Optical fiber vibration sensing method and system based on chirped pulse input and phi-OTDR sensing

Abstract

The invention belongs to the field of vibration monitoring, and particularly relates to an optical fiber vibration sensing method and system based on chirped pulse input and phi-OTDR sensing, long-distance optical fiber vibration detection can be effectively carried out by adopting a phi-OTDR technology, and particularly, extra arrangement or installation of a plurality of sensors for sensing optical fibers is not needed in a large-range area. The frequency and phase adjustment of the chirped pulse enables the signal to be transmitted farther, and the reflected signal can maintain enough strength for accurate vibration detection. By adjusting the frequency and the phase of the chirped pulse signal, the sensing signal can be more accurately controlled at different frequencies and time points, and the fine control improves the identification capability of the optical fiber vibration position, so that the vibration source in the optical fiber can be more accurately positioned, and the accuracy of the optical fiber vibration position is improved. And a relatively high spatial resolution can be maintained in a long distance.

Description

Technical Field

[0001] The invention belongs to the field of vibration monitoring, and in particular relates to an optical fiber vibration sensing method and system based on chirped pulse input and Φ-OTDR sensing. Background Art

[0002] From the perspective of signal intensity, Brillouin scattered light is mainly used for the detection of distributed strain and temperature, while Raman scattered light is mainly sensitive to temperature effects. The detection principle of the distributed optical fiber vibration system is based on the phase-sensitive optical time domain reflectometer (Φ-OTDR) technology first proposed by Taylor HF et al. in 1993. The laser light source has the characteristics of high coherence and ultra-narrow linewidth, and the micro-vibration signal is measured through the interference effect of backward Rayleigh scattered light.

[0003] At present, the commonly used method for surveying the optical cable route is to use a radio frequency detector. The transmitter needs to be connected to the metal reinforcement core of the optical cable (or clamped in the outer sheath of the optical cable) to emit a specific radio frequency signal. The tester can detect the signal conducted by the metal in the underground optical cable by holding the receiver at the corresponding position of the ground optical cable route, thereby obtaining the actual route of the optical cable. The grounding requirements for the optical cable line are high, and the transmitter needs to be installed in the well. It only supports short-distance operations of a few kilometers. Long-distance operations require frequent installation of transmitters in the well, which has high labor costs. Later routing data needs to be manually sorted and entered. This technology relies on the metal reinforcement core of the optical cable to transmit radio frequency signals and is not suitable for use with power communication optical cables. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned insufficiency of long-distance detection and to provide an optical fiber vibration sensing method and system based on chirped pulse input and Φ-OTDR sensing.

[0005] In order to achieve the above object, the present invention adopts the following technical solution: In a first aspect, the present invention provides an optical fiber vibration sensing method based on chirped pulse input and Φ-OTDR sensing, comprising the following steps: generating a chirped pulse signal; Adjust the frequency and phase of the chirped pulse signal according to the sensing requirements; The adjusted chirped pulse signal is amplified and guided into the sensing optical fiber; Continuously receiving chirped pulse signals reflected from different receiving positions in the sensing optical fiber; Perform aggregate analysis on the received chirped pulse signal to obtain the vibration position in the sensing optical fiber; Feedback the vibration position in the sensing optical fiber to the host computer.

[0006] A further improvement of the present invention is that the specific method for adjusting the frequency and phase of the chirped pulse signal according to the sensing requirements is as follows: Adjusting the light source frequency of the chirped pulse signal to adjust the frequency of the chirped pulse signal; The excitation voltage of the chirped pulse signal is adjusted to adjust the phase of the chirped pulse signal.

[0007] A further improvement of the present invention is that the specific method of performing aggregate analysis on the received chirped pulse signal to obtain the vibration position in the sensing optical fiber is as follows: De-noising all received chirp pulse signals; Perform time domain analysis on the denoised chirp pulse signal to obtain the time delay of each receiving position, generate a time domain signal, perform Fourier transform on the time domain signal, and obtain the time domain information of each receiving position; Perform short-time Fourier transform on the denoised chirp pulse signal to obtain time-frequency distribution, and perform wavelet transform on the time-frequency distribution to obtain local characteristic information of each receiving position; According to the time domain information of each receiving position and the local characteristic information of each receiving position, the vibration position in the sensing optical fiber is obtained by performing aggregate analysis in combination with the phase of the chirped pulse signal.

