Multi-parameter distributed optical fiber sensing system and method based on chirped pulse

Abstract

The invention provides a chirp pulse-based multi-parameter distributed optical fiber sensing system and method, and relates to the technical field of optical fiber sensing, and the system comprises a chirp laser source module and a sensing detection module. The chirp laser source module is used for generating chirp laser and modulating and testing a laser source; the sensing detection module is used for receiving Raman scattering signals and Rayleigh scattering signals generated after square linear chirped pulses of the laser source are injected into the optical fibers, and calculating temperature parameters and strain parameters of the optical fibers by combining the principle that Raman scattering is only sensitive to temperature. A chirped pulse is introduced into an optical fiber to serve as a system light source, and the characteristic that the frequency of the chirped pulse linearly changes along with time and the change of the optical path difference between scattering centers caused by the uniform refractive index change # imgabs0 # can be compensated through the pulse frequency change # imgabs1 # is utilized, so that rapid co-location / ectopic synchronous measurement of a plurality of parameters along the optical fiber is realized. Especially, temperature and strain measurement is realized.

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 in the fiber. The core principles of this technology include light scattering effects such as Rayleigh scattering, Brillouin scattering and Raman scattering. Rayleigh scattering is mainly used for temperature and strain measurement; Brillouin scattering is very sensitive to temperature and strain changes and is often used for long-distance measurement; Raman scattering is suitable for high-precision temperature measurement. Distributed fiber optic sensing technology has the advantages of high sensitivity, long-distance monitoring, distributed measurement, anti-electromagnetic interference and high durability. It is widely used in oil and gas pipeline monitoring, earthquake monitoring, civil engineering structure health monitoring and power cable temperature monitoring.

[0003] In order to meet the needs of complex application scenarios, multi-parameter distributed fiber optic sensing technology has emerged, which can monitor multiple physical parameters at the same time. It realizes the simultaneous measurement of multiple physical parameters by introducing multiple light scattering effects or multi-core optical fibers. For example, by simultaneously measuring Brillouin scattering and Raman scattering signals, strain and temperature information can be extracted respectively; by utilizing the mode interference characteristics of multimode optical fiber, multi-parameter measurement can be achieved. Multi-parameter distributed fiber optic sensing technology has the advantages of comprehensive information acquisition, high-precision measurement, application flexibility and cost-effectiveness, but it also increases the complexity of data processing and analysis. At the same time, complex optical and electronic equipment also increase the cost and maintenance difficulty of the system. 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 the present application is achieved through the following technical solutions: The system comprises: a chirped laser source module and a sensor detection module; the chirped laser source module is connected to the sensor 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 parameters and strain parameters of the optical fiber by receiving the Raman scattering signal and Rayleigh scattering signal generated by the square linear chirp pulse of the laser source injected into the optical fiber, and combining the principle that Raman scattering is only sensitive to temperature.

[0006] Optionally, 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 test unit includes: coupler 1, delay optical fiber, coupler 2, detector, and oscilloscope; 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; the laser diode of the laser source is controlled by a controller; 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; The output terminal 5 of the optical amplifier is connected to the input terminal 8 of the coupler 1; 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; 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.

[0007] 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; 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; the laser diode of the laser source is controlled by a controller; 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; The output terminal 5 of the optical amplifier is connected to the input terminal 15 of the amplifier 1 for adjusting the input power; 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; 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; the output port 32 of the filter 2 is connected to the input end 33 of the wavelength division multiplexer; 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.

[0008] Optionally, the detector unit includes: a gain detector 1, a gain detector 2, and a photoelectric detector; The 1650 port of the wavelength division multiplexer is connected to the input end of the gain detector 1 of the detector unit; The 1450 port of the wavelength division multiplexer is connected to the input end of the gain detector 2 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 gain detector 1 , the gain detector 2 and the photodetector are connected to the input end 37 of the oscilloscope.

[0009] 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.

[0010] A multi-parameter distributed optical fiber sensing method based on chirped pulses, the method comprising the following steps: S1: Test the laser source to obtain test parameters under a specific modulation state; generate a linear chirp signal through the test parameters; S2: The linear chirp signal is passed through an optical amplifier controlled by a signal generator to generate nanosecond-level square linear chirp 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 reflection signal; the reflection signal includes: a Raman scattering signal and a Rayleigh scattering signal; S4: According to 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.

[0011] Optionally, step S3 includes: The specific method of processing the optical fiber includes: placing an optical fiber vibration source at a preset distance of the optical fiber to vibrate the optical fiber to generate deformation; and setting a heating device at the tail end of the optical fiber to heat the optical fiber.

