Optical fiber vibration sensor based on super-operating wavelength light source and weak vibration measurement method

Abstract

The invention relates to the field of optical fiber vibration sensors, and provides an optical fiber vibration sensor based on an ultra-operating wavelength light source and a weak vibration measurement method, the optical fiber vibration sensor comprises a three-section optical fiber, an optical fiber fixing module, a vibration conduction rod, a laser and a photoelectric detector; two ends of the measuring section optical fiber are welded with the transmission section optical fiber, bending loss exists when the vibration measuring section optical fiber is bent, and the transmission section optical fiber ensures lossless transmission of optical signals. As the center deflection of the measuring section optical fiber is increased and the total loss is increased, the bending light intensity loss of the detecting section optical fiber is amplified through the super-operating wavelength light source, and the three-section optical fiber structure enables optical signals to be transmitted remotely, so that remote measurement is realized; the conversion between the optical signal and the vibration information is realized through demodulation calculation; the device can measure the vibration frequency and amplitude at the same time, and has the advantages of low cost, high measurement precision, simple operation and strong anti-interference performance.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber vibration sensors, and in particular to an optical fiber vibration sensor based on a super-operating wavelength light source and a weak vibration measurement method. Background Art

[0002] Weak vibration measurement has important applications and significance in scientific research and production life. For example, it can be used to measure and control tiny vibrations of precision instruments, monitor vibrations in infrastructure construction, and measure weak vibrations in the environment to assess their impact on human health.

[0003] Due to the optical fiber's resistance to bending loss, existing optical fiber vibration sensors almost all use the principle of light interference to achieve vibration measurement. However, these optical fiber vibration sensors are relatively complex to manufacture and install, are expensive, and require the use of specialized equipment such as spectrometers to analyze the wavelength and intensity of light. The calculation process is complex and the operation is difficult.

[0004] Among the many methods for analyzing optical signals, the simplest is to detect changes in light intensity. Techniques that increase optical fiber bending loss are key to measuring vibrations by detecting changes in light intensity, thereby simplifying the structure of optical fiber vibration sensors and reducing their cost. However, a simple, low-cost, and easy-to-use optical fiber vibration sensor based on a super-operating wavelength light source is currently lacking. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides an optical fiber vibration sensor based on a super-working wavelength light source and a weak vibration measurement method.

[0006] The present invention provides an optical fiber vibration sensor based on a super-working wavelength light source, comprising a three-section optical fiber, an optical fiber fixing module, a vibration conducting rod, a laser, and a photoelectric detector;

[0007] The three-section optical fiber is formed by fusion-joining a transmission section optical fiber and a measurement section optical fiber with the same core and cladding diameters. The first and last sections are the transmission section optical fibers, and the middle section is the measurement section optical fiber. The operating wavelength range of the transmission section optical fiber includes the wavelength of the laser light source; the operating wavelength range of the measurement section optical fiber is less than the wavelength of the laser light source.

[0008] The body of the optical fiber fixing module is provided with a transversely arranged linear slot, and the measuring segment optical fiber of the three-segment optical fiber is arranged in the linear slot to ensure that the optical fiber remains straight. The body of the optical fiber fixing module is provided with a through hole extending vertically, and the through hole intersects the linear slot at right angles. The portions of the measuring segment optical fiber located at both ends of the through hole are fixed by the linear slot.

[0009] The vibration transmission rod is inserted into the through hole from the bottom of the optical fiber fixing module, and the upper end of the vibration transmission rod is located inside the through hole of the optical fiber fixing module and contacts the optical fiber of the measuring section; the lower end of the vibration transmission rod is located in the same plane as the bottom surface of the optical fiber fixing module, or exceeds the bottom surface of the optical fiber fixing module;

[0010] The laser and photoelectric detector are respectively arranged on both sides of the optical fiber fixing module. The transmission section optical fiber at one end of the three-section optical fiber is connected to the output end of the laser, and the transmission section optical fiber at the other end of the three-section optical fiber is connected to the input end of the photoelectric detector.