[0008] A further improvement of the present invention is that the specific method of performing time domain analysis on the denoised chirp pulse signal to obtain the time delay of each receiving position, generating a time domain signal, and performing Fourier transform on the time domain signal to obtain the time domain information of each receiving position is as follows: Get the phase change of the chirped pulse signal after denoising , and the time delay caused by the propagation and reflection of the chirped pulse signal in the sensing fiber, according to the phase change of the denoised chirped pulse signal , and the delay caused by the propagation and reflection of the chirped pulse signal in the sensing fiber, the delay at each receiving position is obtained for

[0009] in, is the distance from the vibration position to the receiving position, is the propagation speed of the chirped pulse signal; The phase change caused by the chirped pulse signal being vibrated when propagating in the sensing optical fiber is:

[0010] in, is the instantaneous frequency change value of the chirp pulse signal, is the signal acquisition time; For the denoised chirp pulse signal With reference signal After comparison, the time domain signal is obtained :

[0011]

[0012] in, is the variation of the amplitude of the chirp pulse signal after denoising over time, is the phase of the reference signal; For time domain signals Take the Fourier transform:

[0013] in, For the time domain information of each receiving location, is the frequency of the chirped pulse signal, Is an imaginary unit.

[0014] A further improvement of the present invention is that a specific method of performing a short-time Fourier transform on the denoised chirped pulse signal to obtain a time-frequency distribution and performing a wavelet transform on the time-frequency distribution to obtain local characteristic information of each receiving position is as follows: For the denoised chirp pulse signal Perform short-time Fourier transform to obtain the time-frequency distribution :

[0015] in, is the short-time Fourier transform, is the size of the vector, is the windowing function, is the frequency of the chirped pulse signal, is the time position; Time-frequency distribution Perform wavelet transform to obtain local characteristic information of each receiving position :

[0016] in, For the mother wavelet, is the scale factor, is the translation factor, For time.

[0017] A further improvement of the present invention is that, according to the time domain information of each receiving position and the local characteristic information of each receiving position, the specific method of performing aggregate analysis in combination with the phase of the chirped pulse signal to obtain the vibration position in the sensing optical fiber is as follows: Combining the time domain information of each receiving position with the local characteristic information of each receiving position to obtain signal characteristics; Obtaining the phase difference at each receiving position according to the signal characteristics; According to the phase difference of each receiving position, the vibration position in the sensing optical fiber is calculated by using the interpolation method based on multi-point signals.

[0018] In a second aspect, the present invention provides an optical fiber vibration sensing system based on chirped pulse input and Φ-OTDR sensing, comprising a pulse transmitting unit and a plurality of vibration sensing units, wherein the pulse transmitting unit is connected to a sensing optical fiber, the plurality of vibration sensing units are connected to different positions of the sensing optical fiber, and the pulse transmitting unit and all the vibration sensing units are connected to a signal driver; The pulse transmitting unit includes: A chirped pulse generator, used for generating a chirped pulse signal; A modulator for adjusting the frequency and phase of the chirped pulse signal; An optical fiber amplifier, used for amplifying the adjusted chirped pulse signal; A pulse signal transmitter, used for sending the amplified chirped pulse signal to the sensing optical fiber; The vibration sensing unit includes: A pulse signal receiver is used to receive the chirped pulse signal reflected from the sensing optical fiber and send it to the detector; A detector is used to analyze the chirped pulse signal reflected from the sensing optical fiber and generate the vibration position information of the optical fiber; The acquisition card is used to collect the vibration position information of the optical fiber and send it to the host computer; The modulator and the acquisition card are both connected to a signal driver, which is used to obtain a control signal and adjust the working parameters of the modulator and the acquisition card according to the control signal.

[0019] A further improvement of the present invention is that the effective sensing distance of the pulse transmitting unit is for:

[0020]

[0021]

[0022] in, is the maximum sensing distance of the sensing fiber affected by the stimulated Brillouin scattering effect, is the maximum sensing distance of the sensing optical fiber, is the optical power of the sensing fiber causing stimulated Brillouin scattering effect, is the Brillouin gain coefficient, is the effective core area of ​​the sensing optical fiber, is the equivalent working distance of the sensing optical fiber, is the Brillouin linewidth in the sensing fiber, is the incident light width of the sensing fiber, is a constant coefficient.

