Temperature and strain decoupling rapid measurement device and method based on chaotic optical frequency comb

Abstract

The invention belongs to the field of distributed optical fiber sensing, and discloses a chaos optical frequency comb-based temperature and strain decoupling rapid measurement device and method.In the device, continuous pump light output by a continuous wave pump light laser sequentially passes through a first optical fiber amplifier, an optical isolator, a polarization controller and an optical fiber ring cavity and then is output into a chaos optical frequency comb; the chaos optical frequency comb is divided into two beams after main peak power is eliminated through the notch filter, the two beams of light are incident to the first polarization beam splitter after forming mutually perpendicular polarization through the fast axis polarizer and the slow axis polarizer respectively, enter the polarization-maintaining sensing optical fiber through the polarization-maintaining circulator after being combined through the first polarization beam splitter, and then enter the polarization-maintaining sensing optical fiber through the polarization-maintaining circulator. After Brillouin scattering occurs in the polarization-maintaining sensing optical fiber, generated scattered light is output by the polarization-maintaining circulator and is polarized and separated by the second polarization beam splitter, and the two separated light beams are respectively received by a photoelectric detector and are subjected to photoelectric conversion. According to the invention, cross sensitivity of temperature and strain can be solved, the measurement range is expanded, and frequency sweep is not needed.

Description

Technical Field

[0001] This invention relates to the field of distributed optical fiber sensing, specifically to a rapid measurement device and method for temperature and strain decoupling based on chaotic optical frequency combs. This method aims to ensure spatial resolution and measurement accuracy while addressing the cross-sensitivity problem of temperature and strain, expanding the measurement range of temperature and strain changes, and overcoming the time-consuming nature of traditional frequency sweeping methods. Background Technology

[0002] Distributed fiber optic sensing technology boasts advantages such as wide-area, long-distance, and high-precision measurement, and has been widely applied in monitoring the health status of large infrastructure projects such as bridges, dams, high-voltage transmission lines, and gas pipelines. Based on different scattering mechanisms, distributed fiber optic sensing technology can be divided into three categories: Rayleigh scattering, Brillouin scattering, and Raman scattering-based distributed fiber optic sensing technologies. Compared to Raman scattering-based distributed fiber optic sensing technology, which can only measure temperature, Rayleigh scattering- or Brillouin scattering-based distributed fiber optic sensing technologies can measure both temperature and strain. The sensing mechanism of Brillouin scattering-based fiber optic sensing technology is based on the linear relationship between the Brillouin frequency shift and temperature or strain. Rayleigh scattering-based fiber optic sensing technology compensates for the phase change of the light pulse in the fiber caused by external temperature or strain by changing the frequency (or wavelength) of the light pulse, and measures based on the linear relationship between the changed frequency (or wavelength) and temperature or strain. However, both the Brillouin frequency shift and the change in the light pulse frequency have a linear relationship with temperature and strain, making them indistinguishable. Therefore, the cross-sensitivity to temperature and strain is an important problem that needs to be solved in the field of distributed fiber optic sensing.

[0003] Fiber optic sensing, dual-frequency shift measurement, scattering fusion, and dual-parameter measurement are common methods for addressing the cross-sensitivity of temperature and strain. However, fiber optic sensing requires the simultaneous and parallel laying of two optical fibers, making it difficult to use in practical applications. Opt. Lett ., 1994 , 19(2).); The dual-frequency shift measurement method utilizes two Brillouin scattering peaks with different sensitivity coefficients in special optical fibers to achieve decoupling of temperature and strain. However, the sensitivity coefficients of the same type of special optical fiber are almost identical, so its measurement accuracy cannot be guaranteed. The scattering fusion method utilizes two scattering effects to achieve temperature and strain decoupling, but different scattering signals need to be distinguished during signal acquisition, which increases the control complexity of the system. At the same time, it has the disadvantages of low signal-to-noise ratio and limited measurement distance. J. Light. Technol. , 2021 , 39(18).); The dual-parameter method achieves the decoupling of temperature and strain by using two parameters that change linearly with temperature and strain. Currently, it mainly utilizes Brillouin frequency shift or Rayleigh dispersion frequency shift and birefringence frequency shift to construct dual parameters. For the extraction of birefringence frequency shift, the Brillouin dynamic grating technology is mainly used ( Technol. Lett., 2010 , 22(18) : 1364-1366. ) or Rayleigh scattering spectrum cross-correlation technique, however, using Brillouin dynamic grating technology to extract birefringence frequency shift requires double-end access and precise control, making the measurement system relatively complex; using Rayleigh scattering spectrum cross-correlation technique to extract birefringence frequency shift, the coherent detection signal will be limited by the coherent optical frequency modulation bandwidth, making the temperature strain measurement range small ( Opt. Express , 2017 , 25(14). );Using chaotic low coherence detection signal, since the wavelength is tunable through a manually tunable fiber optic grating filter, the tuning process is very time-consuming (ZL202310563830.4). Summary of the Invention

