Laser vibration meter series reciprocating type optical frequency modulation calibration device and traceability method

Abstract

The invention discloses a laser vibration meter series reciprocating type optical frequency modulation calibration device and a traceability method, and belongs to the field of photoelectric measurement. The calibration device comprises a calibrated laser vibration meter, a first acousto-optic modulator, a second acousto-optic modulator, a lens, a first sinusoidal signal source, a second sinusoidal signal source, an FM signal source, a first plane mirror, a second plane mirror, a lambda / 4 wave plate, a first polarizing beam splitter, a second polarizing beam splitter, a third polarizing beam splitter, a photoelectric detector, a data acquisition system and a lambda / 2 wave plate. The reversibility characteristic of an optical path is utilized, a linear measuring optical path structure is used, output frequency translation and modulation control of the laser vibration meter are achieved in a secondary optical frequency modulation mode of the same set of optical devices in combination with secondary optical frequency translation, and modulated laser is completely returned to the laser vibration meter in an original path. The effect of the laser Doppler effect of vibration is simulated, a calibration value of the vibration speed is obtained based on a Doppler frequency shift formula, and the calibration value is traced to the time frequency quantity of a data acquisition system.

Description

Technical Field

[0001] The invention relates to a laser vibrometer serial reciprocating optical frequency modulation calibration device and a traceability method, belonging to the technical field of photoelectric measurement. Background Art

[0002] Laser vibrometer is a universal, basic vibration and shock measuring instrument with wide frequency range, wide amplitude range, high precision, non-contact, no additional interference and influence on the measured object, and can provide velocity, acceleration, displacement change waveforms over time.

[0003] The metrological calibration of laser vibrometers has always been a difficult problem in the industry. The main reasons are: 1) Its excitation is the value of motion, and the measurement principle used is based on the laser Doppler effect. It is necessary to perceive the physical motion speed through the change of light frequency, and the output is given in the form of electrical signal acquisition data, involving different aspects such as mechanical motion, light frequency control, and electronic measurement. 2) Since the frequency range, amplitude range and accuracy of photoelectric measurement are much higher than the frequency range, amplitude range and accuracy of mechanical motion values, there has been a lack of suitable excitation sources for its metrological calibration and performance evaluation, and it is difficult to find devices and equipment that meet the requirements. 3) Usually, its metrological calibration is carried out through the excitation of a "standard vibration table", and the value measurement is carried out with a "standard laser vibrometer", and other laser vibrometers are metrologically calibrated. Since the vibration table is a physical motion device of electromechanical structure, it is limited by physical and mechanical principles, as well as material and machining capabilities. Compared with photoelectric measuring instruments such as laser vibrometers, its stability is not easy to reach very high, the frequency band is narrow, and the amplitude can reach a relatively large value at low frequency, while at high frequency, the amplitude can only achieve a very small value, and the accuracy is also low, which is not easy to meet the technical requirements for metrological traceability of laser velocity measurement. Although people have been using standard laser vibrometers to calibrate other laser vibrometers, the uncertainty caused by the characteristics of the vibration table and the limitations caused by its amplitude and frequency range are still the main problems in the metrological calibration of laser vibrometers. 4) On the other hand, using standard laser vibrometers to trace other laser vibrometers still has a logical problem in itself, that is, the metrological calibration problem of the standard laser vibrometer itself cannot be solved.

[0004] In response to these problems, “A laser vibrometer series reciprocating optical frequency modulation calibration device” proposes a solution using optical frequency regulation to perform metrological calibration, which can solve the metrological problems of the laser vibrometer and rely on the linear characteristics of the modulation process of the acousto-optic modulator to trace the laser vibrometer back to the time-frequency value of the RF signal source. However, it is not the direct laser light parameter value itself, while the value used for direct calibration belongs to the laser parameter value, and there is an inconsistency between the two. Summary of the invention

[0005] In response to the absolute traceability demand for "a laser vibrometer serial reciprocating optical frequency modulation calibration device", the purpose of the present invention is to provide a laser vibrometer serial reciprocating optical frequency modulation calibration device and a traceability method, which utilizes the reversibility characteristics of the optical path, uses a "one"-shaped measurement optical path structure, and uses the secondary optical frequency modulation method of the same set of optical devices combined with the secondary optical frequency translation to achieve the output frequency translation and modulation control of the laser vibrometer, thereby simulating the laser Doppler effect caused by different vibration waveform values, and returns the modulated laser to the calibrated laser vibrometer in its original path, so as to achieve the effect of simulating the laser Doppler effect of vibration in the best way, and finally realize the calibration traceability of the laser vibrometer based on the laser Doppler velocity measurement principle. Compared with the electromechanical vibration table excitation method, the present invention does not require a mechanically moving vibration table and a standard laser vibrometer, as well as additional auxiliary facilities such as a vibration isolation foundation, so it can be portable, have a wide frequency range, and a wide amplitude range, and can achieve the calibration traceability of the laser vibrometer with high accuracy and stability.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] The invention discloses a laser vibrometer serial reciprocating optical frequency modulation calibration device, comprising a calibrated laser vibrometer, a first acousto-optic modulator, a second acousto-optic modulator, a lens, a first sinusoidal signal source, a second sinusoidal signal source, an FM signal source, a first plane reflector, a second plane reflector, a λ / 4 wave plate, a first polarization beam splitter, a second polarization beam splitter, a third polarization beam splitter, a photoelectric detector, a data acquisition system, and a λ / 2 wave plate.