[0023] A further improvement of the present invention is that the spatial resolution of the vibration sensing unit is for:

[0024]

[0025]

[0026]

[0027] in, is the first spatial resolution, is the second spatial resolution, is the third spatial resolution, is the speed of light in vacuum, is the optical pulse width in the sensing fiber, is the refractive index of the sensing optical fiber core material, is the detection bandwidth of the vibration sensing unit, is the sampling rate of the vibration sensing unit.

[0028] A further improvement of the present invention is that the maximum detectable frequency of the vibration sensing unit for:

[0029]

[0030]

[0031] in, is the speed of light in vacuum, is the refractive index of the sensing optical fiber core material, is the effective sensing distance of the pulse transmitting unit, is the time interval of the chirped pulse signal generated by the chirped pulse generator, is the trigger frequency of the vibration sensor unit.

[0032] Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts Φ-OTDR technology to effectively perform long-distance optical fiber vibration detection, especially in a large area, without the need to arrange the sensing optical fiber additionally or install multiple sensors. The frequency and phase adjustment of the chirped pulse enables the signal to be transmitted farther, and the reflected signal can maintain sufficient strength for accurate vibration detection. The present invention can more accurately control the sensing signal at different frequencies and time points by adjusting the frequency and phase of the chirped pulse signal. This fine control improves the recognition ability of the present invention for the optical fiber vibration position, so that the present invention can more accurately locate the vibration source in the optical fiber and maintain a high spatial resolution over a long distance. In the long-distance transmission process of the present invention, the optical signal is easily affected by noise and external interference. By using chirped pulse signals and precise signal aggregation analysis methods, the present invention can effectively filter out noise, enhance the stability and reliability of the signal, and improve the anti-interference ability in long-distance detection. The present invention can realize real-time analysis of chirped pulse signals received from different positions in the optical fiber, and timely feedback vibration information to the host computer. This enables the present invention to respond quickly when a vibration event occurs, which is helpful for real-time monitoring and analysis, and is particularly suitable for security and industrial monitoring environments that require rapid response. The present invention avoids the reliance of traditional sensing systems on a large number of sensors by optimizing the optical fiber sensing system and combining chirped pulse technology, thereby reducing the deployment and maintenance costs of the present invention. This is particularly important for deployment over long distances and in complex environments, and can reduce manual intervention and system complexity. In summary, while overcoming the limitations of long-distance detection, the present invention improves the sensitivity, accuracy, anti-interference ability, and real-time response capability of the present invention, and is suitable for vibration monitoring and safety assurance in large-scale and complex environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a flow chart of Example 1; Figure 2 This is a system diagram of Example 2. DETAILED DESCRIPTION

[0034] In order to further understand the content of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the embodiments are only for explaining the present invention and are not intended to limit it.

[0035] Embodiment 1: See also Figure 1 , an optical fiber vibration sensing method based on chirped pulse input and Φ-OTDR sensing, comprising the following steps: S1, generates a chirped pulse signal.

[0036] S2, adjust the frequency and phase of the chirped pulse signal according to the sensing requirements.

[0037] S3, amplifies the adjusted chirped pulse signal and guides it into the sensing optical fiber.

[0038] S4, continuously receiving chirped pulse signals reflected from different receiving positions in the sensing optical fiber.

[0039] S5, performing aggregation analysis on the received chirped pulse signal to obtain the vibration position in the sensing optical fiber.

[0040] S6, feeding back the vibration position in the sensing optical fiber to the host computer.

[0041] This embodiment improves the transmission distance and detection accuracy of the signal by adjusting the frequency and phase of the chirped pulse, and overcomes the shortcomings of the traditional optical fiber sensing system in long-distance detection. This embodiment can effectively detect the vibration position within a long distance range, and has high spatial resolution and anti-interference ability. By performing aggregate analysis on the received signals, this embodiment can feed back vibration information to the host computer in real time to ensure timely response. This embodiment simplifies sensor deployment, reduces costs, and has strong stability and reliability in complex environments. It is suitable for large-scale, real-time monitoring and safety protection scenarios.