[0004] To address the technical problems of insufficient measurement accuracy, limited measurement distance, small temperature measurement range, or low measurement efficiency in existing methods for decoupling temperature and strain, this invention proposes a rapid measurement device and method for decoupling temperature and strain based on a chaotic optical frequency comb. This method achieves rapid measurement of temperature and strain by decoupling based on the cross-correlation of Rayleigh scattering spectra using a chaotic optical frequency comb.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a rapid measurement device for temperature and strain decoupling based on chaotic optical frequency comb, comprising: a continuous wave pump laser, a first fiber amplifier, an optical isolator, a polarization controller, a fiber optic loop cavity, a notch filter, a second fiber amplifier, an optical coupler, a fast axis polarizer, a slow axis polarizer, a first polarization beam splitter, a polarization-maintaining circulator, a third fiber amplifier, a second polarization beam splitter, a first photodetector, a second photodetector, a data acquisition card, and a computer; The continuous wave pump light output from the continuous wave pump laser passes through a first fiber amplifier, an optical isolator, and a polarization controller in sequence before entering the fiber ring cavity. The fiber ring cavity outputs a chaotic optical frequency comb based on nonlinear effects. The chaotic optical frequency comb, after having its main peak power eliminated by a notch filter, is split into two beams by a second fiber amplifier and an optical coupler. The two beams are polarized perpendicularly by a fast-axis polarizer and a slow-axis polarizer, respectively, and then incident on a first polarization beam splitter. After being combined by the first polarization beam splitter, the beams enter a polarization-maintaining sensing fiber through a polarization-maintaining circulator. Brillouin scattering occurs in the polarization-maintaining sensing fiber, and the resulting scattered light is output by the polarization-maintaining circulator and amplified by a third fiber amplifier. The beams are then polarized and separated by a second polarization beam splitter. The two separated beams are received by a first photodetector and a second photodetector, respectively, and undergo photoelectric conversion.

[0006] The aforementioned rapid measurement device for temperature and strain decoupling based on chaotic optical frequency comb further includes a bandpass filter, which is disposed between the first optical fiber amplifier and the optical isolator to suppress ASE noise generated by the first optical fiber amplifier.

[0007] The output end of the first polarization beam splitter is connected to the input end of the polarization-maintaining circulator via a polarization-maintaining fiber jumper; the reflective end of the polarization-maintaining circulator is connected to the polarization-maintaining sensing fiber via a polarization-maintaining fiber jumper; the output end of the polarization-maintaining circulator is connected to the input end of the third fiber amplifier via a polarization-maintaining fiber jumper; the output end of the third fiber amplifier is connected to the input end of the second polarization beam splitter via a polarization-maintaining fiber jumper; and the reflective and transmissive ends of the second polarization beam splitter are connected to the first photodetector and the second photodetector via polarization-maintaining fiber jumpers, respectively.

[0008] The aforementioned rapid measurement device for temperature and strain decoupling based on chaotic optical frequency comb further includes a fast-axis analyzer and a slow-axis analyzer, which are respectively disposed at the reflection end and the transmission end of the second polarization beam splitter.

[0009] The reflecting end and the transmitting end of the second polarization beam splitter are respectively connected to the fast-axis analyzer and the slow-axis analyzer via polarization-maintaining fiber jumpers. The fast-axis analyzer and the slow-axis analyzer are respectively connected to the first photodetector and the second photodetector via polarization-maintaining fiber jumpers.

[0010] The fiber optic ring cavity has a nonlinear coefficient γ greater than 10 W. -1 km -1 Nonlinear optical fiber formation with a free spectral range of 1-5 GHz.

[0011] The aforementioned rapid measurement device for temperature and strain decoupling based on chaotic optical frequency comb also includes a data acquisition card and a computer, wherein the computer is connected to a first photodetector and a second photodetector through the data acquisition card; The data acquisition card is used to acquire the first detection signal and the second detection signal detected by the first photodetector and the second photodetector, respectively. The computer is used to perform cross-correlation calculations on the same echo signals of the first and second detection signals corresponding to the same spatial location to obtain the shift of the birefringence correlation peak. The Rayleigh correlation peak shift is obtained by cross-correlation calculation of two adjacent echo signals from the first or second detection signal corresponding to the same spatial location. And based on the shift of the birefringence-related peak Rayleigh correlation peak shift Demodulation yields temperature and strain information along the polarization-maintaining sensing fiber.

[0012] The demodulation formula is: ; in, and These represent the change in temperature and the change in strain, respectively. and These represent the temperature coefficient and strain sensitivity coefficient of the birefringence frequency shift, respectively. and These represent the temperature coefficient and strain sensitivity coefficient of Rayleigh scattering radio frequency shift, respectively.