[0008] Among them, the calibrated laser vibrometer, the second polarization beam splitter, the first acousto-optic modulator, the first polarization beam splitter, the second acousto-optic modulator, the lens, the λ / 4 wave plate, and the first plane reflector constitute an "I"-shaped measurement optical path structure.

[0009] The laser with a frequency of f1 generated by the calibrated laser vibrometer is split into two paths by the second polarization beam splitter.

[0010] The output frequency of the first sinusoidal signal source is f B The sinusoidal signal controls the first AOM to work at the -1 diffraction order, generating -f B frequency offset.

[0011] The second sinusoidal signal source outputs a sinusoidal signal with a frequency of Ω, which controls the FM signal source to generate a carrier frequency of f B , a frequency deviation of Δf, and a modulation frequency of Ω, controls the second AOM to work at the +1 diffraction order, and generates +f for the laser passing through the second AOM B +f dThe laser frequency shift.

[0012] The vertex of the diffraction angle of the output light of the second AOM is located at the focal length position of the lens.

[0013] The transmitted light that passes through the second polarization beam splitter is converted into a frequency of f1-f by the first acousto-optic modulator. B Then it passes through the first polarization beam splitter and the second acousto-optic modulator and becomes a laser with a frequency of f1+f d The fan-shaped space scanning shape-changing path laser passes through the lens and becomes a translational space scanning shape-changing path laser. Then it passes through the λ / 4 wave plate, is reflected by the first plane reflector, passes through the λ / 4 wave plate again, passes through the lens, converges to the second acousto-optic modulator, passes through the second acousto-optic modulator, and becomes a frequency of f1+f B +2f d The laser is split into two beams by the first polarization beam splitter.

[0014] After the first beam passes through the first polarization beam splitter, it passes through the first acousto-optic modulator and becomes a frequency of f1+2f d The laser passes through the second polarization beam splitter and returns to the calibrated laser vibrometer for measurement and analysis.

[0015] The frequency of the second beam is f1+f B +2f d After the laser is reflected by the polarization beam splitter, it passes through the λ / 2 wave plate and the third polarization beam splitter, and after interference with the laser beam with a frequency of f1 reflected by the second plane reflector, it is detected by the photodetector.

[0016] The other reflected light from the second polarization beam splitter is reflected by the second plane reflector and the third polarization beam splitter, and the frequency of the light coming from the λ / 2 wave plate is f1+f B +2f d The transmitted light beams interfere and are detected by the photodetector.

[0017] The frequency of the photodetector output is f B +2f d The FM electrical signal is collected and measured by the data acquisition system and demodulated to f d The signal waveform is used as the standard value for the calibration of the serial reciprocating optical frequency modulation.

[0018] The present invention also discloses a laser vibrometer serial reciprocating optical frequency modulation tracing method, which is implemented based on the laser vibrometer serial reciprocating optical frequency modulation calibration device. A laser vibrometer serial reciprocating optical frequency modulation tracing method, utilizing the reversibility characteristics of the optical path, using a "one"-shaped measuring optical path structure, and combining the "secondary optical frequency modulation method" of the same set of optical devices with the "secondary optical frequency translation" to achieve output frequency translation and modulation control of the laser vibrometer, thereby simulating the laser Doppler effect caused by different vibration waveform values, and returning the modulated laser to the calibrated laser vibrometer in its original path, achieving the effect of simulating the laser Doppler effect of vibration in the best way, thereby achieving calibration traceability of the laser vibrometer based on the laser Doppler velocity measurement principle;

[0019] Furthermore, the specific implementation method of the serial reciprocating optical frequency modulation calibration method is as follows:

[0020] Use two first acousto-optic modulators and second acousto-optic modulators of the same model and specification connected in series;

[0021] The incident light emitted by the calibrated laser vibrometer is firstly frequency-shifted by the first acousto-optic modulator working in the -1 diffraction order, and then optically frequency-modulated by the second acousto-optic modulator working in the +1 diffraction order;

[0022] The reflected light reflected by the first plane reflector is firstly subjected to optical frequency modulation by the second acousto-optic modulator working at the +1 diffraction order, and then frequency-shifted again by the first acousto-optic modulator working at the -1 diffraction order;

[0023] Thus, a frequency signal is used to generate a laser Doppler effect signal waveform that simulates a vibration waveform, thereby completing the frequency shift and modulation control of the measuring laser.

[0024] The first acousto-optic modulator is always performing frequency translation of the incident light and frequency translation of the reflected light at the same time; the second acousto-optic modulator is always performing frequency modulation of the incident light and frequency modulation of the reflected light at the same time.

[0025] Furthermore, P is a laser vibrometer 1 in a stationary state, Q is a vibrating object in relative motion with P and with a velocity v(t), and the vibration displacement equation is:

[0026]

[0027] Where A is the amplitude; Ω is the vibration frequency; is the initial phase of vibration

[0028] Vibration speed:

[0029]

[0030] Peak vibration velocity:

[0031] v m =2πΩA (3)

[0032] The incident light emitted by P is:

[0033] E1(t)=E0 sin(2πf1t) (4)

[0034] The outgoing light reflected by Q is:

[0035] E2(t)=E0 sin(2πf2t+θ0) (5)

[0036] Among them, E0 is the incident light amplitude; f1 is the incident light frequency; f2 is the outgoing light frequency; θ0 is the initial phase of the outgoing light. According to the laser Doppler effect, the outgoing light frequency is:

[0037]

[0038] Doppler frequency shift f d :

[0039]

[0040] The peak value of the vibration velocity v is determined by the modulation frequency deviation Δf using the Doppler frequency shift formula m :

[0041]

[0042] Where Δf is the modulation frequency deviation, c is the speed of light, and λ is the wavelength of the incident laser.

