Multi-point synchronous vibration meter with strong anti-interference performance based on common-arm interference structure

Abstract

The invention relates to a multi-point synchronous vibration meter with strong anti-interference performance based on a common-arm interference structure, and aims to solve the problems that a traditional non-contact vibration meter can only perform single-point vibration measurement and is low in measurement efficiency and measurement signals are easily influenced by environmental factors. The optical energy utilization efficiency and the system compactness are remarkably improved, meanwhile, multiple paths of interference signals are integrated in one system, the frequency division multiplexing technology is adopted, different modulation frequencies are distributed to measuring points at different positions in a measuring light path, multi-point synchronous vibration measurement is achieved, and the data collection flux and the space coverage capacity are effectively improved. Benefited from the common-arm interference optical path structure design of the system, the vibration meter can effectively suppress common-mode noise, the anti-interference capability and stability of the system in a complex environment are enhanced, and an additional active compensation device is not needed.

Description

Technical Field

[0001] This invention belongs to the field of optical coherent vibration measurement technology, and more specifically relates to a multi-point synchronous vibration meter with strong anti-interference performance based on a shared-arm interference structure. Background Technology

[0002] Optical coherence vibrometry (OCV) is a precision vibration measurement technology based on low-coherence interferometry. Traditional fiber-optic OCV systems typically employ a single-point detection mechanism. However, with the increasing demands for detection efficiency and spatial coverage in applications, this traditional single-point detection approach has gradually revealed its limitations: it cannot achieve simultaneous real-time monitoring of multiple locations on a sample, and when monitoring large areas or multiple samples, it often requires cascading multiple OCV systems. This solution not only significantly increases the system's complexity and cost but also introduces a series of engineering challenges such as calibration and data fusion. In the current development of OCV technology, how to achieve multi-channel parallel detection using a single light source and a single spectrometer has become an important research direction and technical bottleneck. Unlike the structure of traditional OCV systems where one sample arm corresponds to one reference arm, multi-channel OCV systems require the introduction of multiplexing technology to distinguish different channels. However, as the number of channels increases, optical energy attenuation becomes significant, limiting the system's signal-to-noise ratio and detection depth, making the achievement of stable and efficient multi-channel detection a serious challenge. Furthermore, in traditional interference optical path structures, the sample arm and the reference arm are usually arranged separately. Environmental vibrations can easily cause minute changes in the optical path in the fiber, resulting in phase noise or even signal degradation in the interference signal, which seriously affects the stability of the system.

[0003] Meanwhile, in order to increase the number of detection channels in the system, it is necessary to effectively address the problem of beam energy attenuation caused by the increase in channels. The most direct approach is to increase the output power of the light source. However, under the current power level limitations of superluminescent diode (SLD) light sources, simply relying on increasing light energy is not feasible. Summary of the Invention

[0004] To address the aforementioned defects and shortcomings of existing technologies, this invention provides a multi-point synchronous vibration meter with strong anti-interference performance based on a shared-arm interference structure. This vibration meter can achieve synchronous detection of different positions of a sample without contact.

[0005] This invention relates to a multi-point synchronous vibration meter with strong anti-interference performance based on a shared-arm interference structure, characterized in that it includes an SLD broadband light source, a bi-N fiber optic coupler, N sets of probe arms, a grating spectrometer, and a computer.

[0006] The SLD broadband light source is used to emit probe light; the input end of the N-to-2 fiber optic coupler is connected to the SLD broadband light source to split the light emitted by the SLD broadband light source into N paths, and the probe end of the N-to-2 fiber optic coupler is connected to N sets of probe arms respectively.

[0007] The probe arm includes a focusing lens, a glass substrate and a beam splitter arranged in sequence. A gold-plated reflector is provided in the central area of ​​the glass substrate, and an unplated transparent window is provided in the outer area of ​​the gold-plated reflector on the glass substrate.

[0008] The grating spectrometer includes a collimating lens, a grating, a focusing lens, and a high-speed linear array camera arranged in sequence. The inlet of the collimating lens is connected to the outlet of a two-to-N fiber coupler. The grating spectrometer is used to acquire and process broadband spectra. The computer processes the multiple coherent signals and analyzes the information detected by each signal.

