Vibration and displacement synchronous measurement device for multi-longitudinal-mode self-mixing effect

Abstract

The invention discloses a vibration and displacement synchronous measurement device for a multi-longitudinal-mode self-mixing effect, and relates to the field of laser measurement. When the vibration reflection module vibrates, the transmitting device transmits laser to the vibration reflection module, receives the laser reflected by the vibration reflection module, forms a self-mixing signal based on the reflected laser, and transmits the self-mixing signal to the signal processing unit; the vibration reflection module is used for reflecting and transmitting the received laser into the resonant cavity of the transmitting device; and the signal processing unit is used for determining the vibration frequency and the displacement change value of the vibration reflection module based on the compensation distance and the self-mixing signal. The system sensitivity can be improved, and synchronous measurement of the vibration frequency and the displacement can be realized.

Description

Technical Field

[0001] The present invention relates to the field of laser measurement, in particular to a vibration and displacement synchronous measurement device of multi-longitudinal mode self-mixing effect. Background Art

[0002] Existing laser self-mixing measurement technology primarily uses semiconductor lasers as light sources. However, semiconductor lasers generally operate in multiple longitudinal modes, resulting in poor monochromaticity and coherence of the laser beam. When operating at long distances, the divergence angle is extremely large, directly limiting the application and working distance of laser self-mixing vibrometer technology. Previous studies on the inherent characteristics of laser self-mixing signals have also found that the laser mode of semiconductor lasers does have a serious adverse effect on the self-mixing signal, even producing waveform discreteness, which directly affects the measurement accuracy and range of the laser self-mixing sensing system. Furthermore, optical measurement systems that use free-space light transmission are susceptible to system stability being affected by environmental factors such as optical platform vibration, temperature changes, air flow, and airborne dust. Furthermore, arranging the optical path in a confined space is also difficult.

[0003] A thorough analysis of the principle of multi-longitudinal-mode laser self-mixing measurement reveals that while multi-longitudinal-mode laser self-mixing sensing technology can severely negatively impact the self-mixing signal, even causing waveform separation, this very characteristic can be exploited to improve the system's measurement accuracy and range. In dual-parameter simultaneous measurement and sensing systems, the laser's internal cavity length inevitably affects system sensitivity, and thus the effective monitoring range. Summary of the Invention

[0004] The purpose of the present invention is to provide a vibration and displacement synchronous measurement device with multi-longitudinal mode self-mixing effect, which can improve the system sensitivity and realize the synchronous measurement of vibration frequency and displacement.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A vibration and displacement synchronous measurement device for multi-longitudinal mode self-mixing effect comprises:

[0007] A transmitting device, a vibration reflection module, a first sliding platform, a second sliding platform and a signal processing unit;

[0008] The transmitting device is located on a first sliding platform; the vibration reflection module is located on a second sliding platform; the first sliding platform and the second sliding platform are located in a straight line, so that the vibration reflection module is located on the outgoing light path of the transmitting device; the transmitting device is connected to the signal processing unit;

[0009] The transmitting device is used for:

[0010] When the vibration reflection module vibrates, emitting laser light to the vibration reflection module;

[0011] receiving the laser reflected by the vibration reflection module;

[0012] The reflected laser forms a self-mixing signal;

[0013] transmitting the self-mixing signal to a signal processing unit;

[0014] The vibration reflection module is used to transmit the received laser reflection to the resonant cavity of the transmitting device;

[0015] The signal processing unit is used to determine the change value of the vibration frequency and displacement of the vibration reflection module based on the compensation distance and the self-mixing signal; the compensation distance is to adjust the first sliding platform to drive the transmitting device and the second sliding platform to drive the vibration reflection module to move along the outgoing light path until the phase delay of the self-mixing signal is an integer multiple of 2π.

[0016] Optionally, the transmitting device includes: a multi-longitudinal mode laser and a detector;

[0017] The output end of the detector is connected to the signal processing unit;

[0018] The multi-longitudinal mode laser is used for:

[0019] When the vibration reflection module vibrates, emitting laser light to the vibration reflection module;

[0020] receiving the laser reflected by the vibration reflection module;

[0021] The reflected laser forms a self-mixing signal;

[0022] The detector is used to convert the self-mixing signal into an electrical signal and transmit the electrical signal to a signal processing unit.

[0023] Optionally, the multi-longitudinal mode laser includes a semiconductor multi-longitudinal mode laser or a fiber multi-longitudinal mode laser.

[0024] Optionally, an attenuator is provided between the transmitting device and the vibration reflection module;

[0025] The attenuator is used to adjust the intensity of the laser reflected into the emitting device.

