A dual-channel micro-displacement detection device, method, and system based on self-mixing interferometry

Abstract

This invention relates to a dual-path micro-displacement detection device, method, and system based on self-mixing interference, belonging to the field of micro-displacement detection. The device includes: a laser, a first photodetector, a beam splitter, a second photodetector, and a lens. The laser emits laser light, which is decomposed into two beams. One beam is incident on the first photodetector, monitoring the real-time change in the laser output power caused by the self-mixing interference of the laser. The other beam is focused onto the surface of the object under test by the lens. The object under test, driven by a PZT (Polymerized Znotherapeutic Tunneling) beam, performs periodic reciprocating motion and reflects light to generate reflected signal light, which is then decomposed into two other beams. One reflected signal light returns to the laser along the original path, causing a real-time change in the laser output power, which is measured and recorded by the first photodetector. The other reflected signal light is reflected into the second photodetector, where it is detected and recorded. The above-described scheme of this invention can achieve accurate detection of micro-displacements.

Description

Technical Field

[0001] This invention relates to the field of micro-displacement detection, and in particular to a dual-path micro-displacement detection device, method, and system based on self-mixing interferometry. Background Technology

[0002] Laser self-mixing interferometry, also known as laser feedback interferometry, refers to the interference phenomenon where the light output from a laser shines on a target object, and the scattered light carrying information about the target object's motion is fed back into the laser, modulating the laser output. Unlike traditional Michelson and Mach-Zehnder interferometers, self-mixing interferometry systems have simple optical paths and do not require complex collimation operations. The self-mixing interference effect occurs as soon as the light reflected from the object being measured returns to the laser. Furthermore, self-mixing interferometry systems are simple in structure, widely applicable, and offer high measurement accuracy. Therefore, since S. Donati et al. proposed using laser self-mixing interferometry for displacement measurement in 1968, laser feedback technology has been applied to various fields, including micro-displacement, vibration, distance, laser linewidth, target object refractive index, and mechanical resonance measurement.

[0003] Since the intensity information of self-mixed interference contains various motion information such as displacement and velocity of the target, processing the self-mixed signal and extracting effective motion information from it is fundamental to monitoring the motion state of the target object. Currently, methods for extracting micro-displacement information of the target object include fringe counting and phase unwrapping methods. Self-mixed interference and traditional interferometry systems have the same sensitivity to intensity changes; a target object moving half a wavelength corresponds to one fringe of the laser self-mixed interference intensity. Furthermore, the intensity change trend of the self-mixed interference is related to the direction of object movement, thus the fringe counting method can effectively read the object's displacement information. However, since one fringe only corresponds to half a wavelength, the fringe counting method cannot provide more precise information about displacements between two half-wavelengths. Phase measurement directly obtains the phase change caused by the external moving object by solving the self-mixed interference signal, effectively avoiding the accuracy problem of the fringe counting method. Common phase unwrapping methods include: phase calculation of the original self-mixed signal, and phase calculation of the self-mixed signal after adding various modulations (current, cavity length, phase) to the laser. The demodulation accuracy has reached a fraction of the wavelength.

[0004] Taking the measurement of an object's reciprocating motion using laser self-mixing interferometry as an example, the most crucial aspect of self-mixing interferometry phase calculation is extracting effective displacement direction transition point information from the original self-mixed signal. Currently, the most commonly used transition point detection method is a fixed-threshold transition point detection algorithm, which processes the original self-mixing interferometry signal. Because moderately fed self-mixing interferometry signals exhibit sawtooth-like fringes, differentiation reveals large extrema at the sawtooth endpoints, with the signs of these extrema related to the direction of motion. Transition point information can be obtained by extracting the self-mixed signal between adjacent differences in sign. However, this method is only applicable to self-mixing interferometry under moderate feedback conditions. Under weak feedback conditions, the self-mixing interferometry signal does not exhibit significant fringe tilt, and the differentiated signal lacks obvious peaks. Therefore, using this fixed method for direction transition point identification is not feasible. Furthermore, significant external noise can also significantly impact the accuracy of this transition point extraction.

