according to the first aspect.

[0016] The technical scheme provided by the embodiment of the present application has at least the following beneficial effects:

[0017] In the embodiment of the present application, the in-phase and quadrature components are extracted by the phase generation carrier technology, which effectively reduces the non-ideal errors caused by PMD and CPD. Then, the Lissajous figure generated by the quadrature signal pair is corrected by using the ellipse fitting algorithm, which eliminates the non-linear errors and makes the signal closer to the ideal quadrature form. This process effectively compensates for the non-ideal factors, ensures the accuracy of phase demodulation, and significantly improves the accuracy and stability of displacement measurement. BRIEF DESCRIPTION OF DRAWINGS

[0018] The accompanying drawings are included to provide a further understanding of the embodiments, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application. In the drawings:

[0019] Figure 1 is a flowchart of a micro-displacement measurement method based on a laser self-mixing interferometer provided by the embodiment of the present application;

[0020] Figure 2is a schematic diagram of an SPM-SMI measurement system provided by the embodiment of the present application.

[0021] Figure 3 is a schematic diagram of an improved demodulation scheme of SPM-SMI provided by the embodiment of the present application.

[0022] Figure 4 is a structural schematic diagram of a micro displacement measurement system based on a laser self-mixing interferometer provided by the embodiment of the present application. DETAILED DESCRIPTION

[0023] In order to make the person in the art better understand the technical solutions in the embodiment of the present application, the technical solutions of the present application will be described clearly and completely in combination with the drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. It should be understood that these descriptions are only exemplary, and are not used to limit the scope of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor should belong to the scope of protection of the present application.

[0024] The micro displacement measurement method based on the laser self-mixing interferometer provided by the embodiment of the present application will be described in detail in combination with the drawings and specific embodiments and application scenarios.

[0025] Referring to the drawings attached to the specification, Figure 1 , a flowchart of the micro displacement measurement method based on the laser self-mixing interferometer provided by the embodiment of the present application is shown.

[0026] Referring to the drawings attached to the specification, Figure 2 , a schematic diagram of an SPM-SMI measurement system provided by the embodiment of the present application is shown.

[0027] Referring to the drawings attached to the specification, Figure 3 , a schematic diagram of an improved demodulation scheme of SPM-SMI provided by the embodiment of the present application is shown.

[0028] The micro displacement measurement method based on the laser self-mixing interferometer provided by the embodiment of the present application can include the following steps:

[0029] S1: obtaining an object to be measured.

[0030] S2: extracting an interference signal containing displacement information of the object to be measured through a sinusoidal phase modulation self-mixing interferometer of a helium-neon laser.

[0031] The sinusoidal phase modulation self-mixing interferometer (SPM-SMI) of the helium-neon laser is a non-contact displacement measurement technology based on optical feedback effect, which has the advantages of high precision, low cost, simple structure, etc. It is widely used in precision measurement and industrial detection fields, especially in the measurement of small displacement, such as MEMS (Micro Electro Mechanical System) devices, vibration monitoring, etc. SPM-SMI combines laser self-mixing interferometer (SMI) and sinusoidal phase modulation technology, which can provide high resolution and high stability of displacement measurement.

[0032] In a possible implementation, the sinusoidal phase modulation self-mixing interferometer of the helium-neon laser specifically comprises:

[0033] A photodetector (PD), a helium-neon laser, an aperture (D), a polarizer (P), a neutral density (ND), a filter, an EOM phase modulator, and a nanometer positioner.

[0034] The photodetector (PD), the helium-neon laser, the aperture (D), the polarizer (P), the neutral density filter (ND), the EOM phase modulator, and the nanometer positioner are sequentially connected.

[0035] In a possible implementation, S2 specifically comprises:

[0036] S201: The helium-neon laser emits light, which is adjusted by the aperture (D), the polarizer (P), and the neutral density filter (ND) in sequence.

[0037] In the embodiment of the present application, the intensity and polarization state of the light beam are adjusted, which helps to optimize the quality of the interference signal and avoid errors caused by too strong or too weak light signals.