[0026] Optionally, a collimator is further provided between the transmitting device and the vibration reflection module;

[0027] The collimator is used to make the laser irradiate the vibration reflection module in parallel.

[0028] Optionally, the vibration reflection module includes: a vibration target and a signal generator;

[0029] The vibrating target is located on the outgoing light path of the transmitting device; the vibrating target is connected to the signal generator;

[0030] The vibrating target is used to transmit the received laser reflection into the resonant cavity of the transmitting device;

[0031] The signal generator is used to provide a vibration signal to the vibration target.

[0032] Optionally, the vibration target includes a speaker or piezoelectric ceramic driven by a signal generator.

[0033] Optionally, the first sliding platform includes a slider and a slide rail;

[0034] The slider is connected to the launching device;

[0035] The slider is slidably arranged on the slide rail; the slide rail is parallel to the output light path of the emitting device; and the slider is used to drive the emitting device to move along the light path direction.

[0036] Optionally, there is a scale on the slide rail.

[0037] Optionally, the signal processing unit includes a computer or an oscilloscope.

[0038] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0039] The present invention discloses a device for synchronously measuring vibration and displacement using the multi-longitudinal mode self-mixing effect. Laser light is emitted by a transmitting device and then reflected back to the transmitting device by a vibration reflection module, generating a self-mixing signal. A signal processing unit is used to determine the change in vibration frequency and displacement of the vibration reflection module based on the compensation distance and the self-mixing signal. This device can improve system sensitivity and achieve synchronous measurement of vibration frequency and displacement. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0041] Figure 1 4 is a structural diagram of a device for synchronously measuring vibration and displacement of multi-longitudinal mode self-mixing effects in an embodiment of the present invention. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] The purpose of the present invention is to provide a vibration and displacement synchronous measurement device with multi-longitudinal mode self-mixing effect, which can improve the system sensitivity and realize the synchronous measurement of vibration frequency and displacement.

[0044] The present invention adopts a multi-longitudinal mode semiconductor laser with a shorter inner cavity length as a light source, which in principle effectively solves the problem that the inner cavity length of the laser itself will inevitably affect the system sensitivity.

[0045] Using multi-longitudinal-mode semiconductor lasers as the light source for laser self-mixing dual-parameter synchronous measurement sensing systems can directly address the high cost of high-precision sensing systems and greatly promote the development and application of self-mixing interferometry systems.

[0046] The measurement method is as follows: the vibrating target vibrates, a multi-longitudinal mode laser is used as the laser light source to be measured, the emitted laser is reflected by the vibrating target, and fed back into the resonant cavity of the multi-longitudinal mode laser to form a self-mixing signal, and the compensation distance is measured. The signal processing unit and the measured compensation distance are used to simultaneously obtain the vibration and displacement values at the vibrating target. This measurement method can simultaneously realize the measurement of vibration and displacement.

[0047] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] like Figure 1As shown, a device for synchronously measuring vibration and displacement based on the self-mixing effect of laser multi-longitudinal modes includes a multi-longitudinal mode laser 1, a vibrating target 2, an attenuator 3, and a signal processing unit 4. The multi-longitudinal mode laser 1 is the laser light source to be measured. The emitted laser passes through the sensing optical fiber and is emitted from one end of the sensing optical fiber to the vibrating target 2. The vibrating target 2 receives the laser emitted by the multi-longitudinal mode laser 1 and reflects it back into the resonant cavity of the multi-longitudinal mode laser 1 through the surface 21 of the vibrating target 2, forming a self-mixing signal. The bottom of the vibrating target 2 is fixed on the slider 8. The vibrating target 2 is provided with an adjustable vibration signal by the signal generator 6. The bottom of the multi-longitudinal mode laser 1 is fixed on the slider 32. The slider 32 is set on the slide rail 33 and can move horizontally along the slide rail 33. The slide rail 33 is in the same straight line as the emitted laser. The attenuator 3 is set on the optical path between the multi-longitudinal mode laser 1 and the vibrating target 2. The self-mixing signal is fed back to the multi-longitudinal mode laser 1. The built-in detector 7 of the multi-longitudinal mode laser 1 converts the received optical signal into an electrical signal. The signal processing unit 4 receives the electrical signal for analysis and processing, and obtains the change values of the vibration and displacement of the environment in which the vibrating target 2 is located.

[0049] The present invention provides a device for synchronously measuring vibration and displacement of a multi-longitudinal mode self-mixing effect, and the device comprises:

[0050] A transmitting device, a vibration reflection module, a first sliding platform, a second sliding platform and a signal processing unit.