[0042] Embodiment 2: See also Figure 2 , an optical fiber vibration sensing system based on chirped pulse input and Φ-OTDR sensing, comprising a pulse transmitting unit and a plurality of vibration sensing units, the pulse transmitting unit being connected to a sensing optical fiber, the plurality of vibration sensing units being connected to different positions of the sensing optical fiber, the pulse transmitting unit and all the vibration sensing units being connected to a signal driver; The pulse transmitting unit includes: A chirped pulse generator, used for generating a chirped pulse signal; A modulator for adjusting the frequency and phase of the chirped pulse signal; An optical fiber amplifier, used for amplifying the adjusted chirped pulse signal; A pulse signal transmitter, used for sending the amplified chirped pulse signal to the sensing optical fiber; The vibration sensing unit includes: A pulse signal receiver is used to receive the chirped pulse signal reflected from the sensing optical fiber and send it to the detector; A detector is used to analyze the chirped pulse signal reflected from the sensing optical fiber and generate the vibration position information of the optical fiber; The acquisition card is used to collect the vibration position information of the optical fiber and send it to the host computer; The modulator and the acquisition card are both connected to a signal driver, which is used to obtain a control signal and adjust the working parameters of the modulator and the acquisition card according to the control signal.

[0043] This embodiment can effectively transmit long-distance vibration signals through frequency and phase modulation of chirped pulse signals, combined with the amplification processing of signals by optical fiber amplifiers, and significantly improves the ability of long-distance monitoring. The vibration sensing unit of this embodiment can provide accurate optical fiber vibration position information by accurately analyzing the reflected chirped pulse signal, with high spatial resolution and positioning accuracy, ensuring that the position of the vibration source can be accurately detected even over a long distance. Through the connection between the acquisition card and the host computer, this embodiment can collect vibration position information in real time and provide timely feedback to ensure rapid response and monitoring, and is suitable for industrial monitoring and safety protection that require rapid response. This embodiment does not rely on multiple sensors, but uses a single optical fiber to cover long-distance areas, reducing hardware requirements and deployment costs. The modulator and acquisition card optimize working parameters through signal drivers to achieve efficient management and operation.

[0044] Embodiment 3: This embodiment is based on the embodiment 1, and further defines the specific method for adjusting the frequency and phase of the chirped pulse signal required for sensing: Adjusting the light source frequency of the chirped pulse signal to adjust the frequency of the chirped pulse signal; The excitation voltage of the chirped pulse signal is adjusted to adjust the phase of the chirped pulse signal.

[0045] By adjusting the frequency of the light source, this embodiment can finely adjust the spectral characteristics of the chirped pulse signal, thereby improving the transmission efficiency of the optical fiber and the penetration of the signal, especially in long-distance transmission, it can reduce signal attenuation and distortion, and ensure the reliability of long-distance detection. By adjusting the excitation voltage of the chirped pulse signal to adjust the signal phase, this embodiment can accurately control the phase characteristics of the chirped pulse, improve the time domain characteristics of the signal, and enable this embodiment to effectively detect vibration signals in a wider frequency range, thereby enhancing the sensitivity of this embodiment to weak vibrations and increasing the accuracy of vibration detection. The flexible adjustment of the light source frequency and excitation voltage in this embodiment enables this embodiment to adjust the working parameters according to different application scenarios, different optical fiber characteristics or environmental conditions, thereby improving the adaptability of this embodiment in complex environments. This adjustment can adapt to different optical fiber materials and different interference environments, ensuring that this embodiment can work stably under a variety of conditions.

[0046] Embodiment 4: This embodiment is based on the embodiment 1, and further defines the specific method of performing aggregate analysis on the received chirped pulse signal to obtain the vibration position in the sensing optical fiber: Step 1: De-noise all received chirp pulse signals.

[0047] Step 2: Perform time domain analysis on the denoised chirp pulse signal to obtain the time delay of each receiving position, generate a time domain signal, perform Fourier transform on the time domain signal, and obtain the time domain information of each receiving position.