[0038] S202: The adjusted light beam is phase-modulated by the EOM phase modulator.

[0039] S203: The phase-modulated light beam is irradiated to the object to be measured, and the feedback light is generated by the nanometer positioner.

[0040] S204: The feedback light passes through the EOM phase modulation, the neutral density filter (ND), the polarizer (P), and the aperture (D) in sequence, enters the cavity of the helium-neon laser, and interferes with the cavity light field to generate an interference signal containing displacement information of the object to be measured.

[0041] Specifically, the system configuration based on the sinusoidal phase modulation self-mixing interferometer is shown in the following figure: Figure 2As shown, the system integrates an EOM phase modulator. Linearly polarized light emitted from the helium-neon laser cavity passes through an aperture (D), a polarizer (P), various neutral density (ND) filters and an EOM (electro-optic modulator), and then is reflected by a nanometer positioner after being amplified by a power amplifier and driven by a signal transmitter. The feedback light returns to the laser cavity and interferes with the intracavity light field, which is a well-known self-mixing effect. The light intensity is modulated by the self-mixing effect, and finally converted into an electrical signal by a photodetector (PD). After being processed by an analog-to-digital converter (ADC), the signal is transmitted to a computer. Combined with the signal demodulation algorithm, the phase demodulation is finally realized. The phase and optical power of the SMI signal can be expressed as:

[0042]

[0043] wherein, represents the external cavity phase without feedback light, represents the external cavity phase with feedback light, and a represents a linewidth enhancement factor, f P (t) represents the laser output power with feedback light, P0 represents the laser output power without feedback light, C represents a linewidth enhancement factor, m represents a modulation depth factor, sin represents a sine function, cos represents a cosine function, and arctan represents an inverse tangent function.

[0044] Let l(t) represent the instantaneous distance between the helium-neon laser and the measured object. The distance is composed of two parts: one part is the initial distance l0 between the measured object and the laser, and the other part is the nanometer-level displacement d(t) realized by the nanometer positioner. It is known that λ0 is the wavelength of the laser, which can be rewritten as:

[0045]

[0046] wherein λ0 represents the initial distance between the measured object and the laser, l(t) represents the instantaneous distance between the helium-neon laser and the measured object, l0 represents the initial distance between the measured object and the laser, and d(t) represents the nanometer-level displacement realized by the nanometer positioner.

[0047] The analysis of the present application is based on the assumption of a weak feedback level, which means that is extremely similar to The high-frequency carrier signal used to drive the electro-optic modulator can be expressed as:

[0048] S c (t) = a1cos(ω c t)

[0049] wherein S c (t) represents the high-frequency carrier signal, a1 represents the amplitude of the carrier signal, and ωc t represents the frequency of the carrier signal.

[0050] Considering the phase modulation effect caused by the EOM, the interference signal obtained by the PD can be represented as:

[0051]

[0052] where S(t) represents the interference signal, A0 represents the DC bias, A1 represents the amplitude of the AC component sensitive to the feedback light intensity, A c represents the round-trip phase modulation depth value, θ c represents the CPD caused by circuit element delay and carrier phase jitter.

[0053] According to the first type Bessel function and the trigonometric function formula, equation (4) can be expanded as:

[0054]

[0055] where J0 represents the zero-order Bessel function, k represents the kth harmonic sideband of the carrier, J 2k represents the even-order Bessel function, J 2k+1 represents the odd-order Bessel function.

[0056] From the formula, it can be seen that the detected phase is modulated in the kth (0, 1,..., N) harmonic sideband of the carrier. Based on this characteristic, the orthogonal signal pair is successfully extracted from the first and second harmonic sidebands of the carrier frequency.

[0057] In the embodiments of the present application, by adjusting the light intensity and polarization state of the light beam, the clarity and stability of the interference signal are ensured. At the same time, the sinusoidal phase modulation and the self-collimation design of the feedback light can significantly improve the demodulation accuracy and reduce the measurement error.