[0051] The transmitting device is located on a first sliding platform; the vibration reflection module is located on a second sliding platform; the first and second sliding platforms are located in a straight line, so that the vibration reflection module is located on the output light path of the transmitting device; the transmitting device is connected to the signal processing unit. The bottom of the multi-longitudinal mode laser 1 is fixed to a slider 32 of the first sliding platform, and the slider 32 of the first sliding platform is set on the slide rail 33 of the first sliding platform and can move horizontally along the slide rail 33 of the first sliding platform.

[0052] The transmitting device is used to: when the vibration reflection module vibrates, emit laser light to the vibration reflection module, receive laser light reflected by the vibration reflection module, form a self-mixing signal based on the reflected laser light, and transmit the self-mixing signal to the signal processing unit. The vibrating target 2 receives laser light emitted by the multi-longitudinal mode laser 1 and feeds it back into the resonant cavity of the multi-longitudinal mode laser 1 through a feedback structure (including reflected and scattered light), forming a self-mixing signal.

[0053] The transmitting device includes: a multi-longitudinal mode laser 1 and a detector 7.

[0054] The multi-longitudinal mode laser 1 includes a semiconductor multi-longitudinal mode laser or an optical fiber multi-longitudinal mode laser.

[0055] The output end of the detector 7 is connected to the signal processing unit 4 .

[0056] The multi-longitudinal mode laser 1 is used to: emit laser light to the vibration reflection module when the vibration reflection module vibrates; receive laser light reflected by the vibration reflection module, and form a self-mixing signal based on the reflected laser light.

[0057] The detector 7 is used to convert the self-mixing signal into an electrical signal and transmit the electrical signal to the signal processing unit 4 .

[0058] The vibration reflection module is used to reflect and transmit the received laser light into the resonant cavity of the transmitting device.

[0059] The vibration reflection module includes: a vibration target 2 and a signal generator 6.

[0060] The vibrating target 2 is located on the outgoing light path of the transmitting device; the vibrating target 2 is connected to the signal generator 6 .

[0061] The vibrating target 2 is used to reflect and transmit the received laser light into the resonant cavity of the transmitting device. The vibrating target 2 comprises a speaker or piezoelectric ceramic driven by a signal generator. The vibrating target 2 is a thin plate driven by a signal generator and is fixed to the slider 8 of the second sliding stage. The slider 8 of the second sliding stage is set on the slide rail of the second sliding stage and can move horizontally along the slide rail of the second sliding stage.

[0062] The signal generator 6 is used to provide a vibration signal to the vibration target 2 .

[0063] The signal processing unit 4 is configured to determine the change in vibration frequency and displacement of the vibration reflection module based on a compensation distance and a self-mixing signal. The compensation distance is the distance traveled by the transmitting device and the vibration reflection module by adjusting the first sliding stage to move the transmitting device and the second sliding stage to move the vibration reflection module along the outgoing optical path until the phase delay of the self-mixing signal reaches an integer multiple of 2π. The signal processing unit includes a computer or an oscilloscope.

[0064] The present invention also provides a method for simultaneously measuring vibration and displacement based on the above-mentioned device for synchronously measuring vibration and displacement based on the laser multi-longitudinal mode self-mixing effect, comprising the following steps:

[0065] Turn on the vibrating target 2, the multi-longitudinal mode laser 1 emits laser light, and by observing the multi-longitudinal mode self-mixing signal on the signal processing unit 4, move the slider so that the waveform of the signal processing unit maintains the same phase or the phase delay is an integer multiple, and record the first compensation distance δL moved by the slider c1 .

[0066] The device and method for synchronously measuring vibration and displacement based on the self-mixing effect of multiple longitudinal modes of laser provided by the present invention are based on the change of the output signal waveform caused by the self-mixing feedback signal of multiple longitudinal modes of laser as the vibration and displacement change, and synchronously measure the vibration and displacement changes of the position to be measured in real time by adjusting the cavity length of the external cavity to track the waveform of the self-mixing signal.

[0067] An attenuator 3 is provided between the transmitting device and the vibration reflection module.

[0068] The attenuator 3 is used to adjust the intensity of the laser reflected into the emitting device.

[0069] A collimator 5 is further provided between the emitting device and the vibration reflection module. The collimator 5 ensures that the laser is emitted in parallel to the surface of the target object.

[0070] The collimator 5 is used to make the laser beam be parallel to the vibration reflection module.

[0071] The first sliding platform includes a sliding block 32 and a sliding rail 33 .

[0072] There are scales on the slide rail 33 .