[0043] Outgoing light phase:

[0044]

[0045] Where θ0 is the initial phase

[0046] Emerging light:

[0047]

[0048] The frequency f2(t) of the outgoing light E2(t) is obtained by superimposing a cosine-law-varying FM light portion with a frequency deviation of Δf and a modulation frequency of Ω on the frequency f1 of the incident light E1(t).

[0049] According to equations (6), (7), (8), and (9), optical frequency modulation calibration traceability of the laser vibrometer is achieved through optical frequency modulation.

[0050] Furthermore, the specific implementation method is:

[0051] The output frequency of the first sinusoidal signal source is fB The sinusoidal signal controls the first AOM to work at the -1 diffraction order, generating -f B The frequency offset of

[0052] The second sinusoidal signal source outputs a sinusoidal signal with a frequency of Ω, which controls the FM signal source to generate a carrier frequency of f B , a frequency deviation of Δf, and a modulation frequency of Ω, controls the second AOM to work at the +1 diffraction order, and generates +f for the laser passing through the second AOM B +f d The laser frequency shift;

[0053] The laser with frequency f1 generated by the calibrated laser vibrometer is split into two paths by the second polarization beam splitter:

[0054] The transmitted light that passes through the second polarization beam splitter is converted into a frequency of f1-f by the first acousto-optic modulator. B Then it passes through the first polarization beam splitter and the second acousto-optic modulator and becomes a laser with a frequency of f1+f d The fan-shaped space scanning shape-changing path laser passes through the lens and becomes a translational space scanning shape-changing path laser. Then it passes through the λ / 4 wave plate, is reflected by the first plane reflector, passes through the λ / 4 wave plate again, passes through the lens, converges to the second acousto-optic modulator, passes through the second acousto-optic modulator, and becomes a frequency of f1+f B +2f d The laser is split into two beams by the first polarization beam splitter;

[0055] After the first beam passes through the first polarization beam splitter, it passes through the first acousto-optic modulator and becomes a frequency of f1+2f d The laser passes through the second polarization beam splitter and returns to the calibrated laser vibrometer for measurement and analysis, giving the vibration velocity v m The velocity measurement result is compared with the vibration velocity peak value v determined by Δf according to formula (9) m In comparison, the calibration traceability of the laser vibrometer is achieved.

[0056] The frequency of the second beam is f1+f B +2f d After the laser is reflected by the polarization beam splitter, it passes through the λ / 2 wave plate and the third polarization beam splitter, and after interference with the laser beam with a frequency of f1 reflected by the second plane reflector, it is detected by the photodetector.

[0057] The other reflected light from the second polarization beam splitter is reflected by the second plane reflector and the third polarization beam splitter, and the frequency of the light coming from the λ / 2 wave plate is f1+f B +2f dThe transmitted light beams interfere and are detected by the photodetector.

[0058] The frequency of the photodetector output is f B +2f d The FM electrical signal is collected and measured by the data acquisition system and demodulated to f d The signal waveform is used as the standard value for the serial reciprocating optical frequency modulation calibration, and the peak value v of the vibration velocity is obtained using formula (9): m The calibration value is used to calibrate the laser vibrometer to be calibrated, and the vibration velocity peak value v is obtained through the data acquisition system. m Trace back to the time frequency quantity.

[0059] Furthermore, a lens is used to convert the fan-shaped spatial scanning light into a parallel shifted spatial scanning light, thereby achieving stable and reliable plane reflection. In addition, the vertex of the diffraction angle of the output light of the second acousto-optic modulator is located at the focal length position of the lens.

[0060] Furthermore, the first AOM and the second AOM respectively work at -2 and +2, -3 and +3 or other diffraction orders to achieve calibration traceability.

[0061] Furthermore, the FM optical frequency signal with heterodyne characteristics and the original measurement light signal are extracted from the first polarization beam splitter and the second polarization beam splitter in the system respectively, the two are beat and demodulated to obtain the standard value of the vibration velocity, and it is traced back to the time and frequency quantity of the data acquisition system to achieve the metrological traceability of the laser Doppler signal parameters, thereby completing the metrological traceability of the laser vibrometer.

[0062] Beneficial effects:

[0063] 1. The present invention discloses a laser vibrometer serial reciprocating optical frequency modulation calibration device and a traceability method. Based on the laser frequency emitted by the calibrated laser vibrometer, the reversible characteristics of the optical path are utilized, and a "one"-shaped measurement optical path structure is used. The secondary optical frequency modulation method of the same set of optical devices is combined with the secondary optical frequency shift to realize the output frequency shift and modulation control of the laser vibrometer, thereby simulating the laser Doppler effect caused by different vibration waveform values, and returning the modulated laser to the calibrated laser vibrometer in its original path, thereby realizing the effect of simulating the laser Doppler effect of vibration in the best way.