[0058] S3: Extracting in-phase and quadrature components from the interference signal to form an orthogonal signal pair by phase generation carrier technology.

[0059] where the phase generation carrier technology (PGC) is a commonly used phase demodulation technology, widely used in interferometric measurement systems, especially in systems such as self-mixing interferometer (SMI), fiber optic sensor and laser interferometer. PGC technology achieves high-precision phase demodulation by multiplying the interference signal with a carrier signal (usually the fundamental frequency and the second harmonic), and then extracting the quadrature signal through low-pass filtering. Its main advantage is that it can overcome the noise in the interference signal, improve the demodulation stability and measurement accuracy.

[0060] Among them, the orthogonal signal pair refers to the phase and amplitude characteristics of two signals in a certain time or frequency range are not interfered with each other and independent of each other. Usually, the phase difference of the two signals is 90 degrees, or they satisfy certain orthogonal relationship in mathematics, so that they can be separated from each other by certain mathematical operation (such as inner product or Fourier transform).

[0061] In a possible implementation, S3 specifically includes:

[0062] S301: using PGC demodulation technology, the interference signal is mixed with a frequency carrier signal and a double frequency carrier signal.

[0063] S302: filtering the mixed interference signal through a low-pass filter to obtain an orthogonal signal pair:

[0064]

[0065] Among them, I(t) represents the in-phase component signal, alpha2 represents the amplitude of the double frequency carrier signal, A1 represents the amplitude of the alternating component sensitive to the feedback light intensity, A C represents the round-trip phase modulation depth value, J2 represents the second Bessel function, A C represents the round-trip phase modulation depth value, theta C represents the modulated phase, represents the external cavity phase without feedback light, Q(t) represents the quadrature component signal, alpha1 represents the amplitude of the one frequency carrier signal, J1 represents the first Bessel function, cos represents the cosine function, and sin represents the sine function.

[0066] In the embodiment of the application, after mixing, the frequency characteristics of the signal change, especially through the low-pass filter, these high-frequency noise components can be effectively filtered out, leaving only useful low-frequency signals. This helps to reduce the noise effect in the system, enhance the signal-to-noise ratio of the signal, and thus improve the accuracy of measurement.

[0067] S4: using an ellipse fitting algorithm to correct the Lissajous figure generated by the orthogonal signal pair to obtain a corrected orthogonal signal pair.

[0068] Among them, the ellipse fitting algorithm is a mathematical method commonly used in signal processing and data analysis, especially in the fields of interference signal, image processing, pattern analysis, etc. Its purpose is to fit an ideal ellipse through a set of data points to compensate for distortion or error in the signal, especially in the correction process of the Lissajous figure generated by the orthogonal signal pair.

[0069] In a possible implementation, S4 specifically includes:

[0070] S401: Draw a Lissajous figure based on the quadrature signal pair.

[0071] Wherein, the Lissajous figure is a special kind of figure proposed by French mathematician Jules Antoine Lissajous in the mid-19th century. This figure is composed of two orthogonal periodic motions on the plane, usually represented as the combination of two sinusoidal signals with a phase difference of 90 degrees at the same time. The Lissajous figure is characterized by reflecting the phase difference, frequency ratio and amplitude ratio between two signals (usually sinusoidal waves), and is widely used in signal analysis, vibration monitoring and measurement systems.

[0072] S402: Perform ellipse fitting on the Lissajous figure by least squares method to obtain the basic parameters of the ellipse, wherein the basic parameters include the length of the horizontal axis, the length of the vertical axis, the coordinates of the center point, and the inclination angle relative to the horizontal axis.

[0073] In one possible implementation, the calculation method of the basic parameters of the ellipse is specifically:

[0074]

[0075] Wherein, θ r represents the inclination angle of the ellipse, a represents the length of the major axis of the ellipse, b represents the length of the minor axis of the ellipse, arctan represents, x p represents the horizontal coordinate of the center point of the ellipse, y p represents the vertical coordinate of the center point of the ellipse, A represents the parameter controlling the horizontal axis of the ellipse, B represents the parameter controlling the inclination angle of the ellipse, C represents the parameter controlling the vertical axis of the ellipse, D represents the parameter controlling the translation of the ellipse in the x-axis direction, E represents the parameter controlling the translation of the ellipse in the y-axis direction, sin represents the sine function, and cos represents the cosine function.