[0011] During use, the laser and photoelectric detector are respectively connected to a controller or a host computer. The laser outputs continuous laser light, and the photoelectric detector detects the output light intensity of the three-section optical fiber in real time. The laser, photoelectric detector and other electrical equipment are respectively connected to a power supply.

[0012] Preferably, the optical fiber fixing module includes a module body and a cover plate, the upper surface of the module body is provided with a linear groove, the lower surface of the cover plate is correspondingly provided with a linear groove, the cover plate is arranged on the upper part of the module body, and the linear grooves of the module body and the cover plate are buckled to form a linear slot; the module body and the cover plate of the optical fiber fixing module are respectively provided with a through hole that passes through from top to bottom, the through holes on the module body and the cover plate are connected, and intersect with the slot hole vertically.

[0013] Preferably, the transmission segment optical fiber may be an ordinary single-mode optical fiber, and the measurement segment optical fiber may be a small numerical aperture single-mode optical fiber, wherein the numerical aperture of the measurement segment optical fiber is smaller than the numerical aperture of the transmission segment optical fiber.

[0014] Preferably, the laser outputs a continuous laser with a wavelength of 1550 nm; the numerical aperture of the transmission section optical fiber is 0.125, and the operating wavelength is 1440-1625 nm; the numerical aperture of the measurement section optical fiber is 0.085, and the operating wavelength is 980-1150 nm.

[0015] Preferably, a groove is provided at the top end of the vibration conducting rod, the measuring section optical fiber is located in the groove, and the groove contacts the lower surface of the measuring section optical fiber.

[0016] Furthermore, the upper portion of the vibration conducting rod is wedge-shaped, so that the bottom surface of the groove is as narrow as possible and the contact area with the measuring section optical fiber is as small as possible, forming a force point rather than a surface.

[0017] Working principle of the present invention:

[0018] The present invention designs a three-section optical fiber with a measuring section optical fiber fused at both ends to a transmission section optical fiber. It only has bending loss when the vibration measuring section optical fiber is bent, and the transmission section optical fiber can ensure lossless transmission of optical signals.

[0019] First, fix the vibration transmission rod to the surface of the vibration source, then adjust the optical fiber fixing module so that the top of the vibration transmission rod just contacts the optical fiber, and then fix the optical fiber fixing module so that the optical fiber fixing module and the vibration source remain relatively stationary during the measurement process.

[0020] During measurement, the lower end of the vibration transmission rod contacts the vibration source, and the vibration of the vibration source is transmitted to the measuring section of the optical fiber through the vibration transmission rod; when the vibration source is above the equilibrium position, the vibration transmission rod will move upward, causing the middle part of the measuring section of the optical fiber to produce an upward deformation; because the linear slots of the optical fiber fixing module fix the two ends of the measuring section of the optical fiber, the measuring section of the optical fiber located at the through hole will bend at this time.

[0021] A controller or host computer controls the laser to emit continuous laser light into the three-segment fiber and controls the photodetector to measure the light intensity at the output end of the three-segment fiber in real time. When the light source wavelength is outside the operating wavelength of the measurement section fiber, light intensity loss is very sensitive to changes in fiber curvature. Furthermore, the center deflection of the measurement section fiber is positively correlated with the total light intensity loss. As the center deflection increases, the total loss of the measurement section fiber increases.

[0022] The present invention realizes the demodulation calculation of vibration frequency and amplitude based on the principle of optical fiber vibration sensing. First, it is necessary to calculate the distribution function of curvature of the measuring section optical fiber at different center deflections with position, and then integrate it with the optical fiber bending loss formula to calculate the total light intensity loss under the deflection; the finite number of deflections and the total light intensity loss are stored in an array.