[0064] 2. The present invention discloses a laser vibrometer serial reciprocating optical frequency modulation calibration device and traceability method. Due to the use of an "I"-shaped reciprocating measurement optical path, the reversibility of the optical path is effectively utilized, the number of optical components used is greatly reduced, the light quality is extremely stable and reliable, the waveform and parameter reproducibility are extremely strong, and the stability problem in the optical frequency regulation process is completely overcome, making it easier to promote and apply. Due to the use of secondary modulation and secondary frequency shift, the simulated vibration amplitude range obtained by the present invention has a doubling effect, thereby expanding the amplitude range.

[0065] 3. The present invention discloses a laser vibrometer serial reciprocating optical frequency modulation calibration device and traceability method. After frequency shift control is performed using an acousto-optic modulator, optical frequency modulation is performed according to the vibration waveform parameters, and the optical frequency modulation is fed back to the calibrated laser vibrometer, so that the waveform of the vibration velocity value is replaced by the waveform of the frequency value, thereby realizing the calibration of the laser vibrometer. Then, the FM optical frequency signal with heterodyne characteristics and the original measurement light signal are extracted from the system respectively, and the two are beat and demodulated to obtain the standard value of the vibration velocity, which is then traced back to the time frequency quantity of the data acquisition system, realizing the metrological traceability of the laser Doppler signal parameters, and then completing the metrological traceability of the laser vibrometer.

[0066] 4. The present invention discloses a laser vibrometer serial reciprocating optical frequency modulation calibration device and traceability method, which realizes the mechanical motion speed value by equivalently realizing the mechanical motion speed value with the frequency value of the electrical signal source, and can overcome the problems of large size, unstable performance, and non-portability of providing an excitation source for the calibrated equipment in the form of mechanical motion, while being portable and high-precision, and realizing on-site measurement and calibration conveniently and quickly.

[0067] 5. The present invention discloses a laser vibrometer serial reciprocating optical frequency modulation calibration device and traceability method, which uses different diffraction orders to calibrate different speed value intervals. Each laser diffraction order has a certain spectrum width, and frequency modulation and control are performed within the spectrum width.

[0068] 6. The present invention discloses a laser vibrometer serial reciprocating optical frequency modulation calibration device and a traceability method, which uses a lens to convert the fan-shaped spatial scanning light output by the acousto-optic modulator into a parallel moving spatial scanning light, and then reflects it through a plane mirror. This can overcome the problems of unstable optical path, fluctuating intensity, light loss, and loss of lock caused by the fan-shaped spatial scanning light output by the acousto-optic modulator, obtain stable, reliable, and reproducible optical characteristics, and thus realize the optical frequency regulation method to calibrate the laser vibrometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 This is a schematic diagram of the laser Doppler effect;

[0070] Figure 2It is a structural schematic diagram of a laser vibrometer serial reciprocating optical frequency modulation calibration device of the present invention;

[0071] Wherein: 1—laser vibrometer, 2—first acousto-optic modulator, 3—second acousto-optic modulator, 4—lens, 5—first sinusoidal signal source, 6—FM signal source, 7—second sinusoidal signal source, 8—first plane reflector, 9—λ / 4 wave plate, 10—first polarization beam splitter, 11—photodetector, 12—data acquisition system, 13—second polarization beam splitter, 14—second plane reflector, 15—λ / 2 wave plate, 16—third polarization beam splitter. DETAILED DESCRIPTION

[0072] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0073] Embodiment 1:

[0074] like Figure 2 As shown, a laser vibrometer serial reciprocating optical frequency modulation calibration device disclosed in this embodiment includes a laser vibrometer 1 to be calibrated, a first acousto-optic modulator 2, a second acousto-optic modulator 3, a lens 4, a first sinusoidal signal source 5, a second sinusoidal signal source 7, an FM signal source 6, a first plane reflector 8, a second plane reflector 14, a λ / 4 wave plate 9, a first polarization beam splitter 10, a second polarization beam splitter 13, a third polarization beam splitter 16, a photodetector 11, a data acquisition system 12, and a λ / 2 wave plate 15.

[0075] The laser light with a wavelength λ=632.8 nm and a frequency f1=c / λ generated by the calibrated laser vibrometer 1 is split into two paths by the second polarization beam splitter 13 .

[0076] The output frequency of the first sinusoidal signal source 5 is f B =100MHz sinusoidal signal, controls the first AOM 2 to work at the -1st diffraction order, and generates -f for the laser passing through the first AOM 2 B =Frequency deviation of -100MHz.

[0077] The second sinusoidal signal source 7 outputs a sinusoidal signal with a frequency of Ω=5MHz, which controls the FM signal source 6 to generate a carrier frequency of f B =100MHz, frequency deviation Δf=20MHz, modulation frequency Ω=5MHz FM voltage signal, control the second acousto-optic modulator 3 to work at the +1st diffraction order, and generate +f for the laser passing through the second acousto-optic modulator 3 B +f d =100MHz+f d The laser frequency shift.

[0078] The vertex of the diffraction angle of the output light of the second AOM 3 is located at the focal length position of the lens 4 .