[0076] S403: Based on the basic parameters, correct the quadrature signal pair using the correction formula to obtain the corrected quadrature signal pair:

[0077]

[0078] Wherein, I N (n) represents the corrected in-phase component signal, n represents the discrete sampling index, θ r represents the inclination angle of the ellipse, a represents the length of the major axis of the ellipse, b represents the length of the minor axis of the ellipse, Q(n) represents the quadrature component signal, I(n) represents the in-phase component signal, sin represents the sine function, and cos represents the cosine function, Q N (n) represents the corrected quadrature component signal.

[0079] In the embodiments of the present application, the generated Lissajous figure is corrected by an ellipse fitting algorithm, which can effectively eliminate signal errors caused by non-ideal factors (such as PMD and CPD), making the corrected quadrature signal pair more stable and accurate. This process not only improves the phase demodulation accuracy and the accuracy of displacement measurement, but also enhances the adaptability and robustness of the system, effectively reducing the influence of external environment and equipment errors, thereby providing more reliable data for precision measurement.

[0080] S5: Phase demodulation is performed on the corrected quadrature signal pair to extract the phase information of the measured object.

[0081] In one possible implementation, S5 specifically includes:

[0082] S501: Division operation is performed on the in-phase component signal and the quadrature component signal in the corrected quadrature signal pair to obtain a component signal ratio.

[0083] S502: Arctangent operation is performed on the component signal ratio to obtain preliminary phase information.

[0084] S503: Phase unwrapping operation is performed on the preliminary phase information to obtain final phase information with continuous phase:

[0085]

[0086] wherein, represents the preliminary phase information, i.e., the external cavity phase without feedback light, Unwrapping represents the phase unwrapping operation, α1 represents the amplitude of the first-order frequency carrier signal, J1 represents the first-order Bessel function, A c represents the round-trip phase modulation depth value, θ c represents the modulated phase, α2 represents the amplitude of the second-order frequency carrier signal, J2 represents the second-order Bessel function, sin represents the sine function, and cos represents the cosine function.

[0087] In the embodiments of the present application, the phase unwrapping operation makes the phase information smooth, avoiding measurement errors caused by periodic jumps, thereby improving the demodulation accuracy.

[0088] S504: The final phase information is output as the phase information of the measured object.

[0089] In one possible implementation, S5 further includes:

[0090] S505: Integration processing is performed on the in-phase component signal and the quadrature component signal in the corrected quadrature signal pair.

[0091] S506: Cross-multiplying the integrated in-phase component signal with the original quadrature component signal in the corrected quadrature signal pair and cross-multiplying the integrated quadrature component signal with the original in-phase component signal in the corrected quadrature signal pair to obtain a mixed in-phase component signal and a mixed quadrature component signal.

[0092] In the embodiment of the present application, by mixing and subtracting different components of the quadrature signal, the system can extract useful information from complex signals and remove interference, thereby improving the stability and robustness of the measurement.

[0093] S507: After subtracting the mixed in-phase component signal and the mixed quadrature component signal, differential processing is performed to obtain the phase information of the object to be measured.

[0094] In the embodiment of the present application, the integral processing and cross-multiplication operation can effectively reduce the noise component of the signal and enhance the accuracy of demodulation. By integral processing of the in-phase component signal (I) and the quadrature component signal (Q), the error caused by high-frequency noise of the signal can be suppressed, and the signal can be made smoother.

[0095] S6: Based on the phase information, the displacement of the object to be measured is determined.

[0096] Specifically, in the laser interferometric measurement system, the displacement of the object has a direct linear relationship with the phase. Through the phase change, the small displacement of the object can be calculated.