[0023] When demodulating the frequency, the approximate value of the vibration frequency at this time is first calculated through fast Fourier transform, and then the sampling frequency and sampling time of the frequency interval are matched. The fast Fourier transform refers to collecting a shorter period of time at a higher sampling frequency, obtaining the frequency interval through fast Fourier transform (FFT), and selecting the appropriate sampling frequency and sampling time according to the frequency interval; then data is collected and peak value judgment is performed through the front-to-back comparison method. Peak value judgment refers to finding the peak value by comparing the front-to-back values and storing the peak value position and size, and recording the peak value position in an array; finally, the vibration period is calculated according to the peak interval and the sampling frequency to obtain the vibration frequency.

[0024] When demodulating the amplitude, the total light intensity loss value is the ratio of the minimum light intensity value to the initial value. According to the size of the peak value and the fiber bending loss formula, the deflection closest to the loss in the array is traversed and the amplitude at this time is calculated by linear interpolation.

[0025] The present invention provides a method for measuring weak vibrations based on an optical fiber vibration sensor, which uses the above-mentioned optical fiber vibration sensor to measure weak vibrations. The measurement method includes the following steps:

[0026] After initialization, the optical fiber vibration sensor starts collecting photoelectric signals. The optical intensity fluctuations caused by the deformation of the measuring section of the three-section optical fiber are linearly converted into analog voltage signals through the photoelectric detector. After analog-to-digital conversion, a discrete voltage sequence is generated and stored in non-volatile memory.

[0027] In view of the non-stationary characteristics of vibration signals, a sliding time window mechanism is used to pre-process the original signal, and digital filtering is used to eliminate environmental noise and enhance the effective signal components;

[0028] Perform a discrete Fourier transform on the preprocessed time domain data to construct a frequency domain complex array containing real and imaginary parts. Calculate the amplitude of each frequency component and locate the fundamental frequency index corresponding to the maximum amplitude. Combined with the dynamically adjusted sampling rate parameter, convert the actual vibration frequency.

[0029] During the vibration frequency demodulation phase, a fast Fourier transform is used to determine the approximate value of the vibration frequency at that time, and then the sampling frequency and sampling time of the frequency interval are matched. An adaptive threshold algorithm is used to identify the extreme points of the voltage waveform: with the current sampling point as the center, a search window of variable length is extended forward and backward (the window width is inversely correlated with the fundamental frequency value). Peak value determination is performed using a forward and backward comparison method. If the voltage value at that point is continuously greater than that of adjacent points within the window range and exceeds the noise floor threshold, it is determined to be a valid peak. The intervals between consecutive peaks are counted to calculate the average vibration period.

[0030] In the amplitude demodulation stage, the first K maximum points are extracted to calculate the normalized intensity ratio. Based on the peak value and the fiber bending loss formula, a reverse search is performed using a pre-calibrated fiber deformation-intensity mapping table (discrete data points are fitted to a piecewise linear function using the least squares method). The current intensity ratio interval is located using the bisection method, and the corresponding physical amplitude is calculated using linear interpolation.

[0031] To achieve dynamic visualization, a circular data cache structure is designed, that is, vibration frequency and amplitude data are stored in a buffer connected end to end according to timestamps. Each update overwrites the oldest data and triggers dual graphics rendering; the original data stream is plotted as a real-time waveform curve, and a trend baseline is generated based on a sliding average algorithm. The two are superimposed to highlight the signal evolution law; key parameters (sampling rate, filter cutoff frequency, peak detection window, interpolation accuracy, etc.) are encapsulated as a configurable structure, which supports online calibration according to the fiber type, vibration coupling coefficient and environmental interference intensity, ensuring the robustness of the algorithm in weak signal detection and strong noise scenarios.

[0032] Preferably, the dynamically adjusted sampling rate parameters are: high-frequency vibrations adopt dense sampling with a short time window, and low-frequency vibrations adopt sparse sampling with a long time window.

