A multi-parameter distributed optical fiber sensing system and method based on chirped pulses

Abstract

The present application provides a multi-parameter distributed fiber optic sensing system and method based on chirped pulses, relating to the field of fiber optic sensing technology. The system comprises: a chirped laser source module and a sensing detection module; the chirped laser source module is used to generate chirped laser light and modulate and test the laser source; the sensing detection module is used to receive Raman scattering signals and Rayleigh scattering signals generated by square linear chirped pulses from the laser source injected into the optical fiber, and, based on the principle that Raman scattering is only sensitive to temperature, calculate the temperature and strain parameters of the optical fiber. By introducing chirped pulses into the optical fiber as the system light source, and utilizing the characteristics that the chirped pulse frequency varies linearly with time and that the change in optical path difference between scattering centers caused by uniform refractive index changes can be compensated by changes in pulse frequency, rapid in-situ / out-of-situ synchronous measurement of multiple parameters along the optical fiber is achieved, particularly the measurement of temperature and strain.

Description

Technical Field

[0001] The present application relates to the field of optical fiber sensing technology, and in particular to a multi-parameter distributed optical fiber sensing system and method based on chirped pulses. Background Art

[0002] Distributed fiber optic sensing technology uses optical fiber as a sensing medium to measure physical parameters along the fiber path by detecting changes in light as it propagates through the fiber. The core principles of this technology include light scattering effects such as Rayleigh scattering, Brillouin scattering, and Raman scattering. Rayleigh scattering is primarily used for temperature and strain measurements; Brillouin scattering is highly sensitive to temperature and strain changes and is often used for long-distance measurements; and Raman scattering is suitable for high-precision temperature measurements. Distributed fiber optic sensing technology offers advantages such as high sensitivity, long-distance monitoring, distributed measurement, immunity to electromagnetic interference, and high durability. It is widely used in oil and gas pipeline monitoring, earthquake monitoring, civil engineering structural health monitoring, and power cable temperature monitoring.

[0003] To meet the demands of complex application scenarios, multi-parameter distributed fiber optic sensing technology has emerged, capable of simultaneously monitoring multiple physical parameters. It achieves simultaneous measurement of multiple physical parameters by introducing multiple light scattering effects or multi-core optical fibers. For example, by simultaneously measuring Brillouin and Raman scattering signals, strain and temperature information can be extracted separately; and by leveraging the interferometric properties of multimode optical fibers, multi-parameter measurement can be achieved. Multi-parameter distributed fiber optic sensing technology offers advantages such as comprehensive information acquisition, high-precision measurement, application flexibility, and cost-effectiveness. However, it also increases the complexity of data processing and analysis. Furthermore, complex optical and electronic equipment increase system costs and maintenance difficulties. Summary of the Invention

[0004] The purpose of the present invention is to provide a multi-parameter distributed optical fiber sensing system and method based on chirped pulses in order to solve the problems of high experimental system complexity, high cost, and difficulty in signal decoupling in the existing multi-parameter distributed optical fiber sensing technology.

[0005] The above-mentioned purpose of this application is achieved through the following technical solutions:

[0006] The system includes: a chirped laser source module and a sensor detection module; the chirped laser source module is connected to the sensor detection module;

[0007] The chirped laser source module is used to generate chirped laser and modulate and test the laser source;

[0008] The sensing detection module is used to calculate the temperature and strain parameters of the optical fiber by receiving the Raman scattering signal and Rayleigh scattering signal generated by the square linear chirped pulse of the laser source injected into the optical fiber and combining the principle that Raman scattering is only sensitive to temperature.

[0009] Optionally, the chirped laser source module includes: a chirped pulse generating unit and a testing unit;

[0010] The chirped pulse generating unit includes: a laser source, a signal generator, an isolator, a controller, and an optical amplifier;

[0011] The test unit includes: coupler 1, delay fiber, coupler 2, detector, and oscilloscope;

[0012] The output terminal 1 of the laser source is connected to the input terminal 2 of the isolator; the output terminal 3 of the isolator is connected to the input terminal 4 of the optical amplifier; a controller is used to control the laser diode of the laser source; a port 6 of the signal generator is connected to the modulation port of the controller, and a port 7 of the signal generator is connected to the modulation port of the optical amplifier;

[0013] The output terminal 5 of the optical amplifier is connected to the input terminal 8 of the coupler 1;

[0014] The output end 9a of the coupler 1 is connected to the input end 10a of the coupler 2; the output end 9b of the coupler 1 is connected to the input end 10b of the coupler 2 via a time-delay optical fiber;

[0015] The output end 11 of the coupler 2 is connected to the input end 12 of the detector; the output end 13 of the detector is connected to the input end 14 of the oscilloscope.