[0013] Furthermore, this invention also provides a rapid measurement method for temperature and strain decoupling based on a chaotic optical frequency comb, implemented according to the aforementioned rapid measurement device for temperature and strain decoupling based on a chaotic optical frequency comb, comprising the following steps: Step 1: Calibrate the measuring device to obtain the temperature coefficient and strain sensitivity coefficient of the birefringence frequency shift, as well as the temperature coefficient and strain sensitivity coefficient of the Rayleigh dispersion frequency shift; Step 2: Collect the first detection signal and the second detection signal obtained by the first photodetector and the second photodetector; Step 3: Perform cross-correlation calculations on the echo signals of the first and second detection signals corresponding to the same spatial location to obtain the birefringence correlation peak shift. The Rayleigh correlation peak shift is obtained by cross-correlation calculation of two adjacent echo signals from the first or second detection signal corresponding to the same spatial location. ; Step 4: Based on the shift of the birefringence correlation peak Rayleigh correlation peak shift Demodulation yields temperature and strain information along the polarization-maintaining sensing fiber (22).

[0014] The demodulation formula is: ; in, and These represent the change in temperature and the change in strain, respectively. and These represent the temperature coefficient and strain sensitivity coefficient of the birefringence frequency shift, respectively. and These represent the temperature coefficient and strain sensitivity coefficient of Rayleigh scattering radio frequency shift, respectively.

[0015] Compared with the prior art, the present invention has the following advantages: 1. This invention proposes a rapid measurement device and method for temperature and strain decoupling based on a chaotic optical frequency comb. Based on the nonlinear effect in the ring cavity, a wideband chaotic optical frequency comb is generated by controlling the wavelength and output power of the pump light. The chaotic optical frequency comb, as a probe light source, has an extremely wide wavelength tuning range, breaking through the frequency modulation bandwidth limitation in coherent optical detection, and effectively expanding the measurement range of temperature and strain. Simultaneously, each frequency signal of the chaotic optical frequency comb is a chaotic optical signal with low coherence, which can significantly suppress the coherent fading of Rayleigh scattering signals, improving signal stability and demodulation accuracy. 2. This invention achieves decoupled sensing of temperature and strain through Rayleigh correlation peak shift and birefringence correlation peak shift. Its structure is simple and easy to operate. 3. This invention replaces the traditional wavelength-tunable chaotic light source with a chaotic optical frequency comb, avoiding the frequency-by-frequency scanning operation achieved through a manually tunable fiber optic grating filter. That is, full-band data can be obtained through a single echo measurement, and all Rayleigh scattering signals at different optical frequencies at a certain location can be quickly extracted, greatly improving the measurement speed. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the rapid temperature and strain decoupling measurement device based on chaotic optical frequency comb provided in an embodiment of the present invention; In the diagram: 1 is a continuous wave pump laser, 2 is the first fiber amplifier, 3 is a bandpass filter, 4 is an optical isolator, 5 is a polarization controller, 6 is a fiber optic loop cavity, 7 is a notch filter, 8 is the second fiber amplifier, 9 is an optical coupler, 10 is a fast-axis polarizer, 11 is a slow-axis polarizer, 12 is the first polarization beam splitter, 13 is a polarization-maintaining circulator, 14 is the third fiber amplifier, 15 is the second polarization beam splitter, 16 is a fast-axis analyzer, 17 is a slow-axis analyzer, 18 is the first photodetector, 19 is the second photodetector, 20 is a data acquisition card, 21 is a computer, and 22 is a polarization-maintaining sensing fiber. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1 like Figure 1As shown, Embodiment 1 of the present invention provides a rapid temperature and strain decoupling measurement device based on chaotic optical frequency comb, comprising: a continuous wave pump laser 1, a first fiber amplifier 2, an optical isolator 4, a polarization controller 5, a fiber optic ring cavity 6, a notch filter 7, a second fiber amplifier 8, an optical coupler 9, a fast axis polarizer 10, a slow axis polarizer 11, a first polarization beam splitter 12, a polarization-maintaining circulator 13, a third fiber amplifier 14, a second polarization beam splitter 15, a first photodetector 18, a second photodetector 19, a data acquisition card 20, and a computer 21.

[0019] In this embodiment, the continuous pump light output from the continuous wave pump laser 1 passes sequentially through the first fiber amplifier 2, the optical isolator 4, and the polarization controller 5 before entering the fiber ring cavity 6. The fiber ring cavity 6 outputs a chaotic optical frequency comb based on nonlinear effects. After the main peak power is eliminated by the notch filter 7, the chaotic optical frequency comb is split into two beams after passing through the second fiber amplifier 8 and the optical coupler 9. The two beams are polarized into mutually perpendicular P and S polarizations by the fast axis polarizer 10 and the slow axis polarizer 11, respectively, and then incident on the first polarization beam splitter 12. After being combined by the first polarization beam splitter 12, the beams enter the polarization-maintaining sensing fiber 22 through the polarization-maintaining circulator 13. After Brillouin scattering occurs in the polarization-maintaining sensing fiber 22, the scattered light is output by the polarization-maintaining circulator 13 and amplified by the third fiber amplifier 14. Then, the beams are polarized and separated by the second polarization beam splitter 15. The two beams of light with P and S polarization are received by the first photodetector 18 and the second photodetector 19, respectively, and undergo photoelectric conversion.

