Multi-longitudinal-mode self-mixing effect speed and micro-angle synchronous measurement device

Abstract

The invention discloses a multi-longitudinal-mode self-mixing effect speed and micro-angle synchronous measurement device, and relates to the technical field of optical detection. The transmitting device transmits laser to the speed reflecting module, receives the laser reflected by the speed reflecting module, forms a self-mixing signal based on the reflected laser, and transmits the self-mixing signal to the signal processing unit; the speed reflection module reflects and transmits the received laser to a resonant cavity of the transmitting device; the signal processing unit determines the speed of the speed reflection module and the change value of the micro angle based on the compensation distance and the self-mixing signal; the compensation distance is the moving distance of the transmitting device when the sliding table is adjusted to drive the transmitting device to move in the direction of the emergent light path until the phase delay of the self-mixing signal is an integral multiple of 2 pi. The system sensitivity can be improved, and speed and micro-angle synchronous measurement can be realized.

Description

Technical Field

[0001] The present invention relates to the field of optical detection technology, in particular to a device for synchronously measuring speed and micro-angle of multi-longitudinal mode self-mixing effects. 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 speed and micro-angle synchronous measurement device for multi-longitudinal mode self-mixing effect, which can improve system sensitivity and realize speed and micro-angle synchronous measurement.

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

[0006] A device for synchronously measuring speed and micro-angle of multi-longitudinal mode self-mixing effects comprises:

[0007] Launching device, velocity reflection module, sliding table and signal processing unit;

[0008] The transmitting device is located on the sliding platform; the speed 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] emitting a laser to the speed reflection module;

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

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

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

[0014] The speed 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 speed and micro-angle change values ​​of the speed reflection module based on the compensation distance and the self-mixing signal; the compensation distance is the movement distance of the transmitting device when the sliding stage is adjusted to drive the transmitting device to move along the output 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] emitting a laser to the speed reflection module;

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

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

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

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

[0030] The speed 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 speed signal for the speed target.

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

[0033] Optionally, the speed reflection module further includes a turntable;

[0034] The speed target is set on the turntable;

[0035] The turntable is used to adjust the angle of the reflective structure in the speed target.

[0036] Optionally, the sliding platform includes a slider and a slide rail;

[0037] The slider is connected to the launching device;

[0038] 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.

[0039] Optionally, the signal processing unit includes a computer or an oscilloscope.

[0040] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0041] The present invention discloses a device for synchronously measuring speed and micro-angle using the multi-longitudinal mode self-mixing effect. Laser light is emitted from a transmitter, which is then reflected back to the transmitter by a velocity reflection module, generating a self-mixing signal. A signal processing unit is used to determine the change in speed and micro-angle of the velocity reflection module based on the compensation distance and the self-mixing signal. This device improves system sensitivity and enables synchronous measurement of speed and micro-angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] 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.

[0043] Figure 1 4 is a structural diagram of a device for synchronously measuring speed and micro-angle of multi-longitudinal mode self-mixing effects in an embodiment of the present invention. DETAILED DESCRIPTION

[0044] 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.

[0045] The purpose of the present invention is to provide a speed and micro-angle synchronous measurement device for multi-longitudinal mode self-mixing effect, which can improve system sensitivity and realize speed and micro-angle synchronous measurement.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] The present invention provides a measurement method comprising the following steps: a speed target generates a speed, a multi-longitudinal mode laser is used as a laser light source to be measured, the emitted laser is reflected by the speed target and fed back into the laser resonant cavity to form a self-mixing signal, the compensation distance is measured, and the speed and micro-angle values ​​of the speed target are simultaneously obtained using a signal processing unit and the measured compensation distance. This measurement method can simultaneously realize the measurement of speed and micro-angle.

[0050] like Figure 1As shown, a device for synchronously measuring speed and micro-angle based on the self-mixing effect of laser multi-longitudinal modes includes a multi-longitudinal mode laser 1, a speed 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 fiber and is emitted from one end of the sensing fiber to the speed target 2. The speed 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 rotating surface 21 of the speed target 2, forming a self-mixing signal. The bottom of the speed target 2 is fixed on the turntable 8. The speed target 2 is provided with an adjustable speed 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 speed target 2. The self-mixing signal is fed back to the multi-longitudinal mode laser 1 , and 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 simultaneously obtains the speed and micro-angle change values ​​of the speed target 2 .