[0016] Optionally, the sensing detection module includes: a laser source, a signal generator, an isolator, a controller, an optical amplifier, an amplifier 1, a filter 1, a circulator, an optical fiber 1, a vibration source, an optical fiber 2, a heating device, an amplifier 2, a filter 2, a wavelength division multiplexer, a detector unit, and an oscilloscope;

[0017] The output terminal 1 of the laser source is connected to the input terminal 2 of the isolator; the output terminal 3 of the isolator is connected to the input terminal 4 of the optical amplifier; a controller is used to control the laser diode of the laser source; a port 6 of the signal generator is connected to the modulation port of the controller, and a port 7 of the signal generator is connected to the modulation port of the optical amplifier;

[0018] The output terminal 5 of the optical amplifier is connected to the input terminal 15 of the amplifier 1 for adjusting the input power;

[0019] The output terminal 16 of the amplifier 1 is connected to the input terminal 17 of the filter 1 for adjusting the input power to avoid nonlinear effects;

[0020] The output end 18 of the filter 1 is connected to the first port 19 of the circulator; the second port 20 of the circulator is connected to the input end 21 of the optical fiber 1; the output end 22 of the optical fiber 1 is connected to the input end 23 of the vibration source, and the output end 24 of the vibration source is connected to the input end 25 of the optical fiber 2; the output end 26 of the optical fiber 2 is connected to the input end 27 of the heating device; the third port 28 of the circulator is connected to the input end 29 of the amplifier 2; the output end 30 of the amplifier 2 is connected to the input port 31 of the filter 2; and the output port 32 of the filter 2 is connected to the input end 33 of the wavelength division multiplexer.

[0021] The output terminal 34 of the wavelength division multiplexer is connected to the input terminal 35 of the detector unit, and the output terminal 36 of the detector unit is connected to the input terminal 37 of the oscilloscope.

[0022] Optionally, the detector unit includes: a gain detector 1, a gain detector 2, and a photoelectric detector;

[0023] The 1650 port of the wavelength division multiplexer is connected to the input end of the gain detector 1 of the detector unit;

[0024] The 1450 port of the wavelength division multiplexer is connected to the input end of the gain detector 2 of the detector unit;

[0025] The 1550 port of the wavelength division multiplexer is connected to the input end of the photodetector of the detector unit;

[0026] The output terminals of the gain detector 1 , the gain detector 2 and the photodetector are connected to the input terminal 37 of the oscilloscope.

[0027] Optionally, the amplifier 1 and the amplifier 2 are erbium-doped fiber amplifiers; the filter 1 and the filter 2 are bandpass filters; the laser source adopts a frequency-stabilized laser; and the controller adopts a standard current and temperature controller.

[0028] A multi-parameter distributed optical fiber sensing method based on chirped pulses, the method comprising the following steps:

[0029] S1: Test the laser source to obtain test parameters under a specific modulation state; generate a linear chirp signal based on the test parameters;

[0030] S2: The linear chirped signal is passed through an optical amplifier controlled by a signal generator to generate nanosecond-level square linear chirped pulses.

[0031] S3: injecting a square pulse signal into the optical fiber and modulating the transmission characteristics of the optical fiber by changing the physical state of the optical fiber or the external environment to obtain a reflected signal; the reflected signal includes: a Raman scattering signal and a Rayleigh scattering signal;

[0032] S4: Based on the nonlinear effect in the optical fiber, the reflected signal is analyzed, and the curves of temperature and strain values ​​changing with time are calculated to complete the distributed optical fiber multi-parameter sensing measurement.

[0033] Optionally, step S3 includes:

[0034] The specific methods of processing the optical fiber include: placing an optical fiber vibration source at a preset distance from the optical fiber to vibrate the optical fiber and generate deformation; and setting a heating device at the tail end of the optical fiber to heat the optical fiber.