[0033] Beneficial effects of the present invention:

[0034] The optical fiber vibration sensor based on a super-working wavelength light source provided by the present invention amplifies the light intensity loss caused by bending of the detection section optical fiber through the super-working wavelength light source, and the three-section optical fiber structure enables long-distance transmission of optical signals, thereby realizing long-distance measurement; the light intensity change is detected in real time by a photoelectric detector; and finally, the conversion of optical signals into vibration information is realized through demodulation calculation. The present invention can not only simultaneously measure the frequency and amplitude of vibration, but also has the advantages of low cost, high measurement accuracy, simple operation, and strong anti-interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic structural diagram of the optical fiber vibration sensor based on the super-working wavelength light source of the present invention.

[0036] Figure 2 This is a structural schematic diagram of the optical fiber fixing module of the optical fiber vibration sensor based on the super-working wavelength light source of the present invention.

[0037] Figure 3 The figure is a schematic diagram of the module body structure of the optical fiber fixing module of the optical fiber vibration sensor based on the super-operating wavelength light source of the present invention.

[0038] Figure 4 This is a schematic diagram of the three-section optical fiber structure of the optical fiber vibration sensor based on the super-working wavelength light source of the present invention.

[0039] Figure 5 The figure is a schematic diagram of the module body structure of the optical fiber fixing module of the optical fiber vibration sensor based on the super-operating wavelength light source of the present invention.

[0040] Figure 6 This is a schematic diagram of the vibration conduction rod structure of the optical fiber vibration sensor based on the super-working wavelength light source of the present invention.

[0041] 1. Three-section optical fiber, 101. Ordinary single-mode optical fiber, 102. Small numerical aperture single-mode optical fiber, 2. Optical fiber fixing module, 201. Module body, 202. Cover plate, 203. Linear groove, 204. Through hole, 3. Vibration conduction rod, 4. Laser, 5. Photodetector. DETAILED DESCRIPTION

[0042] Example 1

[0043] This embodiment provides an optical fiber vibration sensor based on a super-working wavelength light source, comprising a three-section optical fiber 1, an optical fiber fixing module 2, a vibration transmission rod 3, a laser 4, and a photoelectric detector 5; Figure 1-6 As shown:

[0044] The three-section optical fiber 1 is formed by fusion splicing a common single-mode optical fiber 101 having the same core and cladding diameters and a small numerical aperture single-mode optical fiber 102. The first and last sections are common single-mode optical fibers 101, and the middle section is a small numerical aperture single-mode optical fiber 102. The common single-mode optical fiber 101 serves as the transmission section optical fiber, and the small numerical aperture single-mode optical fiber 102 serves as the measurement section optical fiber. In this embodiment, the numerical aperture of the common single-mode optical fiber 101 is preferably 0.125, and the operating wavelength is 1440-1625 nm; the numerical aperture of the small numerical aperture single-mode optical fiber 102 is preferably 0.085, and the operating wavelength is 980-1150 nm.

[0045] The optical fiber fixing module 2 includes a module body 201 and a cover plate 202. The upper surface of the module body 201 is provided with a linear groove 203, and the lower surface of the cover plate 202 is provided with a corresponding linear groove. The cover plate 202 is arranged on the upper part of the module body 201, and the linear grooves 203 of the module body 201 and the cover plate 202 are buckled to form a linear slot. The small numerical aperture single-mode optical fiber 102 of the three-section optical fiber 1 is arranged in the linear slot to ensure that the optical fiber remains straight. The cover plate 202 and the module body 201 are assembled and fixed by screws. The module body 201 and the cover plate 202 of the optical fiber fixing module 2 are provided with a through hole 204 that runs vertically therethrough. The through hole 204 intersects the linear slot at right angles. The portions of the small numerical aperture single-mode optical fiber 102 located at both ends of the through hole 204 are fixed by the linear slot.

[0046] The vibration transmission rod 3 is inserted into the through hole 204 from the lower part of the optical fiber fixing module 2. The upper part of the vibration transmission rod is wedge-shaped. The top of the vibration transmission rod 3 is provided with a groove, which is located inside the through hole 204 of the optical fiber fixing module 2 and contacts the small numerical aperture single-mode optical fiber 102. The small numerical aperture single-mode optical fiber 102 is located in the groove at the top of the vibration transmission rod 3. The lower end of the vibration transmission rod 3 exceeds the bottom surface of the optical fiber fixing module 2.