[0020] Specifically, in this embodiment, the fiber optic ring cavity 6 has a nonlinear coefficient γ greater than 10 W. -1 km -1 A fiber optic ring cavity formed from highly nonlinear optical fibers.

[0021] Furthermore, such as Figure 1 As shown in the figure, the temperature and strain decoupling rapid measurement device based on chaotic optical frequency comb in this embodiment also includes a bandpass filter 3. The bandpass filter 3 is disposed between the first optical fiber amplifier 2 and the optical isolator 4 to suppress ASE noise generated by the first optical fiber amplifier 2.

[0022] The chaotic optical frequency comb is generated as a result of the fiber ring cavity 6 transitioning from a period-doubling bifurcation path to a chaotic system under self-phase modulation. The output end of the continuous wave pump laser 1 is connected to the input end of the first fiber amplifier 2 via a single-mode fiber jumper; the output end of the first fiber amplifier 2 is connected to the input end of the bandpass filter 3 via a single-mode fiber jumper; the output end of the bandpass filter 3 is connected to the input end of the optical isolator 4 via a single-mode fiber jumper; the output end of the optical isolator 4 is connected to the input end of the polarization controller 5 via a single-mode fiber jumper; the polarization controller 5 is connected to the input end of the fiber ring cavity 6 via a single-mode fiber jumper; and the output end of the fiber ring cavity 6 is connected to the input end of the notch filter 7 via a single-mode fiber jumper. The output end of the notch filter 7 is connected to the input end of the second fiber amplifier 8 via a single-mode fiber optic patch cord. The input end of the second fiber amplifier 8 is connected to the input end of the optical coupler 9 via a single-mode fiber optic patch cord. The two output ends of the optical coupler 9 are connected to the input ends of the fast-axis polarizer 10 and the slow-axis polarizer 11 via single-mode fiber optic patch cords, respectively.

[0023] Furthermore, in this embodiment, the output ends of the fast-axis polarizer 10 and the slow-axis polarizer 11 are respectively connected to the input end of the first polarization beamsplitter 12 via polarization-maintaining fiber jumpers; the output end of the first polarization beamsplitter 12 is connected to the input end of the polarization-maintaining circulator 13 via polarization-maintaining fiber jumpers; the reflecting end of the polarization-maintaining circulator 13 is connected to the polarization-maintaining sensing fiber 22 via polarization-maintaining fiber jumpers; the output end of the polarization-maintaining circulator 13 is connected to the input end of the third fiber amplifier 14 via polarization-maintaining fiber jumpers; the output end of the third fiber amplifier 14 is connected to the input end of the second polarization beamsplitter 15 via polarization-maintaining fiber jumpers; and the reflecting end and the transmitting end of the second polarization beamsplitter 15 are respectively connected to the first photodetector 18 and the second photodetector 19 via polarization-maintaining fiber jumpers.

[0024] Furthermore, such as Figure 1 As shown, the rapid measurement device for temperature and strain decoupling based on chaotic optical frequency comb in this embodiment also includes a fast axis analyzer 16 and a slow axis analyzer 17, which are respectively disposed at the reflection end and the transmission end of the second polarization beam splitter 15.

[0025] Furthermore, in this embodiment, the reflecting end and the transmitting end of the second polarization beam splitter 15 are respectively connected to the fast-axis analyzer 16 and the slow-axis analyzer 17 via polarization-maintaining fiber jumpers. The fast-axis analyzer 16 and the slow-axis analyzer 17 are respectively connected to the first photodetector 18 and the second photodetector 19 via polarization-maintaining fiber jumpers. The fast-axis analyzer 16 and the slow-axis analyzer 17 can eliminate signal noise caused by polarization degradation.

[0026] Specifically, the free spectral range of the fiber optic ring cavity 6 is 1-5 GHz. In this embodiment, it is specifically 3 GHz.