[0097] In the embodiment of the present application, based on the demodulated phase change, the linear relationship between the phase and the displacement is used to finally determine the displacement of the object to be measured. The key of this process is to accurately acquire and process the phase information, convert it into displacement data, and ensure effective compensation for noise, error and other factors in the actual measurement process. In this way, high-precision and stable small displacement measurement can be achieved.

[0098] The technical scheme provided by the embodiment of the present application has at least the following beneficial effects:

[0099] In the embodiment of the present application, the in-phase and quadrature components are extracted by the phase generation carrier technology, which effectively reduces the non-ideal error caused by PMD and CPD. Then, the ellipse fitting algorithm is used to correct the Lissajous figure generated by the corrected quadrature signal pair, which eliminates the non-linear error and makes the signal closer to the ideal quadrature form. This process effectively compensates for non-ideal factors, ensures the accuracy of phase demodulation, and significantly improves the accuracy and stability of displacement measurement.

[0100] Reference is made to the accompanying drawings Figure 4 , which shows a structure schematic diagram of a small displacement measurement system based on a laser self-mixing interferometer according to an embodiment of the present application.

[0101] The embodiment of the present application provides a kind of micro displacement measurement system 20 based on laser self-mixing interferometer, comprising: processor 201 and memory 202;

[0102] The memory 202 stores the program or instruction that can be run on the processor 201, the program or instruction is implemented when the processor 201 is executed The steps of the above-mentioned micro displacement measurement method based on laser self-mixing interferometer, and the same technical effect can be achieved, to avoid repetition, the present application will not be described again The present application will not be described again.

[0103] It should be understood that the processor 201 in the embodiment of the present application can be a central processing unit (CPU), and the processor can also be other general-purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), field programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc.The general-purpose processor can be a microprocessor or the processor can also be any conventional processor, etc.

[0104] It should also be understood that the memory 202 in embodiments of the present application can be volatile or nonvolatile memory, or can include both volatile and nonvolatile memory. Nonvolatile memory can be read-only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), electrically EPROM (EEPROM), or flash memory. Volatile memory can be random access memory (RAM), used as external cache. By way of example, and not limitation, many forms of random access memory (RAM) are available, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous dynamic RAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), Synchlink DRAM (SLDRAM), and direct rambus RAM (DR RAM).

[0105] The above-described embodiments can be implemented in part or in whole through software, hardware (e.g., circuitry), firmware, or any combination thereof. When implemented in software, the above-described embodiments can be implemented in the form of a computer program product. The computer program product includes one or more computer instructions or computer programs. When loaded and executed by a computer, the computer instructions or computer programs cause the computer to perform the processes or functions described above according to the embodiments of the present application. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable apparatus. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another computer-readable storage medium, such as from a website, a computer, a server, or a data center to another website, computer, server, or data center through a wired (e.g., infrared, wireless, microwave, or the like) manner. The computer-readable storage medium can be any available medium or a collection of medium accessible by a computer or a data storage device such as a server, data center, or the like, containing one or more of the available medium. The available medium can be a magnetic medium (e.g., a floppy diskette, a hard disk, a magnetic tape), an optical medium (e.g., a DVD), or a semiconductor medium. The semiconductor medium can be a solid-state hard disk.

[0106] It should be understood that the size of the serial number of each process described above in various embodiments of the present application does not mean the order of execution, and the execution order of each process should be determined by its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0107] Those of ordinary skill in the art can realize that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be realized in electronic hardware, or a combination of computer software and electronic hardware. Whether the functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0108] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described devices, apparatuses, and units can refer to the corresponding processes in the foregoing method embodiments, which will not be described here.

[0109] In several embodiments provided by the present application, it should be understood that the disclosed devices, apparatuses and methods can be implemented in other manners. For example, the embodiments of the apparatus described above are merely schematic. For example, the division of the units is only a logical function division. There can be another division manner for the actual implementation, for example, multiple units or components can be combined or integrated into another device, or some features can be ignored or not executed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections between different units, can be indirect couplings or communication connections through some interfaces, devices or units, and can be in electrical, mechanical or other forms.

