A ramp-assisted sensing system and method based on random sampling

Abstract

The application discloses a kind of slope auxiliary sensing system and method based on random sampling, belong to optical fiber sensing technical field, the present application will random sampling technology and slope auxiliary technology be applied in traditional brillouin sensing system, through slope auxiliary technology realizes dynamic strain, i.e. the real-time measurement of vibration signal, simultaneously with the aid of random sampling technology, the frequency range of measurable vibration signal is promoted.Experiment results prove the effectiveness of the proposed sensing system scheme for the frequency measurable range of vibration signal, breaks the long-standing limitation of traditional brillouin sensing system that the frequency of measurable vibration signal is limited by the round-trip time of pulse in optical fiber;And the proposed sensing system is the same as traditional brillouin sensing system, without increasing the complexity of sensing system, which will greatly expand the practical engineering application of brillouin sensing system in ultrahigh frequency vibration signal measurement.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing technology, and more specifically, relates to a slope-assisted sensing system and method based on random sampling. Background Technology

[0002] With the continuous development of the global information age, sensors, with their intelligent perception capabilities of the surrounding environment, have become an important component of the Internet of Things (IoT). Fiber optic sensors have gained widespread attention due to their advantages such as low transmission loss, resistance to electromagnetic interference, corrosion resistance, high sensitivity, and adaptability to harsh environments. Distributed fiber optic sensing systems utilize every point along the fiber optic link as a sensing unit, while the fiber itself serves as the signal transmission carrier, thus enabling distributed continuous measurement along the fiber's length. Given their excellent technical solutions and low cost, distributed sensors are used in numerous fields, including oil pipelines, bridges, dams, tunnels, power lines, buildings, aircraft, earthquake early warning systems, and border defense, making them ideal distributed measurement tools that combine intelligence and environmental protection.

[0003] Brillouin Optical Time Domain Analysis (BOTDA) is widely used in the health monitoring of large-scale buildings because it is sensitive to both temperature and stress, and utilizes the stimulated Brillouin scattering effect in optical fibers to produce high intensity scattered light signals and longer measurement distances.

[0004] Traditional BOTDA sensing systems suffer from time-consuming frequency scanning processes that limit their ability to measure dynamic signals such as dynamic stress and temperature, leading to numerous existing studies. Methods such as ramp-assisted sensing, optical frequency combs, frequency agility, and chirped optical pulses eliminate the frequency sweeping process in traditional Brillouin systems, enabling dynamic signal measurement. Among these, ramp-assisted sensing has become a common solution for dynamic strain sensing due to its convenient implementation, lack of modification to traditional Brillouin sensing systems, and low hardware requirements. However, the narrow linear region of the Brillouin gain spectrum limits the dynamic range of measurable vibration signals. To improve the dynamic range of ramp-assisted BOTDA, various solutions have been proposed in recent years, such as multi-ramp-assisted techniques, Brillouin phase-gain ratio techniques, and Brillouin gain spectrum modulation techniques. These solutions broaden the measurement range of vibration signal intensity, significantly improving the dynamic range of ramp-assisted BOTDA systems. However, there has been little breakthrough in broadening the measurement range of vibration signal frequency. In traditional ramp-assisted BOTDA systems, the measurable vibration frequencies are limited by the round-trip time of the pump pulse in the optical fiber, i.e., the repetition frequency of the pump pulse. In long-distance sensing scenarios, the low repetition frequency of the pump pulse limits the maximum measurable vibration frequency. Furthermore, the increased sensing distance degrades the signal-to-noise ratio of the sensing signal, often necessitating averaging, which further restricts the range of measurable vibration frequencies. Therefore, expanding the frequency measurement range of vibration signals represents a landmark breakthrough in the dynamic measurement of BOTDA systems. Summary of the Invention

[0005] In response to the shortcomings and improvement needs of existing technologies, this invention provides a slope-assisted sensing system and method based on random sampling, aiming to solve the technical problem of limited measurable vibration frequencies in traditional slope-assisted BOTDA systems.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a ramp-assisted sensing system based on random sampling, comprising: a laser, an optical coupler, a first polarization controller, a microwave source, an electro-optic modulator, an optical isolator, a sensing fiber, a semiconductor optical amplifier, an arbitrary waveform generator, an erbium-doped fiber amplifier, a bandpass filter, a first circulator, a second polarization controller, a second circulator, a photodetector, a data acquisition module, and a fiber Bragg grating;

[0007] The output light of the laser serves as the system light source and is split into two beams by the optical coupler, which are used to generate probe light and pump light, respectively.