[0009] The N-to-2 fiber optic coupler uniformly splits the light emitted from the SLD light source into N paths, which are then transmitted to corresponding detector arms. These N detector arms are positioned at different test locations on the sample. After calibration of the sample detection points, each detector arm is adjusted to focus, ensuring the beam is precisely focused and illuminates the N detection points on the sample, and detection is initiated simultaneously. The interference signal generated at each detection point is transmitted to the spectrometer via the main channel. After the broadband optical signal is split by a grating, it is synchronously acquired by a high-speed linear array camera. The computer first performs dispersion compensation on the signal acquired by the camera, and then performs Fourier transform processing to extract the sample vibration information. To distinguish the N different signals, the system introduces a specific optical path difference by inserting glass plates of different thicknesses into the optical path, thereby achieving effective signal differentiation. Each optical signal undergoes an independent optical process without interference. After the N interference signals are simultaneously received by the high-speed linear array camera, Fourier transform processing is performed on the interference signals to extract information from each channel, thus reconstructing the vibration information of each corresponding sample point.

[0010] Furthermore, the aforementioned N sets of probe arms are actually four sets of probe arms, and the two-to-N fiber optic coupler is a two-to-four fiber optic coupler.

[0011] Furthermore, the probe ends of the aforementioned N sets of probe arms can be fitted with glass plates of different thicknesses. These glass plates are made of the same material as the glass substrate with the same refractive index, thereby changing the optical path difference. By using this method, different center frequencies are assigned to each channel, different frequency bands are divided, the problem of interference signal crosstalk between channels is solved, and the N signals are clearly distinguished.

[0012] Furthermore, the surface of the aforementioned beam splitter is coated with a semi-transparent, semi-reflective film with a splitting ratio of 50:50, targeting light in the 700-1000nm wavelength range. The incident light is split at this interface; part of the light is reflected by the beam splitter, refracted 180 degrees for vertical reflection, and the reflected beam passes through the glass substrate again and is precisely focused on the gold film area of ​​the gold-plated mirror. Due to its extremely high reflectivity and excellent response to near-infrared light, the gold film efficiently reflects the beam back along its original path. This reflected light passes through the beam splitter again and returns along its original path as a reference light; another part of the light passes through the beam splitter and continues to propagate downwards, eventually focusing on the surface of the sample under test; after the incident light is reflected or backscattered by different depth layers of the sample, part of the signal light also returns along its original path, passes through the beam splitter and returns to the optical path. Finally, the two beams of reference light and signal light, which originate from the same light source and have undergone almost identical optical paths, converge again at the beam splitter and meet the coherence condition, resulting in interference.

[0013] Furthermore, the light emitted from the aforementioned light source is split into N paths by a two-to-N fiber coupler, each entering a corresponding detector arm. The corresponding lenses in the detector arms focus the light onto the sample. The backscattered signal light from the sample returns along the original beam path after passing through the detector arm. After coherence with the reference light, they are transmitted together onto a main channel and then transmitted to the spectrometer via fiber couplers. The spectrometer receives the signal and transmits it to a computer for signal processing. The interference signal acquired by the system for each path is described as follows:

[0014]

[0015] Among them, P r P is the reference optical power detected by the detector. o Let Γ(z) be the light power emitted by the probe arm and illuminating the probe end face, k(t) be the wave number, which is the time dependent variable, and Γ(z) be the coherence function of the light source.

[0016] The right side of the equation has three terms: the first term is the optical power returned by the reference arm detected by the system detector, called the DC term; the second integral term is the sum of the power of the light returned by each layer of the sample along the detection axis and the light that interferes between the layers of the sample, called the autocorrelation term; the third term is the integral of the light intensity of the interference between the reference light and the light returned by the sample, called the cross-correlation term, which is the useful information in the interference spectrum signal. The information obtained by performing a Fourier transform on this term is the result of converting from wavenumber space to longitudinal coordinates, thereby obtaining the vibration information of the measurement point.