[0005] To effectively locate direction change points under varying feedback conditions, this invention proposes a dual-path displacement detection system based on self-mixing interferometry. One path consists of a laser self-mixing interferometry signal, while the other path comprises a reflected light signal containing external trajectory information and an interference signal. Direction change point identification is achieved by processing the scattered light information. Subsequently, the change point information is used to reconstruct the displacement of the self-mixing interferometry signal, enabling micro-displacement detection. Furthermore, displacement detection can also be achieved through intensity demodulation of the scattered light information. Summary of the Invention

[0006] The purpose of this invention is to provide a dual-path micro-displacement detection device, method, and system based on self-mixing interference to achieve accurate detection of micro-displacements.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] A dual-path micro-displacement detection device based on self-mixing interferometry, the detection device comprising:

[0009] Laser, first photodetector, beam splitter, second photodetector, and lens;

[0010] The laser emits a laser beam, which is split into two beams by the beam splitter. One beam is directly incident on the first photodetector, which directly receives the light emitted by the laser and monitors the real-time changes in the laser output power caused by the laser self-mixing interference. The other beam is focused by the lens onto the surface of the object under test for testing.

[0011] The object under test, driven by a piezoelectric ceramic (PZT), performs a periodic reciprocating motion and reflects light to generate a reflected signal. This reflected signal light is then decomposed into two other light rays by the beam splitter. One of the reflected signal rays returns to the laser along the original path, modulating the laser to produce a self-mixing interference effect, causing the laser output power to change in real time, which is measured and recorded by the first photodetector. The other reflected signal light is reflected into the second photodetector, where it is detected and recorded.

[0012] Optionally, the reflected signal light carries real-time information about the motion trajectory of the externally detected object.

[0013] Optionally, the detection and recording performed by the second photodetector specifically involves recording the light intensity transformation characteristics of the other reflected signal.

[0014] Optionally, the periodic reciprocating motion includes: a fixed-period reciprocating motion and a random-period reciprocating motion.

[0015] Based on the above-described apparatus of the present invention, the present invention further provides a dual-path micro-displacement detection method based on self-mixing interferometry, wherein the detection method is applied to the above-described detection apparatus, and the detection method includes:

[0016] The signal of change in reflected light intensity received by the second photodetector is recorded as the second reflected light signal;

[0017] The timing information of the change point of the motion direction of the object under test and the range of the one-way distance of the round-trip motion are determined based on the second reflected light signal.

[0018] The optical signal received by the first photodetector is acquired and denoted as the first optical signal;

[0019] The first optical signal is filtered.

[0020] Perform a Hilbert transform on the filtered first optical signal to extract phase information;

[0021] Based on the time information of the change point of the motion direction of the object under test and the range of the one-way distance of the round-trip motion, and based on the phase information, the motion displacement of the object under test is reconstructed.

[0022] Optionally, based on the time information of the turning point of the motion direction of the object under test and the one-way distance range of the round-trip motion, and based on the phase information, the motion displacement of the object under test can be reconstructed.

[0023]

[0024] Where l represents the displacement of the object being measured. λ represents the phase of the first optical signal, and λ is the wavelength of the probe laser.

[0025] Based on the detection method described above in this invention, this invention further provides a dual-path micro-displacement detection system based on self-mixing interferometry, the detection system comprising:

[0026] The second reflected light signal acquisition module is used to acquire the reflected light intensity change signal received by the second photodetector, which is denoted as the second reflected light signal;

[0027] The transition point information determination module is used to determine the time information of the transition point of the motion direction of the object under test and the range of the one-way distance of the round-trip motion based on the second reflected light signal.

[0028] The first optical signal acquisition module is used to acquire the optical signal received by the first photodetector, denoted as the first optical signal;

[0029] A filtering module is used to filter the first optical signal;

[0030] The Hilbert transform module is used to perform a Hilbert transform on the filtered first optical signal to extract phase information.

[0031] The reconstruction module is used to reconstruct the motion displacement of the object under test based on the time information of the change point of the motion direction of the object under test and the one-way distance range of the round-trip motion, and based on the phase information.

[0032] The present invention also provides an electronic device, comprising:

[0033] processor;

[0034] The memory stores computer instructions, which, when executed by the processor, implement the aforementioned micro-displacement detection method.

[0035] The present invention also provides a computer-readable storage medium, characterized in that it stores computer instructions thereon, which, when executed by a processor, implement the above-described micro-displacement detection method.