[0047] The laser 4 and the photodetector 5 are respectively arranged on both sides of the optical fiber fixing module 2. The ordinary single-mode optical fiber at one end of the three-section optical fiber 1 is connected to the output end of the laser 4, serving as the input end of the three-section optical fiber. The ordinary single-mode optical fiber at the other end of the three-section optical fiber 1 is connected to the input end of the photodetector 5, serving as the output end of the three-section optical fiber.

[0048] During use, the laser 4 and the photodetector 5 are respectively connected to a controller or a host computer. The laser 4 outputs continuous laser light, and the photodetector 5 detects the output light intensity of the three-section optical fiber 1 in real time. The laser 4, the photodetector 5 and other electrical devices are respectively connected to a power supply.

[0049] The laser 4 outputs a continuous laser with a wavelength of 1550 nm. When the light source wavelength is outside the operating wavelength of the low-numerical-aperture single-mode fiber 102, light intensity loss is very sensitive to changes in fiber curvature. Furthermore, the center deflection of the low-numerical-aperture single-mode fiber 102 is positively correlated with the total light intensity loss. As the center deflection increases, the total loss of the low-numerical-aperture single-mode fiber 102 increases. The low-numerical-aperture single-mode fiber 102 is 15 cm long. The conventional single-mode fiber 101 fused to the ends of the low-numerical-aperture single-mode fiber 102 can be very long. The laser 4 and photodetector 5 can be located far away from the fiber mounting module 2, enabling long-distance measurement.

[0050] Working principle of the present invention:

[0051] The present invention designs a three-section optical fiber with a small numerical aperture single-mode optical fiber 102 and ordinary single-mode optical fiber 101 fused at both ends. It only has bending loss when the small numerical aperture single-mode optical fiber 102 is bent, and the ordinary single-mode optical fiber 101 can ensure lossless transmission of optical signals.

[0052] First, fix the vibration transmission rod 3 to the surface of the vibration source, then adjust the optical fiber fixing module 2 so that the top of the vibration transmission rod 3 just contacts the small numerical aperture single-mode optical fiber 102, and then fix the optical fiber fixing module 2. The fixing method is not limited, as long as the optical fiber fixing module 2 and the vibration source remain relatively stationary during the measurement process.

[0053] During the measurement, the lower end of the vibration transmission rod 3 contacts the vibration source, and the vibration of the vibration source is transmitted to the small numerical aperture single-mode optical fiber 102 through the vibration transmission rod 3; when the vibration source is above the equilibrium position, the vibration transmission rod 3 will move upward to cause the middle part of the small numerical aperture single-mode optical fiber 102 to produce an upward deformation; because the linear slots of the optical fiber fixing module 2 fix the two ends of the small numerical aperture single-mode optical fiber 102, the small numerical aperture single-mode optical fiber 102 located at the through hole 204 will bend at this time.

[0054] The controller or host computer stores a control program that performs the following control and data processing operations:

[0055] The laser 4 is controlled to emit continuous laser light to the three-section optical fiber 1 , and the photoelectric detector 5 is controlled to detect the light intensity at the output end of the three-section optical fiber 1 in real time.

[0056] To achieve demodulation and calculation of vibration frequency and amplitude based on the principle of optical fiber vibration sensing, the curvature distribution function of small numerical aperture single-mode optical fiber 102 at different center deflections must first be calculated. This function is then integrated using the optical fiber bending loss formula to calculate the total light intensity loss at each deflection. The finite number of deflections and the total light intensity loss are stored in an array. Calculating total light intensity loss is a conventional technique.