[0017] Furthermore, by introducing glass plates of different thicknesses into each detection channel, different optical path difference offsets are precisely set for each signal. This operation is equivalent to assigning a unique "carrier" frequency to each channel in the frequency domain. When the optical signals from each channel return and interfere, the interference signals, which were originally concentrated near the zero frequency, are "shifted" to different center frequencies in the spectrum, with each center frequency corresponding to a specific detection channel. By converting them to the frequency domain through Fourier transform, multiple separate peaks can be seen on the spectrum, with each peak corresponding to a detection channel. Using bandpass filters centered on each peak, multiple signals can be clearly extracted in the frequency domain, thus completely solving the problem of crosstalk between inter-channel interference signals and realizing the parallel and independent acquisition of multi-channel vibration information.

[0018] Furthermore, the system undergoes spectral calibration and dispersion compensation, its wavelength data is exported, and the frequency domain information of the acquired coherent signals from each channel is processed by performing Fourier transforms to convert the signals of each channel to the frequency domain. Finally, Fourier transforms are performed on the signals acquired by the system.

[0019]

[0020] Where S(k) is the power spectral density function of the light source, δ(z) is the DC term near zero optical path difference, a(z) is the amplitude of the light returned at the axial coordinate z of the sample, which is symmetrical to a(-z), and the AC term is the result after FFT of the autocorrelation term.

[0021] Furthermore, for the subsequent signal processing, the Hanning window energy centroid correction method is used to obtain the peak data after the Fast Fourier Transform, convert it into displacement information, and plot the displacement-time curve; the Hanning window energy centroid correction algorithm is as follows:

[0022]

[0023] in, Let f be the normalized frequency of the harmonic signal, k be the spectral line number corresponding to the point of maximum amplitude, G be the amplitude corresponding to the i-th spectral line, and f be the frequency of the harmonic signal. s Where N is the sampling frequency and N is the number of sampling points.

[0024] Compared with existing technologies, the outstanding advantages of this invention are:

[0025] 1. The shared-arm interference structure ingeniously combines the two separate arms of the traditional Michelson interferometer into one, and each path strictly follows the principle of shared path. The impact of environmental disturbances on each path of reference light and sample light is the same, which can greatly reduce the impact of environmental disturbances on the detection effect. At the same time, the design of this structure can ensure that the dispersion imbalance is minimized when the interference fringe contrast is high, and the structure is more compact.

[0026] 2. The system adopts a detector arm architecture with N-to-N fiber optic couplers and N shared-arm interference structures, which can realize parallel detection of N detection points. The system introduces frequency division multiplexing technology, which effectively solves the problem of crosstalk between multi-channel signals, so that the signals of all detection points can be acquired and demodulated by a shared spectrometer, thereby enabling the synchronous acquisition of vibration data from multiple points using a single device.

[0027] 3. The fiber optic design gives the system a high degree of spatial flexibility. Each probe arm can be flexibly arranged according to the distribution of the test points. This not only improves the system's degree of freedom of detection, but also enables the simultaneous acquisition of multi-position information of the sample in the same degree of freedom direction, ultimately achieving the goal of simplifying the system structure and significantly reducing costs.

[0028] This invention addresses the shortcomings of traditional non-contact vibration meters, which can only perform single-point vibration measurements, resulting in low measurement efficiency and susceptibility to environmental factors. It innovatively introduces a shared-arm interferometric optical path structure, integrating the reference arm and sample arm into the same optical path. This significantly improves light energy utilization efficiency and system compactness. Simultaneously, it integrates multiple interferometric signals into a single system, employing frequency division multiplexing technology to assign different modulation frequencies to measurement points at different locations in the measurement optical path, achieving multi-point synchronous vibration measurement and effectively enhancing data acquisition throughput and spatial coverage. Thanks to the shared-arm interferometric optical path design, the vibration meter effectively suppresses common-mode noise, enhancing the system's anti-interference capability and stability in complex environments without requiring additional active compensation devices. The system supports flexible placement of probe points, making it suitable for high-precision synchronous monitoring of multi-location vibrations at macroscopic scales. It can be widely applied to structural dynamics characterization and vibration deformation analysis. Attached Figure Description

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0030] Figure 1 This is a schematic diagram of the shared-arm interference structure of the system in this invention;

[0031] Among them: 301, focusing lens; 302, glass substrate; 303, beam splitter; 304, gold-plated reflector; 305, glass plate;

[0032] Figure 2 This is a comparison chart of the noise immunity performance of the shared-arm interference structure and the traditional dual-path interference system;

[0033] Figure 3 This is a schematic diagram of a multi-point synchronous vibration meter with strong anti-interference performance based on a shared-arm interference structure.