[0035] Optionally, step S4 includes:

[0036] S41: Acquire multiple sets of vibration data and temperature data from the Raman scattering signal and the Rayleigh scattering signal;

[0037] S42: processing vibration data and temperature data by clipping and normalizing;

[0038] S43: When processing vibration data and temperature data at different positions of the optical fiber, the specific steps are as follows:

[0039] S43a: using a cross-correlation analysis method, calculating the cross-correlation between each set of vibration data and the first set of vibration data, and determining a maximum offset of the time domain traces between the vibration data;

[0040] Convert the maximum offset of the time domain traces between the vibration data into a time offset, use the offset-stress conversion formula to calculate the stress value corresponding to the time offset, and draw a curve of the stress value changing with time;

[0041] S43b: using a cross-correlation analysis method, calculating the cross-correlation between each set of temperature data and the first set of temperature data, and determining a maximum offset of the time domain traces between the temperature data;

[0042] Convert the maximum offset of the time domain trace between temperature data into time offset; use the offset-temperature conversion formula to calculate the temperature value corresponding to the time offset and draw a curve of temperature change over time;

[0043] S44: When processing vibration data and temperature data at the same position of an optical fiber, the specific steps are as follows:

[0044] S44a: Introduce Raman scattering signal, calculate the intensity ratio of Stokes and anti-Stokes signals, and obtain the actual measured temperature value ;

[0045] S44b: Construct the chirp system equation to represent the combined effects of temperature and strain on the measurement:

[0046] in, Indicates temperature The influence coefficient on the measurement result quantifies the influence of the real temperature T on the temperature value measured by the chirp system equation The effect of temperature on the refractive index change. Indicates strain The influence coefficient on the measurement results quantifies the effect of strain on the refractive index and the temperature value measured by the chirp system equation , indicating the contribution of strain to the refractive index change;

[0047] S44c: Using matrix method, the chirp system equation is transformed into the chirp system matrix;

[0048]

[0049] S44d: The actual measured temperature value , bring in the chirp system matrix to perform inverse operation and solve the actual strain ; Draw the curve of actual temperature and strain value changing with time.

[0050] The beneficial effects of the technical solution provided by this application are:

[0051] 1. Using chirped pulsed light as the light source, multi-parameter measurements are performed through the reflected light signals of the system's Rayleigh scattering and Raman scattering. This solves the problem of conventional fiber-optic distributed sensing systems where temperature and strain parameters are both sensed but difficult to distinguish. Using linear chirped signals for intensity detection eliminates the need for frequency scanning or local oscillators, thereby simplifying the system architecture and enabling long-distance frequency-time mapping of fiber responses. By adjusting the chirp characteristics of the pulse, high-sensitivity and high-resolution temperature and strain measurements can be achieved, with a resolution several orders of magnitude lower than that of the Brillouin scattering method.

[0052] 2. The system's laser source emits a chirped pulsed light signal, which passes through the optical fiber and is modulated by environmental parameters such as temperature, vibration, and strain. The system's receiving end measures not only the reflected Rayleigh scattered signal but also the Raman scattered signal. Analysis of the Rayleigh scattered light signal reveals the combined changes in strain and temperature acting on the optical fiber. Analysis of the Raman scattered light signal accurately interprets the temperature change as a temperature parameter, and then analyzes the temperature and strain separately. This invention eliminates the need for expensive narrow-linewidth lasers and can measure multiple environmental parameters with high precision, offering advantages such as a simple structure and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The present application will be further described below with reference to the accompanying drawings and embodiments, in which:

[0054] Figure 1 is a diagram of a chirped laser source module in an embodiment of the present application;

[0055] Figure 2 This is a diagram of a sensor detection module in an embodiment of the present application;

[0056] Figure 3 It is a step diagram in an embodiment of the present application. DETAILED DESCRIPTION

[0057] In order to have a clearer understanding of the technical features, purposes and effects of this application, the specific implementation methods of this application are now described in detail with reference to the accompanying drawings.

[0058] The embodiments of the present application provide a multi-parameter distributed optical fiber sensing method based on chirped pulses.