[0051] The present invention provides a device for synchronously measuring speed and micro-angle of multi-longitudinal mode self-mixing effects, comprising:

[0052] Launching device, speed reflection module, sliding table and signal processing unit.

[0053] The transmitter is located on a sliding platform; the velocity reflection module is located on the outgoing light path of the transmitter; and the transmitter is connected to the signal processing unit. The bottom of the transmitter is fixed to a slider 32 of the sliding platform, and the slider 32 is mounted on a slide rail 33 and can move horizontally along the slide rail 33.

[0054] The sliding platform includes a slider 32 and a slide rail 33 .

[0055] The slider is connected to the launching device.

[0056] The slider 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 direction.

[0057] The transmitting device is used to transmit laser light to the speed reflection module, receive the laser light reflected by the speed 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 speed reflection module receives the laser light emitted by the transmitting device and feeds it back to the resonant cavity of the multi-longitudinal mode laser 1 of the transmitting device through a feedback structure (including reflected and scattered light) to form a self-mixing signal.

[0058] The transmitting device includes: a multi-longitudinal mode laser 1 and a detector 7.

[0059] Multi-longitudinal mode laser 1, preferably a low-cost semiconductor multi-longitudinal mode laser; but other multi-longitudinal mode lasers can also be used (such as multi-longitudinal mode fiber lasers, which are not susceptible to electromagnetic interference, can emit more stable lasers, and are more suitable for complex working environments).

[0060] The output end of the detector 7 is connected to the signal processing unit 4 .

[0061] The multi-longitudinal mode laser 1 is used in the speed reflection module to receive the laser light reflected by the speed reflection module and form a self-mixing signal based on the reflected laser light.

[0062] The multi-longitudinal mode laser 1 includes a semiconductor multi-longitudinal mode laser or an optical fiber multi-longitudinal mode laser.

[0063] 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 .

[0064] The speed reflection module is used to reflect and transmit the received laser light into the resonant cavity of the transmitting device.

[0065] The speed reflection module includes: a speed target 2 and a signal generator 6.

[0066] The speed target 2 is located on the outgoing light path of the transmitting device and is connected to the signal generator 6. The speed target 2 includes a speaker or piezoelectric ceramic driven by the signal generator.

[0067] The speed target 2 is used to reflect and transmit the received laser light into the resonant cavity of the transmitting device.

[0068] The signal generator 6 is used to provide a speed signal for the speed target 2 .

[0069] The speed reflection module further includes a turntable 8 .

[0070] The speed target 2 is set on the turntable 8 .

[0071] The turntable 8 is used to adjust the angle of the reflective structure in the speed target 2 .

[0072] The signal processing unit 4 is configured to determine the velocity and micro-angle changes of the velocity reflection module based on a compensation distance and a self-mixing signal. The compensation distance is the distance the transmitter moves along the outgoing optical path after adjusting the sliding stage 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.

[0073] The present invention also provides a method for simultaneously measuring speed and micro-angle based on the speed and micro-angle synchronous measurement device of the multi-longitudinal mode self-mixing effect, comprising the following steps:

[0074] Turn on the speed target 1 and the multi-longitudinal mode laser 1, observe the multi-longitudinal mode self-mixing signal on the signal processing unit 4, move the slider 32, make the waveform of the signal processing unit maintain the same phase or phase delay is an integer multiple of 2π, record the compensation distance δL moved by the slider 32 c1 ; At the same time, the Doppler shift The real-time rotation speed can be obtained synchronously through the changes in the spectrum analyzer signal.

[0075] An attenuator 3 is provided between the transmitting device and the speed reflection module.

[0076] The attenuator 3 is used to adjust the intensity of the laser reflected into the emitting device.