[0110] The units described as separate components can or can not be physically separate, and the components shown as units can or can not be physical units, that is, can be located in one place, or can be distributed on multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the embodiments.

[0111] In addition, each functional unit in the various embodiments of the present application can be integrated into a processing unit, or each unit can exist physically, or two or more units can be integrated into one unit.

[0112] If the functions are realized in the form of software function units and sold or used as independent products, they can be stored in a computer readable storage medium. Based on this understanding, the technical solutions of the present application or the parts of the present application that essentially contribute to the prior art or the parts of the technical solutions can be embodied in the form of a software product. The computer software product is stored in a storage medium, and includes a plurality of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the method described in the various embodiments of the present application. The foregoing storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, and various media that can store program codes.

[0113] The embodiments of the present application provide a readable storage medium, which includes: a program or instructions stored on the readable storage medium, the program or instructions are executed by a processor to realize the steps of the above-mentioned micro-displacement measurement method based on a laser self-mixing interferometer, and the same technical effects can be achieved. To avoid repetition, the present application will not be described again.

[0114] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present application, but not to limit them. Although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application. Any changes or replacements that can be easily thought of by those skilled in the art within the technical scope disclosed by the present application should be covered within the protection scope of the present application.

Claims

1. A method for measuring a minute displacement based on a laser self-mixing interferometer, characterized by, The method comprises the following steps: S1: obtaining an object to be measured; S2: extracting an interference signal containing displacement information of the object to be measured by a sinusoidal phase modulation self-mixing interferometer of a helium-neon laser; S3: extracting in-phase and quadrature components from the interference signal by a phase generated carrier technique to form a quadrature signal pair; S4: correcting a Lissajous figure generated by the quadrature signal pair by an ellipse fitting algorithm to obtain a corrected quadrature signal pair; S5: performing phase demodulation on the corrected quadrature signal pair to extract phase information of the object to be measured; S6: determining displacement of the object to be measured based on the phase information.

2. The method of claim 1, wherein the laser self-mixing interferometer is a distributed feedback laser. The sinusoidal phase modulation self-mixing interferometer of the helium-neon laser comprises: a photodetector (PD), a helium-neon laser, an optical diaphragm (D), a polarizer (P), a neutral density (ND), a filter, an EOM phase modulator, and a nanometer positioner. The photodetector (PD), the helium-neon laser, the optical diaphragm (D), the polarizer (P), the neutral density filter (ND), the EOM phase modulator, and the nanometer positioner are sequentially connected.

3. The method of claim 2, wherein the laser self-mixing interferometer is a distributed feedback laser. The S2 specifically comprises: S201: the helium-neon laser emits light, which is sequentially adjusted by the optical diaphragm (D), the polarizer (P), and the neutral density filter (ND); S202: the adjusted light beam is phase-modulated by the EOM phase modulator; S203: the phase-modulated light beam is directed to the object to be measured, and the nanometer positioner generates feedback light; S204: the feedback light sequentially passes through the EOM phase modulator, the neutral density filter (ND), the polarizer (P), the optical diaphragm (D), and enters the cavity of the helium-neon laser, and interferes with the cavity light field to generate an interference signal containing displacement information of the object to be measured.

4. The method of claim 1, wherein the laser self-mixing interferometer is a distributed feedback laser. The S3 specifically comprises: S301: using a PGC demodulation technique, the interference signal is mixed with a frequency-doubled carrier signal and a frequency-tripled carrier signal; S302: the mixed interference signal is filtered by a low-pass filter to obtain a quadrature signal pair: where I(t) represents the in-phase component signal, a2 represents the amplitude of the double-frequency carrier signal, A1 represents the amplitude of the alternating component sensitive to the feedback light intensity, A C represents the phase modulation depth value of the round trip, J2 represents the second-order Bessel function, A C represents the phase modulation depth value of the round trip, θ C represents the phase of the modulation, represents the external cavity phase without feedback light, Q(t) represents the quadrature component signal, a1 represents the amplitude of the single-frequency carrier signal, J1 represents the first-order Bessel function, cos represents the cosine function, and sin represents the sine function.