[0034] The components include: 1. SLD light source; 2. Two-to-N fiber coupler; 3. Probe arm; 7. Collimating lens; 8. Grating; 9. Focusing lens; 10. High-speed linear array camera; 11. Computer; 12. Grating spectrometer.

[0035] Figure 4 This is a schematic diagram of a multi-point synchronous vibration meter measuring the vibration at four arbitrary positions of a cantilever beam;

[0036] Among them: 2. Two-to-N fiber optic coupler; 3. Probe arm; 4. Fixed end; 5. Cantilever beam;

[0037] Figure 5 This is a photograph of a multi-point synchronous vibration meter measuring the vibration of a cantilever beam at four arbitrary positions.

[0038] Figure 6 It is an interference signal diagram of four-point synchronous vibration measurement;

[0039] Figure 7 This is a graph showing the measurement results of the vibration of a cantilever beam at four locations. Detailed Implementation

[0040] The present invention will now be described in detail with reference to the embodiments. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0041] This embodiment provides a multi-point synchronous vibration meter with strong anti-interference performance based on a shared-arm interference structure, including the following steps:

[0042] The basic structure of the probe arm in a shared-arm interferometric structure is as follows: Figure 1As shown, the system includes a focusing lens 301, a glass substrate 302, a beam splitter 303, and a gold-plated reflector 304. The collimated low-coherence parallel beam first enters the focusing lens 301. The core function of this lens is to converge the parallel beam so that it presents a convergent focused state in the rear optical path. This is to form a high-energy-density focal point on the reference plane and the sample surface, thereby improving the detection signal-to-noise ratio. The converged beam then reaches the customized gold-plated reflector 304. This element is not a simple total reflection mirror, but rather a specific area is processed on a K9 glass substrate 302 through a coating process: its central area is coated with a highly reflective gold film, while the outer area retains an unplated transparent window, allowing part of the beam to pass through the unplated window area without damage. The beam passing through the window continues to propagate to the beam splitter 303. The surface of the beam splitter is coated with a semi-transparent and semi-reflective film with a splitting ratio of (50:50) and is designed for light in the 700-1000nm wavelength range. The incident light is split at this interface; a portion of the light (50%) is reflected by the beam splitter and refracted 180 degrees vertically. The reflected beam passes through the glass substrate 302 again and is precisely focused on the gold film area of ​​the gold-plated reflector 304. Due to its extremely high reflectivity and excellent response to near-infrared light, the gold film efficiently reflects the beam back along its original path. This reflected light passes through the beam splitter 303 again and returns along its original path as a reference light. Another portion of the light (50%) passes through beam splitter 304 and continues to propagate downwards, eventually focusing on the surface of the sample under test. After being reflected or backscattered by different depth layers of the sample, part of the signal light also returns along the original path, passing through beam splitter 303 and returning to the optical path. Finally, the two beams of reference light and signal light, which originated from the same light source and have undergone almost identical optical paths, converge again at beam splitter 303 and satisfy the coherence condition, resulting in interference.

[0043] To verify the anti-interference ability and stability of the shared-arm interference structure in a complex environment, the vibration applied in the experiment came from the minute vibrations generated by common equipment such as computer heat sinks, simulating a typical real working environment. Figure 2 More accurate error comparison data were provided to further quantify the performance difference and verify the ability of the shared-arm interference structure to suppress environmental interference.

