A method and apparatus for calibrating a broadband laser vibrometer

Abstract

This invention discloses a broadband laser vibrometer calibration method and apparatus, belonging to the field of optoelectronic measurement technology. The apparatus includes a laser vibrometer, a first acousto-optic modulator, a second acousto-optic modulator, a concave mirror, a first sinusoidal signal source, an FM signal source, and a second sinusoidal signal source. This invention uses two acousto-optic modulators for optical frequency control and processing. One modulator is loaded with a sinusoidal wave to obtain an FM signal, and the -1st order diffraction order of the acousto-optic modulator generates an optical frequency modulation signal. The other modulator is frequency-shifted using the +1st order diffraction order, ensuring the median modulation frequency is at the laser vibrometer's output frequency. The signal is reflected and converged by the concave mirror, returning to the laser vibrometer along the original path, thus obtaining an optical frequency characteristic signal that completely simulates the actual sinusoidal waveform motion. This ensures the optical frequency modulation signal maintains its median frequency upon returning to the laser vibrometer for measurement processing, thereby achieving broadband laser vibrometer calibration and evaluation.

Description

Technical Field

[0001] This invention relates to a broadband laser vibration meter calibration method and device, belonging to the field of photoelectric measurement technology. Background Technology

[0002] Laser vibrometers are general-purpose, fundamental instruments for measuring vibration and impact. They are high-precision, non-contact instruments that do not interfere with or affect the measured object. However, their calibration and performance evaluation have always been challenging issues in the industry, primarily due to the following reasons: 1) Their excitation is a motion quantity (displacement, velocity, acceleration), and the measurement principle is based on the laser Doppler effect, requiring the sensing of physical motion through changes in light frequency. The output is given as electrical signal data, involving different aspects such as mechanical motion, optical frequency control, and electronic measurement. 2) Because the frequency range and accuracy of photoelectric measurements are much higher than those of mechanical motion quantities, suitable excitation sources for calibration and performance evaluation have been lacking, making it difficult to find suitable devices and equipment. 3) Typically, calibration involves excitation using a "standard vibration table," measurement using a "standard laser vibrometer," and calibration of other laser vibrometers. Because a vibration table is a physical motion device of an electromechanical structure, it is limited by physical and mechanical principles, as well as limitations in materials and machining capabilities. Compared with photoelectric measuring instruments like laser vibrometers, its stability is not easily achieved, its bandwidth is narrower, and while its amplitude can reach relatively large values ​​at low frequencies, it can only achieve very small values ​​at high frequencies, resulting in lower accuracy. This makes it difficult to meet the technical requirements for metrological traceability of laser vibrometers. Even with the use of standard laser vibrometers for metrological calibration, the uncertainties caused by the characteristics of the vibration table and the limitations imposed by its amplitude and frequency range remain major problems in the metrological calibration of laser vibrometers. 4) On the other hand, using standard laser vibrometers for metrological traceability of other laser vibrometers also presents technical logic problems; the metrological calibration issues of the standard laser vibrometer itself remain unresolved. Summary of the Invention

[0003] To address the issues in the calibration and performance evaluation of laser vibrometers, such as the limitations imposed by mechanical motion (e.g., vibration table) preventing the technical parameters from fully covering the vibrometer's range and compromising stability, as well as the inability to fully resolve the issue of traceability in standard laser vibrometer calibration, the main objective of this invention is to provide a broadband laser vibrometer calibration method and apparatus. This method can generate a sinusoidal waveform excitation simulating vibration using optical frequency modulation, thereby solving the excitation source problem in the performance evaluation of laser vibrometers and ultimately achieving broadband laser vibrometer calibration and evaluation.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] This invention discloses a broadband laser vibrometer calibration method. For the laser signal emitted by the laser vibrometer, two acousto-optic modulators (AOMs) are used for optical frequency control and processing. One AOM modulates the laser signal with a sinusoidal wave to obtain an FM signal, and uses the -1st order diffraction stage of the AOM to generate an optical frequency modulation signal. The other AOM uses the +1st order diffraction stage of the AOM to perform frequency shifting, ensuring the median modulation frequency is at the laser vibrometer's output frequency. The signal is reflected and converged by a concave mirror, returning to the laser vibrometer along the original path. This obtains the optical frequency characteristic signal that completely simulates actual sinusoidal waveform motion, i.e., generates a sinusoidal waveform excitation simulating vibration. The characteristic signal, which maintains a constant median frequency, returns to the laser vibrometer for measurement and processing, thereby achieving broadband laser vibrometer calibration and evaluation.

[0006] The present invention discloses a broadband laser vibration meter calibration device, comprising a laser vibration meter, a first acousto-optic modulator, a second acousto-optic modulator, a concave reflector, a first sine wave signal source, an FM signal source, and a second sine wave signal source.