[0048] Step three, perform short-time Fourier transform on the denoised chirp pulse signal to obtain time-frequency distribution, and perform wavelet transform on the time-frequency distribution to obtain local characteristic information of each receiving position.

[0049] Step 4: Based on the time domain information of each receiving position and the local characteristic information of each receiving position, an aggregate analysis is performed in combination with the phase of the chirped pulse signal to obtain the vibration position in the sensing optical fiber.

[0050] The denoising process of this embodiment effectively filters out environmental interference and background noise, improves the purity of the signal, and enhances the detection sensitivity and reliability of this embodiment. Through time domain analysis and Fourier transform, this embodiment can obtain more accurate vibration delay information, thereby improving the accuracy of vibration positioning. Short-time Fourier transform and wavelet transform help to extract the local characteristics of the signal, so that this embodiment can identify complex vibration patterns and frequency changes. This embodiment combines the aggregate analysis of time domain information, local characteristics and the phase of the chirped pulse signal to more accurately determine the vibration source of each receiving position, especially in complex environments, to improve the accuracy and resolution of vibration detection. In summary, this embodiment can perform vibration monitoring more accurately and stably in complex and long-distance environments.

[0051] Embodiment 5: This embodiment further defines step 2 in embodiment 4, and the specific method is as follows: Get the phase change of the chirped pulse signal after denoising , and the time delay caused by the propagation and reflection of the chirped pulse signal in the sensing fiber, according to the phase change of the denoised chirped pulse signal , and the delay caused by the propagation and reflection of the chirped pulse signal in the sensing fiber, the delay at each receiving position is obtained for

[0052] in, is the distance from the vibration position to the receiving position, is the propagation speed of the chirped pulse signal; The phase change caused by the chirped pulse signal being vibrated when propagating in the sensing optical fiber is:

[0053] in, is the instantaneous frequency change value of the chirp pulse signal, is the signal acquisition time; For the denoised chirp pulse signal With reference signal After comparison, the time domain signal is obtained :

[0054]

[0055] in, is the variation of the amplitude of the chirp pulse signal after denoising over time, is the phase of the reference signal; For time domain signals Take the Fourier transform:

[0056] in, For the time domain information of each receiving location, is the frequency of the chirped pulse signal, Is an imaginary unit.

[0057] In this embodiment, since the propagation speed of the chirped pulse in the optical fiber is usually slightly lower than the speed of light, the propagation speed of the chirped pulse signal in the sensing optical fiber is for , at some point , the instantaneous frequency change value of the chirp pulse signal The time delay caused by the propagation and reflection of the chirped pulse signal in the sensing fiber is , the phase change of the denoised chirp pulse signal is , and obtain the delay of each receiving position for:

[0058] Calculating Phase Change :

[0059] Computing time domain signals : Reference signal =1, the amplitude of the chirp pulse signal after denoising changes with time is also 1, the phase of the reference signal is 0, then:

[0060] Substituting the phase change ,get

[0061] Expanding using Euler's formula, we get:

[0062]

[0063] Therefore, the time domain signal Approx. .

[0064] For time domain signals Perform Fourier transform to get the frequency domain signal:

[0065] Since the time domain signal is a complex constant, the Fourier transform result will be a Dirac pulse located near the zero frequency point. Therefore, the Fourier transform result is mainly concentrated near the zero frequency, representing the main frequency component of the signal.

[0066] This embodiment obtains the time delay, phase change, time domain signal and Fourier transform result of each receiving position. In this embodiment, the Fourier transform result shows that the frequency components of the signal are mainly concentrated at zero frequency, reflecting the low-frequency characteristics of the signal. In practical applications, the output of the Fourier transform will provide detailed information for the signal components at different frequencies, thereby helping to accurately locate the vibration source.

[0067] Embodiment 6: This embodiment further defines step 3 in embodiment 4, and the specific method is as follows: For the denoised chirp pulse signal Perform short-time Fourier transform to obtain the time-frequency distribution :

[0068] in, (Short-Time Fourier Transform) is short-time Fourier transform, is the size of the vector, is the windowing function, is the frequency of the chirped pulse signal, is the time position; Time-frequency distribution Perform wavelet transform to obtain local characteristic information of each receiving position :

[0069] in, For the mother wavelet, is the scale factor, is the translation factor, For time.