[0059] Please refer to Figure 1 and Figure 2 , Figure 1 and Figure 2 This is a diagram of a chirped laser source module and a sensor detection module of a multi-parameter distributed optical fiber sensing system based on chirped pulses in an embodiment of the present application. The system includes: a chirped laser source module and a sensor detection module; the chirped laser source module is connected to the sensor detection module;

[0060] The chirped laser source module is used to generate chirped laser and modulate and test the laser source;

[0061] The sensing detection module is used to calculate the temperature and strain parameters of the optical fiber by receiving the Raman scattering signal and Rayleigh scattering signal generated by the square linear chirped pulse of the laser source injected into the optical fiber and combining the principle that Raman scattering is only sensitive to temperature.

[0062] Specifically, the light emitted by the laser source is received at wavelengths of 1550nm, 1450nm, and 1650nm. The 1550nm wavelength represents Rayleigh scattering, while the 1450nm and 1650nm wavelengths represent Raman scattering. Raman scattering signals are only sensitive to temperature. The chirped laser source module and the sensor detection module share the same chirped pulse generation unit, which includes a laser source, signal generator, isolator, controller, and optical amplifier.

[0063] The chirped laser source module includes: a chirped pulse generating unit and a testing unit;

[0064] The chirped pulse generating unit includes: a laser source, a signal generator, an isolator, a controller, and an optical amplifier;

[0065] The test unit includes: coupler 1, delay fiber, coupler 2, detector, and oscilloscope;

[0066] The output terminal 1 of the laser source is connected to the input terminal 2 of the isolator; the output terminal 3 of the isolator is connected to the input terminal 4 of the optical amplifier; a controller is used to control the laser diode of the laser source; a port 6 of the signal generator is connected to the modulation port of the controller, and a port 7 of the signal generator is connected to the modulation port of the optical amplifier;

[0067] The output terminal 5 of the optical amplifier is connected to the input terminal 8 of the coupler 1;

[0068] The output end 9a of the coupler 1 is connected to the input end 10a of the coupler 2; the output end 9b of the coupler 1 is connected to the input end 10b of the coupler 2 via a time-delay optical fiber;

[0069] The output end 11 of the coupler 2 is connected to the input end 12 of the detector; the output end 13 of the detector is connected to the input end 14 of the oscilloscope.

[0070] Specifically, a laser device with a continuous emission wavelength of approximately 1550nm generates the light source, driving a temperature current controller to control the laser diode of the laser device to select the laser's center wavelength. Simultaneously, the controller applies a repetitive electrical ramp signal to the laser driver, generating a repetitive electrical ramp signal that introduces linear chirp. An optical amplifier is used to gate the light in the time domain, and its driver is synchronized with the secondary laser current control to generate a linear chirp signal. This component is the chirp generation unit in the entire system. The chirp generation unit is connected to coupler 1. One end of coupler 1 is connected to a length of delay fiber, which is then connected to coupler 2. The other end is directly connected to coupler 2. Finally, the output of coupler 2 is connected to an oscilloscope via a high-bandwidth detector to complete the test of the light source modulation state.

[0071] The sensing detection module includes: a laser source, a signal generator, an isolator, a controller, an optical amplifier, an amplifier 1, a filter 1, a circulator, an optical fiber 1, a vibration source, an optical fiber 2, a heating device, an amplifier 2, a filter 2, a wavelength division multiplexer, a detector unit, and an oscilloscope;

[0072] The output terminal 1 of the laser source is connected to the input terminal 2 of the isolator; the output terminal 3 of the isolator is connected to the input terminal 4 of the optical amplifier; a controller is used to control the laser diode of the laser source; a port 6 of the signal generator is connected to the modulation port of the controller, and a port 7 of the signal generator is connected to the modulation port of the optical amplifier;

[0073] The output terminal 5 of the optical amplifier is connected to the input terminal 15 of the amplifier 1 for adjusting the input power;

[0074] The output terminal 16 of the amplifier 1 is connected to the input terminal 17 of the filter 1 for adjusting the input power to avoid nonlinear effects;

[0075] The output end 18 of the filter 1 is connected to the first port 19 of the circulator; the second port 20 of the circulator is connected to the input end 21 of the optical fiber 1; the output end 22 of the optical fiber 1 is connected to the input end 23 of the vibration source, and the output end 24 of the vibration source is connected to the input end 25 of the optical fiber 2; the output end 26 of the optical fiber 2 is connected to the input end 27 of the heating device; the third port 28 of the circulator is connected to the input end 29 of the amplifier 2; the output end 30 of the amplifier 2 is connected to the input port 31 of the filter 2; and the output port 32 of the filter 2 is connected to the input end 33 of the wavelength division multiplexer.