[0044] A multi-point synchronous vibration meter with strong anti-interference performance based on a shared-arm interference structure, such as Figure 3As shown, the system includes an SLD broadband light source 1, a two-to-N fiber coupler 2, multiple sets of detector arms (the illustration shows four sets, with the two-to-N fiber coupler 2 being a two-to-four fiber coupler), a collimating lens 7, a grating 8, a focusing lens 9, a high-speed linear array camera 10, and a computer 11. The collimating lens 7, grating 8, and focusing lens 9 constitute a grating spectrometer 12. The light emitted from the light source first enters the fiber coupler, which splits the incident light into four paths, achieving efficient and symmetrical division of the light emitted from the light source into four independent beams. The theoretical power of each beam is 25% of the light output power of the light source, ensuring good consistency of the initial light intensity among the detection channels. These four beams are connected to four identical common-arm detector arms through APC-type fiber optic connectors, achieving precise distribution and transmission of light energy. The four detector arms are precisely arranged in space according to the needs of the detection points, so that each beam spot is focused on four different detection points on the surface of the sample to be tested. In the optical path behind the beam splitter and in front of the sample surface, glass plates 305 of different thicknesses are sequentially inserted. These glass plates are made of the same material as the glass substrate used in the gold-plated mirror, and a fixed frequency shift is generated by introducing a controllable optical path difference. When light illuminates the sample, the signal light reflected from the minute displacement caused by vibrations on the sample surface returns along its original path to the detector arm. Inside each detector arm, this signal light encounters a reference light generated by a built-in reference mirror. Since they originate from the same light source and their optical path difference is within the coherence length, they interfere simultaneously, forming four interference signal lights carrying their respective sample point depth information. During demodulation, the interference signal we acquire is a superposition of all these signals at different frequencies.

[0045] This vibration meter can simultaneously acquire vibration amplitude and frequency data at four points, theoretically increasing the detection speed to four times that of traditional single-point systems. The four interference signal beams are combined via fiber optic couplers and transmitted to the spectrometer 12 for synchronous detection and analysis. Upon entering the spectrometer, the mixed multi-channel signal beams are first converted into parallel light by the collimating lens 7 to meet the incident angle requirements of subsequent optical elements. The parallel beams then strike the surface of the diffraction grating 8. The grating, acting as a dispersive element, spatially expands the broadband interference signals containing different frequency components according to wavelength, forming a series of parallel spectral bands. The dispersed spectra are converged by the focusing lens 9 and focused onto the sensor of the high-speed linear array camera 10. The camera's acquisition rate and exposure time are controlled by calculation 11. Finally, a computer processes the four interference signals to reconstruct the surface vibration information of the four corresponding sample points.

[0046] Figure 4 This diagram illustrates the use of a multi-point synchronous vibration meter to measure vibration at four different locations on a cantilever beam. Two detection points are positioned randomly near the fixed end of the cantilever beam, while the other two are located in the middle region of the beam. These points are used to detect the vibration response at their respective locations. A physical diagram of the experimental setup is shown below. Figure 5 As shown, Figure 6 The interference signals from four-point synchronous vibration measurements are displayed, each corresponding to one of the four measurement points and containing interference components of different frequencies. The signals are independent of each other, effectively avoiding crosstalk and superposition issues and ensuring the reliability of multi-channel data. Furthermore, by combining the Hanning window energy centroid method, the peak position changes of each interference signal are accurately identified, and the amplitude response at each of the four measurement points is calculated based on the system's axial resolution. The results are as follows: Figure 7 As shown, the deformation distribution of the cantilever beam under external excitation is clearly reflected, verifying the effectiveness and measurement accuracy of the vibration meter in multi-point synchronous vibration detection.

[0047] The specific steps for the system to perform detection include the following:

[0048] S1. The light emitted from the light source is split into N paths by a two-to-N fiber optic coupler, and each path enters a corresponding detector arm. The corresponding lens in the detector arm focuses the light onto the sample. The backscattered signal light from the sample returns along the original beam path after passing through the detector arm. After coherence with the reference light, they are transmitted together to a main channel and then transmitted to the spectrometer via the fiber optic coupler. The spectrometer receives the signal and transmits it to the computer for signal processing. The interference signal acquired by the system for each path can be described as follows:

[0049]

[0050] Among them, P r P is the reference optical power detected by the detector. o Let Γ(z) be the light power emitted by the probe arm and illuminating the probe end face, k(t) be the wave number, which is the time dependent variable, and Γ(z) be the coherence function of the light source.