5. The method of claim 1, wherein the laser self-mixing interferometer-based micro-displacement measurement method is characterized by, The S4 specifically comprises: S401: based on the quadrature signal pair, a Lissajous figure is drawn; S402: the Lissajous figure is fitted by an ellipse by a least squares method to obtain basic parameters of the ellipse, wherein the basic parameters include a horizontal axis length, a vertical axis length, a center point coordinate, and an inclination angle relative to the horizontal axis; S403: based on the basic parameters, the quadrature signal pair is corrected by a correction formula to obtain the corrected quadrature signal pair: where I N (n) denotes the modified in-phase component signal, n denotes a discrete sample index, θ r denotes an inclination angle of the ellipse, a denotes a length of a major axis of the ellipse, b denotes a length of a minor axis of the ellipse, Q(n) denotes a quadrature component signal, I(n) denotes an in-phase component signal, sin denotes a sine function, and cos denotes a cosine function. Q N (n) denotes the modified quadrature component signal.

6. The method of claim 5, wherein the laser self-mixing interferometer is a distributed feedback laser. The calculation method of the basic parameters of the ellipse is specifically as follows: where θ r represents an ellipse inclination angle, a represents an ellipse major axis length, b represents an ellipse minor axis length, arctan represents, x p represents an ellipse center point abscissa, y p represents an ellipse center point ordinate, A represents a parameter controlling an ellipse transverse axis, B represents a parameter controlling an ellipse inclination angle, C represents a parameter controlling an ellipse ordinate axis, D represents a parameter controlling an ellipse translation in an x-axis direction, E represents a parameter controlling an ellipse translation in a y-axis direction, sin represents a sine function, and cos represents a cosine function.

7. The method of claim 1, wherein the laser self-mixing interferometer is based on a semiconductor laser. The S5 specifically comprises: S501: performing division operation on the in-phase component signal and the quadrature component signal in the corrected quadrature signal pair to obtain a component signal ratio; S502: using an inverse tangent operation on the component signal ratio to obtain preliminary phase information; S503: performing phase unwrapping operation on the preliminary phase information to obtain final phase information with continuous phase: wherein, represents the external cavity phase without feedback light, i.e. the preliminary phase information, Unwrapping represents the phase unwrapping operation, α1represents the amplitude of the first-order frequency carrier signal, J1represents the first-order Bessel function, A c represents the phase modulation depth value of the round trip, θ c represents the modulated phase, α2represents the amplitude of the second-order frequency carrier signal, J2represents the second-order Bessel function, sin represents the sine function, and cos represents the cosine function. S504: outputting the final phase information as the phase information of the object to be measured.

8. The method of claim 1, wherein the laser self-mixing interferometer-based micro displacement measurement method is characterized by, The S5 further comprises: S505: performing integral processing on the in-phase component signal and the quadrature component signal in the corrected quadrature signal pair; S506: cross-multiplying the integral-processed in-phase component signal with the original quadrature component signal in the corrected quadrature signal pair and cross-multiplying the integral-processed quadrature component signal with the original in-phase component signal in the corrected quadrature signal pair to obtain a mixed in-phase component signal and a mixed quadrature component signal; S507: performing differential processing on the mixed in-phase component signal and the mixed quadrature component signal after a subtraction operation to obtain the phase information of the object to be measured.

9. A system for measuring a small displacement based on a laser self-mixing interferometer, characterized in that, comprise: a processor and a memory; the memory stores programs or instructions executable on the processor, and the programs or instructions are executed by the processor to implement the steps of the method for measuring a small displacement based on a laser self-mixing interferometer according to any one of claims 1 to 8.

10. A readable storage medium, characterized by, the readable storage medium stores programs or instructions, and the programs or instructions are executed by the processor to implement the steps of the method for measuring a small displacement based on a laser self-mixing interferometer according to any one of claims 1 to 8.

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