[0079] The transmitted light passing through the second polarization beam splitter 13 is converted into a frequency of f1-f by the first acousto-optic modulator 2. B = f1-100MHz laser; then passes through the first polarization beam splitter 10, and the second acousto-optic modulator 3, and becomes a frequency of f1+f d The fan-shaped space scanning shape-changing path laser passes through the lens 4 and becomes the translational space scanning shape-changing path laser; then passes through the λ / 4 wave plate 9, is reflected by the first plane reflector 8, passes through the λ / 4 wave plate 9 again, passes through the lens 4, converges to the second acousto-optic modulator 3, passes through the second acousto-optic modulator 3, and becomes the frequency f1+f B +2f d =f1+100MHz+2f d The laser light is split into two beams by the first polarization beam splitter 10.

[0080] After the first beam passes through the first polarization beam splitter 10, it passes through the first acousto-optic modulator 2 and becomes a frequency of f1+2f d The laser passes through the second polarization beam splitter 13 and returns to the calibrated laser vibrometer 1 for measurement and analysis.

[0081] The frequency of the second beam is f1+f B +2f d =f1+100MHz+2f d The laser is reflected by the first polarization beam splitter 10, passes through the λ / 2 wave plate 15 and the third polarization beam splitter 16, and is detected by the photodetector 11 after frequency interference with the laser beam with a frequency of f1 reflected by the second plane reflector 14.

[0082] The other reflected light from the second polarization beam splitter 13 is reflected by the second plane reflector 14 and the third polarization beam splitter 16, and the frequency of the light from the direction of the λ / 2 wave plate 15 is f1+f B +2f d =f1+100MHz+2f d The transmitted light beam beats and interferes with each other and is detected by the photodetector 11.

[0083] The frequency of the output of the photodetector 11 is f B +2f d =100MHz+2f d The FM electrical signal is collected and measured by the data acquisition system 12, and the demodulated signal f d The signal waveform, f d The corresponding velocity value peak v m As a standard value for calibration of tandem reciprocating optical frequency modulation.

[0084] This embodiment also discloses a laser vibrometer serial reciprocating optical frequency modulation tracing method, which is implemented based on the laser vibrometer serial reciprocating optical frequency modulation calibration device. A laser vibrometer serial reciprocating optical frequency modulation tracing method, utilizing the reversibility characteristics of the optical path, using a "one"-shaped measurement optical path structure, and combining the "secondary optical frequency modulation method" of the same set of optical devices with the "secondary optical frequency translation" to achieve output frequency translation and modulation control of the laser vibrometer 1, thereby simulating the laser Doppler effect caused by different vibration waveform values, and returning the modulated laser to the calibrated laser vibrometer 1 in its original path, achieving the effect of simulating the laser Doppler effect of vibration in the best way, thereby achieving the calibration traceability of the laser vibrometer 1 based on the laser Doppler velocity measurement principle;

[0085] Furthermore, the specific implementation method of the serial reciprocating optical frequency modulation calibration method is as follows:

[0086] Use two first acousto-optic modulators and second acousto-optic modulators of the same model and specification connected in series;

[0087] The incident light emitted by the calibrated laser vibrometer is firstly frequency-shifted by the first acousto-optic modulator working in the -1 diffraction order, and then optically frequency-modulated by the second acousto-optic modulator working in the +1 diffraction order;

[0088] The reflected light reflected by the first plane reflector is firstly subjected to optical frequency modulation by the second acousto-optic modulator working at the +1 diffraction order, and then frequency-shifted again by the first acousto-optic modulator working at the -1 diffraction order;

[0089] Thus, a frequency signal is used to generate a laser Doppler effect signal waveform that simulates a vibration waveform, thereby completing the frequency shift and modulation control of the measuring laser.

[0090] The first acousto-optic modulator is always performing frequency translation of the incident light and frequency translation of the reflected light at the same time; the second acousto-optic modulator is always performing frequency modulation of the incident light and frequency modulation of the reflected light at the same time.

[0091] Furthermore, P is a laser vibrometer 1 in a stationary state, Q is a vibrating object in relative motion with P and with a velocity v(t), and the vibration displacement equation is:

[0092]

[0093] Where A is the amplitude; Ω is the vibration frequency; is the initial phase of vibration

[0094] Vibration speed:

[0095]

[0096] Peak vibration velocity:

[0097] v m =2πΩA (3)

[0098] The incident light emitted by P is:

[0099] E1(t)=E0 sin(2πf1t) (4)

[0100] The outgoing light reflected by Q is:

[0101] E2(t)=E0 sin(2πf2t+θ0) (5)

[0102] Among them, E0 is the incident light amplitude; f1 is the incident light frequency; f2 is the outgoing light frequency; θ0 is the initial phase of the outgoing light. According to the laser Doppler effect, the outgoing light frequency is:

[0103]

[0104] Doppler frequency shift f d :

[0105]

[0106] The peak value of the vibration velocity v is determined by the modulation frequency deviation Δf using the Doppler frequency shift formula m :

[0107]

[0108] Where Δf is the modulation frequency deviation, c is the speed of light, and λ is the wavelength of the incident laser.

[0109] Outgoing light phase:

[0110]

[0111] Where θ0 is the initial phase

[0112] Emerging light:

[0113]

[0114] The frequency f2(t) of the outgoing light E2(t) is obtained by superimposing a cosine-law-varying FM light portion with a frequency deviation of Δf and a modulation frequency of Ω on the frequency f1 of the incident light E1(t).

[0115] According to equations (6), (7), (8), and (9), optical frequency modulation calibration traceability of the laser vibrometer is achieved through optical frequency modulation.