[0051] The right side of the equation has three terms: the first term is the optical power returned by the reference arm detected by the system detector, called the DC term; the second integral term is the sum of the power of the light returned by each layer of the sample along the detection axis and the light that interferes between the layers of the sample, called the autocorrelation term; the third term is the integral of the light intensity of the interference between the reference light and the light returned by the sample, called the cross-correlation term, which is the useful information in the interference spectrum signal. The information obtained by performing a Fourier transform on this term is the result of converting from wavenumber space to longitudinal coordinates, thereby obtaining the vibration information of the measurement point.

[0052] S2. The shared-arm interference structure consists of a parallel beam, a focusing lens, a beam splitter, and a reflector with a gold film in the center, all on a glass substrate. It integrates the sample arm and the reference arm onto the same probe arm, simplifying the structure.

[0053] S3. Since the interference signal generated by the shared-arm interference structure is at the zero optical path difference position, and combining the principle of frequency division multiplexing (FDM), glass plates of different thicknesses are inserted into the optical path where the incident light from the beam splitter is focused onto the surface of the sample under test. These glass plates are made of the same material as the glass substrate on the gold-plated mirror to ensure consistent refractive index, thereby altering the optical path difference. This method assigns a different center frequency to each channel, dividing it into different frequency bands, resolving crosstalk between channels, and clearly distinguishing the four signals. The specific details of the FDM technique are as follows:

[0054] By introducing glass plates of specific thicknesses for each detection channel, different optical path difference offsets are precisely set for each signal. This operation is equivalent to assigning a unique "carrier" frequency to each channel in the frequency domain. When the optical signals from each channel return and interfere, the interference signals, originally concentrated near zero frequency, are "shifted" to different center frequencies in the spectrum, each center frequency corresponding to a specific detection channel. By converting this to the frequency domain using Fourier transform, multiple separate peaks can be seen on the spectrum, each peak corresponding to a detection channel. Using bandpass filters centered on each peak, multiple signals can be clearly extracted in the frequency domain, thus completely solving the problem of crosstalk between channels and enabling parallel and independent acquisition of multi-channel vibration information.

[0055] S4. Taking advantage of the high spatial flexibility of optical fibers, each probe arm is placed at a different position on the sample, and each probe arm simultaneously detects the sample, acquiring information from different positions on the sample at the same time.

[0056] S5. Perform spectral calibration on the system and compensate for its dispersion. Export the wavelength data and process the frequency domain information of the coherent signals from each channel by performing Fourier transform to convert the signals of each channel to the frequency domain. Perform Fourier transform on the signals acquired by the system:

[0057]

[0058] Where S(k) is the power spectral density function of the light source, δ(z) is the DC term near zero optical path difference, a(z) is the amplitude of the light returned at the axial coordinate z of the sample, which is symmetrical to a(-z), and the AC term is the result after FFT of the autocorrelation term.

[0059] For subsequent signal processing, the Hanning window energy centroid correction method is used to obtain the peak data after the Fast Fourier Transform, convert it into displacement information, and plot the displacement-time curve. Specifically, the Hanning window energy centroid correction algorithm is as follows:

[0060]

[0061] in, Let f be the normalized frequency of the harmonic signal, k be the spectral line number corresponding to the point of maximum amplitude, G be the amplitude corresponding to the i-th spectral line, and f be the frequency of the harmonic signal. s Where N is the sampling frequency and N is the number of sampling points.

[0062] S6. After processing all the collected signals, the vibration information at different points on the sample is reconstructed.

[0063] This invention introduces a shared-arm interferometric structure, which integrates the probe arm and reference arm into the same optical path, eliminating the redundant and independent reference arm design of traditional systems and significantly improving the compactness of the optical path and the efficiency of optical energy utilization. In traditional OCV systems, even with a 2-to-4 fiber coupler, only two parallel measurements can typically be achieved. However, by using the shared-arm interferometric structure of this application and combining it with frequency division multiplexing (FDM) technology for channel differentiation, the system's multiplexing capability is greatly improved. Similarly, combined with a 2-to-4 fiber coupler, four parallel detections can be successfully achieved, significantly increasing the data acquisition throughput per unit time and providing a new technical path for rapid, large-scale OCV monitoring. Furthermore, this structure possesses excellent resistance to environmental interference. Since the reference light and sample light propagate in almost identical optical paths, the effects of external vibrations and temperature changes on the two beams manifest as common-mode noise, which cancels each other out during interference, thereby significantly improving the system's stability and reliability. This characteristic allows the system to maintain high signal quality even in complex operating environments, avoiding complex active compensation mechanisms and reducing system complexity and cost. The system's excellent spatial flexibility extends its application to macroscopic scales. It can be precisely arranged in space as needed, either in a regular matrix distribution or an arbitrary irregular arrangement designed for specific measurement targets, enabling simultaneous monitoring of information at four different locations on a large vibration platform or structural component. For example, it can be located at the four corners of a platform to monitor potential torsional vibrations; or symmetrically arranged at the center and edges to distinguish between rigid body translation and bending deformation. It can also simultaneously collect amplitude data at four different points on a cantilever beam.