[0027] Furthermore, such as Figure 1 As shown, the rapid temperature and strain decoupling measurement device based on chaotic optical frequency comb in this embodiment also includes a data acquisition card 20 and a computer 21. The computer 21 is connected to the first photodetector 18 and the second photodetector 19 through the data acquisition card 20. The data acquisition card 20 is used to acquire the first detection signal and the second detection signal detected by the first photodetector 18 and the second photodetector 19, respectively. The computer 21 is used to perform cross-correlation calculations on the same echo signals of the first and second detection signals corresponding to the same spatial location to obtain the shift of the birefringence correlation peak. The Rayleigh correlation peak shift is obtained by cross-correlation calculation of two adjacent echo signals from the first or second detection signal corresponding to the same spatial location. And based on the shift of the birefringence-related peak Rayleigh correlation peak shift Demodulation yields temperature and strain information along the polarization-maintaining sensing fiber 22.

[0028] The working principle of the embodiments of the present invention is described below.

[0029] a. A continuous-wave pump laser 1 serves as the pump source, outputting continuous light with a center wavelength of 1550 nm. The pump power is gradually increased by adjusting the first fiber amplifier 2, and a bandpass filter 3 is used to suppress ASE noise. An isolator 4 and a polarization controller 5 ensure efficient coupling of the pump light to the fiber ring cavity 6. The free spectral range of the ring cavity is 3 GHz. As the pump power increases to the nonlinear threshold, discrete comb teeth are gradually formed, and the self-phase modulation effect dominates the evolution of the optical field, entering a period-doubling bifurcation. The frequency components on both sides of the single comb teeth become increasingly dense and broadened. Finally, a chaotic optical frequency comb with a single comb line width of 1 GHz and a total bandwidth of approximately 200 GHz is formed in the 3 GHz ring cavity 6 and output. The chaotic optical frequency comb generates 50 low-correlation, crosstalk-free detection channels near 1550 nm.

[0030] b. The generated chaotic optical frequency comb attenuates the pump light power at the main peak of 1550 nm through a notch filter 7, ensuring effective amplification of the subsequent chaotic optical comb. Then, after passing through a second fiber amplifier, it is split into two beams by a coupler 9. One beam enters the input of the fast-axis polarizer 10 and the first polarization beam splitter 12, while the other beam enters the other input of the slow-axis polarizer 11 and the first polarization beam splitter 12. The fast-axis polarizer 10 and the slow-axis polarizer 11 make the polarizations of the two beams orthogonal. The two orthogonally polarized chaotic optical frequency combs are injected into the polarization-maintaining sensing fiber 22 through a polarization-maintaining circulator 13.

[0031] c. The chaotic optical frequency comb generates Rayleigh scattering along the polarization-maintaining sensing fiber 22. The backscattered Rayleigh light is amplified by the polarization-maintaining circulator 13 and then enters the third fiber amplifier 14. After being incident on the second polarization beam splitter 15, it is split into two paths. One end enters the fast axis analyzer 16 and the first photodetector 18, and the other end enters the slow axis analyzer 17 and the second photodetector 19. The backscattered Rayleigh signal is converted into an electrical signal by the photodetector to obtain the first detection signal and the second detection signal. After the first detection signal and the second detection signal are collected by the data acquisition card 20, the computer 21 performs data processing.

[0032] In this embodiment, for the signals within the 50 chaotic optical comb detection channels at each spatial location, only one echo signal between different polarization axes and two echo signals within the same polarization axis need to be extracted. By performing cross-correlation calculations on these two types of signals, the birefringence frequency shift and Rayleigh frequency shift can be obtained, respectively. Finally, based on the above frequency shift information, rapid and large-scale temperature strain decoupling measurement is achieved.

[0033] Specifically, in this embodiment, the generation process of the chaotic optical frequency comb can be simulated by establishing a specific mathematical model to simulate its optical field evolution. The detailed steps are as follows: As a closed loop, the fiber optic ring cavity 6's structure dictates that light waves must satisfy specific phase conditions during propagation within the cavity; that is, the phase difference after one round trip must be an integer multiple of 2π. This resonance condition results in frequency selectivity, meaning that only frequencies meeting specific conditions can stably exist within the cavity. The frequency interval between adjacent resonant modes is: ; (1) Where c is the speed of light in a vacuum. The effective refractive index is L, the circumference of the ring cavity is L, and FSR represents the free spectral range.

[0034] Neglecting the low material loss in fiber ring cavity 6, wave propagation within fiber ring cavity 6 can be described by the nonlinear Schrödinger equation: ; (2) Where E is the normalized amplitude. These are nonlinear coefficients. For group velocity dispersion, z is the coordinate along the propagation direction of the optical fiber; wave follower group velocity The moving reference frame is the time coordinate. In the near-zero dispersion case, the dispersion effect is negligible compared to the nonlinear effect; therefore, the dispersion term in equation (2) can be ignored. At this point, the evolution of the optical field within the ring cavity is mainly modulated by the self-phase effect (SPM).