[0076] The output terminal 34 of the wavelength division multiplexer is connected to the input terminal 35 of the detector unit, and the output terminal 36 of the detector unit is connected to the input terminal 37 of the oscilloscope.

[0077] The detector unit includes: gain detector 1, gain detector 2, and photoelectric detector;

[0078] The 1650 port of the wavelength division multiplexer is connected to the input end of the gain detector 1 of the detector unit;

[0079] The 1450 port of the wavelength division multiplexer is connected to the input end of the gain detector 2 of the detector unit;

[0080] The 1550 port of the wavelength division multiplexer is connected to the input end of the photodetector of the detector unit;

[0081] The output terminals of the gain detector 1 , the gain detector 2 and the photodetector are connected to the input terminal 37 of the oscilloscope.

[0082] Specifically, the power of the detector in the detector unit is adjusted by the attenuator.

[0083] The amplifier 1 and the amplifier 2 are erbium-doped fiber amplifiers; the filter 1 and the filter 2 are band-pass filters; the laser source adopts a frequency-stabilized laser; and the controller adopts a standard current and temperature controller.

[0084] Please refer to Figure 3 , Figure 3 1 is a step diagram of a multi-parameter distributed optical fiber sensing method based on chirped pulses in an embodiment of the present application, the method comprising the following steps:

[0085] S1: Test the laser source to obtain test parameters under a specific modulation state; generate a linear chirp signal based on the test parameters;

[0086] Specifically, the external modulation performance of the laser source needs to be measured before use. First, important parameters such as the frequency shift generated by the light source under a specific modulation state and the chirp change rate are obtained from the light source test system and imported into the data processing code.

[0087] S2: The linear chirped signal is passed through an optical amplifier controlled by a signal generator to generate nanosecond-level square linear chirped pulses.

[0088] S3: injecting a square pulse signal into the optical fiber and modulating the transmission characteristics of the optical fiber by changing the physical state of the optical fiber or the external environment to obtain a reflected signal; the reflected signal includes: a Raman scattering signal and a Rayleigh scattering signal;

[0089] Specifically, based on the nonlinear effects within the optical fiber, the frequency, intensity, and other characteristic quantities of the reflected light signal are analyzed to calculate the time-varying curves of the temperature and strain values ​​sensed by the optical fiber. Specific methods for changing the physical state of the optical fiber or the external environment include: placing an optical fiber vibration source and a heating device at predetermined distances along the optical fiber to modulate the transmission characteristics of the optical fiber to simulate the effects of changes in the real environment on the optical fiber. The reflected signal is received through a wavelength division multiplexer.

[0090] S4: Based on the nonlinear effect in the optical fiber, the reflected signal is analyzed, and the curves of temperature and strain values ​​changing with time are calculated to complete the distributed optical fiber multi-parameter sensing measurement.

[0091] Specifically, the chirp generating unit drives the optical amplifier through a signal generator to generate nanosecond square linear chirped pulses to achieve a specific spatial resolution. An isolator is added between the laser diode and the optical amplifier to prevent the laser from being unstable due to reflection. The optical signal is introduced into the optical fiber through a circulator, and an optical fiber vibration source is placed at a specific distance of the optical fiber, with a disturbance length of several meters. The heating device at the tail end of the optical fiber is used to introduce temperature changes within a specific length range. A wavelength division multiplexer is used at the receiving end to separate signals of different wavelengths. Two highly sensitive detection devices are used to measure Raman scattering signals. A photoelectric detection device with a specific large bandwidth is used to receive Rayleigh scattering signals. Finally, the detection device is connected to the oscilloscope unit for data processing.

[0092] Step S4 includes:

[0093] S41: Acquire multiple sets of vibration data and temperature data from the Raman scattering signal and the Rayleigh scattering signal;

[0094] S42: processing vibration data and temperature data by clipping and normalizing;

[0095] Specifically, each data set was cropped to the same size and normalized. After normalization, the mean of each data set was zero and the standard deviation was one to ensure consistency and accuracy in data processing.