[0077] A collimator 5 is further provided between the transmitting device and the speed reflection module.

[0078] The collimator 5 is used to make the laser light irradiate the speed reflection module in parallel. The collimator 5 ensures that the laser light is emitted in parallel to the surface of the target object.

[0079] The speed and micro-angle synchronous measurement device of the multi-longitudinal mode self-mixing effect provided by the present invention is based on the output signal waveform changes caused by the multi-longitudinal mode laser self-mixing feedback signal changing with the speed and micro-angle, and synchronizes the speed and micro-angle changes of the position to be measured in real time by adjusting the external cavity length to track the self-mixing signal waveform.

[0080] The method for simultaneously measuring speed and micro-angle using the above-mentioned device is as follows: the speed target 2 generates speed, 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 speed 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 speed 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 speed and micro-angle change values ​​of the environment in which the speed target 2 is located. The specific steps are as follows:

[0081] For the laser self-mixing signal of a multi-longitudinal mode laser, different longitudinal modes of the laser 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:

[0082]

[0083] 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.

[0084] When the target's micro-angle changes, there are:

[0085] op tj =op0+δop s +δop c =op0+δ(n s L s )+δ(n c L c )(2)

[0086]

[0087] 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 micro-angle, 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 L is the total geometric length of the actual path of the laser transmission in the sensor unit, 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 a slight angle change, δφ cj To compensate for phase changes, when measuring micro-angle changes, δφ sj =-δφ cj .

[0088] 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:

[0089] op tj =2mn g L0(4)

[0090] 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 speed target changes slightly, 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 micro-angle change can be obtained. s , the phase delay of the outgoing light wave can be expressed as:

[0091] φ=2πnL / λ0=βL(5)

[0092] 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.

[0093] Therefore, the compensation distance δL is measured using c2 , get the change value of the micro angle.

[0094] At the same time, by recording the changes in the number of fringes in the laser self-mixing interference image, the changes in velocity frequency (or amplitude) can be calculated.

[0095] At the same time, due to the Doppler shift:

[0096]

[0097] The real-time rotation speed can be obtained synchronously through the changes in the spectrum analyzer signal.

[0098] The present invention has the following advantages:

[0099] 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 micro-angle information. At the same time, the Doppler frequency shift observed by the spectrum analyzer can synchronously obtain speed information.

[0100] 2. The speed and micro-angle 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.

[0101] 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.

[0102] 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 the speed and micro-angle of multi-longitudinal mode self-mixing effects, characterized in that: The device for synchronously measuring the speed and micro-angle of the multi-longitudinal mode self-mixing effect comprises: Launching device, velocity reflection module, sliding table and signal processing unit; The transmitting device is located on the sliding platform; the speed 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: emitting a laser to the speed reflection module; receiving the laser reflected by the speed reflection module; The reflected laser forms a self-mixing signal; transmitting the self-mixing signal to a signal processing unit; The speed 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 speed and micro-angle change values ​​of the speed reflection module based on the compensation distance and the self-mixing signal; the compensation distance is the movement distance of the transmitting device when the sliding stage is adjusted to drive the transmitting device to move along the output light path until the phase delay of the self-mixing signal is an integer multiple of 2π.

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

5. The device for synchronously measuring the speed and micro-angle 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 speed reflection module; The collimator is used to make the laser irradiate the speed reflection module in parallel.

6. The device for synchronously measuring the speed and micro-angle of multi-longitudinal mode self-mixing effect according to claim 1, characterized in that: The speed reflection module includes: a speed target and a signal generator; The speed target is located on the outgoing light path of the transmitting device; the speed target is connected to the signal generator; The speed 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 speed signal for the speed target.

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

8. The device for synchronously measuring the speed and micro-angle of multi-longitudinal mode self-mixing effect according to claim 6, characterized in that: The speed reflection module also includes a turntable; The speed target is set on the turntable; The turntable is used to adjust the angle of the reflective structure in the speed target.

9. The device for synchronously measuring speed and micro-angle of multi-longitudinal mode self-mixing effect according to claim 1, characterized in that: The 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.

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

Images