[0008] In the detection optical path, the detection light passes sequentially through the first polarization controller, the electro-optic modulator, and the optical isolator before being injected from one end of the sensing optical fiber; wherein, the electro-optic modulator is controlled and fixed at the ramp operating frequency by a microwave source;

[0009] In the pump optical path, the pump light passes through the semiconductor optical amplifier, the erbium-doped fiber amplifier, the bandpass filter, and the second polarization controller, and is then injected from the other end of the sensing fiber; wherein, the randomly sampled and encoded pulse sequence is introduced by the arbitrary waveform generator and then modulated into an optical pulse sequence by the semiconductor optical amplifier;

[0010] The pump light and probe light generate stimulated Brillouin scattering in the sensing fiber and are output by the first circulator. The Stokes light is then filtered out by the second circulator and the fiber Bragg grating, and then enters the photodetector. The signal is then acquired and processed by the data acquisition module.

[0011] Furthermore, the sensing system includes a Brillouin optical time-domain reflectometer, a Brillouin optical time-domain analyzer, a Brillouin correlation domain reflectometer, and a Brillouin correlation domain analyzer.

[0012] Furthermore, the laser is a distributed feedback semiconductor laser with a narrow linewidth.

[0013] Furthermore, the data acquisition module is an oscilloscope.

[0014] In a second aspect, the present invention provides a method for extending the measurement range of vibration signals using the slope-assisted sensing system based on random sampling as described in the first aspect, comprising:

[0015] After a pulse sequence with random sampling pulse code is pre-written in Matlab, it is imported into the arbitrary waveform generator to form an electrical pulse, which is then modulated into an optical pulse by the semiconductor optical amplifier.

[0016] The vibration signal is sampled at the same time during each pump light pulse cycle, and the frequency of the vibration signal is obtained by calculating the spectrum through non-uniform discrete Fourier transform.

[0017] Furthermore, the period of the pump light pulse is random, and each period is longer than the round-trip time of the pulse in the sensing optical fiber.

[0018] Furthermore, the vibration signal x collected by random sampling r (t n The frequency of the vibration signal obtained after calculating the spectrum through non-uniform discrete Fourier transform is:

[0019]

[0020] Wherein, sampling time tn+1 Represented as: t n+1 =t n +T n n = 1, 2, 3, ..., N; T n Let N be the period of the nth sampling point, and N be the total number of sampling points.

[0021] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0022] This invention applies random sampling and ramp-assisted techniques to a traditional Brillouin sensing system. Ramp-assisted techniques enable real-time measurement of dynamic strain, i.e., vibration signals, while random sampling techniques expand the frequency range of measurable vibration signals. Experimental results demonstrate the effectiveness of the proposed sensing system scheme in broadening the measurable frequency range of vibration signals, breaking the long-standing limitation of traditional Brillouin sensing systems on the measurable vibration signal frequency due to the pulse's round-trip time in the optical fiber. Furthermore, the proposed sensing system is identical to traditional Brillouin sensing systems, without increasing system complexity, which will greatly expand the practical engineering applications of Brillouin sensing systems in ultra-high frequency vibration signal measurement. Attached Figure Description

[0023] Figure 1 The diagram below illustrates the principle of the sensing system provided by this invention; (a) shows the principle of the ramp-assisted technology, (b) shows the measurement process of the traditional uniform sampling method, and (c) shows the measurement process of the random sampling method proposed in this invention.

[0024] Figure 2 A schematic diagram of the slope-assisted sensing system based on random sampling provided by the present invention; Figure 2 In the middle: 11-Laser, 12-Optical coupler, 13-First polarization controller, 14-Microwave source, 15-Electro-optic modulator, 16-Optical isolator, 17-Semiconductor optical amplifier, 18-Arbitrary waveform generator, 19-Erbium-doped fiber amplifier, 20-Bandpass filter, 21-First circulator, 22-Second polarization controller, 23-Second circulator, 24-Photodetector, 25-Data acquisition module, 26-Fiber Bragg grating.

[0025] Figure 3 The above is a comparison of the spectra of the 3.5 kHz vibration position demodulated using different sampling methods provided by the present invention, where (a) is uniform sampling and (b) is random sampling. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0027] In this invention, the terms "first," "second," etc. (if present) in the invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0028] This invention proposes a ramp-assisted sensing system based on random sampling, wherein the sensing system includes, but is not limited to, a Brillouin optical time domain reflectometer / analyzer (BOTDR / A) and a Brillouin correlation domain reflectometer / analyzer (BOCDR / A).

[0029] Figure 1 This is a schematic diagram illustrating the principle of the sensing system proposed in this invention. Figure 1 Figure (a) illustrates the principle of the ramp-assisted technique. The Brillouin Gain Spectrum (BGS) is Lorentz-shaped and changes with external temperature or stress, resulting in a Brillouin Frequency Shift (BFS). Therefore, if the frequency difference between the pump light and the probe light is fixed within the linear region at half the height of the Brillouin gain, i.e., the operating frequency, the Brillouin gain will change linearly with changes in external environmental parameters. Real-time recording of the changes in Brillouin gain intensity enables dynamic measurement of vibration signals.