[0096] S43: When processing the vibration data and temperature data at different positions of the optical fiber, the specific steps are as follows:

[0097] S43a: using a cross-correlation analysis method, calculating the cross-correlation between each set of vibration data and the first set of vibration data, and determining a maximum offset of the time domain traces between the vibration data;

[0098] Specifically, the maximum deviation reflects the vibration effect that changes over time. The three-point median filter method is used to remove outliers, making the changes in vibration data smoother and more accurate.

[0099] Convert the maximum offset of the time domain traces between the vibration data into a time offset, use the offset-stress conversion formula to calculate the stress value corresponding to the time offset, and draw a curve of the stress value changing with time;

[0100] Specifically, a curve showing the stress variation over time is drawn to intuitively display the stress variation before and after the linear chirp signal compensation is introduced.

[0101] S43b: using a cross-correlation analysis method, calculating the cross-correlation between each set of temperature data and the first set of temperature data, and determining a maximum offset of the time domain traces between the temperature data;

[0102] Convert the maximum offset of the time domain trace between temperature data into time offset; use the offset-temperature conversion formula to calculate the temperature value corresponding to the time offset and draw a curve of temperature change over time;

[0103] S44: When processing vibration data and temperature data at the same position of an optical fiber, the specific steps are as follows:

[0104] S44a: Introduce Raman scattering signal, calculate the intensity ratio of Stokes and anti-Stokes signals, and obtain the actual measured temperature value ;

[0105] Specifically, Raman scattering is sensitive to temperature changes but not affected by strain, so it can be used to eliminate the influence of strain on temperature measurement.

[0106] S44b: Construct the chirp system equation to represent the combined effects of temperature and strain on the measurement:

[0107] in, Indicates temperature The influence coefficient on the measurement result quantifies the influence of the real temperature T on the temperature value measured by the chirp system equation The effect of temperature on the refractive index change. Indicates strain The influence coefficient on the measurement results quantifies the effect of strain on the refractive index and the temperature value measured by the chirp system equation , indicating the contribution of strain to the refractive index change;

[0108] S44c: Using matrix method, the chirp system equation is transformed into the chirp system matrix;

[0109]

[0110] S44d: The actual measured temperature value , bring in the chirp system matrix to perform inverse operation and solve the actual strain ; Draw the curve of actual temperature and strain value changing with time.

[0111] The detection principle of chirped pulses is as follows:

[0112] Typically, the intensity detected in a fiber optic sensing system will appear as random noise. If the fiber and the measurement conditions do not change over time, this pattern will remain constant and repeatable. When a disturbance affects a certain section of fiber, it will cause a change in the refractive index at that specific location. In traditional schemes, this refractive index change will produce an intensity change in the corresponding part of the power trace. However, the intensity change of the signal is not linearly related to the amplitude of the external disturbance, so it is usually difficult to accurately quantify the amplitude of the disturbance. But uniform refractive index changes The change of optical path difference between scattering centers can be controlled by pulse frequency. movement to compensate.

[0113] Assuming that the refractive index change is small ( << ), then the compensation is given Required for:

[0114]

[0115] in is the center frequency of the pulse, is the effective refractive index of the optical fiber. According to this principle, The system has been proven to be capable of quantitatively measuring temperature and strain with high measurement resolution. However, sweeping the pulse frequency to measure changes in this situation would be time-consuming. Therefore, this system uses linearly chirped probe pulses, enabling simple and time-efficient acquisition of high-precision temperature and strain changes.

[0116] In chirped pulse In the example, the refractive index change can be simply converted into a proportional time shift of the corresponding part of the power trace. In conventional single-mode optical fibers, the measured and temperature ( ) or strain ( ) changes as follows:

[0117]

[0118] in : The center frequency of the optical pulse (unit: Hertz), which represents the main frequency of the optical pulse sent to the optical fiber; Formula (1) is the offset-stress conversion formula, and Formula (2) is the offset-temperature conversion formula.

[0119] : The spectral content or bandwidth of a pulse (unit: Hertz), which represents the range of frequencies contained in the pulse and is determined by the chirp (frequency modulation) of the pulse.