[0116] Furthermore, the specific implementation method is:

[0117] The output frequency of the first sinusoidal signal source 5 is f B =100MHz sinusoidal signal, controls the first AOM 2 to work at the -1st diffraction order, and generates -f for the laser passing through the first AOM 2 B =-100MHz frequency offset;

[0118] The second sinusoidal signal source 7 outputs a sinusoidal signal with a frequency of Ω=5MHz, which controls the FM signal source 6 to generate a carrier frequency of f B =100MHz, frequency deviation Δf=20MHz, modulation frequency Ω=5MHz FM voltage signal, control the second acousto-optic modulator 3 to work at the +1st diffraction order, and generate +f for the laser passing through the second acousto-optic modulator 3 B +f d =100MHz+f d The laser frequency shift;

[0119] The laser light with a frequency of f1 generated by the calibrated laser vibrometer 1 is split into two paths by the second polarization beam splitter 13:

[0120] The transmitted light passing through the second polarization beam splitter 13 is converted into a frequency of f1-f by the first acousto-optic modulator 2. B = f1-100MHz laser; then passes through the first polarization beam splitter 10, and the second acousto-optic modulator 3, and becomes a frequency of f1+f d The fan-shaped space scanning shape-changing path laser passes through the lens 4 and becomes the translational space scanning shape-changing path laser; then passes through the λ / 4 wave plate 9, is reflected by the first plane reflector 8, passes through the λ / 4 wave plate 9 again, passes through the lens 4, converges to the second acousto-optic modulator 3, passes through the second acousto-optic modulator 3, and becomes the frequency f1+f B +2f d =f1+100MHz+2f d The laser light is split into two beams by the first polarization beam splitter 10;

[0121] After the first beam passes through the first polarization beam splitter 10, it passes through the first acousto-optic modulator 2 and becomes a frequency of f1+2f d The laser passes through the second polarization beam splitter 13 and returns to the calibrated laser vibrometer 1 for measurement and analysis, giving the vibration velocity v m The speed measurement result is compared with the vibration speed v determined by Δf according to formula (9) m In comparison, a calibration of the laser vibrometer 1 is achieved.

[0122] The frequency of the second beam is f1+f B +2f d =f1+100MHz+2f dAfter being reflected by the polarization beam splitter 10 , the laser passes through the λ / 2 wave plate 15 and the third polarization beam splitter 16 , and after frequency interference with the laser beam with a frequency of f1 reflected by the second plane reflector 14 , it is detected by the photodetector 11 .

[0123] The other reflected light from the second polarization beam splitter 13 is reflected by the second plane reflector 14 and the third polarization beam splitter 16, and the frequency of the light from the direction of the λ / 2 wave plate 15 is f1+f B +2f d =f1+100MHz+2f d The transmitted light beam beats and interferes with each other and is detected by the photodetector 11.

[0124] The frequency of the output of the photodetector 11 is f B +2f d =100MHz+2f d The FM electrical signal is collected and measured by the data acquisition system 12, and the demodulated signal f d The signal waveform is used as the standard value for the serial reciprocating optical frequency modulation calibration. The calibration value of the vibration velocity is obtained using formula (9) and traced back to the time frequency value of the data acquisition system.

[0125] Furthermore, a lens is used to convert the fan-shaped spatial scanning light into a parallel shifted spatial scanning light, thereby achieving stable and reliable plane reflection. In addition, the vertex of the diffraction angle of the output light of the second acousto-optic modulator 3 is located at the focal length position of the lens 4.

[0126] Furthermore, the first AOM 2 and the second AOM 3 respectively work at -2 and +2, -3 and +3 or other diffraction orders to achieve calibration traceability.

[0127] Furthermore, the FM optical frequency signal with heterodyne characteristics and the original measurement light signal are extracted from the first polarization beam splitter 10 and the second polarization beam splitter 13 in the system, respectively, and the two are beat and demodulated to obtain the standard value of the vibration velocity, which is traced back to the time frequency quantity of the data acquisition system 12 to achieve the metrological traceability of the laser Doppler signal parameters, thereby completing the metrological traceability of the laser vibrometer 1.

[0128] Based on the optical path structure of “a laser vibrometer serially connected reciprocating optical frequency modulation calibration device”, this embodiment constructs a light wave extraction structure to extract a laser signal with heterodyne information. After being received by the photoelectric detector 11, it is converted into an electrical signal. After data acquisition and FM signal demodulation, vibration parameters of the same vibration signal as that fed back to the calibrated laser vibrometer 1 are obtained. By comparing the vibration parameters with the measurement results of the calibrated laser vibrometer 1, the measurement results of the calibrated laser vibrometer 1 can be traced back to the time and frequency quantity of the data acquisition system 12.