[0070] In this embodiment, the chirped pulse signal after denoising , Base frequency Hz, the windowing function uses the Hanning window function, ,in, is the window width, wavelet function Using Morlet wavelet:

[0071] For the denoised chirp pulse signal Perform short-time Fourier transform to obtain the time-frequency distribution :

[0072] Substitute the denoised chirp pulse signal and Hanning window function ,get:

[0073] The above formula is the convolution integral, which is solved by Fast Fourier Transform (FFT) to obtain the time-frequency distribution The value of There will be a prominent peak near Hz, indicating the main frequency part of the chirp pulse signal.

[0074] The scale factor of this example Using invariant scale, translation factor Using translation invariance, , the denoised chirp pulse signal Substituting into the Morlet wavelet function, we get:

[0075] Use MATLAB or Python to calculate the above formula and get the frequency The transformation results near Hz will be concentrated in a local area, indicating that the characteristics of the chirped pulse signal are mainly concentrated in this frequency.

[0076] This embodiment can more accurately capture the time-frequency characteristics and local oscillation mode of the denoised chirp pulse signal by combining short-time Fourier transform and wavelet transform. In time-frequency analysis, short-time Fourier transform provides a global view of the signal frequency changing over time, while wavelet transform can capture the local characteristics of the signal, and is particularly suitable for analyzing signals with time-varying frequencies.

[0077] Embodiment 7: This embodiment further defines step 4 in embodiment 4, and the specific method is as follows: Step 1: Combine the time domain information of each receiving position and the local characteristic information of each receiving position to obtain the signal characteristics.

[0078] Step 2: Obtain the phase difference of each receiving position according to the signal characteristics.

[0079] Step three, according to the phase difference of each receiving position, the vibration position in the sensing optical fiber is calculated using an interpolation method based on multi-point signals.

[0080] This embodiment can more accurately capture the changes in vibration signals by combining time domain information and local characteristic information. This multi-dimensional information fusion provides richer signal features, which helps to accurately determine the location and frequency of vibration. Calculating the phase difference of each receiving position and performing fine calculations through interpolation can effectively reduce the errors caused by signal discretization and enhance the resolution of vibration positioning. This embodiment uses a multi-point signal interpolation method to overcome the error effects caused by a single signal source and reduce the effects caused by noise, signal attenuation or interference. This significantly improves the robustness of this embodiment in complex environments or long-distance transmission. The interpolation method can smooth the signal data and reduce the errors caused by excessive sampling intervals or signal discontinuity, thereby improving the detection accuracy of the vibration position.

[0081] Embodiment 8: This embodiment is an effective sensing distance of the pulse transmitting unit in embodiment 2. Further restrictions were made:

[0082]

[0083]

[0084] in, is the maximum sensing distance of the sensing optical fiber affected by the stimulated Brillouin scattering effect, is the maximum sensing distance of the sensing optical fiber, is the optical power of the sensing fiber causing stimulated Brillouin scattering effect, is the Brillouin gain coefficient, is the effective core area of ​​the sensing optical fiber, is the equivalent working distance of the sensing optical fiber, is the Brillouin linewidth in the sensing fiber, is the incident light width of the sensing fiber, is a constant coefficient.

[0085] The sensing distance parameter is mainly used to characterize the effective sensing area range of the Φ-OTDR system that meets various monitoring requirements. Due to the influence of transmission loss and background noise in the optical fiber, increasing the incident light intensity can increase the optical fiber sensing distance in principle. However, since stimulated Brillouin scattering (SBS) exists during the transmission of optical pulses, when the incident light intensity is greater than the SBS threshold, the energy of the backward Rayleigh scattered light will be transferred to the SBS in large quantities, resulting in a significant reduction in the overall signal-to-noise ratio of this embodiment.

[0086] Embodiment 9: This embodiment improves the spatial resolution of the vibration sensor unit in Embodiment 2. Further restrictions were made:

[0087]

[0088]

[0089]

[0090] in, is the first spatial resolution, is the second spatial resolution, is the third spatial resolution, is the speed of light in vacuum, is the optical pulse width in the sensing fiber, is the refractive index of the sensing optical fiber core material, is the detection bandwidth of the vibration sensing unit, is the sampling rate of the vibration sensing unit.