[0036] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0037] This invention provides a dual-path micro-displacement detection device and method based on self-mixed interferometry. The device includes a laser, a first photodetector, a beam splitter, a second photodetector, and a lens. Based on this device, a micro-displacement detection method is proposed, comprising: first, acquiring the reflected light intensity change signal received by the second photodetector, denoted as the second reflected light signal; then, based on the second reflected light signal, determining the time information of the motion direction change point of the object under test and the one-way distance range of the round-trip motion; next, acquiring the light signal received by the first photodetector, denoted as the first light signal, and extracting the phase information of the first light signal; finally, using the phase information of the first light signal, achieving high-precision reconstruction of the motion displacement of the object under test. That is, firstly, the real-time displacement trajectory of the target can be obtained using the signal acquired by the second photodetector, extracting the position and time of the motion direction change point of the target object, and then using the self-mixed interferometry signal obtained by the first photodetector to perform higher-precision phase unwrapping calculation, ultimately achieving high-precision displacement reconstruction and rapid measurement. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a schematic diagram of the structure of a dual-path micro-displacement detection device based on self-mixing interference according to the present invention;

[0040] Figure 2 This is a flowchart of a dual-path micro-displacement detection method based on self-mixing interference according to the present invention;

[0041] Figure 3 This is a schematic diagram of the actual 16-micron sawtooth wave normalized signal and PZT signal of the present invention. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] The purpose of this invention is to provide a dual-path micro-displacement detection device, method, and system based on self-mixing interference to achieve accurate detection of micro-displacements.

[0044] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] Self-mixed interferometry-based micro-displacement detection methods have been developed for many years, and their measurement accuracy has gradually improved. However, this improvement in accuracy also places higher demands on the detection environment and the original self-mixed interferometric signal. When the self-mixed interferometric signal contains significant noise, and the direction change point cannot be calculated by the algorithm after effective noise reduction, displacement information extraction becomes impossible, or large errors occur during displacement detection.

[0046] Based on this, the present invention proposes a dual-path micro-displacement detection device based on self-mixing interference, such as... Figure 1 As shown, the detection device in this invention includes:

[0047] Laser 1, first photodetector 2, beam splitter prism 3, second photodetector 4, lens 5, and measurement target surface 6 are used. The target under test, driven by piezoelectric ceramics, performs reciprocating translational motion in the axial direction, with a displacement range within tens of micrometers. Figure 1 The dashed lines in the diagram represent the trajectory of the light beam.

[0048] Specifically, the laser 1 mentioned above is a semiconductor laser with a PD terminal, and the beam splitter 3 is a 5 / 5 beam splitter.

[0049] The transmission process of light is as follows:

[0050] The light emitted by laser 1 is split into two beams after passing through a 5 / 5 beam splitter prism 3. One beam is directly incident on the first photodetector 2, which detects the output of the laser. The first photodetector 2 directly receives the light emitted by the laser, and its intensity change is the same as the intensity change caused by the self-mixing interference of the laser. Therefore, the first photodetector can directly monitor the real-time change of the laser's output power. The other beam is focused by lens 5 onto the surface of the object under test for testing. The signal light reflected back from the target object driven by the piezoelectric ceramic PZT carries information about the motion of the externally detected object. This reflected signal light, like the incident light, is split in reverse by the beam splitter prism 3 into two other beams of roughly the same intensity. One of the reflected signal lights returns to the laser 1 along the original path, modulating the laser 1 to produce a self-mixing interference effect, thus changing the output power of the laser 1. The other reflected signal light is reflected into the second photodetector 4, which detects and records the intensity change characteristics of the reflected signal light. The light received by the second photodetector 4 comes from the object.

[0051] Reflection and the trend of light intensity variation are modulated by the motion of external objects. The trend of light intensity variation is related to the trend of the motion of the external object being detected, and the greater the displacement of the external object, the greater the change in light intensity; the two are linearly correlated. Therefore, the signal collected by the second photodetector 4 contains both the curve of the target's displacement over time and describes the magnitude of the displacement. Thus, this invention utilizes this dual-path interferometry system to propose a novel and accurate displacement method. First, the real-time displacement trajectory of the target is obtained using the signal collected by the second photodetector 4, and the position and time of the target's direction of motion change are extracted. Then, the self-mixed interferometric signal obtained by the first photodetector 2 is used for higher-precision phase analysis, ultimately achieving high-precision displacement reconstruction and rapid measurement.

[0052] It should be noted that in the above-mentioned dual-channel interferometric displacement detection system, the signals received by the first photodetector and the second photodetector can be used to directly calculate the displacement of the target. However, due to the influence of external noise, the accuracy of the calculation results of a single signal is limited. Therefore, this invention proposes for the first time a method to combine the two signals to improve the system accuracy.