[0012] Optionally, step S4 includes: S41: acquiring multiple sets of vibration data and temperature data from the Raman scattering signal and the Rayleigh scattering signal; S42: processing the vibration data and the temperature data by clipping and normalizing; S43: When processing the vibration data and temperature data of 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 group of vibration data and the first group of vibration data, and determining the maximum offset of the time domain trace between the vibration data; The maximum offset of the time domain trace between the vibration data is converted into a time offset, and the stress value corresponding to the time offset is calculated using the offset-stress conversion formula, and a curve of the stress value changing with time is plotted; 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 the maximum offset of the time domain trace between the temperature data; Convert the maximum offset of the time domain trace between the temperature data into the 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 the vibration data and temperature data of the same position of the 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:

[0013] 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 is shown in Figure 2. 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 the matrix method, the chirp system equation is transformed into the chirp system matrix;

[0014] S44d: The actual measured temperature value , bring in the chirp system matrix for inverse operation and solve the actual strain ; Draw the curve of actual temperature and strain value changing with time.

[0015] The beneficial effects of the technical solution provided by this application are: 1. Use chirped pulse light as the light source, and perform multi-parameter measurements through the reflected light signals of the system's Rayleigh scattering and Raman scattering. This solves the problem that the temperature and strain parameters of conventional fiber-optic distributed sensing systems are both sensed but difficult to distinguish. Using linear chirp signals for intensity detection, there is no need for frequency scanning or local oscillators, thereby simplifying the system architecture and achieving long-distance frequency-time mapping of fiber response. 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. 2. The laser source transmitting end of the system generates a chirped pulse light signal, which passes through the optical fiber and is modulated by environmental parameters such as temperature, vibration, and strain; the receiving end of the system measures not only the reflected Rayleigh scattering signal, but also the Raman scattering signal. The combined changes in strain and temperature acting on the optical fiber are analyzed by analyzing the Rayleigh scattering light signal, and the temperature change and temperature parameters are accurately analyzed by analyzing the Raman scattering light signal, and then the temperature and strain are analyzed separately. The present invention does not require the use of expensive narrow linewidth lasers, and can measure multiple environmental parameters with high precision, and has the advantages of simple structure and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present application will be further described below with reference to the accompanying drawings and embodiments, in which: Figure 1 is a diagram of a chirped laser source module in an embodiment of the present application; Figure 2 is a diagram of a sensor detection module in an embodiment of the present application; Figure 3 It is a step diagram in an embodiment of the present application. DETAILED DESCRIPTION

[0017] In order to have a clearer understanding of the technical features, purposes and effects of the present application, the specific implementation methods of the present application are now described in detail with reference to the accompanying drawings.

[0018] The embodiments of the present application provide a multi-parameter distributed optical fiber sensing method based on chirped pulses.

[0019] Please refer to Figure 1 and Figure 2 , Figure 1 and Figure 2 It is a chirped laser source module diagram and a sensor detection module diagram of a multi-parameter distributed optical fiber sensing system based on chirped pulses in an embodiment of the present application, wherein the system comprises: a chirped laser source module and a sensor detection module; the chirped laser source module is connected to the sensor 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 parameters and strain parameters of the optical fiber by receiving the Raman scattering signal and Rayleigh scattering signal generated by the square linear chirp pulse of the laser source injected into the optical fiber, and combining the principle that Raman scattering is only sensitive to temperature.

[0020] Specifically, the light emitted by the laser source is received at 1550nm, 1450nm, and 1650nm. The light at 1550nm is a Rayleigh scattering signal, and the light at 1450nm and 1650nm is a Raman scattering signal. Raman scattering signals are only sensitive to temperature. The chirped laser source module and the sensor detection module have the same chirped pulse generation unit, which includes: a laser source, a signal generator, an isolator, a controller, and an optical amplifier.

[0021] The chirped laser source module comprises: 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 test unit includes: coupler 1, delay optical fiber, coupler 2, detector, and oscilloscope; 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; the laser diode of the laser source is controlled by a controller; 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; The output terminal 5 of the optical amplifier is connected to the input terminal 8 of the coupler 1; 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; 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.

[0022] Specifically, a laser device with an emission wavelength of about 1550nm and continuous emission generates a light source, and drives a temperature current controller to control the laser diode of the laser device to select the laser center wavelength; at the same time, the controller applies a repetitive electrical ramp signal in the laser driver to generate a repetitive electrical ramp signal and introduce 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 part is the chirp generation unit in the entire system. The chirp generation unit is connected to coupler 1, one end of which is connected to a delay optical fiber of a certain length and then to coupler 2, and the other end is directly connected to coupler 2. Finally, the output end of coupler 2 is connected to an oscilloscope through a large-bandwidth detector to complete the test of the modulation state of the light source.