[0091] Spatial resolution refers to the minimum distance that the sensing fiber can effectively distinguish at the layout position. It can characterize the positioning accuracy of the Φ-OTDR system for a specific target event and is also one of the main parameters for measuring its system performance. Generally speaking, spatial resolution is mainly affected by the pulse width of the excitation light and should be half of the pulse width. However, spatial resolution is affected by the combined effects of the coherent pulse laser source, signal acquisition system, and analog-to-digital conversion (A / D) components.

[0092] Embodiment 10: This embodiment is a maximum detectable frequency of the vibration sensor unit in embodiment 2. for:

[0093]

[0094]

[0095] in, is the speed of light in vacuum, is the refractive index of the sensing optical fiber core material, is the effective sensing distance of the pulse transmitting unit, is the time interval of the chirped pulse signal generated by the chirped pulse generator, is the trigger frequency of the vibration sensor unit.

[0096] This embodiment restores the external disturbance model by detecting the backward Rayleigh scattered light in the optical fiber. Its essence is to discretely sample the optical fiber as a whole sensing element by exciting pulse light. At the same time, it should be ensured that no aliasing occurs between pulse lights in the optical fiber.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. An optical fiber vibration sensing method based on chirped pulse input and Φ-OTDR sensing, characterized in that: The following steps are involved: generating a chirped pulse signal; Adjust the frequency and phase of the chirped pulse signal according to the sensing requirements; The adjusted chirped pulse signal is amplified and guided into the sensing optical fiber; Continuously receiving chirped pulse signals reflected from different receiving positions in the sensing optical fiber; Perform aggregate analysis on the received chirped pulse signal to obtain the vibration position in the sensing optical fiber; Feedback the vibration position in the sensing optical fiber to the host computer.

2. The optical fiber vibration sensing method based on chirped pulse input and Φ-OTDR sensing according to claim 1, characterized in that: The specific method of adjusting the frequency and phase of the chirped pulse signal according to the sensing requirements is as follows: Adjusting the light source frequency of the chirped pulse signal to adjust the frequency of the chirped pulse signal; The excitation voltage of the chirped pulse signal is adjusted to adjust the phase of the chirped pulse signal.

3. The optical fiber vibration sensing method based on chirped pulse input and Φ-OTDR sensing according to claim 1, characterized in that: The specific method of performing aggregate analysis on the received chirped pulse signal to obtain the vibration position in the sensing optical fiber is as follows: De-noising all received chirp pulse signals; Perform time domain analysis on the denoised chirp pulse signal to obtain the time delay of each receiving position, generate a time domain signal, perform Fourier transform on the time domain signal, and obtain the time domain information of each receiving position; Perform short-time Fourier transform on the denoised chirp pulse signal to obtain time-frequency distribution, and perform wavelet transform on the time-frequency distribution to obtain local characteristic information of each receiving position; According to the time domain information of each receiving position and the local characteristic information of each receiving position, the vibration position in the sensing optical fiber is obtained by performing aggregate analysis in combination with the phase of the chirped pulse signal.

4. The optical fiber vibration sensing method based on chirped pulse input and Φ-OTDR sensing according to claim 3, characterized in that: The specific method of performing time domain analysis on the denoised chirp pulse signal to obtain the time delay of each receiving position, generating a time domain signal, and performing Fourier transform on the time domain signal to obtain the time domain information of each receiving position is as follows: Get the phase change of the chirped pulse signal after denoising , and the time delay caused by the propagation and reflection of the chirped pulse signal in the sensing fiber, according to the phase change of the denoised chirped pulse signal , and the delay caused by the propagation and reflection of the chirped pulse signal in the sensing fiber, the delay at each receiving position is obtained for: in, is the distance from the vibration position to the receiving position, is the propagation speed of the chirped pulse signal; The phase change caused by the chirped pulse signal being vibrated when propagating in the sensing optical fiber is: in, is the instantaneous frequency change value of the chirp pulse signal, is the signal acquisition time; For the denoised chirp pulse signal With reference signal After comparison, the time domain signal is obtained : in, is the variation of the amplitude of the chirp pulse signal after denoising over time, is the phase of the reference signal, is an imaginary unit; For time domain signals Take the Fourier transform: in, For the time domain information of each receiving location, is the frequency of the chirped pulse signal.