[0007] The laser generated by the laser vibrometer passes through a first acousto-optic modulator, which, controlled by a first sinusoidal signal source, generates a +1st-order diffraction frequency shift. The laser then reaches a second acousto-optic modulator, where a sinusoidal signal source generates a sinusoidal signal that modulates the frequency of an FM signal source. This modulated FM signal controls the second acousto-optic modulator, which in turn shifts and modulates the optical frequency transmitted from the first acousto-optic modulator, generating a -1st-order diffracted laser. This laser is reflected and focused by a concave mirror and returns to the second acousto-optic modulator, where it is again frequency-shifted and modulated. Finally, it passes through the first acousto-optic modulator for further frequency shifting before returning to the laser vibrometer. This completes the simulation process of using a sinusoidal waveform generated by the second sinusoidal signal source to excite the laser vibrometer.

[0008] By comparing the measurement results of sinusoidal waveforms of different frequencies obtained by the laser vibrometer with the second sinusoidal signal source, the excitation response characteristics of the laser vibrometer can be obtained, thereby realizing the calibration and performance evaluation of the broadband laser vibrometer.

[0009] Preferably, a concave mirror with spherical features is used to reflect and converge a laser beam that has beam instability characteristics after passing through a second acousto-optic modulator due to the combination of optical frequency modulation and diffraction.

[0010] Preferably, the concave mirror with spherical features used has its center point coinciding with the convergence point of the multiple diffracted laser beams generated by the second acousto-optic modulator.

[0011] Preferably, the first and second acousto-optic modulators used can not only operate at ±1st order diffraction order, but also at ±2nd order diffraction order, ±3rd order diffraction order, and other arbitrary diffraction orders.

[0012] Beneficial effects:

[0013] 1. This invention discloses a broadband laser vibrometer calibration method and apparatus. It uses electrical signals to control optical signals to generate a laser Doppler signal with sinusoidal motion characteristics. Instead of physical mechanical motion to generate Doppler frequency shift, it uses optical frequency control to directly generate an optical frequency modulation signal with motion Doppler characteristics, thus avoiding the difficulty of generating high-quality broadband sinusoidal motion signals through mechanical motion. Therefore, when calibrating or evaluating the sinusoidal motion response characteristics of a laser vibrometer, compared to excitations such as vibration tables, this invention has a wider frequency range and a larger amplitude range.

[0014] 2. The present invention discloses a broadband laser vibration meter calibration method and device, which uses an acousto-optic modulator to shift the frequency, and then uses the acousto-optic modulator to obtain a laser frequency modulation signal waveform by controlling the frequency modulation signal of a sinusoidal waveform. After being focused and reflected by a concave mirror, the laser signal that has been diffracted and diverged is stabilized and converged. After being modulated and frequency shifted again along the original path, it returns, so that the laser signal returns to the laser vibration meter with the characteristic of maintaining the median frequency unchanged, and obtains its response characteristics to sinusoidal waveform motion.

[0015] 3. When a laser beam passes through an acousto-optic modulator and is optically modulated by an arbitrary waveform, diffraction causes frequency-dependent dispersion in the laser beam. Direct transmission to subsequent optical devices can lead to unstable optical path characteristics. To avoid this dispersion problem, this invention discloses a broadband laser vibrometer calibration method and apparatus. This method involves placing the acousto-optic modulator at the center of a concave mirror with spherical features. The reflected beam is then focused back to its original quality, enhancing system stability and doubling the modulation frequency deviation.

[0016] 4. The broadband laser vibration meter calibration method and device disclosed in this invention traces the linear motion signal (linear velocity, linear acceleration) values ​​back to their frequency values ​​through frequency modulation and demodulation technology. Therefore, in principle, it has higher measurement accuracy and stability than mechanical motion excitation. This is because the frequency value is a physical quantity with the highest measurement accuracy achievable in the current metrology industry, far exceeding any other physical quantity. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a broadband laser vibration meter calibration device according to the present invention.

[0018] 1—Laser vibrometer, 2—First acousto-optic modulator, 3—Second acousto-optic modulator, 4—Concave mirror, 5—First sine wave source, 6—FM signal source, 7—Second sine wave source. Detailed Implementation

[0019] To better illustrate the purpose and advantages of the present invention, the invention will be further described below in conjunction with the accompanying drawings and examples.

[0020] Example 1:

[0021] This embodiment discloses a broadband laser vibrometer calibration method that uses two acousto-optic modulators with identical characteristics working together. First, the positive (or negative) diffraction stage of the first acousto-optic modulator shifts the incident laser frequency by a constant value in the positive (or negative) direction. Then, the negative (or positive) diffraction stage of the second acousto-optic modulator, controlled by a sinusoidal frequency modulation signal, obtains the laser frequency modulation signal waveform of the optical frequency modulator. This signal is then reflected and focused by a concave mirror, modulated again by the second acousto-optic modulator, and frequency-shifted by the first acousto-optic modulator. This ensures the optical frequency modulation signal maintains its median frequency constant, returning to the laser vibrometer for measurement processing. The resulting sinusoidal waveform response characteristic waveform is then obtained, generating a sinusoidal excitation that simulates vibration. This process, which maintains the median frequency constant of the optical frequency modulation signal, returns to the laser vibrometer for measurement processing, thereby achieving broadband laser vibrometer calibration and evaluation.