[0073] The slider 32 is connected to the launching device.

[0074] The slider 32 is slidably disposed on the slide rail 33; the slide rail 33 is parallel to the output light path of the emitting device; the slider 32 is used to drive the emitting device to move along the light path. The second sliding platform has a similar structure to the first sliding platform.

[0075] The method for simultaneously measuring vibration and displacement using the above-mentioned device is as follows: the vibrating target 2 vibrates and generates displacement by moving the slider 8, the multi-longitudinal mode laser 1 is used as the laser light source to be measured, the emitted laser passes through the attenuator 3 to the vibrating target 2, and the emitted laser is reflected by the reflective film or the reflective plane 21, and then fed back into the resonant cavity of the multi-longitudinal mode laser 1 to form a self-mixing signal, so that the slider 32 moves slightly along the slide rail 33 to obtain a compensation distance, and the compensation distance makes the waveform maintain the same phase or the phase delay is an integer multiple of 2π, so as to change the distance between the vibrating target 2 and the multi-longitudinal mode laser 1, and obtain a multi-longitudinal mode self-mixing signal with non-discrete waveforms, and at the same time use the attenuator 3 to adjust the intensity of the feedback light, use the detector 7 to collect the laser self-mixing signal, use the signal processing unit 4 to analyze the electrical signal of the received laser self-mixing signal, and use different compensation distances to obtain the change values of the vibration and displacement of the environment in which the vibrating target 2 is located. The specific steps are as follows:

[0076] For the laser self-mixing signal of the multi-longitudinal mode laser 1, the different longitudinal modes of the multi-longitudinal mode laser 1 only interfere with their own modes. The final laser self-mixing signal is the superposition of the laser self-mixing signal intensities formed by each longitudinal mode. According to the related interference mixing theory model, without considering the influence of speckle, the multi-longitudinal mode laser self-mixing signal intensity is:

[0077]

[0078] In formula (1) op tj is the total optical path of the external cavity in mode j, β is the total number of oscillation modes in the multi-longitudinal mode laser, j represents the jth longitudinal mode in the multi-longitudinal mode laser, I0 is the initial total light intensity, ΔI j is the amplitude of the j-mode laser intensity change, ω0 is the angular frequency of the laser, c is the speed of light in vacuum, n g is the group refractive index of the multi-longitudinal mode laser resonant cavity medium, L0 is the cavity length of the multi-longitudinal mode laser resonant cavity, cc represents the complex conjugate of the previous formula. In the calculation, the refractive index change caused by different longitudinal modes in the same material can be ignored.

[0079] When the displacement at the target changes, there is:

[0080] op tj =op0+δop s +δop c =op0+δ(n s L s )+δ(n c L c )(2)

[0081]

[0082] In formula (2), op0 is the initial optical path of the multi-longitudinal mode laser external cavity, δop s is the optical path change caused by displacement, δop c To compensate the optical path, n c is the refractive index of the air in the external cavity, n s is the refractive index of the sensing unit, L s is the total geometric length of the actual path of the laser transmission in the sensor unit, L c is the compensation length, φ in formula (3) 0j is the initial phase of the j-mode laser in the external cavity during one round trip, δφ sj is the phase change caused by displacement change, δφ cj To compensate for phase changes, when measuring displacement changes, δφ sj =-δφ cj .

[0083] When the waveforms of each mode maintain the same phase or the phase delay is an integer multiple of 2π, there is no waveform separation when the self-mixing signals of lasers in different longitudinal modes are superimposed, that is:

[0084] op tj =2mn g L0(4)

[0085] In formula (4), m is the number of external cavity modes of the multi-longitudinal mode laser, which is a positive integer. Therefore, the multi-longitudinal mode laser has a series of special position points, so that the superimposed laser self-mixing signal does not produce waveform discreteness. From formula (2), it can be seen that when the displacement at the target changes, the optical path or phase of the light during transmission will change, resulting in the op s of each mode. tj The laser self-mixing signal waveform after superposition will be separated by changing the position of the external feedback object by adjusting the sliding device to compensate for the optical path or phase change, so that the laser self-mixing signal waveform after superposition can be transformed into a complete waveform again. The phase change can be compensated by measuring the position of the external feedback object, and the optical path change caused by the displacement change can be obtained. s , the phase delay of the outgoing light wave can be expressed as:

[0086] φ=2πnL / λ0=βL(5)

[0087] Where β is the propagation constant of the light wave in the sensing unit, λ0 is the propagation wavelength of the light wave in the sensing medium, and n is the refractive index of the sensing medium.