5. The optical fiber vibration sensing method based on chirped pulse input and Φ-OTDR sensing according to claim 3, characterized in that: The specific method of performing short-time Fourier transform on the denoised chirp pulse signal to obtain the time-frequency distribution and performing wavelet transform on the time-frequency distribution to obtain the local characteristic information of each receiving position is as follows: For the denoised chirp pulse signal Perform short-time Fourier transform to obtain the time-frequency distribution : in, is the short-time Fourier transform, is the size of the vector, is the windowing function, is the frequency of the chirped pulse signal, is the time position; Time-frequency distribution Perform wavelet transform to obtain local characteristic information of each receiving position : in, For the mother wavelet, is the scale factor, is the translation factor, For time.

6. The optical fiber vibration sensing method based on chirped pulse input and Φ-OTDR sensing according to claim 3, characterized in that: According to the time domain information of each receiving position and the local characteristic information of each receiving position, the specific method of obtaining the vibration position in the sensing optical fiber by combining the phase of the chirped pulse signal for aggregation analysis is as follows: Combining the time domain information of each receiving position with the local characteristic information of each receiving position to obtain signal characteristics; Obtaining the phase difference at each receiving position according to the signal characteristics; According to the phase difference of each receiving position, the vibration position in the sensing optical fiber is calculated by using the interpolation method based on multi-point signals.

7. An optical fiber vibration sensing system based on chirped pulse input and Φ-OTDR sensing, characterized in that: It includes a pulse transmitting unit and a plurality of vibration sensing units, wherein the pulse transmitting unit is connected to a sensing optical fiber, the plurality of vibration sensing units are connected to different positions of the sensing optical fiber, and the pulse transmitting unit and all the vibration sensing units are connected to a signal driver; The pulse transmitting unit includes: A chirped pulse generator, used for generating a chirped pulse signal; A modulator for adjusting the frequency and phase of the chirped pulse signal; An optical fiber amplifier, used for amplifying the adjusted chirped pulse signal; A pulse signal transmitter, used for sending the amplified chirped pulse signal to the sensing optical fiber; The vibration sensing unit includes: A pulse signal receiver is used to receive the chirped pulse signal reflected from the sensing optical fiber and send it to the detector; A detector is used to analyze the chirped pulse signal reflected from the sensing optical fiber and generate the vibration position information of the optical fiber; The acquisition card is used to collect the vibration position information of the optical fiber and send it to the host computer; The modulator and the acquisition card are both connected to a signal driver, which is used to obtain a control signal and adjust the working parameters of the modulator and the acquisition card according to the control signal.

8. The optical fiber vibration sensing system based on chirped pulse input and Φ-OTDR sensing according to claim 7, characterized in that: Effective sensing distance of the pulse transmitter for: in, is the maximum sensing distance of the sensing fiber affected by the stimulated Brillouin scattering effect, is the maximum sensing distance of the sensing optical fiber, is the optical power of the sensing fiber causing stimulated Brillouin scattering effect, is the Brillouin gain coefficient, is the effective core area of ​​the sensing optical fiber, is the equivalent working distance of the sensing optical fiber, is the Brillouin linewidth in the sensing fiber, is the incident light width of the sensing fiber, is a constant coefficient.

9. The optical fiber vibration sensing system based on chirped pulse input and Φ-OTDR sensing according to claim 7, characterized in that: Spatial resolution of the vibration sensing unit for: in, is the first spatial resolution, is the second spatial resolution, is the third spatial resolution, is the speed of light in vacuum, is the optical pulse width in the sensing fiber, is the refractive index of the sensing optical fiber core material, is the detection bandwidth of the vibration sensing unit, is the sampling rate of the vibration sensing unit.

10. The optical fiber vibration sensing system based on chirped pulse input and Φ-OTDR sensing according to claim 7, characterized in that: Maximum detectable frequency of the vibration sensor unit for: in, is the speed of light in vacuum, is the refractive index of the sensing optical fiber core material, is the effective sensing distance of the pulse transmitting unit, is the time interval of the chirped pulse signal generated by the chirped pulse generator, is the trigger frequency of the vibration sensor unit.

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