[0129] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A laser vibrometer serial reciprocating optical frequency modulation calibration device, characterized in that: The invention comprises a calibrated laser vibrometer (1), a first acousto-optic modulator (2), a second acousto-optic modulator (3), a lens (4), a first sinusoidal signal source (5), a second sinusoidal signal source (7), an FM signal source (6), a first plane reflector (8), a second plane reflector (14), a λ / 4 wave plate (9), a first polarization beam splitter (10), a second polarization beam splitter (13), a third polarization beam splitter (16), a photoelectric detector (11), a data acquisition system (12), and a λ / 2 wave plate (15); The laser light with a frequency of f1 generated by the calibrated laser vibrometer (1) is split into two paths by a second polarization beam splitter (13); The output frequency of the first sinusoidal signal source (5) is f B The sine signal controls the first acousto-optic modulator (2) to work at the -1 diffraction order, and generates -f for the laser passing through the first acousto-optic modulator (2). B The frequency offset of The second sinusoidal signal source (7) outputs a sinusoidal signal with a frequency of Ω, and controls the FM signal source (6) to generate a carrier frequency of f B , a frequency deviation of Δf and a modulation frequency of Ω, controls the second acousto-optic modulator (3) to work at the +1 diffraction order, and generates +f for the laser passing through the second acousto-optic modulator (3). B +f d The laser frequency shift; The vertex of the diffraction angle of the output light of the second acousto-optic modulator (3) is located at the focal length position of the lens (4); The transmitted light passing through the second polarization beam splitter (13) is converted into a light having a frequency of f1-f by passing through the first acousto-optic modulator (2). B Then it passes through the first polarization beam splitter (10) and the second acousto-optic modulator (3) and becomes a frequency of f1+f d The laser beam is a fan-shaped space scanning shape-changing path laser beam; it passes through the lens (4) to become a translational space scanning shape-changing path laser beam; it then passes through the λ / 4 wave plate (9), is reflected by the first plane reflector (8), passes through the λ / 4 wave plate (9) again, passes through the lens (4), converges to the second acousto-optic modulator (3), passes through the second acousto-optic modulator (3), and becomes a laser beam with a frequency of f1+f B +2f d The laser light is split into two beams by a first polarization beam splitter (10); After the first beam passes through the first polarization beam splitter (10), it passes through the first acousto-optic modulator (2) and becomes a beam with a frequency of f1+2f d The laser light passes through a second polarization beam splitter (13) and returns to the calibrated laser vibrometer (1) for measurement and analysis; The frequency of the second beam is f1+f B +2f d After the laser is reflected by the first polarization beam splitter (10), it passes through the λ / 2 wave plate (15) and the third polarization beam splitter (16), and after frequency interference with the laser beam combination with a frequency of f1 reflected by the second plane reflection mirror (14), it is detected by the photoelectric detector (11); The other reflected light, which is reflected by the second polarization beam splitter (13), is reflected by the second plane reflector (14) and the third polarization beam splitter (16) in sequence, and the frequency of the light coming from the direction of the λ / 2 wave plate (15) is f1+f B +2f d The transmitted light beam beats and interferes, and is detected by a photodetector (11); The frequency of the photodetector (11) output is f B +2f d The FM electrical signal is collected and measured by the data acquisition system (12) and demodulated to f d The signal waveform, f d The corresponding peak velocity v m As a standard value for calibration of tandem reciprocating optical frequency modulation.

2. A laser vibrometer serial reciprocating optical frequency modulation tracing method, based on a laser vibrometer serial reciprocating optical frequency modulation calibration device as claimed in claim 1, characterized in that: By utilizing the reversibility of the optical path, a laser vibrometer (1) to be calibrated, a second polarization beam splitter (13), a first acousto-optic modulator (2), a first polarization beam splitter (10), a second acousto-optic modulator (3), a lens (4), a λ / 4 wave plate (9), and a first plane reflector (8) are used to form a "I"-shaped round-trip measurement optical path structure; the output frequency translation and modulation control of the laser vibrometer (1) are realized by combining "secondary optical frequency modulation" with "secondary optical frequency translation" of the same set of optical components, thereby simulating the laser Doppler effect caused by different vibration waveform values, and returning the modulated laser to the laser vibrometer (1) in its original path, thereby simulating the laser Doppler effect of vibration in the best way, thereby realizing the calibration of the laser vibrometer (1) based on the laser Doppler velocity measurement principle; The first polarization beam splitter (10) and the second polarization beam splitter (13) are used to extract the measurement light simulating the vibration laser Doppler effect and the incident light emitted by the calibrated laser vibrometer (1) from the measurement light path, respectively, and perform beam combination, beat frequency, interference, measurement, and demodulation to obtain the simulated velocity value v in the laser parameter. m and trace it back to the time frequency quantity of the data acquisition system (12), thereby completing the value traceability of the calibrated laser vibrometer (1); The specific implementation method of the serial reciprocating optical frequency modulation calibration method is as follows: Using two first acousto-optic modulators (2) and second acousto-optic modulators (3) of the same model and specification connected in series; The incident light emitted by the calibrated laser vibrometer (1) is firstly frequency-shifted by a first acousto-optic modulator (2) working at the -1st diffraction order, and then optically frequency-modulated by a second acousto-optic modulator (3) working at the +1st diffraction order; The reflected light reflected back by the first plane reflector (8) is firstly subjected to optical frequency modulation by the second acousto-optic modulator (3) working at the +1st diffraction order, and then frequency-shifted again by the first acousto-optic modulator (2) working at the -1st diffraction order; Thus, the frequency signal is used to generate a laser Doppler effect signal waveform simulating the vibration waveform, and the frequency translation and modulation control of the measuring laser are completed; The first acousto-optic modulator (2) is always performing frequency translation of the incident light and frequency translation of the reflected light at the same time; the second acousto-optic modulator (3) is always performing frequency modulation of the incident light and frequency modulation of the reflected light at the same time.