[0120] : Pulse width (unit: seconds), which indicates the duration of the light pulse in time.

[0121] : Time offset (unit: seconds), which indicates the displacement of the optical signal on the time axis due to strain or temperature change.

[0122] : Frequency offset (unit: Hertz), which indicates the frequency that needs to be adjusted to compensate for the change in the refractive index of the optical fiber.

[0123] : Strain change (dimensionless), which represents the strain in the optical fiber caused by external forces or changes in environmental conditions. The spectral content or bandwidth of a linear chirp signal represents the frequency variation of a single light pulse as it propagates through an optical fiber.

[0124] Used to describe compensation for changes in the refractive index of optical fibers The desired frequency shift allows the system to measure changes in temperature or strain along the fiber.

[0125] Similar to Brillouin scattering time-domain detection systems, temperature and stress changes both affect the system's refractive index, so their effects overlap. If temperature and strain occur at different locations, the chirp system can directly measure their respective changes. However, if temperature and strain information at the same location is desired, this system incorporates a Raman scattering-based temperature measurement system to mitigate the crosstalk caused by the two changes. Raman scattering is only sensitive to temperature, and the Raman system measures temperature changes, which can then be used to determine stress changes.

[0126] The above are merely exemplary embodiments of the present disclosure and are not intended to limit the scope of the present disclosure. In other words, any equivalent variations and modifications made in accordance with the teachings of the present disclosure are still within the scope of the present disclosure. Those skilled in the art will readily conceive of other embodiments of the present disclosure after considering the disclosure and the practical implications thereof.

[0127] This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include common knowledge or customary techniques in the art not described herein. The description and examples are to be considered as exemplary only, and the scope and spirit of the present disclosure are to be defined by the claims.

Claims

1. A multi-parameter distributed optical fiber sensing method based on chirped pulses, implemented based on a multi-parameter distributed optical fiber sensing system based on chirped pulses, characterized in that: The method comprises the following steps: S1: Test the laser source to obtain test parameters under a specific modulation state; generate a linear chirp signal based on the test parameters; S2: The linear chirped signal is passed through an optical amplifier controlled by a signal generator to generate nanosecond-level square linear chirped pulses. S3: injecting a square pulse signal into the optical fiber and modulating the transmission characteristics of the optical fiber by changing the physical state of the optical fiber or the external environment to obtain a reflected signal; the reflected signal includes: a Raman scattering signal and a Rayleigh scattering signal; S4: Based on the nonlinear effect in the optical fiber, the reflected signal is analyzed and the time-varying curves of temperature and strain values ​​are calculated to complete the distributed optical fiber multi-parameter sensing measurement. Step S4 includes: S41: Acquire multiple sets of vibration data and temperature data from the Raman scattering signal and the Rayleigh scattering signal; S42: processing vibration data and temperature data by clipping and normalizing; S43: When processing vibration data and temperature data at different positions of the optical fiber, the specific steps are as follows: S43a: using a cross-correlation analysis method, calculating the cross-correlation between each set of vibration data and the first set of vibration data, and determining a maximum offset of the time domain traces between the vibration data; Convert the maximum offset of the time domain traces between the vibration data into a time offset, use the offset-stress conversion formula to calculate the stress value corresponding to the time offset, and draw a curve of the stress value changing with time; S43b: using a cross-correlation analysis method, calculating the cross-correlation between each set of temperature data and the first set of temperature data, and determining a maximum offset of the time domain traces between the temperature data; Convert the maximum offset of the time domain trace between temperature data into time offset; use the offset-temperature conversion formula to calculate the temperature value corresponding to the time offset and draw a curve of temperature change over time; S44: When processing vibration data and temperature data at the same position of an optical fiber, the specific steps are as follows: S44a: Introduce Raman scattering signal, calculate the intensity ratio of Stokes and anti-Stokes signals, and obtain the actual measured temperature value ; S44b: Construct the chirp system equation to represent the combined effects of temperature and strain on the measurement: in, Indicates temperature The influence coefficient on the measurement result quantifies the influence of the real temperature T on the temperature value measured by the chirp system equation The effect of temperature on the refractive index change. Indicates strain The influence coefficient on the measurement results quantifies the effect of strain on the refractive index and the temperature value measured by the chirp system equation , indicating the contribution of strain to the refractive index change; S44c: Using matrix method, the chirp system equation is transformed into the chirp system matrix; S44d: The actual measured temperature value , bring in the chirp system matrix to perform inverse operation and solve the actual strain ; Draw the curve of actual temperature and strain value changing with time.