[0088] Therefore, the compensation distance δL is measured c2 , and obtain the displacement change value.

[0089] At the same time, by recording the changes in the number of fringes in the laser self-mixing interference image, the changes in vibration frequency (or amplitude) can be calculated.

[0090] The present invention has the following advantages:

[0091] 1. The structure is simple. It only needs to observe the intensity change waveform of the output signal and track and compensate it through the external cavity to obtain the displacement information. At the same time, the vibration information can be obtained synchronously by counting the fringes.

[0092] 2. The vibration and displacement sensing units are located at the same position, which is a better intrinsic measurement solution and reduces the interference of other sensitive factors on the measurement system.

[0093] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0094] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A device for synchronously measuring vibration and displacement of multi-longitudinal mode self-mixing effects, characterized in that: The vibration and displacement synchronous measurement device of the multi-longitudinal mode self-mixing effect comprises: A transmitting device, a vibration reflection module, a first sliding platform, a second sliding platform and a signal processing unit; The transmitting device is located on a first sliding platform; the vibration reflection module is located on a second sliding platform; the first sliding platform and the second sliding platform are located in a straight line, so that the vibration reflection module is located on the outgoing light path of the transmitting device; the transmitting device is connected to the signal processing unit; The transmitting device is used for: When the vibration reflection module vibrates, emitting laser light to the vibration reflection module; receiving the laser reflected by the vibration reflection module; The reflected laser forms a self-mixing signal; transmitting the self-mixing signal to a signal processing unit; The vibration reflection module is used to transmit the received laser reflection to the resonant cavity of the transmitting device; The signal processing unit is used to determine the change value of the vibration frequency and displacement of the vibration reflection module based on the compensation distance and the self-mixing signal; the compensation distance is to adjust the first sliding platform to drive the transmitting device and the second sliding platform to drive the vibration reflection module to move along the outgoing light path until the phase delay of the self-mixing signal is an integer multiple of 2π.

2. The device for synchronously measuring vibration and displacement of multi-longitudinal mode self-mixing effect according to claim 1, characterized in that: The transmitting device includes: a multi-longitudinal mode laser and a detector; The output end of the detector is connected to the signal processing unit; The multi-longitudinal mode laser is used for: When the vibration reflection module vibrates, emitting laser light to the vibration reflection module; receiving the laser reflected by the vibration reflection module; The reflected laser forms a self-mixing signal; The detector is used to convert the self-mixing signal into an electrical signal and transmit the electrical signal to a signal processing unit.

3. The device for synchronously measuring vibration and displacement of multi-longitudinal mode self-mixing effect according to claim 2, characterized in that: The multi-longitudinal mode laser includes a semiconductor multi-longitudinal mode laser or an optical fiber multi-longitudinal mode laser.

4. The device for synchronously measuring vibration and displacement of multi-longitudinal mode self-mixing effect according to claim 1, characterized in that: An attenuator is provided between the transmitting device and the vibration reflection module; The attenuator is used to adjust the intensity of the laser reflected into the emitting device.

5. The device for synchronously measuring vibration and displacement of multi-longitudinal mode self-mixing effect according to claim 1, characterized in that: A collimator is further provided between the transmitting device and the vibration reflection module; The collimator is used to make the laser irradiate the vibration reflection module in parallel.

6. The device for synchronously measuring vibration and displacement of multi-longitudinal mode self-mixing effect according to claim 1, characterized in that: The vibration reflection module includes: a vibration target and a signal generator; The vibrating target is located on the outgoing light path of the transmitting device; the vibrating target is connected to the signal generator; The vibrating target is used to transmit the received laser reflection into the resonant cavity of the transmitting device; The signal generator is used to provide a vibration signal to the vibration target.

7. The device for synchronously measuring vibration and displacement of multi-longitudinal mode self-mixing effect according to claim 6, characterized in that: The vibration target includes a speaker or piezoelectric ceramic driven by a signal generator.

8. The device for synchronously measuring vibration and displacement of multi-longitudinal mode self-mixing effect according to claim 1, characterized in that: The first sliding platform includes a slider and a slide rail; The slider is connected to the launching device; The slider is slidably arranged on the slide rail; the slide rail is parallel to the output light path of the emitting device; and the slider is used to drive the emitting device to move along the light path direction.

9. The device for synchronously measuring vibration and displacement of multi-longitudinal mode self-mixing effect according to claim 8, characterized in that: There are scales on the slide rail.

10. The device for synchronously measuring vibration and displacement of multi-longitudinal mode self-mixing effect according to claim 1, characterized in that: The signal processing unit includes a computer or an oscilloscope.

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