[0035] Therefore, let the complex amplitude of the light field be: ; (3) in, This represents the instantaneous power within the ring cavity at time T. When losses are ignored and only SPM is considered, the instantaneous power remains constant along z. Let z represent the phase corresponding to position z. Integrating the light field from the starting point (z=0) to the ending point (z=L) of the loop, we can obtain the cumulative phase of the light field after one revolution: ; (4) The expression for the complex amplitude after the light field has propagated one revolution is: ; (5) Let the complex amplitudes of the optical field before and after the nth coupling at the reference point of the annular cavity (at the coupler) be respectively... , ,but: ; (6) For each complete propagation cycle of the optical field, the coupling between the output port of the ring cavity and the optical field input to the straight waveguide of the fiber ring can be described by a matrix equation: ; (7) in This represents the complex amplitude at the input port of the coupled straight waveguide of the fiber optic loop. This represents the complex amplitude of the cavity field before the (n+1)th coupling. Let be the complex amplitude at the output port of the straight waveguide after the nth coupling, under continuous pumping. (constant); , Let these represent the self-coupling coefficient and the cross-coupling coefficient, respectively, satisfying... .

[0036] Substituting the mapping equation (5) of the optical field inside the ring into (6), we can obtain the nonlinear mapping equation that drives the evolution of the entire ring cavity system: ; (8) This equation establishes the iterative relationship of the light field in its loop propagation.

[0037] Based on this iterative equation, the evolution of the optical field within the ring cavity can be divided into three stages: 1) When the pump power is less than the nonlinear threshold power, the nonlinear term of the iterative equation is approximately zero, and the optical field evolution iterative equation can be simplified to a linear equation, and the system converges to a stable point.

[0038] 2) When the pump power is greater than the nonlinear threshold, a discrete frequency comb structure is generated on both sides of the pump light with FSR as the interval.

[0039] 3) As the pump power further increases, the system becomes unstable and undergoes a period-doubling bifurcation, causing the optical field intensity to begin oscillating periodically. This oscillation translates into a periodic shift in instantaneous frequency: ; (9) in, Phase of the light field The instantaneous frequency shift that occurs as time t changes. Here, L is the nonlinear coefficient, and L is the length of the annular cavity. The power is the intracavity power. As the frequency components become more complex with the periodic oscillations, when the pump power exceeds the cumulative bifurcation point, the system will transition to a chaotic state. The phase diffusion causes the comb bandwidth to broaden, thus generating a single chaotic continuous spectrum. The linewidth of the single chaotic optical comb is approximately 1 GHz.

[0040] The above theoretical derivation assumes zero-group velocity dispersion, in which case the transition between different power levels of the same mode is instantaneous, thus the resulting chaotic optical frequency comb can theoretically have an infinitely wide spectral bandwidth. However, finite dispersion... It has a smoothing effect on time-domain waveforms, therefore the attenuation of the spectrum approximately follows... , This represents the offset relative to the pump frequency. Indicates the light field at frequency shift The magnitude of the spectral power at that location.

[0041] In this device, the final width of the chaotic optical frequency comb can be extended by adjusting a smaller group velocity dispersion, a higher pump power, and a nonlinear coefficient. The spectral width of the chaotic optical frequency comb is defined as the full-width frequency range corresponding to a power drop of 3 dB relative to the pump frequency.

[0042] In this embodiment, the total bandwidth of the chaotic optical frequency comb should not be less than 200 GHz, the linewidth of a single chaotic optical frequency comb is about 1 GHz, exhibiting continuous chaotic spectrum characteristics, the free spectral range of the fiber ring cavity 6 is 3 GHz, and at least 50 low-correlation, crosstalk-free chaotic optical comb detection channels are generated near 1550 nm.

[0043] In practice, the extraction of birefringence frequency shift involves incidenting the chaotic optical frequency comb signal onto the polarization-maintaining fiber 22, recording the echo signals along the fast and slow axes at each spatial location, and then performing cross-correlation calculations on the same echo signals along the slow and fast axes at each spatial location to obtain the birefringence correlation peak shift. This represents the change in birefringence frequency shift at a certain location. Further analysis of how this shift changes with temperature and strain yields the temperature coefficient of the birefringence frequency shift. and strain sensitivity coefficient The extraction of Rayleigh dispersion frequency shift involves recording the echo signals of two incident chaotic optical frequency combs at each spatial location, performing cross-correlation calculations on the two echo signals within the fast axis (or slow axis) at each spatial location, and obtaining the Rayleigh correlation peak shift. This represents the change in Rayleigh scattering frequency shift, thus obtaining the temperature coefficient of Rayleigh scattering frequency shift. and strain sensitivity coefficient .

[0044] In practice, the Rayleigh scattering frequency shift exhibits zero frequency shift in the correlation spectrum in the unstrained region, while the correlation peak shifts to lower frequencies in the strain-applied region. Applying a small strain to the strain gauge, the corresponding change in fiber length using the displacement platform is 3 uε, with a corresponding fiber length change of 0.03 mm and a strain increase interval of 0.5 uε. Linear fitting is performed on the measured experimental results to obtain the strain sensitivity coefficient of the Rayleigh scattering frequency shift. .