[0053] Based on the above-described device, the present invention further proposes a detection method, such as... Figure 2 As shown, the method includes:

[0054] S1: Obtain the signal of change in reflected light intensity received by the second photodetector, denoted as the second reflected light signal.

[0055] S2: Based on the second reflected light signal, determine the time information of the change point of the motion direction of the object under test and the range of the one-way distance of the round-trip motion.

[0056] The signal L detected by the second photodetector is proportional to the real-time displacement I of the target (i.e., the displacement curve of the piezoelectric ceramic PZT). Therefore, the signal from the second photodetector can be extracted (using methods such as wavelet transform, empirical mode decomposition, and trajectory envelope) and fitted with a pre-known target displacement calibration value to obtain the following linear relationship between the two in this system:

[0057] L=aI+d

[0058] Where L is the measured value of the second photodetector; a is the calculated fitting slope coefficient; I is the actual displacement value; and d is the fitting coefficient. The system can be calibrated beforehand by using the known target position to obtain the system-specific a and d values. Then, in the actual measurement, the signal from the second photodetector is used to perform a preliminary measurement of the unknown displacement to be measured, and the position and time of the target motion direction change point are obtained.

[0059] Actual 16μm sawtooth wave normalized signal and PZT signal as follows Figure 3 As shown:

[0060] Figure 3 The solid black line in the middle represents the data measured by the second photodetector, and the dashed line at the bottom represents the displacement signal of the piezoelectric ceramic PZT, i.e., the real-time position of the target under test.

[0061] S3: Acquire the optical signal received by the first photodetector, and denot it as the first optical signal.

[0062] S4: Filter the first optical signal.

[0063] S5: Perform a Hilbert transform on the filtered first optical signal to extract phase information.

[0064] The position of the target can be initially measured using the signal from the second photodetector alone. However, in order to achieve higher precision (nanometer level), this invention utilizes the laser output power change signal (i.e., laser self-mixing interference signal) measured by the first photodetector, based on the signal from the second photodetector, to achieve higher resolution phase calculation.

[0065] S6: Based on the time information of the change point of the motion direction of the object under test and the one-way distance range of the round-trip motion, and based on the phase information, the motion displacement of the object under test is reconstructed.

[0066] The specific calculation formula is as follows:

[0067]

[0068] Where l represents the displacement of the object being measured. λ represents the phase of the first optical signal, and λ is the wavelength of the probe laser.

[0069] Furthermore, the present invention also provides an electronic device, comprising:

[0070] processor;

[0071] The memory stores computer instructions, which, when executed by the processor, implement the aforementioned micro-displacement detection method.

[0072] Based on the above-described method of this invention, this invention also provides a dual-path micro-displacement detection system based on self-mixing interferometry, the detection system comprising:

[0073] The second reflected light signal acquisition module is used to acquire the reflected light intensity change signal received by the second photodetector, which is denoted as the second reflected light signal;

[0074] The transition point information determination module is used to determine the time information of the transition point of the motion direction of the object under test and the range of the one-way distance of the round-trip motion based on the second reflected light signal.

[0075] The first optical signal acquisition module is used to acquire the optical signal received by the first photodetector, denoted as the first optical signal;

[0076] A filtering module is used to filter the first optical signal;

[0077] The Hilbert transform module is used to perform a Hilbert transform on the filtered first optical signal to extract phase information.

[0078] The reconstruction module is used to reconstruct the motion displacement of the object under test based on the time information of the change point of the motion direction of the object under test and the one-way distance range of the round-trip motion, and based on the phase information.

[0079] The present invention also provides a computer-readable storage medium, characterized in that it stores computer instructions thereon, which, when executed by a processor, implement the above-described micro-displacement detection method.