[0023] 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; 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; the laser diode of the laser source is controlled by a controller; 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; The output terminal 5 of the optical amplifier is connected to the input terminal 15 of the amplifier 1 for adjusting the input power; 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; 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; the output port 32 of the filter 2 is connected to the input end 33 of the wavelength division multiplexer; 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.

[0024] The detector unit comprises: a gain detector 1, a gain detector 2, and a photoelectric detector; The 1650 port of the wavelength division multiplexer is connected to the input end of the gain detector 1 of the detector unit; The 1450 port of the wavelength division multiplexer is connected to the input end of the gain detector 2 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 gain detector 1 , the gain detector 2 and the photodetector are connected to the input end 37 of the oscilloscope.

[0025] Specifically, the power of the detector in the detector unit is adjusted by the attenuator.

[0026] 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.

[0027] Please refer to Figure 3 , Figure 3: 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: S1: Test the laser source to obtain test parameters under a specific modulation state; generate a linear chirp signal through the test parameters; 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.

[0028] S2: The linear chirp signal is passed through an optical amplifier controlled by a signal generator to generate nanosecond-level square linear chirp 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 reflection signal; the reflection signal includes: a Raman scattering signal and a Rayleigh scattering signal; Specifically, according to the nonlinear effect in the optical fiber, the characteristic quantities such as the frequency and intensity of the reflected light signal are analyzed, and the temperature and strain values ​​of the optical fiber sensing are calculated to obtain the time curve. The specific method of changing the physical state of the optical fiber or the external environment includes: placing an optical fiber vibration source and a heating device at a preset distance of the optical fiber to modulate the transmission characteristics of the optical fiber to simulate the impact of changes in the real environment on the optical fiber. Receive the reflected signal through a wavelength division multiplexer; S4: According to 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.

[0029] Specifically, the chirp generating unit drives the optical amplifier through a signal generator to generate square linear chirp pulses at the nanosecond level 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 a 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.

[0030] Step S4 includes: S41: acquiring multiple sets of vibration data and temperature data from the Raman scattering signal and the Rayleigh scattering signal; S42: processing the vibration data and the temperature data by clipping and normalizing; Specifically, each set of data is cropped to the same size and normalized. After normalization, the mean of each set of data is zero and the standard deviation is one to ensure the consistency and accuracy of data processing.

[0031] S43: When processing the vibration data and temperature data of 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 group of vibration data and the first group of vibration data, and determining the maximum offset of the time domain trace between the vibration data; 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 change of vibration data smoother and more accurate.

[0032] The maximum offset of the time domain trace between the vibration data is converted into a time offset, and the stress value corresponding to the time offset is calculated using the offset-stress conversion formula, and a curve of the stress value changing with time is plotted; Specifically, a curve of stress variation over time is drawn to intuitively display the stress variation before and after the introduction of the linear chirp signal compensation.

[0033] 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 the maximum offset of the time domain trace between the temperature data; Convert the maximum offset of the time domain trace between the temperature data into the 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 the vibration data and temperature data of the same position of the 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 ; 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.

[0034] S44b: Construct the chirp system equation to represent the combined effects of temperature and strain on the measurement:

[0035] 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 is shown in Figure 2. 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 the matrix method, the chirp system equation is transformed into the chirp system matrix;

[0036] S44d: The actual measured temperature value , bring in the chirp system matrix for inverse operation and solve the actual strain ; Draw the curve of actual temperature and strain value changing with time.

[0037] The detection principle of chirped pulses is as follows: Typically, the intensity detected in a fiber optic sensing system will appear as random noise. This pattern will remain constant and repeatable if the fiber and the measurement conditions do not change over time. When a disturbance affects a section of fiber, it causes 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 in the optical path difference between the scattering centers caused by the pulse frequency movement to compensate.

[0038] Assuming that the refractive index change is small ( << ), then the compensation is given Required for:

[0039] 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 able to quantitatively measure temperature / strain with high measurement resolution. In this case, if the pulse is frequency-scanned to measure the change, the measurement takes a long time. Therefore, this system uses a linear chirped probe pulse to obtain high-precision temperature and strain changes in a simple and time-saving manner.

[0040] 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:

[0041] in : The center frequency of the optical pulse (unit: Hz), 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.

[0042] : The spectral content or bandwidth of a pulse (in Hertz), which represents the range of frequencies contained in the pulse and is determined by the chirp (frequency modulation) of the pulse.

[0043] : Pulse width (unit: seconds), which indicates the duration of the light pulse in time.

[0044] : Time offset (unit: seconds), which indicates the displacement of the light signal on the time axis due to strain or temperature change.