3. A laser vibrometer serial reciprocating optical frequency modulation tracing method as claimed in claim 2, characterized in that: P is a laser vibrometer (1) in a stationary state, Q is a vibrating object in relative motion with P and with a velocity v(t), and its vibration displacement equation is: Where A is the amplitude; Ω is the vibration frequency; is the initial phase of vibration Vibration speed: Peak vibration velocity: v m =2πΩA (3) The incident light emitted by P is: E1(t)=E0 sin(2πf1t) (4) The outgoing light reflected by Q is: E2(t)=E0 sin(2πf2t+θ0) (5) Among them, E0 is the incident light amplitude; f1 is the incident light frequency; f2 is the outgoing light frequency; θ0 is the initial phase of the outgoing light. According to the laser Doppler effect, the outgoing light frequency is: Doppler frequency shift f d : The peak value of the vibration velocity v is determined by the modulation frequency deviation Δf using the Doppler frequency shift formula m : Where Δf is the modulation frequency deviation, c is the speed of light, and λ is the wavelength of the incident laser. Outgoing light phase: Where θ0 is the initial phase Emerging light: The frequency f2(t) of the outgoing light E2(t) is the frequency f1 of the incident light E1(t), with a cosine-law-varying FM light part superimposed on it. According to equations (6), (7), (8), and (9), optical frequency modulation calibration of the laser vibrometer is achieved through optical frequency modulation.

4. A laser vibrometer serial reciprocating optical frequency modulation tracing method as claimed in claim 3, characterized in that: The specific implementation method is: The output frequency of the first sinusoidal signal source (5) is f B The sine signal controls the first acousto-optic modulator (2) to work at the -1 diffraction order, and generates -f for the laser passing through the first acousto-optic modulator (2). B The frequency offset of The second sinusoidal signal source (7) outputs a sinusoidal signal with a frequency of Ω, and controls the FM signal source (6) to generate a carrier frequency of f B , a frequency deviation of Δf and a modulation frequency of Ω, controls the second acousto-optic modulator (3) to work at the +1 diffraction order, and generates +f for the laser passing through the second acousto-optic modulator (3). B +f d The laser frequency shift; The laser light with a frequency of f1 generated by the calibrated laser vibrometer (1) is divided into two paths by a second polarization beam splitter (13): The transmitted light passing through the second polarization beam splitter (13) is converted into a light having a frequency of f1-f by passing through the first acousto-optic modulator (2). B Then it passes through the first polarization beam splitter (10) and the second acousto-optic modulator (3) and becomes a frequency of f1+f d The laser beam is a fan-shaped space scanning shape-changing path laser beam; it passes through the lens (4) to become a translational space scanning shape-changing path laser beam; it then passes through the λ / 4 wave plate (9), is reflected by the first plane reflector (8), passes through the λ / 4 wave plate (9) again, passes through the lens (4), converges to the second acousto-optic modulator (3), passes through the second acousto-optic modulator (3), and becomes a laser beam with a frequency of f1+f B +2f d The laser light is split into two beams by a first polarization beam splitter (10); After the first beam passes through the first polarization beam splitter (10), it passes through the first acousto-optic modulator (2) and becomes a beam with a frequency of f1+2f d The laser passes through the second polarization beam splitter (13) and returns to the calibrated laser vibrometer (1) for measurement and analysis to give the vibration velocity v m The speed measurement result is compared with the vibration speed v determined by Δf according to formula (9) m In comparison, a laser vibrometer (1) is calibrated; The frequency of the second beam is f1+f B +2f d After the laser is reflected by the first polarization beam splitter (10), it passes through the λ / 2 wave plate (15) and the third polarization beam splitter (16), and after frequency interference with the laser beam combination with a frequency of f1 reflected by the second plane reflection mirror (14), it is detected by the photoelectric detector (11); The other reflected light, which is reflected by the second polarization beam splitter (13), is reflected by the second plane reflector (14) and the third polarization beam splitter (16) in sequence, and the frequency of the light coming from the direction of the λ / 2 wave plate (15) is f1+f B +2f d The transmitted light beam beats and interferes, and is detected by a photodetector (11); The frequency of the photodetector (11) output is f B +2f d The FM electrical signal is collected and measured by the data acquisition system (12) and demodulated to f d The signal waveform is used as the standard value for the serial reciprocating optical frequency modulation calibration. The calibration value of the vibration velocity is obtained using formula (9) and traced back to the time frequency value of the data acquisition system.

5. A laser vibrometer serial reciprocating optical frequency modulation tracing method as claimed in claim 4, characterized in that: The fan-shaped spatial scanning light is converted into parallel shifted spatial scanning light by using a lens, thereby achieving stable and reliable plane reflection; and the vertex of the diffraction angle of the output light of the second acousto-optic modulator (3) is located at the focal length position of the lens (4).

6. A laser vibrometer serial reciprocating optical frequency modulation tracing method as claimed in claim 5, characterized in that: The first acousto-optic modulator (2) and the second acousto-optic modulator (3) respectively work at -2 and +2, -3 and +3 or other diffraction orders to realize calibration traceability.

7. The laser vibrometer serial reciprocating optical frequency modulation tracing method as claimed in claim 2, characterized in that: An FM optical frequency signal with heterodyne characteristics and an original measurement optical signal are extracted from the first polarization beam splitter (10) and the second polarization beam splitter (13), the two are beat and demodulated to obtain a standard value of vibration velocity, and the value is traced back to the time frequency quantity of a data acquisition system, thereby achieving metrological traceability of laser Doppler signal parameters and completing metrological traceability of a laser vibrometer (1).

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