[0080] The above-described dual-path micro-displacement detection device, method, and system based on self-mixing interferometry of the present invention have the following beneficial effects:

[0081] The method for micro-displacement detection based on self-mixed interferometry has been developed for many years, and the measurement accuracy has gradually improved. However, with the improvement of measurement accuracy, the requirements for the detection environment and the original self-mixed interferometric signal are also higher. When the self-mixed interferometric signal has a large amount of noise, and the direction change point cannot be calculated by the algorithm after effective noise reduction, displacement information cannot be extracted, or large errors occur during displacement detection. The dual-path micro-displacement detection system based on laser self-mixed interferometry can effectively avoid this problem. Even when there is a lot of noise in the laser self-mixed signal (first photodetector) and the change point cannot be extracted, the comprehensive method in this invention can still be used for displacement reconstruction. Because the intensity modulation information of the second photodetector is almost unaffected by external conditions, tests have shown that even with a lot of external noise, the overall change in the intensity of the second photodetector signal still changes linearly with the external displacement. The displacement curve and the position of each inflection point of the detected target can be reconstructed very accurately, and then the self-mixed interferometric signal can be used. Therefore, the extraction of the direction change point by the method in this invention is almost unaffected.

[0082] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0083] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A dual-path micro-displacement detection device based on self-mixing interference, characterized in that, The detection device includes: Laser, first photodetector, beam splitter, second photodetector, and lens; The laser emits a laser beam, which is split into two beams by the beam splitter. One beam is directly incident on the first photodetector, which directly receives the light emitted by the laser and monitors the real-time changes in the laser output power caused by the laser self-mixing interference. The other beam is focused by the lens onto the surface of the object under test for testing. The object under test, driven by a piezoelectric ceramic (PZT), performs a periodic reciprocating motion and reflects light to generate a reflected signal. The reflected signal light is then decomposed into two other light rays by the beam splitter. One of the reflected signal rays returns to the laser along the original path, modulating the laser to produce a self-mixing interference effect, causing the laser output power to change in real time, which is measured and recorded by the first photodetector. The other reflected signal light is reflected into the second photodetector, which is then detected and recorded.

2. The dual-path micro-displacement detection device based on self-mixing interference according to claim 1, characterized in that, The reflected signal light carries real-time information about the trajectory of the externally detected object.

3. The dual-path micro-displacement detection device based on self-mixing interference according to claim 1, characterized in that, The detection and recording performed by the second photodetector specifically involves recording the light intensity transformation characteristics of the other reflected signal.

4. The dual-path micro-displacement detection device based on self-mixing interference according to claim 1, characterized in that, The periodic reciprocating motion includes: reciprocating motion with a fixed period and reciprocating motion with a random period.

5. A dual-path micro-displacement detection method based on self-mixing interferometry, characterized in that, The detection method is applied to the detection device as described in any one of claims 1-4, and the detection method includes: The signal of change in reflected light intensity received by the second photodetector is recorded as the second reflected light signal; The timing information of the change point of the motion direction of the object under test and the range of the one-way distance of the round-trip motion are determined based on the second reflected light signal. The optical signal received by the first photodetector is acquired and denoted as the first optical signal; The first optical signal is filtered. Perform a Hilbert transform on the filtered first optical signal to extract phase information; Based on the time information of the change point of the motion direction of the object under test and the range of the one-way distance of the round-trip motion, and based on the phase information, the motion displacement of the object under test is reconstructed.

6. The dual-path micro-displacement detection method based on self-mixing interferometry according to claim 5, characterized in that, Based on the time information of the change point of the motion direction of the object under test and the one-way distance range of the round-trip motion, and based on the phase information, the motion displacement of the object under test is reconstructed. Where l represents the displacement of the object to be measured. λ represents the phase of the first optical signal, and λ is the wavelength of the probe laser.

7. A dual-path micro-displacement detection system based on self-mixing interferometry, characterized in that, The detection system includes: The second reflected light signal acquisition module is used to acquire the reflected light intensity change signal received by the second photodetector, which is denoted as the second reflected light signal; The transition point information determination module is used to determine the time information of the transition point of the motion direction of the object under test and the range of the one-way distance of the round-trip motion based on the second reflected light signal. The first optical signal acquisition module is used to acquire the optical signal received by the first photodetector, denoted as the first optical signal; A filtering module is used to filter the first optical signal; The Hilbert transform module is used to perform a Hilbert transform on the filtered first optical signal to extract phase information. The reconstruction module is used to reconstruct the motion displacement of the object under test based on the time information of the change point of the motion direction of the object under test and the one-way distance range of the round-trip motion, and based on the phase information.

8. An electronic device, characterized in that, include: processor; A memory that stores computer instructions that, when executed by a processor, implement the method as described in any one of claims 5-6.

9. A computer-readable storage medium, characterized in that, It stores computer instructions that, when executed by a processor, implement the method as described in any one of claims 5-6.

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