[0057] When demodulating the frequency, the approximate value of the vibration frequency at this time is first calculated through fast Fourier transform, and then the sampling frequency and sampling time of the frequency interval are matched. The fast Fourier transform refers to collecting a shorter period of time at a higher sampling frequency, obtaining the frequency interval through fast Fourier transform (FFT), and selecting the appropriate sampling frequency and sampling time according to the frequency interval. This is the existing technology; then data is collected, and peak value judgment is performed through the front-to-back comparison method. Peak value judgment refers to finding the peak value by comparing the front-to-back values and storing the peak value position and size, and recording the peak value in an array; finally, the vibration period is calculated according to the peak interval and the sampling frequency to obtain the vibration frequency. This is the existing technology.

[0058] When demodulating the amplitude, the total light intensity loss value is the ratio of the minimum light intensity value to the initial value. According to the size of the peak value and the fiber bending loss formula, the deflection closest to the loss in the array is traversed and the amplitude at this time is calculated by linear interpolation. This is the existing technology.

[0059] The calculation steps of the optical fiber bending loss formula are as follows:

[0060] The refractive indices of the core, cladding, and coating are n1, n2, and n3, respectively. The coating radius is assumed to be infinite, and the radii of the core and cladding are a and b, respectively. The Cartesian coordinate system (X, Y) of the fiber cross section has its origin coincident with the fiber axis. The fiber is assumed to be bent in the plane at Y = 0, with a bending radius of R.

[0061] Under the weakly guided approximation, the transverse field distribution ψ(x,y) in a bent fiber satisfies the two-dimensional scalar equation as follows:

[0062]

[0063] where k = 2π / λ, λ and β are the wavelength and the complex propagation constant of the leaky fundamental mode, respectively; is the square of the effective refractive index profile in the bent fiber:

[0064]

[0065] Where n(x,y) represents the refractive index distribution in the straight fiber; the “effective” bending radius R is different from the actual bending radius R exp The difference lies in the elasto-optical correction factor based on the material.

[0066] In the q region (q is 2 and 3, representing the region 2 cladding region and region 3 coating region), the Fourier transform of the coordinate Y is:

[0067]

[0068] where ζ is the variable corresponding to coordinate Y in the Fourier transform. The corresponding field is represented by a Fourier integral and is valid over the entire interval -∞ < y < +∞;

[0069]

[0070] where A i and B i are Airy functions, and their variable X q is defined as:

[0071]

[0072] The unknown coefficients D q (ζ) and H q (ζ) can be determined by the boundary conditions.

[0073] Oscillations in the bend loss curve occur only for sufficiently large curvatures, i.e., when R is less than the critical bend radius R c ;

[0074] <00叭77>

[0075] where: <叭000180>

[0076] Using Vassallo's simple perturbation formula, the bend loss of the coated fiber is: <00叭82>

[0077]

[0078] where:

[0079]

[0080] 2α B is the conventional bend loss of the fiber with an infinite cladding. For a step-index fiber with a core refractive index of n1:

[0081]

[0082] where: [[ID=?9]]

[0083] When the value of K is large, the integral is approximated as (π / 8L 2 ) 1 / 2 times the integrand:

[0084] <00Q0203>

[0085] where:

[0086]

[0087] Example 2

[0088] This embodiment provides a method for measuring weak vibrations based on an optical fiber vibration sensor. The optical fiber vibration sensor of the first embodiment is used to measure weak vibrations. The method includes the following steps:

[0089] After initialization, the optical fiber vibration sensor starts collecting photoelectric signals. The light intensity fluctuation caused by the deformation of the small numerical aperture single-mode optical fiber 102 in the three-section optical fiber 1 is linearly converted into an analog voltage signal through the photodetector 5. After analog-to-digital conversion, a discrete voltage sequence is generated and stored in the non-volatile memory.

[0090] In view of the non-stationary characteristics of vibration signals, a sliding time window mechanism is used to pre-process the original signal, and digital filtering is used to eliminate environmental noise and enhance the effective signal components;

[0091] When the frequency changes significantly for the first time or when it does, a discrete Fourier transform should be performed on the preprocessed time domain data to construct a frequency domain complex array containing real and imaginary parts. The amplitude of each frequency component is calculated and the fundamental frequency index corresponding to the maximum amplitude is located. The actual vibration frequency is converted based on the dynamically adjusted sampling rate parameter (high-frequency vibration uses short-time window dense sampling, low-frequency vibration uses long-time window sparse sampling).