[0030] Figure 1 Image (b) shows the measurement process of the traditional uniform sampling method. For signal processing in traditional uniform sampling, the pump pulse light samples the vibration signal once within each identical period, at sampling time t. n+1 Represented as:

[0031] t n+1 =t n +T0,n=1,2,3,…,N

[0032] Where T0 is the pulse period. Therefore, the vibration signal sampling rate is the pulse repetition frequency. Then sample the vibration signal x u (t n After calculating the spectrum using Fast Fourier Transform (FFT), the frequency of the vibration signal is measured.

[0033]

[0034] According to the Nyquist sampling theorem:

[0035]

[0036] Where f sampling f is the signal sampling rate. signal The frequency of the vibration signal is the sampling rate, or pulse repetition frequency. This rate determines the upper limit of the measured vibration signal frequency. Therefore, traditional uniform sampling methods have limited frequency measurement ranges and cannot be used to measure high-frequency vibration signals. Figure 1 The spectrum on the right side of (b) is shown.

[0037] Figure 1 Image (c) illustrates the measurement process of the random sampling method proposed in this invention. For signal processing using random sampling, the period of the pump pulse light is random, but each period must be longer than the round-trip time of the pulse in the optical fiber to achieve distributed measurement across the entire fiber. Vibration signals are sampled at the same time in each period, with the sampling time t... n+1 Represented as:

[0038] t n+1 =t n +T n n = 1, 2, 3, ..., N

[0039] Where T n Let x be the period of the nth sampling point. The vibration signal x is collected through random sampling. r (t n The frequency of the vibration signal is obtained by calculating the spectrum through Non-uniform Discrete Fourier Transform (NUDFT).

[0040]

[0041] The maximum measurable frequency of random sampling is determined by the randomness of the period, reaching the order of hundreds of kHz or even MHz. Therefore, the measurable frequency of random sampling exceeds the frequency limit determined by the pulse repetition frequency in uniform sampling, such as... Figure 1 The spectrum on the right side of (c) is shown. The dynamic Brillouin distributed sensor, utilizing random sampling and ramp-assisted techniques, enables ultra-high frequency vibration signal measurement, representing a breakthrough in extending frequency response.

[0042] Figure 2 This is a schematic diagram of the slope-assisted sensing system based on random sampling provided by the present invention. Since signal processing technology does not modify the sensing system, the system is essentially a traditional sensing system. This embodiment takes the traditional BOTDA system as an example.

[0043] Laser 11 outputs a narrow linewidth laser of 1550nm, which is split into two beams by optical coupler 12: probe beam and pump beam.

[0044] In the detection optical path, the detection light is injected into the sensing optical fiber after passing through the first polarization controller 13, the electro-optic modulator 15 and the optical isolator 16 in sequence. The electro-optic modulator 15 is controlled and fixed at the ramp operating frequency by the microwave source 14. The function of the optical isolator 16 is to isolate the pump light injected from the other end of the sensing optical fiber from entering the detection optical path and damaging the electro-optic modulator 15.

[0045] In the pump optical path, the pump light sequentially passes through a semiconductor optical amplifier 17, an erbium-doped fiber amplifier 19, a bandpass filter 20, and a second polarization controller 22 before being injected into the other end of the sensing fiber. The random sampling pulse code is pre-programmed in Matlab and imported into an arbitrary waveform generator 18 to form electrical pulses. These electrical pulses are then modulated into optical pulses by the semiconductor optical amplifier 17. The optical pulse sequence is then amplified by the erbium-doped fiber amplifier 19 and filtered by the bandpass filter 20 to remove spontaneous emission noise generated by the erbium-doped fiber amplifier 19 before being injected into the sensing fiber from the other end. It is noteworthy that the period of the random sampling coded pulse must be greater than the round-trip time of the pulse within the fiber to achieve distributed measurement across the entire fiber.

[0046] A 1-m long vibration point was set at 5.2km of the sensing fiber to verify the experimental effect, and polarization-related Brillouin gain fluctuations were suppressed by a second polarization controller 22. The pump light and probe light generated stimulated Brillouin scattering in the sensing fiber, and the backscattered signal was output through a first circulator 21. The Stokes frequency component was then filtered out by a second circulator 23 and a fiber Bragg grating 26 before being input to a photodetector 24. Finally, the signal was acquired and processed by a data acquisition module 25.