[0045] In practice, simultaneous measurement of temperature and strain is achieved by establishing a coefficient matrix between two parameters—birefringence frequency shift and Rayleigh dispersion frequency shift—and temperature and strain. (10) (11) Therefore, temperature and strain information can be demodulated simultaneously: (12) Specifically, considering the known calibrated sensitivity coefficient , , , When the bandwidth of the chaotic optical frequency comb used for detection At 200 GHz, the maximum temperature change that can be measured within the sensing range. Maximum strain change for: ; (13) ;(14) Therefore, the maximum measurement range for temperature is approximately 115 ℃, and the maximum measurement range for strain is approximately 1300 ℃. .

[0046] In traditional frequency sweep systems, the time required to completely reconstruct the Rayleigh scattering spectrum Influence parameters include average number of times Number of scans Duration of each frequency Ignoring frequency switching time, that is: ; (15) Therefore, in traditional frequency sweeping systems, if a probe beam with a pulse width of 20 ns is used in a 100m polarization-maintaining sensing fiber, it would take approximately 1 minute to perform 500 sweeps on average for 400 frequencies. However, the device in this embodiment eliminates the need for frequency sweeping during measurement, significantly reducing measurement time and enabling rapid measurement of temperature strain decoupled from its original parameters.

[0047] Example 2 Embodiment 2 of the present invention provides a rapid measurement method for temperature and strain decoupling based on chaotic optical frequency comb, which is implemented according to the rapid measurement device for temperature and strain decoupling based on chaotic optical frequency comb described in Embodiment 1, and includes the following steps: Step 1: Calibrate the measuring device to obtain the temperature coefficient and strain sensitivity coefficient of the birefringence frequency shift, as well as the temperature coefficient and strain sensitivity coefficient of the Rayleigh dispersion frequency shift; Step 2: Collect the first detection signal and the second detection signal obtained by the first photodetector (18) and the second photodetector (19); Step 3: Perform cross-correlation calculations on the echo signals of the first and second detection signals corresponding to the same spatial location to obtain the birefringence correlation peak shift. The Rayleigh correlation peak shift is obtained by cross-correlation calculation of two adjacent echo signals from the first or second detection signal corresponding to the same spatial location. ; Step 4: Based on the shift of the birefringence correlation peak Rayleigh correlation peak shift Demodulation yields temperature and strain information along the polarization-maintaining sensing fiber (22).

[0048] Specifically, in step 4, the demodulation formula is: (16) in, and These represent the change in temperature and the change in strain, respectively. and These represent the temperature coefficient and strain sensitivity coefficient of the birefringence frequency shift, respectively. and These represent the temperature coefficient and strain sensitivity coefficient of Rayleigh scattering radio frequency shift, respectively.

[0049] Using formula (16), the shift of birefringence-related peaks can be determined. Rayleigh correlation peak shift The changes in temperature and strain are obtained, enabling rapid measurement of temperature and strain through decoupling.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A rapid measurement device for temperature and strain decoupling based on chaotic optical frequency comb, characterized in that, include: Continuous wave pump laser (1), first fiber amplifier (2), optical isolator (4), polarization controller (5), fiber ring cavity (6), notch filter (7), second fiber amplifier (8), optical coupler (9), fast axis polarizer (10), slow axis polarizer (11), first polarization beam splitter (12), polarization maintaining circulator (13), third fiber amplifier (14), second polarization beam splitter (15), first photodetector (18), second photodetector (19), data acquisition card (20), computer (21); The continuous pump light output from the continuous wave pump laser (1) passes through the first fiber amplifier (2), the optical isolator (4), and the polarization controller (5) in sequence before entering the fiber ring cavity (6). The fiber ring cavity (6) outputs a chaotic optical frequency comb based on nonlinear effects. After the chaotic optical frequency comb is filtered by a notch filter (7) to eliminate the main peak power, it is split into two beams after passing through a second fiber amplifier (8) and an optical coupler (9). The two beams are polarized perpendicularly by a fast-axis polarizer (10) and a slow-axis polarizer (11) and then incident on a first polarization beam splitter (12). After being combined by the first polarization beam splitter (12), they enter the polarization-maintaining sensing fiber (22) through a polarization-maintaining circulator (13). After Brillouin scattering occurs in the polarization-maintaining sensing fiber (22), the scattered light is output by the polarization-maintaining circulator (13) and amplified by a third fiber amplifier (14). Then, it is polarized and separated by a second polarization beam splitter (15). The two beams are received by a first photodetector (18) and a second photodetector (19) and undergo photoelectric conversion.