[0092] When the frequency changes slightly, during the vibration frequency demodulation stage, it is only necessary to use fast Fourier transform to calculate the approximate value of the vibration frequency at that time, and then match the sampling frequency and sampling time of the frequency interval. An adaptive threshold algorithm is used to identify the extreme points of the voltage waveform: with the current sampling point as the center, a search window of variable length is extended forward and backward (the window width is inversely correlated with the fundamental frequency value). Peak value determination is performed through the forward and backward comparison method. If the voltage value at this point is continuously greater than the adjacent points within the window range and exceeds the noise floor threshold, it is determined to be a valid peak. The interval between consecutive peaks is counted to calculate the average vibration period.

[0093] In the amplitude demodulation stage, the first K maximum points are extracted to calculate the normalized intensity ratio. Based on the peak value and the fiber bending loss formula, a reverse search is performed using a pre-calibrated fiber deformation-intensity mapping table (discrete data points are fitted to a piecewise linear function using the least squares method). The current intensity ratio interval is located using the bisection method, and the corresponding physical amplitude is calculated using linear interpolation.

[0094] To achieve dynamic visualization, a circular data cache structure is designed, that is, vibration frequency and amplitude data are stored in a buffer connected end to end according to timestamps. Each update overwrites the oldest data and triggers dual graphics rendering; the original data stream is plotted as a real-time waveform curve, and a trend baseline is generated based on a sliding average algorithm. The two are superimposed to highlight the signal evolution law; key parameters (sampling rate, filter cutoff frequency, peak detection window, interpolation accuracy, etc.) are encapsulated as a configurable structure, which supports online calibration according to the fiber type, vibration coupling coefficient and environmental interference intensity, ensuring the robustness of the algorithm in weak signal detection and strong noise scenarios.

Claims

1. An optical fiber vibration sensor based on a super-operating wavelength light source, characterized in that: It includes three-section optical fiber, optical fiber fixing module, vibration transmission rod, laser, and photoelectric detector; The three-section optical fiber is formed by fusion-joining a transmission section optical fiber and a measurement section optical fiber with the same core and cladding diameters. The first and last sections are the transmission section optical fibers, and the middle section is the measurement section optical fiber. The operating wavelength range of the transmission section optical fiber includes the wavelength of the laser light source. The operating wavelength range of the measurement section optical fiber is smaller than the wavelength of the laser light source, and the numerical aperture of the measurement section optical fiber is smaller than the numerical aperture of the transmission section optical fiber. The body of the optical fiber fixing module is provided with a transversely arranged linear slot, and the measuring segment optical fiber of the three-segment optical fiber is arranged in the linear slot; the body of the optical fiber fixing module is provided with a through hole extending vertically, and the through hole intersects the linear slot at right angles; the portions of the measuring segment optical fiber located at both ends of the through hole are fixed by the linear slot; The vibration transmission rod is inserted into the through hole from the bottom of the optical fiber fixing module, and the upper end of the vibration transmission rod is located inside the through hole of the optical fiber fixing module and contacts the optical fiber of the measuring section; the lower end of the vibration transmission rod is located in the same plane as the bottom surface of the optical fiber fixing module, or exceeds the bottom surface of the optical fiber fixing module; The laser and photoelectric detector are respectively arranged on both sides of the optical fiber fixing module. The transmission section optical fiber at one end of the three-section optical fiber is connected to the output end of the laser, and the transmission section optical fiber at the other end of the three-section optical fiber is connected to the input end of the photoelectric detector.

2. The optical fiber vibration sensor based on a super-operating wavelength light source according to claim 1, characterized in that: The optical fiber fixing module includes a module body and a cover plate. The upper surface of the module body is provided with a linear groove, and the lower surface of the cover plate is correspondingly provided with a linear groove. The cover plate is arranged on the upper part of the module body, and the linear grooves of the module body and the cover plate are buckled to form a linear slot hole; the module body and the cover plate of the optical fiber fixing module are respectively provided with a through hole that passes through from top to bottom. The through holes on the module body and the cover plate are connected and intersect with the slot hole vertically.