[0045] : Frequency offset (unit: Hertz), which indicates the frequency that needs to be adjusted to compensate for the change in refractive index in the optical fiber.

[0046] : 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 in an optical fiber.

[0047] 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.

[0048] Similar to the Brillouin scattering time-domain detection system, temperature and stress changes both affect the refractive index of the system, so the effects of the two on the system will overlap. If the temperature and strain occur at different locations, the chirp system can be used to directly obtain their respective changes. If you want to obtain temperature-strain information at the same location, this system introduces a temperature test system based on Raman scattering to solve the crosstalk caused by the two changes. Raman scattering is only sensitive to temperature. The temperature change is obtained through the Raman system, and then the stress change is solved.

[0049] The above are only exemplary embodiments of the present disclosure and cannot be used to limit the scope of the present disclosure. That is, any equivalent changes and modifications made according to the teachings of the present disclosure are still within the scope of the present disclosure. After considering the disclosure of the specification and the truth of practice, those skilled in the art will easily think of other embodiments of the present disclosure.

[0050] This application is intended to cover any variation, use or adaptation of the present disclosure, which follows the general principles of the present disclosure and includes common knowledge or customary technical means in the art not described in the present disclosure. The description and examples are to be regarded as exemplary only, and the scope and spirit of the present disclosure are defined by the claims.

Claims

1. A multi-parameter distributed optical fiber sensing system based on chirped pulses, characterized in that: The system comprises: a chirped laser source module and a sensor detection module; the chirped laser source module is connected to the sensor 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 parameters and strain parameters of the optical fiber by receiving the Raman scattering signal and Rayleigh scattering signal generated by the square linear chirp pulse of the laser source injected into the optical fiber, and combining the principle that Raman scattering is only sensitive to temperature.

2. A multi-parameter distributed optical fiber sensing system based on chirped pulses as claimed in claim 1, characterized in that: The chirped laser source module comprises: 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 test unit includes: coupler 1, delay optical fiber, coupler 2, detector, and oscilloscope; 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; the laser diode of the laser source is controlled by a controller; 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; The output terminal 5 of the optical amplifier is connected to the input terminal 8 of the coupler 1; 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; 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.

3. The multi-parameter distributed optical fiber sensing system based on chirped pulses according to claim 1, characterized in that: 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; 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; the laser diode of the laser source is controlled by a controller; 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; The output terminal 5 of the optical amplifier is connected to the input terminal 15 of the amplifier 1; The output terminal 16 of the amplifier 1 is connected to the input terminal 17 of the filter 1; 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; the output port 32 of the filter 2 is connected to the input end 33 of the wavelength division multiplexer; 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.

4. A multi-parameter distributed optical fiber sensing system based on chirped pulses as claimed in claim 3, characterized in that: The detector unit comprises: a gain detector 1, a gain detector 2, and a photoelectric detector; The 1650 port of the wavelength division multiplexer is connected to the input end of the gain detector 1 of the detector unit; The 1450 port of the wavelength division multiplexer is connected to the input end of the gain detector 2 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 gain detector 1 , the gain detector 2 and the photodetector are connected to the input end 37 of the oscilloscope.

5. A chirped pulse-based multi-parameter distributed optical fiber sensing system as claimed in claim 4, characterized in that: 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.

6. A chirped pulse-based multi-parameter distributed optical fiber sensing method, implemented based on a chirped pulse-based multi-parameter distributed optical fiber sensing system as claimed in claims 1 to 5, 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 through the test parameters; S2: The linear chirp signal is passed through an optical amplifier controlled by a signal generator to generate nanosecond-level square linear chirp 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 reflection signal; the reflection signal includes: a Raman scattering signal and a Rayleigh scattering signal; S4: According to 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.

7. The multi-parameter distributed optical fiber sensing method based on chirped pulses according to claim 6, characterized in that: Step S4 includes: S41: acquiring multiple sets of vibration data and temperature data from the Raman scattering signal and the Rayleigh scattering signal; S42: processing the vibration data and the temperature data by clipping and normalizing; S43: When processing the vibration data and temperature data of 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 group of vibration data and the first group of vibration data, and determining the maximum offset of the time domain trace between the vibration data; The maximum offset of the time domain trace between the vibration data is converted into a time offset, and the stress value corresponding to the time offset is calculated using the offset-stress conversion formula, and a curve of the stress value changing with time is plotted; 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 the maximum offset of the time domain trace between the temperature data; Convert the maximum offset of the time domain trace between the temperature data into the 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 the vibration data and temperature data of the same position of the 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 is shown in Figure 2. 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 the 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 for inverse operation and solve the actual strain ; Draw the curve of actual temperature and strain value changing with time.

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