2. The rapid measurement device for temperature and strain decoupling based on chaotic optical frequency comb according to claim 1, characterized in that, It also includes a bandpass filter (3), which is disposed between the first fiber amplifier (2) and the optical isolator (4) to suppress ASE noise generated by the first fiber amplifier (2).

3. The rapid measurement device for temperature and strain decoupling based on chaotic optical frequency comb according to claim 1, characterized in that, The output end of the first polarization beam splitter (12) is connected to the input end of the polarization-maintaining circulator (13) via a polarization-maintaining fiber jumper; the reflection end of the polarization-maintaining circulator (13) is connected to the polarization-maintaining sensing fiber (22) via a polarization-maintaining fiber jumper; the output end of the polarization-maintaining circulator (13) is connected to the input end of the third fiber amplifier (14) via a polarization-maintaining fiber jumper; the output end of the third fiber amplifier (14) is connected to the input end of the second polarization beam splitter (15) via a polarization-maintaining fiber jumper; the reflection end and the transmission end of the second polarization beam splitter (15) are respectively connected to the first photodetector (18) and the second photodetector (19) via polarization-maintaining fiber jumpers.

4. The rapid measurement device for temperature and strain decoupling based on chaotic optical frequency comb according to claim 1, characterized in that, It also includes a fast-axis analyzer (16) and a slow-axis analyzer (17), which are respectively disposed at the reflecting end and the transmitting end of the second polarization beam splitter (15).

5. The rapid temperature and strain decoupling measurement device based on chaotic optical frequency comb according to claim 4, characterized in that, The reflecting end and the transmitting end of the second polarization beam splitter (15) are respectively connected to the fast axis analyzer (16) and the slow axis analyzer (17) through polarization-maintaining fiber jumpers. The fast axis analyzer (16) and the slow axis analyzer (17) are respectively connected to the first photodetector (18) and the second photodetector (19) through polarization-maintaining fiber jumpers.

6. The rapid measurement device for temperature and strain decoupling based on chaotic optical frequency comb according to claim 1, characterized in that, The fiber optic ring cavity (6) has a nonlinear coefficient γ greater than 10 W. -1 km -1 Nonlinear optical fiber formation with a free spectral range of 1-5 GHz.

7. The rapid temperature and strain decoupling measurement device based on chaotic optical frequency comb according to claim 1, characterized in that, It also includes a data acquisition card (20) and a computer (21), wherein the computer (21) is connected to the first photodetector (18) and the second photodetector (19) through the data acquisition card (20); The data acquisition card (20) is used to acquire the first detection signal and the second detection signal detected by the first photodetector (18) and the second photodetector (19) respectively; The computer (21) is used to perform cross-correlation calculations on the same echo signals of the first and second detection signals corresponding to the same spatial location to obtain the birefringence correlation peak shift. The Rayleigh correlation peak shift is obtained by cross-correlation calculation of two adjacent echo signals from the first or second detection signal corresponding to the same spatial location. And based on the shift of the birefringence-related peak Rayleigh correlation peak shift Demodulation yields temperature and strain information along the polarization-maintaining sensing fiber (22).

8. The rapid measurement device for temperature and strain decoupling based on chaotic optical frequency comb according to claim 7, characterized in that, The demodulation formula is: ； in, and These represent the change in temperature and the change in strain, respectively. and These represent the temperature coefficient and strain sensitivity coefficient of the birefringence frequency shift, respectively. and These represent the temperature coefficient and strain sensitivity coefficient of Rayleigh scattering radio frequency shift, respectively.

9. A rapid measurement method for temperature and strain decoupling based on a chaotic optical frequency comb, implemented by a rapid measurement device for temperature and strain decoupling based on a chaotic optical frequency comb according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Calibrate the measuring device to obtain the temperature coefficient and strain sensitivity coefficient of the birefringence frequency shift, as well as the temperature coefficient and strain sensitivity coefficient of the Rayleigh dispersion frequency shift; Step 2: Collect the first detection signal and the second detection signal obtained by the first photodetector (18) and the second photodetector (19); Step 3: Perform cross-correlation calculations on the echo signals of the first and second detection signals corresponding to the same spatial location to obtain the birefringence correlation peak shift. The Rayleigh correlation peak shift is obtained by cross-correlation calculation of two adjacent echo signals from the first or second detection signal corresponding to the same spatial location. ; Step 4: Based on the shift of the birefringence correlation peak Rayleigh correlation peak shift Demodulation yields temperature and strain information along the polarization-maintaining sensing fiber (22).

10. The rapid measurement method for temperature and strain decoupling based on chaotic optical frequency comb according to claim 9, characterized in that, The demodulation formula is: ； in, and These represent the change in temperature and the change in strain, respectively. and These represent the temperature coefficient and strain sensitivity coefficient of the birefringence frequency shift, respectively. and These represent the temperature coefficient and strain sensitivity coefficient of Rayleigh scattering radio frequency shift, respectively.

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