3. The optical fiber vibration sensor based on a super-operating wavelength light source according to claim 1, characterized in that: The laser outputs a continuous laser with a wavelength of 1550nm; the numerical aperture of the transmission section optical fiber is 0.125, and the operating wavelength is 1440-1625nm; the numerical aperture of the measurement section optical fiber is 0.085, and the operating wavelength is 980-1150nm.

4. The optical fiber vibration sensor based on a super-operating wavelength light source according to claim 1, characterized in that: The top end of the vibration conducting rod is provided with a groove, the measuring section optical fiber is located in the groove, and the groove contacts the lower surface of the measuring section optical fiber.

5. The optical fiber vibration sensor based on a super-operating wavelength light source according to claim 1 or 4, characterized in that: The upper part of the vibration conducting rod is wedge-shaped.

6. A method for measuring weak vibrations based on an optical fiber vibration sensor, characterized in that: The optical fiber vibration sensor according to any one of claims 1 to 5 is used to measure weak vibrations, and the measurement method comprises the following steps: After initialization, the optical fiber vibration sensor starts collecting photoelectric signals. The optical intensity fluctuations caused by the deformation of the measuring section of the three-section optical fiber are linearly converted into analog voltage signals through the photoelectric detector. After analog-to-digital conversion, a discrete voltage sequence is generated and stored in non-volatile memory. In view of the non-stationary characteristics of vibration signals, a sliding time window mechanism is used to pre-process the original signal, and digital filtering is used to eliminate environmental noise and enhance the effective signal components; Perform a discrete Fourier transform on the preprocessed time domain data to construct a frequency domain complex array containing real and imaginary parts. Calculate the amplitude of each frequency component and locate the fundamental frequency index corresponding to the maximum amplitude. Combined with the dynamically adjusted sampling rate parameter, convert the actual vibration frequency. During the vibration frequency demodulation phase, a fast Fourier transform is used to approximate the vibration frequency at that moment, and then the sampling frequency and sampling time of that frequency interval are matched. An adaptive threshold algorithm is used to identify the extreme points of the voltage waveform: with the current sampling point as the center, a search window of variable length is extended forward and backward, and peak value determination is performed using a forward and backward comparison method. If the voltage value at that point is continuously greater than that of adjacent points within the window range and exceeds the noise floor threshold, it is determined to be a valid peak, and the intervals between consecutive peaks are counted to calculate the average vibration period. In the amplitude demodulation stage, the first K maximum points are extracted to calculate the normalized intensity ratio. Based on the peak value and the fiber bending loss formula, a reverse search is performed through the pre-calibrated fiber deformation-intensity mapping table. The current intensity ratio interval is located using the bisection method, and the corresponding physical amplitude is calculated using linear interpolation. To achieve dynamic visualization, a circular data cache structure is designed. That is, the vibration frequency and amplitude data are stored in a buffer connected end to end according to timestamps. Each update overwrites the oldest data and triggers dual graphics rendering. The original data stream is plotted as a real-time waveform curve, and a trend baseline is generated based on a sliding average algorithm. The two are superimposed and displayed to highlight the signal evolution law. Key parameters are encapsulated as a configurable structure to support online calibration based on the fiber type, vibration coupling coefficient, and environmental interference intensity.

7. The method for measuring weak vibrations based on an optical fiber vibration sensor according to claim 6, wherein: The dynamically adjusted sampling rate parameters are: high-frequency vibrations adopt dense sampling with a short time window, and low-frequency vibrations adopt sparse sampling with a long time window.

8. The method for measuring weak vibrations based on an optical fiber vibration sensor according to claim 6, wherein: The key parameters include sampling rate, filter cutoff frequency, peak detection window, and interpolation accuracy.

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