[0022] like Figure 1 As shown, this embodiment discloses a broadband laser vibration meter calibration device, which consists of a laser vibration meter 1, a first acousto-optic modulator 2, a second acousto-optic modulator 3, a concave reflector 4, a first sine wave signal source 5, an FM signal source 6, and a second sine wave signal source 7.

[0023] The laser generated by the laser vibrometer 1 passes through the first acousto-optic modulator 2, which is controlled by the first sinusoidal signal source 5 to generate a +1st order diffraction frequency shift. The laser then reaches the second acousto-optic modulator 3, where the second sinusoidal signal source 7 generates a sinusoidal signal to frequency modulate the FM signal source 6, producing a modulated FM signal that controls the second acousto-optic modulator 3 to shift and modulate the optical frequency transmitted from the first acousto-optic modulator 2, generating a -1st order diffracted laser. This laser is reflected and focused by the concave mirror 4 and returns to the second acousto-optic modulator 3, where it is again frequency-shifted and modulated. It then passes through the first acousto-optic modulator 2 again for frequency shifting before returning to the laser vibrometer 1. This completes the simulation process of using the sinusoidal waveform generated by the second sinusoidal signal source 7 to excite the laser vibrometer 1.

[0024] By comparing the measurement results of sinusoidal waveforms of different frequencies obtained by the laser vibration meter 1 with the second sinusoidal signal source 7, the excitation response characteristics of the laser vibration meter 1 can be obtained, thereby realizing the calibration and performance evaluation of the broadband laser vibration meter.

[0025] The first acousto-optic modulator 2 and the second acousto-optic modulator 3 used can not only operate at ±1st order diffraction order, but also at ±2nd order diffraction order, ±3rd order diffraction order, and other arbitrary diffraction orders.

[0026] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description 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 within the scope of protection of the present invention.

Claims

1. A calibration method for a broadband laser vibrometer, characterized in that: For the laser signal emitted by the laser vibrometer, two acousto-optic modulators (AOMs) are used for optical frequency control and processing. One AOM is used to apply a sinusoidal modulation to obtain an FM signal, and the -1st diffraction stage of the AOM generates an optical frequency modulation signal. The other AOM is used to shift the frequency by applying the +1st diffraction stage of the AOM, so that the median of the modulation frequency is at the output frequency of the laser vibrometer. The signal is reflected and converged by a spherical concave mirror and returns to the laser vibrometer along the original path, thereby obtaining the optical frequency characteristic signal that completely simulates the actual sinusoidal waveform motion. That is, the sinusoidal waveform excitation that simulates vibration is generated, and the optical frequency modulation signal returns to the laser vibrometer with the median frequency unchanged for measurement and processing, thus realizing the calibration and evaluation of the broadband laser vibrometer.

2. A broadband laser vibrometer calibration device, used to implement the broadband laser vibrometer calibration method as described in claim 1, characterized in that: It includes a laser vibrometer (1), a first acousto-optic modulator (2), a second acousto-optic modulator (3), a concave mirror (4), a first sine wave source (5), an FM signal source (6), and a second sine wave source (7); The laser generated by the laser vibrometer (1) passes through the first acousto-optic modulator (2), which is controlled by the first sinusoidal signal source (5) to generate +1 order diffraction frequency shift. Then it reaches the second acousto-optic modulator (3). The second sinusoidal signal source (7) generates a sinusoidal wave signal to frequency modulate the FM signal source (6) and generate a modulated FM signal to control the second acousto-optic modulator (3). The light frequency transmitted from the first acousto-optic modulator (2) is shifted and modulated to generate -1 order diffracted laser. After the laser reaches the concave mirror (4) and is reflected and focused, it returns to the second acousto-optic modulator (3) and is shifted and modulated again by the second acousto-optic modulator (3). Then, it passes through the first acousto-optic modulator (2) again to shift the frequency and return to the laser vibrometer (1). The simulation process of using the sinusoidal waveform generated by the second sinusoidal signal source (7) to excite the laser vibrometer (1) to vibrate is completed. By comparing the measurement results of sinusoidal waveforms of different frequencies obtained by the laser vibrometer (1) with the second sinusoidal signal source (7), the excitation response characteristics of the laser vibrometer (1) can be obtained, thereby realizing the calibration and performance evaluation of the broadband laser vibrometer.

3. The broadband laser vibrometer calibration device as described in claim 2, characterized in that: Using a concave mirror 4 with spherical features, the reflection and convergence of a laser beam with beam instability after passing through a second acousto-optic modulator (3) is achieved due to the combination of optical frequency modulation and diffraction.

4. The broadband laser vibrometer calibration device as described in claim 2, characterized in that: The concave mirror 4 with spherical features used has its center position coincide with the convergence point of the multiple diffracted laser beams generated by the second acousto-optic modulator (3).

5. The broadband laser vibrometer calibration device as described in claim 2, characterized in that: The first acousto-optic modulator (2) and the second acousto-optic modulator (3) used can not only operate on ±1 diffraction orders, but also on any other diffraction orders.

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