[0047] Figure 3To measure the spectrum of a 3.5 kHz vibration applied to a 1 m vibration point at a distance of 5.2 km fiber using a slope-assisted BOTDA system employing both conventional uniform sampling and the random sampling technique proposed in this invention, 5 s of Brillouin gain signals were acquired for both methods. The uniform sampling period was 100 μs, with 50,000 periods; the random sampling period was 80–160 μs, with a random interval of 1 μs, and 41,400 periods. Based on the uniform sampling period of 100 μs, the sampling rate can be calculated to be 10 kHz. To enhance the signal-to-noise ratio of the vibration signal, the uniform sampling scheme underwent 10 averaging operations, reducing the number of sampling points to 5000, and simultaneously reducing the sampling rate to 1 kHz. Due to the limitations of the Nyquist sampling theorem, the maximum measurable frequency of the uniform sampling scheme is half the sampling rate, 500 Hz. For the random sampling scheme, the maximum measurable frequency is determined by the randomness of the period, typically reaching the order of several hundred kHz or even MHz. The uniform sampling measurement results are as follows... Figure 3 As shown in (a), the vibration frequency of 3.5 kHz exceeds the measurable frequency range of the uniform sampling scheme, making the vibration frequency unmeasurable. The random sampling measurement results are as follows... Figure 3 As shown in (b), a vibration frequency peak of 3.5 kHz was successfully measured within a frequency range of 5 kHz. This fully verifies the ability of the ramp-assisted BOTDA sensing system based on random sampling to measure high-frequency vibration signals that exceed the range of uniform sampling.

[0048] In summary, dynamic Brillouin distributed sensing systems based on ramp-assisted technology have many performance parameters that require optimization for vibration signals, such as vibration intensity, vibration frequency, and vibration signal-to-noise ratio. Although significant work has been done and results have been achieved in improving the vibration intensity measurement range, research on expanding the vibration frequency measurement range is still limited. The ramp-assisted sensing system based on random sampling proposed in this invention expands the vibration frequency measurement range, overcoming the limitation of traditional ramp-assisted sensing systems on pulse round-trip time. This greatly improves the application capability of Brillouin sensors in practical engineering applications of high-frequency vibration signal measurement. Furthermore, this technology requires no changes to the system device, has a simple system structure, and achieves distributed measurement simply through software data processing, demonstrating broad application prospects.

[0049] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A slope-assisted sensing method based on random sampling, characterized in that, include: After pre-programming a random sampling pulse code pulse sequence in Matlab, it is imported into an arbitrary waveform generator to form an electrical pulse, which is then modulated into an optical pulse by a semiconductor optical amplifier. The vibration signal is sampled at the same time in each pump light pulse cycle, and the frequency of the vibration signal is obtained by calculating the spectrum through non-uniform discrete Fourier transform. The period of the pump light pulse is random, and each period is longer than the round-trip time of the pulse in the sensing fiber. Vibration signals collected by random sampling The frequency of the vibration signal obtained after calculating the spectrum using the non-uniform discrete Fourier transform is: Among them, sampling time Represented as: , ; For the first n The period of each sampling point N This represents the total number of sampling points; The sensing method is implemented by a sensing system, which includes: Laser, optical coupler, first polarization controller, microwave source, electro-optic modulator, optical isolator, sensing fiber, semiconductor optical amplifier, arbitrary waveform generator, erbium-doped fiber amplifier, bandpass filter, first circulator, second polarization controller, second circulator, photodetector, data acquisition module, and fiber Bragg grating; The output light of the laser serves as the system light source and is split into two beams by the optical coupler, which are used to generate probe light and pump light, respectively. In the detection optical path, the detection light passes sequentially through the first polarization controller, the electro-optic modulator, and the optical isolator before being injected from one end of the sensing optical fiber; wherein, the electro-optic modulator is controlled and fixed at the ramp operating frequency by a microwave source; In the pump optical path, the pump light passes through the semiconductor optical amplifier, the erbium-doped fiber amplifier, the bandpass filter, and the second polarization controller, and is then injected from the other end of the sensing fiber; wherein, the randomly sampled and encoded pulse sequence is introduced by the arbitrary waveform generator and then modulated into an optical pulse sequence by the semiconductor optical amplifier; The pump light and probe light generate stimulated Brillouin scattering in the sensing fiber and are output by the first circulator. The Stokes light is then filtered out by the second circulator and the fiber Bragg grating, and then enters the photodetector. The signal is then acquired and processed by the data acquisition module.

2. The slope-assisted sensing method based on random sampling according to claim 1, characterized in that, The sensing system includes a Brillouin optical time-domain reflectometer, a Brillouin optical time-domain analyzer, a Brillouin correlation domain reflectometer, and a Brillouin correlation domain analyzer.

3. The slope-assisted sensing method based on random sampling according to claim 1, characterized in that, The laser is a distributed feedback semiconductor laser with a narrow linewidth.

4. The slope-assisted sensing method based on random sampling according to claim 1, characterized in that, The data acquisition module is an oscilloscope.

Images