Claims

1. A strong anti-interference performance multipoint synchronous vibrometer based on common-arm interference structure, characterized in that: The system comprises an SLD broadband light source (1), a two-division N fiber coupler (2), N groups of detection arms (3), a grating spectrometer (12) and a computer (11); The SLD broadband light source is used for emitting detection light; the input end of the two-division N fiber coupler is connected with the SLD broadband light source, so as to divide the light emitted by the SLD broadband light source into N paths, and the detection end of the two-division N fiber coupler is connected with the N groups of detection arms respectively, The detection arm (3) comprises a focusing lens (301), a glass substrate (302) and a light splitting plate (303) arranged in sequence, a gold-coated mirror (304) is arranged in the central region of the glass substrate (302), and the peripheral region of the gold-coated mirror on the glass substrate (302) is a transparent window without gold coating; The grating spectrometer (12) comprises a collimating lens (7), a grating (8), a focusing lens (9) and a high-speed linear array camera (10) arranged in sequence, the input end of the collimating lens (7) is connected with the output end of the two-division N fiber coupler, and the grating spectrometer (12) is used for acquiring and processing wide-band spectrum; the computer (11) processes the multiple coherent signals and analyzes the information of each detection; The two-division N fiber coupler (2) uniformly divides the light emitted by the SLD light source (1) into N paths and transmits them to the corresponding detection arms respectively, the N groups of detection arms are arranged at different to-be-detected positions of the sample, after the calibration of the sample detection points is completed, the detection arms are adjusted to the focusing state, so that the light beams are accurately focused and irradiated to the N detection points of the sample, and then the detection is started simultaneously; the interference signals generated by each detection point are transmitted to the spectrometer (12) through the main channel, after the wide-band light signals are split by the grating (8), the high-speed linear array camera (10) synchronously collects, the computer (11) firstly performs dispersion compensation on the signals collected by the camera, and then performs Fourier transform processing to extract the information of sample vibration; in terms of distinguishing the N different signals, the system introduces specific optical path differences by inserting glass sheets (305) with different thicknesses in the optical path, so as to effectively distinguish the signals; each light signal experiences an independent optical process and does not interfere with each other; After the N-path interference signals are received by the high-speed linear array camera, Fourier transform processing is performed on the interference signals to extract the information of each channel, so as to reconstruct the vibration information of each corresponding sample point.

2. The strong anti-interference performance multipoint synchronous vibration meter based on the common-arm interference structure of claim 1, wherein: The N groups of detection arms are four groups of detection arms, and the two-division N fiber coupler (2) is a two-division four-fiber coupler.

3. The strong anti-interference performance multipoint synchronous vibration meter based on the common-arm interference structure of claim 1, wherein: The detection end of the N groups of detection arms can be inserted with glass sheets with different thicknesses, the glass sheets are made of the same material as the glass substrate (302) in terms of refractive index, so as to change the optical path differences of different signals; So as to obviously distinguish the N-path signals.