2. The multi-parameter distributed optical fiber sensing method based on chirped pulses according to claim 1, wherein: The multi-parameter distributed optical fiber sensing system based on chirped pulses comprises: a chirped laser source module and a sensing detection module; the chirped laser source module is connected to the sensing detection module; The chirped laser source module is used to generate chirped laser and modulate and test the laser source; The sensing detection module is used to calculate the temperature and strain parameters of the optical fiber by receiving the Raman scattering signal and Rayleigh scattering signal generated by the square linear chirped pulse of the laser source injected into the optical fiber and combining the principle that Raman scattering is only sensitive to temperature.

3. The multi-parameter distributed optical fiber sensing method based on chirped pulses according to claim 2, characterized in that: The chirped laser source module includes: a chirped pulse generating unit and a testing unit; The chirped pulse generating unit includes: a laser source, a signal generator, an isolator, a controller, and an optical amplifier; The testing unit includes: a first coupler, a delay optical fiber, a second coupler, a detector, and an oscilloscope; The output end of the laser source is connected to the input end of the isolator; the output end of the isolator is connected to the input end of the optical amplifier; a controller is used to control the laser diode of the laser source; a first port of the signal generator is connected to the modulation port of the controller, and a second port is connected to the modulation port of the optical amplifier; The output end of the optical amplifier is connected to the input end of the first coupler; The first output end of the first coupler is connected to the first input end of the second coupler; the second output end of the first coupler is connected to the second input end of the second coupler via a time-delay optical fiber; The output end of the second coupler is connected to the input end of the detector; the output end of the detector is connected to the input end of the oscilloscope.

4. The multi-parameter distributed optical fiber sensing method based on chirped pulses according to claim 2, wherein: The sensing detection module includes: a laser source, a signal generator, an isolator, a controller, an optical amplifier, a first amplifier, a first filter, a circulator, a first optical fiber, a vibration source, a second optical fiber, a heating device, a second amplifier, a second filter, a wavelength division multiplexer, a detector unit, and an oscilloscope; The output end of the laser source is connected to the input end of the isolator; the output end of the isolator is connected to the input end of the optical amplifier; a controller is used to control the laser diode of the laser source; a first port of the signal generator is connected to the modulation port of the controller, and a second port is connected to the modulation port of the optical amplifier; The output end of the optical amplifier is connected to the input end of the first amplifier; The output end of the first amplifier is connected to the input end of the first filter; The output end of the first filter is connected to one port of the circulator; the second port of the circulator is connected to the input end of the first optical fiber; the output end of the first optical fiber is connected to the input end of the vibration source, and the output end of the vibration source is connected to the input end of the second optical fiber; the output end of the second optical fiber is connected to the input end of the heating device; the third port of the circulator is connected to the input end of the second amplifier; the output end of the second amplifier is connected to the input port of the second filter; and the output port of the second filter is connected to the input end of the wavelength division multiplexer. The output end of the wavelength division multiplexer is connected to the input end of the detector unit, and the output end of the detector unit is connected to the input end of the oscilloscope.

5. The multi-parameter distributed optical fiber sensing method based on chirped pulses according to claim 4, characterized in that: The detector unit includes: a first gain detector, a second gain detector, and a photoelectric detector; The 1650 port of the wavelength division multiplexer is connected to the input end of the first gain detector of the detector unit; The 1450 port of the wavelength division multiplexer is connected to the input end of the second gain detector of the detector unit; The 1550 port of the wavelength division multiplexer is connected to the input end of the photodetector of the detector unit; The output ends of the first gain detector, the second gain detector and the photodetector are connected to the input end of the oscilloscope.

6. The multi-parameter distributed optical fiber sensing method based on chirped pulses according to claim 5, characterized in that: The first amplifier and the second amplifier are erbium-doped fiber amplifiers; the first filter and the second filter are bandpass filters; the laser source adopts a frequency-stabilized laser; and the controller adopts a standard current and temperature controller.

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