4. The common-arm interferometric structure based strong anti-interference performance multipoint synchronous vibrometer according to claim 1, characterized in that: The surface of the beamsplitter (303) is coated with a semi-transparent and semi-reflective film, which has a beamsplitting ratio of 50:50 and is for light in the 700-1000 nm band. The incident light is split at the interface. Part of the light is reflected by the beamsplitter, is reflected vertically by 180 degrees, and the reflected light beam passes through the glass substrate (302) again and is accurately focused on the gold film area of the gold-coated mirror (304). The gold film has a very high reflectivity and a good response to near-infrared light, so it efficiently reflects the light beam back along the original path. The reflected light passes through the beamsplitter (303) again and returns along the original path as reference light. The other part of the light transmits through the beamsplitter (303) and continues to propagate downward, and is finally focused on the surface of the sample to be measured. After the incident light is reflected or backscattered by the different depth layer structures of the sample, part of the signal light returns along the original path, transmits through the beamsplitter (303) and returns to the optical path. Finally, the reference light and the signal light, which originate from the same light source and have experienced almost the same optical path, recombine at the beamsplitter (303) and satisfy the coherence condition, and interference occurs.

5. The common-arm interferometric structure based strong anti-interference performance multipoint synchronous vibration meter according to claim 1, 2, 3 or 4, characterized in that: The light emitted by the light source is split into N paths by a two-way N-fiber coupler and enters the corresponding detection arms; The signal light backscattered by the sample is focused on the sample by the corresponding lens in the detection arm, returns along the original beam path through the detection arm, and after being coherent with the reference light, is transmitted to a main channel. The signal light is transmitted to the spectrometer by the fiber coupler, and the signal is received by the spectrometer and transmitted to the computer for signal processing. The system collects the interference signal of each path as follows: where P r is the reference light power detected by the detector, P o is the light power emitted by the detection arm and incident on the detection end face, k(t) is the wave number, which is a dependent variable of time, and Γ(z) represents the coherence function of the light source. The right side of the equation has three terms: the first term is the power of the light returned by the reference arm detected by the system detector, called the direct current term; the second integral term is the accumulation of the power of the light returned by each layer of the sample along the detection axis and the light that interferes between each layer of the sample, called the autocorrelation term; the third term is the integral of the light intensity that interferes between the reference light and the light returned by the sample, called the cross-correlation term, which is the useful information in the interference spectrum signal. The information obtained after Fourier transform of this term is the result of converting from wave number space to longitudinal coordinate, thereby obtaining the vibration information of the measurement point.

6. The strong anti-interference performance multipoint synchronous vibration meter based on the common-arm interference structure of claim 3, wherein: By introducing glass sheets of different thicknesses into each detection channel, different optical path difference offsets are accurately set for each channel, which is equivalent to assigning a unique "carrier" frequency to each channel in the frequency domain. When the light signals of each channel return and interfere, the interference signals originally concentrated around zero frequency are "shifted" to different center frequencies in the frequency spectrum, with each center frequency corresponding to a specific detection channel. By Fourier transform, the signals are converted to the frequency domain, and multiple separate peaks can be seen on the frequency spectrum, with each peak corresponding to a detection channel. Using a bandpass filter centered on each peak, the multi-channel signals can be clearly extracted in the frequency domain, thereby completely solving the interference signal crosstalk problem between channels and achieving parallel and independent acquisition of multi-channel vibration information.

7. The common-arm interferometric structure based strong anti-interference performance multipoint synchronous vibrometer according to claim 1, characterized in that: Also including the system is spectrally calibrated and its dispersion is compensated, its wavelength data export, the signal processing of the acquisition of each channel coherent signal frequency domain information, Fourier transform, the signal of each channel is converted to the frequency domain, the signal collected by the system is Fourier transformed: Wherein, S(k) is the power spectral density function of the light source, δ(z) is the zero optical path difference near the direct current term, a(z) is the amplitude of the returned light at the axial coordinate z of the sample, which is symmetrical with a(-z), and the AC term is the result after the autocorrelation term FFT.

8. The strong anti-interference performance multipoint synchronous vibration meter based on the common-arm interference structure of claim 7, wherein: For the subsequent signal processing process, the peak value data after fast Fourier transform is obtained by using the Hann window energy barycenter correction method, which is converted into displacement information and a displacement-time curve is drawn; the Hann window energy barycenter correction algorithm is: wherein, is the normalized frequency of the harmonic signal, k is the spectral line number corresponding to the maximum point of the spectral line amplitude, G is the amplitude corresponding to the i-th spectral line, f s is the sampling frequency, and N is the number of sampling points.

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